Demyan E. Prokopchuk

Structural properties of trans hydrido–hydroxo M(H)(OH)(NH2CMe2CMe2NH2)(PPh3)2 (M = Ru, Os) complexes and their proton exchange behaviour with water in solution

We report the synthesis of Ru(II) and Os(II) trans hydrido-hydroxo complexes by reacting the unsaturated amido complexes MH(NHCMe2CMe2NH2)(PPh3)2 (M = Ru, Os) with stoichiometric amounts of water. Proton exchange is rapid at room temperature between the amine/water/hydroxide moieties which leads to signal averaging of the NMR properties which can be slowed at low temperature in order to see resonances of separate complexes. These compounds can also be cleanly converted back to their starting complexes by dehydration in the presence of 3 Å molecular sieves. X-ray crystal structures of these Ru(II) and Os(II) trans hydrido-hydroxo complexes reveal that the unit cell contains an additional molecule of water trapped in the crystal lattice which hydrogen bonds with a neighbouring hydroxo ligand, forming a water bridged dimer in the solid state. Although there are many cases of oxidative addition of water to transition metal complexes, relatively few cases are well characterized where water addition occurs via metal-ligand cooperation (bifunctional addition) without altering the oxidation state of the metal center.

Catalytic N2 Reduction to Silylamines and Thermodynamics of N2 Binding at Square Planar Fe

The geometric constraints imposed by a tetradentate P4N2 ligand play an essential role in stabilizing square planar Fe complexes with changes in metal oxidation state. The square pyramidal Fe0(N2)(P4N2) complex catalyzes the conversion of N2 to N(SiR3)3 (R = Me, Et) at room temperature, representing the highest turnover number of any Fe-based N2 silylation catalyst to date (up to 65 equiv N(SiMe3)3 per Fe center). Elevated N2 pressures (>1 atm) have a dramatic effect on catalysis, increasing N2 solubility and the thermodynamic N2 binding affinity at Fe0(N2)(P4N2). A combination of high-pressure electrochemistry and variable-temperature UV-vis spectroscopy were used to obtain thermodynamic measurements of N2 binding. In addition, X-ray crystallography, 57Fe Mössbauer spectroscopy, and EPR spectroscopy were used to fully characterize these new compounds. Analysis of Fe0, FeI, and FeII complexes reveals that the free energy of N2 binding across three oxidation states spans more than 37 kcal mol-1.

Intramolecular CH/OH Bond Cleavage with Water and Alcohol Using a Phosphine‐Free Ruthenium Carbene NCN Pincer Complex

Transition metal complexes that exhibit metal-ligand cooperative reactivity could be suitable candidates for applications in water splitting. Ideally, the ligands around the metal should not contain oxidizable donor atoms, such as phosphines. With this goal in mind, we report new phosphine-free ruthenium NCN pincer complexes with a central N-heterocyclic carbene donor and methylpyridyl N-donors. Reaction with base generates a neutral, dearomatized alkoxo-amido complex, which has been structurally and spectroscopically characterized. The tert-butoxide ligand facilitates regioselective, intramolecular proton transfer through a CH/OH bond cleavage process occurring at room temperature. Kinetic and thermodynamic data have been obtained by VT NMR experiments; DFT calculations support the observed behavior. Isolation and structural characterization of a doubly dearomatized phosphine complex also strongly supports our mechanistic proposal. The alkoxo-amido complex reacts with water to form a dearomatized ruthenium hydroxide complex, a first step towards phosphine-free metal-ligand cooperative water splitting.

Reactivity of an All‐Ferrous Iron–Nitrogen Heterocubane under Reductive and Oxidative Conditions

The reactivity of the all-ferrous FeN heterocubane [Fe4 (Ntrop)4 ] (1) with i) Brønsted acids, ii) σ-donors, iii) σ-donors/π-acceptors, and iv) one-electron oxidants has been investigated (trop = 5H-dibenzo[a,d]cyclo-hepten-5-yl). 1 showed self-re-assembling after reactions with i) and proved surprisingly inert in reactions with ii) and iii), with the exception of CO. Reductive and oxidative cluster degradation was observed in reactions with CO and TEMPO, respectively. These reactions yielded new cluster compounds, namely a trinuclear bis(μ3 -imido) 48 electron complex in the former case and a tetranuclear all ferric μ-oxo-μ-imido species in the latter case. Characterization techniques include NMR and in situ IR spectroscopy, single crystal X-ray analysis, Mössbauer spectroscopy, cyclic voltammetry, magnetic susceptibility measurements, and DFT calculations.