Tungsten bimetallic complexes

Reduction of the compounds of molybdenum and tungsten (VI). The first reaction of this group that was studied was the reduction of tungsten phenox-ide by the alkaline metals (Li, Na, K) in inert solvents that led to bimetallic complexes of W(V) [600] ... 

In addition to the bimetallic complexes of rhenium and alkaline metals formed as byproducts in the exchange reactions of rhenium halids with alkali alkoxides (such as, for example, LiReO(OPr )5 xLiCl(THF)2 [519]) there has been recently prepared a number ofbimetallic complexes ofrhenium and molybdenum, rhenium and tungsten, and rhenium and niobium [904, 1451]. The latter are formed either due to the formation of a metal-metal bond, arising due to combination of a free electron pair on rhenium (V) and a vacant orbital of molybdenum (VI) atom or via insertion of molybdenum or tungsten atoms into the molecular structure characteristic of rhenium (V and VI) oxoalkox-ides. The formation of the compounds with variable composition becomes possible in the latter case. 

The photochemical synthesis of the tungsten carbonyl metallocarborane [Eq. (18) ] is also effective in the preparation of the molybdenum carbonyl analog. The resulting air-sensitive complexes show chemical behavior similar to the cyclopentadienyl analogs, C5H5M(CO)3, in that they undergo protonation with anhydrous HOI and met.hylation with CH3I. They also react further with metal hexacarbonyls to afford bimetallic complexes 54) ... 

Redox activity of bimetallic complexes based on tris(3,5-dimethylpyrazolyl)-borato molybdenum(II) and tungsten(II) nitrosyls. Complexes derived from ethane-1,2-diol and the crystal structure of anti [Mo(NO) HB(3,5-Me2C3HN2)3 -(0CH2CH20)]24CHCl3... 

Scheme 76. Synthesis of bimetallic tungsten-rhodium complexes with bridging alkylidyne groups (R = C6H4Me-4, Me L = PPh3, X = Pp6 L = 2 cod, X = Bp4).

W(C3Et3)(0CMe2CMe20)(0CMe3) gave the desired tungsten-rhodium bimetallic complex. In addition, several closely related bimetallics were also reported. While alkynyl-substituted tetramethylcyclopentadienyl metal compounds might be useful in syntheses of OTM-containing polymers, the use of 2-4 in the construction of polymers was not discussed. 

A1 Obaidi, N., Chaudhury, M., Clague, D., Jones, C.J., Pearson, J.C., McCleverty, J.A., and Salam S.S. (1987) Monometallic, homo- and hetero-bimetallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato molybdenum and tungsten nitrosyls, part 4. The effects of ligating atom type on reduction potentials of monometallic complexes, J.ChemSoc., Dalton Trans., 1733-6. 

Figure 4 shows the remarkable structural similarity between the bimetallic carbene (1 2) and alkoxy complexes formed from diverse paths 1,2 addition of Zr-H to a carbonyl bound to tungsten (eq. 1) and 1,1 addition of Re-H to a zirconium-bound acetyl (eq. 2). 

Complex formation of molybdenum and tungsten alkoxides with the alkoxides of other metals formation of bimetallic alkoxides... 

The complex formation of tungsten alkoxides with the alkoxides of other metals than the alkali, bismuth, and rhenium (see Section 12.21) has not been investigated in detail, and therefore the major attention below will be paid to the description of the bimetallic alkoxides of molybdenum. 

Stable zirconium, platinum, molybdenum, and tungsten complexes of cyclooctyne, a zirconium complex of cydoocta-5-enyne, and a bimetallic molybdenum complex of cyclocta-3,7-dienyne have been discussed in earlier reviews.28 More recently, two stable zirconocene complexes of cycloocta-trienyne (275 and 276) have been prepared101 by /3-hydride elimination from 274 in the presence of PMe2R [Eq. (45)]. 

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