Palladium complexes containing rigid bidentate nitrogen ligands as catalysts for carbon [sbnd]carbon bond formation

Abstract

Zerovalent Pd(Ar-BIAN)(dimethyl fumarate) and divalent PdCl 2(Ar-BIAN) complexes containing the rigid bidentate nitrogen ligand bis(arylimino)acenaphtene (Ar-BIAN; Ar = C 6H 5, p-MeC 6H 4, p-MeOC 6H 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 °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 formed 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.