Synthesis of Highly Branched Polyethylene Using “Sandwich ”(8?p ?Tolyl naphthyl α?diimine)nickel(II)Catalysts
Danfeng Zhang,?Enrico T.Nadres,?Maurice Brookhart,*,§and Olafs Daugulis *,?
?
Shanghai Key Laboratory of Advanced Polymeric Materials,School of Materials Science and Engineering,East China University of Science and Technology,Shanghai 200237,China ?
Department of Chemistry,University of Houston,Houston,Texas 77204-5003,United States §
Department of Chemistry,University of North Carolina at Chapel Hill,Chapel Hill,North Carolina 27599-3290,United States
*
Supporting Information weights and narrower PDIs.They yield the most highly branched PE 8-aryl-1-naphthylamines provides ready access to a new class of α-ideally positioned to provide steric bulk at the axial sites.
Since the demonstration in 1995that cationic α-diimine complexes of Ni(II)and Pd(II)bearing bulky aryl substituents (Figure 1)are catalysts for polymerization of ethylene,α-
ole ?ns,and certain polar vinyl monomers,1,2there has been intense interest in these basic systems and in their variants,both neutral and cationic.3?5The key to generating high polymer from the cationic diimine complexes and related systems is the incorporation of ortho aryl substituents that,due to the perpendicular arrangement of the aryl ring and the square coordination plane of the metal,are positioned in axial sites above and below the square plane.Virtually all of the Ni and Pd catalysts that have been developed since the initial discovery have incorporated this design feature into the ligand.This concept has also been extended to cobalt and iron systems as well.6
Ole ?n polymerizations employing palladium-based α-diimine catalysts are normally initiated using well-de ?ned cationic monoalkyl species bearing a weakly coordinating ligand,L,as
shown in Figure 1.While polymerizations using well-de ?ned cationic nickel complexes have been achieved,the di ?culty in preparing these species has led to initiation via activation of more stable nickel dihalides 2by methyl aluminoxane or other alkyl aluminum activators.
Polymerization of ethylene by palladium diimine complexes of type 1produces high molecular weight polymers exhibiting highly branched structures.Branching numbers between 90and 125per thousand carbons are typically observed.Hyper-branched polyethylenes can be produced at low ethylene pressures and higher temperatures.8Nickel catalysts are considerably more active than palladium species;turnover frequencies up to 3×106/h have been demonstrated.1,4,7These systems produce branched polyethylenes,and the extent of branching can be controlled by variation of pressure and temperature.High pressures and lower temperatures produce more linear material,while lower pressures and higher temperatures can lead to PE with branching densities approaching 124/1000C.
Mechanistic studies of well-de ?ned systems for both Ni and Pd complexes have established the general mechanism shown in Scheme 1with the following key features:9(a)The metal alkyl species are 16-electron β-agostic complexes.(b)The resting states are alkyl ethylene complexes in the case of Pd systems.For Ni systems the resting state depends on temperature and ethylene pressure and can be the alkyl ethylene,the β-agostic complex,or a mixture of these species.(c)For Ni,chain-walking (β-elimination and addition with opposite regiochemistry)is competitive with ethylene trapping,and thus for Ni the extent of branching is dependent on
Received:July 17,2013
Published:September 10,
2013
Figure 1.Palladium and nickel diimine catalysts.
ethylene pressure.Increasing temperature increases the rate of chain-walking (a ?rst-order process)relative to ethylene trapping (a second-order process).(d)Trapping of the agostic alkyl complex is irreversible in the case of Ni,but reversible in the case of Pd.This feature is responsible for generation of hyperbranched PE at low ethylene pressures.(e)The most critical mechanistic feature of these systems is that the bulky axial substituents greatly retard the rate of chain transfer relative to the rate of propagation,thus giving rise to high molecular weight polymers.Initially slow chain transfer was ascribed to an associative mechanism where the function of bulky substituents on the diimine ligand was to retard the rate of displacement of ole ?n from an intermediate alkyl ole ?n complex.However,DFT calculations suggest that chain transfer occurs from the resting state in an intramolecular process.10Steric crowding of this transition state by axially positioned substituents raises the barrier to chain transfer.
Several groups have introduced other ortho-substituents into the bis(aryl)-α-diimine nickel catalysts (Figure 2).11?13For
example,Coates and co-workers have reported the preparation of the C 2-symmetric system 3bearing a single ?CH(Me)-(mesityl)substituent on the two ortho positions.Catalyst 3polymerizes propylene at ?78°C to yield isotactic PP.At 22°C,amorphous,regioirregular PP is produced.The very narrow M w /M n values at each temperature allow preparation of unique PP block polymers.11Moody and co-workers as well as Rieger have examined catalysts of type 4bearing aryl substituents at
both ortho positions.12Such systems exhibit higher thermal stabilities than alkyl-substituted complexes of type 1and 2(R ′=alkyl).A similar series of Ni catalysts bearing ortho-difuryl substituents has also been reported.13
In studies directed at signi ?cantly increasing the bulk of axial substituents and thermal stability of catalysts,Guan and co-workers have prepared nickel catalysts 5derived from cyclophane-type ligands where linkages to opposing ortho positions provide a rigid axial cap.Indeed,these systems display much improved temperature stability.14
In this article,we report the preparation of and ethylene polymerization by Ni catalysts derived from 8-p -tolyl naphthyl-α-diimines of general structure 6(Figure 3).When coordinated
to a square planar metal complex,this ligand adopts C 2symmetry.The tolyl substituents lie perpendicular to the naphthyl rings and are nearly coplanar with the square coordination plane,thus capping the axial sites in a “sandwich-like ”arrangement.This geometry is in contrast to that generated from ortho-substituted aryl complexes 1or 2,where the R ′substituent is pointed away from the square plane at an angle.
2.RESULTS AND DISCUSSION
2.1.Synthesis of Diimine Ligands.8-p -Tolylnaphthale-nylamine was synthesized by using known C ?H bond functionalization methodology.15The synthetic procedure is summarized in Scheme 2.Picolinic acid 1-naphthylamide was coupled with 4-iodotoluene to yield N -(8-p -tolylnaphthalen-1-yl)picolinamide.The reaction requires Pd(OAc)2as catalyst and stoichiometric AgOAc for halide removal and proceeds in the absence of solvent.Amide hydrolysis yields 8-p -tolylnaph-thalenylamine (Scheme 2).Yields of each step are high,and the amine is readily puri ?ed.Synthesis of 2,3-butanedione diimine ligand 9was accomplished in 40%yield.
The synthesis of the corresponding imine derived from acenaphthenequinone was somewhat more problematic.Reaction of amine 8with acenaphthenequinone in the presence
Scheme 1.General Mechanistic
Considerations
Figure 2.Hindered diimine
catalysts.
Figure 3.(8-p -Tolyl naphthyl α-diimine)nickel(II)catalyst.
Scheme 2.Synthesis of Ligand
9
of formic acid a ?orded predominately monoimine.The monoimine structure was supported by the lack of C 2symmetry in the 1H and 13C NMR spectra as well as signals for a carbonyl carbon at 188.3ppm and an imine carbon at 158.0ppm (Figure S4).However,the desired bis(8-p -tolylnaphthylimino)-acenaphthene 11was successfully prepared by the “template method ”of Rosa (Scheme 3).16a [Bis(8-p -tolylnaphthylimino)-acenaphthene]ZnCl 210was synthesized by the reaction of 8-p -tolylnaphthylamine 9and acenaphthenequinone in the presence of ZnCl 2to give 10as a bright orange-red solid in 72%https://www.doczj.com/doc/3b11621188.html,plex 10exhibits poor solubility in most common solvents such as toluene,methanol,diethyl ether,and methylene chloride.
Complex 10was subsequently treated with an aqueous solution of potassium oxalate to provide the free bis(8-p -tolylnaphthylimino)acenaphthene 11as an orange powder in 87%yield.Recrystallization from toluene/pentane gave bright orange crystals of high purity characterized by 1H and 13C NMR spectroscopy.
2.2.Catalyst Synthesis.The nickel(II)dibromide complexes 12and 13are readily prepared from reaction of the α-diimine ligands 9and 11with (DME)NiBr 2(Scheme 4).Characterization of these complexes is di ?cult because of their poor solubility in common solvents and the fact that they are paramagnetic,eliminating the use of high-resolution NMR spectroscopic analysis.Purity and identity were established by elemental and mass spectrometric analysis as well as X-ray di ?raction analysis.X-ray-quality crystals of 13were obtained by slow di ?usion of pentane into a methylene chloride solution of 1
3.An ORTEP diagram of 13is shown in Figure
4.The complex crystallizes with a molecule of CH 2Cl 2solvent,which is veri ?ed by elemental analysis.The nickel center,as expected,shows a distorted tetrahedral arrangement of ligands around the
nickel center.The tolyl groups lie perpendicular to the naphthyl planes and are positioned such that when the square planar Ni(II)catalyst is generated upon addition of MMAO,the aryl rings will e ?ectively shield the axial coordination sites.Interestingly,the Br1?Ni1?Br1angle is 112.3(3)°.In similar nickel dihalide-diimine complexes the corresponding angles typically are 117?125°.7,11a,b,16b
2.3.Ethylene Polymerization.Ethylene polymerizations were carried out by activation of dibromides 12and 13in toluene using modi ?ed methyl alumoxane (MMAO)in a 1000:1Al:Ni ratio.Polymerizations run at low ethylene pressure (1atm)su ?er from monomer mass transport limitations,which caused measured catalyst turnover frequen-cies (TOFs)to be lower than intrinsic TOFs.Consequently,the polymerizations were performed at 8atm and above.Low catalyst loadings were also used to minimize mass transport problems.Polymerizations using 12and 13are compared with literature data for other aryl diimine catalysts.1,4a,7Additionally,direct comparisons of polymerization data for 12and 13were made with catalyst 14(Figure 5).
Turnover frequencies were calculated as mol PE formed/mol Ni/time.As a consequence,they represent an average TOF over the polymerization time.Since at higher temperatures catalysts decay over the course of the polymerization,measured average TOFs decrease with time.Branching numbers were determined by using 1H NMR spectroscopy.17Polymerization results are summarized in Tables 1,2,and 3.
Table 1summarizes polymerizations at 25°C under 8,13.6,27.2,and 40.8atm of ethylene pressure.Several trends are apparent.First,there is a signi ?cant pressure dependence of the TOFs measured based on 30min runs.In the case of 12an increase of the pressure from 8.0to 13.6atm results in a 1.4-fold increase in TOF (57to 82×103/h,entries 3and 4).A
Scheme 3.Bis(8-p
-tolylnaphthylimino)acenaphthene
Scheme 4.Synthesis of Complexes 12and
13
Figure 4.Crystal structure of 13.Selected bond lengths (?)and angles (deg):Ni1?Br1 2.363(5),Ni1?N1 2.028(2),N1?C11.277(4),Br1i ?Ni1?Br1112.3(3),N1?Ni1?N182.5(14),C1?N1?Ni1
111.7(19).
Figure 5.Standard catalyst.
Table1.E?ect of C2H4Pressure on Catalyst Activities and Polymer Properties a
2142513.6301047 6.3 3.659?5496 312258305745.7 1.393?5444 4122513.6308248.0 1.579?5257 5122527.23012791.2 1.75374 6122540.81022669.3 1.84392 71325830138101.9 1.885?5347 8132513.630297114.5 1.98055 9132527.230568178.1 1.871?5463
a Reaction conditions:toluene(200mL),1000equiv of Al/equiv of Ni,catalyst(1.6μmol).
b Molecular weight was determined by GPC in trichlorobenzene at135°C.
c Branching numbers were determine
d by using1H NMR spectroscopy.Se
e Experimental Section for details.
Table2.E?ects of Reaction Temperature on Catalyst Activities and Polymer Properties a
2145083092514.8 2.160?5261 3145013.610250015.8 2.164?5561 412258305745.7 1.393?5444 512508304216.2 2.4119?61 6122513.6308248.0 1.579?5257 7125013.6304948.6 1.7115?58 8127013.6303025.4 1.9125?63 9122527.23012791.2 1.75374 10125027.23011090.9 1.799?54 11127027.2304032.6 2.1124?61 12122540.81022669.3 1.84392 13125040.83016477.9 2.081?5538 14127040.8309148.3 1.9109?59 151325830138101.9 1.885?5347 1613508308410.9 4.2137?63 171370830189.3 3.7152?66 18132513.630297114.5 1.98055 19135013.63012974.8 2.2116?59 20137013.6303936.8 2.0149?64
a Reaction conditions:toluene(200mL),1000equiv of Al/equiv of Ni,catalyst(1.6μmol).
b Molecular weights of the polymers were determined by GPC(using a universal calibration)in trichlorobenzene at135°C.
c Branching numbers were determine
d using1H NMR spectroscopy.Se
e Experimental Section for details.
Table3.E?ect of Reaction Time on Polymerization Properties and Catalyst Activities a
2142513.6301047 6.3 3.659?5496 312258305745.7 1.393?5444 412258607951.2 1.392?5441 51225812012992.1 1.687?5245 612508304216.2 2.4119?61 712508603230.5 1.8119?61 8125081202420.0 3.9118?61 913508308410.9 4.2137?63 1013508603725.2 2.1133?62 11135081202382.9 1.9130?62
a Reaction conditions:toluene(200mL),1000equiv of Al/equiv of Ni,catalyst(1.6μmol).
b Molecular weights of the polymers were determined by GPC(using a universal calibration)in trichlorobenzene at135°C.
c Branching numbers were determine
d by using1H NMR spectroscopy.Se
e Experimental Section for details.
further doubling of the pressure results in a1.5-fold increase in TOF(entry4vs entry5).In the case of13,the TOF is nearly proportional to pressure(entries7?9).Studies on the diimine palladium complexes have shown that the catalyst resting state is the alkyl ole?n complex and that chain growth is thus independent of ethylene pressure.1,9For nickel dimine catalysts, the resting state can be the alkyl ethylene species,theβ-agostic complex,or a mixture of these species.9The results here suggest that the major resting state of the catalyst is the agostic alkyl complex,leading to an essentially?rst-order dependence on ethylene pressure.8,18
The activity of the acenaphthyl-based catalyst13is about2?3times that of12,possessing a dimethyl backbone(entries3?6vs7?9).This di?erence is consistent with previous observations.1,7Catalysts12and13are less active than ortho-dialkyl-substituted aryl analogues such as14.1,4a,7For example,14exhibits a TOF frequency at8atm ethylene of ca.
8.5×105vs1.4×105/h for13under similar conditions(entry 1vs7).The TOF determined for the acenaphthenequinone-derived cyclophane catalyst5(M=NiBr2)reported by Guan is 14×105/h at30°C,8atm ethylene,measured over10min.14a The molecular weight distributions of polyethylenes generated from12and13at25°C are in the1.3?1.9range and are more narrow than generally observed for14and related catalysts.7,21 Polymer molecular weights for12and13are higher than those obtained with14,with M n exceeding106g/mol for13(entries 7?9).In contrast,catalysts of type5produce polyethylene with M n ca.3×105under similar conditions.14a
The most notable feature of these catalysts is the high branching number of the polyethylenes produced.For catalysts 12and13the branching numbers are93and85,respectively, at25°C/8atm ethylene(entries3and7).These numbers are substantially higher than those for14(entry1)and related systems.7The branching density for polymer produced by acenaphthenequinone-derived nickel paracyclophane catalyst5 at similar conditions was reported to be ca.70.14a Similar to other nickel diimine catalysts,the branching number decreases and T m increases with increasing ethylene pressure.For example,in the case of12,branching decreases smoothly from93at8atm ethylene to43at40.8atm ethylene,while T m increases from44°C to92°C(entries3and6).
Table2summarizes the e?ects of varying temperature on catalyst activities and polymer properties.For comparison, some of the data from Table1are repeated in Table2.For both catalysts12and13the30min turnover frequencies drop quite signi?cantly as temperature is increased from25°C to70°C.For example,the average TOF for12at13.6atm ethylene decreases from82×103/h at25°C to49×103/h at50°C to 30×103/h at70°C(entries6?8).Similarly,the TOF for catalyst13at13.6atm decreases from297×103/h at25°C to 129×103/h at50°C to39×103/h at70°C(entries18?20). Since the TOF is dependent on ethylene concentration,a signi?cant portion of this decrease is due to decreased solubility of ethylene.However,examining the turnover frequency as a function of time indicates that some of this decrease results from increased catalyst decay rates at higher temperatures as shown below.This behavior is consistent with the behavior of standard ortho-dialkyl-substituted aryl diimine catalysts.1,2,7,9 Polymer branching increases dramatically with temperature, as seen with standard diimine catalysts.For example,catalyst12 at13.6atm produces PE with branching numbers of79at25°C,115at50°C,and125at70°C(entries6?8).A similar trend is seen for catalyst13(entries15?17and18?20).In both cases,polymerization at a temperature of70°C results in polymers with125?150branches per1000C and are the most highly branched polyethylenes yet obtained with nickel catalysts.These branching numbers rival those obtained with palladium catalysts.1,8,18The DSC traces for these highly branched polymers are exhibited in the Supporting Information (Figures S7?11)and show very broad,ill-de?ned melting transitions.Above ca.100branches per1000C,the polymers are completely amorphous.The increase in branching with an increase in temperature results from an increase in the rate of chain-walking relative to the rate of insertion.Since the rate of chain growth is essentially second-order and will exhibit a negativeΔS?,an increase in temperature will result in a less rapid increase in the chain growth rate relative to the rate of chain-walking.This is magni?ed by the fact that ethylene solubility decreases with increasing temperature.
Table3shows the e?ect of varying time on the average TOF. These data show that the catalyst lifetimes are moderately short in the25?70°C temperature range.For example,at50°C the average TOF for12is42×103/h at8atm over30min.It drops to32×103/h over60min(entries6and7).Translating this to turnover numbers,the TON after30min is21800, which increases only an additional10300to32100after another30min.Catalyst13is even less stable in that the TON at8atm,30min is essentially the same as the TON at60min (entries9and10).These stabilities are similar to those exhibited by standard ortho-dialkyl-substituted aryl diimine catalysts.7In contrast,the paracyclophane catalyst5shows much better stability in the50?70°C range.14a
3.SUMMARY AND CONCLUSIONS
Nickel(II)α-diimine dibromide complexes incorporating8-p-tolylnaphthylimino groups have been prepared and used as ethylene polymerization catalysts by activation with modi?ed methylalumoxane.These complexes possess C2symmetry,as illustrated by the crystal structure of13.By virtue of the naphthyl group perpendicular to the plane of the diimine ligand and the tolyl group perpendicular to the naphthyl group,the two tolyl groups cap the two axial sites of the square planar cationic polymerization catalyst.19Examination of the crystal structure of13and related standard arylα-diimine catalysts7,9b,11a,b,16b possessing alkyl groups in the ortho positions suggests that such a cap provides increased steric bulk in the axial positions of these catalysts.
The features of12and13as ethylene polymerization catalysts are consistent with increased axial bulk relative to standard diimine catalysts2.Increasing the steric bulk results in lower rates of chain transfer relative to chain propagation rates, and thus higher molecular weights and more narrow PDIs are observed compared with polymers produced with“standard”nickel diimine catalysts such as14under similar conditions.As observed with14,the PE produced is branched,and branching densities decrease with ethylene pressure and increase with increasing temperature.Furthermore,as noted earlier,increas-ing axial bulk results in increasing the branching density. Catalysts12and13yield the most highly branched PE produced from Ni catalysts seen to date.Branching densities are comparable to those produced with diimine palladium catalysts.1,8,18Although the thermal stabilities of12and13are comparable to those of14,the turnover frequencies are reduced by a factor of2?3,resulting in reduced productivity. The closest structural analogue to12and13is the paracyclophane catalyst5.The cyclophane catalysts are
signi?cantly thermally more stable and under similar conditions exhibit higher turnover frequencies but produce PE with somewhat lower molecular weights and branching densities. These comparisons suggest that the tolyl cap in12and13 provides greater steric shielding compared with the bridging para-cyclophane structure.
The easy synthesis of8-aryl-1-naphthylamines provides access to a new class ofα-diimine-based nickel and palladium catalysts in which the8-substituent is ideally positioned to provide steric bulk in the axial sites.We are exploring the behavior of nickel and palladium diimine catalysts by employing this new class of ligands in the polymerization of ethylene. Mechanistic studies of the polymerization processes are in progress.
4.EXPERIMENTAL SECTION
General Procedures.All manipulations of air-and water-sensitive compounds were carried out using standard Schlenk,high-vacuum, and glovebox techniques.Argon and nitrogen were puri?ed by passing through columns of BASF R3-11catalyst(Chemalog)and4?molecular sieves.THF was distilled under a nitrogen atmosphere from sodium/benzophenone prior to use.Diethyl ether,pentane,methylene chloride,and toluene were passed through columns of activated alumina and degassed by either freeze?pump?thaw methods or purging with argon.Methanol was distilled under a nitrogen atmosphere from Mg prior to use.Dichloromethane-d2for NMR was dried with CaH2and vacuum transferred into a sealed?ask.The MMAO used was a6.42%Al solution of modi?ed methylaluminoxane in heptane,d=0.73g/mL,containing23?27%isobutyl groups, purchased from Akzo Nobel.1H and13C NMR spectra were recorded at400,500,and600MHz.High-temperature NMR analysis of polyethylene was performed on a Bruker-DRX-500at120°C.1H and 13C NMR spectra were referenced with solvent peaks.Elemental analyses were performed by Robertson Microlit Laboratories Inc. (Madison,NJ,USA)or Atlantic Microlabs Inc.(Norcross,GA,USA). High-temperature gel permeation chromatography(GPC)was performed in1,2,4-trichlorobenzene at135°C using a PL220GPC equipped with a PLgel MIXED-B column,10μm particle size,300mm long.The M n and M w data were obtained by comparison with a polystyrene standard.Di?erential scanning calorimetry(DSC)was recorded on a TA Instruments DSC Q200.Samples were heated to 200°C,cooled rapidly to?100°C,and then scanned from?100to 200°C with scan rate of10°C/min.
N-(Naphthalen-1-yl)picolinamide.1-Naphthylamine(7.2g,50 mmol)in pyridine(10mL)was added dropwise in15min to a stirred solution of picolinic acid(6.2g,50mmol)in pyridine(14mL)at50°C.Triphenylphosphite(13mL,50mmol)was added to the resulting mixture followed by stirring at110°C for4h.The mixture was cooled to room temperature followed by addition of distilled water(50mL) and dichloromethane(50mL).The mixture was placed in a500mL Erlenmeyer?ask,and aqueous H2SO4(150mL;concentrated H2SO4/ water,1/1v/v)was added.The mixture was shaken,and the layers were separated.The organic layer was washed with aqueous H2SO4(2×100mL).The acidic aqueous layers were combined and neutralized with solid sodium bicarbonate.The tan solids formed were?ltered and washed thoroughly with distilled water,then recrystallized from methanol to a?ord tan needles(10.9g,87%).This compound is known.201H NMR(400MHz,CDCl3,ppm):δ10.77(s,1H),8.70(d, J=8.2Hz,1H),8.36(d,J=8.2Hz,1H),8.36(d,J=7.8Hz,1H), 8.09(d,J=8.2Hz,1H),7.95?7.88(m,2H),7.70(d,J=8.2Hz,1H), 7.61?7.50(m,4H).
N-(8-p-Tolylnaphthalen-1-yl)picolinamide(7).N-(Naphthalen-1-yl)picolinamide(5.1g,20.5mmol),4-iodotoluene(17.5g,80.3 mmol),AgOAc(5.1g,30.5mmol),and Pd(OAc)2(101mg,0.45 mmol)were placed in a Kontes?ask.The resulting suspension was stirred at140°C for24h.After dilution with dichloromethane(ca.40 mL)and column chromatography(hexanes/ethyl acetate,90/10,then hexanes/ethyl acetate,65/35),the solvent was evaporated to give light brown crystals(6.45g,91%yield).R f=0.50(hexanes/ethyl acetate, 65/35),mp=123?124°C(hexanes).1H NMR(400MHz,CDCl3, ppm):δ9.61(s,1H),8.23(dd,J=7.7,1.5Hz,1H),8.18?8.16(m, 1H),8.10?8.08(m,1H),7.86(dd,J=8.4,1.5Hz,1H),7.80?7.74 (m,2H),7.58?7.54(m,1H),7.48?7.44(m,1H),7.32?7.24(m,4H), 6.96(d,J=7.7Hz,2H),2.80(s,3H).13C NMR(100MHz,CDCl3, ppm):δ162.0,150.0,147.4,139.9,137.8,137.0,136.6,135.6,133.0, 130.5,129.2,128.9,128.6,126.5,126.0,125.7,125.1,125.0,122.6, 121.9,21.2.FT-IR(neat,cm?1):ν1689,1493,1433,814,764,751, 716,697.Anal.Calcd for C23H18N2O(388.4g/mol):C,81.63;H, 5.36;N,8.28.Found:C,81.54;H,5.35;N,8.23.
8-p-Tolylnaphthalen-1-amine(8).N-(8-p-Tolylnaphthalen-1-yl)picolinamide(10.1g,30mmol)was re?uxed for6h in ethanolic NaOH solution(12g NaOH,300mmol in EtOH/H2O,10/1v/v,120 mL).The reaction mixture was cooled and diluted with an equal volume of water.The product was extracted with dichloromethane(3×60mL).The combined organic layers were combined,dried with MgSO4,and concentrated.After chromatography(hexane/ethyl acetate/triethylamine,94/5/1),beige crystals were obtained(7.0g, quantitative yield).R f=0.16(hexane/ethyl acetate/triethylamine,94/ 5/1),mp=73?74°C(hexanes).1H NMR(400MHz,CDCl3,ppm):δ7.75(d,J=8.1Hz,1H),7.38?7.22(m,7H),7.13(d,J=7.0Hz, 1H),6.60(d,J=7.3Hz,1H),3.74(s,2H),2.42(s,3H).13C NMR (100MHz,CDCl3,ppm):δ143.8,140.6,138.4,137.3,135.9,129.2, 128.8,128.6,128.4,126.6,124.7,121.0,119.1,111.4,21.4.FT-IR (neat,cm?1):ν3490,3393.1615,1579,1522.Anal.Calcd for C17H15N233.3g/mol):C,87.52;H,6.48;N,6.00.Found:C,87.44; H,6.42;N,5.96.
Bis(8-p-tolylnaphthylimino)butadiene(9).A25mL Schlenk ?ask was charged with a solution of8-p-tolylnaphthalenylamine(0.59 g,2.53mmol)in methanol(2mL),molecular sieves(4?),and2,3-butanedione(0.106g,1.23mmol).Acetic acid(3?5drops)was added to the reaction mixture followed by re?uxing the solution for2days. The formed precipitate was?ltered and washed with dry methanol (3?5times)until the color of methanol washings was faint.The solid residue was dried under vacuum,dissolved in dry methylene chloride, and?ltered,and the solution was evaporated under vacuum to yield yellow diimine product(0.26g,40%).1H NMR(600MHz,CD2Cl2):δ7.86(d,J=8.1Hz,2H,f),7.69(d,J=8.1Hz,2H,c),7.51(t,J=7.8 Hz,2H,b),7.46(t,J=7.8Hz,2H,e),7.18(d,J=6.9Hz,2H,d),7.07 (d,J=7.7Hz,4H,g),7.02(d,J=7.3Hz,4H,h),6.40(d,J=7.1Hz, 2H,a),2.40(s,6H,i),1.28(s,6H,j).13C NMR(151MHz,CD2Cl2):δ166.8(C N),149.0(C?N),142.1,139.9,136.3,135.8,129.8, 129.4,128.5,128.4,126.2,125.6,124.9,124.0,115.0,21.5,15.6.
Bis[(8-p-tolylnaphthylimino)acenaphthene](11).In a300mL three-necked round-bottom?ask ZnCl2(0.86g,6.25mmol)and acenaphthenequinone(1g,5.5mmol)were suspended in glacial acetic acid(10mL).8-p-Tolylnaphthylamine(2.91g,12.5mmol)was added, and the reaction mixture was re?uxed under stirring for30min.The solution was allowed to cool to room temperature,and a bright orange-red solid precipitated.The solid was separated by?ltration and washed with acetic acid(3×10mL)and diethyl ether(8×15mL), to remove remaining acetic acid.Drying under vacuum gave
pure
bright orange-red,poorly soluble solid 10(2.96g,72%).ESI:m /z 613.3[L +H]+;635.3[L +Na]+;721.0[M ?2CH 3]+;1333.4[M +L +H]+.The procedure for removal of the zinc from the zinc diimine complex follows a literature precedent.16a Bis[(8-p -tolylnaphthylimino)acenaphthene]zinc dichloride 10(2.5g, 3.35mmol)was suspended in methylene chloride (200mL),and a solution of potassium oxalate (1.84g,10mmol)in water (10mL)was added.The reaction mixture was stirred vigorously for 15min.A white precipitate of zinc oxalate was generated in the aqueous phase.The two phases were separated,and the organic layer was washed with water (3×20mL)and dried with MgSO 4.After ?ltration the solvent was removed under vacuum to a ?ord the product as an orange powder (1.79g,87%).1H NMR (600MHz,CD 2Cl 2):δ7.93(d,J =7.8Hz,2H,f),7.83(d,J =7.9Hz,2H,j),7.78(d,J =8.2Hz,2H,c),7.64(t,J =7.7Hz,2H,k),7.44(t,J =7.7Hz,2H,e),7.22?7.14(m,6H,g ′,h ′b),7.04(d,J =6.9Hz,2H,d),6.88(d,J =6.6Hz,2H,l),6.41(d,J =7.2Hz,2H,a),5.95(d,J =7.5Hz,2H,g),5.85(d,J =7.5Hz,2H,h),2.17(s,6H,i).13C NMR (151MHz,CD 2Cl 2):δ159.4,149.2,141.3,140.9,139.7,135.8,135.7,130.9,130.1,130.0,129.4,128.4,128.3,127.7,127.5,127.3,126.2,125.5,124.9,122.8,122.5,114.5,21.4.Bis[(8-p -tolylnaphthylimino)(2,3-dimethyl)butadiene]·NiBr 2(12).A 50mL Schlenk tube was charged with imine 9(238mg,0.53mmol)and (DME)NiBr 2(154mg,0.5mmol)in an argon-?lled glovebox.The tube was placed under argon,and CH 2Cl 2(20mL)was added via syringe.The red reaction mixture was stirred at room temperature for 2days.The supernatant liquid was removed,and the remaining brown-red solid was washed with ether (3×8mL)and dried under reduced pressure at room temperature for about 5h.Yield:289mg (79%).Anal.Calcd for C 38H 32Br 2N 2Ni ·CH 2Cl 2:C,57.12;H,4.18;N,3.42.Found:C,58.32;H,4.19;N,3.55.22ESI:m /z 517.26[L1+H]+;575.18[M ?2Br +H]+;655.12[M ?Br +2H]+;773.55[M +K]+.
Bis[(8-p -tolylnaphthylimino)acenaphthene]·NiBr 2(13).A 50mL Schlenk tube was charged with imine 10(515mg,0.84mmol)and (DME)NiBr 2(247.0mg,0.8mmol)in an argon-?lled glovebox.The tube was placed under argon,and CH 2Cl 2(25mL)was added via syringe.The red reaction mixture was stirred at room temperature for 2days.The supernatant liquid was removed,and the brown-red solid was washed with ether (3×25mL)and dried under reduced pressure at room temperature for 5h to provide 13as a red solid (589mg,88%).Anal.Calcd for (C 46H 32Br 2N 2Ni ·CH 2Cl 2):C,61.61;H,3.74;N,3.06.Found:C,62.33;H,3.61;N,3.06.22ESI in CH 2Cl 2:m /z 613.2[L +H]+;635.2[L +Na]+;745.1[M ?Br +4H]+;909[M +2H]+.ESI in MeOH:m /z 613.2[L +H]+;635.2[L +Na]+;745.1[M ?Br +4H]+;1357.4[L2M ?Br +4H]+.
General Procedure for Polymerizations.A 1000mL Parr autoclave was heated under vacuum at 60°C for several hours followed by cooling and back ?lling with ethylene.Toluene (200mL)was added,the autoclave was sealed,and the ethylene pressure was raised to ca.8atm and maintained for about 15min.The reaction temperature was established.The autoclave was then vented,and the precatalyst solution/suspension (1.6μmol catalyst)was rapidly added followed by MMAO (1.6mL;Al:Ni =1000).The autoclave was sealed and rapidly pressurized to the desired ethylene pressure with fast stirring.The temperature was maintained by a water circulator,and no exotherms were noted by using 12and 13as catalysts.A small exotherm (<10°C)was occasionally observed using 14as a catalyst.The reaction was quenched by venting the autoclave followed by addition of HCl/methanol (5%v).The precipitated polymers were ?ltered from solution and dried under vacuum.
Crystallographic Structural Determination.Crystals of 13suitable for X-ray crystallography were grown by slow di ?usion of pentane into a room-temperature saturated solution of 13in CH 2Cl 2.Single crystals were mounted in oil on the end of a ?ber.Intensity data were collected on a Bruker SMART 1K di ?ractometer with a CCD detector using Mo KR radiation of wavelength 0.71073?.The structure was solved by direct methods and re ?ned by least-squares techniques using the NRCVAX57suite of programs.All non-hydrogen atoms were re ?ned to ride on the atoms to which they were bonded.
ASSOCIATED CONTENT
*
Supporting Information NMR spectra of new compounds and polyethylene;DSC data for polymers.This material is available free of charge via the Internet at https://www.doczj.com/doc/3b11621188.html,.
■AUTHOR INFORMATION
Corresponding Authors
*E-mail:olafs@https://www.doczj.com/doc/3b11621188.html,.
*E-mail:mbrookhart@https://www.doczj.com/doc/3b11621188.html,.
Notes
The authors declare no competing ?nancial interest.
■ACKNOWLEDGMENTS
This research was supported by NSF (grant CHE-1010170to M.B.),the Welch Foundation (Grant No.E-1571to O.D.),and the Norman Hackerman Advanced Research Program (to O.D.).D.Z.thanks the China Scholarship Council for a Visiting Scholar Research Fellowship.We thank Dr.Peter S.White for help with collecting and solving the X-ray structure of 13and Mr.Qian Chen for providing GPC analyses.
■
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(21)We cannot rule out some broadening due to mass transfer e?ects,but we have attempted to minimize such e?ects by using very low catalyst loadings(1.6μmol)in large solvent volumes(200mL) with high stirring rates.
(22)Although these results are outside the range viewed as establishing analytical purity,they are provided to illustrate the best
values obtained to date.