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(S₂C ₂B₁₀H₁₀)] (IS; Cp: cyclopentadienyl) with ethynylferrocene in CH₂Cl₂ at ambient temperature leads to [CpCo(S₂C₂B₁₀)H₉)-(CH ₂CFc)] (2S; Fc: ferrocenyl) and 1,2,4-triferrocenylbenzene. 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 [(CH₂CFc)(S₂C₂B ₁₀H₉)] (38). On the other hand, 2S can take a free CpCo fragment to form [(CpCo)₂(S₂C₂B ₉H₈)-(CHCFc)] (4S) containing a nido-C₂B ₉ unit. In sharp contrast, [CpCo(Se₂C₂B ₁₀H₁₀)] (1Se) does not react with the alkyne in CH ₂Cl₂, but in MeOH [(CHCFc)(Se₂C ₂B₁₀H₁₀)] (5Se) is generated without the presence of a CpCo unit. The reaction of 1 with di methyl acetylenedicarboxylate at ambient temperature leads to insertion compounds [CpCo(E₂C ₂B₁₀H₁₀)((MeO₂C)-C=C(CO ₂Me)}] (6S, E = S; 6Se, E = Se). Upon heating, 6S rearranges to two geometrical isomers [CpCo-(S₂C₂B₁₀H ₉){(MeO₂C)C=CH(CO₂Me)}] (7S) and [CpCo(S ₂C₂B₁₀H₉)((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 B-CH 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(S₂C ₂-B₁₀H₈){(MeO₂C)C=CH(CO ₂Me)}₂] (9S) and [CpCo(S₂C₂B ₁₀H₈){(MeO₂C)-CHC(CO₂Me)}{(MeO ₂C)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(S₂C₂B₁₀H ₈){CH=CH(CO₂Me)}-{(MeO₂C)C=CH(CO ₂Me))] (11S). In contrast, 6Se does not rearrange. All new complexes 2S-4S, 5Se, 6Se, and 7S-11S were characterized by NMR spectroscopy ( ¹H, ¹¹B, ¹³C) and X-ray structural analyses were performed for 2S-4S, 5Se, 6Se, and 7S-9S.