Room Temperature Hydration Of Alkynes Catalyzed By(Isocyanide)gold Complexes And Carbene Gold Complexes

The hydration of alkynes is one of the important and the highest atomic economy methods(with 100%)to convert alkynes into carbonyl compounds,which is also known as one of the benchmark to measure the catalytic activity of gold complexes and is of great interest by the researchers.Mercury(?)salts had been traditionally used to catalyze the hydration of alkyne with effective and reliable conversions.However,mercury(?)salts are toxic,difficult recycle and treat,and also harmful to products and environment.It is difficult for mercury catalysts to meet the increasing requirement of environmental protection and their widespread using in modern industry is also forbidden.Even though Br(?)nsted acids were also found to have catalytic activity for the hydration of alkynes,the processes require,in most cases,stoichiometric or excess amounts of acids and only electron-rich alkynes as the substrates can lead to high conversions.To overcome the disadvantages of mercury(?)salts and Br(?)nsted acids,a variety of organometallic catalysts were explored,such as complexes containing Pt,Ag,Ru,Au,and even bimetallic catalysts in the past thirty years.Among them,the unique catalytic ability of gold(?)and gold(?)has attracted many attentions,because gold centers show high affinity to activate C=C triple bonds through nucleophilic attack.Though gold complexes were thought to be potential and excellent catalysts for alkynes hydration,most of the reactions catalyzed by gold complexes require high reaction temperature,such as 120 ? for the hydration catalyzed by gold/N-heterocyc lic carbenes(Au-NHC)/AgSbF6,Au-NHC/HSbF6,100-150? fur Bis(phosphane)gold(I),100? for NaAuCl4,80 ? for Au-NHC and Au-SH/SO3H-PMO(Et),70? for(Ph3P)AuCH3 in the presence of H2SO4,65? for abnormal Au-NHC,and reflux temperature.Obviously,it is still a challenge to develop more effective gold catalysts that can catalyze for hydration of alkyries even at room temperature.Room temperature hydration is of great significance,since it benefits to the energy-saving processes and helps to overcome byproducts and enhance the selectivity of the reaction.In the past decade,an increasing number of studies have focused on the preparation of gold isocyanide complexes(RNC-Au)and the investigation of their structure and properties.RNC-Au complexes were studied more on optical properties and liquid crystals.By far,RNC-Au complexes were mainly used as the starting materials for the synthesis of other novel catalysts.As far as we known,there were almost no examples that RNC-Au complex was directly used as catalyst in not only alkynes hydration but also other reactions.In this work,we selected two simple structures of(isocyanide)gold(?)as catalysts to catalyze the hydration of alkynes from the two aspects of experiment and theory.In addition,two NHC-Au catalysts,as well as two NAC-Au catalysts were also chosen as the catalysts to hydrate alkynes,and the comparison with RNC-Au complexes in catalytic activity was made.The contents and results are summarized as follows:(1)The two gold isocyanide complexes(CyNC)AuCl(Cat-1)and(2,6-Me2C6H3)AuCl(Cat-2),two NHC-gold(?)complexes IMesAuCl[IMes=(2,4,6-trimethylphenyl)imidazol-2-ylidene]and IPrAuCl[IPr-(1,3-bis(diisopropyl)imidazol-2-yliene],two NAC-gold(I)complexes,chloro[(cyclohexy lamino)(diethy lamino)methy lene]-gold(NAC1)and chloro[(diethylamino)[(2,6-dimethylphenyl)amino)]methylene]-gold(NAC2)were synthesized according the general literature procedures.The six synthetic complexes were characterized by elemental analysis,1H-NMR,13C-NMRand ESI.Their molecular structures were confirmed.(2)The hydration of phenylacetylene was selected as a probe to investigate the activity of the catalyst.The reaction conditions were optimized from the factors of cocatalyst,solvent,amount of catalyst,volume ratio of solvent and water.The optimized conditions are:0.5mmol substrate,5mol%cat-1,5mol%KB(C6F5)4,methanol as solvent,the volume ratio of 1:1,room temperature,and 24h reaction time.To explore the substrate scope of this catalytic system,the hydration of different alkynes was investigated under the standard conditions.Cat-1 was found to show excellent catalytic reactivity at room temperature for a wide range of substrates,including electron-rich and electron-deficient alkynes,aromatic and non-aromatic alkynes.In total seventeen alkynes were investigated,and the isolated or GC yields of fifteen alkynes are larger than 95%.Cat-2 was also investigated and its catalytic ability was compared with that of Cat-1 in the hydration of 4-methoxyphenylacetylene.The reaction catalyzed by Cat-2 or Cat-1 can proceed quite well at room temperature in the 8 hours.The Cat-1 showed slightly high activity than Cat-2.This is the first report about the catalytic activity of(isocyanide)gold as precursor for synthesis of carbine gold which show the comparable activity with the carbine gold.(3)To further understand the hydration mechanism catalyzed by Cat-1,a DFT based theoretical investigation of transition and active species was performed.Hydration mechanism of the reaction catalyzed by gold isocyanide was proposed.(4)Under the optimal conditions and the same amount of catalysts,RNC-Au,NHC-Au and NAC-Au with the different anions(BF4-.SbF6-and B(C6F5)4-)as counterion were respectively used to catalyze the hydration of phenylacetylene.According to the kinetic performance in the hydration,IPrAuCl/KB(C6F5)4 was found to show the best catalytic activity.NACl/KB(C6F5)4 and NAC2/KB(C6F5)4 were also more active than the reported ones in literature.The reaction time was shortened from 5 days to 7 hours for the catalysts with B(C6F5)4-counterion.0.5mol%IPrAuCl/KB(C6F5)4 were tested to catalyze the hydration of four alkynes(cyclohexylacetylene,4-methoxyphenylacetylene,2-propynylbenzene,and 1-octyne)with excellent yields within four hours.The catalyst system IPrAuCl/KB(C6F5)4 shows better adaptation and can be recycled and reused at least six times in the hydration of phenylacetylene.There are few reports about the hydration of alkynes for IPrAuCl/KB(C6F5)4 at the room temperature and the recyclability.This thesis presents creative research on the hydration of alkynes,new catalyst systems and catalytic mechanism have been proposed,and more mild catalytic conditons have been obtained.It is expected that this thesis can be helpful in promoting the technical advance of alkyne hydration process either theoretically or experimentally.