A belt-shaped [8]­cycloparaphenylene (CPP) and an enantioenriched Möbius-shaped [10]­CPP have been synthesized by high-yielding rhodium-catalyzed intramolecular cyclotrimerizations of a cyclic dodecayne and a pentadecayne, respectively. This Möbius-shaped [10]­CPP possesses stable chirality and isolated with high enantiomeric purity. It is evident from the reaction Gibbs energy calculation that the above irreversible cyclotrimerizations are highly exothermic; therefore establishing that the intramolecular alkyne cyclotrimerization is a powerful route to strained cyclic molecular strips.

The mechanical motion of materials has been increasingly explored in terms of bending and expansion/contraction. However, the locomotion of materials has been limited. Here, we report walking and rolling locomotion of chiral azobenzene crystals, induced thermally by a reversible single-crystal-to-single-crystal phase transition. Long plate-like crystals with thickness gradient in the longitudinal direction walk slowly, like an inchworm, by repeated bending and straightening under heating and cooling cycles near the transition temperature. Furthermore, thinner, longer plate-like crystals with width gradient roll much faster by tilted bending and then flipping under only one process of heating or cooling. The length of the crystal is shortened above the transition temperature, which induces bending due to the temperature gradient to the thickness direction. The bending motion is necessarily converted to the walking and rolling locomotion due to the unsymmetrical shape of the crystal. This finding of the crystal locomotion can lead to a field of crystal robotics.

Planar chiral zigzag-type [8]- and [12]­cyclophenylene (CP) belts have been synthesized in good yields with high ee values of 98% and 83%, respectively, by the rhodium-catalyzed enantioselective intramolecular sequential cyclotrimerizations of the corresponding cyclic polyynes. The observed high enantioselectivity arises from the regioselective formation of a rhodacycle intermediate from an unsymmetric triyne unit. The X-ray crystal structural analysis of the racemic planar chiral zigzag-type [8]­CP belt revealed that the uneven molecules mesh with each other to form a one-dimensional columnar packing structure, in which one column contains single enantiomers, giving two types of chiral columns [(S)- and (R)-form columns] arranged alternately. The ring strain of the zigzag-type [8]­CP belt was smaller than that of the armchair-type [8]­CPP belt despite its smaller ring size, due to the presence of the strain-relieving m-terphenyl moieties. The effect of the number of the benzene rings of the zigzag-type CP belts on absorption and emission peaks was small due to interruption of π-conjugation at the m-phenylene moieties. However, the bending effect on the absolute fluorescence quantum yield as well as absorption and emission peaks was significant. Concerning chiroptical properties, the modest anisotropy dissymmetry factors of ECD and CPL were observed in the [8]­CP belt.

The visible-light responsive Cu(I)-complex photosensitizers were developed by introducing various aromatic substituents at the 4,7-positions of a 2,9-dimethyl-1,10-phenanthroline (dmp) ligand in a heteroleptic Cu I (dmp)(DPEphos) + -type complexes (DPEphos = [2-(diphenylphosphino)phenyl]ether) for photocatalytic CO 2 reduction. Introducing biphenyl groups (Bp-) on the dmp ligand enhanced the molar extinction coefficient (ε) of the metal-to-ligand charge transfer (MLCT) band in the visible region (ε = 7,500 M −1 cm −1 ) compared to that of the phenyl (Ph-)-containing analog (ε = 5,700 M −1 cm −1 at λ max = 388 nm). However, introducing 4-R-Ph- groups (R = the electron-withdrawing groups NC-, or NO 2 -) led to a red shift in the band to λ max = 390, 400, and 401 nm, respectively. Single-crystal X-ray analysis showed the Ph- groups were twisted because of the steric repulsion between the 2,6-protons of the Ph- groups and 5,6-protons of the dmp ligand. The result strongly indicated that the π-conjugation effect of the 4-R-Ph- groups is so weak that the lowering of the energy of the dmp π * orbitals is small. However, when 4-R-ph- was substituted by a 5-membered heterorings, there was a larger red shift, leading to an increase in the ε value of the MLCT absorption band. Thus, the substitution to 2-benzofuranyl- groups resulted in visible-light absorption up to 500 nm and a shoulder peak at around 420 nm (ε = 12,300 M −1 cm −1 ) due to the expansion of π-conjugation over the substituted dmp ligand. The photocatalytic reaction for CO 2 reduction was tested using the obtained Cu I complexes as photosensitizers in the presence of a Fe(dmp) 2 (NCS) 2 catalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1 H -benzo[d]imidazole as a sacrificial reductant, which showed improved CO generation.

The synthesis of C- and C-symmetrical [8]cycloparaphenylene (CPP)-octacarboxylates has been achieved via macrocyclization by the rhodium-catalyzed intermolecular stepwise cross-cyclotrimerization and subsequent reductive aromatization. The C-symmetrical octa-tert-butyl [8]CPP-octacarboxylate forms a dimer in which eight ester moieties face each other. The dimers are aligned so as to make a one-dimensional column with a channel structure inside. Both absorption and fluorescence maxima of [8]CPP-octacarboxylates in CHCl were significantly blue-shifted compared to those of [8]CPP due to the presence of eight electron-withdrawing ester moieties.

It has been established that a strongly electrophilic η 5 -cyclopentadienylrhodium complex, [Cp E RhCl 2 ] 2, is capable of reacting with aliphatic alkenes in the presence of a silver salt and cesium acetate at room temperature to give the corresponding π-allyl complexes in high yields. The use of an alkenyltosylamide as the alkene also afforded the corresponding π-allyl complex. Treatment of the thus obtained π-allyl complex with a silver(I) salt and copper(II) acetate afforded the allylic amination product, which proves the intermediacy of this π-allyl complex in the rhodium(III)-catalyzed intramolecular oxidative allylic amination. ■ INTRODUCTIONAllylic substitution through transition-metal π-allyl complexes as represented by the Tsuji−Trost reaction is an important bond-forming transformation in organic synthesis. 1 The π-allyl complexes are typically generated by the reactions of transitionmetal complexes with allylic compounds possessing heteroatom-containing leaving groups. 1 On the other hand, generation of the π-allyl complexes through deprotonation of aliphatic alkenes with the transition-metal complexes is a direct and atom-economical process and is involved in allylic sp 3 C−H functionalization as a key step. 2−7 Especially, allylic sp 3 C−H functionalization via (π-allyl)palladium(II) complexes has been extensively studied and the proposed (π-allyl)palladium-(II) intermediates have been isolated and well characterized. 2−4 Recently, (π-allyl)rhodium(III) complexes 8−12 have been proposed as key intermediates in rhodium(III)-catalyzed allylic sp 3 C−H functionalization. 13−16 For example, Cossy and co-workers reported the cationic Cp*Rh III -catalyzed intramolecular oxidative allylic amination of alkenyltosylamides leading to cyclic amines at elevated temperature (83°C), while the corresponding (π-allyl)rhodium(III) intermediates have not been isolated and characterized (Scheme 1). 14 In 2012, we developed the method for the synthesis of the electron-deficient cyclopentadienyl rhodium(III) complex [Cp E RhCl 2 ] 2 (1), bearing two ethoxycarbonyl groups on the cyclopentadienyl moiety, and have disclosed its high catalytic activity toward the oxidative sp 2 C−H functionalization reactions of electron-rich arenes. 17 In these reactions, sp 2 C−H bond cleavage through concerted metalation−deprotonation might be accelerated as a result of a strong interaction between the aromatic π bond and the highly electrophilic rhodium(III) center. Similarly, the deprotonation of the allylic sp 3 C−H bond would be accelerated by strong interaction of an electron-rich alkene with the electrophilic rhodium(III) center. In this paper, we disclose the generation and isolation of π-allyl complexes from aliphatic alkenes and [Cp E RhCl 2 ] 2 (1) in the presence of a silver salt and cesium acetate at room temperature. An alkenyltosylamide-derived (π-allyl)rhodium(III) complex (R = (CH 2 ) 4 NHTs, Scheme 2) was also prepared, and its intermediacy in the rhodium(III)-catalyzed intramolecular

The synthesis of alternating donor-acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. These alternating donor-acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO-LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.

The control of two-dimensional layered crystalline and/or liquid crystalline phases for π-extended organic molecules is crucial for expanding the potential of organic electronic materials and devices. In this work, we develop unique solution-processable organic semiconductors based on the unsymmetric substitution of [1]­benzothieno­[3,2-b]­[1]­benzothiophene (BTBT) with two different substituents, namely, phenylethynyl (PE) and normal alkyl with different chain lengths n (−C n H2n+1), both of which exhibit structural flexibility while maintaining the rod-like nature over the entire molecule. A distinctive layered solid crystalline phase, analogous to the smectic liquid crystalline phase, is obtainable in PE-BTBT-C n at n = 6, where the substituent lengths are almost the same. The BTBT moiety maintains a rigid layered-herringbone (LHB) packing, whereas the molecular long axis exhibits a complete orientational disorder. We refer to this packing as disordered LHB (d-LHB), the unique geometry of which can be analyzed by the emerging technique of microcrystal electron diffraction crystallography. The intermolecular core–core interactions stabilize the d-LHB packing, enabling a relatively high field-effect mobility of approximately 3 cm2 V–1 s–1. In contrast, PE-BTBT-C n with longer alkyl chains (n = 8, 10, 12) exhibits higher mobility of approximately 7 cm2 V–1 s–1 by constituting bilayer-type LHB (b-LHB), which is associated with the unsymmetrical length of the substituents. We discuss the correlation and competition among the d-LHB, b-LHB, and smectic liquid crystalline phases based on the structural, thermal, and transistor characteristics. These findings demonstrate the controllability of various phases in layered organic semiconductors.