Migratory insertion reactions of indenyliridium dialkyls and alkyl and aryl hydrides

Article abstract of DOI:10.1021/om00041a014

This paper reports the migratory insertion chemistry of indenyliridium complexes described in the companion paper. Complexes of general formula (η⁵-Ind)(PMe₃)Ir(R)(R′), where R = alkyl or aryl and R′ = alkyl, aryl, or hydride (4-6) react with dative ligands L such as tert-butylisocyanide and CO. These transformations lead to η⁵ to η¹ isomerization of the indenyl ligand, giving octahedral iridium complexes of general formula (η¹-Ind)(PMe₃)(L)₂Ir(R)(R′) (8, 9, 11). Treatment of the methyl aryl and dimethyl η¹-indenyl complexes 9a, 9d, and 9e with trimethylamine oxide removes CO, allowing the indenyl ligand to reestablish η⁵-coordination by inducing CO migratory insertion to give acyl complexes 10. Reaction of η¹-indenyl aryl and methyl hydrides 6 (as well as the dihydride (η⁵-Ind)(PMe₃)IrH₂ (7)) with CO leads to reductive elimination of arene, methane, or H₂ rather than migratory insertion, forming (η¹-Ind)(CO)₃(PMe₃)Ir (12) as the organometallic product. In contrast, treatment of methyl and aryl hydrides 6 with alkynes leads to the methyl vinyl complexes (η⁵-Ind)(PMe₃)Ir(Me)(CR=C(R′)(H)) (13) and reaction of 6a with ethylene gives the methyl ethyl complex (η⁵-Ind)(PMe₃)Ir(Me)(Et) (14). Isotope labeling, stereochemical, and kinetic studies have been carried out on the insertion reaction of 6a with 3,3-dimethyl-1-butyne. The results of these experiments are most consistent with a mechanism involving initial reversible coordination of alkyne to the metal center (probably with concurrent η⁵-η³ isomerization of the indenyl ligand) followed by irreversible migration of the metal-bound hydrogen to the tert-butyl-substituted carbon of the alkyne and then rapid recoordination of the indenyl group.