Reduction of Terphenyl Co(II) Halide Derivatives in the Presence of Arenes: Insertion of Co(I) into a C–F Bond

Reduction of [(3,5-iPr2-Ar*)­Co­(μ-Cl)]2 (3,5-iPr2-Ar* = -C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with KC8 in the presence of various arene molecules resulted in the formation of a series of terphenyl stabilized Co­(I) half-sandwich complexes (3,5-iPr2-Ar*)­Co­(η6-arene) (arene = toluene (1), benzene (2), C6H5F (3)). X-ray crystallographic studies revealed that the three compounds adopt similar bonding schemes but that the fluorine-substituted derivative 3 shows the strongest cobalt-η6-arene interaction. In contrast, C–F bond cleavage occurred when the analogous reduction was conducted in the presence of C6F6, affording the salt K­[(3,5-iPr2-Ar*)­Co­(F)­(C6F5)] (4), in which there is a three-coordinate cobalt complexed by a fluorine atom, a C6F5 group, and the terphenyl ligand Ar*-3,5-iPr2. This salt resulted from the formal insertion of a putative 3,5-iPr2-Ar*Co species as a neutral or anionic moiety into one of the C–F bonds of C6F6. Reduction of [(3,5-iPr2-Ar*)­Co­(μ-Cl)]2 in the presence of bulkier substituted benzene derivatives such as mesitylene, hexamethylbenzene, tert-butylbenzene, or 1,3,5-triisopropylbenzene did not afford characterizable products.