SYNTHESES AND STRUCTURES OF ISOPROPYL AND (BIS(TRIMETHYLSILYL)METHYL) ANTIMONY RINGS AND CATENA-TRISTIBANES AND CATENA-TETRASTIBANES BY REACTION OF ORGANOANTIMONY RINGS WITH DISTIBANES

The syntheses and the structures of selected organoantimony rings (RSb)n and the formation of catena-stibanes by reaction of organoantimony rings with distibanes are reported. The syntheses include the preparation of i-PrSbBr2 and the reaction of this intermediate with magnesium to form (i-PrSb)4 and (i-PrSb)5. The isopropylantimony rings are stable in solution but polymerize in the absence of solvent. [(Me3Si)2CHSb]4 is, however, stable in the solid state with respect to polymerization. This four-membered ring has been obtained in the form of orange crystals from a solution of the dehalogenation products of the corresponding dichloride. The H-1 NMR data of (i-PrSb)4 and (i-PrSb)5 in solution are in accordance with the cyclic structure with the substituents adopting a maximum of trans positions. The structure of [(Me3Si)2CHSb]4 has been determined by single-crystal X-ray diffractometry as that of a strongly folded cyclotetrastibane (115.4-degrees) in the all-trans configuration. The Sb-Sb distances alternate between short and long (2.83, 2.87 angstrom), and the molecule on the whole approximates C2 symmetry. The crystal data with Mo K-alpha radiation are as follows: triclinic, space group P1BAR, a = 12.361 (1) angstrom, b = 12.981 (1) angstrom, c = 17.337 (2) angstrom, alpha = 108.18 (1)-degrees, beta = 90.82 (1)-degrees, gamma = 102.82 (1)-degrees, Z = 2, and R = 0.0362. The study of the reactivity of organoantimony rings with distibanes led to the formation of the first examples of catena-tri- and catena-tetrastibanes. The tristibanes (Me2Sb)2SbR, with R = Et, Pr, t-Bu, [Me3Si]2CH, and 2,4,6-Me3C6H2, are formed by reaction of an excess of Me4Sb2 with the corresponding rings (RSb)n. Action of an excess of Et4Sb2 with (EtSb)5 or (PrSb)5 gives (Et2Sb)2SbEt or (Et2Sb)2SbPr. (Ph2Sb)2SbEt and (Ph2SbSbEt)2 are formed by the reaction of Ph4Sb2 with (EtSb)5. catena-Stibanes derived from difficulty accessible antimony rings are better obtained by dehalogenation of appropriate mixtures of organoantimony bromides or by salt elimination; Me2SbBr and MeSbBr2 react with magnesium to give (Me2Sb)2SbMe, and Ph5Sb3 is obtained by reaction of PhSbCl2 and Ph2SbLi or Ph2SbNa in liquid NH3. The novel catena-tri- and catena-tetrastibanes have been characterized by H-1 NMR and mass spectra. They exist in equilibrium with distibanes and cyclostibanes.