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Synlett 2003(1): 0079-0082
DOI: 10.1055/s-2003-36230
LETTER
© Georg Thieme Verlag Stuttgart · New York

Sterically Encumbered Porphyrins by Suzuki Reactions of a 5,15-Bis(4,6-dichloropyrimidin-5-yl) Derivative

W. Maes, W. Dehaen*
Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium
Fax: +32(16)327439; e-Mail: wim.dehaen@chem.kuleuven.ac.be;
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Publication History

Received 22 October 2002
Publication Date:
18 December 2002 (online)

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Abstract

The high yielding synthesis of novel four picket fence porphyrins via palladium catalyzed Suzuki cross-coupling reactions of 5,15-bis(pyrimidinyl)porphyrin 1 and commercially available arylboronic acids is described.

Key words

porphyrins - Suzuki cross-coupling - palladium - arylations - steric hindrance

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Experimental Details, Representative Procedure for Porphyrin 2a: To a mixture of porphyrin 1 (100 mg, 0.12 mmol) and Pd(PPh3)4 (4 mg, 3 mol%) in toluene (7.5 mL), phenylboronic acid (87 mg, 0.72 mmol) was added, immediately followed by aq Na2CO3 (2 M, 1 mL). The mixture was flushed with N2 for 5 min and the reaction mixture was then heated under reflux for 24 h. After cooling, the reaction mixture was evaporated under reduced pressure to dryness. To the reaction mixture H2O (50 mL) was added and the aq layer was extracted with CH2Cl2 (3 × 50 mL). The organic layers were collected, dried over MgSO4 and evaporated in vacuum. Purification by column chromatography (silica gel, CH2Cl2/EtOAc: 10/1) furnished the pure compound 2a as a purple solid (83 mg, 70%). Rf = 0.3 (CH2Cl2/EtOAc 10/1). 1H NMR (400 MHz, CDCl3): δ = -2.58 (sbr, 2 H), 1.61 (s, 12 H), 2.57 (s, 6 H), 6.48 (t, 8 H), 6.60 (t, 4 H), 7.00 (d, 8 H), 7.19 (s, 4 H), 8.32 (d, 4 H), 8.53 (d, 4 H), 9.75 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ = 21.3, 21.4, 112.4, 118.4, 127.4, 127.7, 127.8, 129.4, 130.2, 131.2, 137.6, 137.9, 138.8, 139.2, 146.5, 158.4, 168.2. MS (electrospray): 1007.5 [(M+) + H]. UV/VIS (CH2Cl2): λmax = 432.6 (log ε = 5.586), 528.2 (log ε = 4.271), 564.3 (log ε = 4.025), 603.0 (log ε = 3.829), 662.2 (log ε = 3.673).
The optical spectra are extremely similar to the one of the starting porphyrin 1 but are red-shifted for about 12-16 nm. Suslick et al. [3] reported the same red-shift (ca. around 30 nm) for their porphyrin compared to the tetraphenylporphyrin.

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All arylboronic acids were purchased from Acros.