Propeller, Linear, Cruciform and Stellate Spiro-bicarbazolium Salts.

A general synthetic approach to halogenated tetraaryl-ammonium salts has been developed and illustrated crystallographically. Bromide ammonium salts used as common synthetic intermediates together with Suzuki coupling of these bromides to a family of boronic acids provided a simplified strategy for arylation. Resolution of the C2 subset of spiro-bicarbazolium derivatives led to the first examples of enantiopure spiro-bicarbazoliums and the assignment of their absolute configuration by comparison of computational and experimental electronic circular dichroism (ECD) spectra. An ECD comparison with Prelog's spirobifluorenes is provided. The absolute configuration of the meta-bromide spiro-bicarbazolium salt was confirmed by anomalous scattering. Cruciform and stellate tetra-substituted salts provide a test of the limits of the methodology, and their structures suggest them to be candidates for MOF building blocks.

Room-Temperature Multiple Phosphorescence from Functionalized Corannulenes: Temperature Sensing and Afterglow Organic Light-Emitting Diode.

Corannulene-derived materials have been extensively explored in energy storage and solar cells, however, are rarely documented as emitters in light-emitting sensors and organic light-emitting diodes (OLEDs), due to low exciton utilization. Here, we report a family of multi-donor and acceptor (multi-D-A) motifs, TCzPhCor, TDMACPhCor, and TPXZPhCor, using corannulene as the acceptor and carbazole (Cz), 9,10-dihydro-9,10-dimethylacridine (DMAC), and phenoxazine (PXZ) as the donor, respectively. By decorating corannulene with different donors, multiple phosphorescence is realized. Theoretical and photophysical investigations reveal that TCzPhCor shows room-temperature phosphorescence (RTP) from the lowest-lying T1 ; however, for TDMACPhCor, dual RTP originating from a higher-lying T1 (T1 H ) and a lower-lying T1 (T1 L ) can be observed, while for TPXZPhCor, T1 H -dominated RTP occurs resulting from a stabilized high-energy T1 geometry. Benefiting from the high-temperature sensitivity of TPXZPhCor, high color-resolution temperature sensing is achieved. Besides, due to degenerate S1 and T1 H states of TPXZPhCor, the first corannulene-based solution-processed afterglow OLEDs is investigated. The afterglow OLED with TPXZPhCor shows a maximum external quantum efficiency (EQEmax ) and a luminance (Lmax ) of 3.3 % and 5167 cd m-2 , respectively, which is one of the most efficient afterglow RTP OLEDs reported to date.

Cooperative Weak Dispersive Interactions Actuate Catalysis in a Shape-Selective Abiological Racemase.

A simple abiological host-guest system demonstrates racemase activity with catalytic rate enhancements of 104 without employing traditional functional groups. Cooperative weak interactions enhanced through shape-complementarity between the catalyst active site and the reaction transition state drive this activity, as proposed by Pauling for enzymes. In analogy to the Jencks' concept of catalytic antibodies, it is shown that a hapten resembling the planar transition state of the bowl inversion acts as a potent inhibitor of this catalytic process. In contrast, no substrate/product inhibition is detected, and a relatively weak binding of the substrate is observed (Ka ≈ 102 M-1 at 293 K). This simple box-and-bowl system demonstrates that shape selectivity arising from cooperative dispersive forces suffices for the emergence of a catalytic system with an enzyme-like thermodynamic profile.

An S10-Symmetric 5-Fold Interlocked [2]Catenane.

The reaction of sym-pentakis(4-aminothiophenyl)corannulene with 2-formyl-6-methylpyridine and CuI or 2-formyl-1,10-phenanthroline and MII (M = Co, Zn) yields an S10-symmetric 5-fold interlocked [2]catenane of two interpenetrating [CuI5L2]5+ cages or D5-symmetric [MII5L2]10+ cages, respectively. The new structures were characterized by X-ray crystallography, NMR spectroscopy, and mass spectrometry. Density functional theory computations point to dispersive energies on par with traditional covalent bond energies. Subcomponent exchange reactions favored formation of the [CoII5L2]10+ cage over the [CuI10L4]10+ catenane. The single cage and catenane each cocrystallized with a corannulene guest to form a bowl-in-bowl substructure.

X-ray Crystallography and Unexpected Chiroptical Properties Reassign the Configuration of Haliclonadiamine.

Haliclonadiamine and papuamine are bis-indane marine natural products isolated from the marine sponge Haliclona sp. Their relative structures were previously reported to differ by inversion at only one of their eight shared stereocenters. Here X-ray crystallography shows the opposite to be true: papuamine has a 1R,3S,8R,9S,14S,15R,20S,22R configuration, while haliclonadiamine has a 1S,3R,8S,9R,14R,15S,20R,22R configuration. Paradoxically the ECD of each structure displays a negative Cotton effect. X-ray crystallography reveals the two structures adopt similar conformations of their 13-membered macrocyclic core that comprises a configurationally relevant diene. B97x-D/Def2-TZVPP-(MeOH)-calculated ECD supports the diene configuration with the macrocycle dominating the ECD Cotton effect for haliclonadiamine and papuamine. Additional crystallographic and chiroptical analyses of three sponge samples from geographically distant locations indicate this pair of natural products always exists as a configurationally related couple. The co-discovery of a biosynthetic precursor, halichondriamine C, present in these same Haliclona samples must be considered when discussing any biosynthetic pathway. Taken together, this work justifies a reassignment of haliclonadiamine's structure and opens the question of how this complex stereochemical relationship between haliclonadiamine and palauamine arises biosynthetically.

Fluorous Corannulenes: Ab initio Predictions and the Synthesis of sym-Pentafluorocorannulene.

Ten sym-penta and deca-X substituted corannulenes (1-10; X=H, F, CH3 , or CF3 ) define a library of fluorous compounds comprising high symmetry non-planar aromatic compunds. They provide a group of structurally similar, yet physically distinct structures manifesting special chemical behavior related to their degree of fluorination. Owing to their bowl forms, corannulene derivatives are distinct from planar polynuclear aromatic compounds; they have relatively high dipole moments, accept 1-4 electrons, and display room temperature fluorescence as well as low temp phosphorescence. Electronic structure theory predicts the bowl inversion barrier and physical properties. The syntheses of sym-pentafluorocorannulene by an efficient late stage fluorination affords a key derivative to calibrate predictions.

One-Pot Domino Carbonylation Protocol for Aromatic Diimides toward n-Type Organic Semiconductors.

Aromatic diimides are one of the most important chromophores in the construction of n-type organic semiconductors, which lag far behind their p-type counterpart but are necessary for ambipolar transistors, p-n junctions and organic complementary circuits. Herein, we establish a facile one-pot domino synthetic protocol for aromatic diimides via palladium-catalyzed carbonylation of tetrabromo aromatic precursors. Taking tetrabromocorannulene (TBrCor) and tetrabromo-2,7-di-tert-butylpyrene (TBrPy) as the typical examples, we obtained diimide derivatives in yields of about 50 %, one order of magnitude higher than that of the traditional multi-step diimidization. As demonstrated in the case of corannulene diimide, the efficient diimidization not only allows the LUMO levels to be lowered significantly but also provides an ordered and closer packing structures, opening up possibilities to the development of n-type semiconducting materials based on a variety of aromatic systems.

Synthesis of Modified Nucleoside Oligophosphates Simplified: Fast, Pure, and Protecting Group Free.

Phosphoramidite analogues of modified cyclotriphosphates provide a general and step-economical synthesis of nucleoside triphosphates and analogues on scale without the need for protecting groups. These reagents enable rapid access to pure nucleoside oligophosphates and a range of other analogues that were previously difficult to obtain (e.g., NH, CH2, CCl2, and CF2 replacements for O, phosphono- and phosphoimidazolides, -morpholidates, -azidates, and -fluoridates). DFT calculations demonstrate that the selectivity of the cyclotriphosphate opening reactions proceeds via an in-line substitution mechanism that displaces the least charged leaving group.

Corannurylene Pentapetalae.

Despite the great advances in the synthesis of diverse nonplanar graphenoids, investigations into the relationship between structural features and intermolecular interactions still present significant challenges. Herein, the novel nonplanar graphenoid structure, corannurylene pentapetalae (CRP), obtained via bottom-up syntheses of hybridization between perylene diimide (PDI) planar fragments and a corannulene curved core, is presented. Single crystal studies reveal a D5-symmetric as well as a C2-symmetric graphenoid corannurylene pentapetalae. The D5-symmetric structure has a unique honeycomb lattice with two chiral honeycomb layers alternately stacked, whereas the C2-symmetric CRP forms dimer units via π-π stacking. Transistor devices demonstrate that, without any π-π stacking, the honeycomb lattice of the D5-symmetric CRP has the potential to also facilitate electron transport.

Fivefold Symmetry and 2D Crystallization: Self-Assembly of the Buckybowl Pentaindenocorannulene on a Cu(100) Surface.

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion-enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two-dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C-H⋅⋅⋅π bonding.

Graphene Grown from Flat and Bowl Shaped Polycyclic Aromatic Hydrocarbons on Cu(111).

The growth of carbon layers, defective graphene, and graphene by deposition of polycyclic aromatic hydrocarbons (PAHs) on Cu(111) is studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Two different PAHs are used as starting materials: the buckybowl pentaindenocorannulene (PIC) which contains pentagonal rings and planar coronene (CR). For both precursors, with increasing sample temperature during deposition, porous carbon aggregates (350 °C), dense carbon layers (400-450 °C), disordered defective graphene (500 °C-550 °C), and extended graphene (≥600 °C) are obtained. No significant differences for defective graphene grown from PIC and CR are observed. C 1s X-ray photoelectron spectra of PIC and CR derived samples grown at 350-550 °C exhibit a characteristic C-Cu low binding energy component. Preparation at ≥600 °C eliminates this C-Cu species and only C-C bonded carbon remains.

1,2,3- versus 1,2-Indeno Ring Fusions Influence Structure Property and Chirality of Corannulene Bowls.

Annulated corannulenes 3-5 form via distinct synthetic pathways: (i) Pd-catalyzed sp3 CH insertion, (ii) Pd-catalyzed aryl coupling, and (iii) silyl cation-promoted C-F activation/CH insertion. Crystal structure, redox, and photophysical studies elucidate the differing influence of 1,2,3- versus 1,2-indeno ring fusions. Mono and dianions of 3-5 are characterized. Resolution of 4 gives enantiopure forms, allowing assessment of the bowl-inversion barrier.

Kurt†M. Mislow (1923-2017).

Kurt M. Mislow, Hugh Stott Taylor Professor of Chemistry Emeritus at Princeton University, died peacefully on October 5th, 2017 at the age of 94. Through the use of non-numerical mathematical models to conceptualize molecular form and function, Mislow pioneered the development of a modern stereochemistry, with contributions including the chiroptical properties of biaryls, resolution of phosphine oxides, and the use of NMR spectroscopy for the study of stereodynamic processes.

Chiral Atropisomeric Indenocorannulene Bowls: Critique of the Cahn-Ingold-Prelog Conception of Molecular Chirality.

Chiral corannulenes abound, but suffer generally from configurational lability associated with bowl-to-bowl inversion, thus obviating questions of stereogenicity and stereoelement construction. In contrast, peri-annulated corannulenes show greatly increased barriers for bowl-to-bowl inversion; specifically indenocorannulenes invert on a time scale too slow to observe by normal NMR methods and raise the possibility of creating chiral atropisomeric bowl-shaped aromatics. Two methods for preparing indenocorannulene from simple 2-haloarylcorannulenes-silyl cation C-F activation, and Pd-mediated C-Cl activation[5] -enable the synthesis of an array of such chiral atropisomeric indenocorannulenes. Resolution of the enantiomers by high-performance liquid chromatography over chiral support phases motivates the study of chiroptical properties, the assignment of absolute "Cartesian" configuration, and the assessment of configurational stability. These studies bring into question any systematic assignment of nontrivial stereoelements (i.e. not the molecule in its entirety) and refute any assertion of congruence between "Cahn-Ingold-Prelog elements" and the physical or "Cartesian" basis of chirality.

Pentaindenocorannulene: Properties, Assemblies, and C60 Complex.

Pentaindenocorannulene (C50 H20 , 1), a deep bowl polynuclear aromatic hydrocarbon, accepts 4 electrons, crystallizes in columnar bowl-in-bowl assemblies and forms a nested C60 @12 complex. Spectra, structures and computations are presented.

Half a century of the Bürgenstock Conference: a pilgrim's tale.

"…︁ The Bürgenstock program always allows for important scientific discussion. It is clear that this meeting is valuable for the scientific community as it is on one hand important for its deep historical significance, and on the other hand crucial for what it preserves of great scientific tradition for future generations. Every meeting contained a lesson learned and further brought together the family of stereochemists …︁" Read more in the Editorial by Jay S. Siegel.

Extended Corannulenes: Aromatic Bowl/Sheet Hybridization.

Among sheet/sheet polynuclear aromatic hydrocarbon (PAH) hybrids, a buckybowl-graphene hybrid has been used as a model to explore the effects of physical properties of PAHs with distinct planar and bowl regions. Activation of a C(Ar)-F bond was used to synthesize this corannulene/graphenic hybrid. Photophysical and voltammetric studies together with high-level computations revealed curvature and extended π-effects on the properties of these materials.

Phase behavior of a designed cyclopropyl analogue of monoolein: implications for low-temperature membrane protein crystallization.

Lipidic cubic phases (LCPs) are used in areas ranging from membrane biology to biodevices. Because some membrane proteins are notoriously unstable at room temperature, and available LCPs undergo transformation to lamellar phases at low temperatures, development of stable low-temperature LCPs for biophysical studies of membrane proteins is called for. Monodihydrosterculin (MDS) is a designer lipid based on monoolein (MO) with a configurationally restricted cyclopropyl ring replacing the olefin. Small-angle X-ray scattering (SAXS) analyses revealed a phase diagram for MDS lacking the high-temperature, highly curved reverse hexagonal phase typical for MO, and extending the cubic phase boundary to lower temperature, thereby establishing the relationship between lipid molecular structure and mesophase behavior. The use of MDS as a new material for LCP-based membrane protein crystallization at low temperature was demonstrated by crystallizing bacteriorhodopsin at 20 °C as well as 4 °C.

Gear-meshed tiling of surfaces with molecular pentagonal stars.

The assembly of the chiral pentagonal-star-shaped 1,3,5,7,9-pentaphenylcorannulene on a Cu(111) surface has been studied with scanning tunneling microscopy. Two different long-range ordered phases coexist at 60 K, most likely racemic and homochiral phases. The principal motifs emulate a network of meshed gears. One of the observed structures resembles the densest packing of five-fold symmetric stars.