Accessing Alkyl- and Alkenylcyclopentanes from Cr-Catalyzed Ethylene Oligomerization Using 2-Phosphinophosphinine Ligands

Abstract

Desilylation of the 2-phosphinophosphinine 2-PPh 2-3-Me-6-SiMe 3-PC 5 H 2 with HCl gave 2-PPh 2-3-Me-PC 5 H 3 , demonstrating the late-stage modification of this bidentate heterocyclic ligand. Group 6 metal carbonyl complexes of these ligands showed κ 2-binding and very small bite-angles of 65.1-68.3°, and also demonstrated that the donor properties of 2phosphinophosphinines can be tuned readily by the presence of the SiMe 3 group which gives a more π-accepting phosphinine ligand. The properties of 2-phosphinophosphinines were compared to bidentate diphosphorus ligands computationally, contextualizing them in the Ligand Knowledge Base for bidentate P,P donor ligands (LKB-PP) and were found to occupy an area of ligand space adjacent to Ar 2 PN(R)NAr 2 ligands that have been successfully used in ethylene oligomerization reactions, but with well-separated properties in the second principal component. Testing 2-phosphinophosphinines in Cr-catalyzed ethylene oligomerization reactions showed key differences to standard PNP ligands in that a high proportion of alkyl-and alkenyl-cyclopentanes were formed. This demonstrates that the different donor properties of 2-phosphinophosphinines influence the reactivity of the key 7-membered metallacycle postulated in the metallacyclic reaction mechanism, generating products from isomerization and subsequent ethylene insertion. Alkyl-and alkenyl-cyclopentanes represent new products for the key industrial feedstock ethylene, with the alkenes having potential as new monomers, comonomers or additives for plastics. Computational evaluation of ligand properties and the resulting property maps can play a role in suggesting future ligand developments to change the selectivity of this industriallyrelevant system in the pursuit of new products generated from ethylene.

Computational Ligand Descriptors for Catalyst Design

“…124 Ligand maps can be used in their own right to select alternative ligands and set novel designs into context, as demonstrated for fluorophosphines 106 and a range of unusual ligand designs. 97,127 Going beyond a comparison of ligand properties, such maps can also be used to explore the sampling of ligand space by a set of ligands, either, as is the case in this review, driven by commercial and data availability, or for the Design of Experiments (DoE) 56,200 and the identification of areas of ligand space that correspond to favourable catalyst performance, as described by both us 96 and others 200 for LKB-P. 96 Such applications crucially depend on the availability of suitable experimental data. Here, catalyst screening with designed ligand sets, followed by several iterations of data analysis and further screening, are perhaps most promising.…”

Two isomers of a bis(diphenylphosphino)phosphinine, and the synthesis and reactivity of Ru arene/Cp* phosphinophosphinine complexes

“…Pyridylphosphinine ligands coordinated to Pd, Pt, 29 Rh and Ir 30 readily react with water or alcohols across a localised PQC double bond, with Pd/Pt complexes demonstrating syn-addition 31 but antiaddition for Ir and Rh. 30 We have explored the chemistry of BH3protected phosphinophosphinine ligands, 16,19 and BH3 protection of the PPh2 does not increase the reactivity of the phosphinine unit. BH3 does not coordinate to the phosphinine, and hence does not lead to enhanced reactivity of the phosphinine with H2O, because phosphinines are not basic (pKa E 16) 2b and so protonation is also not a feature of their chemistry as it is for phosphines.…”

“…16 Prior to this study, 2-phosphinophosphinine ligands were only characterised as bridging ligands. 8,17 Further examples of 1 as a small-bite angle 18 chelating ligand were subsequently described in a series of group 6 tetracarbonyl complexes, with 1 also able to influence the selectivity of Cr-catalysed ethylene oligomerisation reactions, 19 as well as in the Rh-catalysed hydroboration of carbonyls. 20 We now describe the extension of the synthetic route used to synthesise 1 to give bis(diphenylphosphino)phosphinines.…”

MAO‐free and extremely active catalytic system for ethylene tetramerization

“…Herein, we report another type of MAO‐free and extremely active catalytic system, whose activity is more than 10 times that of the original MAO‐based Sasol system. Catalyst development for ethylene oligomerization is still an active research topic in both academia and industry …”