I. Chemoselective catalytic hydrogenation of alpha, beta-unsaturated aldehydes and ketones using soluble copper(I) hydrides II. Free radical alkylation of titanium(III) allyl and propargyl complexes

The first part of the thesis pertains to the chemoselective catalytic hydrogenation of alpha,beta-unsaturated aldehydes and ketones to allylic alcohols using phosphine stabilized Cu(I) hydrides. The investigation has determined that dimethylphenylphosphine and 1-phenylphospholane derived copper(I) hydride catalyst systems give excellent 1,2-selectivity for the reduction of alpha,beta-unsaturated aldehydes and ketones, except in the case of some simple cyclic conjugated enones. Bidendate phosphines, trialkylphosphines and racemic dimethylbinaphthylphosphines do not generate selective and active copper(I) hydride catalysts. Interestingly, the racemic methylalkylphenylphosphine-derived catalyst series also gives good 1,2-selectivity and catalytic activity for most conjugated enal and enone substrates. More importantly, such chiral phosphine ligands can be made in nonracemic forms, and the chiral phosphines can potentially be used for future asymmetric copper(I) hydride catalyst research. The experimental results also demonstrate that catalyst selectivity and catalytic activity is very sensitive to the phosphine ligand structure; even a very small change in the phosphine ligand structure can dramatically change the catalytic reaction. In addition, changes in the reaction conditions, including the solvent, hydrogen pressure, phosphine concentration and tert-butanol co-solvent concentration, also affect the catalytic reaction. The investigation of the achiral and racemic ligands provides some basic data not only defining the ligand structure-catalyst activity relationship, but also for the development of asymmetric copper(I) hydride reduction catalysts.;The second part of the thesis describes an investigation of free radical alkylation of titanium(III) allyl and propargyl complexes. A new one-pot synthesis of titanacyclobutane complexes via Cp*2TiCl provides a very convenient method for the preparation of various beta-substituted titanacyclobutane complexes. Continued research on the intramolecular free radical cyclization of titanium(III) propargyl complexes demonstrates that the full series of bicyclic titanacyclobutene complexes with ring sizes from five to ten can all be made in high yield. Careful investigations of ancillary ligand effects find that the Cp* is not the only effective ligand for the free radical alkylation of titanium(III) propargyl complexes; the tBuCp, Cp, and 1,3-bis-TMSCp ligand sets also lead to the formation of titanacyclobutene complexes in good to excellent yields. More importantly, the investigation also shows that radical addition to these eta3-propargyl complexes is significantly facilitated by the use of stronger electron-donor ancillary ligands. The Cp* and bis-TMSCp ligand sets form titanacyclobutene complexes in high yield, while the less electron-rich tBuCp and Cp ancillary ligands lead to titanacyclobutene complexes in somewhat lower yield. Steric hindered ligands do not inhibit the radical addition reaction. An investigation of the functionalization of the titanacyclobutene complexes shows that only the Cp ligand derived titanacyclobutene complexes undergo facile ketone and isocyanide insertion reactions. Hydrolysis of the ketone insertion product generates useful organic molecules after demetallation.