A Novel Silica-Supported Palladium Catalyst for a Copper-Free Sonogashira Coupling Reaction

Abstract

3-Aminopropyl functionalised silica gel may be readily transformed into a stable immobilised palladium catalyst. This ­catalyst was then successfully employed in a series of fast, copper-free Sonogashira coupling reactions.

Key words

silica - palladium - catalyst - copper-free cross-coupling - Sonogashira - aryl iodides

References

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11

Aldrich reference 36, 425-8.

13

Matrex Silica 60 (37-70 mesh).

19

These studies were conducted on a Mettler TG50 Thermogravimetric Analyser. The decomposition weight loss was measured over the range 200-650 °C at a temperature rate increase of 20.0 °C min^-1.

21

Representative Experimental Procedure: the Synthesis of Diphenylacetylene. To a small dry glass tube/flask charged with a magnetic stirrer bar, iodobenzene (0.204 g, 1.0 mmol) and phenyl-acetylene (0.102 g, 1.0 mmol) was added piperidine (0.256 g, 3.0 mmol) and catalyst 3 (0.015 g). The reaction vessel was sealed with a septum and heated to a temperature of 70 °C on an oil bath with constant stirring. After about 10 min the contents were cooled and decanted into a separating funnel. The residual supported catalyst was washed with Et₂O (3 × 10 cm³) and the washings added to the separating funnel. Then, H₂O (20 mL) was added to the separating funnel and the organic layer was separated neutralised, by washing with dilute HCl (15% v/v), washed with H₂O (2 × 15 mL), dried over anhyd MgSO₄ and the organic solvent removed, in vacuo, to afford the crude product (0.1602 g, 90%). This was characterised by GC-MS which confirmed that the yield of diphenylacetylene (85%), IR and NMR spectroscopy using an authentic sample for reference purposes.

22

The yields of coupled products obtained from reactions involving supported palladium catalysts are often superior to those obtained from the corresponding homogeneous reaction.

23

This work was carried out by A. Al-Saardi as part of an MChem undergraduate final year project at Kingston University.