Metallaborane chemistry. Part 11. Lower rotational barriers in seven-vertex than in twelve-vertex carbaplatinaboranes: synthesis, and molecular and crystal structures of [closo-1,1-(Et3P)2-2,3-Me2-1,2,3-PtC2B4H4] and [closo-1,1-(Et3P)2-1,2,4-PtC2B4H6]

Geoffrey K. Barker, Michael Green, F. Gordon A. Stone, Alan J. Welch

Research output: Contribution to journalArticle

Abstract

Sealed-tube pyrolysis of [nido-μ4,5-{trans-(Et3P)2Pt(H)}-μ 5,6-H-2,3-Me2-2,3-C2B4H4] affords the closo-carbametallaborane [1,1-(Et3P)2-2,3-Me2-1,2,3-PtC 2B4H4], structurally characterised by X-ray diffraction. Crystals are monoclinic, space group P21/a, Z = 4, in a unit cell with lattice parameters a = 15.691(6), b = 10.118(6), c = 15.949(6) Å, and β = 115.76(3)°. Using 7 437 data collected at 215 K on a four-circle diffractometer, refinement converged at R 0.067. The molecule has a highly distorted pentagonal-bipyramidal cage with a novel (C2v) conformation of the Pt(PEt3)2 fragment. In contrast, pyrolysis of [nido-μ4,5-{trans-(Et3P)2 Pt(H)}-μ5,6-H-2,3-C2B4H6] proceeds with separation of the cage carbon atoms, affording[closo-1,1-(Et3p)2-1,2,4-PtC2B 4H6], which may alternatively be prepared directly from 1,6-C2B4H6 or 5-Me3N-2,4-C2B4H6. A crystallographic study of this closo-carbametallaborane confirms the cage carbon positions. Crystals are monoclinic, space group P21/n, with eight molecules in a unit cell of dimensions a = 16.045(7), b = 17.354(5), c = 16.918(6) Å, and β = 117.11(3)°. Refinement converged to R 0.043 for 8 275 data recorded at 215 K. The two crystallographically independent molecules in the asymmetric unit both have pentagonal-bipyramidal cages, but are related as rotational conformers about the metal-cage axis. Comparison of the molecular parameters of the three seven-vertex cages thus studied with those of analogous 12-vertex (icosahedral) systems suggests that the barrier to rotation of a metal fragment, about the axix linking it to the cage, should be less in the former case, and this has been verified by variable-temperature n.m.r. studies.

Original languageEnglish
Pages (from-to)1186-1199
Number of pages14
JournalJournal of the Chemical Society, Dalton Transactions
Issue number7
DOIs
Publication statusPublished - 1980

ASJC Scopus subject areas

  • Chemistry(all)

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