Synthesis of Early Transition Metal Bisphenolate Complexes and Their Use as Olefin Polymerization Catalysts

Bisphenolate ligands with pyridine- and benzene-diyl linkers have been synthesized and metalated with group 4 and 5 transition metals. The solid-state structures of some of the group 4 complexes have been solved. The titanium, zirconium, hafnium, and vanadium complexes were tested for propylene polymerization and ethylene/1-octene copolymerization activities with methylaluminoxane as cocatalyst. The vanadium(III) precatalyst is the most active for propylene polymerization and shows the highest 1-octene incorporation for ethylene/1-octene copolymerization. The zirconium(IV) precatalyst was the most active for propylene polymerization of the group 4 precatalysts. Titanium(IV) and zirconium(IV) precatalysts with pyridine-diyl linkers provided mixtures of isotactic and atactic polypropylene while titanium(IV) precatalysts with benzene-diyl linkers gave atactic polypropylene only. The hafnium(IV) precatalyst with a pyridine-diyl linker generated moderately isotactic polypropylene

Intramolecular C−H Activation of a Bisphenolate(benzene)-Ligated Titanium Dibenzyl Complex. Competing Pathways Involving α-Hydrogen Abstraction and σ-Bond Metathesis

A titanium dibenzyl complex featuring a ligand with two phenolates linked by a benzene-1,3-diyl group was found to undergo thermal decomposition to give toluene and a cyclometalated dimeric complex. The thermal decomposition followed first-order kinetics and was studied at a number of temperatures to determine the activation parameters (ΔH‡ = 27.2(5) kcal/mol and ΔS‡ = −6.2(14) cal/(mol K)). Deuterated isotopologues were synthesized to measure the kinetic isotope effects. The complexes with deuterium in the benzyl methylene positions decomposed more slowly than the protio analogues. Isotopologues of toluene with multiple deuteration positions were observed in the product mixtures. These data are consistent with competing α-abstraction and σ-bond metathesis

Robotic Lepidoptery: Structural Characterization of (mostly) Unexpected Palladium Complexes Obtained from High-Throughput Catalyst Screening

In the course of a high-throughput search for optimal combinations of bidentate ligands with Pd(II) carboxylates to generate oxidation catalysts, we obtained and crystallographically characterized a number of crystalline products. While some combinations afforded the anticipated (L-L)Pd(OC(O)R)_2 structures (L-L = bipyridine, tmeda; R = CH_3, CF_3), many gave unusual oligometallic complexes resulting from reactions such as C−H activation (L-L = sparteine), P−C bond cleavage (L-L = 1,2-bis(diphenylphosphino)ethane, and C−C bond formation between solvent (acetone) and ligand (L-L = 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene). These findings illustrate potential pitfalls of screening procedures based on assuming uniform, in situ catalyst self-assembly

Chemistry in the Center for Catalytic Hydrocarbon Functionalization: An Energy Frontier Research Center

Selective catalysts that activate small molecules such as hydrocarbons, dioxygen, water, carbon dioxide and dihydrogen are central to new technologies for the use of alternative energy sources. For example, controlled hydrocarbon functionalization can lead to high impact technologies, but such catalysts require a level of molecular control beyond current means. The Center for Catalytic Hydrocarbon Functionalization facilitates collaborations among research groups in catalysis, materials, electrochemistry, bioinorganic chemistry and quantum mechanics to develop, validate and optimize new methods to rearrange the bonds of hydrocarbons, activate and transform water and carbon dioxide, implement enzymatic strategies into synthetic systems and design optimal environments for catalysis

Chemistry in the Center for Catalytic Hydrocarbon Functionalization: An Energy Frontier Research Center

Abstract Selective catalysts that activate small molecules such as hydrocarbons, dioxygen, water, carbon dioxide and dihydrogen are central to new technologies for the use of alternative energy sources. For example, controlled hydrocarbon functionalization can lead to high impact technologies, but such catalysts require a level of molecular control beyond current means. The Center for Catalytic Hydrocarbon Functionalization facilitates collaborations among research groups in catalysis, materials, electrochemistry, bioinorganic chemistry and quantum mechanics to develop, validate and optimize new methods to rearrange the bonds of hydrocarbons, activate and transform water and carbon dioxide, implement enzymatic strategies into synthetic systems and design optimal environments for catalysis

Electrocatalytic CO₂ Reduction with a Homogeneous Catalyst in Ionic Liquid: High Catalytic Activity at Low Overpotential

We describe a new strategy for enhancing the efficiency of electrocatalytic CO₂ reduction with a homogeneous catalyst, using a room-temperature ionic liquid as both the solvent and electrolyte. The electrochemical behavior of <i>fac</i>-ReCl­(2,2′-bipyridine)­(CO)₃ in neat 1-ethyl-3-methylimidazolium tetracyanoborate ([emim]­[TCB]) was compared with that in acetonitrile containing 0.1 M [Bu₄N]­[PF₆]. Two separate one-electron reductions occur in acetonitrile (−1.74 and −2.11 V vs Fc^+/0), with a modest catalytic current appearing at the second reduction wave under CO₂. However, in [emim]­[TCB], a two-electron reduction wave appears at −1.66 V, resulting in a ∼0.45 V lower overpotential for catalytic reduction of CO₂ to CO. Furthermore, the apparent CO₂ reduction rate constant, <i>k</i>_app, in [emim]­[TCB] exceeds that in acetonitrile by over one order of magnitude (<i>k</i>_app = 4000 vs 100 M^–1 s^–1) at 25 ± 3 °C. Supported by time-resolved infrared measurements, a mechanism is proposed in which an interaction between [emim]⁺ and the two-electron reduced catalyst results in rapid dissociation of chloride and a decrease in the activation energy for CO₂ reduction