Interpretation of bond-length data for transition-metal–acetylene complexes, in particular the complex [C5H5NH][TaCl4(PhCCPh)(NC5H5)]

Abstract

By analogy with cyclopropene, a simple metallocene model for transition-metal–acetylene complexes should be described as containing bent bonds. On the basis of this model, a simple method for predicting metal–carbon and carbon–carbon distances is proposed and its application to [C₅H₅NH][TaCl₄(PhCCPh)(NC₅H₅)] is described in detail. It is concluded that the reported structural data for this compound are fully consistent with those expected for a simple bent-bond model, and that there is no compulsion on the basis of bond-length data to invoke a contribution to bonding from four-electron donation from the acetylene to the metal, as was previously proposed.