Ferrocene-bis(phosphinimine) Nickel(II) and Palladium(II) Alkyl Complexes: Influence of the Fe–M (M = Ni and Pd) Interaction on Redox Activity and Olefin Coordination

The synthesis of several novel nickel­(II) and palladium­(II) ferrocene-bis­(phosphinimine) alkyl complexes containing iron–nickel and iron–palladium interactions is reported. The redox behavior of all complexes was evaluated electrochemically and chemically; in addition, reactions with weak nucleophiles, such as acetonitrile and olefins, were also investigated. DFT calculations were performed to understand the electronic structure of the alkyl metal complexes

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

Engineered Photochromism in Crystalline Salicylidene Anilines by Facilitating Rotation to Reach the Colored <i>trans</i>-Keto Form

The photochromism of crystalline salicylidene anilines regularly occurs by a volume-conserving bicycle pedal motion that transposes the relative position of the two atoms of the central imine bond while leaving the original salicyladehyde and aniline rings unchanged. Considering the challenges involved in the preparation of packing structures that are conducive to the bicycle pedal process, we tested a design based on a structural strategy that is known to facilitate the rotation of phenyl rings in the solid state, allowing the molecules to be photoreactive. Three salicylidene aniline molecular rotors linked to bulky trityl, tetraphenylmethyl, or pentiptycene stators were prepared and crystallized, and their solid state photochromism was confirmed. In one case, isomorphous crystals of a deuterium labeled deoxo-salicylidene aniline model system were analyzed by solid state ²H NMR to confirm that the corresponding packing structure is conducive to fast rotation in the solid state

Structure–Kinetics Correlations in Isostructural Crystals of α‑(<i>ortho</i>-Tolyl)-acetophenones: Pinning Down Electronic Effects Using Laser-Flash Photolysis in the Solid State

Aqueous suspensions of nanocrystals in the 200–500 nm size range of isostructural α-(<i>ortho</i>-tolyl)-acetophenone (<b>1a</b>) and α-(<i>ortho</i>-tolyl)-<i>para</i>-methylacetophenone (<b>1b</b>) displayed good absorption characteristics for flash photolysis experiments in a flow system, with transient spectra and decay kinetics with a quality that is similar to that recorded in solution. In contrast to solution measurements, reactions in the solid state were characterized by a rate limiting hydrogen transfer reaction from the triplet excited state and a very short-lived biradical intermediate, which does not accumulate. Notably, the rate for δ-hydrogen atom transfer of <b>1a</b> (2.7 × 10⁷ s^–1) in the crystalline phase is 18-fold larger than that of <b>1b</b> (1.5 × 10⁶ s^–1). With nearly identical molecular and crystal structures, this decrease in the rate of δ-hydrogen abstraction can be assigned unambiguously to an electronic effect by the <i>para-</i>methyl group in <b>1b</b>, which increases the contribution of the ³π,π* configuration relative to the reactive ³n,π* configuration in the lowest triplet excited state. These results highlight the potential of relating single crystal X-ray structural data with absolute kinetics from laser flash photolysis

Redox Control of Group 4 Metal Ring-Opening Polymerization Activity toward l‑Lactide and ε‑Caprolactone

The activity of several group 4 metal alkoxide complexes supported by ferrocene-based ligands was controlled using redox reagents during the ring-opening polymerization of l-lactide and ε-caprolactone. Switching in situ between the oxidized and reduced forms of a metal complex resulted in a change in the corresponding rate of polymerization. Opposite behavior was observed for each monomer used. One-pot copolymerization of the two monomers to give block copolymers was also achieved

Structure–Reactivity Correlations and Mechanistic Understanding of the Photorearrangement and Photosalient Effect of α‑Santonin and Its Derivatives in Solutions, Crystals, and Nanocrystalline Suspensions

The synthesis, crystal packing and photochemical reactions of α-santonin (<b>1a</b>) and its methyl, ethyl, <i>n</i>-propyl, and <i>n</i>-butyl derivatives (<b>1b</b>–<b>e</b>) are described to explore the effect that a photochemically benign yet structurally significant synthetic modification can have on the solid-state photochemical reactivity. The structures of the derivatives were determined using single crystal X-ray diffraction and compared against the packing of α-santonin. A cage dimer (<b>12a</b>) found exclusively upon irradiation of <b>1a</b> in the solid state was not found when the other derivatives were exposed to light, because the alkylation proved to perturb the crystal packing away from an optimal dimerization alignment. Using a high-speed camera, we monitored the photosalient effect of α-santonin and found it to occur at an angle orthogonal to the <i>b</i>-axis of the unit cell, which we suspect is caused by the formation of the cage dimer <b>12</b>. The photochemistry of <b>1a</b>–<b>e</b> in solution and crystalline suspensions was also analyzed. The solution photochemistry was in accord with literature precedence, and the crystalline suspensions yielded a variety of photoproducts including a tertiary alcohol (<b>7b</b>–<b>e</b>), which is not commonly observed in neutral water. An exocyclic alkene photoproduct (<b>8b</b>) was also discovered, and its presence is hypothesized to be caused by an intermolecular deprotonation caused by a water molecule present in the crystal

Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms

Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms

Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms

Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

We report the synthesis and characterization of four molecular rotors <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted 1,4-phenylene rotators, respectively, that are axially linked through the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol) stators. Crystallization experiments using solvent mixtures of hexanes–ethyl acetate and acetonitrile–dichloromethane gave rise to polymorphic, pseudopolymorphic, and isomorphic crystals. Whereas two solids were obtained for compound <b>2</b>, four were indentified in the cases of compounds <b>3</b> and <b>4</b>, and three for compound <b>5</b>. The 13 solid forms were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Two sets of isomorphous structures were obtained for solvated and solvent-free structures of compounds <b>3</b>–<b>5</b>. While polymorphic behavior of these compounds arises from their conformational freedom in solution, their isomorphism arises from the closely isosteric relation that exists between hydrogen and fluorine atoms