Selvarajan Nagendran

The first functionalized tris(germylenes) 3 and 4 functioning as tridentate, tripodal ligands are reported through isolation of monomeric Cu( i ) complexes 6 and 7 , respectively. Their catalytic utility in CuAAC reactions is demonstrated.

Bis(germaamides) and their thio- and seleno- analogs are unknown. This work reports the isolation and characterization of the first examples of thio- and seleno-analogs of bis(germaamides) 7 and 8 containing two Ge(E)NR2 moieties (E = S, Se; R = SiMe3). These compounds were obtained by oxidizing the bulky pyrrole-imine dimeric ligand-stabilized bis(aminogermylene) 5 with elemental sulfur and selenium. This study also highlights the first-ever application of the bulky pyrrole-imine dimeric ligand 3 to simultaneously stabilize two low-valent centers (germylenes or stannylenes). Furthermore, the bonding in the thio- and seleno-bis(germaamides) 7 and 8 was investigated in detail using single–crystal X-ray diffraction and DFT calculations.

This study introduces a novel tripodal tris(germylene) 2, stabilized by TREN-tris(aminotroponimine) 1. Compound 2 was synthesized by treating the in situ-generated tri(lithium) salt of compound 1 with GeCl2·(1,4-dioxane). Interestingly, in its reactivity with various carboxylate salts, compound 2 exhibited divergent behavior. The reaction of 2 with sodium acetate and sodium pivalate yielded tris(germylene carboxylates), 3 and 4, respectively. However, 2’s reaction with sodium formate resulted in the unprecedented cationic µ3-oxo-bridged trigermanium derivative 5. It can be considered a hitherto unknown digermylene oxide-stabilized germylene cation, revealing that TREN-based tris(germylenes) can function as tripodal ligands. This aspect is realized in the mononuclear Cu(I) complexes 6 and 7 isolated in the reactions of tris(germylenes) 3 and 4 with CuI, where all three germylenes were coordinated simultaneously with one copper atom, confirming that TREN-based tris(germylene) can indeed function as tripodal ligands. Furthermore, the utility of these copper complexes, 6 and 7, as catalysts in the azide-alkyne cycloaddition (CuAAC) reactions is also demonstrated.

The first examples of air and water stable bis(germylenes) 5–9 and bis(germacarbonyl) compounds 10–12 are reported. Bis(germylene monochloride) 5 is isolated by starting from bis(dipyrromethene) 4, which in turn has been synthesized by oxidizing bis(dipyrromethane) 3 using DDQ. Terephthaldehyde 1 and mesityl pyrrole 2 were the precursors for compound 3. Bis(germylene monochloride) 5 reacts with alcohols and phenol in the presence of a mild base (Cs₂CO₃) to afford bis(germylene alkoxides) 6–7 and bis(germylene phenoxide) 8, respectively. Compound 5′s reaction with sodium pyrrolide has resulted in bis(germylene pyrrolide) 9. Further, compounds 7 and 9 react with elemental sulfur and selenium under ambient conditions, resulting in bis(germacarbonyl) compounds 10–12. The UV‐Vis spectroscopic investigations on compounds 4–12 are done experimentally and computationally.

Guest editors Selvarajan Nagendran, Ramaswamy Murugavel and Eric Rivard introduce the Dalton Transactions “Main group element compounds in materials and catalysis” themed collection.

Catalysis using low‐valent main‐group compounds is usually done under inert conditions; no example of such catalysis has been doable entirely in ambient conditions until now. This aspect is addressed in this work through an air‐ and water‐stable germylene cation [DPMGe][(OH)B(C₆F₅)₃] (2) (DPM=dipyrromethene); it efficiently catalyzes aldehyde and ketone hydrosilylations under ambient conditions. Detailed theoretical studies reveal that compound 2’s stability is bolstered by the interaction between the anion and germanium's frontier orbitals. However, the detachment of the anion (in the solution) alters the capability of compound 2 to render exceptional catalytic efficiency. Compound 2 was synthesized under ambient conditions by the equimolar reaction of DPMGeOH (1) with B(C₆F₅)₃.

The aminotroponiminate (ATI) ligand stabilized germylene cation [(i‐Bu)₂ATIGe][B(C₆F₅)₄] (2) is found to be an efficient low‐valent main‐group catalyst for the cyanosilylation of aldehydes and ketones (ATI=aminotroponiminate). It was synthesized by reacting [(i‐Bu)₂ATIGeCl] (1) with Na[B(C₆F₅)₄]. The catalytic cyanosilylation of diverse aliphatic and aromatic carbonyl compounds (aldehydes and ketones) using 0.075–0.75 mol% of compound 2 was completed within 5–45 min. The catalytic efficiency seen with aliphatic aldehydes was around 15,800 h⁻¹, making compound 2 a capable low‐valent main‐group catalyst for the aldehyde and ketone cyanosilylation reactions. Further, DFT calculations reveal a pronounced charge localization at the germanium atom of compound 2, leading to its superior catalytic performance.

Low‐valent main group compounds that fluoresce in the solid‐state were previously unknown. To address this, we investigated room‐temperature photoluminescence from a series of crystals of germylenes 3–8 in this article; they exhibited emissions nearly reaching the NIR. Germylene carboxylates (3–8) were synthesized by reacting dipyrromethene stabilized germylene pyrrolide (2) with carboxylic acids such as acetic acid, trifluoroacetic acid, benzoic acid, p‐cyanobenzoic acid, p‐nitrobenzoic acid, and acetylsalicylic acid.