SULFUR(IV) COMPOUNDS AS LIGANDS .20. ADDUCT FORMATION AND RING-OPENING OF THIIRANE-1-OXIDE WITH ORGANOTIN HALIDES - CRYSTAL-STRUCTURE OF [(4-FC6H4)2SNCL2(C2H4SO)2]

The organotin halides RnSnX4-n (R = Ph, 4-MeC6H4, 4-FC6H4; X = Cl, Br; n = 0, 1, 2, 3) and Me2SnCl2 form adducts with thiirane-1-oxide. In g eneral, for n = 0, 1, 2 these have a 1:2 stoichiometry and are octahed ral, as shown by a single-crystal structural study of [(4-FC6H4)2SnCl2 (C2H4SO)2] (4c). In 4c the aryl groups are trans to each other and the chloride and sulphoxide ligands mutually cis. The S-O bond is 0.04 an gstrom longer than that in uncoordinated thiirane-1-oxide, whereas the bonds within the three-membered ring are shortened by a similar amoun t. Depending on the reaction conditions, 1:1 adducts [R2SnX2(C2H4SO)] (R = 4-MeC6H4, X = Cl, Br; R = Me, (t)Bu, X = Cl) can also be isolated , while triorganotin halides form only 1:1 complexes. Analogous dimeth ylsulphoxide (DMSO) adducts have been synthesized for comparison. On t he basis of vibrational spectroscopic data it can be concluded that th iirane-1-oxide is a weaker base than DMSO. This is supported by an NMR study of the formation of the 1:1 adduct between Me2SnCl2 and thiiran e-1-oxide (9), which gave the following thermodynamic data: K(eq) = 8. 6 M-1, DELTAH(R) = -20.4 kJ mol-1, DELTAS(R) = -50 J mol-1 K-1. Decomp osition of the thiirane-1-oxide adducts at room temperature gives the thiosulphinic acid esters XC2H4S(O)SC2H4X (X = Cl: 18a, Br: 18b) in hi gh yields.