Neutral and dianionic organoantimony(III) dithiolene complexes:: Syntheses, X-ray crystal structures, and unexpected reactivity

The new neutral PhSb(dmid) (dmid(2-) = 4,5-dithiolato-1,3-dithiol-2-one) complex has been synthesized upon reaction of deprotected 1,3,4,6-tetrathiapentalene-2,5-dione with dichlorophenylstibine. Single-crystal X-ray structure determination shows an original three-dimensional network in the solid state, via Sb --- 0 and Sb --- S secondary interactions, based on an octagonal "Sb4S4" motif Not only PhSb(dmid) but also PhSb(dmit) (dmit(2-) = 4,5-dithiolato-1,3-dithiole-2-thione) reacts with a second 1 equiv of dithiolate to give a series of highly reactive dianionic complexes, unknown so far. One of these complexes, [Me4N](2)[PhSb(dmid)(2)], was structurally characterized by single-crystal X-ray measurements. Both dithiolene ligands, lying in the equatorial plane of a distorted octahedron, are unsymmetrically coordinated, with two Sb-S distances much longer than the other two. These dianionic species reacted with 1 equiv of PhSbCl2 to give, unexpectedly, a series of Sb(V) [Ph2Sb(dithiolene)(2)](-) complexes. The same compounds were obtained directly upon slow addition of 1 equiv of PhSbCl2 on the corresponding dithiolate suspensions. This demonstrates that dianionic [PhSbIII(dithiolene)(2)](2-) species are key intermediates in the synthesis of [Ph2SbV(dithiolene)(2)](-) salts. The single-crystal X-ray structure determination of the tetraethylammonium salts of [Ph2Sb(dmid)(2)](-), [Ph2Sb(dmit)(2)](-), and [Ph2Sb(dmid)(dmit)](-) show a distorted-octahedral coordination geometry for the Sb center with a cis configuration of the phenyl groups. This is preserved also in solution, as established by C-13 NMR. Using the same technique, combined with H-1 NMR, in a scrambling experiment, a fast dithiolene exchange has been emphasized. In the case of the [Ph2Sb(dmid)(2)](-) salt, two polymorphs, with different folding angles along the S --- S hinge, were crystallized.