The Palladium Component of an Immobilized Sonogashira Catalyst System: New Insights by Multinuclear HRMAS NMR Spectroscopy
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© 2014 American Chemical Society. Multinuclear one- and two-dimensional HRMAS NMR spectroscopy has been used to investigate the palladium component of a Sonogashira catalyst system immobilized on silica by diverse bifunctional phosphine linkers incorporating Si(OEt)3 groups. The coordinating strengths of these mono- and bidentate phosphine ligands have been assayed in situ by competition experiments monitored with 31P HRMAS NMR spectroscopy. The ligand best retaining and scavenging the PdCl2 fragment has been determined to be immobilized (EtO)3Si(CH2)3N(CH2PCy2)2, while silica-bound (EtO)3Si(CH2)3NH2 and (EtO)3Si(CH2)3PPh2 led to leaching. The coordinating strengths of the immobilized ligands have been correlated with the catalytic activities of the corresponding immobilized Sonogashira catalyst systems regarding the coupling of phenylacetylene with iodobenzene.
author list (cited authors)
Pope, J. C., Posset, T., Bhuvanesh, N., & Blümel, J.