We have investigated the addition of a simple phosphinoboronate ester, Ph2PBpin (pin = 1,2-O2C2Me4), to 2-diphenylphosphinobenzaldehyde (2-Ph2PC6H4C(O)H) and related aldimine derivatives (2-Ph2PC6H4C(NR)H) as a simple and effective strategy for generating unique diphosphine ligands bearing a pendant Lewis-acid Bpin group. These reactions proceed selectively to give one new product where the phosphide fragment has added to the aldehyde (or imine) carbon atom and the electron-deficient boron group has added to the electron-rich heteroatom. Preliminary studies show these new compounds can ligate to Pd(II) and Pt(II) metal centres. These novel metal complexes, as well as the organic soluble [MCl2(coe)]2 (M = Pd, Pt, coe = cis-cyclooctene) compounds, have been shown to be effective precatalysts in the cyclisation of alkynoic acids to give the corresponding exo-dig cyclic lactones. Reactions employing these metal complexes also generated unusual endo-dig cyclic lactones not traditionally observed in these cyclisation reactions. For instance, reactions of 4-pentynoic acid also afforded significant amounts of α-angelica lactone, a biologically-important compound traditionally prepared via the catalytic dehydration and cyclisation of levulinic acid.

Ambiphilic, Boron, Cyclisations, Palladium, Phosphine, Platinum
Journal of Organometallic Chemistry
Department of Chemistry

Kindervater, M.B. (Meagan B.), Binder, J.F. (Justin F.), Baird, S.R. (Samuel R.), Vogels, C.M. (Christopher M.), Geier, S.J. (Stephen J.), Macdonald, C.L.B, & Westcott, S.A. (Stephen A.). (2019). The phosphinoboration of 2-diphenylphosphino benzaldehyde and related aldimines. Journal of Organometallic Chemistry, 880, 378–385. doi:10.1016/j.jorganchem.2018.11.001