A Robust Nickel Catalyst for Cyanomethylation of Aldehydes: Activation of Acetonitrile under Base-Free Conditions

Manganese-Ketenimine Intermediates as Active Catalysts in the Michael Addition of Unactivated Nitriles to α,β-Unsaturated Ketones

The Michael addition of unactivated nitriles to α,β-unsaturated ketones is a challenging yet desirable strategy for installing alkyl cyano-groups (R-CN) in organic molecules. However, despite formidable efforts, using acetonitrile as a Michael donor in these reactions has remained a significant challenge. Herein, we report a highly active manganese(I) complex [(PCNHCP)Mn(CO)2H] (1), which chemoselectively catalyzes the 1,4-addition of unactivated nitriles (incl. acetonitrile) to α,β-unsaturated ketones. The developed methodology operates under mild conditions, does not require any additives or bases, features low catalyst loadings (1 mol %), fast reaction times (2-8 hours), and is compatible with a wide variety of functional groups, including halides, trifluoromethyl, alkenyl, alkynyl, and (hetero)aryl groups. Extensive mechanistic studies revealed that after base-free activation of the nitrile, either the N-bound manganese-ketenimine (propionitrile or benzyl cyanide) or the C-bound manganese-cyanoalkyl (acetonitrile) complex is formed. The difference in stability of these two species explains why more sterically hindered and presumably less activated nitriles (i.e., propionitrile, and butyronitrile) show higher reactivity than their corresponding more activated congeners (i.e., acetonitrile). Finally, the practicality of our approach was demonstrated through a gram-scale reaction and subsequent derivatizations of the obtained product into important organic motifs such as ene-lactams and tetrahydropyridines.

Regio- and Enantioselective Allylic Cyanomethylation by Synergistic Rhodium and Silane Catalysis

Rh/silane-cocatalyzed regio- and enantioselctive allylic cyanomethylation with inert acetonitrile directly has been developed. Addition of a catalytic amount neutral silane reagent as an acetonitrile anion carrier is essential for the success of this reaction. The synthesis of mono- and bis-allylation products can be switched by adjusting the size of substituents on the silane, ligands, and temperature. Chiral homoallylic nitriles could be synthesized in above 20:1 branch/linear ratio, up to 98% yield and >99% ee.

Diastereoselective Direct Catalytic Asymmetric Mannich-Type Reactions of Alkylnitriles with a Ni(II)-Carbene Complex

Despite recent advances in reactions using alkylnitriles as carbon nucleophiles, diastereoselective direct catalytic asymmetric reactions, in which two consecutive chiral centers could be controlled, remain largely unexplored. Herein, we report the addition of alkylnitriles (such as propionitrile) to imines in the presence of a catalytic amount of a chiral pincer-type Ni-carbene complex and potassium 2,6-di-tert-butyl-4-methylphenoxide (KBHT). BHT and molecular sieves were used as additives to improve the yields, diastereoselectivity, and enantiomeric ratio up to >99%, 90:10 anti/syn, and 97.5:2.5 er, respectively. The Mannich adducts can be readily converted to the corresponding β-amino acids.

Manganese-Pincer-Catalyzed Nitrile Hydration, α-Deuteration, and α-Deuterated Amide Formation via Metal Ligand Cooperation

A simple and efficient system for the hydration and α-deuteration of nitriles to form amides, α-deuterated nitriles, and α-deuterated amides catalyzed by a single pincer complex of the earth-abundant manganese capable of metal–ligand cooperation is reported. The reaction is selective and tolerates a wide range of functional groups, giving the corresponding amides in moderate to good yields. Changing the solvent from tert-butanol to toluene and using D₂O results in formation of α-deuterated nitriles in high selectivity. Moreover, α-deuterated amides can be obtained in one step directly from nitriles and D₂O in THF. Preliminary mechanistic studies suggest the transformations contributing toward activation of the nitriles via a metal–ligand cooperative pathway, generating the manganese ketimido and enamido pincer complexes as the key intermediates for further transformations.

Nickel-Catalyzed C(sp3)-H Functionalization of Benzyl Nitriles: Direct Michael Addition to Terminal Vinyl Ketones

An efficient nickel(0)-catalyzed addition of benzyl nitriles to terminal vinyl ketones via C(sp³)-H functionalization has been developed. The reaction provides a novel and efficient protocol for the synthesis of α-functionalized benzyl nitriles with a wide range of structural diversity under mild reaction conditions while obviating the use of a strong base. The work might be potentially useful toward the development of an enantioselective variant using chiral nitrogen ligands.

Rational design of pincer-nickel complexes for catalytic cyanomethylation of benzaldehyde: A systematic DFT study

The current study dwells upon the efforts to computationally probe a phosphine-free pincer-nickel complex that would demonstrate an efficiency better than the reported phosphine-based pincer-nickel complex (^iPr2 POCN^Et2 )Ni(CH₂ CN) for cyanomethylation reaction. For this purpose, the mechanism of cyanomethylation of benzaldehyde was studied quantum mechanically for a series of 11 pincer-nickel complexes. The energetics of various intermediates and transition states involved in the catalytic cycle for each catalyst was compared with the corresponding energetics of the Miller's catalyst (^iPr2 POCN^Et2 )Ni(CH₂ CN) that is reported to accomplish the cyanomethylation at room temperature. While pincer complexes (^iPr4 NNN)Ni(CH₂ CN) and (^iPr4 NCN)Ni(CH₂ CN) containing strong σ-donating amines were found to fare poorly, pincer-nickel complexes (^iPr2 NCN)Ni(CH₂ CN) and (^dm PheboxNCN)Ni(CH₂ CN) based on weaker σ-donating imines had energetics more favorable than the reported efficient catalyst (^iPr2 POCN^Et2 )Ni(CH₂ CN). While strong trans-influencing C as the pincer central atom was found to be pivotal for lowering the cyanomethylation kinetics, presence of a poor trans-influencing N proved to be detrimental on the overall energetics.

Direct Catalytic Asymmetric Addition of Alkylnitriles to Aldehydes with Designed Nickel-Carbene Complexes

A direct catalytic asymmetric addition of acetonitrile to aldehydes that realizes over 90 % ee is the ultimate challenge in alkylnitrile addition chemistry. Herein, we report achieving high enantioselectivity by the strategic use of a sterically demanding Ni^II pincer carbene complex, which afforded highly enantioenriched β-hydroxynitriles. This highly atom-economical process paves the way for exploiting inexpensive acetonitrile as a promising C2 building block in a practical synthetic toolbox for asymmetric catalysis.

Asymmetric Transfer Hydrogenation of α-Substituted-β-Keto Carbonitriles via Dynamic Kinetic Resolution

A catalytic protocol for the enantio- and diastereoselective reduction of α-substituted-β-keto carbonitriles is described. The reaction involves a DKR-ATH process with the simultaneous construction of β-hydroxy carbonitrile scaffolds with two contiguous stereogenic centers. A wide range of α-substituted-β-keto carbonitriles were obtained in high yields (94%-98%) and excellent enantio- and diastereoselectivities (up to >99% ee, up to >99:1 dr). The origin of the diastereoselectivity was also rationalized by DFT calculations. Furthermore, this methodology offers rapid access to the pharmaceutical intermediates of Ipenoxazone and Tapentadol.

Cu-catalyzed cyanomethylation of imines and α,β-alkenes with acetonitrile and its derivatives

We describe copper-catalyzed cyanomethylation of imines and α,β-alkenes with a methylnitrile source and provide an efficient route to synthesize arylacrylonitriles and β,γ-unsaturated nitriles. This method tolerates aliphatic and aromatic alkenes substituted with a variety of functional groups such as F, Cl, Br, Me, OMe, tert-Bu, NO2, NH2 and CO2H with good to excellent yields (69-98%). These systems consist of inexpensive, simple copper catalyst and acetonitrile with its derivatives (α-bromo/α-iodo-acetonitrile) and are highly applicable in the industrial production of acrylonitriles.

Achiral and chiral NNN-pincer nickel complexes with oxazolinyl backbones: application in transfer hydrogenation of ketones

NNN-based achiral and chiral (oxazolinyl)amido-pincer nickel complexes are developed and employed for the catalytic transfer hydrogenation of ketones.

Recent advances in pincer-nickel catalyzed reactions

Organometallic catalysts have played a key role in accomplishing numerous synthetically valuable organic transformations that are either otherwise not possible or inefficient. The use of precious, sparse and toxic 4d and 5d metals are an apparent downside of several such catalytic systems despite their immense success over the last several decades. The use of complexes containing Earth-abundant, inexpensive and less hazardous 3d metals, such as nickel, as catalysts for organic transformations has been an emerging field in recent times. In particular, the versatile nature of the corresponding pincer-metal complexes, which offers great control of their reactivity via countless variations, has garnered great interest among organometallic chemists who are looking for greener and cheaper alternatives. In this context, the current review attempts to provide a glimpse of recent developments in the chemistry of pincer-nickel catalyzed reactions. Notably, there have been examples of pincer-nickel catalyzed reactions involving two electron changes via purely organometallic mechanisms that are strikingly similar to those observed with heavier Pd and Pt analogues. On the other hand, there have been distinct differences where the pincer-nickel complexes catalyze single-electron radical reactions. The applicability of pincer-nickel complexes in catalyzing cross-coupling reactions, oxidation reactions, (de)hydrogenation reactions, dehydrogenative coupling, hydrosilylation, hydroboration, C-H activation and carbon dioxide functionalization has been reviewed here from synthesis and mechanistic points of view. The flurry of global pincer-nickel related activities offer promising avenues in catalyzing synthetically valuable organic transformations.

Copper-promoted cyanoalkylation/ring-expansion of vinylcyclopropanes with α-C-H bonds in alkylnitriles toward 3,4-dihydronaphthalenes

A copper-promoted oxidative cyanomethylation/ring-expansion of vinylcyclopropanes with α-C(sp3)-H bonds in alkyl nitriles is established for the generation of 1-cyanoethylated 3,4-dihydronaphthalenes. This cyanomethylation/ring-expansion involves a radical pathway and proceeds via cyanomethyl radical formation, radical addition and ring-expansion. This ring-expansion strategy offers a highly atom-economical route for the construction of nitrile-containing 3,4-dihydronaphthalenes, which can be transformed into other useful products under simple conditions.

Cu/Ni-Catalyzed Cyanomethylation of Alkenes with Acetonitrile for the Synthesis of β,γ-Unsaturated Nitriles

We have developed a protocol for the Cu/Ni-catalyzed cyanomethylation of alkenes with acetonitrile for the synthesis of β,γ-unsaturated nitriles. This is the first example of a direct coupling of the alkene sp² C-H bond and the acetonitrile sp³ C-H bond for the preparation of β,γ-unsaturated nitriles. Acetonitrile, an inexpensive and stable solvent, is demonstrated to be a useful cyanomethyl source. The combination of copper and nickel catalysts resulted in a high reaction efficiency.

Aerobic oxidation of primary benzylic amines to amides and nitriles catalyzed by ruthenium carbonyl clusters carrying N,O-bidentate ligands

Four trinuclear ruthenium carbonyl clusters, (6-BrPyCHRO)₂Ru₃(CO)₈ (R = 4-OCH₃C₆H₄, 1a; R = 4-BrC₆H₄, 1b) and (2-OC₆H₄-HC[double bond, length as m-dash]N-C₆H₄R)₂Ru₃(CO)₈ (R = 4-OCH₃, 2a; R = 4-Br, 2b), were synthesized from the reactions of Ru₃(CO)₁₂ with the corresponding N,O-bidentate ligands (two pyridyl alcohols and two Schiff bases) respectively in a ratio of 1 : 2. Three new complexes 1b, 2a and 2b have been fully characterized by elemental analysis, FT-IR, NMR and X-ray crystallography. The catalytic activity of these ruthenium complexes for the aerobic oxidation of primary benzylic amines to amides and nitriles in the presence of t-BuOK was investigated, of which the Schiff base complex 2a was found to exhibit the highest activity.

Recent advances in C–CN and C–H bond activation of green nitrile (MeCN) for organo-complexation, cyanation and cyanomethylation

The use of green and inexpensive organic nitrile (MeCN) as a cyano and cyano-methyl source for organo-complexation, cyanation, and cyanomethylation is reviewed.

Cu2O-catalyzed selective 1,2-addition of acetonitrile to α,β-unsaturated aldehydes

A cyanomethylation of α,β-unsaturated aldehydes with acetonitrile as a nucleophile is disclosed. The reaction is promoted with Cu₂O as an inexpensive catalyst. Mild conditions are used, and the reaction completes within a few minutes.

Free Radical Addition of Nitrile, Ketone, and Ester to Alkyne and the Selectivity Discussion

A general and practical atom transfer radical addition (ATRA) of simple nitriles, ketones, and esters to alkynes was developed. It can allow an efficient access to a wide range of β,γ-unsaturated nitriles, ketones, and esters. The unique chemoselectivity in this system is also discussed.

Template catalysis by manganese pincer complexes: oxa- and aza-Michael additions to unsaturated nitriles

Activation of C[triple bond, length as m-dash]N bonds by metal-ligand cooperation provides a new route for the functionalization of nitriles. Herein, we report the electrophilic activation of unsaturated nitriles by dearomatized manganese pincer complexes for the oxa- and aza-Michael addition reactions under very mild and neutral conditions. Derivatives of acrylonitrile and allyl cyanide furnished the corresponding β-addition products by reacting with alcohols and amines. Mechanistically, the catalysis is mostly ligand based. Reaction of the dearomatized PNN-Mn complex with 2-pentenenitrile or 3-pentenenitrile furnished an enamido-Mn complex. The equilibrium between an enamido complex and a ketimido complex, and reversible C-C bond formation with the ligand are proposed to play central roles in the catalysis.

Reductive C-C Coupling from α,β-Unsaturated Nitriles by Intercepting Keteniminates

We present an atom-economic strategy to catalytically generate and intercept nitrile anion equivalents using hydrogen transfer catalysis. Addition of α,β-unsaturated nitriles to a pincer-based Ru-H complex affords structurally characterized κ-N-coordinated keteniminates by selective 1,4-hydride transfer. When generated in situ under catalytic hydrogenation conditions, electrophilic addition to the keteniminate was achieved using anhydrides to provide α-cyanoacetates in high yields. This work represents a new application of hydrogen transfer catalysis using α,β-unsaturated nitriles for reductive C-C coupling reactions.

"On Water" Direct Organocatalytic Cyanoarylmethylation of Isatins for the Diastereoselective Synthesis of 3-Hydroxy-3-cyanomethyl Oxindoles

An "on water" organocatalytic cyanoarylmethylation of aryl acetonitrile to isatins is developed, giving products in high yields and up to excellent diastereoselectivities. A remarkable enhancement of reaction rates and diastereoselectivities by water was observed under mild conditions. Moreover, this approach provides a highly efficient and environmentally benign access to thermodynamic 3-hydroxy-3-cyanomethyl oxindoles.

An effective preparation of both 1,3-diketones and nitriles from alkynones with oximes as hydroxide sources

An effective phosphine-catalyzed protocol has been established for the syntheses of 1,3-diketones and nitriles from alkynones with oximes as hydroxide surrogates. This method features the use of a phosphine catalyst, compatibility with various functional groups and ambient temperature, which makes this approach very practical. A plausible mechanism was proposed.

Ambient Stable Cyanomethylcopper(III) Complex: a Strong Cu-Csp3 Bond Supported by a PS3-Tripodal Chelator

An organocuprate(III) complex, [Cu(^TMSPS3)(CH₂CN)]^- (2), was identified along with a sequential derivative, [Cu(^TMSPS3)(CN)]^- (3), and an intermediate, [Cu(^TMSPS3)(HN═PPh₃)] (4), formed in a relative transformation. Apical ligands among these complexes all strongly associate with a robust trigonal copper(III) platform. The nature of the ligand binding was spectroscopically and computationally investigated through a series of copper(III) complexes. The bonding along the principal C₃ axis is adaptable, and σ interaction dominates the axial ligand coordination, where the cyanomethyl group exhibits the strongest bonding. Complex 2 is a scarce example of a thermostable aliphatic organocuprate(III) compound, which sheds some light on the organocopper(III) chemistry widely involved in many copper-mediated catalyses.

Cation-controlled catalysis with crown ether-containing transition metal complexes

This Feature Article reviews the structural motifs and catalytic applications of crown ether-containing catalysts and details the development of “pincer-crown ether” ligands for applications in controlled catalysis.

Organocatalytic Decarboxylative Cyanomethylation of Difluoromethyl and Trifluoromethyl Ketones

An efficient organocatalytic method for the synthesis of difluoromethyl and trifluoromethyl substituted β-hydroxynitriles is introduced. The decarboxylative cyanomethylation of fluorinated ketones with readily available cyanoacetic acid gives a variety of tertiary alcohols in high yields and without concomitant water elimination. The reaction occurs in the presence of catalytic amounts of triethylamine, can be upscaled and applied to chlorofluoromethyl ketones and difluoromethyl ketimines.

Activation of Acetonitrile with (C2 F5 )3 PF2 and Amines

Acetonitrile is deprotonated by a combination of the strong Lewis acid (C₂ F₅ )₃ PF₂ and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt₃ ][P(C₂ F₅ )₃ F₂ (CH₂ CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN)₂ ]⁺ and [Ag(MeCN)]⁺ derivatives in which the CH₂ CN substituent of the anion [P(C₂ F₅ )₃ F₂ (CH₂ CN)]^- coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C₂ F₅ )₃ F₂ (CH₂ CN)] shows an uptake of 1.7 equivalents of isobutene from a propane/isobutene mixture. The reaction of (C₂ F₅ )₃ PF₂ with acetonitrile and diethylamine furnishes [P(C₂ F₅ )₃ F₂ {NHC(CH₃ )NEt₂ }]-a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt₂ . Exchange of HNEt₂ with the primary amines H₂ NPh and H₂ NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism.

A multifunctionalized strategy of indoles to C2-quaternary indolin-3-ones via a TEMPO/Pd-catalyzed cascade process

A method for combinative oxidative homo dimerization and cyanomethylation of free indole derivatives catalysed by TEMPO and Pd(OAc)₂ was demonstrated for the first time. This new methodology is both atom and step efficient and is applicable to a broad scope of substrates, allowing the synthesis of a range of synthetically valuable 2-(2-(1H-indol-3-yl)-3-oxoindolin-2-yl)acetonitriles in moderate to excellent yields.

Ruthenium-Catalyzed Aerobic Oxidation of Amines

Amine oxidation is one of the fundamental reactions in organic synthesis as it leads to a variety of value-added products such as oximes, nitriles, imines, and amides among many others. These products comprise the key N-containing building blocks in the modern chemical industry, and such transformations, when achieved in the presence of molecular oxygen without using stoichiometric oxidants, are much preferred as they circumvent the production of unwanted wastes. In parallel, the versatility of ruthenium catalysts in various oxidative transformations is well-documented. Herein, this review focuses on aerobic oxidation of amines specifically by using ruthenium catalysts and highlights the major achievements in this direction and challenges that still need to be addressed.