om500582w_si_001.pdf (3.93 MB)
Air-Stable Chiral Primary Phosphines: A Gateway to MOP Ligands with Previously Inaccessible Stereoelectronic Profiles
journal contribution
posted on 2015-12-17, 05:58 authored by Arne Ficks, William Clegg, Ross W. Harrington, Lee J. HighamThe
air-stable chiral primary phosphines 1a,b facilitate the synthesis of previously inaccessible or hard-to-access
chiral MOP-type ligands 2a,b–5a,b, which can be prepared in one-pot reactions.
These derivatives have been prepared to allow for a unique comparison
of their differing structural and electronic profiles, determined
here by a number of experimental and theoretical studies. Phosphiranes 2a,b and phosphonites 5a,b are electron-poor compounds, with the former possessing exceptional
thermal stability. Conversely, the dimethylarylphosphines 3a,b and bis(dimethylamino)arylphosphines 4a,b are good electron donors, and, in contrast to earlier
reports, the dialkylarylphosphines were found to be remarkably air-stable.
The ligands were coordinated to platinum(II), and the weak trans-influence of the highly strained phosphiranes 2a,b was revealed both in solution and in the
solid state. The steric parameters of the ligands were investigated
by the allyl rotation of their methallylpalladium(II) complexes, which
showed subtle differences in exchange rates. Aryl side-on coordination
of the MOP-backbone to palladium(II) was observed for complexes with
a non-coordinating counterion and structurally analyzed in the case
of ligand 4b. The asymmetric induction and catalytic
activity of 2a,b–5a,b were tested in the hydrosilylation of styrene as well as
the allylic alkylation of (rac)-(E)-1,3-diphenylallyl acetate. Major differences in reactivity were
related back to the electronic parameters of the ligands.