6533b81ffe1ef96bd1278f60

RESEARCH PRODUCT

Stereo and regioselectivity in the phenylation of cationic allylpalladium(II) α-diimine complexes by tetraphenylborate anion

subject

description

The reaction of the cationic complex [Pd(4-methoxy-1,3-η3-cyclohexenyl)(py-2-CHNC6H4OMe-4)]+ (1) with BPh4− in the presence of fumaronitrile yields trans-3-methoxy-6-phenylcyclohexene (2a) and trans-4-methoxy-3-phenylcyclohexene (2b), in ca. 1 : 1 molar ratio. The trans stereochemistry of these products implies that the phenylation of the allyl ligand involves prior transfer of a phenyl group from BPh4− to the metal, followed by reductive coupling of the organic moieties. In the reactions of [Pd(η3-1,1-R1,R2-C3H3)(NN′)]+ (3) [NN′ 4-MeOH4C6NCHCHNC6H4OMe-4; py-2-CHNR (R  C6H4OMe-4, Me, or CMe3), 2,2′-bipyridine (bipy); R1  H, R2  Ph, Me; R1  R2  Me; with BPh4− in the presence of activated olefins, both regioisomers PhCH2CHCR1R2 (4a) and CH2CHCR1R2Ph (4b) are formed with a relative ratio which depends essentially on the allylic substituents: R1  H, R2  Ph, 4a > 98%; R1  H, R2  Me, 4a 75–67%; R1  R2  Me, 4a 64–58%. The regioisomer distribution is very little affected by the nature of the α-diimine, of the activated olefin, and of the solvent. For R1  H and R2  Ph, Me, the olefinic product 4a has a trans (E) geometry. These results have been interpreted in terms of reductive elimination occurring in the intermediate [PdPh(η3-1,1-R1,R2C3H3)(NN′)] with a σ-N monodentate α-diimine ligand.