(Py)₂Co(CH₂SiMe₃)₂ As an Easily Accessible Source of “CoR₂”

(Py)2CoR2 (R = CH2SiMe3) is easily prepared from (Py)4CoCl2 and RLi. It is fairly stable at room temperature and serves as a convenient source of CoR2 for transfer to other ligands. Unfortunately, (Py)2CoR2 was obtained only as an oil, but the structure of the related complex (Py)2CoR′2 (R′ = CH2CMe2Ph) could be confirmed by a single-crystal X-ray diffraction study. Transfer of the CoR2 fragment from (Py)2CoR2 or (TMEDA)CoR2 to diiminepyridine-type ligands (1−6) was studied as a function of ligand steric and electronic properties. Reaction with N-2,6-dimethylphenyl (1) and N-2,4,6-trimethylphenyl (2) ligands produced diamagnetic monoalkyl complexes; the structure of (1)CoR was confirmed by X-ray diffraction. With the less shielding N-phenyl (3) and N-benzyl (4) ligands, 1H NMR indicated formation of diamagnetic CoI alkyl species, but they were not stable enough to allow isolation. Fluorinated ligand 5 appears to be less reactive and−despite its supposedly stronger π-acceptor character−also does not lead to formation of a stable CoI alkyl complex. With PyBOX ligand 6, high-spin dialkyl complex (6)CoR2 was observed by 1H NMR. Based on these observations and DFT calculations, a mechanism is proposed for formation of diiminepyridine CoI alkyls that involves formation of a high-spin κ2 complex, spin flip to give a low-spin κ3 complex, and irreversible loss of an alkyl radical.