Reactions catalyzed by palladium(II) acetate and trifluoroacetic acid (TFA) have a clear preactivation phase. However, the structure of real catalytic species remains unclear. We show that the key species are cyclic trinuclear complexes of composition [Pd₃(OAc)_6−x(OTFA)_x] (x = 1–6) formed by a sequential ligand exchange from [Pd₃(OAc)₆]. Furthermore, we prove that the trinuclear palladium backbone of the precatalyst remains preserved during the first phase of the C–H activation reaction of acetanilides. In other words, the reaction pathway including the trinuclear species should be taken into account in discussion about mechanisms of the reactions catalyzed by palladium acetates.

中文翻译：

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三核物质在乙酸钯/三氟乙酸催化体系中的作用

乙酸钯（II）和三氟乙酸（TFA）催化的反应具有明确的预活化阶段。但是，真正的催化物质的结构仍不清楚。我们表明，键物种的组合物的环状三核配合物[钯₃（OAC）_{6- X}（OTFA）_X ]（X = 1-6）由从[钯顺序配体交换形成₃（OAC）₆]。此外，我们证明，在乙酰苯胺的C–H活化反应的第一阶段中，预催化剂的三核钯主链得以保留。换句话说，在讨论由乙酸钯催化的反应机理时，应考虑包括三核物质在内的反应途径。