Surprising Homolytic Gas Phase Co−C Bond Dissociation Energies of Organometallic Aryl‐Cobinamides Reveal Notable Non‐Bonded Intramolecular Interactions

Aryl‐cobalamins are a new class of organometallic structural mimics of vitamin B(12) designed as potential ‘antivitamins B(12)’. Here, the first cationic aryl‐cobinamides are described, which were synthesized using the newly developed diaryl‐iodonium method. The aryl‐cobinamides were obtained as pairs of organometallic coordination isomers, the stereo‐structure of which was unambiguously assigned based on homo‐ and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt‐center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas‐phase bond dissociation energies (BDEs) of the coordination‐isomeric phenyl‐ and 4‐ethylphenyl‐cobinamides were determined by ESI‐MS threshold CID experiments, furnishing (Co−C [Formula: see text] )‐BDEs of 38.4 and 40.6 kcal mol(−1), respectively, for the two β‐isomers, and the larger BDEs of 46.6 and 43.8 kcal mol(−1) for the corresponding α‐isomers. Surprisingly, the observed (Co−C [Formula: see text] )‐BDEs of the Co(β)‐aryl‐cobinamides were smaller than the (Co−C [Formula: see text] )‐BDE of Co(β)‐methyl‐cobinamide. DFT studies and the magnitudes of the experimental (Co−C [Formula: see text] )‐BDEs revealed relevant contributions of non‐bonded interactions in aryl‐cobinamides, notably steric strain between the aryl and the cobalt‐corrin moieties and non‐bonded interactions with and among the peripheral sidechains.