Enantiopure Chiral Coordination Polymers Based on Polynuclear Paddlewheel Helices and Arsenyl Tartrate

Abstract

Herein, we report the preparation of chiral, one-dimensional coordination polymers based on trinuclear paddlewheel helices [M 3 (dpa) 4 ] 2+ (M = Co(II) and Ni(II); dpa = the anion of 2,2 -dipyridylamine). Enantiomeric resolution of a racemic mixture of [M 3 (dpa) 4 ] 2+ complexes was achieved by chiral recognition of the respective enantiomer by [∆-As 2 (tartrate) 2 ] 2− or [Λ-As 2 (tartrate) 2 ] 2− in N,N-dimethylformamide (DMF), affording crystalline coordination polymers formed from [(∆-Co 3 (dpa) 4 )(Λ-As 2 (tartrate) 2 )]·3DMF (∆-1), [(Λ-Co 3 (dpa) 4 )(∆-As 2 (tartrate) 2 )]·3DMF (Λ-1), [(∆-Ni 3 (dpa) 4 )(Λ-As 2 (tartrate) 2 )]·(4 − n)DMF·nEt 2 O (∆-2) or [(Λ-Ni 3 (dpa) 4 )(∆-As 2 (tartrate) 2 )]·(4 − n)DMF·nEt 2 O (Λ-2) repeating units. UV-visible circular dichroism spectra of the complexes in DMF solutions demonstrate the efficient isolation of optically active species. The helicoidal [M 3 (dpa) 4 ] 2+ units that were obtained display high stability towards racemization as shown by the absence of an evolution of the dichroic signals after several days at room temperature and only a small decrease of the signal after 3 h at 80 • C.

Chiral Octapalladium Chains Supported by Enantiopure P-Stereogenic Linear Tetraphosphines, (R,R)- and (S,S)-Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2

“…Since ( R,R )- and ( S,S )-dpmppm have broad absorption around 250 nm with small |Δε| (∼2 M –1 cm –1 ), the absorption bands with longer wavelengths are derived from MM and ML charge transfers. While the CD spectra for the NIR region around 930 nm were unfortunately not measured as meaningful data due to the extremely high extinction coefficient of the absorption band, the CD spectra together with UV–vis-NIR and 1 H and 31 P­{ 1 H} NMR spectral data (Figures S23–S25) demonstrate that 2 RR and 2 SS are the enantiopure chiral metal chains which are recognized as the longest characterized chiral EMACs, thus far. − As we already reported that the Pd 8 chains with meso - and rac -dpmppm ligands, [Pd 8 ( meso - or rac -dpmppm) 4 (L) 2 ] 4+ (L = CH 3 CN, dmf), are dissociated into two Pd 4 units, [Pd 4 ( meso - or rac -dpmppm) 2 (L) 2 ] 2+ (L = dmf) at higher temperature above 100 °C in dmf, and that they are self-aligned into the original Pd 8 chains at lower temperature below 60 °C, it was confirmed that the CD spectra of 2 RR and 2 SS in CH 3 CN were restored even after heating at around 70 °C, without racemization of P -stereogenic centers of dpmppm ligands.…”

“…The notation of Δ and Λ means the handedness of the tricobalt helix, right ( P ) and left ( M ), respectively. Later, chiral resolution of an analogous trinickel complex, [Ni 3 (dpa) 4 XCl] (X = Cl, OH), was performed by using preparative chiral chromatography, and racemic pairs of [M 3 (dpa) 4 ­(CH 3 CN) 2 ] 2+ (M = Co­(II), Ni­(II)) were resolved by diastereomeric ion pairing with Δ or Λ-[As 2 (tartrate) 2 ] 2– and selective crystallization. , Enantiopure pentanickel strings, Δ- and Λ-[Ni 5 ((−)- or (+)-camnpda) 4 ], were synthesized by introducing the chiral camphorsulfonyl group into a pyridyl-naphthyridyl diamide ligand (camnpda) (Scheme ), which is at present the longest chiral EMAC …”

“…Later, chiral resolution of an analogous trinickel complex, [Ni 3 (dpa) 4 XCl] (X = Cl, OH), was performed by using preparative chiral chromatography, 27 and racemic pairs of [M 3 (dpa) 4 -(CH 3 CN) 2 ] 2+ (M = Co(II), Ni(II)) were resolved by diastereomeric ion pairing with Δ or Λ-[As 2 (tartrate) 2 ] 2− and selective crystallization. 28,29 Enantiopure pentanickel strings, Δand Λ-[Ni 5 ((−)-or (+)-camnpda) 4 ], were synthesized by introducing the chiral camphorsulfonyl group into a pyridyl-naphthyridyl diamide ligand (camnpda) (Scheme 2), which is at present the longest chiral EMAC. 30 In the present study, we have intended to establish optical resolution of rac-dpmppm, with an aim of creating chiral octapalladium chains supported by enantiopure dpmppm ligands, and found an effective synthetic route via a cyclic tetranuclear Pd(II) complex with a chiral bisisocyanide, 1,1′binaphthyl-2,2′-bisisocyanide (Binac), in which chirality of dpmppm and Binac ligands is sorted as (R*,R*) and (R*).…”

Resolution, structures, and vibrational circular dichroism of helicoidal trinickel and tricobalt paddlewheel complexes

“…It has been recently reported that the combination of AsT and [Ni3(dpa)4(CH3CN)2] 2+ in DMF yields chiral onedimensional coordination polymers constructed of axiallybound AsT linking the trimetal units together in an alternating Ni3(dpa)4-AsT motif. 7 However, when the reaction is performed in acetonitrile, discrete trinuclear chiral complexes were obtained. These compounds are isostructural with the cobalt(II) congener ( [Co3(dpa)4(CH3CN)2](PF6)2 (-and -2) and [Ni3(dpa)4(CH3CN)2](PF6)2 (-and -4), respectively.…”