Acceptorless dehydrogenation of alcohols, an important organic transformation, was accomplished with welldefined and inexpensive iron-based catalysts supported by a cooperating PNP pincer ligand. Benzylic and aliphatic secondary alcohols were dehydrogenated to the corresponding ketones in good isolated yields upon release of dihydrogen. Primary alcohols were dehydrogenated to esters and lactones, respectively. Mixed primary/secondary diols were oxidized at the secondary alcohol moiety with good chemoselectivity. The mechanism of the reaction was investigated using both experiment and DFT calculations, and the crucial role of metal−ligand cooperativity in the reaction was elucidated. The iron complexes are also excellent catalysts for the hydrogenation of challenging ketone substrates at ambient temperature under mild H 2 pressure, the reverse of secondary alcohol dehydrogenation.

Hydrogen is an attractive alternative energy vector to fossil fuels if effective methods for its storage and release can be developed. In particular, methanol, with a gravimetric hydrogen content of 12.6%, is a promising target for chemical hydrogen storage. To date, there are relatively few homogeneous transition metal compounds that catalyze the aqueous phase dehydrogenation of methanol to release hydrogen and carbon dioxide. In general, these catalysts utilize expensive precious metals and require a strong base. This paper shows that a pincer-supported Fe compound and a co-catalytic amount of a Lewis acid are capable of catalyzing base-free aqueous phase methanol dehydrogenation with turnover numbers up to 51 000. This is the highest turnover number reported for either a first-row transition metal or a base-free system. Additionally, this paper describes preliminary mechanistic experiments to understand the reaction pathway and propose a stepwise process, which requires metal−ligand cooperativity. This pathway is supported by DFT calculations and explains the role of the Lewis acid cocatalyst.

The iron complex [FeH­(CO) (PNP)] (PNP = N­(CH2CH2PiPr2)2) is a highly active catalyst for ammonia borane dehydrocoupling at room temperature. Mainly linear polyaminoborane is obtained upon release of 1 equiv of H2. Mechanistic studies suggest that both hydrogen release and B–N coupling are metal-catalyzed and proceed via free aminoborane. Catalyst deactivation results from reaction with free BH3 that is formed by aminoborane rearrangement. Importantly, borane trapping with a simple amine allows for the observation of a TON that is unprecedented for a well-defined base metal catalyst.

The coupling of electron- and proton-transfer steps provides a general concept to control the driving force of redox reactions. N splitting of a molybdenum dinitrogen complex into nitrides coupled to a reaction with Brønsted acid is reported. Remarkably, our spectroscopic, kinetic, and computational mechanistic analysis attributes N-N bond cleavage to protonation in the periphery of an amide pincer ligands rather than the {Mo-N -Mo} core. The strong effect on electronic structure and ultimately the thermochemistry and kinetic barrier of N-N bond cleavage is an unusual case of a proton-coupled metal-to-ligand charge transfer process, highlighting the use of proton-responsive ligands for nitrogen fixation.

A simple imine clip-and-cleave concept has been developed for the selective hydroxylation of non-activated CH bonds in aliphatic aldehydes with dioxygen through a copper complex. The synthetic protocol involves reaction of a substrate aldehyde with N,N-diethyl-ethylendiamine to give the corresponding imine, which is used as a bidentate donor ligand forming a copper(I) complex with [Cu(CH CN) ][CF SO ]. After exposure of the reaction mixture to dioxygen acidic cleavage and aqueous workup liberates the corresponding β-hydroxylated aldehyde. The concept for the hydroxylation of trimethylacetaldehyde as well as adamantane and diamantane 1-carbaldehydes was investigated and the corresponding β-hydroxy aldehydes were obtained with high selectivities. The results of low temperature stopped-flow measurements indicate the formation of a bis(μ-oxido)dicopper complex as reactive intermediate. According to density functional theory (DFT, RI-BLYP-D3/def2-TZVP(SDD)/ COSMO(CH Cl )//RI-PBE-D3/def2-TZVP(SDD)) computations CH bonds suitably predisposed to the [Cu O ] core undergo hydroxylation in a concerted step with particularly low activation barriers, which explains the experimentally observed regioselectivities.