Mononuclear/Binuclear [VIVO]/[VVO2] Complexes Derived from 1,3-Diaminoguanidine and Their Catalytic Application for the Oxidation of Benzoin via Oxygen Atom Transfer

Ligands H₄sal-dag (I) and H₄Brsal-dag (II) derived from 1,3-diaminoguanidine and salicylaldehyde or 5-bromosalicylaldehyde react with one or 2 mol equivalent of vanadium precursor to give two different series of vanadium complexes. Thus, complexes [V^IVO(H₂sal-dag) (H₂O)] (1) and [V^IVO(H₂Brsal-dag) (H₂O)] (2) were isolated by the reaction of an equimolar ratio of these ligands with [V^IVO(acac)₂] in MeOH. In the presence of K⁺/Cs⁺ ion and using aerially oxidized [V^IVO(acac)₂], the above reaction gave complexes [K(H₂O){V^VO₂(H₂sal-dag)}]₂ (3), [Cs(H₂O){V^VO₂(H₂sal-dag)}]₂ (4), [K(H₂O){VO₂(H₂Brsal-dag)}]₂ (5), and [Cs(H₂O){V^VO₂(H₂Brsal-dag)}]₂ (6), which could also be isolated by direct aerial oxidation of complexes 1 and 2 in MeOH in the presence of K⁺/Cs⁺ ion. Complexes [(H₂O)V^IVO(Hsal-dag)V^VO₂] (7) and [(H₂O)V^IVO(HBrsal-dag)V^VO₂] (8) were isolated upon increasing the ligand-to-vanadium precursor molar ratio to 1:2 under an air atmosphere. When I and II were reacted with aerially oxidized [V^IVO(acac)₂] in a 1:2 molar ratio in MeOH in the presence of K⁺/Cs⁺ ion, they formed [K(H₂O)₅{(V^VO₂)₂(Hsal-dag)}]₂ (9), [Cs(H₂O)₂{(V^VO₂)₂(Hsal-dag)}]₂ (10), [K₂(H₂O)₄{(V^VO₂)₂(Brsal-dag)}]₂ (11), and [Cs₂(H₂O)₄{(V^VO₂)₂(Brsal-dag)}]₂ (12). The structures of complexes 3, 4, 5, and 9 determined by single-crystal X-ray diffraction study confirm the mono-, bi-, tri-, and tetra-anionic behaviors of the ligands. All complexes were found to be an effective catalyst for the oxidation of benzoin to benzil via oxygen atom transfer (OAT) between DMSO and benzoin. Under aerobic condition, this oxidation also proceeds effectively in the absence of DMSO. Electron paramagnetic resonance and ⁵¹V NMR studies demonstrated the active role of a stable V(IV) intermediate during OAT between DMSO and benzoin.

Crystal structure of (E)-amino(2-(thiazol-2-ylmethylene)hydrazineyl)methaniminium nitrate, C10H16N12O6S2

C10H16N12O6S2, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 7.6977(2) Å, b = 11.5353(3) Å, c = 11.7533(3) Å, α = 67.973(2)°, β = 87.916(2)°, γ = 88.347(2)°, V = 966.69(5) Å3, Z = 2, R gt (F) = 0.0290, wR ref (F 2) = 0.0818, T = 170K.

Crystal structure of bis(2-((E)-5-chloro-2-hydroxybenzylidene)hydrazineyl)methaniminium trifluoroacetate dihydrate, C34H36Cl4N10O12

C34H36Cl4N10O12, triclinic, P 1 ‾ $P‾{1}$ (no. 2), a = 10.3071(3) Å, b = 13.4696(4) Å, c = 16.1893(4) Å, α = 81.467(2)°, β = 77.726(2)°, γ = 82.055(2)°, V = 2158.64(11) Å3, Z = 2, R gt (F) = 0.0539, wR ref (F 2) = 0.1609, T = 170 K.

The crystal structure of (2E,2′E)-,2,2′-bis[1-(2-pyrazinyl)ethylidene]carbonimidic dihydrazide, C13H15N9

C13H15N9, monoclinic, C2/c (no. 15), a = 22.827(5) Å, b = 7.8830(16) Å, c = 16.020(3) Å, β = 98.95(3)°, V = 2847.6(10) Å3, Z = 8, R gt(F) = 0.0416, wR ref(F 2) = 0.1331, T = 293(2) K.

Iminoguanidines: from anion recognition and separation to carbon capture

Iminoguanidines, first reported in 1898, have received renewed attention in the last 5 years due to their ability to recognize and separate anions from competitive aqueous environments. Iminoguanidines display high recognition abilities towards hydrophilic oxyanions (e.g., sulfate, chromate, carbonate) through strong and complementary hydrogen bonding from the guanidinium groups. This feature article reviews the fundamental anion recognition chemistry of iminoguanidines, as well as real-world applications including sulfate removal from seawater and CO₂ capture for climate change mitigations.