Half-sandwich Complexes of Ruthenium; Synthesis and Application to Catalysis

This thesis describes syntheses and catalytic reactivity of several half-sandwich complexes of ruthenium. The neutral ruthenium trihydride complex, Cp(PPri3)RuH3(1), can efficiently catalyse the H/D exchange reaction between various organic substrates and deuterium sources, such as benzene-d6. Moreover, the H/D exchange reactions of polar substrates were also observed in D2O, which is the most attractive deuterium source due to its low cost and low toxicity. Importantly, the H/D exchange under catalytic conditions was achieved not only in aromatic compounds but also in substituted liphatic compounds. Interestingly, in the case of alkanes and alkyl chains, highly selective deuterium incorporation in the terminal methyl positions was observed. It was discovered that the methylene units are engaged in exchange only if the molecule contains a donating functional group, such as O-and N-donors, C=C double bonds, arenes and CH3. The cationic half-sandwich ruthenium complex [Cp(PPri3)Ru(CH3CN)2]+(2) catalyses the chemoselective mono-addition of HSiMe2Ph to pyridine derivatives to selectively give the 1,4-regiospecific, N-silylated products. An ionic hydrosilylation mechanismis suggested based on the experiments. To support this mechanistic proposal, kinetic studies under catalytic conditions were performed. Also, the 1,4-regioselective mono-hydrosilylation of nitrogen containing compounds such as phenanthroline, quinoline and acridine can be achieved with the related Cp*complex [Cp*(phen)Ru(CH3CN)]+(3) (phen = 1,10-phenanthroline) and HSiMe2Ph under mild conditions. The cationic ruthenium complex 2 can also be used as an efficient catalyst for transfer hydrogenation of various organic substrates including carbonyls, imines, nitriles and esters. Secondary alcohols, amines, N-isopropylidene amines and ether compounds can be obtained in moderate to high yields. In addition, other ruthenium complexes, 1,3 and [Cp*(PPri3)Ru(CH3CN)2]+(4), can catalyse transfer hydrogenation of carbonyls although the reactions were sluggish compared to the ones of 2. The possible intermediate, Cp(PPri3)Ru(CH3CN)(H), was characterized by NMR at low temperature and the kinetic studies for the transfer hydrogenation of acetophenone were performed. Recently, chemoselective reduction of acid chlorides to aldehydes catalysed by the complex 2 was reported. To extend the catalytic reactivity of 2, reduction of iminoyl chlorides, which can be readily obtained from secondary amides, to the corresponding imines and aldehydes was investigated. Various substituted iminoyl chlorides were converted into the imines and aldehydes under mild conditions and several products were isolated with moderate yields.

Investigation into the determination of arsenic by direct current plasma atomic emission spectrometer

Improvements have been made on the currently available hydride generator system manufactured by SpectraMetrics Incorporated, because the system was found to be unsatisfactory with respect to the following: 1. the drying agent, anhydrous calcium chloride, 2. the special sample tube, 3. the direction of argon flow through the Buchner funnel when it came to dealing with real sample, that is, with reference only to aqueous extracts of soil samples. Changes that were made on the system included the replacement of anhydrous calcium chloride with anhydrous calcium sulphate and the replacement of the special sample tube with a modified one made from silica. Re-directing the flow of argon through the top of the Buchner funnel appeared to make the system compatible with aqueous extracts of soil samples. The interferences from 1000 ~g/mL of nickel(II) , cobalt(II), iron(III), copper(II) have been eliminated with the aid of 1.4 M hydrochloric acid and 1% (weight/volume) L-cystine. Greater than 90% recovery of 0.3 ~g/mL arsenic signal was achieved in each case. Furthermore, 103% of arsenic signal was accomplished in the presence of 1000 ~g/mL cadmium with 5 M Hel. tVhen each of the interferents was present in solution at 1000 ppm, a recovery of 85% was achieved by using 5 M hydrochloric acid and 3% (weight/volume) L-cystine. Without L-cystine and when 1.4 M hydrochloric acid was used, the recoveries were 0% (Ni), 0% (Co), 88% (Fe), 15% (Cu), 18% (Cd). Similarly, a solution containing 1000 ppm of each interferent gave a zero percent recovery of arsenic. The reduction of trivalent and pentavalent arsenic at a pH less than one has also been investigated and shown to be quantitative if peak areas are measured. The reproducibility determination of a 0.3 Vg/mL standard arsenic solution by hydride generation shows a relative standard deviation of 3.4%. The detection limits with and without Porapak Q have been found to be 0.6 ng/mL and 1.0 ng/mL, respectively.