Lewis Acid-Assisted C(sp 3 )-C(sp 3 ) Reductive Elimination at Gold.

The phosphine-borane i Pr 2 P( o -C 6 H 4 )BFxyl 2 (Fxyl = 3,5-(F 3 C) 2 C 6 H 3 ) 1-Fxyl was found to promote the reductive elimination of ethane from [AuMe 2 (μ-Cl)] 2 . Nuclear magnetic resonance monitoring revealed the intermediate formation of the ( 1-Fxyl )AuMe 2 Cl complex. Density functional theory calculations identified a zwitterionic path as the lowest energy profile, with an overall activation barrier more than 10 kcal/mol lower than without borane assistance. The Lewis acid moiety first abstracts the chloride to generate a zwitterionic Au(III) complex, which then readily undergoes C(sp 3 )-C(sp 3 ) coupling. The chloride is finally transferred back from boron to gold. The electronic features of this Lewis-assisted reductive elimination at gold have been deciphered by intrinsic bond orbital analyses. Sufficient Lewis acidity of boron is required for the ambiphilic ligand to trigger the C(sp 3 )-C(sp 3 ) coupling, as shown by complementary studies with two other phosphine-boranes, and the addition of chlorides slows down the reductive elimination of ethane.