Kinetics and Mechanism of the Gold‐Catalyzed Hydroamination of 1,1‐Dimethylallene with N ‐Methylaniline

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(η 2 ‐H 2 C=C=CMe 2 )] + ( I ), which is in rapid, endergonic equilibrium with the regioisomeric π‐ C2,C3 ‐allene complex [(IPr)Au(η 2 ‐Me 2 C=C=CH 2 )] + ( I′ ). Rapid and reversible outer‐sphere addition of 2 to the terminal allene carbon atom of I′ to form gold vinyl complex (IPr)Au[C(=CH 2 )CMe 2 NMePh] ( II ) is superimposed on the slower addition of 2 to the terminal allene carbon atom of I to form gold vinyl complex (IPr)Au[C(=CMe 2 )CH 2 NMePh] ( 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] 2 [C(=CH 2 )CMe 2 NMePh]} + ( 6 ).