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Aromatic C–F Bond Activation by Rare-Earth-Metal Complexes
C–F bond activation is a challenging
reaction with increasing
importance in synthesis. The strength of the C–F bond and the
shielding effect of the fluorine atom render its activation difficult. Rare-earth metals offer an exceptional
opportunity for this process because the high dissociation energy
of the M–F bond offsets the strength of the C–F bond.
Herein we report a unique reaction for the C–F activation of
aromatic bonds by rare-earth-metal complexes. The strong C–F
bond of perfluorobenzene is cleaved under reducing conditions in the
presence of a rare-earth-metal iodide to form initially an equimolar
mixture of a metal fluoride and a metal perfluorophenyl complex; the
latter eventually undergoes β-F elimination to a metal fluoride.
A similar behavior is observed when inverse sandwich rare-earth-metal
arene complexes react with perfluorobenzene. All compounds were characterized
by X-ray crystallography, multinuclear NMR spectroscopy, and elemental
analysis
Reduction of Diphenylacetylene Mediated by Rare-Earth Ferrocene Diamide Complexes
The synthesis and characterization
of <b>Ln-C</b><sub><b>4</b></sub><b>Ph</b><sub><b>4</b></sub><b>-K</b>, [(NN<sup>TBS</sup>)ÂLnÂ(η<sup>2</sup>-C<sub>4</sub>Ph<sub>4</sub>)]Â[KÂ(THF)<sub><i>x</i></sub>] (Ln = Sc, Y, Lu), rare-earth
metal complexes supported by a ferrocene diamide ligand, NN<sup>TBS</sup> (NN<sup>TBS</sup> = fcÂ(NSi<sup><i>t</i></sup>BuMe<sub>2</sub>)<sub>2</sub>, fc = 1,1′-ferrocenediyl), were accomplished.
The preparation of the half-sandwich compounds, <b>Ln-naph-K</b>, [(NN<sup>TBS</sup>)ÂLnÂ(μ-C<sub>10</sub>H<sub>8</sub>)]Â[KÂ(THF)<sub>2</sub>] (Ln = Sc, Y, Lu, La), was necessary in order to obtain high
yields of rare-earth metallacyclopentadienes. Unlike Y and Lu, La
did not show the same reactivity toward PhCCPh. The characterization
of the new metal complexes was accomplished by NMR spectroscopy, elemental
analysis, and single-crystal X-ray diffraction
Reduction of Diphenylacetylene Mediated by Rare-Earth Ferrocene Diamide Complexes
The synthesis and characterization
of <b>Ln-C</b><sub><b>4</b></sub><b>Ph</b><sub><b>4</b></sub><b>-K</b>, [(NN<sup>TBS</sup>)ÂLnÂ(η<sup>2</sup>-C<sub>4</sub>Ph<sub>4</sub>)]Â[KÂ(THF)<sub><i>x</i></sub>] (Ln = Sc, Y, Lu), rare-earth
metal complexes supported by a ferrocene diamide ligand, NN<sup>TBS</sup> (NN<sup>TBS</sup> = fcÂ(NSi<sup><i>t</i></sup>BuMe<sub>2</sub>)<sub>2</sub>, fc = 1,1′-ferrocenediyl), were accomplished.
The preparation of the half-sandwich compounds, <b>Ln-naph-K</b>, [(NN<sup>TBS</sup>)ÂLnÂ(μ-C<sub>10</sub>H<sub>8</sub>)]Â[KÂ(THF)<sub>2</sub>] (Ln = Sc, Y, Lu, La), was necessary in order to obtain high
yields of rare-earth metallacyclopentadienes. Unlike Y and Lu, La
did not show the same reactivity toward PhCCPh. The characterization
of the new metal complexes was accomplished by NMR spectroscopy, elemental
analysis, and single-crystal X-ray diffraction
Synthesis and Characterization of Paramagnetic Lanthanide Benzyl Complexes
The organometallic chemistry of paramagnetic lanthanides
(Ln, from Ce to Yb) is far less developed compared to that of their
diamagnetic counterparts (Sc, Y, La, and Lu). Lack of available starting
materials and characterization methods are the major obstacles. Herein
we report the synthesis and characterization of trisbenzyl complexes
of neodymium, gadolinium, holmium, and erbium. In addition, we introduce
a direct procedure for the synthesis of lanthanide benzyl and iodide
complexes supported by a ferrocene diamide ligand starting from the
corresponding oxides. All newly synthesized compounds were characterized
by X-ray crystallography, <sup>1</sup>H NMR spectroscopy (except for
gadolinium compounds, which were NMR silent), and elemental analysis
Bimetallic Cleavage of Aromatic C–H Bonds by Rare-Earth-Metal Complexes
A new
type of C–H bond activation mediated by rare-earth metals under
reducing conditions is reported. The synergy between reductants and
rare-earth-metal complexes allows the cleavage of unactivated aromatic
C–H bonds. The reaction between rare-earth-metal iodides supported
by a 1,1′-ferrocenediamide ligand and potassium graphite in
benzene leads to the formation of a 1:1 metal molar ratio of the corresponding
metal hydride and metal phenyl complex. A proposed mechanism involving an inverse sandwich arene bimetallic intermediate is supported
by experimental and computational studies
Tetraanionic Biphenyl Lanthanide Complexes as Single-Molecule Magnets
Inverse sandwich biphenyl complexes
[(NN<sup>TBS</sup>)ÂLn]<sub>2</sub>(μ-biphenyl)Â[KÂ(solvent)]<sub>2</sub> [NN<sup>TBS</sup> = 1,1′-fcÂ(NSi<sup>t</sup>BuMe<sub>2</sub>)<sub>2</sub>; Ln = Gd, Dy, Er; solvent = Et<sub>2</sub>O,
toluene; 18-crown-6], containing a quadruply reduced biphenyl ligand,
were synthesized and their magnetic properties measured. One of the
dysprosium biphenyl complexes was found to exhibit antiferromagnetic
coupling and single-molecule-magnet behavior with <i>U</i><sub>eff</sub> of 34 K under zero applied field. The solvent coordinated
to potassium affected drastically the nature of the magnetic interaction,
with the other dysprosium complex showing ferromagnetic coupling.
Ab initio calculations were performed to understand the nature of
magnetic coupling between the two lanthanide ions bridged by the anionic
arene ligand and the origin of single-molecule-magnet behavior
Topology-Dependent Synthesis, Structures, and Bonding Interactions of Uranium Polyarene Complexes
Metal polyarene complexes have attracted great attention
in recent
years because of their appealing electronic structures and readily
tunable properties and reactivity. While main group and transition
metal polyarene complexes have been well studied with various degrees
of reduction and different coordination modes, f-block metal polyarene
complexes are rare. Here we report the synthesis of a series of uranium
polyarene complexes supported by ferrocene diamide ligands. X-ray
crystallography shows that the structures of uranium polyarene complexes
are dependent on the topology of polyarenes. While linear polyarenes
form mononuclear compounds, nonlinear polyarenes prefer an inverse-sandwich
structure with a μ-η6,η6-coordination
mode. Combined experimental and computational studies unveil that
mononuclear uranium polyarene complexes are best described as bidentate
with a three-center two-electron (3c-2e) σ bond, whereas inverse-sandwich
uranium polyarene complexes are bound through two δ bonds. The
correlation between the topology of polyarenes and the coordination
mode of uranium polyarene complexes can be rationalized by the electronic
structures and bonding interactions as well as the relative energies
of coordination isomers
Topology-Dependent Synthesis, Structures, and Bonding Interactions of Uranium Polyarene Complexes
Metal polyarene complexes have attracted great attention
in recent
years because of their appealing electronic structures and readily
tunable properties and reactivity. While main group and transition
metal polyarene complexes have been well studied with various degrees
of reduction and different coordination modes, f-block metal polyarene
complexes are rare. Here we report the synthesis of a series of uranium
polyarene complexes supported by ferrocene diamide ligands. X-ray
crystallography shows that the structures of uranium polyarene complexes
are dependent on the topology of polyarenes. While linear polyarenes
form mononuclear compounds, nonlinear polyarenes prefer an inverse-sandwich
structure with a μ-η6,η6-coordination
mode. Combined experimental and computational studies unveil that
mononuclear uranium polyarene complexes are best described as bidentate
with a three-center two-electron (3c-2e) σ bond, whereas inverse-sandwich
uranium polyarene complexes are bound through two δ bonds. The
correlation between the topology of polyarenes and the coordination
mode of uranium polyarene complexes can be rationalized by the electronic
structures and bonding interactions as well as the relative energies
of coordination isomers
Two-Electron Oxidations at a Single Cerium Center
Two-electron
oxidations are ubiquitous and play a key role in the
synthesis and catalysis. For transition metals and actinides, two-electron
oxidation often takes place at a single-metal site. However, redox
reactions at rare-earth metals have been limited to one-electron processes
due to the lack of accessible oxidation states. Despite recent advancements
in nontraditional oxidation state chemistry, the low stability of
low-valent compounds and large disparity among different oxidation
states prevented the implementation of two-electron processes at a
single rare-earth metal center. Here we report two-electron oxidations
at a cerium(II) center to yield cerium(IV) terminal oxo and imido
complexes. A series of cerium(II–IV) complexes supported by
a tripodal tris(amido)arene ligand were synthesized and characterized.
Experimental and theoretical studies revealed that the cerium(II)
complex is best described as a 4f2 ion stabilized by δ-backdonation
to the anchoring arene, while the cerium(IV) oxo and imido complexes
exhibit multiple bonding characters. The accomplishment of two-electron
oxidations at a single cerium center brings a new facet to molecular
rare-earth metal chemistry
Increasing H‑Aggregates via Sequential Aggregation to Enhance the Hole Mobility of Printed Conjugated Polymer Films
Solid-state
microstructures of conjugated polymers are
essential
for charge transport in electronic devices. However, precisely modulating
aggregation pathways of conjugated polymers in a controlled fashion
is challenging. Herein, we report a sequential aggregation approach
via selectively modulating side chain aggregation in solution state
and backbone aggregation during film formation to increase H-aggregates
and consequently enhance hole mobility of printed diketopyrrolopyrrole-based
polymer (PDPP-TVT) film. The sequential aggregation is realized by
introducing 1-bromonaphthalene additive into chloroform solvent. The
structural evolution and assembly pathways of PDPP-TVT in initial
solution and during printing were revealed using small-angle neutron
scattering, cryogenic transmission electron microscopy, and time-resolved
optical diagnostics. The results show that the poor interactions between
PDPP-TVT side chains and BrN triggers side chain aggregation to form
large H-aggregate nuclei in initial solution. The additive further
selectively forces backbone aggregation on H-aggregate nuclei during
printing with dynamics increasing from ca. 3 to >1000 s. Such prolonged
growth window and selective growth of H-aggregates produce large fibers
in printed film and therefore 3-fold increase in hole mobility. This
work not only provides a promising route toward high-mobility printed
conjugated polymer films but also reveals the important relationship
between assembly pathways and film microstructure