Antimony lone electronic pair as a stereoelectronic barrier to stibatrane

To examine the effect of 5s2 lone electron pair of antimony atom on the reaction of antimony trifluoride and triethanolamine in the presence of sodium methylate, the crystal structure of the reaction product -2-fluoro-6-(2-hydroxyethyl)-1,3-dioxa-6-aza-2-stibacy-cylooctane (1-fluoro-2-hydrostibatrane) FSb (OCH2CH2)2NCH2CH2OH) was confirmed. In the compound structure, the hydrogen atom of the 2-hydtoxyethyl group of each molecule forms an intermolecular hydrogen bond with the oxygen atom of one of the five-membered SbOCH2CH2N half-cycles in a neighbouring molecule. A geometry of both five-member N-C-C-O-Sb heterocycles, end-capped by transannular N→Sb bond in the 1-fluoro-2-hydrostibatrane molecule, is almost identical. C-O, C-C, N-C interatomic distances and valence angles in two endocyclic units (NCCOSb) are comparable to those observed in RSi(OCH2CH2)3N silatranes. A coordination polyhedron of the Sb atom can be represented as a transition from a bisphenoid to Sb(O3)N trigonal pyramid, with a nitrogen atom at the apex and three oxygen atoms in the base. The N→Sb transannular coordinate bond length is 2.402(4) Å, which is 0.40 Å greater than the Sb-N covalent bond standard length. The Sb-F bond (1.997(4) Å) is 0.12 Å longer than that in the SbF3 molecule, and insignificantly shorter than that of the Sb-Fax (2.028(3) Å) in the SbF3Gly crystalline complex. The fluorine atom substantially strays from the N→Sb axis to the direction of O(1) and O(2) atoms. The oxygen atom of the 2-hydroxyethyl group lies at a distance of 2.899(3) A from that of Sb, intermediate between the valence bond length and the sum of the Van der Waals radii of these atoms. Combined with the F atom position, one can assume the 1-fluoro-2-hydrostibatrane crystal structure as a “frozen” state of the SNi(Sb) type nucleophilic attack of the oxygen atom, uncompleted because of its repulsion by the 5s2 lone electronic pair of antimony atom.

Reactions of Pentaphenylantimony and Penta-Para-Tolylanimony with Calixarene [4-t-BuC6H2OH(S-2)]4

Pentaphenylantimony and penta-para-tolylantimony react with calixarene [4-t-BuC6H2OH(S-2)]4 (СArH) by way of arene elimination and formation of the [Ph4Sb]+[СAr]- × TolH (1), [p-Tol4Sb]+[CAr]- × H2O (2) ionic products with a yield up to 96%. The compound has been identified by IR spectroscopy and X-ray diffraction analysis. According to the X-ray diffraction data, compounds 1 and 2 are ionic complexes with solvate molecules of toluene (1) and water (2). The cation has a tetrahedral coordination of the antimony atom with aryl ligands at the polyhedron vertices; the anion is represented by the deprotonated form of p-tert-butylthiacalix[4]arene. The three tert-butyl groups, the phenyl ring and solvated toluene in the structure of compound 1, and two tert-butyl fragments in the structure of compound 2 are disordered over two positions. The tetrahedral coordination of antimony atoms in the cations of compounds 1 and 2 is slightly distorted. The CSbC angles deviate from the theoretical value and vary within 106.0(4)−117.7(4)° (1), 105.75(15)−112.84(15)° (2). The average Sb–C bond lengths are 2.101(3) and 2.106(4) Å in structures 1 and 2, respectively. The [СAr]- anion is in the cone conformation, the upper rim of which is represented by the tert-butyl groups in the para-position, while the lower one is represented by hydroxy groups, one of which is deprotonated. The СAr–O– bond length (1.318(4) (1) and 1.326(4) (2) Å) is less than the average value of the СAr–OH bond lengths (1.338(4) (1) and 1.343(4) (2) Å), which indicates increasing multiplicity of the bond and localization of a negative charge on the oxygen atom. Intramolecular hydrogen bonds with the neiboring O atom are observed. The H∙∙∙O distances are 2.16, 1.69, 1.77 Å in 1 and 1.92, 1.79, 1.76 Å in 2. Dihedral angles between opposite phenoxide rings are 60.64° and 87.07° (1) and 83.85° and 80.42° (2), which indicates somewhat less symmetric anion in structure 1 than in structure 2. The formation of the crystal spatial structure is due to the formation of hydrogen bonds between ions with participation of oxygen and sulfur atoms, as well as СН∙∙∙π–interactions, while the ions form chains in the crystal of compound 1, and layers in the crystal of compound 2. Complete tables of atom coordinates, bond lengths and valence angles are deposited at the Cambridge Crystallographic Data Center (No. 1850118 (1); No. 2013220 (2); [email protected] or http://www.ccdc.cam.ac.uk/data_request/cif).

The Oxidative Addition Reaction of Tris(2-Methoxy-5-Chlorinephenyl)Antimony With Trifluoropropionic Acid

The interaction of tris(2-methoxy-5-chlorophenyl)antimony with 3,3,3–trifluoropropionic acid in the presence of hydrogen peroxide (1:2:1 mol) in ether proceeds according to the oxidative addition reaction scheme with the formation of bis(3,3,3-trifluoropropionyl)tris(2-methoxy-5-chlorophenyl)antimony [(MeO-2)(Cl-5)C6H3]Sb[OC(O)CH2F3]2. The IR spectra of compound 2, recorded on a Shimadzu IRAffinity-1S Fourier transform IR spectrometer in a KBr pellet in the region of 4000–400 cm–1, contain absorption bands of carbonyl groups, which are shifted to the low-frequency vibration region in comparison with the IR spectra of the initial acids. According to the X-ray diffraction data obtained on a Bruker D8 QUEST diffractometer, compound 1 has the following crystallographic parameters of the unit cell: crystal size 0.23×0.21×0.08 mm3, space group P21/n, а = 8.883(7), b = 21.184(15), c = 13.642(15) Å, α = 90.00°, β = 107.34(3)°, γ = 90.00°, V = 2451(4) Å3, ρcalc = 1.587 g/cm3, Z = 4; crystal 2 has the following crystallographic parameters of the unit cell: 0.3×0.25×0.08 mm3, P21/c, а = 12.00(5), b =16.81(7), c =16.30(9) Å, α =90.00°, β =108.3(3)°, γ =90.00°, V =3121(25) Å3, ρcalc = 1.704 g/cm3, Z = 4. The antimony atom in 2 has a distorted trigonal-bipyramidal coordination with carboxylate ligands in axial positions. The OSbО angles are 174.2(5)°, the sums of the СSbC angles in the equatorial plane are 360°, the axial Sb–O bonds equal 2.073(15), 2.092(15) Å, and the equatorial Sb–С bonds equal 2.05–2.13 Å, which is close to the sum of the covalent radii of the atoms. The intramolecular Sb∙∙∙OМе distances (3.035(3), 3.037(3), 2.992(4) Å (1), 3.03(2), 3.119(17), 3.147(19) Å (2)), as well as Sb∙∙∙OMe for compound 2 (3.232(19), 2.99(2) Å), are much smaller than the sum of the van der Waals radii of atoms.

Palladium-Catalyzed C–H Arylation of Benzofurans with Triarylantimony Difluorides for the Synthesis of 2-Arylbenzofurans

Pd-catalyzed regioselective C–H arylation is a useful tool for the chemical modification of aromatic heterocycles and 2-arylbenzofuran derivatives are of interest as biologically active substances. Herein, the reaction of triarylantimony difluorides with benzofurans under aerobic conditions in 1,2-DCE, using 5 mol% Pd (OAc)2 and 2 eq. of CuCl2 at 80 °C, produced a variety of 2-arylbenzofurans in moderate-to-high yields. The reaction is sensitive to the electronic nature of the substituents on the benzene ring of the triarylantimony difluorides: an electron-donating group showed higher reactivity than an electron-withdrawing group. Single crystal X-ray analysis of tri(p-methylphenyl) antimony difluoride revealed that the central antimony atom exhibits trigonal bipyramidal geometry.