Reactivity studies of H(2), CO and alkenes with non-macrocyclic rhodium(II) systems, and, 'Living' radical polymerization of acrylates

Rhodium(II) porphyrin complexes manifest an unusually diverse reaction chemistry with H{dollar}sb2,{dollar} CO, and hydrocarbons which include formation of metalloformyl complexes, CO reductive coupling and methane activation. Our objectives in this area have encompassed defining the scope of rhodium(II) complexes that can accomplish these thermodynamically difficult substrate reactions and to extend this chemistry to flexible non-macrocyclic ligand arrays which have the potential to manifest more versatile reaction pathways than those available to rigid tetradentate macrocyclic complexes.; Two tetradentate non-macrocyclic rhodium(II) complexes, ((ttbs)Rh) {dollar}sb2{dollar} and ((dbpb)Rh) {dollar}sb2,{dollar} have been synthesized. Reactivity studies of both rhodoum(II) dimers illustrate that rhodium complexes with non-macrocyclic ligands have the thermodynamic capability to accomplish many of the substrate reactions associated with rhodium porphyrins. Reactions of both rhodium(II) dimers with H{dollar}sb2,{dollar} CO, CH{dollar}sb2{dollar} = CH{dollar}sb2{dollar} produce rhodium hydrides, dirhodium ketones and ethylene-bridged complexes, respectively. Observation of the metalloformyl complexes is particularly significant in substantially extending the range of donor site arrays for rhodium which are candidates for promoting a key initial step in CO hydrogenation. Thermodynamic instability of the formyl complexes in the presence of CO with respect to a rhodium(I) dicarbonyl complex currently limits applications of flexible non-macrocyclic ligand complexes as catalysts for CO reduction and hydrogenation.; The second part of the thesis has focused on controlled radical polymerization of vinyl monomers by organometallic complexes. By introducing bromine substituents to the eight pyrrole {dollar}beta{dollar}-positions of the tetramesityl porphyrin ligand, we have synthesized an electron-withdrawing porphyrin cobalt complex ((Br{dollar}sb8{dollar}TMP)Co-R) which has resulted in a weaker Co-C bond than its (TMP)Co-R analog. The weakening of the Co-C bond of (Br{dollar}sb8{dollar}TMP)Co-R has enabled us to conduct controlled radical polymerization of acrylates at lower temperatures (25{dollar}spcirc{dollar}C) rather than 60{dollar}spcirc{dollar}C for the (TMP)Co-R system. Linear increase of molecular weight (M{dollar}rmsb{lcub}n{rcub}){dollar} with monomer conversion and relatively narrow polydispersities ({dollar}sim{dollar}1.1) are indicative of an effective living radical polymerization. The controlled "living" radical polymerization of acrylates by the organocobalt porphyrin complex, (Br{dollar}sb8{dollar}TMP)Co-R, provides another example where an organometallic complex controls radical polymerization through the persistent radical effect. Recognition of the reduction of Co-C bond dissociation energy by introducing electron withdrawing substituents onto the porphyrin ring is important to define the range of metal complexes that can participate in controlled "living" polymerization processes.