Hydrogen bonding or deprotonation: on fluoride ion fluorescence sensing with 1,1′-bi-2-naphthol derivatives

<div><p>The isolation and structural characterisation of two ionic complexes (<i>S</i>)-<b>3</b> and(<i>S</i>)-<b>4</b> based on fluoride ion-mediated deprotonation of 1,1′-bi-2-naphthol (BINOL) derivatives (<i>S</i>)-<b>1</b> and (<i>S</i>)-<b>2</b> have been carried out for the first time. X-ray crystallographic study showed that the deprotonated forms (<i>S</i>)-<b>3</b> and (<i>S</i>)-<b>4</b> adopt remarkably different molecular geometries, bond parameters as well as molecular packing modes from their neutral analogs, in agreement with their significant fluorescence changes upon the addition of fluoride ion, giving insights into the actual mechanism of fluoride ion fluorescence sensing. The deprotonation–protonation processes in two BINOL derivatives were also investigated by both fluorescence measurements and X-ray structural analyses. Such chiral basic compounds can be promising organocatalysts for asymmetric reactions.</p></div

Cobalt-Catalyzed Acceptorless Alcohol Dehydrogenation: Synthesis of Imines from Alcohols and Amines

A cobalt catalyst has been developed for the acceptorless dehydrogenation of alcohols and applied to synthesize imines from alcohols and amines. Deuterium labeling studies suggest that the reaction proceeds by an initial reversible alcohol dehydrogenation step involving a cobalt hydride intermediate

Cobalt-Catalyzed N‑Alkylation of Amines with Alcohols

A well-defined nonprecious metal cobalt­(II) catalyst based on a pincer PNP ligand has been employed for the efficient N-alkylation of both aromatic and aliphatic amines with alcohols. A subtle change of reaction conditions (simply adding 4 Å molecular sieves) was observed to readily switch the resulting products (amines vs imines) with high chemoselectivity. A range of alcohols and amines including both aromatic and aliphatic substrates were efficiently converted to secondary amines in good-to-excellent yields when 2 mol % cobalt catalyst was used. Additional experiments indicate that a hydrogen-borrowing mechanism is responsible for the tandem acceptorless dehydrogenation/condensation/hydrogenation process

Phosphoric Acid-Mediated Synthesis of Vinyl Sulfones through Decarboxylative Coupling Reactions of Sodium Sulfinates with Phenylpropiolic Acids

A novel phosphoric acid -mediated synthesis of vinyl sulfones through decarboxylative coupling reactions of sodium sulfinates with phenylpropiolic acids is described. This transformation is efficient and environmentally friendly

Understanding the Mechanisms of Cobalt-Catalyzed Hydrogenation and Dehydrogenation Reactions

Cobalt­(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt­(II) alkyl complex [(PNHP^Cy)­Co­(CH₂SiMe₃)]­BAr^F₄ (<b>4</b>) (PNHP^Cy = bis­[(2-dicyclohexylphosphino)­ethyl]­amine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N–H group on the pincer ligand in the catalysis via a metal–ligand cooperative interaction, the reactivities of <b>4</b> and [(PNMeP^Cy)­Co­(CH₂SiMe₃)]­BAr^F₄ (<b>7</b>) were compared. Complex <b>7</b> was found to be an active precatalyst for the hydrogenation of olefins. In contrast, no catalytic activity was observed using <b>7</b> as a precatalyst for the hydrogenation of acetophenone under mild conditions. For the acceptorless dehydrogenation of 1-phenylethanol, complex <b>7</b> displayed similar activity to complex <b>4</b>, affording acetophenone in high yield. When the acceptorless dehydrogenation of 1-phenylethanol with precatalyst <b>4</b> was monitored by NMR spectroscopy, the formation of the cobalt­(III) acetylphenyl hydride complex [(PNHP^Cy)­Co^III(κ²-O,C-C₆H₄C­(O)­CH₃)­(H)]­BAr^F₄ (<b>13</b>) was detected. Isolated complex <b>13</b> was found to be an effective catalyst for the acceptorless dehydrogenation of alcohols, implicating <b>13</b> as a catalyst resting state during the alcohol dehydrogenation reaction. Complex <b>13</b> catalyzed the hydrogenation of styrene but showed no catalytic activity for the room temperature hydrogenation of acetophenone. These results support the involvement of metal–ligand cooperativity in the room temperature hydrogenation of ketones but not the hydrogenation of olefins or the acceptorless dehydrogenation of alcohols. Mechanisms consistent with these observations are presented for the cobalt-catalyzed hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols

Understanding the Mechanisms of Cobalt-Catalyzed Hydrogenation and Dehydrogenation Reactions

Cobalt­(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt­(II) alkyl complex [(PNHP^Cy)­Co­(CH₂SiMe₃)]­BAr^F₄ (<b>4</b>) (PNHP^Cy = bis­[(2-dicyclohexylphosphino)­ethyl]­amine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N–H group on the pincer ligand in the catalysis via a metal–ligand cooperative interaction, the reactivities of <b>4</b> and [(PNMeP^Cy)­Co­(CH₂SiMe₃)]­BAr^F₄ (<b>7</b>) were compared. Complex <b>7</b> was found to be an active precatalyst for the hydrogenation of olefins. In contrast, no catalytic activity was observed using <b>7</b> as a precatalyst for the hydrogenation of acetophenone under mild conditions. For the acceptorless dehydrogenation of 1-phenylethanol, complex <b>7</b> displayed similar activity to complex <b>4</b>, affording acetophenone in high yield. When the acceptorless dehydrogenation of 1-phenylethanol with precatalyst <b>4</b> was monitored by NMR spectroscopy, the formation of the cobalt­(III) acetylphenyl hydride complex [(PNHP^Cy)­Co^III(κ²-O,C-C₆H₄C­(O)­CH₃)­(H)]­BAr^F₄ (<b>13</b>) was detected. Isolated complex <b>13</b> was found to be an effective catalyst for the acceptorless dehydrogenation of alcohols, implicating <b>13</b> as a catalyst resting state during the alcohol dehydrogenation reaction. Complex <b>13</b> catalyzed the hydrogenation of styrene but showed no catalytic activity for the room temperature hydrogenation of acetophenone. These results support the involvement of metal–ligand cooperativity in the room temperature hydrogenation of ketones but not the hydrogenation of olefins or the acceptorless dehydrogenation of alcohols. Mechanisms consistent with these observations are presented for the cobalt-catalyzed hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols

Iron/Copper Co-Catalyzed Synthesis of Vinyl Sulfones from Sulfonyl Hydrazides and Alkyne Derivatives

A new approach to the selective synthesis of (<i>E</i>)-vinyl sulfones has been developed via a Fe/Cu co-catalyzed sulfonylation of arylpropiolic acid or phenylacetylene with sulfonyl hydrazides. A variety of vinyl sulfones have been obtained in moderate to good yields, comparable to the best results reported so far. The inexpensive Fe/Cu co-catalyzed method features a simple experimental procedure and good tolerance of substrate

Cobalt-Catalyzed Synthesis of Aromatic, Aliphatic, and Cyclic Secondary Amines via a “Hydrogen-Borrowing” Strategy

The replacement of precious metals with inexpensive, less toxic, and earth-abundant elements in typical noble-metal-mediated organic transformations is a major goal in current synthetic chemistry and industries. The metal-catalyzed N-alkylation of amines with other amines through a “hydrogen-borrowing” principle represents a green and atom-economical reaction for the synthesis of secondary amines. However, catalysts developed thus far that are effective for this process remain quite scarce and are only limited to a few ruthenium and iridium complexes. In this work, we present a cobalt-catalyzed selective alkylation of amines with amines to synthesize a large variety of secondary amines. A range of amine substrates have been converted to the corresponding products through hetero- or homocoupling between amines. Cyclic <i>sec</i>-amines are also achieved from diamine precursors as rare examples

Cobalt-Catalyzed α‑Alkylation of Ketones with Primary Alcohols

An ionic cobalt–PNP complex is developed for the efficient α-alkylation of ketones with primary alcohols for the first time. A broad range of ketone and alcohol substrates were employed, leading to the isolation of alkylated ketones with yields up to 98%. The method was successfully applied to the greener synthesis of quinoline derivatives while using 2-aminobenzyl alcohol as an alkylating reagent

Cobalt(II) Coordination Polymer as a Precatalyst for Selective Hydroboration of Aldehydes, Ketones, and Imines

Highly effective hydroboration precatalyst is developed based on a cobalt­(II)-terpyridine coordination polymer (CP). The hydroboration of ketones, aldehydes, and imines with pinacolborane (HBpin) has been achieved using the recyclable CP catalyst in the presence of an air-stable activator. A wide range of substrates containing polar CO or CN bonds have been hydroborated selectively in excellent yields under ambient conditions