RIGID BIDENTATE NITROGEN LIGANDS IN ORGANOMETALLIC CHEMISTRY AND HOMOGENEOUS CATALYSIS .4. PALLADIUM COMPLEXES CONTAINING RIGID BIDENTATE NITROGEN LIGANDS AS CATALYSTS FOR CARBON-CARBON BOND FORMATION

Zerovalent Pd(Ar-BIAN)(dimethyl fumarate) and divalent PdCl2(Ar-BIAN) complexes containing the rigid bidentate nitrogen ligand bis(arylimino)acenaphtene (Ar-BIAN; Ar = C6H5, p-MeC(6)H(4), p-MeOC(6)H(4)) are efficient catalysts for the cross coupling reaction of various organic halides (including acyl-, allyl-, aryl-, benzyl-, vinyl- and 1,2-dienylhalides) with organomagnesium, -zinc and -tin reagents. Coupling reactions of organic halides with one equivalent of organomagnesium and -zinc reagents, in the presence of 1 mol % of a Pd(Ar-BIAN) catalyst, generally proceed smoothly in THF at 20 degrees C, giving complete conversion of the starting halide within 1-16 hours. Good isolated yields of carbon-carbon coupled products are obtained and the ratio cross/homo coupling varies between 98/2 and 0/100, depending on the substrates used. Reactions employing organotin reagents proceed best in DMF or HMPA and need longer reaction times and/or higher temperatures, as compared to organomagnesium and -zinc reagents, to go to completion. The selectivity for cross coupling is high (generally >99 %) and high isolated yields of cross coupled products can be obtained. In the presence of carbon monoxide (1-5 bar) ketones can be farmed with excellent selectivity and in good yields, as was demonstrated for the carbonylative coupling of benzyl bromide with tetramethyltin or (p-tolyl)trimethyltin. Comparison of some Pd(Ar-BIAN) catalyzed reactions with Pd-phosphine catalyzed reactions reveals that these reactions complement each other: for example, when a Pd(Ar-BIAN) catalyst was employed, the coupling of 2-methylallyl chloride with phenyltributyltin was much faster, whereas the coupling of iodobenzene with vinyltrimethyltin was much slower, as compared to the Pd(PPh(3))(n) catalyzed reactions.