Ion-Pairing Chirality Transfer in Atropisomeric Biaryl-Centered Gold Clusters

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE1 Jan 2021Ion-Pairing Chirality Transfer in Atropisomeric Biaryl-Centered Gold Clusters Kui Xiao†, Yang Xue†, Biao Yang and Liang Zhao Kui Xiao† Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084. , Yang Xue† Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084. , Biao Yang Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084. and Liang Zhao *Corresponding author: E-mail Address: [email protected] Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084. https://doi.org/10.31635/ccschem.020.202000225 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The stereocontrol of chiral metal clusters and nanoclusters has become a focus of interest in metal cluster chemistry due to their promising applications in asymmetric catalysis. Despite being a general chirality transfer strategy, the ion-pairing process is still ambiguous in the course of bestowing chirality to metal clusters. Here we construct a biaryl-centered axially chiral gold-cluster system to study an outside-in ion-pairing chirality transfer process. Four hexanuclear gold(I) clusters, centered by two types of biaryl ligands [(2-indolyl)aniline ( L 1) and biindole ( L 2)], were synthesized via in situ cyclization reactions. In the crystalline state, the biaryl centers showed axial chirality in which the gold atoms were in an asymmetric arrangement. In solution, the chiral phosphates induced an outside-in chirality transfer by significant interactions with the periphery of the biaryl-centered gold clusters. Finally, the chiral resolution of hexa-aurated biindoliums was accomplished via an efficient outside-in chirality transfer process relying on strong aurophilic interaction and extra peripheral coordination. This study not only deepens the understanding of the outside-in ion-pairing chirality transfer process but also provides a new approach for fabricating desired chiral metal clusters by a combination of organometallic transformation and chirality transfer. Download figure Download PowerPoint Introduction Chirality is an intriguing geometrical property of molecules that describes a kind of structure nonsuperimposable with their mirror images. Among many practical methods for asymmetric chemical synthesis, chiral ion-pairing represents a powerful strategy that involves efficient chirality transfer from an enantiomerically pure ionic species to a charged reaction substrate or intermediate.1–4 In the case of metal catalysis with chiral counteranions (e.g., binaphthol-derived phosphates), enhanced electrostatic interaction in specific solvents with low dielectric constants often promotes the enantioselectivity by fixing the enantio-determining transition states.5,6 Besides the asymmetric organic synthesis, the counterion-pairing induction strategy could also be applied to the enantioselective synthesis of charged chiral metal clusters,7 which are regarded as the new generation of chiral catalysts.8–11 In comparison with the commonly used methods such as the employment of chiral ligands in the clustering processes12–16 or the enantio-separation by chiral high-performance liquid chromatography (HPLC),17–21 the ion-pairing strategy is a simple and easily operable way to achieve chiral metal clusters. More importantly, the resulting enantiomerically pure metal clusters, together with chiral counterions might provide dual stereocontrol for the reaction substrates, and thus, enhance the enantioselectivity of asymmetric catalysis efficiently. To date, remarkable achievements have been made in the ion-pairing-induced chiral resolution of molecular coordination complexes and metallasupramolecular cages by the Pfeiffer effect.22–25 However, the application of the chiral counterion-pairing strategy in the synthesis of chiral metal clusters encounters many formidable challenges such as the controllable construction, transfer, and propagation of metal-based chirality. The labile and sophisticated structures and the low-energy requirements for stereoisomeric interconversion26 of chiral metal clusters constitute two key obstacles. Furthermore, the monitoring of the structural variation during the ion-pairing chirality transfer process needs comprehensive techniques such as X-ray single-crystal diffraction (SC-XRD), variable temperature circular dichroism (VTCD),19,26 vibrational circular dichroism (VCD),27 in situ nuclear magnetic resonance (NMR),12,21 and theoretical calculation. We sought to address the chirality transfer details in the ion-induced process to realize the absolute stereocontrol of chiral metal clusters. Herein, we constructed a biaryl-centered gold-cluster system to study an outside-in ion-pairing chirality transfer process. Biaryl compounds are a class of atropisomers whose racemization based on the rotation about the central single bond is dependent on the hindrance of adjacent substitutes and some biaryl-spanning interactions.28 Therefore, we designed a biaryl center with axial chirality and assumed that the chirality of the biaryl-centered metal cluster species would be affected by peripheral counterions through an outside-in chirality transfer, in which the substituent bulkiness and the metal–metal interaction would not be significant enough to restrict the central bond rotation (Scheme 1a). Scheme 1 | (a) A pair of enantiomeric gold-cluster structures with an axially chiral biaryl center. (b) Molecular structures of two in situ generated biaryl ligands used in this study. The colored carbon and nitrogen atoms are in deprotonated form during the formation of the gold metal clusters. Download figure Download PowerPoint Subsequently, we constructed an axially chiral gold-cluster system that contained (2-indolyl)aniline and biindole tetraanions ( L 1 and L 2 in Scheme 1b) as the biaryl centers. The axial chirality of L 1 and L 2 is matched with the specific asymmetric arrangement of gold atoms in the corresponding Au6 and Au4 clusters in crystal structures, while these structures racemized readily in solution. When the external chiral phosphates were introduced to the solution of the biaryl-centered gold-cluster racemates, a significant and compact interaction of phosphate anions with the periphery of the clusters promoted the efficiency of an outside-in chirality transfer, a process that was investigated in detail via characterization using X-ray crystallography, monitoring by NMR, CD, and VCD spectroscopy, and comparing the X-ray crystal structures with those obtained from a conducted theoretical calculation. The absolute stereocontrol of an axially chiral gold cluster via the chiral anion-pairing method was realized finally by strengthening aurophilic interaction and supplementing extra peripheral coordination. The outside-in chirality transfer evidenced in this study provides a promising method to achieve chiral metal clusters with more structural diversity, thus potentiating their future applications in asymmetric catalysis. Experimental Methods Experimental details and characterization methods are available in Supporting Information. Results and Discussion Synthesis and structures of biaryl-centered gold clusters Our synthesis of biaryl-centered gold-cluster compounds relied on an intramolecular nucleophilic attack of an aurated μ3-imido group on a carbon–carbon triple bond. In gold catalysis chemistry, both the π-activation of a 1,2-disubstituted alkynyl group and the activation of a nucleophilic group are essential for the subsequent nucleophilic attack.29–31 We previously found that the NH2 group of 2-(phenylethynyl)aniline could be deprotonated by [(PPh3Au)3(μ3-O)](BF4) ( [Au3O]) to produce a highly nucleophilic μ3-imido trinuclear gold(I) moiety. However, the subsequent nucleophilic attack on the inner alkynyl group was interrupted due to the lack of π-activation of the C≡C.32 Thus, here, we selected purposefully two diamine substrates 1 and 4 containing 1,2-diphenylethyne and 1,4-diphenylbuta-1,3-diyne skeletons, respectively. Treatment of 1 or 4 with two equivalents of [Au3O] led to 2·(BF4) and 5·(BF4) quantitatively, which were isolated as colorless crystals in high yields (85% and 93%, respectively; Scheme 2). X-Ray crystallographic analysis revealed that 2·(BF4) and 5·(BF4) both contained two inversion-related N(AuPPh3)3 moieties (Scheme 2). The composition and structural consistence of 2·(BF4) and 5·(BF4) were confirmed by high-resolution electrospray ionization mass spectrometry (ESI-MS; Supporting Information Figures S1−S2), elemental analysis, and NMR ( Supporting Information Figures S3−S4). Notably, only a single sharp peak was observed in the 31P NMR spectra of 2·(BF4) and 5·(BF4), suggesting that the [N(AuPPh3)3] moieties might rotate freely around the corresponding N–Cphenyl bonds at room temperature. Scheme 2 | Synthetic procedures for 3·(BF4), 6, 7·(BF4), and 8·(BF4). Crystal structures of 2·(BF4) and 5·(BF4) are shown as insets with anions and solvent molecules omitted for clarity. Ph = phenyl and Py = 2-pyridyl. Download figure Download PowerPoint When the solution of 2·(BF4) was kept for 3 days, we found that 85% 2·(BF4) spontaneously transformed into a new complex 3·(BF4) ( Supporting Information Figures S5a). 3·(BF4) was identified as containing a 2-indolylaniline tetraanion moiety L 1 surrounded by a hexagold chain, based on X-ray crystallographic analysis vide infra. Structural scrutiny of 2·(BF4) revealed that the two NAu3 units had close interaction with the central C≡C (Au2-C1 = 3.235 Å and Au3-C1 = 3.327 Å). As the NAu3 unit I activates the C≡C by π-coordination, another NAu3 II would easily attack the activated C≡C from the back side to complete the cyclization spontaneously (Scheme 2). In contrast, upon extending the central alkyne chain in 2·(BF4) to a diyne in 5·(BF4), the carbon–carbon triple bond TB1 activated by the NAu3 unit I was obstructed from the attack of the outlying NAu3 unit II at back side (Scheme 2). Therefore, 1 equiv of silver triflate (AgOTf) was required to supply π-activation to accelerate the 5-to- 6 transformation ( Supporting Information Figures S5b). The product 6 was identified as a hexagold cluster of the tetraanion moiety L 2vide infra. Also, the composition and structural consistence of 3·(BF4) and 6 were confirmed by high-resolution ESI-MS ( Supporting Information Figures S6 and S7), elemental analysis, and NMR ( Supporting Information Figures S8 and S9). Further, we synthesized two more complexes, 7·(BF4) and 8·(BF4), to investigate the influence of provision of extra control on the coordination mode. Complexes 7·(BF4) and 8·(BF4) were prepared by replacing PPh3 (Ph = phenyl) with PPh2Py (Py = 2-pridyl) and adopting a simple and practicable one-pot synthetic method (Scheme 2). By adding 2 equiv of silver tetrafluoroborate to the solution of 1 (1 equiv) and {(PPh2PyAu)3(μ3-O)](BF4) ( [Au3O']), 2 equiv)}, 7·(BF4) was synthesized quantitatively within 5 h, as monitored by 1H NMR spectra ( Supporting Information Figure S10a). Similarly, 8·(BF4) was obtained by applying 3 equiv of silver tetrafluoroborate to the solution of 2 (1 equiv) and [Au3O'] (2 equiv) ( Supporting Information Figure S10b). As similar as the composition of 3·(BF4), complex 7·(BF4) has the formula of [(PPh2PyAu)6( L 2)](BF4)2 based on high-resolution ESI-MS, 1H NMR ( Supporting Information Figures S11 and S13), and elemental analysis. However, due to the bidentate coordination of the PPh2Py ligand, only five PPh2Py ligands were included in the structure of 8·(BF4), as evidenced in the high-resolution ESI-MS and NMR spectra ( Supporting Information Figures S12 and S14). The structures of the axially chiral clusters 3·(BF4), 6 and 8·(BF4) were confirmed by X-ray crystallographic analysis. As shown in Figure 1, the axially chiral cluster cations of all three compounds possessed similar chiral features that include a biaryl center with variable dihedral angles between two aryl planes and a cluster aggregate composed of asymmetrically arranged gold atoms. In the crystal structure of 3·(BF4), three anionic positions of L 1 (N1, N2, and C8) were surrounded by six interconnected gold atoms [2.788(1)−3.211(1) Å] through a μ6-N1,N2,C8-η3,η1,η2 coordination mode (Figure 1a). The phenyl ring and the indolyl ring in L 1 formed a dihedral angle of 82.4°, thus generating a kind of axial chirality. The Au–C [2.118(8)–2.130(8) Å] and Au–N [2.032(8)–2.142(8) Å] distances were comparable to the values in reported gold–indolyl32 and gold−imido complexes.33,34 It is apparent that the equalized C–N and C–C bond lengths of the newly formed five-membered ring indicated the occurrence of the hyperconjugative aromaticity due to the unusual C–Au2 bonding fashion at C8.32,35,36 Furthermore, three gold-containing parts N2–Au6, N1–(Au3–Au4–Au5) and C8–(Au1–Au2) were linked together by twofold moderate aurophilic interactions37–40 [Au2–Au3 = 2.933(1) Å and Au5–Au6 = 3.196(1) Å] to finally constitute a nonplanar asymmetric gold chain. The C2/c space group of 3·(BF4) indicated that two enantiomers of L 1-(AuPPh3)6 coexisted in the crystal structure. In the crystal structure of 6, two different counter anions (a triflate and a tetrafluoroborate) were involved. The biaryl skeleton L 2 therein was featured by two indole rings arising from a two-step cyclization (Figure 1b). Two carbon atoms (C7 and C10) and two indolyl nitrogen atoms (N1 and N2) of L 2 were negatively charged. Each carbon atom connected with a short Au–Au edge (Au1−Au3 = 2.875(1) and Au2−Au4 = 2.910 (1) Å), and two resulting CAu2 units were linked together by threefold aurophilic interactions in the range of 3.026(1)–3.329(1) Å. On the other side of L 2, N1 and N2 span a dimeric gold edge Au5–Au6 [3.145(1) Å]. In this way, the biaryl axial chirality of L 2 (the dihedral angle between two indolyl rings equals to 45.9 °) was fixed by multifold aurophilic interactions. Complex 8·(BF4) shared the same biindole skeleton of L 2 with 6, but the two CAu2 units at C7 and C10 were linked by only onefold strong aurophilic interaction [Au2–Au3 = 2.840(1) Å] due to the bidentate coordination of a PPh2Py ligand (Figure 1c). Accordingly, two indolyl rings of 8·(BF4) constituted a larger dihedral angle of 48.3 °. Figure 1 | Crystal structures and cluster cores of biaryl-centered gold clusters (a) 3·(BF4), (b) 6, and (c) 8·(BF4) with counter anions, hydrogen atoms, and solvent molecules omitted for clarity. Selected bond lengths and distances (Å): 3·(BF4): N1−Au3 2.099(9); N1−Au4 2.032(8); N1−Au5 2.142(8); N2−Au6 2.064(7); C8−Au1 2.130(8); C8−Au2 2.118(8); Au1−Au2 2.788(1); Au2−Au3 2.933(1); Au3−Au4 3.211(1); Au3−Au5 2.987(1); Au4−Au5 2.987(1); Au5−Au6 3.196(1). 6: N1−Au5 2.073(12); N2−Au6 2.042(8); C7−Au1 2.147(11); C7−Au3 2.123(11); C10−Au2 2.111(12); C10−Au4 2.125(10); Au1−Au2 3.296(1); Au1−Au3 2.875(1); Au2−Au3 3.026(1); Au2−Au4 2.910 (1); Au3−Au4 3.329(1); Au5−Au6 3.145 (1). 8·(BF4): N1−Au5 2.045(14); N2−Au6 2.039(16); C7−Au1 2.126(15); C7−Au3 2.109(18); C10−Au2 2.020(18); C10−Au4 2.130(18); Au1−Au3 2.852(1); Au2−Au3 2.840(1); Au2−Au4 2.873(1); Au5−Au6 3.114 (1). Color scheme for atoms: C, gray; N, blue; P, green; Au, yellow. Download figure Download PowerPoint The structures of four axially chiral cluster compounds 3·(BF4), 6, 7·(BF4), and 8·(BF4) in solution were characterized by NMR. As evidenced by ESI-MS mentioned earlier, these four gold-cluster compounds kept intact structures in solution. In the 31P NMR spectrum of 3·(BF4) at room temperature ( Supporting Information Figure S8), four peaks at 36.2, 36.3, 30.9, and 26.2 ppm were assigned to the C(AuPPh3)2, N(AuPPh3), and N(AuPPh3)3 moieties, respectively, as shown in the crystal structure. Notably, the broad peak at 26.2 ppm corresponding to the N(AuPPh3)3 moiety in 3·(BF4) was in sharp contrast to the sharp single peak (27.9 ppm) of the N(AuPPh3)3 in 2·(BF4), suggesting the obstruction of the NAu3–Cphenyl bond rotation in 3·(BF4) due to the presence of adjacent C(AuPPh3)2 and N(AuPPh3) moieties. Moreover, in the low-temperature 31P NMR spectra of 3·(BF4) ( Supporting Information Figure S15), the well-identified four peaks were split into several peaks below –40 °C due to many conformational isomers. Complexes 6 and 8·(BF4) shared a common biindole tetraanion moiety L 2 and a surrounding hexagold cluster, while 6 had six PPh3 ligands and 8·(BF4) consisted of five PPh2Py ligands. However, there were only three peaks in the 31P NMR of 6, in sharp contrast to up to eight peaks in the 31P NMR of 8·(BF4) due to the existence of conformational isomers. This result implied that in solution the structure of 8·(BF4) was rigidified more effectively by the bidentate coordination of PPh2Py. Synthesis of chiral metal clusters by the ion-pairing induction of chiral phosphate anions Next we attempted to acquire chiral gold-cluster compounds by a chiral ion-pairing method (Figure 2a). In view of the positive nature of 3·(BF4), 6, 7·(BF4), 8·(BF4) and their precursors, the enantiomerically pure (R/S)-1,1'-binaphthyl-2,2'-diylphosphates ( R / S -Phos·Na) were selected as the chiral inductors.2,41 In order to reveal the stereocontrol details in the ion-pairing process, we attempted to replace the tetrafluoroborate anions in 2·(BF4) by chiral anions to generate 3·( R -Phos) in situ. A D2O solution of R -Phos·Na was mixed with deuterated dichloromethane (CD2Cl2) solution of 2·(BF4) to produce a biphasic mixture, which was then subjected to three-times washing with D2O to remove the highly water-soluble NaBF4. As evidenced by the 19F NMR monitoring ( Supporting Information Figure S16), the content of BF4− decreased to 7%. The 1H NMR spectrum of the resulting complex [denoted as 2·( R -Phos)] showed a stoichiometric 1∶2 ratio between the positive cluster moiety and the chiral phosphates (Figure 2b). As similar as the 2·(BF4)-to- 3·(BF4) transformation, 2·( R -Phos) underwent a spontaneous transformation to yield 3·( R -Phos) quantitatively. Unfortunately, the attempt to obtain pure 6·( R -Phos) by the same synthetic protocol was unsuccessful. The requirement of silver salt in the 5-to- 6 transformation complicated the synthetic system drastically. Complexes 7·( R -Phos) and 8·( R -Phos) were synthesized directly by anion exchange and solvent extraction from 7·(BF4) and 8·(BF4) (Figure 2a). The proton signals of the phosphate-included cluster compounds were assigned according to the H–H correlated spectroscopy (COSY) NMR spectra ( Supporting Information Figures S18–S21). Figure 2 | (a) Synthetic procedures for the phosphate complexes 3·(R-Phos) and 8·(R-Phos). (b) 1 H-NMR spectra (CD2Cl2, 298 K) of 3·(BF4), 3·(R-Phos), 2·(R-Phos), and 2·(BF4). (c) Chemical shift difference of the H4 (CD2Cl2) in 3·(R-Phos), 7·(BF4), and 3·(BF4) from 293 to 223 K. (d) 1 H-NMR spectra (CD2Cl2, 298 K) of 8·(BF4), 8·(R-Phos), and 8·(S-Phos). (e) Variable-temperature 31 P NMR spectra (CD2Cl2) of 8·(R-Phos) from 20 to –60 °C. H-NMR, proton nuclear magnetic resonance. Download figure Download PowerPoint Although the counter anions were replaced by chiral phosphates, it was still mysterious how efficient the chiral anions were able to transfer chirality to the cationic cluster species. Generally, the process was dependent on the structural rigidity of the cluster cations and the anion–cation interactions. In order to identify the interactions between chiral phosphate anions and the cluster cations in the induction process, we compared the NMR spectra of 3·(BF4), 7·(BF4), and 8·(BF4) with their chiral phosphate counterparts. As shown in Figure two peaks at and corresponding to the and on the indole ring of 3·(BF4) to and ppm in 3·( R a by the R The close and interaction of L and R were confirmed by nuclear spectroscopy NMR ( Supporting Information Figure the and of R revealed strong interaction with the and of the indole ring and the peripheral PPh3 ligands. Similarly, the and on the indole ring of 7·(BF4) from and ppm to and ppm in 7·( R -Phos) ( Supporting Information Figure also by the of R The close interaction between the R and the peripheral PPh3 ligands in 7·( R -Phos) was also confirmed by NMR spectra ( Supporting Information Figure Moreover, and H4 on the ring of L 1 underwent a shift from 7·(BF4) to 7·( R similar to the H4 in 3·(BF4) and 3·( R This shift was to the influence of the surrounding PPh3 ligands due to the conformational by R A strong influence and by anions were also found in the 1H NMR of 8·( R -Phos) and 8·( S -Phos) (Figure the and H4 all underwent a significant shift from and ppm in 8·(BF4) to and ppm in 8·( R -Phos) and and ppm in 8·( S The interaction between the R and the peripheral PPh3 ligands of 8·( R -Phos) was also identified by NMR spectra ( Supporting Information Figure In view of the molecular structures of phosphate anions and the biaryl-centered cluster species and the observed NMR we that the interactions between the cations and the anions were and we compared variable temperature NMR spectra of 3·(BF4), 3·( R and 7·(BF4) ( Supporting Information Figures to investigate the influence of the chiral anions and different peripheral ligands on the structural rigidity of the biaryl-centered gold-cluster species. As shown in Figure the H4 of 3·(BF4) underwent an apparent shift of ppm from 20 °C to °C due to high structural In contrast, the temperature for the H4 both in 3·( R -Phos) and Moreover, in the low-temperature 31P NMR spectra of 3·( R -Phos) ( Supporting Information Figure the well-identified two sharp 31P peaks at and ppm in 3·( R -Phos) were split into many peaks below °C due to the presence of many conformational isomers. However, the split of the 31P NMR peaks as low as –40 °C for 3·(BF4) ( Supporting Information Figure the 31P NMR of 7·(BF4), there were more six 31P NMR peaks at and ppm for conformational at room temperature ( Supporting Information Figure that the chiral anions and new ligands both enhanced the structural rigidity of the biaryl-centered gold-cluster species due to the of extra interactions. Further, we the solution structure of 8·( R -Phos) to the of the chiral anions and PPh2Py on the biaryl-centered gold-cluster species. temperature from 20 °C to the 31P NMR of 8·( R -Phos) four peaks at and ppm (Figure This was different with the 3·(BF4), 3·( R and 7·(BF4) In 8·( R -Phos) and 8·( S -Phos) had NMR spectra and all could be assigned (Figure suggesting that were formed during the ion-pairing chirality transfer process. Furthermore, the VCD spectrum of 8·( R -Phos) at the in which and from the R anions and the other five and were assigned to the chiral metal cluster cations of 8·( R -Phos) ( Supporting Information Figure that chiral phosphate anions could a complete ion-pairing chirality transfer to acquire chiral gold-cluster cations of with high enantiomeric of the chirality transfer process In order to the chirality transfer between chiral phosphate anions and different biaryl-centered gold-cluster we monitored the structural variation details of cluster cations by and NMR. Four equiv R -Phos·Na were to the solution of clusters in and the was to complete the chiral to Supporting Information Figure the of R -Phos·Na to 7·(BF4) and 8·(BF4) significant of in the of and the 7·( R -Phos) and 8·( R -Phos) showed similar with that of the R -Phos·Na at as shown in Supporting Information Figure which indicated the structural of the cluster cations in the anion exchange process. Figures and close between the spectra of the of chiral phosphate anions of 3·(BF4), 5·(BF4), and 6 and R / S The lack of new and variation a chirality transfer from chiral phosphate anions to the cationic cluster low efficiency in chirality transfer could to the and labile nature of these clusters. In contrast, the spectra of R / S -Phos·Na and 8·(BF4): R / S -Phos·Na significant for the at and and which were to the cluster in theoretical vide infra. When the dichloromethane of R / S -Phos·Na and 8·(BF4): R / S -Phos·Na were the corresponding (Figure high chirality transfer efficiency of and is in with their structural by the NMR Furthermore, the proton signals of the R in the NMR spectra of 8·(BF4): R -Phos·Na underwent a significant and the positions to complex 8·( R that an outside-in chirality transfer between the chiral phosphate anions and the cluster species in and The subsequent resolution process the chirality transfer and enantiomerically pure gold-cluster species. Figure 3 | (a) Chirality induction process between and monitored by 1 H-NMR spectra (CD2Cl2, 298 (b) spectra of 3·(BF4) and 7·(BF4) = with equiv) in (c) spectra of 5·(BF4), 6 and 8·(BF4) = with equiv) in (d) monitoring for the chirality transfer process of 7·(BF4) = and 8·(BF4) with equiv) in in 2 CD, circular Download figure Download PowerPoint Finally, we into the between the induced chirality and the cluster structures of and The spectra of 7·( R -Phos) and 8·( R -Phos) similar to those of R -Phos·Na and 8·(BF4): R -Phos·Na in the of ( Supporting Information Figures and However, in contrast to the at in the spectrum of 7·( R -Phos) (Figure there were two more at and in the spectrum of 8·( R -Phos) (Figure It is that R / S -Phos·Na had with and Thus, in order to reveal the of the new we conducted theoretical on the cluster cations of 7·( R -Phos) and 8·( R -Phos) by using crystal structures of 3·(BF4) and 8·(BF4) The between the and spectra of 3·(BF4) and 8·(BF4)

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