Mechanisms of syn-Insertion of Alkynes and Allenes into Gold鈥揝ilicon Bonds: A Comprehensive Experimental/Theoretical Study

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• 作者：Maximilian Joost ; Laura Estevez ; Sonia Mallet-Ladeira ; Karinne Miqueu ; Abderrahmane Amgoune ; Didier Bourissou
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：July 23, 2014
• 年：2014
• 卷：136
• 期：29
• 页码：10373-10382
• 全文大小：507K
• ISSN：1520-5126

文摘

A detailed mechanistic study is reported for the syn-insertion of alkynes and allenes in the Au鈥揝i bonds of complexes (R₃P)Au鈥揝iR鈥睵h₂ (R = Ph, Me and R鈥?= t-Bu, Ph). Kinetic experiments indicate that (i) the reaction is first-order in alkyne and gold silyl complex and (ii) it requires a rather low enthalpy of activation and a relatively large negative entropy of activation [螖H^{鈥?/sup> = 13.7 (卤1.6) kcal路mol鈥? and 螖S鈥?/sup> = 鈭?2.0 (卤5.0) cal路mol鈥?路K鈥? for the reaction of (Ph₃P)Au鈥揝i(t-Bu)Ph₂ with methyl propiolate], in line with a bimolecular associative transformation. The different mechanistic pathways have been explored by DFT calculations. Accordingly, the reaction is found to proceed via a two-step inner-sphere mechanism: (i) first, the alkyne coordinates to the gold silyl complex to form a 蟺-complex; (ii) the subsequent migratory insertion step is rate determining and occurs in a concerted manner. Provided dispersion effects are taken into account (B97D functional), the enthalpy of activation estimated theoretically [螖H鈥?/sup> = 11.5 kcal路mol鈥?] is in good agreement with that measured experimentally. The influence of the 蟺 substrate (methyl propiolate, dimethyl acetylene dicarboxylate, phenyl acetylene, ethyl 2,3-butadienoate) has been analyzed theoretically, and the regioselectivity of the insertion has been rationalized. In particular, the unexpected selectivity observed experimentally with the allene is shown to result from the insertion of the terminal nonactivated C鈺怌 double bond into the Au鈥揝i bond of (Ph₃P)Au鈥揝iPh₃, followed by an original isomerization (Au/Si exchange process). This study provides unambiguous evidence for coordination鈥搃nsertion at gold and thereby strongly supports the possible occurrence of inner-sphere mechanisms during the functionalization of alkynes and allenes.}