Synthesis of copper(II) halide dimers with 2-amino-5-methylpyridine and serendipitous copper catalyzed synthesis of 3-bromo-2-ethyl-5-methyl-1H-pyrrolo[2,3-b]pyridine

Abstract

Reaction of CuX₂·nH₂O (X = Cl, n = 2; X = Br, n = 0) with 2-amino-5-methylpyridine (5MAP) in acetonitrile yielded [(5MAP)₂CuX₂]₂ (1, Cl; 2, Br). The compounds are isomorphous and crystallize in the monoclinic space group P2₁/n as bihalide bridged dimers. Variable temperature magnetic measurements show very weak exchange in the two compounds (-2.1(1) K) which may correlate with previously proposed magnetostructural correlations for bihalide bridged Cu(II) dimers. In attempts to prepare 2 in 2-butanone as solvent, [(3-Br-2-Et-5-Mepyrpy)(CH₃CO₂)₄Cu₂] (3) was serendipitously isolated (3-Br-2-Et-5-Mepyrpy = 3-bromo-2-ethyl-5-methyl-7H-pyrrolido[2,3-b]pyridinium). The bicyclic ligand was synthesized in situ by condensation of 5MAP with the solvent; the acetate ions were generated by copper(II) catalyzed Baeyer-Villiger oxidation of the solvent. A mechanism for the synthesis is proposed. The resulting Cu-paddlewheel compound exhibits strong (-400 K) antiferromagnetic interactions.

Keywords:

• Cu(II) Halides
• magnetism
• solvent oxidation
• pyrrolopyridine

Additional information

Funding

The authors are grateful to the National Science Foundation for grants to purchase the SQUID magnetometer (IMR-0314773) and toward the purchase and construction of a helium recycling system (NSF DMR-1905950). Contributions from SEQENS toward the purchase of the powder X-ray diffractometer are also greatly appreciated.