Unusual strong ortho effects in the rearrangement of binuclear gold(I) complexes

Ab-initio calculations using the binuclear model compounds [Au2X2(mu-L)2] (L = C6H4PH2, 5-MeC6H4PH2, and 6-MeC6H4PH2 and X = Cl, Br, and I) show that the 6-methyl substituent energetically favors isomerization to a gold(I)/gold(III) species and also sterically blocks the C-C coupling reaction of this complex. These findings are in excellent agreement with experimental data for this system. Furthermore, these results demonstrate that partial opening of the Au(III)-P bond is the key step in the sequence leading to C-C coupling.