Mechanism of hydrogenolysis of an iridium-methyl bond: Evidence for a methane complex intermediate

Jesús Campos; Sabuj Kundu; Dale R. Pahls; Maurice Brookhart; Ernesto Carmona; Thomas R. Cundari

doi:10.1021/ja310982v

Mechanism of hydrogenolysis of an iridium-methyl bond: Evidence for a methane complex intermediate

Jesús Campos, Sabuj Kundu, Dale R. Pahls, Maurice Brookhart, Ernesto Carmona, Thomas R. Cundari

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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).

Original language	English (US)
Pages (from-to)	1217-1220
Number of pages	4
Journal	Journal of the American Chemical Society
Volume	135
Issue number	4
DOIs	https://doi.org/10.1021/ja310982v
State	Published - Jan 30 2013
Externally published	Yes

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title = "Mechanism of hydrogenolysis of an iridium-methyl bond: Evidence for a methane complex intermediate",

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).",

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T1 - Mechanism of hydrogenolysis of an iridium-methyl bond

T2 - Evidence for a methane complex intermediate

AU - Campos, Jesús

AU - Kundu, Sabuj

AU - Pahls, Dale R.

AU - Brookhart, Maurice

AU - Carmona, Ernesto

AU - Cundari, Thomas R.

PY - 2013/1/30

Y1 - 2013/1/30

N2 - 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).

AB - 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).

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Mechanism of hydrogenolysis of an iridium-methyl bond: Evidence for a methane complex intermediate

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