Pnictogen-based vanadacyclobutadiene complexes

The reactivity of the V[triple bond, length as m-dash]C ^t Bu multiple bonds in the complex (dBDI)V[triple bond, length as m-dash]C ^t Bu(OEt₂) (C) (dBDI^2- = ArNC(CH₃)CHC(CH₂)NAr, Ar = 2,6- ⁱ Pr₂C₆H₃) with unsaturated substrates such as N[triple bond, length as m-dash]CR (R = Ad or Ph) and P[triple bond, length as m-dash]CAd leads to the formation of rare 3d transition metal compounds featuring α-aza-vanadacyclobutadiene, (dBDI)V(κ²- C , N - ^t BuCC(R)N) (R = Ad, 1; R = Ph, 2) and β-phospha-vanadacyclobutadiene moieties, (dBDI)V(κ²- C , C - ^t BuCPCAd) (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 - ^t BuCC(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 - ^t BuCC(H)C ^t Bu) (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.