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Synthesis and characterization of metallodendritic palladium-biscarbene complexes derived from 1,1′-methylenebis(1,2,4-triazole)†
Valentín Hornillos,Abel de Cózar,Pilar Prieto,Sonia Merino,Miguel A. Maestro,Enrique Díez-Barra,Juan Tejeda
Dalton Transactions Pub Date : 03/07/2011 00:00:00 , DOI:10.1039/C0DT01535K
Abstract

The syntheses of first generation dendritic compounds bearing 1,1′-alkane-1,1-diylbis(4-butyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene)palladium(II) dibromide on the periphery are described. The metallabiscarbene moieties have also been studied separately from the dendrimer. These compounds display a non-symmetric boat-to-boat conformational equilibrium that has axial and equatorial arrangements. The predominance of the axial conformer in the equilibrium is supported by DFT calculations. The X-ray solid state structures of axial conformers of 3-hydroxy- and 3-mesyloxy-1,1′-propane-1,1-diylbis(4-butyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene)palladium(II) dibromide are reported. These complexes display modest catalytic activity in the Heck reaction with activated aryl bromides and the dendritic catalysts were more active than the corresponding non-dendritic mononuclear species, a finding indicative of a cooperative effect.

Graphical abstract: Synthesis and characterization of metallodendritic palladium-biscarbene complexes derived from 1,1′-methylenebis(1,2,4-triazole)
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