Ionic Liquid-Grafted Mn(III)-Schiff Base Complex: A Highly Efficient and Recyclable Catalyst for the Epoxidation of Chalcones

Abstract

A new Mn(III)-Schiff base complex with imidazolium phase tag was synthesized and employed as an efficient and recyclable catalyst for the epoxidation of chalcones with MCPBA/NMO. It can be recovered and reused (at least five times) without any loss of activity.

Mn(III)-Schiff base complex - imidazolium - catalyst

References

1 Jørgensen KA. Chem. Rev.  1989,  89:  431 

2 Porter MJ. Skidmore J. Chem. Commun.  2000,  1215 

3a Katsuki T. J. Mol. Catal. A: Chem.  1996,  113:  87 

3b Katsuki T. Coord. Chem. Rev.  1995,  140:  189 

3c Cozzi PG. Chem. Soc. Rev.  2004,  33:  410 

3d Khavrutskii IV. Musaev DG. Morokuma K. Proc. Natl. Acad. Sci. U.S.A.  2004,  101:  5743 

4a Baley DC. Langer SH. Chem. Rev.  1995,  95:  477 

4b Ley SV. Baxendale IR. Bream RN. Jackson PS. Leach AG. Longbottom DA. Nesi M. Scott JS. Storer RI. Taylor SJ. J. Chem. Soc., Perkin Trans. 1  2000,  3815 

5a Minutolo F. Pini D. Salvadori P. Tetrahedron Lett.  1996,  37:  3375 

5b Canali L. Cowan E. DeLeuze H. Gibson CL. Sherrington DC. Chem. Commun.  1998,  2561 

5c Sellner H. Karjalainen JK. Seebach D. Chem.-Eur. J.  2001,  7:  2873 

6a Parton RF. Vankelecom IFJ. Tas D. Janssen KBM. Knops-Gerrits P.-P. Jacobs PA. J. Mol. Catal. A: Chem.  1996,  113:  283 

6b Janssen KBM. Laquiere I. Dehaen W. Parton RF. Vankelecom IFJ. Jacobs PA. Tetrahedron: Asymmetry  1997,  8:  3481 

7a Heinrichs C. Holderich WF. Catal. Lett.  1999,  58:  75 

7b Gbery G. Zsigmond A. Balkus KJ. Catal. Lett.  2001,  74:  77 

8 Pozzi G. Cinato F. Montanari F. Quici S. Chem. Commun.  1998,  877 

9 Song CE. Roh EJ. Chem. Commun.  2000,  837 

10a Yao Q. Zhang Y. Angew. Chem. Int. Ed.  2003,  42:  3395 

10b Audic N. Clavier H. Mauduit M. Guillemin J.-C. J. Am. Chem. Soc.  2003,  125:  9248 

11a Lee S. Zhang YJ. Piao JY. Yoon H. Song CE. Choi JH. Hong J. Chem. Commun.  2003,  2624 

11b Geldbach TJ. Dyson PJ. J. Am. Chem. Soc.  2004,  126:  8114 

12 Baleizão C. Gigante B. Garcia H. Corma A. Tetrahedron Lett.  2003,  44:  6813 

13a Brasse CC. Englert U. Salzer A. Organometallics  2000,  19:  3818 

13b Favre F. Olivier-Bourbigou H. Commereuc D. Saussine L. Chem. Commun.  2001,  1360 

13c Bronger RPJ. Silva SM. Kamer PCJ. van Leeuwen PWNM. J. Chem. Soc., Dalton Trans.  2004,  1590 

14 Sirieix J. Ossberger M. Betzemeier B. Knochel P. Synlett  2000,  1613 

15a Xiao J.-C. Twamley B. Shreeve JM. Org. Lett.  2004,  6:  3845 

15b Corma A. García H. Leyva A. Tetrahedron  2004,  60:  8553 

16 Zhao D. Fei Z. Geldbach TJ. Scopelliti R. Dyson PJ. J. Am. Chem. Soc.  2004,  126:  15876 

17 A similar procedure for the synthesis of aminopropyl-type ionic liquid has been reported: Bates ED. Mayton RD. Ntai I. Davis JH. J. Am. Chem. Soc.  2002,  124:  926 

18

Synthesis of Imidazolium-Tagged Ligand(3).
A mixture of salicylaldehyde (1.22 g, 10 mmol), 2 (2.71 g, 10 mmol) and ionic liquid [bmim][PF₆] (2.84 g, 10 mmol) was stirred at r.t. for 1 h. After completion of the reaction, as indicated by TLC, the reaction mixture was diluted with EtOH (20 mL). The precipitate was then filtered and dried to afford 3.01 g (80% yield) of ligand 3 as a pale yellow solid; mp 129-130 °C. FT-IR (KBr): ν_max = 3416, 3152, 3093, 2914, 2867, 1637, 1618, 1568, 1505, 1470, 1287, 1163, 1100, 848 cm^-1. ¹H NMR (500 MHz, CD₃COCD₃): δ = 4.01 (s, 3 H, CH ₃), 4.18 (t, 2 H, J ₁ = 5.81 Hz, J ₂ = 5.49 Hz, NCH ₂), 4.80 (t, 2 H, J ₁ = 5.64 Hz, J ₂ = 5.83 Hz, NCH ₂), 6.83-7.33 (m, 4 H, Ph), 7.70 (s, 1 H, NCH), 7.80 (s, 1 H, NCH), 8.55 [s, 1 H, N(H)CN], 9.10 (s, 1 H, CH), 12.60 (s, 1 H, OH).

19

Synthesis of Ionic Liquid-Grafted Mn(III)-Schiff Base Complex(4).
To a solution of ligand 3 (0.50 g, 1.30 mmol) in EtOH (20 mL) was added Mn(OAc)₂·4H₂O (0.16 g, 0.65 mmol). After 4 h of refluxing, 0.04 g of LiCl (0.65 mmol) was added and the reaction mixture was further refluxed for 2 h until the starting material had been completely consumed as judged by TLC. On completion of the reaction, the reaction mixture was cooled to r.t. The precipitate was collected by filtration, washed with EtOH (10 mL), and dried to give compound 4 as brown powder (0.43 g, 77% yield). FT-IR (KBr): ν_max = 3167, 3110, 2976, 1611, 1545, 1478, 1439, 1136, 835, 754, 634, 472 cm^-1. ¹H NMR (500 MHz, DMSO-d ₆): δ = 4.00 (s, 3 H, CH ₃), 4.15 (t, 2 H, J ₁ = 5.76 Hz, J ₂ = 5.70 Hz, NCH ₂), 4.75 (t, 2 H, J ₁ = 5.73 Hz, J ₂ = 5.86 Hz, NCH ₂), 6.85-7.35 (m, 4 H, Ph), 7.65 (s, 1 H, NCH), 7.75 (s, 1 H, NCH), 8.50 [s, 1 H, N(H)CN], 9.01 (s, 1 H, CH). MS (ESI): m/e (%) = 693 (8), 360 (50), 319 (80), 229 (100). Anal. Calcd for C₂₆H₃₀N₆O₂MnClP₂F₁₂: C, 37.20; H, 3.60; N, 10.02. Found: C, 37.13; H, 3.52; N, 9.91.

20

General Procedure for the Epoxidation of Chalcones. To a well-stirred solution of chalcone (1 mmol), NMO (0.17 g, 1.5 mmol) and catalyst 4 (8 mg, 0.01 mmol) in MeCN (10 mL) at -25 °C was added MCPBA (0.26 g, 1.5 mmol) in four equal portions over a 2-min period. The homogeneous mixture was stirred at -25 °C until chalcone had been completely consumed (monitored by TLC), followed by removal of MeCN on a rotary evaporator. The residue was then extracted with Et₂O (3 × 10 mL). The combined extracts were washed with sat. Na₂SO₃ (3 × 10 mL), dried over Na₂SO₄, filtered, and concentrated to afford essentially pure products.
Compound 6f: mp 138-139 °C. FT-IR (KBr): ν_max 3112, 3045, 1672, 1600, 1519, 1487, 1408, 1358, 1215, 1089, 1036, 864 cm^-1. ¹H NMR (500 MHz, CD₃COCD₃): δ = 7.43-7.60 (m, 4 H, Ph), 7.45 (d, J = 15.7 Hz, 1 H, CH-CH), 7.80 (d, J = 15.7 Hz, 1 H, CH-CH), 8.15-8.35 (m, 4 H, Ph). MS (GC-MS): m/z (%) = 303 (1), 287 (70), 252 (100), 207 (15), 179 (25), 165 (45), 102 (30), 76 (20).
Compound 6g: mp 188-191 °C. FT-IR (KBr): ν_max = 3364, 3171, 3045, 2972, 1626, 1540, 1328, 1235, 1149, 844 cm^-1. ¹H NMR (500 MHz, CD₃COCD₃): δ = 2.95 [s, 6 H, N(CH₃)₂], 6.90 (d, J = 15.5 Hz, 1 H, CH-CH), 7.65-7.57 (m, 4 H, Ph), 7.80 (d, J = 15.5 Hz, 1 H, CH-CH), 8.25-8.35 (m, 4 H, Ph). MS (GC-MS): m/z (%) = 312 (1), 296 (100), 250 (25), 207 (3), 179 (25), 165 (20), 105 (10), 76 (10).
Compound 6h: mp 212-213 °C. FT-IR (KBr): ν_max = 3112, 2999, 2906, 1646, 1586, 1520, 1493, 1448, 1334, 1202, 1103, 1036, 924 cm^-1. ¹H NMR (500 MHz, CD₃COCD₃): δ = 6.01 (s, 2 H, OCH ₂O), 6.82-7.25 (m, 3 H, Ph), 7.30 (d, J = 15.5 Hz, 1 H, CH-CH), 7.75 (d, J = 15.5 Hz, 1 H, CH-CH), 8.15-8.35 (m, 4 H, Ph). MS (GC-MS): m/z (%) = 313 (1), 297 (100), 250 (25), 207(5), 175 (25), 145 (30), 105 (8), 76 (10).