Molybdenum, and Tungsten Complexes

Treatment of the black intermediate obtained from the reaction between CrCls and phenyl Grignard in diethyl ether with COa, followed by hydrolysis and acidification, yielded the cation [(ir-CeHgCOOH)-(77-CgH5C6H5)Cr] . No [(7r-CgH5COOH)2Cr] was isolated, presumably due to its decomposition into free benzoic acid under the conditions employed 43). 

Trialkyl and triaryl Cr(III) compounds are effective in promoting the cyclic trimerization of disubstituted acetylenes to aromatic hydrocarbons 222, 457). In the reaction of Ph3Cr -3THF with 2-butyne, the bisarene complexes of hexamethylbenzene and 1,2,3,4-tetramethylnaphthalene are obtained, as well as the free aromatic hydrocarbons 222). It is clear that a phenyl substituent has been incorporated in the formation of the coordinated and uncoordinated 1,2,3,4-tetramethylnaphthalene. Al- 

Bisarene cations of Cr, Mo, and W are best synthesized by the reaction of aromatic hydrocarbon, metal halide, aluminum trihalide and aluminum metal at elevated temperature. Aromatic hydrocarbons, such as benzene, toluene, mesitylene, and hexamethylbenzene have been employed (Table III). The method is not applicable, however, when the aromatic hydrocarbon is itself reactive under Friedel-Crafts conditions. The bisarene cations are readily reduced to the neutral compounds by aqueous dithionite or, in the case of Mo and W, by alkaline disproportionation, e.g. 152), 

The yield of bisarene complex prepared under Fischer-Hafner conditions appears to decrease in the order Cr Mo W for a given arene, the yield in the case of (CeH8)2W being only 2% 152). The neutral bisarene complexes are readily oxidized back to their cations by iodine 152) and, in the case of Cr, by oxygen 192) or AICI3 208)  

Several modifications of the aluminum method are known. The cation [(MeCeHg)2Cr] has been prepared by the reduction of Cr(acac)3 with R3AI (R = Et, i-Bu) or (i-Bu)2A1H in toluene 333). Bisarene cation complexes of Cr, Mo, and W have been prepared directly by the reaction of aromatic hydrocarbon, AICI3, HCl, and the metal powder 70). 

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Very recently, synthesis and structure of molybdenum and tungsten complexes of the relatively unhindered disilene Si2Me4 were reported. The x-ray structure of 84 shows a metallacyclosilane structure with W — Si = 2.606(2) A and Si —Si = 2.260(3) A. The W — Si bond length is within the range of various estimates of the Si and W covalent radii and the Si —Si distance falls midway between the expected values for a single (2.35 A) and a double bond (2.14 A) (Fig. 13). 

The chemistry of silylene-metal complexes has developed in quite another direction, however, from reactions of disilyl-metal complexes, leading to complexes of otherwise unstable disilenes such as Me2Si=SiMe2. Molybdenum and tungsten complexes have been particularly well investigated by Berry and co-workers,103 and platinum complexes have also been isolated.104 Readers interested in this field are directed to a 1992 review of silylene, silene, and disilene-metal complexes.105... 

The electrocatalytic properties of several parent dinitrogen or hydrazido-containing molybdenum and tungsten complexes with dppe ligand have also been investigated. Each of these complexes yielded NH3, in chemical yields which ranged from 1% to 36% per mole of complex.318... 

Hidai, M. (1999) Chemical nitrogen fixation by molybdenum and tungsten complexes, Coord. Chem. Rev., 185-186, 99-108. 

Compound 79 reacts with 0(CH2)4 and NCMe in the presence of CFsSOsMe, like the iron complex 11 and the molybdenum and tungsten complexes 45 and 46, to give zwitterionic compounds [2-NO-2-PEt3-7-L-c/ow-2,l-CoCBioHio] [L = 0(CH2)4 (83), NCMe (84)]. Interestingly, the acetonitrile reaction gave in addition to 84 small amounts of the imine complex [7- N(Me) = C(H)Me -2-NO-2-PEt3-c/oio-2,l-CoCBioHio] (85), a product related to the iron and nickel compounds 34 and 78, respectively. The latter pair were the only products when 11 and 75, respectively, were... 

The properties and reactions of the molybdenum and tungsten complexes [(Tt-Cp)M(CO)2(N CPhBu )] Ci.sely resemble those of the corresponding di-t-butylmethyleneamino-complexes, steric hindrance preventing bridging by the methyleneamino-groups. The complexes react with iodine to form [(jr-Cp)-M(CO)l2(NCPhBu )] as expected however, in contrast to all other such... 

CYCLOPENTADIENYL)NITROSYL chromium, MOLYBDENUM, AND TUNGSTEN COMPLEXES... 

A family of molybdenum and tungsten complexes with the formula [M(Cp)(C0)2(PR3)(0=CEt2)]BAr4 [Ar = 3,5-6isftrifluoro-methyl)phenyl] are known to operate through this mechanism. In most of the cases, the rate-limiting step was the ketone displacement for H2 in order to form the active dihydride (55,56). An... 

BClFjIrOP jnHjj, Iridium(III), carbonyl-chloromethyl[tetrafluoroborato-(1 - )]bis[triphenylphosphine)-, 26 118 BF4, Borate(l-), tetrafluoro-molybdenum and tungsten complexes, 26 96-105... 

C4H 2OSi, Silane, methoxytrimethyl-, 26 44 CH4N, Propane, 2-isocyant-2-methyl-ruthenium complex, 26 275 C][l,4]-dithiin-2-thione, 26 389 CHfc, 1,3-Cyclopentadiene cobalt complex, 26 191-197, 309 chromium, molybdenum, and tungsten complexes, 26 343 iron complex, 26 232-241 mercury-molybdenum-ruthenium complex, 26 333... 

Upon acidification or neutralization of solutions containing phosphate anions with other anions, such as those of molybdenum and tungsten, complexes are formed which can readily be crystallized as salts, called phosphomolybdates, phosphotiingstates, etc. 

The chemistry of pyrrol-1-ylbenzylidene pentacarbonyl chromium, molybdenum and tungsten complexes was investigated. Reaction with electrophilic alkenes gives l-(phenylcyclo-propyl)pyrroles Under photolytic decarbonylation conditions 2 + 2 cycloaddition products were obtained with nucleophilic alkenes, cyclic dienes and imines. <950M2522>... 

Anionic chromium hydride complexes proved to be efficient hydrogen atom donors. Newcomb determined PPN+ HCr(CO)5 to be an efficient radical initiator and reducing agent for radicals and determined the kinetics of the hydrogen abstraction reaction [214]. In line with the observation that 3d metal complexes are much more prone to radical pathways than the corresponding 4d and 5d complexes, an increase of the extent of competing S -pathways for the bromide abstraction was found for molybdenum and tungsten complexes compared to the chromium complex. 

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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