ARGAZZI ROBERTO (IT)
SCANDOLA FRANCO (IT)
BIGNOZZI CARLO ALBERTO (IT)
ARGAZZI ROBERTO (IT)
SCANDOLA FRANCO (IT)
| WO1994004497A1 | 1994-03-03 |
DEMAS J N ET AL: "Preparation and thin-layer chromatography of cis-dicyanobis(2,2'-bipyridine)ruthenium(II)", INORG. CHEM. (INOCAJ);69; VOL.8 (3); PP.674-5, WASHINGTON STATE UNIV.;PULLMAN; WASH., XP000615837
BIGNOZZI C A ET AL: "Bis(bipyridine)ruthenium(II) cyano-bridged polymeric cations", INORG. CHIM. ACTA (ICHAA3,00201693);84; VOL.86 (2); PP.133-6, UNIV. FERRARA;IST. CHIM.; FERRARA; 44100; ITALY (IT), XP000613457
ARGAZZI R ET AL: "Enhanced Spectral Sensitivity from Ruthenium(II) Polypyridyl Based Photovoltaic Devices", INORG. CHEM. (INOCAJ,00201669);94; VOL.33 (25); PP.5741-9, CNR;CENTRO DI STUDIO SU FOTOREATTIVITA E CATALISI; FERRARA; 44100; ITALY (IT), XP000612748
Field of the invention
The present invention refers to a process for the preparation of mononuclear compounds of general formula (I) and (II)
Ru(dcbH 2 ) 2 (X) 2 (I)
Ru(dcbH 2 ) 2 (Y) (II) wherein : dcbH 2 is 4, -dicarboxy-2,2'-bipyridine; X is a mono-dentate ligand and Y is a bi-dentate ligand useful as inorganic dyes for the sensibilisation of semiconductors of type n, as for example titanium dioxide. Such dyes are used, for example, in photoelectrochemical regenerating cells based on nanocrystalline electrods of titanium dioxide. State of the art
In literature [see: M.Z.Nazeeruddin et al. J.Am.Chem.Soc. 1993. H5.
6382; Heimer T.A. et al. J.Phys.Chem. 1993, 97. 11987; Argazzi R. et al. Inorg. Chem. 199*4, 33. 57*^1] processes for the preparation of compounds of formula (I) and (II) as above said are described comprising, as reaction intermediate, the complex Ru(dcbH 2 ) 2 ( c l)2t or its deprotonated form Ru(dcb) 2 (Cl) , obtained by neutralisation of
Ru(dcbH 2 )(Cl) 2 .
The above said complex is obtained by reaction of RuClo hydrate , commercially available , with dcbH 2 . in organic solvents , as for example DMF, at boiling point. Although the reaction itself runs with good yield, the quantity of final product obtained is limited because
of the low solubility of the ligand dcbH 2 and, moreover, the process involves the use of toxic organic solvent with the related problems.
Summary of the invention
The object of the present invention is a process for the preparation of mononuclear compounds of general formula (I) and (II)
Ru(dcbH 2 ) 2 (X) 2 (I)
Ru(dcbH 2 ) 2 (Y) (II) wherein: dcbH 2 is 4 ,4 ' -dicarboxy-2 , 2 ' -bipyridine X is a mono-dentate ligand
Y is a bi-dentate ligand wherein : a) a pentachlororuthenium complex or ruthenium trichloride hydrate is reacted with an excess of potassium or sodium oxalate b) the mixture of step (a) is added with an excess of 4,4'dicarboxy-
2,2-bipyridine, in the form of sodium or potassium salt, in order to obtain the complex Ru(deb) - > (C 2 0 / !) c) the complex of step (b) is reacted with an excess of mono-dentate ligand (X) or bi-dentate ligand (Y) d) the final product is precipitated by adding acid.
Detailed description of the invention
The present invention allows to overcome the above said problems by a process comprising as reaction-intermediate the complex
Ru(dcb) (C 2 0* j ) , wherein deb represents the bianionic form of the ligand 4. '-dicarboxy-2,2'-bipyridine. The process gives high yields allowing the preparation of high quantities of final compounds in aqueous solution and in mild reaction conditions.
The process according to the present invention can be represented by the following reactions:
Ru(dcb) 2 (C 2 0 il ) Z|" + 2 X " > Ru(dcb) 2 (X) 2 i+"
Ru(dcb) 2 (X) 2 i|" + 4 H + > Ru(dcbH 2 )(X) 2 The complex Ru(dcb) 2 (C 2 0 * j ) can be prepared by various methods. Examples of such methods are reported hereinafter.
The synthesis of the intermediate Ru(dcb) (C 2 0 * | ) puts no limit to the production of the wanted dyes; it can in fact be prepared in high quantities with high yield. Moreover, such intermediate can be prepared in aqueous solution and in mild conditions. According to an embodiment of the present invention the commercial product pentachlororuthenium hydrate K 2 Ru(Cl)c is reacted in water with an excess (10-30 folds, preferably 20 folds) of sodium- or potassium- oxalate at 60 β - 100'C, preferably 80 * C. The sodium or potassium salt of 4,4'-dicarboxy-2,2'-bipyridine (Na 2 dcb or K 2 dcb) is added and let react in order to obtain the complex Ru(dcb) 2 (C 2 0* ) 4" ; the complex Ru(dcbH ) 2 ( C 0 4 ι ) is thereafter precipitated by adding an acid, preferably HClOi, and isolated. The obtained complex is dissolved in water by adding NaOH up to neutrality and reacted for 3"6 hours, preferably 4 hours, with an appropriated excess of mono-dentate ligand (X) or bi-dentate ligand (Y), at 60° - 100 β C, preferably 80"C, and the final product is precipitated by adding an acid. According to a different embodiment of the invention ruthenium trichloride Ru(Cl) hydrate, commercially available, is reacted at reflux temperature in aqueous solution with an excess (3-6 folds, preferably 4 folds) of sodium or potassium oxalate in the presence of
ethyl alcohol. The ligand Na 2 dcb or K 2 dcb is added, preferably 50°C and drop by drop, and the mixture is heated at 60° - 100'C, preferably
80 β C.
At this point two different reaction-pathways can be followed: -(1) the complex Ru(dcbH 2 ) 2 (C 2 θ4) is isolated by adding an acid, preferably perchloric acid, and thereafter reacted with an excess of the mono-dentate ligand (X) or bi-dentate ligand (Y) as described above; or -(2) an excess of mono-dentate ligand (X) or bi-dentate ligand (Y) is added directly in the solution and the heating is continued for some hours at 60 β -100 * C, preferably 8θ"C; the product is thereafter precipitated by adding an acid.
In the present invention mono-dentate ligand means, for example, an halide, thiocyanate (NCS~), cyanide CN " etc.; bi-dentate ligand means, for example, polypyridine, dithiocarbamate, alpha'-bipyridine possibly substituted. 1,10-phenanthroline, ethylenediamine, etc..
The invention will be better understood in the light of the following examples. EXAMPLE 1
10 g of K 2 Ru(Cl)c hydrate are reacted for 1 hour with 100 g of potassium oxalate and 15 g. of the sodium salt of 4,4'-dicarboxy-2,2'- bipyridine (Na dcb) in 600 ml distilled water at 80°C. The solution is acidified and 15 g of Ru(dcbH 2 ) 2 (C^) precipitate (yield 83 ). The product is neutralized with NaOH and dissolved in 500 ml of distilled water.
37 g of NaNCS are added and reacted at 75 * C for 4 h. Acid is added up
to the total precipitation of product. The solid is dissolved in acetone and the solution is filtered and dried on rotating evaporator. According to the above described procedure 14 g of Ru(dcbH 2 ) 2 (NCS) 2 are obtained, corresponding to the conversion of Ru(dcbH ) 2 (C 2 0^) into the final product with a yield of 90 . EXAMPLE 2
10 g of RuCl hydrate are reacted with 27 g of potassium oxalate in 300 ml distilled water. To the solution 0 ml of ethyl alcohol are added and the mixture is refluxed for 4 h. This procedure permits to obtain the complex which can be isolated or directly reacted in the same aqueous solution with 22 g Na 2 dcb, for 4 h at 80 β C. The adding of an acid to the reaction mixture allows to obtain 19 g of the intermediate Ru(dcbH 2 ) 2 (C 2 0* j ) (yield 73 ). The product can be converted, for example, in Ru(dcbH 2 ) 2 (NCS) 2 as described in Example 1.
Alternatively, the solution containing the complex prepared as above described, is directly reacted with 22 g Na dcb for 4 h at 80 β C and thereafter with 44 g NaNCS at 80°C for 4 h. The product is finally isolated by adding acid. The solid is dissolved in acetone and the solution filtered and dried on rotating evaporator. By this procedure 19 g of Ru(dcbH ) (NCS) 2 are obtained, corresponding to the total conversion of ruthenium trichloride into the final product with a yield of 70%. EXAMPLE 10 g of RuClo are reacted with 27 g of potassium oxalate in 300 ml distilled water. To the solution 60 ml of ethyl alcohol are added and the solution is refluxed for 4 h. The reaction mixture is cooled to
room temperature and pH adjusted to 7 by adding NaOH IM. The reaction mixture is heated to 50°C and a solution containing 22 g of Na ? dcb in 350 ml of distilled water is added thereto. The addition is performed drop by drop in 2 hours. The reaction mixture is heated to 70 β C and let react for 2 more hours. The solution is cooled to room temperature and filtered.
To the filtered solution 700 ml of HC10 /j 2M are added under stirring. The precipitate is separated by centrifugation and washed twice with 300 ml HClO- j 0.5 M (each). The precipitate is suspended in 300 ml acetone/ether (3:1) and the stirring maintained for 15 minutes.
The above said procedure permits to obtain 22 g of oxalate-complex Ru(dcbH 2 ) 2 (C 0 /j ) (yield 84%). The product is converted in the dye Ru(dcbH) 2 (NCS) 2 as described hereinafter. 22 gr of Ru(dcbH) 2 (C 2 0/) are dissolved in 500 ml distilled water by adding NaOH IM up to pH 1.
50 g of NaNCS are added to the solution and the mixture kept at 70°C for 4 h. The mixture is cooled to room temperature and HCl 2M is added up to pH 1-1.5 under stirring. The precipitate is collected by centrifugation and resuspended in HCl IM under stirring for 30 minutes. The step is repeated twice until the eentrifugated solution is pale yellow or almost colourless.
The precipitate, Ru(dcbH 2 ) 2 (NCS) 2 is eentrifugated. dissolved in acetone and the solution is filtered and evaporated in rotating evaporator. 22 g of Ru(dcbH 2 ) 2 (020 * 4)2 are obtained (yield 95% calculated on Ru(dcbH 2 ) 2 (C 2 0ii)).