Large-scale CO hydrogenation could offer a renewable stream of industrially important C chemicals while reducing CO emissions. Critical to this opportunity is the requirement for inexpensive catalysts based on earth-abundant metals instead of precious metals. We report a nickel-gallium complex featuring a Ni(0)→Ga(III) bond that shows remarkable catalytic activity for hydrogenating CO to formate at ambient temperature (3150 turnovers, turnover frequency = 9700 h), compared with prior homogeneous Ni-centered catalysts. The Lewis acidic Ga(III) ion plays a pivotal role in stabilizing catalytic intermediates, including a rare anionic d Ni hydride. Structural and in situ characterization of this reactive intermediate support a terminal Ni-H moiety, for which the thermodynamic hydride donor strength rivals those of precious metal hydrides. Collectively, our experimental and computational results demonstrate that modulating a transition metal center via a direct interaction with a Lewis acidic support can be a powerful strategy for promoting new reactivity paradigms in base-metal catalysis.

A porous metal-organic framework Zr6O4(OH)4(L-PdX)3 (1-X) has been constructed from Pd diphosphinite pincer complexes ([L-PdX](4-) = [(2,6-(OPAr2)2C6H3)PdX](4-), Ar = p-C6H4CO2(-), X = Cl, I). Reaction of 1-X with PhI(O2CCF3)2 facilitates I(-)/CF3CO2(-) ligand exchange to generate 1-TFA and I2 as a soluble byproduct. 1-TFA is an active and recyclable catalyst for transfer hydrogenation of benzaldehydes using formic acid as a hydrogen source. In contrast, the homogeneous analogue (t)Bu(L-PdTFA) is an ineffective catalyst owing to decomposition under the catalytic conditions, highlighting the beneficial effects of immobilization.

The controlled conversion of hydrocarbons to functionalized products requires selective C-H bond cleavage. This perspective provides an overview of 1,2-CH-addition of hydrocarbons across d(0) transition metal imido complexes and compares and contrasts these to examples of analogous reactions that involve later transition metal amide, hydroxide and alkoxide complexes with d(6) and d(8) metals.

Large-scale implementation of carbon neutral energy sources such as solar and wind will require the development of energy storage mechanisms. The hydrogenation of CO into formic acid or methanol could function as a means to store energy in a chemical bond. The catalyst reported here operates under low pressure, at room temperature, and in the presence of a base much milder (7 pK units lower) than the previously reported CO hydrogenation catalyst, Co(dmpe)H. The Co(I) tetraphosphine complex, [Co(L3)(CHCN)]BF, where L3 = 1,5-diphenyl-3,7-bis(diphenylphosphino)propyl-1,5-diaza-3,7-diphosphacyclooctane (0.31 mM), catalyzes CO hydrogenation with an initial turnover frequency of 150(20) h at 25 °C, 1.7 atm of a 1:1 mixture of H and CO, and 0.6 M 2-tert-butyl-1,1,3,3-tetramethylguanidine.

The water-soluble Ni bis(diphosphine) complex [NiL 2 ](BF 4 ) 2 (L = 1,2-[bis(dimethoxypropyl)phosphino]ethane and the corresponding hydride, [HNiL 2 ]BF 4 , were synthesized and characterized. These complexes were specifically designed for CO 2 hydrogenation. For HNiL 2 + , the hydricity (ΔG°H − ) was determined to be 23.2(3) kcal/mol in aqueous solution. On the basis of the hydricity of formate, 24.1 kcal/mol, the transfer of a hydride from HNiL 2 + to CO 2 to produce formate is favorable by 1 kcal/mol. Starting from either NiL 2 2+ or HNiL 2 + in water, catalytic hydrogenation of CO 2 was observed with NaHCO 3 (0.8 M) as the only additive. A maximum turnover frequency of [4.0(5)] × 10 −1 h −1 was observed at 80 °C and 34 atm of a 1:1 mixture of CO 2 and H 2 . This report demonstrates the use of a homogeneous first-row transition-metal catalyst for CO 2 hydrogenation in water using NaHCO 3 as an inexpensive, readily available base.

A critical scientific challenge for utilization of CO is the development of catalyst systems that function in water and use inexpensive and environmentally friendly reagents. We have used thermodynamic insights to predict and demonstrate that the HCo (dmpe) catalyst system, previously described for use in organic solvents, can hydrogenate CO to formate in water with bicarbonate as the only added reagent. Replacing tetrahydrofuran as the solvent with water changes the mechanism for catalysis by altering the thermodynamics for hydride transfer to CO from a key dihydride intermediate. The need for a strong organic base was eliminated by performing catalysis in water owing to the change in mechanism. These studies demonstrate that the solvent plays a pivotal role in determining the reaction thermodynamics and thereby catalytic mechanism and activity.

No abstract

Discovery chemists routinely identify purpose-tailored molecules through an iterative structural optimization approach, but the preparation of each successive candidate in a compound series can rarely be conducted in a manner matching their thought process. This is because many of the necessary chemical transformations required to modify compound cores in a straightforward fashion are not applicable in complex contexts. We report a method that addresses one facet of this problem by allowing chemists to hop directly between chemically distinct heteroaromatic scaffolds. Specifically, we show that selective photolysis of quinoline N -oxides with 390-nanometer light followed by acid-promoted rearrangement affords N -acylindoles while showing broad compatibility with medicinally relevant functionality. Applications to late-stage skeletal modification of compounds of pharmaceutical interest and more complex transformations involving serial single-atom changes are demonstrated.