Organoantimony(I) Compounds Incorporating the Bulky Rind Groups: Selective Synthesis and Characterization of Distibene and Cyclotetrastibane

The bulky Rind-substituted dihalostibanes, (Rind)­SbX2 (1-X2) [X = Cl and Br; Rind = Eind (a: R1 = R2 = Et) and EMind (b: R1 = Et, R2 = Me)], were prepared by the reaction of SbCl3 with a mixture of (Rind)Li and LiBr in THF (Rind = 1,1,7,7-tetra-R1-3,3,5,5-tetra-R2-s-hydrindacen-4-yl). The reduction of 1-X2 with lithium naphthalenide (LiNaph) or Li metal was carried out to access organoantimony­(I) compounds. The treatment of the bulky Eind-based dihalostibane, (Eind)­SbX2 (1a-X2), with LiNaph in THF afforded a distibene, (Eind)­SbSb­(Eind) (2a), featuring an SbSb double bond. In contrast, the less bulky EMind-based dihalostibane, (EMind)­SbX2 (1b-X2), reacted with Li metal in THF to yield a four-membered ring compound, cyclotetrastibane, Sb4(EMind)4 (3b). The molecular structures and electronic properties of the resulting Sb­(I) species were investigated both experimentally and theoretically.