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International audience; Molecular-level multielectron handling toward electrical storage is a worthwhile approach to solar energy harvesting. Here, a strategy which uses chemical bonds as electron reservoirs is introduced to demonstrate the new concept of "structronics" (a neologism derived from "structure" and "electronics"). Through this concept, we establish, synthesize, and thoroughly study two multicomponent "super-electrophores": 1,8-dipyridyliumnaphtha-lene, 2, and its N,N-bridged cyclophane-like analogue, 3. Within both of them, a covalent bond can be formed and subsequently broken electrochemically. These superelectrophores are based on two electrophoric (pyridinium) units that are, on purpose, spatially arranged by a naphthalene scaffold. A key characteristic of 2 and 3 is that they possess a LUMO that develops through space as the result of the interaction between the closely positioned electrophoric units. In the context of electron storage, this "super-LUMO" serves as an empty reservoir, which can be filled by a two-electron reduction, giving rise to an elongated C−C bond or "super-HOMO". Because of its weakened nature, this bond can undergo an electrochemically driven cleavage at a significantly more anodicyet accessiblepotential, thereby restoring the availability of the electron pair (reservoir emptying). In the representative case study of 2, an inversion of potential in both of the two-electron processes of bond formation and bond-cleavage is demonstrated. Overall, the structronic function is characterized by an electrochemical hysteresis and a chemical reversibility. This structronic superelectrophore can be viewed as the three-dimensional counterpart of benchmark methyl viologen (MV).

Umbrella-like inversion of pyramidalized amines proceed through a planar transition state (TS). Stabilization of the TS through N(lone-pair) → σ*(C–C) “negative hyperconjugation” in diamino-o-carbo...

On the basis of density functional theory computations of the well-known chiral Au38(SR)24 nanocluster and its Pd- and Ag-doped derivatives, we propose here a mechanism for chiral inversion that does not require the breaking of a metal-sulfur bond at the metal-ligand interface but features a collective rotation of the gold core. The calculated energy barriers for this mechanism for Au38 and Pd-doped Au38 are in the range of 1-1.5 eV, significantly lower than barriers involving the breakage of Au-S bonds (2.5 eV). For Ag-doped Au38, barriers for both mechanisms are similar (1.3-1.5 eV). Inversion barriers for a larger chiral Au144(SR)60 are much higher (2.5-2.8 eV). Our computed barriers are in good agreement with racemization barriers estimated from existing experiments for bare and doped Au38. These results highlight the sensitivity of chiral inversion to the size, structure, and metal composition of the metal core and sensitivity to the detailed structure of the metal-thiolate interface. Our work also predicts that enantiopure Au144(SR)60 clusters would be promising materials for applications requiring high resistance to chiral inversion.

A series of pyrenes sandwiched by axially chiral 1,1′-binaphthyls were synthesized. Among them, (R,R)-3 possessing 2-hydroxy-3,3′-dimethylbinaphthyls exhibited solvent-dependent inversion of the si...

Transmetalation between Pd(Br)(PhA)(PCyp3)2 (Ph = phenyl, Cyp = cyclopentyl) and Cu(CaHMePhB)(NHC) (NHC = 1,3-bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene) is an important elementary step in recently reported catalytic cross-coupling reaction by Pd/Cu cooperative system. DFT study discloses that the transmetalation occurs with inversion of the stereochemistry of the CaHMePhB group. In its transition state, the CaHMePhB group has almost planar structure around the Ca atom. That planar geometry is stabilized by conjugation between the π* orbital of the PhB and the 2p orbital of the Ca. Another important factor is activation entropy (ΔS°‡); retention transmetalation occurs through Br-bridging transition state, which is less flexible than that of the inversion transmetalation because of the Br-bridging structure, leading to a smaller activation entropy in the retention transition state than in the inversion transition state. For CaHMeEt group, transmetalation occurs in a retention manner. In the planar C...

Bowl-shaped π-conjugated compounds, or buckybowls, are a novel class of sp(2)-hybridized nanocarbon materials. In contrast to tubular carbon nanotubes and ball-shaped fullerenes, the buckybowls feature structural flexibility. Bowl-to-bowl structural inversion is one of the unique properties of the buckybowls in solutions. Bowl inversion on a surface modifies the metal-molecule interactions through bistable switching between bowl-up and bowl-down states on the surface, which makes surface-adsorbed buckybowls a relevant model system for elucidation of the mechano-electronic properties of nanocarbon materials. Here, we report a combination of scanning tunneling microscopy (STM) measurements and ab initio atomistic simulations to identify the adlayer structure of the sumanene buckybowl on Au(111) and reveal its unique bowl inversion behavior. We demonstrate that the bowl inversion can be induced by approaching the STM tip toward the molecule. By tuning the local metal-molecule interaction using the STM tip, the sumanene buckybowl exhibits structural bistability with a switching rate that is two orders of magnitude faster than that of the stochastic inversion process.

Synthesis of a series of corannulene derivatives with varying bowl depths has allowed for a study correlating the structure (bowl depth) and the energy of bowl inversion. Substituents placed in the peri positions are repulsive and flatten the bowl, thus causing a decrease in the bowl inversion barrier. Conversely, annelation across the peri positions causes a deepening of the bowl, thus an increase in the bowl inversion barrier. Barriers between 8.7 and 17.3 kcal/mol have been measured, and their structures have been calculated using a variety of ab initio methods. The energy profile of an individual corannulene derivative is assumed to fit a mixed quartic/quadratic function from which an empirical correlation of bowl depth and inversion barrier that follows a quartic function is derived. Structure/energy correlations of this type speak broadly of the nature of enzymatic and catalytic activation of substrates.

Azaboradibenzo[6]helicene, a new semiconductor material possessing helical chirality, has been synthesized via a tandem bora-Friedel–Crafts-type reaction. Unprecedented carrier inversion between the racemate (displaying p-type semiconductivity) and the single enantiomer (displaying n-type semiconductivity) was observed and can be explained by changes in the molecular packing induced by helical homochirality.

The helical tetranuclear complex [LZn(3)La(OAc)(3)] having two benzocrown moieties was designed and synthesized as a novel molecular leverage for helicity control and helix inversion. Short alkanediammonium guests H(3)N(+)(CH(2))(n)NH(3)(+) (n = 4, 6, 8) preferentially stabilized the P-helical isomer of [LZn(3)La(OAc)(3)], while the longer guest H(3)N(+)(CH(2))(12)NH(3)(+) caused a helix inversion to give the M-helical isomer as the major isomer. The differences in the molecular lengths were efficiently translated into helical handedness via the novel molecular leverage mechanism using the gauche/anti conversion of the trans-1,2-disubstituted ethylenediamine unit.

The asymmetric synthesis of (S)-(+)-cryptaustoline was accomplished and found to differ in sign of rotation with the natural «S»-(-)-material. The previously assigned absolute configuration was found to be incorrect and is now corrected. The reversal in stereochemistry came about through an unusual manner involving (S)-(+)-laudanosoline (3) cyclizing to (R)-(-)-cryptaustoline ((-)-1c). The mechanism was explored by oxidation of a series of deuterio derivatives of laudanosoline, all of which retained deuterium in the resultant cryptaustoline

Dynamic EPR spectroscopy has been used to investigate the inversion of 1,3-dioxolan-2-yl and [2-D]-1,3-dioxolan-2-yl radicals. The former shows no detectable line broadening down to 93 K, which implies "instant" inversion on the EPR time scale, but the latter shows a temperature-dependent EPR spectrum from which the inversion rate constants have been deduced. These rate constants give rise to a curved Arrhenius plot which, together with the large primary isotope effect, indicates that the inversion proceeds by quantum-mechanical tunneling. To investigate the transition quantitatively, an ab initio UHF-MO calculation has been carried out, yielding the molecular geometry and the normal-mode frequencies in the equilibrium and transition state, as well as an inversion barrier height of ca. 2500 cm -1. The inversion is found to be dominated by two vibrational degrees of freedom, namely, a ring-bending mode in addition to the CH α-bending mode. The potential of the latter mode is approximated by a modified quartic double-minimum potential. The former mode is treated semiclassically: it modifies the quartic potential via an anharmonic cross-term yielding a series of quartic potentials, one for each state of the ring-bending mode, weighted by the Boltzmann population of the state. The observed rate constants can be fitted accurately to the CH α-level splittings generated by this model. The resulting effective one-dimensional inversion barrier compares favorably with the corresponding barrier deduced quantum-chemically.

The dynamics of pyramidal nitrogen inversion can be controlled by reversible redox switching in trans-2,3-diphenylaziridines bearing a suitable 1,4-naphthaquinone substituent. In the reduced form, an intramolecular H-bond significantly raises the inversion barrier slowing this molecular motion by >50-fold. The experimental findings are further supported by DFT calculations.

The natural alkaloid cryptaustoline is (13R,7S)-(−)-1 due to the heretofore unprecedented inversion while the formamidine route led to the expected (13S,7R)-(+)-1

On etudie l'inversion sur le silicium du tetrakis-trifluoromethyl-3,3,3',3' spirobi-1,1' benzooxasilole-2,1

Determination des structures cristallines d'un spirane spirobi-benzoaxasilole et d'un phenylsiliconate. Mesure par spectrometrie RMN de 19 F des vitesses de permutation de coordinat