Merging Pincer Motifs and Potential Metal-Metal Cooperativity in Cobalt Dinitrogen Chemistry: Efficient Catalytic Silylation of N2 to N(SiMe3 )3

Using a pyrazolate-bridged dinucleating ligand that provides two proximate pincer-type PNN binding sites ("two-in-one pincer"), different synthetic routes have been developed towards its dicobalt(I) complex 2 that features a twice deprotonated ligand backbone and two weakly activated terminal N2 substrate ligands directed into the bimetallic pocket. Protonation of 2 is shown to occur at the ligand scaffold and to trigger conversion to a tetracobalt(I) complex 4 with two end-on μ1,2 -bridging N2 ; in THF 4 is labile and undergoes temperature-dependent N2 /triflate ligand exchange. These pyrazolate-based systems combine the potential of exhibiting both metal-metal and metal-ligand cooperativity, viz. two concepts that have emerged as promising design motifs for molecular N2 fixation catalysts. Complex 2 serves as an efficient (pre)catalyst for the reductive silylation of N2 into N(SiMe3 )3 (using KC8 and Me3 SiCl), yielding up to 240 equiv N(SiMe3 )3 per catalyst.

Enhanced Activation of Coordinated Dinitrogen with p-Block Lewis Acids

This Concept article highlights recent research on Lewis acid adducts of dinitrogen complexes, including our contributions. After a reminder of the early works, it is demonstrated that such kind of species offers a new platform for dinitrogen functionalization as well as valuable models for the understanding of elementary steps of (bio)catalytic cycles. When possible, parallels regarding this mode of activation from the orbital point of view are drawn between the different systems discussed herein.

Electrocatalytic Azide Oxidation Mediated by a Rh(PNP) Pincer Complex

One-electron oxidation of the rhodium(I) azido complex [Rh(N3 )(PNP)] (5), bearing the neutral, pyridine-based PNP ligand 2,6-bis(di-tert-butylphosphinomethyl)pyridine, leads to instantaneous and selective formation of the mononuclear rhodium(I) dinitrogen complex [Rh(N2 )(PNP)]+ (9+ ). Interestingly, complex 5 also acts as a catalyst for electrochemical N3- oxidation (Ep ≈-0.23 V vs. Fc+/0 ) in the presence of excess azide. This is of potential relevance for the design of azide-based and direct ammonia fuel cells, expelling only harmless dinitrogen as an exhaust gas.

Metalloradical Reactivity of RuI and Ru0 Stabilized by an Indole-Based Tripodal Tetraphosphine Ligand

The tripodal, tetradentate tris(1-(diphenylphosphanyl)-3-methyl-1H-indol-2-yl)phosphane PP3 -ligand 1 stabilizes Ru in the RuII , RuI , and Ru0 oxidation states. The octahedral [(PP3 )RuII (Cl)2 ] (2), distorted trigonal bipyramidal [(PP3 )RuI (Cl)] (3), and trigonal bipyramidal [(PP3 )Ru0 (N2 )] (4) complexes were isolated and characterized by single-crystal X-ray diffraction, NMR, EPR, IR, and ESI-MS. Both open-shell metalloradical RuI complex 3 and the closed-shell Ru0 complex 4 undergo facile (net) abstraction of a Cl atom from dichloromethane, resulting in formation of the corresponding RuII and RuI complexes 2 and 3, respectively.

Catalytic NH3 Synthesis using N2 /H2 at Molecular Transition Metal Complexes: Concepts for Lead Structure Determination using Computational Chemistry

While industrial NH₃ synthesis based on the Haber-Bosch-process was invented more than a century ago, there is still no molecular catalyst available which reduces N₂ in the reaction system N₂ /H₂ to NH₃ . As the many efforts of experimentally working research groups to develop a molecular catalyst for NH₃ synthesis from N₂ /H₂ have led to a variety of stoichiometric reductions it seems justified to undertake the attempt of systematizing the various approaches of how the N₂ molecule might be reduced to NH₃ with H₂ at a transition metal complex. In this contribution therefore a variety of intuition-based concepts are presented with the intention to show how the problem can be approached. While no claim for completeness is made, these concepts intend to generate a working plan for future research. Beyond this, it is suggested that these concepts should be evaluated with regard to experimental feasibility by checking barrier heights of single reaction steps and also by computation of whole catalytic cycles employing density functional theory (DFT) calculations. This serves as a tool which extends the empirically driven search process and expands it by computed insights which can be used to rationalize the various challenges which must be met.