3 research outputs found
Robust, Chiral, and Porous BINAP-Based Metal–Organic Frameworks for Highly Enantioselective Cyclization Reactions
We
report here the design of BINAP-based metal–organic frameworks
and their postsynthetic metalation with Rh complexes to afford highly
active and enantioselective single-site solid catalysts for the asymmetric
cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs
of UiO topology, BINAP-MOF (<b>I</b>) or BINAP-dMOF (<b>II</b>), were prepared using purely BINAP-derived dicarboxylate linkers
or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate
linkers, respectively. Upon metalation with RhÂ(nbd)<sub>2</sub>BF<sub>4</sub> and [RhÂ(nbd)ÂCl]<sub>2</sub>/AgSbF<sub>6</sub>, the MOF precatalysts <b>I</b>·RhÂ(BF<sub>4</sub>) and <b>I</b>·RhÂ(SbF<sub>6</sub>) efficiently catalyzed highly enantioselective (up to 99%
ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes,
respectively. <b>I</b>·Rh catalysts afforded cyclization
products at comparable enantiomeric excesses (ee’s) and 4–7
times higher catalytic activity than the homogeneous controls, likely
a result of catalytic site isolation in the MOF which prevents bimolecular
catalyst deactivation pathways. However, <b>I</b>·Rh is
inactive in the more sterically encumbered Pauson–Khand reactions
between 1,6-enynes and carbon monoxide. In contrast, with a more open
structure, Rh-functionalized BINAP-dMOF, <b>II</b>·Rh,
effectively catalyzed Pauson–Khand cyclization reactions between
1,6-enynes and carbon monoxide at 10 times higher activity than the
homogeneous control. <b>II</b>·Rh was readily recovered
and used three times in Pauson–Khand cyclization reactions
without deterioration of yields or ee’s. Our work has expanded
the scope of MOF-catalyzed asymmetric reactions and showed that the
mixed linker strategy can effectively enlarge the open space around
the catalytic active site to accommodate highly sterically demanding
polycyclic metallocycle transition states/intermediates in asymmetric
intramolecular cyclization reactions
Robust, Chiral, and Porous BINAP-Based Metal–Organic Frameworks for Highly Enantioselective Cyclization Reactions
We
report here the design of BINAP-based metal–organic frameworks
and their postsynthetic metalation with Rh complexes to afford highly
active and enantioselective single-site solid catalysts for the asymmetric
cyclization reactions of 1,6-enynes. Robust, chiral, and porous Zr-MOFs
of UiO topology, BINAP-MOF (<b>I</b>) or BINAP-dMOF (<b>II</b>), were prepared using purely BINAP-derived dicarboxylate linkers
or by mixing BINAP-derived linkers with unfunctionalized dicarboxylate
linkers, respectively. Upon metalation with RhÂ(nbd)<sub>2</sub>BF<sub>4</sub> and [RhÂ(nbd)ÂCl]<sub>2</sub>/AgSbF<sub>6</sub>, the MOF precatalysts <b>I</b>·RhÂ(BF<sub>4</sub>) and <b>I</b>·RhÂ(SbF<sub>6</sub>) efficiently catalyzed highly enantioselective (up to 99%
ee) reductive cyclization and Alder-ene cycloisomerization of 1,6-enynes,
respectively. <b>I</b>·Rh catalysts afforded cyclization
products at comparable enantiomeric excesses (ee’s) and 4–7
times higher catalytic activity than the homogeneous controls, likely
a result of catalytic site isolation in the MOF which prevents bimolecular
catalyst deactivation pathways. However, <b>I</b>·Rh is
inactive in the more sterically encumbered Pauson–Khand reactions
between 1,6-enynes and carbon monoxide. In contrast, with a more open
structure, Rh-functionalized BINAP-dMOF, <b>II</b>·Rh,
effectively catalyzed Pauson–Khand cyclization reactions between
1,6-enynes and carbon monoxide at 10 times higher activity than the
homogeneous control. <b>II</b>·Rh was readily recovered
and used three times in Pauson–Khand cyclization reactions
without deterioration of yields or ee’s. Our work has expanded
the scope of MOF-catalyzed asymmetric reactions and showed that the
mixed linker strategy can effectively enlarge the open space around
the catalytic active site to accommodate highly sterically demanding
polycyclic metallocycle transition states/intermediates in asymmetric
intramolecular cyclization reactions
Computational Design Principles of Two-Center First-Row Transition Metal Oxide Oxygen Evolution Catalysts
Computational screens
for oxygen evolution reaction (OER) catalysts
based on Sabatier analysis have seen great success in recent years;
however, the concept of using chemical descriptors to form a reaction
coordinate has not been put under scrutiny for complex systems. In
this paper, we examine critically the use of chemical descriptors
as a method for conducting catalytic screens. Applying density functional
theory calculations to a two-center metal oxide model system, we show
that the Sabatier analysis is quite successful for predicting activities
and capturing the chemical periodic trends expected for the first-row
transition metal series, independent of the proposed mechanism. We
then extend this analysis to heterodimer metallic systemsî—¸metal
oxide catalysts with two different catalytically active metal centersî—¸and
find signs that the Sabatier analysis may not hold for these more
complex systems. By performing a principal component analysis on the
computed redox potentials, we show (1) that a single chemical descriptor
inadequately describes heterodimer overpotentials and (2) mixed-metal
overpotentials cannot be predicted using only pure-metal redox potentials.
We believe that the analysis presented in this article shows a need
to move beyond the simple chemical descriptor picture when studying
more complex mixed metal oxide OER catalysts