Vanadocene, synthesis

Electrochemical studies on V(II) complexes have been relatively few compared to the quantity of work on higher oxidation states. The recent discovery of a general synthesis has improved the availability of data on derivatives of vanadocene [15, 16]. For example, Ef values of L2V decrease in the order L = indenyl (—2.38 V versus Cp2Fe/TFlF)> Cp (—2.72 V versus... 

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. 

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." ... 

In the case of low-valent vanadium compounds, metathesis or hydrovanadation is used for the synthesis of organovanadium compounds. Treatment of vanadocene with halomethane results in the formation of the methyl-substituted halo-vanadocene (95) (Scheme 53). The dianion species (96) is similarly used for this purpose (Scheme 54). ... 

Isomerization of alkenes is catalyzed by bis(j7 -allyl)(jj -cyclopentadienyl)vanadium(IV). Cyclohexene nndergoes catalytic stereoselective aerobic oxidation with CpV(CO)4. Reductive coupling (see Reductive Coupling) of aldehydes and aldimines is catalyzed by a Cp-substituted vanadium compound in the presence of a chlorosilane and zinc or aluminum. Vanadocene or bis( ] -cyclopentadienyl)dimethylvanadium(IV) catalyzes the synthesis of 1,2-diphenyldisilane and 1,2,3-triphenyltrisilane from phenylsilane. ... 

Precursor Incorporation Studies. Studies of the incorporation of tritiated precursors of the DNA, RNA, or protein synthesis, i.e. of thymidine, uridine, or leucine, into the acid-insoluble fraction of EAT cells were accomplished after in vivo as well as in vitro treatment with (C5H5)2MCl2 (M Ti, V). In all experiments, the nucleic acid metabolism turns out to be much more sensitive to the metallocene dihalide action than the protein metabolism (33, 34). In particular, treatment with vanadocene dichloride induces an extended and persistent suppression of the DNA synthesis without signs of regeneration processes (Figure 2). 

Figure 2. Incorporation rates related as percentage to the controls ( ) of [methyU Hjthy-midine (left), [5- H]uridine (middle), and h-[4,5- H]leucine (right) as a measure of the DNA, RNA, and protein synthesis activities respectively after a 90-min treatment of EAT cells with vanadocene...

The major interest in these metallocenes involves their use as catalysts in the synthesis of a number of stereoregular vinyl polymers such as polyethylene and polypropylene. They are also being investigated for their biological activities. Because one of the major driving forces for the synthesis of polymeric derivatives is their biological activity, we will briefly review some of this effort focusing on vanadocene dichloride, since that is the compound most often studied. 

Malik, Duncan, Tomalia, and Esfand [29] reported the use of a variety of amine and acid-containing polymers that chelated platinum forming cisplatin derivatives. They also reported the synthesis of similar dendritic-antineoplastic drugs using vanadocene dichloride. The structure from the poly(propyleneimine) dendrimers contains units are shown in (5) and (6). 

Recently we reported the synthesis of vanadocene polyethers [30] from the reaction of vanadocene with diols forming products with structure shown in (7). 

Dorer, B. Prosenc, M. -Ft. Rief, U. Brintzinger, H. H. Synthesis and structure of titanocene, zireono-cene, and vanadocene dichloride complexes with two ethanediyl bridges. Organometallics 1994,13,... 

After in vivo and in vitro treatment with titanocene or vanadocene dichloride, precursor incorporation studies showed a pronounced and persistent inhibition of nucleic acid synthesis, especially of DNA synthesis. 

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