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>_<b>4</b><b>Ph</b>_<b>4</b><b>-K</b>, [(NN^TBS)­Ln­(η²-C₄Ph₄)]­[K­(THF)_<i>x</i>] (Ln = Sc, Y, Lu), rare-earth metal complexes supported by a ferrocene diamide ligand, NN^TBS (NN^TBS = fc­(NSi^<i>t</i>BuMe₂)₂, fc = 1,1′-ferrocenediyl), were accomplished. The preparation of the half-sandwich compounds, <b>Ln-naph-K</b>, [(NN^TBS)­Ln­(μ-C₁₀H₈)]­[K­(THF)₂] (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>_<b>4</b><b>Ph</b>_<b>4</b><b>-K</b>, [(NN^TBS)­Ln­(η²-C₄Ph₄)]­[K­(THF)_<i>x</i>] (Ln = Sc, Y, Lu), rare-earth metal complexes supported by a ferrocene diamide ligand, NN^TBS (NN^TBS = fc­(NSi^<i>t</i>BuMe₂)₂, fc = 1,1′-ferrocenediyl), were accomplished. The preparation of the half-sandwich compounds, <b>Ln-naph-K</b>, [(NN^TBS)­Ln­(μ-C₁₀H₈)]­[K­(THF)₂] (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, ¹H 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^TBS)­Ln]₂(μ-biphenyl)­[K­(solvent)]₂ [NN^TBS = 1,1′-fc­(NSi^tBuMe₂)₂; Ln = Gd, Dy, Er; solvent = Et₂O, 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>_eff 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