Tetracarbonyl vanadium

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 mononuclear metal carbonyls contain only one metal atom, and they have comparatively simple structures. For example, nickel tetracarbonyl is tetrahedral. The pentacarbonyls of iron, ruthenium, and osmium are trigonal bipyramidal, whereas the hexacarbonyls of vanadium, chromium, molybdenum, and tungsten are octahedral. These structures are shown in Figure 21.1. 

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. 

R366 M. Herberhold, A. M. Dietel, J. Peuker, A. Pfeifer and W. Milius, Sandwich and Half-Sandwich Complexes Derived from Pentamethyl-cyclopentadienyl Tetracarbonyl Vanadium, Cp V(CO)4 , Appl Orga-nomet. Chem., 2000,14, 519... 

The only known syntheses of cyclopentadienylvanadium tetracarbonyl, C6H6V(CO)4, are based on the reaction of bis(cyclopentadienyl)vanadium with carbon monoxide under pressure. The procedure given below is based on this reaction but avoids isolation of pyrophoric bis-(cyclopentadienyl)vanadium by direct carbonylation of the solution obtained from vanadium(III) chloride and cyclopentadienylsodium. 

Vanadium, Niobium, and Tantalum.—High-pressure carbonylation of [CpNbCy in the presence of Na-Cu-Al affords high yields ca. 90%) of [CpNb(CO)4], and the preparation can be carried out on a large scale ca. 35 g) irradiation of this product in solution in THF affords [CpNb(CO)3(THF)], which is a useful intermediate for the preparation of complexes of the type [CpNb(CO)3L] e.g., reactions with CO and to afford a labelled tetracarbonyl. A study of... 

Both halides and oxyhalides may be prepared from the tetracarbonyl, 4.23 [250, 251]. The vanadium(IIl) chloride, 4.24, is prepared by the redistri-... 

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