Sterically hindered electron-withdrawing ligands: The reactions of N-carbazolyl phosphines with rhodium and palladium centres

Article abstract of DOI:10.1039/b408841g

The series of N-carbazolyl phosphines PPh_3-n(NC ₁₂H₈)_n (n = 1, L¹; n = 2, L ²; n = 3, L³) has been synthesised using BuLi to generate the N-carbazolyl lithium salt, followed by reaction with the appropriate chlorophosphine. The reactions between [Rh(μ-Cl)(CO)₂]₂ and four equivalents of L¹ or L² gave [RhCl(CO)(L ¹)₂] 1 and [RhCl(CO)(L²)₂] 2, though attempts to synthesise the analogous complex using L³ resulted in the formation of [Rh(μ-Cl)(CO)(L³)]₂ 3 instead. The inability of L³ to cleave the chloride bridges can be related to its considerable steric requirements. The electronic properties of L^1-3 were assessed by comparison of the (CO) values of the [Rh(acac)(CO)(L ^1-3)] complexes 4-6. The increase in number of N-carbazolyl substituents at the phosphorus atom results in a decrease of the σ-donor and increase in the π-acceptor character in the order L¹ < L² < L³. In the reactions of L^1-3 with [PdCl₂(cod)] only L¹ was able to displace cod from the metal centre and form [PdCl₂(L¹)₂] 7. The use of [PdCl₂(NCMe)₂] instead of [PdCl₂(cod)] resulted in the formation of the complexes [PdCl₂(L¹) ₂] 7 from L¹, the cyclometallated complex [Pd(μ-Cl){P(NC₁₂H₈)₂(NC₁₂H ₇)-κ²P,C}]2 8 from L³, and a mixture of [PdCl₂(L²)₂] 9 and [Pd(μ-Cl){PPh(NC ₁₂H₈)(NC₁₂H₇)-κ²P, C}]₂ 10 from L². The reaction of L³ with [Pd(OAc)₂] produced the cyclometallated complex [Pd(μ-O ₂CCH₃){P(NC₁₂H₈)₂(NC ₁₂H₇)-²P,C}]₂11. The reaction of L³ with [Pd₂(dba)₃]·CHCl₃ produced the 14-electron complex [Pd(L³)₂] 12. The X-ray crystal structures of six complexes are reported, all of which show the presence of C-H...Pd hydrogen bonding.

Full text of DOI:10.1039/b408841g

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F U L L P A P E R
Sterically hindered electron-withdrawing ligands: the reactions of
N-carbazolyl phosphines with rhodium and palladium centres
Andrew D. Burrows,* Mary F. Mahon and Maurizio Varrone
Department of Chemistry, University of Bath, Claverton Down, Bath,
UK BA2 7AY. E-mail: a.d.burrows@bath.ac.uk
Received 10th June 2004, Accepted 16th August 2004
First published as an Advance Article on the web 3rd September 2004
The series of N-carbazolyl phosphines PPh3−n(NC12H8)n (n = 1, L1; n = 2, L2; n = 3, L3) has been synthesised using
BuLi to generate the N-carbazolyl lithium salt, followed by reaction with the appropriate chlorophosphine. The
reactions between [Rh(l-Cl)(CO)2]2 and four equivalents of L1 or L2 gave [RhCl(CO)(L1)2] 1 and [RhCl(CO)(L2)2]
2, though attempts to synthesise the analogous complex using L3 resulted in the formation of [Rh(l-Cl)(CO)(L3)]2 3
instead. The inability of L3 to cleave the chloride bridges can be related to its considerable steric requirements. The
electronic properties of L1–3 were assessed by comparison of the m(CO) values of the [Rh(acac)(CO)(L1–3)] complexes
4–6. The increase in number of N-carbazolyl substituents at the phosphorus atom results in a decrease of the r-
donor and increase in the p-acceptor character in the order L1 < L2 < L3. In the reactions of L1–3 with [PdCl2(cod)]
only L1 was able to displace cod from the metal centre and form [PdCl2(L1)2] 7. The use of [PdCl2(NCMe)2]
instead of [PdCl2(cod)] resulted in the formation of the complexes [PdCl2(L1)2] 7 from L1, the cyclometallated
complex [Pd(l-Cl){P(NC12H8)2(NC12H7)-j2P,C}]2 8 from L3, and a mixture of [PdCl2(L2)2] 9 and [Pd(l-
Cl){PPh(NC12H8)(NC12H7)-j2P,C}]2 10 from L2. The reaction of L3 with [Pd(OAc)2] produced the cyclometallated
complex [Pd(l-O2CCH3){P(NC12H8)2(NC12H7)-j2P,C}]2 11. The reaction of L3 with [Pd2(dba)3]·CHCl3 produced the
14-electron complex [Pd(L3)2] 12. The X-ray crystal structures of six complexes are reported, all of which show the
presence of C–HPd hydrogen bonding.
In this paper we report the syntheses of the full series of N-
Introduction
carbazolyl phenyl phosphines PPh3−n(NC12H8)n (n = 1, L1; n = 2,
It is widely recognised that the properties of transition metal
complexes, including their catalytic activity and selectivity, can
L2; n = 3, L3) and their coordination chemistry with rhodium(I),
palladium(II) and palladium(0) metal centres.
be controlled by changing the steric and electronic attributes of
the ligands.1 A recent protocol for developing stereoelectronic
Synthesis of N-carbazolyl phosphines L1–3
maps for phosphorus ligands concluded that bulky electron-
Beller and co-workers have recently described the synthesis
of PPh2(NC12H8) L1 and P(NC12H8)3 L3 from the reaction
of PClPh2 or PCl3 with carbazole in the presence of
NEt3.18 In our hands it proved difficult to isolate pure
samples of the ligands using this method, though on react-
ing two equivalents of carbazole with one equivalent of
PCl2Ph it was possible to isolate and fully characterise the
chlorophosphine PClPh(NC12H8) which together with L2 was
the main product in the crude reaction mixture. Unexpectedly,
and in contrast to most chlorophosphines, PClPh(NC12H8) is a
moderately air- and moisture-stable solid which readily crystal-
lised from cold hexane (−25 °C). The 31P{1H} NMR spectrum
of PClPh(NC12H8) is composed of a singlet at d 99.0, whereas
the 1H and 13C{1H} NMR spectra clearly indicate the presence
of one carbazolyl and one phenyl substituent.
poor phosphines were largely unknown, and suggested these
would be useful targets.2 Sterically demanding ligands are able
to stabilise metals with low coordination numbers and/or un-
usual oxidation states,3 the former being classically illustrated
by low valent complexes containing Group 10 metals. Thus with
small ligands, the preferred coordination number in complexes
of Ni(0), Pd(0) and Pt(0) is four, giving rise to the 18-electron
complexes [M(PR3)4].4 However complexes with lower coordi-
nation numbers can be isolated with bulky phosphines such as
7
PCy3,5 PBut3,6 P(o-Tol)3 and PPh2Np (Np = naphthyl).8 The
ability of bulky phosphorus ligands to stabilise coordinatively
unsaturated metals in low oxidation states has great potential in
catalysis, and bulky phosphorus ligands give rise to high activities
in the rhodium-catalysed hydroformylation of olefins.9
Bearing in mind the properties of bulky phosphines and
the relative dearth of sterically-demanding electron-poor
ligands, we sought to prepare and study phosphorus ligands
containing bulky functionalised N-pyrrolyl substituents. N-
Pyrrolyl phosphines are of interest due to their strong electron-
withdrawing character,10 and we have recently reported the
chemistry of such ligands functionalised with keto,11,12 cyano,13
aza14 and diphenylphosphino15 groups. An increase in the steric
bulk of the N-pyrrolyl functionality can be achieved either by
substitution at the a position or by using fused ring systems.
Using the former approach, the series of (2,5-dimethyl-N-
pyrrolyl)phenyl phosphines PPh3−n(NC4H2Me2-2,5)n has been
prepared,16 whereas using the fused ring strategy, tri-N-indolyl
phosphine has been synthesised in a stepwise manner from PF3
and the N-indolyl lithium salt.17 N-Indolyl and N-carbazolyl
phosphines have also been reported by Beller and co-workers,
who used them as modifying ligands in rhodium-catalysed
hydroformylation reactions.18 However, no studies on the
coordination chemistry of these ligands have been published.
The successful syntheses of L1–3 were performed using
an analogous method to that reported for the syntheses of
PPh2(NC4H3CN-2) and P(NC4H4)2(NC4H3CN-2).13 Thus
carbazole was reacted with BuLi to generate the N-
carbazolyl lithium salt, which was subsequently reacted with
PClnPh3−n (n = 1–3). This method enabled L1–3 to be isolated as
crystalline materials in good yields. The ligands L2 and L3 are
air- and moisture-stable in the solid state and in solution, and
do not react with methanol. In contrast L1 is air- and moisture-
sensitive decomposing, when not handled in inert conditions,
to Ph2PP(O)Ph2 via hydrolysis of the P–N bond.
The compounds L1–3 were fully characterised by multinuclear
NMR spectroscopy and microanalysis. The 31P{1H} NMR
spectra showed single resonances at d 32.7 for L1, d 52.9 for
L2 and d 77.6 for L3, the values for L1 and L3 in agreement
with those previously reported.18 The observed progressive
increase in chemical shift with increase in the number of
carbazolyl rings is in agreement with the reduced r-basicity
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0
3 3 2 1

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of the phosphines as the number of N-carbazolyl substituents
at the phosphorus atom is increased. In a similar manner to
N-pyrrolyl substituents, N-carbazolyl substituents cause a
broadening of the 31P NMR line widths. The line width for
L3 is ca. 70 Hz which is comparable with that reported for
P(NC4H4)3 (64 Hz).10 The 31P NMR line widths of these ligands
are influenced by the quadrupolar nitrogen nuclei and this
serves as a useful diagnostic tool indicating the formation of
P–N bonded products.
a dichloromethane solution. The molecular structure of
trans-[RhCl(CO)(L2)2] is shown in Fig. 2 and selected bond
distances and angles are given in Table 1. The asymmetric
unit contains half of a molecule of the metal complex and
two partial occupancy molecules of dichloromethane. The
metal centre is located on an inversion centre and consequently
the chloride and the carbonyl ligands are disordered in a
50:50 ratio across this symmetry element. The tendency for
rhodium complexes to crystallise in forms that involve disorder
of chloride and carbonyl ligands across inversion centres has
been previously reported for both mononuclear19 and binuclear12
complexes. The metal adopts a distorted square planar geometry
with cis angles between 88.4(3) and 91.6(3)°. The L2 ligands in
2·1.6CH2Cl2 adopt crystallographic cone angles20 of 171°, and
the sums of the angles around N(1) and N(2) are consistent with
the presence of small pyramidal distortions. The supramolecular
structure of 2·1.6CH2Cl2 is dominated by C–Hp interactions.
1
The H and 13C{1H} NMR spectra of L1–3 were assigned
1
on the basis of H–1H and 13C–1H NMR correlation experi-
ments using the numbering scheme shown in Fig. 1. All the
signals were sharp at ambient temperature suggesting that the
carbazolyl rings are free to rotate. In the 1H NMR spectra small
5JHP couplings were observed between the phosphorus atom and
the chemically equivalent H4 and H5 protons and confirmed by
5
1H–31P NMR correlation experiments. Similar JHP couplings
were seen in the spectra of 7-aza-N-indolyl phosphines.14
Fig. 1 Numbering scheme for the carbazolyl ring.
The reactions of L1–3 with [Rh(l-Cl)(CO)2]2
The reactions of four equivalents of L1 or L2 with [Rh(l-
Cl)(CO)2]2 gave the complexes trans-[RhCl(CO)(L1)2]
1
and trans-[RhCl(CO)(L2)2] 2. The products precipitated
out of solution on the addition of hexane, and were
purified by recrystallisation from dichloromethane–hexane.
The 31P{1H} NMR spectra of 1 and 2 both contain doublets,
confirming the expected trans geometry. The carbonyl stretch-
ing frequencies were observed in the IR spectrum at 1992 cm−1
for 1 and at 2000 cm−1 for 2 and are similar to those reported
for the related N-pyrrolyl phosphine complexes trans-[RhCl-
(CO){PPhn(NC4H4)3−n}2] (n = 2, 1992 cm−1; n = 1, 2007 cm−1).10
Thus the replacement of N-pyrrolyl with N-carbazolyl seems
to have little effect on the electronic properties of the ligand.
The reaction between four equivalents of L3 and [Rh(l-
Cl)(CO)2]2 proceeded differently from the analogous reactions
using L1 and L2, and after a few minutes the formation of a
yellow precipitate 3 was observed. The 31P{1H} NMR spectrum
of 3 consists of a doublet at d 90.0 with JPRh 257 Hz. The H
NMR spectrum showed distinctive signals for all the protons
of the carbazolyl ring with the signal assigned to the chemi-
cally equivalent H1 and H8 protons shifted to low field (d 7.75)
compared with those in the free ligand (d 7.11–7.19). In the IR
spectrum the m(CO) absorption was observed at 2015 cm−1. Com-
pound 3 is only sparingly soluble, which prevented the carbonyl
carbon from being observed in the 13C{1H} NMR spectrum.
When the filtrate solvent was removed under reduced pres-
sure, a white powder was observed which was revealed by
NMR spectroscopy to be unreacted L3, suggesting 3 contains a
phosphine:rhodium ratio of less than 2:1. The identity of 3 was
subsequently revealed by X-ray crystallographic studies to be the
chloro-bridged dimer [Rh(l-Cl)(CO)(L3)]2. Repetition of the re-
action using only two equivalents of L3 led to 3 as the only solid
product. Attempts to obtain trans-[RhCl(CO)(L3)2] using a sig-
nificant excess of ligand, higher temperature and/or prolonged
reaction time were unsuccessful. Since P(NC4H4)3 readily reacts
with [Rh(l-Cl)(CO)2]2 to form trans-[RhCl(CO){P(NC4H4)3}2],
the inability of L3 to form the analogous complex trans-
[RhCl(CO)(L3)2] is likely to be a consequence of its steric bulk.
Fig. 2 Molecular structure of trans-[RhCl(CO)(L2)2]·1.6CH2Cl2
(2·1.6CH2Cl2) with thermal ellipsoids shown at the 30% probability
level and solvent molecules removed for clarity.
Single crystals of [Rh(l-Cl)(CO)(L3)]2·2CH2Cl2 (3·2CH2Cl2)
were grown from the slow diffusion of hexane into a dichloro-
methane solution. The molecular structure is shown in Fig. 3
and selected bond distances and angles are given in Table 1. The
asymmetric unit contains half a molecule of the dimer and a
molecule of dichloromethane. The complex lies about an inver-
sion centre and the remainder is generated by symmetry. The
complex consists of two rhodium centres in distorted square
planar coordination geometries linked together by two bridging
chlorides and with the phosphorus ligands mutually trans along
the RhRh axis. The cis angles around each rhodium atom lie
between 83.995(19) and 93.39(2)°. The Rh(1)Rh(1) distance
of 3.590 Å indicates the absence of a metal–metal bond.
1
1
The planar conformation adopted by 3 contrasts with those
reported for a number of other chloro-bridged rhodium(I)
dimers, which have structures bent along the ClCl axis
The X-ray crystal structures of trans-[RhCl(CO)-
(L2)2]·1.6CH2Cl2 (2·1.6CH2Cl2) and [Rh(l-
Cl)(CO)(L3)]2·2CH2Cl2 (3·2CH2Cl2)
Single crystals of trans-[RhCl(CO)(L2)2]·1.6CH2Cl2 (2·1.6-
CH2Cl2) were grown from the slow diffusion of hexane into
Fig. 3 Molecular structure of [Rh(l-Cl)(CO)(L3)]2·2CH2Cl2
(3·2CH2Cl2) with thermal ellipsoids shown at the 30% probability level
and solvent molecules removed for clarity.
3 3 2 2
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0

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Table 1 Selected bond lengths and angles for 2·1.6CH2Cl2a and 3·2CH2Cl2b
2·1.6CH2Cl2a
3·2CH2Cl2b
Rh(1)–P(1)
Rh(1)–Cl(1)
2.311(3)
2.384(15)
Rh(1)–P(1)
Rh(1)–Cl(1)
Rh(1)–Cl(1)
Rh(1)–C(1)
C(1)–O(2)
P(1)–N(101)
P(1)–N(201)
P(1)–N(301)
2.2030(6)
2.4142(5)
2.4167(5)
1.819(2)
Rh(1)–C(1)
C(1)–O(1)
P(1)–N(1)
P(1)–N(2)
1.75(4)
1.11(7)
1.708(10)
1.696(9)
1.146(3)
1.7039(19)
1.7081(19)
1.6894(19)
C(1)–Rh(1)–P(1)
C(1)–Rh(1)–P(1)
P(1)–Rh(1)–Cl(1)
P(1)–Rh(1)–Cl(1)
C(1)–Rh(1)–Cl(1)
89.6(15)
90.4(15)
88.4(3)
91.6(3)
177.3(17)
C(1)–Rh(1)–P(1)
C(1)–Rh(1)–Cl(1)
P(1)–Rh(1)–Cl(1)
Cl(1)–Rh(1)–Cl(1)
P(1)–Rh(1)–Cl(1)
C(1)–Rh(1)–Cl(1)
Rh(1)–Cl(1)–Rh(1)
93.04(7)
89.35(7)
93.39(2)
83.995(19)
176.74(2)
170.83(7)
96.004(19)
a Primed atoms generated by the symmetry operation −x + 1/2, −y + 3/2, −z. b Primed atoms generated by the symmetry operation −x, −y +
1, −z + 1.
and shorter metal–metal distances. For example the com-
plex [Rh(l-Cl)(CO)(PPhMe2)]2 has a RhRh distance of
3.167 Å.21 Recently the nature of such interactions and
their significance in determining non-planar geometries has
been addressed by means of structural analysis and MO
calculations on a series of complexes of the general formula
[L2M(l-X)2ML2].22 This analysis suggested that bending is
energetically favourable for rhodium(I) complexes, but since
the stabilisation is small (2–3 kJ mol−1) steric repulsion between
bulky terminal substituents could lead to the formation of
planar structures. This is not always the case, however, and the
complex [Rh(l-Cl)(But2PCH2PBut2)]2 adopts a bent structure
with a short metal–metal distance of 3.26 Å, despite the pre-
sence of very bulky phosphorus ligands.23 In this case it has
been suggested that the conformation adopted is influenced by
packing effects. Folding along the ClCl axis increases the gap
between the bulky tert-butyl groups on one side of the molecule
thus creating space for ‘embedding’ of the tert-butyl groups of
a neighbouring molecule of the complex.
Geometrical calculations give a crystallographic cone angle
of 191° for L3 in 3. Small pyramidal distortions were observed
at the nitrogen atoms N(101) and N(201) in 3, with the values
for the sums of the angles around these nitrogen atoms 356.3°
and 351.3° respectively, whilst that for N(301) is 358.6°. This
is consistent with the P–N bonds to N(101) and N(201) being
significantly longer than those to N(301). Deviations of the sum
of the angles around nitrogen atoms from the ideal value of
360° are related to the presence of C–Hp and pp stacking
interactions which dominate the packing in the crystal structure.
The carbazolyl rings containing N(101) and N(301) are both
involved in pp stacking interactions with the shortest CC
distances of 3.41 and 3.48 Å respectively.
microanalysis. In addition the crystal structure of 5 was deter-
mined by X-ray crystallography. The reactions were monitored
by IR spectroscopy, which demonstrated increased reaction
times on going from L1 to L3. The synthesis of 6 was particularly
problematic because complete conversion in dichloromethane
could only be obtained after more than 48 h under reflux using
an excess of ligand. This excess proved to be difficult to separate
from the desired product preventing analytically pure sample of
6 from being obtained via this route. Optimum reaction condi-
tions were established using refluxing acetone as solvent, as
the excess ligand crystallises on cooling to room temperature,
leaving the product in solution.
31P{1H} NMR and IR spectroscopic data for complexes 4–6
are given in Table 2 together with those for related complexes.
The phosphorus chemical shift is in all cases shifted downfield
from the free ligands, and the 1JPRh coupling constant increases
with the number of N-carbazolyl substituents at the phosphorus
atom. A similar trend has been observed for the series of phenyl
N-pyrrolyl phosphines.24 Trends in the IR data for 4–6 are also
similar to those observed for the N-pyrrolyl phosphines, with
m(CO) increasing with the number of N-carbazolyl substituents.
Together the NMR and IR data support the assertion that the
order of decreasing p-accepting and increasing r-donating
1
ability is L3 > L2 > L1. The JPRh data for N-pyrrolyl and N-
carbazolyl phosphines suggest very similar electronic characters,
though the IR data suggest PPh2(NC4H4) and PPh(NC4H4)2 are
more electron-withdrawing than L1 and L2.
The X-ray crystal structure of [Rh(acac)(CO)(L2)] 5
The X-ray crystal structure of complex [Rh(acac)(CO)(L2)]
5 is shown in Fig. 4 and selected bond angles and distances
are given in Table 3. The rhodium centre adopts a distorted
square planar coordination geometry with cis angles ranging
from 89.08(9)° to 91.02(10)°. The Rh(1)–P(1) bond distance
of 2.2108(8) Å is longer than that found in the structures of
[Rh(acac)(CO){P(NC4H4)3}] [2.166(1) Å]24 and [Rh(acac)-
(CO){P(NC8H4Me)3CH}] [2.1783(12)]26 but shorter than that
in the structure of [Rh(acac)(CO)(PPh3)] [2.244(2) Å].27 This
is in agreement with the spectroscopic data in Table 4 which
indicates L2 is a weaker r-donor/stronger p-acceptor than PPh3,
but a stronger r-donor/weaker p-acceptor than P(NC4H4)3 or
P(NC8H4Me)3CH. This is consistent with the number of N-
carbazolyl groups present on L2. The Rh–O bond distances in
5 differ due to the different trans influences of the phosphine
and carbonyl ligands. The Rh(1)–O(2) bond distance in 5
can be compared to those reported for [Rh(acac)(CO)(PPh3)]
[2.087(4) Å], [Rh(acac)(CO){P(NC4H4)3}] [2.054(2) Å] and
[Rh(acac)(CO){P(NC8H4Me)3CH}] [2.043(3) Å]. The observed
trend leads to the same order of phosphine electronic properties
as that based on Rh–P distances.
The reactions of L1–3 with [Rh(acac)(CO)2]
In order to compare IR data, it was desirable to have mono-
nuclear carbonyl rhodium complexes for the complete
series of N-carbazolyl phosphines. Complexes of the type
[Rh(acac)(CO)(L)] were expected to be less sterically crowded
than [RhCl(CO)(L)2] since only one phosphine ligand is present
in each complex. Moreover such complexes have previously been
prepared for the entire series of N-pyrrolyl phenyl phosphines24
and for the bulky phosphatri(3-methyl-N-indolyl)methane
P(NC8H4Me)3CH
and
tri(3-methyl-N-indolyl)phosphine
P(NC8H5Me)3 ligands,25,26 so a good amount of data are
available for comparison.
The reaction of one equivalent of L1, L2 or L3 with [Rh-
(acac)(CO)2] in dichloromethane produced the complexes
[Rh(acac)(CO)(L1)] 4, [Rh(acac)(CO)(L2)] 5 and [Rh(acac)-
(CO)(L3)] 6 in good yields. All the complexes were fully
characterised on the basis of IR and NMR spectroscopy and
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0
3 3 2 3

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Table 2 Spectroscopic data for complexes 4–6 and related compounds
d(31P)
1JPRh/Hz
m(CO)/cm−1
Ref.
[Rh(acac)(CO){PPh2(NC12H8)}] 4
[Rh(acac)(CO){PPh(NC12H8)2}] 5
[Rh(acac)(CO){P(NC12H8)3}] 6
[Rh(acac)(CO){PPh2(NC4H4)}]
[Rh(acac)(CO){PPh(NC4H4)2}]
[Rh(acac)(CO){P(NC4H4)3}]
[Rh(acac)(CO){P(NC8H5Me)3}]
[Rh(acac)(CO){P(NC8H4Me)3CH}]
[Rh(acac)(CO){P(OPh)3}]
71.1
98.1
101.1
90.0
104.7
102.5
97.4
65.9
212.1
48.6
190
216
255
194
218
251
248
243
293
180
1990a
1997a
2012a
2000b
2009b
2012b
2005a
2024a
2006b
1975b
This work
This work
This work
24
24
24
26
26
53
52
[Rh(acac)(CO)(PPh3)]
a CH2Cl2. b KBr.
Table 3 Selected bond lengths and angles for 5 and 8·ꢀCH2Cl2a
Table 4 Selected bond lengths and angles for 11·2ꢁCH2Cl2
5
8·ꢀCH2Cl2a
Pd(1)–P(1)
Pd(1)–C(2)
Pd(1)–O(1)
Pd(1)–O(3)
Pd(2)–P(2)
Pd(2)–C(38)
Pd(2)–O(4)
Pd(2)–O(2)
P(1)–N(1)
P(1)–N(2)
P(1)–N(3)
P(2)–N(4)
P(2)–N(5)
P(2)–N(6)
2.2199(11)
1.996(4)
2.078(3)
2.137(3)
2.1943(10)
1.987(4)
2.075(3)
2.126(3)
1.681(3)
1.707(4)
1.684(3)
1.683(4)
1.694(4)
1.688(3)
Pd(3)–P(3)
Pd(3)–C(78)
Pd(3)–O(5)
Pd(3)–O(7)
Pd(4)–P(4)
Pd(4)–C(114)
Pd(4)–O(8)
Pd(4)–O(6)
P(3)–N(7)
P(3)–N(8)
P(3)–N(9)
P(4)–N(10)
P(4)–N(11)
P(4)–N(12)
2.2051(11)
1.986(5)
2.072(3)
2.124(3)
2.1938(10)
1.989(5)
2.076(3)
2.133(3)
1.691(4)
1.685(3)
1.688(3)
1.681(4)
1.692(3)
1.689(4)
Rh(1)–P(1)
Rh(1)–C(36)
Rh(1)–O(1)
Rh(1)–O(2)
C(36)–O(3)
P(1)–N(1)
2.2108(8)
1.792(3)
2.036(2)
2.071(2)
1.166(4)
1.712(3)
1.705(3)
Pd(1)–P(2)
Pd(1)–C(23)
Pd(1)–Cl(1)
Pd(1)–Cl(1)
P(2)–N(1)
P(2)–N(2)
P(2)–N(3)
2.2159(18)
1.991(8)
2.3875(17)
2.433(2)
1.694(6)
1.679(6)
1.701(6)
P(1)–N(2)
C(36)–Rh(1)–P(1)
C(36)–Rh(1)–O(2)
O(1)–Rh(1)–O(2)
O(1)–Rh(1)–P(1)
C(36)–Rh(1)–O(1)
O(2)–Rh(1)–P(1)
91.02(10)
89.82(12)
89.08(9)
90.01(7)
176.97(12)
178.26(7)
C(23)–Pd(1)–P(2)
C(23)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(1)
C(23)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(1)
Cl(1)–Pd(1)–Cl(1)
Pd(1)–Cl(1)–Pd(1)
84.36(19)
93.0(2)
170.60(7)
178.87(19)
96.37(7)
86.41(7)
93.59(7)
C(2)–Pd(1)–O(1)
O(1)–Pd(1)–O(3)
C(2)–Pd(1)–P(1)
O(3)–Pd(1)–P(1)
O(1)–Pd(1)–P(1)
C(2)–Pd(1)–O(3)
C(38)–Pd(2)–O(4)
O(4)–Pd(2)–O(2)
C(38)–Pd(2)–P(2)
O(2)–Pd(2)–P(2)
O(4)–Pd(2)–P(2)
C(38)–Pd(2)–O(2)
90.15(17)
87.13(13)
82.76(15)
99.34(10)
169.21(9)
175.14(15)
91.42(15)
89.80(13)
84.13(12)
92.98(10)
164.48(9)
173.35(15)
C(78)–Pd(3)–O(5)
O(5)–Pd(3)–O(7)
C(78)–Pd(3)–P(3)
O(7)–Pd(3)–P(3)
O(5)–Pd(3)–P(3)
C(78)–Pd(3)–O(7)
C(114)–Pd(4)–O(8)
O(8)–Pd(4)–O(6)
C(114)–Pd(4)–P(4)
O(6)–Pd(4)–P(4)
O(8)–Pd(4)–P(4)
C(114)–Pd(4)–O(6)
89.46(17)
91.28(14)
83.97(14)
94.46(9)
169.02(9)
174.61(13)
91.46(17)
91.03(14)
82.95(13)
93.25(9)
a Primed atoms generated by the symmetry operation −x + 1, −y +
1, −z + 2.
169.17(9)
171.64(14)
observed to react with [PdCl2(cod)], even on reflux. However,
L3 reacts with [PdCl2(NCMe)2] to give the cyclometalled com-
plex [Pd(l-Cl){P(NC12H8)2(NC12H7)-j2P,C}]2 8, which was
isolated in good yield (77%) as a crystalline material.
The formation of the cyclometallated complex 8 is likely to
be a consequence of the high steric requirement of L3, which
places the carbazolyl hydrogen atom H1 close enough to the
metal centre so that the C–H bond is activated towards the
metal insertion reaction. Cyclometallated complexes have
been reported for a number of other bulky phosphorus ligands
28
including P(o-Tol)3 and PNp3.29 Such compounds have at-
tracted attention recently as catalysts for various transition
metal catalysed C–C bond formation reactions. Pre-formed or
in situ-generated cyclometallated palladium complexes of the
Fig. 4 Molecular structure of [Rh(acac)(CO)(L2)] (5) with thermal
30
31
phosphine ligands P(o-Tol)3 and PNp3 have been reported
to be excellent catalysts for Heck-type coupling reactions,
and cyclometallated ligands based on phosphites32,33 and phos-
phinites34 have very high activities in Suzuki and Heck reactions.
In order to investigate the generality of cyclometallation
reactions with carbazolyl phosphines, the reactions between
L1 or L2 and [PdCl2(NCMe)2] were also investigated. The
reaction of L1 with [PdCl2(NCMe)2] proceeded similarly to
the reaction of this ligand with [PdCl2(cod)], and complex
7 was isolated as a yellow powder. In contrast, the reaction
between two equivalents of L2 and [PdCl2(NCMe)2] produced
more than one compound. After crystallisation, both orange
crystals and a yellow powder were obtained, and these were
separated manually. The orange and yellow products were
identified as [PdCl2(L2)2] 9 and [PdCl{PPh(NC12H8)(NC12H7)-
j2P,C}]2 10 respectively on the basis of NMR spectroscopy
ellipsoids shown at the 30% probability level.
The sums of the angles at the nitrogen atoms in 5 are 355.4°
and 358.4°, thus indicating the presence of small pyramidal
distortions. Geometric calculations give a crystallographic cone
angle for L2 in this structure of 181°, slightly larger than that
observed in 2·1.6CH2Cl2. The extended structure is dominated
by the presence of C–Hp interactions.
Palladium(II) complexes of L1–3
The reaction of two equivalents of L1 with one equivalent of
[PdCl2(cod)] in dichloromethane produced complex [PdCl2(L1)2]
7 in good yield. The 31P{1H} NMR spectrum of 7 showed a
singlet at d 51.3 which is shifted downfield compared to that
of the free ligand. In contrast with L1, neither L2 nor L3 were
3 3 2 4
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0

View Article Online
and microanalysis. The 31P{1H} NMR spectrum of 9 showed
a single resonance at d 70.0, whereas the H NMR spectrum
falls towards the lower end of the wide range of Pd–PR3 bond
lengths.36 Similar short Pd–P distances have been reported for
the structures of the related cyclometallated complexes such
as [Pd(l-OAc){o-CH2C6H4P(o-Tol)2-j2P,C}]2 [2.216(1) Å].28
The Pd(1)–C(23) bond distance of 1.991(8) Å is long for a
palladium–carbon bond36 and can be compared with the value
in the structure of [Pd(l-Cl){P(OC6H3But2-2,4)2(OC6H2But2-
2,4)-j2P,C}]2 [2.1668(17) Å].32
The angles around P(1) and N(2) are of interest in
evaluating the distortions concomitant with cyclometallation.
The large value of C(13)–N(2)–P(1) [140.9(5)°] compared with
C(24)–N(2)–P(1) [112.9(5)°] suggests that formation of the
cyclometallated ring can be obtained by bending the carbazolyl
ring in the direction of the metal centre. N(2) does not have
a significant pyramidal distortion, as reflected by the sum of
angles around this atom being 359.9°. Small pyramidal distor-
tions are observed for the other nitrogen atoms N(1) and N(3),
and these have their origins in interactions observed in the
extended structure. Indeed, all of the carbazolyl rings present in
8 are involved in pp stacking interactions.
1
showed distinctive signals for the protons of the carbazolyl and
phenyl rings of L2. Compound 10 was not very soluble, but the
31P{1H} NMR spectrum showed a singlet at d 86.8, whereas
1
the H NMR showed an overlapping group of signals in the
aromatic region that were consistent with the reduced symmetry
engendered by the cyclometallation. The ligand L2 therefore
shows a coordination behaviour towards [PdCl2(NCMe)2] that
is midway between those observed for L1 and L3. The lower
steric requirement of L2 compared with L3 means that the for-
mer is still able to coordinate at the metal centre but at the same
time the higher steric requirement with respect to L1 renders
formation of a cyclometallated complex possible under the mild
reaction conditions used.
Since cyclometallated complexes of palladium are
an important group of complexes35 it was decided to
develop
a more rational method towards obtaining a
cyclometalled palladium complex of L3. It was also desirable
that such a complex would present a higher solubility than
8 to facilitate potential use in catalysis. One possible way of
increasing the solubility of 8 is to replace the bridging chlorides
with bridging acetate ligands, so Pd(OAc)2 was used instead
of [PdCl2(NCMe)2]. The reaction of one equivalent of L3
with Pd(OAc)2 in warm toluene produced the complex [Pd(l-
O2CCH3){P(NC12H8)2(NC12H7)-j2P,C}]2 11 in good yield (90%).
The complex was isolated as a yellow powder, which exhibited
a good solubility in various organic solvents. Recrystallisation
from dichloromethane–hexane produced crystals suitable for
X-ray crystallographic studies. The 31P{1H} NMR spectrum
of 11 showed a sharp single resonance at d 85.5. The 1H NMR
spectrum showed complex signals for the aromatic protons,
which integrated well with the signal for the protons of the
bridging acetates to give a ratio of 46:6.
Crystals of [Pd(l-O2CCH3){P(NC12H8)2(NC12H7)-j2P,C}]2·-
2ꢁCH2Cl2 (11·2ꢁCH2Cl2) were obtained by slow diffusion of
hexane into a dichloromethane solution. The asymmetric unit
contains two crystallographically independent molecules of the
complex and 4ꢀ molecules of dichloromethane. The structure of
one of the complex molecules is reported in Fig. 6 and selected
bond distances and angles for both molecules are reported
in Table 4. The two complex molecules in 11 show minor
differences in the bond lengths and angles, of which the most
significant are the PdPd distances, Pd(1)Pd(2) 3.0245(4)
Å and Pd(3)Pd(4) 3.1681(4) Å. These are shorter than the
PdPd distance in the structure of 8 due to the geometry
imposed by the bridging acetate ligands. Pyramidal distortions
on the nitrogen atoms are largely absent.
The X-ray crystal structures of [Pd(l-Cl){P(NC12H8)2(NC12H7)-
j2P,C}]2·ꢀCH2Cl2 (8·ꢀCH2Cl2) and [Pd(l-O2CCH3)-
{P(NC12H8)2(NC12H7)-j2P,C}]2·2ꢁCH2Cl2 (11·2ꢁCH2Cl2)
Crystals of [Pd(l-Cl){P(NC12H8)2(NC12H7)-j2P,C}]2·ꢀCH2Cl2
8 suitable for X-ray crystallographic studies were obtained by
slow diffusion of hexane into a dichloromethane solution. The
asymmetric unit consisted of half a molecule of the complex
and a partial occupancy dichloromethane molecule. The com-
plex lies about an inversion centre and the remaining portion
was generated by symmetry. The molecular structure is shown
in Fig. 5 and selected bond distances and angles are given in
Table 3. The coordination geometry at each metal centre is
distorted square planar with the cis angles between 84.36(19)
and 96.37(7)°.
Fig. 6 Molecular structure of one of the independent molecules
present in the crystal structure of [Pd(l-O2CCH3){P(NC12H8)2-
(NC12H7-j2P,C}]2·2ꢁCH2Cl2 (11·2ꢁCH2Cl2) with thermal ellipsoids
shown at the 30% probability level and solvent molecules removed for
clarity.
The PdPd distance of 3.514 Å rules out the presence
of a metal–metal interaction in agreement with formal
electron counting. The Pd(1)–P(1) distance of 2.2159(18) Å
The angles between the two coordination planes are 43° and
50° in the two independent molecules, based on Pd(1) and Pd(3)
respectively. This allows intramolecular pp interactions to
occur, with the closest inter-plane CC distance at 3.27 Å.
The PdPd distances and inter-coordination plane angles
are similar to those in the analogous compound based on
P(o-Tol)328 whereas the coordination planes in the PBut(o-Tol)2
analogue are further apart [PdPd 3.41 Å, angle 60°].37 The
supramolecular structure of 11·2ꢁCH2Cl2 shows the presence
of pp stacking and C–Hp interactions.
The synthesis and characterisation of [Pd(L3)2] 12
Since bulky phosphorus ligands have been extensively used for
the formation of coordinatively unsaturated complexes of tran-
sition metals in low oxidation states it was of interest to extend
our studies on the coordination chemistry of L3 to palladium(0)
Fig. 5 Molecular structure of [Pd(l-Cl){P(NC12H8)2(NC12H7-
j2P,C}]2·ꢀCH2Cl2 (8·ꢀCH2Cl2) with thermal ellipsoids shown at the
30% probability level and solvent molecules removed for clarity.
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0
3 3 2 5

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Table 5 Selected bond lengths and angles for 12·2C7H8a
centres. Thus L3 was reacted with [Pd2(dba)3]·CHCl3 with the
aim of isolating either the 14-electron complex [Pd(L3)2] or
the 16-electron complex [Pd(dba)(L3)2]. The stabilities of these
Pd(0) complexes of L3 are expected to benefit not only from the
steric bulk of the ligand but also from its strong p-accepting
character.
Pd(1)–P(1)
P(1)–N(1)
P(1)–N(2)
P(1)–N(3)
2.2341(6)
1.712(2)
1.707(2)
1.699(2)
Pd(2)–P(2)
P(2)–N(4)
P(2)–N(5)
P(2)–N(6)
2.2408(6)
1.707(2)
1.717(2)
1.700(2)
P(1)–Pd(1)–P(1)
180.0
P(2)–Pd(2)–P(2)
180.0
When a dichloromethane solution of [Pd2(dba)3]·CHCl3
was added to a dichloromethane solution containing four
equivalents of L3, a change in colour from dark red to
yellow occurred after 2 h stirring. The addition of diethyl ether
afforded precipitation of a yellow powder, which was formulated
a Primed atoms generated by the symmetry operation −x, −y, −z. Double
primed atoms generated by the symmetry operation −x, −y, −z + 1.
1
on the basis of 31P{1H} NMR, H NMR and IR spectroscopy
and microanalysis as [Pd(L3)2] 12. The 31P{1H} NMR spec-
trum of 12 is composed of a single resonance at d 75.1 slightly
1
upfield of the free ligand. The H NMR spectrum showed the
expected signals for the carbazolyl substituents and the absence
of signals for dba.
Crystals of 12 suitable for X-ray diffraction studies were
obtained by reacting [Pd2(dba)3]·CHCl3 with L3 in toluene
instead of dichloromethane. These crystals are much more
stable than those obtained from dichloromethane and can be
stored for weeks without significant decomposition. Moreover
toluene solutions of 12 are considerably more stable than those
in dichloromethane and on standing at ambient temperature
under inert atmosphere do not result in the formation of
palladium black. However they are not thermally stable as
evidenced by the rapid formation of palladium black as soon as
the temperature is increased to ca. 80 °C.
No intermediates of the type [Pd(dba)(L3)2] were observed in
the 31P{1H} NMR spectra. This contrasts with observations made
on the bulky polyaromatic phosphines PPh2Np, PPhNp2 and
PPh2An (An = anthracenyl).8 Under similar reaction condi-
tions these ligands are unable to completely displace dba
from [Pd2(dba)3]·CHCl3 leading to complexes of the type
[Pd(dba)(L)2], even with excess phosphine. The ligand PNp3
does not displace any dba from [Pd2(dba)3]·CHCl3 even using
forcing conditions. The inability of the polyaromatic phosphines
to form 14-electron complexes similar to 12 was attributed to
their large steric demands. If this is the case, the ability of L3 to
form 12 despite its even greater steric demand must be attributed
to its increased p-acceptor character.
Fig. 7 Molecular structure of one of the independent molecules
present in the crystal structure of [Pd(L3)2]·2C7H8 (12·2C7H8) with
thermal ellipsoids shown at the 30% probability level and solvent
molecules removed for clarity.
[2.285(3) Å],38 [Pd(PCy3)2] [2.26 Å],39 [Pd{PBut2(C5H4FeCp)}2]
[2.2764(7) Å],40
[Pd{PCy2(C6H4{Ph-2})}2]
[2.2744(11),
2.2778(11) Å]41 and [Pd{P(C6H3Mes2-3,5}2] [2.2838(9) Å]42—
reflecting the greater p-acceptance of L3. The metal centre in
12 is completely enclosed by the carbazolyl substituents such
that coordination of another ligand to the metal centre without
drastic rearrangements would seem not possible. This may be
taken as indirect evidence to explain the inability to synthesise
trans-[RhCl(CO)(L3)2] and [PdCl2(L3)2] on steric grounds. The
supramolecular structure of 12·2C7H8 is dominated by C–Hp
interactions.
The X-ray crystal structure of [Pd(L3)2]·2C7H8 (12·2C7H8)
Yellow single crystals of [Pd(L3)2]·2C7H8 (12·2C7H8)
suitable for X-ray analysis were grown from a toluene
solution. The crystallographic study revealed that the
asymmetric unit contains two crystallographic independent
halves of the complex and two molecules of toluene. Both
palladium atoms lie on inversion centres, and the remaining
portions of each molecule are generated by symmetry. The
structure of one of the independent complex molecules is
shown in Fig. 7 and selected bond distances and angles for
both molecules are reported in Table 5. There are no chemically
important differences in the bond distances and angles of two
molecules. The presence of the inversion centres ensures linear
coordination geometries with the carbazolyl substituents of the
two phosphorus atoms assuming a staggered conformation. The
ligands assume rotor conformations and intramolecular C–Hp
interactions are present between the two phosphine ligands on
each complex. The ligands adopt crystallographic cone angles
of 209° in both independent molecules, which is considerably
larger than the value observed in 3·2CH2Cl2, reflecting the
greater steric demands of the rotor conformation.
Intramolecular C–HM interactions
All of the crystal structures reported in this paper show evidence
of intramolecular C–HM interactions, details of which are
given in Table 6. These interactions are all best described as
C–HM hydrogen bonds as opposed to agostic43 or pseudo-
agostic44 interactions. The description as hydrogen bonds is
based partly on the geometric parameters and partly on the
nature of the d8 and d10 metal centres, both of which present
filled orbitals for interaction with the C–H bonds. The C–HM
interactions herein generally exhibit angles at hydrogen between
134 and 144°, typical of this type of hydrogen bond, the
exceptions being compounds 5 and 12·2C7H8. In the structure
of 5, one of the acac oxygen atoms also acts as a hydrogen
bond acceptor, and the interaction is best described as an
intramolecular multi-centre hetero-acceptor hydrogen bond.44 In
12·2C7H8 the C–HPd interactions are notably less directional
and involve all of the carbazolyl rings. Short metal–hydrogen
distances were also observed in the structures of [Pd{P(o-
Tol)3}2]7 and [Pd{PtBu3}2]7 and are likely to be a feature of all
such coordinatively unsaturated molecules with bulky ligands.
The observations of C–HM hydrogen bonding parallel the
ease of cyclometallation in the palladium complexes of L2 and
L3, where these interactions can be regarded as intermediates
on the pathway to C–H activation. It is notable that there is no
evidence for any of the C–HM interactions observed in the
The sums of the angles around the nitrogen atoms are
in the range 352.7–358.3° suggesting the presence of small
pyramidal distortions for some of the carbazolyl groups. The
Pd–P distances of 2.2341(6) Å and 2.2408(6) Å are shorter
than those in the structures of the other complexes of the type
[PdL2] that have been structurally characterised—[Pd{P(o-
Tol)3}2] [2.276(1) Å],7 [Pd(PBut2Ph)2] [2.285(2) Å],6 [Pd(PBut3)2]
3 3 2 6
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0

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Table 6 Intramolecular C–HM and C–HO hydrogen bonds present in the crystal structures of 2·1.6CH2Cl2, 3·2CH2Cl2, 5, 8·ꢀCH2Cl2,
11·2ꢁCH2Cl2 and 12·2C7H8
Hydrogen bond
CX/Å
HX/Å
C–HX/°
2·1.6CH2Cl2
3·2CH2Cl2
5
C(15)–H(15)Rh(1)
C(312)–H(312)Rh(1)
C(14)–H(14)Rh(1)
C(14)–H(14)O(1)
C(11)–H(11)Pd(1)
C(14)–H(14)Pd(1)
C(59)–H(59)Pd(2)
C(99)–H(99)Pd(3)
C(135)–H(135)Pd(4)
C(11)–H(11)Pd(1)
C(14)–H(14)Pd(1)
C(26)–H(26)Pd(1)
C(38)–H(38)Pd(2)
C(50)–H(50)Pd(2)
C(62)–H(62)Pd(2)
3.458
3.402
3.378
3.322
3.436
3.199
3.150
3.259
3.168
3.385
3.181
3.260
3.190
3.366
3.266
2.65
2.68
2.77
2.40
2.65
2.43
2.40
2.51
2.37
2.96
2.70
2.71
2.73
2.99
2.70
144
134
122
162
140
138
136
136
141
108
112
118
111
105
119
8·ꢀCH2Cl2
11·2ꢁCH2Cl2
12·2C7H8
solid state being retained in solution. In all of the complexes
the 1H NMR spectra showed H1 and H8 to be equivalent.
redissolved in THF (50 cm3). PClPh2 (2.76 g, 12.5 mmol) was
added dropwise and the reaction mixture was stirred for 3 h.
The solution was filtered and the solvent was evaporated under
reduced pressure. The resulting white solid was washed with
hexane and dried under reduced pressure. Recrystallisation from
THF–hexane at −25 °C gave colourless crystals of L1. Yield:
4.17 g (95%). Calc. for C24H18NP: C, 82.0; H, 5.16; N, 3.99.
Found: C, 81.8; H, 5.27; N, 3.90%. 31P{1H} NMR (161.8 MHz,
Conclusions
The series of N-carbazolyl phosphines PPh3−n(NC12H8)n (n = 1,
L1; n = 2, L2; n = 3, L3) has been synthesised via formation
of the N-carbazolyl lithium salt, which was subsequently
reacted with the chlorophosphines PClnPh3−n (n = 1–3). The
N-carbazolyl group has similar electronic properties to the N-
pyrrolyl group, while being more sterically demanding. Thus
these ligands form a series of bulky electron-withdrawing
phosphines, which are an under-represented class of ligand.2
The variation in stereoelectronic properties on increasing the
number of N-carbazolyl groups is manifested in differences
in reactivity to water, and also in the products observed from
reaction with rhodium(I) and palladium(II) centres. Differences
in the products of the reaction with [Pd2(dba)3]·CHCl3 and an
excess of phosphine between L3 and polyaromatic phosphines
reflects the importance of both steric and electronic factors in
determining the reaction products. The observation of C–HM
hydrogen bonds is observed with rhodium(I), palladium(II)
and palladium(0). These hydrogen atoms can be readily
activated with palladium(II) as reflected by the facile synthesis
of cyclometallated products.
1
CDCl3): d 32.7 (s). H NMR (399.8 MHz, CDCl3): d 8.21 (m,
2H, H4,5), 7.71 (m, 2H, H1,8), 7.61 (m, 4H, Ho), 7.44–7.39 (m,
10H, Hm, Hp, H2,7, H3,6). 13C{1H} NMR (100.5 MHz, CDCl3):
d 143.5 (d, 2JCP 7 Hz, C10,13), 134.1 (d, 1JCP 13 Hz, Ci), 131.0 (d,
2JCP 20 Hz, Co), 129.0 (s, Cp), 128.4 (d, 3JCP 6 Hz, Cm), 125.8 (s,
C11,12), 125.4 (s, C2,7), 120.5 (s, C4,5), 119.9 (s, C3,6), 113.6 (d, 3JCP
12 Hz, C1,8).
Synthesis of di-N-carbazolylphenylphosphine L2
As for L1 using carbazole (3.00 g, 17.9 mmol), BuLi (7.2 cm3 of
2.5 M hexane solution, 18.0 mmol) and PCl2Ph (1.61 g, 9.0 mmol).
Recrystallisation from boiling acetone gave colourless crystals
of L2. Yield: 3.16 g (80%). Calc. for C30H21N2P: C, 81.8; H,
4.81; N, 6.36. Found: C, 81.6; H, 4.80; N, 6.30%. 31P{1H} NMR
(121.5 MHz, CDCl3): d 52.9 (s). 1H NMR (300.2 MHz, CDCl3):
d 8.05–8.01 (m, 4H, H4,5), 7.62–7.55 (m, 4H, H1,8), 7.54–7.48 (m,
3H, Hm, Hp), 7.46–7.43 (m, 2H, Ho), 7.43–7.24 (m, 8H, H2,7,
H3,6). 13C{1H} NMR (75.5 MHz, CDCl3): d 143.2 (d, 2JCP 7 Hz,
C10,13), 132.4 (d, 1JCP 6 Hz, Ci), 131.3 (d, 3JCP 22 Hz, Cm), 130.6 (s,
Cp), 129.5 (d, 2JCP 6 Hz, Co), 126.4 (s, C11,12), 126.2 (s, C2,7), 121.4
(s, C3,6), 120.3 (s, C4,5), 113.8 (d, 3JCP 14 Hz, C1,8).
Experimental
General experimental
Reactions were routinely carried out using Schlenk-line
techniques under pure dry dinitrogen or argon, using dry
dioxgen-free solvents unless noted otherwise. Microanalyses
(C, H and N) were carried out by Mr Alan Carver (University of
Bath Microanalytical Service). Infrared spectra were recorded
on a Nicolet 510P spectrometer as KBr pellets, Nujol mulls on
KBr discs or in solutions using KBr cells. NMR spectra were
recorded on JEOL EX-270, Varian Mercury 400 and Bruker
Avance 300 spectrometers referenced to TMS or 85% H3PO4. The
complexes [Rh(l-Cl)(CO)2]2,45 [Rh(acac)(CO)2],46 [PdCl2(cod)],47
Synthesis of tri-N-carbazolylphosphine L3
As for L1 using carbazole (3.00 g, 17.9 mmol), BuLi (7.2 cm3
of 2.5 M hexane solution, 18.0 mmol), PCl3 (3.0 cm3 of 2.0 M
dichloromethane solution, 6.0 mmol). Recrystallisation from
boiling acetone gave colourless crystals. Yield: 2.98 g (94%).
Calc. for C36H24N3P: C, 81.6; H, 4.57; N, 7.93. Found: C,
81.2; H, 4.49; N, 7.93%. 31P{1H} NMR (161.8 MHz, CDCl3):
1
d 77.6 (s). H NMR (399.8 MHz, CDCl3): d 8.07 (d ps quin,
49
[PdCl2(NCMe)2]48 and [Pd2(dba)3]·CHCl3 were prepared by
3
4
5
5
6H, JHH 8.0 Hz, JHH 1.6 Hz, JHH 0.8 Hz, JHP 0.8 Hz, H4,5),
7.28–7.24 (m, 6H, H3,6), 7.19–7.11 (m, 12H, H1,8, H2,7). 13C{1H}
NMR (75.5 MHz, CDCl3): d 142.1 (d, 2JCP 10 Hz, C10,13), 127.2
(s, C2,7), 126.9 (s, C11,12), 122.3 (s, C4,5), 120.7 (s, C3,6), 113.4 (d,
3JCP 13 Hz, C1,8).
standard literature methods. Carbazole was recrystallised from
boiling acetone before use, whereas triethylamine was distilled
over potassium.
Synthesis of N-carbazolyldiphenylphosphine L1
Isolation of N-carbazolylchlorophenylphosphine
A 2.5 M hexane solution of BuLi (5.0 cm3, 12.5 mmol) was
added dropwise to a stirred THF–hexane solution (50 cm3)
of carbazole (2.10 g, 12.6 mmol) at −78 °C. The reaction
mixture was allowed to warm to room temperature and stirred
for 2 h. Hexane was added to precipitate a white powder,
which was isolated by filtration, washed with hexane and then
A THF solution (40 cm3) of triethylamine (1.02 g, 10.1 mmol),
carbazole (1.50 g, 9.0 mmol) and PCl2Ph (0.6 cm3, 4.4 mmol)
was stirred for 24 h. The solution was separated by filtra-
tion and the solvent eliminated under reduced pressure. The
resulting white powder was extracted with hexane from which
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0
3 3 2 7

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the compound crystallised at −25 °C. Yield: 0.410 g (30%).
Calc. for C18H13ClNP: C, 69.8; H, 4.23; N, 4.52. Found: C,
70.0; H, 4.41; N, 4.45%. 31P{1H} NMR (161.8 MHz, CDCl3):
CO), 143.2 (d, J 2 Hz), 132.7 (d, J 12 Hz), 131.9 (s), 131.1 (s),
128.6 (d J 11 Hz), 126.7 (d, J 4 Hz), 125.8 (s), 121.6 (s), 120.0 (s),
116.7 (d, J 4 Hz), 101.1 (d, J 2 Hz, CH), 27.9 (d, J 6 Hz, CH3),
26.7 (s, CH3).
1
d 99.0 (s). H NMR (399.8 MHz, CDCl3): d 8.05–8.03 (m, 2H,
H4,5), 7.67–7.64 (m, 2H, Ho), 7.55–7.54 (m, 2H, H1,8), 7.46–7.42
(m, 3H, Hm, Hp), 7.37–7.30 (m, 4H, H2,7, H3,6). 13C{1H} NMR
(75.5 MHz, CDCl3): d 141.2 (d, 2JCP 9 Hz, C10,13), 135.9 (d, 3JCP
27 Hz, C11,12), 129.9 (d, JCP 6 Hz, Ci), 129.3 (d, JCP 2 Hz Co),
128.7 (d, 3JCP 20 Hz Cm), 128.0 (d, 4JCP 3 Hz Cp), 125.1 (s, C2,7),
121.1 (s, C3,6), 119.3 (s, C4,5), 113.1 (d, 3JCP 14 Hz, C1,8).
Synthesis of [Rh(acac)(CO)(L2)] 5
A dichloromethane solution (30 cm3) of [Rh(acac)(CO)2]
(0.166 g, 0.64 mmol) and L2 (0.284 g, 0.64 mmol) was heated
at reflux for 6 h after which half of the solvent was removed
under reduced pressure, resulting in the formation of a yellow
precipitate. Hexane was added, resulting in the formation of
more precipitate, which was isolated by filtration and washed
with hexane. Yield: 0.380 g (88%). Calc. for C36H28N2O3PRh:
C, 64.5; H, 4.21; N, 4.18. Found: C, 64.2; H, 4.19; N, 4.12%. 1H
1
2
Synthesis of trans-[RhCl(CO)(L1)2] 1
[Rh(l-Cl)(CO)2]2 (0.077 g, 0.20 mmol) was added with stirring to
a dichloromethane solution (20 cm3) of L1 (0.280 g, 0.80 mmol).
After 2 h stirring the solvent was removed under reduced pres-
sure and the resulting yellow powder washed with diethyl ether
and dried under reduced pressure. Yield: 0.313 g (90%). Calc.
for C49H36ClN2OP2Rh: C, 67.7; H, 4.17; N, 3.22. Found: C,
67.7; H, 4.21; N, 3.29%. 31P{1H} NMR (161.8 MHz, CD2Cl2):
d 59.4 (d, 1JPRh 137 Hz). 1H NMR (399.8 MHz, CD2Cl2): d 8.02
3
NMR (399.8 MHz, CDCl3): d 8.04 (d, 4H, JHH 7.6 Hz, H4,5),
7.89 (d, 4H, 3JHH 8.4 Hz, H1,8), 7.81–7.76 (m, 2H, Ho), 7.43–7.39
(m, 1H, Hp), 7.33–7.28 (m, 2H, Hm), 7.28–7.24 (m, 4H, H3,6),
7.16–7.11 (m, 4H, H2,7), 5.27 (s, 1H, CH), 2.04 (s, 3H, CH3), 1.04
(s, 3H, CH3). 13C{1H} NMR (100.5 MHz, CDCl3): d 187.8 (dd,
1JCRh 76 Hz, 2JCP 26 Hz, CO), 187.0 (s, CO), 185.7 (s, CO),
142.3 (d, 2JCP 4 Hz, C10,13), 133.7 (dd, 2JCRh 63 Hz, 1JCP 4 Hz, Ci),
132.1 (d, 2JCP 15 Hz, Co), 131.3 (d, 3JCP 2 Hz, C11,12), 127.9 (d, 3JCP
12 Hz, Cm), 126.6 (d, 4JCP 4 Hz, Cp), 125.9 (s, C2,7), 121.8 (s, C3,6),
119.5 (s, C4,5), 116.0 (d, 3JCP 4 Hz, C1,8), 100.6 (d, 3JCRh 2 Hz, CH),
27.4 (d, 3JCRh 5 Hz, CH3), 25.4 (s, CH3).
3
(d, 4H, JHH 7.6 Hz, H4,5), 7.84–7.79 (m, 8H, Ho), 7.75 (d, 4H,
3JHH 8.4 Hz, H1,8), 7.50–7.39 (m, 12H, Hm, Hp), 7.26–7.22 (m,
4H, H3,6), 7.13–7.09 (m, 4H, H2,7). 13C{1H} NMR (100.5 MHz,
1
2
CD2Cl2): d 185.9 (dt, JCRh 75 Hz, JCP 16 Hz, CO), 142.8 (s,
C10,13), 133.3 (s, Cp), 131.4 (m, Co, Ci), 128.7 (m, Cm), 126.8 (s,
C11,12), 125.5 (s, C2,7), 121.7 (s, C3,6), 120.1 (s, C4,5), 116.2 (s, C1,8).
IR (CH2Cl2, cm−1): 1992s [m(CO)].
Synthesis of [Rh(acac)(CO)(L3)] 6
An acetone solution (20 cm3) of [Rh(acac)(CO)2] (0.040 g,
0.16 mmol) and L3 (0.106 g, 0.20 mmol) was heated at reflux for
8 h. On cooling the excess of L3 slowly precipitated. The solu-
tion was separated by filtration and the solvent eliminated under
reduced pressure. The resulting yellow powder was washed with
hexane and dried under reduced pressure. Yield: 0.100 g (85%).
Calc. for C42H31N3O3PRh: C, 66.4; H, 4.11; N, 5.53. Found: C,
66.2; H, 4.10; N, 5.43%. 1H NMR (399.8 MHz, CDCl3): d 7.98
(d, 6H, 3JHH 8.0 Hz, H4,5), 7.74 (d, 6H, 3JHH 8.4 Hz, H1,8), 7.27–
7.21 (m, 6H, H3,6), 7.07–7.03 (m, 6H, H2,7), 5.17 (s, 1H, CH), 1.96
(s, 3H, CH3), 0.81 (s, 3H, CH3).
Synthesis of trans-[RhCl(CO)(L2)2] 2
As for 1 using [Rh(l-Cl)(CO)2]2 (0.088 g, 0.23 mmol) and
L2 (0.400 g, 0.91 mmol). Yield: 0.460 g (97%). Calc. for
C61H42ClN4OP2Rh·ꢀCH2Cl2: C, 67.8; H, 3.98; N, 5.14. Found:
C, 67.8; H, 4.01; N, 5.24%. 31P{1H} NMR (121.5 MHz, CDCl3):
d 86.4 (d, 1JPRh 159 Hz). 1H NMR (300.2 MHz, CDCl3): d 8.01
(d, 8H, 2JHH 7.6 Hz, H4,5), 7.85–7.78 (m, 4H, Ho), 7.61 (dm, 8H,
2JHH 8.4 Hz, H1,8), 7.46–7.41 (m, 2H, Hp), 7.32–7.21 (m, 12H,
H3,6, Hm), 7.04–6.91 (m, 8H, H2,7). 13C{1H} NMR (100.5 MHz,
1
2
CD2Cl2): d 186.1 (dt, JCRh 75 Hz, JCP 15 Hz, CO), 142.5 (m,
C10,13), 134.0 (m, Cp), 131.9 (m, Co, Ci), 128.5 (m, Cm), 127.2 (m,
C11,12), 126.3 (s, C2,7), 122.4 (s, C3,6), 120.2 (s, C4,5), 116.4 (s, C1,8).
IR (CH2Cl2, cm−1): 2000s [m(CO)].
Synthesis of [PdCl2(L1)2] 7
[PdCl2(cod)] (0.230 g, 0.81 mmol) was added to a dichloro-
methane solution (30 cm3) of L1 (0.605 g, 1.72 mmol) with
stirring. After a few minutes a yellow precipitate started to
form. Stirring was continued for a further 2 h and the precipitate
isolated by filtration, washed with hexane and dichloromethane,
then dried under reduced pressure. Yield: 0.423 g (60%). Calc.
for C48H36Cl2N2P2Pd·CH2Cl2: C, 61.0; H, 3.97; N, 2.90. Found:
C, 61.4; H, 3.97; N, 3.10%. 31P{1H} NMR (109.3 MHz, CD2Cl2):
Synthesis of trans-[Rh(l-Cl)(CO)(L3)]2 3
[Rh(l-Cl)(CO)2]2 (0.031 g, 0.08 mmol) was added with stirring to
a dichloromethane solution (20 cm3) of L3 (0.085 g, 0.16 mmol).
After ca. 15 min a yellow precipitate started to form. The reac-
tion mixture was stirred overnight and the precipitate isolated by
filtration, washed with small portions of dichloromethane and
dried under reduced pressure. Yield: 0.095 g (85%). Calc. for
C74H48Cl2N6O2P2Rh2·ꢁCH2Cl2: C, 63.1; H, 3.46; N, 5.95. Found:
C, 63.0; H, 3.48; N, 5.91%. 31P{1H} NMR (161.8 MHz, CD2Cl2):
d 90.0 (d, 1JPRh 257 Hz). 1H NMR (399.8 MHz, CD2Cl2): d 8.00
(d, 12H, 3JHH 8.0 Hz, H 4,5), 7.75 (d, 12H, 3JHH 8.0 Hz, H1,8), 7.25
(ps t, 12H, 3JHH 8.0 Hz, H3,6), 7.03 (ps t, 12H, 3JHH 8.0 Hz, H2,7).
IR (CH2Cl2, cm−1): 2015s [m(CO)].
1
2
d 51.3 (s). H NMR (270.2 MHz, CD2Cl2): d 8.02 (d, 4H, JHH
2
7.6 Hz, H4,5), 7.84–7.79 (m, 8H, Ho), 7.75 (d, 4H, JHH 8.4 Hz,
H1,8), 7.50–7.39 (m, 12H, Hp, Hm), 7.26–7.22 (m, 4H, H3,6),
7.13–7.09 (m, 4H, H2,7).
Formation of [Pd(l-Cl){P(NC12H8)2(NC12H7)-j2P,C}]2 8
A dichloromethane solution (20 cm3) of L3 (0.100 g, 0.19 mmol)
and [PdCl2(NCMe)2] (0.048 g, 0.19 mmol) was stirred for 4 h at
room temperature. The solution was layered with hexane and
left at ambient temperature. After 2 days small orange crystals
were present which were separated by filtration. Yield 0.096 g
(77%). Calc. for C72H46Cl2N6P2Pd2·CH2Cl2: C, 61.5; H, 3.39; N,
5.89. Found: C, 61.3; H, 3.44; N, 5.85%.
Synthesis of [Rh(acac)(CO)(L1)] 4
A dichloromethane solution (20 cm3) of [Rh(acac)(CO)2]
(0.100 g, 0.39 mmol) and L1 (0.141 g, 0.40 mmol) was stirred
for 4 h after which the solvent was removed under reduced pres-
sure. The resulting yellow powder was crystallised from hexane
at −25 °C. Yield: 0.200 g (89%). Calc. for C30H25NO3PRh:
C, 62.0; H, 4.33; N, 2.41. Found: C, 61.4; H, 4.99; N, 2.20%.
Formation of [PdCl2(L2)2] 9 and [Pd(l-Cl){PPh(NC12H8)-
(NC12H7)-j2P,C}]2 10
1H NMR (399.8 MHz, CDCl3): d 8.10 (d, 2H, JHH 8.4 Hz,
3
3
H4,5), 8.06 (dm, 2H, JHH 7.6 Hz, H1,8), 7.74–7.68 (m, 4H, Ho),
[PdCl2(NCMe)2] (0.059 g, 0.23 mmol) was added to a dichloro-
methane solution (20 cm3) of L2 (0.200 g, 0.45 mmol) with
stirring. The mixture was stirred for 8 h and the solvent removed
under reduced pressure. The resulting yellow powder was washed
7.44–7.40 (m, 2H, Hp), 7.38–7.33 (m, 4H, Hm), 7.28–7.24 (m,
2H, H2,6), 7.20–7.15 (m, 2H, H3,7), 5.38 (s, 1H, CH), 2.09 (s, 3H,
CH3), 1.39 (s, 3H, CH3). 13C{1H} NMR (75.5 MHz, CDCl3): d
189.4 (dd, 1JCRh 76 Hz, 2JCP 26 Hz, CO), 187.7 (s, CO), 186.1 (s,
3 3 2 8
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0

View Article Online
with diethyl ether, dissolved in dichloromethane and layered
with hexane. On standing orange crystals and a yellow powder
separated out of solution. The crystals and the powder were
separated manually. 9: Calc. for C60H42Cl2N4P2Pd·ꢁCH2Cl2:
C, 67.0; H, 3.97; N, 5.19. Found: C, 66.9; H, 3.94; N, 5.26%.
1
31P{1H} NMR (109.3 MHz, CD2Cl2): d 70.0 (s). H NMR
2
(300.2 MHz, CD2Cl2): d 8.03 (d, 8H, JHH 7.6 Hz, H4,5), 7.67–
7.43 (m, 6H, Ho, Hp), 7.50 (d, 8H, 2JHH 8.4 Hz, H1,8), 7.28–7.21
(m, 12H, Hm, H3,6), 7.02–6.96 (m, 8H, H2,7). 10: Calc. for
C60H40Cl2N4P2Pd2·CH2Cl2: C, 58.7; H, 3.39; N, 4.49. Found: C,
58.5; H, 3.42; N, 4.38%. 31P{1H} NMR (109.3 MHz, CD2Cl2):
d 86.8 (s).
Synthesis of [Pd(l-O2CCH3){P(NC12H8)2(NC12H7)-j2P,C}]2 11
L3 (0.172 g, 0.32 mmol) was added to a toluene solution
(20 cm3) of Pd(OAc)2 (0.071 g, 0.32 mmol) with stirring. The
solution which had rapidly changed colour form dark red to
yellow was heated at 50 °C for 10 min and then allowed to
cool to ambient temperature. Stirring was continued for 1 h,
after which half of the solvent was evaporated under reduced
pressure and hexane added to precipitate a yellow powder. The
precipitate was isolated by filtration, washed with hexane and
dried under reduced pressure. Yield: 0.198 g (90%). Calc. for
C76H52N6O4P2Pd2·ꢀCH2Cl2: C, 64.2; H, 3.73; N, 5.87. Found: C,
64.4; H, 4.05; N, 5.42%. 31P{1H} NMR (161.8 MHz, CD2Cl2): d
85.5 (s). 1H NMR (399.8 MHz, CD2Cl2): d 7.87 (br, 8H), 7.60 (d,
4H, J 8.0 Hz), 7.14–7.06 (m, 12H), 7.00–6.97 (m, 4H), 6.83 (br,
8H), 6.71–6.66 (m, 6H), 6.27–6.24 (m, 2H), 5.87–5.82 (m, 2H),
2.01 (s, 6H, CH3). 13C{1H} NMR (100.5 MHz, CD2Cl2): d 180.4
(s, CO2), 140.3 (m), 136.5 (m), 133.5 (m), 133.5 (s), 128.7 (s),
127.2 (s), 126.1 (s), 124.7 (s), 122.8(s), 122.6(s), 121.8 (s), 121.0
(s), 120.4 (m), 118.1 (m), 116.8 (s), 115.8 (s), 115.5 (s), 25.3 (s,
CH3). IR (Nujol, cm−1): 1577s, 1560s [m(CO2)].
Synthesis of [Pd(L3)2] 12
A toluene solution (20 cm3) containing [Pd2(dba)3]·CHCl3
(0.130 g, 0.13 mmol) and L3 (0.266 g, 0.50 mmol) was stirred
for 4 h with the formation of a pale yellow powder. This was
separated by filtration, washed with small amounts of toluene
and dried under reduced pressure. Yield: 0.278 g (95%). Calc.
for C72H48N6P2Pd·2C7H8: C, 76.5; H, 4.78; N, 6.23. Found: C,
76.5; H, 4.82; N, 6.36%. 31P{1H} NMR (161.8 MHz, CD2Cl2):
d 75.1 (s). 1H NMR (399.8 MHz, CD2Cl2): d 8.01 (d, 12H, 2JHH
7.6 Hz, H4,5), 7.16 (d, 12H, 2JHH 8.4 Hz, H1,8), 7.13–7.09 (m, 12H,
H3,5), 6.50–6.46 (m, 12H, H2,6). 13C{1H} NMR (75.5 MHz,
CD2Cl2): d 138.7 (m), 129.7 (s), 128.9 (s), 126.0 (s), 123.1 (s),
120.6 (s).
Crystallography
Single crystals of compounds 2·1.6CH2Cl2, 3·2CH2Cl2, 5,
8·ꢀCH2Cl2, 11·2ꢁCH2Cl2 and 12·2C7H8 were analysed using a
Nonius Kappa CCD diffractometer and molybdenum radiation
throughout. Details of the data collections, solutions and
refinements are given in Table 7. The structures were solved using
SHELXS-9750 and refined using SHELXL-97.51 Absorption
corrections (semi-empirical from equivalent reflections) were
applied to data for 2·1.6CH2Cl2, 3·2CH2Cl2, 11·2ꢁCH2Cl2 and
12·2C7H8. [Max./min. transmission factors 0.94 0.83, 0.92 0.87,
0.94 0.83 and 0.97 0.84 respectively]. Convergence was routine
throughout with the exception of the observations below.
Despite valiant recrystallisation efforts, the optimum
quality crystal for 2·1.6CH2Cl2 was of mediocre quality, and very
thin. Early fall-off in diffracting power is reflected in R(sigma),
R(int), final residuals for these data and the anomalously large
residual electron density maximum in the Difference Fourier
map within 1.505 Å of H(11). Structural solution revealed
that the asymmetric in this structure unit contains one half of
a molecule of the metal complex, with the metal located at an
inversion centre. Consequently, the chloride and carbonyl ligands
D a l t o n T r a n s . , 2 0 0 4 , 3 3 2 1 – 3 3 3 0
3 3 2 9

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R. W. Harrington, M. F. Mahon, M. T. Palmer, F. Senia and
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are disordered in a 1:1 ratio about this symmetry element. The
asymmetric unit was also found to contain two dichloromethane
fragments, each at 0.4 occupancy. These solvent fragments are
proximate to crystallographic symmetry elements and hence are
disordered. Partial solvent atoms were refined isotropically, and
hydrogen atoms were omitted therein.
In 3·2CH2Cl2 the asymmetric unit was also seen to consist
of one half of a molecule of 3 plus one molecule of dichloro-
methane. The solvent chlorine atoms were disordered but
readily modelled. Nonetheless, analysis of the least squares
output indicated that the largest shifts were associated with
the partial solvent carbons [C(40), C(40B)]. Consequently, the
positional coordinates of these partial occupancy atoms were
fixed in the final convergence run.
The asymmetric unit in 11·2ꢁCH2Cl2 was seen to comprise
two molecules of 11 in addition to four and a half molecules
of dichloromethane. Three of the solvent molecules [i.e. those
based on C(153), C(154) and C(155)] were seen to exhibit full
site occupancy with no disorder. However, the solvent molecule
based in C(156) exhibited 50% occupancy and the chlorines
therein were best modelled as being evenly distributed over
3 sites each at 0.33 occupancy. The remaining solvent mole-
cule was also disordered. Optimum refinement was achieved
by treating this dichloromethane as being shared between 3
sites based on C(157) (50%), C(158) (25%) and C(159) (25%).
Carbon chlorine bond distances were restrained to being the
same within individual disordered fragments, as were the
ADPs in the individual fragments of the molecule based on
C(157)–(159). However, analysis of the least squares output
indicated that the most diffuse region of the electron density
map surrounded the partial solvent carbons [C(157), C(158),
C(159)], which also registered the largest shifts. Consequently,
the positional coordinates of these partial occupancy atoms
were not refined in the final convergence run.
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The asymmetric unit in 12·2C7H8 was seen to be equivalent to
two independent halves of the palladium complex, in addition
to two full molecules of toluene. One of the toluene molecules
is slightly disordered, but attempts to model this disorder did
not afford any significant improvement in convergence.
Crystallographic data for compounds 2·1.6CH2Cl2,
3·2CH2Cl2, 5, 8·ꢀCH2Cl2, 11·2ꢁCH2Cl2 and 12·2C7H8 have
been deposited as CCDC 241491–241496.
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See http://www.rsc.org/suppdata/dt/b4/b408841g/ for crystal-
lographic data in .CIF or other electronic format.
Acknowledgements
The EPSRC is thanked for financial support.
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