No abstract

PCNP diphosphines, in conjunction with Cr(acac)3, are excellent ethylene oligomerisation catalysts with high activity and selectivity towards both 1-hexene and 1-octene formation.

Oxidation of N, N-di-n-butyldithiocarbamato (buzdtc) complexes of Cum, NiOI), ZnOI), Cd(I1) and Hg(II) is reported. Oxidation of Ni(bu2dtc)z with Clz, Brz, or of NiXz (X = CI, Br, Nos) with N,N,N',N'-tetra-n-butylthiuram disulfide (burtds) gives complexes of composition mi(buzdtc)3]X. These compounds are diamagnetic and dissolve in nitrobenzene as 1 : 1 electrolytes, their W spectra resemble that of the iso-electronic Co(buzdtc)s. The experimental data are in accord witli the assumption that in these compounds N i O (low spin d6) is surrounded by 6 S atoms in octahedral symmetry. The analogous selenium compound tris(N, N-di-n-butyldiselenocarbamato) nickelQV) bromide, having the same properties as the thio compounds, can also be prepared. Oxidation of Cu(buzdtc) with Clz or Brz yields paramagnetic products with the composition CuXa(buzdtc), in which Cu also has the formal oxidation number + 4, but the structure of these compounds is still obscure. Oxidation of Zn(buzdtc)z and the corresponding Cd and Hg compounds yields products, the analysis of which suggests the composition MXz(buzdtc)z (M = Zn, Cd or Hg, X = Br or I), but infrared studies indicate that the dithiocarbamato ligands of the starting substances are oxidized to buctds, which in the reaction products is coordinated to the metal in its normal oxidation state + 2.

The effect of ethylene tetramerisation ligand structures on 1‐octene selectivity is well studied. However, by‐product formation is less understood. In this work, a range of PNP ligand structures are correlated with the full product selectivity and with catalyst activity. As steric bulk on the N‐substituent increases, the product selectivity shifts from >10 % to < 3% of both C6 cyclics and C16+ by‐products. 1‐Octene peaks at ca. 70%. Thereafter, only 1‐hexene increases. Similar selectivity changes were observed for ortho‐Ph‐substituted PNP ligands. The C10‐14 selectivity was less affected by the ligand structure. The ligand effect on the changes in selectivity is explained mechanistically. Lastly, an increase in ligand steric bulk was found to improve catalyst activity and reduce polymer formation by an order of magnitude. It is proposed that steric bulk promotes formation of cationic catalytic species which are responsible for selective ethylene oligomerisation.