The properties and reactions of hydroxymethyl and hydride complexes are surveyed with an emphasis on their aqueous chemistry; then the syntheses and reactions found for macrocyclic cobalt complexes of these ligands are presented. The hydroxymethyl-cobalt(III) complex was prepared by addition of the photogenerated CH 2OH radical to the cobalt(II) macrocycle N-meso-CoHMD 2+ (HMD = 5,7,7,12,14,14-hexamethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene) in 0.1 M perchloric acid and characterized by an X-ray crystallographic study and spectroscopic characterization in solution. Acidic aqueous solutions are fairly stable and the complex decomposes, with formaldehyde elimination, by a base-catalyzed pathway. At 25°C, formaldehyde elimination proceeds with the rate law -d[N-meso-CoHMD(CH 2OH) 2+]/dt = k I[N-meso-CoHMD(CH 2OH) 2+]/[H +], with k I = (3.5 ± 0.5) × 10 -9 M s -1 at pH 4-7 and 0.5 M ionic strength to yield the hydride complex, N-meso-CoHMD(H) 2+ and CH 2O. In a subsequent stage, N-meso-CoHMD 2+ and H 2 form with the rate law -d[N-meso-CoHMD(H) 2+]/dt = (2 ± 1) × 10 -7 [N-meso-CoHMD(H) 2+] 2/[H +] s -1 at pH 4.5-8 and 0.5 M ionic strength. Ultimately, the N-meso complex isomerizes to yield N-rac-CoHMD 2+ with previously observed kinetics.
- Hydride complex
- Hydroxymethyl complex
- Water reduction mechanism
ASJC Scopus subject areas
- Physical and Theoretical Chemistry