Photoredox Catalysis by 21-Thiaporphyrins: A green and Efficient Approach for C-N Borylation and C-H Arylation.

The photocatalytic C-N borylation and C-H arylation mostly depend on the ruthenium and iridium complexes or eosin Y and the use of porphyrin catalysts is still in infancy. A series of novel 21-thiaporphyrins (A2B2 and A3B type) were synthesized having carbazole/phenothiazine moieties at their meso-positions and screened as catalysts for C-N borylation and C-H arylation. This paper demonstrates the 21-thiaporphyrin catalyzed C-N borylation and het-arylation of anilines under visible light. The method utilizes only 0.1 mol% of 21-thiaporphyrin catalyst under blue light for the direct C-N borylation and het-arylation reactions. A variety of substituted anilines were used as source for expensive and unstable aryl diazonium salts in the reactions. The heterobiaryls and aryl boronic esters were obtained in decent yields (up to 88%). Versatility of the 21-thiaporphyrin catalyst was tested by thiolation and selenylation of anilines under similar conditions. Mechanistic insight was obtained from DFT studies, suggesting that 21-thiaporphyrin undergo an oxidative quenching pathway. The photoredox process catalyzed by 21-thiaporphyrins offers a mild, efficient and metal-free alternative for the formation of C-C, C-S, and C-Se bonds in aryl compounds; it can also be extended to borylation reaction.

Signatures of non-trivial band topology in LaAs/LaBi heterostructure.

In this article, we investigate non-trivial topological features in a heterostructure of extreme magnetoresistance (XMR) materials LaAs and LaBi using density functional theory. The proposed heterostructure is found to be dynamically stable and shows bulk band inversion with non-trivial Z2 topological invariant and a Dirac cone at the surface. In addition, its electron and hole carrier densities ratio is also calculated to investigate the possibility to possess XMR effect. Electrons and holes in the heterostructure are found to be nearly compensated, thereby facilitating it to be a suitable candidate for XMR studies.

Rational Design of a 3D MnII -Metal-Organic Framework Based on a Nonmetallated Porphyrin Linker for Selective Capture of CO2 and One-Pot Synthesis of Styrene Carbonates.

A 3D MnII -porphyrin metal-organic framework (MOF), [{Mn2 (TCPP)⋅2H2 O}⋅DMF]n (MOF1) (TCPP=5,10,15,20-tetrakis(4-benzoate)porphyrin), was constructed; it exhibits an interesting 3D framework structure with two types of 1D channels of dimensions of 3.94×8.37 Å2 and 4.66×4.93 Å2 running along the crystallographic a axis. Owing to the presence of a nonmetallated porphyrin cavity, MOF1 exhibits selective storage of CO2 with an isosteric heat of adsorption value of 32.1 kJ mol-1 , which is further supported by theoretical calculations with the calculated binding energy (BE) of 29.78 kJ mol-1 . Interestingly, the nonmetallated nature of the porphyrin ligand was exploited for implantation of coordinatively unsaturated FeIII ions to generate a FeIII @MOF1 framework, which acts as an efficient recyclable catalyst for the oxidation of styrenes to the corresponding epoxides in the presence of PhIO as an oxidant at room temperature. Moreover, the one-pot synthesis of styrene carbonates from styrenes and CO2 was also achieved using FeIII @MOF1 as a catalyst. The rational design of a porous MnII -porphyrin MOF for the selective capture of CO2 and the one-pot synthesis of styrene carbonates at mild conditions is reported.

Hydrogen sorption efficiency of titanium decorated calix[4]pyrroles.

Hydrogen is a promising and the most environmentally friendly energy carrier due to its renewable nature and it is expected to replace fossil fuels. The hydrogen storage properties of Ti decorated calix[4]pyrrole (CXP) and octamethylcalix[4]pyrrole (MeCXP) have been reported. The structure, stability and hydrogen loading efficiency of Ti decorated CXP and MeCXP have been studied based on density functional theory with the Minnesota 06 (M06) functional and the 6-311G(d,p) basis set. Ti binds with the pyrrole rings of CXP and MeCXP from outside of each ring by Dewar coordination. It is found that Ti decorated CXP and MeCXP have hydrogen wt% 9.7 and 10.5 respectively. The usable hydrogen wt% is found to be 6.35 and 5.20 for CXP and MeCXP respectively. The stability of Ti decorated CXP and MeCXP is studied by calculating global reactivity parameters, which follow maximum hardness and minimum philicity principles. The calculated adsorption and desorption energy values are found to be low and decrease on H2 adsorption in both the Ti decorated systems. The molecular dynamics simulations indicate that the hydrogen starts releasing at 273 K and all the hydrogen molecules are released by 473 K from both the systems. These predictions pave the way to reversibly store hydrogen efficiently with high gravimetric storage capacity in CXP and MeCXP systems.

Low-energy rotational inelastic collisions of H(+) + CO system.

The quantum mechanical state-to-state rotational excitation cross sections have been computed using the ab initio ground electronic state potential energy surface of the system [M. Mladenovic and S. Schmatz, J. Chem. Phys. 109, 4456 (1998)] computed at coupled-cluster single and double and triple perturbative excitations method using correlation-consistent polarized valence quadruple zeta basis set where the asymptotic potential have been computed using the dipole moment, quadrupole moment, and the molecular polarizability components and fitted to this interaction potential. The anisotropy of the surface has been analyzed in terms of the multipolar expansion coefficients for the rigid-rotor surface. The integral cross sections for rotational excitations have been computed by solving close-coupled equations at very low collision energies (5-200 cm(-1)) and the corresponding rates have been obtained for a range of low temperatures (5-175 K). The j = 0 → j(') = 1 rotational excitation cross section (and rate) is found to be the dominant followed by the j = 0 → j(') = 2 in these collision energies. The close-coupling, coupled-state, and infinite-order sudden approximations coupling calculations have been performed in the energy range of 0.1-1.0 eV using vibrational ground potential. The rotational cross sections have been obtained by performing computationally accurate close-coupling calculations at 0.1 eV using vibrationally averaged potential (ν = 1) and compared with the results of vibrational ground potential.

Hydrogen multicenter bonds and reversible hydrogen storage.

A new strategy for reversible hydrogen storage based on the properties of hydrogen multicenter bonds is proposed. This is demonstrated by carrying out ab initio calculations of hydrogen saturation of titanium and bimetallic titanium-aluminum nanoclusters. Hydrogen saturation leads to the formation of exceptionally and energetically stable hydrogen multicenter bonds. The stabilization results from sharing of the hydrogen atom electron density with the frontier orbitals of the metal cluster. The strength of the hydrogen multicenter bonds can be modulated either by varying the degree of hydrogen loading or by suitable alloying. Mode-specific infrared excitation of the vibrational modes associated with the multicenter hydrogen bonds can release the adsorbed hydrogen, thereby enabling efficient reversible hydrogen storage. The possible formation of hydrogen multicenter bonds involving titanium atoms and its implication to hydrogen adsorption/desorption kinetics in hydrogen cycled Ti-doped NaAlH(4) is also discussed.

Nature of hydrogen interaction and saturation on small titanium clusters.

This work explores the nature of interaction and saturation of hydrogen molecules on small titanium clusters using ab initio calculations. Molecular dynamics simulations and ensuing charge density maps were used to gain insight into the key steps involved in dissociation of the hydrogen molecule on the metal clusters. The mechanistic insights gleaned from these simulations were subsequently utilized to obtain realistic models of the hydrogen saturated titanium clusters. It was found that the most stable hydrogen saturated titanium clusters involve hydrogen multicenter bonds. The observed peaks in the experimental mass and photoelectron spectra of hydrogen saturated titanium clusters are attributed to structures possessing hydrogen multicenter bonds. Hydrogen multicenter bonds are also ascribed to the origin of the broad shoulder in the vibrational spectra of hydrogen cycled Ti-doped NaAlH4 reported in a recent study.

Vibrationally inelastic collisions in H+ +CO system: comparing quantum calculations with experiments.

State-resolved cross beam experiments [H. Udseth et al., J. Chem. Phys. 60, 3051 (1974); J. Krutein and F. Linder, J. Chem. Phys. 71, 599 (1979); G. Niedner-Schatteburg and J. P. Toennies, Adv. Chem. Phys. LXXXII, 553 (1992)], coupled with proton energy loss spectroscopy for the inelastic scattering of H(+) from CO in the collision range of 10-30 eV show very low vibrational excitation of the target molecule. Stimulated by the experimentally observed low vibrational inelasticity in the system the ground and the first two low-lying excited electronic potential-energy surfaces have been computed using the ab initio multireference configuration interaction method. Quantum dynamics has been performed on the ground potential energy surface in the framework of vibrational close-coupling rotational infinite-order sudden approximation. The various computed dynamical attributes such as differential and integral cross sections, and average vibrational energy transfer are analyzed in detail, and compared successfully with the available experimental results.