Bimetallic systems. Part 13. Platinum–manganese carbonyl complexes containing bridging Ph2PCH2PPh2(dppm) ligands: crystal structure of [(OC)3Mn(µ-dppm)2PtH(Br)]BF4

Abstract

Treatment of [MnCl(CO)5] with Ph2PCH2PPh2(dppm) gives cis,mer-[MnCl(CO)2(dppm-PP′)(dppm-P)](1b). Treatment of complex (1b) with [Pt(PPh3)4] under an atmosphere of CO gives [(OC)3Mn(µ-dppm)2PtCl](2c), with a manganese–platinum bond. The complex [(OC)3Mn(µ-dppm)2PtBr](2d) was made similarly. Complexes (2c) and (2d) are protonated reversibly with strong acids (HBF4, toluene-p-sulphonic acid, or CF3CO2H), e.g. (2d) gives [(OC)3Mn(µ-dppm)2PtH(Br)]BF4 whose crystal structure was determined (see below). Treatment of complex (1b) with trans-[PtH(Cl)(PPh3)2] gave a deep red-purple complex, [Cl(OC)2Mn(µ-dppm)2PtH(Cl)](4a); the corresponding dibromide [Br(OC)2Mn(µ-dppm)2PtH(Br)](4b) was made similarly. When the chloro-complex (1b) was treated with trans-[PtH(Br)(PPh3)2] or the corresponding bromocomplex (1a) with trans-[PtH(Cl)(PPh3)2] the same mixture of [Cl(OC)2Mn(µ-dppm)2PtH(Br)] and [Br(OC)2Mn(µ-dppm)2PtH(Cl)] was produced in each case, showing that intramolecular halogen scrambling occurs. Treatment of the dichloro-complex (4a) with TIBF4 under an atmosphere of CO caused rapid conversion into the orange salt, [(OC)3Mn(µ-dppm)2 PtH(Cl)]BF4(3a). The corresponding bromide tetrafluoroborate (3b) was prepared similarly as were [(OC)3Mn(µ-dppm)2PtH(X)]PF6(X = Cl or Br), using TIPF6–CO. The salt (3a) was deprotonated by sodium methoxide to give the metal–metal-bonded complex [(OC)3Mn(µ-dppm)2PtCl](2c). Many of the above-mentioned complexes showed broad 31P-{1H} n.m.r. patterns at 20 °C for the manganese-bonded P nuclei, due to quadrupole broadening by the Mn nucleus (I= 5/2). At lower temperatures, e.g. –50 °C, the resonances were much sharper because of more rapid relaxation of the Mn nucleus. N.m.r. and i.r. spectroscopic data are given. Crystals of the title compound are monoclinic, space group P21/n with a= 1 309.2(2), b= 2 657.2(4), c= 1 571.4(2) pm, and β= 97.37(1)°; final R factor 0.055 4 for 5 781 observed reflections. The structure shows the two metal centres are 287.1 (4) pm apart and are bridged by the two dppm ligands giving an eight-membered ring in the boat conformation.