?.synthesis And Catalytic Properties Of Novel[PSiP]Pincer Iron Nitrogen Complexes And Cobalt Hydrido Chlorides ?.fabrication And Properties Of Controllable Self-Assembled Stimuli-Responsive Systems Based On Dynamic Covalent Bonds

Supporting ligands have played an important role in regulating the electrical and steric properties of metal complexes.The design and synthesis of novel supporting ligands is an important prerequisite for the development of transition metal complexes.Pincer ligands stabilize their metal complexes through meridional structure.The electrical and steric properties of transition metal complexes can be conveniently modified by changing the substituents on pincer ligands.Transition metal complexes supported by pincer ligands are usually structurally stable and have diverse properties.It often shows remarkable catalytic effects in many kinds of catalytic reactions.Recently,silyl-based[PSiP]pincer ligands have developed rapidly,but their types are few.The formations of metal-silyl complexes are achieved by activating the Si-H bond of[PSiP]pincer ligands.On the one hand,the unique feedback bond between Si and the metal center is conducive to the stability of the transition metal complexes.On the other hand,the trans-effect of Si is beneficial to activating the para-coordinate groups and producing coordinate vacancy,which contribute to improving the reactivity of complexes.Therefore,it is of great significance to construct novel[PSiP]pincer ligands and their transition metal complexes.Isopropyls,with strong electron-donating ability,are beneficial to increase the electron density of metal centers.It is helpful to obtain highly reactive and catalytically active transtion metal complexes,especially nitrogen complexes,which have potentials for the nitrogen fixation under mild conditions.Therefore,the constructions of novel isopropyl-substituted[PSiP]pincer ligands and the corresponding inexpensive transition metal complexes have important research values in organosilicication,nitrogen fixation and homogeneous catalytic reactions.Under the guidance of the above research objectives,we have designed and synthesized two novel isopropyl-substituted N-heterocyclic[PSiP]pincer ligands.And on this basis,we have synthesized a series of PMe3 supported iron nitrogen complexes and cobalt hydrido chlorides,focusing on the chemical properties and catalytic applications of the new complexes.The specific research contents are mainly carried out from the following three aspects:1.On the basis of phenyl-substituted N-heterocyclic[PSiP]pincer ligands,new types of N-heterocyclic[PSiP]pincer ligands L3 and L4,C6H4(NCH2P'Pr2)2SiRH(R=Ph,Me),were designed and synthesized.The isopropyl-substituted pincer ligands L3 and L4 showed distinct properties from the phenyl-substituted pincer ligands L1 and L2.Specifically,the solubilities and the activities of L3 and L4 were significantly increased.2.Different from the phenyl-substituted pincer ligands L1 and L2,isopropyl-substituted pincer ligands L3 and L4 reacted with Fe(PMe)4 in nitrogen atmosphere,obtaining two nitrogen-coordinated iron hydrides 5 and 7,respectively.Their single crystal structures were analyzed by X-ray single crystal diffraction.It is proved that the introduction of strong electron-donating substituents is beneficial to the formation of nitrogen complexes.By comparing the iron nitrogen complex 5 with the analogue iron hydride 3 supported by PMe3,we found that they had similar lengths of Fe-H bonds.Although the isopropyls are beneficial to enhance the electron density of the metal centers,the N2 ligands in nitrogen complexes can share the electrons of Fe centers through the feedback bonds.As a result,the nitrogen complexes were stable at a certain degree.Nitrogen complexes 5 and 7 barely reacted with Fe(PMe)4 in argon,and the PMe3 could not exchange with the N2 ligands in nitrogen complex 7.The above results showed that the N2 ligands were tightly bound to Fe centers in nitrogen complexes 5 and 7.However,CO,which is also conducive to forming feedback bonds with the metal centers,could replace the N2 ligands in nitrogen complex 7 to form an iron carbonyl complex 9,whose molecular structures were also determined.In terms of catalytic applications,nitrogen complexes 5 and 7 had both efficient effects on silication of nitrogen at room temperature.The nitrogen complex 7 was slightly better than nitrogen complex 5.On the effect of nitrogen complex 7,61 equiv of N(SiMe3)3 was achieved after 65 hours,under 1800 equiv of KCs and Me3SiCl.Moreover,the nitrogen complex 5 and iron hydride 3 had very similar catalytic effects on the reaction of dehydrating amides to nitriles,which leaded to reasonable speculations about the catalytic mechanism.3.The cobalt hydrido chlorides 10 and 11 were obtained from the reaction of isopropyl-substituted[PSiP]pincer ligands L3 and L4 with CoCl(PMe)3,respectively.Due to the strong electron-donating of isopropyl,cobalt hydrido chlorides 10 and 11 have longer Co-H bonds than the phenyl-substituted cobalt hydrido chlorides 4 and 2.In terms of catalytic applications,the catalytic effects on hydrosilylation of alkenes of cobalt hydrido chlorides supported by the N-heterocyclic[PSiP]ligands and silylene ligands were preliminarily investigated.The results showed that the phenyl-substituted cobalt hydrido chlorides 4 and 2,the isopropyl-substituted cobalt hydrido chloride 11 and the silylene-supported cobalt hydrido chloride 12,were all efficient on hydrosilylation of alkenes at a certain degree,but the selectivitis were average.Among them,the cobalt hydrido chloride 12 supported by silylene ligand was beneficial to the formation of anti-Markovnikov products,while the cobalt hydrido chloride 11 substituted by isopropyl was beneficial to increase the ratio of Markovnikov products.Supramolecular stimuli-responsive self-assembled systems have potential applications in intelligent materials,biochemistry and other fields.The introduction of dynamic chemical bonds is conducive to design and synthesize novel supramolecular self-assembled nanomaterials with a certain of stability and reversible stimuli-response.In this part,we selected small-molecule aldehydes,biomolecular amino acids and peptides to construct pH-responsive supramolecular self-assembled systems via dynamic imine bonds,and realized multiple reversible control of the morphologies and performances.Mainly study from the following two aspects:1.The ?-amino acid,11-aminoundecanoic acid(AUA),and small molecule aldehydes,benzaldehyde(BA)and naphthalene formaldehyde(NA),were selected as the starting reactants to construct Ph-responsive self-assembled systems via dynamic imine bonds.Since the formation and fracturation of imine bonds were pH reversible,the corresponding supramolecular self-assembled systems realized the reversible modification of multiple responses from vesicles to fibers to supramolecular gels.2.Isomerous phthalaldehydes(OPA,PPA,MPA)and peptides(GlyGly)were selected to constructe pH-responsive vesicles and supramolecular gels systems with different morphologies and properties.The formation and fracturation of dynamic imine bonds in the building blocks were directly affected by changing the pH of the systems.And then the pH-reversible supramolecular self-assembled systems with diverse morphologies and properties were realized.The molecular structures played an important role in dynamic chemical reactions and supramolecular self-assembled behaviors.And the interactions between dynamic chemical reactions and supramolecular self-assembled behaviors were discussed by comparing the differences involving the different isomers.In the process of study,the morpholoies and performances of supramolecular self-assembled systems were studied in detail by means of TEM,SEM,DLS,FTIR,SAXS,etc.,and the formation mechanisms were also discussed and reasonably speculated.