Nitrous oxide as diazo transfer reagent.

Nitrous oxide, commonly known as "laughing gas", is formed as a by-product in several industrial processes. It is also readily available by thermal decomposition of ammonium nitrate. Traditionally, the chemical valorization of N2O is achieved via oxidation chemistry, where N2O acts as a selective oxygen atom transfer reagent. Recent results have shown that N2O can also function as an efficient diazo transfer reagent. Synthetically useful methods for synthesizing triazenes, N-heterocycles, and azo- or diazo compounds were developed. This review article summarizes significant advancements in this emerging field.

Well-Defined Iron Sites in Crystalline Carbon Nitride.

Carbon nitride materials can be hosts for transition metal sites, but Mössbauer studies on iron complexes in carbon nitrides have always shown a mixture of environments and oxidation states. Here we describe the synthesis and characterization of a crystalline carbon nitride with stoichiometric iron sites that all have the same environment. The material (formula C6N9H2Fe0.4Li1.2Cl, abbreviated PTI/FeCl2) is derived from reacting poly(triazine imide)·LiCl (PTI/LiCl) with a low-melting FeCl2/KCl flux, followed by anaerobic rinsing with methanol. X-ray diffraction, X-ray absorption and Mössbauer spectroscopies, and SQUID magnetometry indicate that there are tetrahedral high-spin iron(II) sites throughout the material, all having the same geometry. The material is active for electrocatalytic nitrate reduction to ammonia, with a production rate of ca. 0.1 mmol cm-2 h-1 and Faradaic efficiency of ca. 80% at -0.80 V vs RHE.

Synthesis of Cyclometalated Gold(III) Complexes via Catalytic Rhodium to Gold(III) Transmetalation.

A catalytic method to synthesize a broad array of cyclometalated (C^N)gold(III) complexes is reported here. An unprecedented Rh-to-AuIII transmetalation allows the facile transfer of (C^N) ligands between these two metals in a redox-neutral process. The reaction employs commercially available precursors and proceeds under mild and environmentally benign conditions. Both experimental and computational studies support a multistep transmetalation from rhodium to gold as the underlying mechanism for these transformations. This process involves first, a rate-determining transfer of the C ligand followed by the subsequent incorporation of the N donor to form the monocyclometalated (C^N)gold(III) species.

Synthesis and Characterization of Bidentate (P

A new family of cationic, bidentate (P^N)gold(III) fluoride complexes has been prepared and a detailed characterization of the gold-fluoride bond has been carried out. Our results correlate with the observed reactivity of the fluoro ligand, which undergoes facile exchange with both cyano and acetylene nucleophiles. The resulting (P^N)arylgold(III)C(sp) complexes have enabled the first study of reductive elimination on (P^N)gold(III) systems, which demonstrated that C(sp2 )-C(sp) bond formation occurs at higher rates than those reported for analogous phosphine-based monodentate systems.

Mechanistic Insights into C(sp2 )-C(sp)N Reductive Elimination from Gold(III) Cyanide Complexes.

A new family of phosphine-ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary 12/13 C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp2 )-C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp3 )-C(sp3 ), C(sp2 )-C(sp2 ), and C(sp3 )-C(sp2 ) bond formation processes taking place on gold(III) species.

Oxidant speciation and anionic ligand effects in the gold-catalyzed oxidative coupling of arenes and alkynes.

The mechanism of the gold-catalyzed oxidative cross-coupling of arenes and alkynes has been studied in detail combining stoichiometric experiments with putative reaction intermediates and DFT calculations. Our data suggest that ligand exchange between the alkyne, the Au(i)-catalyst and the hypervalent iodine reagent is responsible for the formation of both an Au(i)-acetylide complex and a more reactive "non-symmetric" I(iii) oxidant responsible for the crucial Au(i)/Au(iii) turnover. Further, the reactivity of the in situ generated Au(iii)-acetylide complex is governed by the nature of the anionic ligands transferred by the I(iii) oxidant: while halogen ligands remain unreactive, acetato ligands are efficiently displaced by the arene to yield the observed Csp2-Csp cross-coupling products through an irreversible reductive elimination step. Finally, the nature of competitive processes and catalyst deactivation pathways has also been unraveled. This detailed investigation provides insights not only on the specific features of the species involved in oxidative gold-catalyzed cross couplings but also highlights the importance of both ancillary and anionic ligands in the reactivity of the key Au(iii) intermediates.

κ3 -(N

Gold(III) carboxylate species, stabilized by a κ3 -(N^C^C) ligand template, are presented herein. A η1 -AuIII -C(O)-OH species has been characterized under cryogenic conditions as a result of the nucleophilic attack of an ammonium hydroxide onto a dinuclear µ-CO2 -κ3 -(N^C^C)AuIII precursor. Thermal decomposition for these species proceeds by an unusual decarbonylation process, in contrast to typical decarboxylation pathways observed in related metallocarboxylic acids.

γ-Functionalizations of Amines through Visible-Light-Mediated, Redox-Neutral C-C Bond Cleavage.

Cleavage of unstrained C-C bonds under mild, redox-neutral conditions represents a challenging endeavor which is accomplished here in the context of a flexible, visible-light-mediated, γ-functionalization of amines. In situ generated C-centered radicals are harvested in the presence of Michael acceptors, thiols and alkyl halides to efficiently form new C(sp3 )-C(sp3 ), C(sp3 )-H and C(sp3 )-Br bonds, respectively.

Gold-Catalyzed Direct Oxidative Arylation with Boron Coupling Partners.

An efficient synthesis of biaryls through a gold-catalyzed oxidative cross-coupling of arenes with strong electron-deprived aryl boronates is presented herein. Regio- and chemocontrol are achieved by the selective activation of these coupling partners by gold at different oxidation states. Under reaction conditions devoid of basic additives or directing groups, the role of acetato ligand as an internal base has been revealed as a key parameter for expanding the reaction scope in these transformations.