The Studies On Derivatives Of NHC Functionalized By N-containing Heterocyclic Ring

This thesis mainly involves the studies on the derivatives of N-heterocyclic carbenes (NHCs) functionalized by ferrocenyl, N-containing heterocyclic ring and bis(pyrazol-1-yl)methyl fragment. The results are as follows:1. Ferrocenyl-substituted N-heterocyclic carbene (NHC) transition metal complexes have received considerable attention in recent years owing to their extensive applications in homogenous catalysis or electrochemical investigation. On the other hand, NHCs with additional donor groups are drawing more and more attention. Owing to the introduction of the additional donor atoms on the side-arm of NHCs, these functionalized NHCs often exhibit novel coordination modes and reactivity patterns in the reactions with transition metals, and provide relatively stable and efficient catalysts or catalyst precursors. In this paper, a series of NHC-Ag complexes derived from N-ferrocenylmethyl-N-(pyridylmethytl)imidazolium iodides have been synthesized and characterized by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction. The coordination modes of NHCs in these complexes significantly depended on the relative position of nitrogen in heterocyclic ring. For example, reaction of N-ferrocenylmethyl-N’-(2-pyridylmethyl)imidazolium iodide with Ag2O yielded rare2D staircase coordination polymers. Reaction of N-ferrocenylmethyl-N’-(3-pyridylmethyl)imidazolium iodide with Ag2O gave a dimeric NHC-Ag complex through bridging iodide. While N-ferrocenylmethyl-N’-(4-pyridylmethyl)imidazolium iodide with Ag2O yielded novel1D chain coordination polymers with a repeating16-membered macrocyclic unit. However, In these NHC-Ag complexes,2-and4-pyridyl-substituted NHCs act as bridging bidentate ligands through the pyridyl nitrogen and carbene carbon atoms, while3-pyridyl-substituted NHC only acts as a monodentate ligand through the carbene carbon atom. An I/Cl exchange reaction was observed upon recrystallization of these NHC silver iodides in CH2Cl2. In addition, when BF4-or PF6-was used as the counterion, only mononuclear (NHC)2AgX (X=PF6or BF4) complexes were obtained. Carbene palladium complexes were obtained in the reactions of corresponding ferrocenyl and quinolyl or pyrazolyl bisfunctionalized imidazolium with Pd(OAc)2under air-and moisture-free conditions. In the meanwhile the reactions in air led to oxidation and decomposition of the ligand, yielding novel Pd-NO2complexes while no similar result was observed in the reaction of analogous reacntion of pyridinyl and ferrocenyl bisfunctionalized imidazolium with Pd(OAc)2. Preliminary searching was also conducted for the source of nitrogen dioxide.2. The functionalized bis(pyrazol-1-yl)methanes by organic functional groups on the bridging carbon atom have drawn extensive attention in recent years, owing to their versatile coordination chemistry towards main group and transition metals. We reason that NHCs bearing bis(pyrazol-1-yl)methyl fragment can unite the privileges and act as very useful ligands for transition metals. Herein, a series of N-heterocyclic carbene silver and palladium complexes derived from N-[bis(pyrazol-1-yl)methyl] phenyl-N’-benzylimidazolium and N-[bis(pyrazol-1-yl)methyl]phenoxymethylene-N’-benzylimidazolium salts have been synthesized and characterized by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction. These NHCs with bis(pyrazol-1-yl)methyl groups show three different coordination modes in these complexes. For example,N-[bis(pyrazol-1-yl)methyl]phenyl-N’-benzylimidazol-2-ylidene (L) and N-[bis(3,5-dimethylpyrazol-l-yl)methyl]phenyl-N’-benzylimidazol-2-ylidene (L’) act as a monodentate ligand through the carbene carbon in cationic [L2Ag][AgCl2] and [L’4Ag3Br2][AgBr2] complexes. A bridging [C,N] bidentate coordination mode, through one pyrazolyl nitrogen and the carbene carbon atoms to two palladium centers, was observed in macrocyclic complex L’2Pd2Br2. While in the coordination polymer [L2Ag2]n[PF6]2n and macrocyclic complex [L’2Ag2][PF6]2, L and L’act as bridging [C,N,N] tridentate ligands through two pyrazolyl nitrogen and the carbene carbon atoms. Although N-[bis(pyrazol-1-yl)methyl]phenoxymethylene-N’-benzylimidazol-2-ylidene (L") also acts as a bridging [C,N] bidentate ligand in L"2Ag2Cl2and [C,N,N] tridentate ligand in L"2Ag2X2(X=BF4or PF6), like L’ and L in L’2Pd2Br2as well as [L2Ag2]n[PF6]2n and [L’2Ag2][PF6]2, respectively, a obvious difference among them is present. L" prefers to coordinate to two silver atoms in the form of head (carbene)-to tail (nitrogen) coordination mode, while L and L’ show head (carbene)-to head (carbene) and tail (nitrogen)-to tail (nitrogen) coordination modes to two silver atoms. Additionally, the luminescence properties of these silver complexes have been studied.3. The three-component coupling reaction of alkyne, aldehyde and amine to generate propargylamines catalyzed by transition metals has attracted considerable attention in recent years. Silver complexes exhibited superior catalytic effectiveness for this three-component coupling reaction, but only several NHC-Ag systems were exploited as catalysts for the reaction, and most of them were mononuclear silver complexes. Herein, we find that our NHC-Ag complexes exhibit excellent catalytic activity in the three-component coupling reaction of phenylacetylene, aldehyde and piperidine to generate propargylamines, and the catalyzed reactions can be carried out in air.