Author: Hung, Mei-yuen
Title: Synthesis and characterization of osmium dihydrogen and ruthenium indenyl complexes
Degree: M.Phil.
Year: 1999
Subject: Complex compounds
Osmium compounds
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Biology and Chemical Technology
Pages: x, 180 leaves : ill. ; 30 cm
Language: English
Abstract: The pentacoordinated complex Os(PPh3)3Cl2 reacts with KTp in isopropanol at room temperature to give TpOsCl(PPh3)3 (2), which reacts with dppe and dppp in dioxane to give TpOsCl(dppe) 3 and TpOsCl(dppp) 4, respectively. The X-ray structure of compound 2 has been determined and it shows that the Tp ligand is coordinated in tridentate form. The compound crystallized in the monoclince space group with a = 10.328(0), b = 24.957(5), c= 17.321(0)A, b=92.81o and z= 4. The structure has been refined to R = 0.036, R' = 0.046. Protonation of TpOsH(Ls) (L2 = (PPh3)2 6, dppe 7, dppp 8) with HBF4 produce the corresponding dihydrogen complexes [TpOs(n2-H2)(L2)]BF4(L2 = (PPh3)2 9,dppe 10, dppp11). The pseudo-aqueous pKa values of 9 - 11 have been determined in dichloromethane, and they indicate that [TpOs(n2-H2)(L2)]BF4 are more acidic than the Cp analogues trans-[CpOsH2(L2)]BF4. Protonation of the n5-indenyl ruthenium complexes (n5-C9H7)RuH(L2); [L2 = dppm (16), dppe (17), dppp (18 PPh3)(19)] in CD2Cl2 at -60oC with trifluoromethanesulfonic acid leads to the formation of the dihydrogen (n2-H2) complexes or trans-dihydride monocations or mixture of both depending on the size of the chelating rings of the phosphine ligands. 1H NMR study of the protonation of 16 - 19 with HBF4 revealed the initial formation of the dihydrogen complexes [(n5-C9H7)Ru(n2-H2)(L2)]BF4 (L2 = dppm 20, dppe 21, dppp 23) or dihydride complexes [n5-C9H7]RuH2(L2)]BF4; (L2 = dppe 22, dppp 24, (PPh3)2 25)which slowly transformed irreversibly into [(n6-C9H8)RuH(L2)]+ (26-29). Proton abstraction from (26-29) with triethylamine in dichloromethane regenerated (16-19). The reactivity of (n5-C9H7)RuH(dppm) 16 has been examined for its ability to activate C-H bonds. The complex activates aromatic C-H bonds of common solvent like benzene, toluene, chlorobenzene, nitrobenzene and pyridine under thermal condition, as probed by catalytic H/D exchange between H2 and the deuterated solvents; the C-H activation is further evidenced by the H/D exchange among H2, D2O, and the non-deuterated solvents. Mechanisms involving o-metathesis steps are proposed to account for the H/D exchange. It is found that the electron-withdrawing substituents on the aromatic rings enhance the H/D exchange reactions between D2O and the aromatic solvents in the D2O/H2/solvent systems. This is in accord with increased acidity of the aryl hydrogens with electron-withdrawing substituents. The fD values (fD = fraction of D in the organic solvents that undergo C-H activation) of mono-substituted benzenes increase in the order NH2<CH3<H~Cl<NO2 for the 16 catalyzed H/D exchange reactions, this trend is in consonance with the electron withdrawing ability of the substituents on the aromatic rings. Selectivity in C-H activation is observed in benzene derivatives. Lack of H/D exchange in the ortho positions of toluene, chlorobenzene, nitrobenzene is attributable to steric hindrance of the substituents; and the high ortho selectivity in pyridine is due to the neighboring group participation effect. In addition, 16 is found to be an effective catalyst for the hydration of benzonitrile under thermal condition. A mechanism involving external and internal attack of the carbon atom of the benzonitrile is proposed.
Rights: All rights reserved
Access: open access

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