The reactivity of antimony and bismuth N,C,N-pincer compounds toward K[BEt3H] – the formation of heterocyclic compounds vs. element–element bonds vs. stable terminal Sb–H bonds

Abstract

The oxidative addition of CF₃SO₃CH₂Si(CH₃)₃ (Np^SiOTf) toward organopnictogen(I) N,C,N-pincer compounds, i.e. [2,6-(DippNCH)₂C₆H₃]E (1-E, where E = Sb, Bi; Dipp = 2,6-iPr₂C₆H₃) produced compounds [2,6-(DippNCH)₂C₆H₃]E(Np^Si)(OTf) (2-E, where E = Sb, Bi). By analogy, the in situ reduction of [2,6-(Me₂NCH₂)₂C₆H₃]ECl₂ (3-E, where E = Sb, Bi) followed by treatment with Np^SiOTf or MeI gave compounds [2,6-(Me₂NCH₂)₂C₆H₃]E(R)(X) (R/X = Np^Si/OTf 4-E, where E = Sb, Bi; R/X = Me/I 5-Sb). The reactivity of these compounds toward 1 eq. of K[BEt₃H] was examined showing remarkable differences depending both on the ligand backbone and the pnictogen used. Thus in the case of 2-E, the addition of the hydride across the imino-function was achieved thereby yielding azapnicta-heterocyclic compounds [2-(DippNCH₂)-6-(DippNCH)C₆H₃]E(Np^Si) (6-E, where E = Sb, Bi). The same reaction of 4-Bi produced dibismuthine {[2,6-(Me₂NCH₂)₂C₆H₃]Bi(Np^Si)}₂ (7-Bi), but in the case of 4/5-Sb the analogous distibines {[2,6-(Me₂NCH₂)₂C₆H₃]Sb(R)}₂ (R = Np^Si7-Sb, Me 8-Sb) were not formed directly and hydrides [2,6-(Me₂NCH₂)₂C₆H₃]Sb(R)H (R = Np^Si9-Sb, Me 10-Sb) could be isolated instead. Nevertheless, heating of both 9-Sb and 10-Sb led to an activation of a labile Sb–H bond and the formation of distibines 7/8-Sb.