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Title: Intermolecular and intramolecular Ru-H...H-X dihydrogen-bonding interaction in some ruthenium complexes
Authors: Lam, Yat-fai
Degree: M.Phil.
Issue Date: 2002
Abstract: The Tp and Tpm (Tp = hydridotris(pyrazole)borate, Tpm = trispyrazolylmethane) supported ruthenium hydride complexes, TpRu(PPh3)2H (34) and [TpmRu(PPh3)2H](BF4) (35), have been examined for their abilities to form intermolecular hydrogen bonding. Acidic alcohols such as TEE, HFIP and PFTB (TFE = trifluoroethanol, HFIP = hexafluoroisopropyl alcohol and PFTB perfluoro-tert-butyl alcohol) have been chosen to react with the complexes in order to investigate the existence of hydrogen-bonding interaction of the type ROH H-M. The interaction is monitored by variable-temperature NMR spectroscopy and T1 measurement of the hydride and n2-dihydrogen ligands. My work shows the presence of equilibria between the intermolecular hydrogen-bonded intermediate and n2-dihydrogen complexes at different temperatures. The 1H NMR hydride signal of TpRu(PPh3)2H disappeared as excess HFIP was added at 228K while an upfield broad signal assignable to a n2-H2 ligand was observed. After the temperature was raised to 263K, an upfield signal assignable to the hydrogen-bonded intermediate became observable and its intensity increased with increase in temperature. This phenomenon is in line with other complexes containing dihydrogen bonds which show enhanced M-H H-X interaction as the temperature is lowered. Since the acidity of the acidic alcohol increase from TFE, HFIP, PFTB; equilibria between the hydrogen bonded intermediate and the dihydrogen complex is observed with the addition of HFIP to 34 in variable temperature NMR (VT-NMR) spectroscopy. There are no interaction detected for 35 with any acidic alcohol in the 1H NMR spectra. The second part of my research concerns the chemistry of intramolecular hydrogen bonding between the pendent amino group and the hydride ligand in the aminocyclopentadienyl ruthenium complexes, and studies of their reactivities. The starting aminocyclopentadienyl ruthenium phosphite complex CpNRu[P(OPh)3]2Cl (40)(CpN=[2-(N,N-dimethylamino)ethyl]cyclopentadienyl) was obtained by reflux of CpNRu(PPh3)2Cl with triphenylphosphite in toluene solution. The ortho-metalated complexes [CpNRu(P(OPh)3)(P(OC6H4)(OPh)2] (41) was prepared by reactions of 40 with excess silver triflate in THF solution and followed by column chromatography using neutral alumina. Acidification of 41 with HBF4.Et2O yielded the protonated ortho-metalated complex [CpNH+RU(P(OPh)3)(P(OC6H4)(OPh)2] (42). Application of 25 bar of hydrogen pressure to 41 and 42 in chlorobenzene yielded different results. Complex 42 gave the corresponding hydride complex [CpNH+Ru((P(OPh)3))2H] (43) but no reaction for 41 was observed even with prolonged heating at elevated temperature. The complex CpNRu(P(OPh)3)2H (44) was prepared by reacting 43 with KOH in ethanol solution. However, 2D-NOESY experiments show that there is no hydride-proton interaction between the Ru-H and N-H+ moieties in 43. The catalytic activity of the CpN complex 43, toward hydrogenation of carbon dioxide was also studied. It was found that, although similar in structure to previously reported dppm analogue [CpNH+Ru(dppm)H](BF4) which catalyzes CO2 hydrogenation albeit in low rate, 43 showed no catalytic activity. We attribute the lack of activity of 43 to decreased hydridicity of the hydride ligand in the complex due to the presence of the low donating phosphite ligand.
Subjects: Hong Kong Polytechnic University -- Dissertations
Ruthenium compounds
Hydrogen bonding
Pages: xi, 84 leaves : ill. ; 30 cm
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