Upscaling the Synthesis of Highly Active Ethylene Tetramerization Catalysts [iPrN(PAr2)2-CrCl2][B(C6F5)4] Bearing Long-Alkylsilyl Substituents.

In response to a request for kilogram-scale synthesis of the highly active ethylene tetramerization catalyst [iPrN-(PAr2)2-CrCl2]-[B-(C6F5)4] (Ar = C6H4-p-Si-(octyl)3), a shortened synthetic route to the ligand iPrN-(PAr2)2 was developed. p-ClC6H4Si-(octyl)3 was efficiently synthesized in a one-pot procedure from readily available 1-chlorooctane using Mg, SiCl4, and p-ClC6H4MgBr. Subsequent conversion to the corresponding Grignard reagent, ClMgC6H4-p-Si-(octyl)3, followed by reaction with iPrN-(PCl2)2, afforded the desired PNP ligand. This new synthetic route enabled the preparation of a series of ligands, iPrN-[P-(C6H4-p-SiR3)2]2 (R = decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl), which could not be accessed by the previously reported synthetic method developed for the octyl analogue. The corresponding chromium complexes, [iPrN-(PAr2)2-CrCl2]-[B-(C6F5)4], were evaluated in ethylene tetramerization. The complex bearing -Si-(decyl)3 substituents exhibited 1.5-fold higher catalytic activity than the parent -Si-(octyl)3 analogue, while maintaining comparable selectivity toward 1-octene and producing a slightly lower amount of polyethylene byproduct.