Preparation of N,N‘-Disilylated 1,8-Diaminonaphthalene Chelates and Their Group 4 Metal Complexes for Ethylene Polymerization

Abstract

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 1a, b with n -BuLi yields the dilithiated products ( 2a, b ) in 78−85% yield. The reaction of 2a, b with TiCl 4 produces diamidotitanium(IV) dichlorides, {1,8-C 10 H 6 (NSiMe 3 ) 2 }TiCl 2 ( 3a ) and {1,8-C 10 H 6 (NSi( i -Pr) 3 ) 2 }TiCl 2 ( 3b ). The crystal structure of 3a shows that the complex has an unusually large Cl−Ti−Cl angle (120.5°). Meanwhile, the bulkier substituents on the nitrogen atoms of 3b are significantly away from the naphthalene plane. The reaction of 2a, b with ZrCl 4 produces a bis(diamido)zirconium(IV) complex {1,8-C 10 H 6 (NSiMe 3 ) 2 } 2 Zr ( 4a ) and a diamidozirconium(IV) dichloride {1,8-C 10 H 6 (NSi( i -Pr) 3 ) 2 }ZrCl 2 ( 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.