Lantern-Type Divanadium Complexes with Bridging Ligands: Short Metal-Metal Bonds with High Multiple Bond Orders

Torsion Effects Beyond the δ Bond and the Role of π Metal-Ligand Interactions

Previous studies on bimetallic paddlewheel compounds have established a direct correlation between metal-metal distance and ligand torsion angles, leading to the rule that higher torsion results in longer metal-metal bond distances. Here, the new discovery based on diarylformamidinate Ru₂⁵⁺ paddlewheel compounds [Ru2Cl(DArF)4] that show an opposite behavior is reported: higher torsions lead to shorter metal-metal distances. This discovery challenges the assumption that internal rotation solely impacts the δ bond. By combining experimental and theoretical techniques, it is demostrated that this trend is associated with previously overlooked π metal-ligand interactions. These π metal-ligand interactions are a direct consequence of the paddlewheel structure and the conjugated nature of the bidentate ligands. This findings offer far-reaching insights into the influence of equatorial ligands and their π-conjugation characteristics on the electronic properties of paddlewheel complexes. That this effect is not exclusive of diruthenium compounds but also occurs in other bimetallic cores such as ditungsten or dirhodium is demonstrated, and with other ligands showing allyl type conjugation. These results provide a novel approach for fine-tuning the properties of these compounds with significant implications for materials design.

Vanadium pyridonates: dimerization, redox behaviour, and metal-ligand cooperativity

The synthesis, structure, and reactivity of vanadium pyridonate complexes are described. Vanadium(III) pyridonate complexes were accessed through protonolysis and reduction of a tetrakis(amido)vanadium(IV) starting material. Bis(pyridonate) vanadium(IV) precursors could be isolated depending on the amount of proteoligand added. The targeted vanadium(III) species tend to form dimers, but monomeric complexes can be achieved in the presence of neutral donors such as amines or pyridine derivatives or through the use of sterically demanding proligands. The reduction process is proposed to involve dimeric intermediates and be mediated by the amine released from protonolysis, thereby forming the corresponding imine as a byproduct. Isolated amine complexes of vanadium(III) are presented. In contrast, bis(amidate)vanadium(IV) complexes were not found to undergo a similar reduction. This work informs on design principles for the synthesis and application of new vanadium pyridonate catalysts for transformations involving dimerization and PCET for changes in oxidation state.

A supported Cr-Cr sextuple bond in an all-metal cluster

Herein, we report a distinct Cr-Cr sextuple bond with ultra-short length stabilized by equatorial alkali metals. Bonding analyses indicate that the two desired 4p-pi bonds failed to be formed but...