13 research outputs found
Sustainable Synthesis of Silicon Precursors Coupled with Hydrogen Delivery Based on Circular Economy via Molecular Cobalt-Based Catalysts
The
development of a circular economy is a key target to reduce
our dependence on fossil fuels and create more sustainable processes.
Concerning hydrogen as an energy vector, the use of liquid organic
hydrogen carriers is a promising strategy, but most of them present
limitations for hydrogen release, such as harsh reaction conditions,
poor recyclability, and low-value byproducts. Herein, we present a
novel sustainable methodology to produce value-added silicon precursors
and concomitant hydrogen via dehydrogenative coupling by using an
air- and water-stable cobalt-based catalyst synthesized from cheap
and commercially available starting materials. This methodology is
applied to the one-pot synthesis of a wide range of alkoxy-substituted
silanes using different hydrosilanes and terminal alkenes as reactants
in alcohols as green solvents under mild reaction conditions (room
temperature and 0.1 mol % cobalt loading). We also demonstrate that
the selectivity toward hydrosilylation/hydroalkoxysilylation can be
fully controlled by varying the alcohol/water ratio. This implies
the development of a circular approach for hydrosilylation/hydroalkoxysilylation
reactions, which is unprecedented in this research field up to date.
Kinetic and in situ spectroscopic studies (electron paramagnetic resonance,
nuclear magnetic resonance, and electrospray ionization mass spectrometry),
together with density functional theory simulations, further provide
a detailed mechanistic picture of the dehydrogenative coupling and
subsequent hydrosilylation. Finally, we illustrate the application
of our catalytic system in the synthesis of an industrially relevant
polymer precursor coupled with the production of green hydrogen on
demand
[Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb)A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies
The divalent lanthanide borohydrides [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb) have been prepared
in a straightforward
approach. The europium compound shows blue luminescence in the solid
state, having a quantum yield of 75%. Nonradiative deactivation of
C–H and B–H oscillator groups could be excluded in the
perdeuterated complex [Eu(BD<sub>4</sub>)<sub>2</sub>(<i>d</i><sub>8</sub>-THF)<sub>2</sub>], which showed a quantum yield of 93%.
The monocationic species [Ln(BH<sub>4</sub>)(THF)<sub>5</sub>][BPh<sub>4</sub>] and the bis(phosphinimino)methanides [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Ln(BH<sub>4</sub>)(THF)<sub>2</sub>] have
been prepared from [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>]. They show significantly lower or no luminescence. Using the diamagnetic
compound [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Yb(BH<sub>4</sub>)(THF)<sub>2</sub>], we performed a 2D <sup>31</sup>P/<sup>171</sup>Yb HMQC experiment
[Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb)A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies
The divalent lanthanide borohydrides [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb) have been prepared
in a straightforward
approach. The europium compound shows blue luminescence in the solid
state, having a quantum yield of 75%. Nonradiative deactivation of
C–H and B–H oscillator groups could be excluded in the
perdeuterated complex [Eu(BD<sub>4</sub>)<sub>2</sub>(<i>d</i><sub>8</sub>-THF)<sub>2</sub>], which showed a quantum yield of 93%.
The monocationic species [Ln(BH<sub>4</sub>)(THF)<sub>5</sub>][BPh<sub>4</sub>] and the bis(phosphinimino)methanides [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Ln(BH<sub>4</sub>)(THF)<sub>2</sub>] have
been prepared from [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>]. They show significantly lower or no luminescence. Using the diamagnetic
compound [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Yb(BH<sub>4</sub>)(THF)<sub>2</sub>], we performed a 2D <sup>31</sup>P/<sup>171</sup>Yb HMQC experiment
[Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb)A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies
The divalent lanthanide borohydrides [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb) have been prepared
in a straightforward
approach. The europium compound shows blue luminescence in the solid
state, having a quantum yield of 75%. Nonradiative deactivation of
C–H and B–H oscillator groups could be excluded in the
perdeuterated complex [Eu(BD<sub>4</sub>)<sub>2</sub>(<i>d</i><sub>8</sub>-THF)<sub>2</sub>], which showed a quantum yield of 93%.
The monocationic species [Ln(BH<sub>4</sub>)(THF)<sub>5</sub>][BPh<sub>4</sub>] and the bis(phosphinimino)methanides [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Ln(BH<sub>4</sub>)(THF)<sub>2</sub>] have
been prepared from [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>]. They show significantly lower or no luminescence. Using the diamagnetic
compound [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Yb(BH<sub>4</sub>)(THF)<sub>2</sub>], we performed a 2D <sup>31</sup>P/<sup>171</sup>Yb HMQC experiment
[Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb)A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies
The divalent lanthanide borohydrides [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb) have been prepared
in a straightforward
approach. The europium compound shows blue luminescence in the solid
state, having a quantum yield of 75%. Nonradiative deactivation of
C–H and B–H oscillator groups could be excluded in the
perdeuterated complex [Eu(BD<sub>4</sub>)<sub>2</sub>(<i>d</i><sub>8</sub>-THF)<sub>2</sub>], which showed a quantum yield of 93%.
The monocationic species [Ln(BH<sub>4</sub>)(THF)<sub>5</sub>][BPh<sub>4</sub>] and the bis(phosphinimino)methanides [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Ln(BH<sub>4</sub>)(THF)<sub>2</sub>] have
been prepared from [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>]. They show significantly lower or no luminescence. Using the diamagnetic
compound [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Yb(BH<sub>4</sub>)(THF)<sub>2</sub>], we performed a 2D <sup>31</sup>P/<sup>171</sup>Yb HMQC experiment
[Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb)A Highly Luminescent Material. Synthesis, Properties, Reactivity, and NMR Studies
The divalent lanthanide borohydrides [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Eu, Yb) have been prepared
in a straightforward
approach. The europium compound shows blue luminescence in the solid
state, having a quantum yield of 75%. Nonradiative deactivation of
C–H and B–H oscillator groups could be excluded in the
perdeuterated complex [Eu(BD<sub>4</sub>)<sub>2</sub>(<i>d</i><sub>8</sub>-THF)<sub>2</sub>], which showed a quantum yield of 93%.
The monocationic species [Ln(BH<sub>4</sub>)(THF)<sub>5</sub>][BPh<sub>4</sub>] and the bis(phosphinimino)methanides [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Ln(BH<sub>4</sub>)(THF)<sub>2</sub>] have
been prepared from [Ln(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>]. They show significantly lower or no luminescence. Using the diamagnetic
compound [{(Me<sub>3</sub>SiNPPh<sub>2</sub>)<sub>2</sub>CH}Yb(BH<sub>4</sub>)(THF)<sub>2</sub>], we performed a 2D <sup>31</sup>P/<sup>171</sup>Yb HMQC experiment
Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation
Artificial photosynthesis (AP) promises
to replace society’s
dependence on fossil energy resources via conversion of sunlight into
sustainable, carbon-neutral fuels. However, large-scale AP implementation
remains impeded by a dearth of cheap, efficient catalysts for the
oxygen evolution reaction (OER). Cobalt oxide materials can catalyze
the OER and are potentially scalable due to the abundance of cobalt
in the Earth’s crust; unfortunately, the activity of these
materials is insufficient for practical AP implementation. Attempts
to improve cobalt oxide’s activity have been stymied by limited
mechanistic understanding that stems from the inherent difficulty
of characterizing structure and reactivity at surfaces of heterogeneous
materials. While previous studies on cobalt oxide revealed the intermediacy
of the unusual Co(IV) oxidation state, much remains unknown, including
whether bridging or terminal oxo ligands form O<sub>2</sub> and what
the relevant oxidation states are. We have addressed these issues
by employing a homogeneous model for cobalt oxide, the [Co(III)<sub>4</sub>] cubane (Co<sub>4</sub>O<sub>4</sub>(OAc)<sub>4</sub>py<sub>4</sub>, py = pyridine, OAc = acetate), that can be
oxidized to the [Co(IV)Co(III)<sub>3</sub>] state. Upon addition
of 1 equiv of sodium hydroxide, the [Co(III)<sub>4</sub>] cubane is
regenerated with stoichiometric formation of O<sub>2</sub>.
Oxygen isotopic labeling experiments demonstrate that the cubane core
remains intact during this stoichiometric OER, implying that
terminal oxo ligands are responsible for forming O<sub>2</sub>. The
OER is also examined with stopped-flow UV–visible spectroscopy,
and its kinetic behavior is modeled, to surprisingly reveal that O<sub>2</sub> formation requires disproportionation of the [Co(IV)Co(III)<sub>3</sub>] state to generate an even higher oxidation state, formally
[Co(V)Co(III)<sub>3</sub>] or [Co(IV)<sub>2</sub>Co(III)<sub>2</sub>]. The mechanistic understanding provided by these results
should accelerate the development of OER catalysts leading to increasingly
efficient AP systems
Chiral Rare Earth Borohydride Complexes Supported by Amidinate Ligands: Synthesis, Structure, and Catalytic Activity in the Ring-Opening Polymerization of <i>rac</i>-Lactide
The monoamidinato bisborohydride rare earth complexes
[Ln{(<i>S</i>)-PEBA}(BH<sub>4</sub>)<sub>2</sub>(THF)<sub>2</sub>] (Ln = Sc (<b>1</b>), La (<b>2</b>), Nd (<b>3</b>), Sm (<b>4</b>), Yb (<b>5</b>), Lu (<b>6</b>)) were isolated as crystalline materials upon treatment of potassium <i>N</i>,<i>N</i>′-bis((<i>S</i>)-1-phenylethyl)benzamidinate
((<i>S</i>)-KPEBA) with the homoleptic trisborohydrides
[Sc(BH<sub>4</sub>)<sub>3</sub>(THF)<sub>2</sub>] and [Ln(BH<sub>4</sub>)<sub>3</sub>(THF)<sub>3</sub>] (Ln = La, Nd, Sm, Yb, Lu), respectively.
Compounds <b>1</b>–<b>6</b> are unique examples
of enantiopure borohydride complexes of the rare earth metals. Different
ionic radii of the metal centers were selected to cover the whole
range of these elements with respect to the extent of the coordination
sphere. All new complexes were thoroughly characterized by <sup>1</sup>H, <sup>13</sup>C{<sup>1</sup>H}, <sup>11</sup>B, and <sup>15</sup>N NMR and IR spectroscopies, also including single-crystal X-ray
diffraction structure determination of each compound. The scandium,
lanthanum, samarium, and lutetium complexes <b>1</b>, <b>2</b>, <b>4</b>, and <b>6</b> were found active in
the ring-opening polymerization of <i>rac</i>-lactide under
mild operating conditions, providing atactic α,ω-dihydroxytelechelic
poly(lactic acid) (PLA; <i>M</i><sub>n,SEC</sub> up to 18
800 g·mol<sup>–1</sup>). Most of the polymerizations proceed
with a certain degree of control that is directed by molar mass values
and relatively narrow dispersities (1.10 < <i>Đ</i><sub>M</sub> < 1.34), within a moderate monomer-to-initiator ratio
Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation
Artificial photosynthesis (AP) promises
to replace society’s
dependence on fossil energy resources via conversion of sunlight into
sustainable, carbon-neutral fuels. However, large-scale AP implementation
remains impeded by a dearth of cheap, efficient catalysts for the
oxygen evolution reaction (OER). Cobalt oxide materials can catalyze
the OER and are potentially scalable due to the abundance of cobalt
in the Earth’s crust; unfortunately, the activity of these
materials is insufficient for practical AP implementation. Attempts
to improve cobalt oxide’s activity have been stymied by limited
mechanistic understanding that stems from the inherent difficulty
of characterizing structure and reactivity at surfaces of heterogeneous
materials. While previous studies on cobalt oxide revealed the intermediacy
of the unusual Co(IV) oxidation state, much remains unknown, including
whether bridging or terminal oxo ligands form O<sub>2</sub> and what
the relevant oxidation states are. We have addressed these issues
by employing a homogeneous model for cobalt oxide, the [Co(III)<sub>4</sub>] cubane (Co<sub>4</sub>O<sub>4</sub>(OAc)<sub>4</sub>py<sub>4</sub>, py = pyridine, OAc = acetate), that can be
oxidized to the [Co(IV)Co(III)<sub>3</sub>] state. Upon addition
of 1 equiv of sodium hydroxide, the [Co(III)<sub>4</sub>] cubane is
regenerated with stoichiometric formation of O<sub>2</sub>.
Oxygen isotopic labeling experiments demonstrate that the cubane core
remains intact during this stoichiometric OER, implying that
terminal oxo ligands are responsible for forming O<sub>2</sub>. The
OER is also examined with stopped-flow UV–visible spectroscopy,
and its kinetic behavior is modeled, to surprisingly reveal that O<sub>2</sub> formation requires disproportionation of the [Co(IV)Co(III)<sub>3</sub>] state to generate an even higher oxidation state, formally
[Co(V)Co(III)<sub>3</sub>] or [Co(IV)<sub>2</sub>Co(III)<sub>2</sub>]. The mechanistic understanding provided by these results
should accelerate the development of OER catalysts leading to increasingly
efficient AP systems
Mechanistic Investigations of Water Oxidation by a Molecular Cobalt Oxide Analogue: Evidence for a Highly Oxidized Intermediate and Exclusive Terminal Oxo Participation
Artificial photosynthesis (AP) promises
to replace society’s
dependence on fossil energy resources via conversion of sunlight into
sustainable, carbon-neutral fuels. However, large-scale AP implementation
remains impeded by a dearth of cheap, efficient catalysts for the
oxygen evolution reaction (OER). Cobalt oxide materials can catalyze
the OER and are potentially scalable due to the abundance of cobalt
in the Earth’s crust; unfortunately, the activity of these
materials is insufficient for practical AP implementation. Attempts
to improve cobalt oxide’s activity have been stymied by limited
mechanistic understanding that stems from the inherent difficulty
of characterizing structure and reactivity at surfaces of heterogeneous
materials. While previous studies on cobalt oxide revealed the intermediacy
of the unusual Co(IV) oxidation state, much remains unknown, including
whether bridging or terminal oxo ligands form O<sub>2</sub> and what
the relevant oxidation states are. We have addressed these issues
by employing a homogeneous model for cobalt oxide, the [Co(III)<sub>4</sub>] cubane (Co<sub>4</sub>O<sub>4</sub>(OAc)<sub>4</sub>py<sub>4</sub>, py = pyridine, OAc = acetate), that can be
oxidized to the [Co(IV)Co(III)<sub>3</sub>] state. Upon addition
of 1 equiv of sodium hydroxide, the [Co(III)<sub>4</sub>] cubane is
regenerated with stoichiometric formation of O<sub>2</sub>.
Oxygen isotopic labeling experiments demonstrate that the cubane core
remains intact during this stoichiometric OER, implying that
terminal oxo ligands are responsible for forming O<sub>2</sub>. The
OER is also examined with stopped-flow UV–visible spectroscopy,
and its kinetic behavior is modeled, to surprisingly reveal that O<sub>2</sub> formation requires disproportionation of the [Co(IV)Co(III)<sub>3</sub>] state to generate an even higher oxidation state, formally
[Co(V)Co(III)<sub>3</sub>] or [Co(IV)<sub>2</sub>Co(III)<sub>2</sub>]. The mechanistic understanding provided by these results
should accelerate the development of OER catalysts leading to increasingly
efficient AP systems