Treatment of N-heterocyclic silylene Si[N(tBu)CH]2 and [(η3-C3H5)PdCl]2 in toluene led to the formation of mononuclear complex (η3-C3H5)Pd{Si[N(tBu)CH]2}Cl, the silicon analogue to N-heterocyclic carbene complex (η3-C3H5)Pd{C[N(tBu)CH]2}Cl. Complex was characterized with 1H NMR , 13C NMR and Elemental analyses. In this paper, the important dichloride precursor to the N-heterocyclic silylene, SiCl2{N[(2,6-iPr)2C6H3]CH}2 was synthesized with a new method without using HSiCl3. The diimine reacts with dilithium naphthalene in THF resulting in the dilithium derivative, which reacts with SiCl4 to give the dichloride precursor. The product was obtained in excellent yield and characterized by IR and 1H NMR spectrum.N-heterocyclic silylene is currently an area of heavy research activity. This paper is focusing on the catalysis of palladium–(N-heterocyclic silylene) complexes, which is a type of catalyst with potential value. By using palladium N-heterocyclic silylene complex as the primary catalyst, styrene and aryl bromide as reactants ,sodium acetate as base ,tetrabutyl ammonium bromide as phase transfer catalyst, react in N,N-dimethyl acetamide .In addition, through change some factors such as temperature, reaction time, and reactants, then test the product by GC and GC-MS to analysis the catalytic behaviour of the palladium-(N-heterocyclic silylene) complexes.From the experimental datum, The effect of temperature on Heck reaction was investigated by using p-bromoacetophenone and styrene as reactant at 80 and 140℃, respectively. It reveals that the Pd(II) catalyst (η3-C3H5)Pd{Si[N(tBu)CH]2}Cl was activated in situ by NaOAc in DMA at high temperature (140℃) to achieve a good yield, whereas a moderate yield of coupling product was obtained at a lower temperature (80 oC) for a longer time.The effect of substituents of aryl bromides on Heck reaction was preliminarily investigated with the reaction of styrene and some selected aryl bromides p-bromoacetophenone, p-bromoanisole and p-bromotoluene, respectively, under the same reaction conditions. It reveals that the time for p-bromoacetophenone which bears an electron-withdrawing substituent was shorter (about 4 h) than those of other bromides, meanwhile this case gives the highest yield ( about 99%). In contrast, p-bromoanisole and p-bromotoluene which contain electron-donating substituents show a lower yield (60%, 48%, respectively) in a longer time. Unfortunately, treatment of p-chloroacetophenone and styrene under similar Heck reaction conditions led to no formation of the expected product.A comparison of the catalytic activity of the corresponding palladium–(N-heterocyclic carbene) complex was performed. Considering of that the coupling reaction of styrene and p-bromoacetophenone catalysed by complex gave the highest yield, a corresponding reaction was conducted for complex under the same condition. It was found that the reaction gave the product in a yield of about 91% which was little lower than that of for complex (99%). However, on coupling product was found for other corresponding reactions.In conclusion, palladium–(N-heterocyclic silylene) complex exhibits higher activity and selectivity in the Heck reaction of aryl bromides with styrene on small amount of using, and can reach to higher yield. |