Ruthenium N Heterocyclic Carbene And Ruthenium Acetylide Complexes Supported By Macrocyclic Porphyrin Or Tetradentate Schiff Base Ligands

Download or read book Ruthenium-N-Heterocyclic Carbene and Ruthenium Acetylide Complexes Supported by Macrocyclic Porphyrin Or Tetradentate Schiff Base Ligands written by Ka-Ho Chan and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Ruthenium-N-heterocyclic Carbene and Ruthenium Acetylide Complexes Supported by Macrocyclic Porphyrin or Tetradentate Schiff Base Ligands: Synthesis, Structure and Catalytic Applications" by Ka-ho, Chan, 陳嘉豪, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled RUTHENIUM-N-HETEROCYCLIC CARBENE AND RUTHENIUM ACETYLIDE COMPLEXES SUPPORTED BY MACROCYCLIC PORPHYRIN OR TETRADENTATE SCHIFF BASE LIGANDS: SYNTHESIS, STRUCTURE AND CATALYTIC APPLICATIONS Submitted by Chan Ka Ho for the degree of Doctor of Philosophy at The University of Hong Kong in March 2015 Transition metal-catalyzed C-C and C-N bond formation reactions are important transformations in synthetic organic chemistry. In the endeavor of this thesis to develop robust/versatile catalysts for these reactions, the trans effect imposed by N-heterocyclic carbene (NHC) and acetylide ligand onto ruthenium complexes supported by macrocyclic porphyrin or tetradentate Schiff-base ligands was studied. The catalytic activity of these novel ruthenium complexes towards carbene and/or nitrene transfer and insertion reactions was also explored. II A series of bis(NHC)ruthenium(II) porphyrin complexes [Ru (Por)(NHC) ] were synthesized by deprotonation of imidazolium salt using a strong base. These complexes displayed unprecedentedly high catalytic activity towards carbene/nitrene transfer and insertion reactions, including alkene cyclopropanation and aziridination, carbene C-H, S-H, N-H and O-H insertions, and nitrene C-H insertion with product -1 turnover frequency up to 1950 min . Carbene modification of N-terminus of peptide o II at 37 C was achieved. Chiral [Ru (D -Por)(NHC) ] catalyst led to highly 4 2 enantioselective carbene/nitrene transfer and insertion reactions with up to 98% ee. DFT calculations revealed that the strong σ-donor strength of trans axial NHC ligand stabilizes the formation of metal-carbene and metal-nitrene intermediate from decomposition of diazo compounds and organic azides, which is crucial for the transition metal-catalyzed oxidative C-C and C-N bond formation reactions to proceed under mild reaction conditions. II A series of ruthenium Schiff-base complexes cis-β-[Ru (Schiff-base)(CO) ] were synthesized and characterized. These complexes showed high catalytic activity towards enantioselective cyclopropanation, carbene C-H and Si-H bond insertions. II t The cis-[Ru (2-CPh -4- Bu-Schiff-base)(CO) ]-catalyzed intermolecular 3 2 cyclopropanation of styrene with EDA in CH Cl afforded desired cyclopropane 2 2 product in 90% isolated yield and 95% ee with a product turnover number of 9000. Excellent trans- and high enantioselectivity were observed with wide substrate scope, including conjugated, electron-rich, electron-deficient and aliphatic terminal alkenes. Carbene C-H and Si-H insertion reactions proceeded smoothly with II t cis-[Ru (2-CPh -4- Bu-Schiff-base)(CO) ] as catalyst, giving the desired products in 3 2 82-97% yields with excellent enantioselectivity (up to 99% ee). The same complex was also catalytically active towards intramolecular cyclopropanation and intramolecular alkyl carbene sp C-H bond insertion to give cis-products with up to 99:1 cis: trans ratio and with excellent enantioselectivities (up to 98% ee). DFT calculations on the intermolecular cyclopropanation catalyzed by II cis-β-[Ru (Schiff-base)(CO) ] revealed that among the ruthenium-carbene intermediates possibly involved in the reactions, the cis-β species are more stable than their trans isomer with