Lead-vanadium bonds

Analogous compounds possessing lead-vanadium bonds were also prepared376 ... 

Application of equation (10c) to the observed single-bond radii of scandium, titanium and vanadium (1-439,1-324,1-224 A) leads to 20, 27 and 35 % of d character, respectively (table 5). The gradual increase presumably results from the increasing stability of the 3d orbitals relative to 4s and 4p. 

I can say, for example, that it tends to form chemical bonds to five other atoms at a time, but can tolerate fewer and, at a push, more. It is a metal, probably quite a soft one, heavier than iron but lighter than lead. Many of its compounds - its combinations with other elements - will be coloured. It will be apt to form bonds to other niobium atoms - so-called metal-metal bonds. It will behave chemically in a similar manner to the element vanadium, but will be more similar still to tantalum. 

Approximate TS structures were located based on the pathways shown in Fig. 31 using the SEAM search algorithm. However, for associative interchange, this leads to an inconsistency in that in order to have different connectivities in reactant and product states, there are only six explicit M-0 bonds while the TS should have seven. Consequently, the seventh ligand is explicitly connected and the structure reoptimized using a simple Newton-Raphson procedure. For vanadium, the SEAM structure is sufficiently good for this procedure to locate a true first-order saddle point (Fig. 32, left) (73). 

The Ji-complexes formed between chromium(O), vanadium(O) or other transition metals, and mono- or poly-fluorobenzene show extreme sensitivity to heat and are explosive [1,2], Hexafluorobenzenenickel(O) exploded at 70°C [3], and presence of two or more fluorine substituents leads to unstable, very explosive chromium(O) complexes [1]. Apparently, the aryl fluorine atoms are quite labile, and on decomposition M—F bonds are formed very exothermically. Laboratory workers should be wary of such behaviour in any haloarenemetal Ji-complex of this type [1]. However, in later work, no indications of explosivity, or indeed of any complex formation, were seen [4]. Individually indexed compounds are ... 

Of great industrial interest are the copolymers of ethene and propene with a molar ratio of 1/0.5, up to 1/2. These EP-polymers show elastic properties and, together with 2-5 wt% of dienes as third monomers, they are used as elastomers (EPDM). Since they have no double bonds in the backbone of the polymer, they are less sensitive to oxidation reactions. As dienes, ethylidenenorbomene, 1,4-hexadiene, and dicyclopentadiene are used. In most technical processes for the production of EP and EPDM rubber in the past, soluble or highly disposed vanadium components are used [69]. Similar elastomers can be obtained with metallocene/MAO catalysts by a much higher activity which are less colored [70-72]. The regiospecificity of the metallocene catalysts toward propene leads exclusively to the formation of head-to-tail enchainments. The ethylidenenor-bornene polymerizes via vinyl polymerization of the cyclic double bond and the tendency to branching is low. The molecular weight distribution of about 2 is narrow [73]. 

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