Publisher: American Chemical Society (ACS)

Issue: 6

License:

Publication date(s): 2018/03/26 (print) 2018/03/14 (online)

Pages: 1062-1073

Volume: 37 Issue: 6

Journal: Organometallics

Link: https://pubs.acs.org/doi/pdf/10.1021/acs.organomet.8b00063

URL: http://dx.doi.org/10.1021/acs.organomet.8b00063

Desilylation of the 2-phosphinophosphinine 2-PPh₂-3-Me-6-SiMe₃-PC₅H₂ with HCl gave 2-PPh₂-3-Me-PC₅H₃, demonstrating the late-stage modification of this bidentate heterocyclic ligand. Group 6 metal carbonyl complexes of these ligands showed κ² binding and very small bite angles of 65.1–68.3°, and also demonstrated that the donor properties of 2-phosphinophosphinines can be tuned readily by the presence of the SiMe₃ group, which gives a more π accepting phosphinine ligand. The properties of 2-phosphinophosphinines were compared to those of 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 Ar₂PN(R)NAr₂ 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 from standard PNP ligands in that a high proportion of alkyl- and alkenylcyclopentanes were formed. This demonstrates that the different donor properties of 2-phosphinophosphinines influence the reactivity of the key seven-membered metallacycle postulated in the metallacyclic reaction mechanism, generating products from isomerization and subsequent ethylene insertion. Alkyl- and alkenylcyclopentanes 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 industrially relevant system, in the pursuit of new products generated from ethylene.