(Indenyl)ruthenium complexes containing 1,1′-bis(diphenylphosphanyl)- ferrocene (dppf) and thiolato ligands: Synthesis, X-ray structure analysis, electrochemistry and magnetic studies

Article abstract of DOI:10.1002/ejic.200600879

The reaction of [(Ind)Ru(dppf)Cl] (Ind = η⁵-C ₉H₇) (2) with RSNa {R = Me, Et, Ph, Ph ₂P(CH₂)₂) proceeds in MeOH to give [(Ind)Ru(dppf)(SR)] {R = Me (3), Et (4), Ph (5), Ph₂P(CH ₂)₂ (7)}, as well as [(Ind)Ru(dppf)H] (6), in all cases except for R = Ph. This R-dependence of the product mixture was rationalised on a RS^-/MeOH ? MeO^-/RSH equilibrium involving the interaction of thiolate (RS^-) with MeOH, and the relative nucleophilicities of RS^- versus MeO^-; 6 arose from β-H elimination from an OMe derivative. Cyclic voltammetric measurements on 2, 3, 4 and 5, as well as the Cp (η⁵-C₅H₅) and Cp* (η⁵-C₅Me₅) analogues of 2, indicated that the formal oxidation potentials for [LRu(dppf)Cl] complexes {L = Ind (2), Cp (2A) and Cp* (2B)} occurred in the order Cp* < Ind < Cp, correlating with the more electron-donating groups lowering the oxidation potentials. EPR experiments performed on the one-electron oxidised forms of 3 and 5 indicated paramagnetic compounds with g values close to 2, while the two-electron oxidised forms of 3 and 5 were diamagnetic. All the complexes were characterised spectroscopically, and 5 and 6 also crystallographically. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200600879

FULL PAPER
DOI: 10.1002/ejic.200600879
(Indenyl)ruthenium Complexes Containing 1,1Ј-Bis(diphenylphosphanyl)-
ferrocene (dppf) and Thiolato Ligands: Synthesis, X-ray Structure Analysis,
Electrochemistry and Magnetic Studies
Sin Yee Ng,[a] Weng Kee Leong,*[a] Lai Yoong Goh,*[a] and Richard D. Webster[b]
Keywords: (Indenyl)ruthenium / Thiolates / dppf / Cyclic voltammetry / ESR / Ruthenium
The reaction of [(Ind)Ru(dppf)Cl] (Ind = η5-C9H7) (2) with
RSNa {R = Me, Et, Ph, Ph2P(CH2)2} proceeds in MeOH to give
[(Ind)Ru(dppf)(SR)] {R = Me (3), Et (4), Ph (5), Ph2P(CH2)2 (7)},
as well as [(Ind)Ru(dppf)H] (6), in all cases except for R = Ph.
This R-dependence of the product mixture was rationalised
dation potentials for [LRu(dppf)Cl] complexes {L = Ind (2),
Cp (2A) and Cp* (2B)} occurred in the order Cp* Ͻ Ind Ͻ
Cp, correlating with the more electron-donating groups low-
ering the oxidation potentials. EPR experiments performed
on the one-electron oxidised forms of 3 and 5 indicated para-
on a RS–/MeOH ↔ MeO–/RSH equilibrium involving the in- magnetic compounds with g values close to 2, while the two-
teraction of thiolate (RS–) with MeOH, and the relative nu-
cleophilicities of RS– versus MeO–; 6 arose from β-H elimi-
nation from an OMe derivative. Cyclic voltammetric mea-
surements on 2, 3, 4 and 5, as well as the Cp (η5-C5H5) and
Cp* (η5-C5Me5) analogues of 2, indicated that the formal oxi-
electron oxidised forms of 3 and 5 were diamagnetic. All the
complexes were characterised spectroscopically, and 5 and 6
also crystallographically.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
the Group 6, 7 and 9 metals.[6] Recently reports of a few
(indenyl)Ru complexes carrying N-containing ligands have
emerged,[7] but to date there is only one report of examples
carrying S-donor ligands, viz. EtS and EtMeS.[8]
Introduction
The development of the chemistry of indenyl complexes
of ruthenium(II) could be considered to date from the high-
yield synthesis of [(Ind)Ru(PPh3)2Cl] (Ind = η5-C9H7) (1),[1]
In recent work, we have performed a comparative
study of the reactivity of [(η6-C6Me6)Ru(dppf)Cl] and
[CpRu(dppf)Cl] (2A) with various nucleophiles, including S
donor ligands.[9] It is therefore of interest to include the
indenyl analogue of these in the comparison. This paper
describes the reactions of [(Ind)Ru(dppf)Cl] (2) with simple
alkyl/aryl monothiolates, RS– (R = Me, Et and Ph), to com-
pare with reported analogous reactions of [(Ind)Ru(PPh3)2-
Cl] (1) with EtSNa,[8] and the comparative electrochemistry
studies of [LRu(dppf)Cl] {L = Ind (2), Cp (2A) and Cp*
(2B)} and [LRu(LЈ2)Cl] (L = Ind, Cp and Cp*; LЈ2 = dppm,
dppe and dppf).
which superseded [(Ind)Ru(CO)2]2,
a low-yield com-
pound,[2] as the common source material for the synthesis
of (indenyl)ruthenium complexes. A recently improved syn-
thesis of [(Ind)Ru(COD)Cl][3] has provided yet another al-
ternative starting material. The initial interest in the indenyl
ligand stems from its resemblance to η5-cyclopentadienyl
Cp/Cp* ligands, the ‘pillar’ ligands of transition-metal or-
ganometallic chemistry; subsequent interest was heightened
by the observation of the so-called indenyl effect, an en-
hancement of reactivity of the complex brought about by
facile ring slippage from η5 to η3 involving aromatisation
of the benzene ring.[4]
In the last decade Gimeno’s group have carried out inten-
sive studies, with emphasis on reactivity, including catalytic Results and Discussion
aspects, particularly of vinylidene and allenylidene deriva-
[(Ind)Ru(dppf)Cl] (2) was synthesised from phosphane
tives of ruthenium half-sandwich complexes.[5] Prior to
these, there had been limited reports from various groups
on studies of indenyl complexes of Fe, followed by those of
substitution of [(Ind)Ru(PPh3)2Cl] (1), following a pub-
lished procedure for the Cp analogue.[1]
[a] Department of Chemistry, National University of Singapore,
3 Science Drive, Singapore 117543
Fax: +65-6779-1691
Chloro Substitution
(a) Reaction of 2 with RSNa [R = Me (3), Et (4), Ph
(5)] and Solvent Dependence
E-mail: chmgohly@nus.edu.sg
chmlwk@nus.edu.sg
[b] Division of Chemistry and Biological Chemistry, Nanyang
Technological University,
The reaction of 2 with an excess of RSNa in alcoholic
solvent (MeOH or EtOH) at room temperature gave
Singapore 637616
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S. Y. Ng, W. K. Leong, L. Y. Goh, R. D. Webster
FULL PAPER
[(Ind)Ru(dppf)(SR)] in R-dependent yields. (NOTE: with 1
This postulation is in agreement with our observation
equiv. of RSNa, the reaction at r.t. did not reach comple- that the reaction of 2 with MeSNa will not proceed in THF,
tion even after 18 h.) In the cases of R = Me and Et, a despite refluxing for 2 h, but went to completion within
hydride complex, [(Ind)Ru(dppf)H] (6), was also isolated in 15 min at 65 °C upon addition of 1/5 volume of MeOH. We
about 20% yield (Scheme 1).
similarly carried out, on an NMR scale, Hidai’s reaction of
1, using MeSNa, and found that in refluxing THF, [(Ind)-
Ru(PPh3)2(SMe)] was the only product, while in refluxing
MeOH, the hydride species [(Ind)Ru(PPh3)2H] was also
2
formed [1H NMR (C6D6): δ = –15.39 (t, JHP = 33.8 Hz)
2
vs. lit. values in CDCl3: δ = –15.40 (t, JHP = 31.6 Hz)[1]].
This indicates that nucleophilic substitution of Cl– with
MeS– in THF is feasible in 1 but not in 2, suggestive of
the presence of a stronger Ru–Cl bond, which necessitates
assistance from MeOH for cleavage. It is likely that 2, like
[CpRu(PPh3)2Cl] (1A), the Cp analogue of 1, shows ap-
preciable ionic behaviour in MeOH, as shown in Equa-
tion (2).
[CpRu(PPh3)2Cl] + MeOH h [CpRu(PPh3)2(MeOH)]+ + Cl– (2)
Indeed, the MeOH complex had been isolated as the
–
BPh4 salt,[17] and nucleophilic displacement of chloride in
1A by nitriles, tertiary phosphanes or phosphites has been
shown to proceed by displacement of the weakly bound
MeOH.[18] Such a dissociative tendency of the Ru–Cl bond
will facilitate the dissociative pathways found to operate in
substitution reactions of both Cp and indenyl complexes
of Ru.[19] Incidentally, we have noted that the majority of
reported reactions of (Ind)Ru complexes have been carried
out in MeOH. In this present system, we have also ob-
served, in a small-scale NMR tube reaction, that the solvent
derivative of 2, [(Ind)Ru(dppf)(CH3CN)]PF6 (2S), reacted
with MeSNa in THF at r.t. to give 3 as the sole product. In
fact, Stone and co-workers had established that increasing
donor ability of phosphane ligands strengthens the Ru–Cl
bond sufficiently that displacement of chloride in [CpRu-
(L)2Cl] (L = phosphane) cannot be effected.[20] Hence the
observed stronger Ru–Cl bond in 2 versus its Cp analogue
2A and versus its bis(PPh3) analogue 1 [here dppf vs.
(PPh3)2] is in agreement with the recent finding that the
indenyl ligand is more electron-donating than Cp towards
Ru,[13] as is also confirmed by CV measurements in this
study (see cyclic voltammetric and EPR measurements sec-
Scheme 1.
The latter complex was not anticipated, as hydride for-
mation was not reported in the preparation of [(Ind)-
Ru(PPh3)2(SEt)] from the reaction in refluxing THF of
[(Ind)Ru(PPh3)2Cl] (1) with NaSEt,[8] or in similar synthe-
ses of [CpRu(PPh3)2(SR)] (R = 1-C3H7, CHMe2 and 4-
C6H4Me).[10] Very recently, Gimeno and co-workers ob-
tained mono- and diphosphane analogues of 6 from the
reaction of [(Ind)Ru(P-P)Cl] {P-P = diphosphanes (dppm,
dppe) or bis(PR3)} with an excess of MeONa in MeOH.[11]
The formation of metal hydrides from alkoxide precursors
by β-hydrogen elimination is a well-established phenome-
non.[12,13] Invoking the role of alkoxide in this reaction in-
volving the use of thiolates in MeOH will require the par-
ticipation of an equilibrium represented by Equation (1).
K
RS– + MeOH h MeO– + RSH
(1)
In such a situation the competition of nucleophiles RS– tion).
and MeO– in displacement of X from [(Ind)Ru(dppf)X] (X
Complex 5 crystallises with one CH2Cl2 and 0.5 MeOH
= Cl or MeOH) comes into play. This will depend on their in the orthorhombic Fdd2 space group, while 6 crystallises
relative nucleophilicities (RS– Ͼ MeO–), as well as the pre- in the monoclinic P21/n space group. Their molecular struc-
ponderance of one species over the other, a direct conse- tures are very similar to those of their respective Cp ana-
quence of the equilibrium constant K. This is in agreement logues,[9b,21] and are illustrated in the ORTEP diagrams
with the order of pKa’s in MeOH of the thiols as follows: shown in Figures 1 and 2. The metal centres are coordi-
MeSH (14.3)[14] Յ EtSH (14.4)[15] Ͼ PhSH (10.9).[16] Thus, nated to η5-Ind, η2-dppf and η1-thiophenolate/hydrido li-
under similar concentrations of reactants, [MeO–] in equi- gands. Selected bond parameters are compared with those
librium (2) from PhS– will be about two orders of magni- of the Cp analogues in Table 1.
tude lower than that from RS– (S = Me or Et). This is
The Ru–S distances in 5 and its Cp analogue are compar-
in agreement with the observed absence of metal hydride able and longer than in other examples of Ru–S(thiolate)
formation for the R = Ph case. When both RS– (R = Me bonds [2.30 Å (av.)].[23] The Cp rings of dppf in 5 are almost
and Et) and MeO– are present, the higher nucleophilicity eclipsed (syn periplanar) to each other, with a torsional an-
of the former anions qualitatively accounts for the prepon- gle (τ) of 2.1°. The phenyl ring on thiophenolate is almost
derance of metal thiolate over metal hydride products.
parallel to the phenyl ring on P1, while the phenyl ring of
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(Indenyl)Ru Complexes Containing dppf and Thiolato Ligands
FULL PAPER
and P–Ru–H angles of 80.19(2)° and 85.28(2)°. Compared
to the eclipsed conformation in 5, the Cp rings of the dppf
in 6 adopt a more stable syn clinal (gauche) configuration.
This is facilitated because the smaller terminal hydride re-
lieves the steric stress around the Ru centre, enabling the
dppf ligand to orientate to the lower-energy syn clinal con-
figuration with a torsional angle (τ) of 39.67°. The benzen-
oid ring of the indenyl ligand was predicted to arrange itself
trans to the hydride, the higher trans-influence ligand,[4d] as
shown in Figure 3.
Figure 1. ORTEP diagram of 5. Thermal ellipsoids are drawn to
50% probability level. Hydrogen atoms are omitted for clarity.
Figure 3. Top view of 6.
–
(b) Reaction of 2 with the Mixed-Donor Ligand S(CH2)2-
PPh2
The reaction in MeOH of 2 with Ph2P(CH2)2S–, a ‘hy-
brid’ ligand with two coordinating sites, resulted in a mix-
ture of [(Ind)Ru(η2-dppf){κ1S-S(CH2)2PPh2}] (7) and 6 in
54% and 15% yields respectively (Scheme 2), indicating an
equilibrium between Ph2P(CH2)2S– and Ph2P(CH2)2SH in
MeOH. This reaction cannot be effected in THF at r.t. or
at reflux, as previously observed. The amount of 6 isolated
suggested that the pKa of Ph2P(CH2)2SH is similar to that
of EtSH (see Scheme 1).
Figure 2. ORTEP diagram of 6. Thermal ellipsoids are drawn to
50% probability level. Except for the metal hydride atom H1, all
other hydrogen atoms are omitted for clarity.
1
The H NMR and 31P NMR spectra of 7 indicate that
the Ru centre is coordinated to η5-Ind, η2-dppf and κ1S-2-
(diphenylphosphanyl)ethylthiolate [Ph2P(CH2)2S–]; the co-
thiophenolate in the Cp analogue points away from the ordinated phosphorus atoms of dppf resonate at δ = 56.1,
phenyl rings on dppf. This is probably because of the steric while the low-field 31P signal (δ = –14.8 ppm) of the hybrid
bulk of the indenyl ligand, which restricts the orientation ligand pertains to a noncoordinating PPh2 entity, in agree-
of the thiophenolate ligand in 5.
ment with the higher nucleophilicity of thiolato sulfur, and
The hydride ligand in 6 is located in the electron density hence its better coordinative capability to the RuII centre
map and refined with a Ru–H bond length of 1.499(6) Å when compared to phosphane P. The mixed-donor ligand
Table 1. Selected bond lengths [Å] and angles [°].
Complex
5·CH2Cl2·0.5MeOH
[CpRu(dppf)(SPh)][9b]
6
[CpRu(dppf)H][21]
∆ [Å][22]
0.192
6.88
9.87
–
–
–
0.1205
5.19
7.56
–
–
–
Hinge angle (HA) [°][22]
Fold angle (FA) [°][22]
C*–Ru1[a]
Ru1–P1
Ru1–P2
Ru1–X
1.939
–
1.923
–
2.2523(12)
2.3085(12)
X = S1; 2.4193(12)
2.284(3)
2.302(3)
X = S1; 2.434(4)
2.2446(9)
2.2553(9)
X = H; 1.499(6)
2.263(4)
2.246(3)
X = H; 1.30
P1–Ru1–P2
P1–Ru1–X
P2–Ru1–X
97.54(4)
X = S1; 86.21(4)
X = S1; 86.08(4)
99.02(10)
X = S1; 89.29(11)
–
98.68(3)
X = H; 80.19(2)
X = H; 85.28(2)
99.1(1)
–
–
[a] C* = centroid of the five-membered ring, C1, C2, C3, C3a and C7a.
Eur. J. Inorg. Chem. 2007, 463–471
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465

S. Y. Ng, W. K. Leong, L. Y. Goh, R. D. Webster
FULL PAPER
processes at low temperatures, although at room tempera-
ture the third (most-positive) oxidation processes were only
partially chemically reversible, suggesting chemical instabil-
ity of the triply oxidised species. The expression “chemical
reversibility”, when used in connection with cyclic voltam-
ox
metry experiments, relates to the ratio of the oxidative (ip
)
red
to reductive peak currents (ipred). The ipox/ip
ratio ap-
proaches unity for a fully chemically reversible process.
Complexes 2, 2A and 2B displayed two chemically revers-
ible oxidation processes, except for 2A, where the second
more positive process was only partially chemically revers-
ible at a scan rate of 100 mVs–1 (suggesting instability of
the more highly oxidised state). At scan rates Ͼ100 mVs–1,
red
the ipox/ip
ratio for the second process of 2A became
closer to one. Complexes 3, 4 and 5 also displayed one
chemically irreversible reduction process at about –2.5 V
versus Fc/Fc+ (data not shown), with a similar current mag-
nitude to the first oxidation process (indicating that the
same number of electrons were transferred).
Table 2 lists the reversible oxidation potentials (Er1/2) that
were calculated from CV data under conditions where the
Scheme 2.
red
ipox/ip ratios were equal to unity and using the relation-
displaced neither the indenyl ligand nor dppf, indicating the
stronger chelating effect of the dppf ligand versus
Ph2P(CH2)2S–.
ship (3)
ox
Er1/2 = (Ep + Epred)/2
(3)
ox
red
where Ep and Ep are the anodic and cathodic peak po-
tentials, respectively. In situations where no reverse peak
was observed, only the peak potential is given. Voltam-
metric data from reports on several other related com-
pounds are also given in Table 2. The ∆E values for several
of the literature compounds are very large (ϾϾ100 mV),
indicating complicated electrochemical behaviour, and sug-
gesting that the reported Er1/2 values do not correspond
closely to the formal potentials.
Cyclic Voltammetric and EPR Measurements
Cyclic voltammograms obtained at a GC electrode in
0.5 m solutions of 3, 4, 5, 2, 2A and 2B in CH2Cl2 at
233 K are shown in Figure 4. On the CV timescale, com-
plexes 3, 4 and 5 displayed chemically reversible oxidation
ox
red
In most instances where the Ep and Ep peak separa-
tion (∆E) could be measured, the values obtained were close
to that expected for a one-electron transfer (Table 2). There
were some variations detected in the peak current intensities
for equivalent concentrations of different compounds (Fig-
ure 4), but this is likely to be due to differences in diffusion
coefficients, as the peak currents appear to approximately
inversely correlate with the size of the molecules. Coulome-
try measurements made during exhaustive controlled po-
tential electrolysis (CPE) experiments at 233 K for the first
oxidation process of 3 and 5, at applied potentials 100 mV
more positive than the Er1/2 values, confirmed the transfer
of one electron per molecule, see Equation (4) in the Exp.
Sect. The one-electron oxidised species were stable for at
least 2–3 h at 233 K in CH2Cl2 and could be reversibly re-
duced back to their starting materials. The electrolysis ex-
periments were performed at low temperatures to ensure
increased stability of the oxidised compounds (compared to
at ambient temperatures).
Free dppf is oxidised at about +200 mV more positive
than ferrocene.[24] The product of this one-electron oxi-
dation is not as stable as the Fc/Fc+ system and moderate
Figure 4. Cyclic voltammograms performed at a 1-mm diameter
planar GC electrode in CH2Cl2 (0.25  Bu4NPF6) at 233 K at a
scan rate of 100 mVs–1 for 0.5 m (a) 3, (b) 4 (c) 5, (d) 2, (e) 2A
and (f) 2B. CVs in (b), (c), (d), (e) and (f) are offset by –2, –4,
–6, –8 and –10 µA respectively.
red
scan rates of around 3 Vs–1 are needed to obtain ipox/ip
ratios equal to unity.[24] When dppf is coordinated to other
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(Indenyl)Ru Complexes Containing dppf and Thiolato Ligands
FULL PAPER
Table 2. Cyclic voltammetric data obtained at a scan rate of 100 mVs–1 at a 1-mm diameter glassy carbon electrode at 233 K in CH2Cl2
with 0.25  Bu4NPF6 as the supporting electrolyte, together with some literature data.
Compound
Oxidation process[a]
Reduction process
Ep [V][b]
ox
Ep [V][c]
red
Er1/2 [V][d]
∆E [mV][e]
Ep [V][c]
red
[(η5-Ind)Ru(PPh3)2Cl] 1
[(η5-Ind)Ru(dppf)Cl] 2
–0.01
–0.03
+0.51
–0.51
+0.32
+0.74
66[13]
72
77
62
56
+0.010
+0.553
–0.480
+0.344
+0.771
–0.062
+0.476
–0.542
+0.288
+0.702
not detected
[(η5-Ind)Ru(dppf)(SMe)] 3
[(η5-Ind)Ru(dppf)(SEt)] 4
[(η5-Ind)Ru(dppf)(SPh)] 5
69
–2.620
–2.610
–0.498
+0.364
+0.776
–0.560
+0.300
+0.708
–0.53
+0.33
+0.74
62
64
68
–0.351
+0.464
+0.784
–0.416
+0.399
+0.718
–0.38
+0.43
+0.75
65
65
66
–2.548
[(η5-Ind)Ru(dppe)Cl]
[(η5-Ind)Ru(dppm)Cl]
[(η5-Cp)Ru(dppf)Cl] 2A
–0.03
–0.07
+0.11
+0.48
+0.05
+0.03
+0.10
–0.08
+0.45
–0.13
–0.03
–0.30
–0.12
64[13]
62[13]
71
+0.144
+0.521
0.073
+0.436
not detected
85
[(η5-Cp)Ru(dppe)Cl]
110[27]
340[27]
360[27]
65
[(η5-Cp)Ru(dppm)Cl]
[(η5-Cp)Ru(PPh3)2Cl] 1A
[(η5-Cp*)Ru(dppf)Cl] 2B
–0.050
+0.486
–0.115
+0.408
not detected
78
[(η5-Cp*)Ru(dppe)Cl]
[(η5-Cp*)Ru(PPh3)2Cl]
[(η5-Ind)Ru(dppf)H] 6
270[27]
240[27]
66
–0.262
–0.072
–0.328
–0.174
102
not detected
[a] All potentials are relative to the Fc/Fc+ redox couple. Data from literature reports[13,27] that were vs. SCE have been converted to vs.
Fc/Fc+ by adding 0.46 V (corrections for differences in temperature have not been made). [b] Ep = oxidative peak potential. [c] Ep
=
ox
red
ox
ox
reductive peak potential. [d] Er1/2 = (Ep + Epred)/2. [e] ∆E = |Ep – Epred|.
metal ions through the phosphorus atoms, the oxidation
The Er1/2 values of the complexes (Table 2) indicate ease
potential increases to about +0.5 V versus Fc/Fc+ and the of oxidation of the complexes as follows: for [LRuCl(dppf)]
stability of the oxidised dppf is substantially improved so complexes (L = Ind, Cp and Cp*), Cp* Ͻ Ind Ͻ Cp, in
that ipox/ipred ratios equal to unity are obtained at slow scan agreement with the decreasing electron-donor capability of
rates of 100 mVs–1 (similar to Fc/Fc+).[24,25] In the light of the corresponding ligands. Similar trends have been ob-
these previous observations,[24,25] we conclude that the oxi- served for the dppe, dppm, (PPh3)2 and (PMe2Ph)2 ana-
dation process that occurs at +0.32–0.51 V versus Fc/Fc+ logues.[13,27] The data also show [(Ind)RuCl(dppf)SMe] (3)
in the CV’s of 3, 4, 5, 2, 2A and 2B (i.e., the second process) is more easily oxidised than its Ph analogue 5, in agreement
is likely to be associated with the one-electron oxidation with decrease of electron density at the metal centre in 5,
of [dppf] to [dppf]+. Therefore, the first oxidation process caused by delocalisation into the Ph ring.
observed in the CV’s in Figure 4 is associated with the for-
EPR experiments were performed at 10 K on frozen sam-
mal oxidation of Ru2+ to Ru3+ (although it is likely some ples of 3+ and 5+ that were produced by electrochemically
electron delocalisation occurs). The conclusion that the first oxidising the starting materials by one electron at a con-
process is associated with localised oxidation of the Ru cen- stant potential at 233 K (Figure 5). The spectrum obtained
tre is consistent with a similar first oxidation potential for for 5+ showed additional hyperfine structure, suggesting
3, 4 and 5 (ca. –0.45 V vs. Fc/Fc+) and for 2, 2A and 2B that the unpaired electron was partially delocalised, poss-
(ca. 0 V vs. Fc/Fc+) (Figure 4), as the potential is likely to ibly on the Ph group bonded to the S. Complex 3+ did not
be most sensitive to the substituents coordinated directly to display hyperfine structure, possibly because the unpaired
the ruthenium. The third oxidation process for 3, 4 and 5 electron was less able to be accommodated about the methyl
is possibly again centred on the ruthenium ion, as an Ru3+
-
group bonded to the sulfur. Interaction of the unpaired
to-Ru4+ redox transformation is to be expected (although electron with the 31P atoms (I = ½, 100% abundance) is
the exact location of the oxidation process is difficult to also possible, as has been observed in diastereomeric [(η6-
determine from CV experiments). Complexes 2, 2A and 2B arene)RuIII(P-As)Cl] complexes in which the ruthenium
may also be further oxidised, but at a more positive poten- atom is a chiral stereocentre.[26] EPR spectra of 3+ or 5+
tial than 3, 4 and 5 (additional oxidation processes were not were not detected at room temperature, indicting that the
detected within the solvent/electrolyte potential window).
unpaired electron was mainly localised on the metal ion,
Eur. J. Inorg. Chem. 2007, 463–471
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467

S. Y. Ng, W. K. Leong, L. Y. Goh, R. D. Webster
FULL PAPER
rather than on the organic ligands. The further one-electron because of instability of oxidised 6 in CH2Cl2. At 293 K,
oxidation of 3+ and 5+ at 233 K (two electrons overall) pro- only one chemically irreversible oxidation process was de-
duced compounds that did not give an EPR signal at 10 K tected at about +0.6 V versus Fc/Fc+.
and above, either because they were diamagnetic or were
[(Ind)Ru(dppf)H] (6) was approximately 0.3 V easier to
paramagnetic with rapid relaxation times. Complex 4+ was oxidise than the corresponding Cl complex, [(Ind)Ru(dppf)-
not examined by EPR spectroscopy because the cyclic vol- Cl] (2) (Table 2), which is a similar trend seen for other η5
tammetry experiments indicated that its electrochemical be- organometallic compounds containing the dppf ligand and
haviour was essentially identical to 3+ (Figure 4).
Cl or H.[28]
Conclusions
Chloro substitution of [(Ind)Ru(dppf)Cl] (2) with thio-
lates (RS–) in MeOH was found to yield both thiolato deriv-
atives and a hydrido complex, [(Ind)Ru(dppf)H] (6), the
yield of which is both solvent- and R-dependent. From ob-
servations that the reaction could not proceed in the ab-
sence of MeOH, it was rationalised that 6 was formed by
β-H elimination from ligated MeO–, the latter being formed
in equilibrium amounts by an interaction between RS– and
MeOH. The product mixture therefore reflected the relative
nucleophilicity of RS– and MeO–. Voltammetry experi-
ments indicated that the formal oxidation potentials for
[LRu(dppf)Cl] compounds (L = Ind, Cp and Cp*) occurred
in the order Cp* Ͻ Ind Ͻ Cp, with a 200 mV difference
between the Cp* and Cp compounds. For [(Ind)Ru(LЈ)Cl]
Figure 5. Continuous wave X-band EPR spectra obtained at 10 K
with microwave frequency of 9.44 GHz and microwave power of
0.2 mW after the exhaustive electrochemical one-electron oxidation compounds {LЈ = dppm, dppe, dppf, (PPh3)2}, the formal
of (a) 3 to 3+ and (b) 5 to 5+ at –0.2 V vs. Fc/Fc+ in CH2Cl2 (with
0.25  Bu4NPF6) at 233 K.
potentials decreased in the order dppm Ͻ dppe/dppf Ͻ
(PPh3)2, although the total difference in oxidation potential
spanning all the different diphosphanes [(Ind)Ru(LЈ)Cl] was
Cyclic voltammograms of [(Ind)Ru(dppf)H] 6 obtained
in CH2Cl2 solutions at 233 K at a GC electrode are dis-
played in Figure 6. The compound displayed two chemi-
a relatively small 60 mV. EPR experiments on 3+ and 5+ at
10 K indicated that the monocations were paramagnetic
and the dications were EPR silent.
cally reversible (or quasireversible) oxidation processes at
about –0.3 and –0.1 V versus Fc/Fc+. The second oxidation
process had smaller peak currents than the first process,
which may be caused by interactions between the oxidised
Experimental Section
compound and the electrode surface. On a Pt electrode,
only one drawn out oxidation process was detected be-
tween –0.2 and 0.2 V, indicating that the oxidation pro-
cesses were strongly influenced by the nature of the elec-
trode surface. The cyclic voltammetry significantly changed
from that shown in Figure 6 as the temperature was raised,
General: All reactions were carried out using conventional Schlenk
techniques under inert nitrogen or argon in an M. Braun Labmas-
ter 130 Inert Gas System.
NMR spectra were measured with a Bruker 300 FT NMR spec-
trometer; for 1H and 31P spectra, chemical shifts were referenced
to residual solvent in the deuterio-solvents. IR spectra in KBr pel-
lets were measured in the range 4000–400 cm–1 by means of a
BioRad FTS-165 FTIR instrument. Mass spectra were run on a
Finnigan Mat 95XL-T (FAB) or a Finnigan-MAT LCQ (ESI) spec-
trometer. Elemental analyses were performed by the microanalyti-
cal laboratory in-house.
[(Ind)Ru(PPh3)2Cl] (1)[1] and Ph2P(CH2)2SH[29] were prepared by
published methods. [(Ind)Ru(dppf)Cl] (2) was synthesised from
phosphane substitution of 1, while [(Ind)Ru(dppf)(CH3CN)]PF6
(2S) was derived from 2 by reaction with NaPF6 in refluxing
CH3CN.[30] All other chemicals were obtained commercially and
used without any further purification. All solvents were dried with
sodium/benzophenone and distilled before use. Celite (Fluka AG)
and silica gel (Merck Kieselgel 60, 230–400 mesh) were dried at
140 °C overnight before chromatographic use.
Figure 6. Cyclic voltammograms recorded at 100 mVs–1 of a
1.2 m CH2Cl2 solution of 6 with 0.5  Bu4NPF6 at a 1-mm planar
GC electrode at 233 K.
Electrochemical Studies: Voltammetric experiments were conducted
with a computer-controlled Eco Chemie µAutolab III potentiostat.
Solutions of electrogenerated compounds for the EPR experiments
468
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(Indenyl)Ru Complexes Containing dppf and Thiolato Ligands
FULL PAPER
were prepared in a divided controlled potential electrolysis cell sep-
arated with a porosity no. 5 (1.0–1.7 µm) sintered glass frit. The
working and auxiliary electrodes were identically sized Pt mesh
plates symmetrically arranged with respect to each other. A silver
wire reference electrode (isolated by a salt bridge containing 0.5 
Bu4NPF6 in CH3CN) was positioned to within 2 mm of the surface
of the working electrode. The electrolysis cell was jacketed in a glass
sleeve and cooled to 233 K (for improved stability of the oxidised
compounds) using a Lauda RL6 variable temperature methanol-
circulating bath. The volumes of both the working and auxiliary
electrode compartments were approximately 20 mL each. The
number of electrons transferred during the bulk oxidation process
was calculated from Equation (4)
SEt]+, 655 [M – SEt – Ind]+. C45H40FeP2RuS (831.73): calcd. C
65.0, H 4.9, S 3.9; found C 65.5, H 5.1, S 3.4.
1
Data for 5: H NMR (C6D6): δ = 3.62, 3.79, 3.88 and 4.06 (each s,
2 H, C5H4), 5.25 (s, 1 H, Ind), 5.64 (s, 2 H, Ind), 6.38–6.40, 6.94–
6.97 (each 4-line m, 2 H, Ind), 7.04–7.58 (m, 20 H, Ph) ppm.
31P{1H} NMR (C6D6): δ = 54.9 (s, dppf) ppm. FAB+-MS: m/z (%)
= 880 [M]+, 771 [M – SPh]+, 655 [M – SPh–Ind]+. C49H40FeP2RuS
(879.77): calcd. C 66.9, H 4.6, S 3.6; found C 67.3, H 4.8, S 4.1.
Small-Scale Reactions of 1 with MeSNa in MeOH and THF – Ef-
fect of Solvent: MeSNa (2 mg, 0.029 mmol) was added to a red
solution or suspension of 1 (5 mg, 0.006 mmol) in the selected sol-
vent (1 mL), and the mixture was refluxed. After the reaction, the
product mixture was evacuated to dryness and the respective resi-
1
dues extracted with toluene, for examination by H and 31P NMR
N = Q/nF
(4)
spectroscopy.
where N is the number of mols of the starting compound, Q is the
charge (coulombs), n is the number of electrons and F is the Fara-
day constant (96485 Cmol–1). The electrolysed solutions were
transferred under vacuum into cylindrical 3-mm (id) EPR tubes
that were immediately frozen in liquid N2. EPR spectra were re-
corded with a Bruker ESP 300e spectrometer in a TE102 cavity at
10 K using liquid He cooling.
(i) In MeOH: A reflux for 1 h produced a suspension of dark green
solids in a faint yellow supernatant. The spectra indicated the prod-
uct was a mixture of [(Ind)Ru(PPh3)2(SMe)] (3P) and the hydride
species [(Ind)Ru(PPh3)2H] [1H NMR (C6D6): δ = –15.39 ppm (t,
2
2JHP = 33.8 Hz), cf. lit. values in CDCl3: δ = –15.40 ppm (t, JHP
= 31.6 Hz)[1]] in the ratio of 1:1.
(ii) In THF: The solution changed slowly to dark green during
reflux (2 h). The spectra indicated that [(Ind)Ru(PPh3)2(SMe)] (3P)
was the sole product.
Synthesis of [(Ind)Ru(dppf)(SR)] {R = Me (3), Et (4), Ph (5)}: RSNa
{0.25 mmol: R = Me, 17 mg; R = Et [freshly prepared in situ from
EtSH (19 µL) and MeONa obtained from 6 mg Na in 2 mL
MeOH]; R = Ph, 33 mg} was added to a red suspension of [(Ind)-
Ru(dppf)Cl] (2) (50 mg, 0.062 mmol) in MeOH (5 mL) and the
mixture was stirred, whereupon the colour of the suspension
changed immediately to green. After stirring at r.t. for 18 h, the
solvent was removed in vacuo and the residue was extracted using
toluene (2ϫ5 mL). The extract was concentrated to about 2 mL
and then loaded onto a silica gel column (2ϫ5 cm) prepared in n-
hexane. Elution gave two fractions: (i) a yellow eluate in toluene
(about 8 mL), which yielded [(Ind)Ru(dppf)H] (6) (for the reaction
in which R = Me, 9 mg, 19% yield; R = Et, 8 mg, 16% yield); (ii)
a green eluate in toluene/THF (20:1, about 10 mL), which yielded
[(Ind)Ru(dppf)(SR)] {R = Me (3), 40 mg, 79% yield; R = Et (4),
33.5 mg, 65% yield; R = Ph (5), 52 mg, 96% yield}; (iii) an orange-
red eluate in THF (3 mL), which gave 2 in trace amounts.
1
Data for 3P: H NMR (C6D6): δ = 2.23 (s, 3 H, SMe), 4.30 (s, 2
H, Ind), 5.22 (s, 1 H, Ind), 6.88–7.47 (m, 34 H, Ind and Ph) ppm.
31P{1H} NMR (C6D6): δ = 50.2 (s, PPh3) ppm.
Reaction of 2 with MeONa (in THF/MeOH): Complex 2 (10 mg,
0.012 mmol) as a red solid was added to a suspension of dry
MeONa [freshly prepared from Na (6 mg, 0.26 mmol) in MeOH
(4 mL)] in THF (5 mL), and the slurry stirred at r.t. The 1H and
31P NMR spectra in C6D6 of aliquots of the reaction mixture at
2 h, and after reflux for an additional 4 h, revealed that the reaction
did not proceed. MeOH (1 mL) was then added into the mixture
and stirring continued at r.t. A slow colour change from orange-
red to yellow occurred within 1 h. The 1H and 31P NMR spectra of
an aliquot in C6D6 showed the formation of 6 as the sole product.
2
Data for 6: 1H NMR (C6D6): δ = –15.4 (t, JHP = 33 Hz, 1 H),
Compound 3 was also formed from the reaction of [(Ind)-
Ru(dppf)(CH3CN)]PF6 (2S) with MeSNa as follows: MeSNa
(2 mg, 0.029 mmol) was added to a yellow solution of 2S (5 mg,
0.005 mmol) in THF (2 mL) and the mixture was stirred at r.t. The
colour of the mixture slowly changed from yellow to green in 4 h.
The 1H and 31P NMR spectra of an aliquot of the product mixture
showed the sole presence of 3.
Data for 3: 1H NMR (C6D6): δ = 1.96 (s, 3 H, SMe), 3.36, 3.89,
3.92 and 4.06 (each s, 2 H, C5H4), 5.29 (s, 1 H, Ind), 5.60 (s, 2 H,
Ind), 7.04–7.58 (m, 24 H, Ind and Ph) ppm. 31P{1H} NMR (C6D6):
δ = 56.0 (s, dppf) ppm. FAB+-MS: m/z (%) = 818 [M]+, 771 [M –
SMe]+, 655 [M – SMe – Ind]+. C44H38FeP2RuS (817.70): calcd. C
64.6, H 4.7, S 3.9; found C 64.7, H 4.8, S 3.9.
3.77 (s, 4 H, C5H4), 4.13 and 4.27 (each s, 2 H, C5H4), 4.34 (s, 2
H, Ind), 5.75 (s, 1 H, Ind), 6.28–6.31, 6.80–6.83 (each 4-line m, 2
H, Ind), 7.12–7.19, 7.28–7.33 and 8.03–8.08 (each m, total 20 H,
Ph) ppm. 31P{1H} NMR (C6D6): δ = 62.9 (s, dppf) ppm. ESI+-MS:
m/z (%) = 772 [M + H]+. C43H36FeP2Ru (771.61): calcd. C 66.9, H
4.7; found C 66.9, H 4.5.
Synthesis of [(Ind)Ru(dppf){S(CH2)2PPh2}] (7): Ph2P(CH2)2SH
(54 µL, 0.25 mmol) was added into excess NaH in THF (5 mL) and
the suspension was stirred at r.t. overnight. The suspension was
filtered through Celite into
a red suspension of 2 (50 mg,
0.06 mmol) in MeOH (10 mL). The reaction mixture was stirred at
r.t. for 18 h. A slow colour change from red suspension to dark
green solution was observed. The solvent was removed in vacuo,
and the residue extracted with toluene (2ϫ5 mL). The toluene ex-
tract was concentrated to about 1 mL and loaded onto a silica gel
column (2ϫ10 cm) prepared in n-hexane. Elution gave two frac-
tions: (i) a yellow eluate in toluene (about 4 mL), which gave 6
(7 mg, 15% yield); and (ii) a dark green eluate in toluene/diethyl
ether (1:1, about 10 mL), which yielded [(Ind)Ru(dppf){S(CH2)2-
PPh2}] (7) (34 mg, 54% yield).
(Note: The proton resonances of the five-membered ring of Ind in
this complex, as in others in this work, appear as singlets, although
couplings are anticipated, most probably because these are too
small to be resolved using the 300-MHz instrument.)
3
Data for 4: 1H NMR (C6D6): δ = 1.62 (t, JHH = 7.4 Hz, 3 H,
3
SCH2CH3), 2.16 (q, JHH = 7.4 Hz, 2 H, SCH2CH3), 3.63, 3.89,
3.94 and 4.06 (each s, 2 H, C5H4), 5.27 (s, 1 H, Ind), 5.70 (s, 2 H,
Ind), 7.04–7.57 (m, 24 H, Ind and Ph) ppm. 31P{1H} NMR (C6D6): Data for 7: 1H NMR (C6D6): δ = 2.31–2.39 and 2.75–2.80 (each
δ = 56.1 (s, dppf) ppm. FAB+-MS: m/z (%) = 832 [M]+, 771 [M –
m, 2 H, CH2), 3.64, 3.88, 3.92 and 4.06 (each s, 2 H, C5H4), 5.18
Eur. J. Inorg. Chem. 2007, 463–471
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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469

S. Y. Ng, W. K. Leong, L. Y. Goh, R. D. Webster
FULL PAPER
Table 3. Crystal and structure refinement data.
5·CH2Cl2·0.5MeOH
6
Formula
Formula mass
C50.50H44Cl2FeO0.50P2RuS
980.68
C43H36FeP2Ru
771.58
Space group (crystal system)
Crystal system
Unit cell dimensions
a [Å]
Fdd2
orthorhombic
P21/n
monoclinic
27.452(3)
56.029(7)
11.8603(7)
15.3521(10)
b [Å]
c [Å]
α [°]
11.6643(14)
90
18.9672(12)
90
β [°]
γ [°]
90
90
17941(4)
16
1.452
0.933
8016
0.36ϫ0.12ϫ0.10
2.08–26.37
0 Յ h Յ 34, 0 Յ k Յ 70, –14 Յ l Յ 14
60968
9164
0.9125–0.7300
9164/3/520
98.300(2)
90
3417.4(4)
4
1.500
0.991
1576
0.26ϫ0.14ϫ0.06
2.17–26.37
–14 Յ h Յ 14, 0 Յ k Յ 19, 0 Յ l Յ 23
27911
6985
0.9429–0.7827
6985/0/428
Cell volume [Å3]
Z
Dcalcd. [gcm–3]
Absorption coefficient [mm–1]
F(000) electrons
Crystal size [mm]
θ range for data collection [°]
Index ranges
Reflections collected
Independent reflections
Max. and min. transmission
Data/restraints/parameters
Gof
1.203
1.053
Final R indices [I Ͼ 2σ(I)]
R indices (all data)
Largest diff. peak and hole [eÅ–3]
R1 = 0.0440, wR2 = 0.1091
R1 = 0.0462, wR2 = 0.1102
0.954 and –0.522
R1 = 0.0465, wR2 = 0.0927
R1 = 0.0640, wR2 = 0.0994
0.618 and –0.443
(s, 1 H, Ind), 5.67 (s, 2 H, Ind), 7.03–7.05 (m, 8 H, Ph), 7.42 (br.
R. D. W. thanks the Australian National University for financial
s, 5 H, Ph), 7.56–7.61 (m, 7 H, Ph) ppm. 31P{1H} NMR (C6D6): δ support.
= –14.8 [s, S(CH2)2PPh2], 56.1 (s, dppf) ppm. FAB+-MS: m/z (%)
= 1016 [M]+, 771 [M – S(CH2)2PPh2]+. C57H49FeP3RuS (1015.90):
[1] L. A. Oro, M. A. Ciriano, M. Campo, C. Foces-Foces, F. H.
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CCDC-621607 (for 5·CH2Cl2·0.5MeOH) and -621608 (for 6) con-
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Acknowledgments
Support from the National University of Singapore under Aca-
demic Research Fund grant No. R-143-000-209-112 to L. Y. G. and
a research scholarship to S. Y. N. from the Institute of Chemical
and Engineering Sciences (ICES) are gratefully acknowledged.
470
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Eur. J. Inorg. Chem. 2007, 463–471

(Indenyl)Ru Complexes Containing dppf and Thiolato Ligands
FULL PAPER
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Received: September 20, 2006
Published Online: November 27, 2006
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