A Donor-Stabilized Zwitterionic 'Half-Parent' Phosphasilene and Its Unusual Reactivity towards Small Molecules.

The stabilization of the labile, zwitterionic 'half-parent' phosphasilene 4 L′SiPH (L′=CH[(CCH₂)CMe(NAr)₂]; Ar=2,6- iPr₂C₆H₃) could now be accomplished by coordination with two different donor ligands (4-dimethylaminopyridine (DMAP) and 1,3,4,5-tetramethylimidazol-2-ylidene), affording the adducts 8 and 9, respectively. The DMAP-stabilized zwitterionic 'half-parent' phosphasilene 8 is capable of transferring the elusive parent phosphinidene moiety (:PH) to an unsaturated organic substrate, in analogy to the 'free' phosphasilene 4. Furthermore, compounds 4 and 8 show an unusual reactivity of the SiP moiety towards small molecules. They are capable of adding dimethylzinc and of activating the SH bonds in H₂S and the NH bonds in ammonia and several organoamines. Interestingly, the DMAP donor ligand of 8 has the propensity to act as a leaving group at the phosphasilene during the reaction. Accordingly, treatment of 8 with H₂S affords, under liberation of DMAP, the unprecedented thiosilanoic phosphane LSiS(PH₂) 16 (L=HC(CMe[2,6- iPr₂C₆H₃N])₂). Compounds 4 and 8 react with ammonia both affording L′Si(NH₂)PH₂ 17, respectively. In addition, the reaction of 8 with isoproylamine, p-toluidine, and pentafluorophenylhydrazine lead to the corresponding phosphanylsilanes L′Si(PH₂)NHR (R= iPr 18 a; R=C₆H₅CH₃ 18 b, R=NH(C₆F₅) 18 c), respectively. [ABSTRACT FROM AUTHOR]