Metallaborane chemistry. Part 10. Insertion of zerovalent platinum species into bridging boron–hydrogen–boron bonds of 2,3-dicarba-nido-hexaborane(8), 2,3-dimethyl-2,3-dicarba-nido-hexaborane(8), and monocarba-nido-hexaborane(9); molecular and crystal structure of [nido-µ4,5-{trans-(Et3P)2Pt(H)}-µ5,6-H-2,3-C2B4H6]

Abstract

Reaction of [Pt₂(µ-cod)(PEt₃)₄](cod = cyclo-octa-1,5-diene) with 2,3-dicarba-nido-hexaborane(8), 2,3-dimethyl-2,3-dicarba-nido-hexaborane(8), and monocarba-nido-hexaborane(9) affords respectively, [nido-µ_4,5-{trans(Et₃P)₂Pt(H)}-µ_5,6-H-2,3-CB₅H₆], [nido-µ_4,5-{trans-(Et₃P)₂Pt(H)}-µ_5,6-H-2,3-Me₂-2,3-C₂B₄H₄], and [nido-µ_4,5-{trans-(Et₃P)₂Pt(H)}-(µ_3,4-H)(µ_5,6-H)-2-CB₅H₆]. The molecular structure of [nido-µ_4,5-{trans-(Et₃P)₂Pt(H)}-µ_5,6-H-2,3-C₂B₄H₆] has been established by a single-crystal X-ray diffraction study. Four molecules crystallise in the monoclinic space group P2₁/m with cell dimensions a= 10.970(4), b= 11.587(3), c= 9.459(3)Å, and β= 114.47(2)°. The molecular structure has been elucidated by the analysis of 5 106 diffractometer-measured reflection intensities, and refined by least squares to R 0.043. The cage core atoms of the molecule maintain a nido pentagonal-pyramidal geometry, with adjacent facial carbon atoms. Both pentagonal B–B links are bridged, one by hydrogen and the other by a trans-(Et₃P)₂Pt(H) fragment, the latter demonstrating insertion by the metal nucleophile into a bridging B₂H function of the nido-carbaboranes. All cage hydrogen atoms have been located and positionally refined. The ¹H, ¹¹B, and ³¹P n.m.r. spectra of the new compounds have been recorded, and the results are discussed in terms of the molecular structures of the carbaplatinaboranes.