MANGANESE BASED CATALYST, ITS PROCESS OF PREPARATION AND THEIR USE IN PROCESS OF HYDROGENATION REACTIONS FIELD OF THE INVENTION The present invention provides a novel manganese based catalyst of Formula I, its process of preparation, and their use in a process of hydrogenation of different substrates. More particularly, the present invention provides a process of hydrogenation where the novel manganese catalyst of Formula I is used for hydrogenation of various substrates of Formula IIA or IIB such as α,β-unsaturated ketones, aldehydes, imines, etc. BACKGROUND AND PRIOR ART OF THE INVENTION In modern synthetic organic chemistry, chemo- and regioselective hydrogenation of α,β- unsaturated ketones, aldehydes and imines is always a challenging procedure. The catalytic reduction of polar multiple bonds via molecular hydrogen plays a significant role. Use of catalytic procedures in combination with hydrogen gas displays an attractive option to develop efficient and cleaner processes. In last few years, well-defined Mn(I) complexes were introduced as powerful players in field of sustainable hydrogenation chemistry, being active for hydrogenation of not only aldehydes, ketones, esters, CO2, and carbonates but also nitrogen-containing compounds such as imines, nitriles, amides, and heterocycles. Many of these transition-metal catalyzed hydrogenations rely on metal−ligand bifunctional catalysis (metal−ligand cooperation), where complexes contain electronically coupled hydride and acidic hydrogen atoms. An effective way of bond activation by metal−ligand cooperation involves aromatization/dearomatization of the ligand in pincer complexes in which a central pyridine-based backbone is connected with −CH ₂ PR ₂ and/or −CH ₂ NR ₂ substituents. This has resulted in the development of novel and unprecedented iron and manganese catalysis, where this type of cooperation plays a key role in the heterolytic cleavage of H2. An overview of well-defined manganese complexes for hydrogenation reactions is depicted by Stefan Weber et al in the journal “Organometallics 2021, 40, 1388−1394”. An alternative way to activate dihydrogen was recently described in this publication. This article also discloses about the Mn(I) alkyl carbonyl complexes which are known to undergo insertions to form highly reactive acyl intermediates which are able to activate dihydrogen, thereby forming the 16e− Mn(I) hydride catalysts. Accordingly, bisphosphine manganese tricarbonyl complexes containing alkyl ligands could be employed for the additive-free hydrogenation of alkenes and nitriles. The reaction conditions are very harsh to achieve the hydrogenation of alkenes and nitriles. Manganese catalysts and their use in hydrogenation of ketones is disclosed in the US patent application number ‘US2022119329A1’ wherein hydrogenation of ketones involves higher pressure and temperature conditions. Chemo- and regioselective hydrogenation of alkenes and carbonyls under mild conditions is crucial to achieve sustainable synthesis. Most of the known catalysts for hydrogenation of various substrates such as α,β-unsaturated ketones, aldehydes and imines requires expensive catalysts and/or harsh reaction conditions (high H ₂ pressure and high reaction temperature). Therefore, there is a need to provide a chemo and regioselective hydrogenation catalyst useful for the hydrogenation of various substrates such as α,β-unsaturated ketones, aldehydes, imines, etc. OBJECTS OF THE INVENTION The main objective of the present invention is to provide a novel manganese catalyst of Formula I, for a catalytic hydrogenation processes. Another objective of the present invention is to provide a process of preparation of said manganese based catalyst of formula I. Yet another objective of the present invention is to provide a process for hydrogenation of various substrates such as α,β-unsaturated ketones, aldehydes and imines by using said manganese catalyst (of Formula I). BRIEF DESCRIPTION OF DRAWINGS Fig 1: The synthetic scheme explaining general process of hydrogenation of substrates such as α,β-unsaturated ketones, aldehydes and imines by using the manganese catalyst (of Formula I). Fig 2: The synthetic scheme explaining process of preparation of the manganese based catalyst of formula I. Fig 3: ORTEP (Oak Ridge Thermal-Ellipsoid Plot Program) of compound Mn-2 showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Selected bond length (Å): Br1 ^Mn1, 2.5916(7); Mn1 ^C9, 1.773(4); Mn1 ^C10, 1.797(4); Mn1 ^N3, 2.011(3); Mn1 ^N1, 2.012(3); Mn1 ^P1, 2.2462(12). Selected bond angles ( ^): N3 ^Mn1 ^P1, 160.49(11); C10 ^Mn1 ^N1, 175.88(16); C9 ^Mn1 ^Br1, 175.54(14); C9 ^Mn1 ^C10, 87.40(19); C9 ^Mn1 ^N1, 96.23(16); N1 ^Mn1 ^Br1, 84.57(9). Fig 4: Product Scope and Scheme of Mn-Catalyzed C=C Bond Hydrogenation of α,β– Unsaturated Ketones ( ^a Reaction Conditions: Substrate, α,β-unsaturated ketone (0.20 mmol), Mn-3 (0.005 g, 0.01 mmol, 5 mol%), K3PO4 (0.0043 g, 0.02 mmol), MeOH (1.0 mL), H ₂ (5 bar). Yields are of isolated compounds. ^b Reaction at 50 ^o C. ^c Mixture of MeOH : DCM (4 : 1) used. ^d Reaction at 10 bar H ₂ and 50 ^o C.). Fig 5: Product Scope and Scheme of Mn-Catalyzed Hydrogenation of Aldehydes and Imines ( ^a Reaction Conditions: Substrate (0.20 mmol), Mn-3 (0.005 g, 0.01 mmol, 5 mol%), K ₃ PO ₄ (0.0043 g, 0.02 mmol), H ₂ (5 bar), MeOH (1.0 mL). Yield of isolated compounds. ^b Obtained as a mixture of E and Z isomers. ^c Mixture of MeOH:DCM (4:1) used. ^c Reaction performed 50 ^o C). SUMMARY OF THE INVENTION In one aspect, the present invention provides a novel manganese catalyst of Formula I or its isomeric forms, for hydrogenation of various substrates such as α,β-unsaturated ketones, aldehydes, and imines (of Formula IIA or IIB): Formula I wherein, Mn is manganese atom or manganese ion in oxidation state (I), moieties attached to Mn are selected from heteroaryl groups of pyridine and diazole, one or more carbon monoxide groups, and -PR ³ R ⁴ -NR ² , wherein said nitrogen of -PR ³ R ⁴ -NR ² is attached to said heteroaryl, and X group; R ¹ is selected from the group consisting of hydrogen, alkyl, aryl, alkylaryl, alkoxy, cycloalkyl, alkyl cycloalkyl, and alkylcarboxy; R ² is selected from the group consisting of hydrogen, and alkyl; R ³ is selected from the group consisting of alkyl, unsubstituted aryl, substituted aryl, and cycloalkyl; R ⁴ is selected from the group consisting of alkyl, unsubstituted aryl, substituted aryl, and cycloalkyl; and X is selected from the group consisting of halides, organosulfonate oxoanion (Triflate), boron trifluoride, and tetrafluoroborate; wherein R ¹ and R ² may be identical or different, and R ³ and R ⁴ are the substituents of phosphine moiety. The present disclosure also provides a process of preparation of a novel manganese catalyst (Formula I) under mild conditions which comprises reacting compound of formula III with substituted pentacarbonylmanganese [Mn(CO) ₅ X] at room temperature of 25 to 30 ^o C to yield a novel manganese catalyst (Formula I), Formula III wherein R ¹ , R ² , R ³ , R ⁴ and X are same as defined above under formula I. In another aspect, the present invention relates to a process of preparation of the manganese based catalyst complex of Formula I, the process comprising steps of: a) reacting a ligand compound of formula III with substituted pentacarbonylmanganese [Mn(CO)5X] with a solvent in a container to obtain a reaction mixture Formula III wherein R ¹ , R ² , R ³ , R ⁴ and X are same as defined above under formula I; b) stirring the reaction mixture of step a) under inert atmosphere at a temperature in the range of 27-80 ^o C for a time period of up to 48 hrs; c) purifying the mixture of step b) to obtain the manganese catalyst of Formula I. In an embodiment, the ligand compound of formula III used in step a) is selected from N-(diphenylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine (L1), N-(di-n- propylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine (L2), N-(di-tert- butylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine (L3) and N-(di-tert- butylphosphaneyl)-N-methyl-6-(1H-pyrazol-1-yl)pyridin-2-amin e (L4). In an embodiment, the solvent used in step a) is selected from tetrahydrofuran, 2-methyl tetrahydrofuran and toluene. In another aspect, the present invention provides a process for hydrogenation of substrate selected from α, β-unsaturated ketone, aldehyde and imine (of Formula IIA or IIB), by using the manganese based catalyst complex of Formula I, the process comprising steps of: (i) preparing a mixture of the substrate of Formula IIA or IIB in presence of Mn-catalyst of Formula I and a base in dry vial with stir bar Formula IIA Formula IIB; wherein A, B, Y and X of formula IIA and R1, R2 and R3 of formula IIB is same as defined under formulas IVA and IVB; (ii) transferring the reaction vial of step i) in an autoclave under argon atmosphere; (iii) adding a polar solvent in vial of step ii) and pressurizing the autoclave with H ₂ gas followed by venting for five times; (iv) pressurizing the autoclave with H2 gas of pressure ranging between 5-50 bar, and stirring the mixture with speed of 500-800 rpm at temperature in the range of 27-50 ºC for time period of 1 to 24 hrs to obtain crude hydrogenated compound; and (v) purifying the crude compound of step iv) to obtain desired hydrogenated compounds of formula IV or Formula IVA Formula IVB Wherein in formula IVA: X is oxo group (O) or nitrogen (NR ¹ ) group, where R ¹ is alkyl or aryl moiety; R is hydrogen, alkyl (C1-C10), (un)substituted aryl, (un)substituted heteroaryl, alkene, alkyne; A and Y is independently selected from hydrogen, alkyl (C1- C10), (un)substituted aryl, (un)substituted heteroaryl, alkene, alkyne, ferrocene, alkoxy, where the substituted aryl or heteroaryl maybe further substituted with aryl, alkoxy, alkyl, halogen, nitro, cyano, aryl ether, alkyl ether, aryl alkyl ether, CF3, (un)substituted amino, alkyl amino, aryl amino, ferrocene, alkoxy alkyl ether, alkyne alkyl ether, alkylene alkyl ether, hydroxyl, cyclic saturated or unsaturated ring of aryl or heteroaryl with number of rings from 0 to 4; B is selected from hydrogen, alkene, alkyne, alkyl, aryl, heteroaryl, ferrocene, halogen; and A and B optionally together may form saturated or unsaturated ring of aryl or heteroaryl which may further be substituted with hydrogen, alkyl, aryl, heteroaryl, hydroxyl, alkylhydroxyl, alkyl aryl ether, aryl alkyl ether, nitro, cyano, and halogen; and in formula IVB: X is oxo group (O) or nitrogen (NR ³ ) group, where R ³ is alkyl or aryl moiety; R ¹ is selected from hydrogen, alkyl (C1-C10), (un)substituted aryl, (un)substituted heteroaryl, alkene, alkyne, ferrocene, alkoxy, where the substituted aryl or heteroaryl maybe further substituted with aryl, alkoxy, alkyl, halogen, nitro, cyano, aryl ether, alkyl ether, aryl alkyl ether, CF3, (un)substituted amino, alkyl amino, aryl amino, ferrocene, alkoxy alkyl ether, alkyne alkyl ether, alkylene alkyl ether, hydroxyl, cyclic saturated or unsaturated ring of aryl or heteroaryl with number of rings from 0 to 4; R ² is selected from hydrogen, alkene, alkyne, alkyl, aryl, heteroaryl, ferrocene, halogen; and R ¹ and R ² optionally together may form saturated or unsaturated ring of aryl or heteroaryl which may further be substituted with hydrogen, alkyl, aryl, heteroaryl, hydroxyl, alkylhydroxyl, alkyl aryl ether, aryl alkyl ether, nitro, cyano, and halogen. In an embodiment, the novel hydrogenated compounds of formula IVA and/or IVB are selected from the group consisting of: (i) 1-(3-(Allyloxy)phenyl)-3-phenylpropan-1-one (2a) , (ii) 3-Phenyl-1-(3-(prop-2-yn-1-yloxy)phenyl)propan-1-one (2b) (iii) 1-(3-(Oxiran-2-ylmethoxy)phenyl)-3-phenylpropan-1-one (2c) (iv) 2-(4-Acetylphenoxy)-1,3-diphenylpropan-1-one (2d) . In an embodiment, the base used in said hydrogenation process is selected from the group consisting of potassium carbonate, potassium phosphate, potassium hydroxide, tripotassium phosphate potassium tert-butoxide, sodium tert-butoxide, sodium carbonate, cesium carbonate, sodium hydroxide, lithium carbonate, lithium hydroxide, calcium hydroxide, potassium bicarbonate, sodium bicarbonate, sodium methoxide, lithium bicarbonate and tertiary amines. In an embodiment, the polar solvent used in said hydrogenation process is selected from simple alcohols, such as C1-10 hydrocarbyl alcohol, saturated aliphatic C1-8alcohol, polyvalent alcohol; ether based solvent, aliphatic or aromatic hydrocarbon solvent, and halogenated hydrocarbon solvent, or mixtures thereof. In an embodiment, the purification of step v) of said hydrogenation process is done by concentrating the crude hydrogenated compound and subjecting it to column chromatography on silica gel wherein petroleum ether and ethyl acetate is used as solvent media in a ratio of 70:1 respectively, for separation and purification, to yield desired hydrogenated compounds of formula IVA or IVB. The Mn-catalyzed process for hydrogenation of present invention is not limited to process of hydrogenation of substrates such as ketones but may be applicable to hydrogenation process of other substrates too e.g. alkenes, any carbonyl containing substrates, aldehydes and imides, etc. DETAILED DESCRIPTION OF THE INVENTION: “Alkyl” as used herein is collection of carbon atoms that are covalently linked together in normal, secondary, tertiary or cyclic arrangements, i.e., in linear, branched, cyclic arrangement or some combination thereof. An alkyl substituent to structure is chain of carbon atoms that is covalently attached to structure through sp ³ carbon of substituent. The alkyl substituents, as used herein, contains one or more saturated moieties or groups and may additionally contain unsaturated alkyl moieties or groups, i.e., substituent may comprise one, two, three or more independently selected double bonds or triple bonds of combination thereof, typically one double or one triple bond if such unsaturated alkyl moieties or groups are present. Unsaturated alkyl moieties or groups include moieties or groups as described below for alkenyl, alkynyl, cycloalkyl, and aryl moieties. Saturated alkyl moieties contain saturated carbon atoms (sp ³ ) and no aromatic, sp ² or sp carbon atoms. The number of carbon atoms in an alkyl moiety or group can vary and typically is 1 to about 50, e.g., about 1-30 or about 1-20, unless otherwise specified, e.g., C1-8 alkyl or C1-C8 alkyl means an alkyl moiety containing 1, 2, 3, 4, 5, 6, 7 or 8 carbon atoms and C _1-6 alkyl or C ₁ -C ₆ means an alkyl moiety containing 1, 2, 3, 4, 5 or 6 carbon atoms. When an alkyl substituent, moiety or group is specified, species may include methyl, ethyl, 1-propyl (n-propyl), 2-propyl (iso-propyl, —CH(CH3)2), 1-butyl (n-butyl), 2- methyl-1-propyl (iso-butyl, —CH ₂ CH(CH ₃ ) ₂ ), 2-butyl (sec-butyl, —CH(CH ₃ )CH ₂ CH ₃ ), 2-methyl-2-propyl (t-butyl, —C(CH3)3), amyl, isoamyl, sec-amyl and other linear, cyclic and branch chain alkyl moieties. Unless otherwise specified, alkyl groups can contain species and groups described below for cycloalkyl, alkenyl, alkynyl groups, aryl groups, arylalkyl groups, alkylaryl groups and the like. Cycloalkyl as used herein is a monocyclic, bicyclic or tricyclic ring system composed of only carbon atoms. The term “cycloalkyl” encompasses a monocyclic or polycyclic aliphatic, non-aromatic radical, wherein each of the atoms forming the ring (i.e. skeletal atoms) is a carbon atom. The number of carbon atoms in an cycloalkyl substituent, moiety or group can vary and typically is 3 to about 50, e.g., about 1-30 or about 1-20, unless otherwise specified, e.g., C _3-8 alkyl or C3-C8 alkyl means an cycloalkyl substituent, moiety or group containing 3, 4, 5, 6, 7 or 8 carbon atoms and C _3-6 alkyl or C3-C6 means an cycloalkyl substituent, moiety or group containing 3, 4, 5 or 6 carbon atoms. Cycloalkyl substituents, moieties or groups will typically have 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms and may contain exo or endo- cyclic double bonds or endo-cyclic triple bonds or a combination of both wherein the endo-cyclic double or triple bonds, or the combination of both, do not form a cyclic conjugated system of 4n+2 electrons; wherein the bicyclic ring system may share one (i.e., spiro ring system) or two carbon atoms and the tricyclic ring system may share a total of 2, 3 or 4 carbon atoms, typically 2 or 3. Unless otherwise specified, cycloalkyl substituents, moieties or groups can contain moieties and groups described for alkenyl, alkynyl, aryl, arylalkyl, alkylaryl and the like and can contain one or more other cycloalkyl moieties. Thus, cycloalkyls may be saturated, or partially unsaturated. Cycloalkyls may be fused with an aromatic ring, and the points of attachment to the aromatic ring are at a carbon or carbons of the cycloalkyl substituent, moiety or group that is not an aromatic ring carbon atom. Cycloalkyl groups include groups having from 3 to 10 ring atoms. Cycloalkyl substituents, moieties or groups include cyclopropyl, cyclopentyl, cyclohexyl, adamantly or other cyclic all carbon containing moieties. Cycloalkyls further include cyclobutyl, cyclopentenyl, cyclohexenyl, cycloheptyl and cyclooctyl. Cycloalkyl groups may be substituted or unsubstituted. Depending on the substituent structure, a cycloalkyl substituent can be a monoradical or a diradical (i.e., an cycloalkylene, such as, but not limited to, cyclopropan-1,1-diyl, cyclobutan-1,1-diyl, cyclopentan-1,1-diyl, cyclohexan-1,1-diyl, cyclohexan-1,4-diyl, cycloheptan-1,1-diyl, and the like). When cycloalkyl is used as a Markush group (i.e., a substituent) the cycloalkyl is attached to a Markush formula with which it is associated through a carbon involved in a cyclic carbon ring system carbon of the cycloalkyl group that is not an aromatic carbon. “Alkylamine” as used herein means —N(alkyl)xHy group, moiety or substituent where x and y are independently selected from group x=1, y=1 and x=2, y=O. Alkylamine includes—N(alkyl) _x H _y groups where x=2 and y=0 and alkyl groups taken together with nitrogen atom to which they are attached form a cyclic ring system. “Alkenyl” or “alkene” as used herein means a substituent, moiety or group that comprises one or more double bond moities (e.g., —CH═CH—) or 1, 2, 3, 4, 5 or 6 or more, typically 1, 2 or 3 such moieties and can include an aryl moiety or group such as benzene, and additionally comprises linked normal, secondary, tertiary or cyclic carbon atoms, i.e., linear, branched, cyclic or any combination thereof unless the alkenyl moiety is a vinyl moiety (e.g., —CH═CH2). An alkenyl moiety, group or substituent with multiple double bonds may have the double bonds arranged contiguously (i.e. a 1, 3 butadienyl moiety) or non-contiguously with one or more intervening saturated carbon atoms or a combination thereof, provided that a cyclic, contiguous arrangement of double bonds do not form a cyclically conjugated system of 4n+2 electrons (i.e., aromatic). The number of carbon atoms in an alkenyl group or moiety can vary and typically is 2 to about 50, e.g., about 2-30 or about 2-20, unless otherwise specified, e.g., C2-8 alkenyl or C2-8 alkenyl means an alkenyl moiety containing 2, 3, 4, 5, 6, 7 or 8 carbon atoms and C _2-6 alkenyl or C ₂ -6 alkenyl means an alkenyl moiety containing 2, 3, 4, 5 or 6 carbon atoms. Alkenyl moieties or groups will typically have 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. When an alkenyl moiety, group or substituent is specified, species include, by way of example and not limitation, any of the alkyl or cycloalkyl, groups moieties or substituents described herein that has one or more double bonds, methylene methylmethylene (═CH—CH3), ethylmethylene (═CH—CH2—CH3), ═CH—CH2—CH2—CH3, vinyl (—CH═CH2), allyl, 1-methylvinyl, butenyl, iso-butenyl, 3-methyl-2-butenyl, 1-pentenyl, cyclopentenyl, 1-methyl-cyclopentenyl, 1-hexenyl, 3-hexenyl, cyclohexenyl and other linear, cyclic and branched chained all carbon containing moieties containing at least one double bond. When alkenyl is used as a Markush group (i.e., a substituent) the alkenyl is attached to a Markush formula with which it is associated through an unsaturated carbon of a double bond of the alkenyl moiety or group unless specified otherwise. “Alkynyl” or “alkyne” as used herein means a substituent, moiety or group that comprises one or more triple bond moieties (i.e., —C≡C—), e.g., 1, 2, 3, 4, 5, 6 or more, typically 1 or 2 triple bonds, optionally comprising 1, 2, 3, 4, 5, 6 or more double bonds, with the remaining bonds (if present) being single bonds and comprising linked normal, secondary, tertiary or cyclic carbon atoms, i.e., linear, branched, cyclic or any combination thereof, unless the alkynyl moiety is ethynyl. The number of carbon atoms in an alkenyl moiety or group can vary and typically is 2 to about 50, e.g., about 2-30 or about 2-20, unless otherwise specified, e.g., C _2-8 alkynyl or C ₂ -8 alkynyl means an alkynyl moiety containing 2, 3, 4, 5, 6, 7 or 8 carbon atoms. Alkynyl groups will typically have 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. When an alkynyl moiety or group is specified, species include, by way of example and not limitation, any of the alkyl moieties, groups or substituents described herein that has one or more double bonds, ethynyl, propynyl, butynyl, iso-butynyl, 3-methyl-2-butynyl, 1-pentynyl, cyclopentynyl, 1-methyl-cyclopentynyl, 1-hexynyl, 3-hexynyl, cyclohexynyl and other linear, cyclic and branched chained all carbon containing moieties containing at least one triple bond. When an alkynyl is used as a Markush group (i.e., a substituent) the alkynyl is attached to a Markush formula with which it is associated through one of the unsaturated carbons of the alkynyl functional group. “Aryl” as used here means an aromatic ring system or a fused ring system with no ring heteroatoms comprising 1, 2, 3 or 4 to 6 rings, typically 1 to 3 rings, wherein the rings are composed of only carbon atoms; and refers to a cyclically conjugated system of 4n+2 electrons (Huckel rule), typically 6, 10 or 14 electrons some of which may additionally participate in exocyclic conjugation (cross-conjugated (e.g., quinone). Aryl substituents, moieties or groups are typically formed by five, six, seven, eight, nine, or more than nine, carbon atoms. Aryl substituents, moieties or groups are optionally substituted. Exemplary aryls include C ₆ -C ₁₀ aryls such as phenyl and naphthalenyl and phenanthryl. Depending on the structure, an aryl group can be a monoradical or a diradical (i.e., an arylene group). Exemplary arylenes include, but are not limited to, phenyl-1,2-ene, phenyl-1,3-ene, and phenyl-1,4-ene. When aryl is used as a Markush group (i.e., a substituent) the aryl is attached to a Markush formula with which it is associated through aromatic carbon of the aryl group. “Arylalkyl” as used herein means a substituent, moiety or group where an aryl moiety is bonded to an alkyl moiety, i.e., -alkyl-aryl, where alkyl and aryl groups are as described above, e.g., —CH2—C6H5 or —CH2CH(CH3)—C6H5. When arylalkyl is used as a Markush group (i.e., a substituent) the alkyl moiety of the arylalkyl is attached to a Markush formula with which it is associated through a sp ³ carbon of the alkyl moiety. “Alkylaryl” as used herein means substituent, moiety or group where alkyl moiety is bonded to aryl moiety, i.e.,-aryl-alkyl, where aryl and alkyl groups are as described above, e.g. —C ₆ H ₄ —CH ₃ or —C ₆ H ₄ —CH ₂ CH(CH ₃ ). When alkylaryl is used as Markush group (i.e., substituent), aryl moiety of alkylaryl is attached to Markush formula with which it is associated through sp ² carbon of the aryl moiety. “Substituted alkyl”, “substituted cycloalkyl”, “substituted alkenyl”, “substituted alkynyl”, substituted alkylaryl”, “substituted arylalkyl”, “substituted heterocycle”, “substituted aryl” and the like as used herein mean alkyl, alkenyl, alkynyl, alkylaryl, arylalkyl heterocycle, aryl or other group or moiety as defined or disclosed herein that has substituent(s) that replaces hydrogen atom(s) or substituent(s) that interrupts carbon atom chain. Alkenyl and alkynyl groups that comprise substituent(s) are optionally substituted at carbon that is one or more methylene moieties removed from double bond. “Heterocycle” or “heterocyclic” or “heteroaryl” as used herein means a cycloalkyl or aromatic ring system wherein one or more, typically 1, 2 or 3, but not all of the carbon atoms comprising the ring system are replaced by a heteroatom which is an atom other than carbon, including, N, O, S, Se, B, Si, P, typically N, O or S wherein two or more heteroatoms may be adjacent to each other or separated by one or more carbon atoms, typically 1-17 carbon atoms, 1-7 atoms or 1-3 atoms. Heterocycles includes heteroaromatic rings (also known as heteroaryls) and heterocycloalkyl rings (also known as heteroalicyclic groups) containing one to four heteroatoms in the ring(s), where each heteroatom in the ring(s) is selected from O, S and N, wherein each heterocyclic group has from 4 to 10 atoms in its ring system, and with the proviso that the any ring does not contain two adjacent O or S atoms. Non-aromatic heterocyclic, substituents, moieties or groups (also known as heterocycloalkyls) have at least 3 atoms in their ring system and aromatic heterocyclic groups have at least 5 atoms in their ring system and include benzo-fused ring systems. Heterocyclics with 3, 4, 5, 6 and 10 atoms include aziridinyl azetidinyl, thiazolyl, pyridyl and quinolinyl, respectively. Nonaromatic heterocyclic substituents, moieties/groups are pyrrolidinyl, tetrahydrofuranyl, dihydrofuranyl, tetrahydrothienyl, oxazolidinonyl, tetrahydropyranyl, dihydropyranyl, tetrahydrothiopyranyl, piperidinyl, morpholinyl, thiomorpholinyl, thioxanyl, piperazinyl, aziridinyl, azetidinyl, oxetanyl, thietanyl, homopiperidinyl, oxepanyl, thiepanyl, oxazepinyl, diazepinyl, thiazepinyl, 1,2,3,6- tetrahydropyridinyl, pyrrolin-2-yl, pyrrolin-3-yl, indolinyl, 2H-pyranyl, 4H-pyranyl, dioxanyl, 1,3-dioxolanyl, pyrazolinyl, dithianyl, dithiolanyl, dihydropyranyl, dihydrothienyl, dihydrofuranyl, pyrazolidinyl, imidazolinyl, imidazolidinyl, 3- azabicyclo[3.1.0)hexanyl, 3azabicyclo[4.1.0)heptanyl, 3H-indolyl and quinolizinyl. Aromatic heterocyclic includes, by way of example and not limitation, pyridinyl, imidazolyl, pyrimidinyl, pyrazolyl, triazolyl, pyrazinyl, tetrazolyl, furyl, thienyl, isoxazolyl, thiazolyl, oxazolyl, isothiazolyl, pyrrolyl, quinolinyl, isoquinolinyl, indolyl, benzimidazolyl, benzofuranyl, cinnolinyl, indazolyl, indolizinyl, phthalazinyl, pyridazinyl, triazinyl, isoindolyl, pteridinyl, purinyl, oxadiazolyl, thiadiazolyl, furazanyl, benzofurazanyl, benzo-thiophenyl, benzothiazolyl, benzoxazolyl, quinazolinyl, quinoxalinyl, naphthyridinyl and furopyridinyl. Non-aromatic heterocycles may be substituted with one or two oxo (═O) moieties and includes pyrrolidin-2-one. “Heteroaryl” as used herein means an aryl ring system wherein one or more, typically 1, 2 or 3, but not all of the carbon atoms comprising the aryl ring system are replaced by a heteroatom which is an atom other than carbon, including, N, O, S, Se, B, Si, P, typically, oxygen (—O—), nitrogen (—NX—) or sulfur (—S—) where X is —H, protecting group or C _1-6 optionally substituted alkyl, wherein heteroatom participates in conjugated system either through pi-bonding with adjacent atom in ring system or through lone pair of electrons on heteroatom and may be optionally substituted on one or more carbons or heteroatoms, or combination of both, in manner which retains cyclically conjugated system. Examples of heteroaryls include by way of example and not limitation pyridyl, thiazolyl, pyrimidinyl, furanyl, thienyl, pyrrolyl, pyrazolyl, purinyl, imidazolyl, benzofuranyl, indolyl, isoindoyl, quinolinyl, isoquinolinyl, benzimidazolyl, pyridazinyl, pyrazinyl, benzothiopyran, benzotriazine, isoxazolyl, pyrazolopyrimidinyl, quinoxalinyl, thiadiazolyl, and triazolyl. Heterocycles that are not heteroaryls include, by way of example and not limited to, tetrahydrothiophenyl, tetrahydrofuranyl, indolenyl, piperidinyl, pyrrolidinyl, 2-pyrrolidonyl, tetrahydroquinolinyl, tetrahydroisoquinolinyl, decahydroquinolinyl, octahydroisoquinolinyl, 2H-pyrrolyl, 3H-indolyl, 4H-quinolizinyl, imidazolidinyl, imidazolinyl, pyrazolidinyl, piperazinyl, quinuclidinyl, morpholinyl and oxazolidinyl. Monocyclic heteroaryls include, by way of example and not limitation, pyridinyl, imidazolyl, pyrimidinyl, pyrazolyl, triazolyl, pyrazinyl, tetrazolyl, furyl, thienyl, isoxazolyl, thiazolyl, oxazolyl, isothiazolyl, pyrrolyl, pyridazinyl, triazinyl, oxadiazolyl, thiadiazolyl, and furazanyl. Heteroaryls include those substituents, moieties or groups containing 0-3 N atoms, 1-3 N atoms or 0-3 N atoms, 0-1 O atoms and 0-1 S atoms. A heteroaryl may be monocyclic or bicyclic. The ring system of a heteroaryls ring typically contains 1-9 carbons (i.e., C1-C9 heteroaryl). Monocyclic heteroaryls include C ₁ -C ₅ heteroaryls. Monocyclic heteroaryls include those having 5-membered or 6- membered ring systems. Bicyclic heteroaryls include C6-C9 heteroaryls. Depending on the structure, a heteroaryl group can be a monoradical or a diradical (i.e., a heteroarylene group). “Ether” as used herein in the terms “aryl ether, alkyl ether, aryl alkyl ether, alkoxy alkyl ether, alkyne alkyl ether, and alkylene alkyl ether” mean an organic moiety, group or substituent that comprises or consists of 1, 2, 3, 4 or more —O— moieties, usually 1 or 2, wherein no two —O— moieties are immediately adjacent (i.e., directly attached) to each other. Typically, ethers comprise an organic moiety containing 1-50 carbon atoms, 1-20 carbon atoms or 1-8 carbon atoms and 0 to 10 independently selected heteroatoms (e.g., O, S, N, P, Si), typically 0-2. An ether moiety, group or substituent includes organic moiety-O— wherein the organic moiety is as described herein for alkyl or optionally substituted alkyl group. When ether is used as a Markush group (i.e., a substituent) the oxygen of the ether functional group is attached to a Markush formula with which it is associated. When ether is a used as substituent in a Markush group it is sometimes designated as an “alkoxy” group. Alkoxy includes C1-C4 ether substituents such as, by way of example and not limited to, methoxy, ethoxy, propoxy, iso-propoxy and butoxy. Ether further includes those substituents, moieties or groups that contain one (excluding ketal) or more —OCH2CH2O—, moieties in sequence (polyethylene or PEG moieties). “Halogen” or “halo” as used herein means fluorine, chlorine, bromine or iodine. “Hydroxyl” as used herein means –OH, and the “alkylhydroxyl” means –OH is attached to alkyl groupl; wherein alkyl group is as defined above. “Haloalkyl” as used herein means an alkyl substituent moiety or group in which one or more of its hydrogen atoms are replaced by one or more independently selected halide atoms. Haloalkyl includes C1-C4 haloalkyl. Example but non-limiting C1-C4 haloalkyls are —CH2Cl, CH2Br, —CH2I, —CHBrCl, —CHCl—CH2Cl and —CHCl—CH2I. “Haloalkylene” as used herein means an alkylene substituent, moiety or group in which one or more hydrogen atoms are replaced by one or more halide atoms. Haloalkylene includes C1-C6 haloalkylenes or C1-C4 haloalkylenes. “Fluoroalkyl” as used herein means an alkyl in which one or more hydrogen atoms are replaced by a fluorine atom. Fluoroalkyl includes C ₁ -C ₆ and C ₁ -C ₄ fluoroalkyls. Example but non-limiting fluoroalkyls include —CH3F, —CH2F2 and —CF3 and perfluroalkyls. “Fluoroalkylene” as used herein means an alkylene in which one or more hydrogen atoms are replaced by a fluorine atom. Fluoroalkylene includes C ₁ -C ₆ fluoroalkylenes or C ₁ -C ₄ fluoroalkylenes. The term “heteroalkyl” refers to an alkyl group in which one or more skeletal atoms of the alkyl are selected from an atom other than carbon, e.g., oxygen, nitrogen, sulfur, phosphorus or combinations thereof. In one aspect, a heteroalkyl is a C1-C6 heteroalkyl. As used herein, the term “alkylene”, employed alone or in combination with other terms, refers to a divalent alkyl linking group. Examples of alkylene groups include, but are not limited to, ethan-1,2-diyl, propan-1,3-diyl, propan-1,2-diyl, butan-1,4-diyl, butan-1,3- diyl, butan-1,2-diyl, 2-methyl-propan-1,3-diyl, and the like. As used herein, the term “alkoxy”, employed alone or in combination with other terms, refers to a group of formula —O-alkyl, wherein the alkyl group as defined above. Example alkoxy groups include but not limited to methoxy, ethoxy, propoxy (e.g., n- propoxy and isopropoxy), t-butoxy, and the like. As used herein, the term “alkylalkoxy”, employed alone or in combination with other terms, refers to a group of formula —alkyl- O-alkyl, wherein the alkyl group is as defined above. As used herein, the term “alkylamino” refers to a group of formula —NH(alkyl), wherein the alkyl group is as defined above. As used herein, the term “arylamino” refers to a group of formula —NH(aryl), wherein the aryl or aromatic group is as defined above. As used herein, the term “alkoxycarbonyl” refers to a group of formula —C(O)O-alkyl, wherein the alkyl group is as defined above. As used herein, the term “alkylcarbonylamino” refers to a group of formula — NHC(O)-alkyl, wherein the alkyl group is as defined above. As used herein, the term “alkylsulfonylamino” refers to a group of formula —NHS(O)2- alkyl, wherein the alkyl group is as defined above. As used herein, the term “aminosulfonyl” refers to a group of formula —S(O) ₂ NH ₂ . As used herein, the term “alkylaminosulfonyl” refers to a group of formula — S(O)2NH(alkyl), wherein the alkyl group is as defined above. As used herein, the term “aminocarbonyl”, employed alone or in combination with other terms, refers to a group of formula —NHC(O)-. As used herein, the term “alkylaminocarbonyl”, employed alone or in combination with other terms, refers to a group of formula —alkyl-NHC(O)- or —NHC(O)-alkyl-. As used herein, the term “alkylacylamino”, employed alone or in combination with other terms, refers to a group of formula —alkyl-C(O)-alkyl/aryl/heteroparyl-NH2. As used herein, the term “aminocarbonylamino”, employed alone or in combination with other terms, refers to a group of formula —NHC(O)NH ₂ . As used herein, the term “sulfanyl” or “thio” refers to a group of formula —SH. As used herein, the term “alkylthio” or “alkylsulfanyl” refers to a group of formula —S-alkyl, wherein the alkyl group is as defined above. As used herein, the term “arylthio” or “arylsulfanyl” refers to a group of formula —S-aryl, wherein the aryl group is as defined above. As used herein, the term “heteroarylthio” or “heteroarylsulfanyl” refers to a group of formula —S-heteroaryl, wherein the heteroaryl group is as defined above. As used herein, the term “sulfonyl” refers to a group of formula —S(O) ₂ -. As used herein, the term “alkylsulfonyl” refers to a group of formula —S(O)2-alkyl, wherein the alkyl group is as defined above. As used herein, the term “arylsulfonyl” refers to a group of formula —S(O) ₂ -aryl, wherein the aryl group is as defined above. As used herein, the term “heteroarylsulfonyl” refers to a group of formula —S(O)2-heteroaryl, wherein the heteroaryl group is as defined above. As used herein, the term “sulfonyloxy” refers to a group of formula —S(O) ₂ -O-. As used herein, the term “alkylsulfonyloxy” refers to a group of formula —S(O) ₂ -O-alkyl, wherein the alkyl group is as defined above. As used herein, the term “sulfinyl” refers to a group of formula —S(O)-. As used herein, the term “alkylsulfinyl” refers to a group of formula —S(O)-alkyl, wherein the alkyl group is as defined above. As used herein, the term “arylsulfinyl” refers to a group of formula —S(O)-aryl, wherein the aryl group is as defined above. As used herein, the term “amino” refers to a group of formula —NH ₂ . As used herein, the term “carbamyl” to a group of formula —C(O)NH2. As used herein, the term “carbonyl”, employed alone or in combination with other terms, refers to a —C(O)— group. As used herein, the term “alkylcarboxy” refers to a group of formula —C(O)OH connected with at least one of alkyl group. As used herein, the term “dialkylamino” refers to a group of formula —N(alkyl)2, wherein the two alkyl groups each is as defined above. As used herein, the term “alkyl cycloalkyl” refers to a group of formula —alkyl attached to cycloalkyl group, wherein the alkyl and cycloalkyl groups each are as defined above. As used herein, “haloalkoxy” refers to a group of formula —O-haloalkyl where alkyl and halo/halogen is as defined above. An example haloalkoxy group is OCF3. In some embodiments, the haloalkoxy group is fluorinated only. As used herein, the term “haloalkyl”, employed alone or in combination with other terms, refers to an alkyl group having from one halogen atom to 2 s+1 halogen atoms which may be the same or different, where “s” is the number of carbon atoms in the alkyl group, wherein the alkyl and halo is as defined above. As used herein, “haloaryl” refers to a group of formula — halo-aryl where aryl and halo/halogen is as defined above. The compounds described herein can be asymmetric (e.g., having one or more stereocenters). All stereoisomers, such as enantiomers, geometric isomers, and diastereomers, are intended unless otherwise indicated. Compounds of the present invention that contain asymmetrically substituted carbon atoms can be isolated in optically active or racemic forms. Methods on how to prepare optically active forms from optically inactive starting materials are known in the art, such as by resolution of racemic mixtures or by stereoselective synthesis. Many geometric isomers of olefins, C═N double bonds, and the like can also be present in the compounds described herein, and all such stable isomers are contemplated in the present invention. Cis and trans geometric isomers of the compounds of the present invention are described and may be isolated as a mixture of isomers or as separated isomeric forms. In some embodiments, the compound has the (R)-configuration. In some embodiment, compound has (S)-configuration. The term, “compound,” used herein is meant to include all stereoisomers, geometric iosomers, tautomers, and isotopes of structures depicted. Compounds herein identified by name or structure as one particular tautomeric form are intended to include other tautomeric forms unless otherwise specified. All compounds, and pharmaceutically acceptable salts thereof, can be found together with other substances such as water and solvents (e.g. hydrates and solvates) or can be isolated. The expressions, “ambient temperature” and “room temperature” or “rt” as used herein, are understood in the art, and refer generally to a temperature, e.g. a reaction temperature, that is about the temperature of the room in which the reaction is carried out, for example, a temperature from about 20° C. to about 30° C. In general embodiment, the present invention relates to the mixed-donor (PN ³ N)Mn(I) complexes (catalyst of formula I) for the chemoselective hydrogenation of C=C, C=O and C=N bonds using 5 bar H ₂ and a mild base K3PO4 at room temperature (refer Figure 1). The notable features of the present invention are: (i) use of 3 ^rd most abundant transition metal as a catalyst, (ii) excellent chemoselectivity in the reduction of C=C, C=O and C=N bonds, (iii) hydrogenation using 5 bar H2 and at room temperature (27 ^o C), (iv) use of mild base and atom-efficient H2 source, and (v) broad substrates scope with excellent tolerance of hydrogen-sensitive functionalities. In an embodiment, the present invention provides a manganese based catalyst complex of Formula I, for hydrogenation of substrate wherein the substrate is select from α, β- unsaturated ketone, aldehyde and imine (of Formula IIA or IIB); the formula I is represented by: Formula I wherein, Mn is manganese atom or manganese ion in oxidation state (I); moieties attached to said Mn are selected from heteroaryl rings, one or more carbon monoxide groups, -PR ³ R ⁴ -NR ² and X, wherein said nitrogen of -PR ³ R ⁴ -NR ² is further attached to said one of heteroaryl rings, and wherein said heteroaryl rings are selected from pyridine and diazole; wherein R ¹ is selected from the group consisting of hydrogen, (C1-C4)alkyl, aryl, alkyl aryl, alkoxy, cycloalkyl, alkyl cycloalkyl, and alkylcarboxy; R ² is selected from the group consisting of hydrogen and (C1-C4)alkyl; R ³ is selected from group consisting of (C1-C4)alkyl, unsubstituted aryl, substituted aryl and cycloalkyl; R ⁴ is selected from the group consisting of(C1-C4)alkyl, unsubstituted aryl, substituted aryl and cycloalkyl; and X is selected from the group consisting of halide, organosulfonate oxoanion (triflate), boron trifluoride, and tetrafluoroborate; wherein R ¹ and R ² may be identical or different, and R ³ and R ⁴ are substituents of phosphine moiety. In another embodiment, the Mn complex of formula I is defined by R1 being hydrogen, R2 being hydrogen or C1-C4alkyl, R3 being C1-C4alkyl or aryl, R4 being C1-C4alkyl or aryl, and X being halogen. Said Mn based catalyst comprises a mixed-donor ligand with different electronic features of donating center which suitably administer the electronic requirement at the metal center (Mn) and stabilize the active catalytic species. Moreover, the presence of NH on the side-arm could facilitate the non-innocent behavior of ligand via aromatization/dearomatization approach leading to the heterolytic activation of molecules. In another embodiment, the present disclosure provides a process of preparation of a novel manganese catalyst (Formula I) under mild conditions which comprising reacting compound of formula III and substituted pentacarbonylmanganese [Mn(CO) ₅ X] at room temperature to yield a novel manganese catalyst (Formula I) Formula III wherein R ¹ , R ² , R ³ , R ⁴ and X are same as defined above under formula I. In an additional embodiment, the present disclosure provides a process of preparation of novel manganese catalyst of Formula I, the steps comprising: a) reacting 0.16-0.24 mmol of compound of formula III with 0.16-0.24 mmol of substituted pentacarbonylmanganese [Mn(CO) ₅ X] in a container such as round bottom flask with a solvent to obtain a reaction mixture Formula III wherein R ¹ , R ² , R ³ , R ⁴ and X are same as defined above under formula I; b) stirring the reaction mixture under inert atmosphere at temperature in the range of 27- 80 ^o C for a time period of up to 48 hrs; c) purifying the mixture to obtain the manganese catalyst of Formula I. In preferred embodiment, the compound of formula III used in step a) is selected from N- (di-tert-butylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amin e (L3), N-(di-n- propylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine (L2), N- (diphenylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine (L1), and N-(di-tert- butylphosphaneyl)-N-methyl-6-(1H-pyrazol-1-yl)pyridin-2-amin e (L4). In another preferred embodiment, the solvent used in step a) is selected from THF (tetrahydrofuran), 2-methyl THF, and toluene. In another preferred embodiment, the amount of compound of formula III used in the reaction is inert atmosphere in step a) is attained by argon or helium. In yet another preferred embodiment, the amount of compound of formula III used in the reaction is 0.16 mmol, 0.20 mmol or 0.24 mmol. In yet another preferred embodiment, amount of compound of formula III and substituted pentacarbonylmanganese used in reaction is 0.16 mmol, 0.20 mmol or 0.24 mmol respectively. In another embodiment, the novel manganese catalyst (Formula I) for hydrogenation of α, β-unsaturated ketones, aldehydes and imines (of Formula IIA or IIB), is selected from group consisting of: 1. N-(diphenylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine-M n(CO) ₂ Br complex(1a) (Mn-1) 2. N-(di-iso-propylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-am ine-Mn(CO)2Br complex (1b) (Mn-2) 3. N-(di-tert-butylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-am ine Mn(CO)2Br complex (1c) (Mn-3) 4. N-(di-tert-butylphosphaneyl)-N-methyl-6-(1H-pyrazol-1-yl)pyr idin-2-amine Mn(CO) ₂ Br complex (1d) (Mn-4) . Interestingly considering the characterization data of all complexes Mn-1 to Mn-3 and 1d, it displayed three IR peaks for carbonyls ranging between 1857-2053 cm ^-1 . Similarly, closer look at the ¹³ C{ ¹ H}-NMR spectra of complexes indicate the three carbonyl signals. Moreover, and ¹³ C{ ¹ H}-NMR spectra of all complexes display two sets of peaks. All these observations support formation of two geometrical isomeric species in each complex Mn-1, Mn-2, Mn-3 and 1d. Considering presence of three signals for carbonyls in each complexes, inventors noted that one isomer of Mn-complex would have two carbonyls that are trans to –Br and –N _py ligands accounting for two peaks (as indicated in X-ray structure), whereas the other isomer would have two carbonyls trans to each other and display a single carbonyl peak (refer, Figure 2). All the complexes are further characterized by ESI-MS that show two prominent isotopic masses for ⁷⁹ Br and ⁸¹ Br containing complexes. The molecular structure of Mn-2 was confirmed by a single crystal X-ray study (Figure 3). As expected, the coordination geometry around the manganese is distorted octahedral with –Br and one –CO unit trans to each other, making the C9 ^Mn1 ^Br angle almost linear (175.54(15) ^o ). Mn1 ^C10 bond length [1.797(4) Å] is slightly longer than Mn1 ^C9 bond length [1.773(4) Å], which is due to greater trans influence of –N _py than –Br. The process for hydrogenation of various substrates such as α, β-unsaturated ketones, aldehydes, and imines (of Formula IIA or IIB) by using a novel manganese catalyst (Formula I) are successfully done and represented in detail in figures 3 and 4. These figures 3 and 4 enlist the hydrogenated compounds from substrates using said manganese catalyst (Formula I) namely compounds 4 to 55 with yields ranging from 33 to 97% or 60 to 97% of yield. The characterization data for these compounds 4-55 are well determined using 1H-NMR, C13-NMR and HRMS, and the same are in line with the data as reported in the literature known reports. In another embodiment of present invention, a substrate i.e. α, β-unsaturated ketones, aldehyde, ketone or imine (of Formula IIA or IIB) is hydrogenated to yield hydrogenated product (Formula IV), Formula IV wherein X is oxo group (O) or or nitrogen (NR ¹ ) group, where R ¹ is alkyl or aryl moiety; R is hydrogen, alkyl (C1-C10), (un)substituted aryl, (un)substituted heteroaryl, alkene, alkyne; A and Y is independently selected from hydrogen, alkyl (C1-C10), (un)substituted aryl, (un)substituted heteroaryl, alkene, alkyne, ferrocene, alkoxy, where the substituted aryl or heteroaryl maybe further substituted with aryl, alkoxy, alkyl, halogen, nitro, cyano, aryl ether, alkyl ether, aryl alkyl ether, CF3, (un)substituted amino, alkyl amino, aryl amino, ferrocene, alkoxy alkyl ether, alkyne alkyl ether, alkylene alkyl ether, hydroxyl, cyclic saturated or unsaturated ring of aryl or heteroaryl with number of rings from 0 to 4; B is selected from hydrogen, alkene, alkyne, alkyl, aryl, heteroaryl, ferrocene, halogen; and A and B together may form saturated or unsaturated ring of aryl or heteroaryl which may further be substituted with hydrogen, alkyl, aryl, heteroaryl, hydroxyl, alkylhydroxyl, alkyl aryl ether, aryl alkyl ether, nitro, cyano, halogen. The hydrogenated products catalyzed by the novel manganese catalyst (Formula I) of α,β-unsaturated ketones, aldehydes, and imines (of Formula IIA or IIB) is selected from group consisting of: (i) 1-(3-(Allyloxy)phenyl)-3-phenylpropan-1-one (2a) (ii) 3-Phenyl-1-(3-(prop-2-yn-1-yloxy)phenyl)propan-1-one (2b) (iii) 1-(3-(Oxiran-2-ylmethoxy)phenyl)-3-phenylpropan-1-one (2c) (iv) 2-(4-Acetylphenoxy)-1,3-diphenylpropan-1-one (2d) In preferred embodiment, the present disclosure provides a process for hydrogenation of various substrates such as α, β-unsaturated ketones, aldehydes, and imines (of Formula IIA or IIB) by using a novel manganese catalyst (Formula I) comprises of: (i) Reacting a substrate such as α, β-unsaturated ketones (Formula IIA) in presence of Mn-catalyst (Formula I) (1-5 mol%), base (2-10 mol%) in dry vial with stir bar, inside the glove box; (ii) Transferring the reaction vial to an autoclave under argon atmosphere; (iii) Adding polar solvent and pressurizing autoclave with H2 (5-50 bar) and venting for five times; (iv) Pressurizing the autoclave with 5-50 bar H ₂ and stirring (500-800 rpm) at room temperature (27-50 ^o C) for 1-24 h; (v) After reaction time, the reaction mixture is concentrated and subjected to column chromatography on silica gel wherein petroleum ether and ethyl acetate is present in the ratio of 70:1 respectively, after separation and purification, to yield desired hydrogenated products. The base is selected from the group consisting of potassium carbonate, potassium phosphate, potassium hydroxide, potassium tert-butoxide, sodium tert-butoxide, sodium carbonate, cesium carbonate, sodium hydroxide, lithium carbonate, lithium hydroxide, calcium hydroxide, potassium bicarbonate, sodium bicarbonate, sodium methoxide, lithium bicarbonate and tertiary amines, most preferably base used in the present invention is Tripotassium phosphate. Solvents used in the present invention include simple alcohols, such as C1-10 hydrocarbyl alcohols, often saturated aliphatic C1-8alcohols, for example, ethanol, isopropanol and tert-butanol; polyvalent alcohols such as ethylene glycol, propylene glycol, 1,2-propanediol and glycerol; ethers, for example tetrahydrofuran (THF) 1,4- dioxane, methyl tert-butyl ether, cyclopentyl methyl ether; aliphatic and aromatic hydrocarbon solvents, for example C5-12alkanes, benzene, toluene and xylene and halogenated (typically chlorinated) hydrocarbon solvents, for example dichloromethane and chlorobenzene, or mixtures thereof, in particular, mixtures of alcohols, for example ethanol or isopropanol, and hydrocarbon solvents such as hexanes, xylenes (i.e. isomeric mixtures) or toluene. According to particular embodiments of present invention, methanol is used as a solvent. Suitable temperature to conduct the reaction at step i) is in the range of 20 °C-40 °C. In particularly useful embodiment, reaction at step i) is conducted at 27°C and the duration of hydrogenation reaction is quite low, preferably time requires is 1 hour to 5 hours. The methods of the invention, as is typical for hydrogenation reactions, are conducted in the presence of hydrogen gas, under pressure. Generally, the pressure at which the reactions are conducted is in the range of about 1 bar (100 kPa) to about 100 bar (10,000 kPa), for example from about 20 bar (2,000 kPa) to about 80 bar (8,000 kPa), although higher or lower pressures may on occasion be convenient, pressure at which hydrogenation reaction of the present invention is carried out is much lower, 5 bar. According to one aspect of the present invention, catalyzing the hydrogenation of various substrates especially ketones require low catalyst loading. According to one aspect of present invention, compound comprising a charged or neutral complex of formula (I), wherein —N is substituted one or more times with the second electron donating group and at least one of R ¹ and R ² are substituted one or more times with the first electron donating group. According to one aspect of the present invention, form of Mn-catalyst and compound of Formula (I) is amorphous. The Mn catalyst with an acidic NH on the ligand backbone. This acidic NH initiate the catalytic process by the aromatization/dearomatization process and make the present system the best catalysts at room temperature. It also selectively hydrogenates one double bond over the other. According to one aspect of the present invention, ligands are tridentate attached to Mn complex represents tridentate neutral or anionic ligand. Specifically, the present invention provides a chemoselective hydrogenation of C=C, C=O and C=N bonds in α,β-unsaturated ketones, aldehydes and imines at room temperature using the Mn catalyst of formula I at 5.0 bar H2. Amongst the Mn catalysts disclosed, the ^t Bu-substituted complex Mn(CO)2Br shows an exceptional chemoselective catalytic reduction of unsaturated bonds in a wide range of α,β-unsaturated ketones/aldehydes/imines. This hydrogenation tolerates a range of highly sensitive functionalities, such as halides (-F, -Cl, -Br, -I), alkoxy, hydroxy and epoxide, including hydrogen sensitive moieties like acetyl, nitrile, nitro, unconjugated alkenyl and alkynyl groups. C=C bond is chemoselectively hydrogenated in α,β-unsaturated ketones, whereas aldehyde’s C=O bond and imine’s C=N bond are preferentially reduced over C=C bond using developed Mn catalyst. Comprehensive mechanistic investigation by controlled studies endorsed the non- innocent behaviour of ligand in the Mn-catalyst and supported a de- aromatization/aromatization pathway by retaining the oxidation state of Mn(I). The DFT energy calculations highlighted a probable rate-influencing H2 activation with facile progress of other elementary steps. Particularly, the H2 provided a hydride-source and solvent alcohol (e.g. MeOH, propanol, etc.) gave proton-source for the hydrogenation reaction. Proposed mechanistic cycle was unanimously supported by the DFT energy calculations. In a nutshell, the present invention provides an efficient protocol for the chemoselective hydrogenation of C=C, C=O and C=N bonds in α,β-unsaturated ketones, aldehydes and imines catalyzed by the well-defined pincer-ligated Mn(I) complex of formula I. The employment of a mild base, moderate H2 pressure and room temperature (27 ^o C) in the Mn-catalyzed hydrogenation are highly advantageous to the commonly employed KO ^t Bu base and extreme reaction conditions. The mixed donor Mn(I) complexes of formula I, ^ ³ -( ^R2 PN ³ N ^Pyz )Mn(CO)2Br (R = Ph, ⁱ Pr, ^t Bu) were synthesized and meticulously characterized by various techniques. Though both the ⁱ Pr and ^t Bu-substituted Mn(I) complexes are efficient for the hydrogenation of α,β-unsaturated ketones, the ( ^tBu2 PNN ^Pyz )Mn(CO) ₂ Br complex as a catalyst provided exceptional chemoselectivity for the reduction of C=C bond (1,4-hydrogen addition). Thus, using the beneficial molecular hydrogen and a mild K3PO4 base, the ( ^tBu2 PNN ^Pyz )Mn(I) catalyst could hydrogenate diverse unsaturated ketones to saturated ketones at room temperature with the compatibility of sensitive functionalities, such as halides ( ^F, ^Cl, ^Br, ^I), alkoxy, hydroxy, epoxide, acetyl, nitrile, nitro, unconjugated alkenyl and alkynyl groups. The C=O bond in aldehydes and C=N bond in imines were preferentially hydrogenated (1,2- hydrogen addition) over the C=C bond using the Mn-3 catalyst. EXAMPLES The ligand precursor 6-(1H-pyrazol-1-yl)pyridin-2-amine, ligands L1 and L3 were prepared according to the previously described procedures (refer, D. Gong et al., J. Mol. Catal. A Chem., 2014, 395, 100-107; H. Chen et al., Polym. Chem., 2017, 8, 1805-1814; and D. Gong et al., Dalton Trans., 2016, 45, 19399-19407) Example 1: Synthesis of N-(di-iso-propylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin- 2-amine (L2): In 50 mL oven dried Schlenk flask, 6-(1H-pyrazol-1-yl)pyridin-2-amine (0.20 g, 1.25 mmol) was dissolved in THF (10 mL) followed by addition of freshly distilled Et3N (0.21 S4 mL, 1.5 mmol) under inert atmosphere. Reaction mixture was cooled to 0ºC and chlorodiisopropylphosphine (0.21 g, 1.37 mmol) was added dropwise. The reaction mixture was allowed to room temperature and stirred for 1 h. Further reaction mixture was cooled to -78ºC and n-BuLi (0.94 mL, 1.5 mmol; 1.6 M in THF) was added dropwise resulting in colorless solution. Then reaction was allowed to room temperature and stirred for 1 h, followed by heating at 60 ºC for 16 h. Volatiles were evaporated under vacuum and 30 mL of toluene was added into it. Filtration and evaporation of toluene extract gave N-(diiso-propylphosphaneyl)-6-(1H-pyrazol-1- yl)pyridin-2-amine (L2; 0.27 g, 78%) as colorless liquid.1H-NMR (500 MHz, C6D6): δ = 8.65 (d, J = 2.1 Hz, 1H, Ar–H), 7.68-7.66 (m, 2H, Ar–H), 7.13 (t, J = 8.1 Hz, 1H, Ar– H), 6.95 (dd, J = 7.9, 2.2 Hz, 1H, Ar–H), 6.14 (dd, J = 2.4, 1.5 Hz, 1H), 4.55 (br s, 1H, NH), 1.41 (d sept, J = 6.9, 1.7 Hz, 2H, CH), 0.90 (dd, J = 16.2, 7.3 Hz, 6H, CH3), 0.86 (dd, J = 11.0, 7.0 Hz, 6H, CH3). 13C{1H}-NMR (125 MHz, C6D6): δ = 160.4 (d, J = 20.0 Hz, Cq), 151.4 (Cq), 142.2 (CH), 140.6 (CH), 127.0 (CH), 107.7 (CH), 106.4 (d, J = 17.2 Hz, CH), 103.0 (CH), 26.8 (d, J = 12.4 Hz, 2C, CH), 19.2 (CH3), 19.0 (CH3), 17.5(CH3), 17.4(CH3).31P{1H}-NMR(162 MHz, C6D6):48.6 (s). Example 2: N-(Di-tert-butylphosphaneyl)-N-methyl-6-(1H-pyrazol-1-yl)pyr idin-2- amine (L4): In 50 mL round bottom flask, N-(di-tert-butylphosphaneyl)-6-(1H-pyrazol- 1- yl)pyridin-2-amine (0.10 g, 0.33 mmol) in THF (5 mL) was cooled to -20 oC and n- BuLi (0.25 mL, 0.40 mmol; 1.6 M in hexane) was added followed by the addition of MeI (0.055 g, 0.39 mmol). The reaction mixture was allowed to the room temperature and stirred for overnight. The volatiles were evaporated under vacuo and 20 mL of water was added. The organic layer was extracted in EtOAc and the crude product was subjected to the column chromatography on silica gel (petroleum ether/EtOAc:10/1) to yield L3Me (0.071 g, 68%) as white solid.1H-NMR (500 MHz, CDCl3): δ = 8.30 (d, J = 2.4 Hz, 1H, Ar–H), 7.66 (s, 1H, Ar–H), 7.36 (dt, J = 7.9, 2.1 Hz, 1H, Ar–H), 7.04 (d, J = 7.5 Hz, 1H, Ar–H), 6.51 (d, J = 8.1 Hz, 1H), 6.37 (t, J = 2.1 Hz, 1H, Ar–H), 1.83 (d, J = 11.1 Hz, 3H, CH3), 1.34 (d, J = 14.1 Hz, 18H, CH3). 13C{1H}-NMR (100 MHz, CDCl3): δ = 164.4 (d, J = 9.2 Hz, Cq), 149.8 (Cq), 140.9 (CH), 138.6 (d, J = 3.8 Hz, CH), 126.3 (CH), 116.1 (d, J = 22.1 Hz, CH), 106.5 (CH), 98.5 (CH), 36.4 (d, J = 65.6 Hz, 2C, Cq), 27.2 (6C, CH3), 5.6 (d, J = 42.0 Hz, CH3).31P{1H}- NMR (162 MHz, CDCl3): 36.9 (s) Example 3: Synthesis and characterization of Mn-catalyst (1a)(Mn-1): In a 25 mL round bottom flask N-(diphenylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2- amine (L1, 0.084 g, 0.24 mmol) and Mn(CO) ₅ Br (0.067 g, 0.24 mmol) was added inside the glove box. The reaction flask was taken out and THF (3 mL) was added. Reaction mixture was stirred under inert atmosphere at room temperature (27 ºC) for 20 h. Within this time complex has been precipitated out. The solvent was evaporated under vacuum and solid was washed with hexane (3 mL X 3 times) and dried under vacuum to give yellow powder of Mn-1 complex (0.090 g, 70 %). FT-IR (νCO, cm-1): 1935, 1865, 1857. 1H-NMR (500 MHz, DMSOd6): (one isomer): δ = 10.34 (br s, 1H), 9.15 (br s, 1H), 8.57 (br s, 1H), 8.10 (br s, 1H), 7.77- 7.42 (m, 11H), 7.28 (br s, 1H), 6.92 (br s, 1H); (other isomer): δ = 10.02 (br s, 1H), 8.99 (br s, 1H), 8.22 (br s, 1H), 7.96 (br s, 1H), 7.77- 7.42 (m, 11H), 7.16 (br s, 1H), 6.77 (br s, 1H). 13C{1H}-NMR (125 MHz, DMSO-d6): (for both isomers) δ = 229.3, 225.3, 223.8, 160.0, 147.4, 146.1, 144.9, 141.5, 139.9, 136.2, 130.9, 129.8, 129.5, 128.9, 128.1, 127.7, 127.0, 125.7, 110.9, 106.7, 99.3. 31P NMR (162 MHz, DMSO-d6, ppm): 136.89 (s), 134.54 (s). ESI-MS (–ve mode): m/z [M– H]– Calcd for [C22H17 79BrMnN4O2P–H] 532.9569, Found 532.9575; m/z [M–H]– Calcd for [C22H1781BrMnN4O2P–H] 534.9549, Found 534.9554. Example 4: Synthesis and characterization of Mn-catalyst (1c)(Mn-2): This catalyst was synthesized following the procedure similar to the synthesis of Mn-1 (example 1), using N-(di-iso-propylphosphaneyl)-6-(1Hpyrazol-1-yl)pyridin-2-ami ne (L2; 0.060 g, 0.217 mmol) and Mn(CO)5Br (0.060 g, 0.218 mmol). The complex Mn-2 was obtained as an orange powder. Yield: 0.090 g (89%). FT-IR (νCO, cm-1): 1940, 1872, 1857. 1H-NMR (400 MHz, DMSO-d6): (one isomer): δ = 9.15 (br s, 1H), 8.92 (br s, 1H), 8.49 (br s, 1H), 7.94 (br s, 1H), 7.53 (br s, 1H), 7.03 (br s, 1H), 6.91 (br s, 1H), 1.30-1.18 (m, 14H); (other isomer): δ = 9.13 (br s, 1H), 8.80 (br s, 1H), 8.10 (br s, 1H), 7.79 (br s, 1H), 7.40 (br s, 1H), 6.91 (br s, 1H), 6.72 (br s, 1H), 1.18-1.09 (m, 14H). 13C{1H}-NMR (100 MHz, DMSO-d6): (one isomer): δ = 230.2 (d, J = 15.3 Hz, CO), 226.6 (d, J = 22.9 Hz, CO), 161.0 (d, J = 9.5 Hz, Cq), 147.4 (Cq), 146.1 (CH), 141.1 (CH), 130.9 (CH), 111.4 (CH), 106.5 (CH), 98.8 (CH), 29.7, 26.4, 18.1, 17.4; (other isomer): δ = 227.0 (d, J = 19.1 Hz, CO), 225.8 (d, J = 22.9 Hz, CO), 160.6 (d, J = 9.5 Hz, Cq), 147.4 (Cq), 144.3 (CH), 139.5 (CH), 129.3 (CH), 110.6 (CH), 105.2 (CH), 98.1 (CH), 26.5, 25.8, 17.3, 16.5. 31P{1H}-NMR (162 MHz, DMSO-d6, ppm): 159.8 (s), 158.4 (s). ESI-MS (–ve mode): m/z [M–H]– Calcd for [C16H21 79BrMnN4O2P–H] 464.9882, Found 464.9887; m/z [M–H]– Calcd for [C16H21 81BrMnN4O2P–H] 466.9862, Found 466.9866. Example 5: Synthesis and characterization of Mn-catalyst (1c) (Mn-3) In a 25 mL round bottom flask N-(di-tert-butylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin- 2-amine (L3, 0.050 g, 0.16 mmol) and Mn(CO)5Br (0.045 g, 0.16 mmol) was added inside the glove box. The reaction flask was taken out and THF (3 mL) was added. Reaction mixture was stirred under inert atmosphere at room temperature (27 ^o C) for 48 h. By the time the color of reaction mixture was changed from yellow to red. The reaction mixture was concentrated to 0.5 mL. Then hexane was added through the wall to give the orange precipitate of the desired complex. Then the solid was washed with hexane (10 mL x 3 times) and dried under vacuum to give orange solid of complex (0.064 g, 82 %). Note: The synthesized Mn-3 is sensitive to light, hence stored in brown colored vial. FT-IR (νCO, cm-1): 2053, 1959, 1930. ³¹ P NMR (162 MHz, CD ₂ Cl ₂ , ppm): 178.51 (s), 175.26 (s). ³¹ P NMR (162 MHz, CD3OD, ppm): 176.62 (s), 171.27 (s). ¹ H- NMR (200 MHz, CD3OD): δ = 8.46 (d, J = 24.3 Hz, 1H, Ar–H), 7.79 (s, 1H, Ar–H), 7.56 (s, 1H, Ar–H), 7.07 (s, 1H, Ar–H), 6.75 (s, 1H, Ar–H), 6.44 (d, J = 18.3 Hz, 1H, Ar–H), 2.95 (s, 1H, NH), 0.96 (t, J = 14.5 Hz, 18H, CH ₃ ). ESI-MS (–ve mode): m/z [M– H]– Calcd for [C18H25 79BrMnN4O2P–H] 493.0195, Found 493.0197; m/z [M–H]– Calcd for [C18H25 81BrMnN4O2P–H] 495.0175, Found 495.0178. Elemental anal. Calcd for C ₁₈ H ₂₅ BrMnN ₄ O ₂ P: C, 43.66; H, 5.09; N, 11.31. Found: C, 43.37; H, 5.26; N, 11.04. IR (νCO, cm ^-1 ): 1959, 1930. Example 6: Synthesis and characterization of Mn-catalyst (1d) (Mn-4): This complex was synthesized following the procedure similar to the synthesis of Mn-1, using N-(di-tert-butylphosphaneyl)-N-methyl-6- (1H-pyrazol-1-yl)pyridin-2-amine (L4, 0.042 g, 0.132 mmol) and Mn(CO)5Br (0.036 g, 0.131 mmol), and the reaction mixture was stirred at room temperature (27 ºC) for 16 h. The complex Mn-3Me was obtained as an orange powder. Yield: 0.060 g (85%). FT-IR (νCO, cm1 ): 2018, 1924, 1901. 1H- NMR (500 MHz, acetone-d6): δ = 8.67 (br s, 1H, Ar–H), 8.21 (br s, 1H, Ar–H), 7.45 (br s, 1H, Ar–H), 7.02 (br s, 1H, Ar–H), 6.73 (br s, 1H, Ar–H), 6.63 (br s, 1H, Ar–H), 1.93 (s, 3H, CH3), 1.43 (d, J = 12.8 Hz, 18H, CH3).13C{1H}-NMR (125 MHz, DMSO-d6): δ = 224.2 (CO), 223.9 (CO), 223.1 (CO), 164.9 (Cq), 148.3 (Cq), 144.0 (CH), 138.1 (CH), 129.7 (CH), 112.0 (CH), 110.5 (CH), 96.4 (CH), 36.2 (d, J = 63.6 Hz, 2C Cq), 25.8 (d, J = 30.5 Hz, 6C, CH3), 5.1 (d, J = 42.0 Hz, CH3). 31P{1H}-NMR (162 MHz, acetoned6): 41.5 (s). Example 7: General procedure for hydrogenation of substrates. A substrate such as α, β-unsaturated ketones or aldehydes or imines (of Formula IIA or IIB) in presence of Mn-catalyst (Formula I) (5mol%), base (10 mol%) was reacted in dry vial with stir bar, inside the glove box. Reaction vial was transferred to autoclave under argon atmosphere. Polar solvent was added and pressurized autoclave with H2 (5 bar) and vented for five times. The autoclave was pressurized with 5 bar H ₂ and stirred (700 rpm) at 27 ^o C for 1 h. After reaction time, reaction mixture was concentrated and subjected to column chromatography on silica gel where petroleum ether & ethyl acetate was used in ratio of 70:1, after separation and purification, yielded desired hydrogenated products. Table 1. Optimization of Reaction Parameters

^a Reaction Conditions: 4a (0.042 g, 0.20 mmol), base (0.02 mmol), [Mn] catalyst (0.01 mmol, 5 mol %), solvent (1.0 mL). ^b GC conversion, isolated yield is given in parentheses. ^c 20% allylic alcohol was observerd. ^d Using 6.0 mol% K3PO4. ^e Using 3 mol% of Mn-3. ^f Using 3 mol% of Mn-3 and 6 mol% of K3PO4. bpy = 2,2’-bipyridine, phen = 1,10-phenanthroline, dppf = 1,1′-bis(diphenylphosphino)ferrocene, dppbz = 1,2- bis(diphenylphosphino)benzene. All three manganese complexes contain mixture of two geometrical isomers. Example 8: Synthesis of 1,3-diphenylpropan-1-one: To a dry vial with stir bar was introduced catalyst I (0.005 g, 0.01 mmol), K3PO4 (0.0043 g, 0.02 mmol), and (E)-chalcone (0.042 g, 0.202 mmol) inside the glove box. The reaction vial was transferred to an autoclave under argon atmosphere. Then MeOH (1.0 mL) was added and the autoclave was pressurized with H2 (5 bar) and vented for five times. Finally, the autoclave was pressurized with 5 bar H ₂ and stirred (700 rpm) at room temperature (27 ^o C) for 1 h. After reaction time, the reaction mixture was concentrated and subjected to column chromatography on silica gel (petroleum ether/EtOAc: 70/1) to yield 1,3-diphenylpropan-1-one (0.041 g, 97%) as white solid. ¹ H-NMR (500 MHz, CDCl ₃ ): δ = 7.95 (d, J = 7.4 Hz, 2H, Ar–H), 7.54 (t, J = 7.4 Hz, 1H, Ar–H), 7.44 (t, J = 7.6 Hz, 2H, Ar–H), 7.31-7.18 (m, 5H, Ar–H), 3.29 (t, J = 7.7 Hz, 2H, CH2), 3.06 (t, J = 7.7 Hz, 2H, CH2). ¹³ C{ ¹ H}-NMR (125 MHz, CDCl3): δ = 199.4 (CO), 144.4 (Cq), 137.0 (C _q ), 133.2 (CH), 128.8 (2C, CH), 128.7 (2C, CH), 128.6 (2C, CH), 128.2 (2C, CH), 126.3 (CH), 40.6 (CH ₂ ), 30.3 (CH ₂ ). HRMS (ESI): m/z Calcd for C ₁₅ H ₁₄ O + H ⁺ [M + H] ⁺ 211.1117; Found 211.1115. Example 9: Synthesis of 1-(3-(Allyloxy)phenyl)-3-phenylpropan-1-one (2a) (15): The representative procedure was followed, using substrate (E)-1-(3-(allyloxy)phenyl)-3- phenylprop-2-en-1-one (0.053 g, 0.201 mmol) and the reaction mixture was stirred at room temperature (27 oC) for 3 h. Purification by column chromatography on silica gel (petroleum ether/EtOAc: 50/1) yielded 1-(3-(Allyloxy)phenyl)-3-phenylpropan-1-one (0.039 g, 73%) as yellow oil.1H-NMR (400 MHz, CDCl3): δ = 7.54 (d, J = 7.8 Hz, 1H, Ar–H), 7.51-7.50 (m, 1H, Ar–H), 7.35 (t, J = 7.9 Hz, 1H, Ar–H), 7.30 (t, J = 7.3 Hz, 2H, Ar–H), 7.26-7.19 (m, 3H, Ar–H), 7.12 (dd, J = 8.3, 2.0 Hz, 1H, Ar–H), 6.10-6.01 (m, 1H, CH), 5.43 (dd, J = 17.3, 1.5 Hz, 1H, CH), 5.31 (dd, J = 10.6, 1.4 Hz, 1H, CH), 4.57 (d, J = 5.3 Hz, 2H, CH2), 3.28 (t, J = 7.7 Hz, 2H, CH2), 3.06 (t, J = 7.6 Hz, 2H, CH2). 13C{1H}-NMR (100 MHz, CDCl3): δ = 199.4 (CO), 159.3 (Cq), 141.7 (Cq), 138.7 (Cq), 133.3 (CH), 130.1 (CH), 129.0 (2C, CH), 129.0 (2C, CH), 126.6 (CH), 121.3 (CH), 120.6 (CH), 118.4 (CH2), 113.8 (CH), 69.4 (CH2), 41.0 (CH2), 30.6 (CH2). HRMS (ESI): m/z Calcd for C18H18O2 + H+ [M + H]+ 267.1380; Found 267.1373. Example 10: Synthesis of 3-Phenyl-1-(3-(prop-2-yn-1-yloxy)phenyl)propan-1-one (2b) (16): The representative procedure was followed, using substrate (E)-3-phenyl-1-(3-(prop-2- yn-1-yloxy)phenyl)prop-2-en-1-one (0.053 g, 0.202 mmol) and the reaction mixture was stirred at room temperature (27 ^o C) for 3 h. Purification by column chromatography on silica gel (petroleum ether/EtOAc: 50/1) yielded 3-Phenyl-1-(3-(prop-2-yn-1- yloxy)phenyl)propan-1-one (0.037 g, 69%) as yellow oil.1H-NMR (400 MHz, CDCl3): δ = 7.57 (d, J = 8.1 Hz, 2H, Ar–H), 7.38 (t, J = 7.9 Hz, 1H, Ar–H), 7.30 (t, J = 7.4 Hz, 2H, Ar–H), 7.26-7.16 (m, 4H, Ar–H), 4.73 (d, J = 2.3 Hz, 2H, CH2), 3.28 (t, J = 7.7 Hz, 2H, CH2), 3.06 (t, J = 7.6 Hz, 2H, CH2), 2.53 (t, J = 2.2 Hz, 1H, CH). 13C{1H}-NMR (100 MHz, CDCl3): δ = 198.9 (CO), 157.9 (Cq), 141.4 (Cq), 138.4 (Cq), 129.8 (CH), 128.7 (2C, CH), 128.6 (2C, CH), 126.3 (CH), 121.6 (CH), 120.4 (CH), 113.7 (CH), 78.2 (Cq), 76.1 (CH), 56.1 (CH2), 40.7 (CH2), 30.3 (CH2). HRMS (ESI): m/z Calcd for C18H16O2 + H+ [M + H]+ 265.1223; Found 265.1217. Example 11: Synthesis of 1-(3-(Oxiran-2-ylmethoxy)phenyl)-3-phenylpropan-1-one (2c) (17): The representative procedure was followed, using substrate (E)-1-(3-(oxiran-2- ylmethoxy)phenyl)-3-phenylprop-2-en-1-one (0.057 g, 0.203 mmol) and the reaction mixture was stirred at room temperature (27 oC) for 4 h. Purification by column chromatography on silica gel (petroleum ether/EtOAc: 30/1) yielded 1-(3-(Oxiran-2- ylmethoxy)phenyl)-3-phenylpropan-1-one (0.039 g, 68%) as yellow oil. 1H-NMR (400 MHz, CDCl3): δ = 7.56 (d, J = 7.8 Hz, 1H, Ar–H), 7.50 (t, J = 1.9 Hz, 1H, Ar–H), 7.36 (t, J = 7.9 Hz, 1H, Ar–H), 7.30 (t, J = 7.3 Hz, 2H, Ar–H), 7.26-7.19 (m, 3H, Ar–H), 7.14 (dd, J = 2.5, 0.6 Hz, 1H, Ar–H), 4.30 (dd, J = 11.0, 2.9 Hz, 1H, CH), 3.97 (dd, J = 11.0, 5.9Hz, 1H, CH), 3.39-3.35 (m, 1H, CH), 3.29 (t, J = 7.6 Hz, 2H, CH2), 3.06 (t, J = 7.6 Hz, 2H, CH ₂ ), 2.92 (t, J = 4.5 Hz, 1H, CH ₂ ), 2.67 (dd, J = 4.9 Hz, 2.63 Hz, 1H, CH ₂ ). ¹³ C{ ¹ H}-NMR (100 MHz, CDCl ₃ ): δ = 199.1 (CO), 158.9 (C _q ), 141.4 (C _q ), 138.4 (C _q ), 129.9 (CH), 128.7 (2C, CH), 128.6 (2C, CH), 126.3 (CH), 121.4 (CH), 120.3 (CH), 113.2 (CH), 69.1 (CH2), 50.2 (CH), 44.7 (CH2), 40.7 (CH2), 30.3 (CH2). HRMS (ESI): m/z Calcd for C ₁₈ H ₁₈ O ₃ + H ⁺ [M + H] ⁺ 283.1329; Found 283.1223. Example 12: Synthesis of 2-(4-Acetylphenoxy)-1,3-diphenylpropan-1-one (2d) (40): The representative procedure was followed, using substrate (Z)-2-(4-acetylphenoxy)-1,3- diphenylprop-2-en-1-one (0.069 g, 0.202 mmol) and the reaction mixture was stirred at room temperature (27 oC) for 3 h. Purification by column chromatography on silica gel (petroleum ether/EtOAc: 30/1) yielded 2-(4-Acetylphenoxy)-1,3-diphenylpropan-1-one (0.040 g, 57%) as yellow solid. 1H-NMR (500 MHz, CDCl3): δ = 8.04 (d, J = 7.9 Hz, 2H, Ar–H), 7.82 (d, J = 8.8 Hz, 2H, Ar–H), 7.61 (t, J = 7.4 Hz, 1H, Ar–H), 7.48 (t, J = 7.8 Hz, 2H, Ar–H), 7.32-7.23 (m, 5H, Ar–H), 6.84 (d, J = 8.9 Hz, 2H, Ar–H), 5.61 (dd, J = 7.4, 5.3 Hz, 1H, CH), 3.36-3.34 (m, 2H, CH2), 2.48 (s, 3H, CH3). 13C{1H}-NMR (125 MHz, CDCl3): δ = 197.4 (CO), 196.8 (CO), 161.5 (Cq), 136.6 (Cq), 134.4 (Cq), 134.2 (CH), 131.2 (Cq), 130.8 (2C, CH), 129.5 (2C, CH), 129.1 (2C, CH), 128.9 (2C, CH), 128.8 (2C, CH), 127.3 (CH), 115.1 (2C, CH), 81.8 (CH), 39.4 (CH2), 26.5 (CH3). HRMS (ESI): m/z Calcd for C23H20O3 + H+ [M + H]+ 345.1485; Found 345.1478. ADVANTAGES OF THE INVENTION ^ The present invention provides process of hydrogenation wherein the novel manganese catalyst used for hydrogenation of various substrates such as α,β- unsaturated ketones, aldehydes, and imines (of Formula IIA or IIB). ^ Hydrogenation of various substrates such as α,β-unsaturated ketones , aldehydes, and imines (of Formula IIA or IIB) is carried out at room temperature and low H2 pressure, wherein lower temperature conditions are quite suitable to yield high purified and selectively hydrogenated products. ^ Use of 3 ^rd most abundant transition metal as catalyst. ^ Excellent chemoselectivity in the reduction of C=C, C=O and C=N. ^ Hydrogenation at pressure of 5 bar H2 and room temperature. ^ Use of mild base and atom-efficient H ₂ source. ^ Provides broad substrates scope with excellent tolerance of hydrogen-sensitive functionalities. ^ Using the sustainable molecular hydrogen and a mild K3PO4 base, the Mn catalyst of formula I hydrogenate diverse unsaturated ketones at room temperature with the compatibility of sensitive functionalities, such as halides (- F, -Cl, -Br, -I), alkoxy, hydroxy, epoxide, acetyl, nitrile, nitro, unconjugated alkenyl and alkynyl groups. ^ Additionally, a wide range of heteroarenes like indole, pyrrole, furan, thiophene, and pyridine derived unsaturated ketones could be chemoselectively hydrogenated to the corresponding saturated ketones. ^ The C=O bond in aldehydes and C=N bond in imines were preferentially hydrogenated over the C=C bond using the Mn catalyst at an extremely mild reaction conditions.