Ylides vanadium

It might have been expected that the reactions could lead to vanadium ylides instead of the pentaalkyls, but this was obviously not the case. From the literature it is not clear whether or not true vanadium (Y) compounds have been used as starting materials in at least some of the reactions to warrant the appropriate oxidation state. The problems associated with the vanadium pentahalides (except for the fluoride) and other VX6 compounds may well be the reason for the difficulties arising in the syntheses. If these difficulties can be overcome, there should be a chance for a successful preparative procedure according to one of the following pathways ... 

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

Considering the presently available knowledge on vanadium(V) compounds, reaction (58b) seems to be more attractive, as compounds of types (RO)3VO, (RO)3V=NR, etc., are well documented for both R = alkyl and R = silyl (4, 81), whereas only very few VX6 species are known. The pertinent chemistry of the congeners niobium and tantalum offers examples for pentacoordination as well as for ylide formation. 

In this article the author has been using the traditional ylide-ylene nomenclature as well as the modern phosphorane-arsorane-stiborane formalism. No attempt has been made to discriminate between one or the other of these modalities because it is felt that both offer a sufficiently clear description of at least those species that are derived from the main Group Vb elements. (Fortunately no Nli,s or BiR5 had to be given names.). However, when this procedure was followed with the vanadium, niobium, and tantalum compounds, an interesting problem arose because the authors... 

Novel vanadium, e.g. (94), and titanium, e.g. (95), complexes of phosphonium ylides have been prepared by the reaction of methylenetriphenylphosphorane with appropriately co-ordinated metal halides. A variety of silver complexes... 

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