Copper(I) chemistry of n-heterocyclic carbenes: Synthesis and homogeneous catalysis applications

Thisthesisconsists of threeparts. Thefirstpart is a concisereview on N-heterocycliccarbenecopper(I) complexes. Inthesecondpart, theexperimentaldetailsaregiven. Inthethirdpart, synthesis, characterizationandcatalyticstudies of copper(I) complexescontaining benzimidazol-2-ylidene ligandsarepresented.1-{(ethoxycarbonyl)methyl}-3-aryl benzimidazoliumbromidesalts(II-IV)wereobtainedbythereaction of 1-{(ethoxycarbonyl)methyl}benzimidazole(I)withbulkybromidecompounds (RBr: R = CH2C6H3(OMe)2-3,5; CH2CH2C6H3(OMe)2-3,4; CH2C6H3But2-3,5). Treatment of benzimidazolewith 3,5-dimethoxybenzyl bromideledtobenzimidazoliumbromide salt (VIII). Benzimidazoliumbromide salt (XI)wassynthesizedbythereaction of 1-(3,5-di-t-butylbenzyl)benzimidazole(X)with3,5-di-t-butylbenzyl bromide (Scheme 1).Scheme 1.Synthesis of benzimidazoliumbromidesaltsNeutral [(NHC)CuBr] complexes(V, VI, IX)weresynthesizedbydeprotonationof benzimidazoliumsalts(II,III, VIII)with Cu2O.Thereaction of [Cu(CH3CN)4]BF4complexwithVIII salt andNaOButgavethecompoundIX, too. Toprepare a mono(carbene)copper(I) complex, thereaction of thecompound(IV)with Cu2O resulted in theformation of a newbis(carbene)copper(I) complex(VII) (Scheme 2).Scheme 2.Synthesis of NHC-copper(I) complexes(V, VI, VII, IX)Bis(carbene)copper(I) complex(XII)wassynthesizedbythereaction of thebenzimdazolium salt (XI)withNaOButand [Cu(CH3CN)4]BF4 (Scheme 3).Scheme 3.Synthesis of copper(I)complex(XII)Catalyticactivities of thesynthesized NHC-Cu(I) complexes(V, VI, IX, XII) in the [3+2] cycloadditionreactions of someorganicazidesand terminal alkyneswerestudied (Scheme 4). All of thesecomplexesgavethe1,4-disubstituted-1H-1,2,3-triazoles in shorttimesandgoodyields. Itwasfoundthatthecomplexescontaininglessbulkygroupsshowedhighercatalyticactivities.R1CH2CO2EtCH2CO2EtBnPhR2Phn-BuPhPhŞema 4. [3+2] cycloadditionreactions of azidesand terminal alkynes