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

The phosphine-borane i Pr2 P( o -C6 H4 )BFxyl2 (Fxyl = 3,5-(F3 C)2 C6 H3 ) 1-Fxyl was found to promote the reductive elimination of ethane from [AuMe2 (μ-Cl)]2 . Nuclear magnetic resonance monitoring revealed the intermediate formation of the ( 1-Fxyl )AuMe2 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(sp3 )-C(sp3 ) 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(sp3 )-C(sp3 ) coupling, as shown by complementary studies with two other phosphine-boranes, and the addition of chlorides slows down the reductive elimination of ethane.