Diversification of ligand families through ferroin-neocuproin metal-binding domain manipulation

Article abstract of DOI:10.1039/b905988a

Derivatization of 5,5′-bis(3-hydroxyphenyl)-2,2′-bipyridine to give two new ligands, 3 and 4, which possess terminal alkene functionalities is described. The syntheses and characterization of the palladium(ii) complexes [Pd(3)₂][BF₄]

Full text of DOI:10.1039/b905988a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Diversification of ligand families through ferroin–neocuproin metal-binding
domain manipulation
Edwin C. Constable,* Catherine E. Housecroft,* Markus Neuburger, Pirmin J. Ro¨sel and Silvia Schaffner
Received 25th March 2009, Accepted 20th April 2009
First published as an Advance Article on the web 18th May 2009
DOI: 10.1039/b905988a
Derivatization of 5,5¢-bis(3-hydroxyphenyl)-2,2¢-bipyridine to give two new ligands, 3 and 4, which
possess terminal alkene functionalities is described. The syntheses and characterization of the
palladium(II) complexes [Pd(3)2][BF4]2 and [Pd(4)2][BF4]2, and the related [Pd(2)2][BF4]2 in which 2 is
5,5¢-bis(3-methoxyphenyl)-2,2¢-bipyridine are reported. The labile nature of the ligand leads to
[Pd(2)2][BF4]2 co-crystallizing with the free ligand as [Pd(2)2][BF4]2·2; in the solid state, the ligands in
the [Pd(2)2]2+ cation distort (a ‘bow-incline’ distortion) to alleviate bpy H6 ◊ ◊ ◊ H6 repulsions. Compound
2 has been converted to 5,5¢-bis(3-methoxyphenyl)-6-methyl-2,2¢-bipyridine (5) and
5,5¢-bis(3-methoxyphenyl)-6,6¢-dimethyl-2,2¢-bipyridine (6) to produce ligands suited to forming
air-stable, copper(I) complexes of type [CuL2]+. [Cu(5)2][PF6] and [Cu(6)2][PF6] have been prepared and
characterized, and the single crystal structures of 6 and [Cu(5)2][PF6]·0.1C2H4Cl2·0.15CH2Cl2 are
described. By altering the conditions under which 2 is methylated, competitive formation of
5,5¢,5¢¢,5¢¢¢-tetrakis(3-methoxyphenyl)-2,2¢:3¢,3¢¢:2¢¢,2¢¢¢-quaterpyridine occurs.
Introduction
Diaryl-functionalized 2,2¢-bipyridines (bpy), 1,10-phenanthro-
lines (phen) and 2,2¢:6¢,2¢¢-terpyridines are commonly utilized
scaffolds in metallosupramolecular chemistry. The aryl groups
bear substituents which can be further elaborated or which
contain desired functionalities, and the metal-binding domain
provides the recognition features for interaction with specific metal
centres. The development of the metal-ion templated synthesis
of catenanes, knots and other topologically complex systems1
was predicated on the organization of 6,6¢-disubstituted bpy (or
2,9-disubstituted phen) ligands about tetrahedral copper(I) or
silver(I) centres. Although the substituents adjacent to the nitrogen
(neocuproin structure type) are critical for the stability of copper(I)
complexes,2,3 formation of stable complexes with octahedral metal
centres requires that the aryl substituents are attached to other
positions (ferroin structure type). The synthesis of families of
ligands with neocuproin or ferroin metal-binding domains is
time-consuming and we have developed strategies for the direct
conversion of ferroin metal-binding domains to the neocuproin
type.
We have previously reported ligands 1 and 24 (Scheme 1),
and the complexation of 1 with silver(I).5 We have also used 1
as a building block for the formation of a heterotopic ligand
in which the central bpy domain is linked by polyethyleneoxy
spacers to two 2,2¢:6¢,2¢¢-terpyridine (tpy) units. The flexibility
of this ligand permits the binding of iron(II) and formation
of a [1 + 1] ferramacrocycle.6 Apart from these studies, the
complexation of 1 and 2 remains unexplored. In this paper, we
report the formation of two ligands, 3 and 4 (Scheme 1), which
possess terminal alkene functionalities that are ideally suited to
Department of Chemistry, University of Basel, Spitalstrasse 51, CH 4056
Basel, Switzerland. E-mail: catherine.housecroft@unibas.ch; Fax: +41 61
267 1018; Tel: +41 61 267 1008
Scheme 1 Structure of ligands 1 to 4, and numbering schemes for NMR
spectra.
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Grubbs’ coupling and the assembly of polymeric or macrocyclic
species. We extend the diversity in coordination space beyond
commonly studied 1 : 2 tetrahedral and 1 : 3 octahedral species
to 1 : 2 square planar metal centres and describe the preparation
and characterization of palladium(II) complexes of ligands 2–4. We
have made proof-of-principle conversion of 2 to ligands containing
substituents adjacent to the nitrogen donors and describe the air-
stable copper(I) complexes of these new ligands.
(CB4), 112.8 (CB2), 55.2 (CMe). 19F NMR (376 MHz, DMSO-d6) d
(ppm) -148.7 (s). FAB MS m/z 861.1 [Pd(2)2 + F]+ (calc. 861.2),
842.1 [Pd(2)2]+ (calc. 842.2), 474.0 [Pd(2)]+ (calc. 474.1), 369.1 [2 +
H]+ (calc. 369.2). IR (solid, n (cm-1)) 3005 w, 2932 w, 2856 w, 1738
m, 1605 m, 1576 m, 1464 m, 1452 s, 1435 m, 1300 m, 1231 m, 1205
m, 1063 m, 1016 m, 843 m, 837 m, 779 s, 692 s. Found C, 56.53;
H, 4.10; N, 5.41; C48H40B2F8N4O4Pd requires C, 56.69; H, 3.96; N,
5.51%.
Ligand 3
Experimental
Compound 1 (88.4 mg, 260 mmol), allyl bromide (1.0 cm3,
11.5 mmol) and Cs2CO3 (350 mg, 1.07 mmol) were heated in
THF at 100 ◦C in a microwave reactor for 45 min. Purification
by column chromatography (SiO2, CH2Cl2 : MeOH 100 : 1) gave 3
1H and 13C NMR spectra were recorded at room temperature
on Bruker Avance DRX-500 and DPX-400 MHz spectrometers;
chemical shifts are relative to residual solvent peaks with TMS d
1
0 ppm for H and 13C, and relative to CF35Cl3 in CDCl3 for 19F
◦
as a colourless solid (106 mg, 252 mmol, 96%). Mp 135–137 C.
(external reference). Infrared spectra were recorded on a Shimadzu
FTIR-8400S spectrophotometer with solid samples on a Golden
Gate diamond ATR accessory. Electrospray ionisation (ESI) mass
spectra were recorded using Finnigan MAT LCQ or Bruker
esquire 3000plus instruments, and FAB (NBA matrix) and electron
impact (EI) mass spectra using Finnigan MAT 312 and VG 70-
250 instruments, respectively. Electronic absorption spectra were
recorded on a Varian-Cary 5000 spectrophotometer. Microwave
reactions were carried out in a Biotage Initiator 8 reactor. Solvents
were distilled before use, and reactions were carried out under N2.
Electrochemical measurements were carried out using an Eco
Chemie Autolab PGSTAT 20 with a platinum working electrode,
a platinum mesh for the counter electrode, and a silver wire as
the reference electrode. Solutions of the compounds in dry and
degassed MeCN were used in the presence of 0.1 M [n-Bu4N][PF6].
The scan rate for the CV was 150 mV s-1 and ferrocene was added
as an internal standard at the end of every experiment.
1H NMR (500 MHz, CDCl3) d (ppm) 8.91 (d, J = 1.7 Hz, 2H,
HA6), 8.48 (d, J = 8.2 Hz, 2H, HA3), 8.00 (dd, J = 8.3, 2.4 Hz,
2H, HA4), 7.40 (t, J = 7.9 Hz, 2H, HB5), 7.18 (d, J = 7.9 Hz, 2H,
HB6), 7.14 (m, 2H, HB2), 6.91 (ddd, J = 8.2, 2.4, 0.8 Hz, 2H, HB4),
6.03 (m, 2H, Ha), 5.40 (m, 2H, Hc), 5.26 (m, 2H, Hb), 4.56 (m,
4H, He1). 1H NMR (400 MHz, CD3COCD3) d (ppm) 9.00 (d, J =
1.7 Hz, 2H, HA6), 8.59 (d, J = 8.3 Hz, 2H, HA3), 8.21 (dd, J =
8.3, 2.4 Hz, 2H, HA4), 7.40 (t, J = 8.1 Hz, 2H, HB5), 7.37 (m, 4H,
HB2+B6), 7.04 (dd, J = 8.2, 2.4 Hz, 2H, HB4), 6.12 (m, 2H, Ha),
5.47 (m, 2H, Hc), 5.28 (m, 2H, Hb), 4.71 (m, 4H, He1). 13C NMR
(101 MHz, CDCl3) d (ppm) 159.1 (CB3), 154.7 (CA2), 147.7 (CA6),
139.0 (CB1), 136.2 (CA5), 135.2 (CA4), 133.1 (Ca), 130.1 (CB5), 120.9
(CA3), 119.6 (CB6), 117.9 (Cb/c), 114.3 (CB4), 113.7 (CB2), 68.9 (Ce1).
IR (solid, n (cm-1)) 2874 m, 2869 m, 1605 m, 1578 s, 1460 s, 1435
m, 1362 w, 1297 m, 1278 m, 1201 s, 1175 w, 1113 m, 1099 m, 1068
m, 1016 m, 947 m, 934 m, 937 m, 918 m, 841 m, 779 s. EI MS
m/z 421.2 [M]+ (calc. 421.2). Found C, 79.13; H, 6.10; N, 6.31;
C28H24N2O2·0.2H2O requires C, 79.30; H, 5.80; N, 6.61%.
First generation Grubbs’ and Hoveyda–Grubbs’ catalysts and
[Pd(CH3CN)4][BF4]2 were purchased from Aldrich, MeLi from
Acros. Compound 1 was prepared by our previously reported
method.4
[Pd(3)2][BF4]2
The procedure was as for [Pd(2)2][BF4]2 using 3 (64.1 mg,
152 mmol) and [Pd(CH3CN)4][BF4]2 (34.2 mg, 77.0 mmol).
[Pd(3)2][BF4]2 was isolated as a yellow solid (85.1 mg, 75.9 mmol,
Ligand 2
Ligand 2 was prepared according to the literature procedure.4
For comparison with the palladium(II) complex, NMR data were
recorded in DMSO-d6. 1H NMR (400 MHz, DMSO-d6) d (ppm)
9.06 (d, J = 2.1 Hz, 2H, HA6), 8.51 (d, J = 8.3 Hz, 2H, HA3), 8.28
(dd, J = 8.3, 2.3 Hz, 2H, HA4), 7.40 (t, J = 7.8 Hz, 2H, HB5), 7.37
(m, 4H, HB2+B6), 7.03 (dd, J = 8.1, 1.7 Hz, 2H, HB4), 3.86 (s, 6H,
HMe).
1
99.9%). H NMR (500 MHz, CD3COCD3) d (ppm) 9.33 (s, 4H,
HA6), 8.86 (m, 8H, HA3+A4), 7.45 (m, 4H, HB2), 7.41 (m, 8H, HB5+B6),
7.14 (m, 4H, HB4), 6.04 (m, 4H, Ha), 5.39 (m, 4H, Hc), 5.24 (m,
4H, Hb), 4.60 (dt, J = 1.5, 5.2 Hz, 8H, He1). 13C NMR (126 MHz,
CD3COCD3) d (ppm) 160.5 (CB3), 156.2 (CA2), 150.3 (CA6), 141.3
(CA5), 141.0 (CA3/A4), 137.0 (CB1), 134.4 (CHa), 131.6 (CB5), 125.3
(CA3/A4), 120.7 (CB6), 117.8 (CHb/c), 117.1 (CB2), 114.5 (CB4), 69.5
(Ce1). 19F NMR (376 MHz, CD3COCD3) d (ppm) -152.2 (s). IR
(solid, n (cm-1)) 3070 m, 2924 m, 2168 m, 2037 w, 1736 w, 1582
w, 1466 m, 1373 w, 1304 m, 1250 m, 1211 m, 1026 s, 918 m, 841
m, 779 m, 687 m. ESI-MS m/z 1033.9 [Pd(3)2BF4]+ (calc. 1032.3),
965.1 [Pd(3)2F]+ (calc. 965.3), 473.3 [Pd(3)2]2+ (calc. 473.2). Found
C, 60.64; H, 4.49; N, 4.80; C56H48B2F8N4O4Pd requires C, 60.00;
H, 4.32; N, 5.00%.
[Pd(2)2][BF4]2
A solution of 2 (227 mg, 617 mmol) in CH2Cl2 (10 cm3) was
added to a solution of [Pd(CH3CN)4][BF4]2 (137 mg, 308 mmol) in
CH3CN (10 cm3) and stirred at room temperature for 24 h. The
solution turned pale yellow and a yellow precipitate was formed.
Solvent was removed under vacuum to give [Pd(2)2][BF4]2 as a
1
yellow solid (313 mg, 308 mmol, 100%). H NMR (500 MHz,
DMSO-d6) d (ppm) 9.15 (s, 4H, HA6), 8.90 (br, 8H, HA3+A4), 7.43
(m, 8H, HB2+B6), 7.39 (t, J = 7.8 Hz, 4H, HB5), 7.13 (d, J = 7.4 Hz,
4H, HB4), 3.73 (s, 12H, HMe). 13C NMR (126 MHz, DMSO-d6) d
(ppm) 160.1 (CB3), 154.5 (CA2), 149.5 (CA6), 140.1 (CA3/A4), 139.2
(CA5), 135.6 (CB1), 130.5 (CB5), 124.3 (CA3/A4), 119.7 (CB6), 115.4
Ligand 4
Compound 1 (1.63 g, 4.79 mmol), 3-(2-bromoethoxy)prop-1-ene
(1.57 g, 9.63 mmol) and Cs2CO3 (6.24 g, 19.0 mmol) were dissolved
in dry DMF (200 cm3). The reaction mixture was heated at 120 ◦C
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for 4 d. Solvent was removed and the product purified by column
chromatography (SiO2, CH2Cl2 : MeOH 66 : 1). After filtration
over Al2O3, 4 was isolated as a colourless crystalline solid (2.17 g,
4.27 mmol, 89%). Mp 96–98 ◦C. 1H NMR (500 MHz, CDCl3) d
(ppm) 8.97 (d, J = 2.1 Hz, 2H, HA6), 8.54 (d, J = 8.2 Hz, 2H,
HA3), 8.06 (dd, J = 2.3, 8.3 Hz, 2H, HA4), 7.45 (t, J = 7.9 Hz, 2H,
HB5), 7.29 (m, 4H, HB2+B6), 7.03 (dd, J = 8.2, 2.2 Hz, 2H, HB4),
6.00 (m, 2H, Ha), 5.37 (m, 2H, Hc), 5.27 (m, 2H, Hb), 4.27 (m, 4H,
1.6 M solution in hexane, 3.82 mmol) was added dropwise resulting
in an orange coloration. The reaction mixture was allowed to
warm slowly to room temperature and left to stand overnight
after which time the colour became an intense blue-violet. The
reaction mixture was then stirred at 100 ◦C for 30 min and the
resulting orange solution was cooled to room temperature and
extracted with H2O (200 cm3). The aqueous phase was extracted
with CH2Cl2 (3 ¥ 20 cm3) and the combined organic layers were
dried over MgSO4, filtered and stirred in the presence of MnO2
(10 g) for 6 h. Filtration and removal of solvents yielded 5 as a
white solid (1.09 g, 2.85 mmol, 82%). Mp 143–144 ◦C. 1H NMR
(500 MHz, CDCl3) d (ppm) 8.91 (d, J = 2.1 Hz, 1H, HA6), 8.52 (d,
J = 8.2 Hz, 1H, HA3), 8.28 (d, J = 8.0 Hz, 1H, HC3), 8.00 (dd, J =
8.2, 2.3 Hz, 1H, HA4), 7.66 (d, J = 8.0 Hz, 1H, HC4), 7.40 (t, J =
7.9 Hz, 1H, HB5), 7.36 (t, J = 7.9 Hz, 1H, HD5), 7.23 (d, J = 7.5 Hz,
1H, HB6), 7.17 (m, 1H, HB2), 6.94 (m, 3H, HB4+D4+D6), 6.91 (m, 1H,
1
He1), 4.18 (m, 4H, He3), 3.88 (m, 4H, He2). H NMR (400 MHz,
CD3CN–CDCl3) d (ppm) 8.88 (d, J = 2.1 Hz, 2H, HA6), 8.46 (d,
J = 8.3 Hz, 2H, HA3), 8.03 (dd, J = 2.4, 8.3 Hz, 2H, HA4), 7.39 (t,
J = 7.9 Hz, 2H, HB5), 7.24 (m, 2H, HB6), 7.20 (m, 2H, HB2), 6.95
(ddd, J = 8.3, 2.5, 0.8 Hz, 2H, HB4), 5.91 (m, 2H, Ha), 5.29 (m, 2H,
Hc), 5.17 (m, 2H, Hb), 4.19 (m, 4H, He1), 4.07 (m, 4H, He3), 3.80
(m, 4H, He2). 13C NMR (126 MHz, CDCl3) d (ppm) 159.3 (CB3),
154.7 (CA2), 147.7 (CA6), 138.9 (CB1), 136.2 (CA5), 135.2 (CA4), 134.5
(Ca), 130.1 (CB5), 120.9 (CA3), 119.7 (CB6), 117.4 (Cb/c), 114.0 (CB4),
113.6 (CB2), 72.4 (Ce3), 68.4 (Ce2), 67.5 (Ce1). EI MS m/z 508.2
[M]+ (calc. 508.2), 424.2 [M - C5H8O]+ (calc. 424.2), 340.1 [M -
2C5H8O]+ (calc. 340.1). IR (solid, n (cm-1)) 3005 w, 2932 w, 2856
w, 1605 m, 1576 s, 1464 m, 1452 s, 1441 m, 1358 m, 1300 m, 1279
m, 1205 s, 1142 m, 1130 m, 1099 m, 1068 m, 1016 m, 947 m, 937
m, 918 m, 835 m, 781 s, 694 s. Found C, 75.54; H, 6.50; N, 5.39;
C32H32N2O2 requires C, 75.57; H, 6.34; N, 5.51%.
HD2), 3.88 (s, 3H, OMeB), 3.84 (s, 3H, OMeD), 2.62 (s, 3H, Me). 13
C
NMR (126 MHz, CDCl3) d (ppm) 160.4 (CB3), 159.7 (CD3), 155.6
(CA2), 155.4 (CC2), 154.3 (CC6), 147.9 (CA6), 141.6 (CD1), 139.4 (CB1),
138.2 (CC4), 137.0 (CC5), 136.3 (CA5), 135.4 (CA4), 130.4 (CB5), 129.7
(CD5), 121.7 (CD6), 121.2 (CA3), 119.7 (CB6), 118.5 (CC3), 115.0 (CD4),
113.6 (CB4), 113.1 (CD2), 113.0 (CB2), 55.6 (CB-OMe), 55.5 (CD-OMe),
23.9 (CMe). ESI MS: m/z 382.2 [M]+ (calc. 382.2). IR (solid, n
(cm-1)) 3060 w, 2993 w, 2929 w, 2832 w, 1606 m, 1578 m, 1458 s,
1439 m, 1432 m, 1418 m, 1295 m, 1283 s, 1209 s, 1178 m, 1167 m,
1048 m, 1035 m, 1019 m, 841 s, 697 s. Found C, 78.34; H, 5.98; N,
7.13; C25H22N2O2 requires C, 78.51; H, 5.80; N, 7.32%.
[Pd(4)2][BF4]2
The procedure was as for [Pd(2)2][BF4]2 using 4 (100 mg, 197 mmol)
and [Pd(CH3CN)4][BF4]2 (44.1 mg, 99.3 mmol). [Pd(4)2][BF4]2 was
Ligand 6
1
isolated as a yellow solid (129 mg, 99.4 mmol, 100%). H NMR
(500 MHz, CD3CN–CDCl3) d (ppm) 8.76 (s, 4H, HA6), 8.46 (s,
8H, HA3+A4), 7.30 (t, J = 7.9 Hz, 4H, HB5), 7.17 (s, 4H, HB2), 7.14
(d, J = 7.6 Hz, 4H, HB6), 7.00 (dd, J = 8.3, 1.4 Hz, 4H, HB4),
5.86 (m, 4H, Ha), 5.25 (m, 4H, Hc), 5.14 (m, 4H, Hb), 4.07 (m,
8H, He1), 4.01 (d, J = 5.5 Hz, 8H, He3), 3.72 (m, 8H, He2). 13C
NMR (126 MHz, CD3CN–CDCl3) d (ppm) 160.0 (CB3), 155.0
(CA2), 148.9 (CA6), 140.1 (CA3/A4), 136.0 (CA5/B1), 135.8 (CA5/B1),
134.8 (CHa), 131.0 (CB5), 124.7 (CA3/A4), 119.9 (CB6), 117.2 (CHb/c),
116.6 (CB4), 113.4 (CB2), 72.3 (Ce3), 68.6 (Ce2), 67.9 (Ce1). 19F NMR
(376 MHz, CD3COCD3) d (ppm) -152.6 (s). ESI-MS m/z 1157.6
[PdL2Cl]+. IR (solid, n (cm-1)) 3072 w, 2928 w, 2864 w, 1719 m,
1600 m, 1581 m, 1471 s, 1436 m, 1373 w, 1302 m, 1251 w, 1211 m,
1035 s, 1028 s, 936 m, 840 m, 781 s, 690 m. Found C, 60.03; H,
5.15; N, 4.36; C64H64B2F8N4O4Pd requires C, 59.26; H, 4.97; N,
4.32%.
Compound 5 (102 mg, 267 mmol) was dissolved in toluene (30 cm3).
The solution was cooled to -20 ◦C. MeLi (180 mL, 1.6 M solution
in hexane, 293 mmol) was added dropwise and an intense blue
coloration appeared. The reaction mixture was stirred for 1 h at
this temperature, allowed to warm to room temperature and H2O
(5 cm3) was added. The aqueous phase was separated and extracted
with CH2Cl2 (3 ¥ 10 cm3). The combined organic layers were
treated with MnO2 (2 g) and stirred for 5 h at room temperature.
Column chromatography (Al2O3, CH2Cl2) yielded a colourless
fraction from◦which solid 6 was isolated (58.3 mg, 147 mmol, 55%).
J = 7.9 Hz, 2H, HC3), 7.64 (d, J = 7.9 Hz, 2H, HC4), 7.36 (t, J =
7.8 Hz, 2H, HD5), 6.93 (overlapping m, 6H, HD2+D4+D6), 3.84 (s, 6H,
HOMe), 2.60 (s, 6H, HMe). 13C NMR (126 MHz, CDCl3) d (ppm)
159.5 (CB3), 155.2 (CA2), 154.6 (CA6), 141.5 (CB1), 137.9 (CA4), 136.6
(CA5), 129.4 (CB5), 121.5 (CB6), 118.4 (CA3), 114.9 (CB4), 112.7 (CB2),
55.3 (COMe), 23.7 (CMe). ESI MS m/z 397.4 [M + H]+ (calc. 397.2),
419.2 [M + Na]+ (calc. 419.2), 815.6 [2M + Na]+ (calc. 815.4). IR
(solid, n (cm-1)) 3077 w, 3052 w, 2989 m, 2959 m, 2924 m, 2832
m, 1606 m, 1575 m, 1456 m, 1289 m, 1209 s, 1179 m, 1049 m,
1018 m, 879 w, 841 s, 781 s. Found C, 76.12; H, 6.15; N, 6.70;
C26H24N2O2·0.75H2O requires C, 76.17; H, 6.27; N, 6.83%.
1
Mp 185–188 C. H NMR (500 MHz, CDCl3) d (ppm) 8.30 (d,
Attempted ring-closing metathesis
In a typical reaction, [Pd(4)2][BF4]2 or [Pd(5)2][BF4]2 (20 mmol) and
Grubbs’ catalyst (first generation or Hoyveda–Grubbs catalyst
second generation) (2 mmol) were dissolved in CH2Cl2 (20 cm3)
and stirred at room temperature (5–7 days) or heated at reflux
overnight. In additional trials, the solvent was CH3NO2 under the
same conditions. Reactions were also attempted in a microwave
reactor at 60 ◦C for 1.5 h in CH2Cl2. See text.
Compound 7
Compound 2 (1.92 g, 5.21 mmol) was dissolved in toluene
(250 cm3). MeLi (3.9 cm3, 1.6 M solution in hexane, 6.25 mmol)
was added dropwise at room temperature resulting in a blue-violet
solution which was stirred for 30 min at room temperature. Water
Ligand 5
Compound 2 (1.28 g, 3.47 mmol) was◦ dissolved in toluene
(250 cm3). The solution was cooled to -78 C and MeLi (2.4 cm3,
4920 | Dalton Trans., 2009, 4918–4927
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(40 cm3) was added and the organic phase was separated. The
aqueous phase was extracted with CH2Cl2 and the combined
organic layers were dried over MgSO4, filtered and stirred in
the presence of MnO2 (25 g) for 6 h. After filtration, spot thin
layer chromatography showed the presence of two components.
These were separated by column chromatography (Al2O3, CH2Cl2
changing to CH2Cl2 : MeOH 20 : 1). After removal of solvent, 5
(first fraction, 668 mg, 1.75 mmol, 34%) and 7 (second fraction,
621 mg, 814 mmol, 31%) were isolated as colourless solids.
Compound 7: Mp 102–104 C. H NMR (500 MHz, CDCl3) d
(ppm) 8.67 (dd, J = 2.3, 0.7 Hz, 2H, HA6), 7.71 (dd, J = 8.2,
2.3 Hz, 2H, HA4) 7.54 (d, J = 8.2 Hz overlapping s, 4H, HA3+E4),
7.34 (t, J = 7.9 Hz, 2H, HB5), 7.27 (t, J = 7.9 Hz, 2H, HF5), 7.14
(ddd, J = 7.7, 1.4, 0.8 Hz, 2H, HB6), 7.09 (m, 2H, HB2), 6.90 (ddd,
J 8.3, 2.5, 0.7 Hz, 2H, HB4), 6.86 (m, 4H, HF4+F6), 6.79 (m, 2H,
HF2), 3.81 (s, 6H, HB-OMe), 3.72 (s, 6H, HF-OMe), 2.62 (s, 6H, HMe).
13C NMR (126 MHz, CDCl3) d (ppm) 160.1 (CB3), 159.4 (CF3),
156.5 (CA2), 154.5 (CE6), 153.3 (CE2/3), 147.2 (CA6), 140.6 (CF1),
140.4 (CE4), 139.1 (CB1), 136.1 (CE5), 134.9 (CA5), 134.4 (CA4),
131.9 (CE3/2), 130.1 (CB5), 129.3 (CF5), 124.2 (CA3), 121.5 (CF6),
119.5 (CB6), 114.7 (CF2), 113.2 (CB4), 113.0 (CF4), 112.9 (CB2), 55.3
(CB-OMe), 55.2 (CF-OMe), 23.3 (CMe). ESI MS: m/z 763.4 [M + H]+
(calc. 763.3). IR (solid, n (cm-1)) 3001 w, 2932 w, 2831 w, 1599 s,
1578 s, 1450 m, 1424 s, 1363 w, 1285 m, 1211 s, 1163 m, 1037
m, 1013 m, 844, 777 s, 690 s. Found C, 77.36; H, 5.70; N, 7.22;
C50H42N4O4·0.75H2O requires C, 77.35; H, 5.65; N, 7.22%.
[Cu(6)2][PF6] was isolated as a red solid (48.1 mg, 48.0 mmol,
94%). 1H NMR (500 MHz, CD3CN) d (ppm) 8.35 (d, J = 7.1 Hz,
4H, HC3), 7.98 (d, J = 7.3 Hz, 4H, HC4), 7.39 (t, J = 7.8 Hz,
4H, HD5), 6.99 (m, 12H, HD2+D4+D6), 3.80 (s, 12H, OMe), 2.32 (s,
12H, Me). 13C NMR (126 MHz, CDCl3) d (ppm) 159.7, 154.7,
150.5, 139.4, 139.3, 129.8, 129.4, 121.3, 119.9, 114.8, 113.6, 55.4
(COMe), 24.3 (CMe). 19F NMR (376 MHz, CD3CN) d (ppm) -74.1
(d, J = 703 Hz). ESI MS: m/z 856.0 [M - PF6]+ (calc. 855.3)
UV/VIS (CH2Cl2) lmax (nm) 467 (e/6100 dm3 mol-1 cm-1), 320
(61 000), 277 (50 600). Emission (CH2Cl2, lex 350 nm) lmax (nm)
383. IR (solid, n (cm-1)) 3057 w, 2972 w, 2918 w, 2842 w, 1589 m,
1448 m, 1230 w, 1223 m, 1047 w, 1022 m, 831 s, 787 m, 702 m.
E◦(MeCN)/V vs. Fc/Fc+: +0.40 (irreversible). Found C, 62.96;
H, 4.95; N, 5.58; C52H48CuF6N6O6P requires C, 62.36; H, 4.83; N,
5.59%.
◦
1
Crystal structure determination
Data were collected on a Bruker-Nonius Kappa CCD or Stoe
IPDS instrument; data reduction, solution and refinement used
the programmes Stoe IPDS software7 or COLLECT,8 and then
DENZO/SCALEPACK,9 SIR92,10 and CRYSTALS.11 The struc-
tures have been analysed using Mercury v. 1.4.2.12 The ORTEP
figures drawn using Ortep-3 for Windows.13
[Pd(2)2][BF4]2·2
[Cu(5)2][PF6]
C72H60B2F8N6O6Pd, M = 1385.31, yellow plate, triclinic, space
˚
group P-1, a = 8.7623(2), b = 11.1136(2), c = 16.3282(3) A, a =
Ligand 5 (32.0 mg, 83.7 mmol) was dissolved in CH2Cl2 (5 cm3) and
a solution of [Cu(NCMe)4][PF6] (15.7 mg, 42.0 mmol) in CH3CN
(5 cm3) was added. The red solution was stirred for 30 min at
room temperature, filtered over Al2O3, and then the solvent was
removed in vacuo. [Cu(5)2][PF6] was isolated as a red solid (40.1 mg,
41.2 mmol, 98%). 1H NMR (500 MHz, CD3CN) d (ppm) 8.91 (d,
J = 1.7 Hz, 2H, HA6), 8.48 (d, J = 8.4 Hz, 2H HA3), 8.30 (d, J =
8.1 Hz, 2H, HC3), 8.24 (dd, J = 8.3, 1.4 Hz, 2H, HA4), 7.83 (d,
J = 8.0 Hz, 2H, HC4), 7.39 (t, J = 8.0 Hz, 2H, HB5), 7.37 (t, J =
7.9 Hz, 4H, HD5), 7.25 (d, J = 7.8 Hz, 2H, HB6), 7.22 (m, 2H,
HB2), 7.00–6.94 (overlapping, 6H, HB4+D4+D6), 6.93 (m, 2H, HD2),
3.81 (s, 6H, HB-OMe), 3.80 (s, 6H, HD-OMe), 2.39 (s, 6H, HMe). 13C
NMR (126 MHz, CD3CN) d (ppm) 161.4 (CB3), 160.7 (CD3), 156.3
(CC6), 153.7 (CA2), 152.7 (CC2), 148.5 (CA6), 141.5 (CD1), 139.6 (CC4),
139.3 (CC5), 139.0 (CB1), 138.4 (CA5), 136.7 (CA4), 131.4 (CB5/D5),
130.7 (CD5/B5), 122.5 (CA3), 122.3 (CD6), 120.4 (CB6), 119.9 (CC3),
115.8 (CD2), 115.2 (CD4), 114.3 (CB4), 113.6 (CB2), 56.1 (CB-OMe),
56.05 (CD-OMe), 24.6 (CMe). 19F NMR (376 MHz, CD3CN) d (ppm)
-74.03 (d, J = 707). ESI MS: m/z 827.4 [M - PF6]+ (calc. 827.3).
IR (solid, n (cm-1)) 3062 w, 2954 w, 2922 m, 2850 w, 1599 m, 1581
m, 1470 m, 1447 m, 1435 m, 1377 w, 1300 m, 1251 w, 1224 m,
1045 s, 1021 s, 837 s, 786 s, 690 m. UV/VIS (CH2Cl2) lmax (nm)
468 (e/6000 dm3 mol-1 cm-1), 319 (61 000), 277 (50 500). Emission
(CH2Cl2, lex 350 nm) lmax (nm) 379. Found C, 61.39; H, 4.75; N,
5.54; C50H44CuN4O4PF6 requires C, 61.69; H, 4.56; N, 5.76%.
◦
3
˚
75.890(1), b = 77.905(1), g = 89.117(1) , U = 1506.78(5) A , Z =
1, Dc = 1.527 Mg m-3, m(Mo Ka) = 0.396 mm-1, T = 173 K, 13 865
reflections collected (7175 unique). Refinement of 5977 reflections
(430 parameters) with I > 3s(I) converged at final R1 = 0.0274 (R1
all data = 0.0356), wR2 = 0.0285 (wR2 all data = 0.0351), Rint
0.023, gof = 1.1096.
=
Ligand 6
C26H24N2O2, M = 396.49, colourless block, monoclinic, space
˚
group P21/c, a = 10.0276(2), b = 8.1544(1), c = 12.9843(2) A,
◦
3
-3
˚
b = 111.960(1) , U = 984.68(3) A , Z = 2, Dc = 1.337 Mg m ,
m(Mo Ka) = 0.085 mm-1, T = 123 K, 25 410 reflections collected
(4279 unique). Refinement of 2689 reflections (136 parameters)
with I > 3s(I) converged at final R1 = 0.0512 (R1 all data =
0.0728), wR2 = 0.0533 (wR2 all data = 0.0608), Rint = 0.036, gof =
1.0661.
[Cu(5)2][PF6]·0.1C2H4Cl2·0.15CH2Cl2
C50.35H44.70Cl0.50CuF6N4O4P, M = 996.07, red plate, triclinic, space
˚
group P-1, a = 10.3190(8), b = 15.078(1), c = 16.603(1) A, a =
◦
3
˚
90.627(7), b = 98.169(6), g = 106.230(7) , U = 2451.7(4) A ,
Z = 2, Dc = 1.349 Mg m-3, m(Mo Ka) = 0.575 mm-1,
T = 173 K, 59 962 reflections collected (16 938 unique). Re-
finement of 7730 reflections (757 parameters) with I > 2s(I)
converged at final R1 = 0.0916 (R1 all data = 0.1710),
wR2 = 0.0858 (wR2 all data = 0.1181), Rint = 0.128, gof =
1.0181.
[Cu(6)2][PF6]
The method was as for [Cu(5)2][PF6] starting with 6 (40.0 mg,
101 mmol) and [Cu(NCMe)4][PF6] (19 mg, 50.9 mmol).
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Results and discussion
Ligands for palladium(II) complexes
Ligands
3 and 4 were prepared using caesium-directed
Williamson’s methodology by treating 1 with allyl bromide or 3-(2-
bromoethoxy)prop-1-ene, respectively, in the presence of Cs2CO3
in DMF. For 3, the reaction was carried out in a microwave reactor
at 100 ◦C and was complete in less than an hour. For 4, the reaction
mixture was heated at 120 ◦C for 4 d. Both ligands were obtained
in high yield. The EI mass spectrum of each compound exhibited
a parent ion (m/z 421.2 for 3 and 508.2 for 4), and the appearance
of the solution 1H and 13C NMR spectra of 3 and 4 confirmed the
formation of symmetrical ligands. The spectra have been assigned
using COSY, DEPT, HMQC and HMBC techniques. With the
exception of the appearance of signals for the additional methylene
groups in 4, the 1H NMR spectra for 3 and 4 are almost identical,
as are their 13C NMR spectra. However, whereas in 3, the signals
for protons HB2 and HB6 (Scheme 1) appear at d 7.14 and 7.18 ppm,
in 4, they overlap at d 7.29 ppm. Since the 13C NMR spectroscopic
signatures for the aromatic domain of the two ligands are virtually
superimposable, the assignments of signals for CB2 and CB6 in 4
have been made by comparison with those of 3, assigned from the
HMQC spectrum.
Fig. 1 500 MHzNMR spectra of DMSO-d6 solutions of (a) [Pd(2)2][BF4]2
and (b) ligand 2.
for several weeks after which time, X-ray quality yellow plates
had grown. Interestingly, the complex co-crystallized with the free
ligand (which must have originated from the complex) and the
single crystal structure of [Pd(2)2][BF4]2·2 determined. Fig. 2(a)
and Fig. 3 show the centrosymmetric structures of the [Pd(2)2]2+
cation and ligand 2, respectively. Bond distances and angles
within the bpy and phenyl rings are unexceptional. As expected,
the free ligand adopts a transoid conformation, but flips to a
cisoid arrangement upon binding to palladium(II). The C–O
bond distances and C–O–C bond angles in both ligand and
complex (see figure caption) are consistent with delocalization
of p-character from the phenyl ring to the oxygen atom. Two
features of the structure deserve note: the ligand distortion in
[Pd(2)2]2+, and the packing. In [M(bpy)2]n+ complexes and in
Palladium(II) complexes: synthesis and solution characterization
The reaction of [Pd(CH3CN)4][BF4]2 with two equivalents of
ligand 2 in CH3CN produced analytically pure [Pd(2)2][BF4]2
as a yellow solid. The highest mass peaks in the FAB mass
spectrum came at m/z 861.1 and 842.1, and were assigned to
[Pd(2)2 + F]+ and [Pd(2)2]+, respectively. Fragmentation by ligand
loss was also observed. The complex was poorly soluble in most
common solvents, and the NMR spectra were recorded in DMSO-
d6. Compared to signals for the free ligand in DMSO-d6, the
most diagnostic indication of complex formation is the large
shift to higher frequency for the signal for bpy proton HA4.
This presumably reflects the fact that in the square planar Pd(II)
environment, the presence of the methoxy substituents restricts
rotation about the Cpy–CPh bond, and the aryl ring twists out of
the plane of the bpy unit (this is confirmed in the crystal structures
of ligand and complex described below). The bpy protons most
affected by this will be those facing the aryl p-cloud, i.e. HA4
and HA6 (Fig. 1). As Fig. 1 shows, the peaks for the bpy unit
are rather broad compared to those of the free ligand in the
same solvent. Addition of free ligand to an NMR sample of
[Pd(2)2][BF4]2 resulted in further broadening of the signal assigned
to HA3+A4 as well as broadening of the resonance for HB4 and loss
of resolution for the signals for HB2+B6/HB5. In spectra recorded for
[Pd(2)2][BF4]2 plus half and one equivalent of ligand, no signals
arising from the free ligand were observed. This observation is
consistent with that observed by Milani et al., in the DMSO-d6
1
solution H NMR spectrum of [Pd(bpy)2][PF6]2, indicating that
exchange occurs between the free and the coordinated ligand on
the NMR spectroscopic timescale.14
Fig. 2 (a) Molecular structure of the [Pd(2)2]2+ cation in [Pd(2)2][BF4]2·2
with ellipsoids plotted at 50% probability level. Symmetry code a =
-x, -y, -z. Selected bond parameters: Pd1–N1 = 2.033(1), Pd1–N2 =
2.022(1), C1–O1 = 1.427(2), C2–O1 = 1.362(2), C23–O2 = 1.361(2),
Structural characterization of [Pd(2)2][BF4]2·2
a
˚
C24–O2 = 1.428(2) A; N1–Pd1–N2 = 79.21(5), N2 –Pd1–N1 = 100.79(5),
C1–O1–C2 = 118.3(2), C24–O2–C23 = 117.5(1)◦. (b) Distortion of the
A solution of analytically pure [Pd(2)2][BF4]2 in a mixture of
DMF and Et2O in a vial surrounded by Et2O was left at 4 ◦C
bpy units alleviates steric hindrance between H6 protons.
4922 | Dalton Trans., 2009, 4918–4927
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previous structure of 2,4 it lies on the same side of the molecule
as the N atom. This difference probably originates from packing
effects. In 2,4 molecules interact through weak C–Hmethyl ◊ ◊ ◊ O
hydrogen bonds to form interconnected, undulating chains; offset
face-to-face p-stacking occurs between adjacent bpy domains and
between adjacent phenyl rings. In [Pd(2)2][BF4]2·2, ligands and
[Pd(2)2]2+ cations are interleaved to form stacks (Fig. 4(a)) with the
pyridine ring containing atom N1 in [Pd(2)2]2+ is p-stacked over
˚
the bpy unit of the free ligand at a distance of 3.33 A. The stacks
Fig. 3 Molecular structure of the free ligand 2 in [Pd(2)2][BF4]2·2 with
ellipsoids plotted at 50% probability level. Symmetry code a = -x, -y, -z.
Selected bond parameters: C41–C41a = 1.478(3), C36–C38 = 1.482(2),
are connected by non-classical hydrogen bonds between atom O3
of a free ligand and C24H241 of a methyl group of a [Pd(2)2]2+
cation (C24H241 ◊ ◊ ◊ O3 = 2.50 A, C24 ◊ ◊ ◊ O3 = 3.258(2) A,
C24H241 ◊ ◊ ◊ O3i = 135◦, symmetry code i = -1 + x, 1 + y, -1 + z)
(Fig. 4(b)).
i
i
˚
˚
◦
˚
C32–O3 = 1.363(2), C31–O3 = 1.427(3) A; C31–O3–C32 = 117.4(2) .
the absence of electronic factors (i.e. crystal field stabilization
energy), the metal ion is typically in a tetrahedral environment.
However, a square planar environment is preferred for a d8 metal
centre such as palladium(II) or platinum(II). In such a bis(bpy)
complex, steric interactions between the H6 protons on adjacent
ligands lead to one of the two types of distortion illustrated in
Scheme 2.15 A search of the Cambridge Structural Database (v.
5.30)16 using Conquest12 revealed 24 structures containing either a
[Pd(bpy)2]2+ or [Pt(bpy)2]2+ motif, including substituted derivatives
and [M(phen)2]2+ (phen = 1,10-phenanthroline).14,17–34 Excluded
from this set are compounds in which adjacent bpy domains are
connected directly35–37 or indirectly38 through the six-positions. Of
the 24 structures, twelve distort at the metal centre (distortion A
in Scheme 2) and twelve undergo ligand distortion (B in Scheme 2,
the so-called ‘bow-incline’ distortion). These distortions have been
discussed in detail by Marzilli et al.,31 but with a sample size of
only six complexes. In [Pd(2)2]2+, H6 ◊ ◊ ◊ H6 repulsions are relieved
by distortion B as shown in Fig. 2(b).
Fig. 4 (a) Stacking of [Pd(2)2]2+ cations and ligands 2 in[Pd(2)2][BF4]2·2.
(b) Hydrogen bonding between free ligands and cations (see text).
Introduction of terminal alkene functionalities
The reaction of [Pd(CH3CN)4][BF4]2 with two equivalents of
either 3 or 4 resulted in the formation of [Pd(3)2][BF4]2 or
[Pd(4)2][BF4]2, respectively, each isolated as a yellow solid. The two
complexes were characterized by NMR spectroscopic and mass
spectrometric methods, and by elemental analyses. A comparison
1
of the H NMR spectrum of acetone-d6 solutions of ligand 3
and of the palladium(II) complex showed that the most significant
changes were in the chemical shifts of the signals (assigned by
2D techniques) arising from protons HA4 (d 9.00 to 9.33 ppm)
and HA6 (d 8.21 to 8.86 ppm), consistent with the formation of
a square planar palladium(II) complex (see earlier discussion).
Scheme 2 Modes of distortion in [Pd(bpy)2]2+, [Pt(bpy)2]2+ and related
cations.
1
In ligand 2 (Fig. 3), the bpy unit is planar, and the phenyl
substituent is twisted 23.44(9)◦ with respect to this plane. This
compares to 32.2(6) and 32.4(6)◦ in the two independent molecules
of 2 in the previously determined structure of the ligand alone.4
In [Pd(2)2][BF4]2·2 the MeO group is oriented on the side opposite
the N atom of the adjacent pyridine ring (Fig. 3), whereas in the
A comparison of the H NMR spectra of 4 and [Pd(4)2][BF4]2
was made using CD3CN–CDCl3 solutions of the compounds,
and the change in the chemical shift of proton HA4 (d 8.03
to 8.46 ppm) was indicative of coordination. Attempts to grow
X-ray quality crystals of [Pd(3)2][BF4]2 and [Pd(4)2][BF4]2 were
unsuccessful. Our interest in these complexes is the reactivity of
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the terminal alkene functionalities. The application of Grubbs’
catalysts to the formation of macrocyclic species have included
the formation of macrocycles, catenanes and knots templated
within a metal coordination sphere.39–48 Molecular modelling†
indicated that in both [Pd(3)2]2+ and [Pd(4)2]2+, the terminal
alkene chains are long enough to permit ring-closing metathesis
with concomitant formation of a palladium(II)-bound macrocyclic
ligand. However, attempts at ring closure were unsuccessful with
both first generation Grubbs’ and Hoveyda–Grubbs’ catalysts
in CH2Cl2 or CH3NO2 at room temperature or reflux, and
peak in the ESI MS of each ligand corresponded to the parent ion.
1
The symmetrical appearance of the H and 13C NMR spectra of
6 was consistent with methylation at both the 6- and 6¢-positions,
and this is confirmed by the disappearance of the signal assigned
to HA6 on going from 2 to 6 (Fig. 5(a) and (b)). Fig. 5(a) and
(b) also illustrate that the introduction of the methyl substituents
causes the signals for the remaining bpy protons and the ortho-
protons of the phenyl substituent (HD2 and HD6) to shift to lower
frequency. This can be rationalized in terms of a change in the
relative orientations of pyridine and aryl rings (see structural
details below) which results in the ring protons lying over the
p-cloud of the adjacent ring. The resonances for the aryl protons
remote from the bpy unit and for the methoxy protons are only
slightly affected by methylation. The 1H NMR spectrum of 5
(Fig. 5(c)) is readily assigned by comparison with those of 2 and
6 (Fig. 5(a),(b)), and the assignments have been confirmed by 2D
techniques.
1
also under microwave heating conditions. In each case, the H
NMR spectrum of the crude mixture indicated no signs of the
formation of a new double bond. The 1H NMR spectrum of the
crude mixture showed the presence of the unreacted palladium(II)
complex. We propose that the problem lies in the lability of
the palladium(II) complexes which release free ligands capable
of poisoning the catalyst. Although ruthenium carbene catalysts
exhibit an exceptional tolerance towards many functional groups,
catalyst inhibition by complex-formation involving the reagents is
known to be problematical.49,50
An obvious way to circumvent the problem of ligand lability is
to use the more inert platinum(II) analogues of the palladium(II)
complexes described above. We began by attempting to prepare
[Pt(2)2][BF4]2 by reaction of K2PtCl4 with ligand 2 in deionized
water, following the procedure reported for the synthesis of
[Pt(bpy)2][BF4]2.51 However, only starting materials were recov-
ered. The reaction was repeated under more rigorous conditions
(microwave reactor, heating the aqueous mixture at 165 ◦C for
1 h) and this led to the formation of a yellow-brown residue that
was completely insoluble in common solvents. Finally, the solvent
◦
was changed to DMF (microwave reactor, 220 C, 1 h) and this
gave rise to a yellow solid, which was partly soluble in DMSO but
otherwise insoluble in common organic solvents. Because of the
difficulties encountered in characterizing this product, we did not
pursue the syntheses of platinum(II) complexes of ligands 3 and 4.
Fig. 5 Room temperature 500 MHz NMR spectra of CDCl3 solutions of
(a) 2, (b) 6, (c) 5 and (d) 7; * = residual CHCl3. Proton labelling is given
in Schemes 1 and 3.
The ferroin–cuproin interconversion
Single crystals of 6 were grown by slow evaporation of a CDCl3
solution of the ligand. The centrosymmetric molecular structure
of 6 is shown in Fig. 6(a). The plane of the aryl substituent deviates
55.16(6)◦ from the plane of the bpy unit, and so, as expected, 6,6¢-
dimethyl substitution results in a significantly greater twist of the
3-anisyl groups than is observed in 2 (Fig. 3). This deviation affects
the way in which the molecules are able to pack. In 2, p-stacking
is important,4 whereas in 6, there is no analogous stacking, and
the molecules pack so that each 6-methyl or 6¢-methyl substituent
points obliquely towards a pyridine ring on an adjacent molecule
(Fig. 6(b)).
In our initial attempts to synthesize the monomethyl derivative
5, one equivalent of MeLi was added to 2 at room temperature.
After quenching the reaction in water, and oxidation of the
intermediate using MnO2, spot thin layer chromatography showed
the presence of two products. These colourless compounds were
separated by column chromatography, and the first fraction was
identified as 5. The highest mass peak in the ESI MS of the second
product, 7, was observed at m/z 763.4 (i.e. approximately twice the
molecular mass of 5). The CDCl3 solution 1H NMR spectrum of
7 showed the presence of two MeO signals (d 3.81 and 3.72 ppm,
relative integrals 1 : 1), both shifted to lower frequency with respect
In order to broaden the scope of our investigation of 4-coordinate
complexes with ligands related to 2, we turned our attention to
the preparation of copper(I) complexes. The crucial factor for
+
the isolation of air-stable complexes containing an {Cu(bpy)2}
core is the presence of substituents in the 6- and 6¢-positions.2 We
describe here the syntheses of ligands 5 and 6, and their reactions
with copper(I).
Ligand 5 was prepared by methylation of 2 using MeLi
adapting the procedure reported for the methylation of 1,10-
phenanthrolines and 2,2¢-bipyridines.52–55 The optimum yield of
5 (82%) was obtained when MeLi (one equivalent) was added at
-78 ◦C, and the reaction then carried out at room temperature
followed by a period of heating. After quenching the reaction
with water, oxidation with MnO2 resulted in the formation of
5. Ligand 6 was subsequently synthesized by methylation of 5.
Attempts to prepare 6 directly by the reaction of 2 with two or
more equivalents of MeLi were unsuccessful. The highest mass
† Spartan ‘04, Wavefunction Inc.; geometry optimization of the palladium
complex used the crystallographically determined structure of [Pd(2)2]2+
as a starting point.
4924 | Dalton Trans., 2009, 4918–4927
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to the number of resonances in 5. A comparison of the 13C and
DEPT NMR spectra revealed the presence of ten quaternary 13
C
nuclei in 7 compared to nine in 5. The NMR and ESI MS data
are consistent with C–C bond formation between two bpy units
of 5 to produce 7. The equivalence of the bpy units deduced
1
from the H and 13C NMR spectra gave two possibilities: the
formation of a tetramethoxyphenyl derivative of 2,2¢:3¢,3¢¢:2¢¢,2¢¢¢-
or 2,2¢:4¢,4¢¢:2¢¢,2¢¢¢-quaterpyridine (Scheme 4). The singlet in the
1H NMR spectrum can be assigned to either HE3 or HE4, and
the appearance in the NOESY spectrum of a cross peak from
this singlet to the signal for HF2 confirms an assignment of HE4
(Fig. 7). Single crystals of 7 were not forthcoming, but Fig. 8
shows an optimized structure† which indicates C1 symmetry, i.e.
ligand 7 is chiral. To date, attempts at metal complexation using 7
have been unsuccessful.
Fig. 6 (a) Molecular structure of 6 with ellipsoids plotted at 50%
probability. Symmetry operator a = 1 - x, 1 - y, 1 - z. Selected bond
parameters: C1–C1a = 1.484(2), C4–C6 = 1.484(2), C5–C12 = 1.496(2),
˚
C10–O1 = 1.367(2), C13–O1 = 1.429(2) A; C13–O1–C10 = 117.6(1),
C1–N1–C5 = 119.22(9)◦. (b) Packing of molecules of 6; symmetry code
3
2
1
2
i = x, - y, + z.
to those in 5 (d 3.88 and 3.84 ppm). A singlet at d 2.62 ppm
(relative integral with respect to each OMe = 1 : 1) replicated that
in 5. Fig. 5(d) shows the aromatic region of the 1H NMR spectrum
of 7 (see Scheme 3 for atom labelling). Crucial observations that
aid the identification of 7 are a similarity between the phenyl
regions of the spectra of 5 and 7, the appearance of a singlet at
d 7.54 ppm, significant changes in the chemical shifts of signals
for the bpy protons, and the loss of one bpy signal with respect
Scheme 4 Structures of two isomers of quaterpyridine.
Fig. 7 Part of the 500 MHz NMR NOESY spectrum of 7 showing the
HE4–HF2 cross peak.
Scheme 3 Compounds 5–7 with ring and atom labelling for NMR
spectroscopic assignments.
Fig. 8 Optimized C1 structure of 7.
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Copper(I) complexes
Conclusions
Treatment of [Cu(NCMe)4][PF6] with either ligands 5 or 6 led
to the formation of red [Cu(5)2][PF6] or [Cu(6)2][PF6], respectively.
The highest mass envelopes in the ESI mass spectra of the products
were assigned to [M - PF6]+ in each case, with isotope distributions
matching those calculated. The diagnostic changes in the 1H NMR
spectrum on going from 5 (in CDCl3) to [Cu(5)2]+ (in CD3CN)
involve the signals for protons HA4 and HC4. Both signals are
shifted to higher frequency (d 8.00 to 8.24 ppm for HA4, and d
7.66 to 7.83 ppm for HC4), while the remaining signals are little
affected. Similarly, on going from 6 to [Cu(6)2]+, the signal assigned
to HC4 is the only resonance to undergo significant perturbation
(d 7.64 to 7.98 ppm). This mirrors the effects described earlier for
coordination of ligands 2 and 3 to palladium(II).
Crystals of [Cu(5)2][PF6]·0.1C2H4Cl2·0.15CH2Cl2 of X-ray qual-
ity were grown by vapour diffusion of Et2O into a solution of
the complex in a mixture of CH2Cl2 and 1,2-C2H4Cl2. Fig. 9
depicts the structure of the [Cu(5)2]+ cation. The structure suffers
from disorders in the cation, anion and solvent molecules. In the
cation, the methyl group of one ligand is disordered over two sites
modelled with 70% (atom C50 in Fig. 9) and 30% occupancies. In
the other ligand, one methoxyphenyl unit (the one containing atom
O11, Fig. 9) is disordered and has been modelled over two sites
with 70–30% occupancies. Despite the problems associated with
the structure, it confirms that the coordination geometry of the
copper(I) centre is distorted tetrahedral (angle between the least
squares planes of the two bpy domains = 70.0(1)◦). In the ligand
containing atoms N1 and N2, the phenyl ring containing atom
C21 is approximately coplanar with the bpy rings (angles between
the least squares planes of the rings = 6.5(2) and 11.9(5)◦), while
the second phenyl ring is twisted through 67.7(2)◦ with respect
to the bpy unit. The coplanar rings are p-stacked with those
of adjacent cations (alternating distances between least squares
We have described the preparation of two ligands, 3 and 4,
which possess bpy domains terminated in alkene functionalities,
and the syntheses and characterization of [Pd(3)2][BF4]2 and
[Pd(4)2][BF4]2. For the related complex [Pd(2)2][BF4]2 in which 2
is 5,5¢-bis(3-methoxyphenyl)-2,2¢-bipyridine, the labile nature of
the ligand leads to co-crystallization with the free ligand to give
[Pd(2)2][BF4]2·2 in the solid state; rather than undergoing distor-
tion in the coordination sphere towards a tetrahedral geometry,
the H6 ◊ ◊ ◊ H6 repulsions between the two bpy domains in [Pd(2)2]2+
are alleviated by a ‘bow-incline’ distortion within each ligand.
Compound 2 has been converted to 5,5¢-bis(3-methoxyphenyl)-
6-methyl-2,2¢-bipyridine (5) and 5,5¢-bis(3-methoxyphenyl)-6,6¢-
dimethyl-2,2¢-bipyridine (6) to produce ligands capable of forming
air-stable copper(I) complexes. We have described the syntheses
of [Cu(5)2][PF6] and [Cu(6)2][PF6], and the single crystal struc-
tures of 6 and [Cu(5)2][PF6]·0.1C2H4Cl2·0.15CH2Cl2. By altering
the conditions under which 2 is methylated, competitive for-
mation of 5,5¢,5¢¢,5¢¢¢-tetrakis(3-methoxyphenyl)-2,2¢:3¢,3¢¢:2¢¢,2¢¢¢-
quaterpyridine occurs.
Acknowledgements
We thank the University of Basel, the Swiss National Science
Foundation, the Swiss Nanoscience Institute and the Stiftung
Stipendien-Fonds des Verbandes der Chemischen Industrie e. V.
for financial support. Kate Harris and Valerie Jullien are thanked
for recording 500 MHz NMR spectra.
Notes and references
1 Molecular catenanes, rotaxanes and knots, ed. J.-P. Sauvage and
C. Dietrich-Buchecker, Wiley, Weinheim, Germany, 1999.
2 W. W. Brandt, F. P. Dwyer and E. D. Gyarfa, Chem. Rev., 1954, 545,
959.
3 A. A. Schilt, Analytical applications of 1,10-phenanthroline and related
compounds, Pergamon, Oxford, UK, 1969.
˚
planes = 3.49 and 3.66 A). Extensive C–Hphenyl ◊ ◊ ◊ O, C–Hmethyl ◊ ◊ ◊ O
and C–Hbpy ◊ ◊ ◊ F hydrogen bonding contribute to the solid state
packing.
4 E. C. Constable, C. E. Housecroft, B. M. Kariuki and C. B. Smith,
Supramol. Chem., 2006, 18, 305.
5 E. C. Constable, C. E. Housecroft, B. M. Kariuki and C. B. Smith,
Aust. J. Chem., 2006, 59, 30.
6 C. B. Smith, E. C. Constable, C. E. Housecroft and B. M. Kariuki,
Chem. Commun., 2002, 2068.
7 Stoe & Cie, IPDS software v 1.26, Stoe & Cie, Darmstadt, Germany,
1996.
8 COLLECT Software, Nonius BV, 1997–2001.
9 Z. Otwinowski and W. Minor, in Methods in Enzymology, ed.
C. W. Carter, Jr. and R. M. Sweet, Academic Press, New York, USA,
1997, vol. 276, p. 307.
10 A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27,
435.
11 P. W. Betteridge, J. R. Carruthers, R. I. Cooper, K. Prout and D. J.
Watkin, J. Appl. Crystallogr., 2003, 36, 1487.
12 I. J. Bruno, J. C. Cole, P. R. Edgington, M. K. Kessler, C. F. Macrae, P.
McCabe, J. Pearson and R. Taylor, Acta Crystallogr., Sect. B: Struct.
Sci., 2002, 58, 389.
Fig.
9
Molecular structure of the [Cu(5)2]+
cation in
[Cu(5)2][PF6]·0.1C2H4Cl2·0.15CH2Cl2 with ellipsoids plotted at 30%
probability; hydrogen atoms are omitted. For disordered sites (see text),
only the major occupancy atoms are shown. Selected bond parameters:
13 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
14 B. Milani, A. Anzilutti, L. Vicentini, A. Sessanta o Santi, E. Zangrando,
S. Geremia and G. Mestroni, Organometallics, 1997, 16, 5064.
15 E. C. Constable, Adv. Inorg. Chem., 1989, 34, 1.
16 F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58, 380.
17 P. C. Chieh, J. Chem. Soc., Dalton Trans., 1972, 1643.
18 A. Hazell, O. Simonsen and O. Wernberg, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1986, 42, 1707.
Cu1–N1
=
2.014(2), Cu1–N2
˚
=
2.088(3), Cu1–N3
=
2.031(3),
Cu1–N4 = 2.069(3) A; N1–Cu1–N2 = 82.1(1), N1–Cu1–N3 = 134.9(1),
N2–Cu1–N3
=
115.0(1), N1–Cu1–N4
=
126.4(1), N2–Cu1–N4
=
121.7(1), N3–Cu1–N4 = 81.5(1)◦.
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19 S. Maeda, Y. Nishida, H. Okawa and S. Kida, Bull. Chem. Soc. Jpn.,
1986, 59, 2013.
20 T. N. Fedotova, L. Kh Minacheva and G. N. Kuznetsova, Zh. Neorg.
Khim., 2003, 48, 417.
36 E. C. Constable, S. M. Elder, M. J. Hannon, A. Martin, P. R. Raithby
and D. A. Tocher, J. Chem. Soc., Dalton Trans., 1996, 2423.
37 C.-W. Chan, C.-M. Che, M.-C. Cheng and Y. Wang, Inorg. Chem., 1992,
31, 4874.
21 B. R. Clare, C. S. McInnes and A. G. Blackmann, Acta Crystallogr.,
Sect. E: Struct. Rep. Online, 2005, 61, m2042.
22 S. Geremia, L. Randaccio, G. Mestroni and B. Milani, J. Chem. Soc.,
Dalton Trans., 1992, 2117.
38 O. Mamula, A. von Zelewsky, T. Bark, H. Sto¨ckli-Evans, A. Neels and
G. Bernardinelli, Chem.–Eur. J., 2000, 6, 3575.
39 A.-C. Laemmel, J.-P. Collin, J.-P. Sauvage, G. Accorsi and N. Armaroli,
Eur. J. Inorg. Chem., 2003, 467.
23 M. Kato, K. Sasano, C. Kosuge, M. Yamazaki, S. Yano and M. Kimura,
Inorg. Chem., 1996, 35, 116.
24 S. Stoccoro, G. Alesso, M. A. Cinellu, G. Minghetti, A. Zucca, A.
Bastero, C. Claver and M. Manassero, J. Organomet. Chem., 2002, 664,
77.
25 J. R. Stork, D. Rios, D. Pham, V. Bicocca, M. M. Olmstead and A. L.
Balch, Inorg. Chem., 2005, 44, 3466.
26 M. Tominaga, T. Kusukawa, S. Sakamoto, K. Yamaguchi and M.
Fujita, Chem. Lett., 2004, 33, 794.
27 H. Endres, H. J. Keller, W. Moroni, D. Nothe and V. Dong, Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1978, 34, 1823.
28 M. B. Hursthouse, M. A. Mazid and R. D. Gillard, Private Communi-
cation to CSD, 2003, (refcode QAYKOR).
29 R. Palmans, D. B. MacQueen, C. G. Pierpont and A. J. Frank, J. Am.
Chem. Soc., 1996, 118, 12647.
30 V. Dong, H. Endres, H. J. Keller, W. Moroni and D. Nothe, Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem., 1977, 33, 2428.
31 V. Maheshwari, M. Carlone, F. R. Fronczek and L. G. Marzilli, Acta
Crystallogr., Sect. B: Struct. Sci., 2007, 63, 603.
32 P. Wehman, G. C. Dol, E. R. Moorman, P. C. J. Kamer, P. W. N. M.
van Leeuwen, J. Fraanje and K. Goubitz, Organometallics, 1994, 13,
4856.
40 C. O. Dietrich-Buchecker, G. Rapenne and J.-P. Sauvage, Chem.
Commun., 1997, 2053.
41 M. Weck, B. Mohr, J.-P. Sauvage and R. H. Grubbs, J. Org. Chem.,
1999, 64, 5463.
42 G. Rapenne, C. O. Dietrich-Buchecker and J.-P. Sauvage, J. Am. Chem.
Soc., 1999, 121, 994.
43 E. B. Bauer, F. Hampel and J. A. Gladysz, Organometallics, 2003, 22,
5567.
44 D. H. Camacho, E. V. Salo, Z. Guan and J. W. Ziller, Organometallics,
2005, 24, 493.
45 K. H. Song, S. O. Kang and J. Ko, Chem.–Eur. J., 2007, 13, 5129.
46 C. Hamann, J.-M. Kern and J.-P. Sauvage, Inorg. Chem., 2003, 42, 1877.
47 L.-E. Perret-Aebi, A. von Zelewsky, C. Dietrich-Buchecker and J.-P.
Sauvage, Angew. Chem., Int. Ed., 2004, 43, 4482.
48 C. Dietrich-Buchecker, G. Rapenne and J.-P. Sauvage, Coord. Chem.
Rev., 1999, 185–186, 167.
49 M. Schuster and S. Blechert, Angew. Chem., Int. Ed. Engl., 1997, 36,
2036.
50 A. Fu¨rstner, Top. Organomet. Chem., 1998, 1, 37.
51 A. R. Brown, Z. J. Guo, F. W. J. Mosselmans, S. Parsons, M. Schro¨der
and L. J. Yellowlees, J. Am. Chem. Soc., 1998, 120, 8805.
52 M. C. Jimenez-Molero, C. Dietrich-Buchecker and J.-P. Sauvage,
Chem.–Eur. J., 2002, 8, 1456.
53 C. Dietrich-Buchecker, M. C. Jimenez and J.-P. Sauvage, Tetrahedron
Lett., 1999, 40, 3395.
54 C. O. Dietrich-Bucheker, P. A. Marnot and J.-P. Sauvage, Tetrahedron
Lett., 1982, 23, 5291.
55 M. Shaul and Y. Cohen, J. Org. Chem., 1999, 64, 9358.
33 J. Durand, E. Zagrando, C. Carfagna and B. Milani, Dalton Trans.,
2008, 2171.
34 C.-Y. Yue, F.-L. Jiang, D.-Q. Yuan, L. Chen, M.-Y. Wu and M.-C.
Hong, Chin. J. Struct. Chem., 2008, 27, 467.
35 E. C. Constable, S. M. Elder, J. Healy, M. D. Ward and D. A. Tocher,
J. Am. Chem. Soc., 1990, 112, 4590.
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