The study of new,unusual structures and reactivity patterns is of great interest for various field of organic and organometallic chemistry.Metallacycles of electropositive transition metals represent an excellent plat...The study of new,unusual structures and reactivity patterns is of great interest for various field of organic and organometallic chemistry.Metallacycles of electropositive transition metals represent an excellent platform for this purpose.In this work,we present the synthesis,characterisation,and reactivity toward carbodiimides of a set of ring-strained group 4 ansa-metallocene-based 1-metallacyclobuta-2,3-dienes Cp’_(2)M(Me_(3)SiC_(3)SiMe_(3))(M=Ti,Zr;Cp’_(2)=indenyl or tetrahydroindenyl based ansa-Cp ligand).In line with experimental studies,computational analysis of the electronic structure of new and previously reported 1-metallacyclobuta-2,3-dienes for the first time shows that the biradical character of these species not only depends on the metal,but also strongly on the nature of the cyclopentadienyl ligands.In reactions with carbodiimides RNvCvNR,depending on the substituents of the carbodiimide,either 2-aza-1-metallacyclobut-3-ene(R=iPr,Cy,and p-Tol)or 2-aza-1-metallacyclohexa-2,4,5-triene(R=SiMe_(3))complexes were produced.Mechanistic studies by DFT calculations reveal that 1,2-insertion of the carbodiimide followed by migration of a SiMe_(3) group of the metallacycle occurs for R=iPr,Cy,p-Tol,whereas for R=SiMe_(3) insertion is followed by SiMe_(3) migration along the carbodiimide.The reaction of a 2-aza-1-metallacyclobut-3-ene complex with benzophenone produces a zirconocene amidopyridine complex through a series of unprecedented bond activation and formation events,once again demonstrating the potential of early transition metal complexes for activation and transformation of small molecules.展开更多
Herein we report the application of a Co(II)PNN^(H) pincer catalyst system(PNN^(H)=2-(5-(t-butyl)-1Hpyrazol-3-yl)-6-(dialkylphosphinomethyl)pyridine)for the highly E-selective transfer semihydrogenation of internal di...Herein we report the application of a Co(II)PNN^(H) pincer catalyst system(PNN^(H)=2-(5-(t-butyl)-1Hpyrazol-3-yl)-6-(dialkylphosphinomethyl)pyridine)for the highly E-selective transfer semihydrogenation of internal diaryl alkynes using methanol and ammonia borane as hydrogen donors.The catalyst system is highly active(short reaction times,low Co concentration)and operates at very mild conditions(low temperature and transfer hydrogenation conditions).Spectroscopic and computational studies suggest that catalysis occurs via the Co(II)oxidation state,most likely with a Co(II)hydride as the key intermediate.Computational analysis of the reaction mechanism further rationalises the selective formation of E-alkenes and the absence of overreduction to produce alkanes.展开更多
Phosphaalkenes are an emerging class of ligands with unique electronic properties that can be regarded as tuneable variants of the ubiquitous CO ligand.Our group has recently reported the synthesis of the P,N-type pho...Phosphaalkenes are an emerging class of ligands with unique electronic properties that can be regarded as tuneable variants of the ubiquitous CO ligand.Our group has recently reported the synthesis of the P,N-type phosphaalkene ligand quin-CHvPMes^(*)(1,quin=2-quinolinyl)and its coordination chemistry with Rh(Ⅰ)was investigated.展开更多
基金Financial support by the Deutsche Forschungsgemeinschaft(Project No.452714985)is gratefully acknowledgedfinancial support by the China Scholarship Council(CSC,Grant No.202006380016).
文摘The study of new,unusual structures and reactivity patterns is of great interest for various field of organic and organometallic chemistry.Metallacycles of electropositive transition metals represent an excellent platform for this purpose.In this work,we present the synthesis,characterisation,and reactivity toward carbodiimides of a set of ring-strained group 4 ansa-metallocene-based 1-metallacyclobuta-2,3-dienes Cp’_(2)M(Me_(3)SiC_(3)SiMe_(3))(M=Ti,Zr;Cp’_(2)=indenyl or tetrahydroindenyl based ansa-Cp ligand).In line with experimental studies,computational analysis of the electronic structure of new and previously reported 1-metallacyclobuta-2,3-dienes for the first time shows that the biradical character of these species not only depends on the metal,but also strongly on the nature of the cyclopentadienyl ligands.In reactions with carbodiimides RNvCvNR,depending on the substituents of the carbodiimide,either 2-aza-1-metallacyclobut-3-ene(R=iPr,Cy,and p-Tol)or 2-aza-1-metallacyclohexa-2,4,5-triene(R=SiMe_(3))complexes were produced.Mechanistic studies by DFT calculations reveal that 1,2-insertion of the carbodiimide followed by migration of a SiMe_(3) group of the metallacycle occurs for R=iPr,Cy,p-Tol,whereas for R=SiMe_(3) insertion is followed by SiMe_(3) migration along the carbodiimide.The reaction of a 2-aza-1-metallacyclobut-3-ene complex with benzophenone produces a zirconocene amidopyridine complex through a series of unprecedented bond activation and formation events,once again demonstrating the potential of early transition metal complexes for activation and transformation of small molecules.
基金support by the DFG(project code 419924354)is gratefully acknowledged.
文摘Herein we report the application of a Co(II)PNN^(H) pincer catalyst system(PNN^(H)=2-(5-(t-butyl)-1Hpyrazol-3-yl)-6-(dialkylphosphinomethyl)pyridine)for the highly E-selective transfer semihydrogenation of internal diaryl alkynes using methanol and ammonia borane as hydrogen donors.The catalyst system is highly active(short reaction times,low Co concentration)and operates at very mild conditions(low temperature and transfer hydrogenation conditions).Spectroscopic and computational studies suggest that catalysis occurs via the Co(II)oxidation state,most likely with a Co(II)hydride as the key intermediate.Computational analysis of the reaction mechanism further rationalises the selective formation of E-alkenes and the absence of overreduction to produce alkanes.
基金support by LIKAT(PhD fellowship for P.G.)is gratefully acknowledged.
文摘Phosphaalkenes are an emerging class of ligands with unique electronic properties that can be regarded as tuneable variants of the ubiquitous CO ligand.Our group has recently reported the synthesis of the P,N-type phosphaalkene ligand quin-CHvPMes^(*)(1,quin=2-quinolinyl)and its coordination chemistry with Rh(Ⅰ)was investigated.
