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)] (1S; Cp: cyclopentadienyl) with ethynylferrocene in CH2Cl2 at ambient temperature leads to [CpCO(S2C2B10H9)-(CH(2)CFc)] (2S; Fc: ferrocenyl) and 1,2,4-triferrocenyl benzene. In - 2S, 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, 2S loses a CpCo fragment to generate [(CH(2)CFc)(S2C2B10H9)] (3S). On the other hand, 2S can take a free CpCo fragment to form [(CPCO)(2)(S2C2B9H8)-(CHCFc)] (4S) containing a nido-C2B9 unit. In sharp contrast, [CpCo-(Se2C2B10H10)] (1Se) does not react with the alkyne in CH2Cl2, but in MeOH [(CHCFc)(Se2C2B10H10)] (5se) 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)}] (6S, E=S; 6Se, E= Se). Upon heating, 6S rearranges to two geometrical isomers [CpCo(S2C2B10H9)((MeO2C)C=CH(CO2Me)]] (7S) and [CpCo(S2C2B10H9){(MeO2C)- CHC(CO2Me)}] (8S). In both, B-H functionalization takes place at the carborane cage in the position B(3)/B(6), but 7S is a 16e complex with an olefinic unit in a Z configuration, and 8S is an 18e complex containing an alkyl BCH group. Further treatment of 7S 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(S2C2-B10H8){(MeO2C)C=CH(CO2Me)}(2)] (9S) and [CpCo(S2C2B10H8){(MeO2C)- CHC(CO2Me))((MeO2C)C=CH-(CO2Me)}] (10S). Compound 9S is a 16e complex with two olefinic units in E/E configurations, whereas 10S is an 18e species containing both an olefinic substituent and an alkyl B-CH unit. The reaction of 7S with methyl acetylenemonocarboxylate at ambient temperature leads to the sole 16e compound [CpCo(S2C2B10H8){CH=CH(CO2Me)}-{(MeO2C)C=CH(CO2Me)}] (11S). In contrast, 6Se does not rearrange. All new complexes 2S-4S, 5Se, 6Se, and 7S-11S were characterized by NMR spectroscopy (H-1, B-11, C-13) and X-ray structural analyses were performed for 2S-4S, 5Se, 6Se, and 7S-9S.