Diatomic PN - trapped in a cyclo-tetraphosphazene

(Me3Si)(2)NPCl2, which is formally capable of eliminating two equivalents of Me3SiCl, is shown to be a suitable starting material to prepare highly reactive PN species by successive elimination of Me3SiCl. Me3SiCl elimination can be triggered either thermally and/or by addition of a Lewis acid such as GaCl3, thus leading to the formation of a highly labile aminochlorophosphenium cation in [(Me3Si)(2)NPCl][GaCl4] and iminophosphenium salt [Me3Si-N P][GaCl4] upon warming to ambient temperatures. This work describes the synthesis and characterization of a cyclo-tetraphosphazane in [PN(dmb)](4) (5) (dmb = 2,3-dimethyl-1,3-butadiene) obtained by thermal elimination of Me3SiCl from (Me3Si)(2)NPCl2 at 120 degrees C in toluene solution. The reactive intermediate Me3SiN=PCl was trapped with dmb to form the cyclic phosphazane Me3SiN(dmb)PCl, which eventually oligomerizes to give 5. In the presence of dmb or chd (chd = 1,3-cyclohexadiene) (Me3Si)(2)NP(OTf)(2) reacts by eliminating Me3SiOTf to yield the spirocyclic phospholenium salts [Me3SiN(dmb)P(dmb)][OTf] (7) and [Me3SiN(chd)P(chd)][OTf] (8), of which the solid state structures were successfully determined. 7 decomposes when exposed to moisture to give an unprecedented cyclic ammonium phosphinoxide (P(O)H(dmb)(2)NH2][OTf] (9). Tetraphosphazane 5 is shown to be a versatile ligand in transition metal chemistry. It coordinates in an eta(3)-fashion in {[PN(dmb)](4)Mo(CO)(3)} (5 center dot Mo) and is able to coordinate a second metal fragment, exemplified by the formation of the ditungsten comptex{[PN(dmb)](4)W-2(CO)(7)} (5 center dot W-2) with a semi-bridging carbonyl ligand. All compounds were structurally characterized and the bonding situation was investigated by density functional theory and natural bond orbital analysis (NBO).