Mechanistic Insights into C–H Amination via Dicopper Nitrenes

We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl₂NN]­Cu}₂(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl₂NN]­Cu}₂(μ-N^tBu) (<b>3</b>) demonstrate that the terminal nitrene [Cl₂NN]­CuN^<i>t</i>Bu is the active intermediate in C–H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl₂NN]­Cu, both consistent with dissociation of a [Cl₂NN]Cu fragment from <b>3</b> prior to C–H amination. C–H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]₂(μ-NCHRR′) derived from 1° and 2° alkylazides are unstable toward tautomerization to copper­(I) imine complexes [Cu]­(HNCRR′), rendering 1° and 2° alkylnitrene complexes unsuitable for C–H amination

Mechanistic Insights into C–H Amination via Dicopper Nitrenes

We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl₂NN]­Cu}₂(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl₂NN]­Cu}₂(μ-N^tBu) (<b>3</b>) demonstrate that the terminal nitrene [Cl₂NN]­CuN^<i>t</i>Bu is the active intermediate in C–H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl₂NN]­Cu, both consistent with dissociation of a [Cl₂NN]Cu fragment from <b>3</b> prior to C–H amination. C–H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]₂(μ-NCHRR′) derived from 1° and 2° alkylazides are unstable toward tautomerization to copper­(I) imine complexes [Cu]­(HNCRR′), rendering 1° and 2° alkylnitrene complexes unsuitable for C–H amination

Mechanistic Insights into C–H Amination via Dicopper Nitrenes

We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl₂NN]­Cu}₂(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl₂NN]­Cu}₂(μ-N^tBu) (<b>3</b>) demonstrate that the terminal nitrene [Cl₂NN]­CuN^<i>t</i>Bu is the active intermediate in C–H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl₂NN]­Cu, both consistent with dissociation of a [Cl₂NN]Cu fragment from <b>3</b> prior to C–H amination. C–H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]₂(μ-NCHRR′) derived from 1° and 2° alkylazides are unstable toward tautomerization to copper­(I) imine complexes [Cu]­(HNCRR′), rendering 1° and 2° alkylnitrene complexes unsuitable for C–H amination

Mechanistic Insights into C–H Amination via Dicopper Nitrenes

We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl₂NN]­Cu}₂(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl₂NN]­Cu}₂(μ-N^tBu) (<b>3</b>) demonstrate that the terminal nitrene [Cl₂NN]­CuN^<i>t</i>Bu is the active intermediate in C–H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl₂NN]­Cu, both consistent with dissociation of a [Cl₂NN]Cu fragment from <b>3</b> prior to C–H amination. C–H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]₂(μ-NCHRR′) derived from 1° and 2° alkylazides are unstable toward tautomerization to copper­(I) imine complexes [Cu]­(HNCRR′), rendering 1° and 2° alkylnitrene complexes unsuitable for C–H amination

Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols

Nitrite (NO₂^–) and nitroso compounds (E-NO, E = RS, RO, and R₂N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper­(II) nitrito complex [Cl₂NN_F6]­Cu­(κ²-O₂N)·THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [Cu^II]­(κ²-O₂N) that leads to <i>S</i>-nitrosation to give the <i>S</i>-nitrosothiol RSNO and copper­(II) hydroxide [Cu^II]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph₂NH and alcohol ^tBuOH to give Ph₂NNO and ^tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper­(II) thiolate [Cu^II]-SR intermediate formed upon reaction of an additional equiv thiol with [Cu^II]-OH

Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols

Nitrite (NO₂^–) and nitroso compounds (E-NO, E = RS, RO, and R₂N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper­(II) nitrito complex [Cl₂NN_F6]­Cu­(κ²-O₂N)·THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [Cu^II]­(κ²-O₂N) that leads to <i>S</i>-nitrosation to give the <i>S</i>-nitrosothiol RSNO and copper­(II) hydroxide [Cu^II]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph₂NH and alcohol ^tBuOH to give Ph₂NNO and ^tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper­(II) thiolate [Cu^II]-SR intermediate formed upon reaction of an additional equiv thiol with [Cu^II]-OH

Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols

Nitrite (NO₂^–) and nitroso compounds (E-NO, E = RS, RO, and R₂N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper­(II) nitrito complex [Cl₂NN_F6]­Cu­(κ²-O₂N)·THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [Cu^II]­(κ²-O₂N) that leads to <i>S</i>-nitrosation to give the <i>S</i>-nitrosothiol RSNO and copper­(II) hydroxide [Cu^II]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph₂NH and alcohol ^tBuOH to give Ph₂NNO and ^tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper­(II) thiolate [Cu^II]-SR intermediate formed upon reaction of an additional equiv thiol with [Cu^II]-OH

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

Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols

Nitrite (NO₂^–) and nitroso compounds (E-NO, E = RS, RO, and R₂N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper­(II) nitrito complex [Cl₂NN_F6]­Cu­(κ²-O₂N)·THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [Cu^II]­(κ²-O₂N) that leads to <i>S</i>-nitrosation to give the <i>S</i>-nitrosothiol RSNO and copper­(II) hydroxide [Cu^II]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph₂NH and alcohol ^tBuOH to give Ph₂NNO and ^tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper­(II) thiolate [Cu^II]-SR intermediate formed upon reaction of an additional equiv thiol with [Cu^II]-OH

Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols

Nitrite (NO₂^–) and nitroso compounds (E-NO, E = RS, RO, and R₂N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper­(II) nitrito complex [Cl₂NN_F6]­Cu­(κ²-O₂N)·THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [Cu^II]­(κ²-O₂N) that leads to <i>S</i>-nitrosation to give the <i>S</i>-nitrosothiol RSNO and copper­(II) hydroxide [Cu^II]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph₂NH and alcohol ^tBuOH to give Ph₂NNO and ^tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper­(II) thiolate [Cu^II]-SR intermediate formed upon reaction of an additional equiv thiol with [Cu^II]-OH