NCN-Chelated Organoantimony(III) and Organobismuth(III) Phosphonates: Syntheses and Structures

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.

Hexa- and trinuclear organoantimony oxo clusters stabilized by organosilanols

Reactions of Ph2SbCl3 with RSi(OH)3 [where R = tert-Bu, cyclo-C6H11] and Ph2Si(OH)2 in toluene in the presence of triethylamine as a base were performed. Single-crystal X-ray structural elucidation of the products revealed the formation of hexanuclear antimony(V) and mixed-valent antimony (III/V) oxo-hydroxo clusters built up of an incomplete cubane subunit. Interestingly, in all the reactions, at least one Sb-C bond cleavage has been observed, leading to the formation of novel cluster assemblies [(Ph2Sb)4(PhSb)2(C4H9SiO3)2(O)6(OH)2] (1), [(Ph2Sb)4(PhSb)2(C6H11SiO3)2(O)6(OH)2] (2), [(Ph2Sb)(PhSb)2(Ph2SiO2)2(O)3(OH)2](-)Et3NH(+) (3), and [(Ph2Sb)4(Sb)2(Ph2SiO2)2(O)6(OH)2] (4), respectively.

Synthesis of heteroboroxines with MB₂O₃ core (M = Sb, Bi, Sn)--an influence of the substitution of parent boronic acids

The synthesis and structure of stiba-, stanna- and bismaheteroboroxines of a general formula L(E)M[(OBR)2O] supported by a N,C,N-chelating ligand L [where L = C6H3-2,6-(CH2NMe2)2, M, E = Sb, lone pair or Sn, Ph or Bi, lone pair] is reported. The target compounds are prepared by straightforward one-step reactions between oxides (LMO)2 (M = Sb or Bi) or organotin(iv) carbonate L(Ph)Sn(CO3) with four or two molar equivalents of corresponding organoboronic acid. All compounds were characterized with the help of elemental analysis, multinuclear NMR spectroscopy and on several occasions the molecular structure was determined using single-crystal X-ray diffraction analysis. The influence of both the substitution of the parent organoboronic acid and the central atom used on the feasibility of the condensation reaction was addressed. Furthermore, several heteroboroxines containing nitrogen donor functionality (i.e. NH2, NMe2, CN or 4-pyridyl) included in the boronic acid residue were synthesized and characterized with the aim to prepare boroxine-based covalent frameworks (through intermolecular N→B interactions) containing metal atoms in their structures. Although no such intermolecular bonding was detected in solution of these compounds, it was shown that the organotin(iv) heteroboroxine substituted by 4-pyridyl group forms an infinite polymeric chains via N→B interactions in the solid state. This polymer collapsed back to monomeric units upon dissolution.