Reactions of benzyldiphenylphosphine with Pd(II) sources on silica gel

Article abstract of DOI:10.1016/j.jorganchem.2011.06.026

Depending on the conditions used, reactions of benzyldiphenylphosphine (HL¹) with Na₂PdCl₄ on silica gel or with Pd(OAc)₂ on the same absorbent followed by treatment with LiCl provide one or more of the four compounds: the cyclopalladated binuclear complex [(μ-Cl)PdL¹]₂ (1), cis and trans isomers of the coordination complex PdCl₂(HL¹)₂ (3), the binuclear coordination complex [(μ-Cl)PdCl(HL¹)]₂ (4), and compound PdCl₂(HL¹)₃ (5). The 56% yield of complex 1 achieved using the reaction with Na₂PdCl₄ and NaOAc on SiO₂ is higher than that reported for the direct cyclopalladation of PBnPh₂ with Pd(OAc)₂ in AcOH. X-ray diffraction studies of the cyclopalladated dimer 1 and the coordination complex cis-3 are reported.

Full text of DOI:10.1016/j.jorganchem.2011.06.026

Journal of Organometallic Chemistry 696 (2011) 3162e3168
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactions of benzyldiphenylphosphine with Pd(II) sources on silica gel
1
*
Valeria A. Stepanova, Layne M. Egan , Lothar Stahl, Irina P. Smoliakova
Department of Chemistry, 151 Cornell Street, University of North Dakota, Grand Forks, ND 58202-9024, USA
a r t i c l e i n f o
a b s t r a c t
Depending on the conditions used, reactions of benzyldiphenylphosphine (HL1) with Na2PdCl4 on silica
gel or with Pd(OAc)2 on the same absorbent followed by treatment with LiCl provide one or more of the
Article history:
Received 27 April 2011
Received in revised form
17 June 2011
four compounds: the cyclopalladated binuclear complex [(
m
-Cl)PdL1]2 (1), cis and trans isomers of the
-Cl)PdCl(HL1)]2 (4), and
coordination complex PdCl2(HL1)2 (3), the binuclear coordination complex [(
m
Accepted 22 June 2011
compound PdCl2(HL1)3 (5). The 56% yield of complex 1 achieved using the reaction with Na2PdCl4 and
NaOAc on SiO2 is higher than that reported for the direct cyclopalladation of PBnPh2 with Pd(OAc)2 in
AcOH. X-ray diffraction studies of the cyclopalladated dimer 1 and the coordination complex cis-3 are
reported.
Keywords:
Cyclopalladation
Pd(II) complexes of phosphines
Phosphapalladacycles
CeH bond activation on silica gel
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
capable of reacting with Pd(II) sources to give a variety of
compounds. In particular, PBnPh2 can form at least five Pd(II)
Due to growing environmental concerns, chemical synthesis
using either no solvents or their reduced amount is an attractive and
important trend [1]. Recently, mechanochemical approach has been
recognized as a valuable method to perform reactions, including
preparation of metal complexes, without solvents [2,3]. Microwave-
assisted transformations using neat reactants are another way to
lower consumption of chemicals [4]. One more approach is to
perform reactions on silica gel and similar sorbents [5].
complexes, 1e5; four of them, 1e4, have been reported. Two of the
known compounds, 1 [8e12] and 2 [12], contain a five-membered
palladacycle with a CePd bond, while complexes 3 [13e19] and 4
[9,20] have only dative PePd bonds (Chart 1). In general, prepara-
tion and use of cyclopalladated [21,22] and Pd(II) coordination
complexes of phosphines have been subjects of considerable
interest for a few decades. The main application of these complexes
is in catalysis [23], although they have been also used as precursors
for synthesis of valuable organic compounds [24] and other Pd
complexes [25,26]. Therefore, the importance of phosphine-
derived Pd(II) complexes as well as a growing demand for green
approaches in synthesis have warranted our study of reactions of
PBnPh2 with Pd(II) sources on SiO2.
Recently, we reported a general method for cyclopalladation of
N-containing preligands on SiO2 with the use of solvents on the
purification step only [6]. This method allowed preparation of the
corresponding C,N-palladacycles in the yields comparable or even
exceeding those reported for reactions performed under
conventional conditions using solvents. Previously, Tune and
Werner reported the conversion of (
to the cyclopalladated derivative
h
5-C5H5)PdIP(O-ortho-Tol)3
5-C5H5)Pd[P(OC6H3-ortho-
(
h
2. Results and discussions
Me)(O-ortho-Tol)2] during chromatography on SiO2 [7]. To the
best of our knowledge, there have been no other studies related
to the use of P-containing preligands in CeH bond activation on
this or similar absorbents.
Pursuing our interest in chemistry of cyclopalladated and Pd(II)
coordination complexes, we examined reactions of commercially
available benzyldiphenylphosphine, PBnPh2 (HL1), with Pd(OAc)2
and Na2PdCl4 on SiO2. Tertiary monodentate phosphines are
2.1. Reactions of PBnPh2 with Pd(OAc)2 and Na2PdCl4
Two Pd(II) sources, Pd(OAc)2 and Na2PdCl4, were tested in
reactions with PBnPh2 on SiO2 (Scheme 1 and Table 1). Because the
target product was the cyclopalladated complex 1, a 1:1 ratio of
Pd per ligand was used in all experiments unless indicated other-
wise. Two sizes of SiO2 were used, 100e230 and 230e400 mesh. In
some cases, the weak base NaOAc was added to promote cyclo-
palladation. In the experiments with Pd(OAc)2, reactions on SiO2
were followed by treatment with LiCl. Depending on the reaction
conditions used, four different compounds were formed. One of the
* Corresponding author.
E-mail address: ismoliakova@chem.und.edu (I.P. Smoliakova).
Undergraduate researcher.
1
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.06.026

V.A. Stepanova et al. / Journal of Organometallic Chemistry 696 (2011) 3162e3168
3163
Chart 1. Pd(II) complexes with PBnPh2 as a ligand or preligand.
Two sizes of SiO2 were used in the study, 100e230 and 230e400
mesh (particles with the diameter of 63e149 and 37e63 m,
m
respectively). In the experiments with Pd(OAc)2 with or without
NaOAc, there was no significant SiO2 size effect on the product
yields or the product compositions. However, experiments at
120 ꢀC with SiO2 of the larger size,100e230 mesh, provided a much
higher yield of CPC 1 than those with the smaller size (entries 13
and 14).
Scheme 1.
complexes was the target cyclopalladated dimer 1. The remaining
three complexes, 3e5, were coordination complexes with different
ratios of Pd and PBnPh2.
To prove that cyclopalladation of PBnPh2 does not occur with
Na2PdCl4 without SiO2, two experiments were performed. In the
first experiment, a 1:1:1 mixture of PBnPh2, Na2PdCl4 and NaOAc
was heated at 85 ꢀC for 5 h (entry 9, cf. entry 10). The 31P{1H} NMR
spectrum of the mixture showed the presence of the phosphine
oxide, cis-3 and trans-3 with no traces of complexes 1, 4 and 5. In
the other experiment, a 1:1 mixture of PBnPh2 and Na2PdCl4 was
heated at 120 ꢀC for 1 h (entry 15). While the use of these condi-
tions on SiO2 resulted in the formation of the cyclopalladated
complex in a good yield (entry 13), the reaction without the
absorbent provided only complex 3 in 9% yield.
In all experiments, acetone was used at rt to remove complexes
from SiO2. To prove that acetone does not affect the outcome of the
reactions, a 1:1:1 mixture of 1, Na2PdCl4 and NaOAc was mixed
with SiO2 at rt followed by addition of acetone. After filtration, the
acetone solution was analyzed for the presence of complexes 1 and
2e5. The 31P{1H} NMR spectrum contained signals of cis- and trans-
3, the unreacted ligand and the corresponding oxide. No signals of
the cyclopalladated complex 1 and compounds 4 and 5 were
observed. After purification, complex 3 was isolated in 19% yield.
Mixing ligand 1 with Na2PdCl4 in a 1:1 ratio on silica gel followed
Reactions of PBnPh2 with Pd(OAc)2 at 50 ꢀC selectively provided
the dinuclear coordination complex [(m
-Cl)PdCl(HL1)]2, 4, with
yields up to 90% (entries 1 and 2). Attempts at performing similar
experiments at higher temperatures resulted in the formation of Pd
black. It is known that weak bases, particularly NaOAc, promote
cyclopalladation [27]. Addition of NaOAc to the PBnPh2ePd(OAc)2
reaction mixture, as well as increasing the temperature to 85 ꢀC,
resulted in the formation of the dinuclear cyclopalladated complex
[(m
-Cl)PdL1]2, 1, in 14% yield (entry 3).
Na2PdCl4 is known to be a less effective palladating agent than
Pd(OAc)2 and is commonly used in a combination with NaOAc [28].
Reactions of PBnPh2 with Na2PdCl4 without a base at 40e85 ꢀC
provided, at best, only trace amounts of the cyclopalladated
complex 1 (entries 4e8). The major product of these reactions was
the coordination complex PdCl2(HL1)2, 3. Addition of NaOAc and
increasing the temperature while shortening the reaction time
allowed for improvement in the yield of the cyclopalladated
complex up to 56% (entries 10e13).
Table 1
Reactions of PBnPh2 with Pd(OAc)2 and Na2PdCl4 on silica gel.a
Entry
Pd(II) source
Base
SiO2 size, mesh
T, ꢀC
Time, h
Yield of 1, %
Yield of 3, %
Yield of 4, %
Yield of 5, %
1
2
3
4
5
6
7
8
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
Na2PdCl4
230e400c
100e230c
100e230
100e230c
230e400
100e230
230e400
100e230
None
230e400
100e230
100e230
100e230
230e400
None
50
50
85
20
40
40
85
85
85
40
85
85
120
120
120
72
168
168
1
1
1
5
5
5
72
18
168
1
1
1
90
69
6
NaOAc
14
83
77
87
60
68
9
12
8
20
3b
11b
31
13
34
9
10
11
12
13
14
15
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
13
17
21
56
9
51
39
42
42
25
12
a
Yields are given for isolated compounds unless indicated otherwise; 750 mg of SiO2 per 1 mmol of PBnPh2 was used unless indicated otherwise.
The values were estimated using 1H NMR spectra.
375 mg of SiO2 per 1 mmol of PBnPh2 were used.
b
c

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V.A. Stepanova et al. / Journal of Organometallic Chemistry 696 (2011) 3162e3168
by addition of acetone also resulted in the formation of complex 3
only (11% yield after purification). Application of Pd(OAc)2 instead of
Na2PdCl4 in a similar experiment followed by addition of LiCl
provided a complex mixture with no signals of complexes 1 and 3e5.
Thermal stability of the complexes was also studied. Compound
1 was stable on the 100e230 and 230e400 mesh SiO2 at 120 ꢀC for
at least 5 h. Complex 3 did not change its structure at 85 ꢀC for at
least 5 h. Compound 4 was stable at 50 ꢀC for at least 24 h.
mononuclear analogs. It is noteworthy that ligand’s steric bulk is
also known to be an important factor promoting cyclopalladation
[45]. Interestingly, very bulky phosphines are also capable of
reacting with PdCl2 to yield trinuclear coordination complexes,
[(HL)ClPd(m-Cl)2Pd(m-Cl)2PdCl(HL)], instead of dinuclear coordina-
tion or cyclopalladated complexes [46].
In our study, compound 4 was isolated in the highest yield of
90% in the experiment with Pd(OAc)2 after treatment of the reac-
tion mixture with LiCl (entry 1). The complex provided one signal in
the 31P{1H} NMR spectrum, suggesting the presence of only one
isomer. The conformation of the structure of complex 4 was
obtained by X-ray analysis. The results matched the recently pub-
2.2. Cyclopalladated complex (PdClL1)2, 1
Previously, complex 1 and its
m-OAc and m-Br analogs were
synthesized by three different methods. Hiraki et al. obtained 1 in
19% yield by cyclopalladation of PBnPh2 by Pd(OAc)2 in MeOH
under reflux for 3 h [8]. Abicht and Issleib prepared compound 1
lished data for the crystal structure of trans-[(
m
-Cl)PdCl(HL1)]2 [20].
2.5. Coordination complex PdCl2(HL1)3, 5
ꢁ
by reacting the spiro complex 2 with PdCl2 2Et2S in 92% [12].
The same authors converted complex 2 to the
86% using HgBr2 [12]. Ryabov et al. reported preparation of 1 in
m
-Br analog of 1 in
Complexes of this type are relatively rare and unknown for
PBnPh2. For some phosphines, formation of complexes PdCl2(HL)3
was observed using 31P{1H} NMR spectroscopy by adding 1 equiv.
of phosphine HL to a solution of PdCl2(HL)2 [48,49]. The reported
spectrum of PdCl2(PMe3)3 at ꢂ90 ꢀC appeared as an AB2 spin
21% yield using the transmetalation reaction between PBnPh2
and the cyclopalladated complex [(
m
-Cl)PdL2]2 (HL2 ¼ N,N-dime-
thylbenzylamine) in CHCl3eAcOH at rt [11]. Applying different
conditions (PhMeeCF3CO2H, reflux) to the same reaction, Pfeffer’s
group increased the yield of the crude complex 1 to 90% [10]. In
our hands, this procedure provided 52% of 1 after dry-flash chro-
matography using hexane and CH2Cl2 as eluents. In the present
study, the best yield of 56% was obtained when a mixture of the
phosphine, Na2PdCl4 and NaOAc on 100e230 mesh silica gel was
stirred for 1 h at 120 ꢀC.
system,
d
ꢂ6.6 and ꢂ5.3 ppm (CD2Cl2, relative to 62.5% H3PO4) [48],
while the spectrum of PdCl2(PPhMe2)3 at ꢂ60 ꢀC was described as
a sharp doublet and a sharp triplet in a 2:1 ratio at
d 48.6 and
45.2 ppm (CDCl3, 85% H3PO4). Another reported pentacoordinate
complex, PdCl2(PBnMe2)3, was obtained as white crystals by
refluxing a 1:2 ratio of Li2PdCl4 and PBnMe2 in MeOH and con-
verted to [PdCl(PBnMe2)3]BF4 after treatment with NaBF4 [50].
The elemental analysis of compound 5 suggested that its
composition is PdCl2(HL1)3. In orderto get more experimentaldata to
support the proposed structure of complex 5, 31P{1H} NMR spectra of
this compounds were taken at rt as well as at lower temperatures.
Surprisingly, no structure confirmation has been reported for
the cyclopalladated complex except for the IR frequency of the C]O
bond of the acetone adduct 1ꢁ1/2Me2C]O [8]. In the present study,
the structure of complex 1 was supported by 1H, 13C{1H} and 31P
{1H} NMR spectra. The 31P{1H} NMR spectrum of the compound
contained two partly overlapping singlets in ca. 2:3 ratio that
suggests the presence of two isomers, syn and anti. This type of the
31
The P{1H} NMR signal of 5 observed at ꢂ88 ꢀC had a shoulder
suggesting non-equivalency of the phosphine ligands in the
compound. As it was reported for Pd(PPhMe2)3Cl2 [40], the chemical
shift of complex 5 is between those of cis- and trans-3 (Fig. 1).
Attempts to grow crystals of complex 5 failed due to its
decomposition that provided the coordination complex 3 and
BnPh2P ¼ O. The structure of the latter was confirmed by X-ray
crystallographic data.
isomerism is well known for
m-Cl dimeric cyclopalladated
complexes [29]. The X-ray study of complex 1 unambiguously
confirmed its anti geometry in the solid form (see below).
2.3. Coordination complexes cis-PdCl2(HL1)2, cis-3, and trans-
PdCl2(HL)2, trans-3
2.6. X-ray structural analysis of complexes 1 and cis-3
The coordination complex 3 is usually synthesized by reacting
PBnPh2 with PdCl2(NCPh)2 or PdCl2(NCMe)2 in CH2Cl2 or another
solvent [13,14,17]. In solution this complex exists as a mixture of
two geometrical isomers, which undergo reversible thermal
isomerization [17].
The cyclopalladated structure of complex 1 was unambiguously
confirmed by the X-ray diffraction study (Fig. 2). The molecular
In our experiments on SiO2, complex 3 was formed in many
reactions in spite of using a 1:1 ratio of Pd per ligand. The obtained
1H, 13C{1H} and 31P{1H} NMR data were in good agreement with the
previously reported data [16,17,19,30]. 31P{1H} NMR spectra of the
isolated samples in CDCl3 contained either one signal assigned to
the thermodynamically more stable [15,31] cis form or two signals
belonging to cis-3 and trans-3. Similar data have been reported for
other Pd(II) coordination complexes with phosphorus-containing
ligands [32e35].
2.4. Dinuclear coordination complex [(m
-Cl)PdCl(HL1)]2, 4
Dinuclear coordination complexes of phosphorus-containing
ligands are rather common [36e44] and are usually synthesized
by reacting a Pd(II) source with an appropriate ligand in a 1:1 ratio,
i.e. using the same stoichiometry of the reagents as in cyclo-
palladation. In the case of bulky phosphines, the formation of
dinuclear coordination complexes is more favored than their
Fig. 1. 31P{1H} NMR spectra of: (a) a mixture of cis- and trans-3 in CDCl3 at rt, (b)
complex 5 in CDCl3 at rt, and (c) complex 5 at ꢂ88 ꢀC in d6-acetone.

V.A. Stepanova et al. / Journal of Organometallic Chemistry 696 (2011) 3162e3168
3165
ꢀ
however, the difference is smaller than that in IV, 0.020 A and
significantly smaller than in palladacycles with the (sp3)C donor
atom, in which the PdeCl bond trans to the P atom is significantly
ꢀ
shorter, up to 0.088 A [56]. These observations suggest similar trans
influence of the (sp2)C atom and the heteroatom in the PPh2 frag-
ment in complexes 1 and IeIV and a greater trans influence of the
(sp3)C donor atom compared to its sp2-hybridized counterpart [22].
The extent of the palladacycle’s puckering in complex 1 was
estimated by calculating the average intrachelate torsion angle. The
obtained value of 17.2ꢀ is less than that found in (S,S)-I, (R,R)-I and
II, 27.0, 27.2 and 31.4ꢀ [24,51], but typical for other palladacycles
derived from arylphosphines [53].
The X-ray study of complex 3 revealed its cis geometry in the
solid state (Fig. 3). The structure is a CHCl3 solvate. The X-ray
diffraction study of complex 4 was also performed and revealed its
trans geometry in the solid state. Because the molecular structure
of trans-{(m
-Cl)PdCl(HL1)}2 is known [20], our data for complex 4
will be used here only for comparison with other Pd(II) complexes
of PBnPh2 (Table 2).
The majority of available X-ray studies of the coordination
complexes PdCl2(HL)2, where HL is a tertiary phosphine or a similar
P-donor ligand, report their trans geometry in the solid state
[37e42,46,57e59]. X-ray studies of the cis-PdCl2(HL)2 complexes
with P-donor ligands are more rare and include derivatives of
PMe2Ph [60], PMe2(2-Py) [61], PPh(2-Py)2 [62], PPh2(OEt) [63],
P(OPh)3 [64] and a P-monodentate phosphoramidite [65].
The structure of cis-3 showed a distorted square-planar envi-
ronment of the Pd atom. The PePdeP angle was more obtuse than
ClePdeCl by 10.76ꢀ. Such a difference is typical for cis-PdCl2(HL)2
complexes with P-donor ligands [60e62,64]; the only exception is
cis-PdCl2[PPh2(OEt)]2, in which the ClePdeCl angle was greater
than PePdeP by 1.29ꢀ [63]. Parameters of two PBnPh2 ligands as
well as two PdeCl bond lengths in cis-3 were slightly different, e.g.
Fig. 2. The molecular structure of complex 1.
structure of dimer 1 revealed its anti configuration with two P
atoms trans to each other. The same geometry was found in
structures of other chloro-bridged dimers with five-membered
phosphapalladacycles, particularly those with the (sp2)CePd
bond, IeIV (Chart 2) [24,51e53]. The structure of complex 1 is
a CH2Cl2 solvate and consists of two halves, which have minimal
differences in the parameters. Both palladium centers are in dis-
torted square-planar geometry with the dihedral angle of 3.9ꢀ
between the {P(1)ePd(1)eC(1)} and {C(1)ePd(1)eCl(1A)} planes.
For comparison, the value of this angle in complexes (R,R)-I, (S,S)-I,
II and III is 9.8, 9.7, 23.7, 2.6ꢀ, respectively. The {Pd2Cl2} ring in the
structure of dimer 1 was completely flat: the value of the {Pd(1)e
Cl(1)eCl(1A)ePd(1A)} dihedral angle is 180.0ꢀ. In contrast,
complexes (R,R)-I and (S,S)-I with the PPh2 moiety exhibited a very
significant bent of the {Pd2Cl2} fragment, 52.8 and 51.1ꢀ, respec-
tively. Compound IV with the PBut2 group had a less significant
bent of 28.8ꢀ, while reported halogen-bridged (sp3)C,P-cyclo-
palladated complexes exhibited the practically flat {Pd2Hal2}
fragment [54,55] even in the structure with two mesityl substitu-
ents at the donor P atom [56].
ꢀ
one PdeP bond was shorter that the other by 0.0047 A. For
comparison, each of two structures, cis-PdCl2[PPh2(OEt)]2 and cis-
PdCl2(PMe2Ph)2, displayed identical PdeP and PdeCl bonds, while
the difference in two PdeP bonds in cis-PdCl2[PPh2(2-py)]2 was
ꢀ
0.0100 A [60,62,63]. The PdeP and PdeCl bond lengths in cis-3 are
within the range reported for other cis-PdCl2(HL)2 complexes
[60e64].
It is known that both types of coordination complexes,
PdCl2(HL)2 and [(m-Cl)PdCl(HL)]2, can, in some cases, be converted
to the corresponding cyclopalladated complexes [52,66e68].
Coordination of the Pd atom to the heteroatom of HL is recognized
as in initial step of metallation. As one can expect, after palladation,
the PdeP bond in 1 became significantly shorter than in the coor-
ꢀ
ꢀ
dination complexes: by 0.0746 A compared to 3, and by 0.0265 A
Chart 2. Cyclopalladated chloro-bridged dimeric complexes derived from tertiary
phosphines with known molecular structures.
ꢀ
The length of the PdeP bond found in 1, 2.1953(5) A, is within
ꢀ
the range of 2.186e2.217 A reported for the complexes (R,R)-I, (S,S)-
I, II and III with the PPh2 moiety and shorter than in related
complexes with the PdePBut2 fragment [53,55]. The PdeC bond
ꢀ
length of 2.009(2) A in 1 is slightly shorter than those reported for
ꢀ
their PPh2 analogs IeIII, 2.019e2.052 A, but a little bit longer than
ꢀ
in IV, 1.981 and 1.989 A. Two PdeCl bonds in each half of the
ꢀ
structure are slightly different, 2.4267(5) and 2.4393(5) A. These
values are typical for other chloro-bridged phosphapalladacycles
[24,51e53]. The length difference for the PdeCl bonds in 1,
ꢀ
ꢀ
0.0126 A, is greater than that observed in IeIII, 0.001e0.005 A;
Fig. 3. Molecular structure of cis-3. The CHCl3 solvate molecule was omitted for clarity.

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V.A. Stepanova et al. / Journal of Organometallic Chemistry 696 (2011) 3162e3168
Table 2
Selected geometric parameters for complexes trans-1, cis-3 and trans-4.
Angle, ꢀ
ꢀ
Complex
Bond Length, A
PdeP
Pde
m
-Cl
PdeC
PeCH2
PePdeC
ClePdeCl
PePdeCl
trans-1
cis-3
2.1953(3)
2.4393(5)a
2.4267(5)b
2.3509(9)
2.3252(9)
2.4122(5)a
2.3153(4)b
2.2734(4)c
2.009(2)
1.832(2)
82.04(6)
97.75(6)d
178.283(18)
95.104(19)
86.96(3)
2.2652(9)
2.2699(9)
1.864(4)
1.844(4)
1.8325(17)
89.15(3)
85.47(3)
trans-4
85.538(16)d
91.371(17)
176.452(15)
176.349(15)a
95.630(16)b
87.350(17)c
a
Data for the
Data for the
Data for the ClePd cis to the PdeP bond.
Data for the m-ClePdem-Cl angle.
m
-ClePd trans to the PdeP bond.
-ClePd cis to the PdeP bond.
b
m
c
d
compared to 4. The Ph2PeCH2 bond in 1 was compressed as well:
chromatography with the hexane-CH2Cl2 eluent system afforded
cyclopalladated complex 1 (0.201 g, 52% yield) as a very light
yellow solid. Method 2 (preparation on SiO2). In a glove box, PBnPh2
(0.0340 g, 0.123 mmol) was placed into a small flask. Then
Na2PdCl4 (0.0276 g, 0.123 mmol), SiO2 (100e230 mesh, 0.0923 g;
0.750 g of SiO2 per 1.00 mmol of the preligand) and NaOAc
(0.0100 g, 0.123 mmol) were added to the flask and the mixture
was vigorously stirred using a spatula for 1 min. The flask was
topped with cotton and placed in a preheated (120 ꢀC) sand bath to
stir. After 1 h, the reaction mixture was transferred into a glass
filter and the crude dimer was washed from SiO2 with acetone
(5 ꢃ10 mL). The solution was placed on a rotavapor to remove
acetone. The solid residue was dissolved in a minimal volume of
CH2Cl2 and purified using preparative TLC (silica gel, CH2Cl2). Two
compounds were isolated: complex 1 as a light yellow solid in 56%
yield and complex 4 as an off-white powder in 42% yield. Crystals
of 1 suitable for X-ray analysis were obtained using crystallization
from CH2Cl2 at ꢂ5 ꢀC. Rf 0.69 (CH2Cl2), m.p. 197e201 ꢀC (decomp.;
ꢀ
by 0.032 and 0.012 A compared to two corresponding bonds in cis-3
ꢀ
and by 0.009 A compared to 4. The {Pd(1)eCl(1)eCl(1A)ePd(1A)}
dihedral angle in 4 was the same as in complex 1, 180.0ꢀ
3. Conclusions
Depending on the conditions used, reactions of BnPh2P with
Pd(II) sources on silica gel provide one or more of the following
compounds: the cyclopalladated binuclear complex 1 and three
different types of coordination complexes 3e5. The formation of
the cyclopalladated complex 1 is the first example of the solvent-
free phosphine CeH bond activation on silica gel. This method is
expected to be useful for cyclopalladation of other P-containing
preligands.
4. Experimental
2
lit. data [8,12]: 198 and 248 ꢀC). 1H NMR: 3.81 (d, 2H, JHH ¼ 15,
4.1. General methods and materials
CH2), 6.90 (br. s, 2H, H(4,5) of C6H4Pd), 7.01 (d, 1H, 3JHH ¼ 7.9, H(6)
of C6H4Pd), 7.26 (d, 3JHH ¼ 7.9, 1H, H(3) of C6H4Pd); 7.35 (m, 5H, p-
and m-H of PPh2), 7.56 (br. s, 1H, p-H of PPh), 7.64 and 7.74 (br. s,
4H, o-H of PPh2); 31P{1H} NMR: 41.40 and 41.43 in 2:3 ratio (lit.
All reactions were carried out in a glove box using the atmo-
sphere of N2. Purifications by preparative thin-layer chromatog-
raphy (TLC) were carried out using 200 ꢃ 250 mm glass plates with
an unfixed layer of Natland or Merck silica gel 60 (230 mesh).
Analytical TLC was performed on Whatman silica gel 60 (F254) 250
mm precoated plates. Compounds were visualized on TLC plates
using UV light (254 nm) and/or iodine stain. 1H (500 MHz), 13C{1H}
(126 MHz) and 31P{1H} (202 MHz) as well as DEPT, COSYand HMQC
spectra were recorded on a Bruker AVANCE 500 NMR spectrometer.
data [12]:
d 55.95 ppm in CDCl3/d6-DMSO relative to 85% H3PO4).
The 13C{1H} NMR data were not obtained due to a poor solubility of
the complex. Anal. Calcd for C38H32Cl2P2Pd2ꢁCHCl3: C, 49.11; H,
3.49%. Found: C, 48.82; H, 3.48%.
Dichlorobis(benzyldiphenylphosphine)palladium(II) (3). In
a glove box, PBnPh2 (0.0490 g, 0.1773 mmol) was placed in a small
flask. Then Na2PdCl4 (0.0522 g, 0.177 mmol) and SiO2 (100e230
mesh, 0.692 g; 0.375 g per 1.00 mmol of the preligand) were added
and vigorously mixed using a spatula for 1 min. The flask was
topped with cotton and stirred at rt for 1 h. Next, the reaction
mixture was transferred into a glass filter and the crude product
was washed from SiO2 with acetone (5 ꢃ10 mL). The solvent was
removed using a rotavapor, the dry residue was dissolved in
a minimal volume of CH2Cl2 and the product was purified using
preparative TLC (silica gel, CH2Cl2). A mixture of cis- and trans-3
was isolated as a bright yellow solid in 83% yield (0.0534 g). Sample
crystallization from a CDCl3 solution at rt afforded X-ray suitable
crystals of cis-3. Rf 0.8 (cis-3) and 0.3 (trans-3, CH2Cl2), m.p.
200e201 ꢀC (lit. data [15,30]: 205e207 and 182e193 ꢀC). 1H NMR (a
Chemical shifts, d, are reported in ppm with SiMe4 as an internal
standard (1H and 13C) or P(OEt)3 as an external standard (31P). Spin-
spin coupling constants, J, are given in Hz. Spectra of all complexes
were recorded in CDCl3. Hexane, toluene and CH2Cl2 were distilled
over CaH2. Acetone was distilled over KMnO4. PBnPh2 and Na2PdCl4
were purchased from Sigma-Aldrich Co. and used without purifi-
cation. Pd(OAc)2 was also purchased from Sigma-Aldrich Co.; prior
to use, the compound was dissolved in hot benzene, the solution
was filtered and then the solvent was removed under reduced
pressure.
Di-m-chlorobis-{2-[(diphenylphosphino)methyl]phenyl-C,P}
dipalladium(II) (1). Method 1 (preparation in solvent) [11]. In a glove
box, PBnPh2 (0.2300 g, 0.8324 mmol) was placed into an Ar-filled
2
mixture of cis-* and trans-3): 3.95 and 4.12* (t and d, 2H, JHP ¼ 4
50-mL Schlenk flask, then di-(m-chloro)bis-{[2-(N,N-dimethyla-
2
and JHP ¼ 12, CH2), 6.98e7.16 (m, 5H, PBn), 7.32 (m, 4H, m-H of
mino)methyl]phenyl-C,N}dipalladium(II) (0.2138 g, 0.3872 mmol)
was added followed by abs. toluene (6 mL). In several minutes,
CF3COOH (0.07 mL) was added to the flask through the septum. The
reaction mixture was refluxed for 2 h under the Ar atmosphere.
After cooling the mixture to rt, toluene was removed using
PPh), 7.42 (m, 2H, p-H of PPh), 7.50 (m, 4H, o-H of PPh); 31P{1H}
NMR (a mixture of cis-* and trans-3): 15.64* and 5.27 (lit. data for
cis-3: 29.6 [19], 30.27 [17] and 30.29 [30]; for trans-3: 20.06 [16,17]
and 20.03 [30]; all lit. data are for CDCl3 solutions relative to 85%
H3PO4); 13C{1H} NMR (a mixture of cis-* and trans-3): 32.2
a
rotavapor. Purification of the residue using dry-flash

V.A. Stepanova et al. / Journal of Organometallic Chemistry 696 (2011) 3162e3168
3167
(t, 1JCP ¼ 12, CH2) and 39.3* (d, 1JCP ¼ 12, CH2), 126.6e134.1 (PBn and
PPh signals). Anal. Calcd for C38H34Cl2P2PdꢁCDCl3: C, 55.09; H,
4.27%. Found: C, 54.92; H, 4.16%.
with SADABS. The structures were solved by direct methods and
refined by full-matrix least-squares methods on F2 with SHELXL-97
incorporated into in SHELXTL, version 6.14.
Dichlorodi-m-chlorobis(benzyldiphenylphosphine)dipalla-
dium(II) (4). Method 1 (preparation in solvent). In a glove box,
PBnPh2 (0.0310 g, 0.112 mmol) was placed into an Ar-filled 10 mL
Schlenk flask. Then Na2PdCl4 (0.0330 g, 0.112 mmol) was added to
the flask along with abs. toluene (15 mL). The suspension was
stirred for 2 days at rt under the Ar atmosphere. The solvent was
removed and the crude product was purified using dry-flash
chromatography with acetone and CH2Cl2 used as eluents.
Complex 4 was obtained as a bright red solid in 44% yield. Method 2.
In a glove box, PBnPh2 (0.032 g, 0.12 mmol) was weighed in a small
flask. Next, Pd(OAc)2 (0.0263 g, 0.116 mmol) and SiO2 (0.0434 g;
375 mg per 1.00 mmol of the preligand; 100e230 mesh SiO2) were
added and the components were vigorously mixed using a spatula
for approximately 1 min. The flask was topped with cotton and
placed on a sand bath preheated to 50 ꢀC and left to stir for 72 h.
The reaction mixture was transferred into a glass filter and the
crude product was washed from SiO2 using acetone (5 ꢃ10 mL).
Then LiCl (0.0196 g, 0.462 mmol) was added and the mixture was
stirred overnight. After solvent removal on a rotavapor, the crude
product was dissolved in CH2Cl2 (30 mL) and the solution formed
was filtered. Crystallization from a CH2Cl2 solution at rt afforded X-
ray suitable red crystals of complex 4 in 90% yield (23.4 mg). Rf 0.45
(CH2Cl2); m.p. 230e233 ꢀC (decomp.; lit. data [9,47]: 242e243 ꢀC);
1H NMR: 3.83 (d, 2H, 2JHH ¼ 13.0, CH2), 6.83 (d, 2H, 3JHH ¼ 7.2, o-H of
PBn), 7.02 (m, 2H, m-H of PBn), 7.11 (m, 1H, p-H of PBn), 7.30 (m, 4H,
m-H of PPh), 7.44 (m, 2H, p-H of Ph), 7.50 (m, 4H, o-H of PPh);
31P{1H} NMR: 17.11 (lit. data [9,47]: 31.79 and 31.71 ppm, CDCl3-d6-
DMSO relative to 85% H3PO4); 13C{1H} data were not obtained due
to a poor solubility of the complex. Anal. Calcd for C38H34Cl4P2Pd2:
C, 50.31; H, 3.78%. Found: C, 49.82; H, 3.69%.
Acknowledgment
The authors acknowledge financial support from ND EPSCoR
through NSF grant No. EPS-0447679. The Doctoral Dissertation
Assistantship to V.A.S. was provided by ND EPSCoR through NSF
grant No. EPS-0184442.
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