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′SiH 2( 2, R, R′ = Ph; 3, R = Mes, R′ = H) in benzene at room temperature with concomitant release of CH 4gas. These complexes are paramagnetic, with high-spin d 3configurations, 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 2is 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)VCH 2Ph ( 4) with Ph 2SiH 2/Ph 2SiD 2at room temperature. The reaction of 2with Ph 2SiHCl in benzene resulted in silyl group exchange to give Cp(dmpe)VSiClPh 2( 5) in 82% yield. A vanadium(III) silyl complex was obtained by oxidation of 5with Ph 3CCl to give Cp(dmpe)V(Cl)SiClPh 2( 6). The V−Si and V−Cl bond lengths of 6are 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 2with CO afforded Cp(dmpe)V(CO) 2( 7) via homoleptic cleavage of the V−Si bond. The reaction of 5with Li(Et 2O) 3B(C 6F 5) 4generated what appears to be the silylene complex [Cp(dmpe)VSiPh 2]B(C 6F 5) 4, on the basis of elemental analysis. [ABSTRACT FROM AUTHOR]