Bimetallic complexes supported by bis(diphenylphosphino)methane anti and syn to the MnPd bonds

Redox condensation of PPN[Mn2(μ-PPh2)(CO)8] and PdCl2(η2-dppm) gives bimetallic PdMn(μ-PPh2)(μ-dppm)(CO)3(PPh3) (1) with an unexpected formation of PPh3. The latter can be displaced when 1 reacts with free diphosphines (dppm, dppe, dppf) giving PdMn(μ-PPh2)(μ-dppm)(CO)3(Ph2PXP(O)Ph2) (2, XCH2 (2a), C2H4 (2b), C5H4FeC5H4 (2c)) and [PdMn(CO)3(μ-PPh2)(μ-dppm)]2(μ-Ph2PXPPh2) (3a). Complexes 2 are “A-frame”-type bimetallic complexes with an syn-dppm bridging the MnPd bond. In contrast, complex 3a is a “double A-frame” anti-bridged by dppm. As a result, the latter is trans to the MnPd bonds. Both types of dppm bridges are substitutionally inert. Either bridging role is best served by dppm (and not dppe or dppf). The structures of the complexes were derived from NMR analyses of all complexes and X-ray single-crystal diffraction analyses of 1, 2a and 2b. The common and stable “A-frame”-type core in these bimetallics provides a thermodynamic driving force for the opposite transmetallation migration of phosphide and phosphine (dppm) when 1 is formed.