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.

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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