Synthesis And Catalytic Applications Of Iron,Cobalt And Nickel Complexes Supported By N-Heterocyclic Silylenes(NHSis)

Silylenes,the heavier congeners of carbenes,have unique?-donating/?-accepting and steric hindrance properties.Transition metal(TM)complexes containing silylene ligands not only exhibit rich diversity in coordination chemistry,such as coordination modes,spatial properties and electronic structures,but also exhibit high catalytic activity in organic synthesis and homogeneous catalysis.It is considered to be of great value in organosilicon chemistry and applied chemistry.The construction of cheap iron,cobalt and nickel complexes with silylenes coordination is an attractive and challenging subject in organometallic chemistry.Transition metal hydrides have been widely used in the research field of organometallic chemistry.The application value of transition metal hydrides as catalysts or active intermediates in organic catalytic reactions is often explored.Chemists are paying more and more attention to the construction of low-cost metal hydrides with high activity and selectivity and the exploration of their homogeneous catalytic applications through the regulation of electronic and spatial characteristics of cheap metal centers by ligands.This dissertation was divided into six parts.1.The reactions of chlorosilylene L1[:Si(Cl){(NtBu)2CPh}]with Fe(PMe3)4,Co(PMe3)4 and Ni(PMe3)4 resulted in the formation of monovalent metal chlorides 1,3 and 4 via the activation of Si(II)-Cl bond.These complexes are supported by silylene and PMe3 simultaneously.The formation route of mono-electron oxidation addition of metal centers was verified by in-situ mass spectrometry.Due to the decrease of ?-donating ability of ligands and reduction ability of metal centers,only replacement process occured in the reactions of L1 with Ni(COD)2,CoCl(PMe3)3 and CoBr(PMe3)3.Complexes 5,1 and 6 were obatained.The effects of silylene ligands on the electrical and spatial properties of metal complexes were discussed in detail.2.When tert-butoxysilylene L2[:Si(OtBu){(NtBu)2CPh}]was treated with Fe(PMe3)4 and Ni(PMe3)4 respectively,iron hydride 7 was formed through the Csp3-H bond activation and silylene-liagted Ni(0)complexe 8 was constructed by the replacement of PMe3.These results revealed the influence of silylenes on the coordination environment of metal centers.3.Complex 1 reacted with pincer ligand L3 HSiMe(NCH2PPh2)2C6H4 to give the silylene Co(III)hydride 11 through chelate-assisted Si-H activation.Complex 11 was used as an efficient precatalyst for Kumada cross-coupling reactions.Compared with the related complex 10 supported only by trimethylphosphine,complex 6 as catalyst supported by both chlorosilylene and trimethylphosphine exhibited the more efficient performance for the Kumada cross-coupling reactions.A novel catalytic radical mechanism was suggested and experimentally verified.As an intermediate silylene cobalt(II)chloride 11d was isolated and structurally characterized.4.We reported the synthesis of a novel pyridine-based bidentate NHSi ligand L4,and the first bis-chelate disilylene iron hydride[(Si,N)(Si,C)Fe(H)(PMe3)](13)and monosilylene iron hydride[(Si,C)Fe(H)(PMe3)3](14)through Csp2-H activation of the NHSi ligand.DFT calculations indicated the multiple bonding character of the Fe(II)-Si(II)bonds and the ?-back-donation from Fe(II)to Si(II)center.Moreover,the strong ?-donor character of ligand L4 enabled 13 to act as an efficient catalyst for the hydroboration reaction of carbonyl compounds at room temperature.Chemoselective hydroboration was attained under this condition.This might be the first example of hydroboration of ketones and aldehydes catalyzed by silylene hydrido iron complex.A catalytic mechanism was suggested and partially-experimentally verified.Complex 13 was unstable in CO and CO2 atmosphere and ligand dissociation occured.CoCl(PMe3)3 and CoMe(PMe3)4 react with ligand L4 to furnished complexes 21 and 22 by one neutral(Si,N)-chelating coordination and one anionic(Si,C)-chelating coordination,respectively.5.A novel bis(silylene)pincer ligand L5[Si:CSi:]was synthesized and characterized.Fe(PMe3)4 reacted with L5 to give a pincer-type iron hydride 23 by activating the Csp2-H bond.At the same time,due to the influence of silylene on the electrical properties and steric hindrance of metal center,the coordination of N2 molecule was realized,and the formation of pincer-type Fe(I)-N2 complex 24 was detected.Solvent polarity also affected the coordination reaction between L5 and CoCI(PMe3)3.Three different pincer hydido cobalt complexes 25,26 and 27 were isolated in Et2O and THF solutions,respectively.6.The molecular structure of the pincer-type metal complexes 29[[(Ph2P-(C6H4))2P(O)]Fe(H)(PMe3)2 and 30[(Ph2P-(C6H4))2P(O)]Co(PMe3)2 was characterized by X-ray diffraction analysis.The reaction intermediate 30a of L6 with Co(PMe3)4 was detected by IR,in-situ NMR and GC.The catalytic performance of pincer-type Fe,Ni,and Co complexes for the hydrosilylation of aldehydes and ketones was explored.With a catalyst loading of 2 mol%,complex 29 displayed the best catalytic activity for the hydrosilylation by using(EtO)3SiH as the hydrogen source under mild conditions.The novel complexes involved in this dissertation were characterized by IR,NMR,MS and X-ray diffraction analysis.