Electronic and steric factors for elimination reactions in carbenium ions derived from (17.beta.-ethynylestradiol)M2L6 complexes (M2L6 = Co2(CO)6, Mo2Cp2(CO)4. X-ray structure of [Mo2Cp2(CO)4(.mu.-CH.tplbond.CC19H25O)]+BF-4 [Erratum to document cited in CA113(23):212426v]