Carbon-carbon couplings in the reactions of unsaturated Group 4 metal s-cis-butadiene complexes with 2,6-xylyl isocyanide

Abstract

A group of electronically unsaturated (14-electron) diene complexes of Hf and Ti has been reacted with 2,6-xylyl isocyanide. Cp*Hf(diene)Cl (diene = 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-butadiene; Cp* = η-C5Me5) reacts with 2 mol of isocyanide to form the unusual heterospiro complexes Cp*Hf(Cl)N(xy)CCH2C(Me)=C(R)CH=CHN(xy) (R = H, Me; xy = 2,6-xylyl) involving a 1,2-hydrogen shift and a ring closure after insertion of isocyanide into the Hf-diene bond. In Cp*Hf(2,3-dimethyl-1,3-butadiene)R (R = Me, Ph, neopentyl) the size of R determines whether insertion into the Hf-R bond (R = Me) or the Hf-diene bond (R = Ph, neopentyl) takes place. Cp*Ti(2,3-dimethyl-1,3-butadiene)Cl reacts through elimination of the diene ligand and C,C coupling of two isocyanides to form (Cp*TiCl)2[μ-N2C2(xy)2]. This compound crystallizes in space group P21/c with a = 11.111 (8) Å, b = 19.435 (17) Å, c = 8.592 (4) Å, β = 109.68 (5)° at 170 K, Z = 2, and dcalcd = 1.33 g cm-3. The molecule is centered around an approximately planar raftlike Ti2N2C2 structure with a bridging nonlinear (xy)NCCN(xy) ligand. As side products two enediamide complexes deriving from double and triple insertion of isocyanide into the Ti-diene bond could be identified. The difference in reactivity between the Ti and Hf complexes demonstrates the decrease in σ2,π-metallacyclopentene character in Cp*M(diene)Cl going from M = Hf to M = Ti.