Reactivity of a T-shaped cobalt(i) pincer-complex

Abstract

The reactivity of a paramagnetic T-shaped cobalt(I) complex, [(^iPrboxmi)Co], stabilised by a monoanionic bis(oxazolinylmethylidene)-isoindolate (boxmi) NNN pincer ligand is described. The exposure to carbon monoxide as an additional neutral ligand resulted in the square-planar species [(^iPrboxmi)Co(CO)], accompanied by a change in the electronic spin state from S = 1 to S = 0. In contrast, upon treatment with trimethylphosphine the formation of the distorted tetrahedral complex [(^iPrboxmi)Co(PMe₃)] was observed (S = 1). Reacting [(^iPrboxmi)Co] with iodine (I₂), organic peroxides (^tBu₂O₂, (SiMe₃)₂O₂) and diphenyldisulphide (Ph₂S₂) yielded the tetracoordinated complexes [(^iPrboxmi)CoI], [(^iPrboxmi)Co(O^tBu)], [(^iPrboxmi)Co(OSiMe₃)] and [(^iPrboxmi)Co(SPh)], respectively, demonstrating the capability of the boxmi-supported cobalt(I) complex to homolytically cleave bonds and thus its distinct one-electron reactivity. Furthermore, a square-planar cobalt(II) alkynyl complex [(^iPrboxmi)Co(CCAr^F)] was identified as the main product in the reaction between [(^iPrboxmi)Co] and a terminal alkyne, 4-fluoro-1-ethynylbenzene. Putting such species in the context of the previously investigated hydroboration catalysis, its stoichiometric reaction with pinacolborane revealed its potential conversion into a cobalt(II) hydride complex, thus confirming its original attribution as off-cycle species.