Dehydrohalogenation of proton responsive complexes: versatile aggregation via pyrazolate pincer ligand arms

Area of Science:

• Coordination chemistry
• Organometallic chemistry
• Inorganic synthesis

Background:

• Cobalt complexes with bis-(pyrazol-3-yl)pyridine ligands are known.
• Pincer ligands offer unique coordination environments.
• Understanding ligand deprotonation is key to novel complex synthesis.

Purpose of the Study:

• To investigate the reaction of (H2L)CoCl2 with Brønsted bases.
• To explore peripheral NH deprotonation for dianionic pincer ligand formation.
• To characterize the resulting cobalt species and their reactivity.

Main Methods:

• Synthesis and characterization of cobalt complexes.
• Reactions with Brønsted bases and nucleophiles.
• Spectroscopic and structural analysis of products.

Main Results:

• Deprotonation of (H2L)CoCl2 leads to chloride loss and formation of bridged Co2 units.
• Species like [Co2(L)(LH)]2(L), [Co2(L)(HL)]2[Co(L)2], and LiCo2L2Cl were identified.
• Reaction with tBuNC yields monomeric LCo(tBuNC)2 (17 VE species).
• Excess LiN(SiMe3)2 opens the Co2L2 dimer, forming a Co[N(SiMe3)2]2 substructure.

Conclusions:

• Peripheral NH deprotonation is not a direct route to dianionic pincer ligands on d7 cobalt.
• The reaction pathway involves chloride displacement and bimolecular coupling.
• Cobalt complex reactivity is sensitive to base strength and nucleophilic attack.