Development of Nonclassical Photoprecursors for Rh Nitrenes.

Characterization of reactive intermediates in C-H functionalization is challenging due to the fleeting lifetimes of these species. Synthetic photochemistry provides a strategy to generate post-turnover-limiting-step intermediates in catalysis under cryogenic conditions that enable characterization. We have a long-standing interest in the structure and reactivity of Rh nitrene intermediates, which are implicated as transient intermediates in Rh-catalyzed C-H amination.

Copper Complexes with Diazoolefin Ligands and their Photochemical Conversion into Alkenylidene Complexes.

Homometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of Cu complexes with N-heterocyclic diazoolefin ligands.

Oxygen-atom transfer photochemistry of a molecular copper bromate complex.

We report the synthesis and oxygen-atom transfer (OAT) photochemistry of [Cu(tpa)BrO]ClO. spectroscopy and experiments indicate OAT proceeds from a Cu-O fragment generated by sequential Cu-O bond cleavage and OAT from BrO to [Cu(tpa)]. These results highlight synthetic opportunities in M-O photochemistry and demonstrate the utility of experiments to evaluating photochemical reaction mechanisms.

C-H Activation of Inert Arenes using a Photochemically Activated Guanidinato-Magnesium(I) Compound.

UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg} ] 3 (Priso=[(DipN) CNPr ] , Dip=2,6-diisopropylphenyl), in either benzene, toluene, the three isomers of xylene, or mesitylene, leads to facile activation of an aromatic C-H bond of the solvent in all cases, and formation of aryl/hydride bridged magnesium(II) products, [{(Priso)Mg} (μ-H)(μ-Ar)] 4-9. In contrast to similar reactions reported for β-diketiminate coordinated counterparts of 3, these C-H activations proceed with little regioselectivity, though they are considerably faster. Reaction of 3 with an excess of the pyridine, p-NC H Bu (py ), gave [(Priso)Mg(py H)(py ) ] 10, presumably via reduction of the pyridine to yield a radical intermediate, [(Priso)Mg(py ⋅)(py ) ] 11, which then abstracts a proton from the reaction solvent or a reactant.

Iodine-Iodine Cooperation Enables Metal-Free C-N Bond-Forming Electrocatalysis via Isolable Iodanyl Radicals.

Small molecule redox mediators convey interfacial electron transfer events into bulk solution and can enable diverse substrate activation mechanisms in synthetic electrocatalysis. Here, we report that 1,2-diiodo-4,5-dimethoxybenzene is an efficient electrocatalyst for C-H/E-H coupling that operates at as low as 0.5 mol % catalyst loading.

Nitrogen Atom Transfer Catalysis by Metallonitrene C-H Insertion: Photocatalytic Amidation of Aldehydes.

C-H amination and amidation by catalytic nitrene transfer are well-established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C-H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium.

Electronic Structure Analysis and Reactivity of the Bimetallic Bis-Titanocene Vinylcarboxylate Complex, [(CpTi)(OCTMS)].

Multimetallic redox cooperativity features heavily in both bioinorganic and synthetic reactions. Here, the electronic structure of the bimetallic Ti/Ti complex , [(CpTi)(OCTMS)] has been revisited with EPR, confirming a predominantly Ti/Ti electronic structure. Reactions of with 2,6-dimethylphenyl isocyanide (CNXyl), TMSCl, MeI, and BnCl were explored, revealing differential redox chemistry of the bimetallic core.

Nitrene Photochemistry of Manganese N-Haloamides*.

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C-H amination and olefin aziridination catalysis. The reactivity of the transient high-valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of Mn N-haloamide complexes.

Snapshots of Rh-Catalyzed C-H Amination.

While X-ray crystallography routinely provides structural characterization of kinetically stable pre-catalysts and intermediates, elucidation of the structures of transient reactive intermediates, which are intimately engaged in bond-breaking and -making during catalysis, is generally not possible. Here, we demonstrate synthesis of Rh nitrenoids that participate in catalytic C-H amination, and we characterize these transient intermediates as triplet adducts of Rh. Further, we observe the impact of coordinating substrate, which is present in excess during catalysis, on the structure of transient Rh nitrenoids.