ESI-MS Insights into Acceptorless Dehydrogenative Coupling of Alcohols

Acceptorless dehydrogenative coupling (ADC) reactions catalyzed by a series of Ru and Os complexes were studied by ESI-MS. Important ethoxo, 1-ethoxyethanolate, and hydride intermediates were intercepted in the ADC of ethanol to ethyl acetate. Collision-induced dissociation (CID) experiments were applied as a structure elucidation tool and as a probe of the propensity of the reaction intermediates to evolve acetaldehyde, ethyl acetate, and H₂, relevant to the catalytic cycle. The key mechanistic step producing ethyl acetate from the 1-ethoxyethanolate intermediates was documented. Energy-dependent CID experiments demonstrated the importance of a vacant coordination site for efficient production of ethyl acetate. The versatility and potential broad applicability of ESI-MS and its tandem version with CID was further illustrated for the ADC reaction of alcohols with amines, affording amides. A mechanism related to that found for the ester synthesis is plausible, with the key step involving formation of a hemiaminaloxide intermediate

Chemoselective Hydrogenation of Carbonyl Compounds and Acceptorless Dehydrogenative Coupling of Alcohols

OsHCl­(CO)­[κ³-PyCH₂NHC₂H₄NHP<i>t</i>Bu₂] is the first efficient catalyst for chemoselective reduction of challenging unsaturated esters to enols and for acceptorless coupling of amines with MeOH and EtOH affording formamides and acetamides. The NMR, ESI-MS, and DFT data indicate a mechanism proceeding in the metal coordination sphere and producing no free organic intermediates

New Ag(I)–Iminophosphorane Coordination Polymers as Efficient Catalysts Precursors for the MW-Assisted Meyer–Schuster Rearrangement of Propargylic Alcohols in Water

Treatment of the <i>N</i>-thiophosphorylated iminophosphorane ligands (PTA)NP­(S)­(OR)₂ [PTA = 1,3,5-triaza-7-phosphaadamantane, <b>3a</b> and <b>3b</b>] and (DAPTA)NP­(S)­(OR)₂ [DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]­nonane, <b>4a</b> and <b>4b</b>] with an equimolecular amount of AgSbF₆ leads to high-yield formation of the new one-dimensional coordination polymers [Ag­{μ²-<i>N</i>,<i>S</i>-(PTA)NP­(S)­(OR)₂}]_<i>x</i>[SbF₆]_<i>x</i> (<b>5a</b> and <b>5b</b>) and [Ag­{μ²-<i>O</i>,<i>S</i>-(DAPTA)NP­(S)­(OR)₂}]_<i>x</i>[SbF₆]_<i>x</i> (<b>6a</b> and <b>6b</b>), respectively. These new (iminophosphorane)­silver­(I) coordination polymers are efficient catalyst precursors for the Meyer–Schuster isomerization of both terminal and internal alkynols. Reactions proceeded in water, under aerobic conditions and using microwave irradiation as heating source, to afford the corresponding <i>α,β</i>-unsaturated carbonyl compounds in excellent yields, without the addition of any cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min, 99%; 10th cycle 6 h, 97%). ESI-MS analysis of <b>5a</b> in water has been carried out providing valuable insight into the monomeric active species responsible for catalytic activity in water

New Ag(I)–Iminophosphorane Coordination Polymers as Efficient Catalysts Precursors for the MW-Assisted Meyer–Schuster Rearrangement of Propargylic Alcohols in Water

Treatment of the <i>N</i>-thiophosphorylated iminophosphorane ligands (PTA)NP­(S)­(OR)₂ [PTA = 1,3,5-triaza-7-phosphaadamantane, <b>3a</b> and <b>3b</b>] and (DAPTA)NP­(S)­(OR)₂ [DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]­nonane, <b>4a</b> and <b>4b</b>] with an equimolecular amount of AgSbF₆ leads to high-yield formation of the new one-dimensional coordination polymers [Ag­{μ²-<i>N</i>,<i>S</i>-(PTA)NP­(S)­(OR)₂}]_<i>x</i>[SbF₆]_<i>x</i> (<b>5a</b> and <b>5b</b>) and [Ag­{μ²-<i>O</i>,<i>S</i>-(DAPTA)NP­(S)­(OR)₂}]_<i>x</i>[SbF₆]_<i>x</i> (<b>6a</b> and <b>6b</b>), respectively. These new (iminophosphorane)­silver­(I) coordination polymers are efficient catalyst precursors for the Meyer–Schuster isomerization of both terminal and internal alkynols. Reactions proceeded in water, under aerobic conditions and using microwave irradiation as heating source, to afford the corresponding <i>α,β</i>-unsaturated carbonyl compounds in excellent yields, without the addition of any cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min, 99%; 10th cycle 6 h, 97%). ESI-MS analysis of <b>5a</b> in water has been carried out providing valuable insight into the monomeric active species responsible for catalytic activity in water

Imidazole Based Ruthenium(IV) Complexes as Highly Efficient Bifunctional Catalysts for the Redox Isomerization of Allylic Alcohols in Aqueous Medium: Water as Cooperating Ligand

Bis-allyl ruthenium­(IV) complexes containing 1,3 azole β-N-H protic ligands [Ru­(η³:η³-C₁₀H₁₆)­Cl₂L] (C₁₀H₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl) (L = imidazole (<b>1a</b>), benzimidazole (<b>1b</b>)), and <i>N</i>-methylimidazole (<b>1c</b>) are highly active precatalysts in the redox isomerization of allylic alcohols into carbonyl compounds in aqueous medium and in the absence of base. A wide series of primary and secondary allylic alcohols can be isomerized into the corresponding carbonyl compounds. Remarkably, complex <b>1b</b> has been found to be the most efficient catalyst reported to date for the isomerization of 1-octen-3-ol in water leading to a turnover frequency (TOF) value of 60 000 h^–1. Moreover, catalyst <b>1b</b> can be recycled remaining active up to seven cycles. Density functional theory (DFT) calculations give evidence that the hydroxo complexes derived from <b>1a</b>–<b>c</b> species can be formed in aqueous solution and that they can act as the catalytic active species in a bifunctional catalyzed process. This study demonstrate that in water the participation of the β-N-H protic group of the 1,3-azole ligands in the bifunctional catalysis is not required, provided that a water molecule can act as cooperating ligand

Imidazole Based Ruthenium(IV) Complexes as Highly Efficient Bifunctional Catalysts for the Redox Isomerization of Allylic Alcohols in Aqueous Medium: Water as Cooperating Ligand

Bis-allyl ruthenium­(IV) complexes containing 1,3 azole β-N-H protic ligands [Ru­(η³:η³-C₁₀H₁₆)­Cl₂L] (C₁₀H₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl) (L = imidazole (<b>1a</b>), benzimidazole (<b>1b</b>)), and <i>N</i>-methylimidazole (<b>1c</b>) are highly active precatalysts in the redox isomerization of allylic alcohols into carbonyl compounds in aqueous medium and in the absence of base. A wide series of primary and secondary allylic alcohols can be isomerized into the corresponding carbonyl compounds. Remarkably, complex <b>1b</b> has been found to be the most efficient catalyst reported to date for the isomerization of 1-octen-3-ol in water leading to a turnover frequency (TOF) value of 60 000 h^–1. Moreover, catalyst <b>1b</b> can be recycled remaining active up to seven cycles. Density functional theory (DFT) calculations give evidence that the hydroxo complexes derived from <b>1a</b>–<b>c</b> species can be formed in aqueous solution and that they can act as the catalytic active species in a bifunctional catalyzed process. This study demonstrate that in water the participation of the β-N-H protic group of the 1,3-azole ligands in the bifunctional catalysis is not required, provided that a water molecule can act as cooperating ligand

Imidazole Based Ruthenium(IV) Complexes as Highly Efficient Bifunctional Catalysts for the Redox Isomerization of Allylic Alcohols in Aqueous Medium: Water as Cooperating Ligand

Bis-allyl ruthenium­(IV) complexes containing 1,3 azole β-N-H protic ligands [Ru­(η³:η³-C₁₀H₁₆)­Cl₂L] (C₁₀H₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl) (L = imidazole (<b>1a</b>), benzimidazole (<b>1b</b>)), and <i>N</i>-methylimidazole (<b>1c</b>) are highly active precatalysts in the redox isomerization of allylic alcohols into carbonyl compounds in aqueous medium and in the absence of base. A wide series of primary and secondary allylic alcohols can be isomerized into the corresponding carbonyl compounds. Remarkably, complex <b>1b</b> has been found to be the most efficient catalyst reported to date for the isomerization of 1-octen-3-ol in water leading to a turnover frequency (TOF) value of 60 000 h^–1. Moreover, catalyst <b>1b</b> can be recycled remaining active up to seven cycles. Density functional theory (DFT) calculations give evidence that the hydroxo complexes derived from <b>1a</b>–<b>c</b> species can be formed in aqueous solution and that they can act as the catalytic active species in a bifunctional catalyzed process. This study demonstrate that in water the participation of the β-N-H protic group of the 1,3-azole ligands in the bifunctional catalysis is not required, provided that a water molecule can act as cooperating ligand

Imidazole Based Ruthenium(IV) Complexes as Highly Efficient Bifunctional Catalysts for the Redox Isomerization of Allylic Alcohols in Aqueous Medium: Water as Cooperating Ligand

Bis-allyl ruthenium­(IV) complexes containing 1,3 azole β-N-H protic ligands [Ru­(η³:η³-C₁₀H₁₆)­Cl₂L] (C₁₀H₁₆ = 2,7-dimethylocta-2,6-diene-1,8-diyl) (L = imidazole (<b>1a</b>), benzimidazole (<b>1b</b>)), and <i>N</i>-methylimidazole (<b>1c</b>) are highly active precatalysts in the redox isomerization of allylic alcohols into carbonyl compounds in aqueous medium and in the absence of base. A wide series of primary and secondary allylic alcohols can be isomerized into the corresponding carbonyl compounds. Remarkably, complex <b>1b</b> has been found to be the most efficient catalyst reported to date for the isomerization of 1-octen-3-ol in water leading to a turnover frequency (TOF) value of 60 000 h^–1. Moreover, catalyst <b>1b</b> can be recycled remaining active up to seven cycles. Density functional theory (DFT) calculations give evidence that the hydroxo complexes derived from <b>1a</b>–<b>c</b> species can be formed in aqueous solution and that they can act as the catalytic active species in a bifunctional catalyzed process. This study demonstrate that in water the participation of the β-N-H protic group of the 1,3-azole ligands in the bifunctional catalysis is not required, provided that a water molecule can act as cooperating ligand

Experimental Evidence Supporting Related Mechanisms for Ru(II)-Catalyzed Dehydrocoupling and Hydrolysis of Amine-Boranes

A family of ruthenium­(II) half-sandwich complexes was tested for the hydrolytic decomposition of amine-boranes. The analysis of the catalytic results, together with a multilateral approach based on ¹H, ¹¹B NMR, and ESI-MS were used to propose a plausible and conceptually unified mechanism for both the hydrolysis and competitive dehydrogenation of amine-boranes. We propose the intermediacy of solvent-stabilized borenium cations during the catalytic cycle, evolving toward dehydrogenation products in distilled THF or releasing amine-hydroxyboranes in aqueous media. Both reaction pathways would liberate up to 1 equivalent of hydrogen through a metal-catalyzed process, but an out-of-cycle low-barrier hydrolysis of amine-hydroxyboranes would produce the 2 additional equivalents of hydrogen in aqueous solutions. Metal-catalyzed deuteration of (non hydrogen-productive) trisubstituted amine-boranes by using D₂O as deuterium source was observed, and included as part of the mechanism proposal

Catalytic N‑Alkylation of Amines Using Carboxylic Acids and Molecular Hydrogen

A convenient, practical and green N-alkylation of amines has been accomplished by applying readily available carboxylic acids in the presence of molecular hydrogen. Applying an in situ formed ruthenium/triphos complex and an organic acid as cocatalyst, a broad range of alkylated secondary and tertiary amines are obtained in good to excellent yields. This novel method is also successfully applied for the synthesis of unsymmetrically substituted N-methyl/alkyl anilines through a direct three-component coupling reaction of the corresponding amines, carboxylic acids, and CO₂ as a C₁ source