Models for solvation of zirconocene cations: Synthesis, reactivity, and computational studies of phenylsilyl-substituted cationic and dicationic zirconocene compounds

The reactions of the zirconocene compounds [(eta(5)-C5H5)(eta(5)-C5H4SiMe2C6H5)ZrMe2] (1) and [(eta 5C5H4SiMe2C6H4Me 2ZrMe2] (2) with either B(C6F5)(3) or the trityl salt [Ph3C](+)[B(C6F5)(4)](-) in CD2Cl2 were monitored by NMR spectroscopy. In the case of the cationic products [(eta(5)-C5H5)(eta(5)-C5H4SiMe2C6H5)ZrMe](+)[ MeB(C6F5)(3)](-) (4a) and [(eta(5)-C5H4SiMe2C6H4Me)(2)ZrMe](+) X- ( 5a, X) [MeB(C6F5)(3)]-; 5b, X = [ B( C6F5) 4]-), coordination of the arene, bonded through Si to the cyclopentadienyl ring, to the cationic zirconium was observed. However, this coordination is rather weak, and stronger Lewis donors such as the anion or the starting material replace the coordinated arene moiety. The solid-state structures of 1 and 2 were determined by X-ray crystallography. Density functional computations (B3LYP/ECP1 and B3LYP/II level) have revealed that the phenyl groups in [(eta(5)-C5H5)(eta-C5H4SiMe2C6H5)ZrMe](+) (10), [(eta(5)-C5H4SiMe2C6H4Me)(2)Zr](2+) (11), and [(eta(5)-C5H4SiMe2C6H5)(2)Zr](2+) (12) are coordinated via one of the arene carbon atoms. The structural assignments are supported by the good agreement between the experimental NMR shifts and the computed (GIAO-B3LYP/II level) shifts in the case of the cationic compound (10). The structure of the dicationic compound 11 differs significantly from that of 12, indicating a strong influence of the para substituent of the arene ring. Compounds 1 and 2 validate previously suggested models for solvent (arene) adducts in Kaminsky-type polymerization.