ZIRCONOCENE DERIVATIVES WITH PHOSPHINOMETHANIDE LIGANDS - METAL-PROMOTED LIGAND METALATIONS - TUNING OF REGIOSELECTIVITY AND FORMATION OF NOVEL ZIRCONAPHOSPHAHETEROCYCLES

From Cp2ZrCl2 and 2 equiv of the appropriate lithium phosphinomethanides (D)Li[HC-(PMe2)X] (D = -, X = PMe2, 6; D = TMEDA, X = SiMe3, 7), the 1,3-zirconaphosphacyclobutane derivatives Cp2Zr[CH2P(Me)CHX] (10 and 11), containing the first examples of doubly metalated alkylphosphines as chelating ligands, are formed via the known zirconaphosphacyclopropane derivatives Cp2(Cl)Zr[C(H)(PMe2)X] (2 and 3). An intramolecular pathway is deduced from a cross-coupling experiment with Cp2(Cl)Zr[C(H)(PMe2)(SiMe3)], 3 and 6. In contrast, 3 (X = SiMe3) reacts with LiCH2PMe2 (5) to give the substitution product Cp2Zr[C(H)(PMe2)(SiMe3)][CH2PMe2] (13). In the case of 2 (X = PMe2), again metalation occurs with LiR (R = CH3, CH2PMe2, (t)Bu), thereby generating {Cp2Zr[C(PMe2)2]}2 (14). An X-ray diffraction study of the yellow crystals of 14.toluene (monoclinic, space group P2(1)/c, a = 22.558(1) angstrom, b = 8.891(1) angstrom, c = 20.283(1) angstrom, beta = 112.33(1)degrees, V = 3763.0 angstrom3, Z = 4, I = 23-degrees-C, R(w) = 0.042, w = 4F(o)2/sigma2(F(o)2)) shows the diphosphinocarbene ligands to function as eta2(C,P)-mu-(C,P') six-electron ligands to 18e zirconium centers. Only traces of metalation product are observed, however, in the sterically most crowded system Cp2(Cl)Zr[C(PMe2)(SiMe3)2] (4)/(TMEDA){Li[C(PMe2)(SiMe3)2}2 (8). Instead, an oxidative phosphinomethanide coupling (P-C) leads to the phosphorus ylide (Me2P)(Me3Si)2CPMe2=C(SiMe3)2 (15), probably via an external reaction in the ligand sphere. However, a metalation product, Cp2ZrCH2SiMe2C(SiMe3)PMe2 (17), can be obtained via a more indirect route from Cl2Zr[C(PMe2)(SiMe3)2]2 (9) and KCp. Insertion of (t)BuNC into the Zr-C bonds of 11 gives the six-membered heterocycle Cp2ZrC(=Nt-Bu)CH2P(Me)C[=CH(SiMe3)]N(tBu) (19). All compounds were characterized by means of NMR spectroscopy.