Cyclotrimerization Of Terminal Alkynes Catalyzed By Ruthenium Complexes

Cyclotrimerization of terminal alkynes catalyzed by ruthenium complexes can createbenzene derivatives simplely, it is the atom economy method for the synthesis of benzene.The regioseletivity of cyclotrimerization is keynote of the reaction. The thesis focuses onthe cyclotrimerization of alkynes catalyzed by two types of Ru complexes containing Tpand bipy ligands, in order to study the effect of steric effect、eletronic effect of ligands onregioseletivity of cyclotrimerization.The main work can be summarized as follows:1. Cyclotrimerization of terminal alkynes (hexyne phenylacetylene and ethylpropiolate) catalyzed by TpRuCl(PPh3)2is studied. In THF solution, ethyl propiolate iscyclotrimerized, the conversion of1,2,4-tributyl benzene is1.2%, and the regioseletivity ofcyclotrimerization is100%. No cyclotrimerization occurs when hexyne andphenylacetylene are used to be substrates. Adding AgOTf and H2O, ethyl propiolate istransfered to1,2,4-tributybenzene and1,3,5-tributylbenzen, the conversion rate is21%,and molar ratio is4.4:1. In DMF solution, hexyne and phenylacetylene have no catalyzedcyclotrimerization reaction; ethyl propiolate is catalyzed to form1,2,4-tributylbenzene and1,3,5-tributylbenzene, the conversion rate is38%, and the molar ratio is1.77:1. AddingAgOTf and H2O, the conversion rate of ethyl propiolate reaches87%, the molar ration of1,2,4-tributybenzene and1,3,5-tributy benzene is1.84:1. The mechanism can be postulatedthat two ethyl propiolate molecules replace PPh3ligands of TpRuCl(PPh3)2to createπ-alkyne complexes, which is then transferred to Ru heterocyclopentadiene complexes viaoxidative coupling. The Cl in TpRuCl(PPh3)2is replaced by the third ethyl propiolatemolecule, to generate Ru-heterocycloheptatrienes or7-Ru heterobicyclo[2.2.1]-2,5-heptadienes by insertion or diene addition reaction. Benzene derivatives arethen formed by reductive elimination. C2H5OC(O)-in ethyl propiolate has the stongestelectron-withdrawing ability, which is in favor of the formation of catalytic intermediatesand the steric hindrance of Tp affects the regioselectivity of1,2,4-tributybenzene.2. Cyclotrimerization of three terminal alkynes (hexyne, phenylacetylene and ethylpropiolate) catalyzed by [cis-Ru(L)2Cl2]Cl2H2O (L=dmbp, bpda) and[cis-Ru(L)2(H2O)2](CF3SO3)3has been studied. In the presence of water,cyclotrimerization of ethyl propiolate catalyzed by [cis-Ru(bpda)2(H2O)2](CF3SO3)3has higher regioseletivity, the molar ratio of1,2,4-tributybenzene and1,3,5-tributybenzene is9:1. The catalytic mechanism is proposed to to be a [2+2+2] cycloaddition reaction,Ru-heterocycloheptatrienes or7-Ru heterobicyclo[2.2.1]-2,5-heptadienes are postulated tobe the key intermediates. The regioseletivity of cyclotrimerization is affected by theintramolecular hydrogen bond between the hydrated formyl group in the6-position ofbipyridine ligand and the carbonyl in ethyl propiolate ligand.