Synthesis and Reactivity of Cationic Group 4 Tropocoronand Complexes

The tropocoronand complexes [M(TC-3,3)(CH 2 Ph) 2 ] (M = Zr, Hf) react with either oxidants or protic reagents to afford the five-coordinate cations [M(TC-3,3)(CH 2 Ph)] +, in which the benzyl ligand interacts weakly in an η 2 manner with the group 4 metal center. Isocyanides react with the resulting cations to afford ketenimine complexes, whereas benzophenone inserts into the M−C bond to yield [M(TC-3,3){η 1 -OCPh 2 (CH 2 Ph)}] + . These properties reflect the greater electron-releasing character of the tropocoronand ligands compared to cationic zirconium complexes of other tetraaza macrocyclic ligands and to zirconocenes.