Reductive Elimination Leading to C-C Bond Formation in Gold(III) Complexes: A Mechanistic and Computational Study.

摘要: The factors affecting the rates of reductive C-C cross-coupling reactions in gold(III) aryls were studied using complexes that allow easy access to a series electronically modified aryl ligands, as well gold methyl and vinyl complexes, pincer compounds (C^N^C)AuR (R = C6F5, CH=CMe2, Me p-C6H4X, where X OMe, F, H, But, Cl, CF3, or NO2) starting materials (C^N^C 2,6-(4′-ButC6H3)2pyridine dianion). Protodeauration followed by addition 1 equiv. SMe2 leads quantitative generation thioether [(C^N-CH)AuR(SMe2)]+. Upon second pyridine is displaced, which triggers aryl-R elimination. for these cross-couplings increase sequence k(vinyl) > k(aryl) >> k(C6F5) k(Me). Vinyl-aryl coupling particularly fast, 1.15 × 10–3 L mol–1 s–1 at 221 K, while both C6F5 couplings encountered higher barriers bond forming step. Using P(p-tol)3 place greatly accelerates C–C couplings. Computational modelling shows C^N bonded displacement N donor required before ligands can adopt conformation suitable formation, so elimination takes from four-coordinate intermediate. formation rate limiting. In non-chelating case, C(sp2)-C(sp2) three-coordinate cations [(Ar1)(Ar2)AuL]+ almost barrierless, if phosphine.