Four- and eight-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)2NPPh2NSiMe31 yields the four-membered heterocycle [[graphic omitted]SiMe3)]. An improved synthesis of the aminoiminophosphorane 1 is described. The compound TiCl4 reacts with Me3SiOPPh2NSiMe3 unexpectedly with elimination of all Me3p. groups to yield the eight-membered heterocycle [{TiCl2(OPPh2N)}2]. A vanadium-containing dimetallacyclophosphazene [{VCl2(NPPh2N)}2] has been synthesised from [VCl3(NSiMe3)] and CiPPh2NSiMe3. The X-ray structures of [[graphic omitted]SiMe3)]·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.