MONOHYDRIDE COMPLEXES OF W(IV) CONTAINING BULKY SELENOLATE LIGANDS - X-RAY CRYSTAL-STRUCTURE DETERMINATION OF [WH(SEC6H3PR2I-2,6)(3)(PME2PH)(2)]

The complexes [WH(SeR)(3)(L) (PMe2Ph)] (R = C6H3Pr2i-2,6 or C6H2Me3-2, 4,6; L = PMe2Ph, pyridine and N-methylimidazole) have been prepared by reaction of [WH6(PMe2Ph)(3)] or cis-[W(N-2)(2)(PMe2Ph)(4)] with the s elenol HSeR and characterized by FAB mass spectroscopy, (31)p, H-1 and Se-77 NMR, IR and W-Vis spectroscopies. A single crystal X-ray diffra ction study of complex [WH(SeC6H3Pr2i-2,6)(3)(PMe2Ph)(2)] at 178 K rev eals a distorted trigonal bipyramidal geometry of the WSe3P2 core with the hydride located along an Se-P edge of the trigonal bipyramid; the hydride position was refined with a W-H distance of 1.51(6) Angstrom and an H-W-P angle of 53 degrees. This small angle results in a large (2)J(H,P) coupling of 99 Hz. The bulky Se ligands adopt a 'two-up, one -down' arrangement of aryl substituents. The (2)J(SeP) values show a h igh degree of dependence on the P-M-Se angles or the P-M-Se-C dihedral angle, This may be useful for assigning geometries of selenolate comp lexes. Improved syntheses of the starting compounds [WH6(PMe2Ph)(3)] a nd cis-[W(N-2)(2)(PMe2Ph)(4)] are reported.