The coordination behaviour of large natural bite angle diphosphine ligands towards methyl and 4-cyanophenylpalladium(II) complexes

Article abstract of DOI:10.1039/b111596k

The structures of neutral and ionic 4-cyanophenylpalladium(II) and methylpalladium(II) complexes containing bidentate phosphine ligands were investigated in solution and in the solid state. Diphosphine ligands with a xanthene and a ferrocene backbone were used. New bis(dialkylphosphino) substituted Xantphos ligands were synthesised. ¹H NMR and ³¹P NMR spectroscopy, conductivity measurements, UV-Vis spectroscopy, and X-ray crystallography were used to elucidate the structures of the complexes. Subtle changes of the phosphine ligands govern the coordination mode of the ligand. A variety of bidentate cis-, and trans-coordination and terdentate P-O-P, P-S-P and P-Fe-P coordination modes of the ligands were observed.

Full text of DOI:10.1039/b111596k

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The coordination behaviour of large natural bite angle diphosphine
ligands towards methyl and 4-cyanophenylpalladium(II) complexes†
Martin A. Zuideveld,a Bert H. G. Swennenhuis,a Maarten D. K. Boele,a Yannick Guari,a
Gino P. F. van Strijdonck,a Joost N. H. Reek,a Paul C. J. Kamer,a Kees Goubitz,b Jan Fraanje,b
Martin Lutz,c Anthony L. Spekc and Piet W. N. M. van Leeuwen*a
a Institute of Molecular Chemistry, Universiteit van Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands. E-mail: pwnm@science.uva.nl
b Dept. Crystallography, Universiteit van Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands
c Bijvoet Center for Biomolecular Research, Dept Crystal and Structural Chemistry,
Utrecht University Padualaan 8, 3584 CH Utrecht, The Netherlands
Received 20th December 2001, Accepted 11th March 2002
First published as an Advance Article on the web 2nd May 2002
The structures of neutral and ionic 4-cyanophenylpalladium() and methylpalladium() complexes containing
bidentate phosphine ligands were investigated in solution and in the solid state. Diphosphine ligands with a
xanthene and a ferrocene backbone were used. New bis(dialkylphosphino) substituted Xantphos ligands were
synthesised. 1H NMR and 31P NMR spectroscopy, conductivity measurements, UV-Vis spectroscopy, and X-ray
crystallography were used to elucidate the structures of the complexes. Subtle changes of the phosphine ligands
govern the coordination mode of the ligand. A variety of bidentate cis-, and trans-coordination and terdentate
P–O–P, P–S–P and P–Fe–P coordination modes of the ligands were observed.
Introduction
Metal complexes containing chelating phosphine ligands are
active catalysts for a plethora of important reactions.1 The per-
formance of such catalysts is sensitive toward changes in the
ligand environment. In general, steric and electronic properties2
of a ligand strongly influence the rate, the selectivity and the
stability of the catalyst. More recently it has been recognised
that the geometry of ligands around the metal centre also influ-
ences the rate and selectivity of a reaction considerably.3,4
Palladium complexes containing phosphine ligands are
known to catalyse important reactions such as carbon–
carbon5–9 and carbon–heteroatom coupling reactions,10 allylic
substitution reactions,11,12 carbonylation and CO/alkene
copolymerisation reactions.13,14
Basically, all catalytic coupling reactions using chelating
diphosphine ligands proceed via the reaction sequence pre-
Scheme 1 General catalytic cycle of Pd catalysed coupling reactions.
sented in Scheme 1. Firstly, one of the reactants adds oxidatively
to a palladium() species, to form a square planar palladium()
compound. In the next step, a coordination site for the other
substrate has to be created. This vacant site can be created via
dissociation of one of the phosphine moieties or via dissoci-
ation of the anion, XϪ. After coordination of the second
substrate and reductive elimination of the product, the
palladium() species is regenerated. If Y is an alkene, as in
the Heck reaction,15–18 the sequence followed is: insertion,
β-elimination of the product and base-assisted reductive elim-
ination of HX. The reaction pathway depends on the coordinat-
ing and chelating properties of the ligand, the coordinating
properties of XϪ, the substrates and the solvent. Pd() species
are important intermediates in catalytic reactions (Scheme 1)
and have been thoroughly investigated using a wide range of
diphosphine ligands. The crystal structures of (L–L)Pd()-
(alkene) complexes show a large range of P–Pd–P angles from
84.8Њ for (dppe)Pd(dba) to 115.1Њ for (PMe ) Pd(η2-CH ᎐
᎐
2
3
2
CC5Me4), depending on the steric demands of the ligand.19–24
The CO/alkene copolymerisation reaction is a reaction that
proceeds through Pd() intermediates only. The course of the
reaction depends very much on the ligand environment. The use
of monodentate ligands such as triphenylphosphine, which
forms a trans-complex, leads to the selective formation of
methyl propionate. In contrast, the use of cis-chelating diphos-
phine ligands such as 1,2-bis(diphenylphosphino)ethane (dppe)
or 1,3-bis(diphenylphosphino)propane (dppp) produces a high
molecular weight copolymer.13,14
Recently, our group has developed a series of diphosphine
ligands based on xanthene type backbones.25–27 These ligands
were designed to enforce large phosphorus–metal–phosphorus
angles, and have proven to be successful in tuning the activity
and selectivity in the palladium catalysed allylic alkylation,28,29
cross-coupling reaction,30 propionic acid synthesis,31 rhodium
catalysed hydroformylation,25 and the nickel catalysed hydro-
cyanation of alkenes.32 The crystal structures of Pd()-
† Electronic supplementary information (ESI) available: rotatable 3-D
crystal structure diagrams; synthesis details. See http://www.rsc.org/
suppdata/dt/b1/b111596k/
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This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b111596k

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Scheme 2 Ligands used in this study.
Scheme 3 Synthesis of Pd(diphosphine)-complexes 1–6.
(tetracyanoethylene) complexes containing the DPEphos (a),
{[(o-tolyl)3P]Pd(4-C6H4CN)Br}2 with two equivalents of the
Sixantphos (c) and Xantphos (b) ligands have been deter-
mined.33 The widest phosphorus–palladium–phosphorus angle
in these zerovalent palladium complexes containing bidentate
ligands was found to be 104.6Њ.
appropriate diphosphine ligand (Scheme 3).36
The ionic compounds [(L–L)Pd(4-C6H4CN)]ϩ[CF3SO3]Ϫ (4)
were synthesised by salt metathesis of 1 in dichloromethane
with silver triflate. The presence of a coordinating solvent, such
as acetonitrile, was necessary to stabilise the cationic complex
[(L–L)Pd(4-C6H4CN)(CH3CN)]ϩ[CF3SO3]Ϫ (4).37 Compound
4a is not stable and even in the presence of acetonitrile this
complex rapidly decomposes. The other ionic complexes 4 did
not need the stabilisation of a coordinating solvent.
Complexes (L–L)Pd(CH3)(Cl) (L–L = diphosphine ligand, 2)
and (L–L)Pd(CH3)(Br) (3) were prepared by reaction of
(COD)Pd(CH3)(Cl) and (COD)Pd(CH3)(Br) with 1.1 equiv-
alents of the appropriate diphosphine ligand (Scheme 3).38
Ionic complexes [(L–L)PdCH3]ϩ[X]Ϫ (X = CF3SO3 (5),
CF3CO2 (6)) and [(L–L)Pd(CH3)(CH3CN)]ϩ[X]Ϫ (X = CF3SO3
(5), CF3CO2 (6)) were prepared by abstracting the chloride
anion from 2 in dichloromethane–acetonitrile (10 : 1, v/v) using
AgX.38
The effects of Pd() complexes containing ligands inducing
wide bite-angles based on xanthene and ferrocene backbones
on catalysis are not understood completely. Therefore we have
rigorously changed the electronic and steric properties of these
ligands to study the effects on the geometry of the Pd() com-
plexes. In this study we have systematically investigated neutral
and ionic 4-cyanophenylpalladium() and methylpalladium()
complexes in solution and in the solid state. The effects of the
diphosphine ligand, the anion and the methyl and 4-cyano-
phenyl ligands on the structural properties of the palladium
complexes is discussed.
Results
Synthesis
Solution and solid state structures
The syntheses of arylphosphine ligands a–f have been reported
previously (a–f, Scheme 2).25,26,34,35
In view of the flexible ligand properties a variety of coordin-
ation geometries can be envisaged for complexes 1–6 (Scheme
4). To elucidate the structures of the newly synthesised com-
Ligands a-tBu and a-iPr were prepared from the reaction of
2,2Ј-dilithiated diphenyl ether with respectively chlorodi-tert-
butylphosphine and chlorodi-iso-propylphosphine. Ligand
b-Me was prepared by the reaction of methylmagnesium
bromide with 9,9-dimethyl-4,5-bis(dichlorophosphino)xan-
thene. Attempts to synthesise a ligand containing two tert-butyl
groups attached to phosphorus based on the Xantphos back-
bone failed. Neither by starting from the dilithiated backbone,
nor by starting from 9,9-dimethyl-4,5-bis(dichlorophosphino)-
xanthene could the desired ligand be obtained. Probably steric
crowding prevents the coupling of two tert-butyl groups to the
same phosphorus.
1
plexes, H, 13C, 31P NMR spectroscopy, X-ray crystallography,
UV-Vis spectroscopy and conductivity measurements were
performed.
Ligands based on the diphenyl ether backbone. Complex 1a
displays an AB system in the 31P NMR spectra (2JPP = 26.7 Hz)
which implies that the ligand coordinates in a cis fashion to
palladium in solution, similar to previously reported (L–L)-
Pd(Ar)(Br) compounds (cis, neutral, Scheme 4).39–45 Crystals
suitable for X-ray analysis were obtained for compound 1a
from CH2Cl2–hexane (selected data, Table 1). The metal com-
plex has a square planar geometry and the DPEphos ligand in
The neutral complexes (L–L)Pd(4-C6H4CN)(Br) (L–L =
diphosphine ligand, 1a–f ) are readily synthesised by reaction of
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Table 1 Selected bond lengths (Å) and bond angles (Њ) for (L–L)Pd(4-C6H4CN)Br (1a–d) and [(Xantphos)Pd(4-C6H4CN)]ϩ[CF3SO3]Ϫ (4b)
1a
1b
1c
1da
4b
Pd–P1
Pd–P2
Pd–Br
Pd–C1
Pd–O
2.4141(16)
2.2959(17)
2.4709(9)
2.0166(6)
3.441(4)
2.3037(7)
2.3167(7)
2.5339(3)
2.010(3)
2.698(2)
2.2861(16)
2.2916(16)
2.5443(7)
2.006(4)
2.2794(5)
2.2794(5)
2.5580(3)
2.006(3)
2.2912(6)
2.2816(6)
1.966(2)
2.1537(14)
2.714(3)
2.6957(19)
C1–Pd–P2
C1–Pd–P1
P1–Pd–P2
C1–Pd–Br
P2–Pd–Br
P1–Pd–Br
C1–Pd–O
O–Pd–P2
O–Pd–P1
88.82(17)
169.81(17)
100.82(6)
83.24(16)
164.03(5)
88.53(4)
89.73(8)
90.37(8)
150.35(3)
176.12(9)
89.76(2)
89.81(14)
89.94(14)
152.15(5)
178.20(15)
91.18(4)
91.96(2)
91.96(2)
155.05(2)
179.67(10)
87.97(1)
87.97(1)
96.26(7)
96.50(7)
165.15(2)
92.076(19)
89.89(4)
177.63(8)
84.69
83.47(5)
a Compound 1d has crystallographic mirror symmetry.
Scheme 4 Possible geometries for complexes 1–6.
Table 2 Selected bond lengths (Å) and bond angles (Њ) for [(DPE-
phos)Pd(CH3)(CH3CN)]ϩ[CF3SO3]Ϫ (5a) and (DPEphos)PdCH3-
(CF3CO2) (6a)
5a
Pd–P1
Pd–O1
Pd–N
2.443(2)
3.548(5)
2.085(8)
Pd–P2
Pd–C1
2.241(2)
2.076(11)
C1–Pd–P2
C1–Pd–P1
P1–Pd–N
83.1(3)
173.7(3)
89.4(2)
P1–Pd–P2
C1–Pd–N
P2–Pd–N
103.24(7)
84.3(4)
166.9(2)
6a
Pd–P1
Pd–O1
Pd–O2
2.4008(11)
3.531(4)
2.113(3)
Pd–P2
Pd–C1
2.2199(12)
2.092(5)
C1–Pd–P2
C1–Pd–P1
P1–Pd–O2
84.88(15)
173.66(15)
91.01(10)
P1–Pd–P2
C1–Pd–O2
P2–Pd–O2
100.90(4)
83.13(18)
167.90(10)
Fig. 1 Displacement ellipsoid plot of 1a. The ellipsoids are drawn at
the 50% probability level. The hydrogen atoms have been omitted for
clarity.
this complex is chelated in a cis fashion with a P–Pd–P angle of
100.82(6)Њ (Fig. 1).39–45
Suitable crystals of compound 5a for an X-ray analysis were
obtained from CH2Cl2–Et2O (selected data, Table 2). The metal
centre adopts a square planar geometry and the ligand is
coordinated in a cis fashion to palladium (Fig. 2). Acetonitrile
is coordinated to palladium with a Pd–N bond distance of
2.085(8) Å which is similar to other reported N–Pd()
bonds.46,47 The P–Pd–P angle (103.24(7)Њ) is larger than that
observed for its neutral counterparts 1a (100.82Њ) and 6a
(100.90Њ, vide infra). Despite the large bite angle, no out of
plane bending is observed for any of the ligands around the
metal centre.
There is no bonding interaction between palladium and the
oxygen atom of the backbone (d(Pd–O) = 3.441(4) Å). The
analogous ionic Pd(aryl) complex containing the DPEphos
ligand (4a) shows also an AB system in the 31P NMR spectrum
which reflects the cis-coordination. This latter complex, how-
ever, decomposes readily, even in the presence of acetonitrile,
with formation of palladium metal.
The methyl chloride and methyl bromide complexes 2a and
1
3a display a double doublet in the H NMR for the methyl
group and an AB system in the 31P NMR spectra. From this
it can be concluded that the ligand is coordinating in a cis
fashion. Like the ionic arylpalladium complex 4a, the ionic
methylpalladium complex 5a, could only be synthesised in the
presence of acetonitrile. The presence of a coordinating
acetonitrile is confirmed by 1H NMR (δ = 1.79 ppm). The
double doublet in the 31P NMR is in accordance with the
cis-coordination of the ligand in the ionic complex.
The trifluoroacetate complex 6a is also a cis complex in
CH2Cl2 solution as evidenced by the double doublet in the 31P
NMR. In contrast to the complexes with triflate as the counter-
ion, however, this compound is neutral according to conduc-
tivity measurements. Apparently, in CH2Cl2 the trifluoroacetate
anion is coordinated to palladium. When 6a is dissolved in a
dichloromethane–acetonitrile mixture, the compound becomes
ionic as proven by conductivity measurements. Obviously the
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Fig. 2 Displacement ellipsoid plot of 5a. The ellipsoids are drawn at
the 50% probability level. The triflate anion, the non-coordinating
solvent molecule and the hydrogen atoms have been omitted for clarity.
Fig. 3 Displacement ellipsoid plot of 1b. The ellipsoids are drawn at
acetonitrile ligand assists in the dissociation of the trifluoro-
acetate anion from the palladium centre to form compound 5a.
The coordination of the trifluoroacetate anion is confirmed by
X-ray analysis (selected data, Table 2).
The structure of 6a is very similar to that of 1a. The DPE-
phos ligand is coordinated cis to palladium (P–Pd–P angle =
100.90(4)Њ) and the palladium–phosphorus distances are in the
same range. The trifluoroacetate anion is coordinated to pal-
ladium via an oxygen atom of the carboxylate group (Pd–O2 =
2.113(3) Å).
the 50% probability level. The solvent molecule in 1b and the hydrogen
atoms have been omitted for clarity.
square planar geometry. The complexes are neutral and contain
a coordinating bromide anion. The oxygen atom of the ligand
backbone is forced into the apical position and the coordinating
ability of the oxygen atom is obviously not strong enough to
displace the bromide anion to yield an ionic complex. The
structures show a slightly elongated Pd–Br bond (2.53–2.56 Å)
as compared to the cis compounds (Pd–Br = 2.46–2.47 Å). The
dihedral angle between the P–O–P plane and the distorted Pd
square plane is around 77Њ.
The addition of silver triflate to the cis–trans mixtures
resulted in the appearance of one singlet in the 31P NMR spec-
trum, with a chemical shift different from that of the neutral
trans-complexes 1b–e described above. The new complexes 4 are
ionic as proven by conductivity measurements in dichloro-
methane of the isolated complex. Unlike the synthesis of ionic
DPEphos-palladium complexes, the addition of acetonitrile
was not necessary to stabilise the cations. The 1H and 31P NMR
spectra of the ionic complexes 4 did not change when a more
polar solvent such as acetonitrile was added to a CDCl3 solu-
tion of these compounds. Suitable crystals for an X-ray analysis
of 4b were obtained from CH2Cl2–hexane (selected data, Table
1). Complex 4b shows a square planar geometry (Fig. 4). In
the ionic complex the Xantphos ligand coordinates in the
same fashion as 1,8-bis(diphenylphosphino)anthracene.49 The
phosphorus atoms are trans-coordinated (P–Pd–P angle =
165.15(2)Њ) and the Pd–P distances of both phosphorus atoms
are similar (Pd–P1 = 2.2912(6) and Pd–P2 = 2.2816(6) Å). The
oxygen atom of the Xantphos ligand is coordinated to the
metal centre (Pd–O distance = 2.1537(14) Å).31
The complexation behaviour of dialkylphosphine substituted
DPEphos ligands differs from the diphenylphosphine substi-
tuted DPEphos ligand. Complex 2a-tBu, possessing tert-Bu
groups at the phosphorus atoms, shows a singlet in the 31P
1
NMR spectrum (48.3 ppm) and a triplet for PdCH3 in the H
NMR spectrum indicative of a trans-compound (1.44 ppm,
3JPH = 5.1 Hz). Complex 5a-tBu showed the same NMR charac-
teristics. Since both compounds 5a-tBu and 2a-tBu are ionic
according to conductivity measurements, we propose that these
complexes contain a palladium–oxygen bond. In contrast, the
methylpalladium chloride complex 2a-iPr shows NMR charac-
teristics that are very different from the ionic analogue, 5a-iPr,
viz. a singlet in the 31P NMR for the former complex and a
double doublet for the latter compound. Furthermore, complex
2a-iPr is neutral whereas 5a-iPr is ionic. From this we conclude
that in 2a-iPr the ligand is coordinated in a cis fashion, whereas
in complex 5a-iPr the ligand is coordinated in a trans fashion
and a palladium–oxygen bond is present.
Ligands based on xanthene-type backbones. A broadened
singlet in the 31P NMR spectra was observed for compounds
1b–1d at room temperature. An AB system (minor compound)
and a sharp singlet (major compound) appeared at low temper-
atures (Ϫ40 ЊC). From this observation we concluded that in
solution cis–trans isomerisation takes place at room temper-
ature on the NMR time-scale. The cis–trans equilibrium lies
at the side of the trans-compound for 1b–d. Conductivity
measurements in dichloromethane solution showed that these
complexes are neutral. Crystals of 1b–d suitable for an X-ray
analysis were obtained from CH2Cl2–hexane (selected data,
Table 1).
In the solid state, complexes 1b–d, show trans-coordination
modes (trans, neutral, Scheme 4) with P–Pd–P angles which are
in the same range (150.4–155.0Њ, 1b, in Fig. 3). The Pd–P dis-
tances are similar (2.28–2.32 Å) and the Pd–O distances (≈2.7
Å) are in the same range as for a five-coordinate palladium
complex reported by Cavell et al.48 A weak Pd–O bonding
interaction seems to be present. All complexes have a distorted
The methylpalladium complexes containing the xanthene
1
diphosphine ligands 2b–d show broad signals in H NMR and
in 31P NMR spectra at room temperature. At low temperatures
1
(below Ϫ60 ЊC) sharp signals were obtained. The H and 31P
NMR spectra of 2d at different temperatures are shown in
Fig. 5.
In the 31P NMR spectra at low temperature (Ϫ60 ЊC), com-
plex 2c shows an AB system only, whereas complexes 2d, 2b and
3b show an AB system (major compound) and a singlet. The 1H
NMR spectra show a double doublet and a triplet for the
methyl group bonded to palladium. The integration ratio of
the AB system and the singlet in the 31P NMR spectra match
the double doublet to triplet ratio in the 1H NMR spectra. The
chemical shifts of singlets of these compounds do not match
with the shifts of the analogous ionic compounds 5b–d (vide
infra). Furthermore, compounds 2c and 2d did not show
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Table 3 Selected bond lengths (Å) and bond angles (Њ) for (Xantphos)-
Pd(CH3)Cl (2b)
2b
Pd–P1
Pd–Cl
2.2949(16)
2.4290(15)
Pd–P2
Pd–C1
2.2916(15)
2.107(7)
Pd–O
2.658(4)
91.39(19)
92.02(19)
88.82(5)
P1–Pd–P2
C1–Pd–Cl
P2–Pd–Cl
152.61(6)
174.85(19)
90.20(5)
C1–Pd–P2
C1–Pd–P1
P1–Pd–Cl
mixture of CD2Cl2 and CD3CN the equilibrium shifted towards
the cis-complex. The signals in the 31P NMR spectra broaden
upon addition of CD3CN. Lowering the temperature of the
solution results in a sharpening of the signals.
Suitable crystals of 2b for X-ray analysis were obtained from
CH2Cl2–Et2O (selected data, Table 3) The structure of 2b is
similar to compounds 1b–1d. The metal centre adopts a
square planar geometry, and the ligand coordinates in a trans
fashion (P–Pd–P angle = 152.61(6)Њ, Table 3). The palladium–
phosphorus distances are of the same magnitude (Pd–P1 =
2.2949(16) and Pd–P2 = 2.2916(15) Å).
Fig. 4 Displacement ellipsoid plot of 4b. The ellipsoids are drawn at
the 50% probability level. The triflate anion, the solvent molecule and
the hydrogen atoms have been omitted for clarity.
Palladium complexes containing the Thioxantphos ligand, e
are different from the ligands containing oxygen in their ligand
backbone. Compound 1e shows a singlet in the 31P NMR spec-
trum both at 25 ЊC and Ϫ60 ЊC. The addition of silver triflate to
1e did not lead to a change in chemical shift of the singlet,
which suggests that the bromide complex is already ionic. The
methylpalladium complexes show a similar behaviour. Complex
2e gives a singlet in the 31P NMR spectrum (40.5 ppm) and a
1
3
triplet for PdCH3 in the H NMR spectrum (1.08 ppm, JPH
=
8.5 Hz) at room temperature, indicative of a trans-complex. The
NMR spectra did not change when silver triflate was added to a
solution of 2e in CDCl3. The Thioxantphos complexes 1e, and
2e have a molar conductivity in the same range as the ionic
complexes, showing that the bromide and chloride anion are
substituted by the sulfur donor atom in the ligand backbone.
Compound 2b-Me is a pure cis-complex according to the AB
system in the 31P NMR spectrum (Ϫ9.0 ppm and Ϫ13.5 ppm, d,
2JPP = 34.3 Hz). This is confirmed by the double doublet for
3
3
1
PdCH3 (0.66 ppm, JPH = 4.6 Hz and JPH = 7.7 Hz) in the H
NMR spectrum. The triflate analogue 5b-Me, however, turned
out to be a trans-complex. The singlet in the 31P NMR spectrum
1
(Ϫ5.0 ppm), the triplet in the H NMR spectrum (1.21 ppm,
3JPH = 6.6 Hz) and the high molar conductivity confirm that this
is a trans compound and presumably contains a Pd–O bond
analogous to 2b.
Ligands based on the ferrocene-type backbones. Previous
studies showed that dppf behaves generally as a cis-coordin-
ating ligand in methylpalladium() compounds.38 We studied
the complexation behaviour of dialkylphosphine substituted
ferrocene ligands in methylpalladium() complexes. All com-
pounds containing ligand f-tBu (1,1Ј-bis(di-tert-butylphos-
phino)ferrocene), compounds 2f-tBu, 5f-tBu and 6f-tBu, yield
complexes which show a singlet in the 31P NMR spectra (29.3
ppm) and a triplet in the 1H NMR spectra for the PdCH3 group
(1.70 ppm, 3JPH = 4.8 Hz).50 These observations support a trans-
geometry of the ligand in these complexes. The large chemical
shift difference between the α and the β hydrogen atoms of the
cyclopentadienyl rings in the complexes (1.0–1.3 ppm) in com-
parison with the differences in the free ligand (0.14 ppm) indi-
cate that these rings are slightly tilted.51 Such NMR character-
istics indicate that an interaction between palladium and iron is
present in solution. UV-Vis spectra, however, showed only one
absorption around 349 nm, absorptions at higher wavelengths,
typical of Pd–Fe interactions,51 were not observed.
Fig. 5 Variable temperature 1H and 31P NMR spectra of (Thixant-
phos)Pd(CH3)Cl (2d) in CDCl3 from Ϫ60 ЊC to ϩ40 ЊC.
conductivity in CH2Cl2. In contrast, the Xantphos complexes
2b and 3b, showed a molar conductivity of 3.5 and 4.6 S cmϪ2
molϪ1 respectively. Based on this, we assign the signals to the
neutral, cis and the neutral, trans complexes (Scheme 4).
The effect of changing the temperature on the ratio of cis-
compound over trans-compound could only be investigated
over a narrow temperature range (Ϫ90 to Ϫ50 ЊC) due to line-
broadening in the NMR spectra. Over this temperature range,
the ratios do not change.
The complex with the bromide anion, 3b, contains a larger
amount of the trans-compound than the chloride complex, 2b
(cis : trans = 0.90 (3b), 0.52 (2b). When 3b was dissolved in a
Crystals of 5f-tBu suitable for an X-ray analysis were
obtained from CH2Cl2–Et2O (selected data, Table 4). The metal
2312
J. Chem. Soc., Dalton Trans., 2002, 2308–2317

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Table 4 Selected bond lengths (Å) and bond angles (Њ) for [(dtpf )-
PdCH3]ϩ[CF3SO3]Ϫ (5f-tBu)
3.6 Hz). Molecular weight determination in solution showed
that the new compound, 8, is a monomeric cis-compound
analogous to 2f and 2f-iPr.
5f-tBu
Pd–P1
Pd–Fe
2.2862(5)
3.0683(3)
Pd–P2
Pd–C1
2.2979(5)
2.035(3)
Discussion
Neutral complexes containing the DPEphos ligand are cis-
coordinated and show no sign of a palladium–oxygen inter-
action, irrespective of the other coordinating groups. This may
be caused by the preference of the DPEphos ligand for a
smaller bite angle than the other ligands in the Xantphos-
series.25,53 Ionic complexes containing the DPEphos ligand need
a coordinating solvent to stabilise the ionic metal centre. Only
at low temperatures was the cation possessing a palladium–
oxygen bond observed. In the absence of coordinating solvents
DPEphos has the tendency to form a palladium–oxygen bond,
which shows the strength of such a bonding interaction and the
capability of the ligand to coordinate in a trans-fashion. The
crystal structures of complexes with the DPEphos ligand show
that the two phenyl rings of the ligand backbone can rotate
around the carbon–oxygen bond. One of the phenyl rings of
the ligand backbone has a π–π interaction with one of the
phenyl rings bonded to the phosphorus atom. Similar inter-
actions have been reported before in MeO-Biphep metal com-
plexes.54 The bulkiness of the substituents on the phosphorus
atoms is important. tert-Butyl groups on phosphorus (ligand a-
tBu) probably destabilise the cis complex, thus forcing the com-
plex to an ionic trans complex containing a palladium–oxygen
bond. The cis-complexes cannot be formed due to steric crowd-
ing around the metal centre. This is confirmed by the less
crowded iso-propyl substituted ligand, a-iPr, which indeed
coordinates in a cis-fashion. The strength of the palladium–
oxygen bond is illustrated by the fact that in the methyl-
palladium chloride complex, 2a-tBu, the chloride anion is
displaced from the metal centre.
The solid state structures of complexes 1b–d and 2b, which
contain ligands having large bite angles, show that the oxygen
atom of the P–O–P ligand backbone in the trans-complexes is
located at the apical position of the square pyramidal complex.
The weak palladium–oxygen interaction can stabilise the trans-
complex relative to the cis-complex, which lacks such a bonding
interaction. Equilibrium mixtures of the arylpalladium com-
plexes (1b–d) in solution consist mainly of the trans-complex,
whereas the methylpalladium complexes (2b–d) are mainly cis-
coordinated complexes. Three reasons can account for these
observations. The more electron-withdrawing aryl group results
in less electron density at the metal centre. The apical oxygen
atom will therefore coordinate more strongly in the aryl-
palladium complex 1 than in the more electron rich methyl-
palladium complex 2. Furthermore, the π–π interaction between
the phenyl groups on phosphorus and the aryl group attached
to the palladium centre can stabilise the trans-complex relative
to the cis-complex, as such an interaction is absent in methyl-
palladium complexes. In cis-complexes the phenyl rings bonded
to phosphorus cannot be oriented in such a way that a π–π
interaction with the 4-cyanophenyl group is possible due to the
rigidity of the ligand backbone. The methylpalladium com-
plexes lack such a stabilisation and therefore are mainly present
as cis-complexes. A second difference between the methyl-
palladium complexes 2 and the arylpalladium complexes 1 are
the halogen ligands. The methylpalladium complexes contain
chloride ligands, the arylpalladium complexes bromide ligands.
A cis-coordination of the diphosphine ligand would be
relatively more stabilised in complexes containing the smaller
chloride ligands than in complexes containing the larger
bromide ligands.
P–Pd–P
C1–Pd–P1
P1–Pd–Fe
158.21(2)
100.76(7)
79.19(1)
P2–Pd–C1
P2–Pd–Fe
Fe–Pd–C1
100.65(7)
79.47(1)
178.97(8)
Fig. 6 Displacement ellipsoid plot of 5f-tBu. The ellipsoids are drawn
at the 50% probability level. The triflate anion and the hydrogen atoms
have been omitted for clarity.
centre in 5f-tBu adopts a square planar geometry (Fig. 6). Like
the Xantphos ligand in 4b (vide supra), the ferrocene ligand in
5f-tBu behaves as a terdentate ligand. The phosphorus atoms
are trans-coordinated (P–Pd–P angle = 158.21(2)Њ) and the iron
atom of the ligand backbone has a weak interaction with the
palladium centre (Pd–Fe distance = 3.0683(3) Å). Pd–Fe bonds
were found previously in dicationic complexes,51,52 but this is the
first example of a monocationic methylpalladium compound
with a palladium–iron bond. The interatomic Pd–Fe distance
in complex 5f-tBu is larger than other Pd–Fe bonds, such
as [(dppf )Pd(PPh3)][BF4]2 (2.88 Å)51 and [(1,5,9-trithia[9]-
ferrocenophane)Pd(CH3CN)][BF4]2 (2.83 Å)52 which have been
reported by Sato et al., but it is in the same range as that in
[(1,4,7-trithia[7]ferrocenophane)Pd(CH3CN)][BF4]2 (3.10 Å).52
The Pd–P distances are in the range generally found for trans-
coordinating phosphorus atoms (e.g. complexes 1c–e and 4b
(Pd–P1 = 2.2862(5) and Pd–P2 = 2.2979(5) Å)).
The complexes containing ligand f-iPr (1,1Ј-bis(di-iso-
propylphosphino)ferrocene) show NMR characteristics that
are similar to those of the dppf ligand, f. The ionic complex 5f-
iPr shows an AB system in the 31P NMR spectrum (54.1 and
32.7 ppm, 2JPP = 21.3 Hz) and a double doublet in the 1H NMR
spectrum for PdCH3 (0.73 ppm, 3JPH = 4.8 Hz and 3JPH ≈ 1 Hz).
1
According to H NMR spectroscopy, acetonitrile is coordin-
ated to the palladium centre. The singlet in the 31P NMR spec-
trum (4.5 ppm) for the methylpalladium chloride complex 7
(ligand f-Et), the triplet for PdCH3 (0.51 ppm, 3JPH = 5.9 Hz) in
the 1H NMR spectrum and the large chemical shift differences
between the α and β hydrogen atoms of the cyclopentadienyl
rings in the complex (0.75 ppm), suggest a similar coordination
as observed for complex 2f-tBu. Molecular weight determin-
ation in solution, however, showed that 7 is a dimeric com-
pound. When a solution of 7 was allowed to stand at room
temperature in CD2Cl2, a slow reaction occured. A new AB
system appeared in the 31P NMR spectrum (30.1 and 10.7 ppm,
2JPP = 28.2 Hz) and a double doublet for the methyl group
The alkylphosphine ligand b-Me forms a cis-complex only.
The higher electron density on palladium makes a bonding
palladium–oxygen interaction less favourable and therefore the
trans-complex is not observed.
1
3
3
appeared in the H NMR (0.75 ppm, JPH = 7.5 Hz and JPH
=
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Another possible effect of the proximity of the oxygen atom
to the palladium centre may be the stabilisation of an ionic
intermediate that can be formed during the interchange from
the cis- to the trans-complexes (Scheme 5). Only in the case of
observed than those originating from the ferrocene unit. The
solid state structure of 5f-tBu has been determined and this
clearly shows the existence of a palladium–iron interaction, but
the NMR spectra of 2f-tBu and 6f-tBu show the same charac-
teristics in solution as 5f-tBu. These complexes show a large
chemical shift difference between the α and β hydrogens of the
cyclopentadienyl ligand. The methylpalladium chloride com-
plex 2f-tBu is ionic in dichloromethane solution, which indi-
cates that the chloride anion is no longer bonded to palladium
and the fourth coordination site is probably occupied by iron.
These observations indicate that in these complexes a weak Pd–
Fe interaction is present as well (Scheme 6). The main difference
between the complexes described here and the ones described
by Sato, is that the latter complexes are dicationic. The differ-
ence in electrophilicity of the palladium centre can account for
the differences in the UV-Vis spectra. The bulkiness of the
ligand (large tert-butyl groups) hampers a cis-coordination to
palladium. Because the phosphorus atoms are positioned trans,
the iron atom is forced into the proximity of the palladium
centre enforcing the iron–palladium interaction. The slightly
less bulky iso-propyl ligand, f-iPr, leads to the normal cis-
coordination. No spectroscopic evidence was found for a
palladium–iron interaction. The same was observed by Butler
et al. in the crystal structure of (dipf )PdCl2.56 The even less
bulky substituted diphosphine ligand f-Et yields a different
complex again (Scheme 6). The 1H NMR chemical shift differ-
ence of the α and β hydrogens is large, which indicates that
cyclopentadienyl rings are tilted and this suggests the presence
of a palladium–iron bonding interaction. In addition, a triplet
for the methyl group is observed. The large chemical shift
Scheme 5 Possible pathway for cis–trans isomerisation.
complexes 2b and 3b could a significantly higher conductivity
be measured, which would suggest the presence of such an ionic
intermediate; this could, however, not be verified using NMR
spectroscopy. The addition of
a more polar co-solvent
(acetonitrile) to a solution of 3b in dichloromethane led to an
increase of the amount of cis-complex. The polar solvent stabil-
ises the more polar cis-complex. The rate of interconversion
between the cis- and trans-complexes was higher in the more
polar solvent, which could be caused by the stabilisation of the
ionic intermediate (Scheme 5). The molar conductivities of
complex 1e and 2e are of the same magnitude as that of the
complexes with triflate as the counter-ion, which means that the
bromide and chloride anion are not coordinated to the metal
centre. In these complexes the bromide and chloride anions are
substituted by the sulfur ligand of the ligand backbone.55 The
soft sulfur atom can displace the coordinated anions, since it
can bind more strongly to the soft palladium metal centre than
the hard oxygen atom. Addition of acetonitrile or coordinating
anions (chloride or bromide anions) to solutions of ionic com-
plexes having a Pd–O or Pd–S bond did not affect the structure
of the complexes. Such additives apparently cannot compete
with the intramolecular Pd–O and Pd–S bonds.
1
difference between the PdCH3 signals in the H NMR spectra
(1.70 ppm for 2f-tBu and 0.51 ppm for 7) and the low molar
conductivity, indicative of a neutral complex, suggest that a
different complex is formed. Molecular weight determination
in solution proved that 7 is a dimeric compound, analogously
to the previously reported compound [(dppm)Pd(CH3)Cl]2.57
The formation of a dimer is surprising if we consider that
the ligands in compound 2f and 2f-iPr,38 are cis-chelating. The
observation of the slow formation of the monomeric cis-
complex, 8, in dichloromethane solution provided an answer to
this dilemma (Scheme 6).57 Obviously, the dimer is formed as
the kinetic product during the synthesis in benzene, whereas the
cis-complex is the thermodynamically favoured compound.
It has been shown that the iron atom of dppf can coordinate
to palladium and that these complexes which contain a
palladium–iron bond are generally strongly coloured.51,52 The
complexes described in this study, however, are not strongly
coloured and in the visible range no other absorptions were
Scheme 6 Synthesis of Pd-complexes using the ligands f-tBu, f-iPr and f-Et.
2314
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reflections were measured on an Enraf-Nonius CAD4T dif-
Conclusions
fractometer with a rotating anode (λ = 0.71073 Å) at a temper-
ature of 150(2) K. 6143 reflections were unique (Rint = 0.0401).
Absorption correction with PLATON58 (DELABS, µ = 1.799
mmϪ1, 0.57–0.87 transmission). Structure solved with Patterson
methods (DIRDIF-97)59 and refined with SHELXL-9760
against F 2 of all reflections. Non-hydrogen atoms were refined
freely with anisotropic displacement parameters. Hydrogen
atoms were refined as rigid groups. 442 refined parameters, no
restraints. R-values [I > 2σ(I )]: R1 = 0.0508, wR2 = 0.0840.
R-values [all reflections]: R1 = 0.1006, wR2 = 0.0988. Molecular
illustration, structure checking and calculations were per-
formed with the PLATON package.58
Solid state and solution structures of palladium() complexes
bearing diphosphine ligands based on the diphenyl ether,
xanthene and ferrocene backbone have been studied. Subtle
changes in the steric and electronic properties of the diphos-
phine ligands and the electron density on the palladium
metal influence the structure of the palladium complexes
dramatically.
Experimental
Ligand synthesis
The synthesis of all ligands is described in the ESI.
Crystal structure determination of 1b. C48H36BrNOP2Pdؒ0.58
CH2Cl2, FW = 916.27, red–brown plate, 0.28 × 0.22 ×
0.08 mm3, monoclinic, P21/c (no. 14), a = 21.8648(2), b =
10.0742(1), c = 22.7549(2) Å, β = 119.142(1)Њ, V = 4377.76(7) Å3,
Z = 4, ρ = 1.390 g cmϪ3. 78748 reflections were measured on a
Nonius KappaCCD diffractometer with a rotating anode (λ =
0.71073 Å) at a temperature of 150(2) K. 10040 reflections were
unique (Rint = 0.0517). Analytical absorption correction with
PLATON58 (µ = 1.515 mmϪ1, 0.67–0.89 transmission). Struc-
ture solved with Patterson methods (DIRDIF-97)59 and refined
with SHELXL-9760 against F 2 of all reflections. Non-hydrogen
atoms were refined freely with anisotropic displacement
parameters. Hydrogen atoms were refined as rigid groups. 525
refined parameters, 7 restraints. R-values [I > 2σ(I )]: R1 =
0.0357, wR2 = 0.1201. R-values [all reflections]: R1 = 0.0396,
wR2 = 0.1233. Molecular illustration, structure checking and
calculations were performed with the PLATON package.58
Complex synthesis
General remarks. The alkylphosphine ligands used in com-
plex synthesis were used in a larger excess in cases where the
ligand had partially oxidised prior to use. The oxidised alkyl-
phosphine ligands did not coordinate to palladium. Palladium
complexes containing bidentate alkylphosphine ligands could
be handled and stored under ambient conditions.
The detailed syntheses of the complexes are described in the
ESI.
Synthesis of (L–L)Pd(4-C6H4CN)Br (1). A solution of
{[(o-tolyl)3P]Pd(4-C6H4CN)Br}2 (300 mg; 0.25 mmol) and
diphosphine (0.50 mmol, 2.0 equiv.) in dichloromethane (10
mL) was allowed to react overnight at room temperature. The
solution was concentrated in vacuo to ca. 5 mL. Then, 10 mL of
diethyl ether was added which resulted in the formation of
orange crystals. The suspension was filtered and the crystals
dried in vacuo.
Crystal structure determination of 1c. C45H36BrNOP2PdSiؒ
2CH2Cl2, FW = 1052.94, colourless plate, 0.50 × 0.38 × 0.13
mm3, monoclinic, P21/c (no. 14), a = 21.781(3), b = 10.5595(13),
c = 22.522(4) Å, β = 119.206(13)Њ, V = 4521.5(12) Å3, Z = 4,
ρ = 1.547 g cmϪ3. 18205 reflections were measured on an Enraf-
Nonius CAD4T diffractometer with a rotating anode (λ =
0.71073 Å) at a temperature of 150(2) K. 10315 reflections were
unique (Rint = 0.0544). Absorption correction with PLATON58
(DELABS, µ = 1.665 mmϪ1, 0.55–0.86 transmission). Structure
solved with direct methods (SIR97)61 and refined with
SHELXL-9760 against F 2 of all reflections. Non-hydrogen
atoms were refined freely with anisotropic displacement
parameters. Hydrogen atoms were refined as rigid groups. 523
refined parameters, no restraints. R-values [I > 2σ(I )]: R1 =
0.0527, wR2 = 0.1021. R-values [all reflections]: R1 = 0.1077,
wR2 = 0.1256. Molecular illustration, structure checking and
calculations were performed with the PLATON package.58
Synthesis of (L–L)Pd(CH3)Cl (2). To a solution of 0.36 mmol
(COD)Pd(CH3)Cl in 5 mL of benzene, 0.37 mmol (1.05 equiv.)
of ligand (L–L) was added. The solution was stirred for one
hour. The suspension was filtered and the residue was washed
with benzene and diethyl ether. The product was dried in vacuo.
Synthesis of (L–L)Pd(CH3)Br (3). To a solution of 0.36 mmol
(COD)Pd(CH3)Br in 5 mL of benzene, 0.37 mmol (1.05 equiv.)
of ligand (L–L) was added. The solution was stirred for one
hour. The suspension was filtered and the residue was washed
with benzene and diethyl ether. The product was dried in vacuo.
Synthesis of [(L–L)Pd(4-C6H4CN)]؉[CF3SO3]؊ and [(L–L)-
Pd(4-C6H4CN)(CH3CN)]؉[CF3SO3]؊ (4).
A solution of 1
(0.18 mmol) and silver triflate (0.18 mmol) in 10 mL of
CH2Cl2–CH3CN (10 : 1, v/v) was stirred in the dark for one
hour. A suspension of Norit in 5 mL of CH2Cl2 was added and
the reaction mixture was stirred for another hour. The suspen-
sion was filtered and the filtrate was concentrated under
vacuum to ca. 5 mL. 10 mL of diethyl ether was added resulting
in the formation of colourless crystals. The suspension was
filtered and the crystals were dried in vacuo.
Crystal structure determination of 1d. C45H34BrNOP2PdSؒ
CH2Cl2, FW = 969.97, yellow plate, 0.27 × 0.27 × 0.09 mm3,
orthorhombic, Pnma (no. 62), a = 18.4791(1), b = 15.1534(1),
c = 14.9257(1) Å, V = 4179.51(5) Å3, Z = 4, ρ = 1.541 g cmϪ3
.
75073 reflections were measured on a Nonius KappaCCD dif-
fractometer with a rotating anode (λ = 0.71073 Å) at a temper-
ature of 150(2) K. 4971 reflections were unique (Rint = 0.0591).
Absorption correction with PLATON58 (MULABS, µ = 1.691
mmϪ1, 0.77–0.86 transmission). Structure solved with Patterson
methods (DIRDIF-97)59 and refined with SHELXL-9760
against F 2 of all reflections. Non-hydrogen atoms were refined
freely with anisotropic displacement parameters. Hydrogen
atoms were refined as rigid groups. 523 refined parameters, no
restraints. R-values [I > 2σ(I )]: R1 = 0.0267, wR2 = 0.0675.
R-values [all reflections]: R1 = 0.0307, wR2 = 0.0693. Molecular
illustration, structure checking and calculations were per-
formed with the PLATON package.58
Synthesis of ionic methylpalladium complexes (5 and 6).
0.190 mmol 2 was suspended in 2 mL of CH2Cl2–CH3CN
(10 : 1, v/v). 0.191 mmol of AgX (X = CF3SO3, CF3CO2) was
added to the suspension. After stirring for 10 minutes, the sus-
pension was filtered over Celite. Then 10 mL diethyl ether was
added to crystallise the product.
Crystallography
Crystal structure determination of 1a. C43H32BrNOP2Pd, FW
= 826.95, yellow needles, 0.25 × 0.13 × 0.13 mm3, monoclinic,
P21/c (no. 14), a = 20.308(2), b = 10.5695(19), c = 16.309(2) Å,
β = 90.245(9)Њ, V = 3500.6(8) Å3, Z = 4, ρ = 1.569 g cmϪ3. 6387
Crystal structure determination of 2b. C40H35OP2ClPdؒ
C4H10O, FW = 735.5, yellow cube, 0.20 × 0.40 × 0.60 mm3,
J. Chem. Soc., Dalton Trans., 2002, 2308–2317
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monoclinic, P21/n, a = 12.7823(9), b = 17.954(1), c = 16.961(2)
Å, β = 93.290(5)Њ, V = 3886.0(6) Å3, Z = 4, ρ = 1.380 g cmϪ3
structure checking and calculations were performed with the
PLATON package.58
.
7967 reflections were measured on an Enraf-Nonius CAD-4
diffractometer (λ = 1.5418 Å) at room temperature. Analytical
absorption correction with the program ABSCAL (Waten-
paugh and Stewart, 1992) using ψ-scans of the [Ϫ2 6 3] reflec-
tion, with coefficients in the range 1.0–3.04. The structure was
solved with the PATTY option of the DIRDIF-96 program
system.62 Non-hydrogen atoms were refined freely with aniso-
tropic displacement parameters. Hydrogen atoms were calcu-
lated. R-values: [(∆/σ)max = 0.27, S = 0.93] a weighting scheme
w = [10 ϩ 0.001(σ(Fobs))2 ϩ 0.0001/(σ(Fobs))]Ϫ1 was used (R =
0.061, Rw = 0.064. All calculations were performed with
XTAL,63 unless stated otherwise.
Crystal structure determination of 6a. C39H31O3F3P2Pd,
FW = 772.98, colourless cube, 0.30 × 0.40 × 0.50 mm3, triclinic,
P1, a = 10.976(1), b = 11.516(1), c = 15.503(5) Å, α = 98.14(1),
¯
β = 97.05(1), γ = 113.89(1)Њ, V = 1738.2(7) Å3, Z = 2, ρ = 1.48 g
cmϪ3. Final R = 0.078 for 6886 observed reflections. 7751 reflec-
tions were measured on a Enraf-Nonius CAD-4 diffractometer
(λ = 1.5418 Å) at room temperature. Absorption correction
was performed with the program PLATON58 following the
method of North et al. using ψ-scans of five reflections, with
coefficients in the range 0.630–0.978. The structure was solved
by the PATTY option of the DIRDIF-96 program system.62
Non-hydrogen atoms were refined freely with anisotropic dis-
placement parameters. Hydrogen atoms were refined as rigid
groups. The trifluoromethyl group was refined with a disorder
model. R-values: [(∆/σ)max = 0.02, S = 1.05] a weighting
scheme w ≥ [σ2(Fobs2) ϩ (0.1266P)2 ϩ 2.7287P]Ϫ1 was used
(R = 0.0642, wR2 = 0.1761 for I > 2σ(I )). All calculations were
performed with SHELXL-9760 unless stated otherwise.
CCDC reference numbers 133392–133394 and 177711–
177716.
Crystal structure determination of 4b. C46H36BrNOP2Pdؒ
CF3SO3ؒCH2Cl2, FW = 1021.09, colourless block, 0.33 × 0.33 ×
0.24 mm3, monoclinic, P21/n (no. 14), a = 13.2554(10), b =
22.3413(10), c = 15.0667(10) Å, β = 91.984(10)Њ, V = 4459.2(10)
Å3, Z = 4, ρ = 1.521 g cmϪ3. 82840 reflections were measured on
an Nonius KappaCCD diffractometer with a rotating anode
(λ = 0.71073 Å) at a temperature of 150(2) K. The crystal
appeared to be non-merohedrically twinned with a two-fold
rotation around a* as the twin operation. The evaluation of the
data was performed with the program EVAL1464 and the reflec-
tions were not merged. No absorption correction was applied.
The structure was solved by Patterson methods (DIRDIF-97)59
and the non-overlapping reflections. The twin refinement was
performed with SHELXL-9760 against F 2 of all reflections
using the HKLF5 option.65 Non-hydrogen atoms were refined
freely with anisotropic displacement parameters. Hydrogen
atoms were refined as rigid groups. 555 refined parameters, 62
restraints. R-values [I > 2σ(I )]: R1 = 0.0749, wR2 = 0.1941.
R-values [all reflections]: R1 = 0.0956, wR2 = 0.2163. Molecular
illustration, structure checking and calculations were per-
formed with the PLATON package.58
See http://www.rsc.org/suppdata/dt/b1/b111596k/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
This work was supported (M. L., A. L. S.) by the Council
for Chemical Sciences of the Netherlands Organisation for
Scientific Research (CW–NOW) and by the Netherlands
Ministry of Economic Affairs (grant EETK9710) (M. D. K. B.,
G. P. F. v. S.) The help of A. M. M. Schreurs in handling the
twinned structure 4b is kindly acknowledged.
References
Crystal structure determination of 5a. C39H34NOP2Pdؒ
CF3SO3, FW = 850.1, colourless cube, 0.20 × 0.25 × 0.30 mm3,
monoclinic, P21/n, a = 10.8261(6), b = 26.801(2), c = 13.8267(8)
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Crystal structure determination of 5f-tBu. C27H47FeP2Pdؒ
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monoclinic, P21/c (no. 14), a = 11.7515(1), b = 16.9323(2),
c = 16.8170(2) Å, β = 105.8589(6)Њ, V = 3218.88(6) Å3, Z = 4,
ρ = 1.537 g cmϪ3. 53974 reflections were measured on a Nonius
KappaCCD diffractometer with a rotating anode (λ = 0.71073
Å) at a temperature of 150(2) K. 7369 reflections were unique
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=
0.0459). Absorption correction with PLATON58
(MULABS, µ = 1.218 mmϪ1, 0.75–0.82 transmission). Structure
solved with Patterson methods (DIRDIF-97)59 and refined
with SHELXL-9760 against F 2 of all reflections. Non-hydrogen
atoms were refined freely with anisotropic displacement param-
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placement parameters. 540 refined parameters, no restraints.
R-values [I > 2σ(I )]: R1 = 0.0249, wR2 = 0.0561. R-values [all
reflections]: R1 = 0.0323, wR2 = 0.0587. Molecular illustration,
2316
J. Chem. Soc., Dalton Trans., 2002, 2308–2317

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