Metallacycles zirconium compounds

Scheme 13.10 Hydrazinolysis of the metallacyclic zirconium compounds with diphenylhy-drazine, giving the bis(hydrazido) complexes and the corresponding indoles [24].

Cycloreversion of four-membered metallacycles is the most common method for the preparation of high-valent titanium [26,27,31,407,599-606] and zirconium [599,601] carbene complexes. These are usually very reactive, nucleophilic carbene complexes, with a strong tendency to undergo C-H insertion reactions or [2 -F 2] cycloadditions to alkenes or carbonyl compounds (see Section 3.2.3). Figure 3.31 shows examples of the generation of titanium and zirconium carbene complexes by [2 + 2] cycloreversion. 

Phosphoies and other reiated heterocycies are an important class of main group compounds. The chemistry of phosphoies and their preparation has been reviewed extensiveiy by Mathey.3 We provide details here for a simple, one-pot procedure for the preparation of 1-phenyl-2,3,4,5-tetramethylphosphole applying zirconocene chemistry.4 The procedure involves reduction of (ri-C5H5)2ZrCl2 with butyllithium in the presence of 2-butyne which (as reported initially by Negishi, et al. ) forms a zirconium metallacycle. Addition of dichiorophenylphosphine to this reaction mixture produces the phosphole. One other procedure for the preparation of 1-phenyl-... 

Recently the oxidative coupling of olefins and alkynes, not only with late transition metal complexes, but also with low valent early transition metal complexes to give metallacyclopentane or metallacyclopentadiene complexes is attracting increasing attention. For example, titanium(II) and zirconium(II) complexes react with olefins and form metallacycles. Various stoichiometric processes to produce useful compounds that are otherwise unavailable can be produced by exploit-... 

Zirconium metallacycles were found to serve as the precursor compound for the preparation of a variety of main group heterocycles including thiophenes and their 5 -oxides. The zirconium metallacycles (275) and (277) were prepared by treatment of 2,8-decadiyne and diphenylethyne with zirconocene dichloride in the presence of Bu"Li and allowed to react with disulfur dichloride and thionyl chloride, respectively, to give the bicyclic thiophene (276) and the thiophene S -oxide (278)... 

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