Synthesis and reactions of the homoleptic chromium(II) bis-amide [Ph 2PN( iPr)P(Ph)N( iPr)-] 2Cr with relevance to a selective catalytic ethene trimerization system to 1-hexene

Abstract

New organometallic compounds were obtained on the basis of the aminodiphosphinoamine ligand Ph 2PN( iPr)P(Ph)N( iPr)-H (1), which is relevant for the selective ethene trimerization system consisting of ligand 1, CrCl 3(THF) 3, and Et 3Al. This catalytic system produces 1-hexene in more than 90% yield and high purity. Here, we report a more efficient, high-yield synthesis of the recently published homoleptic magnesium complex [Ph 2PN( iPr)P(Ph)N( iPr)-] 2Mg (2) by reaction of n-butylethylmagnesium and 1 in Et 2O. Compound 2 can be used as a reagent to transfer the amide moiety [Ph 2PN( iPr)P(Ph) N( iPr)-] effectively to a chromium or aluminum center. In situ synthesis of the magnesium amide 2 followed by addition of CrCl 2(THF) 2 results in the formation of the homoleptic chromium(II)bis-amide [Ph 2PN( iPr)P(Ph)N( iPr)-] 2Cr (3) by transmetalation. The structure of chromium compound 3 is in some aspects similar to that of the corresponding homoleptic magnesium complex 2. Reacting 2 with ethylaluminum dichloride results in the formation of the respective aluminum amide [Ph 2PN( iPr)P(Ph)N( iPr)-][AlEtCl] (4), for which the direct synthesis of 1 with diethylaluminum chloride was unsuccessful. Additionally, we investigated compound 3 with potentially interesting activators such as Et 2Zn, Et 3Al, and Et 3B to obtain more information about the catalytic properties of these systems. © 2012 American Chemical Society.