Cobalt complexes alkenyl halides

An asymmetric preparation of alkenylcyclopropanes has also been realized by the use of palladium(O) complexes carrying chiral ferrocenylphosphine ligands (equation 22)38. The requisite rt-allyl palladium intermediates can also be generated from allene and meth-ylenecyclopropane derivatives, 1839 and 1940, in the presence of palladium(O) complex and alkenyl or aryl halide (equations 23 and 24). The cobalt complexes, 20, similarly afford the corresponding alkenylcyclopropanes upon exposure to LDA (equation 25)41. 

The first mechanism is. in fact, reminiscent of the well-known copper-catalyzed dimerization of acetylene viny(acetylene being the main by-product of this process. This side reaction can, however, be inhibited to some extent by the use of cobalt salts as additives [IS]. The cyanation of acetylene and of alkenyl halides is also promoted by Co and Ni cyanides and Pd catalysis. A reducing reagent, such as Zn or NaBll4, has been used in conjunction with cobalt cyanide complexes, and the formation of. succinonitrile has been reported to result from the basebase-catalyzed hydrocyanation of acrylonitrile. 

A number of metal complexes of cyclo-octa-1,5-diene are reported from cobalt, palladium, rhodium, iridium, and copper(i) systems. Bis(cyclo-octa-l,5-diene)nickel has been used to couple alkenyl halides. An X-ray study of (356), obtained by proton abstraction from tricarbonylcyclo-octa-l,5-diene-... 

The methodology used for the preparation of a Co-C(j/> ) bond for dienyl cobalt complexes (see below the Diels-Alder reactions in Section 7.01.3.5.4(i)) has been applied for the preparation of alkenylcobaloxime complexes 132 and 133 (Scheme 19). The methodology involved a zinc-mediated coupling of alkenyl halides and trifluoromethanes to (pyr)2(dmgH)2-Co 131 (pyr = pyridine dmgH = dimethylglyoximate). ... 

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