11  Vanadium, niobium and tantalum

Abstract

If activated with Me 3 SiCH 2 MgCl or Bu 2 Mg, the first structurally characterised dichlorooxovanadium() alkoxide, [VOCl 2 OCH 2 CH 2 OPh)], was found to be an effective catalyst for the polymerisation of styrene. The complexes, [V(Bu t 2 pz)Cl 2 (THF) 2 ], [V(Bu t 2 pz) 2 Cl(THF) 2 ] and [V(Bu t 2 pz) 3 (THF)] may be the first examples of η 2 -pyrazolato co-ordination to a d 2 metal centre. The first tantalasilsesequioxanes have been prepared and these include the half-sandwich complexes, [Cy 7 Si 7 O 12 Ta-(NMe 2 ) 2 ], [H 2 NMe 2 ][Ta(Cy 7 Si 7 O 12 ) 2 ] and the first example of a carboranesilsesquioxane hybrid compound, [Cy 7 Si 7 Oi 7 Ta(C 2 B 9 H 11 )]. The first homoleptic naphthalene complex of a third row transition metal, [Na(THF)][Ta(C 10 H 8 ) 3 ], has been prepared by conventional bench methods as opposed to MVS methods. The first hexadecavanadate compound, [{Cu(1,2-pn) 2 } 7 {V 16 O 38 (H 2 O)} 2 ]ؒ4H 2 O, has been prepared and characterised. Co-ordination chemistry VanadiumStructural and conformational changes in [V(O)(acac) 2 ], in frozen solution, have been studied by ENDOR spectroscopy in tandem with DFT calculations. In the absence of a co-ordinating solvent, the expected square pyramidal geometry is observed. In the presence of a co-ordinating solvent, however, a 3 : 2 ratio of co-existent cis-and trans-[V(O)(acac) 2 (solvent)] species is observed. 3 The oxalatooxoperoxo vandium() complexes, (H 3 dien)[VO(O 2 )(C 2 O 4 )]ؒH 2 O, (H 3 tren)[VO(O 2 )(C 2 O 4 )]ؒ3H 2 O, (Hampic) 3 -