Pnictogen-based vanadacyclobutadiene complexes.

The reactivity of the V[triple bond, length as m-dash]C Bu multiple bonds in the complex (dBDI)V[triple bond, length as m-dash]C Bu(OEt) (C) (dBDI = ArNC(CH)CHC(CH)NAr, Ar = 2,6- PrCH) 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(κ- , - BuC(R)N) (R = Ad, 1; R = Ph, 2) and β-phospha-vanadacyclobutadiene moieties, (dBDI)V(κ- , - BuPAd) (3). Complexes 1-3 are characterized using multinuclear and multidimensional NMR spectroscopy, including the preparation of the 50% N-enriched isotopologue (dBDI)V(κ- , - BuCC(Ad)N) (1-N). 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(κ- , - BuC(H) 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.