Small Gold Clusters with Carborane Ligands: Synthesis and Structural Characterization of the Novel Compound [Au_4{(PPh_2)_2C+2B_9H_(10)}_2(AsPh_3)_2]

摘要

The chemistry of homo- or heter opolynuclear gold clusters is still attracting a great deal of interest, and many examples with different nuclearities are known. However, small clusters are poorly represented; the only tetrahedral clusters described thus far are [Au_4I_2(PPh_3)_4] and [Au_4(SnCl_3)_2(PPh_3)_4], in which the two iodine or SnCl_3 groups, respectively, bridge two opposite edges of a tetrahedron of gold atoms, and the recently reported clusters [Au_4L_4](BF_4)_2 (L = PtBu_3, P(mesityl)_3), which show approximate tetrahedral symmetry. All these clusters were minor products (yields 5-15%), with the exception of [Au_4{P(mesityl)_3}_n](BF_4)_2, which was obtained in high yield. The interest in this chemistry is not only focused on the new complexes but also on understanding their formation, and thereby being in a position to develop convenient and reproducible syntheses of a desired product. Here we report the high-yield synthesis of the tetianuclear gold cluster, [Au_4{(PPh_2)_2-C_2B_9H_(10)}_2(AsPh_3)_2] by a novel and unexpected reaction. This complex is the first example of a gold cluster stabilized by arsane ligands. We are currently studying reactions involving partial degradation of the carborane cage in the diphosphane [1,2-(PPh_2)_2-l,2-C_2B_(10)H_(10)] to afford the anionic nido-ligand [7,8-(PPh_2)_2-7,8-C_2B_9H_(10)]~-. Thus, treatment of [AuCl(PR_3)] with the diphosphane in refluxing ethanol led to complexes of the type [Au{(PPh_2)_2C_2B_9H_(10)}(PR_3)]. Here we describe reactions starting from [AuCl(AsPh_3)], in which the more labile ligand plays a decisive role in directing the reactivity.