Thermolysis of Half-Sandwich Vanadium(V) Imido Complexes to Generate Vanadium(III) Imido Species via a Vanadium(IV) Intermediate

Thermolysis of half-sandwich vanadium imido complexes Cp(RN)V(i-Pr2N)Me (R = p-Tol, 1a; R = t-Bu, 1b) results in a mixture of products, including vanadium(IV) dimers [CpVMe](2)(mu-RN)(2), i-Pr2NH, i-PrNCMe2, CH4, and one or more paramagnetic species. In the presence of dmpe (dmpe = bis(dimethylphosphino)ethane), PMe3, or PhSSPh, the initially formed paramagnetic species can be trapped, providing Cp(RN)VL2(R = p-Tol, L-2 = dmpe, 2a; R = t-Bu, L-2 = dmpe, 2b; R = p-Tol, L = PMe3, 3a; R = t-Bu, L = PMe3, 3b; R = t-Bu, L = SPh,4b). This suggests that the initially formed species is [Cp(RN)V]. When generated in situ, [Cp(RN)V] is active in the [2+2+2] cyclotrimerization of PhCCH (R = p-Tol, t-Bu) and PhCCPh (R = t-Bu). Furthermore, the data presented indicate a mechanism in which both [CpVMe](2)(mu-RN)(2) and [Cp(RN)V] originate from a common intermediate, vanadium(IV) imido species [Cp(RN)VMe].