Layered Double Hydroxide-Supported Nanoplatinum: An Efficient and ­Reusable Ligand-Free Catalyst for Heck and Stille Coupling of Iodoarenes

Abstract

A layered double hydroxide-supported nanoplatinum catalyst is employed in the Heck and Stille cross-coupling of a wide range of iodoarenes to give the corresponding cross-coupled products in good to excellent yields. The catalyst is recovered by centri­fugation and reused over a number of cycles with consistent activity.

layered double hydroxides - nanoplatinum - Heck coupling - Stille coupling - iodoarenes

References and Notes

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<A NAME="RD11806ST-7">7</A>

For Heck reaction of iodobenzene with styrene in presence of LDH-Pt⁰ (1.0 mol%) using NaOAc as base at 135 °C for 6 h yield of trans-stilbene: 92% (NMP), 88% (DMF), 89% (DMAc), 10% (MeCN), 0% (xylene).

<A NAME="RD11806ST-8">8</A>

For Heck reaction of iodobenzene with styrene in presence of LDH-Pt⁰ (1.0 mol%) in NMP solvent at 135 °C for 6 h yield of trans-stilbene: 92% (NaOAc), 78% (K₂CO₃), 35% (NaOH), no reaction (Bu₃N).

<A NAME="RD11806ST-9">9</A>

For preparation and characterization of LDH-Pt⁰ catalyst see ref. 5. Loading of Pt in LDH-Pt⁰ is 0.374 mmol of Pt per gram of catalyst. In a typical procedure for Heck coupling using LDH-Pt⁰ as catalyst: in an oven-dried 10-mL round-bottomed flask, iodobenzene (0.5 mmol), styrene (0.75 mmol), NaOAc (1.5 mmol), LDH-Pt⁰ (1.0 mol%), and NMP (3 mL) were taken and stirred at 135 °C under N₂ atmosphere and the reaction was monitored by TLC. After the completion of the reaction, the catalyst was centrifuged and reused. The centrifugate was diluted with Et₂O and washed with sat. aq NaCl solution. The organic layer was dried with Na₂SO₄ and concentrated to get the crude product. Then it was subjected to column chromatography to get the pure product. Isolated yield of trans-stilbene was 92%.
¹H NMR: δ = 7.11 (s, 2 H), 7.21-7.30 (m, 2 H), 7.31-7.41 (t, 4 H, J = 7.54 Hz), 7.47-7.56 (d, 4 H, J = 7.54 Hz).

<A NAME="RD11806ST-10">10</A>

Typical Procedure for Stille Coupling Using LDH-Pt ⁰ as Catalyst.
In an oven-dried 10-mL round-bottomed flask, 4-iodo-anisole (0.5 mmol), phenyltributyl tin (0.75 mmol), LDH-Pt⁰ (1.0 mol%), and NMP (3 mL) were taken and stirred at 100 °C under nitrogen atmosphere and the reaction was monitored by TLC. After the completion of the reaction, the catalyst was centrifuged and reused. The centrifugate was diluted with Et₂O and washed twice with aq 20% KF solution followed by sat. aq NaCl solution. The organic layer was dried with Na₂SO₄ and concentrated to get the crude product. Then it was subjected to column chromatography to get the pure product. Isolated yield of 4-methoxybiphenyl was 94%.
¹H NMR: δ = 3.85 (s, 3 H), 6.93 (d, 2 H, J = 8.9 Hz), 7.20-7.31 (m, 1 H), 7.33-7.44 (t, 2 H, J = 7.4 Hz), 7.46-7.56 (m, 4 H).