Highly cooperative double metalation of a bis(N2O2) ligand based on bipyridine-phenol framework driven by intramolecular π-stacking of square planar nickel(ii) complex moieties

Article abstract of DOI:10.1039/c1dt10124b

Highly cooperative double metalation took place when a novel ligand based on a bipyridine-phenol framework was allowed to react with nickel(ii) acetate. The π-stacking of the square planar metal complex moieties is responsible for the highly cooperative d

Full text of DOI:10.1039/c1dt10124b

Highly-Cooperative Double Metalation of a Bis(N2O2) Ligand Based on
Bipyridine-Phenol Framework Driven by Intramolecular π-Stacking of Square
Planar Nickel(II) Complex Moieties
Shigehisa Akine,* Toshihiko Shimada, Hiroki Nagumo, and Tatsuya Nabeshima*
Supplementary Information

1. Synthesis and characterization of ligands and metal complexes.
Scheme 1. Synthesis of ligands H4L and H2L'. Reagents and conditions: a) [Pd(PPh3)4], Na2CO3,
toluene/H2O, b) (i) n-BuLi, TMEDA, ether (ii) B(OMe)3 (iii) dil. HCl (iv) pinacol, toluene, c) BBr3,
CH2Cl2, d) [Pd(PPh3)4], Na2CO3, toluene/MeOH/H2O, e) HBr, AcOH.

General Procedures. All experiments were carried out under argon atmosphere unless otherwise
noted. Toluene, diethyl ether, and methanol (dehydrated) were used for the organic syntheses.
Aqueous solution of sodium carbonate was degassed prior to use. Dichloromethane and
N,N,N',N'-tetramethylethylenediamine were distilled under argon atmosphere from calcium hydride
prior to use. Commercial chloroform, acetonitrile, and methanol were used without purification
for the synthesis of metal complexes. All chemicals were of reagent grade and used as received.
Column chromatography was performed with Kanto Chemical silica gel 60N (spherical, neutral).
Gel permeation chromatography (GPC) was performed by an LC-9201 equipped with JAI gel 1H +
2H columns (Japan Analytical Industry) with chloroform as eluent. Melting points were
determined on a Yanaco melting point apparatus and not corrected. NMR spectra were recorded
on a Bruker ARX400 (1H, 400 MHz; 13C, 100 MHz) or a Bruker Avance600 (1H, 600 MHz)
spectrometer. Mass spectra (ESI-TOF, positive mode) were recorded on an Applied Biosystems
QStar Pulsar i spectrometer. Absorption spectra were recorded on a JASCO Ubest V660
spectrometer.
6-Bromo-6'-(5-tert-buthyl-2-methoxyphenyl)-2,2'-bipyridine (3)
6,6'-Dibromo-2,2'-bipyridine (1) (0.517 g, 1.65 mmol), 5-tert-butyl-2-methoxyphenylboronic
acid (2) (0.286 g, 1.37 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.0892 g, 0.0772
mmol) were placed in a 50 mL two-necked flask. Toluene (15 mL) and saturated aqueous solution
of sodium carbonate (3 mL) were added to the mixture in one portion. The mixture was stirred at
75 °C for 60 h. After cooling, water and chloroform were added and the organic layer was
separated. The aqueous layer was extracted with chloroform (3 × 30 mL). The combined
organic layer was dried over anhydrous magnesium sulfate and concentrated to dryness. The
crude product was purified by column chromatography on silica gel using chloroform/hexane (2/1,
v/v) as eluent to give 3 (0.276 g, 0.695 mmol, 51%) as colorless crystals, m.p. 112.1–112.9 °C; 1H
NMR (400 MHz, CDCl3): δ=1.38 (s, 9H), 3.86 (s, 3H), 6.97 (d, J = 8.6 Hz, 1H), 7.42 (dd, J = 8.6,
2.6 Hz, 1H), 7.47 (d, J = 7.6 Hz, 1H), 7.66 (t, J = 7.6 Hz, 1H), 7.82 (t, J = 7.9 Hz, 1H), 7.91 (dd, J =
7.9, 0.9 Hz, 1H), 7.98 (d, J = 2.6 Hz, 1H), 8.34 (dd, J = 7.6, 0.9 Hz, 1H), 8.52 ppm (d, J = 7.9 Hz,
13
1H); C NMR (100 MHz, CDCl3): δ=31.56 (CH3), 34.23 (C), 55.73 (CH3), 111.22 (CH), 119.19
(CH), 119.74 (CH), 125.84 (CH), 126.90 (CH), 127.71 (CH), 128.09 (C), 128.36 (CH), 136.57
(CH), 139.13 (CH), 141.41 (C), 143.54 (C), 153.82 (C), 155.07 (C), 155.60 (C), 157.80 ppm (C);
elemental analysis calcd (%) for C21H21BrN2O: C 63.48, H 5.33, N 7.05; found: C 63.31, H 5.49, N
6.87.

(S)-2,2'-(2,2'-Dimethoxy-1,1'-binaphthyl-3,3'-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane)
(4)
To a stirred suspension of (S)-2,2'-dimethoxy-1,1'-binaphthyl (2.52 g, 8.02 mmol) and
N,N,N',N'-tetramethylethylenediamine (3.6 mL, 24 mmol) in diethyl ether (300 mL) was added
n-butyllithium (2.8 M hexane solution, 8.7 mL, 24 mmol) at 0 °C. After the mixture was stirred
for 4 h at room temperature, trimethyl borate (2.7 mL, 24 mmol) was added dropwise at 0 °C. The
reaction mixture was allowed to warm to room temperature and stirred for 2 h. The mixture was
acidified with hydrochloric acid (4 M, 10 mL) and stirred for 1 h. The organic layer was separated,
and the aqueous layer was extracted with diethyl ether. The combined organic layer was
concentrated to dryness to give pale yellow oil. The crude boronic acid was dissolved in toluene
(50 mL) and pinacol (1.92 g, 16.2 mmol) was added to the mixture, which was refluxed with a
Dean-Stark trap for 3 h. After cooling, water (20 mL) was added and the organic layer was
separated. The aqueous layer was extracted with chloroform (3 × 30 mL). The combined
organic layer was dried over anhydrous magnesium sulfate and concentrated to dryness. The
crude product was purified by column chromatography on silica gel using ethyl acetate/hexane (1/5,
v/v) as eluent to give 4 (4.11 g, 7.27 mmol, 91%) as pale yellow crystals, m.p. 124.3–125.2 °C; 1H
NMR (400 MHz, CDCl3): δ=1.40 (s, 24H), 3.45 (s, 6H), 7.11 (d, J = 7.7 Hz, 2H), 7.22 (t, J = 7.7
Hz, 2H), 7.34 (t, J = 7.7 Hz, 2H), 7.90 (d, J = 7.7 Hz, 2H), 8.42 ppm (s, 2H); 13C NMR (100 MHz,
CDCl3): δ=24.85 (CH3), 61.92 (CH3), 83.67 (C), 123 (br, C), 124.40 (CH), 124.71 (C), 125.76 (CH),
127.12 (CH), 128.41 (CH), 130.06 (C), 135.98 (C), 138.64 (CH), 159.74 ppm (C); elemental
analysis calcd (%) for C34H40B2O6•0.25CHCl3: C 69.00, H 6.81; found: C 68.75, H 6.75.
(S)-6',6''-(2,2'-Dimethoxy-1,1'-binaphthyl-3,3'-diyl)bis(6-(5-tert-butyl-2-methoxyphenyl)-2,2'-
bipyridine) (5)
Compound 3 (0.243 g, 0.611 mmol), diboronate ester 4 (0.172 g, 0.303 mmol), and
tetrakis(triphenylphosphine)palladium(0) (0.0346 g, 0.0299 mmol) were placed in a 50-mL
two-necked flask and toluene (10 mL) and saturated aqueous solution of sodium carbonate (2 mL)
were added to the mixture in one portion. The mixture was stirred at 80 °C for 48 h. After
cooling, water was added and the organic layer was separated. The aqueous layer was extracted
with chloroform (3 × 20 mL). The combined organic layer was dried over anhydrous magnesium
sulfate and concentrated to dryness. The crude product was purified by using GPC to give 5
1
(0.173 g, 0.183 mmol, 60%) as colorless crystals, m.p. 161.2–163.4 °C; H NMR (600 MHz,
CDCl3): δ=1.41 (s, 18H), 3.35 (s, 6H), 3.88 (s, 6H), 6.99 (d, J = 8.7 Hz, 2H), 7.28–7.30 (m, 4H),
7.43 (dd, J = 8.7, 2.6 Hz, 2H), 7.45 (ddd, J = 10.2, 6.0, 2.2 Hz, 2H), 7.89 (t, J = 7.8 Hz, 2H), 7.90 (t,
J = 7.9 Hz, 2H), 7.95 (dd, J = 7.9, 1.1 Hz, 2H), 8.06 (d, J = 8.1 Hz, 2H), 8.07 (dd, J = 7.8, 0.9 Hz,

2H), 8.09 (d, J = 2.6 Hz, 2H), 8.59 (dd, J = 7.8, 0.9 Hz, 2H), 8.63 (s, 2H), 8.64 ppm (dd, J = 7.9, 1.1
Hz, 2H); 13C NMR (100 MHz, CDCl3): δ=31.57 (CH3), 34.21 (C), 55.72 (CH3), 61.26 (CH3),
111.27 (CH), 119.03 (CH), 119.55 (CH), 124.62 (CH), 125.08 (CH), 125.23 (CH), 125.78 (CH),
126.05 (C), 126.73 (CH), 126.79 (CH), 128.37 (C), 128.43 (CH), 128.77 (CH), 130.89 (C), 131.85
(CH), 133.63 (C), 134.30 (C), 136.47 (CH), 137.05 (CH), 143.49 (C), 154.29 (C), 155.13 (C),
155.44 (C × 2), 155.72 (C), 156.44 ppm (C); elemental analysis calcd (%) for C64H58N4O4•2H2O: C
78.18, H 6.36, N 5.70; found: C 78.16, H 6.09, N 5.45.
Ligand H4L.
To a stirred solution of 5 (0.173 g, 0.183 mmol) in dichloromethane (15 mL) was added boron
tribromide (0.2 mL, 2.1 mmol) at 0 °C under nitrogen atmosphere. The reaction mixture was
stirred for 4 h at room temperature. After the addition of water at 0 °C, the mixture was stirred for
1 h at room temperature. The organic layer was separated and the aqueous layer was extracted
with chloroform (3 × 50 mL). The combined organic layer was dried over anhydrous magnesium
sulfate and concentrated to dryness to give H4L (0.120 g, 0.135 mmol, 74%) as yellow crystals, m.p.
1
> 300 °C; H NMR (600 MHz, [D6]DMSO): δ=1.25 (s, 18H), 6.87 (d, J = 8.4 Hz, 2H), 7.07 (d, J
=8.4 Hz, 2H), 7.28–7.38 (m, 6H), 7.93 (d, J = 2.4, Hz, 2H), 7.96 (d, J = 8.0 Hz, 2H), 8.08 (t, J = 8.0
Hz, 2H), 8.09 (d, J = 8.0 Hz, 2H), 8.25 (d, J = 8.0 Hz, 2H), 8.28 (d, J = 8.4 Hz, 2H), 8.42 (t, J = 8.0
Hz, 2H), 8.73 (d, J = 8.0 Hz, 2H), 9.02 (s, 2H), 12.60 (s, 2H), 14.06 ppm (s, 2H); 13C NMR (100
MHz, CDCl3): δ=31.48 (CH3), 34.14 (C), 117.83 (CH), 117.89 (C), 118.28 (C), 119.00 (CH),
119.08 (CH), 119.55 (CH), 120.74 (CH), 121.07 (C), 122.89 (CH), 123.03 (CH), 124.60 (CH),
127.47 (CH), 127.48 (CH), 127.55 (C), 128.84 (CH), 129.11 (CH), 135.36 (C), 139.17 (CH),
139.26 (CH), 141.50 (C), 150.91 (C), 151.84 (C), 154.45 (C), 157.13 (C), 157.34 (C), 157.63 ppm
(C); elemental analysis calcd (%) for C60H50N4O4•H2O: C 79.27, H 5.77, N 6.16; found: C 79.55, H
5.69, N 5.98.
Nickel complex [LNi2].
A solution of nickel(II) acetate tetrahydrate (9.6 mg, 38.6 µmol) in methanol (3 mL) and
acetonitrile (3 mL) were added to a solution of H4L (17.2 mg, 19.3 µmol) in chloroform (3 mL),
and the resulting solution was kept at room temperature. From the solution, nickel complex [LNi2]
1
was obtained as dark red crystals (8.0 mg, 6.7 µmol, 35%), H NMR (600 MHz, [D6]DMSO):
δ=1.11 (s, 18H), 5.48 (d, J = 8.7 Hz, 2H), 6.21 (dd, J = 8.7, 2.3 Hz, 2H), 7.03 (d, J = 2.3 Hz, 2H),
7.09–7.12 (m, 4H), 7.15–7.17 (m, 2H), 7.73 (d, J = 7.8 Hz, 2H), 7.81 (d, J = 7.8 Hz, 2H), 7.87 (t, J
= 7.8 Hz, 2H), 7.89 (d, J = 8.3 Hz, 2H), 7.99 (d, J = 7.9 Hz, 2H), 8.23 (t, J = 7.9 Hz, 2H), 8.57 (s,
2H), 8.64 ppm (d, J = 7.9 Hz, 2H); ESI-MS: m/z 1003.3 ([M+H]+); elemental analysis calcd (%) for
C60H46N2O2Ni2•CHCl3•CH3CN•1.5H2O: C 63.49, H 4.48, N 5.88; found: C 63.44, H 4.40, N 5.70.

6-(5-tert-Butyl-2-methoxyphenyl)-6'-(3-methoxynaphthalene-2-yl)-2,2'-bipyridine (6)
Compound 3 (0.394 g, 0.992 mmol), 3-methoxynaphthalen-2-ylboronic acid (0.203 g, 1.01
mmol), and tetrakis(triphenylphosphine)palladium(0) (0.0133 g, 0.0115 mmol) were placed in a
50-mL two-necked flask and toluene (10 mL) methanol (1 mL), and saturated aqueous solution of
sodium carbonate (2 mL) were added to the mixture in one portion. The mixture was stirred at
80 °C for 20 h. After cooling, water (10 mL) was added and the organic layer was separated.
The aqueous layer was extracted with chloroform. The combined organic layer was dried over
anhydrous magnesium sulfate and concentrated to dryness. The crude product was subjected to
chromatography on silica gel using chloroform as eluent and then purified by GPC to afford 6
(0.235 g, 0.495 mmol, 50%) as colorless crystals, m.p. 87.3–89.6 °C; 1H NMR (600 MHz, CDCl3):
δ=1.41 (s, 9H), 3.88 (s, 3H), 4.01 (s, 3H), 6.98 (d, J = 8.7 Hz, 1H), 7.28 (s, 1H), 7.38 (ddd, J = 7.8,
6.9, 1.2 Hz, 1H), 7.42 (dd, J = 8.7, 2.6 Hz, 1H), 7.48 (ddd, J = 7.8, 6.9, 1.2 Hz, 1H), 7.79 (d, J = 7.8
Hz, 1H), 7.84 (t, J = 7.7 Hz, 1H), 7.87 (t, J = 7.8 Hz, 1H), 7.91 (dd, J = 7.7, 1.0 Hz, 1H), 7.92 (d, J
= 7.8 Hz, 1H), 7.93 (dd, J = 7.8, 1.1 Hz, 1H), 8.07 (d, J = 2.6 Hz, 1H), 8.43 (s, 1H), 8.54 (dd, J =
7.7, 1.0 Hz, 1H), 8.55 ppm (dd, J = 7.8, 1.1 Hz, 1H); 13C NMR (100 MHz, CDCl3): δ=31.58 (CH3),
34.23 (C), 55.53 (CH3), 55.74 (CH3), 106.05 (CH), 111.29 (CH), 119.02 (CH), 119.30 (CH), 123.90
(CH), 125.10 (CH × 2), 126.30 (CH), 126.68 (CH), 126.73 (CH), 128.40 (CH), 128.48 (C), 128.49
(CH), 128.87 (C), 130.82 (C), 131.33 (CH), 134.59 (C), 136.37 (CH × 2), 143.51 (C), 154.76 (C),
155.13 (C), 155.31 (C), 155.51 (C), 155.87 (C), 156.24 ppm (C); elemental analysis calcd (%) for
C32H30N2O2•1.25H2O: C 77.32, H 6.59, N 5.64; found: C 77.39, H 6.23, N 5.45.
Ligand H2L'
To a stirred solution of 6 (0.177 g, 0.372 mmol) in acetic acid (7 mL) was added hydrobromic
acid (47%, 0.5 mL) and the resulting solution was refluxed overnight. After cooling, the mixture
was neutralized with saturated aqueous solution of sodium hydrogencarbonate and extracted with
chloroform (3 × 30 mL). The combined organic layer was dried over anhydrous magnesium
sulfate and concentrated to dryness. The residue was recrystallized from chloroform/methanol to
give H2L' (0.142 g, 0.317 mmol, 85%) as yellow crystals, m.p. 249.5–250.5 °C, 1H NMR (600 MHz,
CDCl3): δ=1.39 (s, 9H), 7.03 (d, J = 8.6 Hz, 1H), 7.33 (ddd, J = 8.2, 6.9, 1.2 Hz, 1H), 7.40 (s, 1H),
7.43 (dd, J = 8.6, 2.4 Hz, 1H), 7.46 (ddd, J = 8.2, 6.9, 1.2 Hz, 1H), 7.72 (d, J = 8.2 Hz, 1H), 7.84 (d,
J = 8.2 Hz, 1H), 7.86 (d, J = 2.4 Hz, 1H), 8.03–8.10 (m, 3H), 8.17 (dd, J = 7.1, 1.6 Hz, 1H), 8.20 (d,
J = 7.1 Hz, 1H), 8.21 (d, J = 8.0 Hz, 1H), 8.40 (s, 1H), 13.92 (s, 1H), 13.98 ppm (s, 1H); 13C NMR
(100 MHz, CDCl3): δ=31.57(CH3), 34.25 (C), 112.20 (CH), 117.99 (C), 118.05 (CH), 119.04 (CH),
119.70 (CH), 120.01 (CH), 120.83 (CH), 121.46 (C), 122.99 (CH), 123.51 (CH), 126.04 (CH),
127.56 (CH), 127.60 (CH), 127.71 (C), 128.45 (CH), 129.38 (CH), 135.99 (C), 139.19 (CH),

139.45 (CH), 141.80 (C), 151.98 (C), 152.47 (C), 156.41 (C), 157.28 (C), 157.71 (C), 158.33 ppm
(C); ESI-MS: m/z 447.2 ([M+H]+); elemental analysis calcd (%) for C30H26N2O2: C 80.69, H 5.87,
N 6.27; found: C 80.34, H 6.01, N 6.19.
Nickel complex [L'Ni]
A solution of nickel(II) acetate tetrahydrate (8.4 mg, 33.4 µmol) in methanol (2 mL) was added
to a solution of ligand H2L' (14.7 mg, 32.9 µmol) in chloroform (2 mL) at room temperature. Vapor
phase diffusion of diethyl ether into the solution afforded [L'Ni] (14.1 mg, 23.1 µmol, 70%) as red
needles, 1H NMR (400 MHz, [D6]DMSO): δ=1.32 (s, 9H), 6.87 (d, J = 8.8 Hz, 1H), 7.11 (ddd, J =
8.4, 7.1, 1.4 Hz, 1H), 7.19 (s, 1H), 7.30 (dd, J = 8.8, 2.2 Hz, 1H), 7.33 (ddd, J = 8.4, 7.1, 1.4 Hz,
1H), 7.54 (d, J = 8.4 Hz, 1H), 7.80 (d, J = 8.4 Hz, 1H), 7.81 (s, 1H), 8.23 (t, J = 8.3 Hz, 1H), 8.34 (t,
J = 7.7 Hz, 1H), 8.39 (d, J = 7.7 Hz, 1H), 8.46 (d, J = 8.3 Hz, 1H), 8.49 (d, J = 8.3 Hz, 1H), 8.67 (s,
1H), 8.68 ppm (d, J = 7.7 Hz, 1H); ESI-MS: m/z 503.1 ([M+H]+); elemental analysis calcd (%) for
C30H26N2O2Ni•0.9CHCl3: C 60.78, H 4.11, N 4.59; found: C 60.63, H 4.23, N 4.44.

2. X-ray crystallographic analysis of [LNi2].
Single crystal of [LNi2] suitable for X-ray crystallography was obtained from a suspension of
[LNi2] in methanol/acetonitrile. Intensity data were collected on a Rigaku R-AXIS Rapid
diffractometer with MoKα radiation (λ = 0.71069 Å). The data were corrected for Lorentz and
polarization factors, and for absorption by semiempirical methods based on symmetry-equivalent
and repeated reflections. The structure was solved by Patterson methods (DIRDIF 99) and refined
by full-matrix least-squares on F2 using SHELXL 97. The crystallographic data are summarized in
Table 1.
Table 1. Crystallographic data for [LNi2]•4MeOH•2MeCN
[LNi2]•4MeOH•2MeCN
C68H68N6Ni2O8
1214.70
Formula
Formula weight
Temperature (K)
Crystal size (mm3)
Crystal system
Space group
a (Å)
120
0.50 × 0.25 × 0.10
orthorhombic
P212121
15.6037(4)
27.0324(5)
27.9392(5)
11784.9(4)
8
b (Å)
c (Å)
V (Å3)
Z
Dcalcd
1.369
Collected reflections 115940
Unique reflections
Rint
26976
0.0333
2θmax
54.96
F000
5104
µ (MoKα)
Limiting indices
0.702
–20 ≤ h ≤ 20
–35 ≤ k ≤ 29
–36 ≤ l ≤ 35
Parameters/restraints 1597/110
Flack χ 0.021(7)
Goodness of fit (F2) 1.057
R1 (I > 2σ(I))
wR2 (I > 2σ(I))
R1 (all data)
0.0423
0.1122
0.0451
0.1140
wR2 (all data)

(a)
(b)
Figure 1. X-ray crystal structure of [LNi2] with thermal ellipsoids drawn at 50% probability level.
(a) and (b) denote the two crystallographically independent molecules. Hydrogen atoms and less
occupied disordered atoms are omitted for clarity.