Synthesis and reactivity of cationic group 4 tropocoronand complexes

The tropocoronand complexes [M(TC-3,3)(CH2Ph)(2)] (M = Zr, Hf) react with either oxidants or protic reagents to afford the five-coordinate cations [M(TC-3,3)(CH2Ph)](+), in which the benzyl ligand interacts weakly in an eta(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){eta(1)-OCPh2(CH2Ph)}](+). 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.