Abstract
Chromium(iii) complexes of chelating diphosphines, with PNP or PCNCP backbones, are excellent catalysts for ethylene tetra- and/or trimerisations. A missing link within this ligand series are unsymmetric chelating diphosphines based on a PCNP scaffold. New bidentate PCNP ligands of the type Ph2PCH2N(R)PPh2 (R = 1-naphthyl or 5-quinoline groups, 2a-d) have been synthesised and shown to be extremely effective ligands for ethylene tri-/tetramerisations. Three representative tetracarbonyl Cr0 complexes bearing a single PN(R)P (5), PCN(R)P (6), or PCN(R)CP (7) diphosphine (R = 1-naphthyl) have been prepared from Cr(CO)4(η4-nbd) (nbd = norbornadiene). Furthermore we report a single crystal X-ray diffraction study of these compounds and discuss their structural parameters.
Highlights
There has been considerable interest in developing new homogeneous catalysts for selective ethylene oligomerisations affording, with high selectivity, linear alkenes such as 1-hexene or 1-octene.[1]
As part of our studies regarding the synthesis of PNP and PCNCP ligands,[26,27] we explored a missing counterpart to these two classes, namely PCNP bidentate ligands bearing two electronically different trivalent phosphorus centres
Four unsymmetrical bidentate PCNP ligands have been synthesised in a two-step reaction sequence
Summary
There has been considerable interest in developing new homogeneous catalysts for selective ethylene oligomerisations affording, with high selectivity, linear alkenes such as 1-hexene or 1-octene.[1]. Ligands 2a–d prepared by this route were found to be air stable both in the solid state and in solution. The 31P{1H} NMR spectra were in good agreement with structures based on coordinated symmetrical PNP (5, δ 117.5 ppm) and PCNCP (7, δ 41.0 ppm) ligands along with an AX spectrum for the unsymmetrical fivemembered PCNP chelate complex 6 [δ 67.9 (PCH2), 142.8 (PN), JPP = 32 Hz].
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