Nickel-mediated Polymerization of Methyl Methacrylate

Nickel-mediated Polymerization of Methyl MethacrylateAbstractThe Ni(II) complexes Ni(5-C5H3 R2)(X)(NHC) 1af combined with monoamine oxidase was tested in methylmethacrylate (MMA) polymerisation. The complex 1f, bearing the bulky 2,6-diisopropenylphenyl substituents in the NHC ligand was found to be the most strong in the polymerisation of MMA with TOF up to 200 h-1 resulting in a syndiotactic, high molecular weight PMMAs which stack be explained by non-ionic detergent, MAO-centered polymerization mechanism.IntroductionA great deal of attention is currently creation paid to polymers containing opposite monomers,which may give rise to new high-performance materials with high adhesion and formidability and good dyeing and moisture adsorption properties.1 Metal-based catalysts tolerant of diametrical functionalities, which perform homopolymerization, and if possible copolymerization with nonpolar olefins, argon being sought. Late transition alloy complexes look promising becaus e of their lower oxophilicity,2 and probable tolerance against polar monomers, and against impurities in polar olefins polymerization.Acrylates are polymerized and copolymerized for many diametrical uses including coatings,textiles, adhesives, and paper.3 Commercial poly(methyl methacrylate) has been produced since 1927.4 Like many other polar monomers, acrylates are commonly polymerized by 18radical5 or anionic mechanisms. In addition, polymerization of acrylates with late transition metal complexes has been studied.6 Metallocenegroup IV complexes are known to be excellent for this type of polymerization.Half-sandwich nickel(II) complexes with N heterocyclic carbenes (NHC) of the general formula Ni(5-C5H4R)(X)(NHC) (R = H or alkyl, X= Cl, Br, I) was synthesized by reacting nickelocene or its derivatives and suitable imidazolium salts . The diamagnetic property of these compounds helps in showing some C-C bond forming receptions. But, complexes 1 are very active in aryl dehaloge nation and aryl amination, hydrothiolation of alkynes and oxidation of collateral alcohols as a precatalyst.ExperimentalMaterials and synthesisMethyl methacrylate (MMA)Methyl acrylate (MA),Ni(acac)2,Toluene,Purified THF, and hexane1,3-bis(1,1-dimethylbut-3- enyl)cyclopentadienecomplexes 1ad and 1fNi(5-C5H5)(CH3CN)(IMes)+(PF6) 5Ni(5-C5H5)(Cl) (PPh3)MAO (10% wt. root in toluene)Synthesis of 1eA hexane solution of n-BuLi (2.5 mL, 5.1 mmol) and a THF (5 mL) solution of1,3-bis(1,1-dimethylbut-3-enyl) cyclopentadiene (4.83 mmol) was added and the compartmentalization was move for 2 h at ambient temperature. This solution was added to the solution of Ni(acac)2 (1.199 g, 4.67 mmol) in THF (10 mL) at 78 oC. A color falsify immediately from green to red is observed and a suspension of 1,3-dimesitylimidazolinium chloride12 (1.693 g, 4.96 mmol) in THF (10 mL) was quickly added at this temperature. The reaction mixture was allowed to warm up to ambient temperature and stirred for a further 2 h. The volatiles were removed under reduced pressure. The solid residue was extracted with hexane (20 mL) and filtered through Celite. Complex 1e was unaffectionate by crystallization as a red, microcrystalline solid.Polymerization14mg of Complex 1f(0.0255 mmol) dissolved in 15ml of toluene in a schlenk tube with a magnetic stirrer in it. To this solution, MAO ((5.10 mL, 10% wt. in toluene, 7.65 mmol) which is red in color was added by a hitman tight pipette which results in a brown solution. The obtained brown solution was stirred at ambient temperature for half an hour. Now MMA(2.72 mL, 0.0255 mol) was added and the apparatus is placed in a oil bathe maintaining 50oC with vigorous stirring. The reaction mixture was now quenched with lavishness of CH3OH (200 mL) and then filtered. PMMA was collected by filteration and serve with CH3OH and kept for over night drying. The obtained polymer is purified with small volume of CHCl3 and stirred overnight with 10% aq. HCl. The organi c and the sedimentary phases are separated and the organic phase is poured into excess of CH3OH. A white solid PMMA was isolated by filteration.2.4. CharacterizationNMR spectr at ambient temperature on a Mercury-four hundredBB spectrometer operating at 400 MHz for 1H NMR was recorded and at 101 MHz for 13C NMR was recorded.EI (70 eV) mass spectra on an AMD-604 spectrometer was recorded.MALDI-TOF mass spectra w with a Bruker Daltonics ultrafleXtremeTM mass spectrometer using HABA matrix was recorded.The average molecular weights were measurable on a LabAlliance liquid chromatograph equipped with a Jordi Gel DVB Mixed Bed column (250 mm 10 m) using CH2Cl2 as the mobile phase at 30 -C and calibrated with exemplar PMMAs.2.5. crystallisation grammatical construction determinationThe selected single crystals mounted in inert oil were transferred to the cold gas stream of the diffractometer. Diffraction information was collected at 100(2) K on the Oxford Diffraction Gemini A Ultra di ffractometer with graphite-monochromated Mo-K radiation. booth refinement, data collection, data reduction and analysis were performed with the CrysAlisPRO 13. Empirical absorption correction using spherical harmonics was applied. The structure was solved in monoclinic space group P21/c by direct methodsusing the SHELXS computer program . It is worth noting here that the skew angle is very close to 90-. Full-matrix least-squares refinement against F2 values was carried (SHELXL-97 and OLEX2. plank 1Crystal data, data collection and refinement parameters for complex 1e.Complex 1eEmpirical formula C38H51ClN2NiCrystal size (mm) 0.07 0.07 0.40M(g mol1) 629.96Crystal system MonoclinicSpace group P21/c (no. 14)Z 4F(0 0 0) 1352Temperature (K) 100(2)Dcalc. (g cm3) 1.251Absorption coefficient (mm1) 0.688Radiation Mo-K ( = 0.71073A)range (-) 3.330.0Index range 20 h 20 13 k 13 13 l 13Reflections collected 37,962Unique data 9684, Rint = 0.0355Observed refl. I 2(I) 8195Data/restraints /parameters 9684/17/415Goodness-of-fit on F2 a 1.043Results and discussionSynthesisThe series of Ni(II) complexes 1ad and 1f (Scheme 1) was prepared from nickelocene or 1,1 bis(allyl)nickelocene and the suitable imidazolium salt.Complex 1e bearing the 1,3-disubstituted cyclopentadienyl ligand could not be obtained by this route. thusly, it was synthesized form the pentamethylcyclopentadienyl relation 4e from Ni(acac)2 by the oneness-pot two-step procedure intermediate (5-1,3-R2C5H3)Ni(acac) (Scheme 2).Scheme 1. Ni(II) complexes used in this study, where R = allyl (1d) or 1,1-dimethyl-but-3-en-1-yl (1e) Mes = 2,4,6-trimethylphenyl, Dipp = 2,6-diisopropylphenyl.Scheme 2. The synthesis of complex 1e, where R = 1,1-dimethyl-but-3-en-1-yl,Mes = 2,4,6-trimethylphenyl.From the symmetry of the molecule, it is found that the geometry of the molecule was trigonal planar.The bond angles and the lengths surrounded by nickel and its substituents are approximately same compared to the related c ompounds.Due to week contact between H(29A) heat content of mesityl methyl group C(29) and the chlorine ion H(29A)Cl(1) 2.57 and C(29A)Cl(1) 3.5346(15)A it resulted in the formation of a week intra molecular C HCl hydrogen bond.3.2. PolymerizationPolymerization was performed under the similar environment of the styrene polymerization with an excess of commercial MAO. A toluene solution of complex 1 was treated with an excess of MAO (AlNi = 1001) for 30 min at ambient temperature.Then MMA (MMANi = 10001) was added and the polymerization was devolve in a sealed Schlenk tube for 3 h at 50 -C. The reaction mixture was separated as a homogenous mixture.Molecular structure of complex 1e.Polymerization of methyl methacrylate with complexes 13 and MAOa.The bromide analog 1b displayed slightly higher activity compared to 1a, while complex 1c bearing the alkyl-aryl NHC ligand was sanely more(prenominal) productive than 1b in the productivity of the Ni(Cp)(X)(NHC))/MAO catalytic system.Sub stiuted cyclopentadienyl ligands was examined and complex 1d with allylcyclopentadienyl ligand gave the same result as 1a. It was reasoned that the allyl group might be too small to induce any subject. Therefore complex 1e with two bulky substituents was synthesized and tested to give the same conversion as 1d.By introducing the more bulky 2,6-diisopropylphenyl substituents in the NHC ligand (complex 1f) the yield of PMMA was 34% and when the excess of MAO was increased (AlNi = 3001), the isolated yield of PMMA was increased to 60%.Changing the solvent resulted in a disappointing yield which was predicted to be due to the solubility problem.1H and 13C NMR spectroscopy were used to determine the microstructure of PMMA.Syndiotactic-rich polymers were resulted toluene where atactic PMMA was obtained with hexane and this was because of the formation of MMA polymers via different mechanism in hexane and toluene.Isolated Methanol soluble oligomeric MMA were studied by MALDI-TOF MS which suggests more than one mechanism was operating the reaction.Scheme 3. Rationale for the formation of poly(methyl methacrylate) withNi(Cp)(X)(NHC)/MAO.The structure of Ni complex had considerable effect on the overall yield of MMA with no influence on the molecular weight distribution or tacticity of the resulting polymer and the Al Ni ratio do not effect the tacticity of the polymer.It was supposed that MMA polymerized by co ordinative anionic mechanism described in scheme 3.ConclusionIt can summarized that the complexes 1a-f and 2 can initiate polymerization of MMA in the presence of MAO with TOF up to 200h-1. The results of PMMA with GPC, NMR and MS imply a anionic, MAO-centered mechanism of polymerization catalyzed by Ni(II) species.References1. H. Martin in Ziegler Catalysis (Eds. G. Fink, R. Mlhaupt, H. H. Brintzinger), SpringerVerlag, Berlin, 1995, p 15.2. G. Natta, P. Pino, G. Mazzanti, U. Giannini J. Am. Chem. Soc. 79 (1957) 2975.3. A. Andresen, H.-G. Cordes, J. Herwig, W. Kaminsky, A. Merck, R. Mottweiler, J. Pein, H.Sinn, H.-J. Vollmer Angew. 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