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Preparation of “Constrained Geometry” Titanium Complexes of [1,2]Azasilinane Framework for Ethylene/1-Octene Copolymerization

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Preparation of “Constrained Geometry” Titanium Complexes of [1,2]Azasilinane Framework for Ethylene/1-Octene Copolymerization molecules Article Preparation of “Constrained Geometry” Titanium Complexes of [1,2]Azasilinane Framework for Ethylene/1-Octene Copolymerization Seul Lee, Seung Soo Park, Jin Gu Kim, Chung Sol Kim and Bun Yeoul Lee * Department of Molecular Science and Technology, Ajou University, Suwon 443-749, Korea; [email protected] (S.L.); [email protected] (S.S.P.); [email protected] (J.G.K.); [email protected] (C.S.K.) * Correspondence: [email protected]; Tel.: +82-031-219-1844 Academic Editor: Kotohiro Nomura Received: 27 December 2016; Accepted: 7 February 2017; Published: 9 February 2017 5 t Abstract: The Me2Si-bridged ansa-Cp/amido half-metallocene, [Me2Si(η -Me4C5)(N Bu)]TiCl2, termed a “constrained-geometry catalyst (CGC)”, is a representative homogeneous Ziegler catalyst. CGC derivatives with the [1,2]azasilinane framework, in which the amide alkyl substituent is joined by the Si-bridge, were prepared, and the catalytic performances of these species was studied. Me4C5HSi(Me)(CH2CH=CH2)-NH(C(R)(R’)CH=CH2) (R, R’ = H or methyl; Me4C5H = tetramethylcyclopentadienyl) was susceptible to ring closure metathesis (RCM) when treated with Schrock’s Mo-catalyst to afford -Si(Me4C5H)(Me)CH2CH=CHC(R)(R’)NH- containing a six-membered ring framework. Using the precursors and the products of RCM, various CGC derivatives, i.e., 5 5 [-Si(η -Me4C5)(Me)CH2CH=CHC(R)(H)N-]TiMe2 (13, R = H; 15, R = Me), [-Si(η -Me4C5)(Me) 5 CH2CH2CH2CH2N]TiMe2 (14), [(η -Me4C5)Si(Me)(CH2CH=CH2)NCH2CH=CH2]TiMe2 (16), 5 5 [(η -Me4C5)Si (Me)(CH=CH2)NCH2CH=CH2]TiMe2 (17), and [(η -Me4C5)Si(Me)(CH2CH3)NCH2 CH2CH3]TiMe2 (18), were prepared. The catalytic activity of the newly prepared complexes was lower than that of CGC when activated with [Ph3C][B(C6F5)4]/iBu3Al. However, the catalytic activity of these species was improved by using tetrabutylaluminoxane ([iBu2Al]2O) instead of iBu3Al and the activity of 14/[Ph3C][B(C6F5)4]/[iBu2Al]2O was comparable to that of CGC/[Ph3C][B(C6F5)4]/iBu3Al (4.7 and 5.0 × 106 g/mol-Ti, respectively). Advantageously, the newly prepared complexes produced higher molecular weight poly(ethylene-co-1-octene)s than CGC. Keywords: olefin polymerization; titanium complex; constrained geometry; half-metallocene 1. Introduction Since the discovery of homogeneous metallocene catalysts (single-site polyolefin catalysts) in the 1970s by Kaminsky, their industrial impact has escalated, with current annual production of more than five million tons of polyolefins [1–3]. The initially developed family of metallocene-type catalytic species has expanded to include half-metallocenes constructed with a cyclopentadienyl (Cp) and an amido ligand [4–10], and further to post-metallocenes (or non-metallocenes) comprising non-cyclopentadienyl ligands [11–16]. Among the homogeneous Ziegler catalysts, Me2Si-bridged 5 t ansa-Cp/amido half-metallocenes, a typical example of which is [Me2Si(η -Me4C5)(N Bu)]TiCl2, are termed “constrained-geometry catalysts (CGCs, Chart1)”, and have drawn significant attention from both industry and academia. CGC exhibits excellent catalytic performance, including high activity, high α-olefin incorporation, and high thermal stability [17–22]. We also reported a variety of ansa-Cp/amido half-metallocene congeners bearing the ortho-phenylene-bridge instead of the Me2Si-bridge (1 in Chart1)[ 23,24]. During the course of development of these catalysts, we observed that the tetrahydroquinoline (or tetrahydroquinaldine) derived species (2 in Chart1), in which Molecules 2017, 22, 258; doi:10.3390/molecules22020258 www.mdpi.com/journal/molecules Molecules 2017, 22, 258 2 of 15 the alkyl substituent in the amido ligand is joined to the ortho-phenylene-bridge, exhibited higher Moleculesactivity 2017 and, 22 higher, 258 α-olefin incorporation than the simple ortho-phenylene-bridged ansa-Cp/amido2 of 14 congeners 1 [25–28]. In fact, 2 displays excellent catalytic performance in ethylene/α-olefin 1copolymerization, [25–28]. In fact, 2 thusdisplays enabling excellent its use catalytic in commercial performance processes in ethylene/ [29,30α].-olefin Joining copolymerization, the amide alkyl thussubstituent enabling and itsortho use -phenylene-bridgein commercial processes may afford [29,30]. a highly Joining accessible the amide reaction alkyl sitesubstituent for catalysis, and orthoresulting-phenylene-bridge in higher activity may afford and higher a highαly-olefin accessible incorporation. reaction site This for observationcatalysis, resulting prompted in higher us to activityprepare and CGC higher analogues α-olefin in incorporation. which the amide This alkyl observation substituent prompted is joined us to to prepare the Si-bridge CGC analogues unit to form in whichthe [1,2]azasilinane the amide alkyl framework substituent (Chart is joined1). to Various the Si-bridge CGC derivatives unit to form have the [1,2]azasilinane been reported; framework in most of t (Chartthese cases, 1). Various the Me CGC4C5-unit derivati is replacedves have with been other reported;π-donor in ligands most of or these the N cases,Bu-unit the is Me replaced4C5-unit with is replacedother amides with orother phosphides. π-donor ligands However, or thethe complexesNtBu-unit targetedis replaced in thiswith work other have amides not previouslyor phosphides. been However,prepared [the31– complexes39]. targeted in this work have not previously been prepared [31–39]. Chart 1. Ortho-phenylene-bridged half-metallocene complexes and the complexes targeted in this work. Chart 1. Ortho-phenylene-bridged half-metallocene complexes and the complexes targeted in this work. 2. Results 2. Results 2.1.2.1. Synthesis Synthesis and and Characterization Characterization TheThe present present strategy strategy for for construction construction of the of [1,2 the]azasilinane [1,2]azasilinane framework framework involves involves the ring the closure ring metathesisclosure metathesis (RCM) of (RCM)the two ofolefin the units two olefinattached units to the attached nitrogen to and the silicon nitrogen atoms and (Scheme silicon 1). atoms The precursor (3, Me4C5H-Si(Me)(CH2CH=CH2)-NH(CH2CH=CH2)) for RCM was easily prepared according (Scheme1). The precursor ( 3, Me4C5H-Si(Me)(CH2CH=CH2)-NH(CH2CH=CH2)) for RCM was easily toprepared the scheme according applied to in the the scheme construction applied of the in the prototype construction CGC ligand of the prototypeby using commercially CGC ligand available by using chemicals, tetramethylcyclopentadiene (Me4C5H2), allyl(dichloro)methylsilane ((CH2=CHCH2)(Me)SiCl2), commercially available chemicals, tetramethylcyclopentadiene (Me4C5H2), allyl(dichloro)methylsilane and allylamine. Initial RCM trials of 3 using Ru-catalysts (Grubbs 1st and 2nd generation catalysts ((CH2=CHCH2)(Me)SiCl2), and allylamine. Initial RCM trials of 3 using Ru-catalysts (Grubbs 1st and and2nd Hoveyda–Grubbs generation catalysts catalyst) and Hoveyda–Grubbs for the synthesis catalyst) of 6 were for theunsuccessful synthesis of[40].6 were No ethylene unsuccessful gas was [40]. 1 detectedNo ethylene in the gasreaction was monitored detected in by the H-NMR. reaction Instead, monitored migration by 1 H-NMR.of the double Instead, bond migrationin the allylamine of the unitdouble was bond observed. in the In allylamine contrast, the unit Mo-catalyst was observed. (Schrock In cataly contrast,st, 2 themol Mo-catalyst %) cleanly converted (Schrock catalyst,3 to the desired2 mol % cyclic) cleanly compound converted 6 [41–44].3 to the desiredWhen a cyclicclosed-NMR compound tube6 with[41–44 C].6D When6 was aused, closed-NMR the signal tube of generated ethylene was observed at 5.24 ppm and the vinyl signals that were observed in the spectrum with C6D6 was used, the signal of generated ethylene was observed at 5.24 ppm and the vinyl signals ofthat 3 at were 4.8–5.2 observed ppm inand the 5.7–5.9 spectrum ppm of completely3 at 4.8–5.2 disappeared, ppm and 5.7–5.9 while ppm two completelynew =CH signals disappeared, were observedwhile two at new5.8 and =CH 5.5 ppm signals (Figure were 1). observed The RCM at product 5.8 and 6 5.5could ppm be separated (Figure1). from The the RCM Mo-catalyst product by6 α vacuumcould be distillation separated at from 60 °C. the The Mo-catalyst derivatives by bearing vacuum methyl distillation substituents at 60 at◦ C.the The -position derivatives of the bearing amino groupmethyl (7 substituentsand 8) were also at the successfullyα-position prepared of the amino by RCM group of the (7 correspondingand 8) were also precursors successfully 4 and prepared 5, which wereby RCM prepared of the using corresponding 1-methylallylamine precursors or 1,1-dime4 and 5,thylallylamine which were prepared instead of using allylamine. 1-methylallylamine Hydrogenation or of1,1-dimethylallylamine 6 using a Pd/C catalystinstead afforded of 9 allylamine. bearing the Hydrogenationdesired [1,2]azasilin of 6aneusing framework; a Pd/C catalyst the double afforded bonds9 inbearing the tetramethylcyclopentadiene the desired [1,2]azasilinane units framework; remained the doubleintact during bonds inthe the hydrogenation tetramethylcyclopentadiene process. The 1 characteristicunits remained vinyl intact signals during in the the H-NMR hydrogenation spectrum process.of 6 completely The characteristic disappeared after vinyl hydrogenation. signals in the α However,1H-NMR spectrumhydrogenation of 6 completely of the derivatives disappeared 7 and after 8 bearing hydrogenation. methyl substituent(s) However, hydrogenation at the -position of theof thederivatives amino group7 and was8 bearing unsuccessful; methyl substituent(s) the substrates at re themainedα-position intact of under the amino the identical group was hydrogenation unsuccessful; conditionsthe substrates using remained the Pd/C intact catalyst. under The the five-membered identical hydrogenation analogue conditions11 was also using successfully the Pd/C prepared catalyst. via RCM of the vinylsilane derivative using the same Mo catalyst. Hydrogenation of 11 using the Pd/C catalyst was also successful to afford 12 bearing the [1,2]azasilolidine framework (Scheme 1). Molecules 2017, 22, 258 3 of 15 The five-membered analogue 11 was also successfully prepared via RCM of the vinylsilane derivative using the same Mo catalyst.
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