Synthesis And Reactivity Of Novel Iron,Cobalt And Nickel Complexes Supported By Silylene

The development of organometallic chemistry relies on the synthesis of new complexes,and the synthesis of new complexes depends on the design of new ligands.In the organometallic chemistry,the design of new ligands is based on the ligand framework and changes of the substituents.Silylene and organic phosphines are commonly used substituents in organometallic chemistry,especially N-heterocyclic silylenes(NHSi),have received extensive attention from scientists because of their unique σ-donor and π-accept capabilities.In recent years,metal complexes constructed by silylene as ligands have shown excellent properties in the field of homogeneous catalysis.However,compared to the phosphine ligands,silylene ligands remain limited,which limits the development of silylene chemistry.Therefore,designing new silylene ligands and systematically comparing the differences between silylene ligands and phosphine ligands in the construction of metal complexes and the differences in homogeneous catalytic activities are very meaningful and challenging topics.The N2 fixation under mild conditions by transition metal complexes is generally catalyzed by transition metal dinitrogen complexes and transition metal halides.Because the design and synthesis of transition metal dinitrogen complexes need to fully consider the factors such as electronic property and steric resistance,it is difficult to synthesize transition metal dinitrogen complexes compared with transition metal halides.At present,there are many reports on N2 fixation catalyzed by transition metal halides,but there are no reports on N2 fixation catalyzed by transition metal halides which coordinated by NHSi.Therefore,it is of extreme value to design and synthesize of new transition metal halides coordinated by NHSi and apply them in N2 fixation.Hydrosilylation of alkenes catalyzed by base transition metals instead of noble metals has become one of the research hotspots.In the hydrosilylation of alkenes catalyzed by base transition metal complexes,the complexes supported by pincer ligands are in the majority.There are relatively few reports on hydrosilylation of alkenes catalyzed by chelates supported by bidentate ligands,and there are few reports on the systematic study of the influence of complexes supported by silylene and phosphine ligands on the hydrosilylation of alkenes.Therefore,it is of great significance to design and synthesize new complexes supported by bidentate ligands and to systematically compare the differences between silylene ligands and phosphine ligands in this catalytic reaction.Based on this,this paper will carry out systematic research around the above areas,mainly involving the following five parts:1.Complexes 1-3 supported by bis-silylene were synthesized by the reaction of L1-L3 with FeCl2.Complexes 1-3 have been found to work as effective catalysts to dinitrogen silylation,and complex 3 is the best,up to 381 equiv of N(SiMe3)3 can be produced.Under this optimal catalytic condition,121 equiv and 232 equiv of N(SiMe3)3 can be generated of catalyst 1 and 2,respectively.By stoichiometric reaction and infrared spectrum monitoring,the mechanism of dinitrogen silylation catalyzed by complexes 1-3 is proposed.2.Four-coordinated Ni(0)complexes 11-13 were synthesized by the reactions of L1-L3 with Ni(PMe3)4 in n-pentane.It was found that complexes 11-13 would react further to activate the C(sp3)-H bond in C6D6 solvent,and nickel hydride complexes were formed.In addition,the property of H2 activated by complex 12 were also explored.3.Bidentate phosphine ligands L5,L7 and bidentate silylene ligand L6 were designed and synthesized.Firstly,complexes 16 and 18 were synthesized by the reactions of L-20 supported by bidentate silylene ligand with Co(PMe3)3Cl and Co(PMe3)4Me,respectively.Complexes 17 and 19 were synthesized by the reactions of L5 supported by bidentate phosphine ligand with Co(PMe3)3Cl and Co(PMe3)4Me,respectively.The ligand framework of L-20 and L5 is same.Not only the differences between bidentate silylene ligand L-20 and bidentate phosphine ligand L5 in construction of cobalt complexes were studied,but also the differences of cobalt complexes 16-19 in catalytic hydrosilylation of alkenes were also compared.The experimental results show that the catalytic activity of the complex supported by bidentate phosphine ligand is better than that the complex supported by bidentate silylene ligand,and the complex 19 is best.Secondly,bis-chelate disilylene iron hydride 1-20,20-22 were synthesized by the reaction of L-20,L5-L7 with Fe(PMe3)4,respectively.Not only the differences of ligand framework and substituents in the construction of iron complexes were compared,but also the catalytic effect of complexes 20-21 and 1-20 on the hydroboration of carbonyl compounds was studied.It was found that the ligand framework has little effect on the catalytic reaction,however,the catalytic activity of iron complex supported by bidentate phosphine ligand is better than that supported by silylene ligand.Complex 20 supported by bidentate phosphine ligand has a better catalytic ability.4.Complexes 23 and 24 were synthesized by the reactions of bidentate phosphine ligand L8 and L9 with Co(PMe3)3Cl,respectively.Complexes 23 and 24 have been found to work as effective catalyst to the hydrosilylation of alkenes with the same selectivity and similar conversion.For aryl alkenes,Markovnikov products could be obtained,and for alkyl alkenes,anti-Markovnikov products could be obtained.In the mechanism study,it was found that the ligand did not participate in the catalytic cycle.This explains why the catalytic capacity of complexes 23 and 24 was similar.5.Complex 28 was synthesized by the reaction of L8 with Co(PMe3)4Me.The experimental results show that complex 28 can efficiently and accurately catalyze the hydrosilylation of alkenes under mild conditions(30℃,2.5 h).For aryl alkenes,Markovnikov products can be obtained,and for for alkyl alkenes,anti-Markovnikov products can be obtained.The mechanism study shows that the ligand is not dissociated in the catalytic cycle.