Vanadium complexes cyclopentadienyl

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. 

This section describes the organovanadium compounds containing jj -cyclopentadienyl (Cp) or substituted (Cp ) ligands, which are classified into half-sandwich (see Halfsandwich Complexes), sandwich (see Sandwich Compound), bent sandwich (see Bent Metallocenes), and pseudo-triple decker derivatives. Cyclopentadienyl vanadium compounds are nsed for the synthesis of varions vanadium compounds as mentioned above. Generally, the oxidation state of the cyclopentadienyl vanadium complexes is Irom — 1 to -1-5. 

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

OjNSCyH, 1,2-Benzi othiazol-3(2H)one, 1,1-dioxide, chromium and vanadium complex, 27 307, 309 OjNjWCijHis, Tungsten, tricarbonyltris-(propanenitrile)-, 27 4 0jNaWC,H,2C4Hi 02, Tungstate(l -), tri-carbonyl(n -cyclopentadienyl)-, sodium, compd. with 1,2-dimethoxy-ethane(l 2), 26 343... 

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... 

Table 9.10. Properties of Vanadium Group Cyclopentadienyl Complexes...

Bradley, S. Camm, K. D. Furtado, S. J. Gott, A. L. McGowan, P. C. Podesta, T. J. Thomton-Pett, M. Synthesis and structure of amino-functionahzed cyclopentadienyl vanadium complexes and evaluation of their butadiene polymerization behavior. Organometallics 2002, 21, 3443-3453. 

It has been shown recently that cyclopentadienyl vanadium complexes catalyze the oxidation of benzylic groups by tert-BuOOH [16]. Compound CP2VCI2 (1.12) catalyzes benzylic C-H oxidation selectively and effectively, giving no aromatic oxidation products. The authors assume that intermediate catalytically active species contain Cp rings (Fig. 1.11). 

Vanadium(IV) cyclopentadienyl complexes, [Cp2V(S2CNR2)]", have previously been prepared and studied (674, 675), and more recently a crystallographic and ESR study of [Cp2V(S2CNEt2)][BF4] has been carried out (676). 

Insertions of isocyanide into niobium-carbon bonds follow a path similar to that with vanadium, resulting in the formation of the 7]2-iminoacyl complexes, which can then be involved in further chemistry.175 176 The reaction of acetone with cyclopentadienyl complex 110 under a carbon monoxide atmosphere gives the if -acetone compound 111. Complex 111 subsequently undergoes either stepwise insertion of two isocyanides via 112 or double insertion of the isocyanide to give complex 113 (Scheme 48).177... 

The Tp hgands (i.e., tris(pyrazolyl)borates or scorpionates [13]) are close analogs to the Cp hgands (i.e., -cyclopentadienyl), and in connection with the chemistry of the Tp Cr complexes mentioned above, a recent example of O2-binding from vanadium chemistry is of interest, even though it is formally not organometalhc chemistry Reaction of the V(IV) complex... 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

The ESR spectra of a series of triarylboron anion radicals have been determined and show selective line-broadening effects (95). The radical anions of diborane, generated in an argon matrix at 77 K by irradiation with a-rays have been studied by ESR (121). The vanadium-aluminum complex obtained on mixing dichlorobis(7r-cyclopentadienyl)vanadium with ethylaluminum dichloride, a system that catalyzes the polymerization of ethylene to give a polymer with good characteristics, has been characterized by ESR and ultraviolet studies (44). 

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

Mixed-sandwich complexes with cyclodextrins, 12, 787 iridium cyclopentadienyl complexes, 7, 368 with nickel, synthesis and reactivity, 8, 160 with vanadium, 5, 47... 

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