Catalyst Control of Selectivity in CO₂ Reduction Using a Tunable Heterobimetallic Effect

A tunable bimetallic effect on product selectivity in catalytic CO₂ reduction was identified using <i>N</i>-heterocyclic carbene-ligated Cu complexes. While the monometallic Cu-only system catalyzes hydroboration of CO₂ with pinacolborane to produce formate exclusively, introducing a bimetallic effect with analogous Cu–Fe, Cu–W, and Cu–Mo catalysts produces mixtures of formate and CO. Within a series of isosteric catalysts, the selectivity of CO versus formate was controlled by tuning the electronic nature of the Cu/M pairing, with high selectivity for CO being achieved using a Cu–Mo catalyst

Light-Mediated Synthesis of Aliphatic Anhydrides by Cu-Catalyzed Carbonylation of Alkyl Halides

Acid anhydrides are valuable in the chemical industry for their role in synthesizing polymers, pharmaceuticals, and other commodities, but their syntheses often involve multiple steps with precious metal catalysts. The simplest anhydride, acetic anhydride, is currently produced by two Rh-catalyzed carbonylation reactions on a bulk scale for its use in synthesizing products ranging from aspirin to cellulose acetate. Here, we report a light-mediated, Cu-catalyzed process for producing aliphatic, symmetric acid anhydrides directly by carbonylation of alkyl (pseudo)halides in a single step without any precious metal additives. The transformation requires only simple Cu salts and abundant bases to generate a heterogeneous Cu0 photocatalyst in situ, maintains high efficiency and selectivity upon scale-up, and operates by a radical mechanism with several beneficial features. This discovery will enable the engineering of bulk processes for producing commodity anhydrides efficiently and sustainably

C−C Coupling Reactivity of an Alkylgold(III) Fluoride Complex with Arylboronic Acids

Previously, alkylgold(III) fluorides have been proposed as catalytic intermediates that undergo C−C coupling with reagents such as arylboronic acids in Au(I)/Au(III) cross-coupling reactions. Here is reported the first experimental evidence for this elementary mechanistic step. Complexes of the type (NHC)AuMe (NHC = N-heterocyclic carbene) were oxidized with XeF2 to yield cis-(NHC)AuMeF2 products, which were found to be in equilibrium with their fluoride-dissociated, dimeric [(NHC)AuMe(μ-F)]2[F]2 forms. In one case, a monomeric cis-(NHC)AuMeF2 complex was favored exclusively in solution, and it was found to react with a variety of ArB(OH)2 reagents to yield Ar−CH3 products

Heterobimetallic Control of Regioselectivity in Alkyne Hydrostannylation: Divergent Syntheses of α- and (<i>E</i>)<i>‑</i>β<i>-</i>Vinylstannanes via Cooperative Sn–H Bond Activation

Cooperative Sn–H bond activation of hydrostannanes (Bu3SnH) by tunable heterobimetallic (NHC)­Cu–[MCO] catalysts ([MCO] = FeCp­(CO)2 or Mn­(CO)5) enables the catalytic hydrostannylation of terminal alkynes under mild conditions, with Markovnikov/anti-Markovnikov selectivity controlled by the Cu/M pairing. By using the MeIMesCu–FeCp­(CO)2 catalyst, a variety of α-vinylstannanes were produced from simple alkyl-substituted alkynes and Bu3SnH in high yield and good regioselectivity; these products are challenging to access under mononuclear metal-catalyzed hydrostannylation conditions. In addition, reversed regioselectivity was observed for aryl-substituted alkynes under the Cu/Fe-catalyzed conditions, affording the (E)-β-vinylstannanes as major products. On the other hand, by using the IMesCu–Mn­(CO)5 catalyst, a variety of (E)-β-vinylstannanes were produced from primary, secondary, and tertiary alkyl-substituted alkynes, thus demonstrating divergent regioselectivity for alkyne hydrostannylation controlled by Cu/Fe vs Cu/Mn pairing. Both methods are amenable to gram-scale vinylstannane synthesis as well as late-stage hydrostannylation in a natural-product setting. Mechanistic experiments indicate the syn addition of Bu3SnH to the alkynes and imply the involvement of Sn–H bond activation in the rate-determining step. Two distinct catalytic cycles were proposed for the Cu/Fe and Cu/Mn catalysis based on stoichiometric reactivity experiments

Photochemical Synthesis of Acyl Fluorides Using Copper-Catalyzed Fluorocarbonylation of Alkyl Iodides

Acyl fluorides are important reagents due to their unique balance between reactivity and stability. Here, we report a copper-catalyzed carbonylative coupling strategy for synthesizing acyl fluorides under photoirradiation. Alkyl iodides were transformed in high yields into acyl fluorides by using a commercially available copper precatalyst (CuBr·SMe2) and a readily available fluoride salt (KF) at ambient temperature and mild CO pressure (6 atm) under blue light irradiation

Diverse Thermal and Photochemical Reactivity of an Al–Fe Bonded Heterobimetallic Complex

A heterobimetallic Al–Fe complex, LAl­(Me)­Fp (Fp = FeCp­(CO)2, L is a β-diketiminate), was found to have diverse reaction chemistry including cooperative ring-opening of tetrahydrofuran to form LAl­(Me)­O­(CH2)4Fp, atom transfer with propylene sulfide and elemental sulfur to form LAl­(Me)­(μ-S)­Fp, and group transfer with trimethylsilyl azide to form LAl­(Me)­N3. Photodecarbonylation formed [LAl­(Me)]2(CpFeFeCp)­(μ3:η2-CO)2, which features the FeFe bonded [CpFe­(CO)]2 unit that is the unsaturated analogue of well-known Fp2. Despite Al and Fe being the two most earth-abundant metals, this report represents one of the only surveys of the reactivity behavior of an Al/Fe heterobinuclear complex

<i>E</i>‑Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis

A unique cooperative H₂ activation reaction by heterobimetallic (NHC)­M′-MCp­(CO)₂ complexes (NHC = <i>N</i>-heterocyclic carbene, M′ = Cu or Ag, M = Fe or Ru) has been leveraged to develop a catalytic alkyne semi-hydrogenation transformation. The optimal Ag–Ru catalyst gives high selectivity for converting alkynes to <i>E</i>-alkenes, a rare selectivity mode for reduction reactions with H₂. The transformation is tolerant of many reducible functional groups. Computational analysis of H₂ activation thermodynamics guided rational catalyst development. Bimetallic alkyne hydrogenation and alkene isomerization mechanisms are proposed

C−C Coupling Reactivity of an Alkylgold(III) Fluoride Complex with Arylboronic Acids

Previously, alkylgold(III) fluorides have been proposed as catalytic intermediates that undergo C−C coupling with reagents such as arylboronic acids in Au(I)/Au(III) cross-coupling reactions. Here is reported the first experimental evidence for this elementary mechanistic step. Complexes of the type (NHC)AuMe (NHC = N-heterocyclic carbene) were oxidized with XeF2 to yield cis-(NHC)AuMeF2 products, which were found to be in equilibrium with their fluoride-dissociated, dimeric [(NHC)AuMe(μ-F)]2[F]2 forms. In one case, a monomeric cis-(NHC)AuMeF2 complex was favored exclusively in solution, and it was found to react with a variety of ArB(OH)2 reagents to yield Ar−CH3 products