REACTIONS OF THE BENZONICKELACYCLOPENTENE COMPLEX (ME3P)2NI(CH2CME2-O-C6H4) WITH ALKYNES - SYNTHESIS OF 1,2-DIHYDRONAPHTHALENES

A variety of alkynes have been shown to react with the nickelacyclopentene complex (Me3P)2Ni(CH2CMe2-o-C6H4) in a highly selective manner. The reactions likely proceed with insertion of the alkyne into the Ni-aryl bond of the metallacycle, followed by reductive elimination to give good yields of the corresponding 1,2-dihydronaphthalenes, in addition to nickel side products. Ester and alcohol functionalities are tolerated, but acetylenes that have a halogen substituent provide new organometallic compounds containing an elaborate organic ligand, potentially useful for further synthetic enterprises. The unsymmetrically substituted alkynes RC=CR' yield, in general, a mixture of the 1,2-dihydronaphthalene regioisomers, with the regioselectivity of the reaction being strongly influenced by the nature of the alkyne substituents. Among these, the CO2Me group exhibits the highest selectivity, RC=CCO2Me alkynes giving rise exclusively to one regioisomer. Both the electronic and the steric effects of the R and R' groups must be taken into account to explain the reactivity and regioselectivity observed.