Synthesis, Structures, and Properties of π‑Extended Double Helicene: A Combination of Planar and Nonplanar π‑Systems

The synthesis, structures, and properties of a π-extended double helicene <b>1</b> are described. This double helicene <b>1</b> was synthesized by a four-fold oxidative C–H biphenylation of naphthalene followed by the Scholl reaction or via five steps including the Suzuki–Miyaura cross-coupling reaction and the Scholl reaction. Due to the two helical substructures, <b>1</b> has three isomers, i.e., two enantiomers in a twisted form [(<i>P</i>,<i>P</i>) and (<i>M</i>,<i>M</i>)] and one diastereoisomer in a meso form. X-ray crystallographic analysis of the twisted isomers (<i>twisted</i>-<b>1</b>) revealed a tightly offset packing pattern of (<i>P</i>,<i>P</i>)- and (<i>M</i>,<i>M</i>)-twisted isomers, affording a three-dimensional lamellar stacking structure. A high isomerization barrier (43.5 kcal mol^–1) and the relative thermal stability of <i>twisted</i>-<b>1</b> isomer over <i>meso</i>-<b>1</b> by 0.9 kcal mol^–1 were estimated by DFT calculations. The three isomers were successfully separated by chiral HPLC and characterized by circular dichroism spectroscopy as well as by TD-DFT studies. Electronic state variation resulting from the molecular geometry difference between the two diastereoisomers (<i>twisted</i>-<b>1</b> and <i>meso</i>-<b>1</b>) was observed by UV–vis absorption and fluorescence spectra

Synthesis and Properties of [9]Cyclo-1,4-naphthylene: A π-Extended Carbon Nanoring

The first synthesis of a π-extended carbon nanoring, [9]­cyclo-1,4-naphthylene ([9]­CN), has been achieved. Careful structure–property analyses uncovered a number of unique features of [9]­CN that are quite different from those of [9]­CPP, a simple carbon nanoring

Theoretical Studies on the Structures and Strain Energies of Cycloparaphenylenes

The structures and strain energies of cycloparaphenylenes (CPPs) have been determined by DFT calculation at the B3LYP/6-31G(d) level of theory. Fifteen stable conformations of [12]CPP were found as local minimum structures. It was also found that benzene rings of [12]CPP can rotate rather freely at room temperature. The strain energies of [n]CPP (n = 6−20) were estimated on the basis of the homodesmotic reaction using CPP, biphenyl, and p-terphenyl. It was also found that CPPs have higher strain energy in comparison to cycloparaphenyleneacetylenes (CPPAs)

Syntheses of PBP Pincer Iridium Complexes: A Supporting Boryl Ligand

Syntheses of PBP Pincer Iridium Complexes: A Supporting Boryl Ligan

Aziridinofullerene: A Versatile Platform for Functionalized Fullerenes

An aziridine moiety on the fullerene core can serve as an acid-triggered reacting template for the controlled synthesis of a range of functionalized fullerenes that are otherwise difficult to synthesize in an efficient and selective manner. A copper-catalyzed aziridination of C60 for the practical synthesis of aziridinofullerene 1 and acid-catalyzed reactions of 1 with mono- and bifunctional nucleophiles as well as alkynes are described. The rapid generation of structural diversity in a single chemical operation using the common platform 1 is notable

Synthesis and Structure of [9]Cycloparaphenylene Catenane: An All-Benzene Catenane Consisting of Small Rings

A catenane consisting of two [9]­cyclo­para­phenyl­enes ([9]­CPPs) has been synthesized. Density functional theory calculations suggested that [n]­CPPs (n = 5, 6) are highly strained upon the formation of catenanes compared with the corresponding uncatenated CPPs, whereas [n]­CPP catenanes (n ≥ 7) are not strained. The synthesis of ([9]­CPP)([9]­CPP)­catenane was accomplished via the following route: (i) a spirosilylation, (ii) a nickel(0)-mediated macrocyclization, (iii) a desilylation, and (iv) reductive aromatization reactions. An X-ray diffraction analysis revealed a catenated structure of ([9]­CPP)([9]­CPP)­catenane

<i>para</i>-C–H Borylation of Benzene Derivatives by a Bulky Iridium Catalyst

A highly <i>para</i>-selective aromatic C–H borylation has been accomplished. By a new iridium catalyst bearing a bulky diphosphine ligand, Xyl-MeO-BIPHEP, the C–H borylation of monosubstituted benzenes can be affected with <i>para</i>-selectivity up to 91%. This catalytic system is quite different from the usual iridium catalysts that cannot distinguish <i>meta</i>- and <i>para</i>-C–H bonds of monosubstituted benzene derivatives, resulting in the preferred formation of <i>meta</i>-products. The <i>para</i>-selectivity increases with increasing bulkiness of the substituent on the arene, indicating that the regioselectivity of the present reaction is primarily controlled by steric repulsion between substrate and catalyst. Caramiphen, an anticholinergic drug used in the treatment of Parkinson’s disease, was converted into five derivatives via our <i>para</i>-selective borylation. The present [Ir­(cod)­OH]₂/Xyl-MeO-BIPHEP catalyst represents a unique, sterically controlled, <i>para</i>-selective, aromatic C–H borylation system that should find use in streamlined, predictable chemical synthesis and in the rapid discovery and optimization of pharmaceuticals and materials

Diphenylphosphino- or Dicyclohexylphosphino-Tethered Boryl Pincer Ligands: Syntheses of PBP Iridium(III) Complexes and Their Conversion to Iridium−Ethylene Complexes

Two hydroborane precursors (1b,c) for PBP pincer ligands bearing phenyl or cyclohexyl groups on phosphorus atoms were synthesized, and their complexation reactions with iridium were investigated. Reaction of hydroborane 1b, bearing phenyl groups, with Ir[P(p-tol)3]2(CO)Cl afforded an 18-electron complex, [PhPBP]Ir(H)(CO)Cl (3b), but reactions with other iridium(I) sources gave complicated mixtures. The characteristic IR peaks in 3b compared with the previously reported tBu-PBP derivative 3a were discussed on the basis of theoretical calculations. Complexation of cyclohexyl-substituted hydroborane 1c with [Ir(C2H4)2Cl]2 afforded a 16-electron complex, [CyPBP]Ir(H)Cl (2c). X-ray structure and computational studies on 2c revealed that the hydride ligand is close [B−H = 1.90(5) Å] to the boron atom. Reaction of 2c with LiTMP (TMP = 2,2,6,6-tetramethylpipyridide) under ethylene atmosphere gave monovalent iridium complex [CyPBP]Ir(C2H4) (4c) by a similar procedure to the previously reported [tBuPBP] system. Exposure of a CD2Cl2 solution of 2c to ethylene without additional base resulted in a quantitative formation of the intermediate [CyPBP]Ir(H)(C2H4)Cl (8c), as was characterized by NMR spectroscopy. In contrast, no spectral change was observed in the same procedure using [tBuPBP]Ir(H)Cl (2a) probably due to a difference in steric bulk. The observation of 8c is a rare example of a spectroscopically identified boryl(hydrido)olefin metal complex

All-Benzene Carbon Nanocages: Size-Selective Synthesis, Photophysical Properties, and Crystal Structure

The design and synthesis of a series of carbon nanocages consisting solely of benzene rings are described. Carbon nanocages are appealing molecules not only because they represent junction unit structures of branched carbon nanotubes, but also because of their potential utilities as unique optoelectronic π-conjugated materials and guest-encapsulating hosts. Three sizes of strained, conjugated [<i>n</i>.<i>n</i>.<i>n</i>]carbon nanocages (<b>1</b>, <i>n</i> = 4; <b>2</b>, <i>n</i> = 5; <b>3</b>, <i>n</i> = 6) were synthesized with perfect size-selectivity. Cyclohexane-containing units and 1,3,5-trisubstituted benzene-containing units were assembled to yield the minimally strained bicyclic precursors, which were successfully converted into the corresponding carbon nanocages via acid-mediated aromatization. X-ray crystallography of <b>1</b> confirmed the cage-shaped structure with an approximately spherical void inside the cage molecule. The present studies revealed the unique properties of carbon nanocages, including strain energies, size-dependent absorption and fluorescence, as well as unique size-dependency for the electronic features of <b>1</b>–<b>3</b>

η⁶‑Cycloparaphenylene Transition Metal Complexes: Synthesis, Structure, Photophysical Properties, and Application to the Selective Monofunctionalization of Cycloparaphenylenes

The synthesis, structure, photophysical properties, and reactivity of cycloparaphenylenes (CPPs) coordinated to group 6 transition metal fragments are described. The η⁶-coordination of [9]­CPP or [12]­CPP with M­(CO)₆ (M = Cr, Mo, W) afforded the corresponding [<i>n</i>]­CPP-M­(CO)₃ complexes (<i>n</i> = 9, 12; M = Cr, Mo, W). In the ¹H NMR spectra of these complexes, characteristic upfield-shifted singlet signals corresponding to the four hydrogen atoms attached to the coordinated C₆H₄ ring of the CPPs were observed at 5.4–5.9 ppm. The complex [9]­CPP-Cr­(CO)₃ could be successfully isolated in spite of its instability. X-ray crystallographic analysis and computational studies of [9]­CPP-Cr­(CO)₃ revealed that chromium-CPP coordination occurs at the convex surface of [9]­CPP both in the solid state and in solution. TD-DFT calculations suggested that the emerging high-wavenumber absorption peak upon coordination of [9]­CPP to Cr­(CO)₃ should be assigned to a weak HOMO–LUMO transition. Moreover, by using the complex [9]­CPP-Cr­(CO)₃, a rapid and highly monoselective CPP functionalization has been achieved. The established one-pot method, consisting of complexation, deprotonation, nucleophilic substitution, and decomplexation steps, yielded silyl-, boryl-, and methoxycarbonyl-substituted CPPs in up to 93% yield relative to reacted starting material