it . 12., .'1Y. KTNETTCS OF THE REACTTONS BETI^IEEN TRTETHYLALUMTNÏUM AND UNSATURATED HYDROCA,RBONS A thesís submítted by Roger Malcolm Lough B. Sc. (Ilons . ) candidate for the degree of Doetor of Philosophy DepartmenÈ of Ph]'slcal and Inorganic Chenfstry The University of Adel-aíde Novemþer 1973 TABLB OF CONTENÏS Page No. Section I: Tríalkylaluníniums 1. General 2 2. PreparaËíon of TríalkyJ-aluminiums 4 3. Structure and Bondíng ín Trialkylal-r:mÍníums 4 4. Propertíes of Trialkylaluminír:ms 10 4.1. Thermodynamíc Propertíes 10 4.2. Chemical Properties 1B Section ff : The Reaction of Triethylalumínium h7íth Al-k-l--enes 1. Introduetion 24 1.1. General 24 1..2. Previous Kínetíc Studíes 27 L.2.L. Displ-acemenË 27 L.2.2. Addítíon 28 2. Reactíon of Triethylaluminír¡m wiih 2-Methyl hept-l-ene 36 2.1. Material Hand'J-íng 36 2.2. P.m.r. Measurenents 42 2.2,L. Triethylaluminium-Alken-e n compl-ex 42 2.2.2. Àddition of Tríethyia.iuminium to 2-MethylhepË-1-ene 44 2.3. Results 49 3. Reaction of T::iethy1a1-urníniu.m with Slyrene 55 3.1-. Pre-paratíon of N.m'r. tubes 55 3.2. P.m.r. I'feasuremenËs 55 TA}LE OF CONTENTS (cont . ) Page No. 3.2.L. Tri-ethylaluniníurn-Styrene Complex 55 3.2.2. Addition of Triethylalunínium to Styrene 56 '3.3. Results 59 3.3.1. Triethylalumj-níum-Styrene Complex 59 3.3.2. KinetÍcs of the AddÍtion Reactíon 64 4. Discussíon of Mechanfsm 67 t 4.1. CalculaÈion of the EntroPy Difference IV-III 72 Section III.' ReacLíon of Triethylah:mÍníun wÍth A1k-1-ynes 1. IntroducËion B1 2 . Triethyl-a1-umíníum-Phenylacetylene Complex 88 2.1-. Nature of ConPlex B8 2.2. Esxímation of K" 93 3. DeËernínation of TriethylalunÍniun/Phenyl-acetyl-ene Reactíon Rates 9B 3.1. ?relíminary 98 3.2. Manometry 99 3.3. P.m.r. Spectro'scoPY 1_03 4. Kínetíc Results LO4 4.1. External Orders of Reactíon LO4 4.2. Kinetic Parameters 106 5. DÍscussion of Mechanísm 113 TABLE OT CONTENTS (cont . ) Page No. Seetion IIl.' Reaction of Tríethylal-umínium Ämine Compl-exes with A1-kynes 1. Trialkylalumínium Donor Complexes Lt7. 2. Reactíon of TriethylaLuminium complexes wíth unsaturated Hydrocarbons L24 3. ExperimenËal- L27 3.1-. Purífícati-on of Materials L27 3.2. Kinetíc Measurements L27 4. PossÍble MechanÍsms 131 5. Assocfatlon ComPlexes 133 5 . l-. Triethyl-ah:miníum-amíne Dimer 133 5.1.1. ?.m.r. Studies 133 5.L.2. Ebul-líometry 136 5 . 2 . T x íethy1- a lumin ium-T r Í alkyI arnine -Phenyl a c e tyl ene ' Complex L46 6. Kinetic Results L4B 7. Discussíon of Mechanísm 151 Section V: Conclusion 1. General Surnmary 159 2. Ef.f.eclu of ComplexaËÍon on the ReactiviÈy of Organo- metallics wíth Unsaturated Compounds 163 3. Conclusion L72 TASLE OF COI{TENTS (cont. ) Page No. þpendiæ f - Polynomial Curve Ì'íttíng L76 Appenåín -If - Alkene Rate Co-'efficients 1-78 þpendiæ IIT - Alkyne Rate Co-effícients i-79 Appendtæ IV - Plotting'Programm PLOTT 180 Appendìn 7 - Published Papers 18L Abstz,act The literaLure concernÍng the physícal and thermodynamic propertíes of tríalkylaluminiums and the reactlon of tríeËhylaluminium with terminal alko-nes has been críticall-y reviewed. A detaíled kineËic study of the reaction of triethyl-a1-umíníum wíth styrene and 2-methyl-1--hepËene has been performed using a P.m.r. techni- que. The kinetic parameters obtained have been compared wíth others avaílabl-e for l--allcenes and a co-ordínated mechanism ínvolvlng tIÀto rate determj-níng sËeps to account for the observed parameters is postul-ated. Previols studies of the reactions beËween tríethyLalumínÍum and alkynes have been revíewed and a kÍnetic sËudy of the reaction of Èrie- thylalurníníum wiÈh phenyJ-acetylene performed, usi-ng p.m.r. and" rnanometric techniques. The exj-sÈence of a clonor conplex between alk1'nes aird Ërie- thylalumínÍum has been establíshed. Previousl-y this had on1-y be'en postulated. Finally the kínetícs of the reactíon of two amine complexes of trÍethylaI-umínium u.Íth phenylaceËylene have been ínvestígated and a mechanísm proposed to explaín Ëhe observed kinetíe pal:ameters. This thesis 1s a record of research undertaken in Ëhe Department of Physlcal- and Inorganíc Chemistry at the Uníversity of Adelal-de between March 1971 and September L973. To the best of my knor+ledge and bellef no material contaÍned hereÍn has been acðepted for the award of any other degree or diploma ln any universiËyr or been prevlousl-y publlshed or writËen by another person except when due reference ís made in Èhe text. Roger M. Lough. ACKNOI{LEDGBMENIS Ï am deeply indebted to my suPervisor, Dr. P.E.M. Al]-en, for his guidance and rreverending encouragemenË throughout the duraËíon of this r^¡Ork. I woul-d like to express ny gratitude to Mrs. I. Johnstorr r'rho prepared the diagrams, Mrs. P. Burford who typed this thesis, Mr' G' Duthie and Mr. T. Trivit of the Glassblowing llorkshop, Ifr. K. She-pherdson of the Electronícs Irlorkshop and Mr. A. Bowers and Mr. A. Bastín of the General- !üorkshop for Èheir exPert help in the consËructíon and maíntenance of the given equipment used in the project. A word of appreciation must also be to my research colleagues for their val-uable critícfsms and suggestions' The Conrnonwealth Department of Supply granted me leave of absence Ëo undertake the project and the Conunonweal-th Publíc Servíce Board and Department of EducatÍorr provfded financíal- assistance' To these bodies I am verY grateful-. Finally, I would l-Íke to thank my wife, whose assfstanee- and patience has been inesËímable over the whole course of stucly' SECT]ON I TRIALKYLALUM]NIUMS 1. Synopsis GeneraL - The hístorical- background and industríal uses of organoaluminiums are briefly reviewed and Ëheir relaËÍonshíps to Ziegler-Natta caËalyst,, systems are discussed. Prepaz'ation - A very brief ouÈl-íne of the nethods of preparation of trfal-kylal-umíniums is given. Stzaett¿re and Bondíng - Sorne aspects of the x-ray crystallographic, p.m.r., and mass spectroscopíc evídence for assocÍation are clÍscussed. As a result, two orbital descríptíons of the three-centre, eleetron deficíent bond have been proposed. Ther,nodynanic Pz,operties - The meríts of the varíous values put forwarcl for the enthalpíes and entropies of dissocíation of. LLTEIU and AlrlIeU in the J-iquíd and vapour phase are díscussed. ChemicaL Propez,ties - A very bríef outl-íne of the more ímportant chemical propertles of trialkylaluminiums Ís gíven. 2 r.1. 1. gEII.RAL- Although an organoalumínium compound was synthesized by Ha1-1-iuachs I and Schafarik ín 1859, the study of the chemistry of these compounds remaíned statÍc untÍ1 about 1950. At this time Professor KaxL ZiegLer and hís co-workers utílized aLky1a1umíniums to greatly increase the 2 rate of polymerizaËÍon of eËhylene, whiLe simul-taneousl-y.developi.ng a cheap synthesis for alkylak:miniums dÍrectly from al-umíníum, olefins a J and hydrogen. As a result, the scope of usefulness of crganoaluminirrns in ger:.eral , and alkylal-r:mínir¡ms specífically, has broadened considerably, wíth the conseguenL dramatic increase in the quantíties used in industry and research. Most organoalurniniums are used as components in the various Zieg- ler-NatËa polyrnerízatíon catalysts. These catalysts, formed by combin- íng aluminium with a transition metal eorçcundr are used in preparíng nearly aLl of the comn¡ercial- polyclefin prodt'.ced in Lhe world today. TheÍr maín advant.ages over other polymerLzatJ-,on catalysts are the sËereo- regularity of the resul-Èing poJ-yner - which can be reaclil-y changeC - and the íncreased raËe of reaction r,rhen compared to other catalysts. Organo- al-uminigms, alone, are usecl extensively for the o1-igerm.ization and 1,o1y- merÍzaÊion of the sÍrnpler olefíns. Tríalkylaluminium catalysts, fot 46 example, are used for the dimerization of propylene t-o 2-urethylpent-J--ece. This la-uter compound ís often used as a precursor for isoprene, which ís e:rterisi¡¡ely used in the synthetic rubber industry. 3 r.1. In spíte of this vast use, comParatÍvely l-ittle ís known of the chemist,ry of Èhe organoaluminíums, ín part due to their reactÍve natlrre' The explanation for sl-ereoregular polymer-izaËíon by ziegl'er-NaÈta catalysts has been particularly confused, as rrany theorLes have been proposed over 4-6 7 the lasÈ decade, but recently a clearer Picture seems to be emergÍng' Many patenËs concernlng olefín polymerization appear each year, but as yet there does not seem to be any correlatíon between the nyríad of catalysËs and conditions used, with the resultíng polymer. Thus an understandíng of the basíc reactívíty factors and the mechanísms that are oPeratíng when organoal-umÍniums react wíth unsaËuraËed hydrocarbons coul-d conceívably throw sorne líghÉ on the situatÍon. The purpose of thís thesis is to provide some ínfo:rnatíon towards thís end. TrÍal-kylal-umíníums are one of tlre simplest classes of organo- aluníni-ums, and the resuits deríved from Ëhese compounds have, up to the present, been inteïpreted with less aurbíguity than other organoaluminíums' For this reason, they have been used in thís study. The particular trialkylalumíníum used- triethylaluminíum - was selected mainly on íts ready availabílity and widesiread use as a catalyst and a co-catalysË ' Before examlníng the detaíled kinetics of the reactions of tríethyl-- alunínir:m wíth unsaturatecl hyclrocar:bons' hogever, it ís necessary to revÍew the structure ancl properti.es of Erialkyl-al-uurinfums, so Ëhat the subsequent kíneËic results can, be correcÈl-y ínterpreted. 4 r.213 2. PREPAXATION OF TRIATKYLAI,IIMINIUMS 'Tría1-ky1-aluminiums can be prepared fron olefíns by dlrecÈ synthe- a sís, dísplacement or by a growËh reaction.