Phenyl bismuth β-diketonate complexes: Synthesis and structural characterization

Article abstract of DOI:10.1016/j.jorganchem.2009.04.036

The first examples of arylbismuth diketonate complexes are reported. Phenylbismuth(III) bis(hexafluoroacetylacetonate), BiPh(hfac)₂ (1) and its adducts [BiPh(hfac)₂(L)] (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; L = H₂O (1a), Me₂CO (1b), THF (1c), DMA (N,N-dimethylacetamide) (1d), DMSO (1e), PhCN (1f), as well as a mixed hexafluoroacetylacetonate-trifluoroacetate complex, [BiPh(hfac)(O₂CCF₃)]₂ (2), have been synthesized and characterized. Compound 1 is isolated from the reaction of BiPh₃ with 2 equiv. of Hhfac in dry hexanes. Compound 2 can be synthesized using two different routes: one utilizes the reaction between stoichiometric amounts of 1 and CF₃CO₂H, while the second method involves the interaction of the previously described BiPh₂(O₂CCF₃) (3) with Hhfac. Crystallographic analysis of the [BiPh(hfac)₂(L)] adducts reveals a pentagonal pyramidal geometry around the metal center; similarly, the dinuclear [BiPh(hfac)(O₂CCF₃)]₂ complex is composed of two distorted pentagonal pyramids connected into dimers by the bridging carboxylate groups. The effect of replacing the Lewis base in the coordination sphere of Bi(III) on the coordination polyhedron and crystal packing is discussed. The ¹H and ¹⁹F NMR spectra of the title complexes at room temperature indicate single environments for the hfac group and suggest that they are fluxional in solutions on the NMR time scale. Compounds 1 and 2 are promising starting materials in the chemistry of bismuth(III) and as building blocks for the construction of heterometallic species.

Full text of DOI:10.1016/j.jorganchem.2009.04.036

Journal of Organometallic Chemistry 694 (2009) 2956–2964
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Phenyl bismuth b-diketonate complexes: Synthesis and structural characterization
1
*
Vitalie Stavila , Evgeny V. Dikarev
Department of Chemistry, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The first examples of arylbismuth diketonate complexes are reported. Phenylbismuth(III) bis(hexafluoro-
acetylacetonate), BiPh(hfac)2 (1) and its adducts [BiPh(hfac)2(L)] (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pen-
tanedione; L = H2O (1a), Me2CO (1b), THF (1c), DMA (N,N-dimethylacetamide) (1d), DMSO (1e), PhCN
(1f), as well as a mixed hexafluoroacetylacetonate–trifluoroacetate complex, [BiPh(hfac)(O2CCF3)]2 (2),
have been synthesized and characterized. Compound 1 is isolated from the reaction of BiPh3 with 2 equiv.
of Hhfac in dry hexanes. Compound 2 can be synthesized using two different routes: one utilizes the reac-
tion between stoichiometric amounts of 1 and CF3CO2H, while the second method involves the interac-
tion of the previously described BiPh2(O2CCF3) (3) with Hhfac. Crystallographic analysis of the
[BiPh(hfac)2(L)] adducts reveals a pentagonal pyramidal geometry around the metal center; similarly,
the dinuclear [BiPh(hfac)(O2CCF3)]2 complex is composed of two distorted pentagonal pyramids con-
nected into dimers by the bridging carboxylate groups. The effect of replacing the Lewis base in the coor-
Received 15 March 2009
Received in revised form 24 April 2009
Accepted 24 April 2009
Available online 6 May 2009
Keywords:
Bismuth(III)
b-Diketonates
Crystal structure
Mixed-ligand complexes
Aryl-metal compounds
dination sphere of Bi(III) on the coordination polyhedron and crystal packing is discussed. The 1H and 19
F
NMR spectra of the title complexes at room temperature indicate single environments for the hfac group
and suggest that they are fluxional in solutions on the NMR time scale. Compounds 1 and 2 are promising
starting materials in the chemistry of bismuth(III) and as building blocks for the construction of hetero-
metallic species.
Published by Elsevier B.V.
1. Introduction
The interest in bismuth(III) b-diketonates has mainly arisen
from their utility in different CVD processes. b-Diketonate com-
Despite of the fact that metal b-diketonates represent one of the
oldest and most studied classes of coordination compounds, there
is a continuous interest in exploring their synthesis and properties.
These compounds are useful in a number of applications, mainly
due to their high volatility and solubility in common organic sol-
vents. b-Diketonates proved themselves as very versatile chelating
ligands to form stable complexes with almost all metal ions,
including such electropositive elements as the alkali-earth [1,2]
or lanthanide metals [2,3]. High volatility of metal b-diketonates
is associated with an efficient shielding of the positively charged
metal ions from the intermolecular interactions by surrounding
hydrocarbon or fluorocarbon shells [2]. It is known that in addition
to their ability to chelate the metal ions, b-diketonates can also ful-
fill bridging functions. The degree of oligomerization depends on
many factors, including the nature of the metal ion and the elec-
tronic and steric effects of the ligands. Large metal ions with pro-
nounced electron deficiency tend to favor bridging linkages over
terminal ones, however this tendency is substantially or fully re-
duced in the presence of Lewis bases.
plexes are usually synthesized by methods similar to those de-
scribed for the alkoxides [4]. The metathesis reaction of bismuth
halides with alkali metal salts of the corresponding diketones has
been successfully employed to produce Bi(III) diketonates, how-
ever additional purification steps are usually required to remove
possible halide contamination. An alternative approach is the acid-
olysis reaction of triphenylbismuth with b-diketones. The latter
reaction can be performed in an appropriate solvent or solventless.
The crystal structures of bismuth(III) b-diketonates have been
shown to exhibit considerable diversity. As a consequence of the
pronounced Lewis acidity of the bismuth atom and the Lewis basic
behavior of the diketonate ligands, there is a remarkable tendency
to form oligomers or polymers with one or several bridging atoms.
Thus, in two of the most studied bismuth(III) compounds from this
class, Bi(hfac)3 [5] and Bi(thd)3 [6,7] (Hthd = 2,2,6,6-tetramethyl-
3,5-heptanedione), the ligands display strong chelating and rela-
tively weaker bridging functions; the latter function is responsible
for the assembly of the two complexes into dimers through BiꢀꢀꢀO
interactions. Recently, new research directions have emerged for
bismuth(III) b-diketonate complexes, such as their use in assembly
of heterometallic complexes [5] and polynuclear oxo-clusters [8].
While the chemistry of tris-diketonate bismuth complexes is
well developed, no data are available on the corresponding arylbis-
muth diketonate compounds. These compounds are likely formed
* Corresponding author. Fax: +1 518 442 3462.
E-mail address: dikarev@albany.edu (E.V. Dikarev).
1
Present address: Sandia National Laboratories, 7011 East Avenue, Livermore, CA
94550, United States.
0022-328X/$ - see front matter Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2009.04.036

V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
2957
as intermediates during the reaction of BiPh3 with the correspond-
ing b-diketones. However, their isolation may present difficulties
due to possible formation of polymeric species. This could be due
in part to the large size of Bi(III) (ionic radius 1.03 Å), which allows
for high coordination numbers without significant steric con-
straints, thus favoring the association of Bi(III) centers. In order
to control the oligomerization process, one possibility is to use
the idea of ‘‘solvent control”. In this approach a coordinating sol-
vent forms a stable adduct with the corresponding metal ion, pre-
venting bridging interactions. We attempted to perform the
reaction of BiPh3 with 2 equiv. Hhfac in hexane with subsequent
addition of some coordinating molecules. In this paper, we report
the synthesis and characterization of phenylbismuth(III) hexafluo-
roacetylacetonate, (1), and its adducts [BiPh(hfac)2(L)] (1a–1f), as
well as a dimeric hexafluoroacetate–trifluoroacetate complex,
[BiPh(hfac)(O2CCF3)]2 (2), obtained by two different synthetic pro-
cedures (Scheme 1).
The thermal decomposition of the complexes was investigated
by TGA and the residues were analyzed by X-ray powder diffrac-
tion (XRPD). In all cases, it was found that the compounds undergo
thermal decomposition in two or three stages upon heating and do
not exhibit any apparent mass loss of the diketonates due to sub-
limation. The thermogravimetric plots for 1, 1c and 1e (Fig. 1) are
qualitatively similar in stages of weight loss up to 550 °C. The re-
lease of coordinated Lewis base molecules in the adducts is not ob-
served as a separate step. Compound 1 displays a sharp melting
point at 82–83 °C. The decomposition of 1 proceeds in several steps
and is punctuated by an abrupt mass loss (ꢂ62%) between 195 and
340 °C. The XRPD study of the residue resulted upon thermal
decomposition of 1 in Ar probed the formation of a complex mix-
ture with BiOF being a major phase. The formation of BiOF upon
thermal treatment of fluorine-containing bismuth(III) compounds
has been previously reported in the literature [12,13]. The thermal
decomposition of the adducts 1a–1f somewhat mirrors what was
observed for the thermolysis of 1. In each case, the thermal decom-
position of the complex proceeds in several steps with an abrupt
mass loss that includes removal of the corresponding neutral li-
gand. Interestingly, the thermolysis of 1, 1a–1f and 2 in air at
2. Results and discussion
Triphenylbismuth reacts upon reflux with 2 equiv. of hexaflu-
oroacetylacetone in dry hexanes to produce a yellow solution. Par-
tial removal of the solvent in vacuum and cooling down the
concentrated solution to ꢁ20 °C provides microcrystalline powder
of BiPh(hfac)2 (1), as confirmed by spectroscopic and elemental
analyses. Attempts to grow single crystals of 1 from non-coordinat-
ing solvents were unsuccessful. In the presence of coordinating sol-
vents it turned out that 1 can easily form monoadducts. Thus,
yellow crystalline solids of the corresponding adducts 1a–1f can
be isolated from hexanes solution of 1 in the presence of small
amounts of H2O (1a), Me2CO (1b), THF (1c), DMA (1d), DMSO
(1e), and PhCN (1f). Complex 2 was obtained by subsequent addi-
tion of 1 equiv. of Hhfac and 1 equiv. of trifluoroacetic acid to BiPh3
in hexanes. The same compound can be obtained in a lower yield
from the reaction of BiPh2(O2CCF3) (3) (synthesized as described
in [9]) with 1 equiv. of Hhfac (Scheme 1). All isolated b-diketonate
complexes appear as yellow–orange, air-sensitive, shiny crystalline
solids. They are sparingly soluble in methanol, acetone, diclorome-
thane and chloroform, but less so in diethylether and hydrocar-
bons. The newly-synthesized compounds were characterized by
IR and NMR spectroscopy as well as by single-crystal X-ray diffrac-
tion. The IR spectra exhibit, as expected, the corresponding C@O
hfacꢁ stretches in the range of 1634–1640 cmꢁ1. These bands are
at significantly lower energies than those found for free Hhfac
(1689 cmꢁ1) and are indicative of b-diketonate chelation to Bi(III).
The 1H and 19F NMR spectra of the isolated complexes at room
temperature revealed single environments for the hfacꢁ group sug-
gesting that the diketonate ligands are able to undergo ligand ex-
change processes at a rate that is fast on the NMR time scale.
The ortho, meta, and para-protons of the phenyl group are cen-
tered at ꢂ8.2–8.3 ppm (d), ꢂ7.9–8.0 ppm (t), and ꢂ7.4–7.5 ppm
(t), respectively. The 1H NMR spectra contain no signals of the di-
and triarilated species, which does not support the occurrence of
aryl redistribution reactions. Such reactions are commonly
encountered in the solution chemistry of arylantimony and aryl-
bismuth complexes [10,11].
550 °C for 1 h resulted exclusively in monoclinic a-Bi2O3 (Fig. 2).
The molecular structures of compounds 1a–1f and 2 were
established by single-crystal X-ray diffraction. X-ray quality crys-
tals can be grown directly from the reaction mixtures. All com-
pounds were found to crystallize in the monoclinic crystal
system (P21/c, P21/n or C2/c space groups). The BiPh(hfac)2L ad-
ducts adopt a pentagonal pyramidal geometry with the metal cen-
ter coordinated by the phenyl group, two chelating b-diketonate
Fig. 1. TGA curves of 1 (——), 1c (————) and 1e (ꢀꢀꢀꢀꢀꢀꢀ).
+2Hhfac
-2PhH
+ L
BiPh3
[BiPh(hfac)2]
[BiPh(hfac)2(L)]
+Hhfac
(1)
(2)
+CF3CO2H
-2PhH
BiPh3 + Hhfac
[BiPh(hfac)(O2CCF3)]
[BiPh2(O2CCF3)]
-PhH
Legend: Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione;
L = H2O, Me2CO, THF, DMA, DMSO, PhCN.
Fig. 2. X-ray powder diffraction pattern of the decomposition product of 1 in air
Scheme 1.
and its comparison to a-Bi2O3 phase, JCPDS No. 00-041-1449.

2958
V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
ligands, and a terminal monodentate O- or N- neutral donor. Com-
plex 2 represents a dimer formed by bridging trifluoroacetate
groups. The carboxylate ligand acts in an aniso-bidentate coordina-
tion mode [14,15] to one Bi atom and also performs a bridging
function to the other Bi(III) center of the dimer. The coordination
environment of the six-coordinate bismuth centers in 1a–1f and
2 are best described as pentagonal pyramidal. A void, presumably
occupied by a stereochemically active lone electron pair (SALEP),
can be identified in the coordination polyhedron (Scheme 2). In
other structurally characterized monoaryl-bismuth complexes,
the SALEP is directed opposite to the ipso carbon of the phenyl
group [10]. In terms of the terminology introduced by Shimoni-Liv-
ny et al. [16], the geometry of Bi(III) in 1a–1f and 2 can be regarded
as hemidirected, with a gap in the coordination sphere, as opposed
to holodirected coordination, in which the bonds are directed
throughout the globe of the coordination sphere.
The aryl ligand occupies the apical position of the bismuth coor-
dination sphere, while the basal plane is completed by five oxygen
donors for complexes 1a–1e and 2, or four oxygen and one nitro-
gen donor in complex 1f (Figs. 3–9). The equatorial plane in 1a–
1f is formed by two chelating b-diketonate ligands and a coordi-
nated Lewis base molecule. Complex 2 represents an example of
the relatively rare Bi(III) complexes containing three different sub-
stituents. Each Bi atom in the dimeric unit of 2 is surrounded in the
equatorial plane by two O atoms from one hfac ligand, two O
atoms of a bridging carboxylate group, and one O atom from the
carboxylate ligand attached to the second bismuth atom. The coor-
dination environment of the Bi(III) centers in 2 represents two
fused pentagonal pyramids, similar to those found in 1a–1e, shar-
ing one common edge and connecting O(22) and O(22A) atoms.
Fig. 8 represents this type of coordination polyhedron in 1a com-
pared with the corresponding Bi(III) polyhedra in 2. The open site
Fig. 4. Coordination environment of Bi(III) in 1b.
Scheme 2.
Fig. 5. Coordination environment of Bi(III) in 1c.
of the pyramid, opposed to the aryl group is believed to accommo-
date a SALEP, in which case the coordination polyhedron of Bi(III)
in compounds 1a–1e and 2 could be described as a
w-pentagonal
bipyramid [15] (Fig. 10).
The overall crystal structures of the phenylbismuth diketonate
complexes 1a–1f and 2 are shown in Figs. 3–9, with selected bond
lengths and angles given in Table 2. The Bi–Caryl bond distances in
1a–1f and 2 are within 2.229(5)–2.242(5) Å range, comparable to
those found in other arylbismuth carboxylates [10,17–20]. These
distances are slightly shorter than the average Bi–Caryl bond dis-
tance reported for BiPh3, 2.268 Å [17]. The sum of valence angles
in the equatorial plane of the bipyramid in 1a–1f and
2
(358.9(1)–360.1(2)°) is close to 360°. The Bi(1) atoms in 1a–1e
form two chelate metallocycles Bi(1)O(11)C(12)C(13)C(14)O(12)
and Bi(1)O(21)C(22)C(23)C(24)O(22) with the Bi–O bond distances
between 2.380(4) and 2.518(4) Å. The oxygen atom of the coordi-
nated water molecule in 1a is at 2.456(4) Å, which is shorter than
most of the Bi–Owater bond lengths in bismuth(III) complexes. The
shortest Bi–O distance in 1a–1e is found in the DMA adduct 1d
Fig. 3. Coordination environment of Bi(III) in 1a; thermal ellipsoids are shown at
40% probability level. Only one orientation of the fluorine atoms is depicted.

V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
2959
Fig. 6. Coordination environment of Bi(III) in 1d.
Fig. 8. Coordination environment of Bi(III) in 1f.
Fig. 9. Coordination environment of Bi(III) in 2.
Fig. 7. Coordination environment of Bi(III) in 1e.
(2.331(5) Å), while the longest belongs to the THF adduct 1c
(2.517(3) Å). The Bi–N bond in 1f is 2.703(4) Å, which is slightly
longer than the typical Bi–N coordination bonds. This weak Bi–N
bond is situated in trans position relative to the O(12)–Bi(1)–
O(21) angle.
The Bi–O chelating bonds with the hfac ligand in 2 are asym-
metric (2.278(4) and 2.385(3) Å) and are shorter than the average
value of such bonds found in 1a–1f (2.436 Å). The trifluoroacetate
anion acts in a tridentate-bridging fashion connecting the neigh-
boring bismuth atoms into dimeric units. The Bi(1) atom in 2 is
chelated by the oxygen atoms of the O(21)C(22)O(22) carboxylate
group (Bi–O 2.399(4) and 2.761(4) Å), while the bridging bond Bi–
O(22A) is 2.627(4) Å (Fig. 9). As a result, complex 2 shows the larg-
est distribution in the length of the Bi–O bond distances among the
complexes under investigation. It also exhibits the most variation
in the equatorial angles of the bipyramid (50.5–85.3°), but despite
this, the sum of the five angles (359.3°) is very close to the ideal
planar value. The distortion of the pentagonal pyramidal coordina-
tion around the bismuth atom in 1a–1f is clearly characterized by
Fig. 10. A fragment of the polymeric chain in the structure of 3.
the variation in O–Bi–O angles, but to a lesser extent compared to
2. The C–Bi–O angles in 1a–1f and 2 generally deviate from 90° and
are found in the range of 81.0° to 93.6°. In the crystal structure of
BiPh2(O2CCF3) (3), that we determined for the first time, the car-
boxylate ligand displays a different coordination mode compared
to 2. In 3 the trifluoroacetate group acts as a bidentate bridging
(rather than chelating-bridging) ligand to generate polymeric
chains (Fig. 10). The compound features a disphenoidal [21,22]

2960
V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
Table 1
Crystallographic data for 1a, 1b, 1c, 1d, 1e, 1f, 2, and 3.
1a
1b
1c
1d
1e
1f
2
3
Formula
C16H9BiF12O5
C19H13BiF12O5
C20H15BiF12O5
C20H16BiF12NO5
C18H13BiF12O5S
C23H12BiF12NO4
fw
Cryst syst
Space group
a, (Å)
C26H12Bi2F18O8
787.32
Monoclinic
P21/n
12.092(2)
18.805(4)
12.363(3)
90
C14H10BiF3O2
778.32
Monoclinic
C2/c
20.128(4)
12.996(3)
18.983(4)
90
718.21
Monoclinic
P21/c
10.726(2)
10.602(2)
18.939(4)
90
758.27
Monoclinic
C2/c
20.517(4)
12.818(3)
18.685(4)
90
772.30
Monoclinic
C2/c
20.781(4)
12.905(3)
18.556(4)
90
803.32
Monoclinic
C2/c
26.892(5)
12.623(3)
16.518(3)
90
1212.32
Monoclinic
C2/c
16.294(3)
16.185(3)
12.849(3)
90
476.20
Orthorhombic
P212121
8.800(2)
10.500(2)
15.556(3)
90
b, (Å)
c, (Å)
a
(°)
b (°)
103.88(3)
90
2090.9(7)
4
93.36(3)
90
4906(2)
8
90.94(3)
90
4976(2)
8
114.31(3)
90
2562.0(9)
4
93.52(3)
90
4957(2)
8
111.61(3)
90
5213(2)
8
105.23(3)
90
3270(1)
8
90
90
1437.5(5)
4
2.200
0.71073
173(2)
56.50
c
(°)
V, (Å3)
Z
Dcalc, (gꢀcmꢁ3
)
2.282
2.053
2.056
2.041
2.086
2.047
2.463
k (Mo K
T (K)
a
), (Å)
0.71073
173(2)
56.345
8.565
0.71073
173(2)
56.60
0.71073
173(2)
56.64
0.71073
173(2)
56.54
0.71073
173(2)
56.58
0.71073
173(2)
56.46
0.71073
173(2)
56.54
2hmax (°)
Absorption coefficient
(mmꢁ1
7.307
7.205
7.001
7.316
6.881
10.900
12.296
)
Number of data collected
Unique reflections
Number of params refined
F(0 0 0)
4902
4048
303
1344
5752
4887
322
2864
9928
5093
379
2928
9288
4381
369
1496
9892
4899
358
2944
9939
5145
382
3040
9926
3534
235
2240
6068
3093
190
880
R1 [I > 2
wR2 [I > 2
r
(I)]
(I)]
0.0327
0.0826
1.028
2.685/
ꢁ1.414
0.0391
0.1117
1.048
1.408/ꢁ0.773
0.0303
0.0785
1.056
1.361/
ꢁ0.668
0.0487
0.1330
1.014
2.206/ꢁ1.764
0.0442
0.1214
1.044
2.513/ꢁ1.179
0.0309
0.0833
1.041
1.876/ꢁ0.725
0.0346
0.0926
1.040
1.033/ꢁ1.899
0.0287
0.0654
1.051
2.61/ꢁ1.02
r
Goodness-of-fit (GOF)
qfin (max/min) (e Åꢁ3
)
Table 2
Selected bond lengths (Å) and angles (°) for 1a–f and 2.
1a
1b
1c
1d
1e
1f
2
Bi1–C31
Bi1–O11
Bi1–O12
Bi1–O21
2.238(5)
2.448(4)
2.432(3)
2.432(4)
2.466(3)
2.456(4)
87.5(2)
87.8(2)
87.6(2)
88.6(2)
83.8(2)
72.2(1)
71.6(1)
72.5(1)
72.8(1)
70.5(1)
143.6(1)
143.3(1)
144.0(1)
142.1(1)
144.4(1)
2.242(5)
2.470(4)
2.398(4)
2.380(4)
2.426(4)
2.510(5)
91.1(2)
86.3(2)
84.1(2)
83.2(2)
85.0(2)
73.2(1)
71.6(2)
73.3(2)
72.3(2)
68.7 (2)
144.7(2)
140.9(2)
144.2(2)
140.7(2)
144.9(2)
2.238(4)
2.230(7)
2.241(5)
2.476(4)
2.475(4)
2.441(4)
2.426(4)
2.360(4)
88.7(2)
84.5(2)
83.8 (2)
83.6(2)
88.2(2)
71.7(1)
69.9(1)
71.9(2)
72.8(2)
72.8(2)
141.3(1)
144.9(2)
140.9(1)
143.8(2)
144.3(1)
2.233(4)
2.485(3)
2.339(3)
2.332(3)
2.473(3)
2.703(4)
84.1(1)
87.1(1)
88.2(1)
90.0(1)
89.2(1)
73.0(1)
71.5(1)
74.4(1)
73.2(2)
67.7(1)
144.0(1)
140.5(1)
145.8(1)
140.8(1)
147.5(1)
2.229(5)
2.385(3)
2.278(4)
2.399(4)
2.761(4)
2.627(4)
86.2(1)
89.2(1)
86.7(1)
81.0(1)
85.3(1)
77.5(1)
75.9(1)
50.5(1)
70.1(1)
85.3(1)
152.5(1)
153.0(1)
125.7(1)
162.2(1)
120.5(1)
2.429(3)
2.413(3)
2.388(3)
2.457(3)
2.517(3)
90.3(1)
86.0(1)
85.3(1)
82.1(1)
88.(1)
72.8(1)
69.2(1)
72.4(1)
73.4(1)
71.5(1)
142.0(1)
144.3(1)
140.5(1)
143.8(1)
145.8(1)
2.402(5)
2.466(4)
2.518(4)
2.482(5)
2.331(5)
87.0(2)
83.2(2)
86.8(2)
93.6(2)
84.8(2)
72.5(2)
71.3(1)
70.9(2)
69.8(2)
75.6(2)
143.8(2)
145.1(2)
142.2(2)
146.4(2)
139.0(2)
Bi1–O22
Bi1–EX*
C31–Bi1–O11
C31–Bi1–O12
C31–Bi1–O21
C31–Bi1–O22
C31–Bi1–EX*
O11–Bi1–O12
O12–Bi1–O21
O21–Bi1–O22
O22–Bi1–EX*
EX*–Bi1–O11
O11–Bi1–O21
O11–Bi1–O22
O12–Bi1–O22
O12–Bi1–EX*
O21–Bi1–EX*
*
EX = O(41) for 1a–1e, N(41) for 1f, and O(22A) for 2.
Fig. 11. Coordination polyhedra of bismuth atoms in 1a (a) and 2 (b).

V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
2961
Bi(III) center coordinated by two aryl groups and two oxygen
atoms. The Bi–C distances in 3 are 2.232(5) and 2.243(6) Å, while
the Bi–O distances are 2.358(4) and 2.464(4) Å. The separations ob-
served between two Bi centers in 2 (4.392(4) Å) and 3 (4.431(3) Å)
are less than the sum of van der Waals radii of two bismuth atoms
(4.8 Å [17]). In both compounds the dimerization/polymerization
brings the bismuth atoms into a close intermolecular contact.
Analysis of the data available from the Cambridge Structural
Database indicates that the hemidirected pentagonal bipyramidal
geometry found in complexes 1a–1f and 2 (Fig. 11) is typical for
aryl-bismuth complexes. Thus, the related arylbismuth(bis)salicy-
late adducts [BiPh(Hsal)2(phen)] and [BiPh(Hsal)2(bipy)] display a
phenyl group in the apical position of the Bi(III) coordination poly-
hedron, with the base of the pentagonal pyramid being completed
by three carboxylate oxygen atoms of a mono- and a bidentate
salicylate ligand and two nitrogen atoms of the chelating diamine
phen or bipy ligand [10]. Other structurally characterized Bi-
Ph(O2CR)2 complexes, including [BiPh(O2CCH(CH3)CH2GePh3)2]
[18], [BiPh(O2CC6H2F3-3,4,5)2] [19], and [BiPh{(2-C5H4N)CO2}2]
[20] feature similar coordinations around the Bi(III) center. Inter-
estingly enough, the geometries of the primary coordination
spheres (up to ꢂ2.5 Å) of Bi(III) in Bi(hfac)3 [5] and Bi(thd)3 [6,7]
can also be represented as distorted pentagonal pyramids, if the
secondary bonds are not being taken into account. This suggests
the presence of a SALEP in both Bi(hfac)3 [5] and Bi(thd)3 [6,7];
subsequently, their coordination polyhedra can be viewed as dis-
Significant differences are observed in the way the monoaryl-
bismuth hexafluroacetylacetonate molecules are assembled in
their crystal lattices. The six-coordinate complexes 1a–1f and 2
are linked in their solid-state structures by hydrogen bonds as well
as by secondary and/or van der Waals interactions. Intermolecular
interactions between the bismuth atoms and the adjacent phenyl
groups are present in 1a as it is evident from Fig. 12. This type of
weak p-bonding from the metal to the organic ligand is character-
istic of a number of main group element-aryl complexes and is
indicative of relatively electron-deficient metal centers [23]. The
Bi–centroid contact in 1a is 3.388(4) Å with a slight ring slippage
of the Bi atom away from the line perpendicular to the ring plane.
This distance is somewhat shorter than in [BiPhCl2(THF)] (3.43 Å)
1
[24], [BiPhBr2(THF)]1 (3.47 Å) [25], and [BiPhI2(THF)]1 (3.54 Å)
t
[25], similar to Bi(OSiPh2 Bu)3 (3.34 Å), but much longer than the
shortest Bi–Carene centroid contacts found in Bi(O{2,6-Me2C6H3})3
(2.98 Å) [26] and Bi(OC6F5)3(C6H5CH3)2 (2.96 Å) [27]. It should be
noted, however, that the oxygen atom of the ligand allows addi-
tional flexibility to adopt a favorable conformation for an opti-
mized Bi–arene interaction. The coordination mode can be
considered as roughly g6 with Bi–CPh distances between 3.513(4)
and 3.792(4) Å. The bismuth–aromatic ring centroid distance in
1a is thus closer to the upper range of reported values in the liter-
ature suggesting a rather weak contact. By means of these weak
interactions the Bi(III) centers are capped by phenyl groups that
connect them into a polymeric chain (Fig. 12). The BiꢀꢀꢀBi distance
between the two neighboring atoms in the chain (5.317(5) Å) ex-
torted
w-pentagonal bipyramids [21,22].
Fig. 12. Intermolecular interactions between bismuth atoms and the adjacent phenyl groups in 1a. Fluorine atoms are omitted for clarity.
Fig. 13. Intermolecular interactions between the bismuth atoms and the adjacent diketonate O-atoms in 1e. Fluorine atoms are omitted for clarity.

2962
V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
Fig. 14. Intermolecular interactions between the bismuth atoms and the neighboring N-atoms of PhCN ligands in 1f. Fluorine atoms of the hfac groups are omitted for clarity.
Fig. 15. Intermolecular interactions between the bismuth atoms and the neighboring O and F-atoms in 2.
P
cludes any metal–metal interaction ( rvdW 4.8 Å) [17], while the
corresponding distance between the chains is measured to
10.726(6) Å.
3.356(5) Å) from two different [BiPh(hfac)(O2CCF3)] moieties as
shown in Fig. 15. Similar secondary bonds are observed in Bi(hfac)3
[5], though the contacts in the structure of the latter compound are
considerably shorter (BiꢀꢀꢀO 2.890(3) Å and BiꢀꢀꢀF 3.174(4) Å). It has
to be noted that the aryl groups from each Bi atom of the dimer 2
lie stacked with relatively long inter-ring separations in the range
of 3.8–4.1 Å.
No bismuth–aromatic ring interactions are present in the crys-
tal structures of the other adducts 1b–1f or in 2. In contrast to 1a,
the aryl groups in 1b–1e are oriented away from each other. A clo-
ser look on the crystal packing in the adducts reveals some inter-
esting aspects. It is known that the coordination sphere of Bi(III)
can comprise both primary bonds as well as secondary bonds or
interactions, with interatomic distances shorter than the sum of
van der Waals radii. Thus, in 1b–1e two diketonate oxygen atoms
from the neighboring molecule are involved in weak interactions
with an adjacent Bi(III) atom. Sawyer and Gillespie showed [21]
that in some complexes such weak contacts may form around
the direction of the lone pair, but not directly over it. Fig. 13 shows
the formation of such weak contacts in the structure of 1e. The
Bi(1)ꢀꢀꢀO(12A) and Bi(1)ꢀꢀꢀO(21A) contacts in 1b, 1c, 1d and 1e are
3.525, 3.670, 3.518, 3.474 and, respectively, 3.411, 3.319, 3.750,
3.349 Å. The bismuth(III) lone pair of electrons, if it is considered
stereochemically active, should occupy an axial position trans to
the C(31) atom and being oriented between the O(12A) and
O(21A) atoms. A drastic difference in the secondary bonding is ob-
served in 1f. Only a very weak interaction can be distinguished,
Comparing the packing arrangements of the complexes under
investigation, it is found that when water is coordinated to Bi(III),
the assembly through Bi–arene
p complexation is favored, while
when bulkier O-donor Lewis bases are present, secondary bonding
with additional donor atoms from the neighboring complexes be-
comes more favorable. The dominant motif of assembly in 1b–1f
and 2 through the additional weak bonding appears to prevent
Bi–aryl
p-interactions observed in 1a. It can be argued that the
realization of one or the other weak bonding pattern is dependent
upon the nature and availability of the donor atoms and specific
steric constraints around each bismuth center. Crystal-packing
forces may play an important role as well [10,28]. These results
illustrate that the interactions between Bi atoms in phenylbismuth
b-diketonate compounds are diverse and can involve hydrogen
bonding, Bi–arene
p complexation, as well as a weak secondary
bonding of bismuth(III) centers with a range of donor atoms (N,
involving Bi(III) and
a nitrogen atom of the PhCN ligand
O, F).
(Bi(1)ꢀꢀꢀN(41A) 3.489 Å) from an adjacent molecule (Fig. 14). A
more complex picture is observed in 2, which contains dimers of
[BiPh(hfac)(O2CCF3)]. The dimers are connected in chains by means
of very weak interactions between Bi(III) and one of hfac oxygen
atoms (Bi(1)ꢀꢀꢀO(21B) 3.308(4) Å) and of one F atoms (Bi(1)ꢀꢀꢀF(16H)
3. Conclusions
Monoarylbismuth diketonates have been reported for the first
time, extending the (relatively small) list of metal complexes of

V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
2963
this type. The crystal structures of compounds 1a–1f and 2 show
4.4. Synthesis of [BiPh(hfac)2(Me2CO)] (1b)
that the coordination geometry of the bismuth(III) center takes
the form of a distorted pentagonal pyramid. Depending upon the
nature of the ligands the bismuth atoms are associated through
weak secondary bonding in chains or layers by coordination of
To the hexanes solution of 1 obtained as described above,
200 L dry Me2CO was added via a Hamilton syringe. Yellow crys-
l
tals formed in 58% yield. Anal. Calc. for C20H15F12O5Bi: C, 30.10; H,
1.73. Found: C, 30.60; H, 1.80%. FT-IR (ATR, cmꢁ1): 3180, 3070,
1638, 1553, 1526, 1456, 1433, 1380, 1251, 1192, 1137, 1118,
1090, 1055, 1016, 996, 843, 792, 735, 693, 678, 662, 579. 1H
NMR (CDCl3): 8.24 (d, Ph, 2H), 8.07 (t, Ph, 2H), 7.42 (t, Ph, 1H),
5.97 (s, hfac), 2.19 (s, Me2CO, 6H). 19F NMR (CDCl3): ꢁ76.83 (s, hfac,
12F).
Bi(III) to (i) a phenyl group through weak p-bonding from the me-
tal to the organic ligand as in 1a; (ii) two diketonate oxygen atoms
from the neighboring molecule as in 1b–1e; (iii) a nitrogen atom
from the adjacent molecule as in 1f; or (iv) an oxygen and a fluo-
rine atoms from two different [BiPh(hfac)(O2CCF3)] fragments as
in 2. Thermal decomposition of the complexes in air resulted in
Bi2O3, while under argon BiOF was identified as the major decom-
position product. The complexes are sufficiently soluble to be of
interest as promising building blocks for the construction of het-
erometallic complexes. The presence of aryl functionality offers a
wide variety of possibilities for further functionalization of these
complexes, for instance, through the use of appropriate
metalloligands.
4.5. Synthesis of [BiPh(hfac)2(THF)] (1c)
The yellow solution obtained by reaction of BiPh3 and Hhfac in
hexanes was treated with 200 lL dry THF. Yellow crystals formed
in 71% yield. Anal. Calc. for C20H15F12O5Bi: C, 31.10; H, 1.96. Found:
C, 30.95; H, 2.03%. FT-IR (ATR, cmꢁ1): 3190, 3060, 2980, 1640,
1602, 1554, 1525, 1455, 1358, 1251, 1196, 1137, 1093, 1054,
1023, 997, 917, 862, 809, 795, 768, 733, 694, 661, 581. 1H NMR
(CDCl3): 8.31 (d, Ph, 2H), 8.03 (t, Ph, 2H), 7.42 (t, Ph, 1H), 5.95 (s,
hfac, 2H), 3.98 (m, THF, 4H), 1.96 (m, THF, 4H). 19F NMR (CDCl3):
ꢁ76.92 (s, hfac, 12F).
4. Experimental section
4.1. General procedures
All chemicals, unless otherwise stated, were of reagent grade
and used as received. Acetone was dried over Drierite and distilled
over freshly activated molecular sieves. THF and hexanes were dis-
tilled from sodium-benzophenone ketyl before use. [Bi-
4.6. Synthesis of [BiPh(hfac)2(DMA)] (1d)
The hexanes solution of 1 resulting from the reaction of BiPh3
and Hhfac was treated with 200 lL DMA via a Hamilton syringe.
Ph2(O2CCF3)] (3) was synthesized following
a
previously
Yellow crystals formed in 67% yield. Anal. Calc. for C20H16F12NO5Bi:
C, 31.51; H, 2.05. Found: C, 30.62; H, 1.98%. FT-IR (ATR, cmꢁ1):
3140, 3055, 2995, 1637, 1594, 1554, 1527, 1469, 1433, 1422,
1406, 1336, 1252, 1196, 1134, 1090, 1054, 1028, 996, 969, 795,
770, 751, 734, 693, 662, 614, 580. 1H NMR (CDCl3): 8.45 (d, Ph,
2H), 7.97 (t, Ph, 2H), 7.52 (t, Ph, 1H), 5.87 (s, hfac, 2H), 3.09 (s,
DMA, 6H), 2.22 (s, DMA, 3H). 19F NMR (CDCl3): ꢁ76.96 (s, hfac,
12F).
described procedure [9]. The reported IR data were obtained on a
Perkin–Elmer FT-IR spectrometer using attenuated total reflection
(ATR). NMR spectra were recorded at room temperature in CDCl3
on a Bruker Avance 400 spectrometer, and the 1H and 19F chemical
shifts are reported relative to tetramethylsilane (TMS) and CFCl3,
respectively. Thermogravimetric measurements were carried out
under argon or air at a heating rate of 10°/min using a Mettler To-
ledo TGA instrument. Elemental analysis was performed by Galbra-
ith Laboratories Inc.
4.7. Synthesis of [BiPh(hfac)2(DMSO)] (1e)
4.2. Synthesis of BiPh(hfac)2 (1)
To the hexanes solution obtained by reaction of BiPh3 and Hhfac
as described abobe, 200 lL DMSO was added via a Hamilton syr-
440 mg (1 mmol) commercial BiPh3 was loaded into a Schlenk
flask and 10 mL dry hexanes was added. The mixture was stirred
and heated to reflux to result in a complete dissolution of the solid.
inge. Yellow crystals formed in 85% yield. Anal. Calc. for
C18H13F12SO5Bi: C, 27.78; H, 1.68. Found: C, 28.33; H, 1.76%. FT-
IR (ATR, cmꢁ1): 3190, 3070, 1637, 1554, 1528, 1447, 1337, 1253,
1198, 1135, 1086, 1056, 1022, 997, 926, 799, 764, 741, 726, 689,
662, 579. 1H NMR (CDCl3): 8.25 (d, Ph, 2H), 8.05 (t, Ph, 2H), 7.42
(t, Ph, 1H), 5.91 (s, hfac, 2H), 2.71 (s, DMSO, 6H). 19F NMR (CDCl3):
ꢁ76.85 (s, hfac, 12F).
280 lL (2 mmol) Hhfac was added upon vigorous stirring within
10 min to produce a yellow solution, which was refluxed for addi-
tional 30 min. The solution was filtered under Ar and the filtrate
was concentrated in vacuum and stored at ꢁ20 °C overnight. A yel-
low powder was produced in 65% yield. Anal. Calc. for C16H7F12O4-
Bi: C, 27.45; H, 1.01. Found: C, 27.41; H, 1.10%. FT-IR (ATR, cmꢁ1):
3180, 3060, 1640, 1609, 1556, 1530, 1445, 1339, 1254, 1195, 1141,
1085, 1052, 997, 917, 803, 733, 722, 689, 663, 581. 1H NMR
(CDCl3): 8.26 (d, Ph, 2H), 8.07 (t, Ph, 2H), 7.41 (t, Ph, 1H), 5.95 (s,
hfac, 2H). 19F NMR (CDCl3): ꢁ76.79 (s, hfac, 12F).
4.8. [BiPh(hfac)2(PhCN)] (1f)
The hexanes solution resulting from the reaction of BiPh3 and
Hhfac was reacted with 0.103 g PhCN suspended in hexanes that
was added upon vigorous stirring. Orange crystals formed in 73%
yield from the filtrate. Anal. Calc. for C23H12F12NO4Bi: C, 34.39; H,
1.51. Found: C, 34.07; H, 1.62%. FT-IR (ATR, cmꢁ1): 3185, 3060,
2234, 1636, 1603, 1554, 1528, 1448, 1338, 1253, 1196, 1138,
1088, 1053, 997, 943, 801, 758, 741, 735, 693, 685, 662, 580,
555. 1H NMR (CDCl3): 8.31 (d, Ph, 2H), 8.05 (t, Ph, 2H), 7.49 (t,
Ph, 2H), 7.36–7.74 (m, PhCN, 5H), 5.96 (s, hfac, 2H). 19F NMR
(CDCl3): ꢁ76.83 (s, hfac, 12F).
4.3. Synthesis of [BiPh(hfac)2(H2O)] (1a)
When reagent-grade hexanes were used for the reaction de-
scribed above, yellow crystals of 1a were obtained in 52% yield. The
water in the composition of complex 1a almost certainly arises from
traces of water in the solvent. Anal. Calc. for C16H9F12O5Bi: C, 26.76;
H, 1.26. Found: C, 26.83; H, 1.38%. FT-IR (ATR, cmꢁ1): 3340, 3190,
3070, 2970, 1636, 1606, 1557, 1531, 1453, 1435, 1340, 1249, 1199,
1141, 1086, 1055, 1015, 997, 914, 803, 733, 722, 690, 663, 581. 1H
NMR (CDCl3): 8.25 (d, Ph, 2H), 8.06 (t, Ph, 2H), 7.40 (t, Ph, 1H), 5.95
(s, hfac+H2O, 4H). 19F NMR (CDCl3): ꢁ76.79 (s, hfac, 12F).
4.9. Synthesis of [BiPh(hfac)(O2CCF3)]2 (2)
440 mg (1 mmol) BiPh3 were dissolved in 10 mL hexanes upon
heating. 280 lL (2 mmol) Hhfac was added within 10 min and the

2964
V. Stavila, E.V. Dikarev / Journal of Organometallic Chemistry 694 (2009) 2956–2964
mixture was refluxed for 30 min to form a yellow solution. The
solution was filtered and 200 L HO2CCF3 was added via a Hamil-
Appendix A. Supplementary material
l
ton syringe. Yellow crystals formed in 80% yield. The same com-
pound was isolated in 45% yield from the reaction of
[BiPh2(O2CCF3)] (synthesized by a previously described procedure
[9]) with 1 equiv. Hhfac. Anal. Calc. for C13H6F9O4Bi: C, 25.76; H,
1.00. Found: C, 26.05; H, 1.12%. FT-IR (ATR, cmꢁ1): 3140, 1634,
1602, 1562, 1541, 1433, 1257, 1191, 1156, 1143, 1100, 1075,
942, 853, 816, 794, 743, 726, 664, 609, 584, 562. 1H NMR (CDCl3):
8.29 (d, Ph, 2H), 8.01 (t, Ph, 2H), 7.41 (t, Ph, 1H), 5.95 (s, hfac, 1H).
19F NMR (CDCl3): ꢁ76.78 (s, hfac, 6F), ꢁ77.59 (s, tfa, 3F).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.04.036.
References
[1] D.J. Otway, W.S. Rees, Coord. Chem. Rev. 210 (2000) 279–328.
[2] R.E. Sievers, J.E. Sadlowski, Science 201 (1978) 217–223.
[3] H.C. Aspinall, Chemistry of the f-Block Elements, CRC Press, 2001.
[4] D. Bradley, R. Mehrotra, I. Rothwell, A. Singh, Alkoxo and Aryloxo Derivatives of
Metals, Academic Press, 2001.
[5] E.V. Dikarev, H. Zhang, B. Li, J. Am. Chem. Soc. 127 (2005) 6156–6157.
[6] L. Armelao, G. Bandoli, M. Casarin, G. Depaoli, E. Tondello, A. Vittadini, Inorg.
Chim. Acta 275–276 (1998) 340–348.
4.10. X-ray structural determinations
[7] G.K. Fukin, A.P. Pisarevskii, A.I. Yanovskii, Y.T. Struchkov, Zh. Neorg. Khim. 38
(1993) 1205–1211.
Single-crystals of 1a–1f, 2, and 3 suitable for X-ray crystallogra-
phy were taken as small plates or blocks directly from the reaction
mixtures. The data for all complexes were collected at 173 K on a
Bruker SMART APEX CCD-based X-ray diffractometer equipped
with a Mo-target X-ray tube with 20 s exposure times. Analysis
of the data showed negligible decay during data collection experi-
ments. The frames were integrated with the Bruker SAINT software
package and corrected for absorption effects using empirical meth-
od (SADABS). The structures were solved using direct methods and
refined by full-matrix least-squares on F2 using the Bruker SHELXL
software package. The coordinates of bismuth atoms (and sulfur
atom in 1e) were found in direct method E maps. The remaining
atoms were located after an alternative series of least-squares dif-
ference-Fourier cycles. Hydrogen atoms were included in idealized
positions for structure factor calculations. Anisotropic displace-
ment parameters were assigned to all atoms, except the hydrogens
and disordered fluorines. The fluorine atoms of the CF3 groups
were found to be disordered over two or three rotational orienta-
tions. Relevant X-ray crystallographic data for all compounds are
given in Table 1. Selected bond distances and angles are presented
in Table 2.
[8] E.V. Dikarev, H. Zhang, B. Li, Angew. Chem. Int. Ed. 45 (2006) 5448–5451.
[9] G.B. Deacon, W.R. Jackson, J.M. Pfeiffer, Aust. J. Chem. 37 (1984) 527–535.
[10] V. Stavila, J.C. Fettinger, K.H. Whitmire, Organometallics 26 (2007) 3321–3328.
[11] C.J. Carmalt, A.H. Cowley, A. Decken, N.C. Norman, J. Organomet. Chem. 496
(1995) 59–67.
[12] M. Mehring, Coord. Chem. Rev. 251 (2007) 974–1006.
[13] C.M. Jones, M.D. Burkart, R.E. Bachman, D.L. Serra, S.J. Hwu, K.H. Whitmire,
Inorg. Chem. 32 (1993) 5136–5144.
[14] G.G. Briand, N. Burford, Adv. Inorg. Chem. 50 (2000) 285–357.
[15] G.G. Briand, N. Burford, Chem. Rev. 99 (1999) 2601–2657.
[16] L. Shimoni-Livny, J.P. Glusker, C.W. Bock, Inorg. Chem. 37 (1998) 1853–1867.
[17] C. Silvestru, H.J. Breunig, H. Althaus, Chem. Rev. 99 (1999) 3277–3328.
[18] L. Yu, Y.-Q. Ma, R.-C. Liu, G.-C. Wang, J.-S. Li, Inorg. Chem. Commun. 7 (2004)
410–411.
[19] V.V. Sharutin, I.V. Egorova, T.K. Ivanenko, O.K. Sharutina, M.A. Pushilin, A.V.
Gerasimenko, N.A. Adonin, V.F. Starichenko, Russ. J. Coord. Chem. 30 (2004)
309–313.
[20] P.C. Andrews, G.B. Deacon, P.C. Junk, I. Kumar, M. Silberstein, Dalton Trans.
(2006) 4852–4858.
[21] J.F. Sawyer, R.J. Gillespie, Prog. Inorg. Chem. 34 (1986) 65–113.
[22] R.L. Davidovich, V. Stavila, D.V. Marinin, E.I. Voit, K.H. Whitmire, Coord. Chem.
Rev. 253 (2009) 1316–1352.
[23] H. Schmidbaur, A. Schier, Organometallics 27 (2008) 2361–2395.
[24] W. Clegg, R.J. Errington, G.A. Fisher, R.J. Flynn, N.C. Norman, J. Chem. Soc.,
Dalton Trans. (1993) 637–641.
[25] W. Clegg, R.J. Errington, G.A. Fisher, D.C.R. Hockless, N.C. Norman, A.G. Orpen,
S.E. Stratford, J. Chem. Soc., Dalton Trans. (1992) 1967–1974.
[26] W.J. Evans, J.H. Hain, J.W. Ziller, J. Chem. Soc., Chem. Commun. (1989) 1628–
1629.
Acknowledgment
[27] C.M. Jones, M.D. Burkart, K.H. Whitmire, Angew. Chem. Int. Ed. 31 (1992) 451–
452.
V.S. is grateful to Dr. Bo Li and Haitao Zhang for their help with
single-crystal XRD experiments. Financial support from the Na-
tional Science Foundation (CHE-0718900 and CHE-0619422, X-
ray diffractometer) is gratefully acknowledged.
[28] V. Stavila, R.L. Davidovich, A. Gulea, K.H. Whitmire, Coord. Chem. Rev. 250
(2006) 2782–2810.