The synthesis of less toxic oxidation catalysts is of much interest in green chemistry. Due to a significant untapped potential gold homogeneous catalysis is only now recognized a scientific hotspot[1] with an increasing number of publications appearing on a weekly basis. The significance of AuI and AuIII complexes as homogeneous catalysts for several reactions has been only recently addressed.[2] There is still a need, however, to fully understand reaction mechanisms in order to rationally design more efficient and selective catalysts. One of the areas in homogeneous gold catalysis that has received much less attention has been selective oxidation, particularly using molecular oxygen. Gold(I) complexes have been effective in the oxidation of alcohols (with molecular oxygen)[3] and the oxidation of alkenes.[4] The nature and oxidation state of the active catalytic species is still not known. We are interested in the synthesis of gold compounds in different oxidation states (I and III) with the same set of ligands and their use in different catalytic processes.

We present here the preparation of new gold compounds with tripodal bis(imidazole) thioether ligands that have different heteroatoms (nitrogen and sulfur) than can act as donor atoms to the gold centers. This ligand system can thus stabilize gold(III) and gold(I) complexes and may allow the identification of some reaction intermediates in oxidation reactions. Results for the catalytic studies of the oxidation of alkenes and alcohols will be discussed.

[1]. Nolan, S. P. Nature 2007, 445, 496.

[2]. Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem. Int. Ed. 2006, 45, 78096.

[3]. Guan, B.; Xing, D.; Cai, G.; Wan, X.; Yu, N.; Fang, Z.; Yang, L.; Shi, Z. J. Am. Chem. Soc. 2005, 127, 18004.

[4]. Xing, D.; Guan, B.; Cai, G.; Fang, Z.; Yang, L.; Shi, Z. Org. Lett. 2006, 8, 693.