Palladiumdichloride (ferrocenylethynyl)phosphanes and their use in Pd-catalyzed Heck-Mizoroki- and Suzuki-Miyaura carbon-carbon cross-coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2008.09.040

In this work the synthesis of phosphane selenides (FcC{triple bond, long}C)_nPh_3-nP{double bond, long}Se (2a, n = 1; 2b, n = 2; 2c, n = 3; Fc = ferrocenyl, (η⁵-C₅H₄)(η⁵-C₅H_5<

Full text of DOI:10.1016/j.jorganchem.2008.09.040

Journal of Organometallic Chemistry 693 (2008) 3821–3830
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Palladiumdichloride (ferrocenylethynyl)phosphanes and their use in Pd-catalyzed
Heck–Mizoroki- and Suzuki–Miyaura carbon–carbon cross-coupling reactions
*
Alexander Jakob, Bianca Milde, Petra Ecorchard, Claus Schreiner, Heinrich Lang
Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Lehrstuhl für Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work the synthesis of phosphane selenides (FcC„C)nPh3ꢀnP@Se (2a, n = 1; 2b, n = 2; 2c, n = 3;
Fc = ferrocenyl, (
is described to estimate the
g g
5-C5H4)( 5-C5H5)Fe) from (FcC„C)nPh3ꢀnP (1a, n = 1; 1b, n = 2; 1c, n = 3) and selenium
Received 16 June 2008
Received in revised form 24 September
2008
Accepted 24 September 2008
Available online 30 September 2008
r
-donor properties of these systems by 31P{1H} NMR spectroscopy. Progres-
sive replacement of phenyl by ferrocenylethynyl causes a shielding of the phosphorus atom with increas-
ing of the 1J(31P–77Se) coupling constants.
The palladiumdichloride metal-organic complexes [((FcC„C)nPh3ꢀnP)2PdCl2] (3a, n = 1; 3b, n = 2; 3c,
n = 3) have been used as (pre)catalysts in the Suzuki–Miyaura (reaction of 2-bromo-toluene (4a) and
4-bromo-acetophenone (4b), respectively, with phenyl boronic acid (5) to give 2-methyl biphenyl (6a)
and 4-acetyl biphenyl (6b)) and in the Heck–Mizoroki reaction (treatment of iodobenzene (7) with
tert-butyl acrylate (8) to give E-tert-butyl cinnamate (9)).
The structures of molecules 1a, 1c, 2c, and 3c in the solid state were determined by single X-ray struc-
ture analysis showing that the structural parameters of these systems are unexceptional and correspond
to those of related phosphanes, seleno phosphanes, and palladium dichloride complexes.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Ethynylferrocene
Phosphane
Tolman cone angle
31P–77Se NMR coupling constant
Heck–Mizoroki
Suzuki–Miyaura
1. Introduction
phosphorus and the acceptor carbon atoms are found. This elec-
tronic effect directly affects the steric demand around the phos-
Palladium-catalyzed carbon–carbon cross-coupling reactions
such as the Suzuki–Miyaura [1] and the Heck–Mizoroki [1a–e,2]
reaction are among the most essential transformations in organic
and organometallic chemistry. Recently, very active organometal-
lic and metal-organic systems have been framed amending the sta-
bility and efficiency of the palladium-based catalysts [3]. In this
respect, heterocyclic carbenes, [4] ortho-metallated benzyl thio-
ethers, [5] cyclometallated imine-type derivatives, [6] diverse pal-
ladacycles [7] and a series of electron-rich and, sterically hindered
phosphane palladium complexes [8] were synthesized and applied
as catalysts in C–C bond forming reactions. In the Heck–Mizoroki
phorus atom which causes marked changes in the behavior of
the respective transition metal complexes. These feature sizes are
decisive parameters for the specific design of transition metal com-
pounds used as catalytic active species in homogeneous catalysis.
In this paper we report the synthesis of (ferrocenylethy-
nyl)phosphane selenides and the use of (ferrocenylethynyl)phos-
phane palladium-dichlorides of type [((FcC„C)nPh3ꢀnP)2PdCl2]
(Fc = ferrocenyl, (g g
5-C5H4)( 5-C5H5)Fe) as (pre)catalysts in the
Heck–Mizoroki (the reaction of iodobenzene with tert-butyl acry-
late) and Suzuki–Miyaura reaction (reaction of 2-bromo-toluene
or 4-bromo-acetophenone with phenylboronic acid). The influence
of the electronic (1J(31P–77Se)) and steric (Tolman cone angle) ef-
fects on the catalytic activity of the appropriate organometallic
compounds will be discussed. The basic idea of this work was to
synthesize with the (ferrocenylethynyl)phosphane ligands more
stable phosphane-palladium catalysts for C–C cross-coupling reac-
tions in comparison with, for example, ‘‘(Ph3P)2Pd” which only
shows low stability and activity during the catalytic cycle.
reaction weak
r-donating phosphane ligands are privileged, while
in the Suzuki–Miyaura reaction strong Lewis-basic phosphanes are
essential [1a].
The donor properties of phosphanes (PR3; R = alkyl, aryl, alk-
oxyl) toward selenium acceptors can be quantified by the phos-
phorus–selenium coupling constant (1J(31P–77Se)) as indicated by
31P{1H} NMR spectroscopy [9]. There it was found that an elec-
tron-withdrawing group at the phosphorus atom increases the
coupling constant 1J(31P–77Se) which can be explained by the in-
creased s character of the phosphorus orbital involved in the P–
Se bonding. Consequently, shorter bond distances between the
2. Results and discussion
The
(FcC„C)nPh3ꢀn
[((FcC„C)nPh3ꢀnP)2PdCl2] (n = 1, 2, 3; Fc = (
synthesis
and the respective palladium complexes
5-C5H4)( 5-C5H5)Fe)
of
the
(ferrocenylethynyl)phosphanes
P
* Corresponding author. Tel.: +49 371 531 21210; fax: +49 371 531 21219.
E-mail address: heinrich.lang@chemie.tu-chemnitz.de (H. Lang).
g
g
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.040

3822
A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
were recently reported by Baumgartner et al. [10] and our group
[11]. Whereas the Baumgartner group is interested in the use of
the latter molecules as precursors in the formation of super-molec-
ular assemblies and in the investigation of these systems toward
materials applications, our aim is to make use of these organome-
tallic compounds as (pre)catalysts in carbon–carbon cross-cou-
pling reactions.
To verify the donor ability of (FcC„C)nPh3ꢀnP (1a, n = 1; 1b,
n = 2; 1c, n = 3) these compounds were converted to the corre-
sponding phosphane selenides (FcC„C)nPh3ꢀnP@Se (2a, n = 1; 2b,
n = 2; 2c, n = 3) by the reaction of 1a–1c with elemental selenium
in toluene at 100 °C (Reaction (1)) (see Section 4). After appropriate
work-up, 2a–2c could be isolated as orange to red solids in quan-
titative yield.
The crystal structures of 1a, 1c, and 2c are set-up by one (1a) or
three (1c, 2c) ferrocenyl ethynyl moieties with somewhat de-
formed P–C„C–Fc units (Figs. 1–3). The carbon–carbon triple bond
distances are between 1.176(19) and 1.210(10) Å and are typical
for this type of molecules [10–12]. The two cyclopentadienyl rings
of the ferrocenyl fragments of 1a (1.57, 1.78°), 1c (0.76, 1.19, 2.63°),
and 2c (0.26°) are almost parallel oriented with DꢀFeꢀD0 separa-
tions between 1.6352(1) and 1.6618(3) Å (D = centroid of the
cyclopentadienyl ring C5H5, D0 = centroid of the cyclopentadienyl
ring C5H4).
The phosphorus–carbon bond separations are in the range of
1.743(3) to 1.772(3) Å and are representative for P–C„C units
[10,11,12c]. The other structural parameters are unexceptional
and correspond to those of related compounds [10–12].
C C Ph
3-nP
C C Ph3-nP Se
toluene
100 °C
+
Se
Fe
Fe
ð1Þ
n
n
2a - 2c
1a - 1c
The identities of phosphanes 1a–1c [10,11] and the respective
phosphane selenides 2a–2c have been confirmed by elemental
analysis, IR and NMR spectroscopy (see Section 4).
The overall structure of 2c conforms to a chandelier (Fig. 3),
whereby the P@Se unit is in accordance with the socket and the
ferrocenyl moieties correspond to the candles. This means that
all ferrocene units are positioned on the site of the phosphorus–
selenium bond. Compound 2c thereby possesses the molecular
symmetry C3h. Molecule 2c crystallizes in the rhombohedral non-
centrosymmetric space group R3m and its absolute conformation
was ascertained by refinement of the Flack parameter 0.013(10)
The molecular solid state structures of 1a, 1c, and 2c were addi-
tionally solved by single X-ray structure analysis. Suitable crystals
were obtained by slow diffusion of n-hexane into a concentrated
dichloromethane solution containing either 1a, 1c or 2c at room
temperature. ORTEP diagrams, selected bond distances (Å) and an-
gles (°) are shown in Fig. 1 (1a), Fig. 2 (1c), and Figs. 3 and 4 (2c).
The crystal and structure refinement data are presented in Section
4 (Table 4).
[13]. The ferrocenyl units form a 1D polymer by
p–p interactions
between C5H4 (D1) and C5H5 (D20) (Fig. 4). The distance of the cen-
troid of the cyclopentadienyl rings D and D0 is 3.704 Å and is typical
Fig. 1. ORTEP diagram (50% probability level) of 1a with the atom numbering scheme. (Hydrogen atoms are omitted for clarity.) The asymmetric unit of 1a consists of two
crystallographically independent molecules (molecules A (right) and B (left)). Selected bond distances (Å) and angles (°): Molecule A: P1–C12 1.757(7), P1–C13 1.840(8), P1–
C19 1.833(7), C11–C12 1.210(10), D1-Fe1 1.6488(3), D2–Fe1 1.6521(3); P1–C12–C11 173.7(7), C12–C11–C1 175.3(8), C12–P1–C13 102.4(3), C12–P1–C19 102.4(3), C13–P1–
C19 102.6(3). Molecule B: P2–C36 1.760(8), P2–C3 1.848(8), P2–C43 1.839(8), C35–C36 1.203(11), D3–Fe2 1.6618(3), D4–Fe2 1.6427(3); P2–C36–C35 169.2(7), C36–C35–C25
176.1(8), C36–P2–C37 99.4(4), C36–P2–C43 103.3(4), C37–P2–C43 101.0(3) (D1 = centroids of C1–C5, D2 = centroids of C6–C10, D3 = centroids of C25–C29, D4 = centroids of
C30–C34). Standard uncertainties of the last significant digit(s) are shown in parenthesis.

A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
3823
Fig. 2. ORTEP diagram (50% probability level) of 1c with the atom numbering
scheme. (Hydrogen atoms are omitted for clarity.) Selected bond distances (Å) and
angles (°): P1–C12 1.766(3), P1–C24 1.767(3), P1–C36 1.772(3), C11–C12 1.197(4),
C23–C24 1.198(3), C35–C36 1.193(4), D1–Fe1 1.6398(2), D2–Fe1 1.6342(2), D3–Fe2
1.6496(2), D4–Fe2 1.6447(1), D5–Fe3 1.6470(2), D6–Fe3 1.6421(1); P1–C12–C11
175.6(3), P1–C24–C23 176.5(2), P1–C36–C35 173.6(2), C12-C11–C1 177.9(3), C24–
C23–C13 174.7(3), C36–C35–C25 176.4(3), C12-P1–C24 98.92(12), C12–P1–C36
99.40(12), C24–P1–C36 99.76(12) (D1 = centroids of C1–C5, D2 = centroids of C6–
C10, D3 = centroids of C13–C17, D4 = centroids of C18–C22, D5 = centroids of C25–
C29, D6 = centroids of C30–C34). Standard uncertainties of the last significant
digit(s) are shown in parenthesis.
Fig. 4. ORTEP diagram (50% probability level) of a (selected) part of the polymeric
structure of 2c formed by p–p interactions between the cyclopentadienyl rings D1–
for parallel-displaced geometries [14]. Characteristic for 2c is the
P–Se bond with 2.0991(11) Å, which is identical to that of other
phosphane selenides, for example, tris(m-trifluoromethylphenyl)
phosphane selenide [15] and tris(2-furyl)phosphane selenide
D2’ (3.704 Å; D1 = centroid of C5H4, D2’ = centroid of C5H5 of the second molecule).
(Hydrogen atoms were omitted for clarity). All cyclopentadienyl rings are perfectly
parallel oriented with C–C separations ranging from 3.635 to 3.712 Å. (Label’ refers
to a second, label’’ refers to a third molecule of 2c.)
Fig. 3. ORTEP diagram (50% probability level) of the molecular structure of 2c with the atom numbering scheme. (Hydrogen atoms are omitted for clarity.) Symmetry
transformations used to generate equivalent atoms (indicated with the suffixes A, B, C, D, and E): A: 1 ꢀ y, 1 + x ꢀ y, z; B: ꢀx + y, 1 ꢀ x, z; C: ꢀx + y, y, z; D: x, 1 + x ꢀ y, z; E:
1 ꢀ y, 1 ꢀ x, z. Selected bond distances (Å) and angles (°): P1–Se1 2.0991(11), P1–C8 1.743(3), C7–C8 1.204(4), D1–Fe1 1.6566(2), D2–Fe1 1.6499(2); P1–C8–C7 167.9(2), C8–
C7–C1 180.0(3), C8–P1–Se1 113.64(9), C8–P–C8A 105.00(10). D1 = centroid of C1–C2–C3–C2(C)–C3(C); D2 = centroid of C4–C5–C6–C5(C)–C6(C). Standard uncertainties of
the last significant digit(s) are shown in parenthesis.

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A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
phosphorus atom with increasing of the 1J(31P–77Se) coupling con-
stants. The latter observation shows that the ferrocenylethynyl
building blocks act as electron-withdrawing units in phosphane
selenides. Considering the 1J(31P–77Se) coupling constants in Table
1 these values suggest that in the series of the ferrocenylethynyl
phosphanes, compound 1a in its palladium-complexed form
should be best suited for the Suzuki–Miyaura reaction, while phos-
phane 1c with its more electron-withdrawing character is sup-
posed to be better for the Heck–Mizoroki reaction (vide supra).
In order to explore the possibility of using the palladium-com-
plexed ferrocenylethynyl phosphanes 1a–1c in the Suzuki–Miya-
ura and Heck–Mizoroki reaction, the appropriate coordination
compounds had to be prepared. The synthesis of these systems
succeeds in a straightforward manner by the reaction of 1a–1c
with [(Et2S)2PdCl2] in the molar ratio of 2:1 in dichloromethane
as solvent at room temperature (Reaction (2)). [10,11] After appro-
priate work-up, complexes [((FcC„C)nPh3ꢀnP)2PdCl2] (3a, n = 1;
3b, n = 2; 3c, n = 3) were obtained as dark red solids in excellent
yield.
Table 1
Chemical shifts and 31P–77Se coupling constants of 2a–2c, and Ph3P@Se for
comparison.
Compd.
d [ppm]
1J(31P–77Se) [Hz]
Se@PPh3 [9c]
35.9
4.3
732
746
757
765
2a
2b
2c
ꢀ31.3
ꢀ71.3
[9d], respectively, containing
r
-electron-withdrawing substitu-
ents. As result thereof, the s character of the phosphorus orbital in-
volved in bonding to the selenium atom is increased (see below).
The C–P–C inter-valence angles at P1 (Fig. 3) are in the typical
range for tertiary phosphane selenides [15].
The 31P{1H} NMR data together with the 1J(31P–77Se) coupling
constant for the phosphane selenides 2a–2c are summarized in
Table 1.
Following trends can be seen from Table 1. Progressive replace-
ment of phenyl by ferrocenylethynyl causes a shielding of the
C C Ph3-nP
CH2Cl2
C C Ph
3-nP
PdCl2
[(Et2S)2PdCl2]
+
cis-
2
Fe
Fe
ð2Þ
n
n
2
1a - 1c
3a - 3c
Fig. 5. ORTEP diagram (50% probability level) of 3c with the atom numbering scheme. (Hydrogen atoms and two molecules of trichloromethane are omitted for clarity.)
Selected bond distances (Å) and angles (°): Pd1–Cl1 2.238(4), Pd1–Cl2 2.322(4), Pd1–P1 2.238(4), Pd1–P2 2.251(4), P1–C12 1.738(14), P1–C24 1.732(15), P1–C36 1.760(15),
P2–C48 1.730(14), P2–C60 1.752(14), P2–C72 1.750(14), C11–C12 1.203(19), C23–C24 1.184(19), C35–C36 1.176(19), C47–C48 1.205(19), C59–C60 1.199(19), C71–C72
1.20(2), D1–Fe1 1.6325(7), D2–Fe1 1.6290(6), D3–Fe2 1.6603(7), D4–Fe2 1.6357(6), D5–Fe3 1.6395(7), D6–Fe3 1.6415(8), D7–Fe4 1.6390(6), D8–Fe4 1.6371(6), D9–Fe5
1.6431(6), D10–Fe5 1.6348(6), D11–Fe6 1.6466(8), D12–Fe6 1.6308(7); P1–C12–C11 177.4(13), C12–C11–C1 176.8(15), P1–C24–C23 172.8(14), C24–C23–C13 178.9(14), P1–
C36–C35 175.6(14), C36–C35–C25 176.5(18), P2–C48–C47 165.1(13), C48–C47–C37 177.2(16), P2–C60–C59 177.3(12), C60–C59–C49 177.6(16), P2–C72–C71 169.4(14),
C72–C71–C61 174.9(17) (D1 = centroid of C1–C5, D2 = centroid of C6–C10, D3 = centroid of C13–C17, D4 = centroid of C18 – C22, D5 = centroid of C25–C29, D6 = centroid of
C30–C34, D7 = centroid of C37–C41, D8 = centroid of C42–C46, D9 = centroid of C49–C53, D10 = centroid of C54–C58, D11 = centroid of C61–C65, D12 = centroid of C66–C70;
Standard uncertainties of the last significant digit(s) are shown in parenthesis).

A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
3825
From complex 3c single crystals suitable for X-ray diffraction stud-
ies could be grown from slow diffusion of petroleum ether into a
dichloromethane solution containing 3c at 25 °C.
The structure of 3c in the solid state (Fig. 5) indicates a cis-con-
figuration which is the most favored arrangement in ferrocenyl-
ethynyl phosphane and phenylethynyl phosphane palladium
tration. Quantitative conversion is found for trimetallic Fe2Pd 3a at
a Pd loading of 0.25 mol%, while 3b and 3c show their highest
activities at 0.1 mol%, respectively 0.05 mol% (Table 2). However,
for the common Suzuki catalyst [Pd(OAc)2/PPh3] (10) [17] used
as a reference system best results were obtained with 0.5 mol%
(Table 2).
dichloride
chemistry,
i.e.
[((FcC„C)Ph2P)2PdCl2]
and
From Table 2 and Fig. 7 it is obvious that in the carbon–carbon
cross-coupling reaction of 4b with 5 always a quantitative conver-
sion is found, which originates from the higher reactivity of 4b
compared with 4a. A decrease of reactivity from 3a to 3c is also
observed.
In summary, an efficient and general catalytic protocol for the
carbon–carbon cross-coupling of 2-bromo-toluene (4a) and 4-bro-
mo-acetophenone (4b) with phenyl boronic acid (5) and com-
plexes 3a–3c as palladium (pre)catalysts was established.
Compared with other catalytic active systems in the Suzuki–Miya-
ura reaction including the catalysts developed by Beller, Buchwald,
and Herrmann complexes 3a–3c are less active [19–21]. Neverthe-
less, for all three tested complexes it is obvious that they reach
quantitative conversion during 1 h.
[((PhC„C)Ph2P)2PdCl2]. [10,16] The P–C–C angles are with
165.1(13)–177.4(13)° essentially linear (Fig. 5) which differs from
[((FcC„C)Ph2P)2PdCl2] in which angles of 157.3(6) and 170.7(6)°
are typical and have been explained by the increased steric bulki-
ness within the complex [10]. The ferrocenylethynyl moieties are
not coplanar arranged with the P2PdCl2 plane (r. m. s. deviation
0.0629 Å). All other structural parameters (Fig. 5) correspond to
those of related palladium dichloride complexes [10,16].
Heterobimetallic complexes [((FcC„C)nPh3ꢀnP)2PdCl2] (3a,
n = 1; 3b, n = 2; 3c, n = 3) with different electronic and steric prop-
erties were used as (pre)catalysts in the aforementioned carbon–
carbon cross-coupling reactions.
2.1. Suzuki–Miyaura reaction
Electron-donating phosphane complexes are better suited as
catalytic active systems in the Suzuki–Miyaura reaction [1a]. This
is confirmed by Tables 1 and 2 as well as Figs. 6 and 7, and is ver-
In a model reaction we studied the combination of 2-bromo-tol-
uene (4a) and 4-bromo-acetophenone (4b), respectively, with phe-
nyl boronic acid (5, 1.3 equivalents) in the presence of 3a–3c
(loading of 0.05–0.5 mol% Pd, Table 2), potassium carbonate
(3.0 equiv.) as base and a 2:1 mixture of dioxane-water as solvent
to give the cross-coupled products 2-methyl biphenyl (6a) and 4-
acetyl biphenyl (6b), respectively, under inert gas atmosphere
(Reaction (3)). The catalytic reactions were carried out at 100 °C
in analogy to literature procedures for comparison [3g]. In all reac-
tions complexes 3b and 3c showed an initial reaction period of 5–
20 min to generate the catalytic active species.
ified in the series 3a > 3b > 3c. As outlined earlier (Table 1) the
r-
donor ability of phosphanes can be evaluated by measuring the
magnitude of 1J(31P–77Se) in the 31P NMR spectra [9a,b]. The cou-
pling constants listed in Table 1 nicely correlate with the conver-
sion numbers presented in Table 2 and are in agreement with
the
r-donor ability increasing in the order of 3c > 3b > 3a. This al-
lows in a simple way to decide if individual phosphane palladium
coordination complexes are suitable (pre)catalysts in the Suzuki–
Miyaura reaction by only determining the magnitude of the
31P–77Se coupling constants of the respective phosphane selenides.
[Pd], K2CO3
+
+
(HO)2B
Br
Dioxane/H2O
4a
4b
6a
5
ð3Þ
[Pd], K2CO3
(HO)2B
Br
Dioxane/H2O
O
O
5
6b
All palladium complexes 3a–3c are active in the cross-coupling of
4a and 4b with 5 and show high productivities, especially at low
catalyst concentrations (TONs up to 2000, TON = turnover num-
ber). It is obvious that 3a as well as 3b show optimum performance
at catalyst concentrations of 0.25 and 0.1 mol%, respectively. While
3a is more tolerant toward increased palladium loadings (0.5 vs.
0.25 mol%), 3b shows high activities even at reduced palladium
concentrations (0.1 vs. 0.05 mol%). In contrast, 3c shows an unex-
pected behavior, its productivity is significantly increased with
decreasing palladium loadings.
Kinetic investigations (Fig. 6) with 3a–3c in the Suzuki–Miyaura
cross-coupling of 4a and 4b with 5 showed that 3b and 3c need
somewhat longer induction periods to form the active catalyst.
From Fig. 6 it can be seen that the lower the concentration, the
higher the activity/conversion up to the optimally catalyst concen-
The classification of the appropriate catalyst by considering sterical
arguments (Tolman cone angle) is outlined below.
2.2. Heck–Mizoroki reaction
To appreciate the performance of complexes 3a–3c in the Heck–
Mizoroki carbon–carbon coupling reaction the rate of conversion
and systematic kinetic studies were carried out. As a model reac-
tion we chose the coupling between iodobenzene (7) and tert-butyl
acrylate (8) to give E-tert-butyl cinnamate (9) following the meth-
od described by Boyes and Butler [22]. Thus, 7 and 8 were reacted
in toluene and acetonitrile mixtures of ratio 1:1 between 65 and
100 °C in the presence of NEtiPr2 as a base and [CuI] as reducing
agent with catalyst loadings of 0.25, 0.50, 0.75 and 1.0 mol% (Reac-
tion (4), Table 3, Fig. 8) to test the productivity of the appropriate

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A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
catalytic systems. In addition to these studies, reactions with the
conventional monodendate triphenylphosphane ligands were car-
ried out under similar conditions, so that direct comparison might
be achieved.
As summarized in Table 3 the reactions carried out at higher
temperature produce higher conversion numbers, for example,
the best results were obtained at 100 °C for all compounds. Never-
theless, the determination of the optimum reaction conditions is
[Pd], EtN(iPr)2, [CuI]
O
O
+
I
ð4Þ
toluene/acetonitrile
OtBu
8
OtBu
7
9
not predictable since individual catalysts show a unique behavior,
for example, catalyst 3a has its highest productivity at a palladium
loading of 0.25, 3b at 0.75, and 3c at 0.75 and 0.25 mol% at 100 °C
(Table 3). The maximal possible conversion amounts to ca. 92% (Ta-
ble 3). As consequence of the data presented in Table 3 it can be
concluded that the highest productivity is obtained with the cata-
lyst possessing the highest Lewis-basic and lowest electron-with-
drawing phosphane ligands. This effect is not consistent with the
electronic argumentation used in the Suzuki–Miyaura reaction
(vide supra) and hence, must be different originated. Apart from
electronic effects also steric arguments (Tolman cone angle) must
be considered since these effects are responsible for changing the
molecular properties or parts of it.
The Tolman cone angle is the apex angle of a cylindrical cone
centered 2.28 Å from the center of the phosphorus atom which
touches the van-der-Waals radii of the outermost atoms [23].
Increasing the angle between the phosphane substituents will de-
crease the percentage of the s character in the phosphorus lone-
pair. The Tolman cone angle of PPh3 with 145° was published by
Tolman [24]. The Tolman cone angel for compound 1a was calcu-
Table 2
Conditions of the Suzuki–Miyaura C–C cross-coupling of 4a and 4b with
complexes 3a–3c, and [Pd(OAc)2/PPh3] (10) [17] for comparison.
5
by
Compd.
Conc. [mol%]
Yield biphenyls [%]a
TONb
6a
76.7
6b
6a
6b
10
3a
3b
3c
10
3a
3b
3c
3a
3b
3c
3a
3b
3c
0.5
0.5
0.5
0.5
0.25
0.25
0.25
0.25
0.1
0.1
0.1
0.05
0.05
0.05
153
172
81
86.2
40.7
32.4
35.1
100
98.1
66.2
65
139
395
387
261
1000
1000
719
960
1884
1662
100
100
71.9
48.0
94.2
83.1
100
100
100
100
100
100
1000
1000
1000
2000
2000
2000
a
Yields are determined by 1H NMR spectroscopy with acetyl ferrocene as a
standard relative to 6a and 6b, respectively; 60 min.
b
(Mol product/mol [Pd]).
100
80
100
80
60
60
40
20
0
40
20
0
3a
3b
3c
3a
3b
3c
10
10
0
10
20
30
40
50
60
0
10
20
30
40
50
60
t / min
t / min
100
80
60
40
20
0
100
80
60
40
20
0
3a
3b
3c
3a
3b
3c
0
10 20 30 40 50 60 70
t / min
0
10
20
30
t / min
40
50
60
Fig. 6. Kinetic investigation of 3a–3c in the Suzuki–Miyaura carbon–carbon cross-coupling reaction of 4a with 5 to give 6a. (Top: left, 0.5 mol%; right, 0.25 mol%; bottom: left,
0.1 mol%, right, 0.05 mol% (pre)catalyst.)

A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
3827
100
80
60
40
20
0
100
80
60
40
3a
3b
3c
3a
3b
3c
20
0
0
10
20
30
40
50
60
0
10
20
30
40
50
60
t / min
t / min
Fig. 7. Kinetic investigation of 3a–3c in the Suzuki–Miyaura carbon–carbon cross-coupling reaction of 4b with 5 to give 6b. (Left, 0.1 mol%; right, 0.05 mol% (pre)catalyst.)
Table 3
Conditions of the Heck–Mizoroki C–C cross-coupling reaction of
7 with 8 by
complexes 3a–3c, and [Pd(OAc)2/2 PPh3/[CuI]]a (10) for comparison.
Compd.
Conc. [mol%]
65 °C
100 °C
Yield of 9 [%]b
10
3a
10
3a
3b
3c
10
3a
3b
3c
10
3a
3b
3c
1.0
53.7
38.2
56.1
36.1
11.4
0
53.6
22.7
8.0
31.0
83.4
70.3
68.5
54.9
4.3
81.1
91.1
43.9
0
0.75
0.5
0.5
0.25
34.2
22.0
7.6
47.1
91.8
18.6
4.3
Fig. 8. Schematic view of the different orientations of the ferrocene subunits in 3a–
3c.
0
a
According to the method described by Boyes and Butler [22].
b
cantly are responsible for a larger Tolman cone angle (3a, 168;
3c, 175°; for comparison, PPh3 145° [24]). This emphasizes that
the s character in the phosphorus lone-pair will not be increased
in 3c as stated above, rather the phosphane group acts as an elec-
tron deficient Lewis-base ligand. These results indicate that pre-
sumably the reason for the contrary catalytic behavior of 3a vs.
3c is owed to the higher shielding in 3c resulting in a more hin-
dered attack of the substrates to the catalytic active centre.
The kinetic studies carried out with 3a–3c, and [Pd(OAc)2/2
PPh3/[CuI]] (10) [22] for comparison in a mixture of toluene/aceto-
nitrile of ratio 1:1 at 80 °C and in presence of 0.5 mol% of palladium
are shown in Fig. 9. From these graphs it is obviously that, as out-
lined earlier, 3a is by far the most active and productive catalyst in
the reaction of 7 with 8 to give 9. The conversion rate is 70%. Com-
plexes 3b and 3c show, due to their steric bulkiness, lower activi-
ties. Therefore, we repeated the catalytic reactions once more by
Yields are determined by 1H NMR spectroscopy with acetyl ferrocene as stan-
dard relative to 9; reaction time 32 h.
lated to 168° and for 1c to 175°. Thus, electronic and steric effects
are intimately related [24].
The 1J(31P–77Se) coupling constant (3a, 746 Hz; 3c, 765 Hz)
shows that 3c possesses a higher electron deficiency as 3a. Consid-
ering this, coordination complex 3c should be the better catalyst.
As discussed earlier, however, metal-organic 3a evinces a higher
productivity. This contrary behavior most probably is attributed
to the different orientations of the sandwich substructures present
in the appropriate phosphane ligands, which finally influences the
Tolman cone angle (Fig. 8). From Fig. 8 it can be seen that, when the
sandwich units are positioned to the outside they are not influenc-
ing the angle between the phosphorus substituents, but signifi-
80
70
60
50
40
30
100
80
60
40
3a
20
10
0
3b
3c
10
20
3b
3c
0
10
20
30
t / h
40
50
30 60 90 120 150 180 210
t / h
Fig. 9. Kinetic investigations of 3a–3c in the Heck–Mizoroki carbon–carbon cross-coupling reaction of 7 with 8. (0.5 mol% (pre)catalyst; left, conversion time 0–50 h; right,
conversion time 45–210 h.)

3828
A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
starting from 45 h. After 210 h the conversion rate for 3c is 91%,
while for 3b a quantitative conversion is typical (Fig. 9, right).
However, the catalyst systems reported by, for example, Fu, [25]
Herrmann, [26] and Reetz, [27] are much more active than 3a–3c
and even can be used for less reactive aryl halides under mild
conditions.
performed with the C, H, N analyzer FLASHEA 1112 Series (Thermo
company).
4.3. Reagents
2-Bromo-toluene (4a), 4-bromo-acetophenone (4b), phenyl
boronic acid (5) iodobenzene (7), tert-butyl acrylate (8), and sele-
nium were purchased by ACROS Organics and were used as re-
ceived. The ferrocenylethynyl phosphanes and the respective
palladium(II)chloride complexes (3a–3c) were synthesized as de-
scribed in Ref. [11]. Reagents [(Et2S)2PdCl2] [28] and acetylferro-
cene [29] were prepared in analogy to the respective synthesis
protocol.
3. Conclusion
Within this report, the synthesis of phosphane selenides
(FcC„C)nPh3ꢀnP@Se (n = 1; 2; 3; Fc = ferrocenyl, (
C5H5)Fe) from (FcC„C)nPh3ꢀnP and selenium is described to esti-
mate the
-donor properties of these systems by 31P{1H} NMR
g -
5-C5H4)(g5
r
spectroscopy. Progressive replacement of phenyl by ferrocenyle-
thynyl causes a shielding of the phosphorus atom with increasing
of the 1J(31P–77Se) coupling constants. The appropriate palladi-
umdichloride complexes [((FcC„C)nPh3ꢀnP)2PdCl2] are accessible
by treatment of (FcC„C)nPh3ꢀnP with [(Et2S)2PdCl2]. Single X-ray
structure analysis confirms the cis-configuration of these
molecules.
4.3.1. Synthesis of (FcC„C)Ph2P@Se (2a)
150 mg (0.38 mmol) of (ferrocenylethynyl)diphenyl phosphane
(1a) were dissolved in toluene (30 mL) and 60 mg (0.76 mmol) of
selenium were added. After 12 h of stirring at 100 °C, all volatiles
were removed in oil-pump vacuum and the brown residue was dis-
solved in 20 mL of dichloromethane and filtered through a pad of
Celite. The title compound could be isolated as an orange, chewy
oil by concentrating the solution to 10 mL and addition of petro-
leum ether. Yield: 170 mg (0.36 mmol, 94%).
It could be shown that complexes [((FcC„C)nPh3ꢀnP)2PdCl2] can
successfully be used as (pre)catalysts in Suzuki–Miyaura and
Heck–Mizoroki carbon–carbon cross-coupling reactions. Com-
pared with the [Pd(OAc)2/PPh3] standard system they show signif-
icantly higher activities and productivities. Although, they are less
active than the catalyst systems reported earlier with any combi-
nation of N-heterocyclic carbenes, bulky, electron-rich chelating
bis(phosphines), palladacycles, secondary phosphates or phospho-
nium salts. The obtained catalytic results can be correlated with
electronic (1J(31P–77Se) coupling constants from 31P{1H} NMR spec-
troscopy) and steric parameters (Tolman cone angle vs. angle be-
tween the phosphorus substituents) of the appropriate
phosphane selenides and palladiumdichloride (ferrocenylethy-
nyl)phosphane systems. In general, electron-withdrawing phos-
phane ligands increase the rate of reaction in the Heck–Mizoroki
reaction which may be attributed to the nucleophilic attack at
the more electrophilic phosphorus atom. In contrast, the Suzuki–
Miyaura carbon–carbon cross-coupling reaction electron-rich and
more bulky phosphanes are favored and show the best results.
Anal. Calc. for C24H19FePSe (473.97): C, 60.76; H, 4.04. Found: C,
60.74; H, 4.02%. IR (KBr, cmꢀ1): 2156 (m, P@Se). 1H
mC„C), 559 (m, m
NMR (d, CDCl3): 4.27 (s, 5 H, C5H5), 4.34 (pt, JHH = 1.9 Hz, 2 H, Hb/
a
C5H4), 4.62 (pt, JHH = 1.9 Hz, 2 H, H /C5H4), 7.45–7.53 (m, 6 H,
C6H5), 7.95–8.07 (m, 4 H, C6H5). 13C {1H} NMR (d, CDCl3): 60.8 (d,
JCP = 4 Hz, Ci/C5H4), 70.5 (C5H5), 72.7 (C /C5H4), 72.7 (Cb/C5H4),
a
77.9 (C„C), 109.4 (d, JCP = 26 Hz, C„C), 128.8 (d, JCP = 14 Hz, Co/
C6H5), 131.4 (d, JCP = 11 Hz, Cm/C6H5), 131.9 (d, JCP = 3 Hz, Cp/
C6H5), 133.2 (d, JCP = 26 Hz, Ci/C6H5). 31P {1H} NMR (d, CDCl3): 4.3
(J31P–77Se = 746 Hz).
4.3.2. Synthesis of (FcC„C)2PhP@Se (2b)
Compound 2b was synthesized in the same manner as 2a,
whereby 150 mg (0.30 mmol) of di(ferrocenylethynyl)phenyl
phosphane (1b) were reacted with 45 mg (0.57 mmol) of selenium.
After appropriate work-up, 2b was obtained as an orange solid.
Yield: 160 mg (0.26 mmol, 93%).
Anal. Calc. for C30H23Fe2PSe (605.94): C, 59.41; H, 3.83. Found:
C, 59.77; H, 3.77%. M.p. 142 °C. IR (KBr, cmꢀ1): 2153 (m,
mC„C),
4. Experimental
557 (w, m
P@Se). 1H NMR (d, CDCl3): 4.29 (s, 10 H, C5H5), 4.33 (pt,
a
JHH = 1.9 Hz, 4 H, Hb/C5H4), 4.61 (pt, JHH = 1.9 Hz, 4 H, H /C5H4),
4.1. General data
7.48–7.56 (m, 3 H, C6H5), 8.13–8.22 (m, 2 H, C6H5). 13C {1H} NMR
(d, CDCl3): 60.7 (d, JCP = 5 Hz, Ci/C5H4), 70.3 (d, JCP = 16 Hz, C /
a
All reactions were carried out under an atmosphere of nitrogen
using standard Schlenk techniques. Toluene, petroleum ether, n-
pentane and n-hexane were purified by distillation from sodium/
benzophenone ketyl; dichloromethane was purified by distillation
from calcium hydride. Celite (purified and annealed, Erg. B.6, Rie-
del de Haen) was used for filtrations.
C5H4), 70.5 (C5H5), 72.7 (Cb/C5H4), 79.5 (C„C),106.3 (d, JCP = 8 Hz,
C„C), 128.9 (d, JCP = 15 Hz, Co/C6H5), 129.4 (Cm/C6H5), 130.8 (d,
JCP = 14 Hz, Cp/C6H5), 132.3 (Ci/C6H5). 31P {1H} NMR (d, CDCl3):
ꢀ31.3 (J31P–77Se = 757 Hz).
4.3.3. Synthesis of (FcC„C)3P@Se (2c)
4.2. Instruments
Compound 2c was synthesized in the same manner as 2a,
whereby 150 mg (0.23 mmol) of tri(ferrocenylethynyl)phenyl
phosphane (1c) were reacted with 45 mg (0.57 mmol) of selenium.
After appropriate work-up, 2b could be isolated as an orange solid.
Yield: 145 mg (0.20 mmol, 86%).
Infrared spectra were recorded with a Thermo Electron Corpo-
ration FT-IR spectrometer Nicolet IR 200. 1H NMR spectra were re-
corded with a Bruker Avance 250 spectrometer operating at
250.130 MHz in the Fourier transform mode; 13C{1H} NMR spectra
were recorded at 62.860 MHz; 31P{1H} NMR spectra were recorded
at 101.249 MHz. Chemical shifts are reported in d units (parts per
million) downfield from tetramethylsilane with the solvent as ref-
erence signal (1H NMR: CDCl3 (99.8%), d = 7.26. 13C{1H} NMR:
CDCl3 (99.8%), d = 77.16. 31P{1H} NMR: rel. H3PO4 (85%), d = 0.0;
rel. P(OMe)3, d = 139.0; external). The abbreviation pt in the 1H
NMR spectra corresponds to pseudo-triplet. Microanalyses were
Anal. Calc. for C36H27Fe3PSe (737.91): C, 58.54; H, 3.69. Found:
C, 58.76; H, 3.69%. M.p. 178 °C. IR (KBr, cmꢀ1): 2148 (w,
mC„C),
556 (w, m
P@Se). 1H NMR (d, CDCl3): 4.34 (s, 15 H, C5H5), 4.35 (pt,
a
JHH = 1.9 Hz, 6 H, Hb/C5H4), 4.66 (pt, JHH = 1.9 Hz, 6 H, H /C5H4).
13C {1H} NMR (d, CDCl3): 60.4 (d, JCP = 5 Hz, Ci/C5H4), 70.4 (d,
a
JCP = 23 Hz, C /C5H4), 70.6 (C5H5), 72.7 (d, JCP = 2 Hz, Cb/C5H4),
78.9 (C„C), 105.1 (d, JCP = 40 Hz, C„C). 31P {1H} NMR (d, CDCl3):
ꢀ71.3 (J31P–77Se = 765 Hz).

A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
3829
4.3.4.Suzuki–Miyaura reaction of 2-bromo-toluene (4a) and 4-bromo-
acetophenone (4b), respectively, with phenyl boronic acid (5)
all volatiles were evaporated under reduced pressure. The conver-
sions were determined by 1H NMR spectroscopy.
4.3.4.1. Kinetic investigations.
2-Bromotoluene (500 mg,
2.92 mmol), phenylboronic acid (470 mg, 3.85 mmol), K2CO3
(1.21 g, 8.76 mmol) and 222 mg (0.97 mmol) of acetylferrocene
were dissolved in 10 mL of a dioxane/water mixture (2:1, v/v).
After addition of the appropriate amount (0.5, 0.25, or 0.1 mol%)
of the respective (pre)catalyst (3a–3c, or 10), the reaction mixture
was stirred for 1 h at 100 °C. After 2.5, 5, 10, 20, 30, and 60 min,
samples (1 mL) were taken for characterization, chromatographed
on silica gel with diethyl ether as eluent, and all volatiles were
evaporated under reduced pressure. The conversions were deter-
mined by 1H NMR spectroscopy.
4-Bromo-acetophenone (995 mg, 5.0 mmol), phenylboronic
acid (726 mg, 6.0 mmol), K2CO3 (1.21 g, 8.76 mmol), and acetylfer-
rocene (114 mg, 0.5 mmol) were dissolved in 10 mL of a dioxane/
water mixture (2:1, v/v). After addition of the appropriate (pre)cat-
alyst (3a–3c) (0.1 or 0.05 mol%), the reaction mixture was stirred
for 1 h at 100 °C. After 2.5, 5, 10, 20, 30, and 60 min, samples
(1 mL) were taken for characterization, chromatographed on silica
gel with diethyl ether as eluent, and all volatiles were evaporated
under reduced pressure. The conversions were determined by 1H
NMR spectroscopy.
4.3.5.2. Kinetic investigations. Iodobenzene (654 mg, 5.1 mmol),
tert-butylacrylate (672 mg, 5.2 mmol), EtNiPr2 (672 mg, 5.2 mmol),
and acetylferrocene (114 mg, 0.5 mmol) were dissolved in 20 mL of
a toluene/acetonitrile mixture (1:1, v/v) and loaded with 0.5 mol%
of the respective (pre)catalyst (3a–3c, and 10). Two equivalents of
[CuI] were added in a single potion. The reaction suspension was
stirred at 80 °C and samples (1 mL) were taken in periods of 1 h.
In addition, for (pre)catalysts 3b and 3c the kinetic investigations
were performed by sampling (sample 1 mL) over a period of
208.5 h (at 48.0, 63.35, 90.75, 117.75, 135.5, 143.5, 183.5, and
208.5 h). The samples were chomatographed on silica gel with
diethyl ether as eluent. All volatiles were evaporated from there
samples under reduced pressure. The conversions were deter-
mined by 1H NMR spectroscopy.
5. Crystal structure determinations
The crystal and intensity collection data for 1a, 1c, 2c, and 3c
are summarized in Table 4. All data were collected on a Oxford
Gemini S diffractometer with graphite monochromatized Mo K
a
radiation (k = 0.71073 Å) at 100 K (1a, 1c, 2c) and graphite mono-
chromatized Cu K radiation (k = 1.54 Å) at 110 K (3c) using oil-
4.3.5. Heck–Mizoroki reaction of iodobenzene (7) with tert-butyl
acrylate (8)
4.3.5.1. Conversion dependency on the concentration of the (pre)cat-
a
coated shock-cooled crystals [30]. The structures were solved by
direct methods using SHELXS-97 [31] and refined by full-matrix
least-square procedures on F2 using SHELXL-97 [32]. All non-hydro-
gen atoms were refined anisotropically and a riding model was
employed in the refinement of the hydrogen atom positions.
alyst. Iodobenzene
(612 mg,
3.0 mmol),
tert-butylacrylate
(397 mg, 3.1 mmol), EtNiPr2 (415 mg, 3.2 mmol), and acetylferro-
cene (228 mg, 1.0 mmol) were dissolved in 10 mL of a toluene/ace-
tonitrile mixture (1:1, v/v). After loading with the appropriate
(pre)catalyst (0.25, 0.5, 0.75, and 1.0 mol%) and addition of two
equivalents of [CuI], the suspension was stirred for 16 h at 65
and 100 °C, respectively. Afterward, a sample (2 mL) was taken,
chromatographed on silica gel with diethyl ether as eluent and
6. Supplementary material
CCDC 680846, 680847, 680848 and 680845 contain the supple-
mentary crystallographic data for 1a, 1c, 2c, and 3c. These data can
Table 4
Crystal and intensity collection data for 1a, 1c, 2c and 3c.
1a
1c
2c
3c
Formula weight
Chemical formula
Crystal system
Space group
a (Å)
788.42
658.10
737.06
1732.23
C48H38Fe2P2
Triclinic
C36H27Fe3P
Monoclinic
P21/a
13.2158(7)
11.0527(6)
19.0908(13)
90
92.130(5)
90
2786.7(3)
1.569
C36H27Fe3PSe
Rhombohedral
R3m
18.76270(10)
18.76270(10)
6.9440(2)
90
90
120
2117.05(6)
1.734
1110
C72H54Cl2Fe6P2Pd 2CHCl3
Monoclinic
P21/a
22.9481(6)
12.3827(2)
24.0250(3)
90
92.780(2)
90
6818.9(2)
1.687
ꢀ
P1
5.9812(4)
12.2705(10)
25.979(2)
99.613(7)
92.641(6)
99.733(6)
1847.4(2)
1.417
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
qcalc (g cmꢀ3
F(000)
)
816
1344
3472
Crystal dimensions (mm)
Z
0.3 ꢁ 0.2 ꢁ 0.05
0.4 ꢁ 0.2 ꢁ 0.1
0.4 ꢁ 0.3 ꢁ 0.2
0.1 ꢁ 0.05 ꢁ 0.03
2
4
3
4
Max. and min. transmission
Absorption coefficient (k, mmꢀ1
Scan range (°)
1.04440, 0.94207
0.907
3.18–26.09
ꢀ7 6 h 6 7, ꢀ15 6 k 6 15,
ꢀ32 6 l 6 32
18098
1.00000, 0.87219
1.624
3.08–26.11
ꢀ16 6 h 6 16, ꢀ13 6 k 6 13,
ꢀ23 6 l 6 23
26707
1.00000, 0.85363
2.894
3.19–26.06
ꢀ23 6 h 6 14,
ꢀ18 6 k 6 23, ꢀ8 6 l 6 7
958
0.0127
958/1/73
1.052
0.0151, 0.0393
0.0153, 0.0395
0.013(10)
0.425, ꢀ0.246
1.00000, 0.15934
15.696
3.68–60.72
ꢀ24 6 h 6 25, ꢀ13 6 k 6 13,
ꢀ27 6 l 6 27
10141
0.1508
10141/582/820
1.085
0.0917, 0.2271
0.1408, 0.2543
–
2.900, ꢀ0.979
)
Index ranges
Total reflections
Unique reflections
Rint
7286
0.0314
5531
0.0482
Data/restraints/parameters
7286 /0/469
1.220
0.0825, 0.2018
0.0969, 0.2057
1.291, ꢀ1.305
5531/0/361
1.019
0.0298, 0.0644
0.0520, 0.0768
0.539, ꢀ0.317
Goodness-of-fit on F2
a
R1a, wR2 [I 2
q
(I)]
a
R1a, wR2 (all data)
Largest differences in peak and hole peak in
final Fourier map (e Åꢀ3
)
a
2
2
R1 = [R
(||Fo| ꢀ |Fc|)/
R
|Fo|); wR2 = [
R
(w(Fo ꢀ Fc2)2)/
R
(wFo4)]1/2. S = [
R
w(Fo ꢀ Fc2)2]/(n ꢀ p)1/2. n = number of reflections, p = parameters used.

3830
A. Jakob et al. / Journal of Organometallic Chemistry 693 (2008) 3821–3830
(b) R.P. Pinnell, C.A. Megerle, S.L. Manatt, P.A. Kroon, J. Am. Chem. Soc. 95
(1973) 977;
(c) D.W. Allen, B.F. Taylor, J. Chem. Soc. Dalton Trans. (1982) 51;
(d) D.W. Allen, I.W. Nowell, J. Chem. Soc. Dalton Trans. (1985) 2505.
[10] T. Baumgartner, M. Fiege, F. Pontzen, R. Arteaga-Müller, Organometallics 25
(2006) 5657.
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgement
[11] Jakob, A., Ph. D. Thesis, TU Chemnitz/Germany, 2008.
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We are grateful to the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie for generous financial support.
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