1,2-Addition of Dihydrogen across Rhodium(III)鈥揙Me Bonds

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• 作者：Samantha A. Burgess ; Deepa Devarajan ; Tamara Bola帽o ; Daniel H. Ess ; T. Brent Gunnoe ; Michal Sabat ; William H. Myers
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：May 19, 2014
• 年：2014
• 卷：53
• 期：10
• 页码：5328-5340
• 全文大小：588K
• 年卷期：v.53,no.10(May 19, 2014)
• ISSN：1520-510X

文摘

The Rh(III) complexes [(^tbpy)₂Rh(OMe)(L)][X]_n (^tbpy = 4,4鈥?di-tert-butyl-2,2鈥?bipyridyl; L = MeOH, n = 2, X = OTf (OTf = trifluoromethanesulfonate), TFA (TFA = trifluoroacetate); L = TFA, n = 1, X = OTf) have been shown to activate dihydrogen via net 1,2-addition of the H鈥揌 bond across the Rh^III鈥揙Me bond. The bis(methoxide) complex [(^tbpy)₂Rh(OMe)₂][OTf] was synthesized by addition of CsOH路H₂O in methanol to [(^tbpy)₂Rh(OTf)₂][OTf] in CH₃CN. The addition of HTFA to [(^tbpy)₂Rh(OMe)₂][OTf] leads to the formation of [(^tbpy)₂Rh(OMe)(MeOH)][OTf][TFA], which exists in equilibrium with [(^tbpy)₂Rh(OMe)(TFA)][OTf]. The mixture of [(^tbpy)₂Rh(OMe)(MeOH)][OTf][TFA] and [(^tbpy)₂Rh(OMe)(TFA)][OTf] activates dihydrogen at 68 掳C to give methanol and [(^tbpy)₂Rh(H)(TFA)][OTf]. Studies indicate that the activation of dihydrogen has a first-order dependence on the Rh(III) methoxide complex and a dependence on hydrogen that is between zero and first order. Combined experimental and computational studies have led to a proposed mechanism for hydrogen activation by [(^tbpy)₂Rh(OMe)(MeOH)][OTf][TFA] that involves dissociation of MeOH, coordination of hydrogen, and 1,2-addition of hydrogen across the Rh鈥揙Me bond. DFT calculations indicate that there is a substantial energy penalty for MeOH dissociation and a relatively flat energy surface for subsequent hydrogen coordination and activation.