Different Products of the Reduction of (N),C,N-Chelated Antimony(III) Compounds: Competitive Formation of Monomeric Stibinidenes versus 1H-2,1-Benzazastiboles

The reduction of N,C,N-chelated antimony(III) chlorides [C6H3-2,6-(CH=NR)(2)]SbCl2 (R=Ph (1), tBu (2), Dip (3); Dip=2,6-iPr(2)C(6)H(3)) with an appropriate amount of KC8 or Li[AlH4] resulted in the formation of rare examples of monomeric stibinidenes [C6H3-2,6-(CH=NR)(2)]Sb (R=Ph (4), tBu (5), Dip (6)). Similarly, the reduction of compounds 1 or 2 by two equivalents of K[B(sBu)(3)H] led to the stibinidenes 4 and 5. In contrast, the analogous reaction of compound 3 resulted in the formation of an unprecedented stibinidene [C6H3-2-(CH=NR)-6-(CH2NHR)]Sb (7) (R=Dip), in which the hydrogen atoms that come from the K[B(sBu)(3)H] are incorporated into the ligand backbone. To gain further insight into this intriguing reactivity with K[B(sBu)(3)H] and to assess the influence of the substitution at both the antimony atom and pendant substituents, we prepared compounds [C6H3-2-(CH=NDip)]Sb(Ph)Cl (8) and [C6H2-2-(CH=NDip)-4,6-(tBu)(2)]SbCl2 (9). The treatment of compound 8 with K[B(sBu)(3)H] smoothly led to the 1-Ph-2-Dip-1H-2,1-benzazastibole (11), whereas the reaction of compound 9 with K[B(sBu)(3)H] resulted in either tBu-substituted 1-Cl-2-Dip-1H-2,1-benzazastibole (13) or the formation of unprecedented Sb-Sb dimer bis(2-Dip-1H-2,1-benzazastibole) (12) depending on the reaction stoichiometry. The miscellaneous reactivity of antimony(III) precursors with reducing agents together with the structure and bonding of the resulting products has also been investigated from a theoretical point of view.