Synthesis, structure, and reactivity of Group 4 metallacycles incorporating a Me2C-linked cyclopentadienyl-carboranyl ligand

Abstract

Group 4 metallacycles [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ti[η²-N(Me)CH₂CH₂N(Me)] (1a), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Zr[η²-N(Me)CH₂CH₂N(Me)](HNMe₂) (1b) and [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]M[η²-N(Me)CH₂CH₂CH₂N(Me)] (M = Ti (2a), Zr (2b), Hf (2c)) were synthesized by reaction of [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]M(NMe₂)₂ (M = Ti, Zr, Hf) with MeNH(CH₂)_nNHMe (n = 2, 3). These metal complexes reacted with unsaturated molecules such as 2,6-Me₂C₆H₃NC, PhNCO and PhCN to give exclusively M–N bond insertion products. The M–C_cage bond remained intact. Such a preference of M–N over M–C_cage insertion is suggested to most likely be governed by steric factors, and the mobility of the migratory groups plays no obvious role in the reactions. This work also shows that the insertion of unsaturated molecules into the metallacycles is a useful and effective method for the construction of very large ring systems.