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Mechanism of Hydrogenolysis of an Iridium–Methyl Bond: Evidence for a Methane Complex Intermediate

Author:
Campos, Jesús, Kundu, Sabuj, Pahls, Dale R., Brookhart, Maurice, Carmona, Ernesto, Cundari, Thomas R.
Source:
Journal of the American Chemical Society 2013 v.135 no.4 pp. 1217-1220
ISSN:
1520-5126
Subject:
deuterium, methane, methodology, pyridines
Abstract:
Evidence for key σ-complex intermediates in the hydrogenolysis of the iridium–methyl bond of (PONOP)Ir(H)(Me)⁺ (1) [PONOP = 2,6-bis(di-tert-butylphosphinito)pyridine] has been obtained. The initially formed η²-H₂ complex, 2, was directly observed upon treatment of 1 with H₂, and evidence for reversible formation of a σ-methane complex, 5, was obtained through deuterium scrambling from η²-D₂ in 2-d₂ into the methyl group of 2 prior to methane loss. This sequence of reactions was modeled by density functional theory calculations. The transition state for formation of 5 from 2 showed significant shortening of the Ir–H bond for the hydrogen being transferred; no true Ir(V) trihydride intermediate could be located. Barriers to methane loss from 2 were compared to those of 1 and the six-coordinate species (PONOP)Ir(H)(Me)(CO)⁺ and (PONOP)Ir(H)(Me)(Cl).
Agid:
5389636