Pnictogen-based vanadacyclobutadiene complexes

Abstract

The reactivity of the VC^tBu multiple bonds in the complex (dBDI)VC^tBu(OEt₂) (C) (dBDI²⁻ = ArNC(CH₃)CHC(CH₂)NAr, Ar = 2,6-ⁱPr₂C₆H₃) with unsaturated substrates such as NCR (R = Ad or Ph) and PCAd leads to the formation of rare 3d transition metal compounds featuring α-aza-vanadacyclobutadiene, (dBDI)V(κ²-C,N-^tBuCC(R)N) (R = Ad, 1; R = Ph, 2) and β-phospha-vanadacyclobutadiene moieties, (dBDI)V(κ²-C,C-^tBuCPCAd) (3). Complexes 1–3 are characterized using multinuclear and multidimensional NMR spectroscopy, including the preparation of the 50% ¹⁵N-enriched isotopologue (dBDI)V(κ²-C,N-^tBuCC(Ad)¹⁵N) (1-¹⁵N). Solid-state structural analysis is used to determine the dominant resonance structures of these unique pnictogen-based vanadacyclobutadienes. A systematic comparison with the known vanadacyclobutadiene (dBDI)V(κ²-C,C-^tBuCC(H)C^tBu) (4) is also presented. Theoretical investigations into the electronic structure of 2–4 highlight the crucial role of unique V–heteroatom interactions in stabilizing the vanadacyclobutadienes and identify the most dominant resonance structures.