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
The development of routes and strategies for the design and preparation of complexes of 4d metals in moderate oxidation states is of great importance in magnetochemistry, bioinorganic chemistry, materials chemistry an...The development of routes and strategies for the design and preparation of complexes of 4d metals in moderate oxidation states is of great importance in magnetochemistry, bioinorganic chemistry, materials chemistry and solid-state chemistry. Bidentate ligands containing N or O donors especially phenanthroline have been widely used to form complexes with interesting structural motif. Reaction of M（CO）6 （M = Cr, Mo, W） with phenanthroline has been done in 1935 and produced an interesting stereo structure, but the reaction of MoOE（acac）2 （acac = acetylacetonato） with phenanthroline has not been studied yet. So, in this research, first of all MoOE（acac） 2 was prepared, and then it reacted with bidentate nitrogen donor to lead to produce the complex of [MoOEL2] （L = Phen） and different aspects of this complex were studied. This complex is very active and highly selective epoxidation catalyst. The structure of the product was characterized by various spectral techniques such as elemental analysis, IH NMR, 13C NMR and IR spectroscopy.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The development of routes and strategies for the design and preparation of complexes of 4d metals in moderate oxidation states is of great importance in magnetochemistry, bioinorganic chemistry, materials chemistry and solid-state chemistry. Bidentate ligands containing N or O donors especially phenanthroline have been widely used to form complexes with interesting structural motif. Reaction of M（CO）6 （M = Cr, Mo, W） with phenanthroline has been done in 1935 and produced an interesting stereo structure, but the reaction of MoOE（acac）2 （acac = acetylacetonato） with phenanthroline has not been studied yet. So, in this research, first of all MoOE（acac） 2 was prepared, and then it reacted with bidentate nitrogen donor to lead to produce the complex of [MoOEL2] （L = Phen） and different aspects of this complex were studied. This complex is very active and highly selective epoxidation catalyst. The structure of the product was characterized by various spectral techniques such as elemental analysis, IH NMR, 13C NMR and IR spectroscopy.
