Sterically hindered diphosphines (Ph2P)2C=CHR (R=Me or Ph) and their derivatives

Reactions of (Ph,P),C=CHR (R = Me or Ph) with E (E = S or Se) yielded the corresponding mono- and di-chalcogenides and the mixed S/Se derivatives, lH, 13C and 31P NMR parameters for which are reported. These are rationalized in terms of conformational preferences associated with the relative P-E and phosphorus-lone pair orientations. The complexes [M(CO),{(Ph,P),C=CHR}] (M = Mo or W, R = Me or Ph) have also been prepared and have NMR parameters which can be accounted for similarly. The crystal structure of (Ph,P),C=CHMe has been determined by single-crystal X-ray diffraction and shows that the solid-state conformation is similar to that deduced in solution on the foregoing basis.