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Title: Catalytic C-H bond activation with ruthenium complexes, and their reactivities toward terminal alkynes
Authors: Mak, Chi-chuen Donald
Keywords: Ruthenium compounds
Hong Kong Polytechnic University -- Dissertations
Issue Date: 2001
Publisher: The Hong Kong Polytechnic University
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 130℃. 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 η²-C₆D₆ and Ru-H to give the η²-HD phenyl complex intermediate, and that between η²-H₂ and Ru-C₆D₅ to form the η²-C₆D₅H ligand and Ru-H. THF, diethylether and toluene show regio-selectivities in the H/D exchange reactions. For THF, α C-H bond activation predominates while β 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 ³¹1P {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.
Description: xv, 124 leaves : ill. ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577M ABCT 2001 Mak
Rights: All rights reserved.
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