SYNTHESIS AND STRUCTURE OF PENTAVALENT BISMUTH(V) ALKOXIDES AND LIGAND REDISTRIBUTION EQUILIBRIA IN SOLUTION

The six new pentavalent Bi(V) alkoxide complexes Ph3Bi(OR)(2), 1, Ph3B iBr(OR), 2, and Ph4Bi(OR), 3 (a, R = C6F5; b R = C6Cl5) have been prep ared. Ph4Bi(OR) was synthesized by alcoholysis of BiPh5 with ROH. Ph3B i(OR)(2) and Ph3BiBr(OR) were products of the salt elimination reactio n between Ph3BiBr2 and NaOR. These compounds were characterized spectr oscopically and by single-crystal X-ray diffraction. In the solid stat e, they possess distorted trigonal bipyramidal coordination geometries . Although the mixed species Ph3BiBr(OR) may be isolated in pure form as crystalline solids, they do not exist as pure compounds in solution owing to the very rapid redistribution equilibrium Ph3Bi(OR)(2) + Ph3 BiBr2 reversible arrow 2Ph(3)BiBr(OR). The equilibrium constants were measured using VTNMR spectroscopy. For comparison, the equilibrium con stants for the previously unreported cross-exchange reactions between the dihalides Ph3BiX2 (X = F, Cl, Br) were also measured at 226 K. Tre nds observed in the values of K-eq correlate with the difference in th e electronegativity of the mixed X species. The thermal stabilities of Ph3Bi(OR)(2) were examined in toluene solution and in the solid state . Pyrolysis results in elimination of ROPh for both R = C6F5 and C6Cl5 .