Synthesis, Characterization, and Reactivity of Cyclometalated Gold(III) Dihalide Complexes inAqua Regia

A range of N,C-chelated, cyclometalated gold(III) complexes Au(ppy(R))X(2)have been prepared and characterized by spectroscopic, crystallographic, and computational means. Here,ppy(H)is 2-phenylpyridine dicarboxylic acid (series1),ppy(Et)is diethyl 2-phenylpyridine dicarboxylate (series2), and X is trifluoroacetate OAcF(a), Cl (b), Br (c), or I (d) anion. The dihalo complexes1b-dand2b-dare obtained when Au(ppy(R))(OAcF)(2)(1aand2a) are treated with HNO3/HX mixtures (aqua regia(X)). Good to high yields are obtained with short reaction times (< 30 min) and simple work-up. Notably, the strongly acidic medium does not cause protolytic cleavage of the Au-C or Au-N bonds in the chelate, nor is ester hydrolysis of complexes2b-dseen. Ethylene inserts into an Au-O bond of1aand1b, and the resulting trifluoroacetoxyethyl-Au complexes can be further elaborated inaqua regiawithout cleavage of the two Au-C bonds in the molecule. Facile, mutual halide exchange reactions between complexes with different halides (1band1d,1cand1d) were observed and led to formation of mixed-halide complexes Au(ppy(H))(X)(Y). These exchange reactions occurred with complete stereoselectivity. The stereoisomer produced was the one expected based on the relativetransinfluence of the halides (I > Br > Cl), i.e. the highesttransinfluence halide was locatedtransto N which is the lowesttransinfluence end of the chelate. These thermodynamic preferences were also investigated by DFT computations.