Olefin Hydrosilylation Catalyzed By Cobalt Hydrides

As one of the most widely used homogeneous catalytic reactions in industry,olefin hydrosilylation has attracted more and more attention,but at present,the traditional Pt metal catalyst is still dominant.Although Pt metal catalyst has excellent catalytic performance,it is expensive and toxic.Therefore,in recent years,people have focused on non-precious-metal complexes.Some non-precious-metal complexes have achieved good catalytic transformation,but there are still some disadvantages,such as large amount of catalyst loading,poor universality of substrate,side reactions and so on.There is no doubt that solving these problems depends on our deeper understanding of the reaction mechanism and the in-depth exploration of the design and synthesis of metal complexes.Compared with phosphine ligands and carbene ligands,the non-precious-metal complexes supported by silylene ligands show more and more advantages in homogeneous catalysis,but there are few studies on silylene ligands compared with the former.In particular,the non-precious-metal complexes supported by NHSi ligands catalyzed olefin hydrosilylation.It has been found that cobalt chlorides have excellent catalytic transformation in olefin hydrosilylation.In the study of catalytic reaction mechanism,it is found that the real catalyst is cobalt hydrides.If cobalt hydries can be used as catalysts directly,it will be more helpful to promote the understanding of catalytic mechanism.However,it is usually difficult to separate cobalt hydrides due to the active nature of metal hydrides.Thus,this paper is mainly divided into the following two parts:1.Based on the previous work of our research group,the catalytic activity of cobalt hydrides 1,2 and 3 bearing different pincer ligands on olefin hydrosilylation were studied,and the effects of different phosphine ligands and silylene ligands on the catalytic effect and selectivity were studied in detail.The experimental results show that 1 and 3 have excellent catalytic efficiency and selectivity for olefin hydrosilylation.Compared with complexes 1 and 2 supported by phosphine ligands,the introduction of silylene in silylene complex 3 transforms the selectivity of aromatic olefin hydrosilylation from the Anti-Markovnikov product of 1 to the Markovnikov product.The separation yields of complex 1 for most products are between 76%-94%,and the catalytic effect for aromatic substrates is better than that for aliphatic substrates.The electronic property of the substituents on the phenyl ring of aromatic olefins have little effect on the catalytic results.The hydrosilylation products of aromatic olefins catalyzed by complex 3 are mainly Markovnikov products.The hydrosilylation products of aliphatic olefins are mainly Anti-Markovnikov products.Complex 3 can provides moderate to excellent selectivity with good yields on aromatic olefins with different substituents.The catalytic reaction mechanism was studied in detail by various exploring experiments.The pincer carbonyl cobalt chlorides 9-11 were obtained from the reaction of 1-3 with CO,respectively.2.Two[P,Si]chelated cobalt hydrides 5-6 were synthesized.And the catalytic activity of 5-6 for olefin hydrosilylation was studied in detail.The results show that cobalt hydrides 5-6 with different phosphine ligands have excellent catalytic effect on olefin hydrosilylation,and the selectivity is same.Markovnikov product is main product for aromatic olefins,while Anti-Markovnikov is main product for aliphatic olefins.Under the same conditions,the catalytic effect of 5 is better than 6.The study on the reaction mechanism shows that in this catalytic cycle,the silyl cobalt(Ⅰ)intermediate formed by the reaction of cobalt hydride 5 with silane is the real catalyst.