Efficient Homogeneous Catalysis in the Reduction of CO₂ to CO

The well-defined copper(I) boryl complex [(IPr)Cu(Bpin)] [where IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and pin = pinacolate:  2,3-dimethyl-2,3-butanediolate] deoxygenates CO2 rapidly and quantitatively, affording CO and the borate complex [(IPr)Cu(OBpin)]. The boryl may be regenerated by treatment with the diboron compound pinB−Bpin, giving the stable byproduct pinB−O−Bpin. The use of a copper(I) alkoxide precatalyst and stoichiometric diboron reagent results in catalytic reduction of CO2, with high turnover numbers (1000 per Cu) and frequencies (100 per Cu in 1 h) depending on supporting ligand and reaction conditions

Efficient Homogeneous Catalysis in the Reduction of CO₂ to CO

The well-defined copper(I) boryl complex [(IPr)Cu(Bpin)] [where IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and pin = pinacolate:  2,3-dimethyl-2,3-butanediolate] deoxygenates CO2 rapidly and quantitatively, affording CO and the borate complex [(IPr)Cu(OBpin)]. The boryl may be regenerated by treatment with the diboron compound pinB−Bpin, giving the stable byproduct pinB−O−Bpin. The use of a copper(I) alkoxide precatalyst and stoichiometric diboron reagent results in catalytic reduction of CO2, with high turnover numbers (1000 per Cu) and frequencies (100 per Cu in 1 h) depending on supporting ligand and reaction conditions

Synthesis, Structure, and Alkyne Reactivity of a Dimeric (Carbene)copper(I) Hydride

The monomeric, two-coordinate carbene complex (IPr)CuO-t-Bu (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) reacts readily with silanes such as triethoxysilane, forming a dimeric copper(I) hydride complex (2) with a very short copper−copper distance. Hydrocupration of 3-hexyne by 2 affords a monomeric copper(I) vinyl complex

Catalytic Diboration of Aldehydes via Insertion into the Copper−Boron Bond

Mesitaldehyde reacts cleanly with (IPr)CuB(pin) [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene); pin = 2,3-dimethyl-2,3-butanediolate] to afford the product complex 1, the first well-defined product of carbonyl group insertion into a metal−boron bond. Analysis of 1 by NMR spectroscopy and single-crystal X-ray diffraction indicates the formation of a copper−carbon and a boron−oxygen bond. A copper(I) precatalyst supported by the less sterically demanding ligand ICy (1,3-dicyclohexylimidazol-2-ylidene) achieves the efficient 1,2-diboration of aryl-, heteroaryl-, and alkyl-substituted aldehydes at room temperature

Synthesis, Structure, and Alkyne Reactivity of a Dimeric (Carbene)copper(I) Hydride

The monomeric, two-coordinate carbene complex (IPr)CuO-t-Bu (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) reacts readily with silanes such as triethoxysilane, forming a dimeric copper(I) hydride complex (2) with a very short copper−copper distance. Hydrocupration of 3-hexyne by 2 affords a monomeric copper(I) vinyl complex

Copper(I) β-Boroalkyls from Alkene Insertion: Isolation and Rearrangement

The insertion of alkenes into an (NHC)copper(I) boryl affords isolable β-boroalkyl complexes in high yields; competition experiments using substituted styrenes show that electron-donating substituents slow the reaction. Although the insertion products are stable at ambient temperature, a β-hydride elimination/reinsertion sequence affords a rearranged α-boroalkyl complex on heating

Copper(I) β-Boroalkyls from Alkene Insertion: Isolation and Rearrangement

The insertion of alkenes into an (NHC)copper(I) boryl affords isolable β-boroalkyl complexes in high yields; competition experiments using substituted styrenes show that electron-donating substituents slow the reaction. Although the insertion products are stable at ambient temperature, a β-hydride elimination/reinsertion sequence affords a rearranged α-boroalkyl complex on heating

Catalytic Diboration of Aldehydes via Insertion into the Copper−Boron Bond

Mesitaldehyde reacts cleanly with (IPr)CuB(pin) [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene); pin = 2,3-dimethyl-2,3-butanediolate] to afford the product complex 1, the first well-defined product of carbonyl group insertion into a metal−boron bond. Analysis of 1 by NMR spectroscopy and single-crystal X-ray diffraction indicates the formation of a copper−carbon and a boron−oxygen bond. A copper(I) precatalyst supported by the less sterically demanding ligand ICy (1,3-dicyclohexylimidazol-2-ylidene) achieves the efficient 1,2-diboration of aryl-, heteroaryl-, and alkyl-substituted aldehydes at room temperature

Generation of a Doubly Bridging CO₂ Ligand and Deoxygenation of CO₂ by an (NHC)Ni(0) Complex

The treatment of [(IPr)Ni(μ-Cl)]2 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaOt-Bu and then pinB-Bpin (bis(pinacolato)diboron) gives rise to a mono-NHC−Ni(0) complex, which dimerizes upon crystallization. The same product is prepared by the treatment of [(IPr)Ni(μ-Cl)]2 with Li(BEt)3H, or with NaOt-Bu and then HSi(OEt)3. The treatment of [(IPr)Ni]2 or its monomer with CO2 reduces CO2 to CO generating [(IPr)Ni]2(μ-CO)(μ-η2,η2-CO2). This compound represents an unprecedented symmetric double-bridging mode of CO2

Generation of a Doubly Bridging CO₂ Ligand and Deoxygenation of CO₂ by an (NHC)Ni(0) Complex

The treatment of [(IPr)Ni(μ-Cl)]2 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaOt-Bu and then pinB-Bpin (bis(pinacolato)diboron) gives rise to a mono-NHC−Ni(0) complex, which dimerizes upon crystallization. The same product is prepared by the treatment of [(IPr)Ni(μ-Cl)]2 with Li(BEt)3H, or with NaOt-Bu and then HSi(OEt)3. The treatment of [(IPr)Ni]2 or its monomer with CO2 reduces CO2 to CO generating [(IPr)Ni]2(μ-CO)(μ-η2,η2-CO2). This compound represents an unprecedented symmetric double-bridging mode of CO2