Oxidation of tris(2-methoxyphenyl)antimony with tert-butyl hydroperoxide in the presence of carboxylic acid

Oxidation of tris(2-methoxyphenyl)antimony with tert-butyl hydroperoxide in the presence of a carboxylic acid in tetrahydrofuran or diethyl ether leads to formation of tris(2-methoxyphenyl)antimony bis(chloroacetate) (2-MeOC6H4)3Sb[OC(O)CH2Cl]2 (1), tris(2-methoxyphenyl)antimony bis(2-methoxybenzoate) (2-MeOC6H4)3Sb[OC(O)C6H4(OMe-2)]2 (2), tris(2-methoxyphenyl)antimony bis(2,3-difluorobenzoate) [(2-MeOC6H4]3Sb[OC(O)C6H3F2-2,3]2 (3) and tris(2-methoxyphenyl)antimony bis(pentafluorobenzoate) solvate with benzene [(2-MeOC6H4]3Sb[OC(O)C6F5]2 ∙ ½ PhH (4). Compounds 1-4 isolated after recrystallization from a benzene-octane mixture in the form of single crystals, were characterized by IR spectroscopy and X-ray diffraction (XRD) analysis. The IR spectra contain bands characterizing vibrations of carbonyl groups (1697, 1624, 1655, 1668 cm-1), the SbC3 fragment (440-447 cm-1), the Sb-O bonds (575-536 cm-1), respectively. According to the XRD data, crystals 1 and 4 belong to the triclinic syngony, symmetry group P-1; crystals 2 and 3 belong to the monoclinic syngony, symmetry group P21/n. The uncertainty factors for refinement of the structural data are R1 = 0.0502 (1), R1 = 0.0437 (2), R1 = 0.0409 (3), R1 = 0.0333 (4). In trigonal bipyramidal molecules with electronegative ligands in axial positions, the Sb-C distances are 2.0966(17)-2.1194(18) Å for 1, 2.104(2)-2.126(2) Å for 2, 2.0889(19)-2.1134(19) Å for 3, and 2.109(2)-2.123(2) Å for 4; the OSbO bond angles take the values of 175.15(5)° (1), 171.42(6)° (2), 176.97(6)° (3), and 164.47(6)° (4). The Sb-O distances in 1 [2.1088(15) and 2.1269(15) Å] are comparable with those observed in 2 [2.1137(17) and 2.1232(18) Å], in 3 [2.0880(14) and 2.1063(14) Å] and are slightly different for 4 [2.1035(17) and 2.1460(17) Å]. The solvate molecules of benzene in 4 bind neighboring dicarboxylate molecules [the C∙∙∙H and Cl∙∙∙H distances are 2.84 Å and 3.06 Å, which is less than the sum of the covalent radii of the partner atoms. The antimony atom coordinates the carbonyl oxygen atoms from the side of small equatorial angles (115.31(9)° and 119.59(9)°), while the Sb∙∙∙O=C intramolecular contacts are 3.374(3) and 3.296(3) Å, which is greater than the Sb∙∙∙OMe intramolecular contacts (3.079-3.172 Å). It should be noted that a similar difference in the Sb∙∙∙O and Sb∙∙∙OMe intramolecular contacts is also observed in the first three molecules of the complexes [3.296(3), 3.374(3) Å and 3.102-3.167 Å for 1, 3.010(3), 3.164(3) Å and 3.058-3.202 Å for 2 and 3.190(3), 3.233(3) Å and 3.056-3.120 Å for 3]. The Sb∙∙∙O=C intramolecular contacts between the central metal atom and carbonyl oxygen atom are the largest in 1 and 4, which can be explained by the presence of electroacceptor carboxylate ligands. Complete tables of atomic coordinates, bond lengths and bond angles for the structures have been deposited with the Cambridge Crystallographic Data Centre (No. 2416266 (1), No. 2415652 (2), No. 2415732 (3), No. 2415648 (4), deposit@ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk).