β‑Diketiminato Nickel Imides in Catalytic Nitrene Transfer to Isocyanides

The β-diketiminato nickel­(I) species [Me₃NN]­Ni­(2-picoline) (<b>1</b>) serves as an efficient catalyst for carbodiimide (RNCNR′) formation in the reactions of a range of organoazides N₃R with isocyanides R′NC. [Me₃NN]­Ni­(CNR)₂ (R = ^tBu, Ar (Ar = 2,6-Me₂C₆H₃)) species provide carbodiimides RNCNAr′ upon reaction with Ar′N₃ (Ar′ = 3,5-Me₂C₆H₃). Nitrene transfer takes place via the intermediacy of nickel imides. Reaction of [Me_<i>x</i>NN]­Ni­(2-picoline) (<i>x</i> = 2 or 3) with Ar′N₃ gives the new dinickel imides {[Me_<i>x</i>NN]­Ni}₂(μ-NAr′) (<b>4</b> (<i>x</i> = 3) and <b>5</b> (<i>x</i> = 2)) as deep purple, diamagnetic substances. The X-ray structure of {[Me₂NN]­Ni}₂(μ-NAr′) (<b>5</b>) features short Ni–N_imide distances of 1.747(2) and 1.755(2) Å along with a short Ni–Ni distance of 2.7210(3) Å. These dinickel imides <b>4</b> and <b>5</b> react stoichiometrically with ^tBuNC to provide the corresponding carbodiimides ^tBuNCNAr′ in good yield. Azide transfer takes place upon reaction of <b>1</b> with TMS-N₃ to give the square planar nickel­(II) azide [Me₃NN]­Ni­(N₃)­(2-picoline) (<b>7</b>). Stoichiometric reaction of dinickel dicarbonyl {[Me₃NN]­Ni}₂(μ-CO)₂ with organoazides such as Ar′N₃ is sluggish, indicating that <b>1</b> is not an efficient catalyst for nitrene transfer from organoazides to CO to form isocyanates RNCO

Reaction of Cu^I with Dialkyl Peroxides: Cu^II-Alkoxides, Alkoxy Radicals, and Catalytic C–H Etherification

Kinetic analysis of the reaction of the copper­(I) β-diketiminate [Cl₂NN]Cu ([Cu^I]) with ^tBuOO^tBu to give [Cu^II]–O^tBu (<b>1</b>) reveals first-order behavior in each component implicating the formation of free ^tBuO^• radicals. Added pyridine mildly inhibits this reaction indicating competition between ^tBuOO^tBu and py for coordination at [Cu^I] prior to peroxide activation. Reaction of [Cu^I] with dicumyl peroxide leads to [Cu^II]–OCMe₂Ph (<b>3</b>) and acetophenone suggesting the intermediacy of the PhMe₂CO^• radical. Computational methods provide insight into the activation of ^tBuOO^tBu at [Cu^I]. The novel peroxide adduct [Cu^I]­(^tBuOO^tBu) (<b>4</b>) and the square planar [Cu^III]­(O^tBu)₂ (<b>5</b>) were identified, each unstable toward loss of the ^tBuO^• radical. Facile generation of the ^tBuO^• radical is harnessed in the catalytic C–H etherification of cyclohexane with ^tBuOO^tBu at rt employing [Cu^I] (5 mol %) to give the ether Cy–O^tBu in 60% yield

Reaction of Cu^I with Dialkyl Peroxides: Cu^II-Alkoxides, Alkoxy Radicals, and Catalytic C–H Etherification

Kinetic analysis of the reaction of the copper­(I) β-diketiminate [Cl₂NN]Cu ([Cu^I]) with ^tBuOO^tBu to give [Cu^II]–O^tBu (<b>1</b>) reveals first-order behavior in each component implicating the formation of free ^tBuO^• radicals. Added pyridine mildly inhibits this reaction indicating competition between ^tBuOO^tBu and py for coordination at [Cu^I] prior to peroxide activation. Reaction of [Cu^I] with dicumyl peroxide leads to [Cu^II]–OCMe₂Ph (<b>3</b>) and acetophenone suggesting the intermediacy of the PhMe₂CO^• radical. Computational methods provide insight into the activation of ^tBuOO^tBu at [Cu^I]. The novel peroxide adduct [Cu^I]­(^tBuOO^tBu) (<b>4</b>) and the square planar [Cu^III]­(O^tBu)₂ (<b>5</b>) were identified, each unstable toward loss of the ^tBuO^• radical. Facile generation of the ^tBuO^• radical is harnessed in the catalytic C–H etherification of cyclohexane with ^tBuOO^tBu at rt employing [Cu^I] (5 mol %) to give the ether Cy–O^tBu in 60% yield

Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation

Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru₂(L)₂Cl₃]­PF₆ complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283 000 h^–1 were achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quantitative yields. The described synthetic protocol makes use of air-stable reagents available in multigram quantities, rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems