Vanadium carbonyl derivatives

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). 

The second method is useful for preparing large quantities of vanadium carbonyl derivatives. 

The reaction of and 2 with vanadium carbonyl derivatives has not yet been studied. This would be a possible route to (ri -vinylcyclopentadienyl)tetracarbonylvanadium, However, a number... 

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 rearrangement of a-acetylenic alcohols into a-p ethylenic carbonyl derivates has been extensively studied. Different catalysts have been proposed acid catalysts such as sulfuric, hydrochloric or acetic acids which give rise to unselective rearrangements [1,2] and more recently, oxo derivatives of vanadium, molybdenum or tungsten in liquid phase [3]. 

The stoichiometries of anionic metal carbonyls follow from the requirement of inert gas configuration for the metal atom. It is apparent, for example, why the usual carbonyl anions of vanadium, manganese, and cobalt have the formulas [V(CO)6] , [Mn(CO)5] , and [Co(CO)4]-, respectively. In addition, in almost all neutral metal carbonyl derivatives, such as those prepared by reactions involving alkali metal derivatives of metal carbonyls, the metal atom will also have the inert gas configuration. A very few exceptions will arise in these the metal atom will have one electron less than the inert gas... 

The chemistry of carbonyl derivatives of vanadium [except CsH5V(CO)4] is of very recent origin. Although the properties of vanadium hexacarbonyl were briefly described in 1959 (lid), the first preparation of vanadium hexacarbonyl (from ditoluenevanadium and carbon monoxide) was des-... 

Some triphenylphosphine-substituted anionic derivatives of vanadium carbonyl are known. Treatment of vanadium hexacarbonyl with tri-phenylphosphine in hexane solution gives the orange air-sensitive [(C6H5)jP]2V(CO)4 in 61.2% yield 39). 

Information on the carbonyl chemistry of niobium and tantalum is, to date, very meager. The main difficulty appears to be the reduction of the usual pentavalent derivatives of these metals to the very low formal oxidation states of metal carbonyl derivatives. Nevertheless, the yellow anions [M(C0)6] (M = Nb, Ta) have been obtained by a method analogous to, but more difficult than, one of the preparations of the [VCCO) ]" anion. The method involves reduction of the pentachlorides with sodium metal in diglyme in the presence of high pressures of carbon monoxide (63). The niobium and tantalum derivatives are much more air-sensitive than the analogous vanadium derivative. The niobium derivative has not yet been obtained analytically pure (63). No chemistry of the [Nb(CO)J and the [Ta(CO)6] ions has been reported, even conversion to the neutral carbonyl derivatives [M(CO) (M = Nb or Ta = 1 or 2) or to the carbonyl hydride derivatives HM(CO)6 (M = Nb, Ta) still presenting unsolved problems. 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

Carbonyl—nitrosyl derivatives, vanadium compounds, 5, 7 Carbonyl ylides... 

No carbonyl cations of vanadium with a-donor ligands have been reported. When Lewis bases react with vanadium hexacarbonyl, either a substituted derivative or a hexacarbonylvanadate salt is obtained. The latter is formed by disproportionation, which also produces a carbonyl-free cation. 

The formation of the 17-electron paramagnetic vanadium complex is not surprising in view of the known corresponding carbonyl complex, however the 16-electron titanium derivative is unexpected in view of the ready formation of the 18-electron biscarbonyl and bistrifluorophos-phine metal complexes containing the 5-cyclopentadienyl ligand. The solid-state structure of the PF3 adduct of bis[2,4-dimethyl-(pentadienyl)]titanium has recently been determined (111) and is shown in Fig. 20. The corresponding vanadium complex is isomorphous. The metal-PF3 distances are 2.326(Ti) and 2.275(V) A. 

Vanadium(IV) forms complexes with charged carboxylate, aryloxide and alkoxide functionalities as well as the neutral carbonyl group. The steric crowding of the /-butoxides allowed structural characterization of the tetraalkoxide (96) by gas-phase electron diffraction.475 Vw phenoxide complexes derived from ligands such as 2-(dimethylaminomethyl)phenol and 4-chloro-2-[(dimethylamino)methyl]phenol are active as ethylene and propylene copolymerization agents 476 Complexes with silanoxides have been prepared by the oxidation of Vnl complexes.477... 

The low-valency cyclopentadienyl vanadium complexes are usually stabilized by carbon monoxide, and VCp(CO)4 is the most useful precursor to various low-valency organovanadium complexes. There are a number of synthetic routes to VCp(CO)4. One convenient method is to carry out the reaction between NaCp and VCl3 in THF in situ and then to carbonylate under 60 atm CO pressure at 120 °C [19]. Reduction of preformed vanadocene by potassium, and subsequent carbonylation also gives rise to VCp(CO)4 [20]. These methods, however, cannot be applied to alkyl-substituted cyclopentadienyl derivatives. It is necessary to treat alkyl-substituted cyclopentadiene... 

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