Organic chemistry of dinitrogen and related ligands. Part 7. N-Vinylation or oxidative replacement of the hydrazido(2–) ligand in reactions of [WX(dppe)2(NNH2)]Y (dppe = Ph2PCH2CH2PPh2, X = F or Br, Y = BF4 or Br) with cyanoalkenes. X-Ray crystal structure of [WBr(dppe)2{NC(Br)-C(CN)C(CN)2}]

Abstract

The dinitrogen-derived hydrazido(2–) complexes [WX(dppe)₂(NNH₂)]Y (dppe = Ph₂PCH₂CH₂PPh₂, X = F or Br, Y = BF₄ or Br respectively) react readily with certain polycyanoalkenes such as (CN)₂CCHCl in the presence of base to give vinyldiazenido(1–) complexes, e.g.[WBr(dppe)₂{NNCHC(CN)₂}]. This type of reaction proceeds via the neutral diazenido(1–) complex [WX(dppe)₂(NNH)]. Some more heavily cyano-substituted alkenes, including tetracyanoethene and tetracyanoquinodimethane react differently however, to give complexes in which the hydrazido(2–) ligand is replaced by a novel type of methyleneamido ligand derived from the cyanoalkene and the bromide counter ion of the starting complex. The structure of one such methyleneamido complex, [WBr(dppe)₂{NC(Br)C(CN)C(CN)₂}], has been determined by single-crystal X-ray analysis. The compound crystallises in the monoclinic space group C2/c, with unit-cell parameters a= 26.473(5), b= 14.443(4), c= 30.144(4)Å, β= 102.51(1)°, and Z= 8. The structure was solved by the heavy-atom method and refined to R= 0.043 for 5 021 independent observed reflections.