Reaction of neopentylidene complexes of the type M(CH-t-Bu)(N-2,6-C6H3-i-Pr2)(OR)2 (M = W, Mo) with methyl acrylate and N,N-dimethylacrylamide to give metallacyclobutane complexes

Article abstract of DOI:10.1021/om00111a025

W(CH-t-Bu)(NAr)[OCMe₂(CF₃)]₂ (Ar = 2,6-C₆H₃-i-Pr₂) reacts with methyl acrylate to give the metallacyclobutane complex W[CH(t-Bu)CH₂CH(CO₂Me)](NAr)[OCMe₂(CF ₃)]₂ (1). 1 belongs to the space group P2₁/c with a = 17.323 (3) ?, b = 10.408 (3) ?, c = 18.758 (3) ?, V = 3337 (2) ?³, M_r = 769.52, ρ(calcd) = 1.531 g cm^-3, Z = 4, and μ = 37.33 cm^-1 (R = 0.043, R_w = 0.043). The complex has an approximately square-pyramidal core geometry with the carbonyl oxygen atom bound weakly trans to the apical imido ligand. The four basal sites are occupied by the two alkoxide oxygen atoms and the two α-carbon atoms of the metallacyclobutane ligand. Similar reactions may be carried out between M(CH-t-Bu) (NAr)-[OCMe₂(CF₃)]₂ or M(CH-t-Bu)(NAr)(O-t-Bu)₂ and N,N-dimethylacrylamide to give metallacyclobutane complexes of the type M[CH(t-Bu)CH₂CH(CONMe₂)](NAr)(OR)₂ (OR = OCMe₂(CF₃), O-t-Bu; M = W, Mo). 1 reacts with trimethylphosphine to give W(CH-t-Bu)(NAr)[OCMe₂(CF₃)]₂(PMe₃), but complexes of the type W[CH(t-Bu)CH₂CH(CONMe₂)](NAr)(OR)₂ (OR = OCMe₂(CF₃), O-t-Bu) do not react readily with trimethylphosphine. Differences in reactivity of the methyl acrylate and the dimethylacrylamide tungsten complexes with ethylene are analogous. In contrast, Mo[CH(t-Bu)CH₂CH(CONMe₂)](NAr)(O-t-Bu)₂ is in equilibrium with Mo(CH-t-Bu)(NAr)(O-t-Bu)₂ and free N,N-dimethylacrylamide in solution.