Crystallographic and NMR Studies on Chiral Palladium(II) Allyl Ferrocene-Based P,N Complexes

Abstract

Detailed crystallographic and NMR measurements are reported for several Pd(II) allyl complexes containing chiral ferrocene-based phosphinopyrazole ligands, CpFe{η5-C5H3(1-CH(CH3)(NNC(R1CHCR2)-2-PPh2)}, 1. Relative to similar BINAP, CHIRAPHOS, and diphosphine JOSIPHOS analogs, the major isomer of the β-pinene allyl complex [Pd(η3-C10H15)(1a)]CF3SO3, 2, R1 = R2 = H, shows a surprisingly large trans influence for the PPh2 donor moiety, based on 13C data. The solid-state structure for 2 shows normal bond lengths, although there are indications that the allyl adjusts its position due to the relatively large P,N ligand. The solid- and solution-state structures of [Pd(η3-PhCHCHCHPh)(1g)]PF6, 3g, R1 = adamantyl and R2 = H (99% ee in the enantioselective allylic amination), show the allyl ligand to be strongly rotated, thus placing the terminal allyl carbon proximate to the pyrazole moiety, significantly below the coordination plane. These structural results suggest that, for the enantioselective catalysis using ligands 1, there is an “early” transition state.