Molecular Structures of Substituted Cyclopentadienylcobalt(III) Complexes(η-1, 2, 3-Trimethylcyclopentadienyl) (triphenylphosphine)dimethylcobalt(III) and (η-Methoxycarbonylcyclopentadienyl) (triphenylphosphine)dimethylcobalt(III)

Abstract

In order to elucidate the effect of electron-donating and electron-withdrawing substituents on the cyclopentadienyl group in pianostuhl complexes, the (triphenylphosphine)dimethylcobalt (III) complexes of 1, 2, 3-trimethylcyclopentadienyl [1] J and methoxycarbonylcyclopentadienyl were prepared and their crystals were subjected to X[2-r]a y analyses (Table 2). The substituents were located trans to the phosphine ligand with respect to cobalt (Fig.1, Fig.2). The Co-Me and Co-P bond lengths are shorter in [2] than in [1] (Table 5), in accord. with our qualitative observation that [2] is more stable than [1]. Deviation of the cyclopentadienyl rings from a planar regular pentagon was observed. Geometries of the substituted cyclopentadienyls in the uncomplexed state were optimized by means of ab initio molecular orbital calculations and compared with those found in the complexes (Fig.3). Strong conjugation between the methoxycarbonyl group and the cyclopentadienyl ring was found. Deviation of the cyclopentadienyl group in [1] from planarity (Table 6), and short Co-C (14) distances in [1] and [2] (Table 5) were explained by strong interaction between the metal d_xz and cyclopentadienyl e- orbitals (Fig.4).