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

Group 4 metallacycles [eta(5): sigma-Me2C(C5H4)(C2B10H10)] Ti[eta(2)-N(Me)CH2CH2N(Me)] (1a), [eta(5): sigma-Me2C(C5H4)(C2B10H10)]Zr[eta(2)-N(Me)CH2CH2N(Me)](HNMe2) (1b) and [eta(5): sigma-Me2C(C5H4)(C2B10H10)]M[eta(2)-N(Me)CH2CH2CH2N(Me)] (M = Ti (2a), Zr (2b), Hf (2c)) were synthesized by reaction of [eta(5): sigma-Me2C(C5H4)(C2B10H10)]M(NMe2)(2) (M = Ti, Zr, Hf) with MeNH(CH2)(n)NHMe (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.