Cycloaddition reactions of titanium and zirconium imido, oxo and hydrazido complexes supported by tetraaza macrocyclic ligands ‡

The tetraaza macrocycle-supported titanium and zirconium imido complexes [Ti(NR)(Mentaa)] [R = But, Ph, Tol or 4-C6H4NO2; n = 4 or 8 where H2Mentaa = tetra- or octa-methyldibenzotetraaza[14]annulene, respectively] and [Zr(NC6H3Pri2-2,6)(py)(Me4taa)] react with isocyanates or carbon dioxide to form cycloaddition products generally of the type [M{N(R)C(O)E}(Mentaa)] (M = Ti or Zr, R = aryl or tert-butyl, E = O, NBut or N–aryl). The complex [Zr{N(C6H3Pri2-2,6)C(O)N(But)}(Me4taa)] is also formed by reaction of the bis(arylimide) [Zr(NHC6H3Pri-2,6)2(Me4taa)] with ButNCO. The crystal structures of [Ti{N(Tol)C(O)O}(Me4taa)] (Tol = p-tolyl) and [Zr{N(C6H3Pri2-2,6)C(O)N(But)}(Me4taa)] are described. The tert-butyl imido complexes [Ti(NBut)(Mentaa)] (n = 4 or 8) react with Ph2NNH2 to give the corresponding terminal N,N-diphenylhydrazido derivatives [Ti(NNPh2)(Mentaa)] and these yield the cycloaddition products [Ti{N(NPh2)C(O)O}(Mentaa)] or [Ti{N(NPh2)C(O)N(Tol)}(Me4taa)] with CO2 or TolNCO, respectively. The related titanium oxo complexes [Ti(O)(Mentaa)] (n = 4 or 8) react with p-tolyl isocyanate to form the N,O-carbamate products [Ti{N(Tol)C(O)O}(Mentaa)], and with ditolylcarbodiimide to form the N,N-ureate derivative [Ti{N(Ph)C(O)N(Ph)}(Mentaa)] in which complete rupture of the TiO linkage has occurred. Reaction of the N-phenyl-N-tolyl (asymmetric) ureate [Ti{N(Ph)C(O)N(Tol)}(Me4taa)] with an excess of PhNCO gave quantitative conversion to the N,N-symmetric product [Ti{N(Ph)C(O)N(Ph)}(Me4taa)] and TolNCO. Crossover NMR tube experiments suggest that this reaction occurs via an associative mechanism.