Solvent-Dependent Formation of Di- and Trinuclear Rhodium and Iridium Complexes Bridged by N, N′-Donor Ligands

Abstract

Abstract Reactions of Rh and Ir hydrido complexes, [Rh(H)2(PPh3)2(solv)(EtOH)]ClO4 (solv = Me2CO, 1a; EtOH, 1b) and [Ir(H)2(PPh3)2(Me2CO)2]BF4 (2), with various N,N′-donor bridging ligands, such as pyrazine (pyz), 4,4′-trimethylenedipyridine (tmdp) and di(4-pyridyl) disulfide (dpds), in some solvents were examined, and their reaction products were characterized by X-ray crystal structure analysis, IR, 1H NMR and UV-vis spectra. Rh hydrido complexes, 1a or 1b, formed a dinuclear Rh complex, [Rh2(PPh3)2{(η6-C6H5)PPh2}2](ClO4)2·6CH2Cl2 (3·6CH2Cl2), in dichloromethane with a reductive elimination of hydrogen. The reactions of 1a or 1b with the pyz ligand in dichloromethane and tetrahydrofuran gave triangular Rh3 complexes, [Rh3(PPh3)6(pyz)3](ClO4)3·CH2Cl2 (5·CH2Cl2) and [Rh3(PPh3)6(pyz)3](ClO4)3·EtOH (5·EtOH), respectively, in contrast to the formation of a dinuclear Rh hydrido complex, [Rh2(H)4(PPh3)4(Me2CO)2(pyz)](ClO4)2·EtOH (4·EtOH), in acetone. The reactions of 1a or 1b with the tmdp ligand in dichloromethane and 3-methyl-2-butanone also afforded dinuclear Rh complexes, [Rh2(PPh3)4(tmdp)2](ClO4)2 (6) and [Rh2(PPh3)4(tmdp)2](ClO4)2·4MeCOCHMe2 (6·4MeCOCHMe2), respectively. On the other hand, Ir hydrido complex 2 reacted with pyz and dpds ligands in dichloromethane to afford dinuclear Ir complexes, [Ir2(H)4(PPh3)4(Me2CO)2(pyz)](BF4)2·3CH2Cl2 (7·3CH2Cl2) and [Ir2(H)4(PPh3)4(dpds)2](BF4)2·3CH2Cl2·H2O (8·3CH2Cl2·H2O), respectively, without any reductive elimination of hydrogen. Based on structural studies in solution and in the solid state, it was demonstrated that various Rh and Ir complexes were selectively produced depending on the choice of solvents and N,N′-donor bridging ligands.