Guanidinophosphazenes- Design, Synthesis, and Basicity in THF and in the Gas Phase

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1、PublishedonWeb11/25/2005Guanidinophosphazenes:Design,Synthesis,andBasicityinTHFandintheGasPhaseAlexanderA.Kolomeitsev,*,†IlmarA.Koppel,*,‡ToomasRodima,‡JanBarten,§EnnoLork,†Gerd-VolkerRo¨schenthaler,†IvariKaljurand,‡AgnesKu¨tt,‡IvarKoppel,‡VahurMa¨emets,‡andIvoLeito*,‡Contri

2、butionfromtheInstituteofInorganic&PhysicalChemistry,UniVersityofBremen,LeobenerStrasse,D-28334Bremen,Germany,DepartmentofChemistry,UniVersityofTartu,Jakobi2str,51014Tartu,Estonia,andHansaFineChemicalsGmbH,LeobenerStrasse,NW2C,D-28359Bremen,GermanyReceivedMay31,2005;E-mail:ko

3、lomeit@chemie.uni-bremen.de;ilmar.koppel@ut.ee;ivo.leito@ut.eeAbstract:Aprincipleforcreatinganewgenerationofnonionicsuperbasesispresented.Itisbasedonattachmentoftetraalkylguanidino,1,3-dimethylimidazolidine-2-imino,orbis(tetraalkylguanidino)carbiminogroupstothephosphorusatom

4、oftheiminophosphoranegroupusingtetramethylguanidineoreasilyavailable1,3-dimethylimidazolidine-2-imine.Sevennewnonionicsuperbasicphosphazenebases,tetramethylguani-dino-substitutedatthePatom,havebeensynthesized.Theirbasestrengthsareestablishedintetrahydrofuran(THF)solutionbyme

5、ansofspectrophotometrictitrationandcomparedwiththoseofeightreferencesuperbasesdesignedspeciallyforthisstudy,P2-andP4-iminophosphoranes.Thegas-phasebasicitiesofseveralguanidino-andN¢,N¢,N¢¢,N¢¢-tetramethylguanidino(tmg)-substitutedphosphazenesandtheircyclicanaloguesarecalcula

6、ted,andthecrystalstructuresof(tmg)3PdN-t-Buand(tmg)3PdN-t-BuâHBF4aredetermined.Theenormousbasicity-increasingeffectofthisprincipleisexperimentallyverifiedforthetetramethylguanidinogroupsintheTHFmedium:thebasicityincreasewhenmovingfrom(dma)3PdN-t-Bu(pKR)18.9)to(tmg)3PdN-t-Bu(

7、pKR)29.1)is10ordersofmagnitude.Asignificantlylargerbasicityincrease(upto20powersof10)isexpected(basedonthehigh-leveldensityfunctionaltheorycalculations)toaccompanythesimilargas-phasetransferbetweenthe(dma)3PdNHand(tmg)3PdNHbases.Farstrongerbasicitiesstillareexpectedwhen,inth

8、elattertwocompounds,allthreedimethylamino(ortetrameth-ylguanidino)fragments