PREPARATION, REACTIVITY, AND X-RAY STRUCTURE OF A CATIONIC ALKOXYZIRCONOCENE COMPLEX

The tetrahydrofuran adduct of bis(cyclopentadienyl)-tert-butoxyzirconium(1+) tetraphenylborate (2) was prepared, in high yield, by reaction of tert-butanol with bis(cyclopentadienyl)methyl)zirconium(1+) tetraphenylborate (1). Analogous reactions of compound 1 with less hindered alcohols were complicated by the formation of several compounds of undertermined structure. The structure of compound 2 was determined by X-ray diffraction: triclinic, space group P1BAR, a = 15.564 (2) angstrom, b = 17.253 (4) angstrom, c = 21.647 (3) angstrom, alpha = 106.12 (1)-degrees, beta = 94.71 (1)-degrees, gamma = 101.76 (1)-degrees, V = 5407.3 (17) angstrom 3, Z = 6 with three independent molecules of 2 in the asymmetric unit, R = 0.0483, and R(w) = 0.0652, for 9608 observed reflections with F > 6-sigma-(F). In this structure, the lone pairs on the oxygen atom of the tert-butoxy ligand are involved in significant back-donation to the electron deficient metal center, as revealed by the short Zr-O bonds and near-linear angles at oxygen in the three independent molecules. The exchange of bound and free THF is a higher energy process in solution as compared to that observed for compound 1. Complex 2 catalyzes the Diels-Alder reaction between methyl acrylate and dienes in CH2Cl2 solution under mild conditions.