Synthesis and reactivity of rhodium(1) complexes containing keto-functionalised N-pyrrolyl phosphine ligands

Article abstract of DOI:10.1039/b306292a

The reaction of [Rh(μ-Cl)(CO)₂]₂ with two equivalents of L [L = PR₂{NC₄H₃C(O)Me-2}; R = Ph, L¹; R = NC₄H₄, L²] gave the P,O-chelate complexes [RhCl(CO)(L-κ²P,O)] (1, L = L¹; 2, L = L²), whereas reaction with four equivalents of L gave [RhCl(CO)(L)₂] (3, L = L¹; 4, L = L²). Complexes 3 and 4 are fluxional in solution, and at low temperatures exist predominantly with one of the two keto groups coordinated. Complexes 3 and 4 undergo metal-promoted hydrolysis reactions with adventitious water leading to the diphosphoxane-bridged dimers [RhCl(CO)(μ-PR₂OPR₂)]₂ (5, R = Ph; 6, R = NC₄H₄), with the carbonyl and chloride ligands both terminal and semi-bridging in 5 but solely terminal in 6. Complexes 3 and 4 react with NH₄PF₆ or TIPF₆ to give cis-[Rh(L-κ²P,O)₂] PF₆ (7b, L = L¹; 8, L = L²). These complexes are also formed from the reaction of L with [Rh(μ-Cl)(cod)]₂ in the presence of NH₄PF₆. Complex 8 reacts with CO to give [Rh(CO)(L²)₂]PF₆ 9, with PMe₃ to give [Rh(PMe₃)₂ (L²-κ²P,O)]PF₆ 10, and with [NEt₃Bz]Cl (Bz = CH₂Ph) to give [RhCl(L²-κ¹P)(L²-κ²P,O)] 11. Complexes 2, 5·CH₂Cl₂, 6·C₇H₈, 7b, 8 and 11 have been crystallographically characterised. The electron-withdrawing character of L¹ and L² has led to differences in reactivity from the β-ketophosphine PPh₂CH₂C(O)Ph and the ether-phosphine PPh₂CH₂OMe.

Full text of DOI:10.1039/b306292a

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Synthesis and reactivity of rhodium(I) complexes containing
keto-functionalised N-pyrrolyl phosphine ligands
Andrew D. Burrows,* Ross W. Harrington, Mary F. Mahon, Mark T. Palmer, Francesco Senia
and Maurizio Varrone
Department of Chemistry, University of Bath, Claverton Down, Bath, UK BA2 7AY
Received 3rd June 2003, Accepted 11th August 2003
First published as an Advance Article on the web 28th August 2003
The reaction of [Rh(µ-Cl)(CO)2]2 with two equivalents of L [L = PR2{NC4H3C(O)Me-2}; R = Ph, L1; R = NC4H4, L2]
gave the P, O-chelate complexes [RhCl(CO)(L-κ2P, O )] (1, L = L1; 2, L = L2), whereas reaction with four equivalents of
L gave [RhCl(CO)(L)2] (3, L = L1; 4, L = L2). Complexes 3 and 4 are fluxional in solution, and at low temperatures
exist predominantly with one of the two keto groups coordinated. Complexes 3 and 4 undergo metal-promoted
hydrolysis reactions with adventitious water leading to the diphosphoxane-bridged dimers [RhCl(CO)(µ-PR2OPR2)]2
(5, R = Ph; 6, R = NC4H4), with the carbonyl and chloride ligands both terminal and semi-bridging in 5 but solely
terminal in 6. Complexes 3 and 4 react with NH4PF6 or TlPF6 to give cis-[Rh(L-κ2P, O )2]PF6 (7b, L = L1; 8, L = L2).
These complexes are also formed from the reaction of L with [Rh(µ-Cl)(cod)]2 in the presence of NH4PF6. Complex 8
reacts with CO to give [Rh(CO)(L2)2]PF6 9, with PMe3 to give [Rh(PMe3)2(L2-κ2P, O )]PF6 10, and with [NEt3Bz]Cl
(Bz = CH2Ph) to give [RhCl(L2-κ1P)(L2-κ2P, O )] 11. Complexes 2, 5ؒCH2Cl2, 6ؒC7H8, 7b, 8 and 11 have been
crystallographically characterised. The electron-withdrawing character of L1 and L2 has led to differences in
reactivity from the β-ketophosphine PPh2CH2C(O)Ph and the ether-phosphine PPh2CH2CH2OMe.
solution of PCl(NC4H4)2 15 with 2-acetylpyrrole in the presence
Introduction
of the base NEt3. The ligand L2 was isolated as a colourless
Hybrid ligands, carrying a combination of soft and hard donor
crystalline material and characterised by multinuclear NMR
atoms, continue to attract widespread interest in coordination
and IR spectroscopy. The 31P{1H} NMR spectrum of L2
and organometallic chemistry.1–4 This attention has concen-
showed a singlet at δ 75.1 indicating that the phosphorus is
trated to a large extent on the potential of these ligands to
display hemilabile behaviour on platinum group metal centres,
and the catalytic opportunities that this reversible generation of
vacant coordination sites engenders. The two most important
deshielded relative to L1, which was observed at δ 55.8. This is
consistent with the pyrrolyl rings acting as stronger electron-
withdrawing groups than the phenyl rings, and a similar differ-
ence was reported for the N-pyrrolyl phosphines P(NC4H4)3
classes of P, O-donor ligand that have been studied are ether-
(δ 79.6) and PPh2(NC4H4) (δ 48.1).14
phosphines5–8 and ketophosphines,9–11 and the chemistry of
In the 1H NMR spectrum of L2 the signals for the protons of
these two ligand types can differ due to the greater coordinating
ability of the carbonyl group, with respect to an ether, towards a
late transition metal centre.
We have recently reported the synthesis of the keto-function-
the 2-acetylpyrrolyl ring appeared as distinctive but unresolved
multiplets. The signals for the protons of the non-functional-
ised pyrrolyl rings appeared as an overlapping doublet of
pseudo triplets (pseudo quintet) at δ 6.74 and a pseudo triplet at
alised N-pyrrolyl phosphine ligand PPh2{NC4H3C(O)Me-2}
δ 6.33. The signal for the methyl group was a distinctive singlet
L1,12 and shown that it can act as either a P-donor or a P, O -
at δ 2.35, similar to that observed for L1 at δ 2.43.12 The IR
donor on molybdenum.13 The strong π-acceptor character of
spectrum showed a strong absorption at 1637 cmϪ1 for ν(CO),
N-pyrrolyl phosphines14 leads to an enhanced electronic differ-
which is similar to that reported for L1 [ν(CO) 1643 cmϪ1].
ence between the donor atoms in these ligands, and we reasoned
that this could lead to a differentiation in the reactivity of these
ligands from other ketophosphines such as PPh2CH2C(O)Ph.
In this paper we report the synthesis of the functionalised tri-
Ligand L2 is air and moisture sensitive, decomposing both in
solution and the solid state to yield intractable purple com-
pounds. Ligand L2 reacts rapidly with methanol at ambient
temperature with the formation of (C4H4N)2POMe and 2-acetyl-
pyrrole. The functionalised pyrrole ring is selectively substi-
tuted, which may simply be a consequence of it being a better
(N-pyrrolyl)phosphine ligand P(NC4H4)2{NC4H3C(O)Me-2}
L2, which is anticipated to be a better π-acceptor than L1, and
the rhodium() chemistry of L1 and L2. The use of L1 in the
leaving group than the unfunctionalised pyrrolyl groups. Alter-
rhodium-catalysed hydroformylation of 2-pentene has recently
natively, it is possible that the acetyl functionality plays a role in
been reported by Beller and co-workers.15 Some of the results
determining the selectivity, with hydrogen bond formation to
discussed in this paper have been previously reported in a
the incoming protic nucleophile acting as a directing force in a
preliminary communication.16
manner analogous to the mechanism proposed as an explan-
ation for the high reactivity of N-pyrazolyl phosphines towards
protic reagents.17
Synthesis and characterisation of [RhCl(CO)(L-ꢀ2P,O)]
(1, L ؍ L1; 2, L ؍ L2)
The reaction of [Rh(µ-Cl)(CO)2]2 with two equivalents of L1 or
L2 in dichloromethane gave the P, O -chelate complexes [RhCl-
(CO)(L1-κ2P, O )] 1 and [RhCl(CO)(L2-κ2P, O )] 2 respectively.
Complexes 1 and 2 were characterised on the basis of IR and
multinuclear NMR spectroscopy, and the molecular structure
of 2 was confirmed by a single crystal X-ray crystallographic
study. The IR spectra provided strong evidence for the
Results and discussion
Synthesis of P(NC4H4)2{NC4H3C(O)Me-2} L2
The ligand P(NC4H4)2{NC4H3C(O)Me-2} L2 can be prepared
in an analogous manner12 to L1 via the reaction of a THF
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 3
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
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Table 1 Selected bond lengths (Å) and angles (Њ) for complex 2
coordination of the keto group in the complexes. The ν(C᎐O)
᎐
absorption bands were observed at 1576 cmϪ1 for 1 and 1572
cmϪ1 for 2, both shifted significantly to lower wavenumbers9,12
with respect to the free ligands. The higher frequency of
the metal carbonyl stretch for 2 [ν(CO) 2017 cmϪ1] compared
with 1 [ν(CO) 1989 cmϪ1] is consistent with L2 being a better
π-acceptor than L1, as anticipated from the greater number of
N-pyrrolyl substituents, which reduces the back-donation to the
metal carbonyl.
Rh(1)–O(1)
Rh(1)–P(1)
Rh(1)–Cl(1)
Rh(1)–C(15)
2.0701(12)
2.1474(4)
2.3492(4)
1.8152(19)
P(1)–N(1)
P(1)–N(2)
P(1)–N(3)
C(2)–O(1)
1.7085(14)
1.6965(14)
1.6977(15)
1.248(2)
P(1)–Rh(1)–O(1)
O(1)–Rh(1)–Cl(1)
Cl(1)–Rh(1)–C(15)
C(15)–Rh(1)–P(1)
O(1)–Rh(1)–C(15)
90.66(4)
86.46(4)
91.44(6)
91.46(6)
177.88(7)
P(1)–Rh(1)–Cl(1) 176.136(16)
N(1)–P(1)–Rh(1)
N(2)–P(1)–Rh(1)
N(3)–P(1)–Rh(1)
112.66(5)
115.83(6)
121.34(5)
The 31P{1H} NMR spectra of 1 and 2 both consisted of a
doublet, with that for 1 at δ 93.6 with 1JPRh 178 Hz, and that for
1
1
2 at δ 91.4 with JPRh 237 Hz. The higher value of JPRh in 2 is
torsion angle O(1)–C(2)–C(3)–N(1) is 2.9Њ indicating that the
acyl group is essentially co-planar with the pyrrolyl ring.
The Rh(1)–P(1) bond distance is short compared with those
reported for the complexes [RhCl(CO){PPh2(C6H4NMe2-2)-
κ2P, N }] [2.3308(10) Å22] and [Rh(acac)(CO){P(NC4H4)3}]
[2.166(1) Å23], which is consistent with the electronic character
of L2. The P–N(1) bond distance of 1.7085(14) Å is slightly
longer than the P–N(2) and P–N(3) bond distances, though in
general the P–N bond distances are similar to those observed in
the structure of trans-[RhCl(CO){P(NC4H4)3}2] (av. 1.70 Å).14
The sum of the angles around each of the nitrogen atoms in 2
are all very close to 360Њ consistent with their sp2 hybridisation.
The C(2)–O(1) bond distance is longer than that observed in the
structure of the ligand L1 [1.216(2) Å12] while being comparable
to that in [MoCp(CO)2(L1-κ2P, O )][BF4] [1.251(3) Å13]. This is
indicative of the reduced double bond character of the keto
functionalities upon coordination and is in agreement with the
IR spectroscopic data.
again indicative of L2 being a stronger π-acceptor than L1. In
the H NMR spectra of 1 and 2, the methyl resonances were
1
observed at δ 2.60 for 1 and δ 2.68 for 2, in both cases shifted
downfield with respect to the free ligands which is consistent
with coordination of the keto groups.18 In the 13C{1H} NMR
spectrum of 2 the signal for the metal carbonyl appeared as a
doublet of doublets at δ 183.9 with 1JCRh 78 Hz and 2JCP 19 Hz.
2
The low value of JCP indicates a cis arrangement of the carb-
onyl group relative to the phosphorus, which is consistent with
the two best π-acceptors avoiding a mutually trans arrange-
ment.19 The signal for the acetyl carbon was observed as a
doublet at δ 191.7 with 2JCRh 7 Hz.
These observations can be compared with the analogous
reactions of [Rh(µ-Cl)(CO)2]2 with the ether-phosphines
PPh2(CH2)nOMe (n = 1,20 2, 321) which give the compounds
[RhCl(CO)2{PPh2(CH2)nOMe-κ1P}]. This difference in reactiv-
ity is consistent with the greater coordinating ability of keto
groups with respect to the ether groups in PPh2(CH2)nOMe.
Whereas [RhCl(CO)2(PPh2CH2OMe-κ1P)] is stable to CO loss,
the compounds [RhCl(CO)2{PPh2(CH2)nOMe-κ1P}] (n = 2, 3)
can be converted to [RhCl(CO){PPh2(CH2)nOMe-κ2P, O }] by
purging solutions with nitrogen, though return to a CO atmos-
phere leads to the reformation of [RhCl(CO)2{PPh2(CH2)n-
OMe-κ1P}].21
Crystals of 2 suitable for X-ray crystallographic studies were
grown by slow diffusion of hexane into a dichloromethane solu-
tion. The molecular structure of 2 is shown in Fig. 1, and
selected bond distances and angles are given in Table 1. The
metal centre has a distorted square-planar coordination geom-
etry with cis angles between 86.46(4)Њ and 91.46(6)Њ, and a
ligand bite angle of 90.66(4)Њ. As anticipated from the
spectroscopic data, the ligand adopts a chelating mode, with the
phosphorus atom coordinated trans to the chloride. The
6-membered chelate ring assumes a half chair conformation in
which the atoms O(1), C(2), C(3), N(1) and P(1) are approx-
imately co-planar, with Rh(1) lying outside this plane. The
Synthesis and characterisation of [RhCl(CO)(L1)2] 3 and
[RhCl(CO)(L2)2] 4
The reaction of four equivalents of L1 with [Rh(µ-Cl)(CO)2]2 in
toluene resulted in the evolution of CO and formation of a
yellow solution. After 5 minutes stirring, a yellow precipitate of
[RhCl(CO)(L1)2] 3 began to form, and this was isolated by fil-
tration. A similar reaction of L2 with [Rh(µ-Cl)(CO)2]2 was
carried out in dichloromethane, and in this case the yellow
product [RhCl(CO)(L2)2] 4 was precipitated by addition of
hexane.
The 31P{1H} NMR spectra of 3 and 4 both showed broad
doublets at room temperature, with that for 3 observed at δ 84.4
1
1
with JPRh 158 Hz and that for 4 observed at δ 91.4 with JPRh
198 Hz. While these parameters are consistent with complexes
of the type trans-[RhCl(CO)(L-κ1P)2], the broadness of the
phosphorus resonances reveals the presence of fluxionality on
the NMR timescale. The 1H NMR spectra recorded at ambient
temperature also showed broad signals in agreement with the
compounds being fluxional. Moreover, since the signal assigned
to the protons of the methyl groups in 4 appeared as a broad
singlet at δ 2.43 with a chemical shift intermediate between that
recorded for complex 2 and for the free ligand L2, the fluxional-
ity of the complex is likely to involve coordination and dissoci-
ation of the keto group. Further support for the presence of
such a fluxional process was found in the IR spectra, in which
ν(C᎐O) bands were observed at 1653, 1635 and 1581 cmϪ1, indi-
᎐
cating the presence of both coordinated and uncoordinated
acetyl groups.
In order to investigate the fluxional behaviour of complexes 3
and 4 variable temperature NMR spectra were recorded. On
cooling a CD2Cl2 solution of 3, the doublet in the 31P{1H}
NMR spectra progressively broadened, reaching coalescence at
approximately Ϫ60 ЊC. At Ϫ80 ЊC a complex group of signals
was observed, of which the major component (> 80%) was the
AB part of an ABX system (A, B = 31P; X = 103Rh) centred at
2
1
1
δ 84.8 with JAB 468 Hz, JAX 156 Hz and JBX 158 Hz. In
1
addition a doublet at δ 83.8 with JPRh 149 Hz and two broad
Fig. 1 Molecular structure of [RhCl(CO)(L2-κ2P, O)] 2 with thermal
ellipsoids shown at the 30% probability level.
singlets at δ 87.1 and δ 82.6 were observed. The major com-
ponent can be assigned to either the 4-coordinate complex
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
3718

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2
trans-[Rh(CO)(L1-κ1P)(L1-κ2P, O )]Cl or the 5-coordinate com-
plex [RhCl(CO)(L1-κ1P)(L1-κ2P, O )], both of which contain
chemically inequivalent (terminal and chelating) L1 ligands,
while the A2X spin system is consistent with trans-[RhCl-
(CO)(L1-κ1P)2] which contains magnetically equivalent L1
ligands. The magnitude of 2JPP in the ABX system and 1JPRh in
the A2X and ABX systems implies that the phosphines are
mutually trans in both complexes.
Table 2 JPP coupling constants for complexes of general formulae
trans-[RhX(CO)LLЈ] and trans-[PdI2LLЈ]
L
LЈ
2JPP/Hz
X
Ref.
trans-[RhX(CO)LLЈ]
PMe2Ph
PMe2Ph
PMe2Ph
PMe2Ph
L1-κ1P
PPri3
PEt3
344
348
352
362
468
487
538
726
Cl
Cl
Cl
Cl
43
43
43
43
PEt2Ph
PEtPh2
PPh3
On cooling a CD2Cl2 solution of 4, the 31P{1H} NMR
spectra showed similar behaviour to 3 though with coalescence
occurring at the higher temperature of Ϫ30 ЊC. The 31P{1H}
NMR spectrum of complex 4 recorded at Ϫ70 ЊC is shown in
Fig. 2. As for 3, the major component is the AB part of an ABX
spin system, centred at δ 89.3 with JAB 726 Hz, JAX 200 Hz
and JBX 202 Hz. In addition, doublets are observed at δ 92.4
and δ 85.1 with JAX of 200 and 202 Hz respectively. This indi-
cates the presence of three compounds, of which the predomin-
ant species is either trans-[Rh(CO)(L2-κ1P)(L2-κ2P, O )]Cl or
[RhCl(CO)(L2-κ1P)(L2-κ2P, O )]. As for 3, the high values of
1JPRh and 2JPP exclude the possibility of compounds containing
mutually cis phosphines. For neither 3 nor 4 is it possible to
categorically distinguish between trans-[Rh(CO)(L-κ1P)-
(L-κ2P, O)]Cl and [RhCl(CO)(L-κ1P)(L-κ2P, O )], or indeed a
tight ion pair, on the basis of spectroscopy, though the magni-
L1-κ2P, O
P(OPri)3
P(OPh)3
L2-κ2P, O
L1-κ2P, O
Cl
This work
44
43
PEt2Ph
Cl
L2-κ1P
L2-κ2P, O
This work
trans-[PdI2LLЈ]
PMe3
PBu3
PBu3
PEt3
565
551
758
829
I
I
I
I
45
45
45
45
PMe2Ph
P(OPh)3
P(OPh)3
PMe2Ph
complexes cis-[Rh(L1-κ2P, O )2]PF6 and cis-[Rh(L2-κ2P, O )2]PF6
are formed in high yield following displacement of CO
(vide infra).
1
2
tude of the JPRh coupling constants favours a 4-coordinate
The extremely high value (726 Hz) of JPP between the in-
complex.
equivalent phosphorus atoms observed in the low temperature
31P{1H} NMR spectrum of 4 is unusual but not unprecedented.
2
Indeed it is generally observed that the value of JPP in transi-
tion metal complexes increases with enhancement of their
π-accepting character. Examples are reported in Table 2 for
complexes of the general formulae trans-[RhX(CO)LLЈ] and
trans-[PdI2LLЈ]. Since L2 is a strong π-accepting ligand, the
2
value of JPP for two inequivalent L2 ligands is expected to be
high.
Comparison of the coalescent temperatures for complexes 3
(ca. Ϫ60 ЊC) and 4 (ca. Ϫ30 ЊC) suggests that the keto function-
ality in 4 is more strongly coordinated to the Rh() centre than
that in 3. This is consistent with a reduced electron density at
the metal centre in complex 4, in agreement with L2 being a
better π-acceptor/poorer σ-donor than L1. In a similar manner,
the static nature of the complexes [RhCl(CO){PPh2CH2C(O)-
Ph-κ1P}2]24 is in agreement with L1 and L2 being better
π-acceptor/poorer σ-donor ligands than PPh2CH2C(O)Ph.
Synthesis and characterisation of [RhCl(CO)(ꢁ-PPh2OPPh2)]2 5
and [RhCl(CO){ꢁ-P(NC4H4)2OP(NC4H4)2}]2 6
Dissolution of [RhCl(CO)(L1)2] 3 in dichloromethane leads to a
darkening of colour and precipitation of red crystals after
several hours. These crystals are very poorly soluble, and only a
broad signal at δ 34.7 could be observed in the 31P{1H} NMR
spectrum in CD2Cl2 after several hours acquisition. The IR
spectrum was rather more helpful, with bands observed in the
metal carbonyl region at 1964 cmϪ1 and 1793 cmϪ1 but absent
Fig. 2 a) Simulated 31P{1H} NMR spectrum for trans-[Rh(CO)(L2-
κ1P)(L2-κ2P, O)]Cl. b) 31P{1H} NMR spectrum of [RhCl(CO)(L2)2] 4
recorded at Ϫ70 ЊC.
The high temperature NMR spectra of 4, recorded using d 8-
toluene as solvent, showed that as the temperature rises the
original broad doublet in the 31P{1H} NMR spectrum becomes
progressively sharper. The 31P{1H} NMR spectrum at 50 ЊC
showed a sharp doublet at δ 89.9 with a coupling constant of
209 Hz. This implies that the increase in rate of the fluxional
process makes the two phosphorus atoms in 4 chemically
equivalent. However, it was found that complex 4 is not ther-
mally stable as evidenced by the appearance of new signals in
the 31P{1H} NMR spectrum recorded at 60 ЊC and by an
irreversible change in colour of the solution from yellow to
dark brown.
In contrast to the observations on 3 and 4, the β-ketophos-
phine complex trans-[RhCl(CO){PPh2CH2C(O)Ph-κ1P}2] is not
reported to be fluxional,24 though it can be converted to trans-
[Rh(CO){PPh2CH2C(O)Ph-κ1P}{PPh2CH2C(O)Ph-κ2P, O }]PF6
on reaction with TlPF6. The analogous reactions with 3 and
4 do not give [Rh(CO)(L-κ1P)(L-κ2P, O )]PF6: instead the
from the ν(C᎐O) region. Taken together with the absence of
᎐
1
methyl peaks in the H NMR spectrum, this suggested that
rearrangement of L1 had occurred, with cleavage of the P–N
bond and loss of the acetylpyrrolyl group. The crystals were
identified by X-ray crystallography as the diphosphoxane
complex [RhCl(CO)(µ-PPh2OPPh2)]2ؒCH2Cl2, 5ؒCH2Cl2. The
molecular structure of this compound in shown in Fig. 3, with
selected bond lengths and angles given in Table 3.
The coordination geometry around each rhodium centre in 5
is distorted trigonal bipyramidal, with two phosphorus atoms
from different bridging diphosphoxane ligands arranged trans
to each other in the axial positions. The equatorial positions are
occupied by one terminal and two semi-bridging ligands, which
were identified as carbonyls and chlorides, disordered equally
between the two positions. This is supported by the IR spec-
trum, which shows both terminal and bridging metal carbonyls.
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
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Table 3 Selected bond lengths (Å) and angles (Њ) for complex 5ؒ
The oxygen atom in the PPh2OPPh2 ligand originates from
adventitious water, and this was confirmed by an increase in the
rate of formation of 5 from 3 on use of wet dichloromethane.
The identity of the solvent is not an important factor in the
reaction, and 5 can also be prepared from 3 using wet toluene.
Although uncoordinated L1 is slowly hydrolysed to form PPh2-
P(O)Ph2, hydrolysis of 3 to form 5 is much faster under similar
conditions, suggesting the reaction is metal-promoted. The
chelate complex [RhCl(PPh3)(PPh2OPPh2)] has previously been
prepared from a metal-promoted rearrangement and disrup-
a
CH2Cl2
Rh(1) ؒ ؒ ؒ Rh(1)Ј
Rh(1)–P(1)
Rh(1)–P(2)Ј
Rh(1)–C(26)
Rh(1)–C(27)
2.8683(9)
2.2917(13)
2.2986(13)
1.827(15)
1.83(2)
Rh(1)–Cl(1)
Rh(1)–Cl(2)
P(1)–O(3)
2.360(5)
2.464(5)
1.636(3)
1.651(3)
P(2)–O(3)
P(1)–Rh(1)–P(2)Ј
C(26)–Rh(1)–P(1)
C(26)–Rh(1)–P(2)Ј
177.46(5)
90.8(4)
89.3(4)
Cl(2)–Rh(1)–C(26) 151.7(4)
Rh(1)–C(26)–O(1)
Rh(1)–C(27)–O(2)
P(1)–O(3)–P(2)
176.3(13)
165.7(12)
125.9(2)
tion of mutually cis PPh O CCH᎐CH ligands.32 The trans
᎐
2
2
2
Cl(1)–Rh(1)–C(27) 148.5(4)
orientation of the L1 ligands in 3 disfavours formation of the
analogous monomer [RhCl(CO)(PPh2OPPh2)] on hydrolysis,
instead promoting formation of the dimer 5 in which the trans
orientation of the phosphorus donors in maintained.
a Primed atoms generated by the symmetry operation Ϫx ϩ 1, Ϫy, Ϫz.
In order to examine the generality of this reaction, complex 4
was stirred in wet toluene at 60 ЊC to produce the complex
[RhCl(CO){µ-P(NC4H4)2OP(NC4H4)2}]2 6. Complex 6 was
isolated as a red crystalline material and fully characterised.
The IR spectrum showed the presence of a terminal carbonyl
at 2029 cmϪ1 and the absence of absorption for the acetyl
group. On following the reaction by IR spectroscopy, the
disappearance of the absorption for 4 is accompanied by the
appearance of the absorptions assigned to 6 and 2-acetyl-
1
pyrrole. The H NMR spectrum showed a pseudo-triplet and
a
pseudo-quintet characteristic of the unfunctionalised
N-pyrrolyl phosphorus substituents, but no signal for the
methyl group.
The 31P{1H} NMR spectrum of 6 showed a broad apparent
doublet of triplets centered at δ 107.3 which is consistent with a
dimeric structure. This spectrum is shown in Fig. 4 and can be
interpreted as the partially resolved AAЈ part of an [AAЈX]2
spin system in which X is Rh and A and AЈ are the two chem-
ically equivalent but magnetically inequivalent phosphorus
atoms of P(NC4H4)2OP(NC4H4)2. Although a full analysis of
this spectrum is prevented by the observed broadness, it is pos-
sible to calculate the values of 1JPRh as 186 Hz and 3JPRh as 3 Hz.
Fig. 3 Molecular structure of [RhCl(CO)(µ-PPh2OPPh2)]2ؒCH2Cl2
(5ؒCH2Cl2) with hydrogen atoms and the included solvent omitted for
clarity and thermal ellipsoids shown at the 30% probability level.
Although a 1 : 1 mixture of the complexes [Rh2(CO)2(µ-Cl)2-
(µ-PPh2OPPh2)2] and [Rh2Cl2(µ-CO)2(µ-PPh2OPPh2)2] cannot
be excluded on the basis of the X-ray analysis, a simpler model
contains one compound, [Rh2Cl(CO)(µ-Cl)(µ-CO)(µ-PPh2-
OPPh2)2], present in two positions with equal likelihood. The
related cationic complexes [Rh2(CO)2(µ-Cl)(µ-CO)(µ-L)2]ϩ (L =
dppm, PPh2NHPPh2) have previously been structurally charac-
terised.25–27
Analysis of the Rh–Rh distances from complexes contain-
ing the Rh2(µ-dppm)2 skeleton, show that the distance in 5
[2.8683(9) Å] lies within the ranges observed both for com-
pounds which contain a Rh–Rh bond [2.52–3.01 Å, mean 2.77
Å] and for those in which a Rh–Rh bond is absent [2.83–3.47 Å,
mean 3.16 Å].28,29 The P ؒ ؒ ؒ P separation between the phos-
phorus atoms of the same ligand (2.93 Å) is longer than the
Rh–Rh distance indicating compression along the Rh–Rh
internuclear axis, though this may be a consequence of the
presence of the bridging ligands. These bridges are highly
unsymmetrical, with Rh–C(27) distances of 1.83(2) and 2.69(3)
Å and Rh–Cl(2) distances of 2.464(5) and 2.889(6) Å respect-
ively, hence the ligands are best described as semi-bridging. This
is further reflected in the bond angles, with the bridging carb-
onyl ligands [Rh(1)–C(27)–O(2) 165.7(12)Њ] exhibiting a rel-
atively small deviation from the linear conformation observed
for the terminal carbonyl [Rh(1)–C(26)–O(1) 176.3(13)Њ]. Simi-
lar semi-bridging carbonyl ligands were observed in the struc-
ture of [Rh2(µ-CO)(CO)2(µ-dppm)2].30 The two diphosphoxane
oxygen atoms point in opposite directions in 5 giving a chair
conformation for the Rh2P4O2 ring, as opposed to the boat
conformation observed in the majority of M2P4C2 rings.31
Fig.
4
31P{1H} NMR spectrum of [RhCl(CO){µ-P(NC4H4)2-
OP(NC4H4)2}]2 6.
Single crystals of 6ؒC7H8 were obtained by the slow diffusion
of hexane into a toluene solution. The molecular structure of 6
is shown in Fig. 5, and selected bond distances and angles are
reported in Table 4. In contrast with 5, the carbonyl and the
chloride in 6 are terminally coordinated and there is no disorder
in the dimer. The coordination geometry around each metal
centre is distorted square planar with the angles P(1)–Rh–P(2)Ј
[175.82(2)Њ] and C(17)–Rh–Cl(1) [170.64(8)Њ] deviating slightly
from the ideal value of 180Њ. The Rh ؒ ؒ ؒ Rh distance [3.1177(3)
Å] is considerably longer than that observed for 5 clearly indi-
cating the absence of a Rh–Rh bond. Although further struc-
tural comparisons between 5 and 6 are limited by the disorder
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
3720

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a
Table 4 Selected bond lengths (Å) and angles (Њ) for complex 6ؒC7H8
characterised. The NMR and IR spectral parameters for 7b
are similar to those for 7a, with the addition of signals for
the hexafluorophosphate counterion, suggesting that the
cations in 7a and 7b are identical. The sensitivity of 7a presum-
ably relates to a competing coordination of the chloride to
give [RhCl(L1-κ1P)(L1-κ2P, O )], which is more sensitive than
[Rh(L1-κ2P, O )2]ϩ.
Rh(1) ؒ ؒ ؒ Rh(1)Ј
Rh(1)–P(1)
Rh(1)–P(2)Ј
Rh(1)–C(17)
Rh(1)–Cl(1)
P(1)–N(1)
3.1177(3)
2.2664(5)
2.2624(5)
1.839(3)
2.3719(5)
1.6945(19)
P(1)–N(2)
P(2)–N(3)
P(2)–N(4)
P(1)–O(2)
P(2)–O(2)
1.6733(18)
1.6948(19)
1.6716(19)
1.6176(15)
1.6266(15)
The reaction of four equivalents of L2 with [Rh(µ-Cl)(cod)]2
in the presence of NH4PF6 resulted in the formation of [Rh-
(L2-κ2P, O )2]PF6 8, which was isolated as a yellow crystalline
material following recrystallisation from dichloromethane–
hexane. The 31P{1H} NMR spectrum of 8 showed a sharp
doublet at δ 104.2 with 1JPRh 269 Hz and a septet at δ Ϫ143 for
the PF6Ϫ counterion. Whereas the chemical shifts in the 31P{1H}
NMR spectra of 7 and 8 are very similar, a significant differ-
P(1)–Rh(1)–P(2)Ј
C(17)–Rh(1)–Cl(1) 170.64(8)
C(17)–Rh(1)–P(1)
C(17)–Rh(1)–P(2)Ј
a Primed atoms generated by the symmetry operation Ϫx ϩ 1/2, Ϫy ϩ
1/2, Ϫz.
175.82(2)
P(2)–Rh(1)–Cl(1)Ј
P(1)–Rh(1)–Cl(1)
P(1)–O(2)–P(2)
89.489(19)
91.340(19)
132.42(10)
89.72(7)
90.13(7)
1
ence exists for the values of JPRh. As observed before, this is
consistent with the electronic difference of the two ligands, with
the better π-acceptor ligand giving the higher 1JPRh. As with 7b,
coordination of the keto groups can be inferred from the IR
spectrum, with ν(CO) observed at 1575 cmϪ1 for 8.
The NMR spectra for 7b and 8 are temperature independent,
confirming the absence of fluxionality. In the reactions of
[Rh(µ-Cl)(cod)]2 with L1 and L2 there was no evidence for mixed
cod–phosphine complexes, in contrast to the reactions of the
ether-phosphines PR2CH2CH2OMe (R = Cy, Pri, But and Ph)
which give complexes of the general formulae [Rh(cod)-
(L-κ2P, O )]ϩ or [Rh(cod)(L-κ1P)2]ϩ.33
Complexes 7b and 8 can also be obtained by chloride abstrac-
tion from 3 or 4 with TlPF6 or NH4PF6. These reactions pro-
ceed with isomerisation to give the thermodynamically more
stable product in which the two phosphorus atoms occupy
mutually cis positions. This is in contrast to the reaction of
[RhCl(CO){PPh2CH2C(O)Ph-κ1P}2] with TlPF6 which gives
trans-[Rh(CO){PPh2CH2C(O)Ph-κ1P}{PPh2CH2C(O)Ph-
κ2P, O }]PF6.24 The increased lability of the CO ligand in the
N-pyrrolyl phosphine complexes is a consequence of the
stronger π-acceptor character of these ligands which reduces
the back-donation to CO.
Single crystals of 7b and 8 suitable for X-ray analyses were
obtained by slow diffusion of hexane into dichloromethane
solutions. The structures of the cations of 7b and 8 are shown in
Figs. 6 and 7 respectively, with selected bond distances and
angles reported in Table 5. The structures show the two mole-
cules of L1 or L2 coordinated to the metal centre via the phos-
phorus and oxygen atoms in a distorted square planar geometry
with the cis arrangement of the ligands consistent with the
spectroscopic data. The distortion from square planarity is evi-
dent in the cis angles which range from 81.57(6)Њ to 98.748(18)Њ
for 7b, and from 81.81(7)Њ to 99.04(2)Њ for 8. Crystallographic
bite angles of 89.93(4)Њ and 90.34(4)Њ for L1 in 7b and 87.71(5)Њ
Fig.
5
Molecular structure of [RhCl(CO){µ-P(NC4H4)2OP(NC4-
H4)2}]2ؒC7H8 (6ؒC7H8) with hydrogen atoms and the included solvent
omitted for clarity and thermal ellipsoids shown at the 30% probability
level.
in the structure of 5 it is noteworthy that the Rh–P bond
distances in 6 [2.2664(5) Å and 2.2624(5) Å] are shorter
than those in 5 [2.292(1) Å and 2.299(1) Å], which is consistent
with P(NC4H4)2OP(NC4H4)2 being a better π-acceptor than
PPh2OPPh2. It is notable that in the formation of 6 the P–N
bond to the functionalised pyrrolyl group is selectively cleaved.
No evidence was observed for any product in which one of the
other P–N bonds had been cleaved.
Synthesis and characterisation of [Rh(L1-ꢀ2P,O)2]X (7a, X ؍ Cl;
7b, X ؍ PF6) and [Rh(L2-ꢀ2P,O)2]PF6 8
The reaction of four equivalents of L1 with [Rh(µ-Cl)(cod)]2 in
dichloromethane gave the complex [Rh(L1-κ2P, O )2]Cl 7a, which
was characterised spectroscopically. The 31P{1H} NMR spec-
trum of 7a consisted of a doublet at δ 108.0 with 1JPRh 204 Hz.
The magnitude of this coupling constant suggests that the
phosphorus ligands are orientated mutually cis such that the
phosphorus atoms are both trans to the oxygen atoms. The 1H
NMR spectrum showed a deshielding of the methyl protons
with δ 2.63, consistent with coordination of the keto groups.
This was confirmed by the IR spectrum, which gave a single
band for ν(CO) at 1574 cmϪ1. Complex 7a was found to
decompose readily in solution, precluding a full characteris-
ation. However, the hexafluorophosphate salt, formed on
metathesis with NH4PF6, is stable in solution, and the complex
[Rh(L1-κ2P, O)2]PF6 7b was isolated in the solid state and fully
Fig. 6 Molecular structure of [Rh(L1-κ2P, O )2]PF6 7b, with the phenyl
hydrogen atoms and the anion omitted for clarity and thermal
ellipsoids shown at the 30% probability level.
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
3721

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Table 5 Selected bond lengths (Å) and angles (Њ) for complexes 7b and
8
Table
6
31P{1H} NMR spectral parameters for complex 10.
Chemical shifts are in ppm and coupling constants in Hz
7b
Pa
Pb
Pc
δ(P)
94.2
273
8.3
161
Ϫ12.8
133
Rh(1)–O(1)
Rh(1)–O(2)
Rh(1)–P(1)
2.0880(13)
2.0867(14)
2.1680(5)
Rh(1)–P(2)
P(1)–N(1)
P(2)–N(2)
2.1704(5)
1.7615(16)
1.7525(17)
1JPRh
2JPP
Pa
Pb
49
Pc
Pa
449
49
Pb
P(1)–Rh(1)–P(2)
O(1)–Rh(1)–O(2)
P(1)–Rh(1)–O(1)
98.748(18)
81.57(6)
90.34(4)
P(2)–Rh(1)–O(2)
P(1)–Rh(1)–O(2)
P(2)–Rh(1)–O(1)
89.93(4)
169.36(5)
169.80(4)
On cooling to Ϫ60 ЊC, the broad signal of the new complex in
8
the 31P{1H} NMR spectrum sharpened to give a doublet at
Rh(1)–O(1)
Rh(1)–O(2)
Rh(1)–P(1)
Rh(1)–P(2)
P(1)–N(1)
2.0914(16)
2.0716(16)
2.1411(6)
2.1409(6)
1.7297(19)
P(1)–N(2)
P(1)–N(3)
P(2)–N(4)
P(2)–N(5)
P(2)–N(6)
1.6930(19)
1.690(2)
1.7243(19)
1.692(2)
1
1
δ 84.1 with JPRh 188 Hz. The H NMR spectrum at Ϫ60 ЊC
showed two sharp singlets in the methyl region at δ 2.73 and
δ 2.34, which can be assigned to 8 and the new complex 9
respectively. The chemical shift of the new signal is very similar
to that observed for the free ligand L2, suggesting that in the
newly formed complex L2 is either terminally coordinated
through the phosphorus atom or is chelated with the co-
ordination geometry of the metal centre different from that of
8. Attempts to obtain a low temperature 13C{1H} NMR spec-
trum with a signal to noise ratio high enough to clearly dis-
tinguish signals for the carbonyl carbon were unsatisfactory.
Further insight into the identity of 9 was obtained by repeat-
ing the variable temperature NMR experiments using 13CO.
The 31P{1H} NMR spectrum recorded at Ϫ75 ЊC showed a
1.693(2)
P(1)–Rh(1)–P(2)
O(1)–Rh(1)–O(2)
P(1)–Rh(1)–O(1)
99.04(2)
81.81(7)
87.71(5)
P(2)–Rh(1)–O(2)
P(1)–Rh(1)–O(2)
P(2)–Rh(1)–O(1)
91.99(5)
167.71(5)
171.60(5)
1
sharp doublet of doublets centred at δ 87.3 with JPRh 185 Hz
2
and JPC 20 Hz in addition to the signal for the starting
material. In the 13C{1H} NMR spectrum the coordinated carb-
1
onyl group was observed as a doublet of triplets with JCRh 74
2
Hz and JCP 20 Hz. The multiplicity of the signals observed in
these spectra establish the formula of 9 as [Rh(CO)(L2)2]PF6.
This is consistent with either the 5-coordinate complex [Rh-
(CO)(L2-κ2P, O )2]ϩ or the 4-coordinate complex [Rh(CO)-
(L2-κ1P)(L2-κ2P, O )]ϩ if a fluxional process allowing inter-
conversion of the phosphines is still occurring at this temper-
ature, though in this latter case δ(Me) in the 1H NMR spectrum
would be expected to be similar to that in 4. Penta-coordinate
carbonyl rhodium() complexes containing chelating phos-
phorus ligands have been reported to form from the reaction
of [Rh(dppm-κ2P, P)2]BF4 and [Rh(Ph2PC2H4SPh-κ2P, S )2]BF4
with CO.35,36 However, the reaction of CO with rhodium()
complexes of ether-functionalised phosphines occurs with dis-
placement of the coordinated oxygen atoms to give tricarbonyl
complexes [Rh(CO)3(L-κ1P)2].37 Analogous complexes with L2
can clearly be excluded on the basis of the NMR data.
The addition of one equivalent of PMe3 to a dichloro-
methane solution of 8 occurred with displacement of one mole-
cule of L2 and formation of [Rh(PMe3)2(L2-κ2P, O)]PF6 10.
Complex 10 was characterised on the basis of its 31P{1H} NMR
spectrum, which showed three resonances, at δ 94.2 (ddd),
δ 8.3 (dt) and δ Ϫ12.8 (ddd). Coupling constant information,
together with the assignment, is given in Table 6. A similar
spectrum has recently been reported for the complex [Rh-
(PPh3)2{PPh2NHC(O)Me-κ2P, O }]ϩ.38
Fig. 7 Molecular structure of [Rh(L2-κ2P, O)2]PF6 8, with the pyrrolyl
hydrogen atoms and the anion omitted for clarity and thermal
ellipsoids shown at the 30% probability level.
and 91.99(5)Њ for L2 in 8 suggest that the ligands are essentially
isosteric, in line with previous observations concerning phenyl
and N-pyrrolyl groups.34 The Rh–P distances of 2.1411(6) and
2.1409(6) Å in 8 are significantly shorter than the corre-
sponding distances in 7b [2.1680(5) Å and 2.1704(5)] indicating
the effect of the stronger π-acceptor ligand. The P–N distances
in 7b are longer than those in 8, and in 8 the P–N bonds to the
acetylpyrrolyl group are longer than those to the unfunctional-
ised pyrrolyl groups.
Reactivity of [Rh(L2-ꢀ2P,O)2]PF6
Complexes 7b and 8 are both stable in dichloromethane, in con-
trast to cis-[Rh{PPh2CH2C(O)Ph-κ2P, O }2]PF6 which is slowly
oxidised to [RhCl2{PPh2CH2C(O)Ph-κ2P, O }2]PF6.24 No reac-
tion was observed with either H2 or methyl iodide, though
NMR evidence showed a reaction with CO. When a CD2Cl2
solution of 8 was placed under 10 psi CO the 31P{1H} NMR
spectrum recorded at ambient temperature showed a broad sig-
nal at δ 87.2, in addition to the signal for the starting material.
Increasing the CO pressure to 20 psi resulted in an increase in
intensity of the new signal, though full conversion was not
obtained even after prolonged reaction time (24 h). The
observed reaction is reversible with release of the CO pressure
resulting in complete re-conversion to the starting material. The
1H NMR spectrum under CO showed in addition to the signals
for complex 8 a new set of broad signals. In the aliphatic region
a broad singlet at δ 2.30 was clearly distinguishable from the
sharp signal for the methyl protons of 8.
It did not prove possible to isolate 10 from a mixture contain-
ing 8 and displaced L2, both of which were also observed in the
31P{1H} NMR spectrum.
The reaction of 8 with [NEt3Bz]Cl produced the complex
cis-[RhCl(L2-κ1P)(L2-κ2P, O )] 11, which was isolated following
recrystallisation from dichloromethane–hexane as red crystals.
Complex 11 was fully characterised and its structure was con-
firmed by X-ray crystallography. The 31P{1H} NMR spectrum
recorded at ambient temperature showed a broad doublet at
1
δ 98.2 with JPRh 276 Hz and the absence of the septet typical
Ϫ
1
of PF6 . The high value of JPRh is in agreement with a cis
arrangement of the two phosphorus atoms whereas the appear-
ance of the signal as a broad doublet indicates the presence of a
fluxional process which makes the two phosphorus atoms
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
3722

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1
Table 7 Selected bond lengths (Å) and angles (Њ) for complex 11
chemically equivalent. The H NMR spectrum showed broad
but distinctive signals in the aromatic region and a reasonably
sharp singlet at δ 2.49 assigned to the methyl group. The
observed chemical shift for the protons of the methyl groups is
intermediate between that observed for the coordinated keto
groups in 2 (δ 2.68) and for the non-coordinated keto group in
the free ligand (δ 2.35) as in 4, and is consistent with the equi-
librium process involving coordination and dissociation of the
keto groups. The IR spectrum recorded in dichloromethane
Rh(1)–P(4)
Rh(1)–P(3)
Rh(1)–O(3)
Rh(1)–Cl(1)
P(3)–N(7)
P(3)–N(8)
P(3)–N(9)
P(4)–N(10)
P(4)–N(11)
P(4)–N(12)
2.178(2)
2.1332(18)
2.093(5)
2.3614(19)
1.745(6)
1.705(5)
1.703(7)
1.720(6)
1.709(5)
1.723(5)
Rh(2)–P(1)
Rh(2)–P(2)
Rh(2)–O(2)
Rh(2)–Cl(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)
2.162(2)
2.1353(15)
2.120(6)
2.3416(16)
1.735(5)
1.710(6)
1.710(5)
1.687(6)
1.708(5)
1.721(6)
showed ν(C᎐O) for both the uncoordinated and coordinated
᎐
keto groups at 1642 cmϪ1 and 1592 cmϪ1 respectively, consistent
with the NMR data. Similar bands were observed in the solid
state IR spectrum, giving a good indication that both co-
ordinated and uncoordinated keto groups were also present in
the solid state.
P(4)–Rh(1)–Cl(1)
Cl(1)–Rh(1)–O(3)
P(3)–Rh(1)–O(3)
P(3)–Rh(1)–P(4)
P(3)–Rh(1)–Cl(1)
P(4)–Rh(1)–O(3)
92.17(7)
82.19(14)
88.42(14)
97.58(7)
168.95(7)
173.11(14)
P(1)–Rh(2)–Cl(2)
Cl(2)–Rh(2)–O(2)
P(2)–Rh(2)–O(2)
P(1)–Rh(2)–P(2)
P(2)–Rh(2)–Cl(2)
P(1)–Rh(2)–O(2)
88.25(7)
84.23(13)
86.33(13)
101.22(8)
170.52(9)
170.25(13)
The fluxional behaviour of 11 was studied through variable
1
temperature 31P{1H} and H NMR spectroscopy. As the tem-
perature was lowered the original doublet in the 31P{1H} NMR
spectrum became progressively broader and reached coales-
cence at approximately Ϫ40 ЊC. The spectrum recorded at
Ϫ80 ЊC showed two doublets of doublets at δ 107.2 and δ 88.0
in agreement with the proposed structure of complex 11. The
broadness of the signals allowed a determination of the values
and the uncoordinated keto groups [C(18) ؒ ؒ ؒ O(1) 3.156,
H(18) ؒ ؒ ؒ O(1) 2.27 Å, C(18)–H(18) ؒ ؒ ؒ O(1) 156Њ; C(35) ؒ ؒ ؒ
O(4) 3.385, H(35) ؒ ؒ ؒ O(4) 2.46 Å, C(35)–H(35) ؒ ؒ ؒ O(4) 163Њ].
Conclusions
1
of JPRh (275 and 210 Hz) but only an estimate of the value of
The synthesis and reactions of rhodium() complexes of L1 and
L2 are summarised in Scheme 1. The strong electron-withdraw-
ing character of the N-pyrrolyl phosphine ligands manifests
itself in a number of differences between the chemistry of
these ligands and the reactions previously reported for ether-
phosphines such as PPh2CH2CH2OMe and β-ketophosphines
such as PPh2CH2C(O)Ph. Most notably, the rhodium() centres
in complexes of L1 and L2 are relatively electron poor, so the
keto groups of L1 and L2 tend to be more tightly bound whereas
competing π-acceptors such as CO are more weakly bound.
Complexes of L1 and L2 are less prone to oxidation than those
of PPh2CH2C(O)Ph, again due to the electron-withdrawing
character of the ligands.
1
the cis-2JPP (≈25–30 Hz). The H NMR spectrum recorded at
Ϫ80 ЊC showed very broad signals in the aromatic region and a
relatively sharp signal at δ 2.52 assigned to the methyl groups.
The lack of significant broadening of this signal reveals that
this temperature is too high to observe coalescence. The ether-
phosphine complexes [RhCl(PR2CH2CH2OMe-κ1P)(PR2CH2-
CH2OMe-κ2P, O)] (R = Pri,39 Cy40) have also been reported to be
fluxional, whereas the PPh2CH2C(O)Ph analogue is static at
room temperature.24
The crystal structure of 11 confirmed the formulation pro-
posed on the basis of the spectroscopic data. The unit cell con-
tains two crystallographically independent molecules, though
there are only small changes in the interatomic distances and
angles for the two independent molecules and therefore only
one of these molecules is shown in Fig. 8. Selected bond lengths
and angles are given for both molecules in Table 7. The ligands
are coordinated to the metal centre in a distorted square planar
geometry, with cis angles in the range 82.19(14) to 101.22(8)Њ.
The Rh–P bond distances to the monodentate ligands are
longer [2.178(2) Å and 2.162(2) Å] than to the ligands forming
the chelate rings [2.133(2) Å and 2.135(2) Å]. The latter dis-
tances are slightly shorter than the Rh–P distances observed in
the structures of [RhCl(CO)(L2-κ2P, O )] 2 [2.1474(4) Å] and
[Rh(L2-κ2P, O)2]PF6 8 [av. 2.1410(6) Å]. In both independent
molecules, relatively strong intramolecular C–H ؒ ؒ ؒ O hydro-
gen bonds are observed between a CH group on a pyrrole ring
The differences in the electronic properties of L1 and L2 are
clearly reflected in both structural and spectroscopic data, with
the larger number of electron-withdrawing N-pyrrolyl on L2
leading to this being a poorer σ-donor and better π-acceptor
than L1. However, in the reactions considered here this electro-
nic disparity does not lead to differences in reactivity.
The P–N bonds in L1 and L2 are generally stable to hydrolysis
after coordination, but the metal-promoted hydrolysis of the
P–N bonds in 3 and 4 has been observed to give the diphos-
phoxane complexes 5 and 6. It is noticeable that in the case of 4,
only the bond to the functionalised pyrrole group is cleaved.
Experimental
General experimental
Reactions were routinely carried out using Schlenk-line tech-
niques under pure dry dinitrogen or argon, using dry dioxygen-
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 SiMe4 or 85% H3PO4.
41
42
The complexes [Rh(µ-Cl)(CO)2]2 and [Rh(µ-Cl)(cod)]2 and
15
the ligand precursor PCl(NC4H4)2 were prepared following
the literature methods. The ligand L1 was prepared following
the previously reported method.12
Fig. 8 Molecular structure of one of the independent molecules in
the asymmetric unit in [RhCl(L2-κ1P)(L2-κ2P, O)] 11 with the pyrrolyl
hydrogen atoms omitted for clarity and thermal ellipsoids shown at the
30% probability level.
Syntheses
Synthesis of P(NC4H4)2{NC4H3C(O)Me-2} L2. NEt3 (2.5 cm3,
18.0 mmol), PCl(NC4H4)2 (2.9 g, 14.7 mmol) and 2-acetyl-
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
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Scheme 1 (i) 1 eq. L1 or L2; (ii) 2 eq. L1 or L2; (iii) H2O; (iv) TlPF6 or NH4PF6; (v) 2 eq. L1 or L2 + NH4PF6; (vi) CO; (vii) ϪCO; (viii) PMe3;
(ix) [NEt3Bz]Cl.
pyrrole (1.60 g, 14.7 mmol) were dissolved in THF (40 cm3),
and the mixture stirred overnight. The colourless precipitate of
[NEt3H]Cl was removed by filtration and washed with THF,
and the washings were combined with the filtrate. The volume
of this solution was reduced by approximately one half and
hexane (30 cm3) added. Slow evaporation of the solvent pro-
duced colourless block shaped crystals which were isolated by
filtration and dried under reduced pressure. Yield 3.2 g (80%).
31P{1H} NMR (CD2Cl2, 161.8 MHz): δ 75.1 (s). 1H NMR
(CD2Cl2, 399.8 MHz): δ 7.17 (m, 1H), 6.74 (ps quin, 4H), 6.33
(ps t, 4H), 6.29 (m, 1H), 5.90 (m, 1H), 2.35 (s, 3H). 13C{1H}
H, 4.35; N, 3.66%. 31P{1H} NMR (161.8 MHz, CDCl3): δ 84.4
(d, 1JPRh 158 Hz). 1H NMR (399.8 MHz, CDCl3): δ 7.74 (br m,
3
4
4H), 7.41 (br m, 6H), 7.14 (dd, 1H, JHH 4.0 Hz, JHH 1.6 Hz),
6.45 (br m, 1H), 6.21 (t, 1H, 3JHH 4.0 Hz) 2.40 (s, 3H, Me). IR
(KBr, cmϪ1): 1963s [ν(CO)], 1650vs [ν(C᎐O)]; IR (CH Cl ,
᎐
2
2
cmϪ1): 1981s [ν(CO)], 1650vs [ν(C᎐O)].
᎐
Synthesis of [RhCl(CO)(L2)2] 4. [Rh(µ-Cl)(CO)2]2 (0.161 g,
0.41 mmol) was added to a solution of L2 (0.450 g, 1.66 mmol)
in dichloromethane. After 2 h stirring hexane was added, result-
ing in the formation of a yellow precipitate which was isolated
by filtration, washed with diethyl ether and dried under reduced
pressure. Yield 0.566 g (97%). Calc. for C29H28ClN6O3P2Rh: C,
49.1; H, 3.98; N, 11.8%. Found: C, 48.8; H, 3.96; N, 11.4%.
2
NMR (CDCl3, 100.5 MHz): δ 188.2 (s), 135.9 (d, JCP 2 Hz),
2
2
129.8 (d, JCP 4 Hz), 122.4 (d, JCP 15 Hz), 121.7 (s), 112.8 (s),
112.4 (d, 3JCP 4 Hz), 25.0 (s). IR (KBr, cmϪ1): 1637s [ν(C᎐O)].
᎐
1
31P{1H} NMR (161.8 MHz, CD2Cl2): δ 91.4 (br d, JPRh 198
Synthesis of [RhCl(CO)(L1-ꢀ2P,O)] 1. [Rh(µ-Cl)(CO)2]2
(0.100 g, 0.26 mmol) was added to a stirred solution of L1
(0.151 g, 0.52 mmol) in dichloromethane (10 cm3). After 30 min
stirring, the solvent was evaporated under reduced pressure.
Recrystallisation from dichloromethane–hexane, followed by
toluene–dichloromethane–hexane gave orange crystals of 1.
Yield 0.208 g (88%). Calc. for C19H17ClNO2PRh: C, 49.6; H,
3.51; N, 3.05%. Found: C, 49.6; H, 3.60; N, 2.95%. 31P{1H}
NMR (161.8 MHz, CDCl3): δ 93.6 (d, 1JPRh 178 Hz). 1H NMR
(399.8 MHz, CDCl3): δ 7.65 (m, 1H, C4H3), 7.58–7.47 (m, 10H,
Ar), 6.96 (br m, 1H, C4H3), 6.60 (m, 1H, C4H3), 2.60 (s, 3H,
Hz). H NMR (399.8 MHz, CD2Cl2): δ 7.17 (br, 1H), 7.07 (br,
1
4H), 6.41 (br, 5H), 5.85 (br, 1H), 2.43 (br, 3H, Me). IR (KBr,
cmϪ1): 1997s [ν(CO)], 1653s, 1635s, 1581w [ν(CO)].
Synthesis of [Rh2Cl2(CO)2(ꢁ-PPh2OPPh2)2] 5. Complex 3
(0.200 g, 0.27 mmol) was dissolved in dichloromethane (10
cm3). On standing for 4 h, the initial yellow solution darkened,
and red needle-shaped crystals were precipitated. These were
separated by filtration, washed with dichloromethane and dried
under reduced pressure. Yield 0.101 g (69%). Calc. for
C50H40Cl2O4P4Rh2ؒCH2Cl2: C, 51.5; H, 3.56%. Found: C, 51.1;
H, 3.59%. 31P{1H} NMR (CD2Cl2, 161.8 MHz): δ 34.7 (br). 1H
NMR (CD2Cl2, 399.8 MHz): δ 7.32 (br m). IR (KBr, cmϪ1):
1964s [ν(CO)], 1793s [ν(CO)].
Me). IR (KBr, cmϪ1): 1989vs [ν(CO)], 1576s [ν(C᎐O)].
᎐
Synthesis of [RhCl(CO)(L2-ꢀ2P,O)] 2. [Rh(µ-Cl)(CO)2]2
(0.100 g, 0.26 mmol) was added to a stirred solution of L2
(0.139 g, 0.51 mmol) in dichloromethane. After 2 h, half of the
solvent was evaporated under reduced pressure and hexane was
added to precipitate a yellow powder. Recrystallisation from
dichloromethane–hexane gave yellow crystals of 2. Yield 0.216
g (97%). Calc. for C15H14ClN3O2PRh: C, 41.2; H, 3.22; N,
9.60%. Found: C, 40.8; H, 3.26; N, 9.21%. 31P{1H} NMR (161.8
MHz, CDCl3): δ 91.4 (d, 1JPRh 237 Hz). 1H NMR (399.8 MHz,
CDCl3): δ 7.56 (m, 1H), 6.92–6.85 (m, 5H), 6.57 (m, 1H), 6.45
(m, 4H), 2.68 (s, 3H, Me). 13C{1H} NMR (100.5 MHz, CDCl3):
Synthesis of [Rh2Cl2(CO)2{ꢁ-P(NC4H4)2OP(NC4H4)2}2] 6.
Complex 4 (0.200 g, 0.28 mmol) was dissolved in wet toluene
(10 cm3) and stirred at 60 ЊC for 4 h. A progressive change in the
colour from yellow to deep red was observed. On standing at
ambient temperature for 48 h, red crystals of complex 6 were
deposited. Yield 0.130 g (91%). Calc. for C34H32Cl2N8O4P4Rh2:
C, 40.1; H, 3.17; N, 11.0%. Found: C, 40.3; H, 3.21; N, 11.1%.
31P{1H} NMR (161.8 MHz, CD2Cl2): δ 107.3 (ps dt). 1H NMR
(399.8 MHz, CD2Cl2): δ 6.99 (ps quin, 16H), 6.34, (ps t, 16H).
IR (KBr, cmϪ1): 2029s [ν(CO)].
2
1
2
δ 191.7 (d, JCRh 7 Hz), 183.9 (dd, JCRh 78 Hz, JCP 19 Hz),
133.4 (d, 2JCP 1 Hz), 132.4 (s), 132.0 (d, 2JCP 4 Hz), 123.3 (d, 2JCP
2
11 Hz), 115.3 (s), 114.8 (d, JCP 7 Hz), 27.3 (s, Me). IR (KBr,
Synthesis of [Rh(L1-ꢀ2P,O)2]Cl 7a. L1 (0.119 g, 0.41 mmol)
was added to a solution of [Rh(µ-Cl)(cod)]2 (0.050 g, 0.10
mmol) in dichloromethane (10 cm3) and the mixture stirred for
90 min. The solvent was removed under reduced pressure, and
the solid washed with cold hexane then dried under reduced
pressure. Yield 0.143 g (97%). 31P{1H} NMR (161.8 MHz,
cmϪ1): 2017vs [ν(CO)], 1572s [ν(C᎐O)].
᎐
Synthesis of [RhCl(CO)(L1)2] 3. [Rh(µ-Cl)(CO)2]2 (0.050 g,
0.13 mmol) was added to a solution of L1 (0.151 g, 0.52 mmol)
in toluene (10 cm3) and the mixture stirred for 30 min. The
resulting solution was filtered, and the yellow precipitate
washed with toluene (5 cm3) and hexane (20 cm3) then dried
under reduced pressure. Yield 0.178 g (92%). Calc. for
C37H32ClN2O3P2Rh: C, 59.0; H, 4.28; N, 3.72%. Found: C, 58.7;
1
1
CDCl3): δ 108.0 (br d, JPRh 204 Hz). H NMR (399.8 MHz,
CDCl3): δ 7.88 (m, C4H3), 7.68–6.88 (br m, Ar), 6.67 (br m,
C4H3), 6.37 (br m, C4H3), 2.63 (s, Me). IR (KBr, cmϪ1): 1574s
[ν(C᎐O)].
᎐
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
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Synthesis of [Rh(L1-ꢀ2P,O)2]PF6 7b. NH4PF6 (0.034 g, 0.21
mmol) was added to a solution of 7a formed in situ from [Rh-
(µ-Cl)(cod)]2 (0.050 g, 0.10 mmol) and L1 (0.119 g, 0.41 mmol)
in THF (30 cm3). The mixture was stirred for 2 h, then the
solution was filtered to remove NH4Cl. The solvent was
removed from the filtrate under reduced pressure, and the crude
solid washed with cold diethyl ether and recrystallised from di-
chloromethane–hexane to give orange crystals of 7b. Yield
0.154 g (91%). Calc. for C36H32F6N2O2P3Rhؒ0.25CH2Cl2: C,
50.9; H, 3.83; N, 3.27%. Found: C, 50.9; H, 3.93; N, 3.16%.
31P{1H} NMR (161.8 MHz, CD2Cl2): δ 108.3 (d, 1JPRh 205 Hz),
Ϫ143.0 (sep, 1JPF 711 Hz, PF6). 1H NMR (399.8 MHz, CDCl3):
δ 7.54 (m, 1H, C4H3), 7.42 (m, 2H, Ar), 7.24 (m, 8H, Ar), 6.73
(m, 1H, C4H3), 6.42 (m, 1H, C4H3), 2.71 (s, 6H, Me). IR (KBr,
cmϪ1): 1570s [ν(C᎐O)], 837vs [ν(PF )].
᎐
6
Synthesis of [Rh(L2-ꢀ2P,O)2]PF6 8. NH4PF6 (0.255 g, 1.6
mmol) was added to a dichloromethane solution of L2 (0.854 g,
3.14 mmol) and [Rh(µ-Cl)(cod)]2 (0.380 g, 0.78 mmol). The
mixture was stirred for 3 h, after which the solution was filtered
to remove NH4Cl. The filtrate was evaporated under reduced
pressure to give a yellow powder which was recrystallised from
dichloromethane–hexane to give 8 as yellow crystals. Yield
1.190 g (96%). Calc. for C28H28F6N6O2P3Rh: C, 42.5; H, 3.60;
N, 10.6%. Found: C, 42.5; H, 3.60; N, 10.6%. 31P{1H} NMR
1
(161.8 MHz, CD2Cl2): δ 104.2 (d, JPRh 269 Hz), Ϫ143.0 (sep,
1
1JPF 711 Hz, PF6). H NMR (399.8 MHz, CD2Cl2): δ 7.65 (m,
2H), 6.64 (m, 2H), 6.59 (m, 8H), 6.55 (m, 2H), 6.29 (m, 8H),
2.74 (s, 6H). 13C{1H} NMR (C6D6, 75.5 MHz): δ 193.7 (s),
133.8 (s), 133.6 (m), 123.7 (m), 116.5 (s), 115.2 (m), 26.9 (s). IR
(CH Cl , cmϪ1): 1575s [ν(C᎐O)], 837vs [ν(PF )].
᎐
2
2
6
Synthesis of [RhCl(L2-ꢀ2P,O)(L2-ꢀ1P)] 11. NEt3BzCl (0.028
g, 0.13 mmol) was added to a dichloromethane solution of 8
(0.100 g, 0.13 mmol). The mixture was stirred for 4 h, filtered
then addition of hexane precipitated a red powder which was
isolated by filtration, washed with diethyl ether and dried under
reduced pressure. Recrystallisation from dichloromethane–
hexane gave 11 as red crystals. Yield 0.072 g (84%). Calc. for
C28H28ClN6O2P2Rh: C, 49.4; H, 4.15; N, 12.3%. Found: C, 49.6;
H, 4.22; N, 12.3%. 31P{1H} NMR (161.8 MHz, CD2Cl2): δ 98.2
(br d, 1JPRh 276 Hz). 1H NMR (399.8 MHz, CD2Cl2): δ 7.23 (br
m, 2H), 6.66 (br m, 8H), 6.26 (t, 2H, 3JHH 3.6 Hz), 6.18 (br m,
8H), 5.87 (br m, 2H), 2.49 (br s, 3H). IR (KBr, cmϪ1): 1632s,
1591s [ν(C᎐O)]; IR (CH Cl , cmϪ1): 1642s, 1592s [ν(C᎐O)].
᎐
᎐
2
2
Crystallography
Crystallographic data for compounds 2, 5ؒCH2Cl2, 6ؒC7H8, 7b,
8 and 11 are summarised in Table 8. All data were collected
using a Nonius KappaCCD diffractometer with the exception
of 5ؒCH2Cl2 which were collected on an Enraf-Nonius CAD4.
Full matrix anisotropic refinement was implemented in the final
least-squares cycles for all structures with the specific excep-
tions described below. All data were corrected for Lorentz and
polarisation. Absorption corrections (multiscan) were applied
on the basis of their individual merits to data for 2, 7b and 8
(maximum, minimum transmission factors were 1.03, 0.91;
1.04, 0.97; and 1.02, 0.98; respectively). Hydrogen atoms were
included at calculated positions throughout with the exception
of the solvent moiety in 5ؒCH2Cl2.
The asymmetric unit in 5ؒCH2Cl2 was seen to consist of one
half of a rhodium dimer and one dichloromethane molecule
with half site occupancy. The remaining portion of the dimer
arises via the 1Ϫx, Ϫy, Ϫz transformation. Disorder within the
sample was evident at the early stages of refinement, whereby
the bridging carbonyl and terminal chloride ligands are dis-
ordered in a 1 : 1 ratio with a bridging chloride and terminal
carbonyl respectively. Moreover, proximity of the solvent mole-
cule in the asymmetric unit to an inversion centre also resulted
D a l t o n T r a n s . , 2 0 0 3 , 3 7 1 7 – 3 7 2 6
3725

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13 C. D. Andrews, A. D. Burrows, J. C. Jeffery, J. M. Lynam and
M. F. Mahon, J. Organomet. Chem., 2003, 665, 15.
14 K. G. Moloy and J. L. Petersen, J. Am. Chem. Soc., 1995, 117, 7696.
15 R. Jackstell, H. Klein, M. Beller, K.-D. Wiese and D. Röttger, Eur. J.
Org. Chem., 2001, 3871.
16 A. D. Burrows, M. F. Mahon, M. T. Palmer and M. Varrone,
Inorg. Chem., 2002, 41, 1695.
17 S. Fischer, L. K. Peterson and J. F. Nixon, Can. J. Chem., 1974, 52,
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18 A. D. Burrows, M. F. Mahon and M. T. Palmer, J. Chem. Soc.,
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19 R. G. Pearson, Inorg. Chem., 1973, 12, 712.
20 P. Das, M. Sharma, N. Kumari, D. Konwar and D. K. Dutta,
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in disorder which was successfully modelled. The asymmetric
unit in 6ؒC7H8 was also revealed to be composed of half of one
molecule which straddles an inversion centre in addition to half
of one toluene molecule proximate to a 2-fold rotation axis.
Consequently, the solvent methyl group exhibited disorder,
which was readily modelled. In the refinement of 8, the highest
unassigned peaks in the final difference Fourier electron density
map were proximate to the hexafluorophosphate anion suggest-
ing some disorder. However attempted modelling of any pos-
sible disorder failed to improve the structural refinement. The
data for compound 11 are only of moderate quality, as reflected
in the larger than desirable error on the unit cell parameter, c.
These data were collected at a time when our hardware was
giving an erroneous ‘crash’ error when starting some scan
sequences. This took considerable time to resolve by which time
the sample had degraded, thus the refinement presented is
based on 68% of potential unique data.
23 A. M. Trzeciak, T. Glowiak, R. Grzybek and J. J. Ziólkowski,
J. Chem. Soc., Dalton Trans., 1997, 1831.
CCDC reference numbers 184445, 184446 and 211980–
211983.
See http://www.rsc.org/suppdata/dt/b3/b306292a/ for crystal-
lographic data in CIF or other electronic format.
24 P. Braunstein, Y. Chauvin, J. Nähring, A. DeCian, J. Fischer,
A. Tiripicchio and F. Ugozzoli, Organometallics, 1996, 15, 5551.
25 M. Cowie, Inorg. Chem., 1979, 18, 286.
26 M. M. Olmstead, C. H. Lindsay, L. S. Benner and A. L. Balch,
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27 G. Liehr, G. Szucsänyi and J. Ellermann, J. Organomet. Chem., 1984,
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28 F. H. Allen, Acta Crystallogr., Sect. B, 2002, 58, 380.
29 D. A. Fletcher, R. F. McMeeking and D. Parkin, J. Chem. Inf.
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30 C. Woodcock and R. Eisenberg, Inorg. Chem., 1985, 24, 1285.
31 D. J. Anderson, K. W. Kramarz and R. Eisenberg, Inorg. Chem.,
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Acknowledgements
The authors would like to thank the EPSRC for financial sup-
port and Johnson-Matthey plc for a generous loan of platinum
metals.
32 D. J. Irvine, C. Glidewell, D. J. Cole-Hamilton, J. C. Barnes and
A. Howie, J. Chem. Soc., Dalton Trans., 1991, 1765.
33 E. Lindner, Q. Wang, H. A. Mayer and A. Bader, J. Organomet.
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34 A. D. Burrows, CrystEngComm, 2001, 3, 217.
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37 E. Lindner, Q. Wang, H. A. Mayer, R. Fawzi and M. Steimann,
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