No abstract

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.

The palladium diacetate–aluminium triflate combination is an effective catalyst for the hydromethoxycarbonylation reaction of isolated alkenes and alkynes. However, its application in the hydromethoxycarbonylation of oxygen atom‐bearing alkynes is non‐trivial: the position relative to the alkyne (e.g., allylic, homoallylic) and nature of the oxygen atom determine the success of the transformation. We detail the minimum structural requirements for a successful outcome with ether‐containing alkyne substrates and hydroxyl‐containing analogues. In general, the oxygen atom has a detrimental effect on the outcome of the hydromethoxycarbonylation reaction, which can be overcome in many instances. The presence of the oxygen atom(s) causes decreases in the rate of the reaction compared to aliphatic alkynes and the closer the oxygen atom is to the triple bond, the more pronounced the effect. The chemistry is demonstrated on complex substrates derived from 5 and 6‐carbon sugars in optimised reactions.