Synthesis, characterization, and catalytic evaluation of ruthenium-diphosphine complexes bearing xanthate ligands

Article abstract of DOI:10.1039/c8dt02838a

The reaction of [RuCl₂(p-cymene)]₂ with potassium O-ethylxanthate and a set of nine representative Ph₂P-X-PPh₂ bidentate phosphines (dppm, dppe, dppp, dppb, dpppe, dppen, dppbz, dppf, and DPEphos) afforded monometallic [Ru(S₂COEt)₂(diphos)] chelates 1-9 in 62-96% yield. All the products were fully characterized by using various analytical techniques and their molecular structures were determined by X-ray crystallography. They featured a highly distorted octahedral geometry with a S-Ru-S bite angle close to 72° and P-Ru-P angles ranging between 73° and 103°. Bond lengths and IR stretching frequencies recorded for the anionic xanthate ligands strongly suggested a significant contribution of the EtO⁺CS₂^2- resonance form. ¹H NMR and XRD analyses showed that the methylene protons of the ethyl groups were diastereotopic due to a strong locking of their conformation by a neighboring phenyl ring. On cyclic voltammetry, quasi-reversible waves were observed for the Ru²⁺/Ru³⁺ redox couples with E_1/2 values ranging between 0.65 and 0.80 V vs. Ag/AgCl. The activity of chelates 1-9 was probed in three catalytic processes, viz., the synthesis of vinyl esters from benzoic acid and 1-hexyne, the cyclopropanation of styrene with ethyl diazoacetate, and the atom transfer radical addition of carbon tetrachloride and methyl methacrylate. In the first case, ³¹P NMR analysis of the reaction mixtures showed that the starting complexes remained mostly unaltered despite the harsh thermal treatment that was applied to them. In the second case, monitoring the rate of nitrogen evolution revealed that all the catalysts under investigation behaved similarly and were rather slow initiators. In the third case, [Ru(S₂COEt)₂(dppm)] was singled out as a very active and selective catalyst already at 140 °C, whereas most of the other complexes resisted degradation up to 160 °C and were only moderately active. Altogether, these results were in line with the high stability displayed by [Ru(S₂COEt)₂(diphos)] chelates 1-9.

Full text of DOI:10.1039/c8dt02838a

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DOI: 10.1039/C8DT02838A
Dalton Transactions
ARTICLE
Synthesis, characterization, and catalytic evaluation of
ruthenium–diphosphine complexes bearing xanthate ligands†
Received 00th January 20xx,
Accepted 00th January 20xx
Mohammed Zain Aldin,a Anthony Maho,b Guillermo Zaragoza,c Albert Demonceau,a and Lionel
Delaude*a
DOI: 10.1039/x0xx00000x
The reaction of [RuCl2(p-cymene)]2 with potassium O-ethylxanthate and a set of nine representative Ph2P–X–PPh2
bidentate phosphines (dppm, dppe, dppp, dppb, dpppe, dppen, dppbz, dppf, DPEphos) afforded monometallic
[Ru(S2COEt)2(diphos)] chelates 1–9 in 62–96% yield. All the products were fully characterized by using various analytical
techniques and their molecular structures were determined by X-ray crystallography. They featured a highly distorted
octahedral geometry with a S–Ru–S bite angle close to 72° and P–Ru–P angles comprised between 73° and 103°. Bond
lengths and IR stretching frequencies recorded for the anionic xanthate ligands strongly suggested a significant
contribution of the EtO+=CS22– resonance form. 1H NMR and XRD analyses showed that the methylene protons of the ethyl
groups were diastereotopic due to a strong locking of their conformation by a neighboring phenyl ring. On cyclic
voltammetry, quasi-reversible waves were observed for the Ru2+/Ru3+ redox couples with E1/2 values comprised between
0.65 and 0.80 V vs. Ag/AgCl. The activity of chelates 1–9 was probed in three catalytic processes, viz., the synthesis of vinyl
esters from benzoic acid and 1-hexyne, the cyclopropanation of styrene with ethyl diazoacetate, and the atom transfer
radical addition of carbon tetrachloride and methyl methacrylate. In the first case, 31P NMR analysis of the reaction
mixtures showed that the starting complexes remained mostly unaltered, despite the harsh thermal treatment that was
applied to them. In the second case, monitoring the rate of nitrogen evolution revealed that all the catalysts under
investigation behaved similarly and were rather slow initiators. In the third case, [Ru(S2COEt)2(dppm)] was singled out as a
very active and selective catalyst already at 140 °C, whereas most of the other complexes resisted degradation up to 160
°C and were only moderately active. Altogether, these results were in line with the high stability displayed by
[Ru(S2COEt)2(diphos)] chelates 1–9.
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late ligands.2 Subsequent research efforts carried out in
collaboration with the group of Wilton-Ely at Imperial College
allowed to extend the coordination chemistry of these 1,1-
Introduction
Since 2009, our Laboratory has been investigating the
synthesis, characterization, and complexation of azolium-2-
dithiocarboxylate betaines.1,2 These stable, crystalline inner
salts are the adducts of N-heterocyclic carbenes (NHCs) and
carbon disulfide (Chart 1).3 They form strong M–S bonds with a
wide range of metals through various binding modes.4 As a
result, NHC·CS2 zwitterions are particularly attractive for
designing new molecular architectures based on transition
metals.5 Our first venture in this area focused on ruthenium–
arene complexes containing imidazol(in)ium-2-dithiocarboxy-
dithiolate inner salts to osmium,6 palladium,7 and gold
complexes.8 More recently, we also reported the formation of
mono- and bimetallic metal–carbonyl compounds based on
manganese9 and rhenium10 that featured chelating or bridging
NHC·CS2 ligands, while Neuba and Wilhelm used these sulfur
donors to assemble sophisticated copper coordination
polymers and clusters.11
R
N
N
S
Zwitterions:
Anions:
C
S–
R
NHC•CS2
R
R
RO
RO
S
S
S
N
O
P
S–
S–
S–
R
Dithiocarbamate
Xanthate
Dithiophosphate
Chart 1 Generic structures of common 1,1-dithiolate ligands.
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Apart from azolium-2-dithiocarboxylate zwitterions, other Ph2P–X–PPh2. More specifically, our assortment comprised
View Article Online
related species, such as the dithiocarbamate,12 dithiophos- 1,1-bis(diphenylphosphino)methane (dpDpOmI:),101.1,023-b9/iCs(8dDipT0h2e8n3y8lA-
phate,13 and xanthate anions,14 have long dominated the phosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane
coordination chemistry of 1,1-dithiolate ligands (Chart 1).15 In (dppp), 1,4-bis(diphenylphosphino)butane (dppb), 1,5-bis(di-
particular, the last-mentioned oxygen-containing derivatives phenylphosphino)pentane (dpppe), cis-1,2-bis(diphenylphos-
have been known for more than two centuries. Indeed, the phino)ethene (dppen), 1,2-bis(diphenylphosphino)benzene
term xanthate was coined by Zeise in 1822 to reflect the (dppbz), 1,1'-bis(diphenylphosphino)ferrocene (dppf), and 2,2'-
yellow appearance of various complexes bearing these bis(diphenylphosphino)diphenyl ether (DPEphos) (Chart 2).
ligands,16 which should be more rigorously named O-alkyl (or
aryl) dithiocarbonate anions. Over the years, xanthate salts
have been widely used as flotation collectors in the mining and
PPh2
Ph2P
PPh2
Ph2P
Ph2P
PPh2
metallurgy of non ferrous metal sulfides.17 They have also
been employed as reagents in analytical chemistry18 and to
generate radical species in organic synthesis.19 Contrastingly,
their use as ancillary ligands in homogeneous catalysis is barely
documented, with only a single report describing the electro-
dppm
dppe
dppp
PPh2
PPh2
Ph2P
Ph2P PPh2
Ph2P
catalytic activity of
a ruthenium–xanthate complex in
dppb
dpppe
dppen
tryptophan oxidation.20
In light of our sustained interest for ruthenium catalysts21
and azolium-2-dithiocarboxylate zwitterions,3 we decided to
have a fresh look at the coordination chemistry of Ru(II) and
xanthate ligands in view of potential catalytic applications. In
this contribution, we report on the synthesis and full
characterization of nine ruthenium–diphosphine complexes
bearing O-ethyl dithiocarbonate ligands using efficient and
straightforward synthetic protocols combined with modern
analytical techniques. We also investigated the redox
properties of the [Ru(S2COEt)2(diphos)] chelates obtained by
cyclic voltammetry and we probed their catalytic activity in the
synthesis of vinyl esters, in the cyclopropanation of styrene,
and for atom transfer radical additions.
Fe
O
Ph2P
PPh2
Ph2P
PPh2
PPh2
Ph2P
dppbz
dppf
DPEphos
Chart 2 Diphosphine ligands used in this work.
In a typical experiment, the [RuCl2(p-cymene)]2 dimer (1
equiv.) and small excesses of Ph2P–X–PPh2 (2.2 equiv.) and
KS2COEt (4.4 equiv.) were stirred in THF for 24 h at room
temperature. The resulting suspensions that possibly
contained diphosphine-bridged multimetallic ruthenium–
arene oligomers were then heated to induce the formation of
the
thermodynamically
more
stable
monometallic
[Ru(S2COEt)2(diphos)] chelates 1–9 (Scheme 1). This thermal
treatment was required to achieve high yields of pure
products. It was initially carried out by heating Schlenk flasks in
an oil bath at 80–90 °C for 24 h. Alternatively, we also
performed syntheses using a monomodal microwave reactor
or a pressure reactor. With these equipments, THF could be
heated up to 130 °C and completion was reached within 1 h.
With dppe and dppb, precipitates that formed at room
temperature remained insoluble even when the temperature
was increased to 130 °C, thereby affording low yields of final
products 2 and 4. In these cases, we obtained better results by
reacting first the [RuCl2(p-cymene)]2 dimer with potassium
O-ethylxanthate for 24 h at room temperature before adding
the diphosphine ligand and heating the mixture for 1 h at 130
°C. With this modification of the standard procedure, all the
compounds 1–9 were isolated in satisfactory to excellent yields
after a work-up to remove the various byproducts and excess
reagents.
Results and discussion
Synthesis of [Ru(S2COEt)2(diphos)] complexes
In 1969, Wilkinson and coworkers first reported the synthesis
of cis-[Ru(S2COR)2(PPh3)2] complexes (R = Me, Et) by reacting
[RuCl2(PPh3)3] with either potassium O-methylxanthate or
potassium O-ethylxanthate in refluxing acetone for 12 h.22 In
1975, Critchlow and Robinson showed that [RuH(OAc)(PPh3)3]
was also a suitable starting material for this reaction23 and in
1990 Chakravorty et al. noted that the use of refluxing ethanol
in place of acetone significantly reduced its duration.24
Subsequent work from Ballester and coworkers showed that
[Ru(S2COEt)2(PPh3)2] reacted with tertiary mono- and
diphosphines to afford [Ru(S2COEt)2(PR2R')2] (R2R' = Ph2Me,
PH2Et, or Me2Ph) and [Ru(S2COEt)2(Ph2P(CH2)xPPh2)] (x = 1, 2)
complexes.25
To shorten the two-step procedure employed so far, our
strategy to access [Ru(S2COEt)2(diphos)] complexes involved
the one-pot chelation of both a diphosphine and two O-ethyl-
xanthate ligands onto a ruthenium(II) center. For this purpose,
we elected the readily available [RuCl2(p-cymene)]2 dimer
(p-cymene is 1-isopropyl-4-methylbenzene) as the metal
source, in combination with KS2COEt and a set of nine
representative bidentate phosphines with the generic formula
2 | J. Name., 2012, 00, 1-3
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The 31P NMR spectra of complexes 1–9 recorded in CDCl3
View Article Online
OEt
or CD2Cl2 were particularly simple and nDeOatI:,1w0.i1t0h39o/nCl8yDaT0s2i8n3g8lAe
resonance present in all cases (Table 1). These data indicate a
symmetrical chelation of the metal center by the diphosphine
ligands. The chemical shifts observed were in line with those
reported previously for other types of Ru(diphos) species.27 As
anticipated, the nature and the length of the spacer between
the two phosphorus atoms had a profound influence on the
magnetic properties of these nuclei. Indeed, when a bidentate
phosphine is coordinated to a transition metal, the size and
the topology of the metallacycle are known to induce
significant variations in the 31P NMR chemical shifts.28 Of note,
a reduction of symmetry was detected when looking at the
aromatic region in the 13C{1H} NMR spectra of chelates 1–9.
Thus, two sets of signals were observed for the ipso-, ortho-,
meta-, and para-carbon atoms of the phenyl rings flanking the
Ph2P–X–PPh2 ligands. Additionally, these resonances were split
into multiplets due to 31P–13C coupling interactions.
S
Ru
S
Ph2
P
diphos, 2 EtOCS2K
S
0.5 [RuCl2(p-cymene)]2
S
THF, rt then Δ, 25–48 h
P
Ph2
1: diphos = dppm (96%)
2: diphos = dppe (95%)
3: diphos = dppp (85%)
4: diphos = dppb (96%)
5: diphos = dpppe (93%)
OEt
6: diphos = dppen (73%)
7: diphos = dpbz (62%)
8: diphos = dppf (89%)
9: diphos = DPEphos (93%)
Scheme 1 Synthesis of [Ru(S2COEt)2(diphos)] complexes 1–9.
Structural analysis
1H and 13C NMR analysis of [Ru(S2COEt)2(diphos)] chelates 1–9
provided evidence for the dissociation of p-cymene from the
starting ruthenium dimer and for the incorporation of
diphosphine and O-ethylxanthate ligands in 1:2 stoichiometric
proportions. Strikingly, the methylene protons of the latter
anionic moiety afforded either a complex multiplet or two
1
distinct multiplets centered around 4 ppm on H NMR spec-
The FT-IR spectra of complexes 1–9 were recorded in KBr
pellets. In all cases, the most intense absorption was located
around 1210 cm–1. Another strong vibration was observed at
ca. 1035 cm–1 (Table 2). Based on earlier experimental and
computational studies,29 these two bands were assigned,
respectively, to the stretching of the C–OEt and C–S bonds
within the xanthate anion. It should be pointed out that their
actual wavenumbers suggested a significant contribution of
troscopy. This pattern sharply contrasted with the usual
quartet displayed by the OCH2CH3 group in KS2COEt and in
various organic xanthates with the generic formula RS2COEt.26
–
It is a sign of restricted rotation around the CH3CH2–OCS2
bond leading to diastereotopic methylene protons, as further
evidenced by X-ray crystallography (vide infra). The neigh-
boring methyl group was not affected and resonated as a
triplet around 1.2 ppm as expected. On 13C NMR spectroscopy,
the dithiocarboxylate unit led to a highly deshielded singlet at
ca. 226 ppm (Table 1). This characteristic signal was only
slightly shifted to lower field upon complexation (δ CS2 = 230.3
ppm for KS2COEt in DMSO-d6). It was no further affected by
varying the nature of the diphosphine ligand. These
observations are in line with previous trends evidenced while
studying the coordination chemistry of azolium-2-dithiocarbo-
xylate zwitterions and other 1,1-dithiolate ligands.6–15
2–
the EtO+=CS2 canonical form of the ligand, as further
discussed below. Phenyl rings directly attached to
a
phosphorus atom in the Ph2P–X–PPh2 ligands gave rise to a
characteristic sharp line at 1431 cm–1. Other less informative
absorptions observed on IR spectroscopy included weak C–H
stretching vibration bands between 2800 and 3100 cm–1 for
the various alkyl and aryl substituents of the xanthate and
diphos ligands, as well as weak summation bands arising from
combination and overtone of the aromatic C–H wagging
vibrational modes between 1650 and 2000 cm–1.
Table 1 13C NMR chemical shift of the CS2 group and 31P NMR chemical shift of the
diphos ligand in [Ru(S2COEt)2(diphos)] chelates 1–9 in CDCl3 at 298 K
Table 2 IR stretching vibrations of the [Ru(S2COEt)2(diphos)] chelates 1–9 (spectra
recorded in KBr pellets)
Complex
δ CS2 (ppm)
226.5
δ P (ppm)
3.34
Complex
ν PPh (cm–1)
1430
ν CO (cm–1)
1201
ν CS (cm–1)
1039
[Ru(S2COEt)2(dppm)] (1)
[Ru(S2COEt)2(dppe)] (2)
[Ru(S2COEt)2(dppp)] (3)
[Ru(S2COEt)2(dppb)] (4)
[Ru(S2COEt)2(dpppe)] (5)
[Ru(S2COEt)2(dppen] (6)
[Ru(S2COEt)2(dppbz)] (7)
[Ru(S2COEt)2(dppf)] (8)
[Ru(S2COEt)2(DPEphos)] (9)
226.5
76.61
37.17a
48.18
43.57
80.83
78.39
46.68
43.45
[Ru(S2COEt)2(dppm)] (1)
[Ru(S2COEt)2(dppe)] (2)
[Ru(S2COEt)2(dppp)] (3)
[Ru(S2COEt)2(dppb)] (4)
[Ru(S2COEt)2(dpppe)] (5)
[Ru(S2COEt)2(dppen] (6)
[Ru(S2COEt)2(dppbz)] (7)
[Ru(S2COEt)2(dppf)] (8)
[Ru(S2COEt)2(DPEphos)] (9)
226.6a
226.2
1432
1214
1034
1430
1214
1036
225.7
226.5
226.4
225.0
1431
1211
1036
1431
1217
1037
1431
1214
1034
1431
1217
1035
224.9
1431
1215
1038
1431
1209
1039
a Data recorded in CD2Cl2.
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DOI: 10.1039/C8DT02838A
Fig. 1 ORTEP representations of [Ru(S2COEt)2(diphos)] complexes 1–9 (ellipsoids drawn at the 50% probability level). Co-crystallized solvent molecules and hydrogen atoms
were omitted for clarity.
Dark yellow-brown crystals of complexes 1–9 suitable for monoclinic or triclinic lattice system. Racemic crystals of
X-ray diffraction analysis were easily obtained by slow chelate 3 contained a co-crystallized CH2Cl2 molecule and
evaporation of the mother liquors left after work-up (Fig. 1). belonged to the orthorhombic system. Only the Λ enantiomer
Compounds 1, 4, 5, and 7–9 crystallized as racemates in the of [Ru(S2COEt)2(dppe)] (2) and the
Δ enantiomer of
4 | J. Name., 2012, 00, 1-3
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[Ru(S2COEt)2(dppen)] (6) were present in the samples that we were always shorter than their Ru–S(2) and Ru–S(4)
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analyzed and they both crystallized in the orthorhombic counterparts, which reached 2.46 Å onDaOvI:e1r0a.1g0e3.9/TCh8iDsT00.208738ÅA
P212121 space group. Mononuclear entities featuring a highly difference clearly shows that a phosphine ligand gives rise to a
distorted octahedral geometry around the metal center were greater trans effect than a sulfur-based dithiocarboxylate unit,
observed in all cases (Chart 3). The two xanthate anions in line with earlier observations made on cis-
coordinated the ruthenium atom in a bidentate manner and [Ru(S2COR)2(PPh3)2] complexes.30
displayed similar metrics. Likewise, the two phosphorus atoms
In all the chelates under investigation, the S–Ru–S bite
of the diphosphine ligands were almost equivalent. Hence, angle was almost invariant and equal to 72° (Table 3). Such an
only selected bond lengths and angles pertaining to half the acute angle was mainly responsible for the strong distortion
coordination sphere of complexes 1–9 are listed in Table 3.
from an ideal octahedral geometry observed in complexes 1–9
with a quadratic elongation around 1.03 and an angular
variance comprised between 86 and 124.32 Other ruthenium
chelates based on NHC·CS2 zwitterions2,6,33 or dithiocarbamate
anions27c,27d,30b shared this feature. At about 115°, the S–C–S
bite angle of the O-ethylxanthate ligand was also typical of 1,1-
dithiolate chelates. Assuming that sodium or potassium
C3
C2
O1
C1
C3
C2
O1
C1
S1
Ru
S3
S1
Ru
S3
P1
P2
S2
S2
P1
P2
–
S4
C4
S4
C4
xanthates were valid models for the uncoordinated ROCS2
anions (although substantial M+...S– interionic contacts are
observed in their crystal structures) led to an average S–C–S
angle of 125° for the free ligands.14 Thus, a contraction of 10°
occurred upon chelation. Conversely, comparison of the C–S
distances measured within compounds 1–9 and in NaS2COEt or
KS2COEt did not reveal any significant variation. An average
value of 1.69 Å was obtained in all cases. This figure is almost
halfway between the standard lengths reported for C=S double
bonds (1.60 Å) and C–S single bonds (1.81 Å).34 Likewise, the
average C–O distance in [Ru(S2COEt)2(diphos)] complexes (1.33
Å) was intermediate between common values reported for CO
single and double bonds (1.45 Å and 1.21 Å, respectively).34
Moreover, the deviation from planarity between S(1), S(2),
C(1) and O(1) was very limited. Altogether, these metrics
further support IR spectroscopy measurements that suggested
a significant contribution of the EtO+=CS22– resonance form for
the O-ethylxanthate ligand in complexes 1–9.
O2
C5
C6
O2
C5
C6
Δ enantiomer
Λ enantiomer
Chart 3 Topology of the Δ and Λ enantiomers of [Ru(S2COEt)2(diphos)] chelates 1–9
showing the atom numbering system used for XRD analysis.
The Ru–P distances in complexes 1–5 that contained a
phosphorus atom substituted by two phenyl groups and an
alkyl chain varied between 2.25 and 2.32 Å (Table 3). Slightly
shorter values (2.24 Å) were recorded for complexes 6 and 7
with an ethylene or an ortho-phenylene bridge, whereas
compounds 8 and 9 with a ferrocene or a diphenylether linker
led to a ca. 2.31 Å length that matched the Ru–PPh3 distance
previously determined in various cis-[Ru(S2COR)2(PPh3)2]
complexes (R = Me, Et, iPr).30 As expected, the exact nature of
the spacer between the two phosphorus atoms had a
profound influence on the P–Ru–P angle, which varied
between 73° (with dppm in 1) and 103° (with dppf in 8).
Furthermore, the values recorded in this study were much
closer to the ligand's preferred bite angles (also known as
natural bite angles) than to the metal's own requirements
(90°), thereby indicating that the steric constraints imposed by
the diphosphine ligands dictated the actual geometry of the
complexes.31 At ca. 2.39 Å, the Ru–S(1) and Ru–S(3) distances
Examination of the molecular structures of complexes 1–9
clearly revealed that each phosphorus atom of their
diphosphine ligand had a phenyl ring pointing toward the ethyl
group of the nearest xanthate unit (Fig. 1). Such a spatial
proximity was held responsible for the inequivalence of the
1
methylene protons observed on H NMR spectroscopy (vide
supra). The largest chemical shift differences between the two
diastereotopic protons of the OCHaHbCH3 system were
observed with dppe (2), dppp (3), and dppen (6) (Δδ = 0.13,
0.19, and 0.16 ppm, respectively). These three compounds
Table 3 Selected bond distances (Å) and angles (°) derived from the molecular structures of [Ru(S2COEt)2(diphos)] complexes 1–9a
Complex (diphos)
Ru(1)–P(1)
Ru(1)–S(1)
Ru(1)–S(2)
C(1)–S(1)
C(1)–S(2)
C(1)–O(1)
P(1)–Ru(1)–P(2)
S(1)–Ru(1)–S(2)
S(1)–C(1)–S(2)
S(1)–C(1)–O(1)–C(2)
1 (dppm)
2.268(1)
2.389 (1)
2.451 (1)
1.692(2)
1.697(2)
1.326(2)
73.14(2)
72.23(2)
114.7(1)
–9.5(3)
2 (dppe)
2.256(1)
2.378(1)
2.491(1)
1.681(4)
1.693(4)
1.342(5)
85.88(4)
71.65(4)
115.4(2)
6.8(6)
3 (dppp)
2.265(2)
2.407(2)
2.464(2)
1.714(9)
1.665(9)
1.337(10)
91.31(7)
71.87(8)
115.6(5)
179.0(7)
4 (dppb)
2.283(1)
2.396(1)
2.457 (1)
1.691(2)
1.691(2)
1.331(2)
94.89(2)
71.63(2)
114.2(1)
–178.6(1)
5 (dpppe)
2.315(1)
2.416(1)
2.452(1)
1.693(4)
1.678(4)
1.334(5)
99.26(4)
71.78(3)
115.7(3)
–172.8(3)
6 (dppen)
2.246(1)
2.392(2)
2.463(2)
1.696(4)
1.678(6)
1.339(6)
84.62(5)
72.13(5)
116.1(3)
–178.0(4)
7 (dppbz)
2.244(1)
2.384 (1)
2.462(1)
1.681(3)
1.694(4)
1.329(4)
85.61(3)
72.03(3)
115.2(2)
175.7(3)
8 (dppf)
2.312(1)
2.399(1)
2.450(1)
1.686(4)
1.693(3)
1.329(4)
103.32(3)
71.73(3)
114.5 (2)
–171.6(3)
9 (DPEphos)
2.302(1)
2.408(6)
2.420(1)
1.688(3)
1.687(2)
1.343(3)
96.60(2)
72.15(2)
114.8(1)
4.2(3)
a See Fig. 1 for ORTEP plots and Chart 3 for atom labeling.
This journal is © The Royal Society of Chemistry 20xx
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gave rise to two well-resolved doublets of quadruplet around 4 specifically from an oxidation process that these ligands
View Article Online
2
3
ppm with JH,H = –10.3 Hz and JH,H = 7.1 Hz. All the other undergo when cycled above 1.20 V. ADsOimI: 1i0la.1r03p9h/Ce8nDoTm02e8n3o8nA
chelates led to overlapping second-order multiplets with the was observed by Wilton-Ely and coworkers with bimetallic
exception of [Ru(S2COEt)2(DPEphos)] (9), which exhibited an Ru(II) complexes bearing xanthate and dppm ligands.37 Only for
almost unsplit quadruplet. Variable temperature NMR experi- chelate 1 were additional peaks due to the Ru3+/Ru4+ couple
ments were carried out on a solution of [Ru(S2COEt)2(dppp)] visible at E1/2 = 1.15 V (Fig. 2), in line with earlier literature
(3) in DMSO-d6. A complete coalescence was not observed data.25 Last but not least, the redox chemistry of ferrocene was
even when the sample was heated up to 150 °C, which highlighted
from
the
cyclic
voltammogram
of
indicates that the conformation of the methylene group is [Ru(S2COEt)2(dppf)] (8). The Fe2+/Fe3+ couple gave rise to a
strongly locked by the neighboring phenyl ring. Of note, the half-wave potential of 1.06 V. Similar values were already
complex did not show any sign of thermal decomposition at reported for complexes of the [RuCl2(N–N)(dppf)] type (where
this temperature.
N–N designates bipyridine or phenanthroline ligands).38 Of
note, the E1/2 value for the free 1,1'-bis(diphenylphosphino)-
ferrocene in TBAP/CH2Cl2 electrolyte is 0.70 V vs. Ag/AgCl.38b
Cyclic voltammetry
Cyclic voltammograms of complexes 1–9 were recorded at 100
mV/s in a 0.1 M solution of tetrabutylammonium perchlorate
(TBAP) in dichloromethane. They all featured characteristic,
quasi-reversible waves for the Ru2+/Ru3+ redox couple
centered at a E1/2 value comprised between 0.65 and 0.80 V vs.
Ag/AgCl (Fig. 2 and Table 4). This half-wave potential was
clearly dependent on the diphosphine ligand nature and
increased according to the sequence: 8 (dppf) < 1 (dppm) < 9
(DEPphos) < 5 (dpppe) < 4 (dppb) < 3 (dppp) < 2 (dppe) < 7
(dppbz) < 6 (dppen). Except for [Ru(S2COEt)2(dppm)] (1), there
was a reverse correlation between E1/2 and the P(1)–Ru–P(2)
angles determined by X-ray crystallography, which decreased
from 103 to 73° following the order: 8 (dppf) > 5 (dpppe) > 9
(DPEphos) > 4 (dppb) > 3 (dppp) > 2 (dppe) > 7 (dpbz) > 6
(dppen) > 1 (dppm). Hence, if we exclude complex 1 for being
“too constrained”, a larger bite angle of the diphosphine ligand
led to an easier oxidation of Ru2+ into Ru3+, irrespective of the
exact nature of the linker group between the two phosphorus
atoms. These data emphasize the importance of steric effects
on the electron-donating properties of diphosphine ligands. It
is indeed well-established that the P–M–P angles in metal
chelates with bidentate phosphines are often quite different
from those recorded in complexes featuring two unidentate
phosphines and that geometric constraints imposed by the
linker group may result in significant electronic differences.35
Furthermore, because Ru(III) is slightly smaller than Ru(II) (ionic
radii of 0.68 vs. 0.73 Å, respectively),36 oxidation should be
more difficult to perform with the most crowded ligand
systems, leading to higher E1/2 values. It is also worth
highlighting the progressive increase of the current densities
Ip,ox and Ip,red with the number of methylene units and the
corresponding larger P(1)–Ru–P(2) bite angle within homolo-
gous complexes 2–5, although we don't have any rationale for
this observation.
In addition to the main peaks assigned to the Ru2+/Ru3+
couple, additional signals were detected in some instances.
Thus, we observed the reduction of unidentified by-products
at E values of 0.2–0.3 V on the reverse scan with complexes 1,
3, and 6 (Fig. 2). The reversible oxidation of these compounds
became visible around E = 0.3–0.4 V upon further cycling (not
shown). This electrochemical response was not detected when
the potential was cycled below 1.20 V. It most likely originates
from the redox chemistry of dppm, dppp, and dppen, and
Fig. 2 Cyclic voltammograms of [Ru(S2COEt)2(diphos)] chelates 1–9 dissolved in 0.1 M
TBAP/CH2Cl2 (only the first cycles are displayed).
6 | J. Name., 2012, 00, 1-3
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Table 4 Half-wave potentials for the Ru2+/Ru3+ redox couple determined by cyclic
voltammetrya and diphosphine bite angle of complexes 1–9 determined by XRD
Table 5 Ruthenium-catalyzed synthesis of vinyl esters from benzoic acid and 1-hexynea
View Article Online
DOI: 10.1039/C8DT02838A
O
Ru cat. 1–9 (0.8 mol%)
Complex
E1/2 (V)
0.668
0.769
0.759
0.743
0.740
0.800
0.773
0.645
0.672
P(1)–Ru(1)–P(2) angle (°)
Bun
+
OH
Bun
H
Ph
[Ru(S2COEt)2(dppm)] (1)
[Ru(S2COEt)2(dppe)] (2)
[Ru(S2COEt)2(dppp)] (3)
[Ru(S2COEt)2(dppb)] (4)
[Ru(S2COEt)2(dpppe)] (5)
[Ru(S2COEt)2(dppen] (6)
[Ru(S2COEt)2(dppbz)] (7)
[Ru(S2COEt)2(dppf)] (8)
[Ru(S2COEt)2(DPEphos)] (9)
73
86
91
95
99
85
86
103
97
PhCH3, 160 °C, 30 min
O
O
O
Bun
O
O
O
Ph
+
Ph
+
Ph
Bun
10
11
12
Catalyst
Conversion (%)b
Selectivity (%)b
10
42
11
24
55
19
26
44
46
43
29
41
12
a
Experimental conditions: TBAP in CH2Cl2 (0.1 M), Pt working and counter
electrodes, Ag/AgCl reference electrode, room temperature, scan rate 100 mV/s.
[Ru(S2COEt)2(dppm)] (1)
[Ru(S2COEt)2(dppe)] (2)
[Ru(S2COEt)2(dppp)] (3)
[Ru(S2COEt)2(dppb)] (4)
[Ru(S2COEt)2(dpppe)] (5)
[Ru(S2COEt)2(dppen] (6)
[Ru(S2COEt)2(dppbz)] (7)
[Ru(S2COEt)2(dppf)] (8)
2
10
3
11
5
2
9
11
7
34
25
47
50
32
38
41
44
45
20
34
24
24
16
16
27
14
Catalytic tests
Various types of ruthenium catalysts efficiently promote the
formation of vinyl esters from benzoic acid and 1-hexyne with
excellent selectivities toward either the branched product 10
or its (E) and (Z) linear isomers 11 and 12 (Table 5).39 In
particular, we devised a rapid and straightforward procedure
for the regioselective synthesis of 10 using the readily available
[RuCl2(p-cymene)(PPh3)] complex in toluene at 160 °C under
microwave irradiation.40 This experimental setup was adopted
to probe the catalytic activity of [Ru(S2COEt)2(diphos)] chelates
1–9 in the synthesis of enol esters. As shown in Table 5, low
yields and poor selectivities were obtained in all cases. 31P
NMR analysis of the reaction media left after cooling, using a
sealed capillary tube containing triphenylphosphine oxide in
CD2Cl2 as an external reference (δ = 27.8 ppm), revealed that
the starting complexes remained mostly unaltered, despite the
harsh treatment that was applied to them. Only in the case of
[Ru(S2COEt)2(dppe)] (2) was a new singlet visible at δ = 43.7
ppm, while two small peaks located at δ = 41.8 and 0.6 ppm
were detected with [Ru(S2COEt)2(dppb)] (4) (Fig. S70).† These
structural changes could explain the slightly better yields
achieved with these two catalyst precursors compared with
the other species examined, but we did not further investigate
this possibility.
[Ru(S2COEt)2(DPEphos)] (9)
a Experimental conditions: catalyst (0.004 mmol), benzoic acid (0.5 mmol), 2.6 mL
of a stock solution containing 1-hexyne (0.75 mmol) and isooctane (0.13 mmol) in
b
dry toluene; microwave irradiation at 160 °C for 30 min. Determined by GC
using isooctane as an internal standard.
Next, we shifted our attention to the cyclopropanation of
styrene with ethyl diazoacetate in the presence of chelates 1–9
(Table 6). This reaction is another representative catalytic
process leading to highly valuable intermediates for organic
synthesis, which greatly benefited from the intervention of
ruthenium complexes, sometimes in an asymmetric fashion.41
Our screening was carried out at 60 °C using 0.5 mol% of
catalyst in the presence of air. The diazo compound was slowly
added with a syringe pump over 5 h to minimize its unwanted
dimerization. Despite this precaution, up to 10% of diethyl
maleate and fumarate (14) were formed after a total reaction
time of 50 h, as evidenced by GC analysis. Variations in the
cis/trans ratio for these products were hardly meaningful and
should not be overinterpreted. More importantly, the desired
ethyl 2-phenylcyclopropanecarboxylate (13) was obtained in
high yield (>90%) as a ca. 30/70 mixture of cis and trans
isomers, irrespective of the exact nature of the diphosphine
ligand. Monitoring the release of nitrogen with a gas burette
throughout the reaction course confirmed that all the
complexes under investigation behaved similarly and were
rather slow promoters for the formal carbene insertion
reaction (Fig. S71).† Indeed, it took them about 36 h to reach a
quantitative consumption of ethyl diazoacetate. With the most
efficient [RuCl2(p-cymene)(NHC)] catalyst precursors, for
instance, the reaction was complete in less than 6 h.42
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such as the half-sandwich Ru(II) complex [Cp*RuCl(PPh3)2]45 or
the related Ru(III) derivative [Cp*RuCl2(PPh3)] combined with
Table 6 Ruthenium-catalyzed reactions of styrene and ethyl diazoacetatea
View Article Online
DOI: 10.1039/C8DT02838A
Ph
CO2Et
CO2Et
magnesium as a reducing agent,46 that were already active at
40 or 60 °C, the [Ru(S2COEt)2(diphos)] chelates displayed a
latent behavior. With these compounds, formation of
unsaturated active species occurred only above 100 °C and
was most efficient with the dppm- and dppen-based
complexes 1 and 5, which feature, respectively, highly strained
and rigid 4- and 5-membered diphosphinometallacycles.
Hence, it can be assumed that active species were generated
via partial or total decoordination of the diphosphine ligand
rather than the xanthate ligands.
+
N2
Ru cat. 1–9 (0.5 mol%), 60 °C, 50 h
CO2Et EtO2C
N2
2
Ph
CO2Et
13
14
Catalyst
Cyclopropanes (13)
Dimers (14)
Yield
(%)b
93
94
92
93
94
94
92
Cis/trans
Yield
(%)b
7
Cis/trans
ratiob
1.56
ratiob
0.41
0.42
0.42
0.46
0.47
0.47
0.43
0.44
0.45
Table 7 Ruthenium-catalyzed atom transfer radical addition of carbon tetrachloride to
[Ru(S2COEt)2(dppm)] (1)
[Ru(S2COEt)2(dppe)] (2)
[Ru(S2COEt)2(dppp)] (3)
[Ru(S2COEt)2(dppb)] (4)
[Ru(S2COEt)2(dpppe)] (5)
[Ru(S2COEt)2(dppen] (6)
[Ru(S2COEt)2(dppbz)] (7)
[Ru(S2COEt)2(dppf)] (8)
[Ru(S2COEt)2(DPEphos)] (9)
methyl methacrylatea
6
8
7
6
6
8
7
10
2.60
0.61
0.51
1.41
2.23
0.49
0.91
1.63
Ru cat. 1–9 (0.5 mol%)
+
CCl4
PhCH3, 30 min
CO2Me
Cl
Cl
93
90
Cl3C
Cl3C
+
2
CO2Me
CO2Me
a
Experimental conditions: catalyst (0.005 mmol), styrene (2 mL), ethyl diazo-
acetate (1 mmol) diluted with styrene up to 1 mL and added in 5 h at 60 °C; 50 h
total reaction time at 60 °C. b Determined by GC (relative errors are ± 5%).
15
16
Catalyst
Reaction at 140 °C
Reaction at 160 °C
Yield
(%)b
98
54
10
3
81
18
4
15/16
ratiob
5.93
2.02
1.80
0.58
1.97
1.20
0.89
0.43
0.80
Yield
(%)b
100
96
83
77
83
100
60
50
47
15/16
ratiob
1.98
3.31
2.87
1.48
1.40
4.30
2.26
1.24
1.28
Finally, we investigated the catalytic activity of complexes
1–9 in the atom transfer radical addition (ATRA) of carbon
tetrachloride and methyl methacrylate (MMA). In this reaction,
also known as the Kharasch addition, ruthenium acts as an
halogen carrier in a reversible redox process.43 Experiments
were conducted in a monomodal microwave reactor at
temperatures ranging between 100 and 160 °C (see the ESI for
full details).† As we had demonstrated in 2007, such a device
was very convenient to speed up the transformation by quickly
bringing the reaction mixtures to temperatures well above the
boiling points of the reagents and solvent.44 In all the runs, the
catalyst loading was 0.5 mol% and the halogen derivative was
introduced in a fourfold excess compared to the olefin to
ensure that only the mono- and diaddition products 15 and 16
were obtained, with no significant oligomerization or polyme-
rization of MMA. Under these conditions, [Ru(S2COEt)2(dppm)]
(1) emerged as the most potent catalyst at 140 °C (Table 7).
Indeed, this complex afforded an almost complete conversion
of MMA and a high selectivity toward the monoinsertion
product 15. When the temperature was raised to 160 °C,
several other chelates became active and the proportion of
product 16 increased significantly. 31P NMR analysis of the
reaction mixtures recovered after cooling, using a sealed
capillary tube containing DMSO-d6 for external lock, showed
that only chelates 1 and 5 underwent significant alterations at
140 °C, in line with their greater catalytic activity. Evidence for
the loss of diphosphine ligands from complexes 2, 4, 6, and 8
became only visible at 160 °C, while species 3, 7, and 9 were
even more robust (Fig. S73 and S74).† These results highlight
the high thermal stability of compounds 1–9, which is not
surprising for 18-electron complexes bearing three strongly
chelating ligands. Unlike other ruthenium catalysts for ATRA,
[Ru(S2COEt)2(dppm)] (1)
[Ru(S2COEt)2(dppe)] (2)
[Ru(S2COEt)2(dppp)] (3)
[Ru(S2COEt)2(dppb)] (4)
[Ru(S2COEt)2(dpppe)] (5)
[Ru(S2COEt)2(dppen] (6)
[Ru(S2COEt)2(dppbz)] (7)
[Ru(S2COEt)2(dppf)] (8)
2
5
[Ru(S2COEt)2(DPEphos)] (9)
a
Experimental conditions: catalyst (0.006 mmol), 1.2 mL of a stock solution
containing MMA (1.2 mmol), CCl4 (4.8 mmol), and dodecane (0.18 mmol) in dry
toluene; microwave irradiation at 140 °C or 160 °C for 30 min. Determined by
b
GC using dodecane as an internal standard.
Conclusions
The one-pot reaction of [RuCl2(p-cymene)]2 with potassium
O-ethylxanthate and a set of nine representative diphosphine
ligands was carried out in THF. Recourse to a monomodal
microwave oven or a pressure reactor was found very
convenient to shift equilibria toward the formation of
monometallic [Ru(S2COEt)2(diphos)] chelates 1–9, which were
isolated in satisfactory to excellent yields after a simple work-
up. All the products were fully characterized using various
analytical techniques and their molecular structures were
determined by X-ray diffraction analysis. In the solid state,
they all featured a highly distorted octahedral geometry with a
S–Ru–S bite angle close to 72° and P–Ru–P angles comprised
between 73° and 103°, depending on the nature of the spacer
group between the two phosphorus atoms. Bond lengths and
IR stretching frequencies recorded for the anionic xanthate
8 | J. Name., 2012, 00, 1-3
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Dalton Transactions
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ligands within complexes 1–9 strongly suggested a significant TMS and are referenced from the solvent peaks or TMS for 1H
View Article Online
13
contribution of their EtO+=CS22– resonance form. Moreover, 1H and C. Assignments were established DwOitI:h10t.h10e39h/eCl8pDTo0f2A83P8TA,
NMR and XRD analyses showed that the methylene protons of COSY, HMBC, and HSQC sequences. Infrared spectra were
the ethyl groups were diastereotopic and remained recorded with a Bruker Equinox 55 FT-IR spectrometer.
inequivalent even when the samples were heated up to 150 Electrospray mass spectra were obtained using a Micromass
°C, due to a strong locking of their conformation by a LCT Premier instrument. GC analyses were performed on a
neighboring phenyl ring on the diphos ligand. On cyclic Varian Star 3400 CX gas chromatograph equipped with a
voltammetry, quasi-reversible waves were observed for the RSLM-150 capillary column (25 m × 0.25 mm, 0.25 μm film
Ru2+/Ru3+ redox couple of the nine complexes under thickness) and a flame ionization detector. Elemental analyses
investigation. The E1/2 values spanned the range comprised were carried out in the Laboratory of Pharmaceutical
between 0.65 and 0.80 V vs. Ag/AgCl and could be correlated Chemistry at the University of Liege.
with the P(1)–Ru–P(2) bite angles of the diphosphine ligands
determined by X-ray crystallography.
Synthesis of [Ru(S2COEt)2(diphos)] complexes
The activity of chelates 1–9 was probed in three different A 20 mL Schlenk flask or a 10 mL pressure vial containing a
catalytic processes, namely, the synthesis of vinyl esters from magnetic stirring bar was charged with [RuCl2(p-cymene)]2
benzoic acid and 1-hexyne, the cyclopropanation of styrene (245 mg, 0.40 mmol), a diphosphine (0.88 mmol, 2.2 equiv.),
with ethyl diazoacetate, and the atom transfer radical addition potassium O-ethylxanthate (283 mg, 1.76 mmol, 4.4 equiv.),
of carbon tetrachloride and methyl methacrylate. Only low and THF (8 mL). The reaction mixture was stirred for 24 h at
yields and poor selectivities were obtained in the first case. 31P room temperature. It was then heated with stirring at 80–90
NMR analysis of the reaction mixtures showed that the °C for 24 h in an oil bath or at 130 °C for 1 h using a pressure
starting complexes remained mostly unaltered under the reactor. The color changed from red to yellow-orange. After
experimental conditions adopted, despite the harsh thermal cooling to room temperature, the reaction mixture was
treatment that was applied to them. In the second case, brought back to air. It was centrifuged for 5–10 min and
quantitative conversions of ethyl diazoacetate were achieved filtered through Celite® to remove KCl and the excess of
within 50 h at 60 °C. Monitoring the rate of nitrogen evolution KS2COEt. The solvent was removed under vacuum on a rotary
revealed, however, that all the catalysts screened behaved evaporator. The residue was washed with petroleum ether (3
rather similarly and were slower initiators than other types of × 5 mL) and diethyl ether (2 × 5 mL) to remove p-cymene and
ruthenium complexes. In the ATRA of CCl4 and MMA, the excess of diphosphine, respectively. The crude product was
[Ru(S2COEt)2(dppm)] (1) was singled out as a very active and dissolved in dichloromethane (2–3 mL) and slowly poured into
selective catalyst already at 140 °C. Contrastingly, most of the diethyl ether (20 mL) under vigorous stirring. The precipitate
other complexes investigated in this study resisted degrada- was separated from the supernatant solution and dried under
tion up to 160 °C and were only moderately active. Altogether, high vacuum.
1
these results are in line with the high stability displayed by [Ru(S2COEt)2(dppm)] (1). Yellow solid (560 mg, 96% yield). H
[Ru(S2COEt)2(diphos)] complexes 1–9. Indeed, these 18-elec- NMR (400 MHz, CDCl3): δ = 1.24 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt),
2
tron species are strongly chelated by two xanthate ligands and 4.21 – 4.51 (m, 4 H, CH2 OEt), 4.92 (t, JP,H = 10.2 Hz, 2 H, CH2
one diphosphine. Hence, their potential to release unsatura- dppm), 7.13 – 7.28 (m, 6H, Ph dppm), 7.29 – 7.38 (m, 4H, Ph
ted, catalytically active species should be rather limited.
dppm), 7.38 – 7.50 (m, 6H, Ph dppm), 7.65 – 7.81 (m, 4H, Ph
dppm) ppm. 13C NMR (101 MHz, CDCl3): δ = 14.0 (s, CH3 OEt),
1
50.7 (t, JP,C = 21.6 Hz, CH2 dppm), 66.1 (s, CH2 OEt), 127.9 (t,
3
3JP,C = 4.8 Hz, m-CHar dppm), 128.6 (t, JP,C = 4.9 Hz, m-CHar
Experimental
dppm), 129.0 (s, p-CHar dppm), 130.1 (s, p-CHar dppm), 130.7
General information
2
2
(t, JP,C = 5.1 Hz, o-CHar dppm), 132.2 (t, JP,C = 5.7 Hz, o-CHar
dppm), 134.8 (t, 1JP,C = 17.7 Hz, i-Car dppm), 135.9 (t, 1JP,C = 19.0
Hz, i-Car dppm), 226.5 (s, S2CO) ppm. 31P NMR (162 MHz,
CDCl3): δ = 3.34 (s) ppm. IR (KBr): ν = 3047 (w), 2970 (w), 2916
(w), 1430 (m), 1284 (m), 1201 (s), 1155 (m), 1086 (m), 1039
(m), 737 (m), 720 (m), 697 (m), 537 (m), 509 (m) cm–1. ESI-MS
(CH3CN): m/z calcd for C31H32O2P2RuS4 ([M]+), 727.97983;
found, 727.97887. Calc. for C31H32O2P2RuS4: C, 51.2; H, 4.4; S,
17.6%. Found: C, 51.3; H, 4.6; S, 17.2%.
Unless otherwise specified, all the syntheses were carried out
under a dry nitrogen atmosphere using standard Schlenk
techniques. Solvents were distilled from appropriate drying
agents and deoxygenated prior to use. The [RuCl2(p-cymene)]2
dimer47 and the diphosphines dppm, dppp, dppb, dpppe, dppf,
and DPEphos were purchased from Strem. Potassium O-ethyl
dithiocarbonate and the diphosphines dppe, dppen, and dppbz
were obtained from Aldrich. Reactions under pressure were
carried out using a CEM Discover monomodal microwave oven
or an Anton Paar Monowave 50 reactor. Petroleum ether
refers to the fraction of boiling point 40–60 °C and was
purchased from VWR. 1H, 13C, and 31P NMR spectra were
recorded at 298 K with a Bruker DRX 400 spectrometer
operating at 400.13, 100.62, and 161.85 MHz, respectively.
Chemical shifts are listed in parts per million downfield from
1
[Ru(S2COEt)2(dppe)] (2).‡ Yellow solid (562 mg, 95% yield). H
NMR (400 MHz, CDCl3): δ = 1.15 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt),
2.40 – 2.62 (m, 2 H, CH2 dppe), 2.79 – 3.05 (m, 2 H, CH2 dppe),
2
3
4.08 (dq, JH,H = –10.3, JH,H = 7.1 Hz, 2 H, CH2 OEt), 4.21 (dq,
2JH,H = –10.3, 3JH,H = 7.1 Hz, 2 H, CH2 OEt), 7.08 – 7.25 (m, 10 H,
Ph dppe), 7.32 – 7.46 (m, 6 H, Ph dppe), 7.68 – 7.83 (m, 4 H, Ph
dppe) ppm. 13C NMR (101 MHz, CDCl3): δ = 14.0 (s, CH3 OEt),
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30.2 (dd, 1JP,C = 23.9 Hz, 2JP,C = 21.3 Hz, CH2 dppe), 66.1 (s, CH2 dpppe), 128.0 (s, p-CHar dpppe), 129.5 (s, p-CHar dpppe), 130.5
View Article Online
3
2
2
OEt), 127.2 (t, JP,C = 4.4 Hz, m-CHar dppe), 128.4 (s, p-CHar (t, JP,C = 3.5 Hz, o-CHar dpppe), 134.6 (tD, OJI:P1,C0.=10539.1/CH8Dz,T0o2-8C3H8aAr
dppe), 128.5 (t, JP,C = 4.6 Hz, m-CHar dppe), 130.0 (s, p-CHar dpppe), 135.8 – 136.9 (m, i-Car dpppe), 141.7 – 142.6 (m, i-Car
3
dppe), 130.9 (t, 2JP,C = 4.2 Hz, o-CHar dppe), 133.1 (t, 2JP,C = 4.9 dpppe), 225.7 (s, S2CO) ppm. 31P NMR (162 MHz, CDCl3): δ =
Hz, o-CHar dppe), 135.1 – 136.2 (m, i-Car dppe), 226.5 (s, S2CO) 43.57 (s) ppm. IR (KBr): ν = 3049 (w), 2977 (m), 2924 (w), 2851
ppm. 31P NMR (162 MHz, CDCl3): δ = 76.61 (s) ppm. IR (KBr): ν (w), 1431 (m), 1207 (s), 1121 (m), 1037 (m), 694 (m), 496 (m)
= 3046 (w), 2980 (w), 2890 (w), 1432 (m), 1214 (s), 1100 (m), cm–1. ESI-MS (CH3CN): m/z calcd for C35H40O2P2RuS4 ([M]+),
1034 (m), 738 (m), 693 (m), 523 (m) cm–1. ESI-MS (CH3CN): m/z 784.04243; found, 784.04124. Calc. for C35H40O2P2RuS4: C,
calcd for C32H34O2P2RuS4 ([M]+), 741.99548; found, 741.99518. 53.6; H, 5.1; S, 16.4%. Found: C, 53.8; H, 5.3; S, 15.6%.
Calc. for C32H34O2P2RuS4: C, 51.8; H, 4.6; S, 17.3%. Found: C, [Ru(S2COEt)2(dppen)] (6). Yellow solid (432 mg, 73% yield). 1H
48.4; H, 4.4; S, 16.8%.
NMR (400 MHz, CDCl3): δ = 1.11 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt),
1
2
3
[Ru(S2COEt)2(dppp)] (3). Yellow solid (514 mg, 85% yield). H 4.00 (dq, JH,H = –10.3, JH,H = 7.1 Hz, 2 H, CH2 OEt), 4.16 (dq,
NMR (400 MHz, CD2Cl2): δ = 1.28 (t, JH,H = 7.1 Hz, 6 H, CH3 2JH,H = –10.3, 3JH,H = 7.1 Hz, 2 H, CH2 OEt), 7.04 – 7.24 (m, 10 H,
3
OEt), 1.84 – 2.06 (m, 2 H, CH2CH2CH2 dppp), 2.06 – 2.22 (m, 2 Ph dppen), 7.42 (m, 6 H, Ph dppen), 7.80 (m, 4 H, Ph dppen),
H, PCH2 dppp), 2.66 – 2.86 (m, 2 H, PCH2 dppp), 4.16 (dq, 2JH,H
=
7.85 – 8.04 (m, 2 H, CH=CH dppen) ppm. 13C NMR (101 MHz,
3
–10.3, 3JH,H = 7.1 Hz, 2 H, CH2 OEt), 4.31 (dq, 2JH,H = –10.2, 3JH,H CDCl3): δ = 13.9 (s, CH3 OEt), 66.1 (s, CH2 OEt), 127.2 (t, JP,C
=
= 7.1 Hz, 2 H, CH2 OEt), 7.10 – 7.23 (m, 4 H, Ph dppp), 7.23 – 4.6 Hz, m-CHar dppen), 128.60 (s, p-CHar dppen), 128.64 (t, 3JP,C
7.47 (m, 16 H, Ph dppp) ppm. 13C NMR (101 MHz, CD2Cl2): δ = = 4.6 Hz, m-CHar dppen), 130.2 (s, p-CHar dppen), 131.3 – 131.7
1
14.3 (s, CH3 OEt), 20.6 (s, PCH2CH2 dppp), 29.8 (d, JP,C = 16.8 (m, o-CHar dppen), 132.9 – 133.3 (m, o-CHar dppen), 133.6 (dd,
Hz, PCH2 dppp), 30.0 (d, 1JP,C = 16.7 Hz, PCH2 dppp), 66.7 (s, CH2 1JP,C = 44.7, JP,C = 3.1 Hz, i-Car dppen), 134.6 (dd, JP,C = 45.9,
4
1
3
3
OEt), 127.8 (t, JP,C = 4.4 Hz, m-CHar dppp), 128.2 (t, JP,C = 4.6 4JP,C = 3.4 Hz, i-Car dppen), 150.0 (dd, 1JP,C = 36.6, 2JP,C = 34.2 Hz,
Hz, m-CHar dppp), 129.1 (s, p-CHar dppp), 129.8 (s, p-CHar CH=CH dppen), 226.5 (s, S2CO) ppm. 31P NMR (162 MHz,
dppp), 132.3 (t, 2JP,C = 4.1 Hz, o-CHar dppp), 134.0 (t, 2JP,C = 5.0 CDCl3): δ = 80.83 (s) ppm. IR (KBr): ν = 3043 (w), 2980 (w),
Hz, o-CHar dppp), 136.4 – 137.8 (m, i-Car dppp), 137.8 – 139.2 2420 (w), 2380 (w), 1431 (m), 1217 (s), 1094 (m), 1034 (m),
(m, i-Car dppp), 226.6 (s, S2CO) ppm. 31P NMR (162 MHz, 737 (m), 693 (m), 553 (m) cm–1. ESI-MS (CH3CN): m/z calcd for
CD2Cl2): δ = 37.17 (s) ppm. IR (KBr): ν = 3041 (w), 2980 (w), C32H32O2P2RuS4 ([M]+), 739.98044; found, 739.98105. Calc. for
2937 (w), 2859 (w), 1430 (m), 1214 (s), 1036 (m), 695 (m), 509 C32H32O2P2RuS4: C, 52.0; H, 4.4; S, 17.3%. Found: C, 52.1; H,
(m) cm–1. ESI-MS (CH3CN): m/z calcd for C33H36O2P2RuS4 ([M]+), 4.6; S, 17.1%.
1
756.01116; found, 756.01125. Calc. for C33H36O2P2RuS4: C, [Ru(S2COEt)2(dppbz)] (7). Yellow solid (388 mg, 62% yield). H
52.4; H, 4.8; S, 17.0%. Found: C, 51.8; H, 4.9; S, 16.3%.
NMR (400 MHz, CDCl3): δ = 1.15 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt),
[Ru(S2COEt)2(dppb)] (4).‡ Yellow solid (591 mg, 96% yield). 1H 4.03 – 4.32 (m, 4 H, CH2 OEt), 7.12 – 7.22 (m, 4H, Ph dppbz),
NMR (400 MHz, CDCl3): δ = 1.24 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt), 7.22 – 7.29 (m, 6H, Ph dppbz), 7.32 – 7.41 (m, 6H, Ph dppbz),
1.38 – 1.56 (m, 2 H, PCH2CH2 dppb), 1.69 – 1.95 (m, 2 H, 7.42 – 7.50 (m, 2H, m-CHar C6H4 dppbz), 7.49 – 7.58 (m, 4H, Ph
PCH2CH2 dppb), 2.59 – 2.87 (m, 4 H, PCH2 dppb), 3.94 – 4.33 dppbz), 7.58 – 7.68 (m, 2H, o-CHar C6H4 dppbz) ppm. 13C NMR
(m, 4 H, CH2 OEt), 7.13 – 7.31 (m, 10 H, Ph dppb), 7.30 – 7.49 (101 MHz, CDCl3): δ = 14.0 (s, CH3 OEt), 66.0 (s, CH2 OEt), 127.1
(m, 6 H, Ph dppb), 7.57 – 7.79 (m, 4 H, Ph dppb) ppm. 13C NMR (t, JP,C = 4.7 Hz, m-CHar Ph dppbz), 128.2 (t, JP,C = 4.7 Hz, m-
3
3
(101 MHz, CDCl3): δ = 13.9 (s, CH3 OEt), 24.1 (s, PCH2CH2 dppb), CHar Ph dppbz), 128.8 (s, p-CHar Ph dppbz), 129.5 (s, p-CHar Ph
1
31.7 (t, JP,C = 13.7 Hz, PCH2 dppb), 65.8 (s, CH2 OEt), 126.9 (t, dppbz), 130.0 (s, m-CHar C6H4 dppbz), 132.6 (dd, 2JP,C = 8.6, 4.5
2
3JP,C = 4.2 Hz, m-CHar dppb), 127.88 (s, p-CHar dppb),127.94 (t, Hz, o-CHar Ph dppbz), 133.0 (t, JP,C = 8.6 Hz, o-CHar C6H4
3JP,C = 4.5 Hz, m-CHar dppb), 129.6 (s, p-CHar dppb), 130.9 (t, dppbz), 132.8 – 133.5 (m, i-Car Ph dppbz), 135.7 (dt, 1JP,C = 28.8
4
2JP,C = 3.7 Hz, o-CHar dppb), 134.1 (t, 2JP,C = 4.8 Hz, o-CHar dppb), Hz, JP,C = 9.2 Hz, i-Car Ph dppbz), 146.6 (t, JP,C = 41.7 Hz, i-Car
136.4 – 137.9 (m, i-Car dppb), 139.8 – 141.2 (m, i-Car dppb), C6H4 dppbz), 226.4 (s, S2CO) ppm. 31P NMR (162 MHz, CDCl3): δ
226.2 (s, S2CO) ppm. 31P NMR (162 MHz, CDCl3): δ = 45.18 (s) = 78.39 (s) ppm. IR (KBr): ν = 3050 (w), 2980 (w), 2925 (w),
ppm. IR (KBr): ν = 3051 (w), 2981 (w), 2916 (w), 2849 (w), 1431 2852 (w), 1431 (m), 1217 (s), 1090 (m), 1035 (m), 693 (m), 557
(m), 1211 (s), 1119 (m), 1036 (m), 693 (m), 515 (m) cm–1. ESI- (m), 528 (m) cm–1. ESI-MS (CH3CN): m/z calcd for
MS (CH3CN): m/z calcd for C34H38O2P2RuS4 ([M]+), 770.02678; C36H34O2P2RuS4 ([M]+), 789.99548; found, 789.99564. Calc. for
found, 770.02585. Calc. for C34H38O2P2RuS4: C, 53.0; H, 5.0; S, C36H34O2P2RuS4: C, 54.7; H, 4.3; S, 16.2%. Found: C, 54.6; H,
16.7%. Found: C, 53.2; H, 5.1; S, 15.8%.
4.4; S, 15.9%.
1
[Ru(S2COEt)2(dpppe)] (5). Yellow solid (583 mg, 93% yield). 1H [Ru(S2COEt)2(dppf)] (8). Yellow solid (638 mg, 89% yield). H
NMR (400 MHz, CDCl3): δ = 1.30 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt), NMR (400 MHz, CDCl3): δ = 1.19 (t, 3JH,H = 7.1 Hz, 6 H, CH3 OEt),
1.35 – 1.56 (m, 6 H, PCH2(CH2)3CH2P dpppe), 2.51 – 2.54 (m, 4 4.05 – 4.20 (m, 4 H, CH2 OEt), 4.23 (s, 2 H, Cp dppf), 4.35 (d,
H, PCH2 dpppe), 4.03 – 4.38 (m, 4 H, CH2 OEt), 7.19 – 7.44 (m, 3JP,H = 11.2 Hz, 4 H, Cp dppf), 4.51 (s, 2 H, Cp dppf), 7.18 – 7.38
16 H, Ph dpppe), 7.64 (t, 3JH,H = 8.1 Hz, 4 H, Ph dpppe) ppm. 13
C
(m, 12 H, Ph dppf), 7.49 – 7.74 (m, 8 H, Ph dppf) ppm. 13C NMR
NMR (101 MHz, CDCl3): δ = 13.9 (s, CH3 OEt), 20.8 (s, (101 MHz, CDCl3): δ = 13.9 (s, CH3 OEt), 66.0 (s, CH2 OEt), 70.6
2
PCH2CH2CH2 dpppe), 26.6 (t, JP,C = 5.2 Hz, PCH2CH2 dpppe), (s, m-Cp dppf), 72.7 (t, 2JP,C = 3.2 Hz, o-Cp dppf), 74.0 (s, m-Cp
28.2 (t, 1JP,C = 12.8 Hz, PCH2 dpppe), 65.8 (s, CH2 OEt), 127.0 (t, dppf), 76.2 (t, 2JP,C = 7.0 Hz, o-Cp dppf), 83.0 ('dt', N = 61.7 Hz,
3
3
3JP,C = 4.1 Hz, m-CHar dpppe), 127.7 (t, JP,C = 4.5 Hz, m-CHar i-Cp dppf),§ 126.6 (t, JP,C = 4.4 Hz, m-CHar Ph dppf), 127.3 (t,
10 | J. Name., 2012, 00, 1-3
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3JP,C = 4.4 Hz, m-CHar Ph dppf), 128.7 (s, p-CHar Ph dppf), 129.2 isooctane (0.13 mmol) in dry toluene was added.VTiehweArtvicilaelOwnlianes
2
DOI: 10.1039/C8DT02838A
(s, p-CHar Ph dppf), 134.0 (t, JP,C = 4.6 Hz, o-CHar Ph dppf), capped under nitrogen, heated to 160 °C (monitored by an IR
134.6 (t, 2JP,C = 4.7 Hz, o-CHar Ph dppf), 134.9 ('dt', N = 58.4 Hz, sensor), and held at that temperature for 30 min in a CEM
i-Car Ph dppf),§ 138.1 ('dt', N = 64.4 Hz, i-Car Ph dppf),§ 225.0 (s, Discover instrument with a 170 W microwave power. After
S2CO) ppm. 31P NMR (162 MHz, CDCl3): δ = 46.68 (s) ppm. IR rapid air-cooling by the unit, the reaction mixture was
(KBr): ν = 3046 (w), 2973 (w), 2945 (w), 2899 (w), 1431 (m), analyzed by GC using isooctane as an internal standard.
1215 (s), 1161 (m), 1038 (m), 696 (m) cm–1. ESI-MS (CH3CN):
m/z calcd for C40H38FeO2P2RuS4 ([M]+), 897.96172; found,
Cyclopropanation of styrene
897.96031. Calc. for C40H38FeO2P2RuS4: C, 53.5; H, 4.3; S, A 10 mL vial equipped with a magnetic stirring bar and a
14.3%. Found: C, 52.8; H, 4.4; S, 13.8%.
septum was charged with a [Ru(S2COEt)2(diphos)] complex
[Ru(S2COEt)2(DPEphos)] (9). Yellow solid (654 mg, 93% yield). (0.005 mmol) and styrene (2 mL). The mixture was stirred in an
3
1H NMR (400 MHz, CDCl3) δ = 1.19 (t, JH,H = 7.0 Hz, 6 H, CH3 oil bath thermostated at 60 °C. Ethyl diazoacetate (120 ± 5 mg,
OEt), 3.96 – 4.43 (m, 4 H, CH2 OEt), 6.60 – 7.62 (m, 28 H, Ph 1 mmol) was diluted up to 1 mL with styrene in a 1 mL syringe.
DPEphos) ppm. 13C NMR (101 MHz, CDCl3): δ = 13.9 (s, CH3 This solution was added dropwise to the reaction mixture in 5
OEt), 65.7 (s, CH2 OEt), 123.3 (s, Ph), 126.2 – 126.5 (m, Ph), h using a syringe pump. Stirring was maintained for an
127.2 – 127.7 (m, Ph), 128.4 (s, Ph), 129.0 (s, Ph), 130.7 (s, Ph), additional 45 h at 60 °C. The rate of nitrogen evolution was
133.6 (s, Ph), 133.9 (s, Ph), 159.4 (s, Ph), 224.9 (s, S2CO) ppm. monitored with a water column connected to the reaction
31P NMR (162 MHz, CDCl3): δ = 43.45 (s) ppm. IR (KBr): ν = 3053 flask via the septum and a metallic cannula. After 50 h, the
(w), 2981 (w), 2931 (w), 2888 (w), 1431 (m), 1209 (s), 1039 reaction mixture was analyzed by gas chromatography and its
(m), 694 (m), 518 (m) cm–1. ESI-MS (CH3CN): m/z calcd for composition was established by comparison with authentic
C42H38O3P2RuS4 ([M]+), 882.02170; found, 882.02064. Calc. for samples.
C42H38O3P2RuS4: C, 57.2; H, 4.3; S, 14.5%. Found: C, 56.8; H,
4.4; S, 14.4%.
ATRA of carbon tetrachloride to methyl methacrylate
A 10 mL pressure vial containing a magnetic stirring bar was
charged with a [Ru(S2COEt)2(diphos)] complex (0.006 mmol).
X-Ray crystallography
Crystals of [Ru(S2COEt)2(diphos)] complexes 1–9 suitable for The reactor was purged of air by applying five vacuum/nitro-
XRD analysis were obtained by slow evaporation at –20 °C of gen cycles before a stock solution (1.2 mL) containing methyl
the supernatant solutions left after the final precipitation from methacrylate (1 M), carbon tetrachloride (4 M), and dodecane
CH2Cl2/Et2O. Data were collected on a Bruker APPEX II (0.15 M) in dry toluene was added. The vial was capped with a
diffractometer using Mo-Kα radiation (λ = 0.71073 Å) from a septum under nitrogen, heated to a given temperature
fine focus sealed tube source at 100 K. Computing data and (monitored by an IR sensor) in a CEM Discover instrument, and
reduction was made with the APPEX II software.48 Absorption held at that temperature for 30 min. After rapid air-cooling by
corrections based on the multiscan method were applied.49 All the unit, the reaction mixture was analyzed by gas chromato-
the structures were solved using SIR2004.50 They were refined graphy using dodecane as an internal standard.
by full-matrix, least-squares based on F2 using SHELXL.51 An
empirical absorption correction was applied using SADABS.52
All non-hydrogen atoms were anisotropically refined and the
Conflicts of interest
hydrogen atom positions were calculated and refined using a
riding model (see the ESI† for further information).
There are no conflicts to declare.
Cyclic voltammetry
Acknowledgements
Cyclic voltammograms were recorded at room temperature
using a Biologic SP-200 potentiostat and a classical 3-electrode
setup with 2 Pt foils of 1 cm² as working and counter
electrodes and a REF361 Ag/AgCl reference electrode from
Hach. Complexes 1–9 (10 mg each) were dissolved in a 0.1 M
solution of (Bu4N)(ClO4) in dichloromethane (30 mL). After 10
min of degassing with N2, CV curves were recorded between
0.0 and +1.5 V vs. Ag/AgCl at 100 mV/s (see the ESI† for
further information).
The authors would like to thank Dr Nicolas Smargiasso for the
MS analyses and Mr Stéphane Luts for IR spectroscopy.
Notes and references
‡ For complexes 2 and 4, [RuCl2(p-cymene)]2 (245 mg, 0.40
mmol) and KS2COEt (283 mg, 1.76 mmol, 4.4 equiv.) were stirred
for 24 h at room temperature in THF (8 mL) before adding dppe
or dppb (0.88 mmol, 2.2 equiv.) and heating the mixture for 1 h
at 130 °C. The work-up remained unchanged.
§ For a definition of the N parameter that expresses the shift
difference in Hz between the outer lines of a higher order
spectrum, see: H. Günther, Angew. Chem. Int. Ed. Engl., 1971,
11, 861–874. See also: C. Albrecht, S. Gauthier, J. Wolf, R.
Scopelliti and K. Severin, Eur. J. Inorg. Chem., 2009, 1003–1010.
Synthesis of vinyl esters
A 10 mL pressure vial containing a magnetic stirring bar was
charged with a [Ru(S2COEt)2(diphos)] complex (0.004 mmol)
and benzoic acid (61 mg, 0.5 mmol). The reactor was purged of
air by applying five vacuum/nitrogen cycles before a stock
solution (2.6 mL) containing 1-hexyne (0.75 mmol) and
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View Article Online
DOI: 10.1039/C8DT02838A
diphos = dppm, dppe, dppp, dppb, dpppe,
dppen, dppbz, dppf, DPEphos
OEt
S
Ru
S
Ph2
P
Ph2P
PPh2
S
0.5 [RuCl2(p-cymene)]2
S
P
Ph2
2 EtOCS2K
OEt
9 examples, 62–96% yield
Nine ruthenium chelates with the generic formula [Ru(S2COEt)2(diphos)] were synthesized
and fully characterized. Their catalytic activity was probed in three distinct reactions.