STRUCTURE AND DYNAMICS OF CHIRAL ALLYL COMPLEXES OF PD(II) - NMR-SPECTROSCOPY AND ENANTIOSELECTIVE ALLYLIC ALKYLATION

The idea of NOE 'reporter ligands', be they simple nitrogen chelates o r relatively complicated bidentate phosphine compounds, is explored. T hese NMR experiments lead to a better understanding of subtle (allyl h ybridization, phenyl-phenyl stacking) and gross (three-dimensional asp ects, shape of the chiral pocket) structural features in the chemistry of chiral palladium-allyl complexes. Combined with X-ray crystallogra phy and MM2 calculations, one can learn how the BINAP, CHIRAPHOS and JOSIPHOS families of chiral ligands use steric effects to transfer chi ral information. A relatively rigid chiral pocket seems a necessary, b ut not sufficient, condition, since an intrusive chiral pocket leads t o syn-anti isomers. Two-dimensional exchange NMR has shown unexpected selectivity with respect to allyl isomerization. The eta(3)-eta(1) iso merization can be under either electronic or steric control. The termi nal allyl C-13 chemical shifts in 1,3-diphenylallyl palladium(II) comp lexes of various chelate ligands are discussed.