Octamethyl-1,1‘-diphosphachromocene:  Its Spin Distribution and Oxidation

Abstract

Octamethyl-1,1‘-diphosphachromocene ((Tmp) 2 Cr) was prepared from (Tmp)K and chromium dichloride in 81% yield. According to X-ray analysis, it has a distorted sandwich structure with the P atoms being bent away from chromium. Large 1 H, 13 C, and 31 P NMR shifts established the similarity to chromocenes ( S = 1) and negative spin on the ligands. The signal splitting and temperature-dependent 1 H NMR data revealed that, on the ligand, the spin sits predominantly at the phosphorus and two carbon atoms. In the cyclic voltammetry, two oxidation steps and one reduction were visible. After chemical oxidation, [(Tmp) 2 Cr] + [B(C 6 H 5 ) 4 ] - was isolated in 65% yield. Its EPR spectrum is in accord with a S = 3 / 2 species. The 1 H NMR spectrum resembled those of chromocenium ions. Its analysis and that of the temperature-dependent 1 H NMR spectra indicated a rather uniform spin distribution within the ligands. It was concluded that, in any case, the phosphorus may release spin to neighboring molecules.