Pd- ?³ -C₆H₉ complexes of the Trost modular ligand: high nuclearity columnar aggregation controlled by concentration, solvent and counterion.

ABSTRACT: Under optimised conditions, the Trost modular ligand (TML) series induces high levels of asymmetric induction in an extraordinarily wide range of reactions involving palladium ?-allyl intermediates. Prior mechanistic investigations into reactions involving Pd-?³-C₆H₉ intermediates have focussed on the monomeric 13-membered ring formed via P,P-chelation of the ligand to Pd. However, it is also recognised that ring-opening oligomerisation provides a pool of high nuclearity Pd-?³-C₆H₉ species that, by affording a low level, or even the opposite sense, of asymmetric induction relative to the mononuclear species, are responsible for a reduction in selectivity under non-optimised conditions. Herein we describe an investigation by NMR spectroscopy, molecular mechanics, molecular dynamics, and small-angle neutron scattering (SANS), of a Pd-?³-C₆H₉ cation bearing the 1,2-diaminocyclohexane TML ligand (2). Using both nondeuterated and perdeuterated (D₄₇) isotopologues of the resulting complexes ([1]⁺), we show that a two-stage oligomerisation-aggregation process forms self assembled cylindrical aggregates of very high nuclearity (up to 56 Pd centres). We also investigate how concentration, solvent and counter-anion all modulate the extent of oligomerisation.

SUBMITTER: Racys DT 

PROVIDER: S-EPMC5520773 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature