Triazine-based polyfluorinated triquaternary liquid salts: Synthesis, characterization, and application as solvents in rhodium(I)-catalyzed hydroformylation of 1-octene

Silylation of N-(2-hydroxyethyl)imidazole, HOCH(2)CH(2)Im (1), with hexamethyldisilazane gave N-(2-trimethylsilyloxyethyl)imidazole, Me(3)SiOCH(2)CH(2)Im (2), which underwent quaternization reactions with the alkyl halides and gave three new N-(trimethylsilyloxyethyl) imidazolium halides, Me(3)SiOCH(2)CH(2)Im(+)RX(-), where Im(+) = imidazolium and R/X = Me/I (3), CH2CH2F/Br (4), and CH2CH2CF3/I (5). The ethyl ether, 6, formed from 1 and ethyl bromide was quaternized with CF3CH2CH2I to obtain 7, followed by anion exchange with LiN(SO2CF3)(2) to obtain 8. The metathesis reactions of 3-5 with cyanuric fluoride in acetonitrile at 25 degreesC gave tris[2-(N'-alkylimidazolium)ethoxy] triazine trihalides, N3C3(OCH2-CH(2)Im(+)RX(-))(3), where R/X = Me/I (9), CH2CH2F/Br (10), and CH2CH2CF3/I (11). Two neutral trimeric compounds, N3C3(OCH(2)CH(2)Im)(3) (12) and N3C3(OCH2CH2NMe2)(3) (14), were prepared from reactions of cyanuric fluoride and Me3SiOCH2CH2NMe2 (13), or 2, respectively. The quaternization of 12 with MeI gave tris[oxoethyl(trimethyl)ammonium]triazine, N3C3(OCH2CH2N+Me3I-)(3) (14). Subsequent exchange of the halides in 9-11 and 15 with the weakly coordinating anions of AgOSO2CF3, LiN(SO2CF3)(2), AgNO3, or AgClO4 resulted in new triquaternary salts, 16-23, that were characterized by NMR, elemental analyses, and, for some of the compounds, mass spectroscopy. Physical (melting point and density) and thermal properties of 9-23 determined with a differential scanning calorimeter (DSC) and a thermogravimetric analyzer (TGA) are reported. In Rh(I)-catalyzed hydroformylation of 1-octene, with Ph2P(NMPBTA) (26) [NMPBTA = N-methylpyridinium bis(trifluoromethanesulfonyl)amide] as ligand, the turnover frequency (TOF), conversion, isomer selectivity (n/i), and recyclability were compared when triquaternary salts 17 and 20 or monoquaternary 8 were used as solvents in the biphasic hydroformylation process. A change of 26/Rh(I) ratio from 4 to 20 resulted in a significant increase of n/i selectivity with 17 or 20, but was marginal with 8 as solvent.