The (diphenylphosphino)alkyl-functionalized nucleophilic heterocyclic carbene (NHC) complexes of palladium LPdX2 (L = (3-R1)[1-Ph2P(CH2)2]-imidazol-2-ylidene; R1 = 2,6-Pri 2C6H3, 2,4,6-Me3C6H2; X = CH3 (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)(CH3)2 and Pd(COD)Br2, respectively, and structurally characterized. Interaction of 3a with H(Et2O){B[3,5-(CF3)2C6H2]4} and pyridine or with (CF3)2CHOH and pyridine in CH2Cl2 gave the monocationic complexes [(La)Pd(CH3)(pyridine)]+(A)- (A- = {B[(3,5-CF3)2C6H2)]4}-, (CF3)2CHO-); acetonitrile and benzonitrile analogues can be prepared in an analogous way. Reaction of 4a with AgBF4 in MeCN gave the dicationic complexes [(La)Pd(MeCN)2](BF4)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(Et2O){B[(3,5-CF3)2C6H2)]4} in CH2Cl2 under CO/ethylene acts as a copolymerization catalyst under mild conditions.

Stepwise addition/elimination and concerted mechanisms for the methanolysis of ε-caprolactone, as a model for the initiation and propagation of ring-opening polymerization (ROP), have been investigated computationally using the B3LYP/6-31G* density functional method, with assistance from one or two ancillary methanol molecules. The effects of specific solvation by these extra methanols in cyclic hydrogen-bonded clusters are very significant, with barrier height reductions of about 50 kJ mol(-)(1). However, the effects of bulk solvation as treated by the polarized continuum model are almost negligible. Increasing the ring size lowers the barriers for both the addition and elimination steps of the stepwise mechanism but does not do so for the concerted mechanism; a stepwise mechanism is preferred for methanol-assisted ROP. The essential catalytic role of solvent molecules in this reaction is to avoid the unfavorable accumulation or separation of charges.