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)2Zr(CH3)2 (5a) with HRh(CO)(PPh3)3 (6) leads to methane
evolution and the formation of the early−late heterobimetallic complex [(μ-C5H4−PPh2)2(H3C−Zr−Rh(CO)PPh3)] (7a), which was characterized by X-ray diffraction (d(Zr−Rh) =
2.863(1) Å). The analogous dialkylphosphino-substituted complexes (C5H4−PR2)2Zr(CH3)2
(5b, R = isopropyl; 5c, 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 [(μ-C5H4−PR2)2(μ-CH3−Zr−Rh(PPh3))] (11) and [(μ-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 [(μ-C5H4−PR2)2(μ-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.