Styrenes hydrozirconation

Styrene hydrozirconation led to a ratio for terminal and benzylic zirconocene products of around 85 15 [97]. Experimental evidence on alkyl-substituted styrene suggested that both electronic [98,99] and steric effects [41,86] are important for the formation of the benzyhc and terminal zirconium isomers. Migration of the metal fragment during the reaction of the zirconocene moiety might occur, perturbing the terminal/benzyl regioisomer ratio of the isolated products (Scheme 8-11) [67, 83, 98-102]. 

The amination of styrene, however, led to two products (1-phenyl-1-ethylamine and 2-phenyl-l-ethylamine) in a 1 3 ratio [113], indicating that the hydrozirconation was not completely regioselective [114,115]. Since it is well known that hydrozirconation of trisubsti-tuted alkenes places zirconium at the least hindered carbon of the chain by a process involving zirconium migration, this class of alkenes was not investigated [5,116], On the other hand, hydrozirconation/amination of 3-methyl-l,2-butadiene gave an allylic amine. Reaction of the latter could either occur at the terminal carbon or proceed with... 

The reaction with styrene or 1,3-butadiene under the same conditions (benzene-ether) results in r-butylzircohation (equation 1). However, in reactions conducted in benzene alone, hydrozirconation is observed. 

Nelson, J. E., Bercaw, J. E., Labinger, J. A. An unexpected isotope scrambling process accompanies hydrozirconation of styrene. Organometallics 1989, 8, 2484-2486. 

Alkenylzirconium reagents Hydrozirconation of alkynes with Cp ZifHlCl followed by reaction with iodonium salts constitutes a method for synthesis of styrenes and enynes. In the latter case it can be seen that zirconium prefers attachment to the heterosubstituted carbon atom therefore, 1,1-difiinctionalized 1-alkenes are readily prepared, including those pairing Si/Se and Te/Te. ... 

Zirconium complexes, generated in situ by addition of HZrCp2Cl to alkenes, can be animated with <9-(mesitylenesulfonyl)hydroxylamine an example is shown in Eq. 41.116 When the initial hydrozirconation is not regioselective, as with styrene, mixtures of amines are formed. A reaction that permits animation at the tertiary carbon in a similar substrate is discussed below (Eq. 49). 

Hydrometallations of alkenes and acetylenes such as hydroboration, hydrosila-tion, hydroalumination, hydrostannation and hydrozirconation are useful synthetic reactions. Rhodium-phosphine complexes catalyze hydroboration of substituted styrenes with a catecolborane (Scheme 68). An extensive survey of the phosphine... 

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