Nobbs, J. D., Tay, D. W. P., Yeap, Y. H., Tiong, Y. L., Ye, S., Aitipamula, S., Wang, C., Cheong, C. B., & van Meurs, M. (2023). Dioxaphosphabicyclooctanes: small caged phosphines from tris(hydroxymethyl)phosphine. Dalton Transactions, 52(47), 17954–17965. https://doi.org/10.1039/d3dt02577b
Abstract:
Dioxaphosphabicyclo[2.2.2]octanes (L1–L4) have been prepared in a one-pot reaction from tris(hydroxymethyl)phosphine and various α,β-unsaturated ketones. The non-volatile phosphines oxidise very slowly in air. They possess highly upfield 31P chemical shifts (−59 to −70 ppm), small cone angles (121–140°) and a similar electronic parameter to PPh3. Reaction of L1 with [Rh(acac)(CO)2] gave the complex [Rh(acac)(CO)(L1)] with a ν(C[triple bond, length as m-dash]O) of 1981.5 cm−1, whereas reaction L1 with [Rh(CO)2Cl]2 gave [Rh(CO)(L1)2Cl] with a ν(C[triple bond, length as m-dash]O) of 1979.9 cm−1, remarkably similar to the CO stretching frequencies reported for analogous PPh3 complexes. The cage phosphines were explored as ligands in rhodium catalysed hydroformylation of 1-octene. All of the ligands gave a linear selectivity to n-nonanal of 68%, regardless of the substituents. However the ligand substituents had a significant effect on the catalyst activity, with increased steric bulk around the coordination environment giving a three-fold increase in aldehyde yield. The phosphines undergo ligand subsitution with [Pd(MeCN)2Cl2] forming square planar trans-[Pd(L)2Cl2] complexes. Subsequent reduction with hydrazine furnishes homoleptic tetravalent [Pd(L1)4] which was applied as a catalyst in Suzuki–Miyaura couplings, furnishing the C–C coupled products in moderate yields.
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Funding Info:
This research / project is supported by the A*STAR - Career Development Fund (CDF)
Grant Reference no. : C210812026