Pyrrolylmethyl Functionalized o‑Carborane Derivatives

The reactions of the 16e half-sandwich complex CpCoS2C2B10H10 (1), diazo esters, and various 1,6-diynes (3a–i; PhN­(CH2CCH)2, 4-Me-PhN­(CH2CCH)2, 4-OMe-PhN­(CH2CCH)2, 4-F-PhN­(CH2CCH)2, BzN­(CH2CCH)2, O­(CH2CCH)2, C­(Ac)2(CH2CCH)2, N­(CH2CCH)3, NH­(CH2CCH)­N­(CH2CCH)2) were investigated, in which two novel types of B–H activated products CpCoS2B10H9(CH2CO2Et)­C5H3N­(R)­(CHCHCO2Et) (4a–c; R = Ph, 4-Me-Ph, 4-OMe-Ph) and the key intermediate CpCoS2B10H9(CHCO2Me) (CH2CO2Me) (9) were isolated. 9 features a reactive Co–B bond, which triggers insertion of various 1,6-diynes to further lead to different final products. Substrates 3a–c are activated by the Co–B bond to produce o-carborane derivatives 4a–c which are functionalized by a cobalt-complexed η3-pyrrolylmethyl group. The pyrrole ring is formed by in situ ring closure of 1,6-diynes. Control experiments and isolation of the intermediate CpCoS2B10H9(CHCO2Me)­(CH2CO2Me)­HCCCH2N­(4-Me-Ph)­(CH2CCH) (10) support the proposed mechanism concerning the formation of 4a–c analogues by oxidation. All of the new complexes were characterized by NMR, IR, elemental analysis, and mass spectrometry. The structures of 4a–6a and 9 were determined by single-crystal X-ray diffraction analysis as well.