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 [C 6H 3-2,6-(CH=NR) 2]SbCl 2(R=Ph (1), tBu (2), Dip (3); Dip=2,6-iPr 2C 6H 3) with an appropriate amount of KC 8or Li[AlH 4] resulted in the formation of rare examples of monomeric stibinidenes [C 6H 3-2,6-(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) 3H] led to the stibinidenes 4 and 5. In contrast, the analogous reaction of compound 3 resulted in the formation of an unprecedented stibinidene [C 6H 3-2-(CH=NR)-6-(CH 2NHR)]Sb (7) (R=Dip), in which the hydrogen atoms that come from the K[B(sBu) 3H] are incorporated into the ligand backbone. To gain further insight into this intriguing reactivity with K[B(sBu) 3H] and to assess the influence of the substitution at both the antimony atom and pendant substituents, we prepared compounds [C 6H 3-2-(CH=NDip)]Sb(Ph)Cl (8) and [C 6H 2-2-(CH=NDip)-4,6-(tBu) 2]SbCl 2(9). The treatment of compound 8 with K[B(sBu) 3H] smoothly led to the 1-Ph-2-Dip-1H-2,1-benzazastibole (11), whereas the reaction of compound 9 with K[B(sBu) 3H] 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.