Two novel rhenium complexes derived from [ReO(OMe)Cl2(dpphen)] – Synthesis, crystal structure, spectroscopic and magnetic properties

Ammonia Formation Catalyzed by a Dinitrogen-Bridged Dirhenium Complex Bearing PNP-Pincer Ligands under Mild Reaction Conditions*

A series of rhenium complexes bearing a pyridine-based PNP-type pincer ligand are synthesized from rhenium phosphine complexes as precursors. A dinitrogen-bridged dirhenium complex bearing the PNP-type pincer ligands catalytically converts dinitrogen into ammonia during the reaction with KC₈ as a reductant and [HPCy₃ ]BAr^F ₄ (Cy=cyclohexyl, Ar^F =3,5-(CF₃ )₂ C₆ H₃ ) as a proton source at -78 °C to afford 8.4 equiv of ammonia based on the rhenium atom of the catalyst. The rhenium-dinitrogen complex also catalyzes silylation of dinitrogen in the reaction with KC₈ as a reductant and Me₃ SiCl as a silylating reagent under ambient reaction conditions to afford 11.7 equiv of tris(trimethylsilyl)amine based on the rhenium atom of the catalyst. These results demonstrate the first successful example of catalytic nitrogen fixation under mild reaction conditions using rhenium-dinitrogen complexes as catalysts.

Dinuclear and Mononuclear Rhenium Coordination Compounds upon Employment of a Schiff-Base Triol Ligand: Structural, Magnetic, and Computational Studies

The 1:1 reaction of trans-[Re^IIICl₃(PPh₃)₂(MeCN)] with 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol, H₃L, in toluene gave the dinuclear complex [Re^III₂Cl₄(HL)(PPh₃)]·2C₇H₈ (1·2C₇H₈), while the 1:2 reaction led to the formation of complex [Re^IVCl₂(HL)(PPh₃)] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL^2-, forming chelate rings around the metallic centers. In addition, 1·2C₇H₈ displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex [Re^IVCl₂(HL)(PPh₃)] (2) the two aromatic ligands, HL^2- and PPh₃, occupy axial positions, with the terminal Cl^- ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C₇H₈ and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ²π⁴δ¹δ^*1 bond order of 3 for 1·2C₇H₈. In addition, the absorption spectrum of 1·2C₇H₈ in CH₂Cl₂ was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C₇H₈ is the first dinuclear rhenium complex with a triple metal-metal bond between trivalent rhenium centers.