Sequential reduction and alkyl exchange reactions of bis(imino)pyridine dialkyliron(II) with trimethylaluminum

1 Sequen ial Reduc ion And Alkyl Exchange Reac ions O Bisiminopy idine Dialkyli on(II) Wi h T ime hylaluminum. M. Ángeles Ca es, An onio Rod íguez-Delgado, Pila Palma, Eleu e io Ál a ez and Juan Cámpo a.* Ins i u o de In es igaciones Químicas, CSIC – Uni e sidad de Se illa. c/ Amé ico Vespucio, 49, 41092, Se illa, Spain. Summa y: The sequence o eac ions ensuing when 2,6-bisiminopy idine Fe(II) dialkyl complexes [Fe(CH2SiMe3)2(BIP)] eac wi h ime hylaluminum is desc ibed in de ail. The i s s ep is he educ ion o he dialkyl o he co esponding monoalkyl complex [Fe(CH2SiMe3)(BIP)]. In he p esence o an excess o ime hylaluminum, hese unde go exchange o he emaining CH2SiMe3 g oup o me hyl, and ul ima ely he me hyli on agmen is displaced om he complex, leading o p e iously known pa amagne ic aluminum compounds. The die hyl aluminum complex [AlE 2(iP BIP)] was ob ained when ie hylaluminum was used ins ead o ime hylaluminum. In oduc ion The s udy o i on and cobal complexes wi h 2,6-bis(imino)py idine (BIP) ligands as ca alys s o ole in polyme iza ion has a ac ed much in e es since hei disco e y in 1998.1 As a esul , he main ac o s con olling hei pe o mance and selec i i y a e now easonably well unde s ood.2 Howe e , he in es iga ion o he mechanis ic aspec s o hese ca alys s p o ed e y challenging, and he ue na u e o he ac i e species in ol ed in hese ca aly ic sys ems is s ill being deba ed.3 By analogy wi h o he homogeneous ole in polyme iza ion ca alys s, ea ly mechanis ic p oposals pos ula ed ha ac i a ion o [MX2(BIP)] wi h o ganoaluminum co-ca alys s leads o coo dina i ely unsa u a ed ca ionic Fe(II) o Co(II) alkyl species.4 This p oposal ecei ed a s ong expe imen al suppo om Chi ik, who syn hesized i on5 and cobal 6 complexes o ype [M(R)(S)(iP BIP)]+ (S is a sol en molecule o no ligand; he supe sc ip on he BIP ligand e e s o he a yl subs i uen s on he imine g oups, see Scheme 1) and con i med ha hese complexes do in ac beha e as single-componen ca alys s o e hylene polyme iza ion. Howe e , one o he di icul ies o his classic ac i a ion scheme is ha , while he eac ion o pa amagne ic dihalide complexes [MX2(BIP)] wi h o ganoaluminum compounds is complex and di icul o s udy, he be e -beha ed o ganoli hium o -magnesium eagen s seldom lead o s aigh o wa d alkyla ion.7 F equen ly, he ou come o such eac ions is simul aneous alkyla ion and educ ion, he main p oduc s being unusual neu al o anionic monoalkyl species [M(R)(BIP)]0/-.8-10 This dis inc eac i i y o BIP complexes sugges ed ha ac i a ion o i on o cobal dihalide p ecu so s by o ganoaluminum compounds could also in ol e edox changes.8,9 Al hough he in e mediacy o neu al o e en anionic in e media es in he polyme iza ion eac ion seems a he i s sigh unusual, combined s uc u al, spec oscopic and heo e ical s udies ha e shown ha he abo e-men ioned educed species [M(R)(BIP)]0/- a e p ope ly desc ibed as M(II) complexes con aining singly o doubly educed BIP adical-anion ligands,5b,9,11 he e o e he edox changes a e ligand- a he han me al-cen e ed p ocesses. Since he elec onic 2 s a e and he s e ic en i onmen o he me al cen e in isoelec onic ca ionic, neu al and anionic monoalkyl species is e y simila , i is concei able ha di e en ly cha ged species could play some ole in he polyme iza ion p ocess. So a , no s able alkyli on o alkylcobal complexes ha e been isola ed om he eac ions o i on o cobal p ecu so s wi h o ganoaluminum eagen s. Fo example, Gamba o a s udied he eac ion o he i on complexes [FeCl2(iP BIP)] o [Fe(CH2SiMe3)2(iP BIP)] wi h ime hyl- o ie hylaluminum (hence o h TMA and TEA, espec i ely), bu his led o he isola ion o [AlMe2(iP BIP)] and o he pa amagne ic, NMR-silen aluminum compounds ha a e ca aly ically inac i e, a he han o i on alkyl species.12 In consequence, s udies on ac i a ion p ocesses ha e elied on in si u spec oscopic s udies.13-16 These led o di e en and some imes con adic o y esul s. Thus, using ESI mass spec ome y, Leskelä and co-wo ke s iden i ied he o ma ion o he ca ionic alkyl species [FeMe(THF)(iP BIP)]+ when he co esponding halide p ecu so complex was ea ed wi h MAO in THF,13 bu a combined Mossbaue and UV-VIS analysis o he MAO ac i a ion p oduc s in mo e usual non-pola sol en s led Gibson o p opose ha his p ocess in ol es oxida ion a he han educ ion, p oducing Fe(III) species.14 This conclusion has ound suppo in heo e ical con ibu ions.17 Using NMR, B yliako and Talsi showed ha in e ac ion o i on15 and cobal 16 [MX2(BIP)] complexes wi h MAO o aluminum ialkyls leads o di e en ypes o p oduc s depending on he M / Al a io and he na u e o he o ganoaluminum compounds. Whils MAO gi es ise o ca ionic bime allic species [M(µ-X)(µ-Me)AlMe2(BIP)]+ (whe e X = Cl o Me), TMA and o he aluminum ialkyls cause he educ ion o he complexes, a o ding neu al compounds [M(µ-X)(µ-R)AlR2(BIP)] ha a e signi ican ly less s able han he ca ionic species gene a ed wi h MAO and decompose a oom empe a u e o ul ima ely yield i on- ee aluminum complexes, consis en ly wi h Gamba o a’s esul s.12,15c Bo h neu al and ca ionic bime allic species can be seen as adduc s o he co esponding complexes [M(X)(BIP)]+/0 wi h a ialkylaluminum uni . Conside ing ha bo h MAO and aluminum ialkyls a e e icien ac i a o s, and he p e iously-men ioned simila i y o he me al cen e in ca ionic and neu al monoalkyl complexes, i was sugges ed ha di e en coca alys s could lead o di e en (ca ionic o neu al) ac i e species, a leas in he case o i on complexes.5b,15c This could help explain he s ong in luence o co-ca alys s in he molecula weigh dis ibu ion o polye hylenes ob ained wi h he la e ca alys s. Wi h he aim o con ibu ing o cla i y he ole o aluminum alkyls as educing agen s, we ha e in es iga ed he in e ac ion o he mally s able dialkyls [Fe(CH2SiMe3)2(BIP)] wi h TMA a oom empe a u e as a well-de ined model o he in e ac ion o i on BIP complexes wi h aluminum alkyls, a highly ele an p ocess o ole in polyme iza ion. In his con ibu ion, we show ha hese eac ions ake place h ough a sequence o consecu i e educ ion and alkyl exchange s eps in ol ing neu al i on monoalkyls [Fe(R)(BIP)] (R = CH2SiMe3 o Me), which could be isola ed o de ec ed unde he app op ia e expe imen al condi ions. Resul s and Discussion Some ime ago, we s udied he in e ac ion o he i on dialkyl complex [Fe(CH2SiMe3)2(MesBIP)] (1a) wi h ime hylaluminum (TMA).18 Using 1H NMR, we obse ed ha he eac ion o 1a wi h one equi alen o TMA (i. e., 0.5 Al2Me6) in C6D6, leads o a single p oduc , 2a, mode a ely s able in solu ion a oom empe a u e. This esul was conside ed ele an because e hylene was apidly polyme ized when bubbled h ough he esul ing solu ion. In ha epo , we sugges ed ha complex 2a could be a bime allic Fe/Al complex on he basis o he simila i y o some o i s main 1H signals wi h hose o he species epo ed by B yliako and Talsi.15b Howe e , we la e ound 3 close simila i y wi h he spec a o he monoalkyl complexes [Fe(CH2SiMe3)(E BIP)]10a and [Fe(CH2SiMe3)( iP BIP)],19 epo ed by Chi ik, and his led us o conclude ha 2a could be a membe o he same amily o monoalkyl compounds, as shown in Scheme 1. Ou e o s o isola e 2a om he eac ion o 1a and TMA we e ini ially hwa ed by he acile decomposi ion o he p oduc du ing he wo kup. Howe e , a e a numbe o a emp s, we ound ha 2a is ob ained in high yield (up o 90 %) when s oichiome ic amoun s o 1a and TMA a e combined in oluene a oom empe a u e and he esul ing mix u e is e apo a ed unde acuum in o de o minimize he exposu e o he p oduc o he aluminum byp oduc s du ing he wo kup. As shown in Figu e 1, he NMR spec um o he c ys alline sample o 2a con i ms ha his is he same obse ed in he NMR expe imen . Scheme 1 Figu e 1. 1H NMR spec um o 1a (bo om) and e ec o adding one equi alen o TMA (middle). The spec um o a pu e sample o 2a is shown in he op. The esidual signal o he sol en (C6D6) is ma ked wi h an as e isk. The essen ially quan i a i e eac ion o 1a wi h TMA sugges ed ha his eac ion could be ex ended o ela ed complexes. As men ioned be o e, Gamba o a s udied he eac ion o he bulkie dialkyl complex [Fe(CH2SiMe3)2(iP BIP)] ( 1b) wi h a la ge excess (10 equi ) o TMA, showing i leads o he compound [AlMe2(iP BIP)].14 Howe e , we ound ha i his eac ion is ca ied ou using he p ocedu e de ised o he syn hesis o 2a, he p e iously desc ibed mono ime hylsilyl de i a i e [Fe(CH2SiMe3)(iP BIP)] (2b)19 is ob ained in good yield. Since he c ys al s uc u e o 2b had no been p e iously epo ed, he iden i ies o bo h monoalkyl de i a i es 2 we e con i med wi h X- ay di ac ion s udies (Figu es 2 and 3). The molecule o 2a has no symme y elemen s bu 2b has a c ys allog aphically imposed symme y mi o . Apa om ha , he main bond leng hs and N Fe N N A A SiMe3 Me3Si N Fe N N A A Me3Si N Fe N N Me A A TMA "Me2AlCH2SiMe3" "Me2AlCH2SiMe3" 1a , 1b N Fe N N Me A A Me3Si 2a , 2b a, A = 2,4,6-Me3C6H2 b, A = 2,6-iP 2C6H3 Me· 3b TMA TMA = 1/2 Al2Me6 (•) II II (•) 4 angles a e e y simila in bo h molecules, and close o hose in he ela ed monoalkyl [Fe(CH2SiMe3)(E BIP)].19 Thus, hey bo h exhibi leng hened imino C=N and con ac ed 2,5-py idyl C-CN bonds wi h ega d o he ee BIP ligand, ha can be conside ed as diagnos ic o monoelec onic educ ion o [BIP]•-.5b,11b The 4-coo dina ed Fe cen e can be desc ibed as app oxima ely squa e plana , se e ely dis o ed by he depa u e o he Fe-C bond om he mean coo dina ion plane. In e es ingly, he a ying deg ee o s e ic hind ance exe ed by he MesBIP, E BIP19 o iP BIP ligands has li le e ec on his dis o ion, as he angle o med by he cen al py idine ing, he i on cen e and he me al-bound ca bon a om is almos he same in he h ee compounds (ca. 149º). Figu e 2. X ay c ys al s uc u e o compound 2a. Selec ed bond leng hs (Å) and angles (deg): Fe(1)-N(1), 2.007(5); Fe(1)-C(28), 2.050(5); Fe(1)-N(2), 2.103(5); Fe(1)-N(3), 2.110(6); C(1)-C(6), 1.440(9); C(6)-N(2), 1.323(8); C(5)-C(8), 1.436(10), C(8)-N(3), 1.325(7); N(1)-Fe(1)-C(28), 148.5(2); N(2)-Fe(1)-N(3), 136.68(19). Figu e 3. X ay c ys al s uc u e o compound 2b. Selec ed bond leng hs (Å) and angles (deg): Fe(1)-N(1), 1.992(3); Fe(1)-C(18), 2.025(4); Fe(1)-N(2), 2.190(2); N(2)-C(4), 1.316(3); C(4)-C(1), 1.443(4); N(1)-Fe(1)-C(18), 149.06(14); N(2)-Fe(1)-N(2)’, 142.04(11). Symme y ope a ion o gene a e equi alen a oms: x, -y+1, z. Moni o ing he eac ion o 1b wi h TMA in C6D6 by 1H NMR imp o ed ou unde s anding o he eac ion o he i on and aluminum alkyls (Scheme 1 and Figu e 4). The eac ion o 1b wi h an equi alen amoun o TMA p oceeds mo e sluggishly han in he case o 1a, as he con e sion in o 2b is ca. 50 % 10 min a e mixing he eagen s and eaches 60 % a e 30 min (no e ha NMR expe imen s a e signi ican ly mo e dilu ed han p epa a i e eac ions, which explains why he la e become nea ly comple e in a sho ime). A signi ican decay o he in ensi y o he 2b signals was obse ed a longe eac ion imes. Inc easing he TMA / 1b a io o 2:1 led o he appea ance o a new pa amagne ic species, iden i ied as he monome hyl complex [Fe(Me)(iP BIP)], 3b, by 5 compa ison wi h he spec um o an au hen ic sample o his compound independen ly p epa ed as desc ibed in he li e a u e.10a Mos likely, his p oduc a ises om he alkyl exchange be ween 2b and TMA. Howe e , signals o 2b a e almos inapp eciable in his expe imen whils signi ican amoun s o 1b (ca. 15 %) emained un eac ed. This indica es ha he alkyl exchange be ween 2b and TMA p oceeds as e han he ini ial educ ion o 1b o 2b. In an independen expe imen , we eac ed a pu e sample o 2b wi h 1 equi . o TMA in C6D6. The spec um o he eac ion mix u e showed he o ma ion o 3b, con i ming ha , as ep esen ed in Scheme 1, his complex can be o med om 1b in a s epwise manne , i. e., ia 2b. In con as , ea ing he mesi yl de i a i e 1a wi h wo equi alen s o TMA does no a o d he co esponding me hyl de i a i e, 3a. Moni o ing his eac ion by NMR showed ha he signals o 2a lose in ensi y and ade away wi hin minu es. Ve y likely 3a is ini ially o med, bu i apidly decomposes in he p esence o ee TMA. We con i med ha also 3b has a simila beha io , as i s 1H spec um becomes b oade and decays in he p esence o TMA, a la ge excess (Al/Fe = 50) causing i s immedia e disappea ance. The ins abili y o bo h monome hyl complexes in he p esence o TMA is consis en wi h he p e iously men ioned esul s by Gamba o a.12 Figu e 4. 1H NMR moni o ing o he eac ion o 1b wi h 1 and 2 Eq o TMA. F om bo om o op: 1) Spec um o 1b wi h signal assigna ions; 2) Reac ion wi h 1 equi o TMA, 30 min a e mixing, showing signal assignmen s o 2b; 3) Reac ion wi h 2 Eq o TMA, 5 min a e mixing; 4) Spec um o 3b wi h signal assigmen s. Shadowed ba s highligh he signals o 1b and 3b in he eac ion mix u es. The esidual signal o he sol en (C6D6) is ma ked wi h an as e isk. The diamagne ic egion close o 0 ppm in he 1H NMR spec a o solu ions o 2a, 2b o 3b di ec ly gene a ed om 1a, 1b o 2b and TMA is complex and consis en ly show se e al signals ha can be easonably assigned o he AlCH2SiMe3 moie y o silyl-con aining aluminum species. Fo example, he spec um o Al(CH2SiMe3)3 consis s o wo signals a δ 0.0 and -0.55 ppm.20 The complexi y o his egion can be explained assuming ha he hypo he ical compound [Al(Me)2CH2SiMe3] disp opo iona es in o a mix u e o silyl-con aining alkyls. The ac ha simila Al-con aining p oduc s a e obse ed in he eac ions o TMA wi h compounds 1 and 2 sugges s ha bo h p ocesses in ol e Fe/Al alkyl exchange, bu in he o me case he esul ing mixed i on alkyls [Fe(Me)(CH2SiMe3(BIP)] unde go Fe-Me homolysis, as depic ed in Scheme 1. This ou come is no su p ising, as mos complexes o he ype [MR2(BIP)] a e uns able and decompose wi h ei he M-C bond homolysis o alkyl mig a ion o he BIP ligand.19,21,22 The successi e o ma ion o complexes 2 and 3 can he e o e be seen as a 6 se ies o alkyl exchange eac ions, p obably in ol ing bime allic in e media es simila o hose obse ed by B yliako and Talsi.15 This aises he ques ion o why we did no de ec such in e media es in ou expe imen s. These au ho s showed ha 3b eac s wi h TMA a 253 K a o ding he bime allic de i a i e [Fe(µ- Me)2AlMe2(iP BIP)], 4b,15c bu we did no obse e his no any new p oduc s when 3b was ea ed wi h excess o TMA a oom empe a u e. In o de o add ess his poin , we e isi ed he eac ion o 3b wi h TMA a low empe a u e. We con i med ha , as epo ed by B yliako and Talsi, 3b is cleanly ans o med in o 4b by eac ion wi h 10 Equi o TMA a 253 K. Howe e , only pa ial con e sion was obse ed wi h a TMA / 3b a io 5:1, which indica es ha ei he he o ma ion o 4b is slow, o i is a e e sible p ocess equi ing excess o TMA o shi he equilib ium. Inc easing he empe a u e should accele a e he eac ion o 3b and TMA, he e o e a apid exchange be ween i on monoalkyls and bime allic adduc s and a low associa ion cons an (because dissocia ion is en opy- d i en) could be he causes ha p e en de ec ion o he la e a oom empe a u e. Howe e , he in e mediacy o adduc s o ype 4 can eadily explain he ins abili y o he me hyl complexes in he p esence o TMA (Scheme 2). Scheme 2 To conclude ou s udy, we b ie ly in es iga ed he in e ac ion o 1b wi h wo equi alen s o TEA, as a possible ou e o he co esponding monoe hyl de i a i e, [FeE (iP BIP)]. This compound was no ob ained, bu ins ead he g een, NMR-silen aluminum complex 5 was isola ed in 45 % yield (Eq. 1). The c ys al s uc u e o 5 is shown in Figu e 4. This compound is analogous o he me hyl de i a i e isola ed by Gamba o a om he eac ion wi h excess o TMA, which is bes desc ibed as an Al(III) complex con aining a educed BIP•- adical anion. In ag eemen wi h his p oposal, he leng hs o he imino C=N bonds and he C-C bonds connec ing hese o he cen al Py ing (C1-C6 and C5-C8) a e elonga ed and con ac ed, espec i ely, in compa ison wi h hose in he ee iP BIP ligand. The main di e ence be ween he s uc u es o he dime hyl complex and 5 is in he geome y o he Al cen e , which is bipy amidal igonal in he o me and squa e py amidal in he la e wi h one o he e hyl g oups occupying he apical posi ion. The acile o ma ion o compound 5 con i ms ha displacemen o he i on cen e om BIP complexes by aluminum alkyls is a qui e gene al p ocess and plays an impo an ole in he deac i a ion o i on-based ole in polyme iza ion ca alys s. 3 N Fe N N Me A A Me Al Me2 4 "FeMe2" N Al N N Me A A Me TMA N Fe N N Me A A N Fe N N Me3Si Me3Si 1b N Al N N E E 2 TEA 5 TEA = "AlE 3" - " FeR2" (1) 7 Figu e 5. X ay c ys al s uc u e o compound 5. Selec ed bond leng hs (Å) and angles (deg): Al(1)-N(1), 1.9582(16); Al(1)-N(2), 1.972(2); Al(1)- N(3), 2.1345(18); Al(1)-C(34), 1.972(2); Al(1)-C(36), 1.984(3); C(6)-N(2), 1.311(2); C(8)-N(3), 1.327(2); C(1)-C(6), 1.456(3); C(5)-C(8), 1.450(3); N(1)-Al(1)-C(34), 142.72(10); N(1)-Al(1)-C(36), 103.36(9); N(2)-Al(1)-N(3), 145.36(7); C(34)-Al(1)-C(36), 113.47(11). Conclusions We ha e shown ha he in e ac ion o he mally s able i on(II) bis( ime hylsilylme hyl) complexes 1a,b wi h TMA in ol es h ee dis inc s ages. The dialkyl complexes a e i s educed o he mono( ime hylsily)me hyl de i a i es 2a,b. These a e obus enough, and can be isola ed in good yields when 1a o 1b and TMA a e eac ed in 1:1 a io. P esumably, he ini ial educ ion o he Fe cen e is no di ec ly induced by he o ganoaluminum compound bu is due o he in insic ins abili y o mixed alkyl in e media es a ising om CH2SiMe3/Me exchange, which apidly decomposes unde going Fe-Me bond homolysis. The CH2SiMe3 g oup ha emains in 2a and 2b is eadily exchanged wi h a second equi alen o TMA, a p ocess ha leads o me hyl complexes (3). An excess o TMA causes he displacemen o i on om he BIP ligand, a o ding NMR-silen dialkylaluminum-BIP complexes. The la e p ocess p obably cons i u es a main deac i a ion ou e o he i on polyme iza ion ca alys s. Complexes 3 eac u he wi h o ganoaluminum compounds such as TMA o he p oduc s esul ing om he alkyl exchange, a o ding NMR-silen aluminum species. This p e en ed hei isola ion om he eac ion mix u es, al hough he o ma ion mo e s able de i a i e 3b (bu no 3a) was obse ed using NMR spec oscopy. A simila p ocess akes place when TMA is eplaced wi h highe aluminum alkyls, and complex 5, he e hyl analogue o he p e iously known compound [AlMe2(iP BIP)], was isola ed om he eac ion o 1b wi h wo equi alen s o TEA. The sequence o eac ions o he dialkyls 1 wi h TMA can be ega ded as a se ies o alkyl exchanges be ween he BIP-con aining species and he aluminum alkyls, and p obably in ol e he o ma ion o Fe/Al bime allic species as in e media es. As epo ed p e iously by B yliako , Talsi e al., he educed, elec ically neu al Fe/Al bime allics a e he mally uns able and can only be de ec ed a low empe a u e. The e o e, educed monoalkyl species [Fe(R)(BIP)] a e he mos ele an p oduc s a ising om he in e ac ion be ween Fe(II) BIP complexes and aluminum alkyls a he oom empe a u e and, in consequence, hey a e likely o play some ole in ca alys sys ems gene a ed om Fe(II) p ecu so s and TMA o o he ialkylaluminum compounds. In an ensuing pape we will be analyzing he ole o hese educed species in he mechanism o e hylene polyme iza ion ca alyzed by i on complexes. 8 Expe imen al All manipula ions we e ca ied ou unde oxygen- ee a gon a mosphe e using con en ional Schlenck echniques, o a ni ogen illed glo e box. Sol en s we e igo ously d ied and degassed be o e using. TMA and TEA we e pu chased om Ald ich and used as ecei ed. Compounds 1a and 1b we e p epa ed acco ding o li e a u e p ocedu es.18-19 Mic oanalyses we e pe o med by he Mic oanaly ical Se ice o he Ins i u o de In es igaciones Químicas (Se illa, Spain). In a ed and UV-Vis spec a we e eco ded, espec i ely, on a B uke Vec o 22 and Pe kin-Elme Lambda 12 o Lambda 750 spec opho ome e s and NMR spec a on B uke DRX 300, 400 o 500 MHz spec ome e s. The esonances o he sol en we e used as he in e nal s anda d bu chemical shi s we e epo ed wi h espec o TMS. Magne ic suscep ibili ies we e measu ed a 298 K using a She wood magne ic balance model MSB-Au o, and we e co ec ed o he diamagne ic con ibu ions es ima ed om Pascal’s cons an s.23 [Fe(CH2SiMe3)(MesBIP)], 2a. To a solu ion o complex 1a (627 mg, 1 mmol) in oluene (30 mL), s i ed a oom empe a u e, 1.1 mL o a 1 M solu ion o TMA in oluene (1 mmol “AlMe3” / mL, 1.1 Eq) was added d opwise. Du ing he addi ion, he colo o he mix u e changed om pu ple o g een. The s i ing was con inued o 5 min and hen he solu ion was e apo a ed o d yness. The esidue was ex ac ed in pen ane (2 x 30 mL) and he solu ion was il e ed h ough a pad o celi e. The esul ing g een solu ion was concen a ed o 1/3 o he o iginal olume (app ox. 20 mL) and s o ed a -20 ºC. The p oduc was isola ed as a g een solid by il a ion, washed wi h cold pen ane and d ied unde acuum. Yield, 500 mg, 90 %. X- ay quali y c ys als we e ob ained by ec ys alliza ion om hexane. Anal. Calcd o C31H42N3FeSi: C, 68.87; H, 7.83; N, 7.77. Found: C, 68.80; H, 8.17; N, 7.85. µe (298 K)= 4.3 µB . UV-VIS (E 2O): λmax 360 nm (ε = 4994), λmax 479 nm (ε = 2825), λsh 640 nm (ε = 1285), λsh 687 nm (ε = 1202). 1H NMR (300 MHz, C6D6, 298 K): δ -187.3 (Δν1/2 = 178 Hz, 6H, MeCN), -50.0 (Δν1/2 = 172 Hz, 12H, o-Memes), -11.3 (Δν1/2 = 42 Hz, 4H, m-CHmes), 14.8 (Δν1/2 = 24 Hz, 6H, p-Memes), 33.7 (Δν1/2 = 214 Hz, 9H, SiMe3), 66.0 (Δν1/2 = 96 Hz, 2H, 3,3’-HPy), 331.8 (Δν1/2 = 234 Hz, 1H, 4-HPy). [Fe(CH2SiMe3)(iP BIP)], 2b. To a solu ion o complex 1b (1.56 g, 2.5 mmol) in 30 mL o oluene, s i ed a oom empe a u e, 2.5 mL o a 1 M solu ion o TMA in he same sol en (2.5 Eq “AlMe3”) we e added a oom empe a u e. The colo o he mix u e changed om pu ple o g een. A e 5 min, he ola iles we e emo ed unde acuum, he esidue was ex ac ed in pen ane (3 x 20 mL) and he solu ion was il e ed h ough a pad o celi e. The g een solu ion was concen a ed o ca. 1/3 o i s o iginal olume and s o ed a -20 ºC o se e al days. The p oduc o ms a g een mic oc ys alline ma e ial ha was il e ed, washed wi h cold pen ane and d ied unde acuum. Yield, 1.15 g, 77%. X- ay quali y c ys als we e ob ained by ec ys alliza ion om oluene/pen ane. Anal. Calcd o C37H54N3FeSi·0.5C7H7: C, 72.51; H, 8.71; N, 6.26. Found: C, 72.04; H, 8.17; N, 6.35. µe (298 K)= 4.0 µB. IR (Nujol mull), 1581 (νC=N). UV-VIS (E 2O) : λmax 353 nm (ε = 4919), λmax 465 nm (ε = 2538), λsh 589 nm (ε = 478). 1H NMR (300 MHz, C6D6, 298 K): δ -203.6 (Δν1/2 = 178 Hz, 6H, MeCN), -105.6 (Δν1/2 = 421 Hz, 2H, CHMe2), -31.7 (Δν1/2 = 102 Hz, 6H, CHMeMe), -18.4 (Δν1/2 = 41 Hz, 6H, CHMeMe), -17.4 (Δν1/2 = 28 Hz, 2H, p-CHA ), -10.8 (Δν1/2 = 31 Hz, 4H, m-CHA ), 65.8 (Δν1/2 = 79 Hz, 2H, 3,3’-HPy), 364.2 (Δν1/2 = 211 Hz, 1H, 4-HPy). 9 [AlE 2(iP BIP)], 5. A solu ion o complex 1b (1.60 g, 2.25 mmol) in oluene (30 mL), s i ed a oom empe a u e, was ea ed wi h 4.5 mL o a 1 M solu ion o TEA in he same sol en (4.5 Eq “AlE 3”). The colo o he mix u e changed om pu ple o g een. A e s i ing o 5 min, he solu ion was aken o d yness, and he esidue was ex ac ed in pen ane. The solu ion was il e ed h ough a pad o celi e, concen a ed o ca. 1/3 o he o iginal olume and s o ed a -20 ºC. The p oduc o med c ys als ha we e app op ia e o X- ay di ac ion. Yield, 570 mg, 45 %. Anal. Calcd o C37H53N3Al: C, 78.40; H, 9.48; N, 7.41. Found: C, 78.41; H, 9.92; N, 7.22. IR (Nujol mull): 1581 (νC=N). NMR Moni o ing he eac ions o i on alkyl complexes wi h TMA. Gene al p ocedu e. Gene al p ocedu e: Samples o he i on complexes we e weighed in he glo e box, dissol ed in he equi ed amoun o C6D6 and placed in NMR ubes capped wi h sep a. A 0.1 M s ock solu ion o TMA (con aining 1 Eq “AlMe3” pe mL) was p epa ed in he same sol en , and a sample was placed in a sep um-capped ial. The 1H NMR spec um o he pu e samples was eco ded. The equi ed amoun o he TMA solu ion was aken wi h a gas- igh sy inge om i s ial, and injec ed in o he ube o he co esponding complex. The NMR ube was sealed wi h a small amoun o silicone g ease and pa a ilm and gen ly shaken be o e placing in o he NMR p obe. Moni o ing he eac ion o complexes 1 - 3 wi h TMA a oom empe a u e: Samples con aining 10 µmol o he complexes in C6D6 we e p epa ed as desc ibed and ea ed wi h 100 o 200 µL o he TMA solu ion (Al/Fe = 1 o 2, espec i ely). Fo he eac ion o 3b wi h 50 Eq o TMA, a 1 N solu ion o his eagen was used. Moni o ing he eac ion o 3b wi h TMA a low empe a u e: Two samples con aining 4.5 mg o 3b (8 µmol) in oluene-d8 we e p epa ed in he glo e box and placed in sep um–capped NMR ubes. A 0.2 N solu ion o TMA in he same sol en was simila ly p epa ed. The 3b samples we e cooled o 193 K (-80 ºC) in an ace one – d y ice ba h, and he p esc ibed amoun o he TMA solu ion (200 o 400 µL, Al/Fe = 5 o 10, espec i ely) was added. The sep a we e sealed wi h silicone g ease and pa a ilm and he ubes we e ans e ed o he p e-cooled NMR p obe. Associa ed Con en Expe imen al o he X- ay c ys al s uc u e analyses and c ys allog aphic in o ma ion iles o 2a, 2b and 5. These da a a e a ailable ee o cha ge ia he In e ne a h p://pubs.acs.o g. Acknowledgemen s This wo k was suppo ed by he Go e nmen o Spain (p ojec numbe CTQ2012-30962), he Jun a de Andalucía (p ojec numbe FQM5074) and he Eu opean Union (EU) (FEDER unds). MAC hanks CSIC o a p edoc o al esea ch ellowship (I3P p og am). Re e ences