In this paper a novel ligand of the type [PNPNH] is presented for the application in a new homogeneous highly selective ethene trimerization system for the formation of 1‐hexene, which consists of the chromium source CrCl3(thf)3, the ligand Ph2PN(iPr)P(Ph)N(iPr)H (1), and Et3Al as an activator in toluene. The excellent characteristics of this new system, e.g. very high selectivity to C6 with highest purity of the C6 fraction (>99 % 1‐hexene), activity on a constant level on a long timescale, use of small amounts of Et3Al as a cheap activator, and only very low production of PE, make it to a hot candidate for industrial application. Its organometallic background gives an indication of the nature of the active catalyst species.

An alternative concept for the selective catalytic formation of 1-octene from ethylene via dimeric catalytic centers is proposed. The selectivity of the tetramerization systems depends on the capability of ligands to form binuclear complexes that subsequently build up and couple two separate metallacyclopentanes to form 1-octene selectively. Comparison of existing catalytic processes, the ability of the bis(diarylphosphino)amine (PNP) ligand to bridge two metal centers, and the experimental background support the proposed binuclear mechanism for ethylene tetramerization.

Different organometallic compounds of the new aminodiphosphinoamine ligand Ph2PN(iPr)P(Ph)N(iPr)-H (1) are reported that are relevant model complexes for the selective ethene trimerization system consisting of ligand 1, CrCl3(THF)3, and Et3Al that produces 1-hexene in more than 90% yield and high purity. The lithiation of 1 by n-BuLi in the presence of tetramethylethylenediamine (tmeda) yields the mononuclear compound Ph2PN(iPr)P(Ph)N(iPr)-][Li(tmeda)] (2). Without using tmeda the dinuclear species [Ph2N(iPr)P(Ph)N(iPr)-Li]2 (3) was obtained. By addition of a Grignard reagent to the ligand solution the bis(aminodiphosphinoamide)magnesium complex [Ph2PN(iPr)P(Ph)N(iPr)-]2Mg (4) could be isolated. Reaction of Li[CpCrCl3] with 3 leads to the formation of the model compound CpCrCl[-N(iPr)P(Ph)N(iPr)PPh2] (5), which can be alkylated with Na[Et4Al] to form the corresponding ethyl compound CpCrEt[-N(iPr)P(Ph)N(iPr)PPh2] (7). In THF the formation of EtCrCl2(THF)3 (8) directly from the reaction of CrCl3[Ph2PN(iPr)P(Ph)N(iPr)-H](THF) (6) with Et3Al could be observed. The organometallic chemistry of 1 gives hints on possible species and activation mechanisms in the catalysis, which have to be considered for a better understanding of the catalytic system.

In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl(3)(thf)(3)] (thf=tetrahydrofuran), a Ph(2)P-N(iPr)-P(Ph)-N(iPr)H (PNPNH) ligand (Ph=phenyl, iPr=isopropyl), and triethylaluminum (AlEt(3)) as activator. It could be shown that the initial activity shows a first-order dependency on the ethylene concentration. Also, a first-order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol(-1). At elevated temperatures (ca. 80 degrees C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt(3). After a fast initial phase, a pronounced 'kink' in the ethylene-uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene.

Coordination, deprotonation, rearrangement, and cleavage of Ph(2)PN(iPr)P(Ph)N(iPr)H (1) by trialkylaluminum compounds R(3)Al (R=Me, Et) are reported that are relevant to the selective ethene trimerization system consisting of the ligand 1, CrCl(3)(THF)(3) and Et(3)Al that produces 1-hexene in more than 90% yield and highest purity. With increasing temperature and residence time first the formation of an adduct [Ph(2)PN(iPr)P(Ph)N(iPr)H][AlR(3)] (2), second the aluminum amide [Ph(2)PN(iPr)P(Ph)(AlR(3))N(iPr)][AlR(2)] (3) and third its rearrangement to the cyclic compound [N(iPr)P(Ph)P(Ph(2))N(iPr)][AlR(2)] (4) were observed. The cleavage of 3 by an excess of R(3)Al into an amidophosphane and an iminophosphane could be the reason for its rearrangement to complex 4, as well as to the cyclic dimer [R(2)AlN(iPr)P(Ph)(2)](2) (5). The chemistry of ligand 1 in the presence of alkylaluminum compounds gives hints on possible activation and deactivation mechanisms of 1 in trimerization catalysis.

Tie me catalyst down, support: A selective homogeneous chromium‐based ethene trimerization catalyst is heterogenized by immobilization on a functionalized polymer support. The immobilized catalyst displays good selectivity towards 1‐hexene, and retains high activity for long times on‐stream, combining advantages of homogeneous and heterogeneous catalyst systems.

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