4-MEMBERED AND 8-MEMBERED CYCLIC PHOSPHAZENE DERIVATIVES OF ZIRCONIUM, TITANIUM AND VANADIUM - CRYSTAL-STRUCTURES OF THE COMPLEXES [ZRCL3(ME3SINPPH2NSIME3)].MECN AND [(TICL2(OPPH2N))2].4MECN

The reaction of ZrCl4 with (Me3Si)2NPPh2NSiMe3 1 yields the four-membered heterocycle [activatedZrCl3(Me3SiNPPh2NSiMe3)]. An improved synthesis of the aminoiminophosphorane 1 is described. The compound TiCl4 reacts with Me3SiOPPh2NSiMe3 unexpectedly with elimination of all Me3Si groups to yield the eight-membered heterocycle [{TiCl2(OPPh2N)}2]. A vanadium-containing dimetallacyclophosphazene [{VCl2(NPPh2N)}2] has been synthesised from [VCl3(NSiMe3)] and ClPPh2NSiMe3. The X-ray structures of [activatedZrCl3(Me3SiNPPh2NSiMe3)].MeCN and [{TiCl2-(OPPh2N)}2].4MeCN have been determined. While the cyclic Zr-N distances in the former have to be considered as single bonds, the short Ti-N of the latter (almost planar) suggest double-bond character.