Mono and dinuclear palladium complexes of o-alkyl substituted arylphosphane ligands: Solvent-dependent syntheses, NMR-spectroscopic characterization and X-ray crystallographic studies

Article abstract of DOI:10.1016/j.jorganchem.2007.07.052

Palladium(II) chloride complexes of o-alkyl substituted phosphanes were prepared in various solvents with the phosphane ligands o-methylphenyldiphenylphosphane, o-ethylphenyldiphenylphosphane, o-isopropylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane. The structures of the complexes were characterized by ¹H NMR and ³¹P NMR spectroscopy and elemental analysis. The X-ray structures of PdCl₂(o-methylphenyldiphenylphosphane)₂, PdCl₂(o-isopropylphenyldiphenylphosphane)₂, PdCl₂(o-cyclohexylphenyldiphenylphosphane)₂, PdCl₂(o-phenylphenyldiphenylphosphane)₂, [PdCl₂(o-methylphenyldiphenylphosphane)]₂, [PdCl₂(o-ethylphenyldiphenylphosphane)]₂ and [PdCl₂(o-cyclohexylphenyldiphenylphosphane)]₂ were also determined. We report a systematic, solvent-dependent method to prepare palladium(II) complexes of the aryl phosphines o-methylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane with a desired nuclearity. We demonstrated that chlorinated solvents promote the formation of dinuclear chlorine-bridged palladium complexes for all five ligands. The ligands preferentially form mononuclear palladium complexes in other solvents where the starting materials are only weakly soluble in the solvent.

Full text of DOI:10.1016/j.jorganchem.2007.07.052

Journal of Organometallic Chemistry 692 (2007) 5044–5052
www.elsevier.com/locate/jorganchem
Mono and dinuclear palladium complexes of o-alkyl substituted
arylphosphane ligands: Solvent-dependent syntheses,
NMR-spectroscopic characterization and X-ray crystallographic studies
a,
b
a
Sauli Vuoti *, Matti Haukka , Jouni Pursiainen
a
Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland
Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland
b
Received 2 May 2007; received in revised form 17 July 2007; accepted 23 July 2007
Available online 8 August 2007
Abstract
Palladium(II) chloride complexes of o-alkyl substituted phosphanes were prepared in various solvents with the phosphane ligands
o-methylphenyldiphenylphosphane, o-ethylphenyldiphenylphosphane, o-isopropylphenyldiphenylphosphane, o-cyclohexylphenyldiphe-
nylphosphane and o-phenylphenyldiphenylphosphane. The structures of the complexes were characterized by 1H NMR and
31P NMR spectroscopy and elemental analysis. The X-ray structures of PdCl2(o-methylphenyldiphenylphosphane)2, PdCl2(o-isopro-
pylphenyldiphenylphosphane)2, PdCl2(o-cyclohexylphenyldiphenylphosphane)2, PdCl2(o-phenylphenyldiphenylphosphane)2, [PdCl2-
(o-methylphenyldiphenylphosphane)]2, [PdCl2(o-ethylphenyldiphenylphosphane)]2 and [PdCl2(o-cyclohexylphenyldiphenylphosphane)]2
were also determined. We report a systematic, solvent-dependent method to prepare palladium(II) complexes of the aryl phosphines
o-methylphenyldiphenylphosphane, o-cyclohexylphenyldiphenylphosphane and o-phenylphenyldiphenylphosphane with a desired nucle-
arity. We demonstrated that chlorinated solvents promote the formation of dinuclear chlorine-bridged palladium complexes for all five
ligands. The ligands preferentially form mononuclear palladium complexes in other solvents where the starting materials are only weakly
soluble in the solvent.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Phosphane ligands; Solvent effects; Substitute effects; Arylphosphane
1. Introduction
plexes are used as promoters, catalysts and starting materi-
als [4] in different reactions with promising results.
Dinuclear palladium complexes are structurally different
from their mononuclear analogues, and therefore could
possibly mediate new types of catalytic mechanisms [5].
Since the early nineties, there has been an underlying
interest in modifying the well-established PdCl2(PPh3)2 cat-
alyst using more efficient and selective phosphane ligands
[6]. Palladium and platinum complexes have shown
enhanced catalytic activity and selectivity in carbonylation
and hydrogenation reactions [6–9] when the well estab-
lished triphenylphosphane ligand is replaced by new mod-
ified arylphosphanes. There are also abundant examples of
this in the Suzuki–Miyaura reactions [10]. Replacing the
PPh3 ligand by modified o-alkyl substituted ligands give
Phosphorous containing ligands, such as phosphanes
(PR3) and especially arylphosphanes are one of the most
widely used groups of ligands in palladium chemistry.
These have been used to prepare catalysts for various reac-
tions for decades [1,2]. The general class of dinuclear sym-
[PdCl2P]2 complexes has been known since the early studies
of Mann et al. [3] and their isomerisation and anion
exchange mechanisms have been described in numerous
publications. Pd2Cl4(PPh3)2, the dinuclear analogue of
PdCl2(PPh3)2, and other related dinuclear palladium com-
*
Corresponding author. Tel.: +358 8 5531617; fax: +358 8 5531603.
E-mail address: sauli.vuoti@oulu.fi (S. Vuoti).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.052

S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
5045
promising results in various alkene hydroformylation reac-
tions. We recently observed that the o-alkyl substituents
have significant effects on the activity and selectivity in
the rhodium and ruthenium catalyzed hydroformylation
of propene [11,12]. However, the Rh and Ru complexes
of these ligands could not be crystallized and sometimes
were found to be unstable in solution. In contrast, palla-
dium complexes provide stable square planar surroundings
around the metal ion in studies of the steric nature and
other properties of the o-alkyl substituents (see Figs. 1–5).
In this study we synthesized and characterized new mono-
and dinuclear square planar palladium complexes (see
Scheme 1) of the o-alkyl substituted arylphosphanes o-meth-
ylphenyldiphenylphosphane (1), o-ethylphenyldiphenyl-
phosphane (2), o-isopropylphenyldiphenylphosphane (3),
Fig. 3. Crystal structure of complex 9. The thermal ellipsoids are drawn at
50% probability level.
Fig. 1. Crystal structure of complex 6. The solvent has been omitted for
clarity. The thermal ellipsoids are drawn at 50% probability level.
Fig. 4. Crystal structure of complex 14. Thermal ellipsoids are drawn with
50% probability. The solvent has been omitted for clarity.
C7
C6
C5
C8
C12
C13
C11
C1
C2
C3
C19
C18
C9
P1
C15
C16
Cl4
C17
Pd1
Cl2
Pd2
Cl1
C24
Cl3
C31
C30
C29
P2
C22
C23
C25
C21
C32
C26
C34
C33
Fig. 2. Crystal structure of complex 7. Thermal ellipsoids are drawn with
Fig. 5. Crystal structure of complex 15. Thermal ellipsoids are drawn with
50% probability level.
50% probability. The solvent has been omitted for clarity.

5046
S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
L
Cl
Cl
Cl
L
Pd
Pd
Pd
L
Cl
Cl
L
Cl
[PdClL2] (complexes 11-15)
[PdCl2L]2 (complexes 6-10)
4
4
4
5
3
5
3
5
3
6
2
o-2
6
2
6
2
CH3
CH3
11
1
CH2
11
o-1
CH3
12
1
1
8
P
8
H3C
7
8
P
9
o-2
7
P
9
7
9
10
10
2 (in complexes 7 and 12)
1 (in complexes 6 and 11)
4
3 (in complexes 8 and 13)
4
5
3
5
3
o-2
6
2
o-1
o-2
o-3
6
2
o-1
o-3
o-4
1
1
o-4
o-2
8
o-2
P
8
7
9
P
o-3
7
9
o-3
10
4 (in complexes 9 and 14)
Scheme 1. Structures of the phosphane ligands 1–5 and palladium complexes 6–15.
5 (in complexes 10 and 15)
o-cyclohexylphenyldiphenylphosphane (4) and o-phen-
ylphenyldiphenylphosphane (5). The following dinuclear
palladium complexes were prepared: di-l-chlorodichlor-
obis(o-methylphenyldiphenylphosphane)di- palladium (6),
di-l-chlorodichlorobis(o-ethylphenyldiphenylphosphane)di-
palladium (7), di-l-chlorodichlorobis(o-isopropylphenyldi-
phenylphosphane)di- palladium (8), di-l-chlorodichlorobis-
(o-cyclohexylphenyldiphenylphosphane)di- palladium (9)
and di-l-chlorodichlorobis(o-phenylphenyldiphenylphos-
phane)di- palladium (10). We also prepared the following
mononuclear complexes: dichlorobis(o-methylphenyldiphe-
nylphosphane) palladium (11), dichlorobis(o-ethylphenyldi-
phenylphosphane) palladium (12), dichlorobis(o-isopropyl-
phenyldiphenylphosphane) palladium (13), dichlorobis(o-
cyclohexylphenyldiphenylphosphane) palladium (14) and
dichlorobis(o-phenylphenyldiphenylphosphane) palladium
(15). The X-ray structures of 6, 8–12 and 14 were also
obtained. The lack of control for the formation of complexes
with the desired nuclearity has been recognized as a problem
in various papers [9,10,12–15]. We tested a variety of solvents
in order to clarify the role of solvents and to develop a
method to produce palladium complexes of o-alkyl substi-
tuted arylphosphanes with the desired nuclearity. Reactions
between the o-alkyl substituted phosphane ligands and
PdCl2(cod) (cod = C8H12) were also carried out using differ-
ent Pd:P ratios in order to test the influence of the absolute
concentration of the reaction mixture on the formation of
the complexes.
2. Results and discussion
2.1. Syntheses
A 2:1 reaction of the o-alkyl substituted phosphane
ligands 1, 4 and 5 with PdCl2(cod) in dichloromethane pro-
duced the chlorine-bridged dinuclear palladium complexes
6, 9 and 10 with the general formula [PdCl2L]2 (see Scheme
2). Interestingly, a similar reaction of the o-alkyl substi-
tuted phosphane ligands 1, 4 and 5 with PdCl2(cod) in
diethyl ether produced the mononuclear palladium com-
plexes 11, 14 and 15 with the general formula [PdCl2L2]
(see Scheme 2). For ligands 2 and 3, the reaction in dichlo-
romethane produced the mononuclear complexes 12 and
13 as the main products, and the dinuclear complexes 7
and 8 surprisingly as only side-products. A similar reaction
was obtained when ligands 2 and 3 in diethyl ether pro-

S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
5047
PPh2(C6H4R)
Cl
Cl
Cl
CH2Cl2
Pd
Pd
PPh2(C6H4R)
PPh2(C6H4R)
Cl
Cl
(CH3CH2)2O
Pd
Cl
PPh2(C6H4R)
R = Me, Cyc, Ph
R
PdCl2(cod)
+
P
PPh2(C6H4R)
Cl
Cl
Pd
Pd
Cl
PPh2(C6H4R)
PPh2(C6H4R)
Cl
CH2Cl2
+
Cl
(CH3CH2)2O
Pd
Cl
PPh2(C6H4R)
R = Et, i-Pr
Scheme 2. A general reaction scheme for the preparation of the palladium complexes 6–15.
duced the mononuclear complexes as the main products
correspondingly as the other ligands, but a minor amount
of the dinuclear complexes was once again formed.
The stability of the mononuclear complexes were tested
by an equimolar reaction between the isolated complexes
and PdCl2(cod) at room temperature in dichloromethane.
The reactions produced the dinuclear complex products
as expected. Moreover, it is well known that the dinuclear
complexes [PdCl2L]2 easily undergo bridge-splitting reac-
tions with a variety of neutral ligands to yield mononuclear
derivatives. Therefore the stability of the isolated dinuclear
complexes was studied by a 1:2 reaction between the dinu-
clear complexes and the corresponding ligands at ambient
temperature in dichloromethane and at 135 °C in chloro-
benzene. However, no bridge-splitting reactions could be
observed and the dinuclear complexes remained unreactive.
With all chlorinated solvents (dichloromethane, chloro-
form, chlorobenzene), the only products in the case of the
ligands 1, 4 and 5 were the dinuclear complexes. Even
though the mononuclear complexes were the main prod-
ucts for reactions involving ligands 2 and 3, there was also
a reasonable amount of the dinuclear complex formed. In
order to get further insight into the role of the halogenated
solvents in the reactions, we also carried out the reactions
with ligands 1 and 5 in bromoform and diiodomethane.
The dinuclear complexes 6 and 10 were the only products
formed, which indicates that other halogen containing sol-
vents also promote the formation of dinuclear palladium
complexes. However, we did not observe any introduction
of bromine or iodine in the crystal structures of the dinucle-
ar complexes, which suggests that the solvent itself does not
react.
We also carried out the reactions between PdCl2(cod)
and the phosphane ligands 1–5 with P:Pd ratios 4:1, 1:1,
1:2 and 1:4 both in diethyl ether and dichloromethane, in
order to test the effect of the absolute concentration of
the reaction mixture on the nuclearity of the formed com-
plexes. The reactions still produced only mononuclear
complexes with the ligands 1, 4 and 5 in diethyl ether in
each case. For ligands 2 and 3, all reactions performed in
diethyl ether also seemed to proceed as before. However,
this time the Pd:P 1:4 reactions did not produce any dinu-
clear complexes even as trace side products. In the reac-
tions which occurred in dichloromethane, the ligands 1, 4
and 5 still produced only dinuclear complexes despite the
varied ratios between the ligand and PdCl2(cod). Where
an excess of the PdCl2(cod) was used, the unreacted
PdCl2(cod) could be recovered from the reaction mixture.
For ligands 2 and 3, the results were similar as before, com-
binations of mono and dinuclear complexes were formed
regardless of the Pd:P ratio. Similar results were reported
previously [15,16].
We also carried out the 2:1 and 1:2 Pd:P reactions in tol-
uene, THF, acetone, DMF and methanol for comparison.
For all ligands, the results were similar as for the reactions
in diethyl ether. Correspondingly, using chlorobenzene or
chloroform as a solvent produced similar results as to those
reactions where dichloromethane was used. The nuclearity
of the main product seemed to depend on the used solvent
for ligands 1, 4 and 5, whereas in the case of ligands 2 and
3, a mononuclear complex was always the main product.
An interesting observation was that the starting material
PdCl2(cod) is only slightly soluble in diethyl ether, and the
reaction between it and the phosphanes results in mononu-

5048
S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
˚
clear palladium complexes, which are also only slightly sol-
uble in all solvents. In contrast, the starting material
PdCl2(cod) is readily soluble in dichloromethane and other
halogenated solvents. The reaction between PdCl2(cod)
and the phosphanes results in dinuclear palladium com-
plexes which are also readily soluble in halogenated sol-
vents. The implication is that the formation of PdCl2L2 is
essentially due to the low solubility of PdCl2(cod) resulting
in a P:Pd ratio >2 in solution, and that the low solubility of
the product [PdCl2L2] prevents the reaction with
PdCl2(cod) to form dinuclear complexes. However, this
does not explain the formation of both mononuclear and
dinuclear complexes in dichloromethane observed in the
reactions involving ligands 2 and 3. Conversely, we
observed that the mononuclear complexes 12 and 13 were
notably more insoluble even in halogenated solvents than
the other mononuclear complexes. Therefore a possible
explanation might be that the low solubility prevents a
complete reaction between the mononuclear species and
PdCl2(cod) to form dinuclear complexes.
3.492 A) [17,18] but still well in the range of Pd–Pd dis-
tances found in these types of dimers. In 6 and 9 the bridg-
ing chlorides, terminal chlorides and phosphorus atoms
were found to be coplanar. In 7 a bridging chloride, termi-
nal chloride and P(1) were coplanar. Likewise, a bridging
chloride, terminal chloride and P(2) were coplanar. Two
square planes were formed around Pd(1) and Pd(2). The
angle between the two planes was 48.63(5)°. Such bending
shortened the Pd–Pd distance in 7 compared to that of 6
and 9. In the dinuclear complexes the Pd–Cl bonds trans
to phosphorus (2.4300(5) (6), 2.422(2), 2.427(2) (7) and
˚
2.3205(8) A (9)) were slightly elongated compared to the
corresponding Pd–Cl bonds trans to Cl (2.3165(5) (6),
2.280(2) (7), 2.274(2) (7), and 2.2847(8) A (9)) or compared
˚
to the Pd–Cl in the mononuclear complexes (see Table 1).
A similar effect has been observed with other [PdCl2L]2
compounds, including Pd2Cl4[PPh3]2 [18], Pd2Cl4[PBu3]2
[19] and Pd2Cl4[PCy3]2 [20].
The o-alkyl groups were pointed outside the cone of the
ligand in all structures 6, 7, 8, 9, 11, 13, 14, and 15. This
orientation is also favored in the free ligand [21,22]. The
o-alkyl groups were oriented reasonably close to the Pd
center (shortest intramolecular Pd–H distances were 2.89
2.2. Structural characteristics
˚
In all the obtained crystal structures the palladium
atoms had slightly distorted square planar environments.
All bond lengths and angles were typical for related spe-
cies. The metal-metal distances in the dinuclear compounds
for 9 and 3.29 A for 6). This orientation is expected to be
favored mostly due to the packing effects in solid state. It
is also expected that in solution, rotation about the P–C
bond is relatively free and not strongly restricted by the
other ligands. However, the correlation found between
the solid state orientation and catalytic behavior of the
complexes suggests that the orientation of the o-substituent
˚
6, 7, and 9 varied between 3.2345(7) and 3.4713(5) A (see
Table 1). The Pd–Pd distances were somewhat shorter than
those of the corresponding PPh3 compounds (3.528 or
Table 1
Selected bond lengths and angles for 6 Æ 2(CH2Cl2), 7, 9, 14 Æ (CH2Cl2), and 15 Æ (CH2Cl2)
6 Æ 2(CH2Cl2)
7
9
14 Æ (CH2Cl2) (A)
14 Æ (CH2Cl2) (B)
15 Æ (CH2Cl2)
Pd(1)–Cl(1)
Pd(1)–Cl(1A)
Pd(1)–Cl(2)
Pd(1)–Cl(3)
Pd(1)–Cl(4)
Pd(2)–Cl(2)
Pd(2)–Cl(3)
Pd(2)–Cl(4)
Pd(1)–Pd(2)
Pd(1)–Pd(1A)
Pd(1)–P(1)
2.4300(3)
2.3165(6)
2.2822(5)
2.280(2)
2.3205(8)
2.4111(8)
2.2847(8)
2.3078(10)
2.3085(10)
2.2958(13)
2.2999(10)
2.3039(10)
2.2958(13)
2.422(2)
2.319(2)
2.274(2)
2.324(2)
2.427(2)
3.2345(7)
3.4482(2)
2.2332(5)
3.4713(5)
2.2356(9)
2.2433(18)
2.3203(10)
2.3260(11)
2.3455(10)
2.3150(10)
2.3370(14)
2.3370(14)
Pd(1)–P(2)
Cl(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(1A)
P(1)–Pd(1)–P(2)
89.96(2)
175.36
171.19(4)
169.16(4)
177.98(3)
172.30(4)
180
180
P(1)–Pd(1)–P(1A)
Pd(1)–Cl(3)–Pd(2)
Pd(1)–Cl(4)–Pd(2)
Pd(1)–Cl(1)–Pd(1A)
Cl(1)–Pd(1)–Cl(4)
P(1)–Pd(1)–Cl(3)
Cl(3)–Pd(2)–Cl(4)
Cl(2)–Pd(2)–Cl(3)
P(2)–Pd(2)–Cl(4)
P(1)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1A)
85.89(5)
85.88(5)
93.15(2)
94.37
173.03(7)
178.52(7)
83.27(6)
171.79(7)
178.57(7)
176.71(2)
176.56(2)
90.72(3)
95.93(3)

S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
5049
Table 2
Spectroscopic data for the free and coordinated ligands
Ligand (L)
Free phosphane
31P NMR d (ppm)
[PdCl2L2] 31P NMR
d (ppm)
[PdCl2L]2 31P NMR
d (ppm)
D = dcomplex ꢀ dL
D = dcomplex ꢀ dL
[PdCl2L2]
[PdCl2L]2
1
2
3
4
5
ꢀ10.7
ꢀ14.2
ꢀ13.8
ꢀ13.6
ꢀ11.9
19.6
20.1
20.3
21.0
22.3
29.8
30.0
31.2
29.4
28.4
30.3
34.3
34.1
34.6
34.2
40.5
44.2
45.0
43.0
40.3
can have an effect on the catalytic reactivity of the metal
centre even in solution. We observed such effects on activ-
ity and selectivity in hydroformylation, even though the
specific mechanism remained unclear [22].
Some of the complexes crystallize with a dichlorometh-
ane molecule as a part of the crystal structure. However,
we were not able to detect the signal of the dichloromethane
molecule from the 1H NMR spectra of the purified, isolated
complexes, nor did it appear to be a part of the structure
based on the elemental analysis data. Therefore we do not
believe that the dichloromethane molecule is chemically
bonded to the metal complexes in solution, rather it is intro-
duced into the structure in the crystallization process.
ideal solvent for preparing mononuclear palladium com-
plexes with all five o-alkyl substituted aryl phosphane
ligands 1–5 due to the low solubility of the starting materi-
als and the reaction products. In contrast, chlorine-bridged
dinuclear palladium complexes of ligands 1, 4 and 5 can be
prepared using halogenated solvents. Dinuclear complexes
of ligands 2 and 3 were only acquired as side-products
regardless of the solvent used. It is also possible to prepare
dinuclear palladium complexes by a reaction between a
mononuclear complex and PdCl2(cod).
4. Experimental
4.1. General comments
2.3. Spectroscopic data
The phosphanes used in this study are air- and moisture-
sensitive, both as pure solid compounds or in solution.
Furthermore, without protection the phosphanes showed
observable oxidation within one day. Therefore all reac-
tions were carried out using standard Schlenk techniques
under either a nitrogen or an argon atmosphere. The metal
complexes were stable both as solid compounds and in
solution. Therefore they were isolated and characterized
in air. Diethyl ether, benzene and THF were distilled over
sodium-benzophenone ketyl before use. Nitrogen was bub-
bled through all chlorinated solvents before use. Other
commercial reagents were used as received. The o-substi-
tuted bromobenzenes were obtained from Lancaster and
Aldrich. The diphenylchlorophosphane, n-butyl lithium
(2.5 M solution in hexane), and dichloro(1,5-cyclooctadi-
ene)-palladium (99%) were obtained from Aldrich.
Spectroscopy: The characterization of the complexes was
based on 1H- and 31P–{1H} NMR spectroscopy. NMR
spectra were recorded on a Bruker DPX400 spectrometer
at room temperature in CDCl3 (99.8% D, 0.03% TMS).
85% H3PO4 was used as an external standard for 31P–
{1H} NMR.
1
The H NMR spectra of the complexes are consistent
with the crystal structures and can be assigned on the basis
of the spectra of the free ligands and decoupling experi-
ments. The 1H NMR signals were almost identical to those
of the free phosphane ligands, the chemical shifts had
shifted downfield only slightly [11,21].
The 31P–{1H} NMR data is summarized in Table 2. As
previous results have shown, the individual signals of the
phosphanes in the 31P–{1H} NMR spectra tend to move to
a lower field when a phosphane is coordinated to a metal cen-
ter [11,21,22]. As expected, complexes 6, 9, 10, 11, 14 and 15
showed one sharp signal initially. The reaction mixtures in
the preparation of the complexes 7, 12, 8 and 13 initially
showed the two respective signals of the mononuclear and
the dinuclear complex. However, the complexes can be sep-
arated using column chromatography. The coordination
chemical shifts were quite similar for complexes 6–10 and
for 11–15. In addition to the 1H NMR and elemental analysis
data, this further supports the assumed similar structures for
the complexes 8, 10, and 12, which could not be crystallized.
3. Conclusion
Elemental analyses: C and H analyses were performed
using a Perkin–Elmer 2400 CHNS analyzer from the puri-
fied, solid metal complex powders.
The formation of palladium complexes with unwanted
nuclearity had previously been described as a problem in
various reports. Moreover, the suggested reasons for the
nuclearity of the formed palladium complexes varied in
each case. In this study we report a convenient method to
prepare palladium(II) complexes of o-alkyl substituted
arylphosphanes with the desired nuclearity in good yields
for ligands 1, 4 and 5. Diethyl ether was found to be an
X-ray crystal structure determinations: The crystals were
immersed in perfluoropolyether, mounted in a cryo-loop
and measured at 100–120 K. The X-ray diffraction data
were collected by a Nonius KappaCCD diffractometer
˚
using Mo Ka radiation (k = 0.71073 A). The DENZO-SCALE-
PACK program package [23] was used for cell refinements
and data reductions. Structures were solved by direct meth-

5050
S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
ods using the SHELXS-97 [24] or SIR2002 program [25] with
the WINGX graphical user interface. [26] An empirical
absorption correction was applied to all data using XPREP
in SHELXTL or SADABS programs [27,28] (Tmin/Tmax were:
0.3908/0.4379, 0.8686/0.9448, 0.1992/0.2391, 0.7362/
0.8069, 0.7378/0.9176 for 6 Æ 2(CH2Cl2), 7, 9, 14 Æ (CH2Cl2)
and 15 Æ (CH2Cl2), respectively). Structural refinements
were carried out with SHELXL-97 [24]. Compounds 6, 7
and 9 are dimers, which crystallize in centrosymmetric
space groups. The asymmetric unit of 14 Æ (CH2Cl2) con-
sists of two palladium molecules whereas the asymmetric
unit of 15 Æ (CH2Cl2) contains only half a palladium mole-
cule. In 15 Æ (CH2Cl2) one of the phenyl rings was disor-
dered over two sites with occupancies of ca. 0.6/0.4. A
rigid group fitting with constant C–C distances was applied
to these rings. All hydrogens were placed in idealized posi-
tions and constrained to ride on their parent atom. The
crystallographic data are summarized in Table 3. The
selected bond lengths and angles are shown in Table 1.
PdCl2(cod) with the preferred phosphane ligand in dichlo-
romethane. PdCl2(cod) reacts relatively easily with one mol
equiv. of phosphane ligands in dichloromethane at room
temperature overnight, and produces a chlorine bridged
dinuclear complex of the type [PdCl2L]2. The complexes
11–15 were prepared by a similar reaction of cyclooctadi-
ene (cod) in PdCl2(cod) with 2 mol equiv. of a preferred
phosphane ligand in diethyl ether at room temperature
overnight. The reaction produces mononuclear complexes
of the type [PdCl2L2]. The dinuclear palladium complexes
7 and 8 were acquired only as side-products in reactions
in both diethyl ether and dichloromethane. The yellow
(mononuclear) or orange (dinuclear) precipitates obtained
were filtered and washed with a small amount of hexane
and diethyl ether and dried in vacuo. If necessary, the com-
plexes were further purified by column chromatography
using silica gel and dichloromethane–hexane 2:1 or THF–
hexane 2:1 mixture. The separation of the mono- and dinu-
clear complexes in the synthesis of complexes 7, 8, 12 and
13 was done by column chromatography using silica gel
and a 5:1 dichloromethane–hexane mixture. Single crystals
for X-ray crystallographic analysis were obtained by slow
evaporation of the dichloromethane–hexane or chloroben-
zene–hexane solvent mixture at room temperature.
4.2. Preparation of the ligands
The previously characterized o-alkyl substituted phos-
phane ligands 1–5 were prepared according to a modified
literature method [11,21] at 0 °C from brominated organic
reagents by lithiation with n-butyl lithium and an overnight
reaction with halogenated arylphosphanes. The ligands
were recrystallized from ethanol or a 1:1 mixture of ethanol
and hexane, and if necessary, purified by column chroma-
tography using silica gel and hexane–dichloromethane 2:1
mixture.
4.3.1. Pd2Cl4(o-methylphenyldiphenylphosphane)2 (6)
o-Methylphenyldiphenylphosphane
(0.103 g,
0.37
mmol) and PdCl2(cod) (0.096 g, 0.34 mmol) were dissolved
in dichloromethane (15 ml). The mixture was stirred at
room temperature for 24 h. After filtration of the solution
and purification by column chromatography, the product
isolated was as a dark orange solid. The yield of the prod-
1
4.3. Preparation of the palladium complexes
uct was 0.265 g (0.29 mmol, 86%). H NMR (400 MHz,
CDCl3, see Scheme 1 for numbering): d = 2.38 (3H, s,
3
3
The dinuclear palladium complexes 6, 9 and 10 were
prepared by a substitution of cyclooctadiene (cod) in
H11), 6.90 (1H, dd, JH–H = 7.4 Hz, JH–P = 4.5 Hz, H6),
7.18–7.50 (13H, m, H3ꢀ5
,
H8–10). The 31P–{1H}
Table 3
Crystal Data for 6 Æ 2(CH2Cl2), 7, 9, 14 Æ (CH2Cl2), and 15 Æ (CH2Cl2)
6 Æ 2(CH2Cl2)
40H38Cl8P2Pd2
1077.04
120(2)
0.71073
Triclinic
7
9
14 Æ (CH2Cl2)
15 Æ (CH2Cl2)
Empirical formula
Formula weight
Temperature (K)
k (A)
Crystal system
C
C40H38Cl4P2Pd2
935.24
120(2)
0.71073
Monoclinic
P21/c
19.0114(7)
10.5966(3)
20.5370(7)
90
C48H50Cl4P2Pd2
1043.42
120(2)
0.71073
Monoclinic
P21/n
9.6950(3)
17.3842(6)
14.1760(9)
90
109.316(2)
90
C49H52Cl4P2Pd
951.05
100(2)
C50H42Cl6P2Pd
1023.88
100(2) K
0.71073 A
˚
˚
0.71073
Orthorhombic
Pn21a
Triclinic
ꢀ
ꢀ
Space group
P1
P1
˚
˚
a (A)
9.2435(2)
9.8186(2)
12.5982(10)
107.213(1)
102.265(1)
95.410(1)
1052.02(9)
1
19.8140(4) A
9.6986(3)
9.9748(3)
13.3530(4)
104.921(1)
96.314(1)
112.421(1)
1122.10(6)
1
˚
˚
b (A)
33.9300(7) A
˚
˚
c (A)
13.5630(2) A
a (°)
b (°)
c (°)
90
90
90
9118.3(3)
8
115.746(2)
90
3726.6(2)
4
3
˚
V (A )
2254.7(2)
2
Z
qcalc (Mg/m3)
l (Mo Ka) (mmolꢀ1
Ra1 (I P 2r)
wRb2 (I P 2r)
1.700
1.468
0.0265
0.0601
1.667
1.367
65386
7293
1.537
1.139
0.0364
0.0795
1.386
0.745
0.0416
0.0929
1.515
0.878
0.0696
0.1634
)
P
P
a
R1 ¼ jjF oj ꢀ jF cjj= jF oj.
P
P
2
2
b
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁ.

S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
5051
NMR-data are presented in Table 2. Anal. Calc. for
Pd2Cl4P2C38H34 (800.81): C, 51.96; H, 3.9. Found: C,
51.62; H, 4.30%.
at room temperature for 24 h. After filtration of the solu-
tion and purification by column chromatography, the iso-
lated product was found to be a dark orange solid. The
yield of the product was 0.120 g (77%, 0.12 mmol). 1H
NMR (400 MHz, CDCl3, see Scheme 1 for numbering):
d = 7.0–7.5 (19H, m, H3–6, H8–10, H9, H0–2, H0–3, H0–4).
The 31P-{1H} NMR-data was presented in Table 2. Anal.
Calc. for Pd2Cl4P2C48H38 (924.94): C, 55.25; H, 4.8.
Found: C, 55.15; H, 4.64%.
4.3.2. PdCl2(o-methylphenyldiphenylphosphane)2 (11)
o-Methylphenyldiphenylphosphane (0.3933 g, 1.42
mmol) and PdCl2(cod) (0.208 g, 0.73 mmol) were added in
diethyl ether (30 ml). The mixture was stirred at room tem-
perature for 24 h. After filtration of the solution, the isolated
product was a yellow solid. The yield of the product was
0.485 g (91%, 0.66 mmol). 1H NMR (400 MHz, CDCl3, see
Scheme 1 for numbering): d = 2.39 (3H, s, H11), 6.93 (1H,
4.3.6. Preparation of PdCl2(o-phenylphenyldiphenyl-
phosphane)2 (15)
3
3
dd, JH–H = 7.4 Hz, JH–P = 4.5 Hz, H6), 7.08 (1H, td,
o-Phenylphenyldiphenylphosphane (0.4740 g, 1.4 mmol)
and PdCl2(cod) (0.2014 g, 0.71 mmol) were added in
diethyl ether (30 ml). The mixture was stirred at room tem-
perature for 24 h. After filtration of the solution, the prod-
uct was isolated as a yellow solid. The yield of the product
was 0.521 g (86%, 0.61 mmol). 1H NMR (400 MHz,
CDCl3, see Scheme 1 for numbering): d = 7.0–7.11 (1H,
H6), 7.12–7.5 (18H, m, H3–5, H8–10, H0–2, H0–3, H0–4).
The 31P–{1H} NMR-data are presented in Table 2. Anal.
Calc. for PdCl2P2C48H50 (747.62): C, 67.5; H, 4.49. Found:
C, 67.08; H, 4.37%.
3JH–H = 7.0 Hz, JH–P = 2.1 Hz, H5), 7.20–7.35 (12H, m,
4
H3–4, H8–10). The 31P–{1H} NMR-data are presented in
Table 2. Anal. Calc. for PdCl2P2C38H34 (788.07): C, 62.5;
H, 4.69. Found: C, 62.13; H, 4.62%.
4.3.3. Preparation of Pd2Cl4(o-Cyclohexylphenyldiphenyl-
phosphane)2 (9)
o-Cyclohexylphenyldiphenylphosphane (0.1305 g, 0.38
mmol) and PdCl2(cod) (0.1512 g, 0.53 mmol) were dis-
solved in dichloromethane (15 ml). The mixture was stir-
red at room temperature for 24 h. After filtration of the
solution and purification by column chromatography, the
product isolated was obtained as a dark orange solid.
The yield of the product was 0.310 g, (78%, 0.30 mmol).
1H NMR (400 MHz, CDCl3, see Scheme 1 for number-
ing): d = 1.15–1.25 (2H, m, H0–4), 1.40–1.50 (4H, m,
H0–2), 1.70–1.83 (4H, m, H0–3), 3.60 (1H, m, H0–1),
6.85–6.98 (1H, m, H6), 7.0 (1H, m, H5), 7.32–7.53
(12H, m, H3–4, H8–10). The 31P–{1H} NMR-data are pre-
sented in Table 2. Anal. Calc. for Pd2Cl4P2C48H50
(1043.46): C, 55.25; H, 4.8. Found: C, 54.95; H,
4.54%.
4.3.7. Preparation of PdCl2(o-ethylphenyldiphenyl-
phosphane)2 (7) and Pd2Cl4(o-ethylphenyldiphenyl-
phosphane)2 (12) in Et2O and CH2Cl2
o-Ethylphenyldiphenylphosphane (0.4210 g, 1.45 mmol)
and PdCl2(cod) (0.1977 g, 0.69 mmol) were added in
diethyl ether (30 ml). The mixture was stirred at room tem-
perature for 24 h. After filtration of the solution and sepa-
ration by column chromatography, the isolated complex
(12) was a yellow solid. The yield of the product was
1
0.380 g (74%, 0.51 mmol). H NMR (400 MHz, CDCl3,
see Scheme
1
for numbering): d = 1.16 (3H, t,
3
3JH–H = 7.6 Hz, H12), 2.93 (2H, qd, JH–H = 7.5 Hz,
3
4.3.4. Preparation of PdCl2(o-cyclohexylphenyldiphenyl-
phosphane)2 (14)
3JH–P = 1.6 Hz, H11), 6.91 (1H, dd, JH–H = 7.3 Hz,
3JH–P = 4.2 Hz, H6), 7.08 (1H, td, JH–H = 7.0 Hz,
3
o-Cyclohexylphenyldiphenylphosphane
(0.4837 g,
4JH–P = 2.5 Hz, H5), 7.35–7.56 (12H, m, H3–4, H8–10).
The 31P–{1H} NMR-data are presented in Table 2. Anal.
Calc. for PdCl2P2C40H38 (743.40): C, 63.4; H, 5.05. Found:
C, 63.21; H, 4.98%.
1.40 mmol) and PdCl2(cod) (0.2001 g, 0.70 mmol) were
added in diethyl ether (30 ml). The mixture was stirred at
room temperature for 24 h. After filtration of the solution,
the isolated product was obtainedas a yellow solid. The
yield of the product was 0.515 g (85%, 0.60 mmol). 1H
NMR (400 MHz, CDCl3, see Scheme 1 for numbering):
d = 1.15–1.24 (2H, m, H0–4), 1.25–1.40 (4H, m, H0–2),
1.45–1.64 (4H, m, H0–3), 3.30 (1H, m, H0–1), 6.98–7.09
(2H, m, H5–6), 7.30–7.46 (12H, m, H3–4, H8–10). The
31P–{1H} NMR-data are presented in Table 2. Anal. Calc.
for PdCl2P2C48H50 (866.14): C, 66.4; H, 5.8. Found: C,
66.04; H, 5.44%.
After separation, the isolated complex (7) was isolated
as a dark orange solid. The yield of the product was
0.021 g (6.6%, 0.02 mmol).1H NMR (400 MHz, CDCl3,
see Scheme
1
for numbering): d = 1.17 (3H, t,
4
3JH–H = 7.6 Hz, H12), 2.98 (2H, qd, JH–H = 7.5 Hz,
3JH–P = 1.6 Hz, H11), 6.88 (1H, dd, JH–H = 7.3 Hz,
3
3JH–P = 4.2 Hz, H6), 7.03 (1H, td, JH–H = 7.0 Hz,
3
4JH–P = 2.5 Hz, H5), 7.30 –7.54 (12H, m, H3–4, H8–10).
The 31P–{1H} NMR-data are presented in Table 2. Anal.
Calc. for Pd2Cl4P2C40H38 (991.40): C, 51.36; H, 4.0.
Found: C, 51.11; H, 4.1%.
4.3.5. Preparation of Pd2Cl4(o-phenylphenyldiphenyl-
phosphane)2 (10)
A similar reaction of o-ethylphenyldiphenylphosphane
(0.2046 g, 0.71 mmol) and PdCl2(cod) (0.1983 g, 0.69
mmol) in dichloromethane (15 ml) produced a 58% yield
for 12 and 23% for 7.
o-Phenylphenyldiphenylphosphane
(0.0504 g,
0.15
mmol) and PdCl2(cod) (0.0932 g, 0.33 mmol) were dis-
solved in dichloromethane (15 ml). The mixture was stirred

5052
S. Vuoti et al. / Journal of Organometallic Chemistry 692 (2007) 5044–5052
[2] (a) G. Parkin, Fundamentals 1 (2006);
4.3.8. Preparation of Pd2Cl4(o-isopropylphenyldiphenyl-
phosphane)2 (8) and PdCl2(o-isopropylphenyldiphenyl-
phosphane)2 (13) in Et2O and CH2Cl2
(b) A. Canty, Compounds of Group 10, vol. 8, Elsevier, Essex,
2006.
[3] (a) F.G. Mann, D. Purdie, J. Chem. Soc. (1935) 1549;
(b) F.G. Mann, A.F. Wells, J. Chem. Soc. (1938) 702.
[4] G. Oehme, H. Pracejus, J. Organomet. Chem. 320 (1987) C56–
C58.
[5] M. Beller, T. Riermeier, S. Haber, S. Kleiner, H. Jerg, W. Herrmann,
Chem. Ber. 129 (1996) 1259–1264.
[6] E. Drent, D. Arnoldy, P.H.M. Budzelaar, J. Organomet. Chem. 455
(1993) 247.
o-Isopropylphenyldiphenylphosphane (0.2969 g, 0.98
mmol) and PdCl2(cod) (0.1388 g, 0.49 mmol) were added in
diethylether(30ml). The mixturewasstirredatroomtemper-
ature for 24 h. After filtration of the solution and separation
bycolumnchromatography,complex13wasisolatedasayel-
low solid. The yield of the product was 0.293 g (76%, 0.37
mmol). 1H NMR (400 MHz, CDCl3, see Scheme 1 for num-
bering):d = 1.13(6H, d, 3JH–H = 6.8Hz, H0–2), 3.48(1H, sep,
3JH–H = 6.8 Hz, H0–1), 6.98 (1H, m, H6), 7.11–7.16 (1H, m,
H5), 7.30–7.44 (12H, m, H3–4, H8–10). The 31P–{1H} NMR-
data are presented in Table 2. Anal. Calc. for PdCl2P2C42H42
(786.16): C, 64.1; H, 5.38. Found: C, 64.5; H, 5.57%.
After separation, complex 8 was isolated as a dark
orange solid. The yield of the product was 0.023 g (9.7%,
[7] A.M. Trzeciak, H. Bartosz-Bechowski, Z. Ciunik, K. Niesyty, J.
Ziotkowski, Can. J. Chem. 79 (2001) 752–759.
[8] G. Dekker, A. Buijs, C.J. Elsevier, K. Vrieze, Organometallics 11
(1992) 1937–1946.
[9] A. Dervisi, P.G. Edwards, P. Newman, R. Tooze, S. Coles, M.B.
Hursthouse, J. Chem. Soc., Dalton Trans. (1998) 3771–3776.
[10] A. Littke, G. Fu, Angew. Chem. Int. Ed. 41 (2002) 4176–4211.
[11] H. Riihima¨ki, P. Suomalainen, H. Renius, J. Suutari, S. Ja¨a¨skela¨inen,
A.O.I. Krause, T. Pakkanen, J. Pursiainen, J. Mol. Catal. 200 (2003)
69–79.
[12] A. Moreno, M. Haukka, S. Ja¨a¨skela¨inen, S. Vuoti, J. Pursiainen, T.
Pakkanen, J. Organomet. Chem. 690 (2005) 3803–3814.
[13] S.B. Sembiring, S. Colbran, D. Craig, M. Scudder, J. Chem. Soc.,
Dalton Trans. (1995) 3731–3741.
1
0.02 mmol). H NMR (400 MHz, CDCl3, see Scheme 1
3
for numbering): d = 1.13 (6H, d, JH–H = 6.8 Hz, H0–2),
3.48 (1H, sep,3JH–H = 6.8 Hz, H0–1), 6.94 (1H, m, H6),
7.01–7.11 (1H, m, H5), 7.30–7.42 (12H, m, H3–4, H8–10).
The 31P–{1H} NMR-data are presented in Table 2. Anal.
Calc. for Pd2Cl4P2C42H42 (963.48): C, 52.36; H, 4.4.
Found: C, 52.42; H, 4.30%.
[14] S. Coles, P. Faulds, M. Hursthouse, D. Kelly, G. Ranger, A. Toner,
N. Walker, J. Organomet. Chem. 586 (1999) 234–240.
[15] R.A. Baber, A.G. Orpen, P.G. Pringle, M.J. Wilkinson, R.L. Wingad,
Dalton Trans. (2005) 659–667.
A similar reaction of o-isopropylphenyldiphenylphos-
phane (0.115 g, 0.38 mmol) and PdCl2(cod) (0.1198 g,
0.42 mmol) in dichloromethane (15 ml) produced a 60%
yield for 13and 22% for 8.
[16] J.J. Stone, R.A. Stockland Jr., N.P. Rath, Inorg. Chim. Acta 342
(2003) 236–240.
[17] G. Ferguson, R. McCrindle, A.J. McAless, M. Parvez, Acta Cryst.
B38 (1982) 2679–2681.
[18] C. Sui-Seng, F. Belanger-Gariepy, D. Zargarian, Acta Cryst. E59
(2003) m618.
5. Supplementary material
[19] P.A. Chaloner, S.Z. Dewa, P.B. Hitchcock, Acta Cryst. C51 (1995)
232.
[20] C. Sui-Seng, F. Belanger-Gariepy, D. Zargarian, Acta Cryst. E59
(2003) m620–m621.
[21] H. Riihima¨ki, T. Kangas, P. Suomalainen, H. Renius, S. Ja¨a¨skela¨i-
nen, M. Haukka, A.O.I. Krause, T. Pakkanen, J. Pursiainen, J. Mol.
Catal. 200 (2003) 81–94.
[22] P. Suomalainen, H. Riihima¨ki, S. Ja¨a¨skela¨inen, M. Haukka, J.
Pursiainen, T. Pakkanen, Catal. Lett. 77 (2001) 125–130.
[23] Z. Otwinowski, W. Minor, Processing of X-ray diffraction data
collected in oscillation mode, in: C.W. CarterJr., R.M. Sweet
(Eds.), Methods in Enzymology, Macromolecular Crystallography
Part A, vol. 276, Academic Press, New York, 1997, pp. 307–
326.
CCDC 618821, 618822, 618823, 618824, 618825, 618826,
and 618827 contain the supplementary crystallographic data
for 6, 7, 9, 11, 13, 14, and 15. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgement
[24] G.M. Sheldrick, SHELXL97, Program for Crystal Structure Refine-
ment, University of Go¨ttingen, 1997.
[25] M.C. Burla, M. Camalli, B. Carrozzini, G.L. Cascarano, C. Giaco-
vazzo, G. Polidori, R.J. Spagna, Appl. Cryst. 36 (2003) 1103.
[26] L.J.J. Farrugia, Appl. Cryst. 32 (1999) 837.
Financial support by Tauno To¨nning – foundation and
the Yliopiston apteekin apurahasto are gratefully
acknowledged.
[27] G.M. Sheldrick, SHELXTL v. 6.12, Bruker Analytical X-ray Systems,
Bruker AXS, Inc. Madison, WI, USA, 2002.
References
[28] G.M. Sheldrick, SADABS–Bruker Nonius Scaling and Absorption
[1] E.W. Abel, F.A. Stone, G. Wilkinson, Comprehensive Organometal-
lic Chemistry IINickel Palladium and Platinum, vol. 9, Elsevier,
Essex, 1995.
Correction,
2003.
v 2.10, Bruker Axs Inc., Madison, WI, USA,