Four-coordinate complexes of bis(1-diphenylphosphinoindenyl)iron(II)

Article abstract of DOI:10.1016/j.ica.2006.02.019

Palladium, platinum and rhodium complexes of rac- and meso-bis(1-diphenylphosphinoindenyl)iron(II) (1) are reported. Both rac and meso isomers of {bis(1-diphenylphosphinoindenyl)iron(II)}palladium dichloride (rac- and meso-2) were characterized by X-ray crystallography along with the rac isomer of the Pt analogue (rac-3). NMR analysis of the rhodium complex [{bis(1-diphenylphosphinoindenyl)iron(II)}(cyclooctadiene)rhodium(I)] tetraphenylborate suggests a similar structure in solution. Coupling reactions of n- and sec-BuCl with bromobenzene in THF are catalysed by rac-2 and found to be similar to (PPh₃)₂PdCl₂ but poorer than (dppf)PdCl₂ in diethyl ether.

Full text of DOI:10.1016/j.ica.2006.02.019

Inorganica Chimica Acta 359 (2006) 3596–3604
www.elsevier.com/locate/ica
Four-coordinate complexes of bis(1-diphenylphosphinoindenyl)iron(II)
*
Julian J. Adams, Owen J. Curnow , Glen M. Fern
Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Received 31 October 2005; received in revised form 1 February 2006; accepted 3 February 2006
Available online 6 March 2006
Dedicated to Professor D. Michael P. Mingos in recognition of his outstanding contributions to inorganic chemistry.
Abstract
Palladium, platinum and rhodium complexes of rac- and meso-bis(1-diphenylphosphinoindenyl)iron(II) (1) are reported. Both rac and
meso isomers of {bis(1-diphenylphosphinoindenyl)iron(II)}palladium dichloride (rac- and meso-2) were characterized by X-ray crystallo-
graphy along with the rac isomer of the Pt analogue (rac-3). NMR analysis of the rhodium complex [{bis(1-diphenylphosphinoinde-
nyl)iron(II)}(cyclooctadiene)rhodium(I)] tetraphenylborate suggests a similar structure in solution. Coupling reactions of n- and
sec-BuCl with bromobenzene in THF are catalysed by rac-2 and found to be similar to (PPh3)2PdCl2 but poorer than (dppf)PdCl2 in
diethyl ether.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Phosphine complex; Ferrocene; X-ray structure; Indenyl; Group 10; Rhodium
1. Introduction
ring-slippage, and indenide dechelation with phosphine
coordination to give a zwitterionic intermediate (Scheme
1). To further understand the factors influencing this
unprecedented ferrocene isomerization process, a number
of derivatives were reported [4].
Ferrocenylphosphines continue to be intensively investi-
gated for their utility in homogeneous catalysis; chiral
derivatives are of particular interest for asymmetric cataly-
sis [1]. The introduction of a chiral substituent to a ferro-
cene core or the use of heterotopic, planar chiral ligands
is usually used to create the chirality. Compounds contain-
ing two planar chiral units may exhibit rac and meso iso-
mers. We have reported the preparation of the diindenyl
analogue of 1,10-bis(diphenylphosphino)ferrocene (dppf),
[(1-PPh2-g5-C9H6)2Fe] (1), and the characterization of its
rac and meso isomers by X-ray crystallographic studies of
their tetracarbonylmolybdenum complexes in which the
meso isomer exhibited significant structural distortions
resulting from steric interactions [2]. Further studies on 1
have shown that this indenyl ferrocene undergoes a facile
isomerization in THF from the meso isomer to the rac iso-
mer at ambient temperatures [3] and a number of studies all
point to a mechanism involving THF coordination, indenyl
Ferrocenylphosphines are widely employed in the for-
mation of polymetallic complexes. Of these, 1,10-bis(diph-
enylphosphino)ferrocene (dppf) is the most studied. As a
ligand, dppf is capable of coordination to a variety of tran-
sition metals, with examples of group 5 metalates [5], car-
bonyl complexes of groups 6, 7, and 8 [6], and halo
complexes of the late transition metals being known [7,8].
The success of dppf as a ligand has been attributed to the
different ways the diphosphine can coordinate to a metal
centre, with unidentate, chelate, and bridging coordination
modes possible [9]. The flexibility of the ferrocenyl core
along with the ability of the phosphorus atoms to deviate
from coplanarity with the cyclopentadienyl rings makes
dppf highly adaptable to the individual requirements of
the different metals.
Bimetallic complexes of dppf are known to catalyze a
wide variety of organic transformations [10]. Palladium
and nickel complexes of dppf are effective catalysts for
*
Corresponding author. Fax: +64 3 364 2110.
E-mail address: owen.curnow@canterbury.ac.nz (O.J. Curnow).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.02.019

J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
3597
The 1H NMR spectrum of rac-2 consists of an aromatic
multiplet centred at 6.93 ppm and singlets at 2.53 and
4.70 ppm for the indenyl protons H2 and H3, respectively.
For meso-2, the indenyl protons H2 and H3 were found at
3.95 and 4.65 ppm, respectively. These chemical shifts are
markedly different from those observed for the parent fer-
rocenes (Table 1), with the resonances for the indenyl pro-
tons H2 and H3 shifted upfield for rac-2 and downfield for
meso-2 (relative to rac- and meso-1, respectively). These
changes in chemical shifts, which are considerably greater
than observed for the analogous dppf complex, are indica-
tive of significant conformational changes that have
occurred upon coordination of the phosphorus atoms to
the palladium. As a result, the resonances for the indenyl
proton H3 of both rac- and meso-2 now occur at similar
chemical shifts. These observations will be discussed fur-
ther with respect to the X-ray structural studies. 13C
NMR spectral assignments were based on the spectra of
rac- and meso-1.
The platinum analogue of rac-2, rac-3, was prepared
similarly from rac-1 and (PhCN)2PtCl2. The proton reso-
nances for H2 and H3 appear in positions similar to those
observed for rac-2, an indication that the conformation of
the two complexes in solution is similar. The 13C{1H}
NMR spectrum of rac-3 is consistent with the formation
of the diphosphine-platinum complex. In general, the car-
bon resonances are shifted upfield relative to rac-1. The
31P{1H} NMR spectrum of rac-3 consists of a singlet at
PPh2
PPh2
Ph
Ph
-THF
THF
P
PPh2
PPh2
O
Fe
Fe
O
Fe
meso
h
PP
rac
2
Scheme 1. Isomerisation of [(1-PPh2-g5-C9H6)2Fe] (1) in THF.
the cross-coupling of organic moieties [11], while rhodium,
ruthenium, and palladium complexes are efficient at the
hydrogenation of olefins [12,13]. Platinum complexes of
dppf have been employed as catalysts for the hydrosilyla-
tion of olefins [14]. Derivatives of dppf containing chiral
functionalities have found use in asymmetric catalysis
[15]. The related bis(1-(diphenylphosphino)tetrahydroinde-
nyl)iron(II) has been reported along with the characteriza-
tion of molybdenum, rhodium, and iridium complexes [16].
It is anticipated that palladium complexes of 1 would also
be able to catalyze organic transformations, with the C2
symmetric rac isomer providing interesting possibilities in
the field of asymmetric catalysis. In this paper, we report
on some Pd and Pt complexes of 1, as well as a Rh com-
plex, and assess a Pd complex of rac-1 as a catalyst for
the cross coupling of alkyl Grignard reagents with aryl
bromides.
12.65 ppm flanked by two satellites due to coupling with
2. Results and discussion
1
the 195Pt nucleus. The magnitude of the coupling, JPtP
=
2.1. Synthesis and characterization of the complexes
Table 1
1H NMR chemical shifts (for H2 and H3) and 31P NMR chemical shifts of
Treatment of bisnitrile complexes of palladium and plat-
inum with the appropriate isomer of the diphosphine com-
plex 1 were found to give the desired heterobimetallic
complexes rac- and meso-bis(1-diphenylphosphinoinde-
nyl)iron(II)-cis-dichloropalladium(II) (rac- and meso-2,
respectively) and rac-bis(1-diphenylphosphinoindenyl)-
iron(II)-cis-dichloroplatinum(II) (rac-3) (Scheme 2).
Syntheses of 2 starting from various ratios of rac- and
meso-1 were found to give the same ratio of rac- and
meso-2 compounds, as shown by 31P NMR spectroscopy:
rac-2 exhibits a single resonance at 35.79 ppm in CDCl3
whereas meso-2 exhibits a single resonance at 33.94 ppm.
As with the isomers of 1 [3], the rac isomer is observed
downfield of the meso isomer.
a
the ferrocenes in CDCl3
Compound
H2
H3
31P
dppfb
meso-1
rac-1
(dppf)PdCl2
meso-2
rac-2
4.07
3.48
3.07
4.18
3.95
2.53
2.42
2.81
4.32
3.81
4.92
4.36
4.65
4.70
4.62
4.96
ꢀ17.2
ꢀ26.5
ꢀ22.3
34.9
33.9
35.3
b
rac-3
rac-4
12.7
29.1
a
Chemical shifts are in ppm (d) downfield from Me4Si (1H) and 85%
H3PO4 (
31P); spectra obtained in CDCl3.
b
H2 and H3 refer to the a and b protons of the cyclopentadienyl ring,
respectively. Data from Refs. [17,18].
Ph2
Ph2
P
P
THF
Fe
PdCl2
L2MCl2
Fe
rac-1 or meso-1 +
or
MCl2
P
Ph2
P
Ph2
meso-2
rac-2 (M = Pd)
rac-3 (M = Pt)
L2M =( PhCN)2Pd, (MeCN)2Pt
Scheme 2. Synthesis of Pd and Pt complexes of 1.

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J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
3818 Hz, is indicative of the phosphine being trans to a
chloro ligand and is similar to that observed for
(dppf)PtCl2 (3765 Hz) [18].
suggested that large distortions in the geometry about the
rhodium, caused by the bulkiness of the diphosphine
ligands, was responsible for the inability of the second
diphosphine to displace the remaining NBD ligand
[13,20]. It is anticipated that rac-4 will suffer from similar
steric demands, making substitution of the second COD
ligand more difficult. Interestingly, the homoleptic species
[M(dppf)2]BF4 (M = Rh, Ir) has been prepared via a differ-
ent route and it was found that the geometry around the
iridium atom was severely distorted from square planar
[21].
[(Cyclooctadiene)(rac-bis(1-diphenylphosphinoindenyl)-
iron(II))rhodium(I)]tetraphenylborate (rac-4) was synthe-
sized by the reaction of rac-1 with [Rh(COD)2]BF4 followed
by the addition of NaBPh4 (Scheme 3). Complex rac-4 was
isolated in good yield (84%) as a yellow powder. Although
the reaction was attempted with two equivalents of rac-1,
only a single COD was displaced from the rhodium by the
diphosphine. Chaloner et al. has reported that the addition
of two equivalents of 1,10-bis(diisopropylphosphino)ferro-
cene (disoppf) to [Rh(NBD)2]BF4 led to the exclusive for-
mation of [Rh(NBD)(disoppf)]BF4 [19]. Subsequent
treatment of [Rh(NBD)(disoppf)]BF4 with a 10-fold excess
of dppf produced, exclusively, [Rh(NBD)(dppf)]BF4. It was
The NMR spectra of rac-4 are consistent with the dis-
placement of a single cyclooctadiene from the rhodium pre-
1
cursor. The H NMR spectrum consists of an aromatic
multiplet centred at 7.31 ppm and two singlets 2.81 and
4.96 ppm for H2 and H3, respectively. The resonances
for the CH2 and CH protons of the cyclooctadiene occur
at 2.56 and 4.37 ppm, respectively. The resonances for
H2 and H3 are upfield of those for rac-1, similar to what
was observed for rac-2 and rac-3. This suggests that the
indenyl ligands in rac-4 are adopting a conformation simi-
lar to that of the palladium and platinum complexes, with
H2 positioned over the benzo ring. The 31P{1H} NMR
spectrum of rac-4 consists of a doublet at 29.1 ppm, with
a rhodium-phosphorus coupling constant of 150 Hz. The
Ph2
P
rac-1
+
THF
Fe
Rh
[Rh(COD)2]BF4
P
Ph2
rac-4
Scheme 3.
Table 2
Crystal data and structural refinement parameters for rac-2, meso-2, and rac-3
Compound
rac-2
meso-2
rac-3
Empirical formula
Formula weight (g molꢀ1
T (K)
C
831.79
293(2)
42H32Cl2FeP2Pd
C42H32Cl2FeP2Pd
831.79
158(2)
C42H32Cl2FeP2Pt
920.45
168(2)
)
˚
k (A)
0.71073
0.71073
0.71073
Crystal system
Space group
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
˚
a (A)
12.694(3)
16.070(3)
16.736(3)
90
98.77(3)
90
3374.1(12)
4
1.637
1.248
1680
12.256(7)
16.691(8)
17.105(9)
90
101.461(9)
90
3429(3)
4
1.611
1.228
12.822(5)
16.199(6)
16.964(7)
90
98.669(7)
90
3483(2)
4
1.755
4.705
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg mꢀ3
Absorption coefficient (mmꢀ1
F(000)
)
)
1680
1808
Crystal size (mm)
h Range (ꢁ)
0.45 · 0.20 · 0.09
1.88–26.50
ꢀ15 6 h 6 14, ꢀ19 6 k 6 20,
ꢀ20 6 l 6 20
41499
0.6 · 0.2 · 0.1
2.72–19.00
ꢀ11 6 h 6 11, ꢀ15 6 k 6 11,
ꢀ15 6 l 6 15
20447
0.16 · 0.09 · 0.02
1.75–26.39
ꢀ7 6 h 6 15,
ꢀ20 6 k 6 17, ꢀ21 6 l 6 21
25108
Index ranges
Reflections collected
Independent reflections
Rint
6957
0.0734
2746
0.0866
7104
0.0865
Completeness to h
Absorption correction
Maximum/minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
(26.50ꢁ) 99.4%
multi-scan
0.896/0.604
6957/0/433
1.356
(19.00ꢁ) 99.7%
multi-scan
0.886/0.605
2746/0/433
1.279
(26.39ꢁ) 99.5%
multi-scan
0.912/0.520
7104/0/433
0.897
R indices [I > 2r(I)] (R, Rw)
R indices (all data) (R, Rw)
Final maximum/minimum Dq (e A
0.1359, 0.3167
0.1843, 0.3678
8.601/ꢀ1.521
0.0780, 0.1913
0.0810, 0.1934
1.177/ꢀ0.796
0.0393, 0.0750
0.0825, 0.0967
1.441/ꢀ0.772
ꢀ3
˚
)

J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
3599
values for the chemical shift and coupling constant are sim-
ilar to those previously seen for analogous rhodium–dppf
complexes [22,23].
2.2. X-ray structural analyses
In order to investigate the structural effects of the benzo
substituents, rac-2, meso-2, and rac-3 were characterized by
X-ray crystallography. Crystallographic and refinement
data are given in Table 2 and selected distances and angles
are given in Table 3.
Complexes rac-2 and rac-3 are isomorphous: they crys-
tallize in the monoclinic space group P21/n, with one com-
plete molecule being in the asymmetric unit. The ligand
conformations are essentially the same. Fig. 1 shows the
molecules with the atomic labeling schemes and Fig. 2
shows the views down the M–Fe axes. As expected, the
indenyl ligands are coordinated to the iron atom via their
five-membered rings in an g5-fashion. In order for both
phosphine moieties to coordinate to the metal, the indenyl
ligands adopt a conformation in which the rotation angle
(RA), 172.5ꢁ and 172.3ꢁ, respectively, is considerably
greater than the p-offset conformation observed in rac-1
(RA = 20.8ꢁ) [4]. This conformation places each indenyl
proton H2 near the centre of the six-membered ring of
the other indenyl ligand and accounts for the upfield shift
of these protons in the 1H NMR spectrum: 2.53 and
2.42 ppm, respectively, for rac-2 and 3. The conformations
Fig. 1. ORTEPs of rac-2 (30% ellipsoids) and rac-3 (40% ellipsoids)
showing the atomic labeling schemes.
Fig. 2. Views down the M–Fe axes of rac-2 and rac-3.
Table 3
a
˚
Selected distances (A) and angles (ꢁ) for rac-2, meso-2, and rac-3
Compound
rac-2
meso-2
rac-3
Fe–CNT
Fe–Cx1
Fe–Cx2
Fe–Cx3
Fe–Cx8
Fe–Cx9
Px–Cx1
1.625, 1.643
1.633, 1.630
1.631, 1.651
2.021(10), 1.999(10)
2.036(11), 2.024(11)
2.019(10), 2.046(11)
2.031(10), 2.069(10)
2.029(12), 2.080(11)
1.764(11), 1.815(10)
1.972(14), 1.998(14)
1.970(15), 2.029(15)
2.032(15), 2.064(16)
2.073(16), 2.040(18)
2.078(16), 2.037(17)
1.771(15), 1.764(15)
2.010(7), 2.012(6)
2.033(7), 2.027(7)
2.050(7), 2.051(7)
2.063(7), 2.094(6)
2.069(7), 2.105(7)
1.793(7), 1.825(7)
CNT–Fe–CNT
Fe–Cx1–Px
CNT–Cx1–Px
C11–CNT–CNT–C21
P–M–P
177.2
178.7
177.2
127.4(5), 125.2(5)
178.0, 179.0
29.6
100.21(10)
86.80(10)
126.7(8), 128.2(8)
177.6, 171.5
34.8
100.32(14)
87.57(14)
127.9(3), 125.6(3)
177.7, 178.9
28.9
100.50(7)
85.16(7)
Cl–M–Cl
M–P
M–Cl
P–Cp planef
P–MCl2 plane
2.275(3), 2.282(3)
2.317(3), 2.329(3)
ꢀ0.016, ꢀ0.036
ꢀ0.080, 0.344
0.01, 0.05
2.50, 2.64
4.26
1.85, 2.63
172.5
2.269(4), 2.267(4)
2.310(4), 2.324(4)
+0.038, +0.049
0.020, 0.305
0.08, 0.01
3.65, 3.41
4.90
2.63, 3.39
35.4
2.666(19), 2.2791(19)
2.3491(19), 2.3566(18)
+0.022, ꢀ0.012
ꢀ0.050, 0.290
0.04, 0.07
3.32, 2.29
4.03
1.74, 2.35
172.3
b
˚
Slip-fold parameter D (A)
Hinge angle HA (ꢁ)c
Angle between C5 planes
Fold angle FA (ꢁ)d
Rotation angle RA (ꢁ)e
a
The second number refers to the equivalent parameter for the primed atoms.
b
c
d
e
f
D = average distance of Fe to C8 and C9 minus average distance of Fe to C1 and C3.
HA = angle between planes defined by [C1, C2, C3] and [C1, C3, C8, C9].
FA = angle between planes defined by [C1, C2, C3] and [C4, C5, C6, C7, C8, C9].
RA = angle formed by the intersection of two lines determined by the centroids of the five- and six-membered rings.
A + sign indicates that the P atom is on the side away from the Fe atom.

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J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
of the phenyl rings in the two complexes (illustrated best in
Fig. 2) are very similar. In each case, there is an indenyl
ligand in which one phenyl group is approximately perpen-
dicular to the C5 ring plane (angle between the C11–P1–
C30 plane and the C5 plane = 87.2ꢁ and 85.7ꢁ for rac-2
and rac-3, respectively) and the other is close to the C5
plane and oriented towards the Fe atom (angle between
the C11–P1–C40 plane and the C5 plane = 14.0ꢁ and
12.9ꢁ for rac-2 and rac-3, respectively). The other indenyl
ligand has one phenyl close to the C5 plane, but oriented
away from the Fe atom (angle between the C21–P2–C50
plane and the C5 plane = 17.6ꢁ and 19.2ꢁ for rac-2 and
rac-3, respectively) while the other phenyl group is at about
50ꢁ to the C5 plane (angle between the C21–P2–C60 plane
and the C5 plane = 50.0ꢁ and 49.2ꢁ for rac-2 and rac-3,
respectively). The phenyl groups close to the C5 plane are
oriented away from their ligand’s benzo ring and away
from each other. This minimizes the benzo-phenyl and phe-
nyl–phenyl steric interactions.
Fig. 4. View of meso-2 down the Pd–Fe axis.
Mo(CO)4], in which the axial CO groups in the meso iso-
mer force the P atom out of the plane by 0.230 A,
whereas the CO groups in the rac Mo(CO)4 isomer give rise
˚
The palladium and platinum atoms adopt a distorted
square planar geometry similar to that observed previously
for other diphosphine palladium and platinum complexes
[17,23]. P2 is significantly displaced from the MCl2 plane
to only a small deviation of the P atoms from the C5
˚
planes: 0.048 A away from the Fe atom [2].
˚
by ca 0.3 A, whereas P1 is approximately in the MCl2
2.3. Cyclic voltammetry
plane.
The X-ray structural analysis of meso-2 shows one inde-
pendent molecule in the asymmetric unit. Fig. 3 shows the
molecule with the atomic labeling scheme and Fig. 4 shows
the view down the Pd–Fe axis. The molecular structure of
meso-2 is surprisingly similar to that of rac-2: even the con-
formations adopted by the phenyl groups, best observed by
comparing Figs. 2 and 4, are very similar despite the pres-
ence of a benzo group near the C50–55 phenyl group. The
biggest difference seems to be that P2 is pushed slightly out
Cyclic voltammetry of rac-2 and rac-3 both showed a
single reversible redox process: DEp and Ia/Ic were found
to change only slightly with scan rate and were similar to
ferrocene as an internal standard. The oxidation of the ferr-
ocenyl moiety of rac-2 occurs at 260 mV versus Fc/Fc+, a
potential 320 mV less positive than (dppf)PdCl2 and in
keeping with the electron-rich character of the indenyl
ligand when compared with the cyclopentadienyl ligand
[8,24]. The electrochemistry of rac-3 exhibits a redox pro-
cess at 248 mV versus Fc/Fc+. As would be expected, this
is at a potential 325 mV less positive than (dppf)PtCl2
[8,25].
˚
of the C5 plane away from the Fe atom by 0.049 A, rather
than towards the Fe atom as in rac-2. The similarity
between rac- and meso-2 is in stark contrast to the
Mo(CO)4 analogues, rac- and meso-[Fe(C9H6PPh2)-
2.4. Cross-coupling reactions
Since the reporting of the nickel-phosphine catalyzed
cross-coupling of Grignard reagents with aryl halides in
1972 [26], a wide variety of similar coupling reactions have
been developed and used successfully in organic chemistry
[27]. Palladium catalysts have been found to be particularly
effective at mediating the cross-coupling of Grignard
reagents with aryl halides. However, the introduction of a
secondary alkyl group to aryl halides remains problematic
due to the isomerization of the alkyl group and/or the
reduction of the halide. The catalyst (dppf)PdCl2 was
found to be highly effective at couplings involving second-
ary alkyl groups, with near perfect sec-/n-selectivity [17].
The cross-coupling of n- and sec-butylmagnesium chloride
with bromobenzene was carried out in the presence of rac-
2. The results and reaction conditions are summarized in
Table 4.
Fig. 3. ORTEP of meso-2 showing the atomic labeling scheme (30%
thermal ellipsoids).

J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
3601
Table 4
Cross-coupling of n- and sec-butylmagnesium chloride with bromobenzene in THF
Catalyst
Concentrationb
Chloride
Time (h)
Yield (%)a
sec-BuPh
n-BuPh
Otherc
(Ph3P)2PdCl2
rac-2
rac-2
rac-2
rac-2
1.0
0.5
1.0
0.5
1.0
5.0
1.0
n-BuCl
n-BuCl
n-BuCl
sec-BuCl
sec-BuCl
sec-BuCl
sec-BuCl
16
18
17
1
1
2
34.4
23.8
26.6
10.5
17.6
47.5
46.6
49.2
33.7
44.6
4.2
7.3
25.8
27.9
4.8
24.0
7.4
81.1
63.4
5.3
rac-2
rac-2
18
7.6
a
Yield determined by GLC using an internal standard.
Concentration in mol% of Pd.
Recovered bromobenzene. When the yields of the coupled products were low compared with consumed bromobenzene, variable amounts of benzene
b
c
was detected by GLC.
Complex rac-2 was found to catalyze the reaction of
bromobenzene with n-butylmagnesium chloride to give
n-butylbenzene in a modest yield (45%) after 17 h at a
catalyst loading of 1 mol% of palladium. The reaction,
however, was not selective with considerable amounts of
sec-butylbenzene and benzene also being formed. The
ratio of n- and sec-butylbenzene formed was 63:37.
Decreasing the catalyst loading to 0.5 mol% of palladium
results in a decrease in both yield and selectivity. The
results are similar to those obtained for the equivalent
reaction using (PPh3)2PdCl2, with a n-/sec- ratio of
59:41 observed. Hayashi et al. reported that (dppf)PdCl2
catalyses the coupling of bromobenzene with n-butylmag-
nesium chloride in excellent yield (92%) and with high
selectivity (100%) [17].
3. Conclusions
In this paper, we have described some Pd, Pt and Rh
complexes of the bisplanar chiral ligand 1. Comparison
of the X-ray structures of the rac and meso isomers of
the PdCl2 complex 2 show little effect of the benzo rings:
there is little distortion and the phenyl conformations are
very similar. This is in contrast to the six-coordinate
Mo(CO)4 analogues. Catalytic cross-coupling reactions
with rac-2 in THF showed little difference with
(PPh3)2PdCl2, but a poorer performance than the dppf
analogue in diethylether, although solvent may be a factor
in the poor performance of rac-2 when compared to the
dppf analogue.
The cross-coupling of bromobenzene with sec-butyl-
magnesium chloride was carried out with rac-2 to yield
sec-butylbenzene (47% after 18 h) with a sec-/n- ratio of
63:37, at a catalyst loading of 1 mol% of palladium.
Increasing the catalyst loading to 5 mol% of palladium
reduces the reaction time (2 h for the same yield), without
loss of selectivity. The equivalent reaction with (dppf)PdCl2
produced sec-butylbenzene in excellent yield (95%) and
with high selectivity (100%) [17].
Correlations have previously been made between cata-
lyst activity and the Cl–Pd–Cl bond angle, with small
angles proposed to accelerate the reductive elimination of
the coupled product [17]. The Cl–Pd–Cl bond angle for
rac-2 was determined to be 86.8ꢁ, similar to that of
(dppf)PdCl2. With this small angle, it was anticipated that
coupling reactions catalyzed by rac-2 would proceed with
high yields and selectivity. The results obtained here sug-
gest that the b-hydride elimination is still competing
strongly with the reductive elimination step of the catalytic
cycle, despite the small bond angle. One should note, how-
ever, that due to solubility problems with rac-2, the cross-
coupling reactions were performed in THF and not diethyl
ether as was used in the previous studies. The choice of sol-
vent has been shown to be important for high selectivity,
with reduced sec-/n- ratios and increased amounts of the
reduced aryl halide observed for cross-coupling reactions
performed in THF [28].
4. Experimental
All manipulations and reactions were carried out under
an inert atmosphere (Ar or N2) by use of standard Schlenk
line techniques. Reagent grade solvents were dried and dis-
tilled prior to use: diethylether and tetrahydrofuran from
Na/benzophenone; dichloromethane and petroleum ether
(50–70 ꢁC fraction) from CaH2. Bis(1-(diphenylphosph-
ino)-g5-indenyl)iron(II) [2,3], (PhCN)2PtCl2 [29] and
(PhCN)2PdCl2 [29] were prepared by published procedures.
All other reagents were purchased from Aldrich or Sigma
Chemical Companies. 1H, 13C{1H} and 31P{1H} NMR
spectroscopy data were collected on a Varian UNITY-
300 spectrometer operating at 300, 75 and 121 MHz,
respectively. NOE, 1H–1H COSY, 1H–13C HSQC and
1H–13C HMBC experiments were run on a Varian
INOVA-500 spectrometer operating at 500 and 125 MHz
for 1H and 13C, respectively. Spectra were measured at
ambient temperature with residue solvent peaks as internal
1
standard for H- and 13C{1H}-spectroscopy. Couplings in
the 13C NMR spectra are to phosphorus. 31P{1H} NMR
spectroscopy chemical shifts were reported relative to
external 85% H3PO4, positive shifts representing deshiel-
ding. EI mass spectra were collected on a Kratos
MS80RFA mass spectrometer. Elemental analyses were
carried out by Campbell Microanalytical Services, Univer-
sity of Otago, Dunedin. Cyclic voltammetry was performed

3602
J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
using a PAR 173 Potentiostat coupled to a PAR 175 Uni-
versal Programmer and a Graphtec WX 1200 chart recor-
der. All electrochemical measurements were made with
1 mM solutions in CH2Cl2 with 0.1 M [Bu4N]PF6 electro-
lyte using a three-electrode cell comprising of a platinum-
disk working electrode (1 mm diameter), a platinum-wire
auxiliary electrode, and a Ag/Ag+ (0.01 M AgNO3, 0.1 M
[Bu4N]PF6–CH2Cl2) reference electrode. All potentials
are reported versus the ferrocene/ferrocenium (Fc/Fc+)
couple after referencing to in situ ferrocene. Before use,
the electrodes were polished with 1 lm diamond paste
and cleaned with acetone and distilled water. Electrochem-
ical measurements were made at ambient temperature
under an inert atmosphere.
C2), 65.8 (s, C1), 64.6 (s, C3). 31P{1H} NMR (CDCl3): d
33.94. Mass spectrum (EI, m/z (%)): 831 (2, M+), 795
(35,
M+ꢀCl),
760
(25,
M+ꢀ2Cl),
704
(20,
[(PPh2C9H7)2Pd]+). As with rac-2, low carbon microana-
lytical results where obtained with meso-2 despite good
crystallinity and NMR spectra.
4.3. Preparation of rac-bis(1-diphenylphosphinoindenyl)-
iron(II)-cis-dichloroplatinum(II) (rac-3)
To a solution of rac-1 (0.20 g, 0.30 mmol) in THF
(50 mL) was added (PhCN)2PtCl2 (0.14 g, 0.30 mmol).
After stirring overnight at ambient temperature, the sol-
vent was removed in vacuo. The resulting brown residue
was dissolved in CH2Cl2 (10 mL) and filtered through Cel-
ite. Washing with CH2Cl2 (30 mL) produced a light brown
solution that was then reduced in volume to 10 mL. To this
solution was added diethylether (20 mL). The flask was
then placed in a freezer and left overnight to give a brown
precipitate of rac-3 (0.22 g, 80%). Crystals suitable for X-
ray structural analysis were grown by vapour diffusion of
diethylether into a CH2Cl2 solution.
4.1. Preparation of rac-bis(1-diphenylphosphinoindenyl)-
iron(II)-cis-dichloropalladium(II) (rac-2)
To a solution of rac-1 (0.19 g, 0.29 mmol) in THF
(50 mL) was added (PhCN)2PdCl2 (0.12 g, 0.29 mmol).
After stirring at ambient temperature for 4 h, the solvent
was removed in vacuo. The resulting brown residue was
dissolved in dichloromethane (30 mL) and filtered through
Celite. The Celite was washed with a further 20 mL of
CH2Cl2. The volume was reduced to 15 mL, and diethyle-
ther (25 mL) was added. The flask was placed in a freezer,
and the crystals were collected by filtration to yield 0.18 g
(73%) of rac-2 as brown crystals.
1H NMR (CDCl3): d 8.04 (m, 4H, o-Ph), 7.65 (d,
3
3JHH = 8 Hz, 2H, H7), 7.57 (d, JHH = 8 Hz, 2H, H4),
3
7.53 (m, 4H, o-Ph), 7.37 (t, JHH = 7 Hz, 2H, p-Ph), 7.32
3
(t, JHH = 7 Hz, 2H, p-Ph), 7.26–7.21 (m, 8H, m-Ph), 6.94
3
3
(t, JHH = 8 Hz, 2H, H6), 6.65 (t, JHH = 8 Hz, 2H, H5),
3
3
4.62 (d, JHH = 2 Hz, 2H, H3), 2.42 (d, JHH = 2 Hz, 2H,
1H NMR (CDCl3): d 8.12–6.75 (m, 28H, H4–7 and Ph),
4.70 (s, 2H, H3), 2.53 (s, 2H, H2). 13C{1H} NMR (CDCl3):
H2). 13C{1H} NMR (CDCl3): d 135.66 (t, JPC = 6 Hz,
1
1
ipso-Ph), 135.02 (t, JPC = 5 Hz, ipso-Ph), 131.34 (s, o-
1
1
d 135.8 (t, JPC = 6 Hz, ipso-Ph), 135.3 (t, JPC = 5 Hz,
ipso-Ph), 132.6 (s, o-Ph), 131.2 (s, o-Ph), 129.4–127.9 (m,
C4, C7, m-Ph and p-Ph), 126.5 (s, C5), 124.9 (s, C6), 90.2
Ph), 130.85 (s, o-Ph), 129.83 (s, C7), 128.22 (s, C4),
127.91–127.50 (m, m-Ph and p-Ph), 126.24 (s, C5), 124.85
2
(s, C6), 89.89 (s, C3a), 86.19 (t, JPC = 5 Hz, C7a), 81.37
2
1
(s, C3a), 86.9 (t, JPC = 5 Hz, C7a), 80.4 (s, C2), 70.7 (d,
(s, C2), 71.12 (d, JPC = 68 Hz, C1), 66.33 (s, C3).
1JPC = 8 Hz, C1), 66.7 (s, C3). 31P{1H} NMR (CDCl3): d
35.79. CV (CH2Cl2): E1/2 = 240 mV, DEP = 75 mV. Mass
spectrum (EI, m/z (%)): 831 (4, M+), 705 (81,
[(PPh2C9H7)2Pd]+). Anal. Calc. for C42H32Cl2P2FePd: C,
60.64; H, 3.88. Found: C, 59.12; H, 4.35%.
31P{1H} NMR (CDCl3): d 12.65 (JPtP = 3818 Hz). CV
(CH2Cl2): E1/2 = 248 mV, DEP = 75 mV. Mass spectrum
(EI, m/z (%)): 884 (100, [(PPh2C9H6)2FePtCl]+), 830 (54,
[(PPh2C9H7)2PtCl]+). Anal. Calc. for C42H32Cl2P2FePt:
C, 54.80; H, 3.50. Found: C, 54.24; H, 3.52%.
4.2. Preparation of meso-bis(1-diphenylphosphinoindenyl)-
iron(II)-cis-dichloropalladium(II) (meso-2)
4.4. Synthesis of [bis(diph enylphosphinoindenyl)iron(II)-
(cyclooctadiene)rhodium(I)] tetraphenylborate (rac-4)
To a solution of 1 (meso/rac ratio of 4:1) (0.65 g,
1.0 mmol) in THF (100 mL) was added (MeCN)2PdCl2
(0.26 g, 1.0 mmol). After stirring at ambient temperature
for 2 h, the solvent was removed in vacuo. The resulting
brown residue was dissolved in CH2Cl2 (30 mL) and fil-
tered through Celite. The Celite was washed with a further
20 mL of CH2Cl2. Recrystallisation from CH2Cl2/diethyle-
ther gave red/brown crystals (0.60 g, 70%) of meso-2.
1H NMR (CDCl3): d 8.25–6.65 (m, 28H, H4–7 and Ph),
4.65 (s, 2H, H3), 3.95 (s, 2H, H2). 13C{1H} NMR (CDCl3):
To a solution of rac-1 (0.48 g, 0.73 mmol) in CH2Cl2
(25 mL) was added a solution of [Rh(COD)2]BF4 (0.15 g,
0.36 mmol) in CH2Cl2 (15 mL) and the resulting solution
stirred at ambient temperature for 3 h. the solvent was
removed in vacuo to leave a brown powder. The crude
product was dissolved in CH2Cl2 (5 mL), Na[BPh4]
(0.123 g, 0.36 mmol) was added and the solution stirred
for 10 min. Diethylether was then added to give a yellow
precipitate which was collected by filtration to yield
0.53 g (80%) of rac-4.
1
1
d 136.8 (t, JPC = 6 Hz, ipso-Ph), 134.5 (t, JPC = 5 Hz,
ipso-Ph), 131.9 (s, o-Ph), 130.6 (o-Ph), 128.4–125.0 (m,
C4, C7, m-Ph and p-Ph), 124.1 (s, C5), 124.1 (s, C6), 91.5
1H NMR (CDCl3): d 7.73–6.80 (m, 48H, H4–7 and Ph),
4.96 (s, 2H, H3), 4.37 (m, 4H, COD-CH), 2.81 (s, 2H, H2),
2.56 (m, 8H, COD-CH2). 13C{1H} NMR (acetone-d6): d
134.2 (m, ipso-Ph), 132.7 (m, ipso-Ph), 130.7 (s, o-Ph),
2
2
(t, JPC = 5 Hz, C3a), 90.9 (t, JPC = 5 Hz, C7a), 82.1 (s,

J.J. Adams et al. / Inorganica Chimica Acta 359 (2006) 3596–3604
3603
130.2 (s, o-Ph), 128.2 (s, p-Ph), 127.8–127.1 (m, C4 and 7,
Acknowledgements
m-Ph and COD-CH), 124.9 (s, C5 or 6), 124.3 (s, C5 or
6), 102.4 (m, C7a or 3a), 97.5 (m, C7a or 3a), 90.7 (d,
We thank New Zealand Lotteries Science for the pur-
chase of precious metals and Dr. Alison J. Downard for
the use of electrochemical equipment.
3
1JPC = 3 Hz, C1), 80.1 (s, C2), 67.4 (t, JPC = 3 Hz, C3),
30.1 (s, COD-CH2). 31P{1H} NMR (CDCl3): d 29.1 (d,
1JPRh = 150 Hz). CV (CH2Cl2): E1/2 = 248 mV, DEP =
88 mV. Mass spectrum (EI, m/z (%)): 865 (100, M+), 511
(20, [(PPh2C9H7)Rh(COD)]+). Anal. Calc. for C74H64-
P2BFeRh: C, 75.02; H, 5.44. Found: C, 74.40; H,
5.70%.
Appendix A. Supplementary materials
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Centre: CCDC No. 287920 for rac-2; CCDC No. 287919
for meso-2; and CCDC No. 287918 for rac-3. Copies of
the information may be obtained free of charge from:
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [fax (int. code): +44 1223 336 033 or by e-mail
at deposit@ccdc.cam.ac.uk or from the www at http://
www.ccdc.cam.ac.uk]. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.ica.2006.02.019.
4.5. Cross-coupling of bromobenzene with Grignard reagents
using rac-2
Grignard preparation: To a suspension of activated mag-
nesium turnings (1.28 g, 52.7 mmol) in THF (30 mL) was
added, dropwise, a solution of chlorobutane (5.50 mL,
52.7 mmol) in THF (60 mL). After initiation, the mixture
was refluxed until the magnesium was consumed. The solu-
tion was cooled to ambient temperature and the concentra-
tion of the Grignard verified by titration.
References
Cross-coupling: To
a
solution of bromobenzene
(4 mmol) and Pd catalyst (0.5–5 mol%) in THF (50 mL)
at ꢀ80 ꢁC, was added the butylmagnesium chloride
(8 mmol). The reaction mixture was allowed to warm to
ambient temperature and stirred for a period of time (1–
18 h) as given in Table 4. The reaction mixture was
quenched with 10% aqueous HCl, and an appropriate
internal standard was added to the organic layer, which
was then analysed by GLC. The organic layer and aqueous
phase washings were combined, washed with saturated
NaHCO3 solution, water, and then dried over MgSO4.
The solvent was evaporated and the resulting oil analysed
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