(Diphenylphosphino)alkyl-Functionalized Nucleophilic Carbene Complexes of Palladium

Abstract

The (diphenylphosphino)alkyl-functionalized nucleophilic heterocyclic carbene (NHC) complexes of palladium LPdX 2 (L = (3-R 1 )[1-Ph 2 P(CH 2 ) 2 ]-imidazol-2-ylidene; R 1 = 2,6-Pr i 2 C 6 H 3, 2,4,6-Me 3 C 6 H 2; X = CH 3 ( 3a, b ), X = Br ( 4a, b )) have been synthesized by the reaction of the in situ generated functionalized NHC ligand L a or L b with Pd(tmed)(CH 3 ) 2 and Pd(COD)Br 2, respectively, and structurally characterized. Interaction of 3a with H(Et 2 O){B[3,5-(CF 3 ) 2 C 6 H 2 ] 4 } and pyridine or with (CF 3 ) 2 CHOH and pyridine in CH 2 Cl 2 gave the monocationic complexes [(L a )Pd(CH 3 )(pyridine)] + (A) - (A - = {B[(3,5-CF 3 ) 2 C 6 H 2 )] 4 } -, (CF 3 ) 2 CHO - ); acetonitrile and benzonitrile analogues can be prepared in an analogous way. Reaction of 4a with AgBF 4 in MeCN gave the dicationic complexes [(L a )Pd(MeCN) 2 ](BF 4 ) 2 . Complexes 3 show moderate catalytic activity for the coupling of acrylates with aryl bromides but not chlorides. The cationic species generated in situ from 3a and H(Et 2 O){B[(3,5-CF 3 ) 2 C 6 H 2 )] 4 } in CH 2 Cl 2 under CO/ethylene acts as a copolymerization catalyst under mild conditions.