Synthesis, structural characterisation and catalytic application of dichloro(η 6-p-cymene){diphenyl(3-methyl-2-indolyl)phosphine} ruthenium(II) in the transfer hydrogenation of ketones

Article abstract of DOI:10.1007/s11243-013-9732-6

The synthesis and investigation of ruthenium complexes containing the relatively unexplored ligand, diphenyl-2-(3-methyl)indolylphosphine, is presented herein. The complexes [RuCl₂{PPh₂(C ₉H₈N)}₃], [Ru₂(μ-Cl) ₃(Cl)(MeCN){PPh₂(C₉H₈N)} ₄] and [RuCl₂(η ⁶-p-cymeme){PPh ₂(C₉H₈N)}] have been studied. Single crystals of the latter two complexes have been prepared and investigated by X-ray crystallography. A detailed examination of [RuCl₂(η ⁶-p-cymeme){PPh₂(C₉H₈N)}] has been carried out. This complex was found to be an active catalyst in the catalytic transfer hydrogenation of ketones. Graphical Abstract: The complex, [RuCl ₂(η ⁶-p-cymeme){PPh₂(C₉H ₈N)}], was synthesised and fully characterised by spectroscopic, analytical and structural methods. The complex was also found to be an active catalyst in the transfer hydrogenation of ketones.

Full text of DOI:10.1007/s11243-013-9732-6

Transition Met Chem (2013) 38:641–648
DOI 10.1007/s11243-013-9732-6
Synthesis, structural characterisation and catalytic application
of dichloro(g6-p-cymene){diphenyl(3-methyl-2-indolyl)phosphine}
ruthenium(II) in the transfer hydrogenation of ketones
•
•
•
Yu-Ying Kuo Mairi F. Haddow Ashley L. Jamieson
Gareth R. Owen
Received: 30 April 2013 / Accepted: 15 May 2013 / Published online: 28 May 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract The synthesis and investigation of ruthenium
complexes containing the relatively unexplored ligand,
diphenyl-2-(3-methyl)indolylphosphine, is presented herein.
The complexes [RuCl2{PPh2(C9H8N)}3], [Ru2(l-Cl)3(Cl)-
(MeCN){PPh2(C9H8N)}4] and [RuCl2(g6-p-cymeme){PPh2-
(C9H8N)}] have been studied. Single crystals of the latter two
complexes have been prepared and investigated by X-ray
crystallography. A detailed examination of [RuCl2(g6-p-cy-
meme){PPh2(C9H8N)}] has been carried out. This complex
was found to be an active catalyst in the catalytic transfer
hydrogenation of ketones.
bifunctional catalysts for asymmetric hydrogenation reac-
tions [5–7]. Many ruthenium complexes which are active
hydrogenation and transfer hydrogenation catalysts are
now known [8–31].
For some time now, we have been interested in hydro-
genation reactivity as a means of exploring potential ligand
cooperation effects. Our investigations have focused on the
close proximity of various functional groups to the transi-
tion metal centres. Much of our work has involved B–H
functional groups [32–42], though we have also investi-
gated a relatively unexplored phosphorus ligand containing
an N–H functional group [43]. In this report, we prepared
some group nine complexes containing the ligand, diphe-
nyl-2-indolylphosphine (L) (Fig. 1). This ligand, along
with some related phosphine compounds containing the
same indolyl functional group, was originally developed by
Browning [44]. To date, there have only been a handful of
complexes containing L [43–47], with the only ruthenium
complexes based on the precursor Ru3(CO)12 [45]. In some
of these complexes, the ligand coordinates to the metal
centre via the phosphorus atom, and the pendant NH group
was found to undergo strong hydrogen-bonding interac-
tions with halide co-ligands [44, 46]. Additionally, there
are a number of derivative ligands known [47–58] which
have been utilised as co-ligands in catalytic applications
such as Suzuki–Miyaura coupling of aryl chlorides [50],
asymmetric hydrogenation [51, 52], hydroformylation [52]
and allylic alkylation reactions [53, 54]. We also intro-
duced the g6-coordination mode for L [43].
Introduction
There is currently great interest in ligands which contain
N–H functional groups and their ability to participate
intimately within transformations at the metal centre. Such
cooperation between ligand and metal centre has certainly
led to substantial improvements in many catalytic trans-
formations [1–3]. The role of N–H functional groups in
catalysis has recently been examined in great detail by
Ding [4]. One significant area of interest has been the
development of phosphorus ligands containing NH func-
tionalities. Perhaps one of the most important and early
contributions to this field is the work carried out by Noyori
and co-workers, in which they introduced metal–ligand
The coordination chemistry of L itself however remains
limited, and we therefore wish to report the synthesis of the
first mononuclear ruthenium complexes containing this
ligand along with some preliminary results of the catalytic
performance of a complex in the transfer hydrogenation of
ketones.
Y.-Y. Kuo Á M. F. Haddow Á A. L. Jamieson Á G. R. Owen (&)
The School of Chemistry, Cantock’s Close, Bristol, UK
e-mail: gareth.owen@bristol.ac.uk
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Transition Met Chem (2013) 38:641–648
Cl
L
excess
L
2 RuCl2(PPh3)3
2
Cl
Ru
-6 PPh3
L
L
P
L
2
- 2 L
Cl
N
H
Cl
L
MeCN
L
L
Cl
MeCN
L
Ru
Ru
Ru
Ru
L
L
Cl
Cl
Cl
L
L
Cl
Cl
L
Fig. 1 Diphenyl-2-indolylphosphine, L
Scheme 1 Synthesis and subsequent reactivity of [RuCl2(L)3] with
MeCN
Results and discussion
A wide range of ruthenium complexes bearing ligands with
N–H groups are known to provide effective catalysts within
transfer hydrogenation reactions [1–3, 59–62]. With that in
mind, we set out to explore synthetic methods towards new
ruthenium complexes containing L. Our initial starting
point was the reaction of L with common precursors such
as [RuCl2(COD)]n and [RuCl2(DMSO)4]. The addition of
an excess of L to a solution of the former compound in
various solvents revealed very little indication of phos-
phine coordination to the ruthenium centre even under
forcing conditions, as determined by 31P{1H} NMR spec-
troscopy.1 Reactions involving the latter precursor consis-
tently gave complicated reaction mixtures, with at least 5
coordinated phosphorus ligand environments observed by
31P{1H} NMR spectroscopy. Our attempts to isolate pure
samples from these mixtures were unsuccessful. When
[RuCl2(PPh3)3] was reacted with a fivefold excess of L in
toluene solvent, two broad signals were observed in the
31P{1H} NMR spectrum at 28.4 and 35.3 ppm (d toluene,
unlocked), respectively, along with signals corresponding
to the eliminated free triphenylphosphine (Scheme 1).
These two signals are very similar to the pattern obtained in
the spectrum of related complexes containing three phos-
phorus ligands including the starting material [63–67]. The
species was given the tentative assignment [RuCl2L3], the
two chemical environments originating from the trigonal
bipyramidal complex. As the spectrum was broad, it is
likely that Berry pseudo-rotation is occurring on the NMR
timescale, although exchange between PPh3 and L at
ruthenium cannot be ruled out. Our attempts to isolate a
Fig. 2 Crystal structure of [Ru2Cl4(NCMe)L4]Á2 CHCl3, solvent
molecules and hydrogen atoms {except for hydrogen atoms on indolyl
˚
NH group} has beenomitted for clarity. Selected bonddistances (A) and
angles (°); Ru(1)–N(5) 2.000(6), Ru(1)–P(1) 2.3060(17), Ru(1)–P(2)
2.3064(16), Ru(1)–Cl(3) 2.4124(15), Ru(1)–Cl(1) 2.4477(15), Ru(1)–
Cl(2) 2.4618(15), Ru(2)–P(3) 2.2751(16), Ru(2)–P(4) 2.2795(17),
Ru(2)–Cl(1) 2.3721(15), Ru(2)–Cl(4) 2.4151(16), Ru(2)–Cl(2)
2.5029(15), Ru(2)–Cl(3) 2.5483(15), N(5)–Ru(1)–P(1) 90.08(16),
N(5)–Ru(1)–P(2) 93.27(16), P(1)–Ru(1)–P(2) 100.77(6), P(1)–Ru(1)–
Cl(3) 98.84(6), P(2)–Ru(1)–Cl(3) 94.83(5), N(5)–Ru(1)–Cl(1)
88.15(16), P(1)–Ru(1)–Cl(1) 91.76(6), Cl(3)–Ru(1)–Cl(1) 81.65(5),
N(5)–Ru(1)–Cl(2) 85.98(16), P(2)–Ru(1)–Cl(2) 88.48(5), Cl(3)–
Ru(1)–Cl(2) 83.60(5), Cl(1)–Ru(1)–Cl(2) 79.11(5), P(3)–Ru(2)–P(4)
100.21(6), P(3)–Ru(2)–Cl(1) 91.08(5), P(4)–Ru(2)–Cl(1) 95.91(6),
P(3)–Ru(2)–Cl(4) 95.02(6), P(4)–Ru(2)–Cl(4) 98.96(6), P(4)–Ru(2)–
Cl(2) 83.64(6), Cl(1)–Ru(2)–Cl(2) 79.73(5), Cl(4)–Ru(2)–Cl(2)
93.05(5), P(3)–Ru(2)–Cl(3) 95.76(5), Cl(1)–Ru(2)–Cl(3) 80.36(5),
Cl(4)–Ru(2)–Cl(3) 82.87(5), Cl(2)–Ru(2)–Cl(3) 80.06(5)
1
Mixtures containing [RuCl2(COD)]n and 2 equivalents of L were
heated to reflux in MeCN for several days. The 31P{1H} NMR
spectrum of the reaction mixture revealed mostly free ligand with
only traces of a new species at 13.9 ppm (\10 %) which was likely to
correspond to the target product, RuCl2(COD)L. The lack of
reactivity is presumably due to the inability of L to break the
chloride bridges in the polymeric starting material. Due the this lack
of reactivity, the route was not further explored.
pure sample of [RuCl2L3] from the mixture proved
unsuccessful. During these attempts, we obtained single
crystals of a different compound from an acetonitrile
solution. An X-ray single-crystallographic analysis of the
crystals revealed its identity to be a dinuclear complex with
the composition of [Ru2Cl4(NCMe)L4] (Fig. 2).
123

Transition Met Chem (2013) 38:641–648
643
CH
CH
Cl
Cl
Cl
Ph2P
C2
C6
C5
N
DCM
PPh2
Ru
Cl
Ru
Ru
+
H
Cl
C3
3 h, r.t.
NH
Cl
HC
59 %
Scheme 2 Synthesis of [RuCl2{g6-p-cymene}L]
The structure revealed that the coordination spheres at the
ruthenium metal centres were both based on distorted octa-
hedral geometries, each comprising of 3 bridging chlorides,
2 ligands (L) and one additional terminal chloride on one
ruthenium centre or a coordinated acetonitrile ligand on the
other. The formation of face-sharing bioctahedral Ru(II)
halide complexes has previously been observed in the liter-
ature [68–71]. As shown in Fig. 2, the Ru–Cl bonds trans to
formation of halide-bridged bimetallic complexes is often
regarded as undesirable for catalytic applications [71, 72].
As an alternative, the complex [RuCl2{g6-p-cymene}L]
was targeted. Indeed, this complex was readily obtained via
the straightforward addition of one equivalent of L to one-
half equivalent of the dinuclear precursor [RuCl2{g6-p-
cymene}]2 in DCM solvent (Scheme 2). After 3 h, a red
micro-crystalline solid was isolated in moderate yield fol-
lowing a standard workup (see Experimental Section). The
new complex was fully characterised by spectroscopic and
analytical techniques. The 31P{1H} NMR spectrum con-
sisted of a sharp single peak at 9.48 ppm (d CDCl3). The
IR spectrum of the isolated solid showed bands charac-
teristic of the phosphorus ligand together with a sharp band
at 3,289 cm-1 which was attributed to the stretching mode
of the NH group. Furthermore, mass spectroscopy and
elemental analysis were both consistent with the molecular
composition of the expected product.
˚
phosphorus [Ru(1)–Cl(1) = 2.4477(15) A, Ru(1)–Cl(2) =
˚
2.4618(15) A, Ru(2)–Cl(2) = 2.5029(15) A, Ru(2)–Cl(3) =
˚
˚
2.5483(15) A] are longer than those trans to the terminal
˚
chloride [Ru(2)–Cl(1) = 2.3720(15) A] or the acetonitrile
˚
ligand [Ru(1)–Cl(3) = 2.4124(15) A]. This is due to the lar-
ger transinfluenceofthe phosphorusdonorligands. TheRu–P
˚
bond lengths are in the range 2.2751(16)–2.3064(16) A. It is
worth noting that the NH groups of the indolyl units are all
orientated towards the chloride ligands within the complex
˚
where the shortest NHÁÁÁCl distance is 2.286(1) A [involving
the NH group of P(1) and the bridging chloride Cl(3)]. These
intramolecular interactions may be strong enough to hinder
the rotation of the Ru–P bond, as found in other examples in
the literature [46].
The 1H and 13C{1H} NMR data were consistent with the
formation of [RuCl2{g6-p-cymene}L] confirming that L and
p-cymene were present in a 1:1 ratio. In free p-cymene, the
chemical shifts for all the ring protons are isochronous at
1
The crystal structure gives some insight into the rea-
ction coordinate from [RuCl2L3] to [Ru2Cl4(NCMe)L4]
(Scheme 1). Based on previous reported examples [71], it
is likely that the 14 valence electron intermediate complex,
‘‘Ru(II)Cl2L2’’, is formed in solution via the elimination of
one equivalent of L from the complex. Two of these
unsaturated complexes then associate, forming halide
bridges and the resulting halide-bridged bimetallic com-
plex subsequently receives an acetonitrile molecule to
furnish the electronically saturated face-sharing dimeric
complex observed in the structure. Mass spectroscopy
(ESI?) of the crystalline material showed peaks corre-
sponding to the [RuClL2]? and [RuCl(MeCN)L2]? frag-
ments. On the other hand, the 31P{1H} and 1H NMR
spectra of the crystalline material revealed a number of
poorly resolved signals, indicating that a mixture of species
is reformed when the product is placed in solution. Such
difficulty in determining the correct stoichiometry is
clearly a disadvantage and thus renders the product less
suitable for catalytic investigations. Furthermore, the
7.32 ppm in H NMR, while their corresponding carbon
signals are observed at 126.3 and 129.0 ppm in the 13C{1H}
NMR spectrum [73]. Upon coordination to the ruthenium
centre in [RuCl2{g6-p-cymene}]2, the signals are shifted
upfield to 5.30 ppm (1H) and 80.5 ppm (13C) for C3,5H and
5.44 ppm (1H) and 81.2 ppm (13C) for C2,6H, as a result of
donation of the p-electrons from the aromatic ring to the
metal [74]. The proton and carbon pairs (d 1H, 13C{1H}) in
[RuCl2{g6-p-cymene}L] were confirmed and established by
the heteronuclear 1H/13C correlation experiments. They
were found to be 5.15 ppm (1H) and 85.7 ppm (13C) for
C2,6H and 5.18 ppm (1H) and 90.7 ppm (13C) for C3,5H. Note
that in this case, the trend is reversed, the downfield signals
we found to correspond to the signals ortho to isopropyl
group (C2,6H) and the upfield signals were identified as the
signals ortho to methyl group (C3,5H). Interestingly, this
showed a reverse trend to the corresponding signals for other
ruthenium–cymene complexes from the literature [74]. The
reason for these observations is currently unknown. There is
2
a small difference in the JCP coupling constants of the
123

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Transition Met Chem (2013) 38:641–648
cymene carbon and the phosphorus nuclei (2JCP = 6 Hz for
Table 1 Transfer hydrogenation of ketones using complexes 1, 2, 6
i
and 7 with 0.2 M KOH in PrOH
2
C2,6H and JCP = 4 Hz for C3,5H) which is likely to result
from the respective P–Ru–C angles. The NH signal was
observed at 10.44 ppm in the 1H NMR spectrum, suggesting
its interaction with the chloride ligands. Such interaction
might result in the two phenyl groups of the phosphine to be
held in one position and preventing the cymene ligand from
rotating, as found in a similar complex [RuCl2(p-cymene)
(phosphine)] [74]. This was further confirmed by a single-
crystal diffraction study as outlined below.
Red needle crystals of [RuCl2{g6-p-cymene}L] were
formed by laying hexane on the top of a concentrated DCM
solution of the complex. A single-crystal diffraction study
confirmed the expected product. The Ru–C distances for
each of the cymene ring carbon atoms range between
Run
Substratea
Base (M)
Conversion (%)b
1 h
3 h
24 h
1
2
3
4
5
A
C
A
B
C
i
0.2
8
21
6
21
51
34
18
83
75
98
0.2
0.02
0.02
0.02
94
4
94
50
[99
10 mL of KOH in PrOH, 0.1 mol % catalyst loading, 2 mmol of
substrate, 84 °C
a
A—acetophenone, B—benzophenone, C—cyclohexanone
b
Measured by NMR integration
˚
2.183(7) and 2.228(7) A. These are similar to those found
for other [RuCl2(g6-cymene)(PR3)] (PR3 = organophos-
phorus ligands) compounds the in literature [74–76]. The
Ru(1)–P(1) bond bisects the edge of the C5 and C6 atoms in
the cymene, in order to reduce the intramolecular repul-
ligand is prohibited by the fact that the isopropyl group is
facing towards the same side as Ru(1)–P(1) bond, as all the
others within the literature. This would cause a steric
repulsion between the isopropyl group and the closest
phenyl group to hinder the rotation of cymene. This sup-
ports the evidence obtained from the 13C{1H}-NMR data.
˚
sions, and has a bond length of 2.3618(19) A. This is
longer than the average distance for Ru–P bond in the
[Ru2Cl4(MeCN)L4] structure. Ru–Cl bonds are 2.4152(18)
˚
and 2.404(2) A while angle for Cl(1)–Ru(1)–Cl(2) is
Catalytic studies
87.43(7)°, similar to those published structures. The N(1)
and H(1) in the indolyl group is not orientated to the centre
of two chloride ligands but rather points towards just one of
them [Cl(1)]. The N(1)–H(1)–Cl(1) angle is 141.4° and the
A preliminary investigation was carried out with [RuCl2{g6-
p-cymene}L] to assess its activity in the transfer hydroge-
nation of ketones. The results of our preliminary investiga-
tions, using standard literature procedures,2 are summarised
in Table 1. The reactions were carried out at 84 °C, and the
resulting conversions were recorded at 1, 3 and 24 h intervals
and were determined by the relative integration of the sub-
strates against products in their 1H NMR spectra (see
experimental section for details). Our initial catalytic reac-
tions (runs 1 and 2) were performed using 10 mL of 0.2 M
solution of KOH in iPrOH. As shown, the complex was found
to be an active catalyst for the transfer hydrogenation of
acetophenone and cyclohexanone. The results show that
cyclohexane is hydrogenated more readily than acetophe-
none, as is typically found. In our previous report, we had
highlighted the background catalytic activity of the base
(KOH) [43], and other groups have also described similar
observations [78–80]. We therefore investigated the activity
˚
H(1)–Cl(1) distance is 2.434 A. The corresponding H(1)–
˚
Cl(2) distance is 2.813 A (Fig. 3). The shorter H(1)–Cl(1)
distance is within the range of a hydrogen bond.
The cone angle, defined by the average of three half
angles of each substituent on the phosphorus atom, has
been calculated as 119.56° [77]. The rotation of cymene
2
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 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. Furthermore, all flasks were
thoroughly cleaned with aqua regia and subsequently thoroughly
washed with water and acetone prior to performing the catalytic tests.
Fig. 3 Crystal structure of [RuCl2{g6-p-cymene}L], hydrogen atoms
{except for H(1)} has been omitted for clarity. Selected bond lengths
˚
(A) and angles (°); Ru(1)–P(1) 2.3618(19), Ru(1)–Cl(1) 2.4152(18),
Ru(1)–Cl(2) 2.404(2), C(1)-P(1) 1.806(8), Cl(1)–Ru(1)–Cl(2)
87.43(7), C(1)-P(1)-Ru(1) 118.8(3)
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Transition Met Chem (2013) 38:641–648
645
at lower base concentrations; runs 3–5. The results reveal
that under these conditions, the conversion of the three
ketones, acetophenone, benzophenone and cyclohexanone,
to the respective alcohols is essentially complete within a
24-h period at very low catalyst loadings (0.1 mol %). This
activity is comparable to other known ruthenium–cymene
complexes [26–31]. Furthermore, the results even show that
overall the catalysts perform better at these lower base
concentrations, suggesting that in this case, the base is
involved in catalyst deactivation. Run 5 reveals a significant
conversion (50 %) of cyclohexanone to cyclohexanol within
the first hour.
Me
C5
C8
C3
C4
C9
C6
C7
C2
Ph2P
N
H
Fig. 4 Numbering scheme for L
spectra were referenced internally, to the residual protic sol-
vent (1H) or the signals of the solvent (13C). 31P{1H} 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?
ionisation. Elemental analyses were performed at the micro-
analytical laboratory of the School of Chemistry at the Uni-
versity of Bristol. Infrared spectra were recorded on a Perkin-
Elmer Spectrum 100 FT-IR spectrometer (solid state, neat)
from 4,000 to 650 cm-1. Figure 4 provides the numbering
scheme used to assign the 1H and 13C{1H} NMR spectra.
Conclusions
In summary, we have investigated a series of ruthenium
complexes in our search for suitable and active ruthenium
catalysts containing the ligand diphenyl-2-(3-methyl)ind-
olylphosphine (L). Two such complexes have been struc-
turally characterised. The title complex, [RuCl2{g6-p-
cymene}L], was synthesised in good yield and was fully
characterised by spectroscopic and analytical methods. It
was also found to be an active catalyst for the transfer
hydrogenation of acetophenone, benzophenone and cyclo-
hexanone, even at low catalyst loading and low-base con-
centration (0.1 mol % catalyst and 0.02 M KOH in
iPrOH). The activities are comparable to other ruthenium
complexes at similar catalyst loadings; however, there is
little evidence for a significant enhancement based on the
presence of the N–H functional group.
Reaction of Ru(PPh3)3Cl2 with fivefold excess of L
A Schlenk flask was charged with dichloro-tris(triphenyl-
phosphine)ruthenium (10.0 mg, 0.010 mmol) and L (16.4
mg, 0.052 mmol). Toluene (5 mL) was subsequently added
to the mixture. The resulting brown solution gradually turned
to yellow after stirring at room temperature overnight. An
orange powder was precipitated when hexane (10 mL) was
added into the concentrated mixture. The product was iso-
lated by filtration and then dissolved in acetonitrile. Yellow
crystals suitable for single-crystal X-ray diffraction study
were grown from slow evaporation of the acetonitrile solu-
tion. 31P{1H} NMR of sample prior to exposure to MeCN
(CDCl3, 121.7 MHz) d [ppm] = 28.4 (br, Dm1/2 = 66 Hz),
35.4 (br, Dm1/2 = 162 Hz). MS of crystalline material: ESI?;
767.1 [RuClL2]?, 808.1 [RuCl(MeCN)L2]?.
Experimental section
General remarks
All manipulations were performed by using standard Schlenk
techniques. Solvents (CH2Cl2, MeCN and hexane) were dried
using a Grubbs’ alumina system and were kept in Young’s
Dichloro(g6-p-cymene){diphenyl(3-methyl-2-
indolyl)phosphine}ruthenium(II), RuCl2{g6-p-
cymene}L
´
˚
ampoules under N2 over molecular sieves (4 A). The ligand,
L [44], was synthesised according to the literature procedures.
The deuterated solvent, CDCl3, was degassed by three freeze–
´
A Schlenk flask was charged with di-l-chloro{chloro(g6-p-
cymene)ruthenium} dimer (50.0 mg, 0.081 mmol) and
L (103.0 mg, 0.326 mmol). DCM (10 mL) was subse-
quently added to the mixture. The resulting red solution was
stirred at room temperature for 3 h. A red–orange powder
was precipitated when hexane (10 mL) was added into the
concentrated (2 mL) mixture. The product was isolated by
filtration and then dried under vacuum (59.8 mg,
0.096 mmol, 59 %). Red crystals suitable for single-crystal
X-ray diffraction study were grown from layering hexane
˚
thaw cycles, stirred over 4 A molecular sieves, then vacuum
distilled and stored in Young’s ampoules over 4 molecular
sieves under N2. 1H NMR, 31P{1H} NMR spectra were
recorded on a JEOL Lambda 300 spectrometer operating at
300 MHz (1H), a JEOL ECP300 spectrometer operating at
300 MHz (1H) or a JEOL ECP 400 spectrometer operating at
400 MHz (1H). 13C{1H} NMR, DEPT-135 and hetero-
nuclear correlation experiments spectra were recorded on a
JEOL ECP400 spectrometer operating at 400 MHz (1H), or a
Varian400-MRspectrometeroperatingat400 MHz(1H).The
123

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Transition Met Chem (2013) 38:641–648
upon DCM solution. 1H NMR (CDCl3, 400.2 MHz) d
[ppm] = 0.98 (d, 3JHH = 7.1 Hz, 6H, cyCH(CH3)2), 1.75 (d,
4JPH = 1.2 Hz, 3H, indoleCH3), 1.83 (s, 3H, cyCH3{ring}),
Bruker APEX II diffractometer using Mo–Ka radiation
˚
(k = 0.71073 A) source. Data collections were performed
using a CCD area detector from a single crystal mounted
on a glass fibre. Intensities were integrated [81] from
several series of exposures measuring 0.5° in x or u.
Absorption corrections were based on equivalent reflec-
tions using SADABS [82]. Structures were solved using
ShelLXS and refined against all F2o data with hydrogen
atoms riding in calculated positions using ShelXL [83].
Crystal structure and refinement data are given in Table 2.
For [Ru2Cl4(NCMe)L4], the crystal model contained
residual electron density which could not be identified.
Thus, the data were modelled with the SQUEEZE algo-
rithm as implemented in PLATON, which calculated an
extra 45 electrons per complex. This most likely correlates
with an extra molecule of DCM per molecule of complex.
For [RuCl2{g6-p-cymene}L], the crystal model contained
two independent complexes in the unit cell. One of these
complexes contained disorder in L. Figures 2, 3 and the
graphical abstract have been generated using ORTEP [84]
and POV-Ray software [85]. CCDC 936150 [RuCl2{g6-p-
3
2.70 (sept, JHH = 7.0 Hz, 1H, cyCH(CH3)2), 5.15 (d,
3
3JHH = 6.4 Hz, 2H, cyC2,6H), 5.18 (dd, JHH = 6.3 Hz,
3
4JHH = 1.3 Hz, 2H, cyC3,5H), 7.00 (ddd, JHH = 7.9 Hz,
4
3JHH = 7.1 Hz, JHH = 0.9 Hz, 1H, indoleC6H), 7.17 (ddd,
3
4
indo-
3JHH = 7.6 Hz, JHH = 7.2 Hz, JHH = 0.6 Hz, 1H,
leC7H), 7.38 (ddd, JHH = 8.3 Hz, JHH = 0.9 Hz,
4JHH = 0.9 Hz, 1H, indoleC5H), 7.41–7.48 (m, 7H,
o,p-PPh2CH & indoleC8H), 7.92–8.04 (m, 4H, m-PPh2CH),
10.44 (br, 1H, NH). 31P {1H} NMR (CDCl3, 121.7 MHz) d
[ppm] = 9.48 (s, PPh2). 13C {1H} NMR (CDCl3,
100.5 MHz) d [ppm] = 10.8 (s, indoleCH3), 17.3 (s,
cyCH3{ring}), 21.6 (s, cyCH(CH3)2), 30.2 (s, cyCH(CH3)2),
85.8 (d, JPC = 5.5 Hz, cyC2,6H), 90.7 (d, JPC = 3.9 Hz,
cyC3,5H), 94.9 (s, cyC4CH3), 110.5 (d, JPC = 1.6 Hz,
cyC1CHMe2), 112.2 (s, indoleC5H), 118.7 (s, indoleC8H), 118.8
3
4
1
(s, indoleC6H), 119.0 (d, JCP = 1.6 Hz, indoleCPPh2), 122.2
(s, indoleCCH3), 123.3 (s, indoleC7H), 128.3 (d,
3
indo-
2JCP = 10.9 Hz, o-PPh2CH), 128.6 (d, JCP = 8.6 Hz,
leC4), 130.5 (d, JCP = 2.3 Hz, p-PPh2CH), 132.8 (d,
3JCP = 9.3 Hz, m-PPh2CH), 133.1 (PPh2Cipso), 136.8 (d,
3JCP = 9.3 Hz, indoleC9). MS(ESI): m/z 550.13 [M-
2Cl- ? H?]? (100 %), 586.10 [M-Cl-]? (25 %), 644.06
[M ? Na?]? (95 %). Anal. Calcd. for C31H32Cl2NPRu
(621.54): C, 59.90; H, 5.19; N, 2.25. Found: C, 59.71; H,
4
Table 2 Crystal structure and refinement data for [Ru2Cl4(NC-
Me)L4] and RuCl2{g6-p-cymene}L
Compound
[Ru2Cl4(NCMe)L4] RuCl2{g6-p-
cymene}L
5.02; N, 2.60. IR(cm-1): 3289.1 t(N–H)
.
Colour, habit
Size/mm
Orange prism
0.16 9 0.08 9 0.08 0.12 9 0.10 9 0.06
88H77Cl10N5P4Ru2 C31H32Cl2NPRu
Red rod
Catalyst screening
Empirical formula
M
C
1,885.07
Monoclinic
P21/n
621.52
The catalytic reactions were performed in a Radleys carousel
as follows: A CH2Cl2 solution containing 0.1 mol % of
RuCl2{g6-p-cymene}L 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 lL; benzophenone, 364 mg; cyclohex-
anone, 207 lL) was added, followed by 10 mL of a 0.2 M
(high-base conditions) or a 0.02 M (low-base conditions)
solution of KOH in iPrOH via a syringe, and the mixture was
heated to 84 °C. The reaction was sampled at 1, 3 and 24 h,
and the portion was added into an NMR tube without evap-
oration or filtration. Three drops of D2O were added into the
NMR tube, and the residue analysed by 1H NMR in CDCl3
(with a reaction mixture: CDCl3 ratio of 2: 3 by volume). The
percentage conversions were determined by relative inte-
gration of characteristic resonances of both the products and
the starting materials.
Crystal system
Space group
Monoclinic
P21/c
˚
a/A
14.8514(10)
20.8694(16)
27.755(2)
90.00
22.333(4)
15.4163(18)
17.224(3)
90.00
˚
b/A
˚
c/A
a/°
b/°
c/°
97.320(4)
90.00
111.901(16)
90.00
3
˚
V/A
8,532.2(11)
4
5,502.1(16)
8
Z
l/mm-1
0.790
0.844
T/K
100
100
hmin,max
Completeness
1.22, 27.60
3.55, 25.36
0.988 to h = 27.60° 0.995 to h = 25.36°
Reflections: total/
independent
19592/19592
100233/10038
Rint
0.0000
0.1035
Final R1 and wR2
Largest peak, hole/
0.0722, 0.2032
1.251, -1.314
0.0576, 0.1682
0.724, -0.917
X-ray crystallography
-3
˚
e A
calc/g cm-3
X-ray diffraction experiments on [Ru2Cl4(NCMe)L4] and
[RuCl2{g6-p-cymene}L] were carried out at 100 K on a
q
1.467
1.501
123

Transition Met Chem (2013) 38:641–648
647
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supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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Acknowledgments The authors thank the Royal Society for a Royal
Society Dorothy Hodgkin Research Fellowship for GRO and Johnson
Matthey for the generous loan of ruthenium salts.
36. Tsoureas N, Kuo Y–Y, Haddow MF, Owen GR (2011) Chem
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