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

The reactivity of a paramagnetic T-shaped cobalt(i) complex, [((iPr)boxmi)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 [((iPr)boxmi)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 [((iPr)boxmi)Co(PMe3)] was observed (S = 1). Reacting [((iPr)boxmi)Co] with iodine (I-2), organic peroxides ((Bu2O2)-Bu-t, (SiMe3)(2)O-2) and diphenyldisulphide (Ph2S2) yielded the tetracoordinated complexes [((iPr)boxmi)CoI], [((iPr)boxmi)Co((OBu)-Bu-t)], [((iPr)boxmi)Co(OSiMe3)] and [((iPr)boxmi)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 [((iPr)boxmi)Co(CCArF)] was identified as the main product in the reaction between [((iPr)boxmi)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.