Catalytic C-H bond activation with ruthenium complexes, and their reactivities toward terminal alkynes

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Catalytic C-H bond activation with ruthenium complexes, and their reactivities toward terminal alkynes

 

Author: Mak, Chi-chuen Donald
Title: Catalytic C-H bond activation with ruthenium complexes, and their reactivities toward terminal alkynes
Degree: M.Phil.
Year: 2001
Subject: Ruthenium compounds
Catalysis
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Biology and Chemical Technology
Pages: xv, 124 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1573163
URI: http://theses.lib.polyu.edu.hk/handle/200/4482
Abstract: The Tp (Tp = hydridotris(pyazoleyl)borate) supported ruthenium hydride complexes, TpRuH(PPh3)2(2) and TpRuH(CH3CN)(PPh3) (4), have been examined for their activity in C-H bond activation. These complexes activate C-H bonds of common organic solvents like THF, dioxane, diethylether, benzene, toluene, chlorobenzene under 15 bars of hydrogen pressure at 130C. The C-H activation reactions are evidenced by the catalytic H/D exchange between H2 and the deuterated solvent substrates. The crucial steps of, for example, H/D exchange between H2 and benzene-d6 are a-metathesis between n2-C6D6 and Ru-H to give the n2-HD phenyl complex intermediate, and that between n2-H2 and Ru-C6D5 to form the n2-C6D5H ligand and Ru-H. THF, diethylether and toluene show regio-selectivities in the H/D exchange reactions. For THF, a C-H bond activation predominates while |B C-H bond activation is more important in diethylether. Only the aromatic C-H bonds are activated in the case of toluene. Complex 4 also activates C-H bond in the reaction of H/D exchange among D2O, H2 and organic solvents under similar conditions to yield HD, D2, HDO, H2O and the deuterated solvents, but 2 is not active in similar reactions. We believe that 4 can effect this H/D exchange reaction because it is able to generate the metal deuteride, 4- d1, via its reaction with D2O. The second part of this work concerns the chemistry of ruthenium vinylidene complexes and their reactions. The solvento a-alkyneyl complex TpRu(C=C- Ph) (PPh3) (CH3CN) (12) was readily obtained via reaction of TpRu(=C=CHPh)(PPh3)(Cl) (7) with Et3N. Elimination of HCl from 7 was assisted by the formation of the salt Et3NHCl. The vinylidene complex [TpRu(=C=CHPh)(dppe)](BF4) (11) was synthesized by acidification of TpRu(dppe)H (3) with one equivalent of HBF4H2O, followed by the addition of excess phenyl acetylene. 1H and 31P {1H} NMR spectroscopy fail to detect any ruthenium intermediate species in the course o' the conversion of 3 to 11. However, not all reactions of 1-alkyne with the metal complexes yield the vinylidene complexes, addition of methyl propiolate to TpRu(PPh3)(Cl)(CH3CN) (1) yields the carbonyl complex TpRu(PPh3)(Cl)(CO) (13). The activities of the cationic ruthenium complexes [(Tp)Ru(PPh3)2(CH3CN)]BF4 (8), [(Tpm)Ru(PPh3)2(CH3CN)](BF4)2 (9), and [(Triphos)Ru(CH3CN)](CF3SO3)2 (10) (Tpm = hydrotrispyrazolylmethane; and triphos = MeC(CH2PPh2)3) toward dimerization of alkynes were also studied. They showed catalytic activity toward dimerization of alkynes in the presence of base, NEt3. However, they only catalyzed dimerization of phenylacetaylene with low yield in the absence of base. A mechanistic interpretation of the dimerization of alkynes, in the absence of base, via a cationic vinylidene intermediate, is proposed.

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