Synthesis and characterisation of organometallic imidazolium compounds that include a new organometallic ionic liquid

New imidazolium salts, 1-(prop-2-ynyl)-3-vinyl-3H-imidazol-1-ium bromide, 1a, the tetraphenylborate, 1b, and hexafluorophosphate, 1c, salts of 1a and 3-allyl-1-(prop-2-ynyl)-3H-imidazol-1-ium bromide, 2a, containing alkene and alkyne groups for derivatisation were prepared from commercially available starting materials and fully characterised. New organometallic imidazolium salts, [{(mu)2-HCCCH2 N=C(H)N(CH=CH2)CH=C H}Co2(CO)6]X [X-= BF4-, B(C6H5)4- or PF6-], 3a, 3b or 3c, and [{(mu)2-HCCCH2 N=C(H)N(CH2CH=CH2)CH=C H}Co2(CO)6]BF4, 4a, and a new organometallic ionic liquid, [{(mu)2-HCCCH2 N=C(H)N(CH2CH=CH2)CH=C H}Co2(CO)6]PF6, 4b, were isolated by reacting 1a-c or 2a with Co2(CO)8. The compound 4b, the first ionic liquid bearing an organometallic moiety covalently attached to the cation, melts reversibly at 75-77 °C without decomposition. The imidazolium protons in 1b and 3b are shielded in the 1H NMR as a result of (pi)-interaction with the phenyl rings of the tetraphenylborate anion. The cation-anion contacts (C-H...~ 2.6 (angstrom)) observed in the molecular structure of 3b in the solid state are also maintained in solution, as evidenced in NOE NMR experiments. The molecular structures of 3b and 3c show an alkyne unit bonded to a Co2(CO)6 fragment with the C(identical)C bond perpendicular to the Co-Co bond.