Synthesis and reactivity of the iridium vinylidene Ir=C=CH2[N(SiMe2CH2PPh2) 2]. Formation of carbon-carbon bonds via migratory insertion of a vinylidene unit

Article abstract of DOI:10.1021/om00045a009

The synthesis of the 16-electron iridium vinylidene complex Ir=C=CH₂[N(SiMe₂CH₂PPh₂) ₂] is described by starting from the cyclooctene derivative Ir(η²-C₈H₁₄) [N(SiMe₂CH₂PPh₂)₂] with addition of acetylene. This vinylidene complex reacts with a variety of electrophiles; thus, reaction with AlR₃ (R = Me, Et) or GaMe₃ leads to the formation of the new derivatives Ir(ER₂)CR=CH₂[N(SiMe₂CH₂PPh ₂)₂] (E = Al, R = Me, Et; E = Ga, R = Me). These complexes result from oxidative addition of the ER₃ reagent to the coordinatively unsaturated Ir(I) vinylidene followed by migratory insertion to generate the carbon-carbon bond of the substituted vinyl moiety. Oxidative addition of methyl iodide generates as the final product the allyl iodide derivative Ir(η³-C₃H₅)I[N(SiMe₂CH ₂PPh₂)₂]. This last transformation has been examined in detail using NMR spectroscopy to follow the course of the reaction. A number of intermediates could be observed: the first species is the oxidative adduct Ir=C=CH₂(Me)I[N(SiMe₂CH₂PPh₂) ₂], which undergoes migratory insertion to generate the isopropenyl iodide Ir(CMe=CH₂)I[N(SiMe₂CH₂PPh₂) ₂], which then rearranges to the allyl product. A third intermediate, believed to be an allene-amine derivative of the formula Ir(η²-H₂C=O=CH₂)I[HN(SiMe ₂CH₂PPh₂)₂] is observed but was found not to be on the pathway to the allyl complex. Extension to other alkyl halides was attempted; reactions with ethyl iodide and benzyl bromide do proceed, but the resultant product mixtures are complex. Crystallographic data: Ir=C= CH₂[N(SiMe₂CH₂PPh₂) ₂]·C₆H₅CH₃, triclinic, a = 11.485 (3) A?, b = 115.498 (6) A?, c = 11.047 (5) A?, α = 92.00 (4)°, β = 103.31 (3)°, γ = 85.20 (3)°, Z = 2, space group P1; Ir(η³-C₃H₅)I[N(SiMe₂CH ₂PPh₂)₂], monoclinic, a = 9.571 (4) A?, b = 9.267 (6) A?, c = 39.262 (5) A?, β = 95.22 (3)°, Z = 4, space group P2₁/n; Ir(AlMe₂)CMe=CH₂[N(SiMe₂CH₂PPh ₂)₂], monoclinic, a = 18.823 (6) A?, b = 9.701 (2) A?, c = 21.359 (8) A?, β = 111.78 (2)°, Z = 4, space group P2₁/c; Ir(GaMe₂)CMe=CH₂[N(SiMe₂CH₂PPh ₂)₂], monoclinic, a = 18.816 (4) A?, b = 9.725 (3) A?, c = 21.4429 (4) A?, β = 111.58 (1)°, Z = 4, space group P2₁/c; IrMeI₂[HN(SiMe₂CH₂PPh₂) ₂]·C₆H₆, orthorhombic, a = 36.250 (5) A?, b = 11.368 (12) A?, c = 9.892 (8) A?, Z = 4, space group Pna2₁. The structures were all solved by heavy-atom methods and were refined by full-matrix least-squares procedures to R = 0.027, 0.026, 0.034, 0.034, and 0.032 for 7795, 5050, 5723, 7025, and 2806 reflections with I ≥ 3σ(I), respectively.