Thermal and photochemical transformations of organoiridium phosphide complexes. Mechanistic studies on carbon-phosphorus bond formation to generate cyclometalated hydride complexes by α-hydride abstraction

Article abstract of DOI:10.1021/ja00023a020

The thermal and photolytic transformations of a series of methyliridium(III) phosphide complexes are described. Complexes of the formula Ir(CH₃)PR₂[N(SiMe₂CH₂PPh ₂)₂] (R = Ph, Me) rearrange thermally to generate the corresponding cyclometalated derivatives fac-Ir(η²-CH₂PR₂)H[N(SiMe ₂CH₂PPh₂)₂]; continued thermolysis results in the formation of the iridium(I) phosphine complexes Ir(PMeR₂)[N(SiMe₂CH₂PPh₂) ₂]. Under photolytic conditions the phosphide derivatives rearrange directly to the phosphine complexes with no observable intermediates. The phenylphosphide complex Ir(CH₃)PHPh[N(SiMe₂CH₂PPh₂) ₂] rearranges directly to the phosphine derivative Ir(PHPhMe)[N(SiMe₂CH₂PPh₂)₂] both thermally and photolytically with no observable intermediates. Crystals of Ir(CH₃)PPh₂[N(SiMe₂CH₂PPh ₂)₂] are monoclinic with a = 13.506 (3) A?, b = 13.665 (3) A?, c = 22.816 (7) A?, β= 92.35 (2)°, Z = 4, D_c = 1.454 g cm^-3, and space group P2₁/c. The structure was solved by the Patterson method and refined by full-matrix least-squares procedures to R = 0.034 and R_w = 0.037 for 3993 reflections with I ≥ 3σ(I). Crystals of fac-Ir(η²-CH₂PPh₂)H[N(SiMe ₂CH₂PPh₂)₂] are monoclinic with a = 9.253 (2) A, b = 21.950 (5) A?, c = 20.081 (4) A?, β= 90.74 (2)°, Z = 4, D_c = 1.50 g cm^-3, and space group P2₁/c. The structure was solved by conventional heavy-atom techniques and was refined in blocks (with the Ir atom in every cycle) by using least-squares procedures down to R = 0.0356 and R_w = 0.0370 for 4448 reflections with I ≥ 3σ(I). Mechanistic studies showed that the formation of the cyclometalated hydride does not involve reductive transfer of the methyl and the phosphide ligands to form a phosphine complex followed by intramolecular C-H bond activation, rather C-H bond abstraction occurs first followed then by C-P bond formation. Transition-state arguments are used to rationalize the difference in the reactivity of the phenylphosphide complex for which no cyclometalated intermediate was detected.