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Bis(hydrocarbyl) and alkylidene complexes of iridium Massey, Roberta Lynn


The iridium(m) bis(hydrocarbyl) complexes Ir(R)R'[N(SiMe₂CH₂PPh₂)₂] for R = CH₃, C₆H₅, CH₂Ph, and R' = CH₃, C₆H₅, CH₂Ph, CH₂CMe₃, CH₂SiMe₃ were synthesized in high yields from the hydrocarbyl halide precursors Ir(R)X [N(SiMe₂CH₂PPh₂)₂], where X = I or Br, by reaction with the appropriate organolithium salt LiR’. The geometry of the five-coordinate complexes was determined to be trigonal bipyramidal both in solution, on the basis of NOEDIFF experiments, and in the solid state by comparison to the previously determined X-ray structures of the methyl neopentyl and dibenzyl derivatives. The complexes were found to be thermally stable, however, they did react when exposed to sunlight to give the alkylidene complexes Ir(=CHR)[N(SiMe₂CH₂PPh₂)₂] for R = H, Ph. Although the benzylidene complex (R = Ph) has not yet been isolated in the pure state, the =CHPh ligand was found to be rotating about the Ir=C bond axis on the ¹H NMR time scale with a ΔG‡[sub rot] = 9.3 kcal/mol. The reactivity of the methylidene complex (R = H) was also briefly explored with CH₃I, C₂H₄, C₂H₂, CO, PMe₃, and H₂. On the basis of the observed spectroscopic data, several of these reactions involve carbon-carbon bond formation, and the methylidene carbon appears to be nucleophilic in nature.

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