Copper(I)-Catalyzed Boryl Substitution of Unactivated Alkyl Halides

Borylation of alkyl halides with diboron proceeded in the presence of a copper(I)/Xantphos catalyst and a stoichiometric amount of K(O-<i>t</i>-Bu) base. The boryl substitution proceeded with normal and secondary alkyl chlorides, bromides, and iodides, but alkyl sulfonates did not react. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (<i>R</i>)-2-bromo-5-phenylpentane gave a racemic product. Reaction with cyclopropylmethyl bromide resulted in ring-opening products, suggesting the reaction involves a radical pathway

A Screening Approach for the Discovery of Mechanochromic Gold(I) Isocyanide Complexes with Crystal-to-Crystal Phase Transitions

Mechanoinduced phase transitions of emissive organic crystalline materials have received much attention. Although a variety of such luminescent mechanochromic compounds have been reported, it is challenging to develop mechanochromic compounds with crystal-to-crystal phase transitions in which precise structural information about molecular arrangements can be obtained. Here, we report a screening approach to explore mechanochromic compounds exhibiting a crystal-to-crystal phase transition. We prepared 48 para-substituted (R¹) phenyl­[para-substituted (R²) phenyl isocyanide]­gold­(I) complexes designated <b>R</b>^<b>1</b><b>–R</b>^<b>2</b> (six R¹ and eight R² substituents) and then performed three-step screening experiments. The first screening step was selection of emissive complexes under UV light, which gave 37 emissive <b>R</b>^<b>1</b><b>–R</b>^<b>2</b> complexes. The second screening step involved evaluation of the mechanochromic properties by emission spectroscopy. Twenty-eight complexes were found to be mechanochromic. The third screening step involved preparation of single crystals, reprecipitated powders, and ground powders of the 28 mechanochromic <b>R</b>^<b>1</b><b>–R</b>^<b>2</b> complexes. The changes in the powder diffraction patterns of these complexes induced by mechanical stimulation were investigated. Two compounds exhibited a crystal-to-crystal phase transition upon mechanical stimulation, including the previously reported <b>H–H</b> complex. Single crystals of the as-prepared and ground forms of the newly discovered <b>CF</b>_<b>3</b><b>–CN</b> complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of <b>CF</b>_<b>3</b><b>–CN</b> is caused by formation of aurophilic interactions. Comparison of the crystal structures of <b>CF</b>_<b>3</b><b>–CN</b> with those of the other complexes suggests that the weaker intermolecular interactions in the as-prepared form are an important structural factor for the observed mechanoinduced crystal-to-crystal phase transition

Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aldehydes: An Efficient Route to Enantiomerically Enriched α‑Alkoxyorganoboronate Esters

The first catalytic enantioselective nucleophilic borylation of a CO double bond has been achieved. A series of aldehydes reacted with a diboron reagent in the presence of a copper­(I)/DTBM-SEGPHOS complex catalyst using MeOH as a proton source to give the corresponding optically active α-alkoxyorganoboronate esters with excellent enantioselectivities. Furthermore, the products could be readily converted to the corresponding functionalized chiral alcohol derivatives through stereospecific C–C bond forming reactions involving the stereogenic C–B bond

Mechano-Responsive Luminescence via Crystal-to-Crystal Phase Transitions between Chiral and Non-Chiral Space Groups

Herein, a novel mechano-responsive luminescent (MRL) material based on crystal-to-crystal phase transitions between crystals of a chiral and those of a centrosymmetric space group, accompanied by a change of emission properties, is described. Initially, a gold complex containing a biphenyl moiety, which exhibits an achiral structure in solution, afforded an orange-emitting amorphous phase together with a viscous isotropic oil after evaporation of the solvent. Upon pricking, the orange-emitting oil spontaneously crystallized either in a centrosymmetric or in a chiral space group while simultaneously changing the emission properties. Remarkably, grinding the chiral crystals induced a solid-state phase transition to the achiral crystals under concomitant changes of the emission properties

A Screening Approach for the Discovery of Mechanochromic Gold(I) Isocyanide Complexes with Crystal-to-Crystal Phase Transitions

Mechanoinduced phase transitions of emissive organic crystalline materials have received much attention. Although a variety of such luminescent mechanochromic compounds have been reported, it is challenging to develop mechanochromic compounds with crystal-to-crystal phase transitions in which precise structural information about molecular arrangements can be obtained. Here, we report a screening approach to explore mechanochromic compounds exhibiting a crystal-to-crystal phase transition. We prepared 48 para-substituted (R¹) phenyl­[para-substituted (R²) phenyl isocyanide]­gold­(I) complexes designated <b>R</b>^<b>1</b><b>–R</b>^<b>2</b> (six R¹ and eight R² substituents) and then performed three-step screening experiments. The first screening step was selection of emissive complexes under UV light, which gave 37 emissive <b>R</b>^<b>1</b><b>–R</b>^<b>2</b> complexes. The second screening step involved evaluation of the mechanochromic properties by emission spectroscopy. Twenty-eight complexes were found to be mechanochromic. The third screening step involved preparation of single crystals, reprecipitated powders, and ground powders of the 28 mechanochromic <b>R</b>^<b>1</b><b>–R</b>^<b>2</b> complexes. The changes in the powder diffraction patterns of these complexes induced by mechanical stimulation were investigated. Two compounds exhibited a crystal-to-crystal phase transition upon mechanical stimulation, including the previously reported <b>H–H</b> complex. Single crystals of the as-prepared and ground forms of the newly discovered <b>CF</b>_<b>3</b><b>–CN</b> complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of <b>CF</b>_<b>3</b><b>–CN</b> is caused by formation of aurophilic interactions. Comparison of the crystal structures of <b>CF</b>_<b>3</b><b>–CN</b> with those of the other complexes suggests that the weaker intermolecular interactions in the as-prepared form are an important structural factor for the observed mechanoinduced crystal-to-crystal phase transition

Introduction of a Biphenyl Moiety for a Solvent-Responsive Aryl Gold(I) Isocyanide Complex with Mechanical Reactivation

Luminescent compounds that are sensitive to volatile organic solvents are useful for detection of harmful gases. Although such compounds have been reported, discrimination of various types of volatile organic compounds using one compound remains challenging. We reported a series of gold isocyanide complexes that form various crystalline structures with distinct emission properties, which can be interconverted by mechanical stimulation and solvent addition. Here, we report that introduction of a biphenyl unit into a gold isocyanide scaffold (denoted complex <b>3</b>) enables discrimination of various volatile organic compounds by forming 11 solvent-containing crystal structures <b>3</b>/solvent [solvent can be CHCl₃, pyridine (Py), CH₂Cl₂, CH₂Br₂, dimethylacetamide (DMA), acetaldehyde (AcH), CH₃CN, DMF, (<i>S</i>)-propylene oxide (SPO), <i>rac</i>-propylene oxide (racPO), or acetone] with different emission properties (emission maxima of 490–580 nm). Mechanical stimulation of <b>3</b>/solvent affords amorphous <b>3</b>_{<b>ground</b>} without solvent inclusion. The resulting <b>3</b>_{<b>ground</b>} can again detect volatile compounds by forming <b>3</b>/solvent with concomitant emission color changes. We also afforded a dozen single crystals of <b>3</b>, which include 11 solvated <b>3</b>/solvent and one solvent-free <b>3</b>/none. The molecular arrangements of <b>3</b> in <b>3</b>/solvent and <b>3</b>/none are all different. Comparison of various crystallographic parameters of <b>3</b>/solvent and <b>3</b>/none with their corresponding optical properties indicates that a combination of various structural properties of <b>3</b> affects the optical properties of <b>3</b>. This study reveals that the introduction of a biphenyl moiety could be a useful design to develop versatile indicators for solvents through the formation of multiple luminescent crystal structure

Copper(I)-Catalyzed Borylative <i>exo</i>-Cyclization of Alkenyl Halides Containing Unactivated Double Bond

A borylative <i>exo</i>-cyclization of alkenyl halides has been reported. The reaction includes the regioselective addition of a borylcopper­(I) intermediate to unactivated terminal alkenes, followed by the intramolecular substitution of the resulting alkylcopper­(I) moiety for the halide leaving groups. Experimental and theoretical investigations of the reaction mechanism have also been described. This reaction provides a new method for the synthesis of alkylboronates containing strained cycloalkyl structures from simple starting materials

Computational Insight into the Enantioselective Nucleophilic Borylation of a Polarized CO Double Bond Catalyzed by Diphosphine/Borylcopper(I) Complexes

Density functional theory calculations were performed to validate the proposed reaction mechanism for the enantioselective nucleophilic borylation of a polarized CO double bond in the presence of diphosphine/borylcopper­(I) complexes. Consequently, we successfully elucidated the origin for the regioselectivity and the mechanism for the enantioselectivity of the reaction. We also obtained theoretical explanations for the fact that the presence of a proton source gave a higher reactivity and a better enantioselectivity in the borylation reaction of aldehydes with a copper­(I)/(<i>R</i>)-DTBM-SEGPHOS complex catalyst. This study is particularly valuable toward the development and design of novel enantioselective borylation reactions with polarized carbon–heteroatom double bonds

Computational Insight into the Enantioselective Nucleophilic Borylation of a Polarized CO Double Bond Catalyzed by Diphosphine/Borylcopper(I) Complexes

Density functional theory calculations were performed to validate the proposed reaction mechanism for the enantioselective nucleophilic borylation of a polarized CO double bond in the presence of diphosphine/borylcopper­(I) complexes. Consequently, we successfully elucidated the origin for the regioselectivity and the mechanism for the enantioselectivity of the reaction. We also obtained theoretical explanations for the fact that the presence of a proton source gave a higher reactivity and a better enantioselectivity in the borylation reaction of aldehydes with a copper­(I)/(<i>R</i>)-DTBM-SEGPHOS complex catalyst. This study is particularly valuable toward the development and design of novel enantioselective borylation reactions with polarized carbon–heteroatom double bonds

Anomalous Reactivity of Silylborane: Transition-Metal-Free Boryl Substitution of Aryl, Alkenyl, and Alkyl Halides with Silylborane/Alkoxy Base Systems

An unexpected borylation of organic halides with a silyborane in the presence of an alkoxy base has been observed. This formal nucleophilic boryl substitution can be applied to a broad range of substrates with high functional group compatibility. Even sterically hindered aryl bromides afforded the corresponding boryl compounds in high yields. Preliminary mechanistic studies indicated that this boryl substitution is promoted by neither transition-metal contamination nor a radical-mediated process