Alkenyl zirconium species

Carboalumination of alkynes is possible in the presence of the zirconium catalyst Cp2ZrCl2. The method is particularly attractive for methylalumination using Me3 A1 and can tolerate a wide variety of functional groups. Terminal alkynes react with very good regioselectivity ( 95 5) and excellent stereoselectivity (>98%) in favour of the alkenyl aluminium species, such as 58 (2.69). Mixtures of regioisomers often result when using internal alkynes with two different substituents. 

Very few Ni-allene complexes have been isolated and characterized, but many such species have been postulated as key intermediates in organic transformations catalyzed by Ni precursors. Notable examples of such applications include the cyclization of two arynes and one allene to give 10-methylene-9,l-dihydrophenanthrenes, " the one-pot coupling of allenes with aldehydes and silanes to give allyl silyl ethers, selective [3+2]-cyclization of allenes and Fischer carbenes, regio- and stereoselective, three-component assembly of allenes with aryl iodides and alkenyl-zirconium reagents, and regio- and chemoselective [2+2+2]-cycloaddition of electron-deficient diynes with allenes to polysubstituted benzene derivatives. ... 

Mixed-Metal Systems. Mixed-metal systems, where a zirconium alkyl is formed and the alkyl group transferred to another metal, are a new apphcation of the hydrozirconation reaction. These systems offer the advantages of the easy formation of the Zr—alkyl as well as the versatiUty of alkyl—metal reagents. For example, Cp2ZrRCl (R = alkyl or alkenyl) reacts with AICI3 to give an Al—alkyl species which may then be acylated with... 

A high yield synthesis of zirconoles from alkyl(hydrido)zirconium(iv) species and alkynes has been reported. The suggested mechanism for the reaction, shown in Scheme 5, involves RH elimination rather than initial insertion via an alkyl-(alkenyl)dicyclopentadienylzirconium intermediate. ... 

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