Synthesis, molecular structures, and nuclear magnetic resonance properties of the macropolyhedral metallaboranes [(PMe2Ph)4Pt3B14H16] and [(PMe2Ph)PtB16H18(PMe2Ph)], and a discussion of the bonding at platinum in these and some related platinaborane clusters

Abstract

Thermolysis of [4-(PMe₂Ph)₂-arachno-4-PtB₈H₁₂] in refluxing toluene solution gives the known yellow 14-vertex diplatinaborane [(PMe₂Ph)₂Pt₂B₁₂H₁₈] plus two novel 17-vertex cluster compounds, viz. the green triplatinaborane [(PMe₂Ph)₄Pt₃B₁₄H₁₆](1) and the red monoplatinaborane [(PMe₂Ph)PtB₁₆H₁₈(PMe₂Ph)](2). Crystals of (1), as its 1:1 solvate with CH₂Cl₂, are monoclinic, space group P2₁/c, with a= 1 249.0(3), b= 3 732.6(8), c= 1 072.0(2) pm, β= 104.92(2)°, and Z= 4; the structure was refined using 4 802 independent F_o with I > 2σ(I) to a final R= 0.049, R′= 0.045. Crystals of (2) are also monoclinic, space group P2₁, with a= 992.7(3), b= 1 067.2(2), c= 1 378.7(3) pm, β= 95.08(2)°, and Z= 2; the structure was refined using 1 992 independent F_o with I > 2σ(I) to a final R= 0.0216, R′= 0.0248. These two new macropolyhedral boranes have been further characterized by multielement, multiple resonance, and multidimensional n.m.r. spectroscopy. The metal-to-borane bonding is discussed in terms of the ‘non-conical’ nature of the platinum contribution to the cluster bonding schemes.