Because of the continually rising levels of CO2 in the atmosphere, research for the conversion of CO2 into fuels using carbon-neutral energy is an important and current topic in catalysis. Recent research on molecular catalysts has led to improved rates for conversion of CO2 to formate, but the catalysts are based on precious metals such as iridium, ruthenium and rhodium and require high temperatures and high pressures. Using established thermodynamic properties of hydricity (ΔGH(-)) and acidity (pKa), we designed a cobalt-based catalyst system for the production of formate from CO2 and H2. The complex Co(dmpe)2H (dmpe is 1,2-bis(dimethylphosphino)ethane) catalyzes the hydrogenation of CO2, with a turnover frequency of 3400 h(-1) at room temperature and 1 atm of 1:1 CO2:H2 (74,000 h(-1) at 20 atm) in tetrahydrofuran. These results highlight the value of fundamental thermodynamic properties in the rational design of catalysts.

A dysprosium(III) sandwich complex, [Dy(III)(COT″)(2)Li(THF)(DME)], was synthesized using 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion (COT″). The complex behaves as a single-ion magnet and demonstrates unusual multiple relaxation modes. The observed relaxation pathways strongly depend on the applied static dc fields.

An organometallic building block strategy was employed to investigate the magnetic properties of a Ln III organometallic single-ion magnet (SIM) and subsequent single-molecule magnet (SMM) after coupling two of the monomeric units. New homoleptic Dy III COT″ 2 and Ln III 2 COT″ 3 (Ln = Gd, Dy) complexes have been synthesized. DFT calculations of the bimetallic Dy III complex indicate strong metal−ligand covalency and uneven donation to the Dy III ions by the terminal and internal COT″ 2− (cyclooctatetraenide) rings that correlate with the respective bond distances. Interestingly, the studies also point to a weak covalent interaction between the metal centers, despite a large separation. The ac susceptibility data indicates that both Dy III COT″ 2 and Dy III 2 COT″ 3 act as an SIM and an SMM, respectively, with complex multiple relaxation mechanisms. Ab initio calculations reveal the direction of the magnetic anisotropic axis is not perpendicular to the planar COT″ rings for both Dy III COT″ 2 and Dy III 2 COT″ 3 complexes due to the presence of trimethylsilyl groups on the COT″ rings. If these bulky groups are removed, the calculations predict reorientation of the anisotropic axis can be achieved.

The complex Co­(dmpe)2H catalyzes the hydrogenation of CO2 at 1 atm and 21 °C with significant improvement in turnover frequency relative to previously reported second- and third-row transition-metal complexes. New studies are presented to elucidate the catalytic mechanism as well as pathways for catalyst deactivation. The catalytic rate was optimized through the choice of the base to match the pK a of the [Co­(dmpe)2(H)2]+ intermediate. With a strong enough base, the catalytic rate has a zeroth-order dependence on the base concentration and the pressure of hydrogen and a first-order dependence on the pressure of CO2. However, for CO2:H2 ratios greater than 1, the catalytically inactive species [(μ-dmpe)­(Co­(dmpe)2)2]2+ and [Co­(dmpe)2CO]+ were observed.