Ligand Assisted Co(II)-Catalyzed Multicomponent Synthesis of Substituted Pyrroles and Pyridines.

Herein, we describe a sustainable Co(II)-catalyzed synthesis of pyrroles and pyridines. Using a Co(II)-catalyst [Co (L)Cl] (1 a) bearing redox-active 2-(phenyldiazenyl)-1,10-phenanthroline) (L) scaffold, various substituted pyrroles and pyridines were synthesized in good yields, taking alcohol as one of the primary feedstock. Pyrroles were synthesized by the equimolar reaction of 2-amino and secondary alcohols.

Zn(II)-Stabilized Azo-Anion Radical-Catalyzed Dehydrogenative Synthesis of Olefins.

Herein, we describe a Zn-catalyzed atom-economical, inexpensive, and sustainable method for preparing a broad spectrum of substituted olefins utilizing alcohols as the main precursor. Using a Zn(II) complex [ZnLCl] () of the redox-noninnocent ligand 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (), various ()-olefins were prepared in good yields by coupling alcohols with sulfones and aryl cyanides under an inert atmosphere. Under an aerial atmosphere, vinyl nitriles were isolated in up to 82% yield reacting alcohols with benzyl cyanides in the presence of .

A Phosphine-Free Air-Stable Mn(II)-Catalyst for Sustainable Synthesis of Quinazolin-4(3)-ones, Quinolines, and Quinoxalines in Water.

The synthesis, characterization, and catalytic application of a new phosphine-free, well-defined, water-soluble, and air-stable Mn(II)-catalyst [Mn(L)(HO)Cl](Cl) ([]Cl) featuring a 1,10-phenanthroline based tridentate pincer ligand, 2-(1-pyrazol-1-yl)-1,10-phenanthroline (), in dehydrogenative functionalization of alcohols to various -heterocycles such as quinazolin-4(3)-ones, quinolines, and quinoxalines are reported here. A wide array of multisubstituted quinazolin-4(3)-ones were prepared in water under air following two pathways via the dehydrogenative coupling of alcohols with 2-aminobenzamides and 2-aminobenzonitriles, respectively. 2-Aminobenzyl alcohol and ketones bearing active methylene group were used as coupling partners for synthesizing quinoline derivatives, and various quinoxaline derivatives were prepared by coupling vicinal diols and 1,2-diamines.

Oxygen-Dependent Ligand-Controlled Iron-Catalyzed Chemoselective Synthesis of Olefins and Vinyl Nitriles.

An oxygen-dependent ligand-controlled chemoselective synthesis of vinyl nitriles and -olefins by coupling a variety of alcohols and benzyl cyanides, catalyzed by a well-characterized, air-stable, easy-to-prepare Fe(II) catalyst () bearing a redox-active arylazo pincer () is reported. The azo-moiety of the ligand backbone acts as an electron and hydrogen reservoir, enabling catalyst to efficiently produce a broad spectrum of vinyl nitriles and -olefins in moderate to good yields selectively under an oxygen and argon atmosphere, respectively.

Oxygen Dependent Switchable Selectivity during Ruthenium Catalyzed Selective Synthesis of -Alkylated Indoles and Bis(indolyl)methanes.

Herein, we report a ligand-centered redox-controlled oxygen-dependent switchable selectivity during ruthenium-catalyzed selective synthesis of -alkylated indoles and bis(indolyl)methanes (BIMs). A wide variety of -alkylated indoles and BIMs were prepared selectively in moderate to good isolated yields by coupling a wide variety of indoles and alcohols, catalyzed by a well-defined, air-stable, and easy-to-prepare Ru(II)-catalyst () bearing a redox-active tridentate pincer (). Catalyst efficiently catalyzed the -alkylation of indoles under an argon atmosphere while, under an oxygen environment, exclusively producing the BIMs.

-Alkylation of Amines by C1-C10 Aliphatic Alcohols Using A Well-Defined Ru(II)-Catalyst. A Metal-Ligand Cooperative Approach.

A Ru(II)-catalyzed efficient and selective -alkylation of amines by C1-C10 aliphatic alcohols is reported. The catalyst [Ru(L)(PPh)Cl] () bearing a tridentate redox-active azo-aromatic pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline () is air-stable, easy to prepare, and showed wide functional group tolerance requiring only 1.0 mol % (for -methylation and -ethylation) and 0.

Zn(II)-Catalyzed Multicomponent Sustainable Synthesis of Pyridines in Air.

Herein, we report a Zn(II)-catalyzed solvent-free sustainable synthesis of tri- and tetra-substituted pyridines using alcohols as the primary feedstock and NHOAc as the nitrogen source. Using a well-defined air-stable Zn(II)-catalyst, , featuring a redox-active tridentate azo-aromatic pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (), a wide variety of unsymmetrical 2,4,6-substituted pyridines were prepared by three-component coupling of primary and secondary alcohols with NHOAc. Catalyst is equally compatible with the four-component coupling.

Zn(II)-Catalyzed Selective -Alkylation of Amines with Alcohols Using Redox Noninnocent Azo-Aromatic Ligand as Electron and Hydrogen Reservoir.

We report a sustainable and eco-friendly approach for selective -alkylation of various amines by alcohols, catalyzed by a well-defined Zn(II)-catalyst, Zn()Cl (), bearing a tridentate arylazo scaffold. A total of 57 -alkylated amines were prepared in good to excellent yields, out of which 17 examples are new. The Zn(II)-catalyst shows wide functional group tolerance, is compatible with the synthesis of dialkylated amines via double -alkylation of diamines, and produces the precursors in high yields for the marketed drugs tripelennamine and thonzonium bromide in gram-scale reactions.

A Singlet-Diradical Co(III)-Dimer as a Nonvolatile Resistive Switching Device: Synthesis, Redox-Induced Interconversion, and Current-Voltage Characteristics.

Herein we report a ligand-centered redox-controlled strategy for the synthesis of an unusual binuclear diradical cobalt(III) complex, [Co(L)] (), featuring two three-electron reduced trianionic monoradical 2,9-bis(phenyldiazo)-1,10-phenanthroline ligands () and two intermediate-spin cobalt(III) centers having a Co-Co bond. Controlled ligand-centered oxidation of afforded two mononuclear complexes, [Co(L)(L)] ([]) and [Co(L)] ([]), which upon further ligand-centered reduction yielded a di-azo-anion diradical complex, [Co(L)] (). In complex , two three-electron reduced di-azo-anion monoradical ligands () bridge two intermediate Co(III) centers at a distance of 2.

Ruthenium-Catalyzed Dehydrogenative Functionalization of Alcohols to Pyrroles: A Comparison between Metal-Ligand Cooperative and Non-cooperative Approaches.

Herein, we report the synthesis and characterization of two ruthenium-based pincer-type catalysts, []X (X = Cl, PF) and containing two different tridentate pincer ligands, 2-pyrazolyl-(1,10-phenanthroline) () and 2-arylazo-(1,10-phenanthroline) (, = 2-(phenyldiazenyl)-1,10-phenanthroline; = 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline), and their application in the synthesis of substituted pyrroles via dehydrogenative alcohol functionalization reactions. In catalyst []X (X = Cl, PF), the tridentate scaffold 2-pyrazolyl-(1,10-phenanthroline) () is apparently redox innocent, and all the redox events occur at the metal center, and the coordinated ligands remain as spectators. In contrast, in catalysts and , the coordinated azo-aromatic scaffolds are highly redox-active and known to participate actively during the dehydrogenation of alcohols.

Iron-Catalyzed Metal-Ligand Cooperative Approach toward Sustainable Synthesis of Azines and -Acylhydrazones in Air.

Herein, we describe a metal-ligand cooperative approach for the sustainable synthesis of various aldazines, ketazines, and -acylhydrazones via dehydrogenative functionalization of alcohols with hydrazine hydrate using a simple, easy-to-prepare iron catalyst featuring a redox noninnocent tridentate arylazo backbone. Our catalyst is compatible with both primary and secondary alcohols to produce a wide variety of substituted aldazines, ketazines, and -acylhydrazones in good isolated yields in air. A series of control experiments are performed to elucidate the reaction mechanism.

Ligand centered redox enabled sustainable synthesis of triazines and pyrimidines using a zinc-stabilized azo-anion radical catalyst.

Herein, we report ligand-centered redox controlled Zn(II)-catalyzed multicomponent approaches for synthesizing pyrimidines and triazines. Taking advantage of the ligand-centered redox events and using a well-defined Zn(II)-catalyst (1a) bearing ()-2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L1a) as the redox-active ligand, a wide variety of substituted pyrimidines and triazines were prepared dehydrogenative alcohol functionalization reactions. Pyrimidines were prepared two pathways: (i) dehydrogenative coupling of primary and secondary alcohols with amidines and (ii) dehydrogenative coupling of primary alcohols with alkynes and amidines.

Metal-ligand cooperative approaches in homogeneous catalysis using transition metal complex catalysts of redox noninnocent ligands.

Catalysis offers a straightforward route to prepare various value-added molecules starting from readily available raw materials. The catalytic reactions mostly involve multi-electron transformations. Hence, compared to the inexpensive and readily available 3d-metals, the 4d and 5d-transition metals get an extra advantage for performing multi-electron catalytic reactions as the heavier transition metals prefer two-electron redox events.

Iron-Catalyzed Alkyne-Based Multicomponent Synthesis of Pyrimidines under Air.

An iron-catalyzed sustainable, economically affordable, and eco-friendly synthetic protocol for the construction of various trisubstituted pyrimidines is described. A wide range of trisubstituted pyrimidines were prepared using a well-defined, easy to prepare, bench-stable, and phosphine-free iron catalyst featuring a redox-noninnocent tridentate arylazo pincer under comparatively mild aerobic conditions via dehydrogenative functionalization of alcohols with alkynes and amidines.

Nickel-Catalyzed [4 + 2] Annulation of Nitriles and Benzylamines by C-H/N-H Activation.

Nickel-catalyzed [4 + 2] annulation of benzylamines and nitriles via C-H/N-H bond activation, providing straightforward atom-economic access to a wide variety of multisubstituted quinazolines, is reported. Mechanistic investigation revealed that the in situ formed amidines from the coupling of benzylamines and nitriles direct the nickel catalyst to activate the -C-H bond of the phenyl ring of the benzylamine.

Cobalt complexes of redox noninnocent azo-aromatic pincers. Isolation, characterization, and application as catalysts for the synthesis of quinazolin-4(3H)-ones.

Herein we report the synthesis, characterization and catalytic application of three new cobalt(ii)-complexes of redox noninnocent arylazo ligands, 2-(phenylazo)-1,10-phenanthroline (L), 2-(4-chlorophenylazo)-1,10-phenanthroline (L) and 2,9-bis(phenyldiazo)-1,10-phenanthroline (L) respectively. The reaction of L with CoCl·6HO produced a μ-dichloro bridged binuclear cobalt(ii)-complex [Co(L)Cl] (1a) while the same reaction when carried out with 2-(4-chlorophenyl)azo-1,10-phenanthroline (L) and 2,9-bis(phenyldiazo)-1,10-phenanthroline (L) ligands produced two new mononuclear five-coordinate cobalt(ii)-complexes 1b and 2 respectively. In complex 1a and 1b, the ligands L and L are coordinated to the cobalt(ii)-center in a tridentate mode utilizing all of its nitrogen donor sites while in complex 2 one of the azo-donor sites of the ligand L remain pendant.

Metal-Ligand Cooperative Approach To Achieve Dehydrogenative Functionalization of Alcohols to Quinolines and Quinazolin-4(3)-ones under Mild Aerobic Conditions.

A simple metal-ligand cooperative approach for the dehydrogenative functionalization of alcohols to various substituted quinolines and quinazolin-4(3)-ones under relatively mild reaction conditions (≤90 °C) is reported. Simple and easy-to-prepare air-stable Cu(II) complexes featuring redox-active azo-aromatic scaffolds, 2-arylazo-(1,10-phenanthroline) (), are used as catalyst. A wide variety of substituted quinolines and quinazolin-4(3)-ones were synthesized in moderate to good isolated yields via dehydrogenative coupling reactions of various inexpensive and easily available starting materials under aerobic conditions.

Achieving Nickel Catalyzed C-S Cross-Coupling under Mild Conditions Using Metal-Ligand Cooperativity.

A simple and efficient approach of C-S cross-coupling of a wide variety of (hetero)aryl thiols and (hetero)aryl halides under mild conditions, mostly at room temperature, catalyzed by well-defined singlet diradical Ni(II) catalysts bearing redox noninnocent ligands is reported. Taking advantage of ligand centered redox events, the high-energetic Ni(0)/Ni(II) or Ni(I)/Ni(III) redox steps were avoided in the catalytic cycle. The cooperative participation of both nickel and the coordinated ligands during oxidative addition/reductive elimination steps allowed us to perform the catalytic reactions under mild conditions.

Dehydrogenative Synthesis of Quinolines, 2-Aminoquinolines, and Quinazolines Using Singlet Diradical Ni(II)-Catalysts.

Simple, straightforward, and atom economic methods for the synthesis of quinolines, 2-aminoquinolines, and quinazolines via biomimetic dehydrogenative condensation/coupling reactions, catalyzed by well-defined inexpensive and easy to prepare singlet diradical Ni(II)-catalysts featuring two antiferromagnetically coupled singlet diradical diamine type ligands are described. Various polysubstituted quinolines, 2-aminoquinolines, and quinazolines were synthesized in moderate to good yields from different low-cost and readily accessible starting materials. Several control experiments were carried out to get insight into the reaction mechanism which shows that the nickel and the coordinated diamine ligands participate in a synergistic way during the dehydrogenation of alcohols.

Iron-Catalyzed/Mediated C-N Bond Formation: Competition between Substrate Amination and Ligand Amination.

Iron catalyzed carbon-nitrogen bond formation reactions of a wide variety of nucleophiles and aryl halides using well-defined iron-complexes featuring redox noninnocent 2-(arylazo)-1,10-phenanthroline (L) ligands are reported. Besides substrate centered C-N coupling, C-N bond formation reactions were also observed at the ortho- and para-positions of the phenyl ring of the coordinated azo-aromatic scaffolds affording new tetradentate ligands, 2-N-aryl-(2-arylazo)-1,10-phenanthroline (L), and tridentate ligands, 4 -N-aryl-(2-arylazo)-1,10-phenanthroline (L), respectively. Control experiments and mechanistic studies reveal that the complex [FeLCl] (1) undergoes in situ reduction during the catalytic reaction to produce the monoanionic complex [1], which then acts as the active catalyst.

Accessing Polysubstituted Quinazolines via Nickel Catalyzed Acceptorless Dehydrogenative Coupling.

Two environmentally benign methods for the synthesis of quinazolines via acceptorless dehydrogenative coupling of 2-aminobenzylamine with benzyl alcohol (Path A) and 2-aminobenzylalcohol with benzonitrile (Path B), catalyzed by cheap, earth abundant and easy to prepare nickel catalysts, containing tetraaza macrocyclic ligands (tetramethyltetraaza[14]annulene (MeTAA) or 6,15-dimethyl-8,17-diphenyltetraaza[14]annulene (MePhTAA)) are reported. A wide variety of substituted quinazolines were synthesized in moderate to high yields starting from cheap and easily available starting precursors. A few control reactions were performed to understand the mechanism and to establish the acceptorless dehydrogenative nature of the catalytic reactions.

Redox-Induced Interconversion and Ligand-Centered Hemilability in Ni Complexes of Redox-Noninnocent Azo-Aromatic Pincers.

A series of nickel(II) complexes, namely, [Ni(L)Cl] (1a-c), [Ni(L)](X) {([2a](X), [2b](X)) (X = ClO, I)}, [Ni(L)(OH)](ClO) ([3](ClO)) and [Ni{(L)}] (4a, 4b) featuring the redox-active tridentate azo-aromatic pincer ligand 2-(arylazo)-1,10-phenanthroline (L) were synthesized. The coordinated azo-aromatic ligand showed reversible hemilability depending on its formal oxidation state. On the one hand, in its native state, the unreduced ligand L shows bidentate coordination; the 1,10-phenanthroline moiety binds the central Ni(II) atom in a bidentate fashion, while the azo-chromophore remains pendent.

A nickel catalyzed acceptorless dehydrogenative approach to quinolines.

A general, efficient and environmentally benign, one-step synthesis of substituted quinoline derivatives was achieved by acceptorless dehydrogenative coupling of o-aminobenzylalcohols with ketones and secondary alcohols catalyzed by a cheap, earth abundant and easy to prepare nickel catalyst [Ni(MeTAA)], featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)). A wide variety of substituted quinolines were synthesized in high yields starting from readily available o-aminobenzylalcohols and ketones or secondary alcohols. A few controlled reactions were carried out to establish the acceptorless dehydrogenative nature of the reactions.

Redox Noninnocent Azo-Aromatic Pincers and Their Iron Complexes. Isolation, Characterization, and Catalytic Alcohol Oxidation.

The new redox-noninnocent azoaromatic pincers 2-(arylazo)-1,10-phenanthroline (L) and 2,9-bis(phenyldiazo)-1,10-phenanthroline (L) are reported. The ligand L is a tridentate pincer having NNN donor atoms, whereas L is tetradentate having two azo-N donors and two N-donor atoms from the 1,10-phenanthroline moiety. Reaction of FeCl with L or L produced the pentacoordinated mixed-ligand Fe(II) complexes FeLCl (1) and FeLCl (2), respectively.