Cu(I) and Pb(II) complexes containing new tris(7-naphthyridyl)methane derivatives: Synthesis, structures, spectroscopy and geometric conversion

Article abstract of DOI:10.1039/c0dt01747g

Two novel facial-capping tris-naphthyridyl compounds, 2-chloro-5-methyl-7- ((2,4-dimethyl-1,8-naphthyridin-7(1H)-ylidene)(2,4-dimethyl-1, 8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L¹) and 2-chloro-7-((2-methyl-1,8-naphthyridin-7(1H)-ylidene)(2-methyl-1, 8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L²), as well as their Cu(I) and Pb(II) complexes, [CuL^a(PPh₃)]BF₄ (1) (PPh₃ = triphenylphosphine, L^a = bis(2,4-dimethyl-1,8- naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methane), [CuL ^b(PPh₃)]BF₄ (2) (L^b = bis(2-methyl-1,8-naphthyridin-7-yl)(2-chloro-1,8-naphthyridin-7-yl)methane), [Pb(OL^a)(NO₃)₂] (3) (OL^a = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl) methanol) and [Pb(L^b)₂][Pb(CH₃OH)(NO ₃)₄] (4), have been synthesized and characterized by X-ray diffraction analysis, MS, NMR and elemental analysis. The structural investigations revealed that the transfer of the H-atom at the central carbon to an adjacent naphthyridine-N atom affords L¹ and L² possessing large conjugated architectures, and the central carbon atoms adopt the sp² hybridized bonding mode. The reversible hydrogen transfer and a geometric configuration conversion from sp² to sp³ of the central carbon atom were observed when Pb(II) and Cu(I) were coordinated to L¹ or L². The molecular energy changes accompanying the hydrogen migration and titration of H⁺ to different receptor-N at L¹ were calculated by density functional theory (DFT) at the SCRF-B3LYP/6-311++G(d,p) level in a CH₂Cl₂ solution, and the observed lowest-energy absorption and emission for L¹ and L ² can be tentatively assigned to an intramolecular charge transfer (ICT) transition in nature.

Full text of DOI:10.1039/c0dt01747g

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 7365
www.rsc.org/dalton
PAPER
Cu(I) and Pb(II) complexes containing new tris(7-naphthyridyl)methane
derivatives: Synthesis, structures, spectroscopy and geometric conversion†
Xin Gan,a Shao-Ming Chi,a Wei-Hua Mu,a Jia-Can Yao,a Li Quan,b Cong Li,a Zhao-Yong Bian,b Yong Chenb
and Wen-Fu Fu*a,b
Received 12th December 2010, Accepted 27th April 2011
DOI: 10.1039/c0dt01747g
Two novel facial-capping tris-naphthyridyl compounds, 2-chloro-5-methyl-7-((2,4-dimethyl-1,8-
naphthyridin-7(1H)-ylidene)(2,4-dimethyl-1,8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L1) and
2-chloro-7-((2-methyl-1,8-naphthyridin-7(1H)-ylidene)(2-methyl-1,8-naphthyridin-7-yl))methyl-1,8-
naphthyridine (L2), as well as their Cu(I) and Pb(II) complexes, [CuLa(PPh3)]BF4 (1) (PPh3 =
triphenylphosphine, La = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-
7-yl)methane), [CuLb(PPh3)]BF4 (2) (Lb = bis(2-methyl-1,8-naphthyridin-7-yl)(2-chloro-1,8-naphthy-
ridin-7-yl)methane), [Pb(OLa)(NO3)2] (3) (OLa = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-
methyl-1,8-naphthyridin-7-yl)methanol) and [Pb(Lb)2][Pb(CH3OH)(NO3)4] (4), have been synthesized
and characterized by X-ray diffraction analysis, MS, NMR and elemental analysis. The structural
investigations revealed that the transfer of the H-atom at the central carbon to an adjacent
naphthyridine-N atom affords L1 and L2 possessing large conjugated architectures, and the central
carbon atoms adopt the sp2 hybridized bonding mode. The reversible hydrogen transfer and a
geometric configuration conversion from sp2 to sp3 of the central carbon atom were observed when
Pb(II) and Cu(I) were coordinated to L1 or L2. The molecular energy changes accompanying the
hydrogen migration and titration of H+ to different receptor-N at L1 were calculated by density
functional theory (DFT) at the SCRF-B3LYP/6-311++G(d,p) level in a CH2Cl2 solution, and the
observed lowest-energy absorption and emission for L1 and L2 can be tentatively assigned to an
intramolecular charge transfer (ICT) transition in nature.
1,8-Naphthyridine and its derivatives have been applied in the
Introduction
pharmaceutical,11 molecular recognition12 and fluorescence sensor
Facial-capping tripodal ligands, such as tris(pyridyl)methane,1
tris(pyridyl)amine,2 tris(pyrazolyl)hydroborate3 and tris(pyrid-
yl)phosphine4 derivatives, have been widely used in coordination
and organometallic chemistry.5–8 Furthermore, the tetrapyridyl-
methane ligand and its silver(I) complex with a diamondoid net-
work structure have also been reported by Oda and co-workers.9,10
fields.13 In particular, oligo(naphthyridines) are of significant inter-
est because of their larger number of chelating sites14–16 and higher
complexity, which give rise to interesting applications as functional
materials,17 however, the synthesis of tris-naphthyridyl compounds
has received little attention. Lippard and co-workers synthesized
and reported several multidentate dinucleating ligands containing
the 1,8-naphthyridine moiety as the bridging unit,18 which can link
two metal ions in a similar manner to the syn, syn coordination
mode of bridging carboxylate groups found in nature.19 Cuccia
et al. reported a one-step synthesis of naphthyridine derivatives
containing a macrocycle by the reaction of naphthyridine with urea
or formamindine.20 1,3,5-Tris(1,8-naphthyridine-2-yl)benzene and
its Ru(II) cluster were prepared by Aguirre et al., however,
poor solubility in most solvents limited their application.21 In
contrast, a Ru(II) complex bearing the 2-phenyl-1,8-naphthyridine
aCollege of Chemistry and Chemical Engineering, Yunnan Normal Univer-
sity, Kunming, 650092, P.R. China. E-mail: wf_fu@yahoo.com.cn; Fax: +86
871 5516061; Tel: +86 871 5516063
bKey Laboratory of Photochemical Conversion and Optoelectronic Materi-
als, HKU-CAS Joint Laboratory on New Materials, Technical Institute of
Physics and Chemistry, Chinese Academy of Sciences, Peking, 100190, P.R.
China. E-mail: fuwf@mail.ipc,ac.cn; Fax: +86 10 62554670; Tel: +86 10
82543519
† Electronic supplementary information (ESI) available: X-ray crystallo-
graphic files in CIF format for L1, L2 and complexes 1–4; 1H-NMR of
L1 and L2 as well as complexes 1 and 3; and theoretical computational
details; The absorption spectral changes of titrating [Cu(CH3CN)4]BF4 to
L1 and solid-state emission spectra of L2 are provided. CCDC reference
numbers 804348–804353. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01747g
derivative ligand showed potential as
catalyst.22
a
homogeneous
In the course of syntheses of vinyl-1,8-naphthyridine derivatives
in acetic anhydride the products of substituted hydrogen atoms of
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7365–7374 | 7365
©

View Article Online
both amino and methyl groups located on adjacent naphthyridine-
N by acetyl groups were obtained.23 The underlying approach
presented herein was to develop a type of substitute reaction for
the preparation of a series of new 1,8-naphthyridine derivatives.
In this content, we first report on the synthesis and molecular
structures of novel tripodal ligands with three naphthyridine units.
The ligands exhibit geometric configuration conversions from sp2
to sp3, which was accompanied by a change in color when the
compounds coordinated to Cu(I) or Pb(II) (Scheme 1). In addition,
spectral changes of L1 and L2 with changing pH values and due
to changes in the concentration of Cu+ or Pb2+ were observed.
The effects of different binding positions of H+ as well as H-
transfer at the central carbon of L1 to naphthyridine-N atoms on
the molecular energy changes were explored by DFT calculations.
The intramolecular hydrogen transfer in the presence of a metal
cation provided a variety of intriguing compound structures and
interesting spectroscopic properties.
2-Methyl-7-amino-1,8-naphthyridine and 2,4-dimethyl-7-amino-1,
8-naphthyridine
The 2-methyl-7-amino-1,8-naphthyridine and 2,4-dimethyl-7-
amino-1,8-naphthyridine were synthesized according to reported
procedures.27
2,4-Dimethyl-7-hydroxyl-1,8-naphthyridine and 2-methyl-7-
hydroxyl-1,8-naphthyridine27
1.5 g NaNO2 was added slowly to 2,4-dimethyl-7-amino-1,8-
naphthyridine (5.196 g, 30.0 mmol) in 50 mL of 40% H2SO4 with
vigorous stirring at 258 K. The solution was gradually warmed to
80 ◦C and held at this temperature for 10 min, then cooled to room
temperature. Concentrated NH4OH was then used to adjust the
pH to 7–8. The resulting solution was then extracted five times with
chloroform (5 ¥ 50 mL), the organic fractions were combined and
dried over Na2SO4, and the solvent was evaporated to give 2,4-
dimethyl-7-hydroxyl-1,8-naphthyridine as a yellow solid. Yield:
2.091 g (40%); IR (KBr, nmax/cm-1): 3126br, 2977, 2977w, 2934w,
2855w, 1643vs, 1596 s, 1538 m, 1503 m, 1400vs, 1311 m, 1241w,
1
1196 m, 857 m, 732 m and 485s; MS (EI): m/z: 174 [M]+; H
NMR (400 MHz, CDCl3): d = 2.51 (s, 3H, methyl), 2.59 (s, 3H,
methyl), 6.63 (d, 1H), 6.91 (s, 1H), 7.90 (d, 1H) and 10.03 (s,
1H, OH); elemental analysis calcd (%) for C10H10N2O (174.2):
C 68.95, H 5.79, N 16.08; found: C 68.87, H 5.70, N 16.21.
2-Methyl-7-hydroxyl-1,8-naphthyridine was obtained following
the same procedure as 2,4-dimethyl-7-hydroxyl-1,8-naphthyridine
except that 2-methyl-7-amino-1,8-naphthyridine was used. Yield:
(62%); m.p.: 176–178 ◦C.
2,4-Dimethyl-7-chloro-1,8-naphthyridine and 2-methyl-7-chloro-
1,8-naphthyridine24,25
A mixture of 2,4-dimethyl-7-hydroxyl-1,8-naphthyridine (1.742 g,
10.0 mmol) and 15 mL of POCl3 was refluxed with stirring for
2 h under nitrogen. The resulting solution was cooled to room
temperature, and then added to ice water, neutralized with NH4OH
and extracted into chloroform. The organic phase was dried
over Na2SO4 and evaporated to give a white solid. The crude
product was purified by column chromatography over a silica gel
column using dichloromethane–ethyl acetate (3 : 1, v/v) as the
eluent. Recrystallization of the product from a dichloromethane–
diethyl ether solution afforded a white needle crystal. Yield: 1.445 g
(75%). IR (KBr, nmax/cm-1): 3092 m, 3029w, 2969w, 2925w, 1610vs,
1588vs, 1550 s, 1492 s, 1399vs, 1287 s, 1186 s, 1159 m, 1136vs, 997
s, 903 s, 862 s, 794vs, 601 m and 454m; MS (EI): m/z: 195 [M + 3]+,
194 [M + 2]+, 193 [M]+; elemental analysis calcd (%) for C10H9N2Cl
(192.6): C 62.35, H 4.71, N 14.54; found: C 62.47, H 4.69, N 14.70.
2-Methyl-7-chloro-1,8-naphthyridine was obtained following the
same method as 2,4-dimethyl-7-chloro-1,8-naphthyridine using 2-
methyl-7-hydroxyl-1,8-naphthyridine in place of 2,4-dimethyl-7-
hydroxyl-1,8-naphthyridine. Yield: (67%); m.p.: 215–217 ◦C.
Scheme 1 The chemical structures of ligand L1–2 and complexes 1–4.
Experimental
General methods
Reagents were obtained commercially and used as received with-
out further purification, unless otherwise stated. 2,4-Dimethyl-
7-chloro-1,8-naphthyridine, 2-methyl-7-chloro-1,8-naphthyridine
and [Cu(CH3CN)4]BF4 were synthesized according to literature
methods.24–26 Solvents were dried by the standard procedures and
freshly distilled prior to use. All reactions were performed under
nitrogen. 1H NMR spectra were measured on a Bruker instrument
1
operating at a H frequency of 400 MHz and 298 K. Chemical
shifts (d, ppm) were referenced to tetramethylsilane (Me4Si) for
1H. ESI–MS data were obtained with an APEX II Model FT–
ICR mass spectrograph. MALDI–TOF MS data were obtained
on a Bruker Biflex III Model MALDI–TOF mass spectrometer.
Elemental analyses were performed with an Elementar Vario
EL (Germany) analysis instrument. Absorption spectra were
recorded using a HITACHI U-3010 scanning spectrophotome-
ter, and the corrected emission spectra of solution and solid
materials were obtained on a HITACHI F-4500 fluorescence
spectrophotometer adapted to a right-angle configuration at room
temperature.
2-Chloro-5-methyl-7-((2,4-dimethyl-1,8-naphthyridin-7(1H)-
ylidene)(2,4-dimethyl-1,8-naphthyri din-7-yl))methyl-1,8-
naphthyridine (L1)
A mixture of 2,4-dimethyl-7-chloro-1,8-naphthyridine (1.926 g,
10.0 mmol) and powdered NaH (0.360 g, 15.0 mmol) in 150 mL
7366 | Dalton Trans., 2011, 40, 7365–7374
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
of toluene was refluxed with stirring for 4 h under nitrogen. After
cooling to room temperature, all solvents were removed in vacuum
leaving a red solid. 100 mL water was added and the resulting
solution was extracted with CHCl3 (5 ¥ 50 mL). The organic
fraction was dried over Na2SO4 and the solvent was evaporated
to give the crude product. The red product was purified by
column chromatography over a neutral aluminum oxide column
CDCl3): d = 1.56 (s, 6H, methyl), 7.10 (d, J = 8.0 Hz, 2H), 7.20
(t, J = 6.0 Hz, 6H, phenyl), 7.30 (t, J = 6.0 Hz, 3H, phenyl), 7.52
(s, 1H, methine), 7.98 (d, J = 8.0 Hz, 2H), 8.03 (d, J = 8.0 Hz,
1H), 8.07 (m, 6H, phenyl), 8.30 (d, J = 8.0 Hz, 2H), 8.35 (d, J =
8.0 Hz, 1H), 8.40 (d, J = 8.0 Hz, 1H), 8.57 (d, J = 8.0 Hz, 2H)
and 8.71 (d, J = 8.0 Hz, 1H); MS (MALDI-TOF): m/z 463.7
[M-Cu-PPh3-BF4+H]+, 525.8 [M-PPh3-BF4]+; 788.6 [M-BF4]+;
elemental analysis calcd (%) for C45H34BClCuF4N6P (875.6): C
61.73, H 3.91, N 9.60; found: C 61.54, H 3.79, N 9.71.
◦
using petroleum ether (boiling range 60–90 C) and chloroform
(2 : 1, v/v) as the eluent. Recrystallization of the product from a
dichloromethane–diethyl ether solution ◦afforded a red prismatic
crystal. Yield: 0.875 g (52%); m.p.: >320 C; 1H NMR (400 MHz,
CDCl3): d = 2.41–2.77 (m, 15H, methyl), 6.52–6.62 (m, 1H), 6.76–
6.87 (m, 2H), 7.12–7.18 (m, 1H), 7.39–7.61 (m, 3H), 7.83–7.88 (m,
1H), 8.15–8.45 (m, 1H) and 16.17 (d, 1H, NH); MS (EI): m/z 506
[M+H]+; elemental analysis calcd (%) for C30H25ClN6 (505.0): C
71.35, H 4.99, N 16.64; found: C 71.31, H 5.02, N 16.80.
[PbOLa(NO3)2] (3) (OLa = bis(2,4-dimethyl-1,8-naphthyridin-7-
yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methanol)
A solution(20 mL) of L1 (0.101 g, 0.20 mmol) in 20 mL of
dichloromethane was added dropwise to the solution of Pb(NO3)2
(0.066 g, 0.20 mmol) in 35 mL of methanol, the mixture was stirred
for 48 h at room temperature. The resulting mixture was filtered,
and the filtrate was concentrated down to 10 mL in vacuum.
Addition of diethyl ether gave the complex 3 (0.082 g, 48%) as
2-Chloro-7-((2-methyl-1,8-naphthyridin-7(1H)-ylidene)(2-methyl-
1,8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L2)
1
yellow colored sheet crystals. H NMR (400 MHz, MeOD) d =
The red compound was prepared following the same proce-
dure as L1 except that 2-methyl-7-chporo-1,8-naphthyridine was
used instead of 2,4-dimethyl-7-chloro-1,8-naphthyridine. The red
product was purified by column chromatography over a neutral
aluminum oxide column using chloroform and methanol (100 : 0.8,
v/v) as the eluent. Recrystallization of the product from a
dichloromethane–diethyl ether s◦olution afforded a red prismatic
crystal. Yield: (55%); m.p.: >350 C; 1H NMR (400 MHz, CDCl3):
d = 2.76 (s, 3H, methyl), 2.82 (s, 3H, methyl), 6.80 (dd, J = 8.0 Hz,
2H), 7.07 (d, J = 8.0 Hz, 1H), 7.16 (d, J = 8.0 Hz, 1H), 7.42 (dd,
J = 8.0 Hz, 2H), 7.53 (d, J = 8.0 Hz, 1H), 7.64 (d, J = 8.0 Hz,
1H), 7.75 (dd, J = 8.0 Hz, 2H), 8.02–8.31 (m, 2H) and 16.30 (m,
1H, NH); MS (MALDI–TOF): m/z 463.9 [M + H]+, 485.9 [M +
23]+, 501.9 [M+39]+; elemental analysis calcd (%) for C27H19ClN6
(462.9): C 70.05, H 4.14, N 18.15; found: C 70.26, H 4.06, N 18.33.
0.37 (s, 3H, methyl), 0.51 (s, 3H, methyl), 2.54 (s, 3H, CH3), 2.59
(s, 3H, methyl), 2.82 (s, 3H, methyl), 6.70–6.86 (m, 3H), 8.34 (d,
1H) and 8.64–9.14 (m, 5H); MS (ESI): m/z 521.3 [M - 2NO3 -
Pb + H]+, 727.3 [M - 2NO3 - 1]+; elemental analysis calcd (%)
for C30H25ClN8O7Pb (852.2): C 42.28, H 2.96, N 13.15; found: C
42.11, H 2.85, N 13.39.
[Pb(Lb)2][Pb(CH3OH)(NO3)4] (4)
A solution of Pb(NO3)2 (0.099 g, 0.30 mmol) in 50 mL of methanol
was added to a solution of L2 (0.139 g, 0.30 mmol) in 30 mL of
dichloromethane with stirring for 48 h at room temperature. The
reaction mixture was filtered and the solvent was evaporated in
vacuum. The residue was recrystallized from a dichloromethane–
diethyl ether solution to give colorless crystals suitable for
X-ray structure analysis. Yield: (0.967 g, 39%).1H NMR (400
MHz, MeOD): d = 0.43–0.48 (m, 6H, methyl), 0.52–0.65 (m, 6H,
methyl), 6.87–6.90 (m, 4H), 6.98 (m, 2H), 7.43 (s, 1H, methine),
7.44 (s, 1H, methine), 8.15 (m, 2H), 8.17–8.25 (m, 2H), 8.40 (m,
2H), 8.49 (m, 2H) and 8.59–8.72 (m, 10H); MS (MALDI–TOF):
m/z 1134.4 [M - Pb(NO3)4(CH3OH)2) + H]+; elemental analysis
calcd (%) for C55H42Cl2N16O13Pb2·CH3OH (1652.4): C 40.71, H
2.81, N 13.56; found: C 40.57, H 2.63, N 13.75.
[CuLa(PPh3)]BF4 (1) (La = bis(2,4-dimethyl-1,8-naphthyridin-7-
yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methane)
A mixture of L1 (0.126 g, 0.25 mmol) and [Cu(CH3CN)4]BF4
(78.6 mg, 0.25 mmol) in 40 mL of dichloromethane was stirred
for 4 h under nitrogen at room temperature, then PPh3 (0.066 g,
0.25 mmol) was added slowly and this was followed by further
stirring for 12 h. The resulting solution was filtered and the filtrate
was evaporated to dryness in vacuum affording a pale yellow solid.
Recrystallization of the crude product from a dichloromethane–
diethyl ether solution gave complex 1 as pale yellow prismatic
crystals with a yield of 38% (0.087 g). 1H NMR (400 MHz, CDCl3):
d = 1.49 (s, 6H, methyl), 2.56 (s, 6H, methyl), 2.74 (s, 3H, CH3),
6.91 (s, 2H, naph-6), 7.16 (m, 9H), 7.28–7.30 (m, 2H), 7.35 (s,
1H, Cl-naph-6), 8.07 (s, 6H), 8.17 (d, 1H) and 8.51–8.53 (m, 4H);
MS (ESI): m/z 567.3 [M–PPh3 - BF4 - 1]+, 829.4 (M–BF4 - 1)+;
elemental analysis calcd (%) for C48H40BClCuF4N6P (917.6): C
62.83, H 4.39, N 9.16; found: C 62.95, H 4.25, N 9.40.
X-Ray crystallography
The X-ray diffraction measurements for compounds were carried
out on a Bruker SMART, Bruker XSCANS or Rigaku STATURN
diffractometer using a graphite monochromator with Mo-Ka
radiation (l = 0.071073 nm) at room temperature or 113 K.
A summary of the crystallographic parameters and important
data are given in Table 1. Empirical absorption corrections based
on equivalent reflections were applied. The structures of the
compounds were solved by direct methods using SHELXL-97. All
nonhydrogen atoms were refined anisotropically by the full-matrix
least-squares method on F2 data.28,29 Metal atoms in each complex
were located from the E-maps and other non-hydrogen atoms were
located in successive difference Fourier syntheses. The hydrogen
atoms of the ligands were generated theoretically onto the specific
atoms and refined isotropically with fixed thermal factors.
[CuLb(PPh3)]BF4 (2) (Lb = bis(2-methyl-1,8-naphthyridin-7-yl)(2-
chloro-1,8-naphthyridin-7-yl)methane)
The preparation of complex 2 is similar to that of 1 except that
the ligand L1 is replaced by L2. Yield: (32%). 1H NMR (400 MHz,
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7365–7374 | 7367
©

View Article Online
Table 1 Selected crystallographic and data collection parameters for L1–2 and 1–4
Compound
Formula
L1·CH2Cl2·H2O L2·CH2Cl2
1·CH2Cl2
2·1.25CH2Cl2
3·CH2Cl2·0.5H2O 4·CH3OH
C31H28Cl3N8O7.5Pb C52H34Cl2N16O14Pb2
C31H29Cl3N6O
C28H21Cl3N6
C49H42BCl3-
CuF4N6P
1002.56
C46.23H36.43BCl3.52-
CuF4N6O0.33
987.45
P
Formula weight
T/K
607.95
113(2)
547.86
298(2)
946.15
298(2)
1592.23
293(2)
298(2)
93(2)
Cryst size/mm
Crystal system
Space group
0.32 ¥ 0.28 ¥ 0.22 0.48 ¥ 0.45 ¥ 0.20 0.48 ¥ 0.45 ¥ 0.22
0.30 ¥ 0.30 ¥ 0.17 0.23 ¥ 0.20 ¥ 0.15 0.06 ¥ 0.06 ¥ 0.04
Monoclinic
P21/n
14.956(15)
19.102(19)
16.461(17)
90.00
100.210(17)
90.00
4628(8)
4
1.417
55.04
Monoclinic
P21/c
14.215(4)
11.089(3)
18.409(5)
90.00
Monoclinic
C2/c
31.115(3)
11.6709(15)
16.466(2)
90.00
Monoclinic
C2/c
17.4863(17)
17.5038(18)
31.150(3)
90.00
99.520(2)
90.00
9403.1(15)
8
1.416
45.03
0.727
23875/8198
647
Monoclinic
P21/n
9.8676(10)
19.013(2)
19.500(2)
90.00
Monoclinic
P21/c
12.842(3)
15.845(3)
15.529(3)
90.00
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
101.018(4)
90.00
2848.2(13)
4
119.257(2)
90.00
5216.8(10)
8
93.953(2)
90.00
3649.8(7)
4
90.22(3)
90.00
3159.8(11)
2
3
˚
V/A
Z
rc/g cm-3
1.418
44.45
1.395
54.40
1.722
50.10
1.673
54.13
2qmax (◦)
m/mm-1
0.359
30705/5613
386
0.381
12833/4593
334
0.767
28217/8076
660
4.900
17667/6423
480
5.478
21230/5575
469
Reflections colected/unique
Parameters
Rint
0.0432
1.162
0.0654, 0.1478
0.0622, 0.1455
0.0460
1.011
0.1466, 0.2132
0.0694, 0.1541
-0.463/0.474
0.0751
1.094
0.1415, 0.2476
0.0943, 0.2175
-0.527/0.948
0.0607
1.127
0.0965, 0.2331
0.0789, 0.2138
-0.615/0.823
0.0700
1.076
0.1015, 0.1558
0.0640, 0.1387
-1.908/2.531
0.0570
1.089
0.1018, 0.2405
0.0727, 0.2193
-0.581/1.704
Goodness of fit
R1, wR2[all data]
R1, wR2[I > 2s(I)]
-3
˚
Residual electron density/e A -0.476/0.583
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
R1 = ꢀFo| - |Fcꢀ |Fo|. wR2 = { [w(Fo - Fc2)2]/ [w(Fo2)2]}
Theoretical calculations
All optimizations were carried out in a CH2Cl2 solution with
the Gaussian 03 program package30 at the SCRF-B3LYP/6-
311++G(d,p)31–33 level employing the PCM/Bader model.34 Time-
dependent density functional theory (TD–DFT) at the SCRF-
TD–DFT(B3LYP/6-311++G(d,p) level was also carried out in a
CH2Cl2 solution to predict and verify the absorption spectra of
various species.
Scheme 2 Synthetic route of L1 and L2.
Results and discussion
The central carbon atom appears to adopt sp2 hybridized bonding
character and ex◦ hibits trigonal planar geometry with bond angles
of 117.5–124.9 . Two naphthyridine moieties of L1 formed a
large conjugated plane (dihedral angle of 2.53◦) in which a six-
membered ring is generated by the interaction of N2 and H5 atoms
Preparation and crystal structures of ligands L1 and L2
Our previous report showed that the methyl hydrogen atoms at
the 2-position on the 1,8-naphthyridine moiety are highly reactive
and can be substituted by acetyl groups to form a b-diketone
group, which is accompanied by a 1,3-hydrogen transfer from
the –CH– group to a naphthyridine-N atom.23 In this study, an
intermolecular substitution reaction of 2,4-dimethyl-7-chloro-1,8-
naphthyridine or 2-methyl-7-chloro-1,8-naphthyridine in toluene
under reflux gave the red compounds, L1 or L2, in the presence
of NaH that was used to remove the hydrogen halide by-product.
(Scheme 2).
X-Ray structure analysis and 1H NMR data of the two obtained
compounds, L1 and L2, revealed that they have similar structures
except that L1 has a methyl group at the 4-position on the
naphthyridine ring vs. a hydrogen atom at this position in L2.
Their perspective drawings are depicted in Fig. 1 and selected
bond lengths and angles are presented in Table 2. The transfer of
the H-atom at the central carbon to an adjacent naphthyridine-N
atom generates L1 and L2 possessing large conjugated structures.
˚
with a short distance of 1.973 A, whereas the third naphthyridine
ring in the molecule is nearly perpendicular to the plane with a
dihedral angle of 87.26◦. The carbon double bond distance of
1
˚
1.396 A between C10 and C21 in L is slightly shorter than that
observed in L2, in which there is indicative partial delocalization
of the electron density among C8, C25 and C16 with C8–C25
˚
and C25–C16 bond lengths of 1.413 and 1.416 A, respectively.
1
˚
In comparison with L , a shorter interaction distance of 1.931 A
for N3 and H1 atoms was found in L2 between two coplanar
naphthyridine rings (dihedral angle of 2.41◦), whereas a third
naphthyridine ring was not vertical to their plane and a dihedral
angle of 69.22◦ was observed. In crystalline L2, 1D polymeric
chains involving C3–H3 ◊ ◊ ◊ N6 and C4–H4 ◊ ◊ ◊ N5 H-bonds are
connected through C19–H19 ◊ ◊ ◊ Cl(2) H-bonds to form a 2D
layered architecture (bottom of Fig. 1).
7368 | Dalton Trans., 2011, 40, 7365–7374
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
1–2
˚
Table 2 Selected bond lengths (A) and bond angles (deg) for ligands L and complexes 1–4
L1
C6–C10
1.427(4)
1.369(3)
124.9(2)
176.0(2)
C10–C11
N3–C11
C21–C10–C11
C6–C10–C11–C12
1.504(3)
1.322(3)
117.5(2)
91.6(3)
C10–C21
N3–C6
C6–C10–C11
C21–C10–C11–C12
1.396(4)
1.354(3)
117.6(2)
86.4(3)
N5–C21
C21–C10–C6
C7–C6–C10–C21
L2
C8–C25
N1–C8
C8–C25–C16
C7–C8–C25–C16
1
Cu1–N1
Cu1–P1
1.413(6)
1.354(5)
124.2(4)
175.5(4)
C24–C25
N3–C16
C8–C25–C24
C23–C24–C25–C16
1.499(6)
1.360(5)
117.6(4)
110.4(5)
C16–C25
N5–C24
C16–C25–C24
C23–C24–C25–C8
1.416(6)
1.312(5)
118.0(4)
65.4(6)
2.121(5)
2.200(2)
1.54(1)
112.7(6)
88.7(2)
Cu1–N3
C1–C9
C1–H1
C21–C1–C11
N5–Cu1–N3
2.142(6)
1.50(1)
0.9800
110.4(6)
87.0(2)
Cu1–N5
C1–C11
C2–C1–C11
C2–C1–H1
N1–Cu1–N3
2.106(6)
1.55(1)
110.1(6)
107.8
C1–C21
C2–C1–C21
N5–Cu1–N1
N3–Cu1–P1
2
C1–C2
C1–H1
Cu1–N5
C2–C1–C20
N1–Cu1–N3
N1–Cu1–P1
3
O1–C1
C1–C21
N5–C21
Pb1–N4
Pb1–O2
Pb(1)–O(6)
C11–C1–C2
4
C8–C10
N2–C8
87.4(2)
126.8(2)
1.49(2)
1.000
2.126(4)
107.9(11)
88.52(17)
126.79(12)
C1–C11
Cu1–N1
Cu1–P1
C11–C1–C20
N1–Cu1–N5
1.52(2)
C1–C20
Cu1–N3
C2–C1–C11
C2–C1–H1
N3–Cu1–N5
1.632(12)
2.094(4)
116.7(13)
108.9
2.083(4)
2.191(2)
105.1(11)
88.76(16)
86.30(16)
1.43(2)
1.54(2)
1.33(1)
2.88(1)
2.627(9)
2.963(9)
108.9(9)
C1–C2
N1–C2
Pb1–N1
Pb1–N5
Pb1–O3
O1–C1–C2
C11–C1–C21
1.56(2)
1.32(1)
2.851(9)
2.578(8)
2.69(1)
110.0(9)
110.5(9)
C1–C11
N3–C11
Pb1–N3
Pb1–N6
Pb1–O5
C21–C1–C2
1.53(2)
1.33(1)
2.611(9)
2.81(1)
2.923(8)
111.1(9)
1.514(17)
1.349(14)
2.688(9)
108.9(9)
64.8(3)
C10–C11
N3–C11
Pb1–N3
C8–C10–C20#1
N2#1–Pb1–N3
N5#1–Pb1–N3
1.538(17)
1.344(13)
2.704(9)
111.0(10)
115.2(3)
64.6(3)
C10–C20#1
N5–C20
Pb1–N5
C11–C10–C20#1
N2–Pb1–N5
1.538(15)
1.292(14)
2.706(9)
110.3(9)
115.8(3)
Pb1–N2
C8–C10–C11
N2–Pb1–N3
N3–Pb1–N5
115.4(3)
Symmetry code: #1 -x, -y + 1, -z
Spectral characterization
of the H+ concentration on geometric conversion at the central
carbon atom for both compounds did not occur even though
a large excess of HBF4 was employed. However, the lowest-
energy absorptions of both compounds were red-shifted from
540 nm to 565 nm upon the addition of HBF4 to a solution
of L1 or L2 in methanol (Fig. 2). In addition, the multi-
binding sites of protons, related to the spectral changes, were
examined by theoretical calculations carried out at the SCRF-
B3LYP/6-311++G(d,p) level in a CH2Cl2 solution. The calculated
molecular total energies and relative energies of the proton
associated with N(1–4) and N6 of L1 appear in the Supporting
Information† and Fig. 4, respectively.33 The calculated molecular
total energies were -1947.874666, -1947.877734, -1947.886562,
-1947.883769 and -1947.875389 a.u., respectively, which indicates
that the first site to be bound is the N3 atom of ligand L1. The
spectral changes measured as a function of proton concentration
showed the protonated nitrogen atom on the naphthyridine
ring will be benefit to decrease in the ICT transition energy,
thereby extending the lowest-energy absorption to a longer
wavelength region. Comparison of the theoretical energy gaps
of DEHOMO–LUMO, before and after L1 is protonated, with the
experimental results fully supports this conclusion (Supporting
Information†).
The UV-Vis absorption spectra of L1 and L2 were similar,
with the lowest-energy absorptions at 545 nm in CH2Cl2 and
large extinction coefficients (104 mol-1 dm3 cm-1), and a slight
blue shift was observed with increasing solvent polarity (Fig.
2 and Supporting Information†). A TD–DFT calculation for
L1 showed that its highest occupied molecular orbital (HOMO)
and lowest unoccupied molecular orbital (LUMO) are mainly
localized on the naphthyridine-receptor of the H-transfer and
naphthyridine moiety with the chlorine group, respectively (Sup-
porting Information†). Thus, the lowest-energy absorption bands
observed ranged from 530–545 nm for L1 and L2 in the organic
solvents CH2Cl2, CH3CN and CH3OH were assigned to an ICT
transition. L1 and L2 displayed intense red solid-state emissions
with lmax values of 670 and 663 nm at room temperature
upon excitation at 500 nm, respectively (Fig. 3 and Supporting
Information†). As shown in Fig. 3, both compounds exhibited a
blue shift with lower-energy solution emissions ranging from 580
to 595 nm relative to the emissions in the solid state.
Detailed spectral studies and geometric configuration conver-
sions of L1 and L2 were undertaken at various pH values in a
methanol solution. The results demonstrated that the influence
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7365–7374 | 7369
©

View Article Online
Fig. 3 Room-temperature solid-state emission spectrum (solid line) and
solution emission spectra in CH2Cl2 (dashed dot line), CH3CN (dashed
dot dot line) and CH3OH (dot line) of L1 with excitation at 500 nm.
molecular energy changes of the 1,3-hydrogen transfer for L1,
L1
generated by the 1,5-hydrogen transfer acquired a higher
N(6)
energy of 15.9 kcal mol-1. To realize a opposite change of the
compound geometries at the central carbon atom from the trigonal
plane (L1) to the tetrahedron (L1C(10)), a energy of 9.0 kcal mol-1 is
required. We expected that metal complexes generated throughout
the titration of [Cu(CH3CN)4]BF4 or Pb(NO3)2 to L1 and L2 in
CH3OH solutions at room temperature will give information for
understanding the geometric conversion.
Changes in the absorption spectra of L1 in a CH3OH solution
upon addition of various concentrations of [Cu(CH3CN)4]BF4
were characterized by a clean isosbestic point at 568 nm, and
a decrease in the absorption band at l > 330 nm with a
concomitant development of a new band at 578 nm (Supporting
Information†). This reaction is accompanied by the solution color
change from red to purple. However, the lowest-energy absorption
band decreased when the ratio of Cu(I) : L1 was over 0.4 : 1, and the
subsequent addition of PPh3 (Cu(I) : L1 : PPh3, 1 : 1 : 1 molar ratio)
led to the solution being colorless. Similarly, titrating a CH3OH
solution of Pb(NO3)2 to a solution of L1 gave rise to a significant
color change from red to purple to pale yellow (Fig. 6). The results
cannot forecast the generated complex structures, but indicate a
geometric conversion at the central carbon atom of ligand L1.
Fig. 1 (Top) ORTEP views of L1 and L2 with the atom-labeling scheme.
Ellipsoids represent 50% probability. (Bottom) The 2D layer structure of
L2.
Geometric conversion from sp2 to sp3 via Cu(I) and Pb(II)
complexes
Crystal structures of complexes 1–4 have been determined. The
reaction of equimolar amounts of L1 or L2, [Cu(CH3CN)4]BF4
and PPh3 afforded 1 and 2. A perspective view of the structures
is depicted in Fig. 7. The two complexes were found to have
similar coordination modes, and the geometric configuration of
the central carbon (C1 in 1 and 2) transformed from sp2 to sp3
via a migration of the active hydrogen located at the nitrogen
atoms (H5 and H1 in L1 and L2, respectively). The migration
was due to the chelating coordination between the metal center
and the nitrogen atoms. Fig. 7 shows that the Cu(I) ion in
both complexes is coordinated to three chelating naphthyridine-N
atoms of L1 or L2 and one phosphorus atom from the phosphine
Fig. 2 Changes in the absorption spectra of L1 (5.1 ¥ 10-5 mol dm-3) upon
addition of HBF4 (3.1 ¥ 10-4 mol dm-3) in CH3OH, initial spectrum (solid
line), [HBF4]: 6.0 equiv (dashed dot line). Inset: the absorption spectra of
L2 in CH3OH (solid line), CH3CN (dashed line) and CH2Cl2 (dot line).
Density functional theory calculations showed that the molec-
ular energy of L1 decreased by 9.0 kcal mol-1 upon undergoing an
sp3 to sp2 geometric conversion involving the interaction of the
N2 and H5 atoms between two naphthyridine moieties, whereas
in the case of L1 the energy increased by 8.3 kcal mol-1 relative
N(3)
to that of L1. This computational result is in good agreement
with the crystal structure analysis (Fig. 5). Compared with the
7370 | Dalton Trans., 2011, 40, 7365–7374
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Fig. 4 The calculated molecular relative energies (kcal mol-1) of the proton associated with N(1–4) and N(6) of ligand L1, respectively.
Fig. 5 The calculated molecular relative energies (kcal mol-1) of the hydrogen transfer for central carbon atom C(10) in ligand L1 to N(1–6) atoms, where
L1 denotes L1
.
N(5)
group, thereby completing its tetrahedral geometry. The C–C bond
˚
lengths relevant to C1 are within the range of 1.49–1.63 A and
close to the single bond length. The bond angles at the carbon
atom vary from 105.1 to 116.7◦. Each benzene ring at PPh3 was
inserted between two naphthyridine rings in spatial arrangement
to ensure the lowest steric restriction.
In contrast, Pb(II) complexes 3 and 4 exhibit multiple coordi-
nation environments, and the hydrogen transfer and geometric
configuration conversion from sp2 to sp3 of the central carbon
atoms of L1 and L2 was observed when Pb(II) was coordinated to
them (Fig. 8). The difference between these two complexes was
that the hydrogen atom at the methine position of L1 was oxidised
to a hydroxyl during the reaction. This hydroxylation of a C–
H group at the ligand had previously been observed by reacting
CuBr2 and tris(6-methyl-2-pyridyl)methane under air.35 The three
naphthyridine groups in 3 are inequivalent, two naphthyridine-
N from three naphthyridyl units bind to the Pb center, and the
interactions between the Pb(II) center and the other nitrogen atoms
(N1, N4 and N6) are observed. The N(2) atom is free and not
involved in coordination. Nitrate ions act as terminal ligands as
well as counterions in the complex.
Fig. 6 The absorption spectral changes of titration Pb(NO3)2 to L1 of
CH3OH solution at room temperature ([Pb(NO3)2]: 0–0.4 equiv). Inset:
[Pb(NO3)2]: 0.4–1.0 equiv.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7365–7374 | 7371
©

View Article Online
Fig. 7 ORTEP views of cationic portion of complexes 1 and 2 with atom-labeling scheme. Ellipsoids represent 50% probability. Hydrogen atoms and
solvent molecules are omitted for clarity.
Fig. 8 Molecular views of complexes 3 and 4 with atom-labeling scheme. Ellipsoids represent 50% probability. Hydrogen atoms and solvent molecules
are omitted for clarity.
Crystal structure analysis of complex
it is composed of
cation [Pb(Lb)2]2+,
4
a
revealed that
counteranion
naphthyridine-N (N3, N5, N3A and N5A) moieties are arranged
˚
a
in a rectangular array with Pb–N distances of 2.704 and 2.706 A
[Pb(CH3OH)(NO3)4]2- and the ligand Lb in a tridentate mode with
nitrogen atoms of three naphthyridyl moieties chelating with the
Pb(II) center to form a distorted octahedral geometry. The four
and N–Pb–N angles of 64.6 and 115.4◦. The two nitrogen atoms
are located at opposite faces of the rectangle, and the Pb–N bond
˚
distances of 2.688 A are slightly shorter than those on the PbN4
7372 | Dalton Trans., 2011, 40, 7365–7374
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
plane. The steric hindrance gives rise to dihedral angles between
the axis and the PbN4 of 64.49◦ rather than the ideal geometry of
90◦.
2 J. P. Wibaut and G. L. C. La Bastide, Recl. Trav. Chim. Pays-Bas, 1933,
52, 493; P. L. Dedert, T. Sorrell, T. J. Marks and J. A. Ibers, Inorg.
Chem., 1982, 21, 3506; J. Pe´rez, D. Dorales, L. A. Garc´ıa-Escudero, H.
Mart´ınez-Garc´ıa, D. Miguel and P. Bernad, Dalton Trans., 2009, 375.
3 P. L. Jones, A. J. Amoroso, J. C. Jeffery, J. A. McCleverty, E. Psillakis,
L. H. Rees and M. D. Ward, Inorg. Chem., 1997, 36, 10; H. D. Bari and
N. Zimmer, Inorg. Chem., 2004, 43, 3344.
Conclusion
4 K. Kurtev, D. Ribola, R. A. Jones, D. J. Cole-Hamilton and G.
Wilkinson, J. Chem. Soc., Dalton Trans., 1980, 55; P. A. Anderson,
F. R. Keene, E. Horn and E. R. T. Tiekink, Appl. Organomet. Chem.,
1990, 4, 523.
5 R. T. Jonas and T. D. P. Stack, Inorg. Chem., 1998, 37, 6615; B. B.
Moubaraki, A. Leita, G. J. Halder, S. R. Batten, J P. Ensen, J. D. Smith,
J. D. Cashion, C. J. Kepert, J. F. Le´tard and K. S. Murray, Dalton
Trans., 2007, 4413.
6 M. Kodera, K. Katayama, Y. Tachi, K. Kano, S. Hirota, S. Fujinami
and M. J. Suzuki, J. Am. Chem. Soc., 1999, 121, 11006; M. Kodera, Y.
Tachi, T. Kita, H. Kobushi, Y. Sumi, K. Kano, M. Shiro, M. Koikawa,
T. Tokii, M. Ohba and H. Okawa, Inorg. Chem., 2000, 39, 226.
7 M. C. Cushion, J. Meyer, A. Heath, A. D. Schwarz, I. Ferna´ndez, F.
Breher and P. Mountford, Organometallics, 2010, 29, 1174.
8 J. W. Canary, S. Mortezaei and J. Liang, Chem. Commun., 2010, 46,
5850.
Two novel tripodal naphthyridyl derivatives, L1 and L2, were
prepared and structurally characterized. The crystal structures
showed that the hydrogen atom at the central carbon atom
transfers to an adjacent naphthyridine-N, thereby forming a large
molecular conjugated structure. Furthermore, this transfer was
characterized by a lowest-energy absorption spectrum centered at
~540 nm. The geometric configuration conversion of the central
carbon in both compounds from sp2 to sp3 was induced by the
coordination of Pb(II) and Cu(I) with the naphthyridyl ligands
which chelate in a tridentate mode with three naphthyridine-N
atoms adjacent to the central carbon atom. The conversions were
accompanied by color changes from red to colorless or pale yellow
in organic solvents and confirmed by crystal structure analysis of
complexes 1–4. The results revealed that 1,3-hydrogen migration
from the splitting of the N–H bond to forming a C–H bond is
dependent on the binding modes of L1 and L2 with metal cations.
The chelating mode favors configuration conversion, which was
fully confirmed by spectral changes with various H+, Cu+ and Pb2+
concentrations. The observed absorption spectral red-shift upon
addition of HBF4 reflects the combined H+ to naphthyrindine-
N depression of the p* energy level for intramolecular charge
transfer, and indicates that the central carbon atoms of L1 and L2
still retain their original geometric configuration. In the presence
of the metal cation the naphthyridine-receptor moiety of the H-
transfer was considered to be metal-free when the ratio of the metal
salt with L1–2 was below 0.5 : 1. However, increasing the metal salt
concentration leads to an H-transfer and the formation of the
M–N bond at N–H, and affords the complex with a geometric
configuration conversion of the ligand compared to the original
ligand. Moreover, the molecular energy changes obtained by
density functional theory fully support these experimental results;
free L1 and L2 have higher stability than the other corresponding
five possible compounds. The obtained results presented a new
approach for the capability of L1 and L2 to recognize heavy
metal ions such as Pb2+ and provided a new perspective for the
development of new tripodal naphthyridyl derivatives.
9 K. Matsumoto, M. Kannami and M. Oda, Tetrahedron Lett., 2003, 44,
2861.
10 K. Matsumoto, M. Kannami, D. Inokuchi, H. Kurata, T. Kawase and
M. Oda, Org. Lett., 2007, 9, 2903.
11 Y. Tsuzuki, K. Tomita, K. I. Shibamori, Y. Sato, S. Kashimoto and
K. Chiba, J. Med. Chem., 2004, 47, 2097; Q. D. You, Z. Y. Li, C. H.
Huang, Q. Yang, X. J. Wang, Q. L. Guo, X. G. Chen, X. G. He, T. K.
Li and J. W. Chern, J. Med. Chem., 2009, 52, 5649.
12 T. F. A. de Greef, G. B. W. L. Ligthart, M. Lutz, A. L. Spek, E. W.
Meijer and R. P. J. Sijbesma, J. Am. Chem. Soc., 2008, 130, 5479; F.
Takei, M. Igarashi, M. Hagihara, Y. Oka, Y. Soya and K. Nakatani,
Angew. Chem., Int. Ed., 2009, 48, 7822; N. Minakawa, S. Ogata, M.
Takahashi and A. Matsuda, J. Am. Chem. Soc., 2009, 131, 1644; Y.
Ferrand, A. M. Kendhale, J. Garric, B. Kauffmann and I. Huc, Angew.
Chem., Int. Ed., 2010, 49, 1778.
13 S. H. Lu, S. Selvi and J. M. Fang, J. Org. Chem., 2007, 72, 117; H. M.
Zhang, W. F. Fu, J. Wang, X Gan, Q. Q. Xu and S. M. Chi, Dalton
Trans., 2008, 6817.
14 S. A. Moya, R. Schmidt, R. Pastene, R. Sartori, U. Mu¨ller and G.
Frenzen, Organometallics, 1996, 15, 3463; M. Majumdar, S. K. Patra,
M. Kannan, K. R. Dunbar and J. K. Bera, Inorg. Chem., 2008, 47,
2212; A. Sinha, S. M. W. Rahaman, M. Sarkar, B. Saha, P. Daw and J.
K. Bera, Inorg. Chem., 2009, 48, 11114.
15 I. P. C. Liu, C. H. Chen, C. F. Chen, G. H. Lee and S. M. Peng, Chem.
Commun., 2009, 577; I. P. C. Liu, W. Z. Wang and S. M. Peng, Chem.
Commun., 2009, (29), 4323.
16 J. L. Katz, B. J. Geller and P. D. Foster, Chem. Commun., 2007,
1026.
17 M. F. Mayer, S. Nakashima and S. C. Zimmerman, Org. Lett., 2005, 7,
3005; Y. Y. Sun, J. H. Liao, J. M. Fang, P. T. Chou, C. H. Shen, C. W.
Hsu and L. C. Chen, Org. Lett., 2006, 8(17), 3713; A. Petitjean, L. A.
Cuccia, M. Schmutz and J. M. Lehn, J. Org. Chem., 2008, 73, 2481; H.
F. J. Li, W. F. Fu, L. Li, X. Gan, W. H. Mu, W. Q. Chen, X. M. Duan
and H. B. Song, Org. Lett., 2010, 12, 2924.
Acknowledgements
18 C. He and S. J. Lippard, Tetrahedron, 2000, 56, 8245.
19 C. He and S. J. Lippard, J. Am. Chem. Soc., 2000, 122, 184; C. He, J. L.
DuBois, B. Hedman, K. O. Hodgson and S. J. Lippard, Angew. Chem.,
Int. Ed., 2001, 40, 1484.
This work was financially supported by the National Basic
Research Program of China (973 Program 2007CB613304) and the
foundation (GJHZ200817) for Bureau of International Coopera-
tion of Chinese Academy of Science. We thank the National Natu-
ral Science Foundation of China (NSFC Grant Nos. 20761006 and
21071123) and Program for Changjiang Scholars and Innovative
Research Team in University (IRT0979, Z2009-1-65003).
20 L. Xing, U. Ziener, T. C. Sutherland and L. A. Cuccia, Chem. Commun.,
2005, 5751.
21 J. Gajardo, J. C. Araya, S. A. Moya, A. J. Pardey, V. Guerchais, H. L.
Bozec and P. Aguirre, Appl. Organomet. Chem., 2006, 20, 272.
22 S. A. Moya, J. Gajardo, J. C. Araya, J. J. Cornejo, V. Guerchais, H.
L. Bozec, J. C. Bayo´n, A. J. Pardey and P. Aguirre, Appl. Organomet.
Chem., 2008, 22, 471.
23 W. F. Fu, L. F. Jia, W. H. Mu, X. Gan, J. B. Zhang, P. H. Liu, Q. Y.
Cao, G. J. Zhang, L. Quan, X. J. Lv and Q. Q. Xu, Inorg. Chem., 2010,
49, 4524.
Notes and references
1 J. P. Wilbaut, A. P. de Jonge, H. G. P. van der Voort and H. L. Otto,
Recl. Trav. Chim. Pays-Bas, 1951, 70, 1054; D. L. White and J. W. Faller,
Inorg. Chem., 1982, 21, 3119; A. J. Canty and N. J. Minchin, Aust. J.
Chem., 1986, 39, 1063; F. R. Keene, M. R. Snow, P. J. Stephenson and
E. R. T. Tiekink, Inorg. Chem., 1988, 27, 2040.
24 E. V. Brown, J. Org. Chem., 1965, 30, 1607.
25 G. R. Newkome, S. J. Garbis, V. K. Majestic, F. R. Fronczek and G.
Chiari, J. Org. Chem., 1981, 46, 833.
26 G. Kubas, Inorg. Synth., 1979, 19, 90.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7365–7374 | 7373
©

View Article Online
27 R. A. Henry and P. R. Hammond, J. Heterocycl. Chem., 1977, 14, 1109.
28 G. M. Sheldrick, SHELXS-97, Program for solution of crystal struc-
tures, University of Go¨ttingen, Germany, 1997.
29 G. M. Sheldrick, SHELXL-97 Program for the Refinement of Crystal
Structures, University of Go˝ttingen, Germany, 1997.
30 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C.
Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci,
M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E.
Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D.
Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S.
Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. G. Johnson,
W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, GAUSSIAN 03
(Revision C.02), Gaussian, Inc., Wallingford, CT, 2004.
31 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
32 C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
33 M. P. Andersson and P. Uvdal, J. Phys. Chem. A, 2005, 109, 2937.
34 W. H. Mu, G. A. Chasse and D. C. Fang, Int. J. Quantum Chem., 2008,
108, 1422.
35 M. Kodera, Y. Tachi, T. Kita, H. Kobushi, Y. Sumi, K. Kano, M. Shiro,
M. Koikawa, T. Tokii, M. Ohba and H. Okawa, Inorg. Chem., 2000,
39, 226.
7374 | Dalton Trans., 2011, 40, 7365–7374
This journal is
The Royal Society of Chemistry 2011
©