6 research outputs found
Synthesis and Activity of Six-Membered Cyclic Alkyl Amino Carbene–Ruthenium Olefin Metathesis Catalysts
Ru–cyclic alkyl amino carbene (Ru–CAAC) olefin metathesis catalysts perform extraordinarily in metathesis macrocyclization and ethenolysis, but previous studies have been limited to the use of five-membered CAAC (CAAC-5) ligands. In this work, we synthesized a different group of ruthenium catalysts with more σ-donating and π-accepting six-membered CAAC (CAAC-6) ligands, and their metathesis activity was probed through initiation studies, ring-closing metathesis (RCM), cross-metathesis, and ethenolysis. These catalysts display higher initiation rates than analogous Ru–CAAC-5 complexes but demonstrate lower activity in RCM and ethenolysis
Synthesis and Activity of Six-Membered Cyclic Alkyl Amino Carbene–Ruthenium Olefin Metathesis Catalysts
Ru–cyclic alkyl amino carbene (Ru–CAAC) olefin metathesis catalysts perform extraordinarily in metathesis macrocyclization and ethenolysis, but previous studies have been limited to the use of five-membered CAAC (CAAC-5) ligands. In this work, we synthesized a different group of ruthenium catalysts with more σ-donating and π-accepting six-membered CAAC (CAAC-6) ligands, and their metathesis activity was probed through initiation studies, ring-closing metathesis (RCM), cross-metathesis, and ethenolysis. These catalysts display higher initiation rates than analogous Ru–CAAC-5 complexes but demonstrate lower activity in RCM and ethenolysis
Efficient Z-Selective Olefin-Acrylamide Cross-Metathesis Enabled by Sterically Demanding Cyclometalated Ruthenium Catalysts
The efficient Z-selective cross-metathesis between acrylamides and common terminal olefins has been developed by the use of novel cyclometalated ruthenium catalysts with bulky N-heterocyclic carbene (NHC) ligands. Superior reactivity and stereoselectivity are realized for the first time in this challenging transformation, allowing streamlined access to an important class of cis-Michael acceptors from readily available feedstocks. The kinetic preference for cross-metathesis is enabled by a pivalate anionic ligand, and the origin of this effect is elucidated by density functional theory calculations
Titanocene-Mediated Dinitrile Coupling: A Divergent Route to Nitrogen-Containing Polycyclic Aromatic Hydrocarbons
A general synthetic strategy for
the construction of large, nitrogen-containing
polycyclic aromatic hydrocarbons (PAHs) is reported. The strategy
involves two key steps: (1) a titanocene-mediated reductive cyclization
of an oligo(dinitrile) precursor to form a PAH appended with di(aza)titanacyclopentadiene
functionality; (2) a divergent titanocene transfer reaction, which
allows final-step installation of one or more <i>o</i>-quinone,
diazole, or pyrazine units into the PAH framework. The new methodology
enables rational, late-stage control of HOMO and LUMO energy levels
and thus photophysical and electrochemical properties, as revealed
by UV/vis and fluorescence spectroscopy, cyclic voltammetry, and DFT
calculations. More generally, this contribution presents the first
productive use of di(aza)metallacyclopentadiene
intermediates in organic synthesis, including the first formal [2
+ 2 + 2] reaction to form a pyrazine ring
Titanocene-Mediated Dinitrile Coupling: A Divergent Route to Nitrogen-Containing Polycyclic Aromatic Hydrocarbons
A general synthetic strategy for
the construction of large, nitrogen-containing
polycyclic aromatic hydrocarbons (PAHs) is reported. The strategy
involves two key steps: (1) a titanocene-mediated reductive cyclization
of an oligo(dinitrile) precursor to form a PAH appended with di(aza)titanacyclopentadiene
functionality; (2) a divergent titanocene transfer reaction, which
allows final-step installation of one or more <i>o</i>-quinone,
diazole, or pyrazine units into the PAH framework. The new methodology
enables rational, late-stage control of HOMO and LUMO energy levels
and thus photophysical and electrochemical properties, as revealed
by UV/vis and fluorescence spectroscopy, cyclic voltammetry, and DFT
calculations. More generally, this contribution presents the first
productive use of di(aza)metallacyclopentadiene
intermediates in organic synthesis, including the first formal [2
+ 2 + 2] reaction to form a pyrazine ring