Palladium-Catalyzed Silylation Of Alkynyl Bromides And Benzyl Halides

In the field of organosilicon research,the construction of silicon-carbon bonds is regarded as one of the themes and important cornerstones of organosilicon chemistry.Among them,transition-metal-catalyzed cross-coupling reaction is one of the most direct and effective methods for constructing silicon-carbon bonds.This method has the advantages of mild conditions,high reaction efficiency,and good selectivity.At present,transition-metal-catalyzed cross coupling reactions of hydrosilanes with aryl halides(Csp~2)have become an effective method for the synthesis of structurally diverse aryl silanes with or without silicon-stereogenic silanes.However,previous studies have mainly focused on the cross coupling reactions of aryl halides with hydrosilanes.In contrast,alkyl halides(Csp~3)and alkynyl halides(Csp),as a class of important electrophilic reagents,are rarely or are not used in this reaction.Therefore,the work of this thesis is mainly focused on palladium-catalyzed silicon-carbon cross-coupling reactions involving alkyl halides or alkynyl halides,using hydrosilane as a silicon source.The main results of the research paper are as follows:(1)A novel palladium-catalyzed cross-coupling reaction of alkynyl bromides and dihydrosilanes to access alkynylsilane has been successfully established for the first time.The experimental results show that this reaction is effective for the synthesis of a series of alkynyl bromides and dihydrosilanes or monohydrosilanes,including aryl alkynyl bromide and aliphatic alkynyl bromide,with medium or high yield and good chemical selectivity.In addition,the author also studied the asymmetric version of cross coupling reaction with prochiral dihydrosilanes in the presence of chiral phosphine ligands,and it was found for the first time that the synthesis of silicon-stereogenic alkynylsilane could be achieved with moderate enantioselectivity.It is worth noting that this is the first example of palladium catalyzed C(sp)-Si cross coupling reaction with alkynyl bromides and dihydrosilanes for preparation of various functionalized alkynylsilanes under mild conditions.(2)A novel palladium-catalyzed cross-coupling reaction of alkyl halides and dihydrosilanes to access alkylsilane has also been successfully established for the construction of C(sp~3)-Si bonds in this work.Through optimizing of reaction conditions,including palladium catalysts,phosphine ligands,and other reaction conditions,a palladium-catalyzed cross coupling reaction of benzyl halides with hydrosilanes was successfully established.The reaction can proceed smoothly under mild conditions for a wide range of substrates,including various electron-rich and electron-deficient benzyl bromide derivatives.Secondly,a variety of secondary or tertiary hydrosilanes can also be applied to the cross coupling reaction to achieve the desired alkylsilanes with moderate to good yields.The experimental results of this work provide a general method for the convenient and efficient synthesis of benzylsilanes.In summary,the silicon-carbon cross-coupling reactions of hydrosilanes with benzyl halide(Csp~3)or alkynyl bromide(Csp)have been achieved using a catalytic system composed of palladium with different phosphine ligands,providing a practical approach for the facile synthesis of benzylsilanes and alkynylsilanes with high chemoselectivities and yields in most cases.