Synthesis of mono-, Di-, and tripalladated 1,3,5-benzenetricarboxaldehyde complexes

Article abstract of DOI:10.1021/om9005966

The oxidative addition of 2,4,6-tribromo-1,3,5-benzenetricarboxaldehyde (C₆(CHO)₃Br₃) to 1, 2, or 3 equiv of [Pd(dba)₂] ([Pd₂(dba)₃]?dba) and N^N affords, respectively, the mono-, di-, or t

Full text of DOI:10.1021/om9005966

Organometallics 2009, 28, 6101–6108 6101
DOI: 10.1021/om9005966
Synthesis of Mono-, Di-, and Tripalladated
1,3,5-Benzenetricarboxaldehyde Complexes
ꢀ
Jose Vicente,* Rashmi V. Shenoy, and Eloısa Martınez-Viviente
´ ´ ´
Grupo de Quımica Organometalica, Departamento de Quımica Inorganica, Facultad de Quımica,
ꢀ
Universidad de Murcia, E-30071 Murcia, Spain
ꢀ
Peter G. Jones
€
Institut fu€r Anorganische und Analytische Chemie, Technische Universitat Braunschweig, Postfach 3329,
38023, Braunschweig, Germany
Received July 9, 2009
The oxidative addition of 2,4,6-tribromo-1,3,5-benzenetricarboxaldehyde (C6(CHO)3Br3) to 1, 2, or
3 equiv of [Pd(dba)2] ([Pd2(dba)3] dba) and N∧N affords, respectively, the mono-, di-, or trinuclear
3
complexes [Pd{C6(CHO)3Br2}Br(N∧N)] (N∧N = tmeda = N,N,N0,N0-tetramethylethylenediamine
(1a), tbbpy=4,40-di-tert-butyl-2,20-bipyridine (1b), bpy=2,20-bipyridine, (1c)); [{PdBr(N∧N)}2{μ2-
C6(CHO)3Br}] (N∧N=tmeda (2a), tbbpy (2b)); or [{PdBr(N∧N)}3{μ3-C6(CHO)3}] (N∧N=tmeda
(3a), tbbpy (3b)). The reactions of C6(CHO)3Br3 with a mixture of [Pd(dba)2] and PR3 lead, depending
on the nature of the phosphine and the molar ratio of the reagents, to the mononuclear trans-[Pd{C6-
(CHO)3Br2}Br(PR3)2] (R=Ph (1d), R3=Me2Ph (1e)) or the dinuclear [{trans-PdBr(PMe2Ph)2}2{μ2-
C6(CHO)3Br}] (2e) complex. All attemptstopreparetrinuclearphosphinecomplexesusing thismethod
of synthesis have been unsuccessful. However, displacement of the tbbpy ligand in 3b by an excess of
PMe3 affords the trinuclear complex [{trans-PdBr(PMe3)2}3{μ3-C6(CHO)3}] (3f). The crystal struc-
tures of 1b, 1d, 2a CDCl3, and 2e have been determined by X-ray diffraction studies.
3
Introduction
carbon and carbon-heteroatom bond-forming reactions.1
Suitable substituents ortho to the Pd atom may lead to
cyclopalladated compounds,2-7 influence the reactivity of
the complexes,4-6,8-11 or participate in the formation of
organic compounds.2,4,5,10-13 Consequently, there have
been intensive studies of the synthesis of Pd(II) aryl com-
plexes14,15 and of their reactivity,2,5-7,9,11,12,15,16 to under-
stand the mechanism of such catalytic or stoichiometric
reactions. This rich chemistry of ortho-substituted aryl
Pd(II) complexes has prompted us to explore the possibility
of synthesizing polypalladated benzene derivatives with
functionalized organic substituents ortho to each Pd.
The chemistry of arylpalladium complexes is a topic
of great interest because of the involvement of these com-
pounds in many important palladium-catalyzed carbon-
*To whom correspondence should be addressed. For the synthesis
and properties of compounds, E-mail: jvs1@um.es (J.V.); eloisamv@
um.es (E.M-V.); rashmi@um.es (R.V.S.). Web: http://www.um.es/gqo/.
For X-ray diffraction studies, E-mail: p.jones@tu-bs.de (P.G.J.).
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2009 American Chemical Society
Published on Web 10/02/2009
pubs.acs.org/Organometallics

6102 Organometallics, Vol. 28, No. 20, 2009
Vicente et al.
Although the synthesis and applications of polymetalated
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Article
Organometallics, Vol. 28, No. 20, 2009 6103
Scheme 1
coordination mode has been described as well.40 These
compounds have been proposed as models for benzene
adsorption at a 3-fold site on the surface of a close-packed
metal lattice.38 Very recently, a similar situation has been
described for Pd in a μ3-tripalladium sandwich complex,41
and there are also reports on Pd3 to Pd5 sheets between
polycyclic aromatic hydrocarbon ligands.42 However, there
has been very little research on σ-bonded polymetalated
derivatives of benzene with transition metals. Until recently
the only examples were 1,3,5-C6H3[Mn(CO)5]3 (I),43 1,3,5-
C6H3[Fe(η5-Cp)(CO)2]3 (II),43,44 and 1,3,5-C6H3[Fe(η5-
C5H4Me)(CO)2]3 (III),45 prepared in two steps involving
the reaction of Na[M] ([M]=[Mn(CO)5], [Fe(η5-Cp)(CO)2]
or [Fe(η5-C5H4Me)(CO)2]) with 1,3,5-C6H3(COCl)3 and
subsequent decarbonylation of the resulting 1,3,5-C6H3[C-
(O)M]3 triacyl complexes. Complexes I and II were later
prepared by reaction of 1,3,5-triiodobenzene with 3 equiv of
[KMn(CO)5] or [Fe(η5-Cp)(CO)2]ZnCl, respectively.46 In
2001 our group published the first tripalladated benzene
derivative, prepared by oxidative addition of 1,3,5-triiodo-
mesitylene to 3 equiv of [Pd(dba)2] in the presence of chelat-
ing N-donor ligands.47 Shortly after that, another group
reported the first 3-fold cyclopalladation of a single benzene
ring, 1,3,5-tris(di-2-pyridylamino)benzene.48 Since then
there have been no further reports on the subject, in spite
of its potential for the Pd-mediated synthesis of organic
polycyclic compounds and in the field of metallodendri-
mers.49 With the aim of pursuing these research lines, we
decided to explore the possibility of synthesizing tripalla-
dated benzene derivatives with functionalized ortho substit-
uents, and we wish to report here our first successes,
involving derivatives of 1,3,5-triformylbenzene.
Results and Discussion
2,4,6-Tribromo-1,3,5-benzenetricarboxaldehyde (C6(CH-
O)3Br3) adds oxidatively to [Pd(dba)2] ([Pd2(dba)3] dba) in
3
the presence of chelating nitrogen donor ligands (N∧N) to
give mono-, di-, or trinuclear complexes (Scheme 1). Thus,
the reaction of equimolecular amounts of the three reagents
led to mononuclear complexes [Pd{C6(CHO)3Br2}Br(N∧N)]
(N∧N = tmeda = N,N,N0,N0-tetramethylethylenediamine
(1a), tbbpy = 4,40-di-tert-butyl-2,20-bipyridine (1b), bpy =
2,20-bipyridine (1c)) as the major products. However, 1a was
obtained together with the dinuclear complex [{PdBr-
(tmeda}2{μ2-C6(CHO)3Br}] (2a) and the starting arene, C6-
(CHO)3Br3 (6.5:1:1.8 molar ratio), while 1b was contami-
nated with C6(CHO)3Br3 (3:1 molar ratio). 1c was obtained
as a single product. Mixtures of products were also formed in
most attempts to prepare dinuclear [{PdBr(N∧N)}2{μ2-C6-
(CHO)3Br}] (N∧N = tmeda (2a), tbbpy (2b)) or trinuclear
[{PdBr(N∧N)}3{μ3-C6(CHO)3}] (N∧N=tmeda (3a), tbbpy
(3b)) complexes. Thus, the reaction of C6(CHO)3Br3,
[Pd(dba)2], and N∧N in a ca. 1:2:2 molar ratio afforded the
dipalladated complex 2a or 2b as the major product, together
with the corresponding mononuclear and trinuclear com-
plexes (2a:1a:3a=7:4:1 and 2b:1b:3b=8:3:1 molar ratios).
(40) Lau, J. P.-K.; Lin, Z.-Y.; Wong, W.-T. Angew. Chem., Int. Ed.
2003, 42, 1935.
(41) Murahashi, T.; Fujimoto, M.; Kawabata, Y.; Inoue, R.; Ogoshi,
S.; Kurosawa, H. Angew. Chem., Int. Ed. 2007, 46, 5440.
(42) Murahashi, T.; Fujimoto, M.; Oka, M.; Hashimoto, Y.;
Uemura, T.; Tatsumi, Y.; Nakao, Y.; Ikeda, A.; Sakaki, S.; Kurosawa,
H. Science 2006, 313, 1104. Murahashi, T.; Kato, N.; Uemura, T.; Kurosawa,
H. Angew. Chem., Int. Ed. 2007, 46, 3509.
(43) Hunter, D. J. B.; Szigety, A. B. Organometallics 1989, 8, 2670.
(44) Hunter, A. D. Organometallics 1989, 8, 1118.
(45) Hunter, A. D.; McLernon, J. L. Organometallics 1989, 8,
2679.
(46) Artamkina, G. A.; Shilova, E. A.; Shtern, M. M.; Beletskaya, I.
P. Russ. J. Org. Chem. 2003, 39, 1282. Artamkina, G. A.; Beletskaya, I. P.
Mendeleev Commun. 2003, 13, 43.
(47) Vicente, J.; Lyakhovych, M.; Bautista, D.; Jones, P. G. Organo-
metallics 2001, 20, 4695.
(48) Sumby, C. J.; Steel, P. J. Organometallics 2003, 22, 2358.
(49) Newkome, G. R.; He, E.; Moorefield, C. N. Chem. Rev. 1999, 99,
1689.

6104 Organometallics, Vol. 28, No. 20, 2009
Vicente et al.
Table 1. Crystal Data for Complexes 1b, 1d, 2a CDCl3, and 2e 11/2CH2Cl2
3
3
2a CDCl3
1b
1d
2e 11/2CH2Cl2
3
3
formula
Mr
C27H27Br3N2O3Pd
773.64
0.28 ꢀ 0.16 ꢀ 0.07
monoclinic
P21/c
C45H33Br3O3P2Pd
1029.78
0.35 ꢀ 0.30 ꢀ 0.15
monoclinic
P21/n
C22H35DBr3Cl3N4O3Pd2
964.44
C42.5H50Br3Cl3O3P4Pd2
1291.59
cryst size (mm3)
cryst syst
0.40 ꢀ 0.20 ꢀ 0.05
0.35 ꢀ 0.10 ꢀ 0.05
monoclinic
P21/c
triclinic
P1
space group
cell constants
˚
a (A)
9.0731(9)
19.278(2)
16.026(2)
90
104.348(5)
90
2715.7(5), 4
0.71073
1.892
1512
133
5.129
13.6265(8)
20.8536(12)
14.1963(8)
90
102.804(4)
90
3933.7(4), 4
0.71073
1.739
2032
133
3.642
8.6227(8)
21.058(2)
18.147(2)
90
98.719(4)
90
3256.8(6), 4
0.71073
1.967
1872
133
5.061
10.9157(11)
12.8369(12)
18.423(2)
75.317(4)
80.263(4)
82.055(4)
2448.8(4), 2
0.71073
1.752
1274
133
3.513
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A ), Z
˚
λ (A)
F (calcd) (Mg m-3
F(000)
)
T (K)
μ (mm-1
)
transmissions
θ range (deg)
limiting indices
0.7153-0.4307
1.68-28.28
-12 e h e 12
-25 e k e 25
-21 e l e 21
0.6111-0.4896
1.77-30.52
-19 e h e 19
-29 e k e 29
-20 e l e 20
0.7860-0.4958
1.49-30.52
-12 e h e 12
-30 e k e 30
-25 e l e 25
0.8439-0.5590
1.65-30.51
-15 e h e 15
-18 e k e 18
-26 e l e 26
no. of rflns
measd
indep
Rint
abs cor
no. of data/restraints/params
S (F2)
R1 (I>2(I))
wR2 (all reflns)
largest diff peak (e A
47839
6730
0.1032
multiscan
6730/20/336
1.065
0.0385
0.0911
0.876
94467
12008
0.0315
multiscan
12008/0/487
1.054
0.0222
0.0506
0.729
70474
9944
0.0478
multiscan
9944/0/342
1.122
0.0287
0.0563
1.083
55883
14874
0.0478
multiscan
14874/51/543
1.028
0.0429
0.1056
2.043
-3
˚
)
Similarly, the reaction of C6(CHO)3Br3, [Pd(dba)2], and
tbbpy in a 1:3:3 molar ratio gave the trinuclear complex 3b,
together with a small amount of 2b (5:1 molar ratio). The use
of a ca. 1:4:4 molar ratio of the reagents afforded 3b as a
single product, while for tmeda a 9:1 mixture of 3a and 2a
was obtained. With the ligand bpy, the oxidative addition
reaction in a 1:3:3 or even 1:6:6 molar ratio afforded mix-
tures of two compounds, which according to their 1H NMR
data (in d6-DMSO) seem to be a dinuclear and a trinu-
clear complex, but their insolubility in common solvents
prevented separation. All the other mixtures could be
separated by preparative TLC on silica gel, using as
eluent CH2Cl2 or mixtures of EtOAc/hexane or CH2Cl2/
acetone. The order of elution was always, as expected,
C6(CHO)3Br3 >1>2>3.
The behavior described above contrasts with that repor-
ted for 1,3,5-C6Me3I3,47 which reacts with a mixture
of [Pd(dba)2] and tbbpy or bpy to give tripalladated
[{PdI(N∧N)}3(μ3-C6Me3)], even when substoichiometric
amounts of Pd and N∧N were used. In contrast, oxidative
addition reactions with phosphines instead of chelating N∧N
ligands occurred in a very similar manner with both 1,3,5-
trihalo derivatives. Thus, in the reactions of C6(CHO)3Br3
with [Pd(dba)2] and PPh3 we could only isolate a mono-
nuclear complex, trans-[Pd{C6(CHO)3Br2}Br(PPh3)2] (1d),
when a 1:1:2 molar ratio was used. In this reaction, a ca. 1:1
mixture of cis (not observed in the reaction with 1,3,
5-C6Me3I3) and trans isomers formed, from which the trans
isomer could be separated by crystallization. Similar reac-
tions in 1:2:4 or 1:3:6 molar ratios did not afford the
corresponding di- or trinuclear complexes, but mixtures of
1d and OPPh3. However, the use of the more basic and less
sterically demanding phosphine PMe2Ph allowed the synthe-
sis of trans-[Pd{C6(CHO)3Br2}Br(PMe2Ph)2] (1e) or [{trans-
PdBr(PMe2Ph)2}2{μ2-C6(CHO)3Br}] (2e) when the stoichio-
metric amounts of C6(CHO)3Br3, [Pd(dba)2], and PMe2Ph
were used. With a 1:3:6 ratio of the reactants, a tripalladated
species could not be obtained, but only mixtures of 2e with
other minor unidentified compounds. A final attempt to
obtain a tripalladated derivative with phosphine ligands was
carried out with the less bulky PMe3, but the reaction of
C6(CHO)3Br3 with [Pd(dba)2] and PMe3 in a 1:3:6 ratio
afforded a complicated mixture of compounds. Neverthe-
less, the trinuclear complex [{trans-PdBr(PMe3)2}3{μ3-C6-
(CHO)3}] (3f) could be obtained by displacement of the
tbbpy ligand by PMe3. Therefore, the failure to synthesize
3f by an oxidative addition reaction does not seem to be due
to thermodynamic but to kinetic effects.
Structure of Complexes. The 1H, 13C, and 31P NMR data
of complexes 1-3 agree with the structures proposed in
Scheme 1. The mononuclear complexes (1a-e) show the
expected spectra for the only possible isomer in 1a-c and for
the presence in solution of only the trans isomer of complexes
1d-e (31P NMR). The dinuclear complexes 2a, 2b, and 2e
show two 1:2 singlets for the CHO groups in their 1H and 13
C
NMR spectra, which is consistent with the presence of a C2
symmetry axis (confirmed to a reasonable approximation for
2a in the solid state). The trinuclear PMe3 complex 3f shows a
single resonance for the CHO groups (1H and 13C NMR) and
for the phosphine ligands (31P NMR), an indication that the
molecule has an all trans geometry. In contrast, the other
trinuclear complexes 3a and 3b show in their NMR spectra a
2:1 pattern for all resonances. This observation is consistent
with the structure depicted for these complexes in Scheme 1,
where two of the Br atoms lie on one side of the aryl plane,
while the third Br atom points to the other side, and implies

Article
Organometallics, Vol. 28, No. 20, 2009 6105
Figure 1. Thermal ellipsoid plot (50% probability level) of 1b.
˚
Selected bond lengths (A) and angles (deg): Pd-C(1)=1.994(4),
Pd-N(11) = 2.049(4), Pd-N(21) = 2.099(4), Pd-Br(1) =
Figure 3. Thermal ellipsoid plot (50% probability level) of 2a
˚
2.4234(6), Pd O(1) 2.832(2); C(1)-Pd-N(11) = 95.94(15),
3
3 3 3
CDCl3. Selected bond lengths (A) and angles (deg): Pd(1)-C(1)=
C(1)-Pd-Br(1) = 86.02(12), N(11)-Pd-N(21) = 79.59(14),
1.984(3), Pd(1)-N(1)=2.165(2), Pd(1)-N(2)=2.109(2), Pd(1)-
N(21)-Pd-Br(1)=98.30, C(1)-Pd O(1)=72.0(1).
3 3 3
Br(1)=2.4311(4), Pd(1) O(3)=2.772(2), Pd(2)-C(3)=1.971(3);
3 3 3
Pd(2)-N(3) =2.121(3); Pd(2)-N(4) =2.164 (3), Pd(2)-Br(2) =
2.4313(4), Pd(2) (O1) = 2.806(2), D(99) (O2) = 2.35; C-
(1)-Pd(1)-N(2) = 94.53(10), C(1)-Pd(1)-Br(1) =87.02(8), N-
(1)-Pd(1)-N(2)=84.32(9), N(1)-Pd(1)-Br(1)=94.47(7), C(1)-
3 3 3
3 3 3
Pd(1) O(3)=74.20(9),C(3)-Pd(2)-N(3)=93.79(11),C(3)-Pd-
3 3 3
(2)-Br(2) = 86.97(8), N(3)-Pd(2)-N(4) = 84.33(10), N(4)-
Pd(2)-Br(2)=94.89(7), C(3)-Pd(2) O(1)=73.20(10), C(99)-
3 3 3
D(99) (O2)=153.
3 3 3
Figure 2. Thermal ellipsoid plot (50% probability level) of 1d.
˚
Selected bond lengths (A) and angles (deg): Pd-C(1)=2.0163(15),
Pd-P(1)=2.3426(4), Pd-P(2)=2.3279(4), Pd-Br(1)=2.4865(2),
Pd O(1) = 2.8561(13); C(1)-Pd-P(1) = 89.42(4), C(1)-Pd-
3 3 3
P(2)=91.02(4), P(1)-Pd-Br(1)=91.999(11), P(2)-Pd-Br(1)=
87.891(12), C(1)-Pd O(1)=71.29(5).
3 3 3
Figure 4. Thermal ellipsoid plot (30% probability level) of 2e.
˚
Selected bond lengths (A) and angles (deg): Pd(1)-C(1) =
that the rotation around the Pd-aryl bonds is hindered. No
traces of a second isomer were detected, which is consistent
with the geometry 2a and 2b.
2.023(4), Pd(1)-P(1) = 2.3162(11), Pd(1)-P(2) = 2.3152(11),
Pd(1)-Br(1)=2.5049(5), Pd(1) O(1)=2.865(3), Pd(2)-C(3)
3 3 3
A complete assignment of the aryl 13C chemical shifts has
been made (see Table 1 in the Supporting Information). As
expected, the 13CHO groups appear highly deshielded
(190-202 ppm) and the 13C-Pd nuclei are observed in the
range 170-181 ppm for the complexes with N∧N ligands and
184-189 ppm for the phosphino complexes. The increase in
the number of Pd atoms ortho to a given CHO group (n)
deshields the corresponding 13C-CHO nucleus. Thus, for
n=2 this resonance appears in the range 147-150 ppm, for
n=1 at 137-141 ppm, and for n=0 at values (134-135 ppm)
similar to that in C6(CHO)3Br3 (138.4 ppm). Finally, the
13C-Br nuclei in complexes 2 (130-133 ppm) are slightly
deshielded with respect to those in C6(CHO)3Br3 (124.9
ppm), while in complexes 1 they do not shift significantly
(124-129 ppm). In spite of the tendencies observed, a
=2.033(4), Pd(2)-P(3)=2.3178(11), Pd(2)-P(4)=2.3315(11),
Pd(2)-Br(2) = 2.5080(6); C(1)-Pd(1)-P(1) = 90.41(11), C-
(1)-Pd(1)-P(2) = 91.97(11), P(1)-Pd(1)-Br(1) = 89.78(3),
P(2)-Pd(1)-Br(1) = 87.76(3), C(1)-Pd(1) O(1) = 70.3(1),
3 3 3
C(3)-Pd(2)-P(3)=90.39(11), C(3)-Pd(2)-Pd(4)=87.93(11),
P(3)-Pd(2)-Br(2) =91.23(3), P(4)-Pd(2)-Br(2)=90.55(3).
simplistic interpretation of these 13C chemical shifts in terms
of the electron density should be avoided.50
The 31P NMR spectra of the phosphine complexes 1d, 1e,
2e, 3f show a single 31P resonance, in agreement with the
trans geometry of the complexes. As usual, the 31P chemical
shift decreases in the order PPh3 (δ 21.1 ppm for 1d) >
(50) Martınez-Viviente, E.; Pregosin, P. S.; Tschoerner, M. Magn.
Reson. Chem. 2000, 38, 23.

6106 Organometallics, Vol. 28, No. 20, 2009
Vicente et al.
PMe2Ph (δ -7.5 ppm for 1e and -10.7 ppm for 2e) > PMe3
(δ -18.8 ppm for 3f).
The crystal and molecular structures of the complexes 1b
between the two aryl groups have been established. The
potential of the aldehyde functional groups for further
synthesis will be investigated.
(Figure 1), 1d (Figure 2), 2a CDCl3 (Figure 3), and
3
2e 11/2CH2Cl2 (Figure 4) have been determined by X-ray
Experimental Section
3
diffraction studies (Table 1). Crystals of apparently good
optical quality were also obtained for the PMe3 complex 3f
and gave diffraction patterns corresponding to a hexagonal
cell. However, the structure could only be interpreted as a
pseudomerohedral 3-fold twin in space group P21/c with β=
120°. The refinement proved unsatisfactory, with poor R
values, an impossibly irregular geometry, and considerable
areas of residual electron density presumably corresponding
to disordered solvent. The qualitative nature of the com-
pound was thus confirmed, but the structure is quantitatively
unreliable and we do not present it here.
NMR spectra (1H, 13C, and 31P) were recorded on Bruker
Avance 200, 300, 400, and 600 spectrometers at room tempera-
ture. Chemical shifts are given in ppm (δ) relative to TMS (1H,
13C) or H3PO4 (31P). Infrared spectra were recorded on a Perkin-
Elmer 16F-PC-FT spectrometer with Nujol mulls between
polyethylene sheets. Melting points were determined on a Reich-
ert apparatus and are uncorrected. Elemental analyses were
carried out with a Carlo Erba 1106 microanalyzer. All experi-
ments were conducted under a N2 atmosphere using Schlenk
techniques. CH2Cl2 was distilled before use. “[Pd(dba)2]”52 and
1,3,5-tribromo-2,4,6-benzenetricarbaldehyde53 were prepared
according to literature procedures. tbbpy (Aldrich), tmeda
(Fluka), bpy (Fluka), PPh3 (Fluka), PMe2Ph (Aldrich), and
PMe3 (Aldrich) were used as received.
The four structures solved show somewhat distorted
square planar coordination around the Pd atoms. Mean
deviations from the best plane through Pd and the four
Synthesis of [Pd{C6(CHO)3Br2}Br(tmeda)] (1a). [Pd(dba)2]
(144 mg, 0.25 mmol), tmeda (37 μL, 0.25 mmol), and
C6(CHO)3Br3 (100 mg, 0.25 mmol) were mixed in dry degassed
toluene (15 mL). The resulting mixture was stirred at 60 °C for
1 h until the dark red color of [Pd(dba)2] was no longer observed.
The brownish suspension was then concentrated in vacuo, and
the residue was extracted with CH2Cl2 (20 mL). The extract was
filtered over Celite, and the resulting solution was evaporated to
dryness. Et2O (15 mL) was added to precipitate a bright yellow
solid, which was filtered off and thoroughly washed with Et2O.
The solid obtained is a mixture of complexes 2a, 1a, and
C6(CHO)3Br3 in ca. 1:6.5:2 molar ratio. The products were
separated by preparative TLC on silica gel using a mixture of
CH2Cl2/acetone (5:3) as eluent. The band with Rf=0.91 was
collected, and the product was extracted with acetone (30 mL).
Evaporation of the acetone and addition of Et2O (15 mL)
rendered a solid, which was filtered off, thoroughly washed with
Et2O, and dried in vacuo to give 1a as a yellow solid. Yield: 84
˚
˚
donor atoms are in the range 0.02-0.07 A [0.021 A for
complex 1b, 0.069 A for 1d, 0.069 A (Pd1) and 0.023 A (Pd2)
˚
˚
˚
˚
˚
for 2a, and 0.020 A (Pd1) and 0.056 A (Pd2) for 2e].
Additionally, all complexes show weak interactions between
the Pd atoms and the O atoms of the ortho formyl groups,
with the sole exception of Pd2 in the dinuclear complex 2e.
The Pd O distances for these weak interactions are in the
˚
3 3 3
˚
˚
range 2.77-2.86 A (2.832(3) A for 1b, 2.8561(13) A for 1d,
˚
˚
2.772(2) A (Pd1 O3) and 2.806(2) A (Pd2 O1) for 2a,
3 3 3
3 3 3
˚
and 2.865(3) A (Pd1 O1) for 2e), lower than the sum of the
3 3 3
van der Waals radii (3.15 A).51 Clearly these Pd O inter-
˚
3 3 3
actions do not cause significant deviation from planarity
around the Pd atoms.
The Pd-C bond distances show the following order: 2e
[2.033(4) A (Pd2) and 2.023(4) A (Pd1)] > 1d (2.0163(15) A)
˚
˚
˚
˚
˚
˚
> 1b (1.994(4) A) > 2a [1.984(3) A (Pd1) and 1.971(3) A
(Pd2)]. Although the differences are small, they follow the
order of trans influence: Br > tbbpy/tmeda. The slightly
longer Pd-C bonds in the dinuclear complex 2e compared
with mononuclear 1d (both with Br trans to the aryl group)
might be due to steric effects. In contrast, the Pd-Br bonds
in phosphine complexes 1d and 2e are considerably longer
1
mg (54%). Mp: 214-215 °C. IR: ν(CO) 1697 cm-1 (sb). H
NMR (400 MHz, CDCl3): δ 10.93 (s, 2H, CHO), 10.18 (s, 1H,
CHO), 2.85-2.80 (m, 2H, CH2), 2.80 (s, 6H, Me), 2.72-2.67 (m,
2H, CH2), 2.31 (s, 6H, Me). 13C{1H} NMR (50.3 MHz, CDCl3):
δ 195.2 (2C, CHO), 191.6 (1C, CHO), 173.7 (1C, C1-Pd), 140.9
(2C, C2-CHO), 133.4 (1C, C4-CHO), 128.1 (2C, C3-Br), 63.1
and 59.4 (1C, CH2), 51.4 and 49.6 (2C, Me). Anal. Calcd for
C15H19Br3N2O3Pd: C, 28.99; H, 3.08; N, 4.51. Found: C, 29.06;
H, 2.84; N, 4.30.
˚
˚
˚
[2.4865(2) A for 1d, 2.5049(5) A (Pd1) and 2.5080(6) A (Pd2)
for 2e] than those in tbbpy and tmeda complexes 1b
˚
˚
˚
(2.4234(6) A) and 2a [2.4311(4) A (Pd1) and 2.4313(4) A
(Pd2)], in agreement with the order of trans influence: aryl .
tbbpy/tmeda. Again, the larger Pd-Br distances in the
dinuclear complexes 2e and 2a, compared with 1d and 1b,
respectively, might be due to steric effects. Finally, the Pd-N
bond distances in 1b (Pd-N trans to aryl, 2.099(4) A, Pd-N
trans to Br, 2.049(4) A) and 2a [Pd-N trans to aryl, 2.165(2)
Synthesis of [Pd{C6(CHO)3Br2}Br(tbbpy)] (1b). [Pd(dba)2]
(145 mg, 0.25 mmol), tbbpy (68 mg, 0.25 mmol), and C6-
(CHO)3Br3 (100 mg, 0.25 mmol) were mixed under N2 in dry
degassed toluene (15 mL). The resulting mixture was stirred at
60 °C for 10 min until the dark red color of [Pd(dba)2] was no
longer observed. Workup as for 1a, afforded a yellow solid,
which was filtered off and thoroughly washed with Et2O. This
solid is a mixture of complex 1b and C6(CHO)3Br3 in 3:1 molar
ratio. The products were separated by preparative TLC on silica
gel using CH2Cl2 as eluent. The band with Rf=0.3 was collected,
and complex 1b (yellow solid) was isolated as for 1a. Yield:
111 mg (57%). Single crystals were grown by slow diffusion of
Et2O into a CDCl3 solution of 1b. Mp: 268-270 °C dec. IR:
ν(CO): 1698 cm-1 (sb). 1H NMR (300 MHz, CDCl3): δ 11.11 (s,
˚
˚
˚
˚
˚
A (Pd1), 2.164(3) A (Pd2); Pd-N trans to Br, 2.109(2) A
(Pd1), 2.121(3) A (Pd2)] also show the order of trans
˚
influence aryl > Br and the possible influence of steric effects
in the dinuclear complex.
Conclusion
3
2H, CHO), 10.25 (s, 1H, CHO), 9.27 (d, 1H, tbbpy, JHH=6
Hz), 7.96 (br s, 2H, tbbpy), 7.57 (dd, 1H, tbbpy, JHH=6 Hz,
3
We have synthesized and characterized a novel family of
mono-, di-, and tripalladated benzene derivatives and proved
that our previous report involving methyl ortho substituents
can be extended to complexes with functionalized ortho-
formyl-benzene, although significant differences in reactivity
4JHH=2 Hz), 7.32-7.27 (m, 2H, tbbpy), 1.45 (s, 9H, tBu), 1.38
(52) Takahashi, Y.; Ito, S.; Sakai, S.; Ishii, Y. J. Chem. Soc., Chem.
Commun. 1970, 1065. Heck, R. F. Palladium Reagents in Organic Synth-
esis; Academic Press: New York, 1985.
(53) Anthony, J. E.; Khan, S. I.; Rubin, Y. Tetrahedron Lett. 1997, 38,
3499. Bruns, D.; Miura, H.; Vollhardt, K. P. C. Org. Lett. 2003, 5, 549.
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Article
Organometallics, Vol. 28, No. 20, 2009 6107
(s, 9H, tBu). 13C{1H} NMR (100.6 MHz, CDCl3): δ 194.7 (2C,
CHO), 191.9 (1C, CHO), 170.7 (1C, C1-Pd), 164.5 and 164.4
(1C, C14 and 140 tbbpy), 156.5 and 154.3 (1C, C12 and 120
tbbpy), 150.8 and 150.2 (1C, CH16 and 160 tbbpy), 141.3 (2C,
C2-CHO), 134.0 (C3-CHO), 126.6 (2C, C3-Br), 124.6 and
124.3 (1C, CH15 and 150 tbbpy), 119.2 and 118.5 (1C, CH13 and
130 tbbpy), 35.8 (2C, CMe3), 30.6 and 30.4 (3C, CMe3). Anal.
Calcd for C27H27Br3N2O3Pd: C, 41.92; H, 3.92; N, 3.62. Found:
C, 42.30; H, 3.52; N, 3.38
3JPC = 45 Hz), 132.6 (1C, C4-CHO), 129.9 (s, 2C, para C’s
4
PMe2Ph), 129.5 (vt, 4C, ortho C’s PMe2Ph, 2JPC þ JPC=10 Hz),
5
128.5 (2C, C3-Br), 128.2 (vt, 4C, meta C’s PMe2Ph, 3JPC þ JPC
3
=9 Hz), 13.4 (vt, 4C, PMe2Ph, 1JPC þ JPC=31 Hz). 31P{1H}
NMR (121.4 MHz, CDCl3):
δ -7.5. Anal. Calcd for
C25H25Br3O3P2Pd: C, 38.42; H, 3.22. Found: C, 38.80; H, 3.25.
Synthesis of [{PdBr(tmeda)}2{μ2-C6(CHO)3Br}] (2a). [Pd(dba)2]
(332 mg, 0.57 mmol), tmeda (86 μL, 0.57 mmol), and C6(CHO)3Br3
(100 mg, 0.25 mmol) were mixed in dry degassed toluene (15 mL).
The resulting mixture was stirred at 65 °C for 40 min until the dark
red color of [Pd(dba)2] was no longer observed. Workup as for 1a,
afforded a bright yellow solid, which was filtered off and thoroughly
washed with Et2O. The solid obtained is a mixture of complexes 3a,
2a, and1a in a ca. 1:7:4 molar ratio. The products were separated by
preparative TLC on silica gel using a mixture of CH2Cl2 /acetone
(5:3) as eluent. The band with Rf=0.70 was collected, and complex
2a (yellow solid) was isolated as in the case for 1a. Yield: 109 mg
Synthesis of [Pd{C6(CHO)3Br2}Br(bpy)] (1c). A mixture of
[Pd(dba)2] (112 mg, 0.193 mmol), bpy (31 mg, 0.193 mmol), and
C6(CHO)3Br3 (70 mg, 0.175 mmol) were mixed under N2 in dry
degassed toluene (15 mL). The resulting mixture was stirred at
60 °C for 30 min until the dark red color of [Pd(dba)2] was no
longer observed. Workup as for 1a, afforded a yellow solid,
which was filtered off, thoroughly washed with Et2O and
CH2Cl2, and dried in vacuo to give 1c as a yellow solid. Yield:
78 mg (67%). Mp: 265-266 °C. IR: ν(CO) 1684 (sb) cm-1. 1H
NMR (300 MHz, d6-DMSO): δ 11.01 (s, 2H, CHO), 10.16 (s,
1H, CHO), 9.13 (d, 1H, bpy, 3JHH=5 Hz), 8.66-8.82 (m, 2H,
(40%). Single crystals of 2a CDCl3 were grown by slow
3
diffusion of hexane into a CHCl3 solution of 2a. Mp: 221-
222 °C dec. IR: ν(CO) 1697 (s) and 1676 (s) cm-1. 1H NMR (400
MHz, CDCl3): δ 12.11 (s, 1H, CHO), 10.93 (s, 2H, CHO), 2.82
(s, 6H, Me), 2.80 (s, 6H, Me), 2.82-2.75 (m, 4H, CH2), 2.70-2.65
(m, 4H, CH2), 2.30 (s, 6H, Me), 2.28 (s, 6H, Me). 13C{1H} NMR
(75.4 MHz, CDCl3): δ 200.1 (1C, CHO), 195.8 (2C, CHO), 179.5
(2C, C1-Pd), 150.3 (1C, C2-CHO), 137.4 (2C, C3-CHO), 132.3
(1C, C4-Br), 62.9 and 59.1 (2C, CH2), 51.3 and 51.1 (2C, Me), 49.2
(4C, Me).Anal.CalcdforC21H35Br3N4O3Pd2: C, 29.88; H, 4.18; N,
6.64. Found: C, 30.09; H, 4.22; N, 6.56.
3
bpy), 8.34 (t, 1H, bpy, JHH =8 Hz), 8.3-8.24 (m, 1H, bpy),
7.87-7.82 (m, 1H, bpy), 7.56-7.5 (m, 2H, bpy). 13C{1H} NMR
(75.4 MHz, d6-DMSO): δ 193.7 (2C, CHO), 193.4 (1C, CHO),
170.2 (1C, C1-Pd), 155.9 and 154.1 (1C, C12 and 120 bpy), 150.6
and 149.6 (1C, CH16 and 140 bpy), 140.6 and 140.4 (1C, CH14
and 140 bpy), 140.4 (2C, C2-CHO), 135.0 (1C, C4-CHO),
128.0 and 127.5 (1C, CH15 and 150 bpy), 124.5 (2C, C3-Br),
123.9 and 123.3 (1C, CH13 and 130 bpy). Anal. Calcd for
C19H11Br3N2O3Pd: C, 34.50; H, 1.68; N, 4.24. Found: C,
34.47; H, 1.51; N, 4.13.
Synthesis of [{PdBr(tbbpy)}2{μ2-C6(CHO)3Br}] (2b). [Pd(dba)2]
(332 mg, 0.575 mmol), tbbpy (154 mg, 0.575 mmol), and
C6(CHO)3Br3 (100 mg, 0.25 mmol) were mixed under N2 in dry
degassed toluene (15 mL). The resulting mixture was stirred at
60 °C for 15 min until the dark red color of [Pd(dba)2] was no
longer observed. Workup as for 1a, afforded a yellow solid, which
was filtered off and thoroughly washed with Et2O. This solid is a
mixture of the complexes 3b, 2b, and 1b in a ca. 1:8:2 molar ratio.
The products were separated by preparative TLC on silica gel using
a mixture of EtOAc/hexane (2:3) as eluent. The band with Rf=0.7
was collected, and complex 2b (yellow solid) was isolated as for 1a
Yield: 140 mg (49%). Mp: 268 °C. IR: ν(CO) 1678 cm-1 (sb). 1H
NMR (300 MHz, CDCl3): δ 11.92 (s, 1H, CHO), 11.16 (s, 2H,
CHO), 9.24 (d, 2H, tbbpy, 3JHH=6 Hz), 7.92 (br s, 2H, tbbpy), 7.90
(br s, 2H, tbbpy), 7.59 (d, 2H, tbbpy, 3JHH=6 Hz), 7.49 (dd, 2H,
tbbpy, 3JHH=6 Hz, 4JHH=1 Hz), 7.30 (dd, 2H, tbbpy, 3JHH=6 Hz,
4JHH = 1 Hz), 1.40 (s, 18H, tBu), 1.34 (s, 18H, tBu). 13C{1H}
NMR (75.4 MHz, CDCl3): δ 199.1 (1C, CHO), 196.0 (2C, CHO),
176.1 (2C, C1-Pd), 163.9 and 163.6 (2C, C14 and 140 tbbpy),
156.0 and 154.4 (2C, C12 and 120 tbbpy), 151.1 and 150.6 (2C,
CH16 and 160 tbbpy), 150.0 (1C, C2-CHO), 138.8 (2C,
C3-CHO), 130.3 (1C, C4-Br), 124.8 and 123.9 (2C, CH15 and
150 tbbpy), 118.7 and 118.2 (2C, CH13 and 130 tbbpy), 35.7 (4C,
CMe3), 30.6 and 30.4 (6C, CMe3). Anal. Calcd for
C45H51Br3N4O3Pd2: C, 47.06; H, 4.48; N, 4.88. Found: C, 47.28;
H, 4.72; N, 4.92.
Synthesis of [{trans-PdBr(PMe2Ph)2}2{μ2-C6(CHO)3Br}]
(2e). A mixture of [Pd(dba)2] (144 mg, 0.25 mmol) and C6-
(CHO)3Br3 (50 mg, 0.125 mmol) was stirred for 2-3 min under
N2 in dry degassed toluene (15 mL) at RT. Then PMe2Ph (71 μL,
0.5 mmol) was added, and the resulting mixture was stirred for 2
h under the same conditions. Workup as for 1d, afforded a
brick-red solid, which was filtered off and thoroughly washed
with Et2O. This solid was purified by preparative TLC on silica
gel using a mixture of acetone/n-hexane (4:1) as eluent. The band
with Rf=0.92 was collected, and the product was extracted with
acetone (30 mL). Evaporation of the acetone and recrystalliza-
tion from CH2Cl2/Et2O gave 2e as yellow crystals. Yield: 73 mg
Synthesis of trans-[Pd{C6(CHO)3Br2}Br(PPh3)2] (1d). A mix-
ture of [Pd(dba)2] (216 mg, 0.375 mmol) and C6(CHO)3Br3 (150
mg, 0.375 mmol) was stirred for 2-3 min under N2 in dry
degassed toluene (20 mL) in an ice bath. Then PPh3 (196 mg,
0.75 mmol) was added, and the resulting mixture was stirred for
50 min under the same conditions. The solvent was then
evaporated to dryness, and the residue was extracted with
CH2Cl2 (20 mL). The extract was filtered over Celite, and the
resulting solution was concentrated to a small volume. Et2O
(15 mL) was added to precipitate a yellow solid, which was
filtered off and thoroughly washed with Et2O. Recrystallization
from CH2Cl2/Et2O gave 1d as yellow crystals. Yield: 145 mg
(37%). Single crystals were grown by slow diffusion of ether into
a CHCl3 solution of 1d. Mp: 241-243 °C dec. IR: ν(CO) 1699
cm-1(sb). 1H NMR (300 MHz, CDCl3): δ 10.29 (s, 2H, CHO),
9.85 (s, 1H, CHO), 7.63-7.5 (m, 12H, PPh3), 7.39-7.22 (m,
18H, PPh3). 13C{1H}NMR (75.4 MHz, CDCl3): δ 192.8 (s, 2C,
CHO), 191.1 (s, 1C, CHO), 188.6 (t, 1C, C1-Pd, 2JPC=5 Hz),
138.3 (s, 2C, C2-CHO), 134.7 (vt, 12C, ortho C’s PPh3, 2JPC
þ
4JPC=12 Hz), 133.5 (s, 1C, C4-CHO), 130.8 (s, 6C, para C’s
3
PPh3), 130.1 (vt, 6C, ipso C’s PPh3, 1JPC þ JPC=47 Hz), 128.7
3
5
(s, 2C, C3-Br), 128.2 (vt, 12C, meta C’s PPh3 JPC þ JPC=10
Hz). 31P{1H} NMR (121.4 MHz, CDCl3): δ 21.1. Anal. Calcd
for C45H33Br3O3P2Pd: C, 52.48; H, 3.23. Found: C, 52.43; H,
3.28.
Synthesis of trans-[Pd{C6(CHO)3Br2}Br(PMe2Ph)2] (1e). A
mixture of [Pd(dba)2] (72 mg, 0.125 mmol) and C6(CHO)3Br3
(50 mg, 0.125 mmol) was stirred for 2-3 min under N2 in dry
degassed toluene (15 mL) at RT. Then PMe2Ph (35.5 μL, 0.25
mmol) was added, and the resulting mixture was stirred for 2 h
under the same conditions. Workup as for 1d, afforded an
orange solid, which was filtered off and thoroughly washed
with Et2O. Recrystallization from CH2Cl2/Et2O gave 1e as
orange crystals. Yield: 49 mg (50%). Mp: 108 °C. IR: ν(CO)
1698 and 1688 cm-1 (sb). 1H NMR (400 MHz, CDCl3): δ 10.36
(s, 2H, CHO), 9.90 (s, 1H, CHO), 7.2-7.1 (m, 6H, PMe2Ph),
4
7.0-6.95 (m, 4H, PMe2Ph), 1.78 (vt, 12H, PMe2Ph, 2JPH þ JPH
(50%). Single crystals of 2e 11/2CH2Cl2 were grown by slow
diffusion of Et2O into a CDCl3 solution of 2e. Mp: 219 °C. IR:
3
=8 Hz). 13C{1H}NMR (100.6 MHz, CDCl3): δ 193.4 (s, 2C,
CHO), 190.9 (s, 1C, CHO), 185.8 (t, 1C, C1-Pd, 2JPC=6 Hz),
ν(CO) 1674 (sb) cm-1. 1H NMR (400 MHz, CDCl3): δ 11.18 (t,
1H, CHO, JPH =11 Hz), 10.54 (t, 1H, CHO, JPH =11 Hz),
138.7 (s, 2C, C2-CHO), 133.2 (vt, 2C, ipso C’s PMe2Ph, 1JPC
þ
5
5

6108 Organometallics, Vol. 28, No. 20, 2009
Vicente et al.
7.55-7.49 (m, 8H, PMe2Ph), 7.35-7.26 (m, 12H, PMe2Ph), 1.38
tBu), 1.41 (s, 18H, tBu), 1.38 (s, 9H, tBu), 1.35 (s, 18H, tBu).
13C{1H} NMR (100.6 MHz, CDCl3): δ 200.5 (1C, CHO), 199.7
(2C, CHO), 179.8 (1C, C1-Pd), 179.6 (2C, C3-Pd), 163.4 (1C),
163.3 (2C), 162.9 (1C) and 162.9 (2C) (C14 and 140 tbbpy), 156.3
(2C), 155.5 (1C), 154.6 (1C) and 154.0 (2C) (C12 and 120 tbbpy),
152.6 (1C), 150.6 (2C), 150.6 (2C) and 150.3 (1C) (CH16 and 160
tbbpy), 148.2 (1C, C4-CHO), 148.0 (2C, C2-CHO), 125.4
(1C), 123.8 (2C), 123.6 (2C) and 123.4 (1C) (CH15 and 150
tbbpy), 118.5 (2C), 118.3 (1C), 117.9 (2C) and 117.9 (1C) (CH13
and 130 tbbpy), 35.6 (4C, CMe3), 35.5 (2C, CMe3), 30.5 (6C,
CMe3), 30.5 (3C, CMe3), 30.4 (6C, CMe3), 30.4 (3C, CMe3).
Anal. Calcd for C63H75Br3N6O3Pd3: C, 49.67; H, 4.96; N, 5.52.
Found: C, 49.42; H, 5.08; N, 5.31.
2
4
(vt, 12H, PMe2Ph, 12 H, JPH þ JPH =4 Hz), 1.15 (vt, 12H,
4
PMe2Ph, 12 H, 2JPH þ JPH=4 Hz). 13C{1H}NMR (50.3 MHz,
CDCl3): δ 198.4 (s, 1C, CHO), 194.9 (s, 2C, CHO), 184.9 (t, 2C,
C1-Pd, 2JPC=5 Hz), 148.6 (br s, 1C, C2-CHO), 137.7 (br s, 2C,
1
3
C3-CHO), 133.5 (vt, 4C, ipso C’s PMe2Ph, JPC þ JPC=46
Hz), 133.3 (s, 1C, C4-Br), 131.8 (vt, 8C, ortho C’s PMe2Ph, 2JPC
4
þ JPC=12 Hz), 130.6 (s, 4C, para C’s PMe2Ph), 128.7 (vt, 8C,
5
meta C’s PMe2Ph, 3JPC þ JPC=10 Hz), 15.6 (vt, 4C, PMe2Ph,
3
3
1JPC þ JPC=30 Hz), 14.1 (vt, 4C, PMe2Ph, 1JPC þ JPC=30
Hz). 31P{1H} NMR (121.4 MHz, CDCl3): δ -10.7. Anal. Calcd
for C41H47Br3O3P4Pd2: C, 42.30; H, 4.07. Found: C, 42.62; H,
4.12.
Synthesis of [{PdBr(tmeda)}3{μ3-C6(CHO)3}] (3a). [Pd(dba)2]
(588 mg, 1.0 mmol), tmeda (150 μL, 1.0 mmol), and C6-
(CHO)3Br3 (100 mg, 0.25 mmol) were mixed in dry degassed
toluene (15 mL). The resulting mixture was stirred at 60 °C for
2.5 h until the dark red color of [Pd(dba)2] was no longer
observed. Workup as for 1a, afforded a bright yellow solid,
which was filtered off and thoroughly washed with Et2O. The
solid obtained is a mixture of complex 3a and 2a in a ca. 10:1
molar ratio. The products were separated by preparative TLC
on silica gel using a mixture of CH2Cl2/acetone (5:3) as eluent.
The band with Rf=0.16 was collected, and complex 3a (yellow
solid) was isolated as for 1a. Yield: 235 mg (88%). Mp: 230 °C.
IR: ν(CO) 1655 cm-1 (sb). 1H NMR (600 MHz, CDCl3): δ 11.97
(s, 2H, CHO), 11.77 (s, 1H, CHO), 2.87-2.6 (m, 12H, CH2),
2.80, 2.78, 2.77, 2.34, 2.27, and 2.26 (s, 6H, Me), 2.75-2.6 (m,
12H, CH2). 13C{1H} NMR (150.9 MHz, CDCl3): δ 201.0 (1C,
CHO), 200.8 (2C, CHO), 180.3 (1C, C1-Pd), 180.4 (2C,
C3-Pd), 147.9 (2C, C2-CHO), 147.6 (1C, C4-CHO), 63.2
(2C, CH2), 62.9 (1C, CH2), 59.1 (1C, CH2), 59.0 (2C, CH2), 51.6,
51.5, 50.8, 49.5, 49.2, and 49.1 (2C, Me). Anal. Calcd for
C27H51Br3N6O3Pd3: C, 30.40; H, 4.82; N, 7.88. Found: C,
30.39; H, 5.0; N,7.51.
Synthesis of [{trans-PdBr(PMe3)2}3{μ3-C6(CHO)3}] (3f).
Complex 3b (100 mg, 0.065 mmol) and PMe3 (787 μL of a 1
M solution in toluene, 0.787 mmol) were mixed under N2 in
degassed CH2Cl2 (15 mL) and stirred at RT for 20 h. The
reaction mixture was then filtered over Celite, and the resulting
solution was evaporated to dryness. Et2O (15 mL) was added to
precipitate a pale green solid, which was filtered off and thor-
oughly washed with Et2O. Recrystallization from CH2Cl2/Et2O
afforded pale green crystals of 3f. Yield: 58 mg (75%). Mp:
269 °C. IR: ν(CO) 1658 cm-1 (sb). 1H NMR (400 MHz, CDCl3):
4
δ 11.36 (s, 3H, CHO), 1.23 (t, 54H, PMe3, 54H, 2JPH þ JPH=4
Hz). 13C{1H}NMR (400 MHz, CDCl3): δ 200.2 (s, 3C, CHO),
187.6 (t, 3C, C1-Pd, 2JPC=5 Hz), 147.1 (s, 3C, C2-CHO), 15.7
1
3
(vt, 18C, PMe3, JPC þ JPC = 30 Hz). 31P{1H}NMR (121.4
MHz, CDCl3): δ -18.8. Anal. Calcd for C27H57Br3O3P3Pd3: C,
27.61; H, 4.89. Found: C, 27.60; H, 4.99.
X-ray Structure Determinations. Intensities were registered at
low temperature on a Bruker SMART 1000 CCD diffractometer
˚
using monochromated Mo KR radiation (λ = 0.710 73 A).
Absorption corrections were based on multiscans (program
SADABS). Structures were refined anisotropically using
SHELXL-97.54 Hydrogen atoms were included using rigid meth-
yl groups or a riding model. Special features: In 1b the atom O(2)
is disordered over two positions. For 2e, both dichloromethane
sites are disordered (one over an inversion center).
Synthesis of [{PdBr(tbbpy)}3{μ3-C6(CHO)3}] (3b). [Pd(dba)2]
(562 mg, 0.975 mmol), tbbpy (260 mg, 0.975 mmol), and C6-
(CHO)3Br3 (100 mg, 0.25 mmol) were mixed under N2 in dry
degassed toluene (15 mL). The resulting mixture was stirred at
60 °C for 10 min, until the dark red color of [Pd(dba)2] was no
longer observed. Workup as for 1a, afforded a solid, which was
filtered off, thoroughly washed with Et2O, and dried in vacuo to
give 3b as a yellow solid. Yield: 360 mg (94%). Mp: 250-251 °C
dec. IR: ν(CO): 1660 cm-1 (sb). 1H NMR (400 MHz, CDCl3): δ
11.94 (s, 2H, CHO), 11.88 (s, 1H, CHO), 9.36 (d, 2H, tbbpy, 3JHH
=6 Hz), 9.25 (d, 1H, tbbpy, 3JHH=6 Hz), 8.02 (d, 1H, tbbpy,
3JHH=6 Hz), 7.93 (d, 1H, tbbpy, 4JHH=2 Hz), 7.91-7.88 (m,
Acknowledgment. We thank the Ministerio de Educa-
ꢀ
cion y Ciencia (Spain), FEDER (Project CTQ2007-60808/
BQU), and Fundacion Seneca (04539/GERM/06) for finan-
ꢀ
ꢀ
ꢀ
ꢀ
cial support. R.V.S. is grateful to the Fundacion Seneca for a
grant and to the European Commission for a Marie Curie
Individual Fellowship (IIF).
Supporting Information Available: Table with 13C NMR data
of complexes 1-3. This material is available free of charge via
the Internet at http://pubs.acs.org.
3
5H, tbbpy), 7.72 (d, 2H, tbbpy, JHH = 6 Hz), 7.51 (dd, 2H,
tbbpy, 3JHH=6 Hz, 4JHH=2 Hz), 7.48 (dd, 1H, tbbpy, 3JHH=6
Hz, 4JHH=2 Hz), 7.47 (dd, 1H, tbbpy, 3JHH=6 Hz, 4JHH=2
Hz), 7.23 (dd, 2H, tbbpy, 3JHH=6 Hz, 4JHH=2 Hz), 1.42 (s, 9H,
(54) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.