Metal-Mediated Controllable
Creation of Secondary,
Tertiary, and Quaternary Carbon Centers: A Powerful Strategy for the
Synthesis of Iron, Cobalt, and Copper Complexes with in Situ Generated
Substituted 1‑Pyridineimidazo[1,5‑<i>a</i>]pyridine Ligands
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Abstract
An efficient strategy for the synthesis of a wide variety
of coordination
complexes has been developed. The synthetic protocol involves a solvothermal
in situ metal–ligand reaction of picolinaldehyde, ammonium
acetate, and transition-metal ions, leading to the generation of 12
coordination complexes supported by a novel class of substituted 1-pyridineimidazo[1,5-<i>a</i>]pyridine ligands (<b>L1</b>–<b>L5</b>). The ligands <b>L1</b>–<b>L5</b> were afforded
by metal-mediated controllable conversion of the aldehyde group of
picolialdehyde into a ketone and secondary, tertiary, and quaternary
carbon centers, respectively. Complexes of various nuclearities were
obtained: from mono-, di-, and tetranuclear to 1D chain polymers.
The structures of the in situ formed complexes could be controlled
rationally via the choice of appropriate starting materials and tuning
of the ratio of the starting materials. The plausible mechanisms for
the formation of the ligands <b>L1</b>–<b>L5</b> were proposed