Carbon-sulfur bond formation via alkene addition to an oxidized ruthenium thiolate

Article abstract of DOI:10.1021/ic701078e

Bulk oxidation of [Ru(DPPBT)₃], 1b, (DPPBT = 2-diphenylphosphinobenzenethiolate) in the presence of ethylene yields [(ethane-1,2-diylbis(thio-2,1-phenylene)diphenylphosphine) ruthenium(II)] hexafluorophosphate, [2a]PF₆, from the addition of the alkene across eis sulfur sites. During oxidation, the absorption bands of 1b at 540, 797, and 1041 nm decrease in intensity. The resulting complex [2a]⁺ displays a single redox couple at +804 mV. The +ESI-MS of [2a]⁺ shows a parent ion peak at m/z = 1009.1013, and the ³¹P NMR spectrum displays chemical shift values of δ₁ = 61.0, δ₂ = 40.3, and δ₃ = 37.5 with coupling constants of J₁₂ ≈ J₁₃ ≈ 30 Hz and J₂₃ = 304 Hz. Oxidation of [2a] ⁺ by one electron at a holding potential of +1000 mV yields [(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl phosphine)ruthenium(III)] hexafluorophosphate, [2b][PF₆]₂. The EPR of [2b][PF ₆]₂ displays a rhombic signal with g₁ = 2.09, g₂ = 2.04, and g₃ = 2.03. Oxidation of 1b in the presence of alkenes including 1-hexene, styrene, cyclohexene, and norbornene yields products similar to [2a]⁺. Each of these products was further oxidized to an analogue of [2b]²⁺. Complex [2a]⁺ was also prepared, as the bromide salt, from [PPN][Ru-(DPPBT)₃] (PPN [1a]; PPN = bis(triphenylphosphoranylidene)ammonium) and 1,2-dibromoethane. The complex [2a]Br crystallizes as thin yellow plates in the monoclinic space group P2 ₁/c with unit cell dimensions of a = 10.2565(9) A, b = 13.2338(12) A, c = 38.325(3) A, and β = 93.3960(10)°.

Full text of DOI:10.1021/ic701078e

Inorg. Chem. 2007, 46, 8044−8050
Carbon−Sulfur Bond Formation via Alkene Addition to an Oxidized
Ruthenium Thiolate
Craig A. Grapperhaus,* Kiran B. Venna, and Mark S. Mashuta
Department of Chemistry, UniVersity of LouisVille, LouisVille, Kentucky 40292
Received June 1, 2007
Bulk oxidation of [Ru(DPPBT)3], 1b, (DPPBT
) 2-diphenylphosphinobenzenethiolate) in the presence of ethylene
yields [(ethane-1,2-diylbis(thio-2,1-phenylene)diphenylphosphine) ruthenium(II)] hexafluorophosphate, [2a]PF6, from
the addition of the alkene across cis sulfur sites. During oxidation, the absorption bands of 1b at 540, 797, and
1041 nm decrease in intensity. The resulting complex [2a]+ displays a single redox couple at
+
+
804 mV. The
1009.1013, and the 31P NMR spectrum displays chemical
shift values of δ1 ) 61.0, δ2 ) 40.3, and δ3 ) 37.5 with coupling constants of J12 J13 30 Hz and J23 304
Hz. Oxidation of [2a]+ by one electron at a holding potential of
1000 mV yields [(ethane-1,2-diylbis(thio-2,1-
phenylene)diphenyl phosphine)ruthenium(III)] hexafluorophosphate, [2b][PF6]2. The EPR of [2b][PF6]2 displays a
ESI-MS of [2a]+ shows a parent ion peak at m/z
)
≈
≈
)
+
rhombic signal with g1
) 2.09, g2 ) 2.04, and g3 ) 2.03. Oxidation of 1b in the presence of alkenes including
1-hexene, styrene, cyclohexene, and norbornene yields products similar to [2a]+. Each of these products was
further oxidized to an analogue of [2b]2+. Complex [2a]+ was also prepared, as the bromide salt, from [PPN][Ru-
(DPPBT)3] (PPN [1a]; PPN
[2a]Br crystallizes as thin yellow plates in the monoclinic space group P21/c with unit cell dimensions of a
10.2565(9) Å, b 13.2338(12) Å, c 38.325(3) Å, and â ) 93.3960(10)
) bis(triphenylphosphoranylidene)ammonium) and 1,2-dibromoethane. The complex
)
)
)
°.
Introduction
the metal-sulfur bond.5 As such, metal-coordinated thiyl
radicals can be stabilized by sufficiently bulky groups that
prevent disulfide formation, thereby opening alternate reac-
tion pathways.
Sulfenyl radicals, also commonly referred to as thiyl
radicals, are organosulfur compounds with the general
formula RS•. The reactivity of thiyl radicals with organic
compounds can be consolidated into three major categories:
disulfide formation, H-atom abstraction, and addition to
unsaturated compounds.1 Oxidation of metal thiolates to
disulfides is well known and is often suspected as the aerobic
decomposition pathway.2,3 Recently, much effort has been
directed toward the stabilization and characterization of
metal-coordinated thiyl radicals.4 In contrast to metal-
coordinated phenoxyl radicals, metal-coordinated phenylthiyl
radicals tend to delocalize the unpaired electron density over
The H-atom abstraction path is limited for organic thiyl
radicals by the relatively weak S-H bond of the thiol
product. As such, thiyl radicals can only abstract H atoms
from activated carbon centers, such as the 3′ carbon of the
ribose unit in ribonucleotides.6 In ribonucleotide reductase
(RNR), metal cofactors assist in the generation of a non-
coordinated thiyl radical, which initiates reduction of the
ribose unit.6 However, metal-coordinated thiyl radicals have
an even more limited utility for H-atom abstraction, as metal
coordination stabilizes the radical and destabilizes the S-H
bond of the product.
The addition of organic thiyl radicals to unsaturated
hydrocarbons in C-S bond-forming reactions is well known,
with applications for cis/trans isomerization, sulfide synthesis,
and polymerization.7-10 Alkene addition to oxidized metal-
* To whom correspondence should be addressed. E-mail: grapperhaus@
louisville.edu. Phone: (502)852-5932. Fax: (502)852-8149.
(1) Alfassi, Z. B. S-centered radicals. John Wiley and Sons: Chichester,
1999.
(2) Treichel, P. M.; Rosenhein, L. D. Inorg. Chem. 1984, 23, 4018-4022.
(3) (a) Albela, B.; Bothe, E.; Brosch, O.; Mochizuki, K.; Weyhermuller,
T.; Wieghardt, K. Inorg. Chem. 1999, 38, 5131-5138. (b) D´ıaz, C.;
Araya, E.; Santa Ana, M. A. Polyhedron 1998, 17, 2225-2230.
(4) Ray, K.; Petrenko, T.; Wieghardt, K.; Neese, F. J. Chem. Soc. Dalton
Trans. 2007, 1552-1566.
(5) Kimura, S.; Bill, E.; Bothe, E.; Weyhermuller, T.; Wieghardt, K. J.
Am. Chem. Soc. 2001, 123, 6025-6039.
(6) Stubbe, J. A.; van der Donk, W. A. Chem. ReV. 1998, 98, 705-762.
(7) Walling, C.; Helmreich, W. J. Am. Chem. Soc. 1958, 81, 1144-1148.
8044 Inorganic Chemistry, Vol. 46, No. 19, 2007
10.1021/ic701078e CCC: $37.00
© 2007 American Chemical Society
Published on Web 08/17/2007

Alkene Addition to an Oxidized Ruthenium Thiolate
cally immediately before use as described previously.15 Deuterated
solvents required for NMR experiments were purchased from
Cambridge Isotope Laboratories and used without further purifica-
tion. All reactions were conducted under anaerobic conditions by
using standard Schlenk techniques, unless otherwise specified.
Scheme 1
Physical Methods. NMR spectra were recorded on a Varian 500
MHz spectrometer and referenced to TMS (1H NMR) or 85%
phosphoric acid (31P NMR). For electrochemically generated
complexes, 31P NMR samples were prepared by removal of solvent
under vacuum and extraction of the analyte into deuterated
acetonitrile. The sample was filtered through the fritted septa of
13 mm syringe filter with a 0.2 µm PTFE membrane into the NMR
tube. Electron paramagnetic resonance spectra were collected on a
Bruker EMX EPR spectrometer at 77 K in a Suprasil quartz dewar.
EPR data were simulated using SimPow6.19 Electrospray ionization
(ESI) mass spectra were recorded at the Mass Spectrometry
Application and Collaboration Facility in the Chemistry Department
at Texas A&M University. An Agilent 8453 diode-array spectrom-
eter was used for electronic absorbance measurements.
sulfur complexes has been previously reported, although a
metal-coordinated thiyl radical was not invoked. The addition
of alkenes to an oxidized nickel dithiolene was reported by
Stiefel, although later studies revealed the reactivity was more
complex, vide infra.11-13 Recently, Webster, Goh, and co-
workers reported reported the addition of acrylonitrile to a
ruthenium thiolate upon chemical oxidation.14
Previous results from our laboratory have shown that
oxidation of [Ru(DPPBT)3]- ([1a]-) (DPPBT ) 2-diphe-
nylphosphinobenzenethiolate) proceeds in two one-electron
steps.15 The first oxidation yields the neutral complex 1b,
which has a Ru(III)-thiolate ground state with Ru(II)-thiyl
radical contributions. The second oxidation yields a reactive
intermediate [Ru(DPPBT)3]+, [1c]+. On the basis of recent
DFT investigations, [1c]+ is best described as having a singlet
diradical ground state with significant Ru(II)-dithiyl radical
character.16 The two unpaired electrons sit in nearly orthogo-
nal orbitals, which significantly retards disulfide formation.15
In the presence of methyl ketones, [1c]+ reacts with the enol
tautomer to generate Ru(II)-thioether complexes.17 In this
manuscript, we further report the reaction of [1c]+ with a
variety of alkenes. As shown in Scheme 1, ethylene,
1-hexene, cyclohexene, styrene, and norbornene have been
successfully added to [1c]+ to generate a series of Ru(II)-
dithioether complexes, [2a]+-[6a]+. Preliminary studies with
styrene were previously communicated.16 Each complex can
be further oxidized to the Ru(III) analogue, [2b]2+-[6b]2+.
Complex [2a]+ has been isolated as the bromide salt for
X-ray crystallographic analysis.
Electrochemical Methods. All electrochemical experiments
were performed with an EG&E 273 potentiostat. Potentials are
reported versus a Ag/AgCl reference electrode for which the
ferrocenium/ferrocene redox couple was observed at +460 mV.
Electrochemical and spectroelectrochemical experiments were
performed in a custom cell designed by E. Bo¨the of Max-Planck
Institute fu¨r Bioanorganische Chemie, Mu¨lheim, Germany. The cell
has a quartz window with a path length of 0.5 cm and variable-
temperature jacketed sample holder. The cell was connected to a
VWR 1190A chiller that was set at -34 °C and produced a
temperature of -22 ( 3 °C in the cell. All the measurements were
taken at the above-mentioned temperature unless noted otherwise.
To avoid condensation on the cell during low-temperature condi-
tions, the cell holder was placed in a Plexiglas box fitted with
Dynasil 4000 quartz windows (Pacific Quartz), through which
nitrogen gas was purged. Coulometric and electronic absorption
measurements were done simultaneously with 10 mL of acetonitrile
as solvent and 0.100 M tetrabutylammonium hexafluorophosphate
(TBAHFP) as supporting electrolyte. The electrochemical cell was
purged with nitrogen to prevent oxygen diffusion and also to ensure
thorough solution mixing. For coulometric measurements, a plati-
num mesh was used as working electrode with a Ag0/Ag+ as the
reference electrode. After each oxidation, a glassy carbon electrode
was used to record the square-wave voltammogram (frequency )
60 Hz, pulse height ) 0.025 V).
Chemical Method Synthesis of [(Ethane-1,2-diylbis(thio-2,1-
phenylene)diphenylphosphine)ruthenium(II)] Bromide ([2a]Br).
To a 50 mL Schlenk flask was added 0.092 g (0.061 mmol) of
PPN[1a] and 17 mL of chlorobenzene. The solution was stirred
for 10 min, and then 8.4 µL (0.097 mmol) of 1,2-dibromoethane
was added. The resulting solution was stirred overnight during
which time a dark red color developed. The mixture was then
filtered through Celite, and the dark red filtrate was layered with
diethyl ether to yield [2a]Br as yellow crystals. Yield: 0.0354 g
(54.7%). E1/2 (RuIII/RuII) ) +794 mV. +ESI-MS for C56H46P3S3-
Ru: experimental ) 1009.1015 amu, theoretical ) 1009.1018 amu.
Experimental Section
Materials and Reagents. Solvents were purified and dried using
standard procedures. All chemical reagents were commercially
obtained and used without further purification. The complex [PPN]-
[Ru(DPPBT)3] [1a]- was synthesized according to published
procedures and was stored in a nitrogen atmosphere dry box.18 The
neutral [Ru(DPPBT)3] complex, 1b, was generated electrochemi-
(8) Chatgilialoglu, C.; Ferreri, C.; Ballestri, M.; Mulazzani, Q. G.; Landi,
L. J. Am. Chem. Soc. 2000, 122, 4593-4601.
(9) Ichinose, Y.; Oshima, K.; Utimoto, K. Chem. Lett. 1988, 669-672.
(10) Lalevee, J.; Allonas, X.; Fouassier, J. P. J. Org. Chem. 2006, 71, 9723-
9727.
(11) Wang, K.; Stiefel, E. I. Science 2001, 291, 106-109.
(12) Geiger, W. E. Inorg. Chem. 2002, 41, 136-139.
(13) Harrison, D. J.; Nguyen, N.; Lough, A. J.; Fekl, U. J. Am. Chem.
Soc. 2006, 128, 11026-11027.
(14) Shin, R. Y. C.; Teo, M. E.; Leong, W. K.; Vittal, J. J.; Yip, J. H. K.;
Goh, L. Y.; Webster, R. D. Organometallics 2005, 24, 1483-1494.
(15) Grapperhaus, C. A.; Poturovic, S. Inorg. Chem. 2004, 43, 3292-3298.
(16) Grapperhaus, C. A.; Kozlowski, P. M.; D., K.; Frye, H. N.; Venna,
B. K.; Poturovic, S. Angew. Chem., Int. Ed. 2007, 4085-4088.
(17) Poturovic, S.; Mashuta, M. S.; Grapperhaus, C. A. Angew. Chem.,
Int. Ed. 2005, 44, 1883-1887.
Electrochemical Method Synthesis of [(Ethane-1,2-diylbis-
(thio-2,1-phenylene)diphenylphosphine)ruthenium(II)] Hexaflu-
orophosphate ([2a]PF6). In the custom-designed spectroelectro-
chemical cell containing 0.100 M TBAHFP, 10.0 mL of a 1.3 mM
(18) Grapperhaus, C. A.; Poturovic, S.; Mashuta, M. S. Inorg. Chem. 2002,
41, 4309-4311.
(19) Nilges, M. J. Simpow6.
Inorganic Chemistry, Vol. 46, No. 19, 2007 8045

Grapperhaus et al.
solution of 1b was prepared immediately before use at -22 (
3 °C. Ethylene gas was then purged through the solution during
which time a potential of +0.620 V was applied. Oxidation of the
mixture generated a light yellow solution. After ∼1049 mC (0.83
electron equiv) of charge production, the current decayed to
background levels. The resulting solution contained [2a]+. E1/2
(RuIII/RuII) ) +804 mV. +ESI-MS for C56H46P3S3Ru: experimental
) 1009.1013 amu, theoretical ) 1009.1018 amu.
Electrochemical Synthesis of [(Norbornane-1,2-diylbis(thio-
2,1-phenylene)diphenylphosphine)ruthenium(II)] Hexafluoro-
phosphate ([6a]PF6). Complex [6a]+ was generated in a manner
analogous to [2a]+ with the following exceptions. Prior to oxidation,
0.100 g (1.06 mmol) of norbornene was added and during oxidation
the solution was purged with N2 in place of ethylene. E1/2 (RuIII/
RuII) ) +824 mV. +ESI-MS for C61H52P3S3Ru: experimental )
1075.1478 amu, theoretical ) 1075.1487 amu.
Electrochemical Method Synthesis of [(Ethane-1,2-diylbis-
(thio-2,1-phenylene)diphenylphosphine)ruthenium(III)] Hexaflu-
orophosphate ([2b][PF6]2). In the custom-designed spectroelec-
trochemical cell, a potential of +1.00 V was applied to a freshly
prepared solution of [2a]+ (∼1 mM) at -22 ( 3 °C until the current
decayed to background levels. A green-colored solution of [2b]-
[PF6]2 was obtained after oxidation by 1326 mC (1.05 electron
equiv). Electronic absorption: λmax (ꢀ, cm-1 M-1): 690 nm (3800).
EPR: g ) 2.09, 2.04, and 2.03. [2b]2+ can be reduced to [2a]+ at
an applied potential < +800 mV.
Electrochemical Synthesis of [(Hexane-1,2-diylbis(thio-2,1-
phenylene)diphenylphosphine)ruthenium(II)] Hexafluorophos-
phate ([3a]PF6). Complex [3a]+ was generated in a manner
analogous to [2a]+ with the following exceptions. Prior to oxidation,
2.0 mL (16 mmol) of 1-hexene was added and during oxidation
the solution was purged with N2 in place of ethylene. E1/2 (RuIII/
RuII) ) +792 mV. +ESI-MS for C60H54P3S3Ru: experimental )
1065.1655 amu, theoretical ) 1065.1643 amu.
Electrochemical Synthesis of [(Hexane-1,2-diylbis(thio-2,1-
phenylene)diphenylphosphine)ruthenium(III)] Hexafluorophos-
phate ([3b][PF6]2). Complex [3b][PF6]2 was generated in a manner
analogous to [2b][PF6]2. E1/2 (RuIII/RuII) ) +798 mV. Electronic
absorption: λmax (ꢀ, cm-1 M-1): 682 nm (2700). EPR: g ) 2.08,
2.03, and 2.02. [3b]2+ can be reduced to [3a]+ at an applied potential
< +800 mV.
Electrochemical Synthesis of [(Cyclohexane-1,2-diylbis(thio-
2,1-phenylene)diphenylphosphine)ruthenium(II)] Hexafluoro-
phosphate ([4a]PF6). Complex [4a]+ was generated in a manner
analogous to [2a]+ with the following exceptions. Prior to oxidation,
2.0 mL (20 mmol) of cyclohexene was added and during oxidation
the solution was purged with N2 in place of ethylene. E1/2 (RuIII/
RuII) ) +790 mV. ESI-MS for C60H52P3S3Ru: experimental )
1063.1493 amu, theoretical )1063.1487 amu.
Electrochemical Synthesis of [(Norbornane-1,2-diylbis(thio-
2,1-phenylene)diphenylphosphine)ruthenium(III)]Hexafluoro-
phosphate ([6b][PF6]2). Complex [6b][PF6]2 was generated in a
manner analogous to [2b][PF6]2. Electronic absorption was not
determined due to precipitation [6b][PF6]2 during oxidation. EPR:
g ) 2.09, 2.05, 2.03. [6b]2+ can be reduced to [6a]+ at an applied
potential < +800 mV.
Crystallographic Studies. A thin yellow plate 0.41 × 0.27 ×
0.07 mm3 crystal of [2a]Br was mounted on a 0.05 mm CryoLoop
with Paratone oil for collection of X-ray data on a Bruker SMART
APEX CCD diffractometer. The SMART20 software package (v
5.628) was used to acquire a total of 1868 30-s frame ω-scan
exposures of data at 100 K to a 2θ max ) 56.16° using
monochromated Mo KR radiation (0.71073 Å) from a sealed tube
and a monocapillary. Frame data were processed using SAINT21
(v 6.36) to determine final unit cell parameters a ) 10.2565(9) Å,
b ) 13.2338(12) Å, c ) 38.325(3) Å, R ) 90°, â ) 93.3960(10)°,
γ ) 90°, V ) 5192.8(8) Å3, Z ) 4, and Fcalcd ) 1.501 Mg m-3 to
produce raw hkl data that were then corrected for absorption
(transmission min/max ) 0.65/0.91; µ ) 1.364 mm-1) using
SADABS22 (v 2.02). The structure was solved by Patterson methods
in the monoclinic space group P21/c using SHELXS-9023 and
refined by least-squares methods on F2 using SHELXL-9724
incorporated into the SHELXTL25 (v 6.12) suite of programs. All
non-hydrogen atoms were refined anisotropically. Phenyl H’s were
calculated and assigned U(H) ) 1.2Ueq. For 12,095 unique
reflections (R(int) ) 0.043), the final anisotropic full matrix least-
squares refinement on F2 for 610 variables converged at R1 )
0.0504 and wR2 ) 0.1164 with a GOF of 1.097. Details of data
collection, structure solution, and refinement are given in Table 1.
Results
Synthesis. A series of dithioether/thiolate ruthenium(II)
complexes were prepared upon the one-electron oxidation
of RuIII(DPPBT)3 (1b) in the presence of various alkenes,
Scheme 1. The alkenes employed include ethylene, 1-hexene,
cyclohexene, styrene, and norbornene. Preliminary details
for the preparation of 5a have been previously reported.16
Each of the Ru(II) addition products ([2a]+-[6a]+) were
further oxidized electrochemically to the Ru(III) derivative
([2b]2+-[6b]2+). A detailed description of the oxidation of
1b in the presence of ethylene to generate [2a]+ and its
subsequent oxidation to [2b]2+ is provided below. The related
Electrochemical Synthesis of [(Cyclohexane-1,2-diylbis(thio-
2,1-phenylene)diphenylphosphine)ruthenium(III)] Hexafluoro-
phosphate ([4b][PF6]2). Complex [4b][PF6]2 was generated in a
manner analogous to [2b][PF6]2. E1/2 (RuIII/RuII) ) +782 mV.
Electronic absorption: λmax (ꢀ, cm-1 M-1): 697 (2500). EPR: g
) 2.09, 2.05, 2.02. [4b]2+ can be reduced to [4a]+ at an applied
potential < +800 mV.
Electrochemical Synthesis of [(Phenylethane-1,2-diylbis(thio-
2,1-phenylene)diphenylphosphine)ruthenium(II)] Hexafluoro-
phosphate ([5a]PF6). Complex [5a]+ was generated in a manner
analogous to [2a]+ with the following exceptions. Prior to oxidation,
2.0 mL (17 mmol) of styrene was added and during oxidation the
solution was purged with N2 in place of ethylene. E1/2 (RuIII/RuII)
) +788 mV. +ESI-MS for C62H50P3S3Ru: experimental )
1085.1318 amu, theoretical ) 1085.1331 amu.
Electrochemical Synthesis of [(Phenylethane-1,2-diylbis(thio-
2,1-phenylene)diphenylphosphine)ruthenium(III)] Hexafluoro-
phosphate ([5b][PF6]2). Complex [5b][PF6]2 was generated in a
manner analogous to [2b][PF6]2. E1/2 (RuIII/RuII) ) +808 mV.
Electronic absorption: λmax (ꢀ, cm-1 M-1): 692 nm (2200). EPR:
g ) 2.09, 2.05, 2.03. [5b]2+ can be reduced to [5a]+ at an applied
potential < +800 mV.
(20) SMART (V.5.628); Bruker Advanced X-ray Solutions, Inc.: Madison,
WI, 2002.
(21) SAINT (V6.36); Bruker Advanced X-ray Solutions, Inc.: Madison, WI,
2002.
(22) Sheldrick, G. M. SADABS (V2.02); University Go¨ttingen: Go¨ttingen,
Germany, 2001.
(23) Sheldrick, G. M. SHELXS-90, A46; University of Go¨ttingen: Go¨t-
tingen, Germany, 1990.
(24) Sheldrick, G. M. SHELXL-97; University Go¨ttingen: Go¨ttingen,
Germany, 1997.
(25) SHELXTL (V6.12); Bruker Advanced X-ray Solutions, Inc.: Madison,
WI, 2001.
8046 Inorganic Chemistry, Vol. 46, No. 19, 2007

Alkene Addition to an Oxidized Ruthenium Thiolate
Figure 2. Electronic spectra obtained during oxidation of 1b in the
presence of ethylene. Spectra were obtained on a 1.13 mM acetonitrile
solution approximately every one-tenth of an electron equivalent at
-20 °C.
Figure 1. Square-wave voltammogram of 1b (top) and [2a]+ (bottom)
recorded in acetonitrile with 0.1M TBAHFP at -20 °C. Potentials referenced
to Ag/AgCl.
Table 1. Crystal Data and Structure Refinement for [2a]Br
empirical formula
fw
temp
wavelength (Å)
space group
unit cell dimens
a, (Å)
C56H46BrP3RuS3‚0.75C6H5Cl
1173.41
100(2) K
0.71073
P21/c
Figure 3. Electronic spectra obtained during oxidation of [2a]+ to [2b]2+
Spectra were obtained on a 1.13 mM acetonitrile solution approximately
every one-tenth of an electron equivalent at -20 °C.
.
10.2565(9)
13.2338(12)
38.325(3)
93.3960(10)
5192.8(8)
4
1.501
1.364
observed during the oxidation.15 This is consistent with a
rapid reaction between [1c]+ and ethylene. In the absence
of an appropriately applied potential, 1b is unreactive with
ethylene gas.
b, (Å)
c, (Å)
â, (°)
vol, (Å3)
Z
density, (Mg m-3
)
The square-wave voltammogram of [2a]+, Figure 1
(bottom), reveals a single event at +804 mV assigned as a
RuIII/II couple. Importantly, no other redox events are
observed. The observed potential is shifted by +1155 mV
from the RuIII/II couple of 1b and is similar to that of the
related dithioether/thiolate ruthenium(II) complex, [(methane-
1,2-diylbis(thio-2,1-phenylene)diphenylphosphine)ruthenium-
(II)] ([7a]Cl).18 The potential is also similar to that of the
disulfide product obtained upon oxidation of 1b in acetoni-
trile.15 However, the disulfide complex is thermally unstable
and degrades to a complex mixture upon warming to room
temperature, while solutions of [2a]+ are stable at room
temperature for several weeks with no notable changes in
spectroscopic properties.
Complex [2a]+ was oxidized to its Ru(III) derivative,
[2b]2+, at an applied potential of +1000 mV. The charge
produced during the reaction is consistent with a one-electron
oxidation per ruthenium. The square-wave voltammogram
recorded following oxidation of [2b]2+ is indistinguishable
from [2a]+, as expected. A UV-visible trace recorded during
abs coeff (mm-1
)
cryst size (mm3)
0.41 × 0.27 × 0.07
cryst color, habit
θ range for data collection (°)
index ranges
yellow plate
1.87-28.08
-13 e h e 12
-17 e k e 17
-50 e l e 50
44 978
reflns collected
indep reflns
completeness to θ ) 28.08°
abs correction
12 095 [R(int) ) 0.043]
95.6%
SADABS
0.65 and 0.91
full-matrix least-squares on F2
12 095/0/610
1.097
R1 ) 0.0504, wR2 ) 0.1164
R1 ) 0.0646, wR2 ) 0.1215
1.456 and -0.936
min and max transm
refinement method
data/restraints/params
GOF on F2
final R indices [I > 2σ(I)]a,b
R indices (all data)a,b
largest peak and hole (e Å-3
)
2
2
2
a R1 ) ∑|Fo| - |Fc|/∑|Fo|. b wR2 ) {∑[w(Fo - Fc )2]2/∑[w(Fo )2]}1/2
.
complexes [3a]+/[3b]2+-[6a]+/[6b]2+ were prepared in an
analogous manner.
The precursor complex, 1b, was freshly prepared by bulk
oxidation of [1a]- at an applied potential of +100 mV in
acetonitrile at -20 °C as described previously.15 The square-
wave voltammogram of 1b is shown in Figure 1 (top).
Complex 1b was oxidized by one electron to [1c]+ at an
applied potential of +620 mV while ethylene gas was purged
continuously through the solution. As shown in Figure 2, a
trace of the UV-visible spectra recorded during the oxidation
reveals a decrease in intensity of the bands of 1b at 540,
797, and 1041 nm. After a complete one-electron oxidation,
the spectra did not further change and the current dropped
to background levels. It is important to note that the
characteristic absorbance band of [1c]+, at 850 nm, is not
the oxidation, Figure 3, shows a rise in intensity at λmax
)
690 nm which can be assigned as a thiolate-to-metal charge-
transfer band, consistent with a Ru(III) oxidation state.
Solutions of [2b]2+ can be oxidized back to [2a]+ at an
applied potential < +804 mV.
The oxidation of 1b in the presence of other alkenes also
proceeds via a one-electron oxidation followed by a chemical
step resulting in alkene addition to yield complexes [3a]+-
[6a]+. Further oxidation at +1000 mV yields the corre-
sponding derivatives, [3b]2+-[6b]2+.
The dithioether/thiolate ruthenium(II) complex, [2a]+, can
also be prepared in the direct chemical reaction of [1a]- and
Inorganic Chemistry, Vol. 46, No. 19, 2007 8047

Grapperhaus et al.
Table 2. Properties of Ru(II)-Dithioether Complexes [2a]+-[6a]+
[2a]+
[3a]+
[4a]+
[5a]+
[6a]+
+ESI-MS (m/z)
1009.1013
1065.1655
1063.1493
1085.1317
1075.1478
31P NMR
δ1
61.0
40.3
37.5
30, 30, 304
59.0
40.0
38.8
30, 30, 318
56.2
41.1
38.1
30, 30, 313
56.3 61.0
45.9 40.7
37.5 36.6
30, 30, 300
30, 30, 311
57.3
40.0
37.0
30, 30, 315
δ2
δ3
J12, J13, J23 (Hz)
Voltammetry
E
1/2 (RuIII/RuII) (mV)
+804
+792
+790
+788
+824
Table 3. Properties of Ru(III)-Dithioether Complexes [2b]2+-[6b]2+
display a single absorbance band in the visible region in the
range of 682-697 nm. On the basis of their energies and
molar absorptivities, these bands are assigned as thiolate-
to-metal charge-transfer bands. Since [6b]2+ precipitated from
solution, no absorbance maximum was measured.
[2b]2+
[3b]2+
[4b]2+
[5b]2+
[6b]2+
UV-Vis
λ
max (nm)
690
3800
682
2700
697
2500
692
2200
n/da
ꢀ (M-1 cm-1
)
EPR
g1
g2
The EPR spectrum of a frozen acetonitrile solution of
[2b]2+ was recorded at 77 K in an EPR Suprasil quartz
dewar, Figure 5. The spectrum of [2b]2+ reveals a rhombic
signal with g1 )2.09, g2 )2.04, and g3 ) 2.03, consistent
with an S ) 1/2 spin system. However, the g values cannot
be attributed to Ru(III) by simple rotational relationships and
spin-orbit coupling.28 Additionally, attempts to model the
g values using the approach of Taylor developed for a d5
low-spin heme iron does not yield physically reasonable
results.29 This complexity is attributed to the high covalency
of the Ru-S bond which makes assignment of the oxidation
state difficult. In fact, the observed g values are similar to
those observed for metal-coordinated thiyl radicals.5 The EPR
spectra of [3b]2+-[6b]2+ are all rhombic with g values
similar to those of [2b]2+.
X-ray Crystallographic Analysis. The structure of [2a]-
Br has been determined by single-crystal X-ray techniques.
Details of the data collection and refinement are presented
in Table 1. Complex [2a]Br crystallizes with a 3/4 occupancy
chlorobenzene solvate in the asymmetric unit. An ORTEP30
view of the cation is presented in Figure 6, with selected
bond distances and angles listed in Table 4.
The ruthenium ion of [2a]Br sits in pseudo-octahedral P3S3
donor environment. The phosphorus and sulfur donors
arrange in a meridional fashion, as seen in related complexes.
The thioether sulfur donors S2 and S3 are bridged by the
ethylene linker, while S1 is a thiolate donor. The Ru-S1
bond length is 2.3856(9) Å and is close to previously reported
Ru-Sthiolate bonds.18,27,31 The Ru-S thioether bond lengths
for Ru-S2 and Ru-S3 are 2.3749(9) and 2.3365(9) Å,
respectively. These values are slightly shorter than the
previously reported values of Ru-S2 and Ru-S3 of 2.406-
(1) and 2.358(1) Å, respectively, in [7a]Cl.18 This decrease
in bond length can be attributed to release of geometrical
constraint due to formation of a five-member ring as opposed
2.09
2.04
2.03
2.08
2.03
2.02
2.09
2.05
2.02
2.09
2.05
2.03
2.09
2.05
2.03
g3
a n/d ) not determined due to solubility limitations.
1,2-dibromoethane. In this reaction, the ruthenium-containing
complex, [1a]-, is two electrons more reduced than in the
electrochemical synthesis. Likewise, the 1,2-dibromoethane
is two electrons more oxidized than ethylene. From the
chemical synthesis, single crystals of [2a]+ as the bromide
salt were obtained for X-ray analysis.
Characterization. The spectroscopic properties of [2a]+-
[6a]+ and [2b]2+-[6b]2+ are summarized in Tables 2 and 3,
respectively. The +ESI-MS of [2a]+ displays a parent ion
peak at m/z ) 1009.1013, which is within experimental error
of the theoretical value of 1009.1018. The observed isotopic
envelope well reproduces the theoretical envelope, which is
characteristic of ruthenium, Figure 4. As shown in Table 2
and Figures S1-S4, the +ESI-MS spectra of [3a]+-[6a]+
also show the expected parent ion peaks within 1 ppm.
The 31P NMR spectrum of [2a]+ shows chemical shift
values of δ1 ) 61.0, δ2 ) 40.3, and δ3 ) 37.5 with coupling
constants of J12 ≈ J13 ≈ 30 Hz and J23 ) 304 Hz. This is
consistent with three phosphorus donors arranged in a
meridional fashion about an octahedral Ru(II) ion.18,26,27 The
31P NMR spectra of [3a]+-[6a]+ show coupling constants
and isomeric shift values that are very close to those of [2a]+.
The 31P NMR spectrum of [5a]+ is unique, as it shows two
sets of resonances with nearly equal intensities. This is
attributed to the presence two diastereomers from the
nonselective addition of unsymmetrical styrene to [1c]+.
Notably, only one set of peaks is observed for [3a]+
indicating that either 1-hexene adds selectively or that the
diastereormers cannot be resolved due to the similarities of
their magnetic environments.
The oxidized complex, [2b]2+, owes its green color to a
charge-transfer band at 690 nm. A similar band is observed
in the other oxidized complexes, [3b]2+-[5b]2+, which each
(28) Palmer, G. Electron Paramagnetic Resonance of Metalloproteins. In
Physical Methods in Bioinorganic Chemistry: Spectroscopy and
Magnetism; Que, L., Jr., Ed.; University Science Books: Sausalito,
CA, 2000.
(26) Dilworth, J. R.; Zheng, Y. F.; Lu, S. F.; Wu, Q. J. Transition Met.
Chem. 1992, 17, 364-368.
(27) Dilworth, J. R.; Lu, C. Z.; Miller, J. R.; Zheng, Y. F. J. Chem. Soc.
Dalton Trans. 1995, 1957-1964.
(29) Taylor, C. P. S. Biochim. Biophys. Acta 1977, 491, 137-149.
(30) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(31) Sellmann, D.; Shaban, S. Y.; Heinemann, F. W. Eur. J. Inorg. Chem.
2004, 4591-4601.
8048 Inorganic Chemistry, Vol. 46, No. 19, 2007

Alkene Addition to an Oxidized Ruthenium Thiolate
Figure 6. ORTEP representation of the cation of [2a]Br showing 30%
probability displacement ellipsoids and partial atom-numbering scheme. H
atoms and solvent molecule are omitted.
Figure 4. Experimental (top) and theoretical (bottom) isotopic distribution
of parent ion peak in the +ESI-MS of [2a]+ in acetonitrile.
Table 4. Selected Bond Distances (Å) and Bond Angles (deg) of
[2a]Br
Ru1-S1
Ru1-S2
Ru1-S3
Ru1-P1
Ru1-P2
Ru1-P3
S2-C55
S3-C56
C55-C56
2.3856(9)
2.3749(9)
2.3365(9)
2.3290(9)
2.3965(10)
2.3648(9)
1.836(4)
S1-Ru1-P1
S2-Ru1-P2
S3-Ru1-P3
P1-Ru1-S2
S1-Ru1-S3
P2-Ru1-P3
S2-Ru1-S3
C55-S2-Ru1
C56-S3-Ru1
85.88(3)
83.36(3)
85.55(3)
172.87(3)
173.73(3)
168.81(3)
87.71(3)
104.52(12)
103.59(12)
1.843(4)
1.510(5)
Figure 5. Experimental (top) and simulated (bottom) EPR spectrum of
[2b]2+ at 77 K. Experimental conditions: microwave frequency of 9.6011
GHz, microwave power of 1.978 mW, modulation frequency of 100 kHz,
modulation amplitude of 10 G. Line widths for SIMPOW6 simulated
spectrum : Wx ) 32 G, Wy ) 39 G, Wz ) 37 G.
Scheme 2
to a four-member ring in the methylene-bridged thioether.
The carbon sulfur bond lengths for S(2)-C(55) and S(3)-
C(56) are 1.836(4) and 1.843(4) Å, respectively. The Ru-P
distances range from 2.3290(9) to 2.3965(10) Å and are
comparable to previously reported Ru-P values in related
systems.18,27
Discussion
Oxidation of the formally Ru(III)-trithiolate complex 1b
in the presence of alkenes has been shown to result in C-S
bond formation and isolation of Ru(II)-dithioether products,
[2a]+-[6a]+. On the basis of previous DFT investigations,
the oxidized intermediate [1c]+ is best described as having
a singlet, diradical ground state with significant Ru(II)-
dithiyl radical contributions.16 Since the unpaired electrons
of [1c]+ are in nearly orthogonal orbitals, disulfide formation
is slow. As such, [1c]+ has a suitable lifetime to promote
addition of unsaturated hydrocarbons across interligand cis-
sulfur sites, Scheme 2. Addition of alkenes yields stable
dithioether/thiolate Ru(II) complexes. These results provide
definitive evidence for the addition of alkenes to a metal-
coordinated thiyl radical. Interestingly, no evidence of
H-atom abstraction has been observed, even when styrene
was added to the reaction mixture. The addition of alkenes
to [1c]+ is consistent with the previously reported addition
of methyl ketones.17 Addition of the enol tautomer, Scheme
2, proceeds as an alkene addition. However, deprotonation,
by adventious base or 1b, results in cleavage of one of the
C-S bonds to yield the observed monothioether products.
Previously, Stiefel and co-workers reported the interligand
alkene addition across cis-sulfur sites upon oxidation of
nickel dithiolenes with subsequent alkene dissociation upon
reduction.11 This intriguing result offered promise for the
use of nickel dithiolenes for redox controlled reversible olefin
binding as a means for olefin purification. However,
subsequent studies by Geiger revealed the reaction was more
complex.12 Very recent studies by Fekl and co-workers
indicate that the favored addition of alkenes to nickel
dithiolenes is intraligand, leading to decomposition to
dihydrodithiin and metal decomposition products.13 Our
family of complexes [2a]+-[6a]+ show the desired interli-
gand addition sought in the earlier studies. However, as noted
by Rothlisherger, Ru(II) dithioethers are not favorably
reduced and therefore do not facilitate C-S bond cleavage.32
In fact, complexes [2a]+-[6a]+ do not show any reduction
(32) Magistrato, A.; Maurer, P.; Fassler, T.; Rothlisherger, U. J. Phys.
Chem. A 2004, 108, 2008-2013.
Inorganic Chemistry, Vol. 46, No. 19, 2007 8049

Grapperhaus et al.
event within the solvent window. Further efforts are under-
way to develop a reversible system.
Research Challenge Trust Fund for the purchase of CCD
X-ray equipment and upgrade of our X-ray facility.
Supporting Information Available: +ESI-MS of [3a]+-[6a]+
in pdf format and crystallographic data for [2a]Br in CIF format
(CCDC 649178). This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. This research was supported in part
by the National Science Foundation (CHE-0238137). Ac-
knowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund (43917-AC3)
for partial support of this work. We thank the Kentucky
IC701078E
8050 Inorganic Chemistry, Vol. 46, No. 19, 2007