Metal-ion sensing europium(III) complexes with bidentate phosphine oxide ligands containing a 2,2′-bipyridine framework

Article abstract of DOI:10.1002/hlca.200900143

Novel Eu^III complexes with bidentate phosphine oxide ligands containing a bipyridine framework, i.e., [3,3′-bis(diphenylphosphoryl)-2, 2′-bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu-(hfa) ₃(BIPYPO)]) and [3,3′-bis(diphenylphosphoryl)-6,6′- dimethyl-2,2′-bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(Me-BIPYPO)]), were synthesized for lanthanide-based sensor materials having high emission quantum yields and effective chemosensing properties. The emission quantum yields of [Eu(hfa)₃(BIPYPO)] and [Eu(hfa)₃(Me-BIPYPO)] were 71 and 73%, respectively. Metal-ion sensing properties of the Eu^III complexes were also studied by measuring the emission spectra of Eu^III complexes in the presence of Zn^II or Cu^II ions. The metal-ion sensing and the photophysical properties of luminescent Eu^III complexes with a bidentate phosphine oxide containing 2,2′-bipyridine framework are demonstrated for the first time.

Full text of DOI:10.1002/hlca.200900143

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Helvetica Chimica Acta – Vol. 92 (2009)
Metal-Ion Sensing Europium(III) Complexes with Bidentate Phosphine
Oxide Ligands Containing a 2,2’-Bipyridine Framework
by Yasuchika Hasegawa*, Ryo Hieda, Tetsuya Nakagawa, and Tsuyoshi Kawai*
Graduate School of Materials Science, Nara Institute of Science and Technology, Takayama 8916 – 5,
Ikoma, Nara 630-0101, Japan (phone: þ 81743726171; fax: þ 81743726171;
e-mail: hasegawa@ms.naist.jp, tkawai@ms.naist.jp)
Dedicated to Professor Jean-Claude Bꢀnzli on the occasion of his 65th birthday
Novel EuIII complexes with bidentate phosphine oxide ligands containing a bipyridine framework,
i.e., [3,3’-bis(diphenylphosphoryl)-2,2’-bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu-
(hfa)3(BIPYPO)]) and [3,3’-bis(diphenylphosphoryl)-6,6’-dimethyl-2,2’-bipyridine]tris(hexafluoroacet-
ylacetonato)europium(III) ([Eu(hfa)3(Me-BIPYPO)]), were synthesized for lanthanide-based sensor
materials having high emission quantum yields and effective chemosensing properties. The emission
quantum yields of [Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-BIPYPO)] were 71 and 73%, respectively.
Metal-ion sensing properties of the EuIII complexes were also studied by measuring the emission spectra
of EuIII complexes in the presence of ZnII or CuII ions. The metal-ion sensing and the photophysical
properties of luminescent EuIII complexes with a bidentate phosphine oxide containing 2,2’-bipyridine
framework are demonstrated for the first time.
Introduction. – The design of chemosensors for the selective detection of a specific
analyte such as a cation, anion, or molecule is a topic of considerable interest, due to
their widely ranging application field [1]. Considerable efforts have been devoted to
the elaboration of luminescent chemosensors for various analytes in the last two
decades [1][2]. A large number of luminescent organic dyes [3], metal complexes [4],
and polymers [5] with attached chemosensing units has been reported. We here focus
on lanthanide complexes as luminophores [6]. Luminescent lanthanide complexes with
attached chemosensing units have been also focused upon as effective sensory
molecules [7 – 10]. Parker, Gunnlaugsson, and co-workers have, for example, studied
luminescent lanthanide cyclen complexes for selective detection of HCOꢀ3 anion [7].
Ziessel, Tsukube, and co-workers have reported luminescent lanthanide complexes for
effective halogen-anion and chiral-molecule sensing [8][9].
Those luminescent lanthanide complexes with chemosensing properties are
expected to contain chemosensing units for effective sensing properties. For example,
EuIII complexes with ZnII ion sensing properties have been reported [10], although the
emission quantum yield of the EuIII complex is relatively small (F ¼ 7.4%). Previous
chemosensing lanthanide complexes contained numerous CꢀH chemical bonds close
to the metal center, which led to the radiationless transition via vibrational relaxations
of these complexes [11]. To enhance the emission quantum yields of lanthanide
complexes having chemosensing units, the coordination sites of the organic ligands
should be composed of low-vibrational-frequency (LVF) modes for the suppression of
ꢀ 2009 Verlag Helvetica Chimica Acta AG, Zꢁrich

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vibrational relaxation [11]. In earlier studies, we have reported on the suppression of
radiationless quenching in fluid lanthanide(III) systems by complexing the lanthani-
de(III) ion with diketonato ligands having CꢀF bonds composed of LVF modes, such
as the hexafluoroacetylacetonato (hfa) ligand [12]. Such a LVF ligand, with the CꢀH
bonds replaced by CꢀF bonds, is effective in the suppression of the radiationless
transition via vibrational relaxation in the lanthanide complex. We have also observed
that EuIII complexes with the LVF ligands hexafluoroacetylacetonato (hfa) and triaryl
phosphine oxide (P¼O: 1125 cmꢀ1) show relatively high emission quantum yields
(F > 60% in (D6)acetone) [13][14]. The LVF phosphine oxides with attached
chemosensing units are expected to be promising ligands for luminescent lanthanide
complexes having high emission quantum yields and effective chemosensing properties.
Here, we report on novel luminescent EuIII complexes with bidentate phosphine
oxide ligands containing a 2,2’-bipyridine framework, i.e., [3,3’-bis(diphenylphosphor-
yl)-2,2’-bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)3(BIPYPO)])
and [3,3’-bis(diphenylphosphoryl)-6,6’-dimethyl-2,2’-bipyridine]tris(hexafluoroacetyl-
acetonato)europium(III) ([Eu(hfa)3(Me-BIPYPO)]) (Figs. 1,a and b). The bipyri-
dine frameworks in these bidentate phosphine oxide ligands are expected to perform as
chemosensing units for catching of a metal cation such as a ZnII ion. The metal-ion
sensing properties of [Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-BIPYPO)] were
estimated by measuring the emission spectra of the EuIII complex in the presence of
a ZnII or CuII ion. We also compared the metal-ion sensing and the emission properties
of [Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-BIPYPO)] with those EuIII complexes
containing a 1,1’-biphenyl framework, e.g., [Eu(hfa)3(BIPHEPO)] (Fig. 1,c) [14]. In
the present study, metal-ion sensing and the emission properties of luminescent EuIII
complexes with bidentate phosphine oxide ligands containing a 2,2’-bipyridine
framework are demonstrated for the first time.
Results and Discussion. – Emission Properties. The emission spectra of the EuIII
complexes [Eu(hfa)3(BIPHEPO)], [Eu(hfa)3(BIPYPO)], and [Eu(hfa)3(Me-BIPY-
PO)] in (D6)acetone under excitation at 465 nm (7F0 – 5D2 transition band of EuIII) are
5
shown in Fig. 2. The spectra are normalized with respect to the D0 – 7F1 (magnetic-
dipole) transition at 580 nm that is known to be insensitive to the ligand field [13a].
Emission bands were observed at around 579, 592, 615, 650, and 700 nm, and are
attributed to the f – f transitions 5D0 – 7FJ (J ¼ 0, 1, 2, 3, 4, resp.). The strongest emission
band at around 615 nm (5D0 – 7F2) is due to the electric-dipole transition. [Eu(hfa)3-
(BIPYPO)] and [Eu(hfa)3(Me-BIPYPO)] showed the characteristic narrow emission
band which agreed well with that of [Eu(hfa)3(BIPHEPO)]. The spectral shape of a
hypersensitive transition band is generally affected by the coordination structure of the
EuIII complex [15]. These results indicate that the coordination structures of
[Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-BIPYPO)] in (D6)acetone are much similar
to that of [Eu(hfa)3(BIPHEPO)].
The emission quantum yields of [Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-BIPY-
PO)] in (D6)acetone are summarized in the Table. [Eu(hfa)3(BIPYPO)] and
[Eu(hfa)3(Me-BIPYPO)] show relatively high emission quantum yields (F ꢁ 70%).
The time-resolved emission profiles of [Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-
BIPYPO)] revealed mono-exponential decays with lifetimes in the millisecond time in

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Fig. 1. Chemical structures of a) [Eu(hfa)3(BIPYPO)], b) [Eu(hfa)3(Me-BIPYPO)], and
c) [Eu(hfa)3(BIPHEPO)]
(D6)acetone. The radiative (kr) and nonradiatve (knr) rate constants estimated from the
emission lifetimes and the emission quantum yields are also summarized in the Table.
The radiative and nonradiative rate constants of [Eu(hfa)3(BIPYPO)] and [Eu-
(hfa)3(Me-BIPYPO)] were nearly similar to those of the corresponding [Eu(hfa)3-
(BIPHEPO)]. The radiative and nonradiative processes of [Eu(hfa)3(BIPYPO)] and
[Eu(hfa)3(Me-BIPYPO)] in (D6)acetone might not be affected by introducing the
bipyridine framework in bidentate phosphine oxides. Generally, kinetics of the
radiative rate of the emission from lanthanide complexes depends on the geometrical
symmetry of their coordination structure [13]. We suggest that the geometrical
symmetries of the coordination structure of [Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-
BIPYPO)] are similar to that of [Eu(hfa)3(BIPHEPO)].
In our previous study, we have reported that the coordination geometry of
[Eu(hfa)3(BIPHEPO)] is characterized as a square-antiprism structure (SAP) with
eight coordinating O-atoms (8-SAP), and the two phosphine oxides of the BIPHEPO
ligand are located on one square of the 8-SAP (Fig. 3) [14]. The two phosphine oxide
sites in the BIPYPO and Me-BIPYPO ligands might also be located on one square of
the 8-SAP. We consider that the characteristic structures of BIPYPO and Me-BIPYPO
located in EuIII complexes would provide the best conformation for chelation of a metal
ion such as a bipyridine ligand in the case of transition-metal complexes.
Metal-Ion-Sensing Properties. The emission spectra of [Eu(hfa)3(BIPYPO)] upon
addition of Zn(NO3)2 ion in (D6)acetone under excitation at 465 nm are shown in

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Fig. 2. Normalized emission spectra of a) [Eu(hfa)3(BIPYPO)], b) [Eu(hfa)3(Me-BIPYPO)], and c)
[Eu(hfa)3(Me-BIPHEPO)] in (D6)acetone under 465 nm. Emission spectra were normalized at 592 nm
(5D0 – 7F1).
Table. Characteristics of the Emission Properties of [Eu(hfa)3(BIPYPO)], [Eu(hfa)3(Me-BIPYPO)],
and [Eu(hfa)3(BIPHEPO)]a)
Ff--f [%]
t [ms]
kr [sꢀ1]b)
knr [sꢀ1]c)
[Eu(hfa)3(BIPYPO)]
[Eu(hfa)3(Me-BIPYPO)]
[Eu(hfa)3(BIPHEPO)]
71
73
60
1.16
1.27
1.27
6.0 · 102
5.8 · 102
4.7 · 102
2.5 · 102
2.1 · 102
3.2 · 102
a) The emission quantum yields (Ff–f) and the emission lifetimes (t) in (D6)acetone (1 mm) were
measured by excitation at 465 nm (7F0 – 5D2) and 355 nm (p – p* transition band of the hfa ligands), resp.
b) Radiative rate constant kr ¼ (Ff–f)/t. c) Nonradiative rate constant knr ¼ (1/t) ꢀ kr.
Fig. 4,a. We observed an effective decrease of the emission intensity of [Eu(hfa)3-
(BIPYPO)] upon the addition of ZnII ions. Normalized emission spectra with respect to

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Fig. 3. ORTEP View of the [Eu(hfa)3(BIPHEPO)] single crystal [14] (CF3 groups omitted for clarity)
the magnetic-dipole-transition intensities were not affected by the addition of ZnII ion.
These results indicate that the geometrical structure and radiative rate constant of
[Eu(hfa)3(BIPYPO)] were not affected by the addition of ZnII ion. We also observed
that the decrease ratio upon addition of Zn(OTf)2 (OTfꢀ ¼ trifluoromethanesulfonate)
was the same as that of Zn(NO3)2, and the absorption band of [Eu(hfa)3(BIPYPO)] in
the presence of ZnII ion was not observed in the range from 500 nm to 800 nm. From
these observations, the effective decrease of the emission intensity of [Eu(hfa)3-
(BIPYPO)] on addition of ZnII ion might be due to the increase of the nonradiative
rate constant of the EuIII complex. We consider that formation of dimer or trimer EuIII
complexes combined by ZnII ions in (D6)acetone might lead to an increase of the
nonradiative process as a consequence of the excitation migration or cross-relaxation
between EuIII ions [16]. In contrast, the effective decrease of the emission intensity of
[Eu(hfa)3(BIPHEPO)] which also has a bidentate phosphine oxide ligand but
containing the biphenylene framework was not observed.
We also observed a drastic decrease of the emission intensity on addition of CuII ion
to [Eu(hfa)3(BIPYPO)], although the normalized emission spectra and the absorption
band of [Eu(hfa)3(BIPYPO)] in the range from 500 nm to 800 nm were not changed by
this addition (Fig. 4,b). The decrease ratio on addition of CuII ion was larger than that
of ZnII ion. Previously, Saladini and co-workers have reported that the binding constant
for the formation of a [CuII(bipyridine)] complex (log K ¼ 8.0) is larger than that of
corresponding [ZnII(bipyridine)] complex (log K ¼ 5.3) [17]. It seems that the drastic
decrease of the emission spectra of [Eu(hfa)3(BIPYPO)] on addition of CuII ion is
caused by a strong affinity between the CuII ion and the bipyridine unit in the BIPYPO
ligand.

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Fig. 4. Emission spectra (excitation at 465 nm) of [Eu(hfa)3(BIPYPO)] (1 mm) in the presence of
various concentrations of a) ZnII or b) CuII (0.000, 0.025, 0.050, 0.075, 0.100, 0.125, 0.160, 0.175, and
0.200 equiv. of ZnII or CuII with respect to [Eu(hfa)3(BIPYPO)])
The emission-intensity profiles of [Eu(hfa)3(BIPYPO)], [Eu(hfa)3(Me-BIPY-
PO)], and [Eu(hfa)3(BIPHEPO)] in the presence of ZnII and CuII ions (Fig. 5) show a

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Fig. 5. Emission-intensity profiles of [Eu(hfa)3(BIPYPO)] (1 mm; red dots), [Eu(hfa)3(Me-BIPYPO)]
(1 mm; blue circles), and [Eu(hfa)3(BIPHEPO)] (1 mm; green triangles) in the presence of ZnII and CuII
ions in (D6)acetone excited at 465 nm

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decrease of the emission intensity of [Eu(hfa)3(Me-BIPYPO)] on addition of Zn(II)
and Cu(II) ions; however, the decrease ratios of the emission intensity of [Eu-
(hfa)3(Me-BIPYPO)] were smaller than those of [Eu(hfa)3(BIPYPO)]. We consider
that formation of [Eu(hfa)3(Me-BIPYPO)] with attached ZnII or CuII ions may be
partially prevented by steric hindrance of the Me groups at the bipyridine moiety. The
effective decrease of the emission intensities of [Eu(hfa)3(BIPHEPO)] in the presence
of ZnII and CuII ions was not observed. From these results, we propose that the
BIPYPO is the most useful ligand for luminescent lanthanide complexes having high
emission quantum yields and effective chemosensing properties.
Conclusion. – We successfully synthesized novel EuIII complexes with bidentate
phosphine oxide ligands containing a bipyridine framework, [Eu(hfa)3(BIPYPO)] and
[Eu(hfa)3(Me-BIPYPO)]. Their high emission quantum yields and effective metal-ion
sensing properties were achieved by the coordination of the low-vibrational phosphine
oxide bearing the chemosensing unit. EuIII Complexes with strong luminescence and
effective metal-ion-sensing properties would open up new fields for luminescent
chemosensors.
Experimental Part
General. IR Spectra: Jasco-FT/IR-420 spectrometer; ATR ¼ attenuated total reflection; in cmꢀ1
.
1H-NMR Spectra: Jeol-AL300 spectrometer (300 MHz); chemical shifts d in ppm rel. to Me4Si as an
internal standard, J in Hz. EI- and ESI-MS: Jeol-JMS-700-M station; in m/z.
Optical Measurements. Absorption spectra of EuIII complexes in acetone (1.0 mm) were measured at
r.t. with a Jasco-V-660 spectrophotometer. Emission spectra of EuIII complexes in acetone (1.0 mm) were
measured at r.t. with a Hitachi-F-4500 spectrophotometer. The samples were excited at 465 nm. The
emission lifetime of EuIII complexes were determined with a Q-switched Nd :YAG laser (Spectra Physics
INDI-50, fwhm ¼ 5 ns, l ¼ 1064 nm). Samples were excited by the third harmonic (355 nm) of the
fundamental nanosecond pulse. Emission decays were monitored with a digital oscilloscope (Sony
Tektronix, TDS3052B) synchronized to single-pulse excitation. The emission quantum yields of
[Eu(hfa)3(BIPYPO)] and [Eu(hfa)3(Me-BIPYPO)] were evaluated by utilizing [Eu(hfa)3(BIPHEPO)]
as the standard of Femi ¼ 0.60 [18].
[2,2’-Bipyridine]-3,3’-diol. The [2,2’-bipyridine]-3,3’-diol was obtained by the same method as
previously reported [19]. NiCl2 (3.9 g, 30 mmol), Zn powder (5.9 g, 90 mmol), and Ph3P (32 g,
120 mmol) were dissolved in anh. DMF (150 ml), and the mixture was heated to 508. After 1 h, 2-
bromopyridin-3-ol (5.2 g, 90 mmol) in anh. DMF (100 ml) was added, and the mixture was kept for
another 20 h at 508. The warm mixture was poured into 10n aq. NaOH (100 ml) and vigorously stirred for
30 min. The precipitated Ph3P was filtered and the filtrate again poured into 10n aq. NaOH (50 ml). The
product was precipitated by the addition of conc. HCl soln. to the combined NaOH soln. (pH 4) and
stirring for 30 min. The solid was immediately filtered, washed with distilled H2O, and dried in a
desiccator. The residue was purified by CC (SiO2): [2,2’-bipyridine]-3,3’-diol (0.70 g, 25%). Yellow solid.
Rf (CHCl3) 0.7. 1H-NMR (300 MHz, CDCl3): 8.06 (d, J ¼ 4.5, 2 H); 7.43 (d, J ¼ 7.5, 2 H); 7.30 (dd, J ¼ 4.8,
4.8, 2 H). EI-MS: 188.0586 (Mþ).
[2,2’-Bipyridine]-3,3’-diyl Bis(trifluoromethanesulfonate). To a soln. of [2,2’-bipyridine]-3,3’-diol
(0.57 g, 3.0 mmol) in anh. CH2Cl2 (25 ml) under N2 at r.t. pyridine (1.6 ml, 18 mmol) was added. Then,
trifluoromethanesulfonic anhydride (1.5 ml, 9.0 mmol) was added dropwise (yellow ! red and white
fume). The mixture was stirred at r.t. for 17 h. H2O was added into the soln. and the mixture extracted
with CH2Cl2. The combined org. phase was washed with H2O and brine, dried (MgSO4), and
concentrated and the residue purified by CC (SiO2): [2,2’-bipyridine]-3,3’-diyl bis(trifluoromethanesul-
fonate) (1.3 g, 94%). White solid. Rf 0.4 (hexane/AcOEt 3 :1). FT-IR (ATR): 1587 (pyridine C¼C,

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Helvetica Chimica Acta – Vol. 92 (2009)
C¼N), 1424 (pyridine C¼C, C¼N), 1270 – 1170 (br., S¼O), 1260 – 1070 (br., CꢀF). 1H-NMR
(300 MHz, CDCl3): 8.79 (d, J ¼ 4.5, 2 H); 7.82 (d, J ¼ 8.4, 2 H); 7.58 (dd, J ¼ 4.5, 4.8, 2 H). EI-MS:
451.9570 (Mþ).
3,3’-Bis(diphenylphosphoryl)-2,2’-bipyridine (BIPYPO). Diphenylphosphine (1.8 ml, 10 mmol) was
added to a stirred soln. of [2,2’-bipyridine]-3,3’-diyl bis(trifluoromethanesulfonate) (1.5 g, 3.4 mmol),
Et3N (1.2 ml), and [Pd(OAc)2] (0.31 g, 1.4 mmol) in dry DMF (20 ml) (! instantly red soln.). The soln.
was heated at 908 under N2 for 24 h. H2O was added and the mixture extracted with CH2Cl2. The
combined org. phase was washed with H2O and brine, dried (MgSO4), and concentrated and the residue
dissolved in CH2Cl2. The soln. was cooled to 08, and then 30% H2O2 soln. (7.0 ml) was added. The
mixture was stirred for 12 h and then extracted with CH2Cl2. The combined org. phase was washed with
H2O and brine, dried (MgSO4), and concentrated and the residue purified by CC (SiO2): 3,3’-
bis(diphenylphosphoryl)-2,2’-bipyridine (0.71 g, 38%). Yellow solid. Rf 0.1 (THF). FT-IR (ATR): 1647,
1580 – 1540 (pyridine, C¼C, C¼N), 1460 – 1360 (pyridine, C¼C, C¼N), 1210 – 1160 (br., P¼O), 1140 –
1000. 1H-NMR (300 MHz, CDCl3): 8.26 (td, J ¼ 2.4, 2.4, 2 H); 7.75 – 7.68 (m, 10 H); 7.46 – 7.37 (m, 12 H);
7.11 (dd, J ¼ 4.8, 4.8, 2 H). EI-MS: 556.1470 (Mþ).
[3,3’-Bis(diphenylphosphoryl-kO)-2,2’-bipyridine]tris(1,1,1,5,5,5-hexafluoropentane-2,4-dionato-
kO,kO’)europium(III) ([Eu(hfa)3(BIPYPO)]). [Eu(hfa)3(H2O)2] (0.49 g, 0.60mmol) and 3,3’-bis(di-
phenylphosphoryl)-2,2’-bipyridine (0.28 g, 0.50 mmol) were dissolved in MeOH (100 ml). The soln. was
refluxed and stirred for 12 h and then concentrated. The residue was washed with CHCl3 and Et2O
several times: [Eu(hfa)3(BIPYPO)] (0.43 g, 62%) as a white solid. Recrystallization from acetone/H2O
gave a colorless crystal. FT-IR (ATR): 1680 ꢀ 1630 (s, C¼O), 1580 ꢀ 1430 (pyridine, C¼C, C¼N),
1210 – 1180 (P¼O), 1170 – 1040 (br., CꢀF). 1H-NMR (300 MHz, CDCl3): 8.77 (br., 4 H); 8.37 (br.,
2 H); 8.13 (dd, J ¼ 7.8, 8.4, 2 H); 7.80 (br., 6 H); 7.50 (br., 4 H); 6.76 (br., 4 H); 5.79 (br., 4 H). ESI-MS:
1123.0358 ([M ꢀ (hfa)]þ). Anal. calc. for C49H29EuF18N2O8P2: C 44.26, H 2.20, N 2.11; found: C 44.13, H
1.85, N 2.11.
2-Bromo-6-methylpyridin-3-ol. The 2-bromo-6-methylpyridin-3-ol was obtained by the same method
as previously reported [20]. Bromine (14 ml, 270 mmol) was slowly added to a soln. of 6-methylpyridin-
3-ol (25 g, 230 mmol) in pyridine (300 ml) at 08. The mixture was stirred for additional 20 h at r.t. H2O
was added into the soln., and the mixture was extracted with CH2Cl2. The combined org. phase was
washed with H2O and brine, dried (MgSO4), and concentrated and the residue purified by CC (SiO2): 2-
bromo-6-methylpyridin-3-ol (19 g, 43%). White solid. Rf 0.2 (CHCl3). 1H-NMR (300 MHz, CDCl3): 7.19
(d, J ¼ 8.1, 1 H); 7.02 (d, J ¼ 8.1, 1 H); 2.47 (s, 3 H). EI-MS: 186.9633 (Mþ).
6,6’-Dimethyl[2,2’-bipyridine]-3,3’-diol. As described above for [2,2’-bipyridine]-3,3’-diol, with NiCl2
(6.4 g, 49 mmol), Zn powder (9.8 g, 150 mmol), Ph3P (51 g, 200 mmol), DMF (200 ml), 2-bromo-6-
methylpyridin-3-ol (9.2 g, 49 mmol), and DMF (100 ml). Workup with 10n NaOH (200 and 50 ml): 6,6’-
dimethyl[2,2’-bipyridine]-3,3’-diol (1.2 g, 23%). Yellow solid. Rf 0.7 (CHCl3). 1H-NMR (300 MHz,
CDCl3): 14.75 (s, 2 H); 7.32 (d, J ¼ 8.4, 2 H); 7.12 (d, J ¼ 8.4, 2 H); 2.52 (s, 6 H). EI-MS: 216.0899 (Mþ).
6,6’-Dimethyl[2,2’-bipyridine]-3,3’-diyl Bis(trifluoromethanesulfonate). As described above for [2,2’-
bipyridine]-3,3’-diyl bis(trifluoromethanesulfonate), with 6,6’-dimethyl[2,2’-bipyridine]-3,3’-diol (1.4 g,
6.2 mmol) CH2Cl2 (40 ml), pyridine (3.5 ml, 42 mmol), and trifluoromethanesulfonic anhydride (3.5 ml,
21 mmol): 6,6’-dimethyl[2,2’-bipyridine]-3,3’-diyl bis(trifluoromethanesulfonate) (2.9 g, 96%). White
solid. Rf 0.5 (hexane/AcOEt 3 :1). FT-IR (ATR): 1600 – 1560 (pyridine, C¼C, C¼N), 1450 – 1380
(pyridine, C¼C, C¼N), 1270 – 1170 (br., S¼O), 1170 – 1070 (br., CꢀF), 1145. 1H-NMR (300 MHz,
CDCl3): 7.65 (d, J ¼ 8.7, 2 H); 7.35 (d, J ¼ 8.4, 2 H); 2.67 (s, 6 H). EI-MS: 479.9884 (Mþ).
3,3’-Bis(diphenylphosphoryl)-6,6’-dimethyl-2,2’-bipyridine (Me-BIPYPO). As described above for
3,3’-bis(diphenylphosphoryl)-2,2’-bipyridine, with diphenylphosphine (2.7 ml, 16 mmol), 6,6’-dimeth-
yl[2,2’-bipyridine]-3,3’-diyl bis(trifluoromethanesulfonate) (2.3 g, 5.2 mmol), Et3N (1.7 ml), Pd(OAc)2
(0.47 g, 2.1 mmol), DMF (20 ml), and 30% H2O2 soln. (25 ml; 20 h stirring instead of 12 h). H2O was
added and the mixture extracted with CH2Cl2. The combined org. phase was washed with H2O and brine,
dried (MgSO4), and concentrated. The residue was washed with AcOEt, and solid was filtered: 3,3’-
bis(diphenylphosphoryl)-6,6’-dimethyl-2,2’-bipyridine (0.71 g, 23%). Yellow solid. Rf 0.3 (THF). FT-IR
(ATR): 1600 – 1520 (br., pyridine, C¼C, C¼N), 1450 – 1400 (br., pyridine, C¼C, C¼N), 1341, 1200 –

Helvetica Chimica Acta – Vol. 92 (2009)
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1150 (P¼O), 1150 – 1050. 1H-NMR (300 MHz, CDCl3): 7.71 – 7.64 (m, 8 H); 7.55 – 7.49 (m, 2 H); 7.44 –
7.34 (m, 12 H); 6.90 (d, J ¼ 7.8, 2 H); 2.04 (s, 6 H). EI-MS: 583.1704 ([M ꢀ H]þ).
[3,3’-Bis(diphenylphosphoryl-kO)-6,6’-dimethyl-2,2’-bipyridine]tris(1,1,1,5,5,5-hexafluoropentane-
2,4-dionato-kO,kO’)europium(III) ([Eu(hfa)3(Me-BIPYPO)]). As described for [Eu(hfa)3(BI-
PYPO)], with [Eu(hfa)3(H2O)2] (5.9 g, 7.3 mmol), 3,3’-bis(diphenylphosphoryl)-6,6’-dimethyl-2,2’-
bipyridine (3.6 g, 6.1 mmol), and MeOH (300 ml): [Eu(hfa)3(Me-BIPYPO)] (6.0 g, 73%) as a yellow
white solid. Recrystallization from acetone/H2O gave a colorless crystal. FT-IR (ATR): 1680 – 1630
(C¼O), 1580 – 1460 (br., pyridine, C¼C, C¼N), 1251, 1200 – 1150 (P¼O), 1160 – 1060 (br., CꢀF).
1H-NMR (300 MHz, CDCl3): 8.22 (br., 4 H); 8.06 (dd, J ¼ 8.1, 2 H); 7.67 (br., 6 H); 7.52 (d, J ¼ 7.8, 2 H);
6.96 (br., 4 H); 6.71 (br., 4 H); 5.98 (s, 4 H); 2.40 (s, 6 H). ESI-MS: 1151.0757 ([M ꢀ (hfa)]þ). Anal. calc.
for C51H33EuF18N2O8P2: C 45.12, H 2.45, N 2.06; found: C 45.09, H 2.19, N 2.06%.
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Received April 25, 2009