?-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

Article abstract of DOI:10.1016/0022-328X(94)80199-1

Various ?-alkenyl complexes of the general composition (alkenyl)V(CO)6-np_m (where n = 2,3 and p_m is a potentially m-dentate phosphine coordinated through n of its donor centers, n <*> 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.Reaction of hexacarbonylvanadate with pyridinium bromide and p_m leads to the bromo complexes BrV(CO)6-np_m (n = 2-4).In the case of p_m = Me2PCH2CH2PMe2 (dmpe), the complex Br2V(dmpe) is also formed.The complex I2V(dmpe)2*toluene was obtained as a by-product from the reaction between and perfluoro-isopropyl iodide.The face-capped, trigonal-prismatic complex ClV(CO)2(pepe)2*benzene (pepe = Ph2PCH2CH2PEt2) was obtained from the photo-reaction between HV(CO)4pepe and Cl.Single crystal X-ray diffraction studies were carried out on all three complexes.The 51V NMR chemical shifts for the seven-coordinate complexes XV(CO)np_m have been used to arrange the ligands X in a magnetochemical series of ligand strengths (alkenyl <*> alkyl < SiMe3 < H <*> Br <*> I < O2CR < Cl <*> N3 < CN). Key words: Vanadium; Alkenyl; Phosphine; Crystal structure; Halide