Synthesis and Reactions of the Homoleptic Chromium(II) Bis-amide [Ph2PN(iPr)P(Ph)N(iPr)-]2Cr with Relevance to a Selective Catalytic Ethene Trimerization System to 1-Hexene

New organometallic compounds were obtained on the basis of the aminodiphosphinoamine ligand Ph2PN(Pr-i)P(Ph)N(Pr-i)-H (1), which is relevant for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)(3), and Et3Al. 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 [Ph2PN(Pr-i)P(Ph)N(Pr-i)-](2)Mg (2) by reaction of n-butylethylmagnesium and 1 in Et2O. Compound 2 can be used as a reagent to transfer the amide moiety [Ph2PN(Pr-i)P(Ph)N(Pr-i)-] effectively to a chromium or aluminum center. In situ synthesis of the magnesium amide 2 followed by addition of CrCl2(THF)(2) results in the formation of the homoleptic chromium(II)bis-amide [Ph2PN(Pr-i)P(Ph)N(Pr-i)-](2)Cr (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 [Ph2PN(Pr-i)P(Ph)N(Pr-i)-][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 Et2Zn, Et3Al, and Et3B to obtain more information about the catalytic properties of these systems.