High-Spin Organocobalt(II) Complexes in a Thioether Coordination Environment

Abstract

A series of electronically and coordinatively unsaturated four-coordinate organocobalt(II) complexes, [PhTttBu]Co(R) ([PhTttBu] = phenyltris((tert-butylthio)methyl)borate; R = Me, Et, Ph, Bn) have been prepared by reaction of [PhTttBu]CoCl with the corresponding R2Mg reagent. These high-spin, S = 3/2, complexes have been characterized spectroscopically and several of their structures determined by X-ray diffraction. The R = allyl derivative, [PhTttBu]Co(η3-allyl), is low spin. Reaction of [PhTttBu]Co(R) with CO yielded the acyl adducts [PhTttBu]Co(CO)C(O)R when R = Me, Et, Ph. These five-coordinate, low-spin complexes possess square pyramidal stereochemistry with a thioether occupying the apical position. In contrast, [PhTttBu]Co(R), R = Bn or allyl, reacted with CO generating the brown cobalt(I) dicarbonyl [PhTttBu]Co(CO)2. The latter reaction is proposed to proceed via CO-promoted Co−C bond homolysis. The Ni complex [κ2-PhTttBu]Ni(η3-allyl) shows no reactivity with CO under similar conditions. Each of the [PhTttBu]Co(R) species reacts with NO, generating brown [κ2-PhTttBu]Co(NO)2 in good yield.