Preparation of N,N′-disilylated 1,8-diaminonaphthalene chelates and their group 4 metal complexes for ethylene polymerization

The reaction of 1,8-diaminonaphthalene with trimethylchlorosilane and tri(isopropyl)chlorosilane gives N,N'-disilylated products (1a,b) in moderate yields. Double deprotonation of la,b with n-BuLi yields the dilithiated products (2a,b) in 78-85% yield. The reaction of 2a,b with TiCl4 produces diamidotitanium(IV) dichlorides, {1,8-C10H6(NSiMe3)(2)}TiCl2 (3a) and {1,8-C10H6(NSi(i-Pr)(3))(2)}TiCl2 (3b). The crystal structure of 3a shows that the complex has an unusually large Cl-Ti-Cl angle (120.5 degrees). Meanwhile, the bulkier substituents on the nitrogen atoms of 3b are significantly away from the naphthalene plane. The reaction of 2a,b with ZrCl4 produces a bis(diamido)zirconium(TV) complex {1,8-C10H6(NSiMe3)(2)}(2)Zr (4a) and a diamidozirconium(IV) dichloride {1,8-C10H6(NSi(i-Pr)(3))(2)}ZrCl2 (4b), respectively. The crystal structure of 4b shows that the molecule forms a dimer associated through two chloro bridges in the solid state. Facile monomethylation and transmetalation of 3a to form a dinuclear aluminum complex (5) were observed when it was exposed to trimethylaluminum. The molecular structure of 5 is identified with an independent synthesis and X-ray crystallography. The crystal structure of 5 shows that two nitrogen centers and two aluminum centers comprise a metallacycle in a butterfly shape. In contrast, only monomethylation of 3b occurs at room temperature. However, no sign of methylation was observed for 4b at all. With a modified methylalumoxane (MAO), transfer of methyl and isopropyl groups to 3a and 3b was observed at room temperature. However, the transmetalated product 5 was not observed under the particular conditions. It is found that 3a and 3b show the marginal reactivity for ethylene polymerization in the presence of MAO.