Synthesis and crystal structures of [C₆H₄SC(-..S)-..NNa·3P(NMe₂) ₃O·NaN-..(S-..)CSC₆H₄] and [C₆H₄SC(-..S)-..NLi·pmdien] (pmdien = N,N,N′,N″,N″-pentamethyldiethylenetriamine): Alkali-metal amides from 2-sulfanylbenzothiazole

Reaction of 2-sulfanylbenzothiazole with MBuⁿ (M = Li or Na) in the presence of the Lewis-base donors Me₂NCH₂CH₂NMeCH₂CH ₂NMe₂ (pmdien) and P(NMe₂)₃O gave, respectively, the monomer [C6H4SC(-^..S)-^..NLi·pmdien] and the dimer [C4H4SC(-^..S)-^..NNa·3P(NMe₂) ₃O·NaNA-^.. (S-^..CSC₆H₄], the structures of which have been determined by X-ray crystallography. In common with other structurally characterised sulfanylbenzothiazolate complexes, both the five-co-ordinate metal cations are involved in bridged bonding with the exocyclic S and the amido N. The amido N⁺-M^- is the formal bond making these two structures amide rather than thiolate complexes. In the sodium complex this is clear [N-Na 2.46(1) Å], however, in the lithium case the Li-N bond is exceptionally long [amido N-Li 2.14(1) Å], but an analysis of the bond lengths within the sulfanylbenzothiazolate moiety verifies its amido nature. The two complexes also show rare secondary bonding of the exocyclic S atoms by the alkali-metal cations, exo-S-Li 2.73(1) and exo-S-Na 2.995(1) and 2.951(7) Å.