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Synthesis and physico-chemical properties of diruthenium(III, II) tetra-aryl carboxylato compounds
PolyhedronVol. 7. No. 9. pp. 685-687. 1988 Printed in Great Britain
0277-5387/88 $3.00+.00 Pergamon Press plc
SYNTHESIS AND PHYSICO-CHEMICAL PROPERTIES OF DIRUTHENIUM(III, II) TETRA-ARYL CARBOXYLATO COMPOUNDS BIRINCHI K. D A S and AKHIL R. C H A K R A V A R T Y *
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560012, India (Received 4 November 1987 ; accepted 16 December 1987)
Abstract--Monochloro-tetra-/~-aryl-carboxylatodiruthenium(llI, II) compounds RuzCI (O2CAr)4 (Ar = -C6H5; -C6H4-p-OCH3), are prepared and characterized. The compounds have magnetic moments that correspond to three unpaired spins per dimer. The Ru--Ru bond order is 2.5 and the ground electronic configuration is cr27z462 (6,n,)3. The visible spectral band is observed at ca 450 nm along with a shoulder near 580 nm in DMF solution. The compounds undergo a one-electron Ru(III)Ru(II)--, Ru(II)Ru(II) quasi-reversible reduction in DMF near 0.0 V vs sce.
Since the discovery ~ of diruthenium(III, II) com- netic measurements were carried out by the Farapounds, several carboxylato species were prepared day method using a Cahn R.G. electrobalance. and characterized. 2"3 While the study is thorough Electrochemical studies were performed using a on alkyl-carboxylato complexes, the chemistry Princeton applied research (Par) 370-4 electroof aryl-carboxylato compounds4 has remained chemistry system. A planar Beckman model 39273 virtually unexplored, except in one case where platinum inlaly working electrode, a platinum only magnetic properties of RuzCI(O2CC6H5) 4 wire auxililary electrode and a standard calomel were reported. 4 We have previously shown 5 that reference electrode (sce) were used in three-elecRuzCI(O2CAr) when reacted with P(C6Hs)3 in an trode measurements. All electrochemical data were alcoholic medium, R'CH2OH, forms monomeric obtained at 298 K and are uncorrected for carbonyl compounds by a novel decarbonylation junction potentials. process. In this paper we report the synthesis and physico-chemical properties of two diruthenium Preparation of monochlorotetra-I~-benzoato-diru(III, II) compounds. A comparison has been made thenium(III, II), Ru2CI(O2CCrHs)4 between Ru2CI(O_~CAr)4 and other known 2'3'6 To a solution of 94 mg RuzCI(O2CCH3)4 (0.2 structurally analogous diruthenium compounds. mmol) in 30 cm 3 of a 1:1 methanol-water (v/v) mixture, 146 mg of benzoic acid (1.2 mmol) were EXPERIMENTAL added. The mixture was heated to reflux for 4 h. It Ru2CI(O2CCH3)4 was prepared using a literature was then cooled and filtered. The brown product procedure. 7 Solution electrical conductivity, elec- was washed several times with methanol and then tronic and IR spectra were recorded using a Digisun with diethylether. The compound thus obtained was digital conductivity meter model D1-909, a Hitachi dried in vacuo over P4Oi0 (Yield : 130 mg, ca 90%). U-3400 spectrophotometer, and a Perkin-Elmer ( Found : C, 46.3 ; H, 2.7. Calc. for C28H20OsC1Ru2 : 597 infrared spectrophotometer, respectively. Mag- C, 46.6; H, 2.8). IR spectrum (KBr phase and Nujol mull): 3050(w), 1595(m), 1480(w), 1450(m), 1395(s), 1140(w), 1060(w), 1020(w), 840(m), 710(s), 685(s), 525(s), 385(m), cm-J (s, strong ; m, medium ; *Author to whom correspondenceshould be addressed. w, weak). 685
686
B . K . DAS and A. R. CHAKRAVARTY
Preparation 0/" monochloro-tetra-lt-p-methoxyhenzoatodiruthenium(III, II), Ru2CI(O2CC6H4-p-OCH3)4
on Ru2CI(O2CR)4 (R, alkyl group) and Ru2CI(Ar CONH)n, show the presence of linear or zigzag {-Ru~--CI--Ru_,-],, chains and a relatively weak This was prepared by using the method given R u ~ l bond. In polar solvents the polymer breaks above for the preparation of R u ~ C I ( O 2 C C 6 H s ) 4 into discrete dimeric units. The formation of the (Yield: 150 mg, ca 90%) (Found C, 45.9; H, 3, 3. solvent adduct is well documented 2"6 in diruCalc. for C32H_~8OI2C1Ru_,: C, 46.5; H, 3, 3). IR thenium(III, II) and diruthenium(lI, II) systems. spectrum (KBr phase and Nujol mull): 3055(w), IR spectra of Ru:CI(O2CAr)4 exhibit charac2840(w), 1595(m), 1430(w), 1395(s), 1250(m), teristic symmetric and antisymmetric vibrations of l160(m), 840(m), 765(m), 710(w), 695(w), 635(s), carboxylate ligands. The absence of a Ru--C1 520(w), 450(m), 385(m) cm ~. stretch near 350 cm ~ indicates the involvement of C1 in a bridge to hold dimeric Ru2 units together. Magnetic measurements show the presence of three unpaired spins per Ru2 dimer in accordance j°'j~ with R E S U L T S AND D I S C U S S I O N the ground electronic configuration of a2n462 Brown coloured tetra-arylcarboxylato com- (6"/~*) 3, a characteristic feature of diruthenium(III, pounds, RuzCI(O2CAr)4 are prepared in near II) compounds having ruthenium in the non-intequantitative yields by reacting Ru,CI(O2CCH3)4 gral oxidation state of +2.5 and an R u - - R u bond and ArCO_,H in a boiling 1 : 1 (v/v) methanol-water order of 2.5. Electronic spectra of these compounds mixture. Ru2CI(O2CC6Hs)4 was earlier prepared 4 by in D M F solution display a band near 450 nm along using Ru2CI(O_,CH)4 as the starting material and with a shoulder near 580 nm. While the low energy the reaction time was 7 days. Under refluxing con- absorption could be assigned to an axial ligand ditions we have been able to isolate the product in Ru2 (6* or n*) transition, the higher energy band 4 h. The compounds are sparingly soluble in water is most likely due to the O(n) ---, Ru2(n*) transition and in common organic solvents, but are appre- with the O(n) primarily R u - - O bonding orbital ciably soluble in dimethylformamide ( D M F ) and having appreciable Ru_~-n bonding character.~° The dimethylsulphoxide (DMSO). Physico-chemical O(n) ~ Ruz(n*) transition is reported to occur t~data on Ru2CI(O2CAr)4 are presented in Table 1. at 459 and 445 nm in RuzCI(CF3CONH)4 and In D M F , Ru2CI(O2CAr)4 dissolves slowly and Ru2CI(C6HsCONH)4, respectively, in D M S O soluforms a brown solution. Conductivity measure- tion. The diruthenium(II, II) benzoato compound, ments show the presence of a 1:1 electrolyte in Ru2(O2CC6Hs)a(THF)2 is known 6 to display a solution. The species in the solution is believed to shoulder at 440 nm. The bands observed ~3 in the be [Ru_,(O2CAr)4(DMF)2] +. Structural studies 2"3"8'9 diffuse reflectance spectrum of Ru2(O2CCH3)4C1
Table 1. Physico-chemical data on Ru2CI(O.,CAr)4 compounds Physico-chemical measurements Conductivity~ A, ohm- t cm 2 mol- ~, 298 K Electronic spectra~'h J-nm(~,dm 3 mol-~ cm-~) Magnetic Moment #at, 298 K, (Per Ru) BM #err, 298 K, (per dimer) BM Cyclic voltammetry"" E%8, V (vs sce) AEe,mV v = 50mVs ~ = 100 m Vs -~ = 200 m Vs-~
Ar = -C6H5
Ar = -C6H4-p-OCH 3
75.2
73.8
451 (2200) 580(Sh)
452 (2 I00) 580(Sh)
2.74 3.88
2.67 3.77
0.043 240 250 270
"Solvent, dimethylformamide. bSh, shoulder. ' v, scan rate, AEr, peak to peak separation.
-0.048 210 230 260
Diruthenium(llI, II) tetra-aryl carboxylato compounds at 568(Sh) and 462 nm are proposed ~° to be due to C1 ~ Rtl2(~z* ) and O(~) ~ Ru2(n*) transitions, respecitvely. Cyclic voltammetric studies in a 0.1 M tetrabutylammonium p e r c h l o r a t e - D M F solution of Ru_,CI(O~CAr)4 show a single v o l t a m m o g r a m near 0.0 V vs the sce reference electrode (Table I). Both compounds undergo a quasi-reversible one-electron R u ( I I I ) R u ( I I ) + e ~ Ru(II)Ru(lI) reduction to form a Ru_,(O2CAr)4(DMF)_, species as is evidenced from the constant potential electrolysis carried out at a potential of 200 mV negative to the cathodic peak. The observed shift of the Ru(III)Ru(II)/ Ru(II)Ru(II) couple in going from Ar = C 6 H 5 to Ar = C 6 H 4 - p - O C H 3 , is consistent with the inductive effect of the substituent on the phenyl ring. Addition of electron density to the antibonding 6*n* level is likely to make the system difficult for reduction. A similar effect is known 6 to occur in Ru2(O2CR)4 complexes. A recent report 6 shows that Ru2(O_,CC6Hs)a(THF)_, undergoes a oneelectron oxidation at 0.07 V (vs sce). The observed difference of 30 mV between T H F and D M F adducts could be due to the difference in solvent donating capacity. A comparison a m o n g the reduction potentials of diruthenium(III, II) systems reveals "-'3"t2'la-t6 that E°98 of the Ru(III)Ru(II)/ Ru(II)Ru(II) couple follows the order O,O > O,N > N,N, where O,O; O,N and N,N are three atom anionic bridging ligands having O,O (e.g. carboxylates), O,N (e.g. amides, hydrooxypyridines) and N , N (e.g. aminopyridines) coordination at the equatorial positions. The potential is also dependent on the solvent medium. Highly polar solvents can easily remove axial CI to form axial solvent adducts as is evidenced ~2't4 from electrochemical experiments.
687
Acknowled,qements--We thank Prof. A. Chakravorty, IACS, Calcutta, for obtaining elemental analytical and cyclic voltammetric results, and CSIR, New Delhi for financial support.
REFERENCES 1. T. A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem. 1966, 28, 2285. 2. F. A. Cotton and R. A. Walton, Multiple Bonds Between Metal Atoms. John Wiley (1982). 3. F. A. Cotton and R. A. Walton, Structure and Bonding 1986, 62, 1. 4. M. Mukaida, T. Nomura and T. Ishimori, Bull. Chem. Soc., Japan 1972, 45, 2143. 5. S. K. Mandal and A. R. Chakravarty, Inorg. Chim. Acta. 1987, 132, 157. 6. A. J. Lindsay, G. Wilkinson, M. Motevalli and M. B. Hursthouse, J. Chem. Soc., Dalton Trans. 1985, 2321. 7. R. W. Mitchell, A. Spencer and G. Wilkinson, J. Chem. Soc., Dalton Trans. 1973, 846. 8. A. R. Chakravarty and F. A. Cotton, Polyhedron 1985, 4, 1957. 9. A. R. Chakravarty, F. A. Cotton and D. A. Tocher, Poplyhedron 1985, 4, 1097. 10. J. G. Norman, Jr., G. E. Renzoni and D. A. Case, J. Am. Chem. Soc. 1979, 101, 5256. 11. V. M. Miskowski, T. M. Loehr and H. B. Gray, Inorg. Chem. 1987, 26, 1098. 12. T. Malinsky, D. Chang, F. N. Feldmann, J. L. Bear and K. M. Kadish, Inory. Chem. 1983, 22, 3225. 13. R. J. H. Clark and M. R. Franks, J. Chem. Soc., Dalton Trans. 1976, 1825. 14. F. A. Cotton and E. Pederson, Inory. Chem. 1975, 14, 388. 15. A. R. Chakravarty, F. A. Cotton, D. A. Tocher and J. H. Tocher, Polyhedron 1985, 4, 1475. 16. M. Y. Chavan, F. N. Feldmann, X. Q. Lin, J. L. Bear and K. M. Kadish, Inory. Chem. 1984, 23, 2373.
0277-5387/88 $3.00+.00 Pergamon Press plc
SYNTHESIS AND PHYSICO-CHEMICAL PROPERTIES OF DIRUTHENIUM(III, II) TETRA-ARYL CARBOXYLATO COMPOUNDS BIRINCHI K. D A S and AKHIL R. C H A K R A V A R T Y *
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560012, India (Received 4 November 1987 ; accepted 16 December 1987)
Abstract--Monochloro-tetra-/~-aryl-carboxylatodiruthenium(llI, II) compounds RuzCI (O2CAr)4 (Ar = -C6H5; -C6H4-p-OCH3), are prepared and characterized. The compounds have magnetic moments that correspond to three unpaired spins per dimer. The Ru--Ru bond order is 2.5 and the ground electronic configuration is cr27z462 (6,n,)3. The visible spectral band is observed at ca 450 nm along with a shoulder near 580 nm in DMF solution. The compounds undergo a one-electron Ru(III)Ru(II)--, Ru(II)Ru(II) quasi-reversible reduction in DMF near 0.0 V vs sce.
Since the discovery ~ of diruthenium(III, II) com- netic measurements were carried out by the Farapounds, several carboxylato species were prepared day method using a Cahn R.G. electrobalance. and characterized. 2"3 While the study is thorough Electrochemical studies were performed using a on alkyl-carboxylato complexes, the chemistry Princeton applied research (Par) 370-4 electroof aryl-carboxylato compounds4 has remained chemistry system. A planar Beckman model 39273 virtually unexplored, except in one case where platinum inlaly working electrode, a platinum only magnetic properties of RuzCI(O2CC6H5) 4 wire auxililary electrode and a standard calomel were reported. 4 We have previously shown 5 that reference electrode (sce) were used in three-elecRuzCI(O2CAr) when reacted with P(C6Hs)3 in an trode measurements. All electrochemical data were alcoholic medium, R'CH2OH, forms monomeric obtained at 298 K and are uncorrected for carbonyl compounds by a novel decarbonylation junction potentials. process. In this paper we report the synthesis and physico-chemical properties of two diruthenium Preparation of monochlorotetra-I~-benzoato-diru(III, II) compounds. A comparison has been made thenium(III, II), Ru2CI(O2CCrHs)4 between Ru2CI(O_~CAr)4 and other known 2'3'6 To a solution of 94 mg RuzCI(O2CCH3)4 (0.2 structurally analogous diruthenium compounds. mmol) in 30 cm 3 of a 1:1 methanol-water (v/v) mixture, 146 mg of benzoic acid (1.2 mmol) were EXPERIMENTAL added. The mixture was heated to reflux for 4 h. It Ru2CI(O2CCH3)4 was prepared using a literature was then cooled and filtered. The brown product procedure. 7 Solution electrical conductivity, elec- was washed several times with methanol and then tronic and IR spectra were recorded using a Digisun with diethylether. The compound thus obtained was digital conductivity meter model D1-909, a Hitachi dried in vacuo over P4Oi0 (Yield : 130 mg, ca 90%). U-3400 spectrophotometer, and a Perkin-Elmer ( Found : C, 46.3 ; H, 2.7. Calc. for C28H20OsC1Ru2 : 597 infrared spectrophotometer, respectively. Mag- C, 46.6; H, 2.8). IR spectrum (KBr phase and Nujol mull): 3050(w), 1595(m), 1480(w), 1450(m), 1395(s), 1140(w), 1060(w), 1020(w), 840(m), 710(s), 685(s), 525(s), 385(m), cm-J (s, strong ; m, medium ; *Author to whom correspondenceshould be addressed. w, weak). 685
686
B . K . DAS and A. R. CHAKRAVARTY
Preparation 0/" monochloro-tetra-lt-p-methoxyhenzoatodiruthenium(III, II), Ru2CI(O2CC6H4-p-OCH3)4
on Ru2CI(O2CR)4 (R, alkyl group) and Ru2CI(Ar CONH)n, show the presence of linear or zigzag {-Ru~--CI--Ru_,-],, chains and a relatively weak This was prepared by using the method given R u ~ l bond. In polar solvents the polymer breaks above for the preparation of R u ~ C I ( O 2 C C 6 H s ) 4 into discrete dimeric units. The formation of the (Yield: 150 mg, ca 90%) (Found C, 45.9; H, 3, 3. solvent adduct is well documented 2"6 in diruCalc. for C32H_~8OI2C1Ru_,: C, 46.5; H, 3, 3). IR thenium(III, II) and diruthenium(lI, II) systems. spectrum (KBr phase and Nujol mull): 3055(w), IR spectra of Ru:CI(O2CAr)4 exhibit charac2840(w), 1595(m), 1430(w), 1395(s), 1250(m), teristic symmetric and antisymmetric vibrations of l160(m), 840(m), 765(m), 710(w), 695(w), 635(s), carboxylate ligands. The absence of a Ru--C1 520(w), 450(m), 385(m) cm ~. stretch near 350 cm ~ indicates the involvement of C1 in a bridge to hold dimeric Ru2 units together. Magnetic measurements show the presence of three unpaired spins per Ru2 dimer in accordance j°'j~ with R E S U L T S AND D I S C U S S I O N the ground electronic configuration of a2n462 Brown coloured tetra-arylcarboxylato com- (6"/~*) 3, a characteristic feature of diruthenium(III, pounds, RuzCI(O2CAr)4 are prepared in near II) compounds having ruthenium in the non-intequantitative yields by reacting Ru,CI(O2CCH3)4 gral oxidation state of +2.5 and an R u - - R u bond and ArCO_,H in a boiling 1 : 1 (v/v) methanol-water order of 2.5. Electronic spectra of these compounds mixture. Ru2CI(O2CC6Hs)4 was earlier prepared 4 by in D M F solution display a band near 450 nm along using Ru2CI(O_,CH)4 as the starting material and with a shoulder near 580 nm. While the low energy the reaction time was 7 days. Under refluxing con- absorption could be assigned to an axial ligand ditions we have been able to isolate the product in Ru2 (6* or n*) transition, the higher energy band 4 h. The compounds are sparingly soluble in water is most likely due to the O(n) ---, Ru2(n*) transition and in common organic solvents, but are appre- with the O(n) primarily R u - - O bonding orbital ciably soluble in dimethylformamide ( D M F ) and having appreciable Ru_~-n bonding character.~° The dimethylsulphoxide (DMSO). Physico-chemical O(n) ~ Ruz(n*) transition is reported to occur t~data on Ru2CI(O2CAr)4 are presented in Table 1. at 459 and 445 nm in RuzCI(CF3CONH)4 and In D M F , Ru2CI(O2CAr)4 dissolves slowly and Ru2CI(C6HsCONH)4, respectively, in D M S O soluforms a brown solution. Conductivity measure- tion. The diruthenium(II, II) benzoato compound, ments show the presence of a 1:1 electrolyte in Ru2(O2CC6Hs)a(THF)2 is known 6 to display a solution. The species in the solution is believed to shoulder at 440 nm. The bands observed ~3 in the be [Ru_,(O2CAr)4(DMF)2] +. Structural studies 2"3"8'9 diffuse reflectance spectrum of Ru2(O2CCH3)4C1
Table 1. Physico-chemical data on Ru2CI(O.,CAr)4 compounds Physico-chemical measurements Conductivity~ A, ohm- t cm 2 mol- ~, 298 K Electronic spectra~'h J-nm(~,dm 3 mol-~ cm-~) Magnetic Moment #at, 298 K, (Per Ru) BM #err, 298 K, (per dimer) BM Cyclic voltammetry"" E%8, V (vs sce) AEe,mV v = 50mVs ~ = 100 m Vs -~ = 200 m Vs-~
Ar = -C6H5
Ar = -C6H4-p-OCH 3
75.2
73.8
451 (2200) 580(Sh)
452 (2 I00) 580(Sh)
2.74 3.88
2.67 3.77
0.043 240 250 270
"Solvent, dimethylformamide. bSh, shoulder. ' v, scan rate, AEr, peak to peak separation.
-0.048 210 230 260
Diruthenium(llI, II) tetra-aryl carboxylato compounds at 568(Sh) and 462 nm are proposed ~° to be due to C1 ~ Rtl2(~z* ) and O(~) ~ Ru2(n*) transitions, respecitvely. Cyclic voltammetric studies in a 0.1 M tetrabutylammonium p e r c h l o r a t e - D M F solution of Ru_,CI(O~CAr)4 show a single v o l t a m m o g r a m near 0.0 V vs the sce reference electrode (Table I). Both compounds undergo a quasi-reversible one-electron R u ( I I I ) R u ( I I ) + e ~ Ru(II)Ru(lI) reduction to form a Ru_,(O2CAr)4(DMF)_, species as is evidenced from the constant potential electrolysis carried out at a potential of 200 mV negative to the cathodic peak. The observed shift of the Ru(III)Ru(II)/ Ru(II)Ru(II) couple in going from Ar = C 6 H 5 to Ar = C 6 H 4 - p - O C H 3 , is consistent with the inductive effect of the substituent on the phenyl ring. Addition of electron density to the antibonding 6*n* level is likely to make the system difficult for reduction. A similar effect is known 6 to occur in Ru2(O2CR)4 complexes. A recent report 6 shows that Ru2(O_,CC6Hs)a(THF)_, undergoes a oneelectron oxidation at 0.07 V (vs sce). The observed difference of 30 mV between T H F and D M F adducts could be due to the difference in solvent donating capacity. A comparison a m o n g the reduction potentials of diruthenium(III, II) systems reveals "-'3"t2'la-t6 that E°98 of the Ru(III)Ru(II)/ Ru(II)Ru(II) couple follows the order O,O > O,N > N,N, where O,O; O,N and N,N are three atom anionic bridging ligands having O,O (e.g. carboxylates), O,N (e.g. amides, hydrooxypyridines) and N , N (e.g. aminopyridines) coordination at the equatorial positions. The potential is also dependent on the solvent medium. Highly polar solvents can easily remove axial CI to form axial solvent adducts as is evidenced ~2't4 from electrochemical experiments.
687
Acknowled,qements--We thank Prof. A. Chakravorty, IACS, Calcutta, for obtaining elemental analytical and cyclic voltammetric results, and CSIR, New Delhi for financial support.
REFERENCES 1. T. A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem. 1966, 28, 2285. 2. F. A. Cotton and R. A. Walton, Multiple Bonds Between Metal Atoms. John Wiley (1982). 3. F. A. Cotton and R. A. Walton, Structure and Bonding 1986, 62, 1. 4. M. Mukaida, T. Nomura and T. Ishimori, Bull. Chem. Soc., Japan 1972, 45, 2143. 5. S. K. Mandal and A. R. Chakravarty, Inorg. Chim. Acta. 1987, 132, 157. 6. A. J. Lindsay, G. Wilkinson, M. Motevalli and M. B. Hursthouse, J. Chem. Soc., Dalton Trans. 1985, 2321. 7. R. W. Mitchell, A. Spencer and G. Wilkinson, J. Chem. Soc., Dalton Trans. 1973, 846. 8. A. R. Chakravarty and F. A. Cotton, Polyhedron 1985, 4, 1957. 9. A. R. Chakravarty, F. A. Cotton and D. A. Tocher, Poplyhedron 1985, 4, 1097. 10. J. G. Norman, Jr., G. E. Renzoni and D. A. Case, J. Am. Chem. Soc. 1979, 101, 5256. 11. V. M. Miskowski, T. M. Loehr and H. B. Gray, Inorg. Chem. 1987, 26, 1098. 12. T. Malinsky, D. Chang, F. N. Feldmann, J. L. Bear and K. M. Kadish, Inory. Chem. 1983, 22, 3225. 13. R. J. H. Clark and M. R. Franks, J. Chem. Soc., Dalton Trans. 1976, 1825. 14. F. A. Cotton and E. Pederson, Inory. Chem. 1975, 14, 388. 15. A. R. Chakravarty, F. A. Cotton, D. A. Tocher and J. H. Tocher, Polyhedron 1985, 4, 1475. 16. M. Y. Chavan, F. N. Feldmann, X. Q. Lin, J. L. Bear and K. M. Kadish, Inory. Chem. 1984, 23, 2373.