Ⅰ Synthesis And Reactivity Of Iron And Cobalt Complexes Supported By Novel Bis(silylene)-Based Pincer Ligands Ⅱ Synthesis And Properties Of Organic Optoelectronic Functional Molecules With Boryl And Amino Groups At O,o’-positions Of Biaryl

N-heterocyclic silylenes(NHSi),heavier analogues of N-heterocyclic carbenes(NHC),have unique σ-donating/π-accepting and tunable steric hindrance properties.In recent years,silylenes,which are very important synthons in organosilicon chemistry,have been employed in the activation of small molecules,due to an ambiphilic character and unsaturated coordination.Furthermore,the silylene ligands surpass the steering properties of their phosphine and N-heterocyclic carbene(NHC)analogues and can act as superior ligands in various metal-mediated catalytic transformations.However,compared to the rich structural diversity of NHC and phosphine ligands,multidentate NHSi ligands remain limited,which limits the development of silylene chemistry largely.The synthesis of new bis-silicon(Ⅱ)-based multidentate ligands and their applications in the activation of small molecules as well as in coordination chemistry are an attractive and challenging project in chemistry.Recent years have witnessed the development of N2 fixation under mild reaction conditions catalyzed by transition metal complexes,but it is still in its infancy.In particular,there was only one case of the transition metal dinitrogen(TM-N2)complexes supported by NHSi.It is of great value to construct the TM-N2 complexes supported by NHSi and explore their applications in the catalytic reduction of N2.Herein,we reported the facile synthesis and characterization of novel bis(silylene)-based pincer ligands and their coordination mode toward iron and cobalt.In addition,their applications in homogenous catalysis,N2 fixation and the activation of small molecules were also explored.Specifically,this paper was divided into the following five parts:1.The bis(silylene)-based SiC(sp3)Si pincer ligands L-1,L-3 and L-4 with a different substituent at the middle carbon atom of the preligand dipyrrolmethane were synthesized.To the best of our knowledge,pincer-type silylene ligands with a C(sp3)-atom anchor have not been reported so far.Our work will provide some new strategies and strongly promote the further development of N-heterocyclic silylene chemistry.What’s more,silyl-silylene compound L-2 was also obtained.2.The construction of iron complexes supported by L-1,L-3 and L-4 was explored.Two novel iron hydride complexes,[SiCHSi]Fe(H)(N2)(PMe3)(1)and[SiCHSi]Fe(H)(PMe3)2(2)were synthesized in the reaction of L-1 with Fe(PMe3)4 via the C(sp3)-H bond activation under different inert atmospheres(N2 or argon).1 and 2 are the first examples of bis(silylene)-based hydrido pincer iron complex produced through activation of the C(sp3)-H bond.At the same time 1 is also the first example of TM dinitrogen complex supported by bis-silylene ligand.The interconversion between 1 and 2 was achieved and monitored by 31P NMR spectra and operando IR to understand the transformation from 1 to 2 from a view of kinetic point.The reaction of complex 1 with CO was further studied.Alike,TM-dinitrogen complexes 4 and 6,supported by L-3 and L-4 respectively,were also obtained.Meanwhile,complex 5 was synthesized as a byproduct.The significant effect of meso-substituent was confirmed by comparing the positions of nitrogen stretching vibration peaks in these TM-N2 complexes.3.The construction of cobalt complexes supported by L-1,L-3 and L-4 was explored.By the reactions of L-1 with Co(PMe3)4,CoCl(PMe3)3 and CoMe(PMe3)4,there cobalt complexes 7,9 and 10 were synthesized via the C(sp3)-H bond activation.The reaction of complex 7 with CO was further studied.Treatment of L-4 with CoCl(PMe3)3 in THF afforded complex 8 through the ligand replacement.In addition,L-3 did not react with CoCl(PMe3)3.4.The investigation of catalytic silylation of dinitrogen gas was carried out by using complexes 1 and 4 as catalysts under ambient reaction conditions.The complex 1 has been found to work as an effective catalyst to nitrogen fixation with KCs as a strong reductant and Me3SiCl as the silylating reagent.Further experiments showed that complex 4 worked as a more effective catalyst than 1 under the same reaction conditions.In addition,1 could effectively catalyze the reduction of amide to nitrile and 7 were found effective in promoting alkene hydrosilylation.5.N-heterocyclic silylenes tend to possess an ambiphilic character and behave as Lewis acids as well as Lewis bases.We successfully used them to facilitate small-molecule activation chemistry,such as N-H bond,O2,CO and CO2.All new compounds involved in the dissertation were characterized by NMR,IR,HRMS,elemental analysis and single crystal X-ray diffraction analysis.In recent years,organic fluorophores have found extensive applications in organic light-emitting diodes(OLEDs),organic field-effect transistors(OFETs),nonlinear optics,highly selective fluoride and cyanide sensors,as well as stimuli responsive materials.Triarylborane π-electron materials have gained significantly increasing research interest due to the unique electrical and spatial properties of boron,such as the high Lewis acidity,the strong electron-accepting ability,as well as the stereo feature of trivalent boron center.It has been well demonstrated that triarylboranes would possess large electronic dipoles in the excited state,when an electron-donating group,such as amino,is present.The large electronic dipole would promote intramolecular charge-transfer(CT)and thus the corresponding excellent emission properties,such as a large Stokes shift,a red shift in emission,a high fluorescence efficiency,and significant fluorescence solvatochromism.In order to expand the applications of this class of materials,it is of great value to focus on the construction of new triarylborane π-systems,detailed study of structure-property relationships,and as well as exploration of intriguing emission properties.In this paper,we have carried out the following two aspects of work based on our previous research.1.We have designed and synthesized a novel triarylborane,Br2-BP-BNMe2,which exhibits a very similar structure to the parent compound,BP-BNMe2.In addition,the photophysical properties of Br2-BP-BNMe2 are also very similar to those of BP-BNMe2,in terms of the absorption and emission maxima positions,and fluorescence solvatochromism.In particular,Br2-BP-BNMe2 exhibits unique temperature-dependent fluorescence behavior.At room temperature,this compound is weakly emissive,but its fluorescence turns significantly stronger abruptly at a specific high temperature.In addition,the fluorescence can maintain very intense even after cooling to r.t.The inherent mechanism for the temperature-dependent fluorescence properties was studied by time-resolved fluorescence test,experiments for influence of O2,as well as the detailed comparisons with BP-BNMe2.We speculated that Br2-BP-BNMe2 might enable fluorescence detection of a specific high temperature.Therefore,Br2-BP-BNMe2 would open a new application field for triarylborane-based π-electron materials.2.We have designed and synthesized two new triarylborane-based o,o’-substituted 2,2’-bithienyls,BT-BNMe2 and BT-BNBn2.Similar to BP-BNMe2 and BP-BNBn2,the steric effect of the amino group has great influence on the conformation of the 2,2’-bithienyl skeleton.The amino and boryl groups are located at the same side with a short B…N distance(3.63 A)for the BT-BNMe2.On the contrary,the amino and boryl groups are arranged on the two opposite sides for BT-BNBn2.From BP-BNBn2 to BT-BNBn2,A large shift of 72 nm in emission was observed.However,BT-BNMe2 and BT-BNBn2 emit fluorescence at the close wavelengths,which is quite different from the much red-shifted fluorescence of BP-BNMe2 than BP-BNBn2.The theoretical calculations indicated that the HOMO and LUMO energy levels of BT-BNMe2 and BT-BNBn2 are almost the same.Thus,HOMO-LUMO gaps are similar,which firmly support the experimental results.Our current experimental results about triarylborane-based o,o’-substituted biaryls are believed to provide a reference for the design and synthesis of new triarylborane-based optoelectronic functional molecules.