INTRAMOLECULARLY COORDINATED ARYLMAGNESIUM COMPOUNDS - EFFECTS ON THE SCHLENK EQUILIBRIUM

A series of phenylmagnesium bromides (1, 3-8) with ortho-substituents capable of forming intramolecular coordinative bonds along with the corresponding diarylmagnesium compounds (1a, 3a-6a, 8a) have been synthesized. The thermodynamic parameters DELTA-H(s) and DELTA-S(s) for the Schlenk equilibria (2 ArMgBr half-arrow-right-over-half-arrow-left Ar2Mg + MgBr2) have been determined by variable temperature NMR spectroscopy. Crystal structures were obtained of 5,6,8,9-tetrahydrodibenz[d,g][1,6]oxamagnescein (2a) and bis(2,6-di(methoxymethyl)phenyl)magnesium (4a). The extent of intramolecular coordination in these compounds as determined in the solid state, is used in the discussion of the influence of substituents on the Schlenk equilibrium parameters. Unusual penta- or hexa-coordination is encountered and explained as a consequence of intramolecular coordination.