Synthesis and characterisation of bulky guanidines and phosphaguanidines: precursors for low oxidation state metallacycles

Abstract

Reactions of alkali metal amides or phosphides with the bulky carbodiimide, ArNCNAr (Ar = C₆H₃Prⁱ₂-2,6), followed by aqueous work-ups, have yielded several guanidines, ArNC(NR₂)N(H)Ar (R = cyclohexyl (GisoH) or Prⁱ (PrisoH); NR₂ = cis-NC₅H₈Me₂-2,6 (PipisoH)), a bifunctional guanidine, {ArNCN(H)Ar}₂{μ-N(C₂H₄)₂N} (Pip(GisoH)₂), and two phosphaguanidines, ArNC(PR₂)N(H)Ar (R = cyclohexyl (CyP-GisoH) or Ph (PhP-GisoH)). A very bulky guanidine, ArNC{N(Ar)SiMe₃}N(H)Ar (ArSi-Giso), and an aryl coupled bifunctional guanidine, {ArN(H)C(NPrⁱ₂)NC₆H₂Prⁱ₂-2,6-}₂ (PrisoH)₂, have been prepared by other routes. All compounds have been crystallographically characterised and shown to exist in a number of isomeric forms in the solid state. These appear to be largely retained in solution. The deprotonation of GisoH with BuⁿLi in either hexane or THF led to crystallographically characterised dimeric and monomeric complexes respectively, viz. [Li{Li(κ²-N,N′-Giso)₂}] and [Li(THF)(η¹-N,η³-Ar-Giso)]. Deprotonation of PrisoH and Pip(GisoH)₂ with K[N(SiMe₃)₂] gave the unsolvated polymer, [{K(η¹-N,η⁶-Ar-Priso)}_∞], and the solvated complex, [{K(THF)₂}{Pip(Giso)₂}{K(THF)₃}], respectively.