Structure–chiroptical property relationship of kinetically labile camphor-derivative β-diketone Yb(iii) complexes: do the adducts coexist as diastereomers or not?

Abstract

The present work examines the relationship between the crystal structures and chiroptical properties of four chiral Yb(III) complexes with camphor-derivative β-diketone ligands by means of solid-state circular dichroism (CD) spectroscopy. For the seven-coordinate complexes, [Yb(H2O)(d-hfc)3] (I) and [Yb(H2O)(l-hfc)3] (II) (d/l-hfc− = 3-heptafluorobutyryl-(+)/(−)-camphorate), the Λ- and Δ-diastereomers coexist in their crystals and no apparent bisignate couplets are observed in their solid-state CD spectra. A theoretical study indicates that the ground-state energy difference between the two diastereomers I and II is only 0.913 kcal mol−1, which explains why they could coexist in a crystal environment with the ratio of 1:1. While, eight-coordinate complexes Δ-[Yb(TPPO)2(d-hfc)3]·CHCl3·3C6H12 (III) and Λ-[Yb(TPPO)2(l-hfc)3]·CHCl3·3C6H12 (IV) (TPPO = triphenylphosphine oxide) are enantiopure in the solid-state, and typically negative and positive exciton splitting patterns around 330 nm are observed in their solid-state CD spectra. The solid-state CD spectra of these four complexes are in accordance with their X-ray single-crystal analyses. Besides, their solution CD spectra show that no particular isomer predominates in solution.