Synthesis, Structure, and Magnetic Properties of Linear Trinuclear CuII and NiII Complexes of Porphyrin Analogues Embedded with Binaphthol

: A porphyrin analogue embedded with ( S )-1,1 (cid:48) -bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N 4 O 4 coordination environment that enables a linear array of three metal ions. That is, it provides the square planar O 4 donor set for the central metal site and the distorted square planar N 2 O 2 donor set for the terminal metal sites. In fact, a Cu II3 complex with a Cu(1)–Cu(2) distance of 2.910 Å, a Cu(1)–Cu(2)–Cu(1 (cid:48) ) angle of 174.7 ◦ , and a very planar Cu 2 O 2 diamond core was obtained. The variable-temperature 1 H-NMR study of the Cu II3 complex showed increasing paramagnetic shifts for the naphthyl protons as temperature increased, which suggests strong antiferromagnetic coupling of Cu II ions. The temperature dependence of the magnetic susceptibility indicated antiferromagnetic coupling both for the Cu II3 complex ( J = − 434 cm − 1 ) and for the Ni II3 complex ( J = − 49 cm − 1 ). The linear (L)M( µ -OR) 2 M( µ -OR) 2 M(L) core in a rigid macrocycle cavity made of aromatic components provides robust metal complexes that undergo reversible ligation at the apical sites of the central metal.


Introduction
Porphyrin analogues provide well-preorganized metal sites due to their rigid molecular structure made of aromatic building blocks with extended π-electron delocalization. In particular, the coordination chemistry of porphyrin analogues of a large ring size has extensively been studied and a number of multinuclear metal complexes have been generated [1][2][3]. Ligands for supporting multimetallic units in a designed arrangement of metals are of great importance because an unusual electronic structure and reactivity are expected for such metal assemblies. In fact, the magnetochemistry of dinuclear Cu II complexes of such porphyrin analogues has been studied extensively, and the catalytic activity of dinuclear Co complexes has been reported [4][5][6][7][8][9][10]. However, examples of trinuclear and tetranuclear complexes of porphyrin analogues are still quite limited [11][12][13][14][15][16][17]. It is well known that two parts of mononuclear complexes such as (L)M(OR) 2 are bridged by the third metal to give trinuclear complexes (L)M(µ-OR) 2 M(µ-OR) 2 M(L), where three metals are assembled in a linear array by the multiple µ-alkoxy bridges to generate a M 3 O 4 core with strong metal-metal interaction [18][19][20][21][22][23][24][25][26][27][28][29][30]. These complexes are not When a dipyrrin unit and a 1,1′-binaphthyl unit are combined, such hybrid molecules can generate metal complexes with interesting chiroptical properties ( Figure 1). In the reported compounds, B and C, the 1,1′-binaphthyl unit was substituted with dipyrrin boron complexes and a bisdipyrrin zinc complex, respectively [34,35]. Compound C is a highly diastereoselective (>99% d.r.) helicate, and compound B showed redox-induced switching of the chiroptical signal. Macrocycles, D and E, were prepared via the condensation of tri-and tetrapyrrolic dialdehydes with 1,1′-binaphthyl-2,2′-diamine, and they contain the chiral atropisomeric 1,1′-binaphthyl substructure as a part of the ring system [36]. However, these macrocycles have never been studied extensively. It is also noteworthy that enantioselective recognition of carboxylate anions was achieved by chiral calix [4]pyrroles bearing an (R)-or (S)-1,1′-bi-2-naphthol strap [37]. We previously developed a stable and relatively rigid macrocycle with direct bonding between the binaphthyl ring carbon and the pyrrole ring carbon through a cross-coupling reaction, where four hydroxy groups and two dipyrrins are preorganized to support a linear trinuclear metal system [17]. In that preliminary communication, we reported the X-ray crystal structure of the tricopper complex (S)-5a and showed reversible coordination of the amine to the apical site of the central Cu ion (Figure 1). Here, we describe the chemistry of the trinuclear metal complexes of these porphyrinoid ligands embedded with binaphthol units in detail, including previous results of the X-ray structure and coordination chemistry of (S)-5a. We synthesized an analogous Cu II 3 complex (S)-5b having different alkyl substituents at the macrocycle core from those in (S)-5a, and the corresponding Ni II 3 complexes, (S)-6a and (S)-6b, were also prepared (Scheme 1). In particular, the magnetic properties of these Cu II 3  When a dipyrrin unit and a 1,1 -binaphthyl unit are combined, such hybrid molecules can generate metal complexes with interesting chiroptical properties ( Figure 1). In the reported compounds, B and C, the 1,1 -binaphthyl unit was substituted with dipyrrin boron complexes and a bisdipyrrin zinc complex, respectively [34,35]. Compound C is a highly diastereoselective (>99% d.r.) helicate, and compound B showed redox-induced switching of the chiroptical signal. Macrocycles, D and E, were prepared via the condensation of tri-and tetrapyrrolic dialdehydes with 1,1 -binaphthyl-2,2 -diamine, and they contain the chiral atropisomeric 1,1 -binaphthyl substructure as a part of the ring system [36]. However, these macrocycles have never been studied extensively. It is also noteworthy that enantioselective recognition of carboxylate anions was achieved by chiral calix [4]pyrroles bearing an (R)-or (S)-1,1 -bi-2-naphthol strap [37]. We previously developed a stable and relatively rigid macrocycle with direct bonding between the binaphthyl ring carbon and the pyrrole ring carbon through a cross-coupling reaction, where four hydroxy groups and two dipyrrins are preorganized to support a linear trinuclear metal system [17]. In that preliminary communication, we reported the X-ray crystal structure of the tricopper complex (S)-5a and showed reversible coordination of the amine to the apical site of the central Cu ion (Figure 1). Here, we describe the chemistry of the trinuclear metal complexes of these porphyrinoid ligands embedded with binaphthol units in detail, including previous results of the X-ray structure and coordination chemistry of (S)-5a. We synthesized an analogous Cu II 3 complex (S)-5b having different alkyl substituents at the macrocycle core from those in (S)-5a, and the corresponding Ni II 3 complexes, (S)-6a and (S)-6b, were also prepared (Scheme 1). In particular, the magnetic properties of these Cu II 3 and Ni II 3 complexes are discussed extensively on the basis of paramagnetic 1 H-NMR in solution and magnetic susceptibility in solid state.

Materials and Methods
General: A Varian Inova 400 spectrometer (400 MHz) was used for the 1 H-NMR measurement. Chemical shifts were recorded against (CH3)4Si (0 ppm) as an internal standard. The ultraviolet (UV)-visible and circular dichroism (CD) spectra were measured on a JASCO V-570 spectrometer and J-820F spectropolarimeter, respectively. A YANACO MT-5 CHN recorder was employed for elemental analyses. An Applied Biosystems Mariner mass spectrometer was used for the measurement of electrospray ionization (ESI) time-of-flight (TOF) MS spectra.

Materials and Methods
General: A Varian Inova 400 spectrometer (400 MHz) was used for the 1 H-NMR measurement. Chemical shifts were recorded against (CH 3 ) 4 Si (0 ppm) as an internal standard. The ultraviolet (UV)-visible and circular dichroism (CD) spectra were measured on a JASCO V-570 spectrometer and J-820F spectropolarimeter, respectively. A YANACO MT-5 CHN recorder was employed for elemental analyses. An Applied Biosystems Mariner mass spectrometer was used for the measurement of electrospray ionization (ESI) time-of-flight (TOF) MS spectra.
Magnetic susceptibility: The variable-temperature magnetic susceptibilities were measured on polycrystalline samples (5.32 mg of (S)-5a and 4.24 mg of (S)-6a) with a Quantum Design MPMS SQUID magnetometer operating in a magnetic field of 10,000 gauss at the 5 K intervals between 300 K and 50 K and at 1 K intervals between 50 K and 2 K. The diamagnetic corrections were evaluated from Pascal's constants for all the constituent atoms [41].
Theoretical calculation: Spin density was calculated using the Gaussian 09 program [42]. Initial geometry was obtained from the X-ray structure of (S)-5a, but the axial water ligand on the central Cu atom was removed. The calculation was performed both on the quartet state and on the doublet state without any symmetry restriction by using the density functional theory (DFT) method with unrestricted ωB97XD functional and B3LYP functional, employing a basis set of 6-31G(d) for C, H, N, and O and LANL2DZ for Cu.
Metalation of (S)-4a with Cu(OAc)2·2H2O in CH2Cl2-MeOH containing triethylamine at room temperature for 5 h afforded the trinuclear copper complex (S)-5a in 67% yield. The observed mass of (S)-5a at 1357.08 by ESI-TOF-MS is in accordance with the theory (1357.28 for (M + 2) + ) of the Cu II 3 complex of the hexaanionic (S)-4a with no additional ligand. The UV-vis absorption band of (S)-5a appeared at 614 nm. This is red-shifted by 42 nm with respect to the 572 nm band of (S)-4a. (S)-5a showed a positive CD couplet at 634 nm as a first Cotton effect and split negative peaks at 593 and 569 nm. The trinuclear nickel complex (S)-6a was prepared in 68% yield by refluxing a toluene-MeOH solution of (S)-4a, Ni(OAc)2·4H2O, and triethylamine for 5 h.  Metalation of (S)-4a with Cu(OAc) 2 ·2H 2 O in CH 2 Cl 2 -MeOH containing triethylamine at room temperature for 5 h afforded the trinuclear copper complex (S)-5a in 67% yield. The observed mass of (S)-5a at 1357.08 by ESI-TOF-MS is in accordance with the theory (1357.28 for (M + 2) + ) of the Cu II 3 complex of the hexaanionic (S)-4a with no additional ligand. The UV-vis absorption band of (S)-5a appeared at 614 nm. This is red-shifted by 42 nm with respect to the 572 nm band of (S)-4a. (S)-5a showed a positive CD couplet at 634 nm as a first Cotton effect and split negative peaks at 593 and 569 nm. The trinuclear nickel complex (S)-6a was prepared in 68% yield by refluxing a toluene-MeOH solution of (S)-4a, Ni(OAc) 2 ·4H 2 O, and triethylamine for 5 h. The observed mass of (S)-6a at 1342.18 by
A number of multidentate ligands (L) of a N2O2 donor set are known to form trinuclear complexes, where three metals are assembled by µ-alkoxy bridges ( Figure 4) [48][49][50][51][52][53]. This Cu3O4 core is planar or folded depending on the N2O2 ligand structure and the apical site coordination. X-ray data of such (L)M(µ-OR)2M(µ-OR)2M(L) complexes are shown in Table 1. The Cu3O4 core of 7 and 9 having four-coordinated Cu II ions at both terminal sites is rather unusual [52,53]. (S)-5a is similar to 7 in this sense, but the Cu(1)-Cu(2) distance (2.910 Å) of (S)-5a is the shortest among these linear tricopper complexes. Although the basal plane of the central Cu II ion of 7 is completely planar, the Cu2O2 unit of 7 is less planar than that of (S)-5a, as seen in the deviation (0.060 Å for 7 and 0.012 Å for (S)-5a) of each atom of Cu2O2 from the Cu2O2 mean plane [52]. Two Cu(salen) units are in a crossing arrangement in the tricopper complex 9, as well as two dipyrrin units of (S)-5a, as seen in the side view of Figure 3 [53]. This structural feature leads to the highly distorted square planar geometry of the terminal Cu II ions of (S)-5a and the trigonal bipyramid geometry of the central Cu II ion in the complex 9. As a result, the Cu(1)-Cu(2)-Cu(1′) angle of 9 is 156.2° and the Cu(2)-OH2 distance of 9 (2.177 Å) is shorter than that (2.43 Å) of (S)-5a. The tricopper complex 10 is a rare example having the Cu3O4 unit inside the macrocycle [31], but its intrinsically folded ligand structure causes the Cu(1)-Cu(2)-Cu(1′) angle of 127.8°. X-ray crystallographic studies on the trinuclear complexes of the Ni3O4 core indicated that Ni II ions are usually six-coordinated [25][26][27][28][29][30][54][55][56][57][58]. The complex 8 is a rare example where only the central Ni is six-coordinated [52]. Although we  Table 1. The Cu 3 O 4 core of 7 and 9 having four-coordinated Cu II ions at both terminal sites is rather unusual [52,53]. (S)-5a is similar to 7 in this sense, but the Cu(1)-Cu(2) distance (2.910 Å) of (S)-5a is the shortest among these linear tricopper complexes. Although the basal plane of the central Cu II ion of 7 is completely planar, the Cu 2 O 2 unit of 7 is less planar than that of (S)-5a, as seen in the deviation (0.060 Å for 7 and 0.012 Å for (S)-5a) of each atom of Cu 2 O 2 from the Cu 2 O 2 mean plane [52]. Two Cu(salen) units are in a crossing arrangement in the tricopper complex 9, as well as two dipyrrin units of (S)-5a, as seen in the side view of Figure 3 [53]. This structural feature leads to the highly distorted square planar geometry of the terminal Cu II ions of (S)-5a and the trigonal bipyramid geometry of the central Cu II ion in the complex 9. As a result, the Cu(1)-Cu(2)-Cu(1 ) angle of 9 is 156.2 • and the Cu(2)-OH 2 distance of 9 (2.177 Å) is shorter than that (2.43 Å) of (S)-5a. The tricopper complex 10 is a rare example having the Cu 3 O 4 unit inside the macrocycle [31], but its intrinsically folded ligand structure causes the Cu(1)-Cu(2)-Cu(1 ) angle of 127.8 • . X-ray crystallographic studies on the trinuclear complexes of the Ni 3 O 4 core indicated that Ni II ions are usually six-coordinated [25][26][27][28][29][30][54][55][56][57][58]. The complex 8 is a rare example where only the central Ni is six-coordinated [52]. Although we could not get X-ray data of the Ni 3 complex (S)-6a, very similar UV-vis and CD spectra of (S)-5a and (S)-6a point to their structural similarity. It is considered on the basis of the X-ray structure of (S)-5a that the terminal Ni II ions of (S)-6a are four-coordinated and the central Ni ion is six-coordinated like 8 (vide infra). Coordination of external ligands to the central Ni ion of (S)-6a is suggested by elemental analysis.
Symmetry 2020, 12, x FOR PEER REVIEW 9 of 21 could not get X-ray data of the Ni3 complex (S)-6a, very similar UV-vis and CD spectra of (S)-5a and (S)-6a point to their structural similarity. It is considered on the basis of the X-ray structure of (S)-5a that the terminal Ni II ions of (S)-6a are four-coordinated and the central Ni ion is six-coordinated like 8 (vide infra). Coordination of external ligands to the central Ni ion of (S)-6a is suggested by elemental analysis.

1 H-NMR Spectra of Paramagnetic Trinuclear Complexes
The presence of three d 9 Cu II ions in (S)-5a leads to paramagnetism. The magnetic moment (3.2 B.M.) of (S)-5a was measured by the Evans method in CDCl3 at 293 K. That is close to the spin-only theoretical value (3.0 B.M.) for the molecular system of three noninteracting S = 1/2 electron spins [59][60][61]. It is noteworthy that all the 1 H-NMR signals of (S)-5a are observed owing to the fast electron spin relaxation. Two signals of a 12H-integral at δ = 0.98 and 7.11 ppm at 303 K in CDCl3 are assigned to the methyl protons of the pyrrole β-ethyl and β-methyl group, respectively ( Figure 5, top and Figure S4, Supplementary Materials). The 2D-COSY experiment indicated that two signals of a 4H-integral at δ = 9.61 and 3.28 ppm are associated with the methylene protons of the ethyl group ( Figure S8). Correlation was also observed for three signals at δ = 7.38 (2H), 7.20 (4H), and 6.88 ppm (4H) assigned to the meso-phenyl protons. The naphthyl protons are associated with the remaining five signals of a 4H-integral at δ = 10.79, 7.99, 7.72, 6.80, and 5.25 ppm. Relatively sharp signals at 7.99, 7.72, and 6.80 ppm should be assigned to the 5-, 6-, and 7-naphthyl protons, and broad signals at δ = 10.79 and 5.25 ppm must be due to the 4-and 8-naphthyl protons that are closer to the metal centers (Table S1, Supplementary Materials). Since the four signals are correlated by the COSY cross-peaks that revealed their positional sequence ((7.99)↔ (6.80)↔ (7.72)↔ (5.25)), they are

1 H-NMR Spectra of Paramagnetic Trinuclear Complexes
The presence of three d 9 Cu II ions in (S)-5a leads to paramagnetism. The magnetic moment (3.2 B.M.) of (S)-5a was measured by the Evans method in CDCl 3 at 293 K. That is close to the spin-only theoretical value (3.0 B.M.) for the molecular system of three noninteracting S = 1/2 electron spins [59][60][61]. It is noteworthy that all the 1 H-NMR signals of (S)-5a are observed owing to the fast electron spin relaxation. Two signals of a 12H-integral at δ = 0.98 and 7.11 ppm at 303 K in CDCl 3 are assigned to the methyl protons of the pyrrole β-ethyl and β-methyl group, respectively ( Figure 5, top and Figure S4, Supplementary Materials). The 2D-COSY experiment indicated that two signals of a 4H-integral at δ = 9.61 and 3.28 ppm are associated with the methylene protons of the ethyl group ( Figure S8). Correlation was also observed for three signals at δ = 7.38 (2H), 7.20 (4H), and 6.88 ppm (4H) assigned to the meso-phenyl protons. The naphthyl protons are associated with the remaining five signals of a 4H-integral at δ = 10.79, 7.99, 7.72, 6.80, and 5.25 ppm. Relatively sharp signals at 7.99, 7.72, and 6.80 ppm should be assigned to the 5-, 6-, and 7-naphthyl protons, and broad signals at δ = 10.79 and 5.25 ppm must be due to the 4-and 8-naphthyl protons that are closer to the metal centers (Table S1, Supplementary Materials). Since the four signals are correlated by the COSY cross-peaks that revealed their positional sequence ((7.99)↔(6.80)↔(7.72)↔(5.25)), they are assigned to the 5-, 6-, 7-, and 8-naphthyl protons, respectively (see Scheme 2 for atom numbering). Consequently, the signal at 10.79 ppm with no correlation is assigned to the 4-naphthyl proton.
Symmetry 2020, 12, x FOR PEER REVIEW 10 of 21 assigned to the 5-, 6-, 7-, and 8-naphthyl protons, respectively (see Scheme 2 for atom numbering). Consequently, the signal at 10.79 ppm with no correlation is assigned to the 4-naphthyl proton. Theoretical DFT calculation (6-31G(d), LANL2DZ/ωB97XD) of the spin density for the quartet spin state of (S)-5a on the basis of the X-ray structure indicates that a positive spin appears at the pyrrole β-carbons (C12, C13) and at the naphthyl 6-and 8-carbons, while a negative spin appears at the naphthyl 4-, 5-and 7-carbons (Table 2 and Table S3, Supplementary Materials). It is considered that a negative electron spin at the naphthyl 4-, 5-and 7-carbons induces positive spin polarization at the naphthyl 4-, 5-and 7-protons by way of spin exchange mechanism, while a positive spin at the pyrrole β-carbons (C12, C13) also induces positive spin polarization at the directly attached 16-CH3 and 17-CH2 protons by way of hyperconjugation mechanism [62,63]. This positive spin polarization at the 4-, 5-, and 7-naphthyl protons and the 16-CH3 and 17-CH2 protons is expected to cause a high-frequency shift of their paramagnetic 1 H-NMR signals with respect to their normal diamagnetic chemical shifts; on the other hand, a positive spin at the 6-and 8-naphthyl carbons results in a low-frequency shift for the 6-and 8-naphthyl protons. The observed 1 H-NMR chemical shifts of (S)-5a at 303 K are consistent with the DFT-based paramagnetic 1 H-NMR shifts under the assumption that the paramagnetic shift depends primarily on the contact shift that is directly related to the spin density in the S = 3/2 spin state.  assigned to the 5-, 6-, 7-, and 8-naphthyl protons, respectively (see Scheme 2 for atom numbering). Consequently, the signal at 10.79 ppm with no correlation is assigned to the 4-naphthyl proton. Theoretical DFT calculation (6-31G(d), LANL2DZ/ωB97XD) of the spin density for the quartet spin state of (S)-5a on the basis of the X-ray structure indicates that a positive spin appears at the pyrrole β-carbons (C12, C13) and at the naphthyl 6-and 8-carbons, while a negative spin appears at the naphthyl 4-, 5-and 7-carbons (Table 2 and Table S3, Supplementary Materials). It is considered that a negative electron spin at the naphthyl 4-, 5-and 7-carbons induces positive spin polarization at the naphthyl 4-, 5-and 7-protons by way of spin exchange mechanism, while a positive spin at the pyrrole β-carbons (C12, C13) also induces positive spin polarization at the directly attached 16-CH3 and 17-CH2 protons by way of hyperconjugation mechanism [62,63]. This positive spin polarization at the 4-, 5-, and 7-naphthyl protons and the 16-CH3 and 17-CH2 protons is expected to cause a high-frequency shift of their paramagnetic 1 H-NMR signals with respect to their normal diamagnetic chemical shifts; on the other hand, a positive spin at the 6-and 8-naphthyl carbons results in a low-frequency shift for the 6-and 8-naphthyl protons. The observed 1 H-NMR chemical shifts of (S)-5a at 303 K are consistent with the DFT-based paramagnetic 1 H-NMR shifts under the assumption that the paramagnetic shift depends primarily on the contact shift that is directly related to the spin density in the S = 3/2 spin state. Scheme 2. Spin-state equilibrium of (S)-5a.
Theoretical DFT calculation (6-31G(d), LANL2DZ/ωB97XD) of the spin density for the quartet spin state of (S)-5a on the basis of the X-ray structure indicates that a positive spin appears at the pyrrole β-carbons (C12, C13) and at the naphthyl 6-and 8-carbons, while a negative spin appears at the naphthyl 4-, 5-and 7-carbons (Table 2 and Table S3, Supplementary Materials). It is considered that a negative electron spin at the naphthyl 4-, 5-and 7-carbons induces positive spin polarization at the naphthyl 4-, 5-and 7-protons by way of spin exchange mechanism, while a positive spin at the pyrrole β-carbons (C12, C13) also induces positive spin polarization at the directly attached 16-CH 3 and 17-CH 2 protons by way of hyperconjugation mechanism [62,63]. This positive spin polarization at the 4-, 5-, and 7-naphthyl protons and the 16-CH 3 and 17-CH 2 protons is expected to cause a high-frequency shift of their paramagnetic 1 H-NMR signals with respect to their normal diamagnetic chemical shifts; on the other hand, a positive spin at the 6-and 8-naphthyl carbons results in a low-frequency shift for the 6-and 8-naphthyl protons. The observed 1 H-NMR chemical shifts of (S)-5a at 303 K are consistent with the DFT-based paramagnetic 1 H-NMR shifts under the assumption that the paramagnetic shift depends primarily on the contact shift that is directly related to the spin density in the S = 3/2 spin state. Table 2. Spin density of (S)-5a calculated by DFT (6-31G(d), LANL2DZ/ωB97XD) 1 .

S = 1/2 S = 3/2
Cu (1) Since the 1 H-NMR spectral pattern of (S)-5a is consistent with a D 2 symmetric structure, the apical water ligand observed in the X-ray structure seems to dissociate in solution. Plotting the 1 H-NMR chemical shifts against T −1 on the basis of the variable-temperature (VT) 1 H-NMR data of (S)-5a showed linear correlation, and the chemical shift extrapolated to the point of T −1 = 0 for each proton signal is shown at the left end of the least square approximation line in Figure 6a (Figure S4, Supplementary Materials). Replacement of the pyrrole-β 16-CH 3 group of (S)-5a by the ethyl group in the case of (S)-5b did not affect the position and the temperature dependency of the 1 H-NMR signals due to the naphthyl protons (red circle in Figure 6a,b) and meso-phenyl protons (black triangle in Figure 6a,b) at all. However, signals due to the 17-CH 2 protons at the pyrrole β-position next to the meso-phenyl group slightly shifted from δ = 9.1 and 3.4 ppm for (S)-5a to δ = 10.6 (or 9.7) and 3.7 ppm for (S)-5b at 323 K, while the signals due to the pyrrole β-16-CH 3 protons at δ = 7.0 ppm (filled blue square in Figure 6a) of (S)-5a were replaced by the newly introduced ethyl protons of (S)-5b that appeared at δ = 9.7 (or 10.6) and 7.8 (CH 2 ), and 1.9 (CH 3 ) ppm at 323 K (Figure 6b and Figure S5, Supplementary Materials). Signals due to the naphthyl 6-and 8-protons of (S)-5a and (S)-5b move to the lower-frequency region with increasing temperature, while the signal due to the 4-naphthyl proton moves to the higher-frequency region with increasing temperature. The chemical shifts extrapolated to the point of T −1 = 0 are far from normal diamagnetic chemical shift region of the naphthyl 4-, 6-, and 8-protons in contrast to the relatively normal Curie law profile of the signals due to the pyrrole β-methyl and β-methylene protons of (S)-5a and (S)-5b. This Curie plot profile of (S)-5a and (S)-5b is explained in terms of the temperature-dependent equilibrium of spin states. DFT calculation indicates that the spin density at the central Cu ion has the opposite sign between the quartet spin state (0.64) and the doublet spin state (−0.62) ( Table 2). However, the spin densities at the terminal Cu ions have the same sign for the quartet (0.61) and the doublet (0.60). Accordingly, the spin densities at the pyrrole β-carbons (C12, C13) that are transmitted from the terminal Cu ions have the same sign (positive) for both spin states, but the spin densities at the naphthyl carbons that are transmitted strongly from the central Cu ion show opposite sign for these two spin states. The DFT calculation indicates that the doublet spin state is expected to cause a low-frequency shift for the 1 H-NMR signals of the 4-, 5-, and 7-naphthyl protons and a high-frequency shift for the 6-and 8-naphthyl protons in contrast to the quartet spin state. The observed Curie plot profile of (S)-5a and (S)-5b at low temperatures seems consistent with that expected for the doublet spin state. DFT calculation of (S)-5a in the doublet state using the B3LYP functional showed the nonsymmetric Cu3O4 core in contrast to the symmetric Cu3O4 core obtained by using the ωB97XD functional ( Figure S13 and Table S2, Supplementary Materials), i.e., two Cu(terminal)-Cu(center) distances (2.887 Å and 3.055 Å) in the B3LYP case and a single Cu-Cu distance (2.930 Å) in the ωB97XD case. The calculated spin densities of the Cu II 3 unit in the B3LYP case are Cu(0.5588)-Cu(0.0067)-Cu(−0.0007) in sequence (Table S4, Supplementary Materials). This is quite different from the symmetric spin structure (Cu(0.5977)-Cu(−0.6169)-Cu(0.5977)) of the ωB97XD case. As for the quartet state of (S)-5a, both DFT calculations using the B3LYP and ωB97XD functional resulted in a symmetric Cu3O4 core with a Cu-Cu distance of 2.922 Å and 2.911 Å, respectively, and their calculated spin densities of the Cu II 3 unit are Cu(0.5644)-Cu(0.5190)-Cu(0.5654) in sequence for the B3LYP case and Cu(0.6083)-Cu(0.6366)-Cu(0.6083) in sequence for the ωB97XD case ( Figure S13, Tables S2 and S4, Supplementary Materials). The observed 1 H-NMR paramagnetic shifts for the naphthyl protons of (S)-5a at both limits of high and low temperature are correlated with the calculated spin densities at the naphthyl unit in the S = 3/2 and 1/2 spin state, respectively. This DFT calculation of (S)-5a in the doublet state using the B3LYP functional showed the nonsymmetric Cu 3 O 4 core in contrast to the symmetric Cu 3 O 4 core obtained by using the ωB97XD functional ( Figure S13 and Table S2 Figure S13, Tables S2 and S4, Supplementary Materials). The observed 1 H-NMR paramagnetic shifts for the naphthyl protons of (S)-5a at both limits of high and low temperature are correlated with the calculated spin densities at the naphthyl unit in the S = 3/2 and 1/2 spin state, respectively. This correlation with the spin densities using the ωB97XD functional is much better than those using the B3LYP functional (Table 2 and Table  S4, Supplementary Materials).
The magnetic moment (4.6 B.M.) of (S)-6a was measured using the Evans method in CDCl 3 at 293 K. This is close to the spin only theoretical value (4.9 B.M.) for the molecular system of three noninteracting d 8 (S = 1) Ni II ions. The 1 H-NMR spectrum of (S)-6a at 303 K in CDCl 3 shows two 12H-signals at δ = 0.61 and 2.39 ppm due to the methyl protons of the pyrrole β-ethyl and β-methyl group, respectively ( Figure 5, bottom). The 2D-COSY experiment reveals that two 4H-signals at δ = 1.99 and 1.67 ppm are associated with the diastereotopic methylene protons of the pyrrole β-ethyl group ( Figure S9, Supplementary Materials). The 6H-signal at 7.40 ppm and the 4H-signal at 7.20 ppm are also assignable to the meso-phenyl protons. The remaining five 4H-signals at δ = 24.4, 10.38, 9.14, 4.87 (very broad), and 3.46 ppm are associated with the naphthyl protons. Three relatively sharp signals are associated with 5-, 6-, and 7-naphthyl protons that showed 2D-COSY cross-peaks of the signal at δ = 3.46 ppm against signals at δ = 9.14 and 10.83 ppm. Consequently, the signal at δ = 3.46 ppm is associated with the 6-naphthyl proton, and the signals at δ = 9.14 and 10.83 ppm are associated with the 5-and 7-naphthyl protons. These remarkable paramagnetic shifts in the opposite direction for the closely positioned 5-, 6-, and 7-naphthyl protons are ascribable not to the dipolar term but to the contact term. The directions of these paramagnetic shifts of the 5-, 6-, and 7-naphthyl protons of (S)-6a are similar to those of (S)-5a at 303 K. Therefore, the high-frequency-shifted signal at 24.4 ppm and the low-frequency-shifted signal at 4.87 seem to be associated with the 4-and 8-naphthyl protons, respectively. These remarkable chemical shifts and the temperature dependency of the naphthyl protons are not affected by replacing the pyrrole β-methyl group of (S)-6a by the ethyl group in the case of (S)-6b (Figure 6c,d, and Figures S6 and S7, Supplementary Materials). Since the Curie plots of (S)-6a and (S)-6b show that the chemical shifts extrapolated to the point of T −1 = 0 for all the proton signals are in their normal diamagnetic chemical shift range, the spin state is not greatly affected by temperature change, and the magnetic coupling between nickel ions should be not so important as the case of the copper ions. The proton signals due to the dipyrrin part of (S)-6a and (S)-6b are in the normal diamagnetic chemical shift range, and their temperature dependency is negligible (blue squares in Figure 6a,b). Therefore, the dipolar term of the paramagnetic shift should be negligible in the dipyrrin part not only of (S)-6a and (S)-6b but also of (S)-5a and (S)-5b. It is noteworthy that the spin density is not transferred from the terminal nickel ion to the pyrrole ligand, but the partial spin is transferred to the 1,1 -binaphthol ligand.
The Curie plot of the trinuclear Cu II complexes does not show a normal Curie law profile. The chemical shifts of the 4-, 6-, and 8-naphthyl proton of (S)-5a and (S)-5b move further away from the normal diamagnetic chemical shift range as temperature goes up from 213 K to 323 K, and they are extrapolated to 19.3, 3.3, and 2.3 ppm, respectively, at T −1 = 0 (Figure 6a). This suggests that the magnetic moment of the trinuclear Cu II complexes increases as temperature goes up as a result of decreasing antiferromagnetic coupling interaction. While the chemical shifts of the pyrrole β-methyl and β-ethyl protons of (S)-6a and (S)-6b are not affected at all by the paramagnetism even though those signals are broadened, the corresponding protons of (S)-5a and (S)-5b undergo remarkable paramagnetic shifts. Accordingly, these paramagnetic shifts of (S)-5a and (S)-5b are caused by the contact term that was induced by the electron spin density on the pyrrole β-carbons through π-conjugation. Since the paramagnetic shifts observed for the pyrrole β-methyl and β-methylene protons of (S)-5a and (S)-5b are caused by the partial spin density transferred from the single terminal Cu atom where the spin state does not depend on temperature, their temperature dependency seems to show an ordinary Curie law profile. In fact, these signals are extrapolated to −1.8, 2.5, 4.0, and 0.5 ppm for (S)-5a and 2.0, 2.7, 1.4, 3.3, 1.6, and 0.3 ppm for (S)-5b. On the other hand, the spin density of the 1,1 -binaphthol ligand is derived both from the terminal Cu atom and from the central Cu atom, and their antiparallel spin orientation would be enhanced more at lower temperature due to the antiferromagnetic coupling (Scheme 2).
A pair of Cu atoms with opposite spin causes a counterbalancing effect on the paramagnetic shifts of the binaphthol ligand. Thus, the unusual temperature dependency of the paramagnetic shifts for the binaphthol protons is ascribed to the spin equilibrium between the quartet and doublet.

Magnetic Susceptibility of Trinuclear Complexes
Magnetic susceptibility (χ M ) of the polycrystalline sample of (S)-5a was measured in the temperature range of 2-300 K, and the temperature dependence plot (χ M T vs. T) is shown in Figure 7 after correction for the diamagnetic terms. The χ M T value of 0.72 cm 3 ·mol −1 ·K at 300 K is lower than the 1.125 cm 3 ·mol −1 ·K expected for three noninteracting Cu II ions. As temperature goes down, χ M T decreases monotonously to reach the value of 0.375 cm 3 ·mol −1 ·K at 15 K, which corresponds to an S = 1/2 ground state for g = 2. This behavior indicates an antiferromagnetic coupling in the Cu II 3 core. A further decrease in χ M T below this temperature to 2 K can be attributed to intermolecular interactions between S = 1/2 trinuclear units. Curve fitting for the temperature-dependent susceptibility data was introduced by an expression for a linear trinuclear Cu II complex on the basis of the spin Hamiltonian H = −J(S 1 S 2 + S 2 S 3 ). The theoretical equation for χ M can be expressed by Equation (1), where θ reflects intermolecular interaction at very low temperature, and TIP stands for a temperature-independent paramagnetism [48,64]. A good data fit was obtained for g = 1.970, θ = −0.11 K, J = −434 cm −1 , and TIP = 887 × 10 −6 cm 3 mol −1 , with the agreement factor R defined as i [(χ M T) obs -(χ M T) calc ] 2 / i [(χ M T) obs ] 2 is 5.25 × 10 −5 .

Magnetic Susceptibility of Trinuclear Complexes
Magnetic susceptibility (χM) of the polycrystalline sample of (S)-5a was measured in the temperature range of 2-300 K, and the temperature dependence plot (χMT vs. T) is shown in Figure 7 after correction for the diamagnetic terms. The χMT value of 0.72 cm 3 ·mol −1 ·K at 300 K is lower than the 1.125 cm 3 ·mol −1 ·K expected for three noninteracting Cu II ions. As temperature goes down, χMT decreases monotonously to reach the value of 0.375 cm 3 ·mol −1 ·K at 15 K, which corresponds to an S = 1/2 ground state for g = 2. This behavior indicates an antiferromagnetic coupling in the Cu II 3 core. A further decrease in χMT below this temperature to 2 K can be attributed to intermolecular interactions between S = 1/2 trinuclear units. Curve fitting for the temperature-dependent susceptibility data was introduced by an expression for a linear trinuclear Cu II complex on the basis of the spin Hamiltonian H = −J(S1S2 + S2S3). The theoretical equation for χΜ can be expressed by Equation (1), where θ reflects intermolecular interaction at very low temperature, and TIP stands for a temperature-independent paramagnetism [48,64]. A good data fit was obtained for g = 1. It is well known that the exchange parameter J is linearly related to the Cu-O-Cu angle in the dinuclear complexes (L)Cu II (µ-OR)2Cu II (L) [65]. The J value (−434 cm −1 ) of (S)-5a is in the range (−511, −482.5, −474, −345.5 cm −1 ) [48][49][50][51] reported for the µ-phenoxy-bridged linear trinuclear Cu II complexes having the Cu-O-Cu angle of 101.4°-98.3° including 7 (−314 cm −1 ) [52]. On the other hand, a much weaker J value (−190 cm −1 ) was reported for the bent Cu II 3 complex 9 [53]. It is noteworthy that the antiferromagnetic coupling of (S)-5a is much stronger than the reported dinuclear (J = −87.6 cm −1 ) [2b] and trinuclear (J = −44.1 cm −1 ) [12] Cu II complexes of porphyrin analogues. A similar temperature dependence plot (χMT vs. T) of (S)-6a is shown in Figure 8. The χMT value of 2.50 cm 3 ·mol −1 ·K at 300 K is lower than the 3.00 cm 3 ·mol −1 ·K expected for three noninteracting high-spin (S = 1) Ni II ions. As temperature goes down, χMT decreases monotonously to reach the value of 1.00 cm 3 ·mol −1 ·K at 14 K, which corresponds to the S = 1 ground state for g = 2 per Ni II 3. This magnetic behavior clearly indicates antiferromagnetic coupling in the Ni II 3 core. A further It is well known that the exchange parameter J is linearly related to the Cu-O-Cu angle in the dinuclear complexes (L)Cu II (µ-OR) 2 Cu II (L) [65]. The J value (−434 cm −1 ) of (S)-5a is in the range (−511, −482.5, −474, −345.5 cm −1 ) [48][49][50][51] reported for the µ-phenoxy-bridged linear trinuclear Cu II complexes having the Cu-O-Cu angle of 101.4 • -98.3 • including 7 (−314 cm −1 ) [52]. On the other hand, a much weaker J value (−190 cm −1 ) was reported for the bent Cu II 3 complex 9 [53]. It is noteworthy that the antiferromagnetic coupling of (S)-5a is much stronger than the reported dinuclear (J = −87.6 cm −1 ) [2b] and trinuclear (J = −44.1 cm −1 ) [12] Cu II complexes of porphyrin analogues.
A similar temperature dependence plot (χ M T vs. T) of (S)-6a is shown in Figure 8. The χ M T value of 2.50 cm 3 ·mol −1 ·K at 300 K is lower than the 3.00 cm 3 ·mol −1 ·K expected for three noninteracting high-spin (S = 1) Ni II ions. As temperature goes down, χ M T decreases monotonously to reach the value of 1.00 cm 3 ·mol −1 ·K at 14 K, which corresponds to the S = 1 ground state for g = 2 per Ni II 3 . This magnetic behavior clearly indicates antiferromagnetic coupling in the Ni II 3 core. A further decrease in χ M T below this temperature to 2 K is ascribable to intermolecular interactions between S = 1 trinuclear units. The theoretical equation for χ M on the basis of the spin Hamiltonian H = −2J 1 (S 1 S 2 + S 2 S 3 ) − 2J 2 (S 1 S 3 ) (S 1 = S 2 = S 3 = 1) for a trinuclear nickel(II) complex is expressed by Equation (2), where J 1 and J 2 are exchange parameters between the adjacent two Ni II ions and between the terminal two Ni II ions, respectively [54]. The best fit was obtained at g = 2.20, θ = −2.84 K, J 1 = −49 cm −1 , J 2 = 17 cm −1 , and TIP = 800 × 10 −6 cm 3 mol −1 , with the R factor of 1.68 × 10 −4 . If the magnetic interaction between the terminal Ni ions is neglected (J 2 = 0 cm −1 ), the best fit parameters are g = 2.17, θ = −2.72 K, J 1 = −60 cm −1 , TIP = 2200 × 10 −6 cm 3 mol −1 , and R = 1.60 × 10 −4 .
(2) Symmetry 2020, 12, x FOR PEER REVIEW 15 of 21 − 2J2(S1S3) (S1 = S2 = S3 = 1) for a trinuclear nickel(II) complex is expressed by Equation (2), where J1 and J2 are exchange parameters between the adjacent two Ni II ions and between the terminal two Ni II ions, respectively [54]. (2) Studies on the magnetic properties of dinuclear Ni II complexes having µ-phenoxy bridging ligands have shown that the exchange parameter J is dependent not only on the Ni-O-Ni angles but also on the coordination geometry of Ni ions [66]. That is, an antiferromagnetic exchange gets stronger as a tetragonal distortion from octahedral geometry of the Ni II ions is more enhanced. As far as linear trinuclear µ-phenoxy bridged Ni II complexes are concerned, Ni II 3 cores with coordination numbers of 4-6-4 (complex 8), 5-6-5 (complex 11), and 6-6-6 (complex 12, 13) have been reported and their exchange parameters |J| are less than 10 cm −1 (Figures 4 and 9). The terminal Ni II ions of the complex 8 are in square planar coordination geometry with a low spin state (S = 0), and the central Ni II ion is in an axially elongated octahedral geometry with a high spin state (S = 1) [52]. Replacement of the ClO4 -counter anion of 8 by Clgenerated a linear Ni II 3 complex 11 of 5(square pyramidal)-6(octahedral)-5(square pyramidal) coordination geometry with one Cl − anion coordinating to the axial site of each terminal Ni ion in an N2O2 basal plane of an analogous tetradentate ligand which has a 1,5-diazacyclooctane ring instead of the 1,4-diazacycloheptane ring of 8. The Ni II 3 complex 11 has three noninteracting high-spin Ni II ions at 300 K, and weak antiferromagnetic interaction with the J1 and J2 values of −7.9 and −5.5 cm −1 , respectively, was Studies on the magnetic properties of dinuclear Ni II complexes having µ-phenoxy bridging ligands have shown that the exchange parameter J is dependent not only on the Ni-O-Ni angles but also on the coordination geometry of Ni ions [66]. That is, an antiferromagnetic exchange gets stronger as a tetragonal distortion from octahedral geometry of the Ni II ions is more enhanced. As far as linear trinuclear µ-phenoxy bridged Ni II complexes are concerned, Ni II 3 cores with coordination numbers of 4-6-4 (complex 8), 5-6-5 (complex 11), and 6-6-6 (complex 12, 13) have been reported and their exchange parameters |J| are less than 10 cm −1 (Figures 4 and 9). The terminal Ni II ions of the complex 8 are in square planar coordination geometry with a low spin state (S = 0), and the central Ni II ion is in an axially elongated octahedral geometry with a high spin state (S = 1) [52]. Replacement of the ClO 4 counter anion of 8 by Clgenerated a linear Ni II 3 complex 11 of 5(square pyramidal)-6(octahedral)-5(square pyramidal) coordination geometry with one Cl − anion coordinating to the axial site of each terminal Ni ion in an N 2 O 2 basal plane of an analogous tetradentate ligand which has a 1,5-diazacyclooctane ring instead of the 1,4-diazacycloheptane ring of 8. The Ni II 3 complex 11 has three noninteracting high-spin Ni II ions at 300 K, and weak antiferromagnetic interaction with the J 1 and J 2 values of −7.9 and −5.5 cm −1 , respectively, was reported [54]. Linear Ni II 3 complexes with 6(octahedral)-6(octahedral)-6(octahedral) coordination geometry of noninteracting high-spin Ni II ions were reported. An exchange parameter (J 1 = 4.31 cm −1 ) suggesting a weak ferromagnetic coupling was reported for complex 12 with additional µ 2 -1,3-acetato bridges between the terminal Ni ion and the central Ni ion [55]. A very weak antiferromagnetic interaction (J 1 = −1.7 cm −1 ) was reported for complex 13 of structurally similar coordination geometry to 12 [56]. The magnetic interaction of (S)-6a is much stronger than that of these linear trinuclear Ni II complexes [25][26][27][28][29][30][54][55][56][57][58], which may be attributed to the unique coordination geometry in the terminal Ni II ions of (S)-6a.

Reversible Coordination at Apical Sites of the Trinuclear Complexes
A large number of trinuclear complexes of general formula (L)M(µ-OR)2M(µ-OR)2M(L) are known, and their solid-state chemistry is well documented as noted above. However, study on the solution chemistry of these multinuclear complexes is quite limited, probably because of their reversible decomposition into mononuclear complexes in solution [33,67]. The present M II 3 complexes protected by the rigid macrocycle ligand are expected to show well-defined coordination chemistry without decomposition of the M II 3O4 core. In fact, it was found that the M II 3O4 core is stable even in the presence of a large excess amount of strongly coordinating external ligand molecules. Addition of butylamine to the Cu3 complex (S)-5a in CDCl3 caused chemical shift changes while keeping a D2 symmetric spectral pattern ( Figure 10). The pyrrole β-methyl proton signal (16-CH3 in Scheme 2) shifted from 7.81 ppm to 11.66 ppm at 253 K. Signals of (S)-5a got broader at 0.5 equivalents of butylamine probably due to fast ligand exchange. Then, a single set of signals appeared at two equivalents of butylamine. The CD titration of (S)-5a with butylamine in CH2Cl2 at 25 °C showed a parabola-type titration curve that led to the association constant K = 3.2 × 10 3 M −1 on the basis of fitting with a one-to-one binding isotherm ( Figure S11, Supplementary Materials). This coordination behavior of (S)-5a with butylamine is consistent with the X-ray structure having one apical water ligand at the central Cu II ion. Therefore, it is reasonably assumed that butylamine reversibly binds to either one of the apical sites of the central Cu II ion (Scheme 3).

Reversible Coordination at Apical Sites of the Trinuclear Complexes
A large number of trinuclear complexes of general formula (L)M(µ-OR) 2 M(µ-OR) 2 M(L) are known, and their solid-state chemistry is well documented as noted above. However, study on the solution chemistry of these multinuclear complexes is quite limited, probably because of their reversible decomposition into mononuclear complexes in solution [33,67]. The present M II 3 complexes protected by the rigid macrocycle ligand are expected to show well-defined coordination chemistry without decomposition of the M II 3 O 4 core. In fact, it was found that the M II 3 O 4 core is stable even in the presence of a large excess amount of strongly coordinating external ligand molecules. Addition of butylamine to the Cu 3 complex (S)-5a in CDCl 3 caused chemical shift changes while keeping a D 2 symmetric spectral pattern ( Figure 10). The pyrrole β-methyl proton signal (16-CH 3 in Scheme 2) shifted from 7.81 ppm to 11.66 ppm at 253 K. Signals of (S)-5a got broader at 0.5 equivalents of butylamine probably due to fast ligand exchange. Then, a single set of signals appeared at two equivalents of butylamine. The CD titration of (S)-5a with butylamine in CH 2 Cl 2 at 25 • C showed a parabola-type titration curve that led to the association constant K = 3.2 × 10 3 M −1 on the basis of fitting with a one-to-one binding isotherm ( Figure S11, Supplementary Materials). This coordination behavior of (S)-5a with butylamine is consistent with the X-ray structure having one apical water ligand at the central Cu II ion. Therefore, it is reasonably assumed that butylamine reversibly binds to either one of the apical sites of the central Cu II ion (Scheme 3). appeared at two equivalents of butylamine. The CD titration of (S)-5a with butylamine in CH2Cl2 at 25 °C showed a parabola-type titration curve that led to the association constant K = 3.2 × 10 3 M −1 on the basis of fitting with a one-to-one binding isotherm ( Figure S11, Supplementary Materials). This coordination behavior of (S)-5a with butylamine is consistent with the X-ray structure having one apical water ligand at the central Cu II ion. Therefore, it is reasonably assumed that butylamine reversibly binds to either one of the apical sites of the central Cu II ion (Scheme 3).  UV-vis titration of the Ni3 complex (S)-6a with 0-2.5 equivalents of butylamine showed very subtle spectral changes ( Figure S12, Supplementary Materials). 1 H-NMR titration showed that two signals at 9.2 and 10.5 ppm due to the naphthyl protons of (S)-6a split into four signals that were finally replaced by two signals at 8.3 and 10.2 ppm when 2 equivalents of butylamine were added ( Figure 11). Meanwhile, the signal at 0.60 ppm due to the methyl protons of the pyrrole β-ethyl group of (S)-6a changed to a pair of signals at 0.74 and 0.48 ppm and finally to a single signal at 0.41 ppm. These changes of the splitting pattern from D2 to C2 symmetry and then from C2 to D2 symmetry again are consistent with the stepwise binding of two butylamine ligands to the apical sites of the central Ni II ion (Scheme 3). Thus, butylamine coordination to Ni II is much stronger than to Cu II in CH2Cl2, and it is reasonably considered that (S)-6a contains two methanol ligands when precipitated from methanol.

Conclusions
A 1,1′-bi-2-naphthol unit was embedded in a porphyrinoid macrocycle without reducing UV-vis titration of the Ni 3 complex (S)-6a with 0-2.5 equivalents of butylamine showed very subtle spectral changes ( Figure S12, Supplementary Materials). 1 H-NMR titration showed that two signals at 9.2 and 10.5 ppm due to the naphthyl protons of (S)-6a split into four signals that were finally replaced by two signals at 8.3 and 10.2 ppm when 2 equivalents of butylamine were added ( Figure 11). Meanwhile, the signal at 0.60 ppm due to the methyl protons of the pyrrole β-ethyl group of (S)-6a changed to a pair of signals at 0.74 and 0.48 ppm and finally to a single signal at 0.41 ppm. These changes of the splitting pattern from D 2 to C 2 symmetry and then from C 2 to D 2 symmetry again are consistent with the stepwise binding of two butylamine ligands to the apical sites of the central Ni II ion (Scheme 3). Thus, butylamine coordination to Ni II is much stronger than to Cu II in CH 2 Cl 2 , and it is reasonably considered that (S)-6a contains two methanol ligands when precipitated from methanol. UV-vis titration of the Ni3 complex (S)-6a with 0-2.5 equivalents of butylamine showed very subtle spectral changes ( Figure S12, Supplementary Materials). 1 H-NMR titration showed that two signals at 9.2 and 10.5 ppm due to the naphthyl protons of (S)-6a split into four signals that were finally replaced by two signals at 8.3 and 10.2 ppm when 2 equivalents of butylamine were added ( Figure 11). Meanwhile, the signal at 0.60 ppm due to the methyl protons of the pyrrole β-ethyl group of (S)-6a changed to a pair of signals at 0.74 and 0.48 ppm and finally to a single signal at 0.41 ppm. These changes of the splitting pattern from D2 to C2 symmetry and then from C2 to D2 symmetry again are consistent with the stepwise binding of two butylamine ligands to the apical sites of the central Ni II ion (Scheme 3). Thus, butylamine coordination to Ni II is much stronger than to Cu II in CH2Cl2, and it is reasonably considered that (S)-6a contains two methanol ligands when precipitated from methanol.

Conclusions
A 1,1′-bi-2-naphthol unit was embedded in a porphyrinoid macrocycle without reducing optical purity of the original 1,1′-bi-2-naphthol. The macrocycle core made of sp 2 carbons was relatively rigid and its unidirectional overall helical conformation was stable. This porphyrinoid ligand was preorganized for the linear array of three metal ions in the form of

Conclusions
A 1,1 -bi-2-naphthol unit was embedded in a porphyrinoid macrocycle without reducing optical purity of the original 1,1 -bi-2-naphthol. The macrocycle core made of sp 2 carbons was relatively rigid and its unidirectional overall helical conformation was stable. This porphyrinoid ligand was preorganized for the linear array of three metal ions in the form of (L)M(µ-OR) 2 M(µ-OR) 2 M(L). X-ray crystallography of the Cu II 3 complex showed that a pair of very planar Cu 2 O 2 cores was only slightly off coplanarity (plane-to-plane angle 8.3 • ), and the terminal Cu ions were highly distorted from square planar geometry. 1 H-NMR study on the Cu II 3 complex revealed unusual temperature dependency of the chemical shifts of the naphthyl protons, which were indicative of the strong antiferromagnetic coupling between the Cu atoms. The observed paramagnetic shifts in the pyrrolic ligand and the binaphthyl ligand could be used to estimate spin delocalization from the terminal metal and the central metal, respectively, and these paramagnetic 1 H-NMR data were consistent with the spin densities calculated via DFT using ωB97XD functional. The strong antiferromagnetic coupling observed for both Cu II 3 (J = −434 cm −1 ) and Ni II 3 (J = −49 cm −1 ) complexes could be ascribed to the unique coordination geometry that was also responsible for reversible ligation of butylamine only at the central metal ion without decomposition of the trinuclear core. This apical ligand binding could be studied using well-resolved 1 H-NMR spectra of both Cu II 3 and Ni II 3 complexes. The present multinuclear complexes of an enantiomerically pure helical porphyrin analogue are expected to lead to further exploration of the interesting chemistry of helical multinuclear complexes.