Ruthenium complexes with tridentate PNX (X = O, S) donor ligands

Article abstract of DOI:10.1039/b717025d

The ligands, PhPNXMe (1), PhPNXPh (2), and PhPNSMe (3), (PhPNX = 2-Ph ₂P-C₆H₄CH=NC₆H₄X-2; X = O, S) have been prepared. A range of new ruthenium complexes were synthesised using these and related ligands, namely: [{RuCl(PhPNO)}₂Cl] (4), [Ru(PhPNO)₂] (5), [RuCl(PhPNXR)(PPh₃)]BPh₄ [X = O, R = Me (6); X = O, R = Ph (7); X = S, R = Me (8)], [{RuCl(PhPNX′ R)}₂Cl]X [X′ = O, R = Me, X = Cl^- (9); X′ = S, R = Me, X = BPh₄^- or PF₆^- (10)], and [RuCl(PhPNO-η ⁶C₆H₅)]BPh₄ (11). The catalytic activity of these complexes with respect to the hydrosilyation of acetophenone and the hydrogenation of styrene has been investigated, giving an insight into the requirements for an active complex in these reactions. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b717025d

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www.rsc.org/dalton | Dalton Transactions
Ruthenium complexes with tridentate PNX (X = O, S) donor ligands†
Simon R. Bayly, Andrew R. Cowley, Jonathan R. Dilworth* and Caroline V. Ward
Received 2nd November 2007, Accepted 22nd January 2008
First published as an Advance Article on the web 6th March 2008
DOI: 10.1039/b717025d
=
The ligands, PhPNXMe (1), PhPNXPh (2), and PhPNSMe (3), (PhPNX = 2-Ph2P-C6H4CH
NC6H4X-2; X = O, S) have been prepared. A range of new ruthenium complexes were synthesised using
these and related ligands, namely: [{RuCl(PhPNO)}2Cl] (4), [Ru(PhPNO)2] (5), [RuCl(PhPNXR)-
(PPh3)]BPh4 [X = O, R = Me (6); X = O, R = Ph (7); X = S, R = Me (8)], [{RuCl(PhPNXꢀR)}2Cl]X
[Xꢀ = O, R = Me, X = Cl− (9); Xꢀ = S, R = Me, X = BPh4− or PF6− (10)], and [RuCl(PhPNO-g6C6H5)]-
BPh4 (11). The catalytic activity of these complexes with respect to the hydrosilyation of acetophenone
and the hydrogenation of styrene has been investigated, giving an insight into the requirements for an
active complex in these reactions.
Introduction
Recently the potential for catalytic activity of platinum group
metal complexes incorporating phosphorus–sulfur donor ligands
has been realised.1–3 The differing binding capabilities of the two
donor atoms gives rise to the possibility of group displacement
by substrates and thus hemilability. Recently we synthesised a
Scheme 1 A generalised PhPNX ligand.
series of ruthenium aromatic phosphinothioether complexes and
investigated their catalytic activity towards the hydrosilyation of
acetophenone. Disappointingly such complexes were found to
be essentially inactive.4 It was therefore of interest to synthesise
tridentate aromatic ligands with three heteroatoms, P, N and
X (X = S, O) and investigate the effect of changing denticity
and donor atom type upon coordination chemistry and catalytic
activity.
A review of the literature reveals that little ruthenium chemistry
of this type has been carried out. Previous investigations have been
mostly concerned with ruthenium–PNOH and –PNO− systems.5–7
Some of these ruthenium–PNO complexes have been applied to
the asymmetric transfer hydrogenation of ketones and have been
found to be active, with both conversions and enantioselectivities
often above 70%.7,8
Scheme 2 Formation of thiazoline and thiazole rings.
Results and discussion
This investigation began with the attempted synthesis of PNS tri-
dentate ligand systems (Scheme 1). The literature shows that alde-
hydes react with aminothiolates to form benzothiazolines, which
can subsequently be oxidised to benzothiazoles (Scheme 2).9–11
While thiazolines can ring open in the presence of ions to give
complexes of iminothiolates, the thiazoles cannot.
In an attempt to avoid this ring formation the reaction
of 2-(diphenylphosphino)benzaldehyde was carried out with 2-
aminodisulfide (Scheme 3). However, in our hands this reac-
tion yielded PhP(O)NHS-cyclic (Scheme 4). This structure has
Scheme 3 Attempted synthesis of the disulfide imine.
Chemistry Research Laboratory, University of Oxford, Mansfield Road,
Oxford, UK OX1 3TA. E-mail: jon.dilworth@chem.ox.ac.uk; Tel: +44
(0)1865 285151, +44 (0)1865 285155
† CCDC reference numbers 666144–666152. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b717025d
previously been reported.10 It appears that both oxidation of
phosphorus and reduction of the disulfide bond occurs during the
reaction or subsequent recrystallisation. Attention was therefore
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◦
˚
Table 1 Selected bond lengths (A) and bond angles ( ) for crystallograph-
ically characterised compounds
3
P(1)–C(1)
S(1)–C(14)
C(7)–N(1)
1.848(3)
1.789(3)
1.281(3)
P(1)–C(1)–C(6)
C(7)–N(1)–C(8)
C(1)–C(6)–C(7)
C(13)–S(1)–C(14)
120.28(18)
117.9(2)
120.8(2)
Scheme 4 PhP(O)NHS-cyclic ligand.
102.43(14)
focused on the neutral thioether ligand, PhPNSMe, which does
not undergo cyclisation reactions.
4
Ru(1)–Ru(2)
Ru(1)–Cl(1)
Ru(1)–O(1)
Ru(1)–N(1)
Ru(1)–P(1)
Ru(1)–O(2)
2.7528(5)
2.412(1)
2.115(3)
2.000(3)
2.242(1)
2.141(3)
Cl(1)–Ru(1)–Cl(2)
Ru(2)–Ru(1)–O(1)
Cl(1)–Ru(1)–O(1)
Ru(2)–Ru(1)–N(1)
Ru(2)–Ru(1)–P(1)
Ru(2)–Ru(1)–O(2)
Ru(1)–Cl(1)–Ru(2)
Ru(1)–O(1)–Ru(2)
Cl(1)–Ru(2)–Cl(3)
Ru(1)–Ru(2)–P(2)
93.23(4)
49.28(7)
87.50(8)
116.5(1)
132.33(3)
48.68(7)
69.71(3)
81.29(9)
93.75(4)
127.14(3)
Synthesis of PhPNX ligands
2-(Diphenylphosphino)benzaldehyde,12 PhPNOH9 and PhPNO-
Me13 (1) were synthesised by the literature procedures.9
PhPNOPh (2). The new ligand, 2, was prepared from
the reaction of 2-(diphenylphosphino)benzaldehyde with 2-
phenoxyaniline, in ethanol. Analysis showed the ligand to be
contaminated by small amounts of both starting materials but
attempts at purification by vacuum distillation resulted in decom-
position. However, the ligand was found to be sufficiently pure for
subsequent reaction with ruthenium precursors.
4a
Ru(1)–Cl(1)
Ru(1)–P(1)
Ru(1)–N(1)
Ru(1)–O(1)
O(1)–H(1)
2.3428(8)
2.2463(8)
2.066(3)
2.157(2)
0.87(5)
Cl(1)–Ru(1)–Cl(2)
Cl(2)–Ru(1)–Cl(3)
Cl(1)–Ru(1)–P(1)
Cl(1)–Ru(1)–N(1)
Cl(2)–Ru(1)–N(1)
Cl(1)–Ru(1)–O(1)
P(1)–Ru(1)–O(1)
N(1)–Ru(1)–O(1)
Ru(1)–P(1)–C(1)
96.38(3)
167.60(3)
92.31(3)
171.85(7)
84.07(7)
92.40(7)
174.74(7)
79.5(1)
PhPNSMe (3). Ligand 3 was prepared by the reaction
of 2-(methylmercapto)aniline with 2-(diphenylphosphino)-
benzaldehyde, in chloroform. This ligand has similar solubility
to ligands 1 and 2. The structure of 3 was confirmed by single
crystal X-ray analysis (Fig. 1). Selected bond lengths and angles
for crystallographically characterised compounds are presented
109.85(11)
5
Ru(1)–P(1)
Ru(1)–N(1)
Ru(1)–O(1)
2.2499(8)
2.053(2)
2.097(2)
P(1)–Ru(1)–N(1)
P(1)–Ru(1)–O(1)
N(1)–Ru(1)–O(1)
P(1)–Ru(1)–P(2)
N(1)–Ru(1)–P(2)
O(1)–Ru(1)–P(2)
Ru(1)–P(1)–C(1)
94.43(8)
171.38(8)
80.9(1)
97.00(3)
95.03(7)
90.63(8)
113.12(11)
=
in Table 1. The geometry around the C N bond is essentially
co-planar, with the C(1)–C(6) and C(8)–C(13) phenyl groups trans
to one another. In order for the ligand to be able to coordinate
a metal centre in a tridentate manner, through all three donors,
rotation is required around the N(1)–C(8) bond, rendering the
two phenyl rings cis. All three donors then have the correct
configuration for mer coordination.
MS contains peaks which correspond to the molecular ion and
two further fragments, [RuCl2(PhPNO)]− and [RuCl(PhPNO)]−.
Paramagnetism and lability precluded NMR assignment.
X-Ray analysis of a single crystal grown under nitrogen from
a solution of the isolated solid in dry methanol revealed the
symmetrical dimeric structure of [{Ru2.5/2.5Cl(PhPNO)}2Cl] (4)
(Fig. 2). On standing in air, the solution changes in colour
from purple to brown and after work-up crystals were ob-
tained from methanol/diethyl ether. X-Ray analysis of these
Fig. 1 ORTEP representation of ligand 3 (40% thermal ellipsoids,
hydrogen atoms omitted for clarity).
Synthesis of PhPNX complexes
[{RuCl(PhPNO)}2Cl] (4). Complex 4 was prepared from the
reaction of diruthenium-tetrachlorobis(4-cymene) with PhPNOH,
in methanol. This complex is air sensitive and changes colour from
purple to brown over tens of minutes in the presence of air, in
both the solid state and solution. It is soluble in tetrahydrofuran
and methanol and is insoluble in diethyl ether. Negative ion ES
Fig. 2 ORTEP representation of 4 (40% thermal ellipsoids, hydrogen
atoms omitted for clarity).
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showed them to be [RuIIICl3(PhPNOH)] (4a) (Fig. 3). From
these structures we propose the following decomposition pathway:
[{RuII/IICl(PhPNO)}2Cl]− is initially formed in the reaction and
oxidises to give 4, which subsequently, on prolonged standing in
solution, forms 4a. The analogous reaction using a 1 : 2 ratio of
ruthenium precursor to ligand (based on the number of moles
of dimer), was carried out in the presence of two equivalents
of triethylamine. A brown powder was isolated (40%, assuming
the formulation below). After several hours of standing in air,
the solid became black. Analysis of the brown solid, including
positive ion ES MS, suggests the formation of [RuII(PhPNO)2] (5).
This complex was also prepared using two equivalents of ligand
with [RuCl2(PPh3)2] as discussed below.
A second complex 5a was isolated from the solution after filtering
off 5. ES MS and analytical data were consistent with this being
monoprotonated 5. An X-ray crystal structure confirmed the
coordination about the metal but was not of sufficient quality
to discuss further.
The addition of excess sodium tetraphenylborate in methanol
solution to a sample of the initial reaction mixture does not
produce a precipitate and this supports the formation of a neutral
rather than a charged product. Identical complexes are formed
whether one or two equivalents of ligand are utilised in the
reaction. However, the yield is maximised in the latter. Complex
5 can also be prepared from the reaction of [{RuCl2(cymene)}2]
with one equivalent of ligand in the presence of base.
X-Ray crystal structure of 5. The structure of 5 was confirmed
by single crystal X-ray analysis (Fig. 4). This complex has a mer–
mer configuration with the two nitrogens trans to one another and
the two phosphorus atoms and two oxygens cis. Ru–N, Ru–O and
˚
˚
˚
Ru–P bond lengths in this complex are ∼2.1 A, ∼2.1 A and ∼2.3 A,
respectively. These are very similar to those measured for the
ruthenium dimer 5 and agree with those of other ruthenium(II)–
PNO complexes with similar ligands.6,7
Fig. 3 ORTEP representation of 4a (40% thermal ellipsoids, hydrogen
atoms omitted for clarity).
X-Ray crystal structures of 4 and 4a. A significant feature of the
structure of 4 is the presence of a Ru–Ru bond, indicated by the
˚
Ru–Ru separation of 2.7528(5) A. The total valence electron count
for the dimer is 35 electrons. The Ru–N, Ru–O and Ru–P bond
˚
˚
˚
lengths are ∼2.0 A, ∼2.1 A and ∼2.3 A, respectively. These are in
agreement with those of other ruthenium complexes reported.12–15
˚
All Ru–Cl bond lengths are very similar, at ∼2.4 A. The chloride
shared between the two ruthenium atoms lies equidistant between
them. The equivalent angles on each side of the dimer are also very
similar. For example Cl(1)–Ru(1)–Cl(2) is 93.23(4)◦ and Cl(1)–
Ru(2)–Cl(3) is 93.75(4)◦. Also Ru(1)–Ru(2)–P(2) is 127.14(3)◦ and
Ru(2)–Ru(1)–P(1) is 132.33(3)◦. All these details are consistent
with a delocalised structure with an average oxidation state for
each ruthenium of 2.5.
Fig. 4 ORTEP representation of 5 (40% thermal ellipsoids, hydrogen
atoms omitted for clarity).
Complex 4a exists as two polymorphs. Above temperatures
of ∼220 K the material has a smaller unit cell and at 250 K
the space group is P21/n. The low temperature form, for which
crystallographic data has been analysed, has a space group of
P21/c. The overall geometry about the Ru centres is pseudo-
octahedral, with the PhPNO ligand adopting its familiar mer
Solution spectroscopic studies of the Ru/PhPNO system
Although it is possible to isolate them pure in the solid state,
31P and 1H NMR (CDCl3) spectra show that 4 and 5 form
complex mixtures of species in solution. The Ru/PhPNO system
can participate in a number of potential equilibria (Scheme 5) and
the 31P NMR spectra in particular show resonances consistent
with species of the type shown.
˚
configuration. All Ru–Cl bond lengths are ∼2.3 A and are
consistent with those for other reported ruthenium complexes.
The same is true for the Ru–N, Ru–O and Ru–P bond lengths.12–15
[Ru(PhPNO)2] (5). Reaction of [RuCl2(PPh3)3] with two equiv-
alents of PhPNOH, in methanol under reflux, produced complex
5. In air this complex decomposes rapidly in the solid state and
in solution. It is soluble in methanol and chlorinated solvents and
insoluble in diethyl ether. Positive ion EI MS shows the molecular
ion and also a peak corresponding to the fragment [Ru(PhPNO)]+.
[RuCl(PhPNXR)(PPh3)]BPh4 [XR = OMe (6), OPh (7), SMe
(8)]. Complexes 6, 7 and 8 were synthesised from the reaction
of [RuCl2(PPh3)3] with one equivalent of ligand in methanol.
The three complexes have similar solubilities. All are soluble in
chlorinated solvents, acetonitrile and methanol and are insoluble
in diethyl ether and hexane. Complex 7 changes in colour from
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Scheme 5 Solution chemistry of the Ru/PhPNO system.
red to yellow in acetonitrile, possibly due to coordination of
solvent, and in dichloromethane becomes brown over a period
of several days. Elemental analysis has been carried out and
the results for 6 and 7 agree with the complexes formulated.
Satisfactory values for 8 could not be obtained. Positive ion ESMS
and FAB support the formation of all three complexes.
ESMS (using a solution of the complex in MeCN) attributable to
[RuCl(MeCN)2(PhPNOMe)]+ and [RuCl(MeCN)(PhPNOMe)]+.
In methanol no colour change was observed and a peak corre-
sponding to [RuCl(MeOH)(PhPNOMe)]+ was observed. Complex
9 is insoluble in hexane and diethyl ether. Complex 10 has
a similar range of solubilities but does not show any colour
change in solution. Positive ion FAB and ESMS and elemental
analysis were in agreement with the calculated formula. However,
satisfactory values could not be obtained for 9. Despite this the
HPLC of 9 displays a single peak at RT 1.22 min. Also the IR
spectrum contains an absorption at 1590 cm−1, assigned to the
Each complex also gives an absorption in the IR spectrum due to
−1
the C N stretch. These are observed at 1579 cm and 1638 cm−1
=
for 6, 1580 cm−1 for 7 and 1579 cm−1 for 8. In solution these
species gave rise to complex mixtures due to dissociation and/or
decomposition, precluding NMR assignment.
=
The reaction of PhPNOMe with excess [RuCl2(PPh3)3] in
tetrahydrofuran solution has previously been reported.16 The red
solid obtained was formulated as [RuCl2(PhPNOMe)(PPh3)] (this
is similar to 6 but with the chloride counter-ion now bound to the
metal centre). However, no crystal structure of this compound has
been reported. Its catalytic activity towards the transfer hydro-
genation of acetophenone to 1-phenylethanol was measured (con-
ditions: 82 ◦C, propan-2-ol, acetophenone : ruthenium : NaOH =
500 : 1 : 24) and the yield after four hours was found to be 98%.
The TOF was found to be 730 h−1 and the reaction was not
enantioselective.16
C N stretching frequency. Similarly the IR spectrum of 10 has
an absorption at 1579 cm−1 (like 8 this is also shifted to lower
wavenumber compared to the free ligand).
Solution spectroscopic studies of Ru/PhPNXR (X = O, R = Me,
Ph; X = S, R = Me) systems
Similarly to 4 and 5, complexes 6–10 form complex mixtures
in solution. Possibilities for species formed include the presence
of different geometrical isomers, monomer–dimer equilibria, and
dissociation of triphenylphosphine where present.
[RuCl(PhPNO-g6C6H5)]BPh4 (11). Complex 11 (Scheme 6)
was formed from the reaction of diruthenium-tetrachlorobis(4-
cymene) with PhPNOPh, in methanol. It is soluble in chlorinated
solvents and methanol and is insoluble in hexane and diethyl
[{RuCl(PhPNXꢀR)}2Cl]X [XꢀR = OMe, X = Cl− (9), XꢀR =
−
−
SMe, X = BPh4 or PF6 (10)]. Complexes 9 and 10 were
prepared by reaction of diruthenium-tetrachlorobis(4-cymene)
with ligands 1 and 3, respectively, in methanol solution. Sim-
ilar chloride bridged ruthenium complexes are reported in the
literature.17 Although analogous in formulae and presumably
in structure, complexes 9 and 10 differ from each other in
their sensitivity to oxygen. Upon exposure to air, complex 9
changes in colour from blue to brown over several hours in
the solid state. In contrast complex 10 does not visibly react.
A solution of complex 9 in acetonitrile rapidly changes colour
to red, presumably due to incorporation of acetonitrile. This
is supported by the observation of peaks in the positive ion
Scheme 6 Proposed structure of 11.
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ether. Unlike many of the ruthenium PNX systems, 11 appears
relatively stable in solution and only one species is observed by
NMR and a full spectral assigment can be made. Comparison
the absence of silver triflate, include 4, 5, 7 and 9. In particular
the activity of 5 is surprising as it was anticipated that chelation
by two tridentate ligands would reduce the activity by making
reactive sites unavailable. Interestingly all these complexes contain
PNO donors and presumably the activity is a consequence of the
poor oxygen to metal binding strength. In contrast complexes
containing PNS are essentially inactive. This is attributed to the
much stronger donation of sulfur to ruthenium. HPLC studies of
8 and 10 also suggest stability of these complexes in solution, with
the elution of one major peak in each case. This implies that the
strength of the Ru–X bond (where X is S or O) is important, in
part, in determining catalytic activity.
The addition of silver triflate in these reactions has little effect
or in fact decreases the activity in most cases. Exceptions do exist
however and in the reactions with 9 and 10 with this additive,
higher activities result. We postulate that this is due to abstraction
of chloride from the chloride bridge and generation of vacant
coordination sites for incoming substrate molecules. The activity
is also increased by the addition of silver triflate in the reaction
with 6. Again this is presumably due to chloride abstraction but
as yet we do not have a rationale as to why this is the case for this
complex and not for the analogous species 7 and 8.
From these studies it appears that ligand lability is a critical fac-
tor indetermining catalytic activityandthis inturnis dependenton
the donor set. Oxygen is a much weaker donor to ruthenium than
sulfur. Also ligand denticity seems to play a part. In general, the
complexes with the highest activities above have a single tridentate
ligand, rather than multiple bidentate coordinating ligands. This
is possibly because tridentate ligands can act in a hemilabile mode
and maintain complex stability with two donor atoms, whilst the
third, is detached creating a vacant coordination site. In these
studies the charge of the ligand appears to have little effect upon
activity.
6
with previously reported g -arene chelates confirms the proposed
6
g -coordination of the phenoxy group.18 The 31P NMR spectrum
shows a single peak at 42.8 ppm. The 1H NMR spectrum,
6
measured in d6-DMSO, shows five g -C6H5 resonances for the
inequivalent protons, between 2.4 ppm and 6.0 ppm, each of which
has a JH–H coupling of ∼7 Hz. No JP–H couplings are observed.
6
The six g -C6H5 carbons show six broad signals (up to 19 Hz in
width at half height) in the 13C NMR spectrum, in the region
30–100 ppm. The broad signals may conceal JC–P couplings. The
remaining phenyl resonances occur in typical regions in both the
1H and 13C spectra and the CH signal has a chemical shift of
8.79 ppm in the 1H spectrum (JH–P 1 Hz) and of 175.4 ppm in the
13C spectrum (JC–P 7 Hz).
Catalysis
The newly synthesised complexes were screened for their activity
towards the hydrosilylation of acetophenone to 1-phenylethanol.
Hydrosilylation is generally taken as an indicator of catalytic
activity and when encouraging results were obtained, further
catalysis measurements were made. These included hydrosilylation
with the addition of silver triflate as an activator and the
hydrogenation of styrene to ethylbenzene. It was hoped that the
results would permit some discussion of the dependence of activity
on ligand denticity, charge, donor atom set and ligand steric
requirements.
Hydrosilylation. Catalytic activity towards the hydrosilyla-
tion of acetophenone, to 1-phenylethanol using diphenylsilane
was tested. Four known complexes were used as a stan-
dard: diruthenium-tetrachlorobis(4-cymene), [RuCl2(PPh3)3],19
[RuCl2(dppe)2]20 and [RuCl2(PhPOMe)2].21,22 The method used
was adapted from the procedure described by Uemura, Hidai
et al.23 Silver triflate can act as an activator and improve
enantioselectivity23 and was used in some reactions. The results
are shown in Table 2.
Hydrogenation. Hydrogenation of styrene was used to test
the catalytic activity of complexes towards hydrogenation. This
was carried out in the same way for each sample and in the
absence of catalyst, no conversion was observed. The activity
of [RuCl2(PPh3)3]19 was measured, so that comparisons could be
drawn with the newly synthesised complexes. The results obtained
Complexes with activity higher than [RuCl2(PPh3)3] and
[RuCl2(PhPOMe)2] (TOF of 19 h−1 and 16 h−1, respectively), in
Table 2 Results of catalytic hydrosilylation using Ru/PNX complexes
Catalyst
Conversion (%) (with AgOTf)
TONa (with AgOTf)
[RuCl2(PPh3)3]
[RuCl2(cymene)]2Cl2
[RuCl2(dppe)2]
19
1
0.2
19
1
0.2
[RuCl2(PhPOMe)2]
16
16
[{RuCl(PhPNO)}2Cl]
4
5
20 (13)
22 (11)
6
20 (13)
22 (11)
6
[Ru(PhPNO)2]
[Ru(PhPNO)2]b
[Ru(PhPNO)2]c
0.5
0.4
[RuCl(PhPNOMe)(PPh3)]BPh4
[RuCl(PhPNOPh)(PPh3)]BPh4
[RuCl(PhPNSMe)(PPh3)]BPh4
[{RuCl(PhPNOMe)} Cl]Cl
[{RuCl(PhPNSMe)}22Cl]BPh4
[RuCl(PhPNO-g6C6H5)Cl]BPh4
6
18 (23)
36 (29)
2 (2)
26 (36)
0 (3)
0.5 (0.6)
9 (12)
18 (15)
1 (1)
26 (36)
0 (3)
0.3 (0.4)
7
8
9
10
11
a TON = TOF (h−1). b Product from the reaction of [RuCl2(PPh3)3], PhPNOH and triethylamine—formula unconfirmed. c Product from the reaction of
[{RuCl2(cymene)}2], PhPNOH and triethylamine—formula unconfirmed.
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Table 3 Results of catalytic hydrogenation using Ru/PNX complexes
Catalyst
Conversiona (%)
TON
TOF/h−1
[RuCl2(PPh3)3]
6
0
6
0
5
0
30
0
30
0
13
0
15
0
15
0
6
0
[{RuCl(PhPNO)}2Cl]
4
5
6
7
9
[Ru(PhPNO)2]
[RuCl(PhPNOMe)(PPh3)]BPh4
[RuCl(PhPNOPh)(PPh3)]BPh4
[{RuCl(PhPNOMe)}2Cl]Cl
a Estimated error 0.5%.
are illustrated in Table 3. [RuCl2(PPh3)3] forms [RuCl(H)(PPh3)3]
upon reaction with base and investigations have shown this species
to be very effective in the hydrogenation of terminal alkenes.24,25
Using the procedure described above it was found to have a TON
of 30 and TOF of 15 h−1. These values are relatively low because
of the mild reaction conditions used, low concentration of metal
complex and the absence of base.
Two of the new complexes described are active under these
conditions, 5 and 7. The activity of 5 is comparable to that of
[RuCl2(PPh3)3], which is significant. However it is not clear why
the other ruthenium–PNO complexes are inactive under the same
conditions.
125.7 MHz and 202.4 MHz, respectively, at ambient temperature
unless otherwise stated. 1H and 13C NMR spectra were referenced
internally to residual solvent resonances or tetramethylsilane at
zero ppm (for 1H NMR) and 31P spectra were externally referenced
to 85% H3PO4 at zero ppm.
Electrospray mass spectrometry was performed on a Micromass
LCT Time of Flight Mass Spectrometer. Electron impact mass
spectrometry was performed on a Micromass GCT Time of Flight
Mass Spectrometer, with a heated solid probe. FAB mass spec-
trometry was performed on a Fisons Autospec, using dithiothreitol
and dithioerythritol or m-nitrobenzyl alcohol as the matrix.
HPLC was carried out on a GILSON analytical/preparative
instrument with a UV/VIS detector (k = 250 nm). A reverse-
phase HAMILTON PRP-1 analytical column (4.1 × 150 mm,
10 lm) was used with an isocratic mobile phase of 95 : 5%
acetonitrile : water and a flow rate of 1.5 mL min−1.
Gas chromatography was carried out on a Unicam ProGC gas
chromatogram system using helium as the carrier gas and a flame
ionisation detector (FID) with a hydrogen/air flame. A 2 metre
Carbowax 20M packed column was used.
Elemental analyses were performed by the elemental analysis
department of the Inorganic Chemistry Laboratory, University of
Oxford.
Conclusions
=
Ligands of the type Ph2PC6H4CH NC6H4XR (X = O, R = H, Me,
Ph; X = S, R = Me) react with [{RuCl2(cymene)}2] to give products
with structures highly dependent on the XR group. When XR =
OH a phenoxy bridged dimer is formed whereas with XR = OMe a
triple chloride bridge results. The reaction with XR = OPh yields
6
a complex with a g -bound phenoxy phenyl group. By contrast
reaction of these same ligands with [RuCl2(PPh3)3], generally leads
to monomeric cationic complexes with the retention of PPh3.
In general complexes containing one tridentate ligand were
found to be most active for hydrosilyation. Higher activities were
obtained for alkoxy rather than thioether analogues, suggesting
the dissociation of an oxygen donor atom is a crucial part of the
catalytic cycle. Two of the new complexes (5 and 7) were found to
be reasonably active for hydrogenation, but no structure–activity
relationship could be elucidated.
Crystallography
X-Ray crystallography was performed on a Bruker-Nonius Kap-
paCCD diffractometer, using graphite-monochromated Mo-Ka
˚
radiation (k = 0.71073 A). Single crystals were mounted on a
glass fibre using perfluoropolyether oil and were cooled rapidly to
150 K in a stream of cold nitrogen using an Oxford Cryosystems
CRYOSTREAM unit. Intensity data were processed using the
DENZO-SMN package.27 Structures were solved using the direct-
methods programme SIR92,28 which located all non-hydrogen
atoms. Subsequent full-matrix least-squares refinement was car-
ried out using the CRYSTALS programme suite.29 Coordinates
and anisotropic thermal parameters of all non-hydrogen atoms
were refined. Hydrogen atoms were positioned geometrically
after each cycle of refinement. A 3-term Chebychev polynomial
weighting scheme was applied. Selected bond lengths and angles
are presented in Table 1. Crystallographic data is shown in Table 4.
Experimental
General procedures
Unless otherwise stated, all manipulations were carried out under
an atmosphere of dinitrogen with dry solvents and using Schlenk
line techniques. Solvents were pre-dried over sodium wire or
calcium chloride prior to heating at reflux over the appropri-
ate drying agent/indicator: methanol (magnesium methoxide),
tetrahydrofuran (sodium/benzophenone), toluene (sodium). All
solvents were degassed prior to use. [RuCl2(PPh3)3],19 PhPNOH9
and 2-(diphenylphosphino)-benzaldehyde26 were prepared accord-
ing to literature procedures. All other reagents and solvents were
purchased from commercial sources and were used as received.
1H, 13C and 31P NMR spectra were recorded on a Varian
Mercury-Vx 300 spectrometer at 300.0, 75.4 and 121.4 MHz, re-
spectively, or a Varian Unit 500 MHz spectrometer at 499.9 MHz,
Synthetic procedures
PhPNOPh
(2). 2-(Diphenylphosphino)benzaldehyde
(520 mg, 1.79 mmol) was dissolved in non pre-dried ethanol
(15 mL) with mild heating. An ethanolic solution of 2-
phenoxyaniline (332 mg, 1.79 mmol, in 5 mL ethanol) was added
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Table 4 Crystallographic data for compounds 3, 4, 4a, and 5
Compound
3
4
4a
5
Chemical formula
C26H22NPS
C50H38Cl3N2O2P2Ru2 +
xCH4O (x = 0.691)
1123.54
150
0.71073
Monoclinic
P 21/n
10.8467(2)
33.4618(4)
13.0799(2)
90
95.8351(5)
90
C30H34Cl3NO3PRu
C50H38N2O2P2Ru +
xCH4O (x ∼ 1.63)
914.03
Formula weight
411.50
150
695.01
150
T/K
150
˚
k/A
0.71073
Monoclinic
P 21/a
10.4453(4)
15.2797(6)
13.4194(5)
90
97.7604(6)
90
2122.1
4
0.71073
Monoclinic
P 21/c
16.3162(2)
17.8674(3)
20.7202(3)
90
95.0265(7)
90
6017.3
8
0.71073
Monoclinic
P 21/n
16.4446(2)
12.5025(2)
20.7078(4)
90
93.0930(7)
90
4251.3
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
4722.8
4
1.580
0.924
Z
4
D/Mg m−3
1.288
0.240
1.534
0.873
1.428
0.493
l/mm−1
F000
864.912
0.05 × 0.20 × 0.30
19458
4976
0.090
2252.705
0.12 × 0.17 × 0.17
41954
10882
0.063
591
1.0563
0.0332
0.0352
2832.962
0.08 × 0.10 × 0.14
62008
14138
0.052
1880.535
0.04 × 0.24 × 0.30
45136
10081
0.051
539
1.0213
0.0532
0.0510
Crystal size/mm
Reflections measured
Unique reflections
Rint
Parameters refined
Goodness of fit
R
262
700
1.0530
0.0380
0.0437
1.0300
0.0383
0.0467
wR
dropwise. The reaction mixture was heated under reflux in air for
three hours and after cooling to room temperature, the solvent
was removed in vacuo. PhPNOPh was obtained as a yellow oil
which contained small amounts of unreacted starting materials.
Attempts at purification failed, therfore the crude product was
125.1 (s, CB2), 126.3 (s, CB4), 127.7 [d, CA1 (JC–P 4 Hz)], 128.6–139.2
(Ph), 129.0 [d, CA2 (JC–P 5 Hz)], 131.1 (s, CA4), 133.2 (s, CA3), 158.3
[d, CH (JC–P 25 Hz)].
[{RuCl(PhPNO)}2Cl]
(4). Diruthenium-tetrachlorobis(4-
cymene) (63 mg, 0.10 mmol) and PhPNOH (78 mg, 0.21 mmol)
were suspended in methanol (15 mL) and heated under reflux
overnight. The reaction mixture became purple and after cooling
to room temperature the solvent was removed in vacuo. Diethyl
ether (5 mL) was added and the mixture triturated to yield a
precipitate. This was collected by filtration under nitrogen, washed
with diethyl ether and dried in vacuo. [{RuCl(PhPNO)}2Cl] was
obtained as an air sensitive, purple solid (48 mg, 44%). Elemental
analysis, found (required)%: C 54.46 (56.16), H 3.92 (3.58), N
2.51 (2.62), Cl 10.20 (9.95); Mass spectrum [ES(−)]: m/z 1071
[M]−, 552 [RuCl2(PhPNO)]−, 516 [RuCl(PhPNO)]−.
used in complexation reactions. FTIR (Nujol mull), cm−1: 1697
+
(w), C N stretch; Mass spectrum [ES(+)]: m/z 458 [M] ; 1H
=
NMR: (CDCl3) d 6.30–8.35 (m, Ph, 23H), 9.35 [d, CH, 1H
(JH–P 6 Hz)]; 31P NMR: (CDCl3) d −13.7; 13C NMR: (CDCl3) d
116.4–144.0 (Ph), 160.1 [d, CH (JC–P 25 Hz)]
PhPNSMe (3). 2-(Methylmercapto)aniline (0.27 mL,
2.191 mmol) was dissolved in non pre-dried chloroform (50 mL)
and 2-(diphenylphosphino)benzaldehyde (636 mg, 2.19 mmol),
also dissolved in chloroform (10 mL), was added dropwise to this.
The reaction mixture was heated under reflux in air for four hours,
using a Dean–Stark trap. After cooling to room temperature the
solvent was removed in vacuo to leave a yellow oil. Diethyl ether
(10 mL) was added and the reaction mixture stirred overnight.
A yellow precipitate formed and was collected by filtration in
air, washed with diethyl ether and dried in vacuo. PhPNSMe was
obtained as a yellow powder (548 mg, 61%). Elemental analysis,
[Ru(PhPNO)2] (5). [RuCl2(PPh3)3] (131 mg, 0.14 mmol) and
PhPNOH (104 mg, 0.27 mmol) were suspended in methanol
(15 mL) and the mixture was heated under reflux overnight. The
solution became red and after cooling to room temperature the
solvent was removed in vacuo. Diethyl ether (10 mL) was added and
trituration took place. A red/brown precipitate formed and was
collected by filtration under nitrogen, washed with diethyl ether
and dried in vacuo. [Ru(PhPNO)2] was obtained as an air sensitive,
found (required)%: C 76.01 (75.89), H 5.30 (5.39), N 3.44 (3.40);
−1
=
FTIR (Nujol mull), cm : 1618 (m), C N stretch; Mass spectrum
[ES(+)]: m/z 412 [M]+; HPLC: RT 8.00 min. (broad peak); H
1
red/brown powder (50 mg, 43%). FTIR (Nujol mull), cm−1: 1585,
NMR: (CDCl3) d 2.41 (s, SMe, 3H), 6.46 [m, HB1, 1H (JH–H 8,
1 Hz)], 6.93 [m, HA3, 1H(JH–P 5 Hz, JH–H 8, 1 Hz)], 7.02 [m, HB2,
1H (JH–H 8, 1 Hz)], 7.14 [m, HB3, 1H (JH–H 1 Hz)], 7.16 [m, HB4,
1H (JH–H 1 Hz)], 7.27–7.39 (m, Ph, 10H), 7.33 (m, HA4, 1H), 7.46
[m, HA2, 1H (JH–H 1 Hz)], 8.40 [m, HA1, 1H (JH–P 4 Hz, JH–H 8,
1 Hz)], 9.12 [d, CH, 1H (JH–P 6 Hz)]; 31P NMR: (CDCl3) d −13.7;
13C NMR: (CDCl3) d 14.8 (s, SMe), 117.6 (s, CB1), 124.4 (s, CB3),
+
=
(w), C N stretch; Mass spectrum [EI(+)]: m/z 861.1160 [M] ,
481.5463 [Ru(PhPNO)]+; HPLC: RT 4.13 min.
[RuCl(PhPNOMe)(PPh3)]BPh4 (6). [RuCl2(PPh3)3] (189 mg,
0.20 mmol) and PhPNOMe (78 mg, 0.20 mmol) were suspended in
methanol (15 mL) and the mixture heated under reflux overnight.
The solution became red and after cooling to room temperature,
2196 | Dalton Trans., 2008, 2190–2198
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was filtered in air and a small amount of a brown solid was
removed. A methanolic solution of sodium tetraphenylborate
(337 mg, 0.99 mmol, in 3 mL of non pre-dried methanol) was
added to the filtrate. A red/orange precipitate formed and was
collected by filtration in air, washed with methanol and dried in
vacuo. [RuCl(PhPNOMe)(PPh3)]BPh4 was obtained as an orange
solid (128 mg, 58%). Elemental analysis, found (required)%: C
formed and was collected by filtration in air, washed with diethyl
ether and dried in vacuo. [{RuCl(PhPNSMe)}2Cl]X was obtained
as a red powder (84 mg, 98% X = BPh4−; 30% X = PF6−).
Elemental analysis, found (required)%: (X = BPh4−) C 63.03
(62.92), H 4.54 (4.45), N 1.98 (1.93), Cl 5.45 (7.33); FTIR (Nujol
−1
=
mull), cm : 1579 (w), C N stretch; Mass spectrum [ES(+)]: m/z
1131 [M]+, 1100 [M − Cl]+, 548 [M − (PhPNSMe + 2Cl)]+; HPLC:
RT 0.97 min.
72.62 (73.35), H 5.29 (5.16), N 1.53 (1.26), Cl 3.03 (3.18); FTIR
−1
=
(Nujol mull), cm : 1579 (m), 1638 (m), C N stretch; Mass
spectrum [ES(+)]: m/z 794 [M]+, 758 [M − Cl]+; HPLC: RT
[RuCl(PhPNO-g6C6H5)]BPh4 (11). Diruthenium-tetrachloro-
bis(4-cymene) (127 mg, 0.21 mmol) and PhPNOPh (190 mg,
0.42 mmol) were dissolved in methanol (15 mL) and the mixture
was heated at reflux for five hours. The solution remained
orange. After cooling to room temperature a solution of sodium
tetraphenylborate (377 mg, 1.09 mmol) in non pre-dried methanol
(∼5 mL) was added. An orange precipitate formed which was
collected by filtration in air, washed with methanol and dried
in vacuo. [RuCl(PhPNOPh-g6C6H5)]BPh4 was obtained as an
orange powder (284 mg, 75%). Elemental analysis, found (re-
0.82 min.
[RuCl(PhPNOPh)(PPh3)]BPh4 (7). Procedure as for the syn-
thesis of 7, using [RuCl2(PPh3)3] (685 mg, 0.72 mmol), PhPNOPh
(327 mg, 0.72 mmol) and sodium tetraphenylborate (1.223 g,
3.57 mmol). A red precipitate formed and was collected by
filtration in air, washed with methanol and dried in vacuo.
[RuCl(PhPNOPh)(PPh3)]BPh4 was obtained as a red solid
(494 mg, 59%). Elemental analysis, found (required)%: C 73.90
(74.59), H 4.86 (5.06), N 1.20 (1.19), Cl 2.61 (3.02); FTIR (Nujol
−1
quired)%: C 72.16 (72.33), H 5.32 (4.86), N 1.21 (1.53), Cl 2.58
=
mull), cm : 1580 (w), C N stretch; Mass spectrum [ES(+)]: m/z
−1
=
(3.88); FTIR (Nujol mull), cm : 1580 (m), C N stretch; Mass
856 [M]+, 822 [M − Cl]+, 559 [M − (Cl + PPh3)]+; HPLC: RT
spectrum [FAB(+)]: m/z 594.1 [M]+, 558.1 [M − Cl]+, 482.1 [M −
1.10 min.
(Cl + Ph)]+; HPLC: RT 0.87 min.; 1H NMR: (d6-DMSO) d 2.43 [m,
6
6
g -C6H5 H1, 1H (JH–H 7 Hz)], 4.46 [d, g -C6H5 H2, 1H (JH–H 6 Hz)],
4.83 [d, g -C6H5 H3, 1H (JH–H 6 Hz)], 5.79 [m, g -C6H5 H4, 1H (JH–H
[RuCl(PhPNSMe)(PPh3)]BPh4 (8). Procedure as for the syn-
thesis of 7, using [RuCl2(PPh3)3] (119 mg, 0.12 mmol), PhPNSMe
(51 mg, 0.12 mmol) and sodium tetraphenylborate (212 mg,
0.62 mmol). A red/brown precipitate formed and was collected by
filtration in air, washed with methanol and diethyl ether and dried
in vacuo. [RuCl(PhPNSMe)(PPh3)]BPh4 was obtained as a pink
solid (76 mg, 54%). Elemental analysis, found (required)%: C 73.08
6
6
6
7 Hz)], 5.95 [m, g -C6H5 H5, 1H (JH–H 7 Hz)], 6.73–8.01 (m, Ph,
38H), 8.79 [d, CH, 1H (JH–P 1 Hz)]; 31P NMR: (d6-DMSO) d 42.8;
13C NMR: (d6-DMSO) d 30.1 (s, g -C6H5 H1), 83.5 (s, g -C6H5
6
6
6
6
6
H2), 92.0 (s, g -C6H5 H5), 92.2 (s, g -C6H5 H4), 98.2 (s, g -C6H5
H6), 103.5 (s, g -C6H5 H3), 118.2–155.8 (Ph), 162.4–164.2 (BPh4−),
6
175.4 [d, CH (JC–P 7 Hz)].
(72.31), H 5.08 (5.09), N 1.33 (1.24), Cl 2.12 (3.14); FTIR (Nujol
−1
=
mull), cm : 1579 (w), C N stretch; Mass spectrum [FAB(+)]: m/z
810.3 [M]+, 775.2 [M − Cl]+, 548.0 [M − PPh3]+, 512.0 [M − (Cl +
PPh3)]+; HPLC: RT 0.99 min.
Catalytic hydrosilyation of acetophenone
The method utilised to ascertain the activity of the complexes was
derived from that of Nishibayashi et al.23 The catalyst (0.01 mmol,
1 mol%) was dissolved in tetrahydrofuran (10 mL), in a Schlenk
flask. Acetophenone (117 lL, 1 mmol) was added and the reaction
mixture was heated to 65 ◦C. An excess of diphenylsilane (371 lL,
2 mmol) was added and the flask sealed. Heating continued for a
further one hour. After cooling to room temperature the reaction
mixture was quenched with non pre-dried methanol (1 mL), to
consume the remaining silane. After stirring at room temperature
for 30 minutes, 0.2 M hydrochloric acid (2.5 mL) was added to
hydrolyse the silyl ether. The reaction mixture was stirred overnight
in air and was then analysed by GC.
When utilised as an additive silver triflate (0.0026 g, 0.01 mmol)
was added to the Schlenk flask with the solid complex, before THF
addition. The flask was covered with aluminium foil to prevent
photolytic decomposition of any silver salts.
Percentage conversions were calculated from the ratio of areas
of the eluted peaks of acetophenone and 1-phenylethanol. Cali-
bration using standards showed the two substances to elute in a
1 : 1 ratio when equal amounts of both were injected. No correction
factors were therefore applied to the areas. The temperature profile
for GC analysis: maintain 60 ◦C for 2 min, increase 10 ◦C per min
for 14 min, maintain 200 ◦C for 4 min. Injector temperature:
220 ◦C, detector temperature: 300 ◦C.
[RuCl(PhPNOMe)}2Cl]Cl
(9). Diruthenium-tetrachloro-
bis(4-cymene) (49 mg, 0.08 mmol) and PhPNOMe (63 mg,
0.16 mmol) were dissolved in methanol (15 mL) and the mixture
was heated under reflux overnight. The solution became purple
in colour and after cooling to room temperature the solvent was
removed in vacuo. An oily solid remained and was titurated with
diethyl ether (10 mL) and a precipitate formed. This was collected
by filtration under nitrogen, washed with diethyl ether and dried in
vacuo. [{RuCl(PhPNOMe)}2Cl]Cl was obtained as an air sensitive,
blue/purple solid (62 mg, 68%). FTIR (Nujol mull), cm−1: 1590
=
(m), C N stretch; Mass spectrum [ES(+)], in acetonitrile: m/z 614
[RuCl(MeCN)2(PhPNOMe)]+, 573 [RuCl(MeCN)(PhPNOMe)]+,
in methanol: m/z 564 [RuCl(MeOH)(PhPNOMe)]+; HPLC: RT
1.22 min.
[{RuCl(PhPNSMe)}2Cl]X (X = BPh4−, PF6−) (10). This
complex was formed in a reaction analogous to that used in
the synthesis of 9, but with slight modification. Diruthenium-
tetrachlorobis(4-cymene) (36 mg, 0.06 mmol) and PhPNSMe
(48 mg, 0.12 mmol) were reacted using the procedure described
above and, after cooling to room temperature, a solution of
sodium tetraphenylborate (204 mg, 0.60 mmol) (or ammonium
hexafluorophosphate, 0.60 mmol) in non pre-dried methanol
(∼5 mL) was added to the resulting red solution. A pink precipitate
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Catalytic hydrogenation of styrene
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a Schlenk flask was added styrene (571 lL, 5 mmol) and the
flask sealed. This was degassed using three freeze–pump–thaw
cycles and after warming to room temperature, hydrogen gas
was permitted into the flask at a pressure of 2 atmospheres.
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The temperature profile for GC analysis: maintain 60 ◦C for 2 min,
◦
◦
increase 10 C per min for 14 min, maintain 200 C for 19 min.
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Acknowledgements
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2198 | Dalton Trans., 2008, 2190–2198
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The Royal Society of Chemistry 2008
©