Comparison between PdCl2(PPh3)2- and NiCl2(PPh3)2-catalyzed crosscoupling of aryl halides by intramolecularly stabilized dialkylaluminum reagents

The catalytic activities of PdCl2(PPh3)(2) and of NiCl2(PPh3)(2) in cross coupling of some chloro- and bromoarenes with intramolecularly stabilized aluminum complexes [R2AlOCH2CH2NMe2](2) (R = Ph, PhC=C, PhCH2, Et and i-Bu) are compared. The palladium catalyst promotes clean cross-alkylation of aryl bromides indifferently to the nature of the R groups of the alkylating reagents, but does not activate aryl chlorides. The nickel complex catalyzes cross-alkylation of both aryl bromides and chlorides, provided the R groups do not have beta -hydrogen atoms. Diethyl- and diisobutylaluminum complexes that disproportionate in the presence of the nickel catalyst cause substantial hydrogenolysis of the aryl halides.