The catalytic hydrogenation activity of the readily prepared, coordinatively saturated cobalt(I) precatalyst, (R,R)-( iPr DuPhos)Co(CO) 2 H ((R,R)-iPr DuPhos = (+)-1,2-bis[(2R,5R)-2,5-diisopropylphospholano]benzene), is described. While efficient turnover was observed with a range of alkenes upon heating to 100 °C, the catalytic performance of the cobalt catalyst was markedly enhanced upon irradiation with blue light at 35 °C. This improved reactivity enabled hydrogenation of terminal, di-, and trisubstituted alkenes, alkynes, and carbonyl compounds. A combination of deuterium labeling studies, hydrogenation of alkenes containing radical clocks, and experiments probing relative rates supports a hydrogen atom transfer pathway under thermal conditions that is enabled by a relatively weak cobalt−hydrogen bond of 54 kcal/ mol. In contrast, data for the photocatalytic reactions support light-induced dissociation of a carbonyl ligand followed by a coordination-insertion sequence where the product is released by combination of a cobalt alkyl intermediate with the starting hydride, (R,R)-( iPr DuPhos)Co(CO) 2 H. These results demonstrate the versatility of catalysis with Earth-abundant metals as pathways involving open-versus closed-shell intermediates can be switched by the energy source.

Ultra-fast pre-solvated electron capture has been observed for aqueous solutions of room-temperature ionic liquid (RTIL) surface-stabilized gold nanoparticles (AuNPs; ∼9 nm). The extraordinarily large inverse temperature dependent rate constants (k(e)∼ 5 × 10(14) M(-1) s(-1)) measured for the capture of electrons in solution suggest electron capture by the AuNP surface that is on the timescale of, and therefore in competition with, electron solvation and electron-cation recombination reactions. The observed electron transfer rates challenge the conventional notion that radiation induced biological damage would be enhanced in the presence of AuNPs. On the contrary, AuNPs stabilized by non-covalently bonded ligands demonstrate the potential to quench radiation-induced electrons, indicating potential applications in fields ranging from radiation therapy to heterogeneous catalysis.

Intermediates relevant to cobalt‐catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18‐electron (R,R)‐(iPrDuPhos)Co(CO)2H has been structurally characterized, and it promotes exclusive hydrogenation of styrene in the presence of 50 bar of H2/CO gas (1:1) at 100 °C. Deuterium‐labeling studies established reversible 2,1‐insertion of styrene into the Co−D bond of (R,R)‐(iPrDuPhos)Co(CO)2D. Whereas rapid β‐hydrogen elimination from cobalt alkyls occurred under an N2 atmosphere, alkylation of (R,R)‐(iPrDuPhos)Co(CO)2Cl in the presence of CO enabled the interception of (R,R)‐(iPrDuPhos)Co(CO)2C(O)CH2CH2Ph, which upon hydrogenolysis under 4 atm H2 produced the corresponding aldehyde and cobalt hydride, demonstrating the feasibility of elementary steps in hydroformylation. Both the hydride and chloride derivatives, (X=H−, Cl−), underwent exchange with free 13CO. Under reduced pressure, (R,R)‐(iPrDuPhos)Co(CO)2Cl underwent CO dissociation to form (R,R)‐(iPrDuPhos)Co(CO)Cl.

Divergent reactivity of organometallic rhodium(I) complexes, which led to the isolation of neutral rhodium silylenes, is described. Addition of PhRSiH2 (R=H, Ph) to the rhodium cyclooctene complex (iPrNNN)Rh(COE) (1‐COE; iPrNNN=2,5‐[iPr2P=N(4‐iPrC6H4)]2N(C6H2)−, COE=cyclooctene) resulted in the oxidative addition of an Si−H bond, providing rhodium(III) silyl hydride complexes (iPrNNN)Rh(H)SiHRPh (R=H, 2‐SiH2Ph; Ph, 2‐SiHPh2). When the carbonyl complex (iPrNNN)Rh(CO) (1‐CO) was treated with hydrosilanes, base‐stabilized rhodium(I) silylenes κ2‐N,N‐(iPrNNN)(CO)Rh=SiRPh (R=H, 3‐SiHPh; Ph, 3‐SiPh2) were isolated and characterized using multinuclear NMR spectroscopy and X‐ray crystallography. Both silylene species feature short Rh−Si bonds [2.262(1) Å, 3‐SiHPh; 2.2702(7) Å, 3‐SiPh2] that agree well with the DFT‐computed structures. The overall reaction led to a change in the iPrNNN ligand bonding mode (κ3→κ2) and loss of H2 from PhSiRH2, as corroborated by deuterium labelling experiments.

Rhodium(I) alkene complexes of an NNN-pincer ligand catalyze the hydrogenation of alkenes, including ethylene. The terminal or resting state of the catalyst, which exhibits an unprecedentedly upfield Rh-hydride (1)H NMR chemical shift, has been isolated and a synthetic cycle for regenerating the catalytically active species has been established.