Eight new ruthenium(ii) half-sandwich complexes containing azobenzene-appended pyridine (1), bipyridine (2-5) and phosphine (6 and 7) ligands have been synthesized and fully characterized. UV-vis ...spectroscopic studies showed that the trans-to-cis photoisomerization was strongly inhibited upon coordination to the metal centre in azopyridine-derived ligands 1 and 2, but it remained efficient in azobenzene-appended bipyridine (3-5) and phosphine (6 and 7) ligands. The complexes were tested as precatalysts for photo-controlled hydrogen generation by hydrolytic decomposition of ammonia-borane (AB). In situ irradiation of the reaction mixtures of compounds Ru(p-Cym)(6)ClCl and Ru(p-Cym)(7)ClCl induced a clear change in the catalytic reaction rate, serving as a proof of concept for light-controlled hydrogen generation.
Twelve Ir(iii) triscyclometalated compounds containing up to three azobenzene fragments on their structure have been synthesized based on photochromic 2-phenylpyridyl type ligands . These complexes ...are intended to study the possibility of transferring the photochromicity of the azobenzene fragment to the organometallic compound, and the effect of the substitution pattern, relative distance of the azobenzene to the metal centre, and number of azobenzenes on their properties.
Iridium(iii) cyclometalated complexes have been used as models to study the effect that extended conjugation and substitution pattern has on the photochromic behavior of azobenzene-appended ...2-phenylpyridyl (ppy) ligands. For this purpose four azobenzene-containing ppy ligands were synthesized. With these ligands, nine iridium(iii) complexes containing up to three appended azobenzenes were synthesized. Analysis of their photochromic behaviour by means of UV-vis and (1)H-NMR spectroscopy permitted us to conclude that the light-induced trans-to-cis isomerization of the azobenzene was strongly inhibited upon coordination to the Ir(iii) cation when the electronic conjugation was extended along the whole ligand. The use of an aliphatic spacer unit (either -CH2- or -OCH2-) between the azobenzene and the ppy fragment of the ligand sufficed to disrupt the electronic communication, and obtain photochromic organometallic complexes.
The development of chelating diphosphine ligands has been a prolific research area for several decades, but quite surprisingly, from the plethora of diphosphines that are currently known, only a ...handful of them are able to coordinate preferentially in a
trans-fashion (P–M–P angle close to 180°). The most representative ones, together with their most relevant reactivities and catalytic applications will be presented herein.
Although some sophisticated backbones are currently known, a truly and only
trans-coordinating diphosphine remains elusive. Apparently, the inherent flexibility associated with the required large backbones always left other coordination modes accessible.
Cis-monodentates, dimeric species or bimetallic compounds are additional escape routes for the desired species. Nevertheless, on the way to this illusory goal compounds with surprising and fascinating reactivities and coordination modes have been encountered which surely have contributed to widen the knowledge of coordination chemistry.
Eight new ruthenium(
ii
) half-sandwich complexes containing azobenzene-appended pyridine (
1
), bipyridine (
2-5
) and phosphine (
6
and
7
) ligands have been synthesized and fully characterized. ...UV-vis spectroscopic studies showed that the
trans
-to-
cis
photoisomerization was strongly inhibited upon coordination to the metal centre in azopyridine-derived ligands
1
and
2
, but it remained efficient in azobenzene-appended bipyridine (
3-5
) and phosphine (
6
and
7
) ligands. The complexes were tested as precatalysts for photo-controlled hydrogen generation by hydrolytic decomposition of ammonia-borane (AB).
In situ
irradiation of the reaction mixtures of compounds Ru(
p
-Cym)(
6
)ClCl and Ru(
p
-Cym)(
7
)ClCl induced a clear change in the catalytic reaction rate, serving as a proof of concept for light-controlled hydrogen generation.
Photo-controlled hydrogen generation catalysts were developed based on ruthenium(
ii
) azobenzene-containing half-sandwich complexes.
•Series of phosphonium ILs were rationally designed prepared and characterized.•Excellent conversion up to 99.8% after 5 h reaction was achieved.•Substituents on phosphonium cation plays a key role ...in catalysts performance.•Outstanding catalytic performance in the cycloaddition of CO2 to epoxidized oils.
A series of phosphonium-based ionic liquids have been prepared in one step in a simple way from inexpensive feedstocks. The prepared ionic liquids have been successfully tested as catalysts in the solvent-free cycloaddition reaction of CO2 to an epoxidized soybean oil to obtain carbonated soybean oil that can be potentially employed as bio-monomer in the synthesis for bio-based polymers. The catalytic performance of these ionic liquids was compared to the widely used and benchmark catalyst in CO2 cycloaddition to epoxides reaction, namely tetrabutylammonium bromide at different reaction conditions. The influence of some reaction parameters such as temperature, CO2 pressure, reaction time and catalyst amount was studied. It has been found that the solubility of the prepared ionic liquids in the reaction media (epoxidized soybean oil) is a key factor that limits the catalytic performance of some of the synthesized ionic liquids. All prepared ionic liquids have shown higher thermal stability that the benchmark catalyst and three of them have shown superior catalytic performance. The best results in terms of conversion and selectivity have been obtained with dodecyltriphenylphosphonium bromide (5) achieving almost full conversion (99.8%) and excellent selectivity (84.0%) after 5 h reaction at 160 ºC and 40 bar of CO2. Outstanding results compared to those reported in the literature with similar catalysts in the solvent-free CO2 cycloaddtion to an epoxidized soybean oil to obtain the corresponding carbonated oil have been achieved. Considering the facile synthesis of catalyst 5, the large availability and non-expensive of the feedstocks and its catalytic performance it can be considered a valuable and green alternative for CO2 fixation to epoxidized vegetable oil.
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A
bstract
The NEXT experiment aims at the sensitive search of the neutrinoless double beta decay in
136
Xe, using high-pressure gas electroluminescent time projection chambers. The NEXT-White ...detector is the first radiopure demonstrator of this technology, operated in the Laboratorio Subterráneo de Canfranc. Achieving an energy resolution of 1% FWHM at 2.6 MeV and further background rejection by means of the topology of the reconstructed tracks, NEXT-White has been exploited beyond its original goals in order to perform a neu- trinoless double beta decay search. The analysis considers the combination of 271.6 days of
136
Xe-enriched data and 208.9 days of
136
Xe-depleted data. A detailed background modeling and measurement has been developed, ensuring the time stability of the radiogenic and cosmogenic contributions across both data samples. Limits to the neutrinoless mode are obtained in two alternative analyses: a background-model-dependent approach and a novel direct background-subtraction technique, offering results with small dependence on the background model assumptions. With a fiducial mass of only 3.50 ± 0.01 kg of
136
Xe-enriched xenon, 90% C.L. lower limits to the neutrinoless double beta decay are found in the
T
1
/
2
0
ν
> 5
.
5
×
10
23
−
1
.
3
×
10
24
yr range, depending on the method. The presented techniques stand as a proof-of-concept for the searches to be implemented with larger NEXT detectors.
Iridium(
iii
) cyclometalated complexes have been used as models to study the effect that extended conjugation and substitution pattern has on the photochromic behavior of azobenzene-appended ...2-phenylpyridyl (ppy) ligands. For this purpose four azobenzene-containing ppy ligands were synthesized. With these ligands, nine iridium(
iii
) complexes containing up to three appended azobenzenes were synthesized. Analysis of their photochromic behaviour by means of UV-vis and
1
H-NMR spectroscopy permitted us to conclude that the light-induced
trans
-to-
cis
isomerization of the azobenzene was strongly inhibited upon coordination to the Ir(
iii
) cation when the electronic conjugation was extended along the whole ligand. The use of an aliphatic spacer unit (either -CH
2
- or -OCH
2
-) between the azobenzene and the ppy fragment of the ligand sufficed to disrupt the electronic communication, and obtain photochromic organometallic complexes.
The use of aliphatic-bridging units to append azobenzene fragments on triscyclometalated Ir(
iii
) complexes permits the construction of photoswitchable organometallics.
