Cobalt and Nickel Complexes Bearing 2,6-Bis(imino)phenoxy Ligands:Synthesis and Ethylene Oligomerization Study

Journal of Chemistry, May 2019

A series of new cobalt and nickel complexes MLX2 (M = Co or Ni, X = Cl) bearing 2,6-bis(imino)phenoxy ligands have been synthesized. Treatment of the complexes with methylaluminoxane (MAO) leads to active catalysts for ethylene oligomerization. The oligomers are olefins from C4 to C6.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

http://downloads.hindawi.com/journals/jchem/2006/831367.pdf

Cobalt and Nickel Complexes Bearing 2,6-Bis(imino)phenoxy Ligands:Synthesis and Ethylene Oligomerization Study

http://www.e-journals.net 0973-4945 Cobalt and Nickel Complexes Bearing 2,6-Bis(imino)phenoxy Ligands: Synthesis and Ethylene Oligomerization Study JIAN-LONG DU 0 LI-JUN LI 0 0 College of Chemistry and Environmental Science Hebei University , Baoding 071002 , P.R. China A series of new cobalt and nickel complexes MLX2 (M = Co or Ni, X = Cl) bearing 2,6-bis(imino)phenoxy ligands have been synthesized. Treatment of the complexes with methylaluminoxane (MAO) leads to active catalysts for ethylene oligomerization. The oligomers are olefins from C4 to C6. Nickel; cobalt; 2; 6-bis(imino)phenoxy; ethylene oligomerization Introduction Late-transition metal complex as catalyst for olefin polymerization and oligomerization is an intense subject of academic research and industrial application.1-2 Recent progress was employing cationic Ni(II) bis(imino) complexes as effective catalysts for ethylene oligomerization and polymerization.3-5 Brookhart, Bennett and Gibson had made great contribution to design highly active ethylene polymerization catalysts based on iron (II) and cobalt (II) bearing 2,6-bis(imino)pyridyl ligands.6-8 Moreover, Grubbs reported new neutral Ni (II) salicylaldimiminato complexes as catalysts for the polymerization of ethylene to obtain high molecular weight polyolefin under moderate conditions.9 Modification of the substituents of imino groups results in dramatic changes to the resultant polyolefin.10 Sun also reported a series of salicylaldimiminato complexes as catalysts for the polymerization of ethylene.11 Now we focus on exploring the effect of changing the central pyridyl moiety to phenol. Herein, we report the synthesis of Co(II) and Ni(II) complexes bearing 2,6bis(imino)phenoxy ligands and their ethylene oligomerization activity. EtOH, HAc R2 N OH N R2 CoCl2 or NiCl2 EtOH R2 t-Bu O OH O + NH2 R1 R2 R3 Experimental R1 R3 t-Bu N M OH N Cl Cl R1 R3 R2 R1 R3 t-Bu R1 R3 Scheme 1. Synthetic procedure for the catalysts All manipulations were carried out under an atmosphere of nitrogen using standard Schlenk and Cannula techniques. Using HP-MOD 1106 microanalyzer performed elemental analysis. NMR spectra were recorded on a Bruker spectrometer DMX-300, with TMS as the internal standard. IR spectra were obtained as KBr pellets on a Perkin-Elmer FTIR 2000 spectrometer. Mass Spectra were measured on a Kratos AEI MS-50 instrument using electron impact (EI). Melting points were determined without further correction. Ethylene oligomerization results were recorded on a HP5890 Series II gas chromatograph (HewlettPackard). Compound 2-hydroxy-5-tert-butylisophthaldehyde was prepared according to an established procedure.14 While MAO (1.4mol l-1) was purchased from Albemarle Corp (USA); Nickel or cobalt chloride and all of the anilines were used commercially without further purification unless stated otherwise. Preparation of ligands (L1): To a solution of 2-hydroxy-5-tert-butylisophthaldehyde (0.62 g, 3 mmol) with a few drops of glacial acetic acid in anhydrous ethanol 15 mL under N2 at 50 ?C was added a solution of 2,3-dimethylaniline (0.73 g, 6 mmol) in anhydrous ethanol (10 ml) over a period of 20 min with stirring. Then the mixture was refluxed for additional 2h. Upon cooling to room temperature, the volatiles were removed under vacuum, and the residue was recrystallized from ethanol giving the yellow crystals 0.87 g in 70% yield, mp. 131-133?C. 1H-NMR(CDCl3), ?, ppm: 13.96 (1H, s), 8.79 (2H, br), 6.94-7.16 (6H, m), 2.34-2.36 (12H, m), 1.57 (6H, s), 1.42 (9H, s). IR(KBr), cm-1: 3593 (m), 2963 (s), 1622, 1574 (vs), 1465 (s), + 1377, 1309, 1284, 1239, 1219, 1091, 1035, 1009 (s), 888, 782 (s). EI-MS (m/z): 412 (M , 3.5%), 293 (M+-NAr?, 7.4%), 292 (M+-NAr?-H, 43.7%), 291 (M+-NAr?-2H, 100%), 277 (4.4%), 132 (8.7%), 120 (5.4%), 105 (8.7%). Anal. Calcd For C28H32N2O: C, 81.51; H, 7.82; N; 6.79. Found: C, 81.44; H, 7.81; N, 6.82%. (L2): By using the procedure described above for synthesis of L1, the ligand L2 was obtained by the reaction of 2-hydroxy-5-tert-butylisophthaldehyde with 2, 5-dimethylaniline as a red crystals 1.06 g in 85% yield, mp. 151-153?C. 1H-NMR(CDCl3), ?, ppm: 14.06 (1H, s), 8.79 (2H, br), 6.90-7.15 (6H, m), 2.38 (12H, s), 1.57 (6H, s), 1.42 (9H, s). IR(KBr), cm-1: 3436 (m), 2963 (s), 1617, 1570 (vs), 1465 (s), 1373, 1290, 1218, 1155, 1009 (s), 877, 765(s). EI-MS (m/z): 412 (M+, 6.2%), 292 (M+-NAr?-H, 42.6%), 291 (M+-NAr?-2H, 100%), 277 (4.3%), 132 (6.5%), 120 (6.3%), 105 (7.7%). Anal. Calcd For C28H32N2O: C, 81.51; H, 7.82; N; 6.79. Found: C, 81.55; H, 7.84; N, 6.78%. (L3): By using the procedure described above for synthesis of L1, the ligand L3 was obtained by the reaction of 2-hydroxy-5-tert-butylisophthaldehyde with 3, 5-dimethylaniline as a red powder 0.93 g in 75% yield. mp. 61-62?C. 1H-NMR(CDCl3), ?, ppm: 14.04 (1H, s), 8.86 (2H, br), 6.94 (6H, s), 2.38 (12H, s), 1.57 (6H, s), 1.41 (9H, s). IR(KBr), cm-1: 3486 (m), 2959 (s), 1622, 1579 (vs), 1465 (s), 1359, 1264, 1222, 1150, 1006 (s), 849, 765 (s). EI-MS (m/z): 412 (M+, 100%), 411 (M+-H, 12.8%), 292 (M+-NAr?-H, 52.2%), 291 (M+-NAr?-2H, 18.0%), 277 (5.2%), 132 (9.6%), 120 (3.6%), 105 (22.6%). Anal. Calcd For C28H32N2O: C, 81.51; H, 7.82; N; 6.79. Found: C, 81.52; H, 7.83; N, 6.76%. Preparation of complexes Complex (1): CoCl2?6H2O (1mmol) and L1 (1mmol) were combined in a Schlenk flask under an N2 atmosphere. EtOH (10 mL) was added, and the mixture was stirred at room temperature for 10 hours. The crude product was filtrated, washing with diethyl ether and the product was recrrystallized from ethanol afford complex 1 as a green powder 0.46 g in 85% yield. IR(KBr), cm-1: 3417 (m), 2961 (m), 1636 (vs), 1596 (s), 1537 (s), 1467 (m), 1363, 1325, 1292, 1232, 1071 (s). Anal. Calcd For C28H32N2O?CoCl2?H2O: C, 60.12; H, 5.95; N, 5.01. Found: C, 59.89; H, 6.11; N, 4.97%. Complex (2): Using the procedure described above, the reaction of L2 and CoCl2?6H2O gave complex 2 0.42 g in 78% yield as a green powder. IR(KBr), cm-1: 3438 (m), 2961 (m), 1641 (s), 1616 (s), 1538 (s), 1461 (m), 1362, 1325, 1282(w), 1238, 1060 (s). Anal. Calcd For C28H32N2O?CoCl2: C, 62.00; H, 5.95; N, 5.16. Found: C, 61.89; H, 5.92; N, 5.17%. Complex (3): Using the procedure described above, the reaction of L2 and CoCl2?6H2O gave complex 3 0.44 g in 81% yield as a green powder. IR(KBr), cm-1: 3435 (m), 2960 (m), 1638 (s), 1591(s), 1539 (m), 1479 (m), 1239, 1201, 1145 (m), 1078, 1028 (s). Anal. Calcd For C28H32N2O?CoCl2: C, 62.00; H, 5.95; N, 5.16. Found: C, 61.87; H, 5.87; N, 5.19%. Complex (4): Using the procedure described above, the reaction of L1 and NiCl2?6H2O gave complex 4 0.41 g in 75% yield as a brown powder. IR(KBr), cm-1: 3382 (m), 2961 (m), 1647 (s), 1577 (s), 1537 (m), 1466 (m), 1404? 1357, 1327, 1289, 1233, 1164 (m), 1046 (s). Anal. Calcd For C28H32N2O?NiCl2: C, 62.03; H, 5.95; N, 5.17. Found: C, 62.08; H, 5.93; N, 5.29%. Complex (5): Using the procedure described above, the reaction of L2 and NiCl2?6H2O gave complex 5 0.42 g in 78% yield as a brown powder. IR(KBr), cm-1: 3370 (m ), 2959 (m), 1649 (s), 1539 (s), 1454 (s), 1410, 1354, 1326, 1292 (w), 1238, 1118 (s). Anal. Calcd For C28H32N2O?NiCl2?H2O: C, 60.03; H, 6.12; N, 5.00. Found: C, 60.13; H, 6.10; N, 4.97%. Complex (6): Using the procedure described above, the reaction of L3 and NiCl2?6H2O gave complex 6 0.42 g in 78% yield as a brown powder. IR(KBr), cm-1: 3380 (br), 2960 (m), 1638 (s), 1536 (s), 1364, 1330, 1292(w), 1239, 1200 (m), 1143 (w), 1064, 1024 (s), 853 (s). Anal. Calcd For C28H32N2ONiCl2: C, 62.03; H, 5.95; N, 5.17. Found: C, 62.13; H, 5.70; N, 5.31%. General procedure for ethylene oligomerization A flame dried three-neck round flask was vacuated-filled three times by nitrogen. Then ethylene was charged with 30 ml of freshly distilled toluene and stirred. At the room temperature, the aluminum cocatalyst MAO was added via syringe. The solution was stirred and the precatalyst complex (1 - 6, 5 ?mol in 5ml toluene) was added to the reaction mixture via syringe. After stirred under 1 atm ethylene pressure for 20 min, the oligomerization was terminated by acidified ethanol. An aliquot of the reaction mixture was analyzed using gas chromatrography. Their activity and distribution of the oligomers were collected in Table 1. Results and Discussion Synthesis and characterization 2,6-bis(imino)phenoxy ligands L1 - L3 were prepared in good yields by condensation of one equivalent of the appropriate aniline with one equivalent of 2-hydroxy-5-tertbutylisophthaldehyde (Scheme 1). Compounds L1 - L3 were characterized by microanalysis, 1H-NMR and mass spectrometry. The complexes 1 - 6 were synthesized by dissolving nickel chloride or cobalt chloride in ethanol (Scheme 1), followed by addition of one equivalent of ligand. The complexes precipitated from the reaction solution. After recrystallized from ethanol, the complexes were obtained in good yields and high purity. All the complexes were confirmed with elemental analysis and IR spectroscopy. The elemental analysis results revealed that the components of all complexes were in accord with the formula MLX2. Oligomerization of ethylene Upon treatment with methylaluminoxane (MAO), all of the complexes are active ethylene oligomerization catalysts. Table 1 lists their activity and molecular weight distribution of the oligomers. The nature of the metal center has a major influence on catalytic activities. In general, Ni(II) catalysts are more active than their corresponding Co(II) analogues under the same condition. The most active Ni(II) catalyst is complex 1 (4.57?104 g(ethylene)mol-1 (Ni)h-1), While the Co(II) complexes are about 103 g(ethylene)mol-1(Co)h-1 for oligomerization. Complexes 1 - 3 (4 - 6) revealed that a reduction of steric methyl at the ortho-aryl position resulted in the decrease of their activities, and electronic environmental around the central metal affected the catalytic activities. In the same condition, catalysts 1 (4) are more active than the catalysts 3 (6). Without methyl group in the aryl rings and 3 (6) displays an activity of 1.78?103 (1.98?104) g(ethylene)mol-1(M)h-1, approximately complex 1 (4) with one methyl at the ortho-aryl with an activity of 3.65?103 (4.57?104) g(ethylene)mol-1(M)h-1. The same phenomenon was observed in previously research.12-13 The oligomers are from C4 to C6. The substituents of the complexes affect distribution of the oligomers to some extent. Comparing with the 2,6-bis(imino)pyridyl ligands6-8, when we change the central pyridyl moiety to phenol, their complexes only show oligomerization activity, no polymerization activity; at the same time, the selectivity in ethylene conversion are not very well. Conclusions We have synthesized six cobalt and nickel complexes. Upon treatment with methylaluminoxane, they are all active ethylene oligomerization catalysts. The oligomers are from C4 to C6. Acknowledgements We thank the financial support from Hebei University. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. International Journal of Medicinal Chemistry Hindawi Publishing Corporation ht p:/ www.hindawi.com International Hindawi Publishing Corporation ht p:/ www.hindawi.com International Journal of Photoenergy International Journal of Analytical Chemistry Advances in Physical Chemistry Hindawi Publishing Corporation Hindawi Publishing Corporation ht p:/ www.hindawi.com International Journal of Carbohydrate Chemistry Hindawi Publishing Corporation ht p:/ www.hindawi.com The Scientiifc World Journal Hindawi Publishing Corporation ht p:/ www.hindawi.com Submit your manuscr ipts organic Journal of Hindawi Publishing Corporation ht p:/ www.hindawi.com Theoretical Chemistry Journal of Hindawi Publishing Corporation ht p:/ www.hindawi.com Chromato Research International Journal of Ittle S D , Johnson L K and Brookhart M Chem. Rev ., 2000 , 100 , 1169 . Britovsek G J P , Gibson V C and Wass D F , Angew. Chem. Int. Ed. 1999 , 38 , 428 . Johnson L K , Mecking S and Brookhart M J. Am . Chem. Soc , 1996 , 118 , 267 . Killian C M , Tempel D J and Johnson L K J. Am . Chem. Soc , 1996 , 118 , 11664 . Johnson L K , Killian C M and Brookhart M J. Am . Chem. Soc , 1995 , 117 , 6414 . Mecking S , Johnaon L K , Wang L , Brookhart M J. Am . Chem. Soc , 1998 , 120 , 888 . Small B L , Brookhart M and Bennett A M A, J . Am. Chem. Soc , 1998 , 120 , 4049 . Britovsek G J P , Gibson V C and Kimberley B S, Chem . Commun., 1998 , 849 . Wang C , Friedrich S and Younkin T R Organometallics , 1998 , 17 , 3149 . Small B L and Brookhart M , J. Am. Chem. Soc , 1998 , 120 , 7143 . Wang LY , Sun W-H and Han L Q , J. Organomet . Chem . 2002 , 650 , 59 . Du J L , Han L Q , Cui Y , Li J T , Li Y and Sun W-H Aust. J. Chem ., 2003 , 56 , 703 . Du J L , Li L-J and Li Y F Inorg. Chem . Commun., 2005 , 8 , 246 . Drago R S , Desmond M J , Corden B B and Miller K A J. Am . Chem. Soc. , 1983 , 105 , 2287 .


This is a preview of a remote PDF: http://downloads.hindawi.com/journals/jchem/2006/831367.pdf

Jian-Long Du, Li-Jun Li. Cobalt and Nickel Complexes Bearing 2,6-Bis(imino)phenoxy Ligands:Synthesis and Ethylene Oligomerization Study, Journal of Chemistry, DOI: 10.1155/2006/831367