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.