Catalyst deactivation through “Oxo-assembling”

• First oxo-hydroxo-peroxo-palladium complex.
• Isolated decomposition intermediate in the Heck reaction using palladacycles.
• Comparison of different palladacycles in the Heck reaction.
• NHC-substituted palladacycles.

The catalytic activity of acetato(1,3-diadamantylimidazolin-2-ylidene)[o-(di-o-tolylphosphino)benzyl]palladium(II) in the Heck reaction is reported. Under basic conditions of Ca(OH)2, a hydroxo complex was formed during the reaction. It converts under molecular oxygen conditions to a Pd4-oxo-hydroxo-peroxo-complex. Novel complexes were characterized by spectroscopy and solid state analysis. The stability and conformity of the Pd4-complex was rationalized by DFT-calculations.

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