Strong Lewis acids of air-stable binuclear triphenylantimony(V) complexes and their catalytic application in C–C bond-forming reactions

Utilizing bis(imino)dihydroacridanide pincer ligands in p-block chemistry: synthesis and catalysis of an antimony monocation salt

We present the synthesis and characterization of an Sb(III) monocation salt stabilized by a bulky bis(imino)dihydroacridanide pincer ligand. The Lewis acidity of the Sb cation is quantified using the Guttmann-Beckett method and confirmed by its reaction with 4-dimethylaminopyridine, which forms a Lewis acid-base adduct. This Sb cation exhibits catalytic activity in the cyanosilylation of arylketones. The electronic structure of the Sb cation as well as the mechanism of the catalytic transformation are explored by density functional theory computations.

Structural and Dynamic Properties of Gallium Alkoxides

A comparison of chlorido-gallium functionalized alkoxides as precursors for aerosol-assisted chemical vapor deposition (AACVD) was carried out. Variable-temperature (VT)-NMR studies were used to probe the fluxional behavior of these alkoxides in solution, and hence their utility as precursors. The synthesis involved the initial isolation of the dimer [GaCl(NMe₂)₂]₂ via a salt metathesis route from GaCl₃ and 2 equiv of LiNMe₂. This dimer was then reacted with 4 equiv of HOCH₂CH₂CH₂NEt₂, resulting in the formation of Ga[μ-(OCH₂CH₂CH₂NEt₂)₂GaCl₂]₃ (1). Mass spectrometry and VT-NMR confirmed the oligomeric structure of 1. Tuning of the ligand properties, namely, the chain length and substituents on N, resulted in formation of the monomers [GaCl(OR)₂] (R = CH₂CH₂NEt₂, (2); CH₂CH₂CH₂NMe₂, (3)). VT-NMR studies, supported by density functional theory calculations, confirmed that the ligands in both 2 and 3 possess a hemilabile coordination to the gallium center, owing to either a shorter carbon backbone (2) or less steric hindrance (3). Both 2 and 3 were selected for use as precursors for AACVD: deposition at 450 °C gave thin films of amorphous Ga₂O₃, which were subsequently annealed at 1000 °C to afford crystalline Ga₂O₃ material. The films were fully characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible spectroscopy, and energy dispersive X-ray analysis.

Phosphonium–stibonium and bis-stibonium cations as pnictogen-bonding catalysts for the transfer hydrogenation of quinolines

Bifunctional group 15 dications are effective transfer hydrogenation catalysts, the activity of which culminates in the case of the bis-stibonium dication [o-C₆H₄(SbMePh₂)₂]²⁺.

Digging the Sigma-Hole of Organoantimony Lewis Acids by Oxidation

The development of group 15 Lewis acids is an area of active investigation that has led to numerous advances in anion sensing and catalysis. While phosphorus has drawn considerable attention, emerging research shows that organoantimony(III) reagents may also act as potent Lewis acids. Comparison of the properties of SbPh₃ , Sb(C₆ F₅ )₃ , and SbAr^F ₃ with those of their tetrachlorocatecholate analogues SbPh₃ Cat, Sb(C₆ F₅ )₃ Cat, and SbAr^F ₃ Cat (Cat=o-O₂ C₆ Cl₄ , Ar^F =3,5-(CF₃ )₂ C₆ H₃ ) demonstrates that the Lewis acidity of electron deficient organoantimony(III) reagents can be readily enhanced by oxidation to the +V state-as verified by binding studies, organic reaction catalysis, and computational studies. The results are rationalized by explaining that oxidation of the antimony center leads to a lowering of the accepting σ* orbital and a deeper carving of the associated σ-hole.

Influence of the catalyst structure in the cycloaddition of isocyanates to oxiranes promoted by tetraarylstibonium cations

In the context of our work on electron deficient group 15 cations as Lewis acid catalysts, we have synthesized the triflate salts of a series of tetraarylstibonium cations of general formula [ArSbPh3]+ with Ar = Mes (4+), o-(dimethylamino)phenyl (5+), and o-((dimethylamino)methyl)phenyl (6+). These new cationic antimony derivatives, along with the known [Ph4Sb]+ (1+), 1-naphthyltriphenylstibonium (2+), and [(Ant)SbPh3]+ (3+), have been evaluated as catalysts for the cycloaddition of oxiranes and isocyanates under mild conditions. While all stibonium cations favor the 3,4-oxazolidinone products, the reactivities of 5+ and 6+ are hindered by the ancillary amino donor which quenches the Lewis acidity of the antimony center. A comparison of the other stibonium cations shows that 4+ is the most selective catalyst.

Coordination of a stibine oxide to a Lewis acidic stiborane at the upper rim of the biphenylene backbone

The biphenylene backbone is used to support a stibine oxide stabilized intramolecularly by a SbO → Sb(v) donor–acceptor interaction.

Activation of an Au-Cl Bond by a Pendent SbIII Lewis Acid: Impact on Structure and Catalytic Activity

With the objective of identifying new coordination modes of ambiphilic ligands, we have investigated the bidentate Sb/P ligands (o-(Ph₂ P)C₆ H₄ )SbCl₂ (L^Cl ) and (o-(Ph₂ P)C₆ H₄ )SbPh₂ (L^Ph ). Reaction of these ligands with (tht)AuCl affords the monoligated species L^Cl AuCl (1) and L^Ph AuCl (2), respectively, in which the antimony centers are only weakly engaged with the coordinated gold atom. Treatment of 1 with PPh₃ induces an intramolecular transfer of a chloride ligand from gold to antimony to form the zwitterionic species o-(Cl₃ Sb)C₆ H₄ (Ph₂ P)Au(PPh₃ ) (3). Natural bond orbital (NBO) calculations show that the antimony and gold centers are involved in weak Sb→Au and Au→Sb interactions, the latter reflecting the Lewis acidity of the pendent antimony group. Finally, we demonstrate that the ability of the antimony center in 1 to abstract a gold-bound chloride in the presence of a Lewis basic substrate may be utilized to activate the gold center for the electrophilic cycloisomerization of propargylic amides.

Bipyridine complexes of E3+ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)3 and synthons for EI and EV cations

Triflate salts of trications [(bipy)₂E]³⁺ ([6E][OTf]₃) and [(tbbipy)₂E]³⁺ ([6′E][OTf]₃) (bipy = 2,2′-bipyridine, tbbipy = 4,4′-di-^tbutyl-2,2′-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized.

Triflate salts of trications [(bipy)₂E]³⁺ ([6E][OTf]₃) and [(tbbipy)₂E]³⁺ ([6′E][OTf]₃) (bipy = 2,2′-bipyridine, tbbipy = 4,4′-di-^tbutyl-2,2′-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized. The unique molecular and electronic structures of this new class of complexes involving pnictogen Lewis acids has been assessed in the solid, solution and gas phases to reveal systematic variations in metric parameters, ligand lability and charge concentration. While the Lewis acidity of E³⁺ has the trend E = Bi < Sb < As < P as determined by gas-phase calculations and ¹H NMR spectroscopy, the Lewis acidity of [6E]³⁺ has the trend E = P < As < Sb < Bi according to gas-phase calculations. Derivatives of [6′E][OTf]₃ (E = P, As) are latent sources of E(OTf)₃ as demonstrated by their reactions with dmap, which give the corresponding derivatives of [(dmap)₃E][OTf]₃. The highly oxidizing nature of P(OTf)₃ and As(OTf)₃ is evidenced in reactions of [6′E][OTf]₃ (E = P, As) with phosphines, which give E^I-containing monocations [(R₃P)₂E]¹⁺ and oxidatively coupled dications [R₃PPR₃]²⁺, illustrating new P–P and P–As bond forming strategies. Cations [6′E]³⁺ (E = P, As) are C–H bond activating agents that dehydrogenate 1,4-cyclohexadiene, with higher activity observed for E = P. Combinations of [6′E]³⁺ and ^tBu₃P activate H₂ and D₂ under mild conditions, evidencing frustrated Lewis pair activity. Oxidation of [6′P][OTf]₃ with SO₂Cl₂ gives [(tbbipy)₂PCl₂][OTf]₃, containing a P^V-trication, but there is no evidence of the analogous reaction with [6′As][OTf]₃. The observations highlight new directions in the chemistry of highly charged cations and reveal a rich reactivity for p-block triflates E(OTf)₃, which can be accessed through derivatives of [6E][OTf]₃ and [6′E][OTf]₃.