Acceptorless alcohol dehydrogenation stands out as one of the most promising strategies in hydrogen storage technologies.Among various catalytic systems for this reaction,cost-effective molecular catalysts using phosp...Acceptorless alcohol dehydrogenation stands out as one of the most promising strategies in hydrogen storage technologies.Among various catalytic systems for this reaction,cost-effective molecular catalysts using phosphine-free ligands have gained considerable attention.However,the central challenge for using non-precious metals is to overcome the propensity of reacting by oneelectron pathway.Herein,we synthesized a phosphine-freeη^(5)-C_(5)Me_(5)-Co complex by using the metal-ligand cooperative strategy and compared its activity with analogous catalysts toward acceptorless alcohol dehydrogenation.The catalyst showed excellent performance with a turnover number of 130.4 and a selectivity close to 100%.The improved performance among the class ofη^(5)-C_(5)Me_(5)-Co complexes could be attributed to the more accessible Co center and its cooperation with the redox-active ligand.To further study the systematic structure-activity relationship,we investigated the electronic structures ofη^(5)-C_(5)Me_(5)-Co complexes by a set of characterizations.The results showed that the redox-active ligand has a significant influence on theη^(5)-C_(5)Me_(5)-Co moiety.In the meantime,the proximal O−/OH group is beneficial for shuttling protons.For the catalytic cycle,two dehydrogenation scenarios were interrogated through density functional theory,and the result suggested that the outer-sphere pathway was preferred.The formation of a dihydrogen complex was the rate-determining step with aΔG value of 16.9 kcal∙mol‒1.The electron population demonstrated that theη^(5)-C_(5)Me_(5)ligand played a key role in stabilizing transition states during dehydrogenation steps.This work identified the roles of vital ligand components to boost catalytic performance and offered rationales for designing metal-ligand cooperative nonprecious metal complexes.展开更多
The development of bifunctional catalysts for the efficient hydrogenation and acceptorless dehydrogenation of N‐heterocycles is a challenge.In this study,Ru_(2)P/AC effectively promoted reversible transformations bet...The development of bifunctional catalysts for the efficient hydrogenation and acceptorless dehydrogenation of N‐heterocycles is a challenge.In this study,Ru_(2)P/AC effectively promoted reversible transformations between unsaturated and saturated N‐heterocycles affording yields of 98%and 99%,respectively.Moreover,a remarkable enhancement in the reusability of Ru_(2)P/AC was observed compared with other Ru‐based catalysts.According to density functional theory calculations,the superior performance of Ru_(2)P/AC was ascribed to specific synergistic factors,namely geometric and electronic effects induced by P.P greatly reduced the large Ru‐Ru ensembles and finely modified the electronic structures,leading to a low reaction barrier and high desorption ability of the catalyst,further boosting the hydrogenation and acceptorless dehydrogenation processes.展开更多
A highly efficient photocatalytic dehydrogenative coupling(PDC)of amines to prepare value-added imines has been developed under the mild conditions.A complete conversion of benzylamine with a 99%selectivity of Nbenzyl...A highly efficient photocatalytic dehydrogenative coupling(PDC)of amines to prepare value-added imines has been developed under the mild conditions.A complete conversion of benzylamine with a 99%selectivity of Nbenzylidenebenzylamine could be obtained using the 2%Pt@g-C_(3)N_(4)as photocatalyst in the absence of hydrogen acceptor at room temperature.Moreover,the relationship between the physical properties of different photocatalysts and their activities has been discussed according to the characterization results of the XRD,BET,SEM,TEM,and XPS techniques.Next,the PDC of different amines have been further investigated,where ca.70.2%-99.0%yields of corresponding imines were attained.Finally,based on the experimental results and heterogeneous catalytic principle,a possible reaction mechanism for the PDC of benzylamine is proposed.展开更多
Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in const...Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes. AD reactions also can be utilized for hydrogen production from biomass or its fermentation products (mainly alcohols). Reversible hydrogenation/ dehy-drogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage. In this article, we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments. These reactions include acceptorless alcohol dehydrogenations, reversible dehydrogenation/hydrogenation of nitrogen heterocycles, dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds, and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds. For the catalysts possessing metal-ligand bifunctional active sites (such as 28, 45, 86, 87, and 106 in the paper), the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted-H elimination mechanism. However, methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene, catalyzed by the iridium complex 121, takes place via the-H elimination mechanism, because the Lewis basicity of either the-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity. Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.展开更多
Acceptorless dehydrogenation(AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry.Acceptorless alcohol dehydrogenation(AAD) can serve as a key step in construc...Acceptorless dehydrogenation(AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry.Acceptorless alcohol dehydrogenation(AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes.AD reactions also can be utilized for hydrogen production from biomass or its fermentation products(mainly alcohols).Reversible hydrogenation/dehydrogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage.In this article,we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments.These reactions include acceptorless alcohol dehydrogenations,reversible dehydrogenation/hydrogenation of nitrogen heterocycles,dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds,and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds.For the catalysts possessing metal-ligand bifunctional active sites(such as 28,45,86,87,and 106 in the paper),the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted β-H elimination mechanism.However,methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene,catalyzed by the iridium complex 121,takes place via the β-H elimination mechanism,because the Lewis basicity of either the π-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity.Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.22078269).
文摘Acceptorless alcohol dehydrogenation stands out as one of the most promising strategies in hydrogen storage technologies.Among various catalytic systems for this reaction,cost-effective molecular catalysts using phosphine-free ligands have gained considerable attention.However,the central challenge for using non-precious metals is to overcome the propensity of reacting by oneelectron pathway.Herein,we synthesized a phosphine-freeη^(5)-C_(5)Me_(5)-Co complex by using the metal-ligand cooperative strategy and compared its activity with analogous catalysts toward acceptorless alcohol dehydrogenation.The catalyst showed excellent performance with a turnover number of 130.4 and a selectivity close to 100%.The improved performance among the class ofη^(5)-C_(5)Me_(5)-Co complexes could be attributed to the more accessible Co center and its cooperation with the redox-active ligand.To further study the systematic structure-activity relationship,we investigated the electronic structures ofη^(5)-C_(5)Me_(5)-Co complexes by a set of characterizations.The results showed that the redox-active ligand has a significant influence on theη^(5)-C_(5)Me_(5)-Co moiety.In the meantime,the proximal O−/OH group is beneficial for shuttling protons.For the catalytic cycle,two dehydrogenation scenarios were interrogated through density functional theory,and the result suggested that the outer-sphere pathway was preferred.The formation of a dihydrogen complex was the rate-determining step with aΔG value of 16.9 kcal∙mol‒1.The electron population demonstrated that theη^(5)-C_(5)Me_(5)ligand played a key role in stabilizing transition states during dehydrogenation steps.This work identified the roles of vital ligand components to boost catalytic performance and offered rationales for designing metal-ligand cooperative nonprecious metal complexes.
文摘The development of bifunctional catalysts for the efficient hydrogenation and acceptorless dehydrogenation of N‐heterocycles is a challenge.In this study,Ru_(2)P/AC effectively promoted reversible transformations between unsaturated and saturated N‐heterocycles affording yields of 98%and 99%,respectively.Moreover,a remarkable enhancement in the reusability of Ru_(2)P/AC was observed compared with other Ru‐based catalysts.According to density functional theory calculations,the superior performance of Ru_(2)P/AC was ascribed to specific synergistic factors,namely geometric and electronic effects induced by P.P greatly reduced the large Ru‐Ru ensembles and finely modified the electronic structures,leading to a low reaction barrier and high desorption ability of the catalyst,further boosting the hydrogenation and acceptorless dehydrogenation processes.
基金supported by the National Natural Science Foundation of China(No.21878235).
文摘A highly efficient photocatalytic dehydrogenative coupling(PDC)of amines to prepare value-added imines has been developed under the mild conditions.A complete conversion of benzylamine with a 99%selectivity of Nbenzylidenebenzylamine could be obtained using the 2%Pt@g-C_(3)N_(4)as photocatalyst in the absence of hydrogen acceptor at room temperature.Moreover,the relationship between the physical properties of different photocatalysts and their activities has been discussed according to the characterization results of the XRD,BET,SEM,TEM,and XPS techniques.Next,the PDC of different amines have been further investigated,where ca.70.2%-99.0%yields of corresponding imines were attained.Finally,based on the experimental results and heterogeneous catalytic principle,a possible reaction mechanism for the PDC of benzylamine is proposed.
基金supported by the Chinese Academy of Sciencesthe National Natural Science Foundation of China (20973197 and 21173263)
文摘Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes. AD reactions also can be utilized for hydrogen production from biomass or its fermentation products (mainly alcohols). Reversible hydrogenation/ dehy-drogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage. In this article, we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments. These reactions include acceptorless alcohol dehydrogenations, reversible dehydrogenation/hydrogenation of nitrogen heterocycles, dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds, and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds. For the catalysts possessing metal-ligand bifunctional active sites (such as 28, 45, 86, 87, and 106 in the paper), the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted-H elimination mechanism. However, methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene, catalyzed by the iridium complex 121, takes place via the-H elimination mechanism, because the Lewis basicity of either the-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity. Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.
文摘Acceptorless dehydrogenation(AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry.Acceptorless alcohol dehydrogenation(AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes.AD reactions also can be utilized for hydrogen production from biomass or its fermentation products(mainly alcohols).Reversible hydrogenation/dehydrogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage.In this article,we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments.These reactions include acceptorless alcohol dehydrogenations,reversible dehydrogenation/hydrogenation of nitrogen heterocycles,dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds,and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds.For the catalysts possessing metal-ligand bifunctional active sites(such as 28,45,86,87,and 106 in the paper),the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted β-H elimination mechanism.However,methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene,catalyzed by the iridium complex 121,takes place via the β-H elimination mechanism,because the Lewis basicity of either the π-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity.Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.
