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The palladium phosphine complexes Pd(PPh3)2Cl2/PPh3, Pd(PBu3)2Cl2, and Pd(dppp)2Cl2 (dppp = 1,2-bis(diphenylphosphino)propane) in the presence of zinc metal powder catalyze nitrile-group transfer from organic nitriles RCN (R = Me, Et, n-Pr, Bn, Ph) to bromoarenes to give the corresponding ArCN compounds. Only ortho-disubstituted bromoarenes (1-bromo-2-methylnaphthalene (1), 2-bromo-m-xylene, 2-bromomesitylene (3), 1-bromo-2-methoxynaphthalene, and 9-bromoanthracene) afforded good yields of the cyanation products. Analysis of the reaction mixture of 3 with benzyl cyanide using Pd(PBu3)2Cl2 as the catalyst showed the presence of dibenzyl ketone and a cyclic product, 2,4,6-tribenzyl-5-phenylpyrimidine, in addition to 2,4,6-trimethylbenzonitrile. To understand the mechanistic features of these catalytic reactions, a number of experiments were performed and the results are summarized as follows: (i) the palladium intermediate Pd(PPh3)2(2-Me-Np)Br (6; 2-Me-Np = 2-methylnaphthyl), which can be prepared separate...

Treatment of Pd(PPh3)4 with PhCHCHBr in THF at 45 °C gave [(trans-PhCHCHPPh3)Pd(PPh3)2]+Br- (1), which was found to be converted from Pd(PPh3)2(CHCHPh)Br. X-ray structural analysis shows that 1 adopts a distorted-square-planar geometry with two PPh3 ligands and a (PhCHCHPPh3)+ moiety. The C−C double bond in the latter is π-bonded to the palladium(0) center and occupies two of the four square-planar coordination sites. Under similar reaction conditions, {Pd[trans-PhCHCHP(p-tolyl)3][P(p-tolyl)3]2}+Br- (2) was formed from Pd[P(p-tolyl)3]4 and PhCHCHBr, while [(trans-MeCHCHPPh3)Pd(PPh3)2]+Br- (3) was isolated from the reactions of Pd(PPh3)4 with MeCHCHBr. Treating PhCHCHBr with trans-Pd(PPh3)2(C6H4O-p-CH3)I in THF at ambient temperature led to the formation of (trans-PhCHCHPPh3)Pd(PPh3)X (5) and (p-CH3OC6H4PPh3)+X- (X, mixture of Br and I). Complex 5 (X = Br) can be prepared by treating trans-PhCHCH(PPh3)+Br- with Pd(dba)2 and 1 equiv of PPh3 in CH2Cl2. X-ray analysis shows 5 adopts a distorted-square-planar ...

Treatment of Pd(dba)2 (dba = dibenzylideneacetone) with (trans-RCHCHPPh3)+Br- in dichloromethane afforded [Pd(trans-RCHCHPPh3)2Br]+ (R = CO2Et (4), CO2Me (5), Ph (6)). As shown by the results of the X-ray diffraction, 4 adopts a distorted pentagonal geometry with two EtO2CCHCH(PPh3)+ moieties and a bromide ligand. The C−C double bond in the EtO2CCHCH(PPh3)+ moieties are π-bonded to the palladium(0) center and are coplanar with the bromide ligand and the metal center. Both (EtO2CCHCHPPh3)+ moieties are oriented with the two PPh3 groups trans to each other and the olefin carbon that is attached to PPh3 occupying the coordination site neighboring to the bromide ligand. Treatment of trans-[R1CHCR2(PPh3)]+Br- with Pd(dba)2 in the presence of 1 equiv of PPh3 or P(OPh)3 gave the corresponding palladium complexes Pd[trans-R1CHCR2(PPh3)](L)Br (L = PPh3, R1 = Ph, R2 = H (3). L = PPh3, R1 = Me, R2 = H (7); R1 = CO2Et, R2 = H (8); R1 = CO2Me, R2 = H (9); R1 = H, R2 = Me (10). L = P(OPh)3, R1 = CO2Me, R2 = H (11)) in ...