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-iPr(2)C(6)H(3)) 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 acti-vating 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-iPr(2)C(6)H(3)N])(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 18a; R=C6H5-CH3 18b, R=NH(C6F5)18c), respectively.