Reactions of 16e CpCo Half-Sandwich Complexes Containing a Chelating 1,2-Dicarba-closo-dodecaborane-1,2-dichalcogenolate Ligand with Ethynylferrocene and Dimethyl Acetylenedicarboxylate

The reaction of the 16e half‐sandwich complex [CpCo(S2C2B10H10)] (1 S; Cp: cyclopentadienyl) with ethynylferrocene in CH2Cl2 at ambient temperature leads to [CpCo(S2C2B10H9)(CH2CFc)] (2 S; Fc: ferrocenyl) and 1,2,4‐triferrocenylbenzene. In 2 S, B substitution occurs at the carborane cage in the position B(3)/B(6) with the formation of a CB bond. In the presence of the protic solvent MeOH, 2 S loses a CpCo fragment to generate [(CH2CFc)(S2C2B10H9)] (3 S). On the other hand, 2 S can take a free CpCo fragment to form [(CpCo)2(S2C2B9H8)(CHCFc)] (4 S) containing a nido‐C2B9 unit. In sharp contrast, [CpCo(Se2C2B10H10)] (1 Se) does not react with the alkyne in CH2Cl2, but in MeOH [(CHCFc)(Se2C2B10H10)] (5 Se) is generated without the presence of a CpCo unit. The reaction of 1 with dimethyl acetylenedicarboxylate at ambient temperature leads to insertion compounds [CpCo(E2C2B10H10){(MeO2C)CC(CO2Me)}] (6 S, E=S; 6 Se, E=Se). Upon heating, 6 S rearranges to two geometrical isomers [CpCo(S2C2B10H9){(MeO2C)CCH(CO2Me)}] (7 S) and [CpCo(S2C2B10H9){(MeO2C)CHC(CO2Me)}] (8 S). In both, BH functionalization takes place at the carborane cage in the position B(3)/B(6), but 7 S is a 16e complex with an olefinic unit in a Z configuration, and 8 S is an 18e complex containing an alkyl BCH group. Further treatment of 7 S with dimethyl acetylenedicarboxylate at ambient temperature affords two B‐disubstituted complexes at the carborane cage in the positions of the B(3) and B(6) sites, that is, [CpCo(S2C2B10H8){(MeO2C)CCH(CO2Me)}2] (9 S) and [CpCo(S2C2B10H8){(MeO2C)CHC(CO2Me)}{(MeO2C)CCH(CO2Me)}] (10 S). Compound 9 S is a 16e complex with two olefinic units in E/E configurations, whereas 10 S is an 18e species containing both an olefinic substituent and an alkyl BCH unit. The reaction of 7 S with methyl acetylenemonocarboxylate at ambient temperature leads to the sole 16e compound [CpCo(S2C2B10H8){CHCH(CO2Me)}{(MeO2C)CCH(CO2Me)}] (11 S). In contrast, 6 Se does not rearrange. All new complexes 2 S–4 S, 5 Se, 6 Se, and 7 S–11 S were characterized by NMR spectroscopy (1H, 11B, 13C) and X‐ray structural analyses were performed for 2 S–4 S, 5 Se, 6 Se, and 7 S–9 S. Sandwich course: Reaction of 1 S with HCCFc (Fc: ferrocenyl) leads to 2 S, which converts to 3 S and 4 S in MeOH (see scheme). However, in the case of MeO2CCCCO2Me, the stepwise substitution of the o‐carborane cage at the B(3)/B(6)‐positions leads to 7 S and 9 S, respectively.