31 research outputs found
A Proton-Switchable Bifunctional Ruthenium Complex That Catalyzes Nitrile Hydroboration
A new bifunctional pincer ligand
framework bearing pendent proton-responsive
hydroxyl groups was prepared and metalated with RuÂ(II) and subsequently
isolated in four discrete protonation states. Stoichiometric reactions
with H<sub>2</sub> and HBPin showed facile E–H (E = H or BPin)
activation across a RuÂ(II)–O bond, providing access to unusual
Ru–H species with strong interactions with neighboring proton
and boron atoms. These complexes were found to promote the catalytic
hydroboration of ketones and nitriles under mild conditions, and the
activity was highly dependent on the ligand’s protonation state.
Mechanistic experiments revealed a crucial role of the pendent hydroxyl
groups for catalytic activity
Recyclable Trifluoromethylation Reagents from Fluoroform
We present a strategy to rationally
prepare CF<sub>3</sub><sup>–</sup> transfer reagents at ambient
temperature from HCF<sub>3.</sub> We demonstrate that a highly reactive
CF<sub>3</sub><sup>–</sup> adduct can be synthesized from alkali
metal hydride,
HCF<sub>3</sub>, and borazine Lewis acids in quantitative yield at
room temperature. These nucleophilic reagents transfer CF<sub>3</sub><sup>–</sup> to substrates without additional chemical activation,
and after CF<sub>3</sub> transfer, the free borazine is quantitatively
regenerated. These features enable syntheses of popular nucleophilic,
radical, and electrophilic trifluoromethylation reagents with complete
recycling of the borazine Lewis acid
A Proton-Switchable Bifunctional Ruthenium Complex That Catalyzes Nitrile Hydroboration
A new bifunctional pincer ligand
framework bearing pendent proton-responsive
hydroxyl groups was prepared and metalated with RuÂ(II) and subsequently
isolated in four discrete protonation states. Stoichiometric reactions
with H<sub>2</sub> and HBPin showed facile E–H (E = H or BPin)
activation across a RuÂ(II)–O bond, providing access to unusual
Ru–H species with strong interactions with neighboring proton
and boron atoms. These complexes were found to promote the catalytic
hydroboration of ketones and nitriles under mild conditions, and the
activity was highly dependent on the ligand’s protonation state.
Mechanistic experiments revealed a crucial role of the pendent hydroxyl
groups for catalytic activity
Recyclable Trifluoromethylation Reagents from Fluoroform
We present a strategy to rationally
prepare CF<sub>3</sub><sup>–</sup> transfer reagents at ambient
temperature from HCF<sub>3.</sub> We demonstrate that a highly reactive
CF<sub>3</sub><sup>–</sup> adduct can be synthesized from alkali
metal hydride,
HCF<sub>3</sub>, and borazine Lewis acids in quantitative yield at
room temperature. These nucleophilic reagents transfer CF<sub>3</sub><sup>–</sup> to substrates without additional chemical activation,
and after CF<sub>3</sub> transfer, the free borazine is quantitatively
regenerated. These features enable syntheses of popular nucleophilic,
radical, and electrophilic trifluoromethylation reagents with complete
recycling of the borazine Lewis acid
Stereoretentive Deuteration of α‑Chiral Amines with D<sub>2</sub>O
We
present the direct and stereoretentive deuteration of primary
amines using Ru-bMepi (bMepi = 1,3-(6′-methyl-2′-pyridylÂimino)Âisoindolate)
complexes and D<sub>2</sub>O. High deuterium incorporation occurs
at the α-carbon (70–99%). For α-chiral amines,
complete retention of stereochemistry is achieved when using an electron-deficient
Ru catalyst. The retention of enantiomeric purity is attributed to
a high binding affinity of an imine intermediate with ruthenium, as
well as to a fast H/D exchange relative to ligand dissociation
A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding
A frustrated
Lewis pair accessory functionality is positioned in
the secondary coordination sphere of a terpyridine ligand (Tpy<sup>BN</sup> = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic
acid pinacol ester) to promote directed Lewis acid/base interactions.
Following metalation with VCl<sub>3</sub>, the utility of the metal
Lewis acid/base triad (LABT) is highlighted with N<sub>2</sub>H<sub>4</sub> as a cooperatively coordinated substrate, affording the first
η<sup>2</sup>-[N<sub>2</sub>H<sub>3</sub>]<sup>−</sup> vanadium complex
A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding
A frustrated
Lewis pair accessory functionality is positioned in
the secondary coordination sphere of a terpyridine ligand (Tpy<sup>BN</sup> = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic
acid pinacol ester) to promote directed Lewis acid/base interactions.
Following metalation with VCl<sub>3</sub>, the utility of the metal
Lewis acid/base triad (LABT) is highlighted with N<sub>2</sub>H<sub>4</sub> as a cooperatively coordinated substrate, affording the first
η<sup>2</sup>-[N<sub>2</sub>H<sub>3</sub>]<sup>−</sup> vanadium complex
A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding
A frustrated
Lewis pair accessory functionality is positioned in
the secondary coordination sphere of a terpyridine ligand (Tpy<sup>BN</sup> = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic
acid pinacol ester) to promote directed Lewis acid/base interactions.
Following metalation with VCl<sub>3</sub>, the utility of the metal
Lewis acid/base triad (LABT) is highlighted with N<sub>2</sub>H<sub>4</sub> as a cooperatively coordinated substrate, affording the first
η<sup>2</sup>-[N<sub>2</sub>H<sub>3</sub>]<sup>−</sup> vanadium complex
A Transition Metal Lewis Acid/Base Triad System for Cooperative Substrate Binding
A frustrated
Lewis pair accessory functionality is positioned in
the secondary coordination sphere of a terpyridine ligand (Tpy<sup>BN</sup> = 6-morpholino-2,2′:6′,2″-terpyridine-6″-boronic
acid pinacol ester) to promote directed Lewis acid/base interactions.
Following metalation with VCl<sub>3</sub>, the utility of the metal
Lewis acid/base triad (LABT) is highlighted with N<sub>2</sub>H<sub>4</sub> as a cooperatively coordinated substrate, affording the first
η<sup>2</sup>-[N<sub>2</sub>H<sub>3</sub>]<sup>−</sup> vanadium complex
Simple Ligand Modifications with Pendent OH Groups Dramatically Impact the Activity and Selectivity of Ruthenium Catalysts for Transfer Hydrogenation: The Importance of Alkali Metals
Remarkable differences in selectivity
and activity for ruthenium-catalyzed
transfer hydrogenation are described that are imparted by pendent
OH groups. Kinetic experiments, as well as the study of control complexes
devoid of OH groups, reveal that the pendent OH groups serve to orient
the ketone substrate through ion pairing with an alkali metal under
basic conditions. The deprotonation of the OH groups was found to
modulate the electronics at the metal center, providing a more electron
rich ruthenium center. The effects of the ion pairing between alkali
metals and the pendent alkoxide groups were highlighted by demonstrating
chemoselective transfer hydrogenation of ketones in the presence of
olefins. The results illustrate that a simple ligand modification
(installation of OH groups) imparts dramatic changes to catalysis. Pendent OH groups turn on catalysis
through electronic perturbations at the metal site under basic conditions
and can also change the mechanism of catalysis, the latter of which
can be used to promote chemoselective reductions