SYNTHESIS AND CHARACTERIZATION OF 1,2-BIS(PHOSPHINO)BENZENE (DIPHOS) AND RELATED COMPLEXES OF VANADIUM, CHROMIUM, IRON AND COBALT - X-RAY CRYSTAL-STRUCTURES OF MCL2(DIPHOS)2 (M = V, CR AND FE) AND [FE(DIPHOS)2(MECN)2](BPH4)2

The interaction of transition metal dichlorides with the chelating diphosphine (diphos) ligands 1,2-bis(phosphino) benzene, 1,2-bis(2-propylphosphino) benzene and 1,2-bis(dimethylphosphino) benzene leads to the octahedral complexes trans-MCl2(diphos)2, (M = V, Cr, Fe or Co). Interaction of FeCl2[1,2-(Me2P)C6H4]2 with NaBPh4 in refluxing MeCN gives the nitrile complex trans-[Fe(NCMe)2(diphos)2](BPh4)2, whereas VCl2[1,2-(C3H7PH)2C4H4]2 gives only the complex [V(CNMe)6](BPh4)2. This difference is attributed to the weaker basicity (exemplified by the longer M-P bond lengths) of the secondary phosphine ligand. X-ray crystal structures of the following compounds have been determined: MCl2[1,2-(C3H7PH)2C6H4]2 (M = V, Cr or Fe) and [Fe(NCMe)2{1,2-(Me2P)C6H4)2](BPh4)2. In all cases the octahedral complexes have trans-Cl or MeCN groups.