Substituent dependence of the reactions of [RuCl2(PPh 3)3] with bulky aromatic thiols

Article abstract of DOI:10.1039/b515244e

The reactions of [RuCl₂(PPh₃)₃] with bulky aromatic thiolates were investigated to under their dependence on substituents. The geometry of the Ru metal center was found distorted trigonal bipyramidal with the C and P atoms occupying the axial positions. The thiolate arene groups were directed away from the bulky phosphine ligand to give a cup-like shape to the molecule. The results show that corresponding thiols with ethyl and isopropyl groups give a paramagnetic Ru (III) complex and a tetrahedral Ru (II) complex respectively.

Full text of DOI:10.1039/b515244e

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Substituent dependence of the reactions of [RuCl2(PPh3)3] with bulky
aromatic thiols†‡
Peter T. Bishop,a Andrew R. Cowley,b Jonathan R. Dilworth,*b Andrew J. Saundersb and
John G. Woollard-Shoreb
Received 26th October 2005, Accepted 28th November 2005
First published as an Advance Article on the web 10th January 2006
DOI: 10.1039/b515244e
2,4,6-Trialkylbenzenethiols react with [RuCl2(PPh3)3] to give
Ru products with the alkyl substituents forming M–C r
bonds, carbene, carbene with a S a-heteroatom, agostic
hydrogen interaction or a simple tetrahedral Ru(II) species,
depending on the substituent.
Sterically hindered thiolates have been studied extensively owing to
their ability to generate metal complexes with unusual geometries.1
Such complexes are potentially capable of binding small molecules,
but this ability is a sensitive function of the nature of the
substituents on the thiolate ligand. We have previously reported
the synthesis of complexes of the type [Re(SAr)3(N2)(PPh3)]
(Ar = 2,4,6-Pri3C6H2).2 We now report our attempted syntheses
of analogous Ru systems by the reaction of [RuCl2(PPh3)3]
with aromatic thiolates. Previously complexes of the type
[Ru(SAr)4], [Ru(SAr)4(L)] and [Ru(SAr)4(NO)]− (L = MeOH,
aJohnson-Matthey Technology Centre, Blounts Court, Sonning Common,
Reading, UK RG4 9NH
bChemistry Research Laboratory, University of Oxford, 12 Mansfield Road,
Oxford, UK OX1 3TA. E-mail: jon.dilworth@chem.ox.ac.uk; Fax: 01865-
272690; Tel: 01865-285151
DMSO, ButCN, MeCN or CO, Ar = 2,3,5,6-Me4C6H2 or 2,4,6-
4
Pri3C6H2),3 [Et4N][Ru(SAr)3(C CPh)Cl] (Ar = 2,6-Me2C6H3),
=
† Complex 1: [RuCl2(PPh3)3] (0.60 g; 0.63 mmol) was dissolved in degassed
acetone, Htmt (0.29 g; 1.90 mmol) and triethylamine (0.39 g; 3.86 mmol)
were added. The solution was heated under reflux, MeOH (20 mL) added
and the solution left to give X-ray quality crystals from the reaction
solution. Yield: 0.18 g, 35%. Elemental analysis for C45H47PRuS3 calcd:
C 66.2, H 5.8, found: C 66.2, H 5.9%. Selected data: 1H NMR (300 MHz,
(acetone-d6) d 7.79–7.73 (m, 6H, PPh3), 7.53–7.50 (m, 9H, PPh3), 6.88 (s,
Ph, 2H), 6.60, (s, Ph, 1H), 6.54, (s, Ph, 2H), 6.02, (s, Ph,1H), 2.43 (d, 2H
3JPH = 6.6 Hz, CH2), 2.30 (s, 3H, CH3), 2.25 (s, 6H, CH3), 2.15 (s, 6H, CH3),
[Ru(arene)(SAr)2] (Ar = 2,6-Me2C6H3 or 2,4,6-Pri3C6H2),5 and
5
[Cp*Ru(Sdmp)] (Sdmp = 2,6-dimesitylthiophenol, Cp* = g -
C5Me5)6 have been described. However, reports of Ru(II) com-
plexes of bulky thiolates with tertiary phosphine co-ligands have
been restricted to [Ru(SAr)2(PPh3)] (Ar = 2,6-Ph2C6H3).7
Reaction of [RuCl2(PPh3)3] with 3 equiv. of Htmt (Htmt =
2,4,6-trimethylthiophenol) and triethylamine in dry acetone under
dinitrogen gave a dark coloured solution. Following partial
evaporation of the solvent, the addition of MeOH gave very dark,
almost black crystals of [Ru(SC6H2Me2CH2)(tmt)2(PPh3)] (1) after
standing at room temperature. The isolated yield of crystalline
product was 35%. Spectroscopic data for 1 are consistent with
1
2.02 (s, 3H, CH3), 1.40 (s, 6H, CH3), 31P{ H} NMR (121 MHz, CD2Cl2):
1
d 27.3 (s, Ru–PPh3), 13C{ H} NMR (75 MHz, CD2Cl2): d 30.8 (CH2),
22.0 (CH3), 20.9 (CH3), 20.6 (CH3), 20.5 (CH3), 19.3 (CH3). Complex
2: [RuCl2(PPh3)3] (0.60 g; 0.63 mmol) was dissolved in degassed MeOH
and 2 equiv. of Htmt was added and a two fold excess of triethylamine.
The solution was stirred at room temperature. The solution was filtered to
give the complex and washed with MeOH. Yield: 0.35 g, 57%. Elemental
analysis for C54H50P2RuS2·C3H6O calcd: C 69.6, H 5.7; found: C 68.7, H
5.9%. Selected data: 1H NMR (300 MHz, CD2Cl2) d 14.15 (t, 1H 3JPH
=
T = 150 K. l(Mo-Ka) = 0.617 mm−1, 66 921 reflections measured, 18 115
unique, 13 264 reflections with I > 3r(I) used in refinement (Rint = 0.057).
Final R = 0.0498, wR = 0.0579, GoF = 1.0422. 2: C57H56OP2RuS2, Dark-
7.5 Hz, CH), 7.12–6.97 (m, 30H, PPh3), 6.60 (s, Ph, 2H), 6.07 (s, Ph, 1H),
6.06 (s, Ph, 1H), 2.18, (s, 3H, CH3), 2.17, (s, 3H, CH3), 2.08 (s, 6H, CH3),
1
1.72 (s, 3H, CH3);31P{ H} NMR (121 MHz, CDCl3): d 29.5, (s, Ru–PPh3)
1
46.4, (s, Ru–PPh3), 13C{ H} NMR (75 MHz, CDCl3): d 160.5 (Ru CH),
=
¯
brown fragment, M = 984.22, triclinic; space group ◦P1, a = 11.6056(2),
◦
˚
22.5 (CH3), 20.9 (CH3), 20.3 (CH3), 20.0 (CH3). Complex 3: Synthesized
from equilibrium of 1 and 2. The solution was left to give complex 3 as a
crop of X-ray quality crystals following the addition of cyclohexane. Yield:
approx. 20%. Elemental analysis for C63H60P2RuS3 calcd: C 70.5, H 5.7;
found: C 70.2, H 6.7%. Selected data: 1H NMR (300 MHz, CD2Cl2) d 2.47
(s, 3H, CH3), 2.41 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.23 (s, 3H, CH3), 1.83 (s,
b = 13.4790(2)◦, c = 16.3892(3), A, a = 80.9584(8) , b = 75.9086(8) ,
3
˚
c = 81.6204(8) , V = 2440.24(7) A , Z = 2, T = 150 K. l(Mo-Ka) =
0.512 mm−1, 42 120 reflections measured, 11062 unique, 6861 reflections
with I > 3r(I) used in refinement (Rint = 0.067). Final R = 0.0354, wR =
0.0384, GoF = 1.1137. 3: C75H84P2RuS3, dark brown crystals, M = 1244.71,
¯
˚
triclinic; space g◦roup P1, a = 10.9358(2), b = 13.5984◦(2), c = 23.3454(4) A,
3H, CH3), 1.78 (s, 3H, CH3), 1.69 (s, 3H, CH3), 1.59 (s, 3H, CH3); 31P{ H}
1
◦
3
˚
a = 100.0944(6) , b = 103.0326(6) , c = 103.5247(6) , V = 3191.77(9) A ,
2
Z = 2, T = 150 K. l(Mo-Ka) = 0.437 mm−1, 47 600 reflections measured,
NMR (121 MHz, CD2Cl2): d 47.8 (d, JPP = 15.8 Hz, Ru–PPh3) d 31.8
(d, 2JPP = 15.8 Hz, Ru–PPh3); 13C{ H} NMR (75 MHz, CD2Cl2): d 164.5
1
14495 unique, 8061 reflections with I > 3r(I) used in refinement (Rint
=
=
(Ru C). Complex 4: [RuCl2(PPh3)3] (0.60 g; 0.63 mmol) was dissolved in
0.069). Final R = 0.0489, wR = 0.0567, GoF = 1.1180. 4: C54H66PRuS3,
¯
degassed methanol, Htet (0.37 g; 1.90 mmol) and triethylamine (0.39 g;
3.86 mmol) were added. The solution was stirred for 2 h, filtered and
the filtrate left to give X-ray quality crystals from the reaction solution.
Elemental analysis for C54H66P1RuS3 calcd: C 68.8, H 7.1; found: C 69.3, H
7.4%. ES-MS m/z = 943.3085 (M+). Calc mass for (C54H66P1RuS3) m/z =
943.3108. Complex 5: Htipt (0.30 g; 1.27 mmol) and triethylamine (0.25 g;
2.47 mmol) were added to [RuCl2(PPh3)3] (0.60 g; 0.63 mmol) in acetone
(30 mL) and stirred at room temperature for 30 min. The brown solution
rapidly changed to green and the complex crystallised out as dark green
crystals on standing at 3 ◦C. Elemental analysis for C66H76P2RuS2·C6H12O2
calcd: C 71.3, H 7.3; found: C 70.3, H 6.5%.
dark brown block crystals, M = 943.36, triclinic; space group P1, a =
◦
˚
12.2271(2), ◦b = 12.4745(2), c = 18.4853(2) A, a = 94.6820(6) , b =
◦
3
˚
106.8104(6) , c = 110.8996(6) , V = 2467.02(6) A , Z = 2, T = 150 K.
l(Mo-Ka) = 0.511 mm−1, 33 343 reflections measured, 11 158 unique,
9578 reflections with I > 3r(I) used in refinement (Rint = 0.025). Final
R = 0.0286, wR = 0.0315, GoF = 1.1121. 5: C72H88O2P2RuS2, dark green
¯
block crystals, M = 1212.64, triclinic; space group P1, a = 12.1170(2),
◦
◦
˚
b = 13.7658(2), c = 20.7248(3) A, a = 106.9647(6) , b = 91.7024(6) ,
◦
3
˚
c = 98.7577(6) , V = 3257.86(9) A , Z = 2, T = 150 K. l(Mo-Ka) =
0.397 mm−1, 41 524 reflections measured, 14 748 unique, 10 682 reflections
with I > 3r(I) used in refinement (Rint = 0.043). Final R = 0.0364, wR =
0.0405, GoF = 1.0985. CCDC reference numbers 257071–257073, 287812
and 287813. For crystallographic data in CIF or other electronic format
see DOI: 10.1039/b515244e
‡ Crystal data: 1: C45H47PRuS3, black plate crystals, M = 816.11, triclinic;
¯
˚
space group P1, a = 12.1363(2), b = 16.9452(2), c = 20.2967(2) A, a =
◦
◦
◦
3
˚
84.3205(4) , b = 75.0315(5) , c = 89.0985(5) , V = 4012.42(9) A , Z = 4,
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the presence of the cyclometallated thiolate ligand, the r-bonded
is again approximately trigonal bipyramidal with a PPh3 group
and thiolate sulfur now in the apical sites. The presence of the
carbene ligand is shown by the contraction of the Ru–C7 distance
1
carbon C7 appearing at d 30.8 ppm in the 13C NMR. The H
NMR spectrum shows three resonances each 6H corresponding
to the methyl groups of the two unmetallated ligands. This is due
to restricted rotation about the C–S bond which results in the two
o-Me groups of each thiolate being chemically inequivalent from
each other. The 31P NMR shows as a singlet at d 27.3 ppm due to
the single phosphorus.
˚
˚
from 2.343(6) A in 1 to 1.891(3) A in 2. The air stable complex
˚
=
[Ru( CHPh)(N(PPh2S)2)2] has a Ru–C distance of 1.88(2) A,
typical for Schrock-type carbenes.8
The geometry of the Ru metal centre in 1 is distorted trigonal
bipyramidal with the C and P atoms occupying the axial sites.
The three thiolate arene groups are directed away from the
bulky phosphine ligand to give a cup-like shape to the molecule
reminiscent of that found in [Re(tipt)3(N2)(PPh3)]2 and [Mo-
(tipt)3(CO)2] (tipt = 2,4,6-triisopropylthiolate).1a Metallation of
o-Me groups of aromatic thiolates is well known and has been
reported to occur for the complex [Ru(SC6H-2,3,5,6-Me4)4(NO)]−
on standing in methanol.3
When reaction 1 was repeated with 2 equiv. of thiol, a new
complex [Ru(SC6H2Me2CH)(tmt)(PPh3)2] (2) was isolated as X-
ray quality crystals in 57% yield. An ORTEP representation
of the structure of complex 2 appears in Fig. 1, together with
selected bond lengths and angles. The geometry about the Ru
Scheme 1
The identity of the product as a carbene complex is confirmed
1
by H NMR which shows a low-field triplet of intensity 1H at d
3
=
14.15 ppm assigned to the CH Ru proton ( JHP = 7.5 Hz). In the
13C NMR the low field carbene resonance appears at 160.5 ppm.
The 31P NMR shows a singlet at d 29.5 ppm and a broad peak at
46.4 ppm. The broad nature of the second signal combined with
lack of P–P coupling suggests that one of the phosphine ligands
is dissociating in solution. The o-Me carbons in the 13C NMR
are equivalent on the unmetallated thiolate at d 22.5 ppm, the
remaining methyl resonances appear at 20.9, 20.3 and 20.0 ppm.
The 31P NMR spectrum of the reaction mixture in acetone with
different thiolate ratios shows that both complexes 1 and 2 are
present. The ratios are dependent on stoichiometry; with 2 equiv.
of thiol they are 80% 1 20% 2 and with 3 equiv. of thiol 80% 2 20% 1.
There are two other unidentified Ru(II) species present in solution
in small amounts in each case. Also if pure complex 1 is dissolved
in acetone and PPh3 is added there is a slow conversion to complex
2. Conversely when pure 2 is treated with excess thiol in acetone
solution it is slowly converted to complex 1. The two species are in
equilibrium in the reaction mixtures and are separated by virtue
of their differing solubilities, complex 1 being more soluble than 2.
Fig. 1 ORTEP diagrams of complexes 2 (top) and 3 (bottom). Selected
bond lengths for 2 (A): Ru(1)–C(7) 1.891(3), Ru(1)–S(1) 2.4143(8),
S(1)–C(1) 1.730(3), C(1)–C(6) 1.407(4), C(6)–C(7) 1.433(4). Only the ipso
carbons of PPh3 are shown for clarity.
˚
1268 | Dalton Trans., 2006, 1267–1270
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Over a 24 h period at room temperature in CD2Cl2 solution
the equilibrium mixture of 1 and 2 slowly converts (about 10% as
judged by NMR) to a third species [Ru(SC6H2Me2CSC6H2Me3)-
(tmt)(PPh3)2] (3), and the process can be followed by 31P NMR in
CD2Cl2.
from complex 1 to 2 and 3. All three structures show evidence
for shortening of the C6–C7 bond from the arene ring to the
Ru-bound carbon and asymmetry in the C–C distances within
the ring, this being most pronounced for 3. There is, however, no
evidence from the bond distances for any olefinic interaction of
the arene-CHn groups with the metal as observed in complexes
such as [Ru(1,2-{(CH2)2C6H4)}(PMe2Ph)3].9
The mechanism of formation of complexes 2 and 3 is not known
at this point. By analogy with the formation of a carbene ligand
from a methyl group on iridium10 it possible that formation of
2 from 1 occurs with hydrogen evolution. However, interfering
peaks prevented the observation of the characteristic peak for
H2 in solution by 1H NMR and no hydrogen evolution was
detected by gas-chromatographic analysis. We cannot rule out
proton abstraction from the cation formed from 1 on addition
of phosphine and loss of thiolate anion. We are currently
investigating the details of the mechanism of conversion of 1 to 2.
Chelated carbene complexes with a sulfur co-donor are un-
common and a rare example is the nickel complex with an
imidazoylcarbene ligand bearing two 2-C6H4S substituents at the
1 and 3 positions. This carbene ligand is, however, not obtained
by C–H activation but indirectly from CS2.11
Ruthenium carbene complexes are of course extremely well
known and the complexes described here have some analogy
Scheme 2 Interconversion of complexes.
to the second generation Hoveyda–Grubbs catalysts12 of the
i
=
type [RuCl2( CH-o-OPr C6H4)(4,5-dihydroIMES)] (IMES = 1,3-
The overall geometry about the Ru in complex 3 is again
distorted trigonal bipyramidal with one triphenylphosphine and a
thiolate sulfur in the apical sites. The Ru–S and Ru–P distances are
close to the values found for complex 1. The most striking feature
of the structure is the presence of the new carbene ligand with a
thiolate group replacing the hydrogen on the carbene carbon of
complex 2. Fig. 2 summarises and compares the bond distances
within the chelated methyl and carbene ligands for complexes
1 and 3. The formation of the metal carbene bond is apparent
from the substantial contraction in the Ru–C distance in moving
bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) with the obvious
difference that here the thiolate sulfur is almost certainly more
strongly bound than the 2-alkoxy substituent. There is no reac-
tivity of these thiolate carbene complexes with olefins and other
small molecules.
The reaction of [RuCl2(PPh3)3] with 3 equiv. of Htet (Htet =
2,4,6-triethylthiophenol) in acetone in the presence of triethy-
lamine also did not give the expected complex of the type
[RuL(SAr3)(PPh3)]− core isoelectronic with the known Re com-
plex, but the formally Ru(III) species [Ru(tet)3(PPh3)] (4). Presum-
ably the anionic Ru(II) species is oxidized during the reaction.
Cyclic voltammetry of 4 recorded in DMF confirms a reversible
one-electron reduction at E 1 = −928 mV vs. NHE and no
2
oxidation was observed. The EPR measured on 4 in the solid state
gave a rhombic set of g-values 2.096, 2.044 and 2.014. These EPR
g-values are similar to the Ru(III) complex [Ru(dppbt)3] (dppbt =
2-diphenylphosphinobenzenethiolate) that can be oxidized in
acetonitrile to form the observable metal-coordinated Ru(III)–thiyl
radical complex.13 The reported g-values for coordinated thiyls
with Co, Ga and Fe14 are less anisotropic than 4, but coordination
to a 2nd row metal such as Ru is likely to increase anisotropy.
However, the similarity to the values reported for [Ru(dppbt)3]
suggests that this is a Ru(III) complex rather than containing a
thiyl radical.
The X-ray crystal structure of 4 reveals that a methylene
hydrogen of an ethyl group approaches closely to the Ru and H(2)
is within the range normally found for metal–hydrogen agostic
interactions. As a result of the formation of this chelate ring the
Ru–S(l) bond lies in approximately the same plane as that of
the thiolate aryl group, while the remaining Ru–S bonds adopt
the more usual conformation perpendicular to the corresponding
phenyl rings. The same geometry is seen in [Re(dmt)3(PPh3)]]
(dmt = 2,6-dimethylthiolate),2 where it is clear that a hydrogen
˚
Fig. 2 Selected bond lengths (A) of complexes 1 (left) and 3 (right).
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When the reaction of [RuCl2(PPh3)3] is carried out with
three equivalents of Htipt in acetone a further new complex
[Ru(tipt)2(PPh3)2] (5) can be isolated after partial evaporation
of the solvent. There is no evidence for formation of a complex
with the Ru(SAr)3(PPh3) structural motif, presumably due to the
increased size of the isopropyl substituents. The crystals of 5
exhibit pronounced pleichroism, appearing dark green or reddish–
brown depending on orientation. The overall geometry about the
Ru(II) is distorted tetrahedral with no evidence of any interaction
between the Ru atom and adjacent H atoms. The interplanar angle
between the groups P–Ru–P and S–Ru–S is 66.7◦. The shortest
˚
˚
Ru · · · H distances are 2.93 A (to H(501)) and 3.04 A (to H(321)).
The reactions with Ru(II) of alkyl substituted arylthiolates
show a strong dependence on the alkyl substituent. 2,4,6-
Trimethylbenzenethiol reacts with [RuCl2(PPh3)3] to give a Ru(IV)
complex with a Ru–C bond to a 2-methylene group which is in
a reversible equilibrium with a carbene complex. In solution this
reacts further to give a complex of a carbene with a S a-heteroatom
derived from the S–C coupling of two aromatic thiolate ligands.
The corresponding thiols with ethyl and isopropyl groups give a
paramagnetic Ru(III) complex and a tetrahedral Ru(II) complex
respectively, neither of which have Ru–C bonds.
Acknowledgements
We thank EPSRC EPR national service for the EPR measurements
and Johnson-Matthey for the gift of RuCl3·3H2O.
Notes and references
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Fig. 3 ORTEP diagrams of complex 1 (top), 4 (centre) and 5 (bottom).
Diagram of complex 1 is one of two crystallographically distinct structures.
Only the major orientation of the disordered ethyl or isopropyl groups is
shown for 4 and 5, respectively. Only the ipso carbons of PPh3 are shown
for clarity.
11 D. Sellmann, W. Prechtel, F. Knoch and M. Moll, Organometallics,
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of the one of the methyl substituents approaches closely to Re
˚
(Re–H 2.07 A), as an agostic interaction.
1270 | Dalton Trans., 2006, 1267–1270
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