Kinetics and Mechanism of the Gold-Catalyzed Hydroamination of 1,1-Dimethylallene with N-Methylaniline |
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Authors: | Dr Robert J Harris Kohki Nakafuku Dr Alethea N Duncan Robert G Carden Dr Jacob C Timmerman Prof Dr Ross A Widenhoefer |
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Institution: | Department of Chemistry, Duke University, French Family Science Center, Durham, NC 27708–0346 USA |
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Abstract: | The mechanism of the intermolecular hydroamination of 3-methylbuta-1,2-diene ( 1 ) with N-methylaniline ( 2 ) catalyzed by (IPr)AuOTf has been studied by employing a combination of kinetic analysis, deuterium labelling studies, and in situ spectral analysis of catalytically active mixtures. The results of these and additional experiments are consistent with a mechanism for hydroamination involving reversible, endergonic displacement of N-methylaniline from (IPr)Au(NHMePh)]+ ( 4 ) by allene to form the cationic gold π-C1,C2-allene complex (IPr)Au(η2-H2C=C=CMe2)]+ ( I ), which is in rapid, endergonic equilibrium with the regioisomeric π-C2,C3-allene complex (IPr)Au(η2-Me2C=C=CH2)]+ ( I′ ). Rapid and reversible outer-sphere addition of 2 to the terminal allene carbon atom of I′ to form gold vinyl complex (IPr)AuC(=CH2)CMe2NMePh] ( II ) is superimposed on the slower addition of 2 to the terminal allene carbon atom of I to form gold vinyl complex (IPr)AuC(=CMe2)CH2NMePh] ( III ). Selective protodeauration of III releases N-methyl-N-(3-methylbut-2-en-1-yl)aniline ( 3 a ) with regeneration of 4 . At high conversion, gold vinyl complex II is competitively trapped by an (IPr)Au+ fragment to form the cationic bis(gold) vinyl complex {(IPr)Au]2C(=CH2)CMe2NMePh]}+ ( 6 ). |
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Keywords: | allenes gold hydroamination kinetics mechanisms |
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