Understanding structure/reactivity trends in palladium(II) polymerization catalysts containing heterocyclic ligands

The transition metal-catalyzed polymerization of olefins is of intense technical and commercial interest. Chapter one provides a concise introduction to many of the significant advances made over the past forty years. Variation in catalyst structure has led to the development of single-site homogenous catalysts based group four cyclopentadienyl complexes that allow for control of polymer microstructure, molecular weight, and monomer incorporation. In contrast late metals (Ni and Pd) most often dimerize or oligomerize olefins due to chain transfer rates that competitive with olefin insertion. The development of sterically crowded alpha-diimine Ni and Pd catalysts in the late 1990's that produced high molecular weight polyolefins has sparked an intense push to develop new group ten based olefin polymerization catalysts.; Chapter 2 describes extensive structural, spectroscopic, and reactivity studies of (NN)Pd(Me)(H2C=CH2)+ cationscontaining simple bis(heterocycle)methane ligands (NN). These species containsterically small NN ligands, and are ethylene dimerization catalysts. Theseresults show that (NN)PdMe+ cations are interesting new platformsfor catalyst development.; Chapter 3 describes the incorporation of steric bulk into the bis(heterocycle)methane ligands discussed in Chapter 2. These new sterically bulky (NN)Pd(Me)(H2C=CH2)+ cations produce branched polyethylene which is in contrast to the complexes studied in Chapter 2 which dimerize ethylene to a mixture of butenes. The complexes studied in Chapter 3 give low to high molecular weight polyethylene depending on the nature of the steric bulk incorporated into the ligand.; Chapter 4 concerns the reaction of (hexyl)HC(mim)2 ( 1, mim = N-methyl imidazol-2-yl) with (cod)PdMeCl in C6H6 yields {lcub}(hexyl)HC(mim)2{rcub}Pd(Me)Cl (3). The photochemical reaction of 3 with CH 2Cl2 at 23°C in ambient room light yields {lcub}(hexyl)HC(mim) 2{rcub}Pd(CHCl2)Cl (4). It is proposed that this reaction proceeds by homolytic scission of the Pd-Me bond of 3.