Rhodium and iridium complexes containing diphenyl-2-(3-methyl) indolylphosphine: Synthesis, structure and application in the catalytic transfer hydrogenation of ketones

Article abstract of DOI:10.1039/c0dt00293c

The synthesis and characterisation of a number of group nine complexes containing the recently reported ligand, diphenyl-2-(3-methyl)indolylphosphine, is presented herein. The complexes [RhCl(COD){PPh₂(C ₉H₈N)}] (1), [IrCl(COD){PPh₂(C ₉H₈N)}] (2), [RhCl(NBD){PPh₂(C ₉H₈N)}] (3) and [Rh(COD)(MeCN){PPh₂(C ₉H₈N)}]BF₄ (4) (where COD = 1,5-cyclooctadiene, NBD = 2,5- norbornadiene) have been structurally characterised by X-ray crystallography. The complex [Rh₂(COD)₂{N(Me)C(H)Ph)} {PPh₂(C₉H₈N)}][BF₄]₂ (8) was also isolated and structurally characterised. Complex 8 contains a '[Rh(COD)]' fragment coordinated to the aromatic ring of the indolyl group, providing the first example of a η⁶ coordination mode for this ligand. The synthesised complexes were investigated for their activity in the catalytic transfer hydrogenation of ketones and found to be moderately active catalysts.

Full text of DOI:10.1039/c0dt00293c

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Rhodium and iridium complexes containing
diphenyl-2-(3-methyl)indolylphosphine: synthesis, structure and application in
the catalytic transfer hydrogenation of ketones†
Yu-Ying Kuo, Mairi F. Haddow, Adria´n Pe´rez-Redondo and Gareth R. Owen*‡
Received 12th April 2010, Accepted 8th May 2010
First published as an Advance Article on the web 4th June 2010
DOI: 10.1039/c0dt00293c
The synthesis and characterisation of a number of group nine complexes containing the recently
reported ligand, diphenyl-2-(3-methyl)indolylphosphine, is presented herein. The complexes
[RhCl(COD){PPh2(C9H8N)}] (1), [IrCl(COD){PPh2(C9H8N)}] (2), [RhCl(NBD){PPh2(C9H8N)}] (3)
and [Rh(COD)(MeCN){PPh2(C9H8N)}]BF4 (4) (where COD = 1,5-cyclooctadiene, NBD = 2,5-
norbornadiene) have been structurally characterised by X-ray crystallography. The complex
=
[Rh2(COD)2{N(Me) C(H)Ph)}{PPh2(C9H8N)}][BF4]2 (8) was also isolated and structurally
characterised. Complex 8 contains a ‘[Rh(COD)]’ fragment coordinated to the aromatic ring of the
6
indolyl group, providing the first example of a h coordination mode for this ligand. The synthesised
complexes were investigated for their activity in the catalytic transfer hydrogenation of ketones and
found to be moderately active catalysts.
Introduction
There has been great interest in the development of new complexes
containing mixed phosphorus and nitrogen based ligands for
the catalytic hydrogenation of unsaturated compounds following
the report of the metal–ligand bifunctional catalysts by Noyori
et al.1 Since then, a broad range of such complexes have been
developed2–4 some of which have been shown to hydrogenate ke-
tones with outstanding catalytic activities.5 We became interested
Fig. 1 Diphenyl-2-(3-methyl)indolylphosphine, L.
in this reaction as a means of exploring a potential cooperation
effect from the close proximity of certain functional groups to
the metal centre.6 In the Noyori systems, the coordination of an
NH functional group at the metal centre is key in determining
the enhanced activities.7 We were interested to explore whether
any cooperation effect would result from the presence of an
NH functional group in close proximity to the metal centre. In
principle, the NH group would stabilize resulting hydride species,
perhaps via hydrogen bonding interactions8 or provide a means
of directing substrates towards the metal centre.6 We therefore set
out to prepare some group nine complexes containing the rela-
tively unexplored ligand, diphenyl-2-(3-methyl)indolylphosphine
(L) (Fig. 1).9,10,11
More recently, derivatives of this ligand have been utilized in
the Suzuki-Miyaura coupling of aryl chlorides.12 Several mon-
odentate and bidentate derivative ligands13–16 have been reported
and some of the latter examples have successfully been applied
to asymmetric hydrogenation,14,15 hydroformylation15 and allylic
alkylation reactions.16 Most recently, Pe´rez-Prieto has published
a new C3-symmetric tripodal ligand based on diphenyl-2-(3-
methyl)indolylphosphine.17 The coordination chemistry of this
ligand however remains limited and we therefore wish to report
the synthesis of a range of group nine transition metal complexes
containing this ligand along with their catalytic performance in
the transfer hydrogenation of ketones.
Browning and coworkers reported the synthesis of diphenyl-
2-indolylphosphine in 2004 together with some of its palladium
complexes.9,11 In these complexes the ligand coordinates to the
metal centre via the phosphorus atom and the NH group
was found to provide strong hydrogen bonding interactions
with the coordinated halides.10 A further report provided an
Results and discussion
Synthesis of complexes
The complexes [RhCl(COD)L] (1) and [IrCl(COD)L] (2) were
prepared by the addition of two equivalents of diphenyl-2-
(3-methyl)indolylphosphine11 to dichloromethane solutions of
[RhCl(COD)]2 and [IrCl(COD)]2 respectively (Scheme 1, top).
3
2
unusual bridging coordination mode for the ligand (m , h ).9
The School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK
BS8 1TS. E-mail: gareth.owen@bristol.ac.uk; Fax: +44 (0)117 929 0509;
Tel: +44 (0)117 928 7652
† CCDC reference numbers 772897–772901. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00293c
‡ Royal Society Dorothy Hodgkin Research Fellow.
1
After 3 h stirring at room temperature, the 31P{ H} NMR spectra
of the reaction mixtures showed the complete disappearance of
the signal corresponding to the free ligand and the appearance
of a new signal for the expected products. Both complexes were
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6239–6248 | 6239
©

View Article Online
Scheme 2 Synthesis of complexes [Rh(COD)(NCMe)L]BF4 (4) and
[Ir(COD)(NCMe)L]BF4 (5).
Scheme 1 Synthesis of complexes [RhCl(COD)L] (1) and [IrCl(COD)L]
(2) (top) and [RhCl(NBD)L] (3) (bottom).
iridium complex, [Ir(COD)(NCMe)L]BF4 (5), was also prepared
in good yield via a similar method to that for complex 4 and
was characterised by spectroscopic and analytical methods. Both
complexes 4 and 5 showed limited stability in solution and in the
solid state even when stored under a nitrogen atmosphere.
obtained as analytically pure solids in high yields, following a
standard work up procedure (see Experimental section).
The two compounds were fully characterised by spectroscopic
The corresponding complexes containing two of the phosphine
ligands, [Rh(COD)L2]BF4 (6) and [Ir(COD)L2]BF4 (7), were
readily prepared by a two step procedure (Scheme 3). The chloride
ligand was removed from complexes 1 and 2 by addition of
AgBF4 to their dichloromethane solutions. After 1 h the reaction
mixtures were filtered to remove the precipitated AgCl, and one
1
and analytical methods. The 31P{ H} NMR spectra revealed sharp
1
peaks at 14.1 ppm (d, JPRh = 146 Hz) for 1 and 6.7 ppm (s)
for 2 at downfield chemical shifts relative to the free ligand
1
d = -32.7 ppm.11 The 1H and 13C{ H} NMR data for both
1 and 2 were consistent with the formation of [RhCl(COD)L]
and [IrCl(COD)L]. The IR spectra of 1 and 2 showed bands
characteristic of the ligand together with sharp bands at 3290 cm-1
and 3325 cm-1 (powder film) due to the stretching mode of
the NH group. Mass spectroscopy and elemental analysis were
both consistent with the molecular composition of 1 and 2. In
order to test the effect of a diene with greater ring strain, the
corresponding rhodium norbornadiene complex [RhCl(NBD)L]
(3) was also prepared in a good yield. Complex 3 was synthesised
and fully characterised by analogous methods as those described
for complexes 1 and 2 (Scheme 1, bottom).
1
equivalent of L was added. The 31P{ H} NMR spectra of the
resulting reaction mixtures revealed new signals at 9.1 ppm (d,
1JPRh = 142 Hz) and at 2.2 ppm (s), respectively suggesting
the formation of the targeted products 6 and 7. Addition of
hexane to these mixtures resulted in the precipitation of these
compounds in high yields which were fully characterised. The
1
1H and 13C{ H} NMR data for both 6 and 7 were consistent
with the formation of [Rh(COD)L2]BF4 and [Ir(COD)L2]BF4. The
IR spectra of 6 and 7 showed bands characteristic of the ligand
including bands at 3389 cm-1 and 3379 cm-1, corresponding to N–
H stretching frequencies together with broad bands at 1058 cm-1
and 1056 cm-1 for the BF4 counterions, respectively. The presence
of two phosphine ligands in each complex was confirmed by mass
spectrometry and elemental analysis.
In order to explore this further, complexes containing two
phosphine ligands were targeted.18 Our initial reactions involved
the addition of the phosphine ligands to dichloromethane solu-
1
tions of 1 and 2 followed by addition of AgBF4. The 31P{ H}
NMR spectra of the reaction mixtures were complicated and
consistently revealed a broad peak at -10.1 ppm along with signals
corresponding to starting material and several other peaks. The
broad peak was tentatively assigned as the complex resulting from
coordination of L to the silver salt. In the following reactions, the
silver halide was removed prior to the addition of the second
equivalent of L. Addition of one equivalent of AgBF4 to a
solution of 1 in dichloromethane resulted in the rapid precipitation
of AgCl from the mixture (interestingly no decomposition was
observed even when non-coordinating solvents were utilized).
Scheme
[Ir(COD)L2]BF4 (7).
3 Synthesis of complexes [Rh(COD)L2]BF4 (6) and
1
Following filtration, the 31P{ H} NMR of the resulting filtrate
was recorded which revealed the presence of two new doublet
signals at 11.4 ppm (d, 1JPRh = 154 Hz, major component) and 9.1
In order to explore the interactions of substrates with
the metal centres further we attempted to synthesise the
1
[(d, JPRh = 142 Hz, minor component, < 15% (estimated from
1
31P{ H} integration]. The minor component was later shown to
complex [Rh(COD){N(Me) C(H)Ph}L]BF4. In a similar pro-
=
correspond to [Rh(COD)L2]BF4 (see below). Despite a number
of attempts, we were unable to establish the identity of the major
component within this mixture. When the reaction was carried out
in the presence of MeCN, (or when MeCN was used as a solvent),
a new single broad peak centred at 8.7 ppm (Dn1/2 = 122 Hz)
cedure to that described above, the halide was abstracted
from [RhCl(COD)L] with AgBF4 and one equivalent of
=
N(Me) C(H)Ph was subsequently added to the resulting filtrate.
The 31P{ H} NMR spectrum revealed the presence of a new
1
1
doublet signal at 6.3 ppm (d, JPRh = 145 Hz, C6D6) suggesting
1
was observed in the 31P{ H} NMR spectrum. An orange solid
the formation of our target complex. The proton NMR spectrum
of the isolated solid was also consistent with the formation of the
was isolated from this reaction mixture in high yield following
1
standard workup (see Experimental section). The 1H and 13C{ H}
target product [Rh(COD){N(Me) C(H)Ph}L]BF4. Our attempts
=
NMR data for this compound were consistent with the formation
to purify this compound by recrystallisation led to isolation of
single crystals which were found to be the unexpected complex
of [Rh(COD)(NCMe)L]BF4 (4) (Scheme 2). The corresponding
6240 | Dalton Trans., 2010, 39, 6239–6248
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
◦
˚
Table 1 Selected bond distances (A) and angles ( ) for 1–4
1
2
3
4
Rh(1)–P(1)/Ir(1)–P(1)
Rh(1)–Cl(1)/Ir(1)–Cl(1)
Rh(1)–N(2)
Rh(1)–C(22)/Ir(1)–C(22)
Rh(1)–C(23)/Ir(1)–C(23)
Rh(1)–C(26)/Ir(1)–C(26)
Rh(1)–C(27)/Ir(1)–C(27)
C(22)–C(23)
C(26)–C(27)
P(1)–C(1)
P(1)–Rh(1)–Cl(1)/P(1)–Ir(1)–Cl(1)
P(1)–Rh(1)–N(2)
C(1)–P(1)–Rh(1)/C(1)–P(1)–Ir(1)
Rh(1)–Cl(1)–H(1)–N(1)/Ir(1)–Cl(1)–H(1)–N(1)
2.3077(3)
2.3766(3)
—
2.3064(7)
2.3664(7)
—
2.2884(5)
2.3626(5)
—
2.2981(10)
—
2.063(3)
2.214(4)
2.242(3)
2.132(4)
2.140(4)
1.376(5)
1.383(6)
1.796(4)
—
2.2312(13)
2.2193(13)
2.1326(12)
2.1156(12)
1.3816(19)
1.409(2)
1.8032(13)
90.726(12)
—
2.209(3)
2.196(3)
2.121(3)
2.104(3)
1.395(4)
1.411(4)
1.808(3)
91.33(3)
—
2.2181(19)
2.2177(19)
2.104(2)
2.103(2)
1.372(3)
1.408(3)
1.807(2)
94.034(18)
—
91.06(9)
113.40(13)
—
115.61(4)
92.24
115.54(10)
91.89
114.51(6)
81.21
=
[Rh2(COD)2{N(Me) C(H)Ph)}{PPh2(C9H8N)}][BF4]2 (8). De-
tails of this complex are presented in the following section.
X-Ray crystal structures of complexes 1, 2, 3, 4 and 8
The coordination of diphenyl-2-(3-methyl)indolylphosphine to the
rhodium and iridium centres was further confirmed by single
crystal X-ray diffraction studies for complexes 1–4 and 8. Single
crystals were obtained by layering a dichloromethane solution
of 1 with hexane (Fig. 2) and upon layering a chloroform
solution of 2 with diethyl ether (Fig. 3). Single crystals of 3
were obtained by layering a chloroform solution of the complex
with hexane. The molecular structure of 3 is shown in Fig. 4.
Single crystals of 4 were grown by layering a THF solution with
diethyl ether (Fig. 5). Finally, single crystals of 8 were grown
by layering a dichloromethane solution with hexane and the
molecular structure is shown in Fig. 6. Selected bond lengths and
distances and crystallographic parameters for complexes 1–4 and
8 are highlighted in Tables 1, 2 and 3.
Fig. 2 Molecular structure of [RhCl(COD)L] (1), [hydrogen atoms
{except for H(1)} have been omitted for clarity (thermal ellipsoids drawn
at the 50% level)].
Complexes 1 and 2 are isostructural (and their crystals are
isomorphous). The metals adopt a square planar geometry with
one COD ligand, one chloride ligand and the diphenyl-2-(3-
methyl)indolylphosphine coordinated to the metal centre via
the phosphorus atom. The M–P bond distances in 1 and 2 are
˚
˚
2.3077(3) A and 2.3064(7) A, respectively. The indolyl N–H
functional group is orientated so that it points in the direction
of the chloride ligand. The indolyl ring is twisted with a torsion
angle defined by M (Rh or Ir), Cl(1), H(1) and N(1), of 92.24◦ (1)
◦
˚
Table 2 Selected bond distances (A) and angles ( ) for 8
Rh(1)–P(1)
Rh(1)–N(1)
Rh(1)–C(1)
Rh(1)–C(2)
Rh(1)–C(5)
Rh(1)–C(6)
C(1)–C(2)
2.3192(9)
2.098(3)
2.160(4)
2.151(4)
2.247(4)
2.233(4)
1.389(5)
1.383(6)
1.284(5)
1.807(4)
129.2(3)
91.40(9)
110.41(12)
-4.7(3)
C(5)–C(6)
Fig. 3 Molecular structure of [IrCl(COD)L] (2), [hydrogen atoms {except
for H(1)} have been omitted for clarity (thermal ellipsoids drawn at the
50% level)].
=
N(1) C(10)
P(1)–C(29)
=
Rh(1)–N(1) C(10)
P(1)–Rh(1)–N(1)
C(29)–P(1)–Rh(1)
Rh(1)–P(1)–C(29)–N(2)
and 91.89◦ (2). The positioning of this group is perhaps governed
by steric factors and also by a hydrogen bond interaction of the
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6239–6248 | 6241
©

View Article Online
Table 3 Crystallographic parameters for complexes 1–4 and 8
Complex
1
2
3
4
8
Chemical formula
Formula weight
Crystal system
Space group
C29H30ClNPRh
561.87
Monoclinic
C29H30ClIrNP
651.16
Monoclinic
C28H26ClNPRh
545.83
Monoclinic
C35H41BF4N2OPRh
726.39
Monoclinic
C45H51B2F8N2PRh2
1030.29
Triclinic
¯
P1
11.0623(4)
11.2983(4)
19.1151(7)
98.481(2)
2
100(2)
0.809
32973
10602
P21/c
P21/c
P21/c
P21/c
˚
a/A
10.3430(3)
15.0230(4)
16.3236(5)
105.2310(10)
4
100(2)
0.891
56256
7494
1.076
0.0230
0.0209
0.0240
10.3316(3)
15.0241(5)
16.3586(5)
105.5230(10)
4
100(2)
5.650
22523
5635
1.063
0.0333
0.0211
0.0266
10.3647(2)
13.1993(3)
17.0825(4)
97.6650(10)
4
100(2)
0.939
24809
5298
1.033
0.0318
0.0248
0.0320
9.5738(2)
18.7089(4)
18.5897(4)
91.6770(10)
4
100(2)
0.614
29947
7630
1.018
0.0812
0.0478
0.0876
˚
b/A
˚
c/A
b (◦)
Z
T/K
m/mm-1
No. of data collected
No. of unique data
Goodness of fit on F2
1.076
Rint
.
0.0326
0.0439
0.0594
Final Rindices for (I > 2sI)
Final Rindices for all data
Fig. 6 Crystal structure of complex 8 [the two BF4 counterions and
hydrogen atoms {except for H(2)} have been omitted for clarity (thermal
ellipsoids drawn at the 50% level)].
Fig. 4 Molecular structure of [RhCl(NBD)L] (3) [hydrogen atoms
{except for H(1)} have been omitted for clarity (thermal ellipsoids drawn
at the 50% level)].
NH group with the chlorine. The H(1)–Cl(1) distances are
˚
˚
2.522 A and 2.551 A for complexes 1 and 2, respectively.
The norbornadiene based complex, 3, has a similar structure
to the cyclooctadiene based complexes. The Rh–P bond distance
˚
is 2.2884(5) A. The indolyl ring is twisted with a torsion angle
defined by M (Rh or Ir), Cl(1), H(1) and N(1), of 81.21◦. The
˚
H(1)–Cl(1) distance (2.450 A) is slightly shorter than found in
complexes 1 and 2. The angle defined by the atoms P(1), Rh(1)
and Cl(1) provides an indication of the ring strain of the diene
ligands. The greater strain associated with NBD complex (3) gives
an angle of 94.034(18)◦ while the corresponding angle in the COD
based complex (1) is 90.726(12)◦.
The rhodium centre in complex 4 adopts a square planar
geometry with one COD ligand, one acetonitrile ligand and the
diphenyl-2-(3-methyl)indolylphosphine coordinated to the metal
centre via the phosphorus atom. The Rh–P bond distance is
˚
2.2981(10) A. The indolyl N–H functional group is orientated
so that it points away from the metal centre.
In the case of complex 8, an additional ‘[Rh(COD)]’
Fig. 5 Crystal structure of complex 4·C4H8O [the non-coordinating
solvent molecule, anion and hydrogen atoms {except for H(1)} have been
omitted for clarity (thermal ellipsoids drawn at the 50% level)].
fragment
was
bound
to
the
expected
structure
=
[Rh{N(Me) C(H)Ph)}(COD)L] which was coordinated to
6242 | Dalton Trans., 2010, 39, 6239–6248
This journal is The Royal Society of Chemistry 2010
©

View Article Online
6
the aromatic ring of the indolyl group in a h mode. To the best of
at 9.61 ppm (6) and 9.52 ppm (7). The NH resonances of the
acetonitrile-substituent complexes were located at 9.02 ppm (4)
and 9.09 ppm (5). The chemical shift of this group appears to
be related to its orientation and interactions with neighbouring
groups. The downfield chemical shifts, in the case of the chloride
complexes (1 and 2), are consistent with hydrogen bonding
interactions between the NH group and the halide.10 The chemical
shifts of the corresponding protons on the methyl group of the
ligand are observed between 1.78 and 2.73 ppm. The signals
corresponding to the methyl groups in both complexes 4 and
5 are found at downfield chemical shifts relative to the other
complexes. The solid state structure of complex 4 reveals that the
methyl group is orientated so that it points towards an axial site
our knowledge, this is the first example of the indolylphosphine
ligand adopting a h coordination mode. These six indole carbon
atoms are not all equally separated from this metal atom. The
rhodium centre is furthest away from the quaternary carbon
6
˚
˚
atoms of indolyl [2.398(4) A and 2.393(4) A compared to the range
˚
2.254–2.293 A for the four other carbon atoms]. This has been
observed in previous examples involving indole coordination19
4
and exhibits some distortion towards a h coordination mode
involving a 16-electron species (Fig. 7). The structure reveals
a Rh(1)–P(1) bond length of 2.3192(9) A [c.f . 2.3077(3) A for
1]. The Rh(1)–N(1) and N(1) C(10) distances are 2.098(3) A
and 1.284(5) A, respectively, comparable to other complexes of
˚
˚
˚
=
˚
20
˚
=
the type Rh–{N(R) C(H)Ph}. The phenyl group of the imine
on the rhodium centre [Rh–Cmethyl distance 3.385(4) A] indicating
ligand is in close proximity with one phenyl groups of phosphine
a Rh ◊ ◊ ◊ H–C interaction. Such interactions are supported by a
number of previous examples where a similar downfield shift has
been recorded.21
˚
ligand with a distance between the two centroids of 3.780 A and
the distance between the two closest atoms of 3.442 A.
˚
The olefin protons of the coordinated 1,5-cyclooctadiene ligand
were found at 3.22 ppm and 5.58 ppm for 1, while in complex 2
they were found at 2.81 ppm and 5.21 ppm. The downfield signals
were assigned as those protons which are trans to the phosphine
on the basis of the assignment of related complexes.18c,22 This
was confirmed by a HMQC correlation experiment since their
corresponding carbon signals coupled to the phosphorus trans to
them. In the case of the acetonitrile complexes 4 and 5, only one
particularly broad signal (integrating for 4 protons) corresponding
to the olefin protons of the coordinated 1,5-cyclooctadiene ligands
was observed [4.56 ppm (4) and 4.33 ppm (5)]. This suggests that
there is some fluxional behaviour in these complexes, resulting
from rapid loss and re-coordination of the solvent molecule.23 The
1H NMR spectra of the bis-phosphine complexes also revealed
one chemical environment for the olefin protons as expected.
The signals corresponding to the coordinated 1,5-cyclooctadiene,
suggesting a more symmetric environment and only one broad
signal integrating for four protons, was observed for the olefin
protons in each case (4.74 ppm for 6 and 4.40 ppm for 7).
The IR spectra of these complexes display a characteristic N–
H stretching frequency of indole group – with reduced frequency
relative to the free ligand (3445 cm-1). The ESI+ mass spectra of 1–
7 showed molecular ion peaks for the expected cationic complexes
with the exception of the acetonitrile complex 4 which showed
signs of decomposition during the analysis (see Experimental
section). The molecular composition of the complexes was further
confirmed by elemental analysis.
6
4
Fig.
7
h
and
h
coordination modes for diphenyl-2-(3-methyl)-
indolylphosphine.
Comparison of complexes 1–7
A comparison of selected NMR and IR spectroscopic data for
complexes 1–7 is shown in Table 4. The 31P{ H} NMR spectra of
1
these complexes consists of a single resonance for each complex.
The positively charged complexes (4, 5, 6 and 7) give signals
with upfield chemical shifts compared to the chloro-substituted
complexes (1 and 2). The spectra for the rhodium complexes
showed a doublet signals for each of the corresponding products
with 1JRhP coupling constants ranging between 145–167 Hz, with
the exception of complex 4, where the signal was too broad to allow
for the measurement of the coupling constant (Dn1/2 = 124 Hz).
The 1H NMR spectra of these compounds revealed single
broad peaks for the NH functional groups over a wide range
between 9.02–10.86 ppm (cf. 7.8 ppm for the free ligand). The NH
resonances within the chloro-substituted complexes 1 and 2 were
located at 10.78 ppm and 10.44 ppm, respectively. The complexes
containing two of the phosphine ligands gave NH resonances
Table 4 A comparison of the NMR and IR spectroscopic data for complexes 1–7
1
a
31P{ H}
1Ha (NH)
d (ppm)
1Ha (CH3)
d (ppm)
IRb (N–H stretch)
cm-1
Complex
d (ppm)
1JPRh/Hz
[RhCl(COD)L] (1)
[Rh(COD)L2]BF4 (6)
[RhCl(NBD)L] (3)
[Rh(COD)(MeCN)L]BF4 (4)
[IrCl(COD)L] (2)
[Ir(COD)L2]BF4 (7)
[Ir(COD)(MeCN)L] BF4 (5)
14.1
9.1
15.8
8.7e
6.7
146
142
167
u.rd,e
—
—
—
10.78c
9.61
1.78
1.81
1.82
2.73e
1.79
1.80
2.65e
3290
3389
3267
3372
3325
3379
3364
10.86
9.02e
10.44
9.52
2.2
0.3e
9.09e
a Recorded in CDCl3 unless otherwise stated. b Powder film. c The NH signal of 1 was observed at 10.45 ppm in CD3CN. d Unresolved. e Recorded in
CD3CN.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6239–6248 | 6243
©

View Article Online
Table 7 A comparison of the activities of the COD and NBD complexes
Catalytic studies
under 0.02 M KOH in iPrOH conditions
Complexes 1–3 and 6 and 7 were tested for their activities in
the transfer hydrogenation of ketones using standard literature
procedures.24 Complexes 4 and 5 gave irreproducible results,
presumably due to their instability and so they have not been
included. The results of our preliminary investigations are sum-
marized in Tables 5–7. The reactions were carried out at 84 ◦C
and the resulting conversions were recorded at 1 h, 3 h and
24 h intervals and were determined by the relative integration
Conversion (%)c
Run
Complexa
Substrateb
1 h
3 h
24 h
23
24
25
26
27
28
29
30
31
32
33
34
35
36
1
2
3
6
7
1
2
3
6
7
2
3
6
7
A
A
A
A
A
B
B
B
B
B
C
C
C
C
8
24
24
63
16
26
21
14
43
14
10
17
94
51
73
56
76
90
35
73
53
58
74
50
48
79
99
88
99
11
51
4
17
12
7
26
4
6
13
60
19
34
1
of the substrates against products in their H NMR spectra (see
Experimental section for details). Our initial catalytic reactions
(runs 1–12) were performed using 10 mL of 0.2 M solution of
i
KOH in PrOH (Table 5). As shown, complexes 1, 2, 6 and 7
are active catalyst for the transfer hydrogenation of acetophenone
(A), benzophenone (B) and cyclohexanone (C). Table 5 reveals that
the rhodium and iridium complexes 1, 2, 6 and 7 exhibit similar
activities and hydrogenate cyclohexanone more readily than the
aryl ketones, acetophenone and benzophenone. The conversion
to the respective alcohols is essentially complete within a 24 h
period for all substrates. The bis-phosphine iridium complex (7)
provides the best activity for the conversion of cyclohexanone to
a 10 mL of 0.02 M KOH in PrOH, 0.1 mol% catalyst loading, 2 mmol
of substrate, 84 ◦C. b A – acetophenone, B – benzophenone, C –
cyclohexanone. c Measured by NMR integration.
i
cyclohexanol which is essentially complete within 3 h with a 65%
conversion within 1 h.
Table 5 Transfer hydrogenation of ketones using complexes 1, 2, 6 and 7
with 0.2 M KOH in iPrOH
The role of the base within transfer hydrogenation has previ-
ously been noted (although only in a small number of cases)25
and so the catalytic reactions were carried out under various
concentrations of KOH in iPrOH. Runs 14–22, shown in Table 6,
show that there is indeed a strong dependence of the base
concentration on the observed activities. Our observations confirm
those previously reported25 which show that the base catalyses
the reaction even in the absence of a transition metal catalyst.26
A comparison of catalytic runs 15 and 16 reveals that under
0.2 M KOH/iPrOH conditions the conversion of cyclohexanone
to cyclohexanol was essentially complete after 24 h while under
0.02 M KOH/iPrOH conditions the conversion was 50% after the
same period. A similar result is observed when the reactions were
carried out in the presence of 0.1 mol% of L [cf. 94% (0.2 mol%
KOH) vs. 44% (0.02 mol% KOH) after 24 h (runs 17 and 18,
respectively)]. Run 21 shows that in the presence of 0.1 mol%
of complex 1 the corresponding conversion was 65% after 3 h
compared to only 10% in its absence (run 16). In order to lower
the background effect of the activity of the base, subsequent runs
were performed at lower base concentrations (0.02 M in iPrOH).
Table 7 shows the activities of complexes 1–3, 6 and 7 for
the transfer hydrogenation of substrates A, B and C under the
lower base concentrations. A comparison of the activities of
the related cyclooctadiene and norbornadiene complexes 1 and
3 is also shown. Runs 23–36 show a decrease in activity for
the cyclooctadiene complexes (1, 2, 6 and 7) under the lower
base concentrations and that, in each case, the norbornadiene
complex(3) outperformedthe cyclooctadiene complexes. Complex
3 provided conversions of 90%, 74% and 99% for acetophenone,
benzophenone and cyclohexanone, respectively, after a period of
24 h. This has been attributed to the greater strain of the former
diene resulting in facile generation of the active species. A similar
observation has recently been recorded by Pugin and Pfaltz et al.27
and by Heller.28
Conversion (%)c
Run
Complexa
Substrateb
1 h
3 h
24 h
1
2
3
4
5
6
7
8
1
2
6
7
1
2
6
7
1
2
6
7
A
A
A
A
B
B
B
B
C
C
C
C
15
10
11
21
14
7
24
39
44
54
42
65
30
31
27
45
27
22
44
46
69
69
57
89
86
94
79
92
78
82
76
90
99
99
99
> 99
9
10
11
12
a 10 mL of 0.2 M KOH in PrOH, 0.1 mol% catalyst loading, 2 mmol
of substrate, 84 ◦C. b A – acetophenone, B – benzophenone, C –
cyclohexanone. c Measured by NMR integration.
i
Table 6 A comparison of the effect of base concentration upon the
transfer hydrogenation of ketones
Conversion (%)c
Run Conditionsa
Substrateb 1 h
3 h 24 h
14
15
16
17
18
19
20
21
22
0.1% L/no base
C
C
C
C
C
A
C
C
C
—
23
trace
14
trace
7
44
39
18
—
48
10
39
12
21
69
65
34
—
99
50
94
44
80
99
98
33
0.2M KOH/iPrOH
0.02 M KOH/iPrOH
0.1% L/0.2 M KOH/iPrOH
0.1% L/0.02 M KOH/iPrOH
0.1% L/0.2 M KOH/iPrOH
0.1% 1/0.2 M KOH/iPrOH
0.1% 1/0.02 M KOH/iPrOH
0.1% 1/0.002 M KOH/iPrOH
a 10 mL of KOH in iPrOH, 2 mmol of substrate, 84 ◦C. b A – acetophenone,
C – cyclohexanone. c Measured by NMR integration.
6244 | Dalton Trans., 2010, 39, 6239–6248
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Conclusions
In summary, we have reported the synthesis and characterisation
of a range of group 9 complexes containing the ligand diphenyl-2-
(3-methyl)indolylphosphine (L). For complex 8, a second rhodium
metal centre coordinates to the indolyl moiety of the ligand
6
through a h coordination mode. This is the first example of
Fig. 8 Numbering scheme for L.
such a coordination mode for this ligand. After optimisation,
it was found that the isolated complexes were active catalysts
for the transfer hydrogenation in acetophenone, benzophenone
and cyclohexanone at even at low catalyst loading and low
mixture with stirring. The resulting yellow solution was stirred
at room temperature for 3 h after which time the mixture was
concentrated to approximately 3 mL. A yellow powder was
precipitated when hexane (20 mL) was added. The product was
isolated by filtration and dried under vacuum. Yield: 190.0 mg
(84%). Crystals suitable for a single-crystal X-ray diffraction study
were grown from layering hexane upon CH2Cl2 solution. Anal.
Calcd. for C29H30ClNPRh (561.89): C, 61.99; H, 5.38; N, 2.49.
Found: C, 61.84; H, 5.42; N, 2.56. 1H NMR (CDCl3, 400.2 MHz)
d [ppm] = 1.78 (d, 4JPH = 1.5 Hz, 3H, indoleCH3), 1.92–2.02 (m, 2H,
CODCH2), 2.06–2.17 (m, 2H, CODCH2), 2.38–2.54 (m, 4H, CODCH2),
3.22 (br, 2H, CODCH trans to Cl), 5.58 (br, 2H, CODCH trans to
P), 7.13 (ddd, 3JHH = 8.0 Hz, 3JHH = 6.9 Hz, 4JHH = 1.0 Hz, 1H,
i
base concentration (0.1 mol% catalyst, 0.02M KOH in PrOH).
Complex 3, which is the only complex to contain the NBD
ligand, shows the highest activities while the other complexes show
moderate activities. Nevertheless, the activities are comparable
to other rhodium and iridium systems containing bidentate N-
heterocyclic carbene,3a mixed N-heterocyclic carbene-nitrogen,29
bidentate nitrogen30 and bidentate phosphine31 ligands at low
catalyst loadings (0.1 mol%).
Experimental
indoleC6H), 7.28 (ddd, 3JHH = 8.0 Hz, 3JHH = 7.4 Hz, 4JHH = 1.2 Hz,
3
1H, indoleC7H), 7.37–7.47 (m, 6H, o,p-PPh2CH), 7.49 (ddd, JHH
=
General remarks
8.3 Hz, JHH = 0.9 Hz, JHH = 0.9 Hz, 1H, indoleC5H), 7.57 (dd,
4
4
3JHH = 8.1 Hz, 4JHH = 0.7 Hz, 1H, indoleC8H), 7.59–7.66 (m, 4H, m-
All manipulations were performed in a Braun glovebox with an
O2 and H2O atmosphere of below 5 ppm or by using standard
Schlenk techniques. Solvents (CH2Cl2, THF, Et2O, MeCN and
hexane) were dried using a Grubbs’ alumina system, and were
PPh2CH), 10.78 (br, 1H, NH). 31P { H} NMR (CDCl3, 121.4 MHz)
1
d [ppm] = 14.1 (d, 1JPRh = 146 Hz, PPh2). 13C { H} NMR (CDCl3,
1
100.6 MHz) d [ppm] = 11.2 (s, indoleCH3), 28.9 (d, JRhC = 1.5 Hz,
CODCH2), 33.0 (d, JRhC = 3.1 Hz, CODCH2), 71.6 (d, JRhC = 13.8 Hz,
CODCH trans to Cl), 105.6 (dd, JRhC = 11.5 Hz, JPC = 6.9 Hz,
CODCH trans to P), 112.1 (s, indoleC5H), 119.1 (s, indoleC8H), 119.3 (s,
indoleC6H), 120.0 (d, 1JCP = 1.5 Hz, indoleCPPh2), 120.8 (s,indoleCCH3),
123.8 (s, indoleC7H), 128.5 (d, 2JCP = 10.8 Hz, o-PPh2CH), 129.4 (d,
˚
kept in Young’s ampoules under N2 over molecular sieves (4 A).
Dry n-pentane (<0.05 ppm H2O) was purchased from Fluka and
was stored in a Young’s ampoule under N2 over molecular sieves
11
32
˚
(4 A). The ligand, L, and the complexes, [RhCl(COD)]2 and
[IrCl(COD)]2,33 were synthesised according to standard literature
procedures. [RhCl(NBD)]2 was purchased from STREM and used
as received. The deuterated solvents, CDCl3 and CD3CN, were
3JCP = 7.7 Hz,indoleC4), 130.2 (d, JCP = 2.3 Hz, p-PPh2CH), 130.6
4
(s, PPh2
C
ipso), 133.2 (d, 3JCP = 11.5 Hz, m-PPh2CH), 137.7 (d, 3JCP
=
9.2 Hz, indoleC9). IR: 3289.9 cm-1 (u N–H). MS m/z (ESI)+: 526.11
[M-Cl-]+ (100%).
˚
degassed by three freeze-thaw cycles, stirred over 4 A molecular
sieves then vacuum distilled and stored in Young’s ampoules over
1
1
4 A molecular sieves under N2. H NMR, 31P{ H} NMR spectra
were recorded on a JEOL Lambda 300 spectrometer operating
at 300 MHz (1H), a JEOL ECP300 spectrometer operating at
300 MHz (1H), a JEOL ECP 400 spectrometer operating at
400 MHz (1H) or a Varian VNMR S500 instrument operating
˚
[IrCl(COD)L] (2).
[IrCl(COD)]2 (100.0 mg, 0.148 mmol) and
A
Schlenk flask was charged with
(93.7 mg,
L
0.297 mmol). CH2Cl2 (20 mL) was subsequently added to the
mixture. The resulting orange solution was stirred at room
temperature for 3 h after which time the mixture was concentrated
to approximately 2 mL. A yellow-orange powder was precipitated
when hexane (20 mL) was added. The product was isolated
by filtration and dried under vacuum. Yield: 163.7 mg (84%).
Crystals suitable for single-crystal X-ray diffraction study were
grown from layering Et2O upon CDCl3 solution. Anal. Calcd.
for C29H30ClNIrP (651.20): C, 53.49; H, 4.64; N, 2.15. Found: C,
53.61; H, 4.75; N, 2.69. 1H NMR (CDCl3, 300.5 MHz) d [ppm] =
1.55–1.74 (m, 2H, CODCH2), 1.79 (d, 4JPH = 0.9 Hz, 3H, indoleCH3),
1.85–2.00 (m, 2H, CODCH2), 2.15–2.41 (m, 4H, CODCH2), 2.81 (br,
2H, CODCH trans to Cl), 5.21 (br, 2H, CODCH trans to P), 7.14 (ddd,
3JHH = 7.9 Hz, 3JHH = 6.9 Hz, 4JHH = 1.4 Hz, 1H, indoleC6H), 7.29
(ddd, 3JHH = 7.5 Hz, 3JHH = 7.0 Hz, 4JHH = 1.1 Hz, 1H, indoleC7H),
at 500 MHz (1H). 13C{ H} NMR, DEPT-135, and hetero-nuclear
1
correlation experiments spectra were recorded on a JEOL ECP400
spectrometer operating at 400 MHz (1H), or a Varian 400-
MR spectrometer operating at 400 MHz (1H). The spectra were
referenced internally, to the residual protic solvent (1H) or the
1
signals of the solvent (13C). 31P{ H} NMR spectra are referenced
relative to high frequency of 85% H3PO4. Mass spectra were
recorded on a Bruker Daltonics Apex (7.0 Tesla) FT-ICR-MS
mass spectrometer using ESI+ ionization. Elemental analyses were
performed at the microanalytical laboratory of the School of
Chemistry at the University of Bristol. Infrared spectra were
recorded on a Perkin-Elmer Spectrum 100 FT-IR spectrometer
(solid state, neat) from 4000 cm-1 to 650 cm-1. Fig. 8 shows the
numbering scheme used for assignment of the signals related to L.
3
4
7.38–7.46 (m, 6H, o,p-PPh2CH), 7.49 (dd, JHH = 8.3 Hz, JHH
=
0.6 Hz, 1H, indoleC5H), 7.54–7.65 (m, 5H, m-PPh2CH &indoleC8H),
1
[RhCl(COD)L] (1).
A
Schlenk flask was charged with
10.44 (br, 1H, NH). 31P { H} NMR (CDCl3, 121.7 MHz) d [ppm] =
1
[RhCl(COD)]2 (100.0 mg, 0.202 mmol) and L (127.4 mg,
0.404 mmol). CH2Cl2 (20 mL) was subsequently added to the
6.70 (s, PPh2). 13C { H} NMR (CDCl3, 100.5 MHz) d [ppm] = 11.3
(s, indoleCH3), 29.5 (d, JPC = 1.6 Hz, CODCH2), 33.4 (d, JPC = 3.1 Hz,
Dalton Trans., 2010, 39, 6239–6248 | 6245
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
CODCH2), 54.6 (s, CODCH trans to Cl), 94.7 (d, JPC = 14.0 Hz,
CODCH trans to P), 112.1 (s, indoleC5H), 119.2 (s, indoleC8H), 119.4 (s,
indoleC6H), 120.6 (d, 1JCP = 3.1 Hz, indoleCPPh2), 121.7 (s, indoleCCH3),
[Ir(COD)L(NCMe)]BF4 (5). A Schlenk flask was charged with
[IrCl(COD)L] (2) (50.0 mg, 0.076 mmol). MeCN (10 mL) was
added and then CH2Cl2 (15 mL). AgBF4 (22.4 mg, 0.115 mmol)
was added to the flask in one portion and the flask was
subsequently covered with aluminium foil. The orange cloudy
solution was filtered, hexane (10 mL) was added and all volatiles
were subsequently removed under reduced pressure to provide a
2
123.9 (s, indoleC7H), 128.4 (d, JCP = 10.9 Hz, o-PPh2CH), 129.1 (s,
indoleC4), 129.6 (s, PPh2
C
ipso), 130.4 (d, 4JCP = 2.3 Hz, p-PPh2CH), 133.5
3
3
(d, JCP = 11.7 Hz, m-PPh2CH), 137.4 (d, JCP = 8.6 Hz, indoleC9).
IR: 3324.5 cm-1 (u N–H). MS m/z (ESI)+: 616.18 [M-Cl-]+ (68%),
674.14 [M+Na+]+ (100%).
1
bright orange solid. Yield: 44.0 mg (77%). H NMR (CD3CN,
499.9 MHz) d [ppm] = 1.96 (s, 3H, coordinatedNCCH3), 1.97–2.03 (m,
4H, CODCH2), 2.23–2.35 (m, 4H, CODCH2), 2.65 (br, 3H, indoleCH3),
4.33 (br, 4H, CODCH), 7.17 (dd, 3JHH = 7.5 Hz, 3JHH = 7.0 Hz, 1H,
indoleC6H), 7.29 (dd, 3JHH = 7.8 Hz, 3JHH = 7.2 Hz, 1H, indoleC7H),
7.46 (d, 3JHH = 8.2 Hz, 1H, indoleC5H), 7.50–7.65 (m, 10H, PC6H5),
[RhCl(NBD)L] (3).
[RhCl(NBD)]2 (50.0 mg, 0.108 mmol) and
A
Schlenk flask was charged with
(68.1 mg,
L
0.216 mmol). CH2Cl2 (10 mL) was subsequently added to the
mixture. The resulting yellow solution was stirred at room
temperature for 3 h after which time the mixture was concentrated
to approximately 2 mL. A bright yellow powder was precipitated
when hexane (10 mL) was added. The product was isolated by
filtration and dried under vacuum. Yield: 91.5 mg (77%). Crystals
suitable for single-crystal X-ray diffraction study were grown
from layering hexane upon CDCl3 solution. Anal. Calcd. for
C28H26ClNPRh (545.85): C, 61.61; H, 4.80; N, 2.57. Found: C,
61.40; H, 4.93; N, 2.79. 1H NMR (CDCl3, 400.2 MHz) d [ppm] =
1.34–1.47 (m, 2H, NBDCH2), 1.82 (d, 4JPH = 1.3 Hz, 3H, indoleCH3),
3.06 (br, 2H, NBDCH=CH trans to Cl), 3.78–3.82 (m, 2H, NBDCH),
1
7.71 (d, 3JHH = 7.9 Hz, 1H, indoleC8H), 9.09 (br, 1H, NH). 31P { H}
1
NMR (CD3CN, 121.6 MHz) d [ppm] = 0.3 (s, PPh2). 13C { H}
NMR36 (CD3CN, 100.5 MHz) d [ppm] = 1.6 (coordinatedCH3CN), 11.7
(
indoleCH3), 31.9 (s, CODCH2), 80.9 (d, JPC = 6.2 Hz, CODCH), 113.0
(s, indoleC5H), 118.5 (coordinatedMeCN), 120.1 (indoleCPPh2), 120.6 (s,
indoleC8H), 120.9 (s, indoleC6H), 124.8 (indoleCCH3), 125.6 (s, indoleC7H),
128.5 (PPh2
C
ipso), 130.0 (indoleC4), 130.2 (d, 2JCP = 10.9 Hz, o-PPh2CH),
132.5 (d, JCP = 2.3 Hz, p-PPh2CH), 134.5 (d, JCP = 11.7 Hz, m-
PPh2CH), 136.3 (indoleC9). IR: 3363.6 (u N–H), 1054.5 (u B–F) cm-1.
MS m/z (ESI)+ 616.17 [M+-MeCN]+ (100%), 657.20 [M]+ (25%),
931.28 [M+L]+ (40%).34
4
3
5.34 (br, 2H, NBDCH=CH trans to P), 7.10 (ddd, JHH = 8.0 Hz,
3
4
3
3JHH = 7.0 Hz, JHH = 1.0 Hz, 1H, indoleC6H), 7.25 (ddd, JHH
=
[Rh(COD)L2]BF4 (6). A Schlenk flask was charged with
[RhCl(COD)L] (1) (50.0 mg, 0.089 mmol) and CH2Cl2 (10 mL).
After stirring well and covering flask with foil, AgBF4 (20.8 mg,
0.106 mmol) was added to the Schlenk in one portion. The yellow
solution was filtrated after 1 h of stirring in room temperature. The
colour became yellow-orange initial after addition of L (28.1 mg,
0.089 mmol). After 1 h further of stirring at room temperature, a
yellow powder was precipitated when hexane (20 mL) was added.
The product was isolated by filtration and dried under vacuum.
Yield: 71.0 mg (86%). Anal. Calcd. for C50H48BF4N2P2Rh·2H2O38
(1911.22): C, 62.84; H, 5.38; N, 2.93. Found: C, 62.36; H, 5.60;
3
4
8.1 Hz, JHH = 6.9 Hz, JHH = 0.8 Hz, 1H, indoleC7H), 7.40–7.44
(m, 6H, o,p-PPh2CH), 7.49 (ddd, JHH = 8.3 Hz, JHH = 0.9 Hz,
3
4
4JHH = 0.9 Hz, 1H, indoleC5H), 7.55 (dd, JHH = 8.0 Hz, JHH
=
3
4
0.8 Hz, 1H, indoleC8H), 7.57–7.64 (m, 4H, m-PPh2CH), 10.86 (br, 1H,
1
NH). 31P { H} NMR (CDCl3, 121.4 MHz) d [ppm] = 15.8 (d,
1JPRh = 167 Hz, PPh2). 13C { H} NMR (CDCl3, 100.6 MHz) d
1
[ppm] = 11.0 (s, indoleCH3), 50.6 (d, JRhC = 2.3 Hz, NBDCH), 52.2
(d, JRhC = 11.5 Hz, NBDCH trans to Cl), 63.8 (d, JRhC = 6.2 Hz,
NBDCH2), 85.4 (dd, JRhC = 11.5 Hz, JPC = 5.5 Hz, NBDCH trans
to P), 112.1 (s, indoleC5H), 119.0 (s, indoleC8H), 119.1 (s, indoleCPPh2),
119.3 (s, indoleC6H), 122.0 (s,indoleCCH3), 123.7 (s, indoleC7H), 128.6
1
N, 2.99. H NMR (CDCl3, 300.5 MHz) d [ppm] = 1.81 (s, 6H,
2
3
(d, JCP = 10.8 Hz, o-PPh2CH), 129.2 (d, JCP = 6.9 Hz,indoleC4),
indoleCH3), 2.19–2.30 (m, 4H, CODCH2), 2.61–2.74 (m, 4H, CODCH2),
4.74 (br, 4H, CODCH), 7.10–7.23 (m, 10H, o-PPh2CH &indoleC6H),
7.28–7.41 (m, 14H, m,p-PPh2CH &indoleC7H), 7.54 (d, 3JHH = 8.4 Hz,
2H, indoleC8H), 7.74 (d, 3JHH = 8.0 Hz, 2H, indoleC5H), 9.61 (s, 2H,
4
130.3 (d, JCP = 2.3 Hz, p-PPh2CH), 130.4 (s, PPh2Cipso), 133.1 (d,
3JCP = 11.5 Hz, m-PPh2CH), 137.7 (d, 3JCP = 10.0 Hz, indoleC9). IR:
3266.7 cm-1 (u N–H). MS m/z (ESI)+: 510.09 [M-Cl]+ (100%).
1
NH). 31P { H} NMR (CDCl3, 121.6 MHz) d [ppm] = 9.1 (d,
[Rh(COD)L(NCMe)]BF4 (4). A Schlenk flask was charged
with [RhCl(COD)L] (1) (50.0 mg, 0.089 mmol). MeCN (10 mL)
was added and then CH2Cl2 (15 mL). AgBF4 (25.9 mg,
0.133 mmol) was added to the flask in one portion and the flask
was subsequently covered with aluminium foil. The yellow cloudy
solution was filtered. All volatiles were subsequently removed
under reduced pressure to provide a yellow solid. Yield: 36.0 mg
(62%). Crystals suitable for single-crystal X-ray diffraction study
1
1JPRh = 142 Hz, PPh2). 13C { H} NMR (CDCl3, 100.6 MHz) d
[ppm] = 11.9 (s, indoleCH3), 30.7 (s, CODCH2), 101.2 (dd, JRhC
=
7.7 Hz, JPC = 4.6 Hz, CODCH), 113.4 (s, indoleC5H), 118.8 (s,
indoleC8H), 119.8 (s, indoleCPPh2), 120.2 (s, indoleC6H), 122.0 (virtual
2
t, JCP = 2.3 Hz, indoleCCH3), 125.0 (s, indoleC7H), 128.7 (virtual t,
2JCP = 5.4 Hz, o-PPh2CH),37 129.0 (virtual t, 3JCP = 3.8 Hz, indoleC4),37
3
129.6 (s, PPh2Cipso), 130.3 (s, p-PPh2CH), 132.7 (virtual t, JCP
=
3
5.8 Hz, m-PPh2CH),37 138.5 (virtual t, JCP = 4.6 Hz, indoleC9).37
IR: 3388.9 (u N–H), 1058.4 (u B–F) cm-1. MS m/z (ESI)+: 526.11
[M+-L]+ (95%), 841.24 [M]+ (100%).39
1
were grown from layering Et2O upon THF solution. H NMR
(CD3CN, 300.5 MHz) d [ppm] = 1.96 (s, 3H, coordinatedNCCH3),
2.04–2.15 (m, 4H, CODCH2), 2.37–2.55 (m, 4H, CODCH2), 2.73 (br,
3H, indoleCH3), 4.56 (br, 4H, CODCH), 7.15 (ddd, JHH = 8.1 Hz,
[Ir(COD)L2]BF4 (7). A Schlenk flask was charged with
[IrCl(COD)L] (2) (100.0 mg, 0.153 mmol) and CH2Cl2 (20 mL).
After stirring well and covering flask with foil, AgBF4 (35.8 mg,
0.184 mmol) was added to the Schlenk in one portion. The wine-
red solution was filtrated after 1 h of stirring in room temperature.
The colour became brighter initial after addition of L (48.4 mg,
0.153 mmol). After 1 h further of stirring at room temperature,
3
4
3
3JHH = 7.0 Hz, JHH = 1.1 Hz, 1H, indoleC6H), 7.26 (ddd, JHH
=
3
4
8.2 Hz, JHH = 7.0 Hz, JHH = 1.1 Hz, 1H, indoleC7H), 7.41 (d,
3JHH = 8.3 Hz, 1H, indoleC5H), 7.46–7.63 (m, 10H, PC6H5), 7.69 (d,
3JHH = 8.3 Hz, 1H, indoleC8H), 9.02 (br, 1H, NH). 31P{ H} NMR
1
(CD3CN, 121.6 MHz) d [ppm] = 8.7 (br, Dn1/2 = 122 Hz, PPh2).
IR: 3371.5 (u N–H), 1015.6 (u B–F) cm-1.34,35
6246 | Dalton Trans., 2010, 39, 6239–6248
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
1
a red powder was precipitated when hexane (20 mL) was added.
The product was isolated by filtration and dried under vacuum.
by H NMR in CDCl3 (with a reaction mixture: CDCl3 ratio of
2 : 3 by volume). The percentage conversions were determined by
relative integration of characteristic resonances of the both the
products and the starting materials.
∑
Yield: 131.1 mg (84%). Anal. Calcd. for C50H48BF4IrN2P2 3H2O38
(1071.94): C, 56.02; H, 5.08; N, 2.61. Found: C, 56.12; H, 5.02;
1
N, 2.66. H NMR (CDCl3, 300.5 MHz) d [ppm] = 1.80 (s, 6H,
indoleCH3), 1.92–2.10 (m, 4H, CODCH2), 2.42–2.62 (m, 4H, CODCH2),
4.40 (br, 4H, CODCH), 7.11–7.23 (m, 10H, o-PPh2CH &indoleC6H),
7.26–7.42 (m, 14H, m,p-PPh2CH &indoleC7H), 7.55 (d, 3JHH = 8.0 Hz,
2H, indoleC8H), 7.73 (d, 3JHH = 8.3 Hz, 2H, indoleC5H), 9.52 (s, 2H,
X-Ray crystallography
X-Ray diffraction experiments on 1, 2, 3, 4 and 8 were carried
out at 100 K on a Bruker APEX II diffractometer using Mo-Ka
˚
1
NH). 31P { H} NMR (CDCl3, 121.7 MHz) d [ppm] = 2.2 (s,
radiation (l = 0.71073 A) source. Data collections were performed
1
PPh2). 13C { H} NMR (CDCl3, 100.5 MHz) d [ppm] = 12.0 (s,
using a CCD area detector from a single crystal mounted on a glass
fibre. Intensities were integrated40 from several series of exposures
measuring 0.5◦ in w or j. Absorption corrections were based on
equivalent reflections using SADABS.41 Structures were solved
indoleCH3), 31.1 (s, CODCH2), 89.5 (virtual t, JPC = 5.5 Hz, CODCH),37
113.2 (s, indoleC5H), 118.5 (s, indoleCPPh2), 118.9 (s, indoleC8H), 120.2
2
(s, indoleC6H), 122.4 (virtual t, JCP = 3.1 Hz, indoleCCH3),37 125.0
2
2
(s, indoleC7H), 128.2 (s, PPh2Cipso), 128.6 (virtual t, JCP = 5.5 Hz,
using SHELXS and refined against all Fo data with hydrogen
atoms riding in calculated positions using SHELXTL.42 Crystal
structure and refinement data are given in Table 3.
3
o-PPh2CH),37 128.9 (virtual t, JCP = 3.9 Hz, indoleC4),37 130.7 (s, p-
PPh2CH), 132.9 (virtual t, 3JCP = 4.7 Hz, m-PPh2CH),37 138.2 (virtual
t, 3JCP = 4.3 Hz, indoleC9).37 IR: 3379.2 (u N–H), 1056.0 (u B–F) cm-1.
MS m/z (ESI)+: 616.18 [M+-L]+ (70%), 931.29 [M]+ (100%).
Acknowledgements
=
Synthesis
of
[Rh(COD){N(Me) C(H)Ph}L]BF4
and
solution
The authors thank, the Royal Society for a Royal Society Dorothy
Hodgkin Research Fellowship for GRO and Johnson Matthey for
the generous loan of rhodium and iridium salts.
=
[Rh2(COD)2{N(Me) C(H)Ph}L][BF4]2 (8). To
a
of 1 (50.0 mg, 0.089 mmol) in CH2Cl2 (10 mL), silver
tetrafluoroborate (20.8 mg, 0.106 mmol) was added. The
yellow mixture was filtrated after 1 h of stirring in room
temperature before adding N-benzylidenemethylamine (11.03 mL,
0.089 mmol). After stirring at room temperature overnight, a
yellow powder was precipitated when Et2O (20 mL) was added.
A yellow solid was isolated by filtration and then dried under
vacuum (32.6 mg, 0.032 mmol, 71%, based on the target product,
[Rh(COD){N(Me)=C(H)Ph}L]BF4). Selected data: NMR of
Notes and references
1 (a) H. Doucet, T. Ohkuma, K. Murata, T. Yokozawa, M. Kozawa, E.
Katayama, A. F. England, T. Ikariya and R. Noyori, Angew. Chem., Int.
Ed., 1998, 37, 1703; (b) M. Yamakawa, H. Ito and R. Noyori, J. Am.
Chem. Soc., 2000, 122, 1466; (c) C. A. Sandoval, T. Ohkuma, K. Mun˜iz
and R. Noyori, J. Am. Chem. Soc., 2003, 125, 13490.
2 For selected ruthenium based examples see: (a) S. E. Clapham, A.
Hadzovic and R. H. Morris, Coord. Chem. Rev., 2004, 248, 2201;
(b) R. L. Chowdhury and J.-E. Ba¨ckvall, J. Chem. Soc., Chem.
Commun., 1991, 1063; (c) M. C. MacInnis, D. F. MacLean, R. J.
Lundgren, R. McDonald and L. Turculet, Organometallics, 2007, 26,
6522; (d) S. Gladiali and E. Alberico, Chem. Soc. Rev., 2006, 35, 226;
(e) D. Amoroso, A. Jabri, G. P. A. Yap, D. G. Gusev, E. N. dos Santos
and D. E. Fogg, Organometallics, 2004, 23, 4047; (f) T. Zweifel, J.-V.
Naubron, T. Bu¨ttner, T. Ott and H. Gro¨tzmache, Angew. Chem., Int.
Ed., 2008, 47, 3245; (g) J. S. M. Samec, J.-E. Ba¨ckvall, P. G. Andersson
and P. Brandt, Chem. Soc. Rev., 2006, 35, 237.
1
isolated solid 31P{ H} (C6D6, 121.4 MHz) d [ppm] = 6.3 (d,
1
1JPRh = 145 Hz, PPh2). H NMR (C6D6, 300.5 MHz) d [ppm] =
1.19–2.26 (m, 8H, CODCH2), 1.59 (d, 3H, 1JPH = 1.1 Hz,indoleCH3),
3.15 (br m, 1H, CODCH), 3.60 (br m, 1H, CODCH), 3.86 [s, 3H,
C N(CH3)], 4.33 (br, m, 1H, CODCH), 6.00 (br, m, 1H, CODCH),
=
6.68 (m, 1H, indoleCH), 6.81 (m, 1H, indoleCH) 6.87–7.07 (m, 5H,
PhCH &indoleCH), 7.10–7.26 (m, 3H, PhCH), 7.31–7.45 (m, 5H,
3
PhCH), 7.55 (d, JHH = 8.3 Hz, 1H, indoleCH), 7.89 (br, m 1H,
3
PhCH), 8.77–8.83 (m, 2H, PhCH), 9.02 (d, JRhH = 8.4 Hz, 1H,
3 For selected rhodium and iridium based examples see: (a) M. Albrecht,
R. H. Crabtree, J. Mata and E. Peris, Chem. Commun., 2002, 32; (b) R.
Corbera´n and E. Peris, Organometallics, 2008, 27, 1954.
=
N CH), 11.15 (s, 1H, NH).
Selected data for 8: Crystals for X-ray diffraction study
were grown from layering hexane upon CH2Cl2 solution un-
der a nitrogen atmosphere. MS (ESI)+ of crystals: m/z 526.12
[M2+-imine-Rh+(COD)] (100%), 645.20 [M2+-Rh (COD)] (25%),
736.12 [M2+-imine-H+] (15%), 857.24 [M2+-H+] (30%).
4 For
a review on transfer hydrogenation see: J.-E. Ba¨ckvall,
J. Organomet. Chem., 2002, 652, 105.
5 Examples involving M-NR2 or M-NHR2 groups which provide ex-
ceptionally high activities: (a) F. Zeng and Z. Yu, Organometallics,
2008, 27, 2898; (b) Z. E. Clarke, P. T. Maragh, T. P. Dasgupta, D. G.
Gusev, A. J. Lough and K. Addur-Rashid, Organometallics, 2006, 25,
4113; (c) W. Baratta, E. Herdtweck, K. Siega, M. Toniutti and P. Rigo,
Organometallics, 2005, 24, 1660; (d) A. D. Zotto, W. Baratta, M. Ballico,
E. Herdtweck and P. Rigo, Organometallics, 2007, 26, 5636; (e) M.
Zhao, Z. Yu, S. Yan and Y. Li, J. Organomet. Chem., 2009, 694, 3068;
(f) M. Zhao, Z. Yu, S. Yan and Y. Li, Tetrahedron Lett., 2009, 50, 4624;
(g) F. Zeng and Z. Yu, Organometallics, 2009, 28, 1855.
Catalyst screening
This was performed in a Radleys carousel as follows: a CH2Cl2
solution containing 0.5 mol% of catalyst was transferred to a
Teflon screw top tube which was connected to a Schlenk line.
The solvent was then evaporated under reduced pressure. 2 mmol
of substrate (acetophenone, 157 mL; benzophenone, 364 mg;
cyclohexanone, 207 mL) was added, followed by 10 mL of a 0.2 M
(high base condition) or a 0.02 M (low base condition) solution
6 C. J. Longley, T. J. Goodwin and G. Wilkinson, Polyhedron, 1986, 5,
1625.
7 Examples involving M-NR2 groups which provide moderate activities:
(a) M. S. Rahman, P. D. Prince, J. W. Steed and K. K. Hii,
Organometallics, 2002, 21, 4927; (b) P. Crochet, J. Gimeno, J. Borge
and S. Garc´ıa-Granda, New J. Chem., 2003, 27, 414; (c) M. P. de
Araujo, A. T. de Figueiredo, A. L. Bogado, G. V. Poelhsitz, J. Ellena,
E. E. Castellano, C. L. Donnici, J. V. Comasseto and A. A. Batista,
Organometallics, 2005, 24, 6159.
i
of KOH in PrOH via a syringe and the mixture was heated to
84 ◦C. The reaction was sampled at 1 h, 3 h and 24 h, the portion
was added into NMR tube without evaporation or filtration. 3
drops of D2O was added into NMR tube and the residue analyzed
8 C. P. Lau, S. M. Ng, G. Jia and Z. Lin, Coord. Chem. Rev., 2007, 251,
2223.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6239–6248 | 6247
©

View Article Online
9 E. Lam, D. H. Farrar, C. S. Browning and A. J. Lough, Dalton Trans.,
2004, 3383.
was not removed and a solvent suppression 1H NMR experiment
was performed on the reaction mixture. This method was calibrated,
at several designated ratios, by measuring the relative integration of
substrates to products under the same concentrations as used for the
catalytic reactions.
10 J. O. Yu, C. S. Browning and D. H. Farrar, Chem. Commun., 2008,
1020.
11 J. O. Yu, E. Lam, J. L. Sereda, N. C. Rampersad, A. J. Lough, C. S.
Browning and D. H. Farrar, Organometallics, 2005, 24, 37.
12 C. M. So, C. C. Yeung, C. P. Lau and F. Y. Kwong, J. Org. Chem., 2008,
73, 7803.
25 (a) M. C. Carrio´n, F. A. Jalo´n, B. R. Manzano, A. M. Rodr´ıguez, F.
Sepu´lveda and M. Maestro, Eur. J. Inorg. Chem., 2007, 3961; (b) M. D.
Le Page and B. R. James, Chem. Commun., 2000, 1647.
13 (a) U. Berens, J. M. Brown, J. Long and R. Selke, Tetrahedron:
Asymmetry, 1996, 7, 285; (b) N. V. Artemova, M. N. Chevykalova,
Y. N. Luzikov, I. E. Nifant’ev and E. E. Nifant’ev, Tetrahedron, 2004,
60, 10365.
26 All flasks were thoroughly cleaned with aqua regia and subsequently
thoroughly washed with water and acetone prior to performing the
catalytic tests.
27 B. Gschwend, B. Pugin, A. Bertogg and A. Pfaltz, Chem.–Eur. J., 2009,
14 J. Wassenaar, M. Kuil and J. N. H. Reek, Adv. Synth. Catal., 2008, 350,
15, 12993.
1610.
28 (a) D. Heller, K. Kortus and R. Selke, Liebigs Ann., 1995, 575; (b) A.
Preetz, H.-J. Drexler, C. Fischer, Z. Dai, A. Bo¨rner, W. Baumann, A.
Spannenberg, R. Thede and D. Heller, Chem.–Eur. J., 2008, 14, 1445.
29 (a) A. C. Hillier, H. M. Lee, E. D. Stevens and S. P. Nolan,
Organometallics, 2001, 20, 4246; (b) E. Mas-Marzia´, M. Sanau´ and
E. Peris, Inorg. Chem., 2005, 44, 9961; (c) E. Peris and R. H. Crabtree,
Coord. Chem. Rev., 2004, 248, 2239; (d) A. T. Normand and K. J. Cavell,
Eur. J. Inorg. Chem., 2008, 2781.
15 J. Wassenaar and J. N. H. Reek, Dalton Trans., 2007, 3750.
16 (a) J. Wassenaar, S. van Zutphen, G. Mora, P. Le Floch, M. A.
Siegler, A. L. Spek and J. N. H. Reek, Organometallics, 2009, 28, 2724;
(b) T. D. W. Ciaridge, J. M. Long, J. M. Brown, D. Hibbs and M. B.
Hursthouse, Tetrahedron, 1997, 53, 4035.
17 D. Penno, I. O. Koshevoy, F. Estevan, M. Sana, M. A. Ubeda and J.
Pe´rez-Prieto, Organometallics, 2010, 29, 703.
18 (a) J. Albers, E. Dinjus, S. Pitter and O. Walter, J. Mol. Catal. A: Chem.,
2004, 219, 41; (b) Y. Nishihara, K. Nara, Y. Nishide and K. Osakada,
Dalton Trans., 2004, 1366; (c) P. U. Rani, P. M. Reddy, K. Shanker and
V. Ravinder, Transition Met. Chem., 2008, 33, 153; (d) U. Hintermair,
T. Gutel, A. M. Z. Slawin, D. J. Cole-Hamilton, C. C. Santini and Y.
Chauvin, J. Organomet. Chem., 2008, 693, 2407.
19 N. Feiken, P. S. Pregosin and G. Trabesinger, Organometallics, 1997,
16, 5756.
20 P. Marcazzan, C. Abu-Gnim, K. N. Seneviratne and B. R. James, Inorg.
Chem., 2004, 43, 4820.
21 (a) M. Bortolin, U. E. Bucher, H. Ru¨gger, L. M. Venanzi, A. Albinati,
F. Lianza and S. Trofimenko, Organometallics, 1992, 11, 2514; (b) M. A.
Garralda, R. Herna´ndez, E. Pinilla and M. R. Torres, J. Organomet.
Chem., 1999, 586, 150; (c) W. Yao, O. Eisenstein and R. H. Crabtree,
Inorg. Chim. Acta, 1997, 254, 105; (d) J. C. Lewis, J. Wu, R. G. Bergman
and J. A. Ellman, Organometallics, 2005, 24, 5737; (e) Y. Zhang, J. C.
Lewis, R. G. Bergman, J. A. Ellman and E. Oldfield, Organometallics,
2006, 25, 3515.
30 (a) W. He, P. Liu, B. L. Zhang, X. L. Sun and S. Y. Zhang, Appl.
Organomet. Chem., 2006, 20, 328; (b) G. Zassinovich and G. Mestroni,
J. Mol. Catal., 1987, 42, 81; (c) G. Zassinovich, C. Del Bianco and G.
Mestroni, J. Organomet. Chem., 1981, 222, 323.
31 R. Spogliarich, J. Kasˇpar, M. Graziani and F. Morandini, J. Organomet.
Chem., 1986, 306, 407.
32 J. L. Herde, J. C. Lambert and C. V. Senoff, Inorg. Synth., 1974, 15, 18.
33 G. Giordano and R. H. Crabtree, Inorg. Synth., 1990, 28, 88.
34 This compound rapidly decomposed through loss of coordinating
solvent and so satisfactory elemental analysis could not be obtained.
35 The molecular ion peak, [M+], was not observed for this compound
in the MS-ESI+ spectrum. Signals corresponding to the oxidized
phosphine were observed indicating that the complex had decomposed
during the analysis procedure.
1
36 The signals in 13C{ H} NMR spectra of this complex were poorly re-
solved, even when longer acquisition times or very concentrated NMR
samples were employed. Even so, the location of the carbon signals
1
could be identified by heteronuclear H/13C correlation experiments.
1
22 R. B. Bedford, M. Betham, A. J. M. Caffyn, J. P. H. Charmant, L. C.
Lewis-Alleyne, P. D. Long, D. Polo-Cero´n and S. Prashar, Chem.
Commun., 2008, 990.
The 13C{ H} assignments were therefore made on the basis of HMQC
and HMBC experiments [CD3CN, (400.2, 100.6) MHz].
37 W. H. Hersh, J. Chem. Educ., 1997, 74, 1485.
23 Similar fluxional behaviour has been observed and investigated by:
(a) A. Bru¨ck and K. Ruhland, Organometallics, 2009, 28, 6383; (b) V.
Ce´sar, S. Bellemin-Laponnaz and L. H. Gade, Eur. J. Inorg. Chem.,
2004, 3436; (c) A. S. Weller, M. F. Mahon and J. W. Steed, J. Organomet.
Chem., 2000, 614–615, 113; (d) H. F. Haarman, F. R. Bregman, J.-M.
Ernsting, N. Veldman, A. L. Spek and K. Vrieze, Organometallics, 1997,
16, 54; (e) G. R. Owen, N. Tsoureas, A. Hamilton and A. G. Orpen,
Dalton Trans., 2008, 6039.
24 We found that removal of the solvents by evaporation according to
standard methods led to significant variations in the ratio of substrate
to product. These variations were significant particularly in the case
of cyclohexanone and cyclohexanol. Accordingly, the reaction solvent
38 This compound was hygroscopic if left in the open air for short periods
of time. Accordingly, the microanalysis appears to indicate the presence
of water suggesting hydrogen bonding interactions with the NH groups
of L.
39 The analogous complex [Rh(COD)L2]BPh4 was also prepared but not
1
isolated. 31P{ H} NMR (CDCl3, 121.6 MHz) d [ppm] = 9.2 (d, 1JPRh
=
142 Hz, PPh2).
40 Bruker-AXS SAINT V7.60A.
41 G. M. Sheldrick, SADABS V2008/1-2, University of Go¨ttingen,
Germany.
42 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
6248 | Dalton Trans., 2010, 39, 6239–6248
This journal is
The Royal Society of Chemistry 2010
©