Metalation and Transmetalation Studies on Ph₂PN(ⁱPr)P(Ph)N(ⁱPr)H for Selective Ethene Trimerization to 1-Hexene

Abstract

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.

A survey of pendant donor-functionalised (N,O) phosphine ligands for Cr-catalysed ethylene tri- and tetramerisation

“…Deprotonation of the PNP precursor with n-butyllithium, to generate the PNP derived lithium amide, followed by introduction of cyclohexene oxide (Scheme 2) did lead to ring opening, however rather than the desired N-functionalised compound, the reaction yielded 17 in moderate yields after hydrolytic work up. 31 P NMR spectroscopy of 17 shows two sets of doublets with a 2 J pp splitting of 94 Hz which is comparable with similarly reported compounds. 53,56 Crystals of 17 were grown from a saturated solution in hot methanol ( Fig.…”

“…1 H NMR spectra were internally referenced to the residual solvent peaks, and 13 C NMR spectra to deuterated solvent resonances. 31 P NMR spectra were referenced to triphenylphosphine standard. The liquid products resulting from ethylene oligomerisation were analysed by GC on a Varian 3900 or a Shimadzu GC-2014 utilising helium carrier gas and FID detector.…”

“…Early studies showed that the ligand could readily coordinate to AlR 3 , however an increase in temperature was required to deprotonate the PNPNH ligand backbone. 21,[31][32][33][34] It was also demonstrated that further heating resulted in rearrangement of the ligand backbone to give an NPPN species which was shown to be inactive for ethylene oligomerisation and was speculated to be the mode by which the catalyst deactivated. 21,32 The catalyst's temperature dependence was also demonstrated in kinetic studies where it was shown that at lower temperatures an induction period of~30 minutes is required before trimerisation commences.…”

Activity Enhancement of a Catalyst System for the Selective Trimerization of Ethene to 1‐Hexene by Modification of the Chromium to Chloride to Aluminium Ratio

“…[7] Experimental Section Ph 2 PNA C H T U N G T R E N N U N G (iPr)P(Ph)NA C H T U N G T R E N N U N G (iPr)H was prepared according to a published method. [5,6,16] ) were obtained from Sigma-Aldrich and used without further purification; toluene (>99.9 % purity) was obtained from Merck Chemicals and was dried over sodium with benzophenone and was then distilled in an inert gas atmosphere (Ar); argon 5.0 and ethene 3.0 were purchased from Linde Gas and used as received.…”

Reduction of Bromo- and Iodo-2,6-bis(diphenylphosphanylmethyl)benzene with Magnesium and Calcium

“…Due to this fact the phosphane bases are commonly incorporated into the anions leading to multidentate anions. Nevertheless, a variety of phosphane complexes of magnesium (see e.g., [12][13][14][15][16]) and calcium (see e.g., [15][16][17][18][19]) have been isolated and structurally studied. In order to stabilize magnesium-and calcium-based Grignard reagents, phosphanylmethyl substituents in ortho-position of the arylalkaline earth metal halides seem to be a suitable choice.…”