Yoshihide Nakao

Bidirectional Chemo‐Switching of Spin State in a Microporous Framework

The ins and outs of spin: Using the microporous coordination polymer {Fe(pz)[Pt(CN)(4)]} (1, pz=pyrazine), incorporating spin-crossover subunits, two-directional magnetic chemo-switching is achieved at room temperature. In situ magnetic measurements following guest vapor injection show that most guest molecules transform 1 from the low-spin (LS) state to the high-spin (HS) state, whereas CS(2) uniquely causes the reverse HS-to-LS transition.

Discrete Sandwich Compounds of Monolayer Palladium Sheets

Despite the abundance of “sandwich” complexes, in which two cyclic aromatic hydrocarbon ligands flank a metal center, this motif has not been extended to sheets of multiple metal atoms. We prepared and isolated two such compounds. In the first, three palladium centers form a planar triangular array, capped by chlorides, between two cycloheptatrienyl ligands. In the second, a pentapalladium sheet adopts an edge-sharing triangle-trapezoid skeleton between two naphthacene rings. The compounds were characterized by x-ray crystallography and nuclear magnetic resonance spectroscopy. The nature of bonding in the clusters was analyzed by quantum calculations.

Why Does Fluoride Anion Accelerate Transmetalation between Vinylsilane and Palladium(II)−Vinyl Complex? Theoretical Study

Transmetalation between palladium(II)-vinyl complex and vinylsilane was theoretically investigated with the DFT and MP2 to MP4 methods to clarify the reaction mechanism and the reasons why fluoride anion accelerates the Pd-catalyzed cross-coupling reaction between vinyl iodide and vinylsilane. This transmetalation occurs with a very large activation barrier (45.8 kcal/mol) and a very large endothermicity (25.6 kcal/mol) in the absence of fluoride anion, where the potential energy change resulting from the solvation effect is evident. This is consistent with the experimental fact that this cross-coupling reaction does not proceed well in the absence of fluoride anion. The effects of fluoride anion were investigated in three possible reaction courses. In the first course, fluorovinylsilicate anion is formed before the transmetalation, and it reacts with the palladium(II)-vinyl complex. In the second course, an iodo ligand is substituted for fluoride anion, and then the transmetalation occurs between the palladium(II)-fluoro-vinyl complex and vinylsilane. In the third course, fluoride anion attacks the Si center of vinylsilane in the transition state of the transmetalation between the palladium(II)-iodo-vinyl complex and vinylsilane. Our theoretical calculation suggests that fluorovinylsilicate anion is not formed in the case of trimethylvinylsilane. In the second and third cases, the transmetalation occurs with a moderate activation barrier (E(a)) and a considerably large exothermicity (E(exo)): E(a) = 25.3 kcal/mol and E(exo) = 5.7 kcal/mol in the second course, and E(a) = 12.7 kcal/mol and E(exo) = 24.8 kcal/mol in the third course, indicating that fluoride anion accelerates the transmetalation via the second and third reaction courses. The acceleration of transmetalation by fluoride anion is clearly interpreted in terms of the formation of a very strong Si-F bond and the stabilization of the transition state by the hypervalent Si center, which is induced by the fluoride anion. Our computational results show that hydroxide anion accelerates the transmetalation in a manner similar to that observed with fluoride anion. From these results, we predict that the electronegative anion accelerates this transmetalation because the electronegative group forms a strong covalent bond with the silyl group and facilitates the formation of the hypervalent Si center in the transition state.

Regioselective beta-metalation of meso-phosphanylporphyrins. Structure and optical properties of porphyrin dimers linked by peripherally fused phosphametallacycles.

meso-Diphenylphosphanylporphyrins were successfully prepared via Pd-catalyzed C-P cross-coupling reaction of the corresponding meso-iodoporphyrins with diphenylphosphane. The meso- phosphanylporphyrins underwent regioselective metalation at the beta carbon to produce novel classes of porphyrin dimers linked by peripherally fused phosphametallacycles. A Pd-mononucler complex was structurally characterized by X-ray crystallography, which revealed a flat structure of the Pd-linked porphyrin pi systems. Both experimental and theoretical results demonstrate that the orbital interaction between the pyrrolic ppi orbitals and the metal dpi orbital affects optical and electrochemical properties of the metal-linked coplanar porphyrin dimers.

Multireference Møller–Plesset method with a complete active space configuration interaction reference function

A multireference Moller–Plesset (MRMP) method with a complete active space configuration interaction (CASCI) reference function has been proposed as an accurate and computationally efficient method for treating the ground and excited states of molecules. The CASCI wave function was constructed using the self-consistent field orbitals and used as a reference function of the MRMP to incorporate the remaining dynamical correlation. The advantage in using the CASCI is that it does not require iterations, nor does it encounter convergence difficulties which may be found in complete active space self-consistent field (CASSCF) calculations. The scheme was applied to the potential curves of the ground and low-lying excited states of N2, the potential curve of the ground state of CO, and the vertical valence π–π* excited states of benzene. Excellent agreement between theory, experiment, and some benchmark calculations was obtained. MRMP with CASCI is comparable in accuracy with MRMP with CASSCF. The present scheme...

Thermal Degradation of Methyl beta-D-Glucoside. A Theoretical Study of Plausible Reaction Mechanisms

Thermal conversion of methyl beta-d-glucoside to levoglucosan was studied with the MP4//DFT(B3LYP) method. The first step is conformational change of the reactant to (1)C(4) from (4)C(1). The second step is intramolecular nucleophilic substitution at the anomeric C1, which occurs via one step without oxacarbenium ion intermediate. The DeltaG(0)() value (52.5 kcal/mol) is smaller than the C1-O1 bond energy, indicating the direct homolysis mechanism is clearly ruled out. Bimolecular reaction also occurs with smaller activation energy via the similar transition state.

Selective Formation and Efficient Photocurrent Generation of [70]Fullerene-Single-Walled Carbon Nanotube Composites

For the first time nanocarbon composites with C 70 molecules aligned on the sidewall of single-walled carbon nanotubes (SWNTs) are demonstrated. The C70-SWNT photoelectrochemical devices exhibit efficient photocurrent generation properties that result from selective formation of a single composite film consisting of a SWNT network covered with C70 molecules and high electron mobility through the C 70-SWNT network.

Electronic Structure of Four-Coordinate Iron(I) Complex Supported by a Bis(phosphaethenyl)pyridine Ligand

A 15-electron iron complex with a formal Fe(I) center, [FeBr(BPEP)] (BPEP = 2,6-bis(1-phenyl-2-phosphaethenyl)pyridine), was prepared by one-electron reduction of the dibromide precursor [FeBr(2)(BPEP)]. The single-crystal diffraction analysis revealed a distorted trigonal monopyramidal arrangement around the iron center, and SQUID magnetometry established the S = 3/2 ground state. The Mossbauer isomer shift value (delta = 0.59 mm/s) was consistent with a high-spin Fe(I) center of [FeBr(BPEP)]. DFT calculations for a model complex revealed two highly delocalized molecular orbitals formed by bonding and antibonding interactions between the d(z(2)) (Fe) and pi* (BPEP) orbitals. Orbital occupancy analysis demonstrated the electronic structure with a high-spin Fe(I) center. The effective dpi-ppi interaction between iron and BPEP was concluded to be responsible for the highly distorted structure of [FeBr(BPEP)], with its rather uncommon trigonal monopyramidal configuration.

Theoretical study of first-row transition metal oxide cations

The equilibrium geometries, dissociation energies, and electronic structures of the ground and low-lying excited states for the first-row transition metal oxide cations, MO+ (M=Sc to Zn), have been studied using the multireference singles and doubles configuration interaction (MR–SDCI) and the multireference second-order Moller–Plesset methods. To investigate the applicability of the density functional theory (DFT) to an electronic structure system with a multiconfigurational character, the Becke exchange functional with the Lee–Yang–Parr correlation functional, the Becke exchange functional with the one-parameter progressive correlation functional (BOP), and the Becke three-parameter hybrid exchange functional with the Lee–Yang–Parr correlation functional (B3LYP) methods have also been applied. The DFT predicts the ground state M–O bond lengths in good agreement with the multireference-based methods except for MnO+ and CuO+, which have a multiconfigurational electronic structure. With respect to the diss...

Heteropolynuclear Complexes of 3,5-Dimethylpyrazolate [Pt2M4(Me2pz)8] (M = Ag, Cu). Highly Luminescent Character of the Triplet Excited State Based on Mixed-Metal Cores

The platinum dimer and heteropolynuclear platinum complexes of 3,5-dimethylpyrazolate, [Pt2M4(mu-Me2pz)8] [M = H (1), Ag (2), Cu (3)], were synthesized and structurally characterized. They exhibit yellow, sky-blue, and orange luminescence, respectively, in the solid state. The absorption bands of 2 and 3 are mainly assigned to the combination of the metal-metal-to-ligand charge-transfer and [Pt2 --> Pt2M4] transitions by the time-dependent density functional theory (DFT) method. DFT calculations also indicate that the emissive states of 2 and 3 are 3[Pt2 --> Pt2Ag4] and 3[Cu(d) --> Pt2Cu4], respectively.