Takeshi Yamamoto

A polyquinoxaline-based helical polymer ligand bearing both helical-sense-determining chiral side chains and coordinating diarylphosphino side chains exhibits solvent-dependent formation of P- or M-helical structures, with which either the S- or R-hydrosilylation product was obtained with high (>93% enantiomeric excess) enantioselectivities.

Taking a new turn: An asymmetric Suzuki–Miyaura coupling of 1-bromo-2-naphthalenephosphonic esters with o-methyl-substituted phenylboronic acids proceeds with high enantioselectivity in the presence of high-molecular-weight helically chiral polyquinoxaline-based phosphines (PQXphos) bearing pendant diarylphosphino groups.

Living it up: Helical polyquinoxalines with single and multiple metal-binding sites, prepared by living polymerization of o-diisocyanobenzenes, are used in the asymmetric hydrosilylation of styrenes, resulting in comparable enantioselectivities to those obtained by low-molecular-weight catalyst systems (up to 87 % ee, stereochemistry was determined by a chiral initiator) and a turnover number of almost 1000.

Katalytische Spirale: In Gegenwart helical-chiraler Polychinoxalin-basierter Phosphane (PQXphos) mit hohem Molekulargewicht gelingen hoch enantioselektive Suzuki-Miyaura-Kupplungen von 1-Brom-2-naphthalinphosphonsäureestern mit o-Methylphenylboronsäuren. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is no

Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-aminopyrid-3-yl pendants were synthesized as new helical-polymer-based chiral nucleophilic organocatalysts. The obtained chiral nucleophilic polymer catalysts exhibited high catalytic activity, enantioselectivity, and reusability in asymmetric Steglich rearrangement of oxazolyl carbonate to C-carboxyazlactone. The polyquinoxaline-based, helically chiral DMAP catalyst mediated intramolecular acyl transfer selectively, by contrast with known s

We present an efficient path integral approach for evaluating thermal rate constants within the quantum instanton (QI) approximation that was recently introduced to overcome the quantitative deficiencies of the earlier semiclassical instanton approach [Miller, Zhao, Ceotto, and Yang, J. Chem. Phys. 119, 1329 (2003)]. Since the QI rate constant is determined solely by properties of the (quantum) Boltzmann operator (specifically, by the zero time properties of the flux-flux and delta-delta correla

The semiclassical (SC) initial value representation (IVR) provides a way for including quantum effects into classical molecular dynamics simulations. Implementation of the SC-IVR to the thermal rate constant calculation, based on the reactive flux correlation function formalism, has two major obstacles: (1) the SC integrand may be highly oscillatory with respect to the initial phase space variables; and (2) matrix elements of the Boltzmannized flux operator, which are crucial in generating the i

Post-polymerization CH activation of poly(quinoxaline-2,3-diyl)-based helically chiral phosphine ligands (PQXphos) with palladium(II) acetate afforded chiral phosphapalladacycles quantitatively. In situ generated palladacycles exhibited enantioselectivities up to 94 % ee in the palladium-catalyzed asymmetric ring-opening arylation of 1,4-epoxy-1,4-dihydronaphthalenes with arylboronic acids.

Helical chirality of poly(quinoxaline-2,3-diyl)s bearing a boronyl pendant at the 5-position of the quinoxaline ring was induced by condensation with chiral guests such as a diol, diamine, and amino alcohol. Reversible induction of a single-handed helical structure was achieved by using less than an equimolar amount of chiral amino alcohols to the boronyl pendants. Majority-rule-effect-based chiral amplification on the polyquinoxaline main chain was demonstrated with chiral amino alcohols with l

The quantum instanton approximation for thermal rate constants, a type of quantum transition state theory (QTST), is applied to a model proton transfer reaction in liquid methyl chloride developed by Azzouz and Borgis. Monte Carlo path integral methods are used to carry out the calculations, and two other closely related QTST's, namely, the centroid-density and Hansen-Andersen QTST, are also evaluated for comparison using the present path integral approach. A technique is then introduced that ca

We first show that a simple scaling of fluctuation coordinates defined in terms of a given reference point gives the conventional virial estimator in discretized path integral, where different choices of the reference point lead to different forms of the estimator (e.g., centroid virial). The merit of this procedure is that it allows a finite-difference evaluation of the virial estimator with respect to temperature, which totally avoids the need of higher-order potential derivatives. We apply th

Semiclassical (SC) initial-value representation (IVR) methods are used to calculate the thermal rate constant for the benchmark gas-phase reaction D+H2→DH+H. In addition to several technical improvements in the SC-IVR methodology, the most novel aspect of the present work is use of Cartesian coordinates in the full space (six degrees of freedom once the overall center-of-mass translation is removed) to carry out the calculation; i.e., we do not invoke the conservation of total angular momentum J

Pyrazolylaniline serves as a temporary directing group attached to the boron atom of alkylboronic acids in Ir-catalyzed C(sp³)-H borylation. The reaction takes place at α-, β-, and γ-C-H bonds, giving polyborylated products including di-, tri-, tetra-, and even pentaborylalkanes. α-C-H borylation was generally found to be the preferred reaction of primary alkylboronic acid derivatives, whereas β- or γ-borylation also occurred if β- or γ-C-H bonds were located on the methyl group.

A total of 3261 ab initio energies calculated at the RHF/MP2 level were used to obtain an analytical representation of the potential energy surface (PES) for the title reaction considering all the vibrational degrees of freedom. The analytical potential is constructed by switching three local representations of the PES utilizing a distancelike function, and it reproduces well the ab initio energies up to 20 kcal/mol above the dissociation threshold with the root-mean-square (rms) deviation equal