Tab Ligated Pd/Pd-Ag-NHC Complexes:Design,Synthesis And Catalysis

In recent years,NHCs have been the research hotspot owing to their extraordinary advantages of non-toxic,facile preparation and forming robust M-Ccarbene bonds to construct stable catalysts.In the field of transitional metal NHC complexs,the chemists have been committed to synthesize efficient NHC complexes catalysts with novel structures.In addition,our group have already reported a zwitterionic thiolate ligand(Tab=4-(trimethyammonio)benzenethiolate),which can coordinate towards various metals to form unique complexes.Partial complexes have been successfully used as organic catalysts,photocatalysts,biological fluorescent probe and so on.This thesis combined the advantages of NHCs and Tab by introducing the auxiliary ligand Tab to build M-NHC-Tab complexes.Then we explored catalytic properties of these complexes for Suzuki-Miyaura coupling reactions in water.In this thesis,we stated the reactions of the precursor traps-Pd(IMe)2Cl2(1,IMe =1,3-dimethyl-imidazoline-2-ylidene)with Tab/TabHPF6 in the absence/presence of additional Ag(I)source(AgOTf/[Ag(IMe)2][AgCl2],OTf-=CF3SO3-).We explored their reactivity and isolated nine Pd(?)/Pd(?)-Ag(?)-IMe-Tab complexes,namely,trans-[Pd(IMe)2(Tab)2](OTf)2(2),cis-[Pd(IMe)2(Tab)2](OTf)(Cl)(3a),cis-[Pd(IMe)2(Tab)2](PF6)2·MeCN(3b·MeCN),[Pd4Ag4(IMe)8(Tab)10](OTf)i2(3c),[Pd2(IMe)4(Tab)2](PF6)4·2MeCN(4`2MeCN),[Pd4(IMe)4(Tab)6](OTf)6(Cl)2(5),[Pd4Ag4(IMe)8(Tab)10](PF6)12(6),[Pd(IMe)(Tab)3](PF6)o.75(Cl)1.25·0.5MeCN(7·0.5MeCN)and trans-[Pd(IMe)2(Tab)(TabO2)](OTf)(Cl)0.5MeOH(8·0.5MeOH).Meanwhile,we determined the catalytic performance of complexes 2,5 and 8.The research content mainly includes several parts as follows:1)We summarized the study progress of the vulcanized M-NHC complexes' structures and catalytic properties.2)We synthesized and isolated nine Pd(?)/Pd(?)-Ag(?)-IMe-Tab complexes by liquid phase reactions and diffusion pathway(2,3a-c,4-8).Thereinto,compounds 2,4,5,6,7,8 have been characterized by means of FT-IR,NMR,ESI-MS,EA and X-ray single crystal diffraction.Three byproducts 3a,3b and 3c have been characterized by X-ray single crystal diffraction only.Notably,the Pd-S framework(Pd4S4)of 5 can be considered as a parallelogram wherein each Pd atom is located in every S-S edge's center.And,the overall skeleton of 6 is an oval-shaped unit of Pd4Ag4S10 which is composed by an two edge-fused norbornane-like framework(Pd2Ag4S6)and two PdS2 motifs at the polar positions.5 and 6 both possess typical Pd…Pd(5),Pd…Ag and Ag…Ag(6)separations.3)We carried out the Suzuki-Miyaura coupling reactions in water with 2,5 and 8 acting as the catalysts.5 turned out to be the better one,which can catalyze the reaction of 4-bromoacetophenone and phenylboronic acid efficiently(Yield:99%)with very low Pd loading(0.0005 mol%);5 can catalyze the couplings between various bromide substrates bearing electronwithdrawing and electrondonating substituents and phenylboronic acid with high activity(Yield:41%-99%)in the conditions of 100 ?,6 h and low Pd loading(0.01?0.1 mol%).The good catalytic properties of the compounds mentioned above highlight the potential of applying this type of metallic clusters as catalysts for organic transformations in environmentally benign media.