Synthesis and catalytic reactions of electrophilic late metal complexes

Late transition metal-catalyzed functionalization of organic substrates is a major focus of organometallic chemistry. In particular, mechanistic studies on the cationic Ni(II) and Pd(II) alpha-diimine catalyzed homo- and co-polymerization of ethylene and alpha-olefins and other polar comonomers revealed several key factors affecting catalyst activity, selectivity (polymerization vs. oligomerization vs. dimerization) and stability including large weakly coordinating anions and axial bulk. Separate studies on cationic Co(III) catalysts for the living polymerization of ethylene revealed that these electrophilic complexes also catalyze olefin hydrogenation, dimerization and hydrosilation. This dissertation focuses on mechanistic studies related to Pd(II) catalyzed ethylene oligomerization and Co(III) catalyzed olefin functionalization reactions.;Chapter 2 describes the synthesis and characterization of a Pd(II) ethylene oligomerization catalyst derived from a sterically bulky, chiral phosphine-oxazoline ligand developed in the laboratory of Professor James Morken. This catalyst incorporates a moderate degree of steric bulk in the axial position of the Pd(II) square plane relative to that reported for the highly active Ni(II) and Pd(II) alpha-diimine olefin polymerization catalysts and the Ni(II) and Pd(II) ethylene dimerization catalysts possessing no axial bulk. Catalyst activity as a function of ethylene pressure and reaction temperature as well as investigation of reaction kinetics are discussed in the context of a proposed mechanism for ethylene oligomerization. The moderate degree of steric bulk imparted by the rigid ligand backbone over the axial position of the Pd(II) square plane is responsible for ethylene oligomerization activity. Mechanistic studies have established the mode of chain transfer.;The synthesis and characterization of proposed reaction intermediates in olefin polymerization, hydrosilation and hydrogenation processes catalyzed by electrophilic Co(III)-alkyl complexes is the subject of Chapter 3. Cleavage of the Co-alkyl bond by dihydrogen or silane is postulated to proceed through either an oxidative addition - reductive elimination sequence or a sigma-bond metathesis pathway. To gain further insight into these two pathways, the reactions of cationic Co(III)-ethyl complexes with H2 and silanes have been examined. Low temperature 1H and 29Si NMR experiments used to establish the bonding interactions of these substitutionally labile and thermally unstable sigma-complex intermediates as well as relevant dynamic processes are described.