Syntheses and structures of N,C,N-stabilized antimony chalcogenides

Oxidative addition of diaryldichalcogenides to the diferrocenylphosphenium ion: synthesis, structure and organocatalytic activity

The reaction of the phosphenium ion [Fc2P]+ with dichalcogenides gace rise to the respective phosphonium ions [Fc2P(ChR)2]+ (Ch = S, Se, Te; R = Ph, Fc, biphen), which were employed in chalcogen bond mediated Michael additions.

Advancing metallomimetic catalysis through structural constraints of cationic PIII species

In recent years, the concept of structural constraints on the main-group (MG) centers has emerged as a powerful strategy to enhance their reactivity. Among these, structurally constrained (SC) phosphorus centers have garnered significant attention due to their ability to cycle between two stable oxidation states, P(III) and P(V), making them highly promising for small molecule activation and catalysis. Structural constraints grant phosphorus centers transition metal (TM)-like reactivity, enabling the activation of small molecules by these SC P(III) centers, a reactivity previously inaccessible with conventional phosphines or other phosphorus derivatives. This feature article reviews recent advances in the chemistry of cationic, structurally constrained P(III) (CSCP) compounds, emphasizing their ability to mimic TM behavior in small-molecule activation and catalysis, particularly through the key elementary steps of TM-based catalysis, such as oxidative addition (OA), migratory insertion (MI), ligand metathesis (LM), reductive elimination (RE), etc. The development of these SC cationic P(III) species highlights the interplay between structural constraints and cationic charge, facilitating analogous metallomimetic reactivity in other main-group elements.

Tetra-Cationic Distibane Stabilized by Bis(α-iminopyridine) and Its Reactivity

The work establishes the salt of a tetra-cationic distibane, [L2Sb2][CF3SO3]4 = [1]2[OTf]4 (CF3SO3 = OTf), stabilized by a bis(α-iminopyridine) ligand L, defying the Coulombic repulsion. The synthetic approach involved a dehydrocoupling reaction when a mixture of L and Sb(OTf)3 in a 1:1 ratio was treated with Et3SiH/LiBEt3H as the hydride source. Compound [1]2[OTf]4 was also achieved from [LSbCl][OTf]2 as a precursor and using Et3SiH. Dissolution of [1]2[OTf]4 in polar solvents unveiled the formation of the persistent L-stabilized dicationic Sb(II) radical monomer [1][OTf]2, while the addition of Me3SiOTf regenerated the dimer in the salt [1]2[OTf]4. The homolytic cleavage of the Sb-Sb bond in [1]24+ has manifested in exchange reactions between [1]2[OTf]4 and Ph2Ch2 (Ch = S, Se), giving [LSb(SPh)][OTf]2 = [2][OTf]2 and [LSb(SePh)][OTf]2 = [3][OTf]2, respectively, in acetonitrile. Reaction between [1]2[OTf]4 and p-benzoquinone gave [L2Sb2(C6H4O2)][OTf]4 = [4][OTf]4. An interesting oxygen atom insertion reaction occurred when [1]2[OTf]4 was treated with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) to give [L2Sb2O][ OTf]4 = [5][OTf]4. The oxo-bridged compound [5][OTf]4 was also obtained from exposure of [1]2[OTf]4 in open air. The strong Mn-Mn bond in [Mn2(CO)10] could be cleaved by reacting with [1]2[OTf]4 in the presence of pyridine to form [LSbMn(CO)5][ OTf]2 = [6][OTf]2. On the other hand, the reaction between [Co2(CO)8] and [1]2[OTf]4 gave the oxidative addition product [L2Sb2Co(CO)3][OTf]3 = [7][OTf]3. The compounds were characterized both in the solid and solution states. Computational studies gave a comprehensive understanding of the experimental findings.

Antimony Redox Catalysis: Hydroboration of Disulfides through Unique Sb(I)/Sb(III) Redox Cycling

The stibinidene ArSbI (Ar = [2,6-(tBuN═CH)2-C6H3], 1) reacts with S2Tol2 (Tol = p-tolyl) to form ArSbIII(STol)2 (2), which upon treatment with pinacolborane, regenerates 1. These processes unveil an unprecedented antimony redox catalysis involving Sb(I)/Sb(III) cycling for the hydroboration of organic disulfides. Elementary reaction studies and density functional theory calculations support that the catalysis mimics transition metal processes, proceeding through oxidative addition, ligand metathesis, and reductive elimination. The thiophenols and sulfidoborates generated from the hydroboration of disulfides react in situ with α,β-unsaturated carbonyl compounds with the assistance of 1 as a base catalyst. These tandem reactions establish a one-pot synthetic method for β-sulfido carbonyl compounds, in which a stibinidene functions as a redox catalyst and a base catalyst successively, illustrating the versatility and efficiency of antimony catalysis in organic synthesis.

Recent advances in the stabilization of monomeric stibinidene chalcogenides and stibine chalcogenides

The elucidation of novel bonding situations at heavy p-block elements has greatly advanced recent efforts to access useful reactivity at earth-abundant main-group elements. Molecules with unsaturated bonds between heavier, electropositive elements and lighter, electronegative elements are often highly polarized and competent in small-molecule activations, but the reactivity of these molecules may be quenched by self-association of monomers to form oligomeric species where the polar, unsaturated groups are assembled in a head-to-tail fashion. In this Frontier, we discuss the synthetic strategies employed to isolate monomeric σ2,λ3-stibinidene chalcogenides (RSbCh) and monomeric σ4,λ5-stibine chalcogenides (R3SbCh). These classes of molecules each feature polarized antimony-chalcogenide bonds (Sb = Ch/Sb+-Ch-). We highlight how the synthesis and isolation of these molecules has led to the discovery of novel reactivity and has shed light on fundamental aspects of inorganic structure and bonding. Despite these advances, there are critical aspects of this chemistry that remain underdeveloped and we provide our perspective on yet-unrealized synthetic targets that may be achieved with the continued development of the strategies described herein.

Organopnictogen(III) bis(arylthiolates) containing NCN-aryl pincer ligands: from synthesis and characterization to reactivity

Salt elimination reactions between organopnictogen(III) dichlorides, RPnCl₂ [R¹ = 2,6-(Me₂NCH₂)₂C₆H₃, Pn = Sb (1), Bi (2); R² = 2,6-{MeN(CH₂CH₂)₂NCH₂}₂C₆H₃, Pn = Sb (3), Bi (4); R³ = 2,6-{O(CH₂CH₂)₂NCH₂}₂C₆H₃, Pn = Sb (5), Bi (6)] and 2 equivalents of KSC₆H₃Me₂-2,6 afforded the isolation of a series of new NCN-chelated monoorganopnictogen(III) bis(arylthiolates), RPn(SC₆H₃Me₂-2,6)₂ [R¹, Pn = Sb (7), Bi (8); R², Pn = Sb (9), Bi (10); R³, Pn = Sb (11), Bi (12)]. Compounds 7 and 8 are unstable upon exposure to a dry O₂ atmosphere and their aerobic decomposition yields the monoorganopnictogen(III) oxides, cyclo-[2,6-(Me₂NCH₂)₂C₆H₃Pn(μ-O)]₂ [Pn = Sb (13), Bi (14)] with concomitant formation of the corresponding disulfide, ArS-SAr (Ar = C₆H₃Me₂-2,6). The oxidative addition of elemental sulfur or selenium to 7 undergoes a similar reaction path and gives stable heterocyclic species cyclo-[2,6-(Me₂NCH₂)₂C₆H₃Sb(μ-E)]₂ [E = S (15), Se (16)]. The reaction of 12 with I₂ (1 : 1 molar ratio) gives the diiodide [2,6-{O(CH₂CH₂)₂NCH₂}₂C₆H₃]BiI₂ (17), along with the S-S oxidative coupling by-product, ArS-SAr. The use of an excess of iodine affords the crystallization of a 2 : 1 iodine adduct of 17 (17·0.5I₂), built through halogen bonding. All new compounds were characterized by multinuclear NMR spectroscopy and ESI-MS as well as single crystal X-ray diffraction (except compounds 9 and 10).