Vanadium complexes tris

Several vanadium (V) complexes were also studied by Aliwi [41] in 1988 as possible photoinitiators for the radical polymerization of MMA. These complexes are oxo-tris(ethoxo) vanadium (V), VO(OC2H5)3, oxo-tris-(triphenylsiloxy) vanadium (V), VO(Si(C6Hs)3)3,... 

The same N3O3 coordination sphere is exhibited by tris(picolinato)-vanadium(III) complex, rV(pic)3], the significantly distorted octahedral geometry of which is shown in Figure 7.13... 

The /3-diketonates are usually thermally stable and may be fused or volatilized with little or no decomposition. These complexes were tested by gas-liquid chromatography without evidence for on-column degradation.252 However, some retention of fluorodiketonato complexes was due to reaction in the stationary phase or with active sites.253 The sublimation enthalpy of tris(trifluoroacetylacetonate)vanadium(III) is 118 2kJmol-1 and the evaporation enthalpy is 77.8 0.8 kJ mol-1.254 At 300-470°C there is decomposition of [V(acac)3] acetone, CO and CO2 are the products.255... 

Aromatic polyalcohols act as strong coordinating agents and Table 17 summarizes reported formation constants. The complexes are quite stable this behaviour has been used for the qualitative and quantitative determination of vanadium (e.g. refs. 494 and 495). At pH 3-4, an initial vanadyl catechol complex slowly converts to a tris complex.496 In fact complexes with 1 3 metal-ligand stoichiometry have been isolated (see below), but since in the equilibrium (30) no protons are consumed or liberated, [VO(cat)2]2- and [V(cat)3]2 are not distinguishable by potentiometric studies. 

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

The synthesis, properties, and biological activities of tris(maltolato)vanadium(III) and three analogues have been reported (Table 7). The structures of the [V(ma)3] complex and the ligands are shown in Figure 16. Blood glucose levels in STZ-diabetic rats were determined after 24 hours... 

Vanadium-sulphur ligand complexes have been studied as models of biological vanadium systems (see Vol. 5, p. 42). Tris(diethyldithiocarbamato)vanadium(iii) is more easily reduced and oxidized than its 8-hydroxyquinolinato analogue. It is suggested that this is a reflection of the increased electron density and/or electron mobility in the sulphur ligand. 

The tris-tiron [tiron (20)] complex of vanadium(IV) is formed slowly, with a half-life of several minutes, from aq, both in acidic and in basic solution. The rate-determining step, here as in the production of the earlier-characterized octahedral tris-catechol-vanadium(IV) complex, is believed to be the removal of the vanadyl-oxygen needed for the addition of the third catecholate ligand. Repeat scan spectra indicate a half-life of about 10 minutes for ligand hydrolysis in the binuclear oxo-bridged complex [ V 0(salamhp) 20], salamhp = (21). ... 

Organometallic compounds apart, oxidation states below - -2 are best represented by complexes with tris-bidentate nitrogen-donor ligands such as 2,2 -bipyridyl. Reduction by LiAlH4 in thf yields tris(bipyridyl) complexes in which the formal oxidation state of vanadium is -1-2 to —1. Magnetic moments are compatible with low-spin configurations of the metal but. 

V(IV) complexes with the formula V(R2C fc)4 (R = Me, Et) were studied by Bradley et al. 11,12, 4, 5). The ethyl complex (5) is thermally unstable and air-sensitive. The thermal instability accounts for the formation of the vanadium tris(dithio-carbamate). The tetrakis(dithiocarbamato) complex is isomorphous with 4)... 

The Tp hgands (i.e., tris(pyrazolyl)borates or scorpionates [13]) are close analogs to the Cp hgands (i.e., -cyclopentadienyl), and in connection with the chemistry of the Tp Cr complexes mentioned above, a recent example of O2-binding from vanadium chemistry is of interest, even though it is formally not organometalhc chemistry Reaction of the V(IV) complex... 

The charge at the vanadium in the usual dithiolene complexes may be estimated49 as less than 2, and these complexes are therefore included in the section on low valence states. Various tris(dithiolene) complexes have been isolated and one-electron oxireductions studied by polarographic and voltammetric techniques. Table 3 summarizes methods of preparation and electrochemical behaviour. Schrauzer and co-workers50 correlated electrochemical data with Taft s constants the observed linear correlation reflected the ligand n orbital origin of the orbitals involved in the redox process. 

Figure 4 Electronic configurations of vanadium tris(l, 2-dithiolene) complexes (from ref. 54, based on the scheme in...

From equation (30), whether a tris chelate is formed depends on the donor ability of the ligand. Several vanadium(IV) complexes with 1,2-dihydroxybenzenes formed from solutions of the ligand, VOSO4 and thallium(I) acetate.498 The compounds are of two types (I) T12[V(RC6H302)3] (R = H, 3-Me, 4-Me, 3-MeO) and (II) T12[V0(RC6H302)2] (R = CHO). 

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