Reversible Binding of Hydrogen and Styrene Coordination on a Manganese Phosphenium Complex

Abstract

The reactions of two complexes [(RNHP)Mn(CO)4] (RNHP = N‐arylated N‐heterocyclic phosphenium) with H2 at elevated pressure (≈ 4 bar) were studied by NMR spectroscopy. Irradiation with UV light initialized in one case (5a, R = Dipp) the unselective formation of (RNHP‐H)MnH(CO)4] (6a) via cooperative addition of H2 across the Mn=P double bond. In the other case (5b, R = Mes), addition of H2 was unobservable and the reaction proceeded via decarbonylation to a dimeric species [(RNHP)2Mn2(CO)7] (7b) that was isolated and identified spectroscopically. Taking into account the outcome of further reaction studies under various conditions in the absence and presence of H2, both transformations can be explained in the context of a common mechanism involving decarbonylation to 7a,b as the first step, and the different outcome is attributable to the fact that 7b is unreactive towards both H2 and CO while 7a is not. DFT studies relate this divergence to deviations in the molecular constitution and stability arising from a different level of steric congestion. Preliminary studies suggest further that 5a/H2 as well as 6a enable the photo‐induced hydrogenation of styrene to ethyl benzene, even if the mechanism and possibly catalytic nature of this process remain yet unknown.

N-Heterocyclic Phosphenium Complexes of Vanadium

“…A preliminary exploration of the chemical properties of the new NHP carbonyl vanadates was triggered by our interest in establishing their potential in the activation of molecular hydrogen. As the activation of H 2 by manganese complexes IV R depends critically on the presence of sterically demanding NDipp-substituents, 19 we focused our attention on transformations involving 2a. However, in contrast to IV Dipp , a reaction of 2a with H 2 at atmospheric or elevated pressure (4 bar H 2 ) could be initiated by neither prolonged heating (60 °C) nor irradiation, and only unreacted starting materials were observable by NMR spectroscopy under all conditions.…”

“…RI-DFT calculations were carried out on the bwForCluster Justus 2 with the TURBOMOLE program suite (version 7.5.2020) using the theoretical model established in previous studies. , Energy optimization of molecular structures and calculation of harmonic frequencies were carried out using the ωB97x-D functional with a def2-SVP basis set on isolated molecules, simulating gas-phase conditions, or using a conductor-like screening model with the solvent parameters for THF to simulate solvation effects, respectively. Stationary points located were identified as local minima on the energy hypersurface by harmonic vibrational frequency calculations at the same level.…”

Facile synthesis of five-membered cyclic RE2P–H iron(0) complexes

“…12 Remarkably, this is not the case for six-membered cyclic P–H phosphanes (phosphinanes), having an N- and/or O-substituted P atom. 13 Also mono- and/or diheteroatom-substituted phosphane complexes with a P–H unit present intrinsic problems, and reported synthetic protocols for N/N, 12,14–31 N/O 32–35 or O/O 36–40 substituted phosphane complexes were individually tailored; a general procedure seems to be absent. Early results of diheteroatom-substituted P–H phosphanes focused on their Fe(CO) 4 complexes (Fig.…”