Additions to metal-activated organonitriles

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Hemilability-Driven Water Activation: A NiII Catalyst for Base-Free Hydration of Nitriles to Amides

The Ni^II complex 1 containing pyridyl- and hydroxy-functionalized N-heterocyclic carbenes (NHCs) is synthesized and its catalytic utility for the selective nitrile hydration to the corresponding amide under base-free conditions is evaluated. The title compound exploits a hemilabile pyridyl unit to interact with a catalytically relevant water molecule through hydrogen-bonding and promotes a nucleophilic water attack to the nitrile. A wide variety of nitriles is hydrated to the corresponding amides including the pharmaceutical drugs rufinamide, Rifater, and piracetam. Synthetically challenging α-hydroxyamides are accessed from cyanohydrins under neutral conditions. Related catalysts that lack the pyridyl unit (i.e., compounds 2 and 4) are not active whereas those containing both the pyridyl and the hydroxy or only the pyridyl pendant (i.e., compounds 1 and 3) show substantial activity. The linkage isomer 1' where the hydroxy group is bound to the metal instead of the pyridyl group was isolated under different crystallization conditions insinuating a ligand hemilabile behavior. Additional pK_a measurements reveal an accessible pyridyl unit under the catalytic conditions. Kinetic studies support a ligand-promoted nucleophilic water addition to a metal-bound nitrile group. This work reports a Ni-based catalyst that exhibits functional hemilability for hydration chemistry.

Metal-mediated generation of triazapentadienate-terminated di- and trinuclear μ2-pyrazolate NiIIspecies and control of their nuclearity

Nuclearity control of nickel(ii)–azole systems for the generation of well-defined (azolate)₂Ni^IIspecies.

A novel family of homoleptic copper(i) complexes featuring disubstituted cyanamides: a combined synthetic, structural, and theoretical study

Homoleptic copper(i) complexes featuring disubstituted cyanamides were obtained and characterized using experimental methods and their properties were studied theoretically.

Heteroleptic complexesviasolubility control: examples of Cu(ii), Co(ii), Ni(ii) and Mn(ii) complexes based on the derivatives of terpyridine and hydroxyquinoline

We describe the preparation of synthetically challenging heteroleptic complexes by considering the solubility properties of their corresponding favored homoleptic complexes.

NHC-catalyzed enantioselective synthesis of dihydropyran-4-carbonitriles bearing all-carbon quaternary centers

A LiCl assisted, carbene-catalyzed oxidative reaction for the synthesis of dihydropyran-4-carbonitriles bearing all-carbon quaternary centers was developed.

Palladium-catalyzed tandem addition/cyclization in aqueous medium: synthesis of 2-arylindoles

Pd-catalyzed tandem reaction of potassium aryltrifluoroborates with nitriles for the synthesis of 2-arylindoles in aqueous medium.

Acid-promoted denitrogenative Pd-catalyzed addition of arylhydrazines with nitriles at room temperature

Pd(TFA)₂-catalyzed denitrogenative addition proceeded with selective C–N bond cleavage of arylhydrazines with nitriles under air at room temperature.

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands

A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N₃)₄(L₂). Hypercoordinate azido(tetrazolato) silicon complexes Si(N₃)₂(N₄C-R)₂(L₂), R = CH₃, C₆H₅, 4-C₆H₄CH₃ (4a, 5, 6, 7) and Si(N₃)₂(N₄C-L)₂ (9, L = 2-C₅H₄N), L₂ = 2,2'-bipyridine, 1,10-phenanthroline, with SiN₆ skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N₃)₄(L₂) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b). Tetrazolato ligand linkage isomerism was observed for complex 4a. The crystallographically characterised methyl tetrazolato complexes and plausible configurational and linkage isomers were evaluated by DFT calculations at the B3LYP/6-311G(d,p) level.

Amidine Production by the Addition of NH3 to Nitrile(s) Bound to and Activated by the Lewis Acidic [Re6(μ3-Se)8]2+ Cluster Core

Acetonitrile bound to and activated by the Lewis acidic [Re₆(μ₃-Se)₈]²⁺ cluster core was transformed into acetamidine in quantitative yield using NH₃ as the nucleophile at room temperature. The amidine ligand was removed by treating the cluster-acetamidine complexes with trifluoroacetic acid in CH₃CN, affording amidinium trifluoroacetate and the starting acetonitrile complexes.

Resonance-Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

Resonance-assisted hydrogen bonding (RAHB), a concept introduced by Gilli and co-workers in 1989, concerns a kind of intramolecular H-bonding strengthened by a conjugated π-system, usually in 6-, 8-, or 10-membered rings. This Review highlights the involvement of RAHB as a driving force in the synthesis of organic, coordination, and organometallic compounds, as a handy tool in the activation of covalent bonds, and in starting moieties for synthetic transformations. The unique roles of RAHB in molecular recognition and switches, E/Z isomeric resolution, racemization and epimerization of amino acids and chiral amino alcohols, solvatochromism, liquid-crystalline compounds, and in synthons for crystal engineering and polymer materials are also discussed. The Review can provide practical guidance for synthetic chemists that are interested in exploring and further developing RAHB-assisted synthesis and design of materials.

Formation of a Cationic Vinylimido Group upon C-H Activation of Nitriles by Trialkylamines in the Presence of TaCl5

We report a new CH3CN activation mode where an imido group is directly formed by deprotonation of the nitrile coordinated to the highly Lewis acidic Ta(V) center. The unexpected deprotonation of TaCl5(CH3CN) by NEt3 resulted in isolation of the triethylammonium vinylimido complex [HNEt3][Ta(NC(CH2)NEt3)Cl5]. The reaction is proposed to proceed through rearrangement of the initial nucleophilic carbanion to the electrophilic azaallene/carbocation intermediate. The use of more sterically hindered (i-Pr)CN and weakly nucleophilic N(i-Pr)2Et resulted in the isolation of a vinylimido group formed upon dimerization of deprotonated nitriles, suggesting deprotonation as the first step of the transformation.

Reactivity towards nitriles, cyanamides, and carbodiimides of palladium complexes derived from benzyl alcohol. Synthesis of a mixed Pd2Ag complex

The chelate complex [Pd(κ(2)-C,O-C6H4CH2O-2)(bpy)] () reacts with acetonitrile, cyanamides, or carbodiimides, in the presence of AgOTf (1 : 5 : 1 molar ratio) and residual water, to form complexes [Pd{κ(2)-C,N-C6H4{CH2OC([double bond, length as m-dash]NX)Y}-2}(bpy)](OTf), where X = H, Y = Me (), NMe2 (), NEt2 (), X = R, Y = NHR (R = (i)Pr (), Tol ()), as a result of the insertion of the unsaturated reagent into the O-Pd bond of and the protonation of one of the N atoms. In the absence of AgOTf the reaction of with TolN[double bond, length as m-dash]C[double bond, length as m-dash]NTol (Tol = p-Tolyl) results in the formation of the neutral complex [Pd{κ(2)-C,N-C6H4{CH2OC([double bond, length as m-dash]NTol)NTol}-2}(bpy)] (). Complexes and can be interconverted by deprotonation ( + KO(t)Bu) or protonation ( + KOTf + HOTf) reactions. When the reaction of with TolN[double bond, length as m-dash]C[double bond, length as m-dash]NTol in the presence of AgOTf is carried out in a 1 : 1 : 1 stoichiometric ratio, or for a short period of time, a mixture of and a mixed heterometallic Ag2Pd complex is obtained ( = [Ag(N-)2](OTf)). Complex is the major product when the AgOTf is added before the carbodiimide, and the reaction is stopped immediately. can also be obtained by reaction of with 0.5 equiv. of AgOTf. When complex [PdI(C6H4CH2OH-2)(bpy)] () reacts with (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr in the presence of TlOTf, instead of AgOTf, a ca. 1 : 1 mixture of and [Pd{κ(2)-O,N-OCH2{C6H4{C([double bond, length as m-dash]NH(i)Pr)N(i)Pr}-2}}(bpy)](OTf) () forms. Complex is the result of the insertion of the carbodiimide into the C-Pd bond. Complexes have been extensively characterized by NMR spectroscopy, and the crystal structures of , , and ·2.5CHCl3·0.5Et2O have been determined by X-ray diffraction studies.