We report the synthesis of dianionic OCO-supported NHC and MIC complexes of molybdenum and tungsten with the general formula(OCO)MO₂(OCO=bis-phenolate benzimidazolylidene M=Mo(1-Mo),bis-phenolate triazolylidene M=Mo(2...We report the synthesis of dianionic OCO-supported NHC and MIC complexes of molybdenum and tungsten with the general formula(OCO)MO₂(OCO=bis-phenolate benzimidazolylidene M=Mo(1-Mo),bis-phenolate triazolylidene M=Mo(2-Mo),M=W(2-W)and bis-phenolate imidazolylidene,M=Mo(3-Mo),W(3-W)).These complexes are tested in the catalytic deoxygenation of nitroarenes using pinacol as a sacrificial oxygen atom acceptor/reducing agent to examine the influence of the carbene and the metal centre in this transformation.The results show that the molybdenum-based triazolylidene complex 2-Mo is by far the most active catalyst,and TOFs of up to 270 h⁻¹ are observed,while the tungsten analogues are basically inactive.Mechanistic studies suggest that the superiority of the triazolylidene-based complex 2-Mo is a result of a highly stable metal carbene bond,strongly exceeding the stability of the other NHC complexes 1-Mo and 3-Mo.This is proven by the structural isolation of a triazolylidene pinacolate complex(5-Mo)that can be thermally converted to aμ-oxodimolybdenum(V)complex 7-Mo.The latter complex is very oxophilic and stoichiometrically deoxygenates nitro-and nitrosoarenes at room temperature.In contrast,azoarenes are not reductively cleaved by 7-Mo,suggesting direct deoxygenation of the nitroarenes to the corresponding anilines with nitrosoarenes as intermediates.In summary,this work showcases the superior influence of MIC donors on the catalytic properties of early transition metal complexes.展开更多
Triazolylidenes are an emerging class of mesoionic carbenes with potential as ligands in homogeneous catalysis.In this contribution we present well-defined dicopper(Ⅰ)complexes with di-mesoionic carbenes where the co...Triazolylidenes are an emerging class of mesoionic carbenes with potential as ligands in homogeneous catalysis.In this contribution we present well-defined dicopper(Ⅰ)complexes with di-mesoionic carbenes where the copper centers are held at a distance of about 2.8Å.All complexes display excellent activity as pre-catalysts for the azide–alkyne cycloaddition(click)reaction.Comparisons with analogous mononuclear complexes show the dinuclear pre-catalysts to be twice as active for the same amount of copper used.These results thus point to potentially strong cooperative effects in these dinuclear complexes,and further support the recently established dinuclear reaction pathway for the click reaction.The results presented here provide a synthetic route for generating dinuclear complexes with di-mesoionic carbenes with relatively short metal–metal distances,and opens a general platform for investigating potential cooperative effects in catalysis.展开更多
Rod-shaped neutral carbon ligands such as carbon monoxide and isocyanides play a central role in organometallic chemistry but are relatively weak electron donors compared to N-heterocyclic carbenes.Phosphonioacetylide...Rod-shaped neutral carbon ligands such as carbon monoxide and isocyanides play a central role in organometallic chemistry but are relatively weak electron donors compared to N-heterocyclic carbenes.Phosphonioacetylides(R_(3)PCC)have been proposed as promising candidates for stronger electron donation within the class of sp-hybridized carbon ligands.However,their high reactivity has significantly limited their exploration and isolation.In this study,we report the synthesis and characterization of a novel phosphonioacetylide,MeR_(2)PCC(R=1,3-di-tert-butylimidazolidin-2-ylidenamino).While it is highly labile at ambient temperature,the compound is stable at−40℃ and can be isolated and stored in the form of alkali metal complexes.The latter undergo efficient transmetallation reactions with a variety of electrophiles,enabling the formation of Lewis base adducts with both main group elements and transition metals,including tungsten(0),nickel(0),and rhodium(Ⅰ).These results demonstrate that alkali metal phosphonioacetylides serve as versatile precursors for introducing this highly donating and structurally unique ligand into coordination complexes.展开更多
Insertion of fluorenone into the lanthanum–phosphorus bond of terminal phosphido complexes(PN)2La(PHR)(R=Mes(1a),R=Ph(1b)and R=tBu(1c))results in the formation of light-sensitive hemiphosphinal complexes 2a–c.Upon e...Insertion of fluorenone into the lanthanum–phosphorus bond of terminal phosphido complexes(PN)2La(PHR)(R=Mes(1a),R=Ph(1b)and R=tBu(1c))results in the formation of light-sensitive hemiphosphinal complexes 2a–c.Upon exposure to daylight,the P–C bonds in 2a–c break resulting in the formation of diphospines and a lanthanum bound fluorenonyl-radical.The scope and mechansim of this reaction are experimentally and theoretically evaluated.展开更多
基金funded in whole or in part by the Austrian Science Fund(FWF),Grant-DOI:https://doi.org/10.55776/P34626.
文摘We report the synthesis of dianionic OCO-supported NHC and MIC complexes of molybdenum and tungsten with the general formula(OCO)MO₂(OCO=bis-phenolate benzimidazolylidene M=Mo(1-Mo),bis-phenolate triazolylidene M=Mo(2-Mo),M=W(2-W)and bis-phenolate imidazolylidene,M=Mo(3-Mo),W(3-W)).These complexes are tested in the catalytic deoxygenation of nitroarenes using pinacol as a sacrificial oxygen atom acceptor/reducing agent to examine the influence of the carbene and the metal centre in this transformation.The results show that the molybdenum-based triazolylidene complex 2-Mo is by far the most active catalyst,and TOFs of up to 270 h⁻¹ are observed,while the tungsten analogues are basically inactive.Mechanistic studies suggest that the superiority of the triazolylidene-based complex 2-Mo is a result of a highly stable metal carbene bond,strongly exceeding the stability of the other NHC complexes 1-Mo and 3-Mo.This is proven by the structural isolation of a triazolylidene pinacolate complex(5-Mo)that can be thermally converted to aμ-oxodimolybdenum(V)complex 7-Mo.The latter complex is very oxophilic and stoichiometrically deoxygenates nitro-and nitrosoarenes at room temperature.In contrast,azoarenes are not reductively cleaved by 7-Mo,suggesting direct deoxygenation of the nitroarenes to the corresponding anilines with nitrosoarenes as intermediates.In summary,this work showcases the superior influence of MIC donors on the catalytic properties of early transition metal complexes.
文摘Triazolylidenes are an emerging class of mesoionic carbenes with potential as ligands in homogeneous catalysis.In this contribution we present well-defined dicopper(Ⅰ)complexes with di-mesoionic carbenes where the copper centers are held at a distance of about 2.8Å.All complexes display excellent activity as pre-catalysts for the azide–alkyne cycloaddition(click)reaction.Comparisons with analogous mononuclear complexes show the dinuclear pre-catalysts to be twice as active for the same amount of copper used.These results thus point to potentially strong cooperative effects in these dinuclear complexes,and further support the recently established dinuclear reaction pathway for the click reaction.The results presented here provide a synthetic route for generating dinuclear complexes with di-mesoionic carbenes with relatively short metal–metal distances,and opens a general platform for investigating potential cooperative effects in catalysis.
基金financial support by a doctoral scholarship of the Universität Innsbruckthe support of the DFG(IRTG 2027).
文摘Rod-shaped neutral carbon ligands such as carbon monoxide and isocyanides play a central role in organometallic chemistry but are relatively weak electron donors compared to N-heterocyclic carbenes.Phosphonioacetylides(R_(3)PCC)have been proposed as promising candidates for stronger electron donation within the class of sp-hybridized carbon ligands.However,their high reactivity has significantly limited their exploration and isolation.In this study,we report the synthesis and characterization of a novel phosphonioacetylide,MeR_(2)PCC(R=1,3-di-tert-butylimidazolidin-2-ylidenamino).While it is highly labile at ambient temperature,the compound is stable at−40℃ and can be isolated and stored in the form of alkali metal complexes.The latter undergo efficient transmetallation reactions with a variety of electrophiles,enabling the formation of Lewis base adducts with both main group elements and transition metals,including tungsten(0),nickel(0),and rhodium(Ⅰ).These results demonstrate that alkali metal phosphonioacetylides serve as versatile precursors for introducing this highly donating and structurally unique ligand into coordination complexes.
文摘Insertion of fluorenone into the lanthanum–phosphorus bond of terminal phosphido complexes(PN)2La(PHR)(R=Mes(1a),R=Ph(1b)and R=tBu(1c))results in the formation of light-sensitive hemiphosphinal complexes 2a–c.Upon exposure to daylight,the P–C bonds in 2a–c break resulting in the formation of diphospines and a lanthanum bound fluorenonyl-radical.The scope and mechansim of this reaction are experimentally and theoretically evaluated.
