Vanadium complexes vanadocene

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... 

Bis(cyclopentadienyl)vanadium(II) complexes applications, 5, 39 coordination compounds, 5, 37 vanadocenes, 5, 36... 

Another route to bis( -arene)vanadium(0) compounds is the cocondensation of arenes with vaporized vanadium metal (see Metal Vapor Synthesis of Transition Metal Compounds) On treatment with 1,3-cyclohexadiene and butyllithium, 15-electron vanadocene (5) is converted to 16-electron ( -benzene)( -cyclopentadienyl)vanadium(l) (6) (Scheme 3). Use of potassium naphthalenide affords the corresponding naphthalene complex. 

Bis(j7 -cyclopentadienyl)vanadium (vanadocene, 5, see Metallocene Complexes), which is the key derivative of this series, is characterized by a 15-electron species. Vanadocene is thermally stable under nitrogen but air sensitive. The... 

Since the vanadium center of vanadocenes is electron-deficient, various vanadium derivatives are formed by the attack with PR3, CO, or unsaturated tt-donating hgands/ This reaction provides a useful synthetic method for the synthesis of jj -alkene complexes as described later. Thus formed Cp 2V(CO) (22) is converted to the cyano derivative (23, see Cyanide Complexes of the Transition Metals) on treatment with the isocyanide (Scheme 12). ( -C5Me5)2V is incubated with O2 at -78 °C to yield [(/u.-)] -C5Me503)V(0)]2 via oxygen insertion into the carbon-vanadium bond." ... 

CpV(CO)4, which is a typical half-sandwich complex, is prepared by reduction of vanadocene with sodium or potassium under carbon monoxide. Another route to CpV(CO)4 involves the direct reaction of hexacarbonylvanadium(O) with cyclopentadiene. The Cp ring is disordered between staggered and eclipsed conformations. The distance between the centroid and vanadium is 1.9-2.0 A. 

Side-on coordination of an unsaturated ligand, alkyne or alkene, provides the corresponding complexes in the ) -mode. Vanadium-alkyne complexes like Cp2V(RC=CR) (R = COOMe, CF3) are formed by treatment of vanadocene with alkynes as shown in Scheme 32. (jj -Alkyne)(j) -cyclopentadienyl)bis(trimethylphosphine)vanadium(I) (59) is obtained by reductive coordination of CpVCl2(PMe3)2 (58) with alkyne (Scheme 33). ... 

Cp2V()] -alkene) is synthesized by treatment of vanadocene with aUcene bearing an electron-withdrawing group. The reaction of vanadocene with dimethyl frunarate or dimethyl maleate leads to the formation of the same complex, bis() -cyclopentadienyl)() -dimethyl fumarate)vanadium (72), via isomerization (Scheme 40). 

Researchers at the Wayne Hughes Institute have pioneered work related to the use of metallocene complexes, focusing on vanadocene derivatives, as spermicidal drugs. Briefly, several vanadium salts were found to act as modulators of cellular... 

Caution. Vanadocene, as well as all the vanadium(H) complexes [(F2(/< Cl3)(77ff)6]2[Zn2C/6] and sodium sand, react exothermically with oxygen and water. Therefore, all manipulations should be carried out in a nitrogen-purified atmosphere and in a well-ventilated hood. 

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