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-O-Me-PhN(CH2C=CH)(2), 4-F-PhN(CH2C=CH)(2), BzN(CH2=CH)(2), O(CH2=CH)(2), C(Ac)(2)(CH2C=CH)(2), N(CH2C=CH),, 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 eta(3)-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.