Chirality in Distorted Square Planar Pd(O,N)₂ Compounds

Abstract

Salicylidenimine palladium(II) complexes trans-Pd(O,N)2 adopt step and bowl arrangements. A stereochemical analysis subdivides 52 compounds into 41 step and 11 bowl types. Step complexes with chiral N-substituents and all the bowl complexes induce chiral distortions in the square planar system, resulting in Δ/Λ configuration of the Pd(O,N)2 unit. In complexes with enantiomerically pure N-substituents ligand chirality entails a specific square chirality and only one diastereomer assembles in the lattice. Dimeric Pd(O,N)2 complexes with bridging N-substituents in trans-arrangement are inherently chiral. For dimers different chirality patterns for the Pd(O,N)2 square are observed. The crystals contain racemates of enantiomers. In complex two independent molecules form a tight pair. The (RC) configuration of the ligand induces the same Δ chirality in the Pd(O,N)2 units of both molecules with varying square chirality due to the different crystallographic location of the independent molecules. In complexes and atrop isomerism induces specific configurations in the Pd(O,N)2 bowl systems. The square chirality is largest for complex [(Diop)Rh(PPh3 )Cl)], a catalyst for enantioselective hydrogenation. In the lattice of two diastereomers with the same (RC ,RC) configuration in the ligand Diop but opposite Δ and Λ square configurations co-crystallize, a rare phenomenon in stereochemistry.

Enhancement of Chiroptical Responses of trans‐Bis[(β‐iminomethyl)naphthoxy]platinum(II) Complexes with Distorted Square Planar Coordination Geometry

“…Previously, we subdivided 52 crystal structures of trans ‐bis[(β‐iminomethyl)aryloxy]palladium(II) complexes into two categories, namely step and bowl arrangements, based on the Cambridge Crystallographic Database (Figure 1 ), and found that step complexes with chiral substituents and all the bowl complexes induce chiral distortions in the square planar geometries, resulting in Δ / Λ configuration (Figure 2 ). [23] In the present work, we found that a series of trans ‐bis[(β‐iminomethyl)naphthoxy]platinum(II) complexes ( 1 a – e ) with chiral ligands exhibited structure‐dependent chiroptical properties, and the unique bowl‐shaped structure with Δ / Λ chirality enhanced the chiroptical properties of these complexes (Scheme 1 ). The emission spectra showed a chromogenic change of approximately 40 nm for solid‐state emission based on conformational changes in the crystal.…”

“…ORTEP [24] drawings of ( S,S )‐ 1 a , ( R,R )/( S , S )‐ 1 a , ( R , S ) ‐ 1 a , ( S,S )‐ 1 b – d , and ( R,R )‐ 1 e are shown in Figures 3 and S10, where the chirality angles of square planar geometry O(1)−N(1)−O(2)−N(2) ( ϕ ) and bowl angles θ between the mean planes of the naphthalene rings are provided to express the degree of distortion of the coordination planes. [23] …”

“…Details of the crystal data and the structure refinement are presented in Table S1 (Supporting Information), including analysis of the intermolecular interactions (Figures S11–S17). ORTEP [24] drawings of ( S,S )‐ 1 a , ( R,R )/( S , S )‐ 1 a , ( R , S ) ‐ 1 a , ( S,S )‐ 1 b – d , and ( R,R )‐ 1 e are shown in Figures 3 and S10, where the chirality angles of square planar geometry O(1)−N(1)−O(2)−N(2) ( ϕ ) and bowl angles θ between the mean planes of the naphthalene rings are provided to express the degree of distortion of the coordination planes [23] …”

“…ORTEP [24] drawings of (S,S)-1 a, (R,R)/(S,S)-1 a, (R,S)-1 a, (S,S)-1 b-d, and (R,R)-1 e are shown in Figures 3 and S10, where the chirality angles of square planar geometry O(1)À N(1)À O(2)À N(2) (ϕ) and bowl angles θ between the mean planes of the naphthalene rings are provided to express the degree of distortion of the coordination planes. [23] The molecular structures of (S,S)-1 a, (R,R)/(S,S)-1 a, and (R,S)-1 a are shown in Figures 3a and S10. (S,S)-1 a has a bowl configuration (θ = 49.6°), and the two methyl groups have a syn-orientation (Figure 3a).…”

Sign control of circularly polarized luminescence of chiral Schiff-base Zn(ii) complexes through coordination geometry changes

“…Chiral zinc(II) complexes 1 and 2 were prepared by the reaction of ZnCl 2 with the corresponding optically pure Schiff-base ligands in the presence of t BuOK in MeOH (Scheme S1, ESI †). The complexes were successfully characterized by 1 H and 13 C NMR (Fig. S1-S6, ESI †), nuclear gradient correlation spectroscopy (gCOSY) and Overhauser effect spectroscopy (NOESY).…”