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-(i)Pr(2)-Ar*)Co(μ-Cl) (3,5-(i)Pr(2)-Ar* = -C(6)H-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)-3,5-(i)Pr(2)) with KC(8) in the presence of various arene molecules resulted in the formation of a series of terphenyl stabilized Co(I) half-sandwich complexes (3,5-(i)Pr(2)-Ar*)Co(η(6)-arene) (arene = toluene (1), benzene (2), C(6)H(5)F (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-η(6)-arene interaction. In contrast, C-F bond cleavage occurred when the analogous reduction was conducted in the presence of C(6)F(6), affording the salt K[(3,5-(i)Pr(2)-Ar*)Co(F)(C(6)F(5))] (4), in which there is a three-coordinate cobalt complexed by a fluorine atom, a C(6)F(5) group, and the terphenyl ligand Ar*-3,5-(i)Pr(2). This salt resulted from the formal insertion of a putative 3,5-(i)Pr(2)-Ar*Co species as a neutral or anionic moiety into one of the C-F bonds of C(6)F(6). Reduction of (3,5-(i)Pr(2)-Ar*)Co(μ-Cl) in the presence of bulkier substituted benzene derivatives such as mesitylene, hexamethylbenzene, tert-butylbenzene, or 1,3,5-triisopropylbenzene did not afford characterizable products.