Pt-Mo and Pt-W Mixed-Metal Clusters with Chelating or Bridging Diphosphine Short-Bite Ligands (Ph2P)(2)NH and (Ph2P)(2)N(CH2)(9)CH3: A Combined Synthetic and Theoretical Study

The reactivity of the complexes (PtCl2{Ph2PN(R)PPh2-P,P}] (R = -H, 3; R = -(CH2)(9)CH3, 8) toward group 6 carbonylmetalates Na[MCp(CO)(3)] (M = W or Mo, Cp = cyclopentadienyl) was explored. When R = H, the triangular clusters [PtM2Cp2(CO)(5)(mu-dppa)] (M = W, 4; M = Mo, 5), in which the diphosphane ligand bridges a Pt-M bond, were obtained as the only products. When R = -(CH2)(9)CH3, isomeric mixtures of the triangular clusters [PtM2Cp2(CO)(5){Ph2PN(R)PPh2-P,P}], in which the diphosphane ligand chelates the Pt center (M = W, 11; M = Mo, 13) or bridges a Pt-M bond (M = W, 12; M = Mo, 14), were obtained. Irrespective of the M/Pt ratio used when R = -(CH2)(9)CH3, the reaction of [PtCl2{Ph2PN(R)PPh2-P,P}] with Na[MCp(CO)(3)] in acetonitrile stopped at the monosubstitution stage with the formation of [PtCl{MCp(CO)(3)}{Ph2PN(R)PPh2-P,P}] (R = -(CH2)(9)CH3, M = W, 9; M = Mo, 10), which are the precursors to the trinuclear clusters formed in THF when excess carbonylmetalate was used. The dynamic behavior of the dppa derivatives 4 and 5 in solution as well as that of their carbonylation products 6 and 7, respectively, is discussed. Density functional calculations were performed to study the thermodynamics of formation of 4 and 5 and 11-14, to evaluate the relative stabilities of the chelated and bridged forms and to trace a possible pathway for the formation of the trinuclear clusters.