Unexpected Complexes from meta-Phenylene Bis(tert-butyl Nitroxides) and Gadolinium(III) 1,1,1,5,5,5-Hexafluoropentane-2,4-dionate

摘要

Coordination reaction of the stable ground triplet biradical biphenyl-3,5-diyl bis(tert-butyl nitroxide) and [Gd(hfac)_3(H_2O)_2] unexpectedly gave complexes containing a dimerized diamagnetic ligand via a [3+3] cycloaddition of the benzene rings (hfac= 1,1,1,5,5,5-hexafluoropentane-2,4-dionate). To avoid such dimerization, we introduced a bulkier substituent into the ligand; namely, a new ground triplet biradical 5-mesityl-1,3-phenylene bis(tert-butyl nitroxide) was applied to this complexation scheme. However, an unexpected complex was again obtained in a different way, and the magnetic study revealed that the novel ligand involved was diamagnetic. The crystallographic analysis of the product clarified isomerization from the paramagnetic ligand to a diamagnetic N-tert-butylaminoquinone imine N-oxide ligand as a result of disproportionation from two open-shell nitroxide groups to closed-shell groups, an amine and a nitrone. The present paper reports the first structural evidence for a diamagnetic isomer of m-phenylene-bridged bisnitroxde compounds.