An Active and Recyclable Polystyrene-Supported N-Heterocyclic Carbene-Palladium Catalyst for the Suzuki Reaction of Arylbromides with Arylboronic Acids under Mild Conditions

Abstract

A novel polymer-supported imidazolium salt has been prepared from a bisimidazolium salt and cross-linked chloromethyl polystyrene. The polymer-supported N-heterocyclic carbene-palladium complex, generated from the supported bisimidazolium salt and Pd(OAc)₂, efficiently catalyzed the Suzuki coupling reaction of aryl bromides and arylboronic acids under air in aqueous DMF ­solution at room temperature, giving biaryls in good to excellent yields. The catalyst could be reused several times still retaining high activity.

Suzuki reaction - N-heterocyclic carbene-palladium complex - polymer-supported catalyst - recyclable catalyst

References

1 Kotha S. Lahiri K. Kashinath D. Tetrahedron  2002,  58:  9633 

2a Bedford RB. Cazin CSJ. Hazelwood SL. Angew. Chem. Int. Ed.  2002,  41:  4120 

2b Herrmann WA. Angew. Chem. Int. Ed.  2002,  41:  1290 

2c Littke AF. Dai C. Fu GC. J. Am. Chem. Soc.  2000,  122:  4020 

2d Kataoka N. Shelby Q. Stambuli JP. Hartwig JF. J. Org. Chem.  2002,  67:  5553 

2e Weng Z. Teo S. Koh LL. Hor TSA. Organometallics  2004,  23:  3603 

2f Li JH. Liu WJ. Org. Lett.  2004,  6:  2809 

2g Chen CL. Liu YH. Peng SM. Liu ST. Organometallics  2005,  24:  1075 

3a Parrish CA. Buchwald SL. J. Org. Chem.  2001,  66:  3820 

3b Cammidge AN. Baines NJ. Bellingham RK. Chem. Commun.  2001,  2588 

3c Gordon RS. Holmes AB. Chem. Commun.  2002,  640 

3d Yamada YMA. Takeda K. Takahashi H. Ikegami S. J. Org. Chem.  2003,  68:  7733 

3e Phan NTS. Brown DH. Styring P. Tetrahedron Lett.  2004,  45:  7915 

4a Zhang C. Trudell ML. Tetrahedron Lett.  2000,  41:  595 

4b Grasa GA. Viciu MS. Huang J. Zhang C. Trudell ML. Nolan SP. Organometallics  2002,  21:  2866 

4c Vargas VC. Rubio RJ. Hollis TK. Salcido ME. Org. Lett.  2003,  5:  4847 

4d Navarro O. Kelly RA. Nolan SP. J. Am. Chem. Soc.  2003,  125:  16194 

5a Bedford RB. Cazin CSJ. Hazelwood SL. Angew. Chem. Int. Ed.  2002,  41:  4120 

5b Feuerstein M. Berthiol F. Doucet H. Santelli M. Synlett  2002,  1807 

5c Mori K. Yamaguchi K. Hara T. Mizugaki T. Ebitani K. Kaneda K. J. Am. Chem. Soc.  2002,  124:  11572 

5d Yin J. Rainka MP. Zhang X.-X. Buchwald SL. J. Am. Chem. Soc.  2002,  124:  1162 

5e Littke AF. Schwarz L. Fu GC. J. Am. Chem. Soc.  2002,  124:  6343 

5f Littke AF. Fu GC. Angew. Chem. Int. Ed.  2002,  41:  4176 

6 Schwarz J. Böhm VPW. Gardiner MG. Grosche M. Herrmann WA. Hieringer W. Raudaschl-Sieber G. Chem.-Eur. J.  2000,  6:  1773 

7a Zhao Y. Zhou Y. Ma D. Liu J. Zhang TY. Zhang H. Org. Biomol. Chem.  2003,  1:  1643 

7b Byun JW. Lee YS. Tetrahedron Lett.  2004,  45:  1837 

7c Kim JH. Jun BH. Byun JW. Lee YS. Tetrahedron Lett.  2004,  45:  5827 

8

Procedure for the Preparation of the Bisimidazolium Salt 1.
In a dry nitrogen atmosphere, a mixture of 1,3-dichloro-2-propanol (1.29 g, 10 mmol) and 1-methylimidazole (1.72 g, 21 mmol) was stirred in MeCN (20 mL) at 80 °C for 4 d in an oil bath. The solvent was removed completely under vacuum. Then, CH₂Cl₂ was added to the residue to give a white solid, which was filtered and dried under vacuum affording the salt 1 in 60% yield. ¹H NMR (600 MHz, DMSO-d ₆): δ = 3.88 (s, 6 H, NCH ₃), 4.20 (m, 1 H, CHOH), 4.22-4.51 (br, 4 H, NCH ₂ ), 7.79 (s, 2 H, NCH), 7.87 (s, 2 H, NCH), 9.36 (s, 2 H, NCHN). ¹³C NMR (150 MHz, DMSO-d ₆): δ = 36.23 (NCH₃), 52.17 (CHOH), 68.21 (NCH₂), 123.44 (NCH), 123.77 (NCH), 137.74 (NCHN). HRMS (ESI): m/z calcd for C₁₁H₁₈Cl₂N₄O [M - 2Cl]²⁺: 111.0741; found: 111.0729.

9

Procedure for the Preparation of Polystyrene-Supported Bisimidazolium Salt 2.
A mixture of Merrifield polymer (200 mg 2.7 mmol Cl/g), KI (30 mg, 0.18 mmol), tributylamine (0.3 g, 1.62 mmol) and the bisimidazolium salt 1 (158 mg, 0.54 mmol) dissolved in DMF (10 mL) was stirred for 4 d at r.t. The polymer was filtered off and washed with DMF (6 × 10 mL), MeOH (6 × 10 mL), H₂O (6 × 10 mL), and then dried under vacuum. The loading of the imidazolium groups was determined by means of the nitrogen content obtained from elemental analysis (N, 1.4%, 0.5 mmol imidazolium/g).

10

Procedure for the Preparation of Polystyrene-Supported NHC-Pd Complex 3. In a dry nitrogen atmosphere, a mixture of the imidazolium loaded polymeric support 2 (200 mg, 0.5 mmol imidazolium/g) and Pd(OAc)₂ (22.5 mg, 0.1 mmol) was suspended in DMF (2 mL). To this suspension was added an aqueous solution (2 mL) of Na₂CO₃ (106 mg, 1.0 mmol). The mixture was stirred at r.t. for 30 min, and then agitated for 4 h at 50 °C in an oil bath. After filtration, the polymeric support was washed vigorously with distilled H₂O (10 × 10 mL), MeOH (10 × 10 mL), and dried under reduced pressure to give 3. ICP-AES: 100 µmol Pd/g.

11

Procedure for Measuring the Swelling Properties of the Polystyrene-Supported Bisimidazolium Salt 2 and the Catalyst 3.
The swelling volumes of polymeric supports in various solvents were measured in a fritted column (ID 0.8 cm, length 20 cm). The polymeric support (1.0 g) was swollen in a solvent at r.t. for 2 h, and then washed with a 10-fold volume of each solvent. After filtration, the volume of the polymeric support was measured.

12

Representative Procedure for Suzuki Reaction (Table 2, Entry 14).
The catalyst 3 (20 mg, 2 µmol Pd) was suspended with DMF (2 mL). After a mixture of 4-bromoanisole (63 µL, 0.5 mmol), phenylboronic acid (75 mg, 0.6 mmol), and Na₂CO₃ (265 mg, 2.5 mmol) in distilled H₂O (2 mL) was added, the reaction mixture was stirred at r.t. for 24 h without the protection of inert gas. The catalyst was filtered and washed with distilled H₂O (5 × 4 mL) and Et₂O (5 × 4 mL), and dried in vacuo for use in the next run. The organic portion was dried over MgSO₄ and evaporated under reduced pressure. The biphenyl product (91 mg, yield 99%) was isolated by column chromatography (eluent: n-hexane).