C-I-Selective Cross-Coupling Enabled by a Cationic Palladium Trimer.

While there is a growing interest in harnessing synergistic effects of more than one metal in catalysis, relatively little is known beyond bimetallic systems. This report describes the straightforward access to an air-stable Pd trimer and presents unambiguous reactivity data of its privileged capability to differentiate C-I over C-Br bonds in C-C bond formations (arylation and alkylation) of polyhalogenated arenes, which typical Pd0 and PdI -PdI catalysts fail to deliver. Experimental and computational reactivity data, including the first location of a transition state for bond activation by the trimer, are presented, supporting direct trimer reactivity to be feasible.