HChlmCl ambient-temperature ionic liquids have been investigated through infrared and variable-temperature -NMR spectroscopy as a function of HC1 mole fraction (Im+ = 1 -ethyl-3-methyl-1 //-imidazolium). The infrared spectrum of the dihydrogen trichloride ion, H2CI3-, has been observed, apparently for the first time. The absence of significant molecular HC1 as earlier proposed, is confirmed. Thermodynamic parameters for the reaction H2CI3-+ Cl" ^2HCI2", in which all species are solvated, have been estimated by VT-NMR: AH and AS were determined as -22.8 ± 1.0 kJ moh1 and -31.8 ± 2.9 J K"1 mol"1 respectively. The minimum value of the equilibrium constant for the reaction HC1 + Cl" *=* HC12", is estimated to be on the order of 104-10s L mol"1, considerably larger than that in molecular solvents. Im+ ring proton resonances have a marked dependence on the anion fractions of Cl", HCI2", and H2CI3", with Im-H2 being the most strongly affected. VT-NMR spectra of Im+ indicate that for A^ci < 0.5, all three ring protons are involved in cation-anion interactions while for A'hci > 0.5, Im-H2 is dominant in mediating these. We have interpreted these results in terms of hydrogen-bonded aggregates of anions and cations, the nature of which depends on the ability of the anion population to form hydrogen bonds with Im+. At the extremes we suggest that these aggregates may range from extended structures involving hydrogen bonding to all three ring protons, to ion-pairs involving hydrogen bonding via
The methyl complex [Ir 2 (CH 3 )(CO)(µ-CO)(dppm) 2 ][CF 3 SO 3 ] (1) reacts readily with a variety of alkyne molecules. With alkynes containing electron-withdrawing substituents (RCtCR′; R ) R′ ) CO 2 Me, CF 3 ; R ) CO 2 Me, R′ ) H), the alkyne-bridged products, [Ir 2 (CH 3 )(CO) 2 -(µ-alkyne)(dppm) 2 ][CF 3 SO 3 ], result. With other 1-alkynes (HCtCR, R ) Me, Ph) reaction at -80 °C results in oxidative addition to give acetylide hydrides [Ir 2 H(CH 3 )(CO) 2 (µ-C 2 R)-(dppm) 2 ][CF 3 SO 3 ], which upon warming undergo transfer of the hydride ligand to the β-carbon of the acetylide to give the vinylidene-bridged products. At ambient temperature methane elimination occurs, yielding the acetylide-bridged "A-frames", [Ir 2 (CO) Reaction of 1 with 1 equiv of acetylene proceeds through analogous acetylide and vinylidene intermediates; however under carbon monoxide exchange of a vinylidene hydrogen and the methyl ligand occurs to give a methylvinylidene-bridged hydride [Ir 2 (H)(CO) 3 (µ-CCHMe)(dppm) 2 ][CF 3 SO 3 ]. Reaction of 1 with an excess of acetylene results in the incorporation of two acetylene molecules, giving [Ir 2 (CH 3 , containing terminal methyl and acetylide ligands and bridging hydride and vinylidene groups. Reaction of 1 with a number of internal, nonactivated alkynes results first in the formation of the alkyne-bridged products, which slowly rearrange to the unusual species [Ir 2 H(CO) 2 (µ-CHCRC(H)R)(dppm) 2 ][CF 3 SO 3 ], in which cleavage of two C-H bonds of the methyl group has occurred accompanied by condensation of the resulting methyne group at one end of alkyne linkage and transfer of a hydrogen to the other end. The resulting hydrocarbyl moiety can be viewed as a vinylcarbene. The X-ray structures of three representative products are reported, including one of these vinylcarbenes (R ) C 2 H 5 ).
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