Formation and reactions of zirconaziridines

Coles, Nicholas (1993) Formation and reactions of zirconaziridines. University of Southampton, Doctoral Thesis.

Abstract

The chemistry of η2-imine complexes of the early transition metals is reviewed.

The formation of a series of zirconocene η2-imine complexes (zirconaziridines) from amine precursors, utilizing a C-H activation process is studied. Reaction with an unactivated alkene or alkyne provides a general method for the α-alkylation of amines, without the need of a formal protection/activation - deprotection sequence. The scope and selectivity of this reaction is delineated.

The mechanism of the C-H activation process leading to the zirconaziridine is investigated, including kinetic isotope effect measurements, (k_H/k_D ∼ 8 at 293K), determination of activation parameters (ΔS^++= - 19JK^-1mol^-1; ΔH⁺⁺⁼ 97kJmol^-1),and Hammet-type structure/reactivity correlations. The data obtained is consistent with a concerted pathway via a cyclic 4-memebered transition state - a cyclometallation.

When the zirconaziridine is formed in a non coordinating solvent (benzene), a rearrangement, to form a novel vinyl amido zirconocene hydride complex is observed. This complex is fluxional at room temperature, and the variable temperature n.m.r. spectra obtained may be explained by slow inversion of a pseudo-metallacyclic form, with ΔG^++= 60 kJmol^-1.

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