Copper-Nitrene Complexes in Catalytic CH Amination

Regioselective C-H bond amination by aminoiodanes

A new approach for the direct amination of 2-phenylpyridine derivatives using a diphthalimide-iodane and copper triflate has been developed. A series of different 2-phenylpyridine derivatives were aminated with yields up to 88%. Mechanistic investigations indicate that the reaction proceeds via a copper-mediated single electron transfer.

Unexpected CN bond formation via NaI-catalyzed oxidative de-tetra-hydrogenative cross-couplings between N,N-dimethyl aniline and sulfamides

A direct de-tetra-hydrogenative cross-coupling reaction between C_sp3–H bonds and sulfamide under transition-metal-free conditions is reported to give the corresponding amidines.

A facile approach to synthesize 3,5-disubstituted-1,2,4-oxadiazoles via copper-catalyzed-cascade annulation of amidines and methylarenes

A tandem Cu-catalyzed oxidation–amination–cyclization reaction for synthesizing various 3,5-disubstituted-1,2,4-oxadiazoles from easily available amidines and methylarenes or methylhetarenes is reported.

Utilization of methylarenes as versatile building blocks in organic synthesis

This review attempts to describe the latest developments in the utilisation of methylarenes adopting C–H functionalization strategies and covers all the developments until March 2015.

Bis(σ-B–H) complexes of copper(i): precursors to a heterogeneous amine–borane dehydrogenation catalyst

A series of bis(σ-B–H) complexes of copper(i) have been prepared by displacement of arene solvent from a β-diketiminate copper(i) complex by four-coordinate boranes, H₃B–L (L = NMe₃, lutidine).

Direct oxidative coupling of amidine hydrochlorides and methylarenes: TBHP-mediated synthesis of substituted 1,3,5-triazines under metal-free conditions

Various 2,4,6-trisubstituted 1,3,5-triazines were smoothly formed via TBHP-mediated direct oxidative coupling of amidine and methylarenes.

Computational exploration of the mechanism of copper-catalyzed aromatic C–H bond amination of benzene via a nitrene insertion approach

The mechanism of aromatic C–H amination of benzene via a nitrene insertion approach catalyzed by the Tp^Br3Cu(NCMe) complex was computationally investigated.

Enzyme-controlled nitrogen-atom transfer enables regiodivergent C-H amination

We recently demonstrated that variants of cytochrome P450BM3 (CYP102A1) catalyze the insertion of nitrogen species into benzylic C-H bonds to form new C-N bonds. An outstanding challenge in the field of C-H amination is catalyst-controlled regioselectivity. Here, we report two engineered variants of P450BM3 that provide divergent regioselectivity for C-H amination-one favoring amination of benzylic C-H bonds and the other favoring homo-benzylic C-H bonds. The two variants provide nearly identical kinetic isotope effect values (2.8-3.0), suggesting that C-H abstraction is rate-limiting. The 2.66-Å crystal structure of the most active enzyme suggests that the engineered active site can preorganize the substrate for reactivity. We hypothesize that the enzyme controls regioselectivity through localization of a single C-H bond close to the iron nitrenoid.

Syntheses of a novel fluorinated trisphosphinoborate ligand and its copper and silver complexes. Catalytic activity toward nitrene transfer reactions

A novel fluorinated ligand, the anionic PhB(CH2P(p-CF3C6H4)2)3 (PhBP3 (p-CF3Ph)), has been synthesized and characterized, as well as its corresponding thallium, copper, and silver derivatives. The presence of fluorine atoms in the ligand structure induced the desired effect of enhancing electrophilic character at the metal center, without promoting substantial changes in the ligand skeleton compared with the parent ligand PhB(CH2PPh2)3(-) (PhBP3). Olefin aziridination and C-H amidation reactions have been induced with those complexes as catalyst precursors. The copper derivative catalyzed the olefin aziridination of an array of olefins bearing either electron-donating or electron-withdrawing groups. The silver analogue was found to promote the C-H amidation of a series of substrates in moderate to high yields.

Copper-catalyzed intermolecular amidation and imidation of unactivated alkanes

We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C-H bonds over tertiary C-H bonds and even occur at primary C-H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from β-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C-H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C-H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product.

Metal-free oxidative synthesis of quinazolinones via dual amination of sp3 C–H bonds

A novel metal-free synthesis of quinazolinones via dual amination of sp³ C–H bonds was developed. The sp³ carbon in methylarenes or adjacent to a heteroatom in DMSO, DMF or DMA was used as the one carbon synthon.

n-Bu4NI/TBHP-catalyzed direct amination of allylic and benzylic C(sp3)–H with anilines under metal-free conditions

An efficient n-Bu₄NI/TBHP-catalyzed direct amination of allylic and benzylic C(sp³)–H with anilines under metal-free conditions was developed.

Copper-mediated C(sp2)–H amination using TMSN3 as a nitrogen source: redox-neutral access to primary anilines

A Cu-mediated C–H amination for the preparation of primary anilines under redox neutral conditions is developed.

Organic azides: “energetic reagents” for the intermolecular amination of C–H bonds

This feature article highlights the potentiality of organic azides (RN₃) for the intermolecular amination of sp³ and sp² C–H bonds. A compendium of employed catalytic systems, together with a discussion of involved mechanisms, is provided.

Iron-catalyzed efficient intermolecular amination of C(sp3)–H bonds with bromamine-T as nitrene source

[Fe(N4Py)(CH₃CN)](ClO₄)₂ can efficiently catalyze intermolecular nitrene insertion of sp³ C–H bonds with bromamine-T as the nitrene source, forming the desired tosylprotected amines with NaBr as the by-product.

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.

Selective intermolecular amination of C-H bonds at tertiary carbon centers

C-H insertion: A method for intermolecular amination of tertiary CH bonds is described that uses limiting amounts of substrate and a convenient phenol-derived nitrogen source. Structure-selectivity and mechanistic studies suggest that steric interaction between the substrate and active oxidant is the principal determinant of product selectivity.

Arene C-H amination at nickel in terphenyl-diphosphine complexes with labile metal-arene interactions

The meta-terphenyl diphosphine, m-P2, 1, was utilized to support Ni centers in the oxidation states 0, I, and II. A series of complexes bearing different substituents or ligands at Ni was prepared to investigate the dependence of metal-arene interactions on oxidation state and substitution at the metal center. Complex (m-P2)Ni (2) shows strong Ni(0)-arene interactions involving the central arene ring of the terphenyl ligand both in solution and the solid state. These interactions are significantly less pronounced in Ni(0) complexes bearing L-type ligands (2-L: L=CH3CN, CO, Ph2CN2), Ni(I)X complexes (3-X: X=Cl, BF4, N3, N3B(C6F5)3), and [(m-P2)Ni(II)Cl2] (4). Complex 2 reacts with substrates, such as diphenyldiazoalkane, sulfur ylides (Ph2 S=CH2 ), organoazides (RN3: R=para-C6H4OMe, para-C6H4CF3, 1-adamantyl), and N2O with the locus of observed reactivity dependent on the nature of the substrate. These reactions led to isolation of an η(1)-diphenyldiazoalkane adduct (2-Ph2CN2), methylidene insertion into a Ni-P bond followed by rearrangement of a nickel-bound phosphorus ylide (5) to a benzylphosphine (6), Staudinger oxidation of the phosphine arms, and metal-mediated nitrene insertion into an arene C-H bond of 1, all derived from the same compound (2). Hydrogen-atom abstraction from a Ni(I)-amide (9) and the resulting nitrene transfer supports the viability of Ni-imide intermediates in the reaction of 1 with 1-azido-arenes.