Radical Behavior of CO2versus its Deoxygenation Promoted by Vanadium Aryloxide Complexes: How the Geometry of Intermediate CO2-Adducts Determines the Reactivity

Erythronium Bonds: Noncovalent Interactions Involving Group 5 Elements as Electron-Density Acceptors

Analyses of the Cambridge Structural Database and theoretical calculations (PBE0-D3/def2-TZVP level, atoms-in-molecules, natural bond orbital studies) prove the formation of net attractive noncovalent interactions between group 5 elements and electron-rich atoms (neutral or anionic). These kinds of bonding are markedly different from coordination bonds formed by the same elements and possess the distinctive features of σ-hole interactions. The term erythronium bond is proposed to denote these bonds. X-ray structures of vanadate-dependent bromoperoxidases show that these interactions are present also in biological systems.

Non-redox reactivity of V(ii) and Fe(ii) formamidinates towards CO2 resulting in the formation of novel M(ii) carbamates

Multiple CO2 insertions into the M–N bonds of V(ii) and Fe(ii) bis(formamidinates) led to the isolation of three novel carbamates. The CO2 insertion effectivity depended on the solvent used and the metal centre's coordination sphere geometry.

Linear End-On Coordination Modes of CO2

The second case of linear end-on and evidence for an unprecedented bridging end-on coordination mode of CO₂ have been discovered for vanadium aryloxide complexes of the tetradentate ligand system (ONNO)^2- (ONNO=2,4-Me₂ -2-(OH) C₆ H₂ CH₂ ]₂ N(CH₂ )₂ NMe₂ ). The reaction of divalent (ONNO)V^II (TMEDA) with CO₂ and under the appropriate reaction conditions affords the trivalent (ONNO)V^III (OH)(η¹ -CO₂ ) resulting from an intermediate CO₂ deoxygenation pathway followed by H-atom abstraction from the aromatic solvent, and CO₂ fixation. In contrast, the reduction of trivalent (ONNO)V^III Cl(THF) with K, followed by exposure to CO₂ in ethereal solvent, afforded the dinuclear [(ONNO)V^II ]₂ (μ_, η¹ -CO₂ ).

Reaction of CO2 with a Vanadium(II) Aryl Oxide: Synergistic Activation of CO2 /Oxo Groups towards H-Atom Radical Abstraction

Treatment of divalent (ONNO)V(TMEDA) (1; ONNO=[2,4-Me₂ -2-(OH)C₆ H₂ CH₂ ]₂ N(CH₂ )₂ NMe₂ ) with CO₂ afforded [(ONNO)V]₂ (μ-OH)(μ-formate) (2). Whereas the bridging hydroxo and formate groups both originated from CO₂ , the H atoms present on the two residues were obtained through H-atom radical abstraction from the solvent. DFT calculations revealed an initially linear CO₂ bonding mode, followed by deoxygenation, and highlighted a synergistic effect between the so-formed oxo group and an additional bridging CO₂ residue in promoting radical behavior.