Nitridomanganese(V) Complexes: Design, Preparation, and Use as Nitrogen Atom-Transfer Reagents

Four-Electron Oxidation of Phenols to p-Benzoquinone Imines by a (Salen)ruthenium(VI) Nitrido Complex

Proton-coupled electron-transfer reactions of phenols have received considerable attention because of their fundamental interest and their relevance to many biological processes. Here we describe a remarkable four-electron oxidation of phenols by a (salen)ruthenium(VI) complex in the presence of pyridine in CH3OH to afford (salen)ruthenium(II) p-benzoquinone imine complexes. Mechanistic studies indicate that this reaction occurs in two phases. The first phase is proposed to be a two-electron transfer process that involves electrophilic attack by Ru≡N at the phenol aromatic ring, followed by proton shift to generate a Ru(IV) p-hydroxyanilido intermediate. In the second phase the intermediate undergoes intramolecular two-electron transfer, followed by rapid deprotonation to give the Ru(II) p-benzoquinone imine product.

A complex with nitrogen single, double, and triple bonds to the same chromium atom: synthesis, structure, and reactivity

A complex with single, double and triple bonds between nitrogen and the same metal center has been synthesized, [NCr(NPh)(NPrⁱ₂)₂]^–. The complex shows differential activity, with some electrophiles attacking the imido and others the nitrido.

A nitrogen-based analogue of the Schrock and Clark “yl-ene-yne” complex, W(CBu^t)(CHBu^t)(CH₂Bu^t)(dmpe), has been prepared. The new complex is the nitrido, imido, amido anion [NCr(NPh)(NPrⁱ₂)₂]^–, which was structurally characterized with the [K(crypt-2.2.2)]⁺ counterion. The “Cr–N 1-2-3” complex was prepared from NCr(NHPh)(NPrⁱ₂)₂, which exists as this nitrido–amido tautomer, rather than the bis(imido) Cr(NH)(NPh)(NPrⁱ₂)₂. By selection of electrophile, the nitrido–imido salt K[NCr(NPh)(NPrⁱ₂)₂] can undergo reaction at either the imido or the nitrido to form unusual examples of nitrido or bis(imido) complexes.

Cu-mediated nitrogen atom transfer via CN bond cleavage

A nitrogen atom transfer to organic molecules affording aryl nitriles via Cu-mediated C–N triple bond cleavage is firstly developed.

Oxidation of ascorbic acid by a (salen)ruthenium(VI) nitrido complex in aqueous solution

The oxidation of ascorbic acid (H2A) by [Ru(VI)(N)(L)(MeOH)](+) in aqueous acidic solutions has the following stoichiometry: 2[Ru(VI)(N)] + 3H2A → 2[Ru(III)(NH2-HA)](+) + A. Mechanisms involving HAT/N-rebound at low pH (≤2) and nucleophilic attack at the nitride at high pH (≥5) are proposed.

Formation of heterobimetallic zirconium/cobalt diimido complexes via a four-electron transformation

The reactivity of the reduced heterobimetallic complex Zr((i)PrNP(i)Pr2)3CoN2 (1) toward aryl azides was examined, revealing a four-electron redox transformation to afford unusual heterobimetallic zirconium/cobalt diimido complexes. In the case of p-tolyl azide, the diamagnetic C3-symmetric bis(terminal imido) complex 3 is formed, but mesityl azide instead leads to asymmetric complex 4 featuring a bridging imido fragment.

Reactivity of nitrido complexes of ruthenium(VI), osmium(VI), and manganese(V) bearing Schiff base and simple anionic ligands

Nitrido complexes (M≡N) may be key intermediates in chemical and biological nitrogen fixation and serve as useful reagents for nitrogenation of organic compounds. Osmium(VI) nitrido complexes bearing 2,2':6',2″-terpyridine (terpy), 2,2'-bipyridine (bpy), or hydrotris(1-pyrazolyl)borate anion (Tp) ligands are highly electrophilic: they can react with a variety of nucleophiles to generate novel osmium(IV)/(V) complexes. This Account describes our recent results studying the reactivity of nitridocomplexes of ruthenium(VI), osmium(VI), and manganese(V) that bear Schiff bases and other simple anionic ligands. We demonstrate that these nitrido complexes exhibit rich chemical reactivity. They react with various nucleophiles, activate C-H bonds, undergo N···N coupling, catalyze the oxidation of organic compounds, and show anticancer activities. Ruthenium(VI) nitrido complexes bearing Schiff base ligands, such as [Ru(VI)(N)(salchda)(CH3OH)](+) (salchda = N,N'-bis(salicylidene)o-cyclohexyldiamine dianion), are highly electrophilic. This complex reacts readily at ambient conditions with a variety of nucleophiles at rates that are much faster than similar reactions using Os(VI)≡N. This complex also carries out unique reactions, including the direct aziridination of alkenes, C-H bond activation of alkanes and C-N bond cleavage of anilines. The addition of ligands such as pyridine can enhance the reactivity of [Ru(VI)(N)(salchda)(CH3OH)](+). Therefore researchers can tune the reactivity of Ru≡N by adding a ligand L trans to nitride: L-Ru≡N. Moreover, the addition of various nucleophiles (Nu) to Ru(VI)≡N initially generate the ruthenium(IV) imido species Ru(IV)-N(Nu), a new class of hydrogen-atom transfer (HAT) reagents. Nucleophiles also readily add to coordinated Schiff base ligands in Os(VI)≡N and Ru(VI)≡N complexes. These additions are often stereospecific, suggesting that the nitrido ligand has a directing effect on the incoming nucleophile. M≡N is also a potential platform for the design of new oxidation catalysts. For example, [Os(VI)(N)Cl4](-) catalyzes the oxidation of alkanes by a variety of oxidants, and the addition of Lewis acids greatly accelerates these reactions. [Mn(V)(N)(CN)4]2(-) is another highly efficient oxidation catalyst, which facilitates the epoxidation of alkenes and the oxidation of alcohols to carbonyl compounds using H2O2. Finally, M≡N can potentially bind to and exert various effects on biomolecules. For example, a number of Os(VI)≡N complexes exhibit novel anticancer properties, which may be related to their ability to bind to DNA or other biomolecules.

Iron-mediated intermolecular N-group transfer chemistry with olefinic substrates

We present a chemoselective group transfer reaction from a high-spin ferric imido to olefinic and benzylic substrates.

Manganese nitride complexes in oxidation states III, IV, and V: synthesis and electronic structure

The synthesis and characterization of a series of manganese nitrides in a tripodal chelating tris(carbene) ligand framework is described. Photolysis of [(TIMEN(xyl))Mn(N(3))](+) (where TIMEN(xyl) = tris[2-(3-xylylimidazol-2-ylidene)ethyl]amine) yields the isolable molecular Mn(IV) nitride, [(TIMEN(xyl))Mn(N)](+). Spectroscopic and DFT studies indicate that this Mn(IV) d(3) complex has a doublet electronic ground state. The metal-centered one-electron oxidation of this Mn(IV) species results in formation of the pentavalent Mn(V) nitride, [(TIMEN(xyl))Mn(N)](2+). Unlike previously reported, tetragonal Mn(V) nitrides with a d(2), nonmagnetic S = 0 ground state, this trigonal bipyramidal complex has a triplet ground state S = 1. One-electron reduction of [(TIMEN(xyl))Mn(N)](+) produces the neutral, nonmagnetic trivalent [(TIMEN(xyl))Mn(N)] species with a d(4) low-spin, S = 0, ground state.

New electrophilic addition of α-diazoesters with ketones for enantioselective C-N bond formation

α-Diazoesters were discovered to be good electrophiles in a catalytic asymmetric α-functionalization of ketones for the first time. This reaction also provided a direct and efficient method for C-N bond formation with excellent yields (up to 98%) and enantioselectivities (up to 99% ee) under mild conditions. The application of the electrophilicity of α-diazoesters opens up a novel way to access the diversity of diazo chemistry.

Recent advances in transition metal-catalyzed N-atom transfer reactions of azides

Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon-nitrogen and sulfur-nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N(2) gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C-H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids.