Silicon Or Germanium Based Frustrated Lewis Pairs,Synthesis And Activity

Small molecule activation has very important research significance in the fields of chemistry,chemical engineering and energy,but it is also very challenging.The construction of efficient main group element catalytic systems to activate small molecules has been a leading research topic.Recently,the frustrated Lewis pair?FLP?system is widely used for the activation of small molecules and exhibits properties similar to transition metals.However,the Lewis acid are mainly expensive perfluoroaromatic boranes and derivatives,and their application scope has certain limitations;for example,borane easily forms a stable adduct with alcohol,catalytic hydrogenation of carbonyl compounds is greatly restricted.This project is based on the controllable structure of coordinated saturated organic silicon or germanium compounds,adjustable Lewis acidity,construction frustrated Lewis pairs with organic phosphine.A new type of frustrated Lewis pairs with saturated silane or germane as the Lewis acid and a large hindered organic phosphine as the Lewis base was constructed.The electronic effects of substituents on silicon or germanium atoms in new FLPs and the effects of steric hindrance on their reactivity were systematically studied,and the reaction mechanism for their activation of small molecule compounds was explored.The research content includes the following two parts:1.An attempt was made to synthesize?C₆F₅?₃GeCH₂P^tBu₂ by the reaction of ^tBu₂PCH₂Li?98?with tris?pentafluorophenyl?chlorogermanane,but it was not successful.Finally,an ionic compound?C₆F₅?₂GeCH?C₆F₄?P^tBu₂ was obtained.A new type of frustrated Lewis pair ^tBu₂PCH₂GeCl₃?FLP,Ge/P?was synthesized by reacting ^tBu₂PCH₂Li?98?with germanium tetrachloride.The frustrated Lewis pair was found to have a certain reactivity.^tBu₂PCH₂GeCl₃ is subjected to cycloaddition reaction with alkyne dimethyl butynedioate?MeO₂CC?CCO₂Me?,ethyl propynate?HC?CO₂Et?,olefin maleic anhydride?C₄H₂O₃?;Addition reaction with C=O?S?bond of phenyl isothiocyanate?PhNCS?and p-methylbenzene isocyanate?MePhNCO?,to obtain ionic five-membered ring structure products,in which the reaction of ^tBu₂PCH₂GeCl₃ and p-methylbenzene isocyanate is reversible;^tBu₂PCH₂GeCl₃ reacts with carbon tetrachloride?CCl₄?to break the C-Cl bond to produce an insertion reaction product.2.The reaction of ^tBu₂PCH₂Li?98?with tris?pentafluorophenyl?chlorosilane also failed to obtain the intramolecular frustrated Lewis pair,but the reaction with silicon tetrachloride produced the frustrated Lewis pair ^tBu₂PCH₂SiCl₃?FLP,Si/P?.The frustrated Lewis pair?^tBu₂PCH₂SiCl₃?react with dimethyl butynedioate?MeO₂CC?CCO₂Me?,ethyl propionate?HC?CO₂Et?,maleic anhydride?C₄H₂O₃?,phenyl isothiocyanate?PhNCS?,p-methylbenzene isocyanate?MePhNCO?to obtain the corresponding five-membered ring structure product;^tBu₂PCH₂SiCl₃ performs C-X bond insertion reaction with carbontetrachloride?CCl₄?and benzyl bromide?PhCH₂Br?.The above results show that ^tBu₂PCH₂SiCl₃ has higher activity than ^tBu₂PCH₂GeCl₃ in the reaction with various substrates because the silane with the same structure has stronger Lewis acid than germanane.