OXIDATION OF TRI(O-TOLYL)ANTIMONY BY TERT-BUTYL HYDROPEROXIDE. MOLECULAR STRUCTURES OF BIS[μ2-OXO- TRI(O-TOLYL)ANTIMONY] AND μ2-OXO-BIS[(TERT-BUTYLPEROXY)TRI(O-TOLYL)ANTIMONY]

Tri(o-tolyl)antimony oxidation by equimolar amount of tert-butyl hydroperoxide in diethyl ether led to the formation of bis[μ2-oxo-tri(o-tolyl)antimony] (1). At the molar ratio of reactants 1:2 or 1:4 μ2-oxo-bis[(tert-butylperoxy)tri(o-tolyl)antimony] (2) has been formed. According to the X-ray analysis data, antimony atoms are in the trigonal bipyramidal coordination in molecules 1 and 2. The bond lengths SbO vary within the ranges 1.937(2)2.078(2) Å (1) and 1.975(17)2.216(15) Å (2).

The interactions between triarylantimony and inorganic and organic oxidizing agents were investigated by many authors, for example [14]. The studies of reactions of triarylantimony with hydroperoxides are of great importance, as the products are useful precursors of derivatives with general formula Ar 3 SbХ 2 (Х = acid radical НХ) [510]. It has been found that hydrogen peroxide oxidizes triarylantimony to produce oxide Ar 3 SbO (Ar = Ph, p-Tol) or dihydroxide Ar 3 Sb(OН) 2 (Ar = 2,4,6-Me 3 C 6 H 2 ), depending on the volume of organic radical bonded with antimony atom, it is believed [10,11]. The interaction of triarylantimony with tert-butyl hydroperoxide was studied on the example of triphenylantimony only. The molecular structure of the reaction product was found to depend on the amount of an oxidizing agent. Triphenylantimony oxide was formed at stoichiometric ratio of reactants and may be dimerized or polymerized [1214]. Stable antimony peroxides Ph 3 Sb(OOBu-t) 2 and (Ph 3 SbOOBu-t) 2 О are formed in the presence of the excess of tert-butyl hydroperoxide [15].
The reactions of tri(o-tolyl)antimony with tert-butyl hydroperoxide at various molar ratios of the reactants have been investigated and crystal and molecular structures of the products have been determined in the present paper. The reaction with the molar ratio 1:4 was carried out at the same conditons. The product yield of substance 2 was 87 %. IR spectrum of the substunce 1 was recorded on the Bruker Tensor 27 FT-IR (KBr pellets; 4000400 cm 1 ).

Synthesis of bis[µ 2 -oxo-tri(o-tolyl)antimony] (1).
The X-ray diffraction analyses of crystalline substances 1 and 2 were made on the Bruker D8 QUEST automatic four-circle diffractometer (Mo K  -emission,  = 0.71073 Å, graphite monochromator). The data were collected and analyzed, the unit cell parameters were refined, and the absorption correction was applied using the SMART and SAINT-Plus programs [16]. All calculations for structure determination and refinement were performed using the SHELXL/PC programs [17]. The structures 1 and 2 were determined by the direct method and refined by the least-squares method in the anisotropic approximation for non-hydrogen atoms.
The main crystallographic data and refinement results for structures 1 and 2 are listed in Table 1. The selected bond lengths and bond angles are given in Table 2.  (1) (3)  The full tables of atomic coordinates, bond lengths, and bond angles for the substance 1 was deposited with the Cambridge Crystallographic Data Centre (№ 1052677; deposit@ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk).

Results and Discussion
It has been found that the oxidation of tri(o-tolyl)antimony by tert-butylhydroperoxide at the molar ratio 1:1 in diethyl ether goes with the formation of tri(o-tolyl)antimony oxide with dimeric structure: bis[μ 2 -oxo-tri(o-tolyl)antimony] (1):