C-ON bond homolysis of alkoxyamines triggered by paramagnetic copper(II) salts

Abstract

The metal complexation reactions of bis(hexafluoroacetylacetonato)copper(ii) (Cu(hfac)2) with alkoxyamines (diethyl(2,2-dimethyl-1-(tert-butyl-(1-(pyridine-4-yl)ethoxy)amino)propyl)phosphonate and diethyl (2,2-dimethyl-1-(tert-butyl-(1-(pyridine-2-yl)ethoxy)amino)propyl)phosphonate) were studied. According to X-ray analysis, the molecular and crystal structures of 1:1 complexes depend on the configuration of the free alkoxyamines, that is dimeric (RSSR) and chain-polymeric (RR/SS) structures for para-pyridyl-substituted alkoxyamines, and cyclic unimeric (RS/SR) structure for ortho-pyridyl derivative. The complex (2:1 ratio Cu(hfac)2/alkoxyamine) for ortho-pyridyl-substituted alkoxyamine is not resolved. Upon warming, ortho complexes decomposed into free alkoxyamines and only a weak activation was observed. Upon warming, para complexes decomposed into their corresponding unimers, and then, a 21-fold increase in the rate constant of the C-ON bond homolysis was observed compared to the corresponding free alkoxyamines. Tuning of the homolysis rate constant of the C-ON bond via addition of pyridine is also reported.