Trans influence of cyanide on the structural and electronic properties of a series of organocobalt III (TIM) complexes

• Published in: New journal of chemistry 2024-07, Vol.48 (29), p.13030-13037
• Main Authors: Rodriguez Segura, Leobardo, Ren, Tong
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D4NJ02364A

The trans influence of anionic ligands on the nature of the cobalt–carbon bond in trans -[Co(TIM)RX] + -type complexes (R is a C-bound ligand and TIM is 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) was probed through the incorporation of cyanide as the second monoanionic axial ligand (X). Salt metathesis reactions between KCN and the corresponding halide precursors readily generate trans -[Co(TIM)(C(CH 2 )Ph)(CN)] + (1), trans -[Co(TIM′′)(C(CH 3 )C 6 H 4 -4- t Bu)(CN)] + (2, TIM′′ is the reduced TIM derivative following the formation of an aza-cobalt-cyclopropane moiety), and trans -[Co(TIM)(CH 3 )(CN)] + (3). The molecular structures of 1 and 2 were established via single-crystal X-ray diffraction studies. FT-IR spectroscopy revealed a red-shift in the ν (CN) stretching frequency from 1 to 3 to 2. The absorption spectra of 1–3 exhibit d–d bands which are substantially blue-shifted from their halide precursors as a result of the enhanced ligand field imbued by the cyanide. Cyclic voltammograms of 1 and 3 consist of an irreversible Co 4+/3+ oxidation and an irreversible Co 3+/2+ reduction. In 2, a reversible Co-centered reduction is observed at −1.75 V vs . Fc 1+/0 . Also reported are the crystal structures of trans -[Co(TIM)(CN) 2 ]PF 6 (4), trans -[Co(TIM)(CH 3 )I]PF 6 (5) and trans -[Co(TIM)(CH 3 ) 2 ]PF 6 (6). The π-accepting capabilities of the cyanide reduce the dπ(Co)-π*(imine) backdonation in 4, while the solely strong σ-donating nature of the –CH 3 ligands in 6 exerts a large trans influence and significantly increases the Co-TIM interactions.