Mechanism Study On Iron-catalyzed Hydrosilylation Of Divinyldisiloxane With Silane

The silicone material is widely used in various areas of aerospace,electronics, machinery, chemicals, medicine, etc., and greatlycontributed to the research on various aspects, it has become animportant new material in the national economy. This is mainlyattributed to the valuable properties of silicone materials, such ashigh and low temperature resistance, moisture proof, insulation,corrosion resistance, ageing resistance and physiological inertia, etc.Simultaneously, silicone materials are species diversity, liquid(silicone oil), elastomer (silicone rubber), resin, adhesive, latex, etc.However, silicone materials are not naturally occurring substances.The effective ways of the synthesis of such compounds are necessaryto explore. Hydrosilylation of unsaturated organic compounds andsilicon compounds containing Si─H bond along with catalysts is animportant means of preparing organosilicon compounds, and thetransition metal catalyst is most effective. Over the last few decades,researchers focused on noble transition metal catalysts (Pt, Rh, Ru,Pd, Co, etc.) and catalytic mechanisms, and achieved gratifyingresults. In recent years, researchers increasingly focus on the development and use of the new transition metal catalysts with lowcost, environmentally friendly, high selectivity and activity and othercharacteristics, as well as exploring the corresponding catalyticmechanism of hydrosilylation. However, reaction intermediates aredifficultly detected just by experimental methods, the quantumchemical calculation combining with experimental methods toprovide comprehensive and thorough understanding of reactionmechanisms becomes important and meaningful.A green and cheap iron complex catalyst with good catalyticperformance is chosen in the present paper. The purpose of this workis to clarify the detailed mechanism of iron–catalyzed hydrosilylationof1,3-divinyldisiloxane and Me3SiH at B3LYP level of densityfunctional theory, with the hopes of shedding light on the formation ofimportant intermediates and transition states, as well as the energybarrier of possible pathways, so as to provide theoretical guidance forthe experimental studies. The main contents and results are asfollows.(1) The advances in new reaction mechanisms of olefinhydrosilylation catalyzed by several transition metal complexes arereviewed. In particular, we highlight the different mechanisticpathways of Pd, Rh, Ru, Zr, etc complexes.(2) The16e silyl species CpFe(CO)SiMe3(A), which is preparedfrom the precursor Cp(CO)FeMe (R), is considered to be the activespecies. And there are two possible ways to obtain A, that is path1ofdissociation of methane through transition states TSR1-A and path2of dissociation of acetaldehyde through transition states TSR2-A.Path2is favored due to its relatively stable intermediates and barrier span.(3) On the basis of previous studies on C–C bond cleavage oforganonitriles, one CO ligand in precursor Cp(CO)FeMe (R) is releasedby photolysis to give Cp(CO)FeMe, which reacts with Me3SiH throughoxidative addition of Si–H bond to give a hydride complexCp(CO)FeMe(H)(SiMe3). However, we never located complexCpFe(CO)Me(H)(SiMe3), which may owing to its destability by thesteric repulsion. Instead, a η2-H complex PC1is formed after COdissociation, or forms complex CpFe(CO){C(O)Me}(R2) withoutdecarbonylation.(4) The complete mechanism from A is divided into three parts:(i)coordination of1,3-divinyldisiloxane and insertion of the C=C doublebond into the Fe–Si bond obtaining C;(ii) Due to the steric repulsion ofmethyl in isomer C, a moe stable complex G1obtained through aseries of isomerization from C;(iii) A hydrido-bridged intermediate Kand decomposition transition states TSK-A is important for productformation and catalyst regeneration. Overall, it was found that thedehydrogenative silylation at one vinyl group and hydrogenation atthe other vinyl group of divinyldisiloxane take place. In other words,the hydrogen introduced at the vinyl α-carbon comes from thehydrosilane added, and the hydrogen introduced at the vinyl β-carbonoriginates from the hydrogen on the β-carbon in the other vinyl group.It conforms well with the experimental results.