Carbonyls vanadium

The neutral complexes of chromium, molybdenum, tungsten, and vanadium are six-coordinate and the CO molecules are arranged about the metal in an octahedral configuration as shown in stmcture (3). Vanadium carbonyl possesses an unpaired electron and would be expected to form a metal—metal bond. Steric hindrance may prevent dimerization. The other hexacarbonyls are diamagnetic. 

Nucleophilicity order for R3X, sign of AS " and existence of 7-coordinated vanadium carbonyls, are consistent with an A mechanism. 

Since the discovery of hexacarbonylvanadium(O) and hexacarbonylvanadate( 1-) by Calderazzo and co-workers in 1959 and 1960, these substances have been key precursors to a variety of vanadium compounds, including inorganic noncarbonyl species, organovanadium complexes," and other vanadium carbonyls. Neutral V(CO)6 is of special interest in that it is the only isolable 17-electron homoleptic metal carbonyl and exhibits fascinating chemical properties that are often reminiscent of iodine and classic pseudohalogens. ... 

Few gold compounds contain vanadium-carbonyl fragments or dicyclopentadienyl-niobium fragments, respectively, and no additional interactions between discrete heterometalic cores are present in the crystal of any of them. 

After removal of volatile products, a yellow vanadium carbonyl carbide remains. In all these cases, it seems likely that there is initial electron donation from oxygen to silicon, followed by Si-M bond cleavage. As supporting evidence, two products from the controlled heating of Me3SiCo(CO)4 are reasonable intermediates in such a process (252). 

The known vanadium carbonyl cations are of two types, namely a tetracarbonyl, [AreneV(CO)4]+, and a dicarbonyl, [Cp2V(CO)2]+. The tetracarbonyl derivatives are readily prepared under mild conditions by the reaction of an arene with vanadium hexacarbonyl. The arenes used include benzene, its methyl derivatives 28, 29), naphthalene, and anisole 29). The cation is probably formed by oxidation of the intermediary arene vanadium tricarbonyl. 

The infrared and proton NMR spectra of the vanadium carbonyl cations have been reported (28, 29, 32). The investigation of the reactivity of these cations with nucleophiles is limited to a study of the hydridic reduction of the tetracarbonyl species (31). A mechanism is proposed which involves primary coordination of hydride to vanadium the hydrogen then transfers to an arene carbon atom to form a methylene group, with the hydridic hydrogen in the endo position, viz., The product is 77-cyclohexadienyl-vanadium tetracarbonyl. 

The anion [V(CO)6] formed no Mn—V or Re—V metal-metal bond, probably because of steric effects, although heptacoordinate vanadium carbonyl derivatives exist, thus HV(CO)5(PPh3) (141). 

A variety of vanadium carbonyl compounds are obtained from [V(CO)6] . Use of l-chloropenta-2,4-diene under photoirradiation leads to V(jj -C5H7)(CO)4. The -bonded acyl complex is formed similarly by photoinduced substitution with benzoyl chloride. The rf--C,0 coordination mode is... 

Scalar coupling between and has been reported for phosphine and trialkyl phosphite coordinated vanadium carbonyl complexes. (194) V( V- P) typically ranges from 150 to 350Hz. No stereochemical specificity was found, however. 

V(CO)6] , as well as the related [V(CO)sPPh3] and [V(CO)4L2] anions [L2 = bis(diphenylphosphino)ethane (dppe), bis(dimethylphosphino)ethane (dmpe), and 1,2-dimethylarsenobenzene (diars)], generally produce seven-coordinate, neutral vanadium carbonyl complexes when treated with group IVB halides ... 

Vanadium carbonyl V(CO)g (Oj, involving dynamic Jahn-Teller effect) V—c 2.015 C—O 1.138 ED... 

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