Cr-bonded anionic carbon complexes

Morton et al.135,141) were the first to study the poly(butadienyl)lithium anionic chain end using (b). They found no evidence of 1,2-chain ends and concluded that only 1,4-structures having the lithium cr-bonded to the terminal carbon were present. A later study by Bywater et al.196), employing 1,1,3,4-tetradeuterobutadiene to minimize the complexity of the spectrum that arises from proton-proton coupling, found that the 1 1 adduct with d-9 fert-butyllithium in benzene exists as a mixture of the cis and trans conformers in the ratio 2.6 1. Glaze et al. 36) obtained a highly resolved spectrum of neopentylallyllithium in toluene and found a cis trans ratio of about 3 1. 

The negative charge on the benzylic position of the side chain is stabilized by the electron-withdrawing effect of coordinated Cr(CO)3. In complex 234, attack of a carbanion occurs at the /f-carbon of the double bond to generate the stabilized anion... 

The sequential trans-addition of a carbon nucleophile and a carbon electrophile across an arene double bond in (arene)Cr(CO)3 was first reported in 1983 [35]. Since then this methodology has undergone extensive development, with recent efforts mainly directed towards enantioenriched products [36]. Anionic (cy-clohexadienyl)Cr(CO)3 complexes are very soft nucleophiles and this places restrictions on the electrophiles that can be used in this sequence. Specifically these reactions are successful when carbanion dissociation from the intermediate anionic cyclohexadienyl complex is slow compared to the reaction with the carbon electrophile. The sequential addition is usually carried out as a one-pot reaction and the proposed reaction sequence is that shown in Scheme 11. In contrast to the nucleophile addition/protonation sequence, products form with excellent 1,2-regioselectivity. It is likely that this is due to an irreversible transfer of the acyl, allyl, or propargyl group to one of the two termini of the cyclohexadienyl ligand. 

When the stable complex of COD 120 was treated with malonate or acetoacetate in ether at room temperature in the presence of Na2C03, a facile carbopallada-tion occurred to give the new and stable complex 121. This reaction is the first example of carbopalladation of alkenes in Pd chemistry. The Pd-carbon a-bond in the carbopalladation product 121 is stabilized by coordination of tt-olefin bond. By the treatment of the new complex 121 with a base, the generated malonate anion attacked the Pd-carbon cr-bond, affording the bicyclo[6.1.0]nonane 122. Also treatment of the complex 121 with another molecule of malonate afforded the bicyclo[3.3.0]octane 123 by transaimulation to the tt-olefin bond [14,52]. 

By varying the metal complex anion and RX, a wide variety of metal compounds containing transition metal-carbon cr-bonds have been prepared directly by this reaction. In addition, acyl metal derivatives prepared by this method may be decarbonylated to give alkyl and aryl metal complexes. 

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