η~5-1,2,3-Trisilacyclopentadienyl - A Ligand for Transition Metal Complexes: Rhodium Half-Sandwich and Ruthenium Sandwich

摘要

Coordination chemistry is greatly dominated by the transition metal complexes featuring cyclic polyene ligands, such as cyclo-propenyls η~3-C_3R_3, cyclobutadienes η~4-C_4R_4, cyclopentadienyls η~5-C_5R_5, arenes η~6-C_6R_6, cycloheptatrienyls η~7-C_7R_7, cyclooctatetraenes η~8-C_gR_8, etc. Among them, complexes with cyclopentadienyl ligands are most abundant. One can recall milestone metallocenes known since the synthesis of ferrocene (η~5-H_5C_5)_2Fe by Kelly and Pauson in 1951. Apart from fascinating structures and nonclassical bonding modes, sandwich metallocenes as well as cyclopentadienyl half-sandwich complexes have found widespread utilization in material science: asymmetric catalysis, polymerization of alkenes, and fluorescent materials. Analogues of metallocenes with the heavy group 14 elements (Si, Ge) in the cyclopentadienyl ring are particularly challenging because of the novel physicochemical properties anticipated upon the introduction of metalloid elements. However, untU now, only a few compounds of such type based on the group 4,5, and 8 transition metals have been isolated, including ruthenocenes and ferrocene featuring sila- and germacyclopenta-dienyl ligands. We have also contributed to the field with the recent report on the synthesis of a heavy analogue of ferrocene with a disilagermacyclopentadienyl ligand. In this contribution, we describe the synthesis of two complexes featuring a novel trisila-cyclopentadienyl ligand: Rh half-sandwich (piano-stool) and Ru sandwich (ruthenocene). The former is particularly important, being the first group 9 metal complex with the heavy cyclopentadienyl ligand and the first heavy cyclopentadienyl complex of half-sandwich type.