Syntheses and structures of new blue luminescent B(III) and Al(III) complexes: BPh2(acac-azain) and Al(CH3)(acac-azain)2, acac-azain=1-N-7-azaindolyl-1,3-butanedionato

Article abstract of DOI:10.1016/S0022-328X(01)01017-8

A novel blue luminescent ligand, 1-N-7-azaindolyl-1,3-butanedione (acac-azainH), has been synthesized and characterized structurally. The acac-azainH has a diketone structure in the solid state. The diketone form of acac-azainH is also dominant in solution. The acac-azainH molecule reacts readily with BPh₃ and Al(CH₃)₃ to form chelate complexes BPh₂(acac-azain) (1) and Al(CH₃)(acac-azain)₂ (2), respectively. The structure of 1 was determined by a single-crystal X-ray diffraction analysis. The acac-azainH molecule and compounds 1 and 2 are all blue luminescent but the luminescent efficiency is poor. In solution, compound 2 appears to exist in two isomeric forms.

Full text of DOI:10.1016/S0022-328X(01)01017-8

Journal of Organometallic Chemistry 631 (2001) 175–180
www.elsevier.com/locate/jorganchem
Syntheses and structures of new blue luminescent B(III) and
Al(III) complexes: BPh2(acac-azain) and Al(CH3)(acac-azain)2,
acac-azain=1-N-7-azaindolyl-1,3-butanedionato
Datong Song, Shi-Feng Liu, Rui-Yao Wang, Suning Wang *
Department of Chemistry, Queen’s Uni6ersity, Frost Wing, F318, Kingston, Ontario, K7L 3N6 Canada
Received 4 May 2001; received in revised form 29 May 2001; accepted 30 May 2001
Abstract
A novel blue luminescent ligand, 1-N-7-azaindolyl-1,3-butanedione (acac-azainH), has been synthesized and characterized
structurally. The acac-azainH has a diketone structure in the solid state. The diketone form of acac-azainH is also dominant in
solution. The acac-azainH molecule reacts readily with BPh3 and Al(CH3)3 to form chelate complexes BPh2(acac-azain) (1) and
Al(CH3)(acac-azain)2 (2), respectively. The structure of 1 was determined by a single-crystal X-ray diffraction analysis. The
acac-azainH molecule and compounds 1 and 2 are all blue luminescent but the luminescent efficiency is poor. In solution,
compound 2 appears to exist in two isomeric forms. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Boron; Aluminum; Luminescence; Azaindolyl
precursor molecules for a number of metal and metal
oxide materials. Recently, diketone boron complexes
have been found to be useful electroluminescent materi-
als [4]. Therefore, we investigated the synthesis of an
acac 7-azaindole derivative (1-N-7-azaindolyl-1,3-bu-
tanedione, acac-azainH) and its boron and aluminum
complexes. The results are reported herein.
1. Introduction
Blue luminescent compounds are an important class
of molecules that have been highly sought-after recently
by scientists around the world because of their potential
applications in electroluminescent devices [1]. A few
years ago we reported that 7-azaindole ligands are
capable of binding to boron(III), aluminum(III) or
zinc(II) readily to produce bright blue luminescent com-
plexes [2]. We have demonstrated that some of these
blue luminescent complexes can be used as blue emit-
ters in electroluminescent devices. Our recent efforts
focus on the modification of 7-azaindole ligand so that
more stable and efficient blue emitters could be ob-
tained. Acetylacetonato (acac) and its derivatives
(acac*) are the best known chelate ligands for metal
ions. Metal complexes of acac or acac* often display a
high stability and a high volatility, in comparison to
other chelate complexes [3]. Consequently, many metal
acac and acac* complexes have been frequently used as
2. Experimental
All the starting materials were purchased from
Aldrich Chemical Co. All the syntheses were carried
out under a nitrogen atmosphere. Solvents were freshly
distilled over appropriate drying reagents prior to use.
1H-NMR spectra were recorded on Bruker Advance
300 or 400 MHz spectrometers. Excitation and emis-
sion spectra were recorded on a Photon Technologies
International QuantaMaster Model 2 spectrometer. El-
emental analyses were performed by Canadian Micro-
analytical Service, Ltd, Delta, British Columbia.
Melting points were determined on a Fisher–Johns
melting point apparatus.
* Corresponding author. Fax: +1-613-533-6669.
E-mail address: wangs@chem.queensu.ca (S. Wang).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01017-8

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D. Song et al. / Journal of Organometallic Chemistry 631 (2001) 175–180
2.1. Synthesis of 1-N-7-azaindolyl-1,3-butanedione
(acac-azainH)
After the mixture was cooled to ambient temperature,
the solvent was removed under vacuum. Recrystalliza-
tion from CH2Cl2–hexanes yielded colorless crystals of
1 (0.153 g, yield 83%), m.p. 180–182 °C. 1H-NMR
(CDCl3, 25 °C): l=8.41 (dd, 3J1=4.8 Hz, 3J2=1.5
A solution of diketene (0.420 g, 5 mmol) in 5 ml of
toluene was added dropwise into a solution of 7-azain-
dole (0.590 g, 5 mmol) in 10 ml of toluene over a period
of 10 min. The reaction mixture was then heated to
90 °C for 2 h. After the solvent was removed, the
residue was purified by column chromatography using
1:2 ethyl acetate–hexanes as eluent, yielding colorless
solid of acac-azainH (0.935 g, yield 92.5%), m.p. 77–
3
Hz, 1H, azain), 8.15 (d, J=5.1 Hz,1H, azain), 7.94 (
3
3
dd, J1=7.8 Hz, J2=1.8 Hz, 1H, azain), 7.77 (s, 1H;
CꢀCꢁH), 7.57, 7.25 (m, 11H, phenyl, azain), 6.76 (d zH,
3J=4.2 Hz, 1H, azain), 2.45 (s, 3H; CH3). Anal. Calc.
for C23H19O2N2B: C, 75.41; H, 5.19; N, 7.65. Found: C,
75.23; H, 5.27; N 7.59%.
1
79 °C. H-NMR (CDCl3, 25 °C): the enol isomer, l=
13.90 (s, 1H, OH), 8.41 (d, 3J=4.8 Hz, 1H; azain), 8.07
2.3. Synthesis of Al(CH3)(acac-azain)2 (2)
3
(d zH, J=4.2 Hz, 1H; azain), 7.92 (m zH, 1H; azain),
7.56 (s, 1H; CꢀCꢁH), 7.21 (m, 1H; azain), 6.65 (m, 1H;
After a solution of acac-azainH (1.212 g, 6 mmol) in
35 ml of toluene was cooled down to −78 °C in an
acetone–liquid nitrogen bath, 1 ml of Al(CH3)3 (2
mmol, 2 M solution in toluene) was added dropwise.
The mixture was stirred at −78 °C for 2 h, and then
warmed to ambient temperature and stirred overnight.
The solution was concentrated by vacuum. White pre-
cipitate was recrystallized from toluene–hexanes to af-
azain), 2.23 (s, 3H; CH3); the diketone isomer: 8.32 (d
3
3
zH, J=4.5 Hz, 1H; azain), 8.02 (d zH, J=3.9 Hz,
1H; azain), 7.92 (m zH, 1H; azain), 7.21 (m, 1H; azain),
6.65 (m, 1H; azain), 4.65 (s, 2H; CH2), 2.43 (s, 3H;
CH3). Anal. Calc. for C11H10N2O2: C, 65.35; H, 4.95;
N, 13.86. Found: C, 65.42; H, 4.98; N, 13.92%.
1
ford white crystals of 2 (0.795 g, yield 89%). H-NMR
2.2. Synthesis of BPh2(acac-azain) (1)
(CDCl3, 25 °C): l=8.440 (m, 2H, azain), 8.06 (m, 2H,
azain), 7.88 (m, 2H, azain), 7.63, 7.62, 7.61 (s zH, 2H,
CꢀCꢁH), 7.19 (m, 2H, azain), 6.50 (m, 2H, azain), 2.31,
2.29, 2.28 (s, 6H, CꢁCH3), 0.089 (s, 3H, AlꢁCH3). Anal.
Calc. for C23H21O4N4Al: C, 62.16; H, 4.73; N, 12.61.
Found: C, 61.58; H, 4.26; N, 12.42%.
Triphenylboron (0.121 g, 0.5 mmol) was added to a
solution of acac-azainH (0.100 g, 0.5 mmol) in 15 ml of
THF. The mixture was stirred and refluxed for 4 h.
Table 1
Crystal data and structure refinement parameters
2.4. X-ray crystallography analysis
Compound
Acac-azainH
1
All crystals were mounted on glass fibers. The data
for acac-azainH and 1 were collected on a Bruker
Empirical formula
Formula weight
Space group
C11H10N2O2
202.21
P21/c
C
366.21
P21/c
23H19BN2O2
SMART CCD 1000 X-ray diffractometer and
a
Siemens P4 X-ray diffractometer, respectively, with
graphite-monochromated Mo–Ka radiation, operating
at 50 kV and 30 mA at 293 K. The data collection
range over 2q is 5.10–56.58° for acac-azainH and 4.12–
50.00° for 1, respectively. No significant decay was
observed during the data collection. Data were pro-
cessed on a Pentium PC using the Bruker AXS Win-
dows NT SHELXTL software package (version 5.10) [5].
Neutral atom scattering factors were taken from
Cromer and Waber [6]. Empirical absorption correc-
tions were applied for both crystals. Crystals of both
acac-azainH and 1 belong to the monoclinic space
group P21/c. The structures were solved by direct meth-
ods. All non-hydrogen atoms were refined anisotropi-
cally. The positions of hydrogen atoms for acac-azainH
were located directly from the difference Fourier maps.
The hydrogen atoms in 1 were either determined di-
rectly from the difference Fourier maps or calculated.
The crystal data are summarized in Table 1. Selected
bond lengths and angles for acac-azainH and 1 are
given in Table 2.
,
a (A)
7.6053(14)
13.267(3)
10.049(2)
90
93.331(4)
90
1012.2(3)
4
1.327
294
0.94
56.58
7271
9.978(3)
13.283(5)
14.457(4)
90
96.85(2)
90
1902.6(10)
4
1.279
296
0.81
50
3547
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
T (K)
)
v (cm−1
)
2q, max (°)
Reflections measured
Reflections used
Parameters
2416
176
3343
253
Final R [I\2|(I)]
R1 a=0.0378
wR2 b=0.1067
R1=0.0587
wR2=0.1157
1.040
R1=0.0513
wR2=0.1164
R1=0.0904
wR2=0.1370
1.018
R (all data)
Goodness-of-fit on F2
a R1=SꢀFoꢀ−ꢀFcꢀ/SꢀFoꢀ.
b wR2=[Sw[(Fo2−Fc2)2]/S[w(F2o)2]]1/2
where P=[max(F2o, 0)+2Fc2]/3.
.
w=1/[|2(F2o)+(0.075P)2],

D. Song et al. / Journal of Organometallic Chemistry 631 (2001) 175–180
177
Table 2
,
C(10)ꢁO(2) distances of 1.2118(5) and 1.2127(14) A are
typical of CꢁO double bond lengths, supporting the
diketone structure. The two carbonyl groups of the
diketone are oriented away from each other. One of the
carbonyl groups, adjacent to the indole ring, is copla-
nar with the 7-azaindolyl portion. The N(1)ꢁC(8) bond
,
Selected bond lengths (A) and angles (°)
Acac-azainH
Bond lengths
O(1)ꢁC(8)
O(2)ꢁC(10)
C(8)ꢁC(9)
C(9)ꢁC(10)
C(10)ꢁC(11)
N(1)ꢁC(8)
Bond angles
1.2118(15)
1.2127(14)
1.4876(19)
1.5129(17)
1.483(2)
C(1)ꢁN(1)ꢁC(8)
C(1)ꢁN(1)ꢁC(7)
C(8)ꢁN(1)ꢁC(7)
O(1)ꢁC(8)ꢁN(1)
O(1)ꢁC(8)ꢁC(9)
N(1)ꢁC(8)ꢁC(9)
O(2)ꢁC(10)ꢁC(11)
O(2)ꢁC(10)ꢁC(9)
C(11)ꢁC(10)ꢁC(9)
O(2)ꢁC(10)ꢁC(11)
122.11(12)
106.67(12)
131.22(10)
118.79(13)
122.72(13)
118.48(11)
122.83(13)
120.65(11)
116.51(12)
122.83(13)
,
length of 1.4068(17) A is much shorter than a single
bond length, indicative of the conjugation of the car-
bonyl group with the indole ring. The C(9) atom has a
typical tetrahedral geometry, and the C(8)ꢁC(9) and
C(9)ꢁC(10) bond lengths are typical of single bonds,
consistent with the diketone structure. The behavior of
acac-azainH in solution was examined by 1H-NMR
spectroscopy, which revealed that in solution the dike-
tone form and the enol form are in equilibrium with the
diketone form being the dominant species (ꢀ3:1 ratio).
The diketone form of the acac-azainH molecule is
clearly stabilized by the conjugation of the C(8) car-
bonyl group with the indole ring, as shown by the
crystal structure. The acac-azainH molecule is not sta-
ble in alcohol solution, especially in the presence of
base, which catalyzes the substitution of the 7-azain-
dolyl group in acac-azainH by an alkoxy group to form
the corresponding ester. Similar substitution reactions
for 1,3-diketone molecules have been well documented
[8].
1.4068(17)
1
Bond lengths
O(2)ꢁB(1)
C(7)ꢁB(1)
C(1)ꢁB(1)
O(1)ꢁB(1)
O(2)ꢁC(16)
O(1)ꢁC(14)
N(1)ꢁC(16)
C(16)ꢁC(15)
C(14)ꢁC(15)
C(14)ꢁC(13)
Bond angles
1.546(3)
1.596(3)
1.605(3)
1.528(3)
1.288(3)
1.294(3)
1.382(3)
1.384(3)
1.374(3)
1.488(3)
C(16)ꢁN(1)ꢁC(17)
C(16)ꢁN(1)ꢁC(23)
C(17)ꢁN(1)ꢁC(23)
O(2)ꢁC(16)ꢁN(1)
O(2)ꢁC(16)ꢁC(15)
N(1)ꢁC(16)ꢁC(15)
O(1)ꢁC(14)ꢁC(15)
O(1)ꢁC(14)ꢁC(13)
C(15)ꢁC(14)ꢁC(13)
O(1)ꢁB(1)ꢁO(2)
O(1)ꢁB(1)ꢁC(7)
O(2)ꢁB(1)ꢁC(7)
O(1)ꢁB(1)ꢁC(1)
O(2)ꢁB(1)ꢁC(1)
C(7)ꢁB(1)ꢁC(1)
C(2)ꢁC(1)ꢁC(6)
C(2)ꢁC(1)ꢁB(1)
C(6)ꢁC(1)ꢁB(1)
C(12)ꢁC(7)ꢁC(8)
C(12)ꢁC(7)ꢁB(1)
C(8)ꢁC(7)ꢁB(1)
123.68(19)
128.83(19)
107.42(19)
113.7(2)
122.6(2)
123.7(2)
122.4(2)
115.3(2)
122.3(2)
106.60(17)
108.27(19)
107.43(19)
109.19(19)
108.70(19)
116.23(19)
115.7(2)
120.2(2)
124.2(2)
116.1(2)
121.2(2)
3.1.2. The complexes of acac-azain
Two novel coordination compounds of acac-azain
have been obtained, namely BPh2(acac-azain) (1) and
Al(CH3)(acac-azain)2 (2). Compound 1 was obtained by
the reaction of acac-azainH with BPh3 in a 1:1 ratio
while compound 2 was obtained from the reaction of
acac-azainH with Al(CH3)3 in a 3:1 ratio, intended for
the synthesis of Al(acac-azain)3. Our attempts to syn-
thesize Al(acac-azain)3 by using excess acac-azainH
were unsuccessful, which, we believe, is likely due to the
steric hindrance imposed by the coordinated acac-azain
122.6(2)
Scheme 1.
3. Results and discussion
3.1. Syntheses and structures
3.1.1. The acac-azainH molecule
The synthesis of the acac-azainH ligand was carried
out using a modified literature method reported previ-
ously for related compounds[7] in high yield (Scheme
1). The structure of acac-azainH was determined by a
single-crystal X-ray diffraction analysis. It is well
known that 1,3-diketone molecules have two isomeric
forms—the enol form and the diketone form. As
shown in Fig. 1, the acac-azainH molecule adopts the
diketone form in the solid state. The C(8)ꢁO(1) and
Fig. 1. A diagram showing the structure of acac-azainH with 50%
thermal ellipsoids and labeling schemes.

178
D. Song et al. / Journal of Organometallic Chemistry 631 (2001) 175–180
,
C(15)ꢁC(16) bond lengths (1.374(3) and 1.384(3) A) of
the acac-azain ligand are much shorter than the corre-
sponding ones in the free neutral ligand and are typical
of chelated acac and acac* ligands.
1
Compound 2 was characterized by H-NMR spec-
troscopy and elemental analysis. In solution, compound
2 appears to exist in several isomeric forms, as evi-
denced by the observation of three C–CH3 chemical
shifts (in ꢀ1:1:2 ratio) and three ꢁCꢀCꢁH chemical
1
shifts (in ꢀ1:2:1 ratio) in the H-NMR spectrum of 2
(Only one AlꢁCH3 chemical shift is observed, which
may be due to accidental overlap or the insensitivity of
the AlꢁCH3 group to the location of the 7-azaindolyl
group.). We believe that compound 2 is most likely a
five-coordinate mononuclear species. The most com-
mon coordination geometry for five-coordinate Al(III)
complexes with monodentate or bidentate ligands is
trigonal bipyramidal (tbp) [2a,14]. Assuming that com-
pound 2 adopts the tbp geometry, three geometric
isomers are possible, as shown in Scheme 2. The most
Fig. 2. A diagram showing the structure of 2 with 50% thermal
ellipsoids and labeling schemes.
ligands that prevent the replacement of the third methyl
group. Compound 1 was fully characterized by 1H-
NMR spectroscopy, elemental and single-crystal X-ray
diffraction analyses. Attempts to obtain single-crystals
of 2 were unsuccessful.
1
plausible explanation of the H-NMR spectrum of 2 is
that isomers A and B (Isomer C is the least likely
because of the steric interactions between the two 7-
azaindolyl groups.) coexist in solution. This could also
explain the fact that we have not been able to grow
single-crystals of 2.
The structure of 1 is shown in Fig. 2. The boron
center of 1 has a tetrahedral geometry, similar to those
displayed by BPh2(mqp) and BR2(q) compounds [9,10]
(mqp=2-(4%-methylquinolinyl)-2-phenolato, q=8-hy-
droxylquinolinato). The BꢁC and BꢁO bond lengths are
comparable to those of previously known boron com-
pounds [11–13]. Several crystal structures of diketone
boron compounds have been reported previously [15].
The acac-azain ligand chelates to the boron center
through both oxygen atoms in a typical acac fashion,
forming a six-membered chelate ring with the boron
center. The C(16)ꢁN(1) bond that connects the 7-azain-
dolyl portion with the diketone portion, is shorter than
that of the free neutral ligand. The C(14)ꢁC(15) and
3.1.3. Luminescence
7-Azaindole emits at 360 nm in solution (toluene or
CH2Cl2) and the solid state. In contrast, the acac-
azainH molecule has a broad emission band at u=420
nm in the solid state (excitation at 360 nm), and at
u=429 nm in solution (CH2Cl2, excitation at 306 nm),
as shown in Fig. 3. The excitation band in solution has
ꢀ50 nm blue-shift with respect to that of the solid.
Although the acac-azainH is blue luminescent, it has a
Scheme 2.

D. Song et al. / Journal of Organometallic Chemistry 631 (2001) 175–180
179
to be visibly brighter than compound 1, with the emis-
sion maximum at u=460 nm in solution (CH2Cl2,
excitation at 397 nm). Due to the poor stability of 2, a
reliable quantum yield for 2 could not be obtained. In
the solid state, compound 2 has a broad emission band,
covering 320–560 nm, with the maximum at u=364
nm (excitation at 320 nm) (Fig. 5). Many factors such
as inter-molecular interactions (No parallel p–p stack-
ing was observed in the crystal lattice of 1.) and the
formation of exciplexes could contribute to the ob-
served spectral difference from solution to the solid
state for compounds 1 and 2. The detail is however yet
to be understood.
Previously we have demonstrated that the attachment
of 7-azaindolyl to organic units other than carbonyl
groups, such as phenyl, biphenylyl, or pyridyl, resulted
in the formation of very bright blue luminescent or-
ganic molecules [2f,15]. The unexpected poor emission
efficiency of the acac-azainH molecule and compound 1
is therefore likely caused by the carbonyl groups of the
diketone portion, that perhaps quenches the lumines-
cence of the attached 7-azaindolyl group. The poor
emission efficiency of 1 and the poor stability of 2 make
them unsuitable as emitters for electroluminescent
devices. Therefore, we did not carry out the study of
their performance in electroluminescent devices.
Fig. 3. Excitation and emission spectra of acac-azainH.
In summary, we have demonstrated that the novel
acac-azain ligand is capable of chelating to Al(III) and
B(III) centers but the resulting complexes display blue
luminescence that is too weak for practical applications.
Fig. 4. Excitation and emission spectra of 1.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 164267 and 164268 for acac-
azainH and compound 1, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
Fig. 5. Excitation and emission spectra of 2.
We thank the Natural Sciences and Engineering Re-
search Council of Canada and the Xerox Research
Foundation for financial support.
very low emission efficiency (quantum yield=0.68%,
relative to that of 9,10-diphenylanthracene). The boron
complex 1 has very weak blue luminescence in solution
and the solid state. The emission band maximum of 1 is
at u=419 nm in solution (CH2Cl2, excitation at 295
nm) and u=470 nm in the solid state (excitation at 415
nm) (Fig. 4). The quantum yield of 1 was determined to
be 0.07%, relative to that of 9,10-diphenylanthracene.
The luminescence of the aluminum complex 2 appears
References
[1] (a) C.H. Chen, J. Shi, Coord. Chem. Rev. 171 (1998) 161;
(b) N.X. Hu, M. Esteghamatian, S. Xie, Z. Popovic, A.M. Hor,
B. Ong, S. Wang, Adv. Mater. 11 (1999) 17;

180
D. Song et al. / Journal of Organometallic Chemistry 631 (2001) 175–180
(b) L.G. Hubert-Pfalzgraf, N. Miele-Pajot, R. Papiernik, J.
(c) J.F. Wang, G.E. Jabbour, E.A. Mash, J. Anderson, Y.
Zhang, P.A. Lee, N.R. Armstrong, N. Peryhambarian, B. Kippe-
len, Adv. Mater. 11 (1999) 1266;
Vaissermann, J. Chem. Soc. Dalton Trans. (1999) 4127.
[9] S.F. Liu, C. Seward, H. Aziz, N.X. Hu, Z. Popovic, S. Wang,
Organometallics 19 (2000) 5709.
(d) Y. Kim, J.G. Lee, S. Kim, Adv. Mater. 11 (1999) 1463.
[10] Q Wu, M. Esteghamatian, N.H. Hu, Z. Popovic, G. Enright, Y.
Tao, M. D’Iorio, S. Wang, Chem. Mater. 12 (2000) 79.
[11] (a) K. Niedenzu, H. Deng, D. Knoeppel, J. Krause, S.G. Shore,
Inorg. Chem. 31 (1992) 3162;
[2] (a) W. Liu, A. Hassan, S. Wang, Organometallics 16 (1997)
4257;
(b) S. Gao, Q. Wu, G. Wu, S. Wang, Organometallics 17 (1998)
4666;
(c) J. Ashenhurst, G. Wu, S. Wang, J. Am. Chem. Soc. 122
(2000) 2541;
(d) J. Ashenhurst, S. Wang, G. Wu, J. Am. Chem. Soc. 122
(2000) 3528;
(e) Q. Wu, M. Esteghamatian, N.X. Hu, Z. Popovic, G. Enright,
S.R. Breeze, S. Wang, Angew. Chem. Int. Ed. 38 (1999) 985;
(f) Q. Wu, J.A. Lavigne, Y. Tao, M. D’Iorio, S. Wang, Inorg.
Chem. 39 (2000) 5248.
(b) L.Y. Hsu, J.F. Mariategui, K. Niedenzu, S.G. Shore, Inorg.
Chem. 26 (1987) 143;
(c) W. Kiegel, G. Lubkowitz, S.J. Rettig, J. Trotter, Can. J.
Chem. 69 (1991) 234, 1217, 1227.
[12] (a) G. Heller, Top. Curr. Chem. 131 (1986) 39;
(b) A. Dal Negro, L. Ungaretti, A. Perotti, J. Chem. Soc. Dalton
Trans. (1972) 1639;
(c) H. Binder, W. Matheis, H.-J. Deiseroth, F.-S. Han, Z.
Naturforsch. Sect. B 39 (1984) 1717;
[3] (a) K.C. Joshi, V.N. Pathak, Coord. Chem. Rev. 22 (1977) 37;
(b) J.P. Fackler Jr., Prog. Inorg. Chem. 7 (1966) 362;
(c) D.P. Graddon, Coord. Chem. Rev. 4 (1969) 1;
(d) R.C. Mehrotra, R. Bohra, D.P. Gaur, Metal b-Diketonates
and Allied Derivatives, Academic Press, New York, 1978;
(e) R.E. Sievers, K.J. Eisentraut, C.S. Springer Jr., in: R.F.
Gould (Ed.), Lanthanide/Actinide Chemistry, American Chemi-
cal Society, Washington, DC, 1967 Chapter 11.
[4] K. Yanagi, H. Okada, T. Kato, Jpn. Kokai Tokkyo Koho
(2000) Patent, JP 2000159777.
(d) W. Clegg, N. Noltemeyer, G.M. Shelderick, W. Maringgele,
A. Meller, Z. Naturforsch. Sect. B 35 (1980) 1499.
[13] (a) H. Hopfl, N.P. Hernandez, S.R. Lima, R. Santillan, N.
Farfan, Heteroat. Chem. 9 (1998) 359;
(b) A.T. Balaban, I. Haiduc, H. Hopfl, N. Farfan, R. Santillan,
Main Group Met. Chem. 19 (1996) 385.
[14] (a) S.J. Trepanier, S. Wang, Organometallics 15 (1996) 760;
(b) S.J. Trepanier, S. Wang, Can. J. Chem. 74 (1996) 2032;
(c) S.J. Trepanier, S. Wang, J. Chem. Soc. Dalton Trans. (1995)
2425;
[5] SHELXTL NT Crystal Structure Analysis Package, Version 5.10;
Bruker Axs, Analytical X-ray System, Madison, WI, 1999.
[6] D.T. Cromer, J.T. Waber, International Tables for X-ray Crys-
tallography, vol. 4, Kynoch Press, Birmingham, UK, 1974 Table
2.2A.
[7] J.W. Williams, J.A. Krynitsky, Org. Synth. Collect. 3 (1955) 10,
Wiley, New York.
[8] (a) R.T. Morrison, R.N. Boyd, Organic Chemistry, 5th edn,
Boston, Allyn and Bacon Inc, 1987 Chapter 24;
(d) S.J. Trepanier, S. Wang, Angew. Chem. Int. Ed. Engl. 33
(1994) 1265;
(e) G. Perego, G. Dozzi, J. Organomet. Chem. 74 (1996) 2032;
(f) G. Mu¨ller, C. Kru¨ger, Acta Crystallogr. C40 (1984) 628;
(g) S.J. Trepanier, S. Wang, Organometallics 13 (1994) 2213;
(h) J. Ashenhurst, L. Brancaleon, A. Hassan, W. Liu, H.
Schmider, S. Wang, Q.G. Wu, Organometallics 17 (1998) 3186.
[15] Q. Wu, J.A. Lavigne, Y. Tao, M. D’Iorio, S. Wang, Chem.
Mater. 13 (2001) 71.
.