Tungsten vi Complexes

Molybdenum(vi) and Tungsten(vi) Complexes.—0-Donor Ligands. These comprise the vast majority of studies of this oxidation state for these elements. Vibrational spectra of [ MoO ] , and 

Heats of formation of certain molybdates and tungstates have been estimated. The Mossbauer parameters for the 100 keV transition of in WO3, 

A potentiometric study of polymeric anions of molybdenum in nitrate melts has resolved apparent contradictions in earlier work and confirmed that [Mo207] , rather than [Mo30,o] , is the polymeric anion in equilibrium with [MoOj ] The crystal structure of K2[Mo,07] has been shown to involve chains of M0O4 tetrahedra and MoO octahedra and the dissociation of molten Na2[W207] to Na and a mixture of anions including [W04], [W207] , and has been confirmed. The results of other 

W203(As04)2 st, ASO4 tetrahedra sharing corners with four WOg octahedra 1 

M2[Mo04]-Np[Mo04]2 1 A scheelite structure system A scheelite structure 

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A unique series of mixed guanidinato/alkylimido/azido tungsten(VI) complexes has been synthesized and structurally characterized. As illustrated in Scheme 133, the syntheses start with the readily accessible imido precursor WCl2(NBu )2py2, which is treated successively with either appropriate lithium... 

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

The heat of formation of [MolCOlg] has been determined as -960 + 12 kJ mol by measuring its heat of decomposition. The Mossbauer parameters for the 100 keV transition of in [W(CO)g] and some tungsten(vi) complexes have been measured and discussed in terms of known bonding and structure. Secondary ions [M (CO) ] (M = Mo, m = I or 2 M = W, m = 1—4 n = 0—14) formed by ion-molecule reactions have been observed in the mass spectra of the hexacarbonyls. A mixt u re of [Cr(CO) ] and [MolCO) ] vapours affords [CrMo(CO) ] ( = 5—7). [MofCOl ] and [WICO) ] catalyse the condensation of isocyanates with aldehydes to give imines in high yields. ... 

DIMETHYLPROPYLIDYNE TUNGSTEN(VI) COMPLEXES AND PRECURSORS FOR THEIR SYNTHESES ... 

Tungsten(VI) complexes guanidine, 283 hydroxamic acids, 506 maleic acid, 475 conformation, 467 tartaric acid, 479 NMR, 468... 

Figure 2.28 Examples of oxygen transfer reactions of hydrogen peroxide in the presence of molybdenum (VI) and tungsten(VI) complexes.

Tungsten(VI) complexes, 974-983 alkylidene, 981 alkylidyne, 981 azobenzene, 977 carbon... 

Elliot et al. Inorg. Chem. 25, 1891 (1986)) have now provided complete physical details of the structure reported in Ref. 55. Complete details of the unusual iron structure reported in Ref. 118 are now available (/. Am. Chem. Soc. 108, 5598 (1986)), An unusual tungsten(VI) complex containing both an oxo and a peroxo ligand (cis) has been reported (Yang, C.-H., Dzugan, S. J., Goedken, V. L. J. Chem. Soc., Chem. Common. 1425... 

Figure 2. Synthesis of heterogeneous highly active metathesis catalysts by reaction of Schrock type carbyne tungsten (VI) complexes with silicagel...

TABLE 1. ROMP of cyclopentene (CPE) with the carbyne tungsten (VI) complexes Cl3(dme)WHC Bu (A) and ( BuO)3W=C Bu (B) in different solvents and in bulk pa = polymerization activity [mmol CPE mmol catalyst h ] (calculated from the turnover of monomer after 1 h), trans = trans content of doublebonds (measured via C NMR spectroscopy), temperature 25°C. 

TABLE 5. ROMP of heteroatom substituted norbomenes with carbyne tungsten (VI) complexes Cl3(dme)W=C Bu (A), ( BuO)3WsC Bu (B), Np3W=C Bu (C), nbe = norbomene, nbde = norbomadiene, reaction time 24 h, GPC Polystyrene standard solvent THE, temperature 25°C. 

The results demonstrate that the Schrock type carbyne tungsten(VI) complexes ... 

TABLE 1. Polymerization of 1-Alkynes with the Carbyne Tungsten(VI) Complexes Cl3(dme)WsC Bu (Cl), Np3WsC Bu (Np) and ( BuO)3W=C Bu ( BuO) solvent dichloromethane temperature 25°C molar ratio alkyne/tungsten = 100. 

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