Tetraphenyl derivatives of phosphorus, arsenic and antimony exchange reaction and reduction. Crystal and molecular structure of [(C4H8O2)NaAsPh2]n.

The tetraphenyl derivatives of phosphorus(I1) and arsenic(I1) P2Ph4 and As2Ph4 were found to undergo a relatively fast exchange reaction to the mixed product Ph2PAsPh2, and the corresponding equilibria were studied in benzene, diethyl ether, and chloroform. By measurements of equilibrium constants at different temperatures in benzene as solvent, the reaction was found to be slightly endothermic (W = 1.3 * 0.3 kcal/mol of mixed product formed) with a positive entropy contribution (AS' = +3.5 * 1.0 eu). The corresponding phosphorus and antimony compounds P2Ph4 and Sb2Ph4 undergo exchange to an even lower extent, presumably due to an even more endothermic character of the reaction. Crystal data: CI6Hl8AsNaO2, M,= 340.23, orthorhombic, a = 10.280 (1) A, b = 15.053 (2) A, c = 10.735 (1) A, Z = 4, d(ca1cd) = 1.360 g.~m-~T.h e structure consists of an alternating sequence of dioxane-coordinated sodium atoms and Ph2As groups, giving rise to infinite -Na-As-Na-As- chains parallel to [100]. The chains are almost linear (173.6 (1)') at arsenic and bent (121.5 (1)') at sodium. The geometry around arsenic approximates closely that of a trigonal bipyramid. An electron deficient 2e-3c bond involving arsenic and sodium is suggested, which appears to account also for solvation by more polar solvents such as tetrahydrofuran.