Synthesis, structures, and properties of 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(I) with 1,5-diaza-3,7-diphosphacyclooctanes

Two new 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(1) (2a and 2b) with 1,3,5,7-tetraphenyl-1,5-diaza-3,5-diphosphaccyclooctane (la) and 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane (Ib), respecti vely, were synthesized. Their structures in solution and in the crystalline state were studied. According to the results of X-ray diffraction analysis , the copper(I) atom in molecules 2a and 2b is in a pseudotetrahedral envir onment and is directly coordinated to two P atoms of the diazadiphosphacycl ooctane ligand and two O atoms of the benzosemiquinone ligand. In complex 2 a, ligand la adopts a chair-boat conformation typical of all complexes with eight-membered cyclic 1,5-donors studied previously. Unlike ligand 1a, the ligand in complex 2b adopts a chair-chair (crown) conformation identical w ith that of the Free ligand. Both complexes are paramagnetic in the solid s tate and in solutions. The parameters of the isotropic ESR spectra of compl exes 2a and 26 are typical of four-coordinate o-semiquinone copper(I) compl exes with bidentate bisphosphine ligands. Based on analysis of the isotropi c ESR spectra, it was suggested that compound 2b in solutions exists as two isomers, which differ in the conformation of the eight-membered heterocycl e (chair-boat or chair-chair).