SIGMA-ALKENYL AND HALOGENO COMPLEXES OF VANADIUM (I AND II) - THE CRYSTAL-STRUCTURES OF (CLV(CO)2(PH2PCH2CH2PET2)2.BENZENE, BR2V(ME2PCH2CH2PME2)2 AND I2V(ME2PCH2CH2PME2)2.TOLUENE

Various sigma-alkenyl complexes of the general composition (alkenyl)V( CO6-npm (where n = 2, 3 and p(m) is a potentially m-dentate phosphine coordinated through n of its donor centres, n less-than-or-equal-to m) have been prepared by photo-induced hydrovanadation of the alkynes 2- butyne, 1-hexyne, 3-hexyne and 3,3-dimethyl-1-butyne. In each case the Z isomer is formed exclusively or as the predominant product. Reactio n of hexacarbonylvanadate with pyridinium bromide and p(m) leads to th e bromo complexes BrV(CO)6-npm (n = 2-4). In the case of p(m) = Me2PCH 2CH2PMe2 (dmpe), the complex Br2V(dmpe) is also formed. The complex I2 V(dmpe)2 . toluene was obtained as a by-product from the reaction betw een [Et4N][V(CO)4dmpe] and perfluoro-isopropyl iodide. The face-capped , trigonal-prismatic complex ClV(CO)2(pepe)2 . benzene (pepe = Ph2PCH2 CH2PEt2) was obtained from the photo-reaction between HV(CO)4pepe and [Et4N]Cl. Single-crystal X-ray diffraction studies were carried out on all three complexes. The V-50 NMR chemical shifts for the seven-coord inate complexes XV(CO)npm have been used to arrange the ligands X in a magnetochemical series of ligand strengths (alkenyl congruent-to alky l < SiMe3 < H congruent-to Br congruent-to I < O2CR < Cl congruent-to N3 < CN).