Structural studies of PdCl2L2 complexes with fluorinated phosphines, phosphites, and phosphinites as precursors of benzyl bromide carbonylation catalysts, and and X-ray crystal structure of cis-PdCl2[PPh2 (OEt)]2

Article abstract of DOI:10.1139/v01-075

PdCl₂L₂-type complexes with phosphines (L = PPh_x(C₆F₅)_3-x (x = 0-3)), phosphites (L = P(OMe)₃, P(OPh)₃, P(OEt)₃), and phosphinites (L = PPh₂ (OC₆F₅), PPh₂(O-3,5-F₂ C₆H₃), PPh₂(OEt), PPh₂ (O-n-Bu), PPh₂(O-t-Bu)) were synthesized and characterized by UV-vis and ³¹P NMR methods. PdCl₂L₂ complexes with less sterically demanding phosphines (Θ < 140°) exist as cis isomers, which is confirmed by the X-ray structure of cis-PdCl₂[PPh₂(OEt)]₂. These complexes react with CO in the presence of NEt₃ forming Pd(CO)_xL_y (x + y = 4) type carbonyls characterized by IR spectra. All PdCl₂L₂ complexes studied are active as precursors of benzyl bromide carbonylation catalysts at 40°C and 1 atm CO; however, the activity of the cis isomers is higher than that of the trans isomers. The highest yields of the carbonylation product, phenylacetic acid methyl ester, were obtained using cis-PdCl₂[P(OMe)₃]₂ (92%), cis-PdCl₂[P(OPh)₃]₂ (89%), and cis-PdCl₂[PPh₂(O-n-Bu)]₂ (78%) as catalyst precursors.

Full text of DOI:10.1139/v01-075

752
Structural studies of PdCl2L2 complexes with
fluorinated phosphines, phosphites, and
phosphinites as precursors of benzyl bromide
carbonylation catalysts, and and X-ray crystal
structure of cis-PdCl2[PPh2(OEt)]2
Anna M. Trzeciak, Hubert Bartosz-Bechowski, Zbigniew Ciunik,
Katarzyna Niesyty, and Józef J. Zió»kowski
Abstract: PdCl2L2-type complexes with phosphines (L = PPhx(C6F5)3–x (x = 0–3)), phosphites (L = P(OMe)3, P(OPh)3,
P(OEt)3), and phosphinites (L = PPh2(OC6F5), PPh2(O-3,5-F2C6H3), PPh2(OEt), PPh2(O-n-Bu), PPh2(O-t-Bu)) were syn-
thesized and characterized by UV–vis and 31P NMR methods. PdCl2L2 complexes with less sterically demanding
phosphines (Θ < 140°) exist as cis isomers, which is confirmed by the X-ray structure of cis-PdCl2[PPh2(OEt)]2. These
complexes react with CO in the presence of NEt3 forming Pd(CO)xLy (x + y = 4) type carbonyls characterized by IR
spectra. All PdCl2L2 complexes studied are active as precursors of benzyl bromide carbonylation catalysts at 40°C and
1 atm CO; however, the activity of the cis isomers is higher than that of the trans isomers. The highest yields of the
carbonylation product, phenylacetic acid methyl ester, were obtained using cis-PdCl2[P(OMe)3]2 (92%), cis-
PdCl2[P(OPh)3]2 (89%), and cis-PdCl2[PPh2(O-n-Bu)]2 (78%) as catalyst precursors.
Key words: palladium complexes, fluorinated phosphines, benzyl bromide carbonylation.
Résumé : On a synthétisé des complexes de type PdCl2L2 comprenant des phosphines L = PPhx(C6F5)3–x (x = 0–3),
des phosphites L = P(OMe)3, P(OPh)3 et P(OEt)3 et des phosphinites L = PPh2(OC6F5), PPh2(O-3,5-F2C6H5),
PPh2(OEt), PPh2(OBu) et PPh2(O-t-Bu) et on les a caractérisés par spectroscopie UV–vis et par RMN du 31P. Les com-
plexes PdCl2L2 comportant des phosphines stériquement moins encombrées (θ < 140°) existent sous la forme
d’isomères cis; cette situation a été confirmée par diffraction des rayons du cis-PdCl2[PPh2(OEt)]2. Ces complexes réa-
gissent avec le CO en présence de NEt3 pour former des complexes carbonylés de type Pd(CO)xLy (x + y = 4) qui ont
été caractérisés par spectroscopie IR. À 40°C et 1 atm de CO, tous les complexes de type PdCl2L2 sont actifs comme
précurseurs de catalyseurs pour la carbonylation du bromure de benzyle; toutefois, l’activité des isomères cis est supé-
rieure à celle des isomères trans. Les rendements les plus élevés en produit de carbonylation, le phénylacétate de mé-
thyle, ont été obtenus avec les cis-PdCl2[P(OMe)3]2 (92%), cis-PdCl2[P(OPh)3]2 (89%) et cis-PdCl2[P(OBu)3]2 (78%)
comme précurseurs de catalyseur.
Mots clés : complexes de palladium, phosphines fluorées, carbonylation du bromure de benzyle.
[Traduit par la Rédaction] Trzeciak et al. 759
Introduction
acter of fluorine reduces the basicity of the ligand, as has
been demonstrated for trans-MCl(CO)(PR3)2 (M = Rh, Ir)
by an increase of the ν(CO) frequency in the following series
of PR3 ligands: PPh3 < PPh2(C6F5) < P(C6F5)3 (1). However,
when only two fluorines are present in the phenyl ring of the
phosphine coordinated in complexes of the same type
(PPhx(2,6-F2C6H3)3–x, x = 0–2), the ν(CO) remains constant
and close to the value observed for MCl(CO)(PPh3)2 (1). On
the basis of ligand displacement studies of PtCl2(PR3)2 com-
plexes, phosphorus ligands have been ordered according to
their ligand exchange ability, which increases in the follow-
The electronic and steric properties of fluorine-containing
phosphorus ligands are quite different from those of their
nonfluorinated analogues. The σ-electron-withdrawing char-
Received September 14, 2000. Published on the NRC
Research Press Web site at http://canjchem.nrc.ca on June 30,
2001.
Dedicated to Professor Brian James on the occasion of his
65th birthday.
ing order: P(C6F5)3 < PPh(C6F5)2 < P(2,6-F2C6H3)3
<
A.M. Trzeciak, H. Bartosz-Bechowski, Z. Ciunik, K.
Niesyty, and J.J. Zió»kowski.1 Faculty of Chemistry,
University of Wroclaw, 14 F. Joliot-Curie St., 50–383
Wroclaw, Poland.
PPh2(C6F5) < PPh3 (2). Rhodium and platinum complexes
with fluorinated phosphines, diphosphines, phosphonites,
and phosphinites have been studied (3–5). Examples of
ortho-C–F bond activation in rhodium and iridium complexes
with fluorinated diphosphines have been reported (6, 7).
1Corresponding author (telephone: +48 71 3402-270; fax:
+48 71 3282-348; e-mail: jjz@wchuwr.chem.uni.wroc.pl).
Can. J. Chem. 79: 752–759 (2001)
© 2001 NRC Canada
DOI: 10.1139/cjc-79-5/6-752

Trzeciak et al.
753
Table 1. UV-vis (in CHCl3) and 31P NMR (in CDCl3) data of PdCI2L2 complexes.
UV–vis
(λ, nm)
31P NMR PdCl2L2
(δ, ppm)
31P NMR OPR3
(δ, ppm)
θ (°)a
∆ = δcompl – δL
No.
L
Isomer
1
2
3
4
5
6
7
8
PPh2(O-t-Bu)
PPh3
PCy3
trans
trans (15)
trans (17)
trans
trans
cis
cis
trans
cis
348
345
344
342
342
342
334
333
330
326
320
317
306
305
79.0
23.4
24.8
12.8
79.0
37.5
29.4
13.9
37.7
–3.1
–35.4
–45.1
40.5
–22.5
–2.8
–42.3
47.6
–30.5
–46.3
34.0
28.1
50.0
20.9
27.8
32.9
–3.4
7.9
31.0
31.7
–17.0
–8.0
2.0 (13)
–1.0 (13)
155b
145 (8)
170
158 (8)
145
PPh2(C6F5)
PPh2(OC6F5)
PPh2(O-3,5-F2C6H3)
P(OCH2CF3)3
PPh(C6F5)2
PPh2(OEt)
PPh2(O-n-Bu)
P(OPh)3
79.2
94.8
139
115
–5.93
109.5
109.3
83.7
–26.8
94.8
167 (1), 171 (8)
133 (8)
133
128 (8)
184 (8), 172 (1)
107 (8)
9
10
11
12
13
14
cis
cis (18)
trans (16)
cis
P(C6F5)3
P(OMe)3
c
P(OEt)3
cis
93.1
109 (8)
aCone angle. References are given in parentheses.
bCalculated from the equation θ = 2/3 Σθi /2 (8).
cNot isolated.
The presence of fluorines in the phosphine phenyl ring,
especially in ortho-positions, dramatically changes the steric
properties of the ligand causing an increase of the cone an-
gle (Θ), e.g., from 145° for PPh3 to 184° for P(C6F5)3 (8).
Long chain alkyl fluorinated phosphines, such as
P(CH2CH2(CF2)5CF3)3, are successfully applied for catalytic
processes in highly fluorinated solvents (9, 10).
Scheme 1.
Cl
Cl
PR3
PR3
Cl
R3P
PR3
Pd
Pd
Cl
cis - isomer
trans - isomer
Looking for good modifying ligands for palladium
carbonylation catalysts, we selected fluorinated phosphorus
ligands such as phosphines of the form PPhx(C6F5)3–x (x =
0–2) and phosphinites of the form PPh2(OC6F5) and PPh2(O-
3,5-F2C6H3) for systematic studies of the electronic and
steric effects of ligands on the structural and catalytic prop-
erties of PdCl2L2-type palladium complexes.
It was particularly interesting to test complexes with lig-
ands that are bulky and simultaneously have a strong accep-
tor character (low basicity). Recently, we found a new
Pd(0)–triphenylphosphite complex formation reaction when
PdCl2[P(OPh)3]2 was treated with NEt3 (11). Although
triphenylphosphite is a stronger π-acceptor, it has relatively
small cone angle (Θ = 128°), and the question arises how the
same reaction with NEt3 would proceed in the case of more
bulky fluorinated phosphines. To supplement the series of
complexes under study and to be able to draw more general
conclusions, we prepared palladium complexes with
nonfluorinated phosphites (P(OPh)3, P(OMe)3, P(OEt)3) and
phosphinites (PPh2(OEt), PPh2(O-n-Bu), PPh2(O-t-Bu)) for
comparison.
o
o
Θ (PR3) < 140
Θ (PR3) > 140
Square planar complexes of the PdCl2L2 type can exist as
two isomers, cis and trans (14). Some of the compounds
listed in Table 1, namely PdCl2L2 (L = PPh3, P(C6F5)3,
P(OPh)3, PCy3) had been characterized earlier by X-ray
crystallography (14–18), and the presence of trans-isomers
was confirmed for complexes with bulky ligands, e.g., trans-
PdCl2(PPh3)2 (15), trans-PdCl2[P(C6F5)3]2 (14), and trans-
PdCl2(PCy3)2 (17). The phosphites and phosphinites, on the
other hand, preferentially formed cis-isomers (14), as was
recently confirmed by the structure of cis-PdCl2[P(OPh)3]2
(8) and the structure of cis-PdCl2[PPh2(OEt)]2 in this paper.
On the basis of the literature data (14–18), we assigned cis
or trans geometry for all complexes under study (Table 1)
according to the general rule shown in Scheme 1. The only
doubtful structure is that of PdCl2[PPh2(OC6F5)]2, which de-
composes during recrystallization thereby making it impos-
sible to determine the structure via X-ray crystallography.
The cone angle of the PPh2(OC6F5) ligand, calculated from
the molecular structure of the platinum complex (3), is 145°,
and by analogy with trans-PdCl2(PPh3)2 (Θ for PPh3 = 145°),
we proposed a trans geometry for PdCl2[PPh2(OC6F5)]2.
It is important to note that the presence of only one 31P NMR
signal in the spectrum of each of the palladium complexes
suggested the presence of only one isomer in solution.
Results and discussion
PdCl2L2-type complexes
The palladium complexes that we used for spectroscopic
and catalytic studies were prepared by substitution of
cyclooctadiene (cod) in PdCl2(cod) with a suitable phospho-
rus ligand. All complexes were isolated and characterized by
spectroscopic and analytical methods (Table 1, and see Ex-
perimental).
UV–vis spectra
Spectroscopic data for the PdCl2L2 complexes are pre-
sented in Table 1. All of the complexes display one elec-
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Can. J. Chem. Vol. 79, 2001
Fig. 1. Correlation between the UV–vis band position (λ, nm) of
PdCl2L2 complexes in CHCl3 and the 31P NMR chemical shift
(δ, ppm) of respective phosphine oxides OPR3; 1 PPh2(O-t-Bu),
2 PPh3, 3 PCy3, 4 PPh2(C6F5), 5 PPh2(OC6F5), 6 PPh2(O-3,5-
F2C6H3), 7 P(OCH2CF3)3, 8 PPh(C6F5)2, 9 PPh2(OEt), 10
PPh2(O-n-Bu), 11 P(OPh)3, 12 P(C6F5)3, 13 P(OMe)3, 14
P(OEt)3. cis-PdCl2L2 (᭹), trans-PdCl2L2 (᭺).
Fig. 2. Correlation between the UV–vis band position (λ, nm) of
PdCl2L2 complexes in CHCl3 and the cone angles (θ) of respec-
tive phosphines (L) 1 PPh2(O-t-Bu), 2 PPh3, 3 PCy3, 4
PPh2(C6F5), 5 PPh2(OC6F5), 6 PPh2(O-3,5-F2C6H3), 7
P(OCH2CF3)3, 8 PPh(C6F5)2, 9 PPh2(OEt), 10 PPh2(O-n-Bu), 11
P(OPh)3, 12 P(C6F5)3, 13 P(OMe)3, 14 P(OEt)3. cis-PdCl2L2 (᭹),
trans-PdCl2L2 (᭺).
Another correlation, between the UV–vis band position
(λ) and the phosphine cone angle (Θ), was plotted because of
the estimation of the influence of the steric effect of the
ligand on the spectroscopic properties of palladium com-
plexes (Fig. 2). This correlation is also not satisfactory as it
still shows some deviations from linearity. However, it al-
lows one to conclude that the band position in the spectra of
PdCl2L2 complexes are dependent on both the electronic and
steric properties of ligand L.
tronic transition (λ) in the 300–350 nm region of the UV–vis
spectrum, as similarly reported for other palladium(II) com-
plexes with phosphorus ligands (12). In the group of com-
plexes studied, the band is shifted from 348 nm for
PdCl2[PPh2(O-t-Bu)]3 to 305 nm for PdCl2[PPh2(OEt)]2,
showing a dependence on the type of phosphorus ligand co-
ordinated to palladium. The influence of the phosphorus
ligand on the spectroscopic properties of metal complexes
can be discussed in terms of two types of effects; electronic
and steric, which could not be separated and considered as
totally independent effects. In the group of palladium com-
plexes under study, we can however, discuss the domination
of electronic or steric influence of the ligand on the spectro-
scopic properties of the compound.
31P NMR spectra
The chemical shift of the 31P NMR signal, being strongly
dependent on the kind of phosphorus ligand, is not very in-
formative (Table 1). However, the coordination chemical
shift (∆), defined as the difference in the 31P NMR chemical
shift between coordinated and free phosphine (∆ = δcoord. – δL),
can be used to compare structurally similar complexes with
different phosphorus ligands (8). The coordination chemical
shift can also be used for the estimation of bond strength, as
was demonstrated for PtCl2L2 complexes with fluorinated
phosphines (2).
To characterize the influence of the electronic properties
of the phosphorus ligand coordinated to palladium on the
UV–vis spectrum of the complex, we plotted the relationship
between the band position (λ) and the 31P NMR chemical
shift of phosphine oxides (δOPR ) (13) (Fig. 1).
3
The selection of this parameter was based on
Derenesceyi’s demonstration (13) that the carbonyl stretch-
ing frequency (ν(CO)) of Ni(CO)3PR3, being the measure of
the electronic properties of PR3, is linearly correlated with
the 31P NMR chemical shift of OPR3 (δ). The linear correla-
tion is fairly good only for trans-PdCl2L2 with fluorinated
phosphines (L = PPhx(C6F5)3–x (x = 0–3)) (Fig. 1).
We found that the coordination chemical shift (∆) of com-
plexes under study increases with increase of phosphine
cone angle (Θ) (Fig. 3), as was similarly reported for
RhCl(CO)(PR3)2 complexes (8). The lowest (negative) values
of ∆ were found for complexes with less bulky phosphorus
ligands (Θ < 140°), existing as cis-isomers. The coordina-
tion of these ligands to palladium causes an upfield shift of
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Trzeciak et al.
755
Fig. 3. Correlation between the 31P NMR coordination chemical
shift (∆ = δcoord. – δL) of PdCl2L2 complexes in CHCl3 and the
cone angles (θ) of the phosphorus ligand (L). 1 PPh2(O-t-Bu), 2
PPh3, 3 PCy3, 4 PPh2(C6F5), 5 PPh2(OC6F5), 6 PPh2(O-3,5-
F2C6H3), 7 P(OCH2CF3)3, 8 PPh(C6F5)2, 9 PPh2(OEt), 10
PPh2(O-n-Bu), 11 P(OPh)3, 12 P(C6F5)3, 13 P(OMe)3, 14
P(OEt)3. cis-PdCl2L2 (᭹), trans-PdCl2L2 (᭺).
Table 2. ν(CO) frequencies observed for Pd(CO)xLy (x + y = 4)
complexes in KBr.
L
ν(CO) (cm–1)
PPh2(OEt)
PPh2(OBu)
P(OCH2CF3)3
P(OPh)3
1816 (m), 1876 (vs), 1896 (s), 1916 (vs)
1809 (m), 1846 (s), 1876 (vs), 1896 (vs), 1942 (m)
1876 (vs), 1920 (m)
1810 (m), 1849 (m), 1876 (s), 1893 (s), 1926 (m)
1822 (m), 1883 (vs), 1903 (vs), 1916 (vs)
P(OMe)3
When a tertiary amine was replaced by a secondary one, a
mixture of Pd(0) carbonyls, Pd(CO)x(PPh3)y (x + y = 4), was
identified in the reaction product (eq. [3]) (19):
[3]
PdCl2(PPh3)2 + CO + HNR1R2 + MeOH →
Pd(CO)(PPh3)3 + Pd3(CO)3(PPh3)4
+ H2NR1R2Cl
The PdCl2L2 complexes react with CO in the presence of
NEt3, giving products depending on the phosphorus ligand
used.
Palladium complexes with fluorinated phosphines
(PPhx(C6F5)3–x (x = 0–2)) treated with CO (1 atm) in metha-
nol containing an excess of NEt3 ([NEt3]:[Pd] = 5) did not
give any new products, even after 24 h. In contrast, com-
plexes with less bulky phosphines react with CO forming the
respective palladium carbonyls in about 20 min (eq. [4]).
The carbonyls were identified by IR spectra and showed
ν(CO) bands of terminally bonded CO-ligands at ca.
1900 cm–1 (Table 2).
[4]
PdCl2L2 + CO + NEt3 + MeOH →
Pd(CO)x(L)y + HNEt3Cl
L = PPh2(OEt), PPh2(O-n-Bu), P(OPh)3,
P(OCH2CF3)3, P(OMe)3
the 31P NMR signal as compared with the free ligand and as
a consequence leads to a negative coordination shift. The
highest (positive) values of ∆ were noted for trans-com-
plexes with bulky ligands (Θ > 140°). Changes in coordina-
tion chemical shift (∆) were explained by changes in SPS
angles (angles between substituents on trivalent phosphorus
upon coordination of phosphine to metal) (8).
x + y = 4
It is worth mentioning that carbomethoxy complexes were
not identified during rxn. [3] nor in its final product.
It is reasonable to propose that NEt3 acts as a reducing
agent with respect to all complexes mentioned in rxn. [4],
and the presence of methanol is not necessary, as palladium
carbonyls were also obtained in reactions of
PdCl2[P(OPh)3]2 or PdCl2[PPh2(O-n-Bu)]2 with CO and
NEt3 in CH2Cl2 as a solvent.
Attempts to correlate both the 31P NMR parameters; the
coordination chemical shift (∆) and the chemical shift of
phosphine oxides (δ), failed.
Reactions of PdCl2L2 complexes with CO and NEt3
A PdCl2L2 complex used as a carbonylation reaction cata-
lyst precursor should first undergo reduction to a palla-
dium(0) complex. We recently found that PdCl2[P(OPh)3]2 is
reduced to a Pd(0) species by NEt3, even in aprotic solvents
such as CH2Cl2 or C6H6 (11) (eq. [1]).
Catalytic activity of PdCl2L2 complexes in benzyl
bromide carbonylation
A test of the catalytic activity of PdCl2L2 complexes in
the carbonylation of benzyl bromide to phenylacetic acid
methyl ester was performed under standard conditions of
40°C and 1 atm of CO in MeOH (eq. [5]).
[1]
PdCl2[P(OPh)3]2 + nNEt3 →
Pd[(P(OPh)3]4 + Pd[P(OPh)3]x[(NEt3)]4–x
x = 1–3
Br
[P dCl2L2]
C(O)OMe
+ CO
[5]
The PdCl2(PPh3)2 complex under similar conditions ex-
hibits different reactivity, forming a carbomethoxy complex
(eq. [2]) (19):
NEt3, MeOH
The results are summarized in Fig. 4 in the form of a cor-
relation between the yield of phenylacetic acid methyl ester
and the cone angle of the phosphorus ligand (Θ). It can be
[2]
PdCl2(PPh3)2 + CO + NEt3 + MeOH →
PdCl(C(O)OMe)(PPh3)2 + HNEt3Cl
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Can. J. Chem. Vol. 79, 2001
Fig. 5. Molecular structure of cis-PdCl2[PPh2(OEt)]2 (9).
Fig. 4. Dependence of the benzyl bromide carbonylation reaction
yield on the cone angle (θ) of phosphorus ligand (L) coordinated
in PDCl2L2 complex. 1 PPh2(O-t-Bu), 2 PPh3, 3 PCy3, 4
PPh2(C6F5), 5 PPh2(OC6F5), 6 PPh2(O-3,5-F2C6H3), 7
P(OCH2CF3)3, 8 PPh(C6F5)2, 9 PPh2(OEt), 10 PPh2(O-n-Bu), 11
P(OPh)3, 12 P(C6F5)3, 13 P(OMe)3, 14 P(OEt)3. cis-PdCl2L2 (᭹),
trans-PdCl2L2 (᭺).
geometry with P-Pd-Cl angles of 178.54(3) and 89.40(3)°,
respectively.
The Pd—P distance (2.2474(8) Å) in cis-
PdCl2[PPh2(OEt)]2 is significantly shorter than correspond-
ing Pd—P distances in trans-PdCl2L2 complexes with L =
PPh3 (15), P(C6F5)3 (16), PCy3 (17). In the series of these
complexes, a gradual shortening of Pd—P distances is ob-
served as ligand’s (L) basicity decreases from 2.3628(9) Å
in trans-PdCl2(PCy3)2 (17) to 2.3051(12) Å in trans-
PdCl2[P(C6F5)3]2 (16). The basicity of PPh2(OEt) is ex-
pected to be intermediate between that of PPh3 and P(C6F5)3,
and therefore, the order of decreasing basicity is as follows:
PCy3 > PPh3 > PPh2(OEt) > P(C6F5)3. Thus, the Pd—P bond
in cis-PdCl2[PPh2(OEt)]2 should be longer compared to that
in trans-PdCl2[P(C6F5)3]2, which was not observed. On the
other hand, the Pd—P bond in complex cis-
PdCl2[PPh2(OEt)]2 is only slightly longer than that in cis-
PdCl2(P(OPh)3)2 (2.2299(11) and 2.2314(12) Å, respec-
tively) (18), because of the higher basicity of the PPh2(OEt)
ligand compared with that of P(OPh)3. The observed short-
ening of the Pd—P distance in the cis-PdCl2[PPh2(OEt)]2
and other cis-PdCl2L2 complexes with respect to trans-
PdCl2L2 complexes is consistent with the stronger trans in-
fluence of a phosphorus ligand than that of a chloride ligand.
The Pd—Cl bond length in cis-PdCl2[PPh2(OEt)]2
(2.3430(8) Å) is similar to those found in cis-
PdCl2(P(OPh)3)2 (2.3273(11) and 2.3354(11) Å) (18) and
cis-PdCl2[PPh2(OMe)]2 (2.349(8) and 2.358(6) Å) (21). In
the trans-PdCl2L2 complexes mentioned above the respective
distances are ca. 0.04 Å longer. The conformation of
PPh2(OEt) ligand is slightly different from that of
PPh2(OEt), which is illustrated by smaller Pd-P-O angles,
118.6(7) and 115.5(6)° in cis-PdCl2[PPh2(OMe)]2 (21) and
108.19(10)° in cis-PdCl2[PPh2(OEt)]2.
concluded that palladium complexes with less crowded
phosphorus ligands (P(OMe)3, P(OPh)3, PPh2(O-n-Bu)) ex-
hibit higher catalytic activity, producing ca. 90% of the
phenylacetic acid methyl ester. This is in agreement with the
observation that these complexes undergo easier reduction to
palladium(0) species when treated with CO and NEt3
(eq. [4]). Therefore, the higher catalytic activity can be ex-
plained by the higher concentration of the active form of the
catalyst, a Pd(0) complex, which activates benzyl bromide
by an oxidative addition reaction. It is interesting to note
that palladium complexes with fluorinated phosphines
(PPhx(C6F5)3–x, x = 1 or 2) exhibit higher catalytic activity
than expected on the basis of the correlation presented in
Fig. 4. In these cases, the electronic effect of phosphine
seems to be dominating over the steric effect.
The formation of black palladium metal at the end of
some carbonylation reactions was observed, i.e., in reactions
with cis-PdCl2[P(OCH2CF3)3]2 and cis-PdCl2[P(OPh)3]2.
However, the good yields of carbonylation products in these
reactions show that the benzyl bromide carbonylation reac-
tion is faster than palladium reduction. It was found earlier
(20) that palladium black is not catalytically active.
X-ray crystal structure of cis-PdCl2[PPh2(OEt)]2
The molecular structure of the cis-PdCl2[PPh2(OEt)]2
complex is shown in Fig. 5, and selected bond distances and
angles are given in Table 3. The complex is of square-planar
© 2001 NRC Canada

Trzeciak et al.
Table 3. Selected bond lengths (Å) and an-
757
(~40 min). The reaction mixture was cooled to –30°C and
distilled chlorodiphenyl phosphine (1.8 mL, 2.21 g, 10 mM)
was added. The cooling bath was removed and the whole
mixture was stirred overnight.
gles (°) for PdCI2[PPh2(OEt)]2.
Bond lengths (Å)
Pd(1)—P(1)
Pd(1)—P(1)′
Pd(1)—Cl(1)′
Pd(1)—Cl(1)
P(1)—O(1)
P(1)—C(7)
P(1)—C(1)
O(1)—C(13)
C(13)—C(14)
2.2474(8)
2.2474(8)
2.3430(8)
2.3430(8)
1.620(3)
1.804(4)
1.809(3)
1.409(5)
1.505(6)
The THF was removed on rotary evaporator and the re-
maining oil was dissolved in methanol (30 mL) and evapo-
rated (3 times). The oil was extracted with dry ethyl ether
(3 times), the extracts were collected, and evaporated. The
residue was extracted with hot petroleum ether (PE) (bp 40–
60°C), the extracts were treated with charcoal, and evapo-
rated. The crude phosphine (1.9 g, 54%) was recrystalized
from PE–methanol to give 1.2 g (37.5%) of white crystals.
mp 57–60°C (lit. mp (2) 65–68°C). GC–MS: single peak.
1
MS m/z: 352. H NMR (CDCl3) δ: 7.35–7.45 (m). 31P NMR
Bond angles (°)
(CDCl3) δ: –24.9.
89.97(4)
178.54(3)
89.40(3)
89.40(3)
178.54(3)
91.26(4)
103.11(15)
109.04(14)
105.07(15)
108.19(10)
118.19(11)
112.60(11)
P(1)-Pd(1)-P(1)′
P(1)-Pd(1)-Cl(1)′
P(1)′-Pd(1)-Cl(1)′
P(1)-Pd(1)-Cl(1)
P(1)′-Pd(1)-Cl(1)
Cl(1)′-Pd(1)-Cl(1)
O(1)-P(1)-C(7)
O(1)-P(1)-C(1)
C(7)-P(1)-C(1)
O(1)-P(1)-Pd(1)
C(7)-P(1)-Pd(1)
C(1)-P(1)-Pd(1)
Phenyl di(pentafluorophenyl)phosphine (PPh(C6F5)2): The
compound was obtained in analogous manner as given above
starting from bromopentafluorobenzene (20 mM) and
dichlorophenylphosphine (1.38 mL, 1.82 g, 10 mM). The at-
tempted crystallization failed so the phosphine was purified
chromatographically on basic alumina with ethyl acetate –
hexane (1:1 v/v) as the eluent. The obtained red oil was
frozen at –10°C. A small sample of the waxy substance was
dissolved in dry methanol and allowed to evaporate slowly.
A few reddish crystals obtained were then used to initialize
crystallization of the remaining wax. The reddish crystals
were recrystallized from methanol (2 times) giving the 2.1 g
of the white phosphine (38%). mp 68°C, (lit. (2) mp 68–
70°C) GS–MS-MS m/z: 442. 31P NMR (CDCl3) δ: –46.4.
Note: Symmetry transformations used to generate
equivalent atoms (′): –x + 1, y, –z + 1/2.
Experimental
Syntheses of phosphinous esters and their palladium
complexes (PdCl2L2)
General
All syntheses were conducted under dry dinitrogen using
Our attempts to synthesize pentafluorophenyl esters of
(di)phenyl phosphinous acid by the literature method (ap-
plied for the synthesis of 2,6-difluorophenyldiphenyl
phosphinite) (3) using pentafluorophenol, triethyl amine, and
chlorodiphenyl phosphine failed. Based on NMR analysis
(data not shown) we suppose that because of its acidic prop-
erties pentafluorophenol forms an adduct with the amine
rather then reacting with chlorophosphine. Increasing the ra-
tio of phenol and amine to chlorophosphine led to inhomo-
geneous mixture, which was very difficult to separate and
purify. An additional problem of very fast hydrolysis of es-
ters by atmospheric humidity was also observed. We, there-
fore, decided to use a less convenient indirect way based on
the application of sodium methanolate for generation of ap-
propriate phenolate, which in turn reacts with stoichiometric
amounts of chlorodiphenyl phosphine in ethyl ether.
the Schlenk technique. Ethyl ether and THF were dried prior
the use by distilling over sodium. Methanol was distilled
over Mg, triethylamine was dried over KOH and distilled.
C6H6 and CH2Cl2 have been purified according to the stan-
dard methods (22). Compounds C6H5CH2Br, PClPh2, and
PCl2Ph were purchased from Aldrich and used without puri-
fication. P(C6F5)3 was purchased from Strem Chemicals.
PdCl2(cod) was obtained according to the literature method
(23).
NMR spectra were recorded with Bruker 300 spectrome-
ter and chemical shifts are given vs. TMS (1H) and vs. 85%
H3PO4 (31P). Abbreviations used in multiplicities are: singlet
(s), doublet (d), triplet (t), quartet (q), and virtual quartet
(vq). IR spectra were measured with FT-IR Nicolet Impact
400 instrument. UV–vis spectra were measured with an HP
4852 Diode Array spectrophotometer. GC–MS analyses
were carried out with HP 5890 II linked to an HP 5971 A
mass detector.
Preparation of sodium salts of phenols Na(OC6F5) and
Na(O-3,5-F2C6H3): Metallic sodium was reacted with dry
methanol. When all the metal was dissolved, a stochiometric
amount of appropriate phenol was added, mixed, and then
the methanol was removed on rotary evaporator. To the
white product was added dry ethyl ether, mixed, evaporated
(3 times), and dried in vacuo.
Ligand syntheses
Syntheses of fluorophenyl phosphines (2)
Diphenyl pentafluorophenyl phosphine (PPh2(C6F5)): Bromo-
pentafluorobenzene (2.46 g, 10 mM) was added to a suspen-
sion of activated magnesium (0.3 g, 1.2 equiv) in freshly
distilled THF (100 mL). The reaction mixture was stirred
and heated under reflux until almost all magnesium reacted
Preparation of pentafluorophenyl diphenylphosphinite and
PdCl2[PPh2(OC6F5)]2 (5): Dry sodium pentafluorophenolate
(0.486 g, 2.3 mM) was dissolved in a Schlenk flask in dry
ethyl ether and cooled. A solution of of chlorodiphenyl-
© 2001 NRC Canada

758
Can. J. Chem. Vol. 79, 2001
1
PdCl2[PCy3]2 (3): H NMR (CDCl3) δ: 1.24 (s), 1.68 (m),
1.95 (d), 2.49 (m, CH2). Anal. calcd. for C36H66Cl2P2Pd:
C 58.6, H 9.0; found: C 58.0, H 8.5.
phosphine (0.42 mL, 0.52 g, 2.3 mM) in ethyl ether (10 mL)
of was added at once. The formation of sodium chloride oc-
curred immediately. The mixture was stirred overnight. The
NaCl was filtered off and solid PdCl2(cod) (0.5 equiv) was
added to the filtrate. The mixture was stirred 30 min and the
yellow product was filtrated off and dried. 1H NMR (CDCl3)
δ: 7.22 (t), 7.36 (t), 7.55 (q, Ph). Anal. calcd. for
C36H20Cl2F10O2P2Pd: C 47.3, H 2.2; found: C 47.5, H 2.6.
PdCl2[P(OCH2CF3)3]2 (7): Anal. calcd. for C12H12Cl2F18O6P2Pd:
C 17.3, H 1.5; found: C 17.1, H 1.2.
PdCl2[P(OMe)3]2 (13): Compound 13 was obtained in reac-
tion of PdCl2(cod) with a fourfold excess of P(OPh)3 in
MeOH (yield 50%). H NMR (CDCl3) δ: 1.2 (s, CH3). Anal.
1
Preparation of (3,5-difluorophenyl) diphenylphosphinite and
PdCl2[PPh2(O-3,5-F2C6H3)]2 (6): Dry sodium 3,5-difluoro-
phenolate (0.746 g, 5.2 mM) was allowed to react at 0°C
with chlorodiphenyl phosphine (0.66 mL, 0.86 g, 3.9 mM)
for 2 days. The insoluble salts were filtered off and the solu-
tion was used immediately to prepare the palladium complex
(6) by the method given for (5). Yield: 78%. 1H NMR
(CDCl3) δ: 6.1 (dd, JH,F = 8 Hz, JH,H = 2.0 Hz), 6.5 (dt, 3,5-
F2C6H3), 7.38 (t), 7.51 (vt), 7.75 (vq, Ph). Anal. calcd. for
C36H26Cl2F4O2P2Pd: C 53.7, H 3.3; found: C 52.7, H 3.3.
calcd. for C6H18Cl2O6P2Pd: C 16.3 H 4.1; found: C 16.9, H
4.3.
Reactions of PdCl2L2 complexes with CO and NEt3
In the typical experiment, MeOH (1 mL) and NEt3 (ca.
0.01 mL) were added consecutively under dinitrogen to the
palladium complex (0.05 g). The Schlenk tube was filled
twice with CO and the solution was stirred under CO atmo-
sphere for 30 min. The resulting precipitate of palladium
carbonyl complex was filtrated off, dried, and analyzed by
IR. The products decompose in the presence of air in ca.
30 min.
Preparation of tert-butyl diphenylphosphinite and
PdCl2[PPh2(O-t-Bu)]2 (1): PPh2(O-t-Bu) was prepared by
reacting potassium tert-butanolate (0.634 g, 5.2 mM) with
chlorodiphenyl phosphine (0.70 mL, 0.86 g, 3.9 mM) for 2
days. To the filtrated ether solution was added PdCl2(cod)
(0.5 equiv), and the complex (1) was isolated after 10 h of
stirring of the mixture as a dark yellow powder (yield 85%).
1H NMR (CDCl3) δ: 0.2 (CH3), 7.22 (t), 7.34 (d), 7.54 (q,
Ph). Anal. calcd. for C32H48Cl2O2P2Pd: C 54.6, H 6.9;
found: C 54.7, H 6.3.
Carbonylation reaction of benzyl bromide
To the thermostated glass reactor (40°C), was added under
a N2 atmosphere MeOH (1.5 mL), NEt3 (1.5 mL), and
benzyl bromide (0.5 mL), the mixture was stirred for 1 min
and then the catalyst (2.45 × 10–5 mol) in small teflon vessel
was added. The reactor was connected with the CO-
container (1 atm), flushed twice with CO, and left for 2 h
with magnetic stirring. After that time, the reaction mixture
was treated with HCl up to pH ca. 7. The reaction products
were extracted with ethyl ether (1 mL) and analyzed by GC–
MS.
Preparation of ethyl diphenylphosphinite and PdCl2[PPh2(OEt)]2
(9): PPh2(OEt) was synthesized analogously to the butyl an-
alog using sodium ethanolate (0.316 g, 4.6 mM) and
chlorodiphenyl phosphine (0.83 mL, 1.03 g) in ether
(30 mL) for 3 days. The addition of PdCl2(cod) (0.5 equiv)
and stirring of the mixture for 30 min allowed the formation
of complex (9) with 90% yield. The crystals for X-ray stud-
X-ray crystallography
X-ray crystal data, together with refinement details, are
given in Table 4. All measurements of crystal were per-
formed on a Kuma KM4CCD κ-axis diffractometer with
graphite-monochromated Mo Kα radiation. The crystal was
positioned at 65 mm from the KM4CCD camera, and 612
frames were measured at 0.75° intervals with a counting
time of 20 s. The data were corrected for Lorentz and polar-
ization effects. No absorption correction was applied. Data
reduction and analysis were carried out with the Kuma Dif-
fraction (Wroclaw) programs. The structure was solved by
direct methods (program SHELXS 97 (24)) and refined by
the full-matrix least-squares method on all F2 data using the
SHELXL 97 (25) programs. Nonhydrogen atoms were re-
fined with anisotropic thermal parameters; hydrogen atoms
were included from geometry of molecules and ∆ρ maps but
were not refined.
ies were obtained by recrystallization of the yellow powder
1
from CH2Cl2–EtOH. H NMR (CDCl3) δ: 0.96 (t, JH,H
=
7 Hz, CH3), 3.67 (q, CH2), 7.38 (m), 7.48 (m), 7.76 (m, Ph).
Anal. calcd. for C28H30Cl2O2P2Pd: C 52.7, H 4.7; found: C
52.1, H 4.4.
Other syntheses
The other PdCl2L2 complexes have been obtained in reac-
tion of PdCl2(cod) with 2 mol equiv of phosphorus ligands
in C6H6, CH2Cl2, or (C2H5)2O. Depending on the solubility
they have been isolated as precipitates or after solvent evap-
oration. In all cases the products have been washed by ethyl
ether and dried in vacuo. The preparation and spectroscopic
data of PdCl2[PPh2(O-n-Bu)]2 (10) and PdCl2[P(OPh)3]2
(11) are reported in ref. 11.
Conclusions
1
PdCl2[PPh2(C6F5)]2 (4): H NMR (CDCl3) δ: 7.42 (t), 7.51
The attempts to correlate the spectroscopic (UV–vis, 31P
(t), 7.86 (q, Ph). Anal. calcd. for C36H20Cl2F10P2Pd: C 49.0,
H 2.3; found: C 49.9, H 3.0.
NMR) data of PdCl2L2 complexes with the steric and elec
tronic parameters of phosphorus ligands (L) show a domi
-
-
nating influence of the steric over the electronic effect.
Correlations between 31P NMR coordination chemical shifts
(∆) and the cone angles (Θ) of L on the other are not per-
fect, but strong enough to show the tendency and directions
1
PdCl2[PPh(C6F5)2]2 (8): H NMR (CDCl3) δ: 7.40 (t), 7.48
(t), 7.83 (q, Ph). Anal. calcd. for C36H10Cl2F20P2Pd: C 40.7,
H 1.0; found: C 40.7, H 1.0.
© 2001 NRC Canada

Trzeciak et al.
759
Table 4. Crystal data and structure refinement.
2. R.D.W. Kemmitt, D.I. Nichols, and R.D. Peacock. J. Chem.
Soc. A, 2149 (1968).
3. M.J. Atherton, J. Fawcett, A.P. Hill, J.H. Holloway, E.G.
Hope, D.R. Russell, G.C. Saunders, and R.M.J. Stead. J.
Chem. Soc. Dalton Trans. 1137 (1997).
Empirical formula
C28H30O2Cl2P2Pd
FW
318.88
T (K)
100(1)
λ (Å)
Crystal system
Space group
0.71073
Orthorhombic
Pbcn
4. M.J. Atherton, J. Fawcett, J.H. Holloway, E.G. Hope, D.R.
Russell, and G.C. Saunders. J. Chem. Soc. Dalton Trans. 2217
(1997).
5. M.J. Atherton, K.S. Coleman, J. Fawcett, J.H. Holloway, E.G.
Hope, A. Karacar, L.A. Peck, and G.C. Saunders. J. Chem.
Soc. Dalton Trans. 4029 (1995).
6. M.J. Atherton, J. Fawcett, J.H. Holloway, E.G. Hope, A.
Karacar, D.R. Russell, and G.C. Saunders. J. Chem. Soc. Dal-
ton Trans. 3215 (1996).
7. M.J. Atherton, J. Fawcett, J.H. Holloway, E.G. Hope, S.M.
Martin, D.R. Russell, and G.C. Saunders. J. Organomet.
Chem. 555, 67 (1998).
8. C.A. Tolman. Chem. Rev. 77, 314 (1977).
9. U.S.A. Patent. 5 463 082 (1995).
10. J.J.J. Juliette, I.T. Horvath, and J.A. Gladysz. Angew. Chem.
Int. Ed. Engl. 36, 1610 (1997).
11. A.M. Trzeciak and J.J. Ziólkowski. Monatsh. Chem. 131, 1281
(2000).
12. A.W. Verstuyft, D.A. Redfield, L.W. Cary, and J.H. Nelson.
Inorg. Chem. 15, 1128 (1976).
a (Å)
b (Å)
c (Å)
V (Å3)
10.5041(6)
16.4709(10)
15.1275(11)
2617.2(3)
4
1.619
1.061
1296
0.15 × 0.10 × 0.10
Kuma KM4CCD
3.42–28.74
–14–8, –21–21, –19–19
17459
3217 (0.0384)
3217/160
0.0296, 9.32, 3
1.141
Z
Dc (Mg m–3)
µ (mm–1)
F(000)
Crystal size (mm)
Diffractometer
θ range for data collection (°)
h, k, and l ranges
Reflections collected
Independent reflections (Rint)
Data/parameters
Weighting scheme: a, b, ca
GoF (F2)
13. T.T. Derenesceyi. Inorg. Chem. 20, 665 (1981).
14. A.T. Hutton and C.P. Morley. In Comprehensive coordination
chemistry. The synthesis, reactions, properties and application
of coordination compounds. Vol 5. Edited by G. Wilkinson.
Pergamon Press, New York. 1987.
Final R1/wR2 indices (I > 2σI)
Largest diff. peak and hole (e Å–3)
aw = 1/[σ2(Fo2) + (aP)2 + bP] where P = [Max(Fo2, 0) + Fc2]/c.
0.0484/0.0975
1.480/–1.022
15. G. Ferguson, R. McCrindle, A.J. McAlees, and M. Parvez.
Acta Crystallogr. Sect. B: Struct. Sci. B38, 2679 (1982).
16. B. Bertsch-Frank, and W. Frank. Acta Crystallogr. Sect. C:
Cryst. Struct. Commun. C52, 328 (1996).
17. S.J. Sabounchei, A. Naghipour, and J.F. Bichley. Acta Cryst.
C56, e280 (2000).
18. V.V. Grushin, C. Bensimon, and H. Alper. Inorg. Chem. 33,
4804 (1994).
19. M. Hidai, M. Kokura, and Y. Uchida. J. Organomet. Chem. 52,
431 (1973).
of changes. The most important conclusion of the reported
studies is the finding that the catalytic activity of PdCl2L2
complexes in the carbonylation of benzyl bromide also de-
pends mainly on the steric properties of L and thus on the
cis–trans geometry of the starting complex. Complexes with
less sterically hindered ligands (phosphites, phosphinites)
having cis structure are more active than those with bulky
ligands (Θ > 140°, e.g., PCy3, PPh2(O-t-Bu)). An exception
should, however, be noted for complexes with bulky fluori-
nated phosphines (PPhx(C6F5)3–x, x = 0–2), which are trans-
isomers that exhibit unexpectedly high catalytic activity.
20. A.M. Trzeciak and J.J. Ziólkowski. J. Mol. Catal. A: Chem.
154, 93 (2000).
21. D.R. Powell and R.A. Jacobson. Cryst. Struct. Comm. 9, 1023
(1980).
22. D.D. Perrin, W.L.F. Armarego, and D.R. Perrin. Purifcation of
laboratory chemicals. Pergamon, Oxford, England. 1986.
23. F.A. Cotton. Inorg. Synth. XIII, 52 (1972).
24. G.M. Sheldrick. SHELXS 97. Program for solution of crystal
structures. University of Göttingen, Germany. 1997.
25. G.M. Sheldrick. SHELXL 97. Program for crystal structure re-
finement. University of Göttingen, Germany. 1997.
Acknowledgments
This work was supported by KBN (State Committee for
Research) project 3T09A 061 15. The authors would like
thank Ms. Iwona Lankiewicz for technical assistance.
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© 2001 NRC Canada