Reactivity of bis(long chain substituted β-diketonato)palladium(II) [Pd(OOR2)2] towards HBF4: Formation of luminescent [BF2(OOR2)] derivatives. X-ray structure of [1,3-di(4-n-butoxyphenyl)propane-1,3-dionato]difluoroboron(III)

Article abstract of DOI:10.1016/j.inoche.2004.06.011

Reactions of [Pd(OO^R2)₂] (OO^R2 = 1,3-di(4-n-alkyloxyphenyl)propane-1,3-dionato; R = C₆H ₄OC_nH_2n+1, n = 14, 16, 4) with N,N′-bidentate ligands of the type bis(4-n-alkyloxyphenyl)-1-(pyridin-2- yl)-1H-pyrazol (pypz^R2) in the presence of HBF₄ gave rise to new dioxoborane derivatives [BF₂(OO^R2)] (1-3) as major products. Compounds 1-3 were also isolated by reaction of [Pd(OO ^R2)₂] and HBF₄, as well as by reaction of the corresponding β-diketones or sodium β-diketonates with HBF ₄. The new oxoboranes [BF₂(OO^R2)] (1-3) showed intense yellow or blue luminescence in the solid state and in the solution, respectively. The X-ray structure of 3 containing the shortest chain (R = C ₆H₄OC₄H₉) evidenced the chelating coordination of the β-diketonate ligand to the acceptor BF₂ group in a boron tetrahedral environment. The molecules were packed in layers showing weak Ca-Ha?F bifurcated interactions, which were responsible for a bi-dimensional network.

Full text of DOI:10.1016/j.inoche.2004.06.011

Inorganic Chemistry Communications 7 (2004) 974–978
www.elsevier.com/locate/inoche
Reactivity of bis(long chain substituted
b-diketonato)palladium(II) [Pd(OOR2)2] towards HBF4: formation
of luminescent [BF2(OOR2)] derivatives. X-ray structure of
[1,3-di(4-n-butoxyphenyl)propane-1,3-dionato]difluoroboron(III)
a
a,
a
a
M.J. Mayoral , M. Cano *, J.A. Campo , J.V. Heras ,
E.Pinillaa,b, M.R. Torres
b
a
´ ´ ´
Departamento de Quımica Inorganica I, Facultad de Ciencias Quımicas, Universidad Complutense, E-28040 Madrid, Spain
´ ´
Laboratorio de Difraccion de Rayos-X, Facultad de Ciencias Quımicas, Universidad Complutense, E-28040 Madrid, Spain
b
Received 5 March 2004; accepted 15 June 2004
Available online 28 July 2004
Abstract
Reactions of [Pd(OOR2)2] (OOR2 = 1,3-di(4-n-alkyloxyphenyl)propane-1,3-dionato; R = C6H4OCnH2n+1, n = 14, 16, 4) with
N,N0-bidentate ligands of the type bis(4-n-alkyloxyphenyl)-1-(pyridin-2-yl)-1H-pyrazol (pypzR2) in the presence of HBF4 gave rise
to new dioxoborane derivatives [BF2(OOR2)] (1–3) as major products. Compounds 1–3 were also isolated by reaction of [Pd(OOR2)2]
and HBF4, as well as by reaction of the corresponding b-diketones or sodium b-diketonates with HBF4. The new oxoboranes
[BF2(OOR2)] (1–3) showed intense yellow or blue luminescence in the solid state and in the solution, respectively. The X-ray struc-
ture of 3 containing the shortest chain (R = C6H4OC4H9) evidenced the chelating coordination of the b-diketonate ligand to the
acceptor BF2 group in a boron tetrahedral environment. The molecules were packed in layers showing weak C–Hꢀ ꢀ ꢀF bifurcated
interactions, which were responsible for a bi-dimensional network.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: b-Diketonate; Boron difluorides; Luminescence; X-ray structure
Bis(b-diketonato) metal complexes containing long
chain substituents on the b-diketonate ligand have been
proved to have liquid crystal properties [1,2]. Among
them, symmetrical palladium(II) derivatives of the type
to get lower melting and clearing temperatures [2]. On
this approach, we are now interested in the preparation
of unsymmetrical palladium(II) complexes containing
both b-diketonate and bidentate N,N0-donor mesogenic
ligands.
[Pd(OOR2)2]
(OOR2 = 1,3-di(4-n-alkyloxyphenyl)pro-
pane-1,3-dionato; R = C6H4OCnH2n+1, n = 10, 12, 14)
have shown discotic mesophases in the temperature
range of ca. 85–160 ꢁC [3,4].
In a previous work, we have described the liquid crys-
tal behaviour of the 3,5-bis(4-n-alkyloxyphenyl)-1-(pyri-
din-2-yl)-1H-pyrazol ligands (pypzR2; R = C6H4OCn
H2n+1, n = 12, 14, 16, 18) as well as that of the related
Pd-complexes of formula [PdCl2(pypzR2)] [5].
A reduction of the molecular symmetry by building
unsymmetrical materials has been used as a strategy
Following these results, our actual purpose deals
with the study of new palladium materials containing
mixed 1-(pyridin-2-yl)pyrazol and b-diketonate meso-
genic ligands. In particular, we have tried the synthesis
*
Corresponding author. Fax: 34-91-3944352.
E-mail address: mmcano@quim.ucm.es (M. Cano).
1387-7003/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.06.011

M.J. Mayoral et al. / Inorganic Chemistry Communications 7 (2004) 974–978
975
of cationic palladium(II) complexes of the type [Pd-
(OOR2)(pypzR2)]+ (R = C6H4OCnH2n+1, n = 14, 16, 4).
RMN and analytical data [7] allowed us to establish
their identity with those obtained through the route a
(Scheme 1).
In order to understand the role of the palladium in
these reactions, we have also explored the reactivity of
the free b-diketones or the sodium b-diketonates to-
wards HBF4 or NaBF4 [10] (Scheme 2). All of these es-
says gave rise to the corresponding adducts [BF2(OOR2)]
(1–3), which were clearly identified by their yellow lumi-
nescence in the solid state, and characterized by spectro-
scopic and analytical techniques [7]. These results
exclude the requirement of the Pd derivatives to produce
Synthetic and characterization work
The reaction of [Pd(OOR2)2] with pypzR2
(R = C6H4OCnH2n+1, n = 14,16) in the presence of
HBF4 was carried out [6] (Scheme 1, route a). Surpris-
ingly, duꢁring the course of the reaction, degradation of
the BF4 group occurs, giving rise to deep-yellow
compounds I that seem luminescent to the naked eye,
and they were characterized as [BF2(OOR2)] (R =
C6H4OCnH2n+1, n = 14 (1), 16 (2)) [7]. The expected
unsymmetrical derivatives [Pd(OOR2)(pypzR2)]BF4 (II)
were also formed but they were isolated in a low yield.
An analogous reaction with ligands containing shorter
chains, i.e., between [Pd(OOR2)2] and pypzR2
(R = C6H4OC4H9), was also investigated [6], the oxobo-
rane complex [BF2(OOR2)] (3) being again the main
product [7]. It was crystallized from dichloromethane/
hexane solutions giving rise to deep-yellow crystals,
which were adequate for X-ray purposes [8].
ꢁ
the degradation of the BF4 group.
Thus, the formation of [BF2(OOR2)] merits a further
comment. This emerges by considering the observed pal-
ladium deposition when [Pd(OOR2)2] was allowed to re-
act with HBF4, and consequently the formation of these
adducts [BF2(OOR2)] should occur with liberation of
HF or NaF.
The IR spectra of 1–3 contain bands due to the coor-
dinated CO groups of the b-diketonate ligand in the
1540–1560 cmꢁ1 interval. They were bathochromically
shifted with respect to those of the starting bis(b-diketo-
nato)palladium complexes [Pd(OOR2)2] (ca. 1584–1590
cmꢁ1) in agreement with a stronger coordination of
the carbonyl group to the boron atom than to the
All new chelates [BF2(OOR2)] (1–3) were also isolated
by the reaction of [Pd(OOR2)2] and HBF4 in dichloro-
methane solution [9] (Scheme 1, route b). The IR,
Scheme 1.
Scheme 2.

976
M.J. Mayoral et al. / Inorganic Chemistry Communications 7 (2004) 974–978
transition-metal [11]. The highest shift was observed for
3. This fact suggests that the steric consequences of the
substituents should be responsible for the variation of
the donor–acceptor interaction between the BF2 group
and the b-diketonate ligand, this interaction being
stronger for 3 containing the shortest chains and weaker
for 1 and 2.
All three compounds 1–3 are intensely luminescent
both in the solid state and in solution, this property be-
ing previously observed in several (b-diketonato)boron
derivatives [11–13], as it has been proved for the related
compound [BF2(OOPh2)] (OOPh2 = 1,3-di(phenyl)pro-
pane-1,3-dionato), which presents a strong luminescence
at 77 K and at room temperature [11,12]. Compounds
1–3 show an intense yellow or blue emission for the sol-
ids and the solutions, respectively, which can be ob-
served with the naked eye.
distances and angles. Boron atom is tetrahedrally coor-
dinated to two F atoms and the two O atoms of the
chelating b-diketonate ligand, giving rise to a boracycle
defined by the B1–O1–O2–C1–C2–C3 atoms.
The charge distribution around the boron atom is not
symmetrical, as reflected by the distances B1–O1 and B1–
˚
O2 of 1.52(1) and 1.42(1) A. The C–C bond distances in
the 1,3-dicarbonyl group are slightly different between
˚
them (C1–C2 1.32(1) A, C2–C3 1.43(1) A; mean value
˚
˚
1.37(1) A), showing again the unsymmetrical charge dis-
tribution. The C–O bond distances (mean value of
˚
1.31(1) A) are considerably longer than those found in
metal chelates [16–19], indicating the stronger bond of
the b-diketonate ligand with the BF2 group, as it was also
deduced from the m(CO) frequencies (see above).
The B1–O1–O2–C1–C2–C3 cycle is almost planar
˚
(the maximum deviation of 0.04(1) A is shown by B1),
Blue luminescent compounds are an important class
of materials because of their potential applications in lu-
minescent devices [14] and some (b-diketonato)boron
complexes have been found to be useful electrolumines-
cent materials [15].
The above results open us to new expectations for the
synthesis and study of the luminescent behaviour of the
family of (b-diketonato)difluoroboron compounds con-
taining successive enlargement of the alkyl chain on
the diketonate ligand. We are now involved in the opti-
cal studies of these compounds, which will be reported
in the future.
with the benzene-substituent ring planes slightly twisted
at angles of 10.9(3)ꢁ (C4–C9) and 12.4(3)ꢁ (C14–C19).
Therefore, the molecule could be defined as almost pla-
nar, in contrast with the envelope conformation of the
related compounds [2-(4-methoxyphenyl)-3-phenyl-3-
oxopropanalato-O,O0]difluoroboron(III) [17] and [2,
3-bis(3,4-dimethoxyphenyl)-3-oxopropanalato-O,O0]di-
di- fluoroboron(III) [20], but it is similar to that reported
for benzoylacetonatodifluoroboron(III) [19]. This plan-
arity could be surprising in view of the steric require-
ments involved, although it has been demonstrated
that high crowding can be tolerated in a planar system
[21]. Thus, the mutual repulsion between the H2 with
the H19 and H5 could probably be limited by an oppos-
ing repulsion between O1 and H9 and O2 and H15, and
it could be the reason that C3–C14–C19 and C3–C14–
C15, and C1–C4–C9 and C1–C4–C5 angles show slight
differences (7.4(7)ꢁ and 4.9(6)ꢁ, respectively).
Crystal structure of [BF2ðOOR2Þ] (R = C6H4OC4H9, 3)
A perspective view of the molecule is depicted in
Fig. 1, showing the atomic numbering and selected bond
Fig. 1. Perspective ORTEP plot of 3. Hydrogen atoms have been omitted for clarity. The thermal ellipsoids are at 35% probability level. Selected
˚
bond lengths (A) and angles (ꢁ): B1–F1, 1.41(1); B1–F2, 1.33(1); B1–O1, 1.52(1); B1–O2, 1.42(1); C1–O1, 1.311(6); C3–O2, 1.308(6); C1–C2, 1.32(1);
C2–C3, 1.43(1); F1–B1–F2, 107.2(4); F1–B1–O1, 104.0(9); F1–B1–O2, 110(1); F2–B1–O1, 109(1); F2–B1–O2, 113(1); O1–B1–O2, 113.0(3); C1–C2–
C3, 122.1(3).

M.J. Mayoral et al. / Inorganic Chemistry Communications 7 (2004) 974–978
977
Fig. 2. View of the molecular packing through b axis.
[5] M.J. Mayoral, M.C. Torralba, M. Cano, J.A. Campo, J.V. Heras,
Inorg. Chem. Commun. 6 (2003) 626.
The molecular packing is represented in Fig. 2. It
could be described as a layer-like distribution, with the
layers situated almost parallel to the (201) direction.
The molecules within a layer are parallel and show the
same head-to-head orientation, but a head-to-tail in re-
lation to those of neighbouring layers. Weak C–Hꢀ ꢀ ꢀF
interactions between the layers are observed, implicating
the F atoms in a bifurcated form [C8ꢀ ꢀ ꢀF1 (x,ꢁy,zꢁ1/2),
[6] To a dichloromethane solution (20 ml) of [Pd(OOR2)2] (0.05
mmol), prepared according to the described procedures [3,22], was
added the stoichiometric amount of the corresponding pypzR2
ligand [5,18]. After few minutes of stirring, a slight excess of
HBF4 ÆOEt2 was also added. The solution was stirred for 24 h at
room temperature. Then, the mixture was filtered off, and the solid
obtained was recrystallized in dichloromethane/hexane giving rise
to [BF2(OOR2)] and [Pd(OOR2)(pypzR2)]BF4 as major and minor
products, respectively.
˚
˚
3.20(1) A; C10ꢀ ꢀ ꢀF1 (x, ꢁy + 1, zꢁ1/2), 3.37(1) A;
[7] BF2(OOR2)] (R = C6H4OC14H29, 1): IR(KBr, cmꢁ1): 1561 m(CO).
1H NMR (CDCl3, 25ꢁ, d ppm, J Hz): 8.11 (d, J = 8.8, Ho); 7.01 (s,
CH); 6.99 (d, J = 8.8, Hm); 4.07 (t, J = 6.6, CH2O); 1.82–1.27 (m,
(CH2)12); 0.88 (t, J = 6.6, CH3). Anal. calc. for C43H67BF2O4:
C, 74.1; H, 9.7. Found: C, 73.8; H, 9.6%. [BF2(OOR2)]
(R = C6H4OC16H33, 2): IR(KBr, cmꢁ1): 1561 m(CO). 1H NMR
(CDCl3, 25ꢁ, d ppm, J Hz): 8.11 (d, J = 8.7, Ho); 7.01 (s, CH); 7.00
(d, J = 8.7, Hm); 4.07 (t, J = 6.3, CH2O); 1.83–1.27 (m, (CH2)14);
0.88 (t, J = 6.3, CH3). Anal. calc. for C47H75BF2O4: C, 75.0; H,
10.0. Found: C, 75.1; H, 9.7%. [BF2(OOR2)] (R = C6H4OC4H9, 3):
IR(KBr, cmꢁ1): 1545 m (CO). 1H NMR (CDCl3, 25ꢁ, d ppm, J Hz):
8.12 (d, J = 9.0, Ho); 7.02 (s, CH); 7.01 (d, J = 9.0, Hm); 4.09 (t,
J = 6.4, CH2O); 1.83 (m, CH2); 1.50 (m, CH2); 0.97 (t, J = 7.1,
CH3). Anal. calc. for C23H27BF2O4: C, 66.4; H, 6.1. Found: C,
66.5; H, 6.2%.
˚
C16ꢀ ꢀ ꢀF2 (x, ꢁy, z + 1/2), 3.22(1) A; C20ꢀ ꢀ ꢀF2 (x,
˚
ꢁy + 1, z + 1/2), 3.39(1) A]. As a consequence, a bi-
dimensional network could be defined.
Supplementary material
Crystallographic data of 3 have been deposited with
the Cambridge Crystallographic Data Centre (CCDC
Deposition No. 232492).
Acknowledgement
[8] Yellow prismatic single crystals (0.30 · 0.08 · 0.08 mm) were
obtained from dichloromethane/hexane solution. Crystal data:
Financial support from the DGI/MCyT of
Spain (Project No. BQU2003-07343) is gratefully
acknowledged.
˚
C
CCD diffractometer (operating at 50 kV and 20 mA); monoclinic,
23H27BF2O4; Mr 416.26; T 293(2) K; k 0.71073 A; Bruker-Smart
˚
space group Cc, a = 25.892(2), b = 7.1634(7), c = 13.067(1) A,
3
b = 110.620(2)ꢁ, V = 2268.4(4) A , Z = 4, Dc = 1.219 g cmꢁ3, l
˚
(mmꢁ1) = 0.092. The data were collected over a hemisphere of the
reciprocal space by combination of three exposure sets. The cell
parameters were determined and refined by least-squares fit of all
reflections collected [range = 1.68–29.46ꢁ; index range = (ꢁ25, ꢁ9,
ꢁ17) to (35, 9, 9)]. Each exposure of 20 s covered 0.3ꢁ in x. The
first 50 frames were recollected at the end of the data collection to
monitor crystal decay. No appreciable decay in the intensities of
standard reflections was observed. The structure was solved by
direct methods and refined by full-matrix least-squares on F2 [23].
Anisotropic thermal parameters were used in the last cycles of
refinement for all non-hydrogen atoms with some exceptions. All
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˚
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