PHOSPHIDO-BRIDGED, HETERODINUCLEAR, HETEROTRINUCLEAR, AND HETEROTETRANUCLEAR COMPLEXES OF PALLADIUM AND PLATINUM WITH TRANSITION-METALS - CRYSTAL-STRUCTURE OF [((OC)4MN(MU-PPH2))2PT(PPH3)] (MN-MN, 2-MN-PT)

Two methodologies have been used for the synthesis of phosphido-bridged heterometallic complexes of palladium or platinum with transition metals. First, trinuclear mixed-metal chain complexes trans-[Pd{m(CO)}2(NCPh)2] (m = Cr(CO)2Cp, Mo(CO)2Cp, W(CO)2Cp, Mn(CO)4) were reacted with 3 equiv of secondary phosphines PR2H (R = Ph, Cy), affording the dinuclear complexes activated m(mu-PR2)Pd(PR2H)2 (1-6). When the complexes trans[Pt{m(CO)}2(NCPh)2] were reacted with 2 equiv of PCy2H, dinuclear complexes of the type activated m(mu-PCy2)Pt(CO)(PCy2H) were obtained. We have generally observed that oxidative addition of the P-H bond of PR2H coordinated to Pt across a metal-metal bond is easier when R = Ph than R = Cy. The second method used involved the in situ reaction of a metallophosphine R2P-m(CO) with a Pt(0) complex. The terminal phosphine ligand which is trans with respect to the mu-PR2 bridging ligand appears to be preferentially replaced by an incoming CO ligand. The new complex [{(CO)4 activated Mn(mu-PPh2)}2Pt(PPh3)] (19a) was best prepared and isolated by substitution of the ethylene ligands of [Pt(C2H4)2(PPh3)] by "Ph2P-Mn(CO)4" fragments, generated from Ph2P-Mn(CO)5. Crystals of 19a.C7H8 are triclinic, space group P1BAR, with Z = 2 in a unit cell of dimensions a = 13.275 (5) angstrom, b = 17.718 (6) angstrom, c = 11.970 (3) angstrom, alpha = 94.61 (2)-degrees, beta = 107.89 (2)-degrees, and gamma = 97.74 (2)-degrees. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares on the basis of 6612 observed reflections to R = 0.0401 and R(w) = 0.0531. Although 19a is closely related to its carbonyl analogue [{(CO)4 activated Mn(mu-PPh2)}2Pt(CO)], which has a bent-chain structure, it displays a weak Mn-Mn bonding interaction, thus resulting in a closed rather than an open structure. The triangular metal framework has Pt-Mn distances of 3.082 (1) and 2.987 (1) angstrom and an Mn-Mn edge of 3.245 (2) angstrom. Two phosphido ligands almost symmetrically bridge the Pt-Mn edges, four terminal carbonyl groups are bonded to each Mn atom, and a PPh3 ligand completes the coordination around the Pt atom. The 3c-4e bonding in 19a has been analyzed by extended Huckel calculations and compared with that in [{(CO)4 activated Mn(mu-PPh2)}2Pt(CO)]. Heterotetranuclear, bent-chain complexes W-Pt-Pt-W (21) and Mn-Pt-Pt-Mn (22) have been prepared by the reaction of [PtCl(mu-PPh2)(PPh2H)]2 with Na[W(CO)3Cp] or Na[Mn(CO)5], respectively.