Transition Metal Chlorides Are Lewis Acids toward Terminal Chloride Attached to Late Transition Metals

Two
different neutral tridentate imine-donor pincer ligands interact with
excess MCl2 (M = Co or Cu) to form compounds of the same
stoichiometry, (LMCl2)2·MCl2, where the assembling force is the electron richness of the terminal chlorides on the LMCl2 unit. Finite aggregation
occurs for M = Co, but for M = Cu, an infinite polymeric structure
is adopted, all because MCl2 is bifunctional, which thus bridges multiple MCl units. The bis-pyrazolylpyridine
ligand has two acidic NH protons, and both of these are involved in
intramolecular hydrogen bonds. The generality of this Lewis acid aggregation
is discussed.