Characterization of a diferrous terminal hydride mechanistically relevant to the Fe-only hydrogenases

Reduction of diferrous dithiolato complexes with hydride donor reagents affords the first example of the previously elusive terminal diferrous hydride, [Fe2(edt)(mu-CO)(H)(CO)(PMe3)4]PF6 (edt = S2C2H4). Crystallographic characterization shows that this model contains an asymmetrical semi-bridging CO trans to a terminal hydrido, as indicated in the Hred state in the D. desulfuricans enzyme. The model reacts with protons to yield H2 and rearranges via an intramolecular process to the isomeric mu-hydrido isomer, which is unreactive toward protons.     

Chiral (Diphosphonite)platinum Complexes in Asymmetric Hydroformylation

The chiral diphosphonite ligand (11bR,11′bR)‐4,4′‐(9,9‐dimethyl‐9H‐xanthene‐4,5‐diyl)bis[dinaphtho[2,1‐d:1′,2′‐f][1,3,2]dioxaphosphepin] ((R,R)‐XantBino; (R)‐ 1 ), based on a rigid xanthene backbone, was applied in the Pt/Sn‐catalyzed hydroformylation of styrene ( 4a ), 4‐methylstyrene ( 4b ), vinyl acetate ( 4c ), and allyl acetate ( 4d ), by using a Pt/Sn ratio of 1 : 1. High ee of up to 80% were observed, along with good regioselectivities towards the desired branched aldehydes. For styrene, an interesting inversion in the stereoselection process was observed at elevated temperatures, and a mechanism is proposed considering the temperature dependence of the regioselectivity. The complex [PtCl₂{(S,S)‐XantBino}] ((S)‐ 2 ) was characterized by X‐ray crystal‐structure analysis, revealing an unusual out‐of‐plane ligand coordination of the metal fragment. The complex [PtCl(SnCl₃){(R,R)‐XantBino}] ((R)‐ 3 ) was characterized by means of ³¹P‐NMR spectroscopy.     

Understanding the role of sodium during adsorption: a force field for alkanes in sodium-exchanged faujasites

We have developed a united atom force field able to accurately describe the adsorption properties of linear alkanes in the sodium form of FAU-type zeolites. This force field successfully reproduces experimental adsorption properties of n-alkanes over a wide range of sodium cation densities, temperatures, and pressures. The force field reproduces the sodium positions in dehydrated FAU-type zeolites known from crystallography, and it predicts how the sodium cations redistribute when n-alkanes adsorb. The cations in the sodalite cages are significantly more sensitive to the n-alkane loading than those in the supercages. We provide a simple expression that adequately describes the n-alkane Henry coefficient and adsorption enthalpy as a function of sodium density and temperature at low coverage. This expression affords an adequate substitute for complex configurational-bias Monte Carlo simulations. The applicability of the force field is by no means limited to low pressure and pure adsorbates, for it also successfully reproduces the adsorption from binary mixtures at high pressure.     

Uncatalyzed Oxidative C−H Amination of 9,10-Dihydro-9-Heteroanthracenes: A Mechanistic Study

A new method for the one-step C−H amination of xanthene and thioxanthene with sulfonamides is reported, without the need for any metal catalyst. A benzoquinone was employed as a hydride (or two-electron and one-proton) acceptor. Moreover, a previously unknown and uncatalyzed reaction between iminoiodanes and xanthene, thioxanthene and dihydroacridines (9,10-dihydro-9-heteroanthracenes or dihydroheteroanthracenes) is disclosed. The reactions proceed through hydride transfer from the heteroarene substrate to the iminoiodane or benzoquinone, followed by conjugate addition of the sulfonamide to the oxidized heteroaromatic compounds. These findings may have important mechanistic implications for metal-catalyzed C−H amination processes involving nitrene transfer from iminoiodanes to dihydroheteroanthracenes. Due to the weak C−H bond, xanthene is an often-employed substrate in mechanistic studies of C−H amination reactions, which are generally proposed to proceed via metal-catalyzed nitrene insertion, especially for reactions involving nitrene or imido complexes that are less reactive (i.e., less strongly oxidizing). However, these substrates clearly undergo non-catalyzed (proton-coupled) redox coupling with amines, thus providing alternative pathways to the widely assumed metal-catalyzed pathways.     

On the Mechanism Behind the Instability of Isoreticular Metal–Organic Frameworks (IRMOFs) in Humid Environments

Increasing the resistance to humid environments is mandatory for the implementation of isoreticular metal–organic frameworks (IRMOFs) in industry. To date, the causes behind the sensitivity of [Zn₄(μ₄‐O)(μ‐bdc)₃]₈ (IRMOF‐1; bdc=1,4‐benzenedicarboxylate) to water remain still open. A multiscale scheme that combines Monte Carlo simulations, density functional theory and first‐principles Born–Oppenheimer molecular dynamics on IRMOF‐1 was employed to unravel the underlying atomistic mechanism responsible for lattice disruption. At very low water contents, H₂O molecules are isolated in the lattice but provoke a dynamic opening of the terephthalic acid, and the lattice collapse occurs at about 6 % water weight at room temperature. The ability of Zn to form fivefold coordination spheres and the increasing basicity of water when forming clusters are responsible for the displacement of the organic linker. The present results pave the way for synthetic challenges with new target linkers that might provide more robust IRMOF structures.