[Tpy2Co][Co(CO)4]: a mixed-valent cobalt(III)/cobalt(-I) com-plex based on phenyl-tris-(pyridin-2-yl)borate (Tpy-).

Tris(pyridin-2-yl)borates are an emerging class of scorpionate ligands. Distinguished by their robustness and nucleophilicity, they have promise as alternatives to tris-(pyrazol-yl)borates in coordination chemistry, materials ap-plications, and catalysis. In this article, bis-[phenyl-tris-(pyridin-2-yl)borato]cobalt(III) tetra-carbonyl-cobalt(-I) di-chloro-methane monosolvate, [Co(C21H17BN3)2][Co(CO)4]·CH2Cl2 or [Tpy2Co][Co(CO)4]·CH2Cl2, was prepared by the reaction of hy-dro-gen phenyl-tris-(pyridin-2-yl)borate (TpyH), tri-ethyl-amine, and Co(CO)4I. Single-crystal X-ray diffraction resulted in a homoleptic com-plex consisting of the diamagnetic [Tpy2Co]+ cation and the tetra-car-bonyl-cobaltate {[Co(CO)4]-} counter-ion. The unusual CoIII/Co-I mixed-valence com-position presumably results from disproportionation. [Tpy2Co][Co(CO)4] represents the first mixed-valence tris-(pyridin-2-yl)borate com-plex.