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Hydrogen uptake and release in arene-cycloalkane pairs provide an attractive opportunity for on-board and off-board hydrogen storage. However, the efficiency of arene-cycloalkane pairs currently is limited by unfavorable thermodynamics for hydrogen release. It is shown here that the thermodynamics can be optimized by replacement of H in the -OH group of cyclohexanol and phenol with alkali or alkaline earth metals. The enthalpy change upon dehydrogenation decreases substantially, which correlates with the delocalization of the oxygen electron to the benzene ring in phenoxides. Theoretical calculations reveal that replacement of H with a metal leads to a reduction of the HOMO-LUMO energy gap and elongation of the C-H bond in the α site in cyclohexanolate, which indicates that the cyclohexanol is activated upon metal substitution. The experimental results demonstrate that sodium phenoxide-cyclohexanolate, an air- and water-stable pair, can desorb hydrogen at ca. 413 K and 373 K in the solid form and in an aqueous solution, respectively. Hydrogenation, on the other hand, is accomplished at temperatures as low as 303 K.

Gold-catalyzed intermolecular alkyne oxidation has attracted much synthetic attention, but mostly suffering undesired over-oxidation. Recent experiments demonstrated that over-oxidation could be dramatically suppressed in zinc(II)-catalyzed intermolecular alkyne oxidation/CH functionalization. By means of first-principle density functional theory calculations, we explored the mechanism of the M-catalyzed intermolecular alkyne oxidations (M = Zn(OTf)2 and Au+ PR3 ) as well as the effects of oxidants, temperature, and metal catalysts on chemoselectivity, in an effort to disclose the origin of the extraordinary chemoselectivity pertaining to zinc catalysis. Our calculations indicate that the Zn-catalyzed intermolecular alkyne oxidation/CH functionalization proceeds by a Friedel-Crafts alkylation mechanism rather than metal carbene insertion mechanism. The chemoselectivity of CH functionalization against over-oxidation in Zn catalysis, in comparison with gold catalysis, can be jointly controlled by four factors: (1) the use of less nucleophilic N-oxide, (2) the enhanced electrophilicity and carbocationic nature of the carbenic site in the α-oxo metal carbenoid intermediate, (3) enhanced steric repulsion to incoming oxidant exerted by bulky ancillary ligand in the close nearby of the carbenic site to disfavor intermolecular over-oxidation and (4) the large negative value of activation entropy in the intermolecular over-oxidation pathway, that jointly give rise to lower activation free energy for the intramolecular cyclization/CH functionalization pathway than for the intermolecular over-oxidation pathway. © 2018 Wiley Periodicals, Inc.

Alkali metals have been widely employed as catalyst promoters; however, the promoting mechanism remains essentially unclear. Li, when in the imide form, is shown to synergize with 3d transition metals or their nitrides TM(N) spreading from Ti to Cu, leading to universal and unprecedentedly high catalytic activities in NH3 decomposition, among which Li2NH-MnN has an activity superior to that of the highly active Ru/carbon nanotube catalyst. The catalysis is fulfilled via the two-step cycle comprising: 1) the reaction of Li2NH and 3d TM(N) to form ternary nitride of LiTMN and H2, and 2) the ammoniation of LiTMN to Li2NH, TM(N) and N2 resulting in the neat reaction of 2 NH3⇌N2+3 H2. Li2NH, as an NH3 transmitting agent, favors the formation of higher N-content intermediate (LiTMN), where Li executes inductive effect to stabilize the TM-N bonding and thus alters the reaction energetics.

Calculation of large complex systems remains to be a great challenge, where there is always a trade-off between accuracy and efficiency. Recently, we proposed the extended our own n-layered integrated molecular orbital (ONIOM) method (XO) (Guo, Wu, Xu, Chem. Phys. Lett. 2010, 498, 203) which surmounts some inherited limitations of the popular ONIOM method by introducing the inclusion-exclusion principle used in the fragmentation methods. The present work sets up general guidelines for the construction of a good XO scheme. In particular, force-error test is proposed to quantitatively validate the usefulness of an XO scheme, taking accuracy, efficiency and scalability all into account. Representative studies on zeolites, polypeptides and cyclodextrins have been carried out to demonstrate how to strive for high accuracy without sacrificing efficiency. As a natural extension, XO is applied to calculate the total energy, fully optimized geometry and vibrational spectra of the whole system, where ONIOM becomes inapplicable.

CAS [KGCX2-YW-806, KJCX2-YW-H21, 2009AA05Z108, 2010CB631304]; US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]

A new algorithm for nonorthogonal valence bond (VB) method is presented by using symmetric group approach. In the present algorithm, a new function, called paired-permanent-determinant (PPD), is defined, which is an algebrant and has the same symmetry of a corresponding VB structure. The evaluation of a PPD is carried out by using a recursion formula similar to the Laplace expansion method for determinants. An overlap matrix element in the spin-free VB method may be obtained by evaluating a corresponding PPD, while the Hamiltonian matrix element is expressed in terms of the products of electronic integrals and sub-PPDs. In the present work, some important properties of PPDs are discussed, and the primary procedure for the evaluation of PPD is deduced. Furthermore, the expressions for evaluating both the overlap and Hamiltonian matrix elements are also given in details, which are essential to develop an efficient algorithm for nonorthogonal VB calculations. In the present study, some further effective technical considerations will be adopted, and a new ab initio VB program will be introduced. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 287–297, 1998

Fundamental Research Funds for the Central Universities [2010121014]; National Natural Science Foundation of China [21133004]