Paramagnetic Vanadium Silyl Complexes: Synthesis, Structure, and Reactivity

Vanadium silyl complexes of the type Cp(dmpe)VSiHRR′ are formed by reaction of Cp(dmpe)VMe (1) with RR′SiH2 (2, R, R′ = Ph; 3, R = Mes, R′ = H) in benzene at room temperature with concomitant release of CH4 gas. These complexes are paramagnetic, with high-spin d3 configurations, and exhibit broad 1H NMR resonances. They possess three-legged piano-stool geometries, and each silicon atom adopts a tetrahedral structure with no agostic V···HSi interaction. The V−Si bond length of 2 is 2.5629(8) Å, and the V−P bond lengths are 2.4613(8) and 2.4621(8) Å. A KIE value of 2.1 ± 0.1 was observed for the reaction of Cp(dmpe)VCH2Ph (4) with Ph2SiH2/Ph2SiD2 at room temperature. The reaction of 2 with Ph2SiHCl in benzene resulted in silyl group exchange to give Cp(dmpe)VSiClPh2 (5) in 82% yield. A vanadium(III) silyl complex was obtained by oxidation of 5 with Ph3CCl to give Cp(dmpe)V(Cl)SiClPh2 (6). The V−Si and V−Cl bond lengths of 6 are 2.573(1) and 2.388(1) Å, respectively. The Si−Cl bond length of 2.160(1) Å is longer than those typically observed (ca. 2.023 Å). Reaction of 2 with CO afforded Cp(dmpe)V(CO)2 (7) via homoleptic cleavage of the V−Si bond. The reaction of 5 with Li(Et2O)3B(C6F5)4 generated what appears to be the silylene complex [Cp(dmpe)VSiPh2]B(C6F5)4, on the basis of elemental analysis.