Chemistry of metal-metal-bonded early-late heterobimetallics:: Cooperative reactions of functional groups at a persistent organometallic Zr-Rh framework

The reaction Of (C5H4-PPh2)(2)Zr(CH3)(2) (5a) with HRh(CO)(PPh3)(3) (6) leads to methane evolution and the formation of the early-late heterobimetallic complex [(mu-C5H4-PPh2)(2)-(H3C-Zr-Rh(CO)PPh3)] (7a), which was characterized by X-ray diffraction (d(Zr-Rh) = 2.863(1) Angstrom). The analogous dialkylphosphino-substituted complexes (C5H4-PR2)(2)Zr(CH3)(2) (5b, R = isopropyl; 5e, R = cyclohexyl) react with the hydrido-rhodium reagent 6 to initially form the analogous bimetallic (Zr-Rh) complexes 7b,c, respectively. However, these complexes are not stable at ambient temperature in toluene solution, due to an equilibration with the products [(mu-C5H4-PR2)(2) mu-CH3-Zr-Rh(PPh3))] (11) and [(mu-C5H4-PR2)(2)(H3C-Zr-Rh(CO)(2))] (10). Treatment of the initially formed complexes 7b,c with carbon monoxide rapidly leads to the formation of the H3C(Zr-Rh)-dicarbonyl complexes 10b,c. The product 10c was characterized by X-ray crystal structure analysis. The systems 7b,c are not stable in dichloromethane. They react readily with the solvent by abstraction of two chlorine atoms to yield the compounds [(mu-C5H4-PR2)(2)(mu-O=C(CH3))(Cl-Zr-Rh-Cl)] (12b,c). Both products were characterized by X-ray diffraction. A cooperative action of the involved metals is assumed to account for the observed reactions at the intact heterobimetallic Zr-Rh framework.