Supported Ni catalysts have been studied for the first time during dimerization of butenes by operando EPR and in situ XAS at 353 K and up to 16 bar. Single Ni^I/Ni^II shuttles were identified as active sites, whereby the conversion of initial Ni^I to Ni^II by oxidative addition of butene is obviously faster than the re-reduction of Ni^II to Ni^I by reductive elimination of the C8 product, rendering the equilibrium percentage of Ni^I small. At p ≦ 2 bar, Ni^I single sites form inactive Ni⁰ aggregates, while this is suppressed at higher pressure (≈ 12 bar). A reaction mechanism is proposed

The synthesis of [Ph₂PN(ⁱPr)P(Ph)NH(R)] (R = ⁱPr, Et) (1, 2) is described and the structure of 2 has been determined by single-crystal X-ray analysis. Compound 1 readily reacts with chromium(0), nickel(0), nickel(II), palladium(II), platinum(II) and iron(II) complexes to give four-membered rings (3–10) via P,P′ coordination. The molecular structures of [Cr(CO)₄{Ph₂PN(ⁱPr)P(Ph)NH(R)-P,P′}] (R = ⁱPr, Et) (3, 4), [Cr(CO)₃(NCCH₃){Ph₂PN(ⁱPr)P(Ph)NH(ⁱPr)-P,P′}] (5), [Ni{Ph₂PN(ⁱPr)P(Ph)NH(ⁱPr)-P,P′}₂] (6), cis-[MX₂{Ph₂PN(ⁱPr)P(Ph)NH(ⁱPr)-P,P′}] (M = Ni, Pd, Pt; X = Cl or Br) (7, 8, 9) and trans-[Fe(NCCH₃)₂{Ph₂PN(ⁱPr)P(Ph)NH(ⁱPr)-P,P′}₂](BF₄)₂ (10) have been determined by X-ray diffraction. In the solid state, these complexes show tight phosphine bite angles in the range 67.89(2)° to 74.97(4)° and the central nitrogen atom adopts an almost planar (sp²) geometry. Complexes 3, 5, 6, 7 and 10 are tested for their catalytic activity in ethylene oligomerisation. Additionally, complex 10 is tested in hydrogenation of olefins.