Photolytic activation of NiXL explains how Ni-mediated cross coupling begins.

Nickel photocatalysis has recently become vital to organic synthesis, but how the NiXL pre-catalyst (X = Cl, Br; L = bidentate ligand) becomes activated to NiXL has remained puzzling and is typically addressed on a case-by-case basis. Here, we reveal a general mechanism where light induces photolysis of the Ni-X bond, either via direct excitation or triplet energy transfer. Photolysis produces NiXL and a halogen radical, X.

Mixed Valence {NiNi} Clusters as Models of Acetyl Coenzyme A Synthase Intermediates.

Acetyl coenzyme A synthase (ACS) catalyzes the formation and deconstruction of the key biological metabolite, acetyl coenzyme A (acetyl-CoA). The active site of ACS features a {NiNi} cluster bridged to a [FeS] cubane known as the A-cluster. The mechanism by which the A-cluster functions is debated, with few model complexes able to replicate the oxidation states, coordination features, or reactivity proposed in the catalytic cycle.

Iron(iv) alkyl complexes: electronic structure contributions to Fe-C bond homolysis and migration reactions that form N-C bonds from N.

High-valent iron alkyl complexes are rare, as they are prone to Fe-C bond homolysis. Here, we describe an unusual way to access formally iron(iv) alkyl complexes through double silylation of iron(i) alkyl dinitrogen complexes to form an NNSi group. Spectroscopically validated computations show that the disilylehydrazido(2-) ligand stabilizes the formal iron(iv) oxidation state through a strongly covalent Fe-N π-interaction, in which one π-bond fits an "inverted field" description.

Evaluating Diazene to N Interconversion at Iron-Sulfur Complexes.

Biological N reduction occurs at sulfur-rich multiiron sites, and an interesting potential pathway is concerted double reduction/ protonation of bridging N through PCET. Here, we test the feasibility of using synthetic sulfur-supported diiron complexes to mimic this pathway. Oxidative proton transfer from μ-η : η-diazene (HN=NH) is the microscopic reverse of the proposed N fixation pathway, revealing the energetics of the process.

Mechanism of Nitrogen-Carbon Bond Formation from Iron(IV) Disilylhydrazido Intermediates during N Reduction.

We recently reported a reaction sequence that activates C-H bonds in simple arenes as well as the N-N triple bond in N, delivering the aryl group to N to form a new N-C bond ( , 221). This enables the transformation of abundant feedstocks (arenes and N) into N-containing organic compounds. The key N-C bond forming step occurs upon partial silylation of N.

Cobalt-Carbon Bonding in a Salen-Supported Cobalt(IV) Alkyl Complex Postulated in Oxidative MHAT Catalysis.

The catalytic hydrofunctionalization of alkenes through radical-polar crossover metal hydrogen atom transfer (MHAT) offers a mild pathway for the introduction of functional groups in sterically congested environments. For M = Co, this reaction is often proposed to proceed through secondary alkylcobalt(IV) intermediates, which have not been characterized unambiguously. Here, we characterize a metastable (salen)Co(isopropyl) cation, which is capable of forming C-O bonds with alcohols as proposed in the catalytic reaction.

Iron Complexes of a Proton-Responsive SCS Pincer Ligand with a Sensitive Electronic Structure.

Sulfur/carbon/sulfur pincer ligands have an interesting combination of strong-field and weak-field donors, a coordination environment that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a proton-responsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex.