Ruthenium(II) thiol and H2S complexes: Synthesis, characterization, and thermodynamic properties

Article abstract of DOI:10.1021/ic3004118

The known, green, five-coordinate species trans-RuCl₂(P-N) (PPh₃) react with R′SH thiols to give yellow cis-RuCl ₂(P-N)(PPh₃)(R′SH) products (P-N = o-diphenylphosphino-N,N′-dimethylaniline; R′ = alkyl). The MeSH and EtSH compounds are structurally characterized, with the former being the first reported for a transition metal-MeSH complex, while the thiol complexes with R′ = ⁿPr, ⁱPr, ⁿPn (pentyl), ⁿHx (hexyl), and Bn (benzyl) are synthesized in situ. Other trans-RuX₂(P-N)(PR₃) complexes (X = Br, I; R = Ph, p-tolyl) are synthesized, and their H₂S adducts, of a type reported earlier by our group, are also prepared. Thermodynamic data are presented for the reversible formation of the MeSH and EtSH complexes and the H₂S analogues. The Ru^IICl₂(P-N)(PPh₃) complex in solution decomposes under O₂ to form [Ru^IIICl(P-N)] ₂(μ-O)(μ-Cl)₂.

Full text of DOI:10.1021/ic3004118

Article
pubs.acs.org/IC
Ruthenium(II) Thiol and H2S Complexes: Synthesis, Characterization,
and Thermodynamic Properties
Erin S. F. Ma, Steven J. Rettig,† Brian O. Patrick, and Brian R. James*
Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
S
* Supporting Information
ABSTRACT: The known, green, five-coordinate species trans-
RuCl2(P−N)(PPh3) react with R′SH thiols to give yellow cis-
RuCl2(P−N)(PPh3)(R′SH) products (P−N = o-diphenylphosphino-
N,N′-dimethylaniline; R′ = alkyl). The MeSH and EtSH compounds
are structurally characterized, with the former being the first reported for
a transition metal−MeSH complex, while the thiol complexes with R′ =
nPr, iPr, nPn (pentyl), nHx (hexyl), and Bn (benzyl) are synthesized in situ. Other trans-RuX2(P−N)(PR3) complexes (X = Br, I;
R = Ph, p-tolyl) are synthesized, and their H2S adducts, of a type reported earlier by our group, are also prepared.
Thermodynamic data are presented for the reversible formation of the MeSH and EtSH complexes and the H2S analogues. The
RuIICl2(P−N)(PPh3) complex in solution decomposes under O2 to form [RuIIICl(P−N)]2(μ-O)(μ-Cl)2.
complexes (eq 1).4,5 These papers4,5 mention in a sentence the
INTRODUCTION
■
coordination of thiols, alcohols, H2O, CO, and SO2, but the
chemistry of these systems has been described only in Ph.D.
dissertations and at a conference.6 This current paper focuses
mainly on the thiol products, including crystallographic data for
the L = MeSH and EtSH complexes, and compares their
properties with those of the corresponding H2S adduct.5 The
structure with MeSH is surprisingly the first reported for any
transition-metal complex containing this thiol.
Our group has recently reported on thiol complexes of the
formulation trans- RuII(porp)(RSH)2, where porp represents
the dianionic ligand of a porphyrin and R is an alkyl or phenyl
group;1 this paper also discusses the potential of these
complexes as models for Fe−S bonds in heme proteins because
systems that contain proximal S-donor ligands at a heme center
are involved in many biological catalytic and/or structural
processes.2 The studies required an extensive literature search
for metal−thiol complexes, and it became clear that examples of
coordinated thiols (and H2S), in general, are relatively rare,
especially structurally characterized species. This is because the
attempted coordination of thiols (and H2S) commonly results
in the formation of the respective thiolato/hydrosulfide ligand
via deprotonation, or hydridothiolato species via oxidative
addition, with the thiol or H2S adduct usually considered as an
intermediate.3
There are about one dozen reported structures of ruthenium
thiol complexes, in which the thiol contains no other functional
binding sites. Some of these structures are included in several
reports7 on CpRuII-RSH complexes, exemplified by [CpRu-
(PPh3)2(RSH)]+, where R is a range of alkyl groups (including
Me and Ph); structures of this type (sometimes containing
7a
7b
n
other phosphines or phosphites) are with R = Pr, tBu,
The recent study1 brought to mind earlier work from our
group on thiol binding to RuII that was completed in the late
1990s; however, this was never published and so is presented
here. The findings evolve from the reactivity of the five-
coordinate species trans-RuCl2(P−N)(PR3) toward small
molecules, where P−N = o-diphenylphosphino-N,N′-dimethy-
laniline (see eq 1) and R = phenyl or p-tolyl.4,5 The structurally
sBu,7f iBu,7f PhCH2CH2,7e Ph,7g and PhCH(SH)Me.7h
Structures of Ru(H)2(CO)(IMes)2(nPrSH)8 and Ru(porp)-
(CPh2)(EtSH)9 containing carbene ligands have also been
reported [IMes = 1,3-(2,4,6-trimethylphenyl)imidazol-2-yli-
dene and porp = dianion of meso-tetrakis(pentafluorophenyl)-
porphyrin], although the former was later shown to be a
hydridothiolato complex.8b Other ruthenium thiol complexes,
not structurally characterized, include the 2,7-dimethyl-
octadienediyl species [(η3:η3-C10H16)RuIVCl2(RSH)] (R =
10
i
t
Me, Et, Pr, Bu, Ph), and the 1,2-bis(diphenylphosphino)-
ethane species trans-[Ru(H)(PhSH)(dppe)2]+, which was
made by protonation of the neutral thiolate species using
HBF4;11 similarly made were the related pyridine-2- and
quinoline-8-thiol species.12
characterized p-tolyl complex has approximately square-
pyramidal geometry with trans-chlorides, the monodentate
phosphine, and −NMe2 in the equatorial positions and the
chelate P atom in the apical position.4 We have published
details on the coordination of H2, N2, H2S, and N2O (defined
here as L) at the vacant site to generate cis-RuCl2(P−N)(PR3)L
Received: February 22, 2012
Published: April 11, 2012
© 2012 American Chemical Society
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Inorganic Chemistry
Article
Ph), 3.17 (6H, s, N(CH3)2). [PN and P refer to the P−N and PPh3
ligands respectively.]
EXPERIMENTAL SECTION
■
General Procedures. Unless stated otherwise, all manipulations
were performed under an O2-free, Ar or N2 atmosphere at ambient
temperatures using standard Schlenk techniques. Commercially
available compounds, including the thiols, SPPh3, and OPPh3, were
supplied by Aldrich; MeSH was obtained as a liquid and was stored at
0 °C. Anhydrous H2S was obtained from Matheson Gas Co. and O2
(USP grade) from Union Carbide Canada Ltd. The thiols and H2S
were used as received. Spectral- or analytical-grade solvents were
refluxed, distilled over appropriate drying agents,13 and then purged
free of O2 prior to use. Deuterated solvents, obtained from Cambridge
Isotope Laboratories, were stored over activated molecular sieves
(Fisher, 4 Å, 4−8 mesh); for the preparation of O2-sensitive
complexes, the deuterated solvents were deoxygenated (via a
freeze−pump−thaw method) and stored under Ar. Reactions with
the odoriferous and toxic materials, especially H2S and MeSH (bp 6
°C), were carried out in a well-ventilated fumehood.
RuI2(P−N)(PPh3) (1c). Yield: 348 mg, 86%. Anal. Calcd for
C38H35NI2P2Ru: C, 49.47; H, 3.82; N, 1.52. Found: C, 49.21; H,
2
3.78; N, 1.58. 31P{1H} NMR (CDCl3): δ 89.18 (d, PN, JPP = 35.56
Hz), 53.6 (d, P, 2JPP = 35.56 Hz). 1H NMR (CDCl3): δ 7.8−6.9 (29H,
m, Ph), 3.48 (6H, s, N(CH3)2).
RuBr2(P−N)(P(p-tolyl)3) (1b′). Yield: 202 mg, 53%. Anal. Calcd for
C41H41NBr2P2Ru: C, 56.56; H, 4.75; N, 1.61. Found: C, 57.09; H,
4.86; N, 1.75. 31P{1H} NMR (CDCl3): δ 84.56 (d, PN, 2JPP = 35.5 Hz),
2
1
47.48 (d, P, JPP = 35.5 Hz). H NMR (CDCl3): δ 8.0−6.6 (26H, m,
Ph), 3.12 (6H, s, N(CH3)2), 2.30 (9H, s, p-CH3).
RuI2(P−N)(P(p-tolyl)3) (1c′). Yield: 300 mg, 72%. Anal. Calcd for
C41H41NI2P2Ru: C, 51.05; H, 4.28; N, 1.45. Found: C, 51.05; H, 4.25;
2
N, 1.48. 31P{1H} NMR (CDCl3): δ 89.27 (d, PN, JPP = 35.8 Hz),
2
1
51.27 (d, P, JPP = 35.8 Hz). H NMR (CDCl3): δ 7.8−6.7 (26H, m,
Ph), 3.46 (6H, s, N(CH3)2), 2.30 (9H, s, p-CH3).
cis-RuBr2(P−N)(P(p-tolyl)3)(SH2) (2b′). This complex was pre-
pared in a manner similar to that described for 2a,5b by stirring 1b′
(100 mg, 0.11 mmol) in acetone (3 mL) under 1 atm of H2S at rt. The
precipitated yellow product was filtered off and subsequently dried
under vacuum for 1 h. Yield: 86 mg, 78%. Anal. Calcd for
C41H43NBr2SP2Ru·acetone: C, 54.89; H, 5.13; N, 1.45. Found: C,
NMR spectra were recorded, unless stated otherwise, at room
temperature (rt ∼ 25 °C) on Varian XL300 (300.0 MHz for H and
1
121.4 MHz for 31P) or Bruker AMX500 (500.0 MHz for 1H and 202.5
MHz for 31P) instruments. Residual deuterated solvent proton
(relative to external SiMe4) or external P(OMe)3 (δ 141.0 relative
to 85% H3PO4) was used as a reference (s = singlet, d = doublet, t =
triplet, q = quartet, and m = multiplet); J values are reported in hertz
(Hz); samples were prepared in 5 mm NMR tubes equipped with
poly(tetrafluoroethylene) and J. Young valves (Aldrich). Calibrated 1H
NMR probes were used to determine the temperatures used for van’t
Hoff analyses. ATLI Mattson Genesis FTIR and Bomem Michelson
far-IR spectrophotometers were used to record spectra in the ranges
500−4000 cm−1 (KBr) and 200−3000 cm−1 (CsI). UV−vis spectra
were recorded on a Hewlett-Packard 8452A diode-array spectropho-
tometer, equipped with a thermostatted compartment using an
anaerobic 1 cm quartz cell, joined to a side-arm flask for the mixing
of solutions. Differential scanning calorimetry (DSC) data were
collected on a TA 910S instrument, with 2−5 mg samples being
heated under N2 (flow rate = 40 cm3 min−1) at a rate of 5 °C min−1 up
to 500 °C. Microanalyses were performed in this department on a
Carlo Erba 1106 instrument.
55.11; H, 5.23; N, 1.49. 31P{1H} NMR (CDCl3): δ 53.41 (d, PN, 2JPP
=
2
1
29.2 Hz), 44.58 (d, P, JPP = 29.2 Hz). H NMR (CDCl3): δ 8.0−6.6
(26H, m, Ph), 3.68 (3H, s, NCH3), 2.99 (3H, s, NCH3), 2.18 (9H, s,
p-CH3), 2.04 (6H, s, acetone), 0.95 (2H, br s, SH2). IR: νSH 2495 s,
2449 s; νCO 1707 (acetone).
In Situ Syntheses of cis-RuI2(P−N)(PR3)(SH2) (R = Ph, p-tolyl).
Exposure of a CDCl3 solution of RuI2(P−N)(PR3) to 1 atm H2S at rt
turned the color from red to brown; NMR spectra were measured
within 10 min because the in situ species decomposed over ∼1 h, with
generation of broad-line spectra.
R = Ph (2c). 31P{1H} NMR: δ 56.0 (d, PN, 2JPP = 25.8 Hz), 49.5 (d,
2
1
P, JPP = 25.8 Hz). H NMR: δ 8.2−6.5 (29H, m, Ph), 4.16 (3H, s,
NCH3), 2.20 (3H, s, NCH3), ∼0.95 (SH2, overlapping with the δ 1.0
signal of free H2S).
R = p-tolyl (2c′). 31P{1H} NMR: δ 56.2 (d, PN, 2JPP = 25.8 Hz), 47.5
(d, P, 2JPP = 25.8 Hz). 1H NMR: δ 8.2−6.5 (26H, m, Ph), 4.15 (3H, s,
NCH3), 2.91 (3H, s, NCH3), 2.22 (9H, s, p-CH3), ∼0.90 (SH2,
overlapping with the δ 1.0 signal of free H2S).
The complexes RuCl2(PR3)3 (R = Ph,14 p-tolyl15), RuX2(P−
N)(PPh3) [X = Cl (1a),4a Br (1b)];5b RuCl2(P−N)(P(p-tolyl)3)
(1a′);4a cis-RuX2(P−N)(PPh3)(SH2) [X = Cl (2a), Br (2b)];5b and cis-
RuCl2(P−N)(P(p-tolyl)3)(SH2) (2a′)4a were prepared by literature
methods. Complexes 2a, 2b, and 2a′ were all isolated with an acetone
solvate molecule. [a−c labeling indicates PPh3 complexes with chloro,
bromo, and iodo ligands, respectively; the corresponding P(p-tolyl)3
complexes are labeled a′−c′; the five-coordinate precursors are all
labeled 1, and the H2S adducts are correspondingly labeled 2.]
RuX2(P−N)(PR3) Complexes. The new complexes RuI2(P−
N)(PPh3) (1c) and RuX2(P−N)(P(p-tolyl)3) [X = Br (1b′), I (1c′)]
were prepared by a method similar to that used for the PPh3 analogues
1a and 1b.4a,5b A solution of P−N (0.44 mmol) in acetone (10 mL)
was added to a suspension of RuCl2(PR3)3, where R = Ph or p-tolyl
(0.44 mmol), in acetone (10 mL), and the mixture was stirred at 50 °C
for 30 min. Excess NaX (25 equiv) was then added to the resulting
dark-green solution. The mixture, containing a suspension of NaX and
NaCl, was stirred at rt for 24 h. The salts were filtered off through
Celite, and the solvent was removed in vacuo; CH2Cl2 (10 mL) was
then added to dissolve the dark-green (Br species) or dark-red residue
(I species), and the solution was filtered through Celite. The filtrate
volume was reduced to ∼5 mL before hexanes was added to
precipitate the product that was filtered off and washed with hexanes
(2 × 10 mL); drying under vacuum gave the products in 51−86%
yield. Previously unreported elemental analysis and NMR data for 1b
are given below.
cis-RuCl2(P−N)(PPh3)(MeSH) (3). A solution of MeSH (0.5 mL,
9.0 mmol) in acetone (2 mL) was cooled to 0 °C, purged with N2 for
1 min, and then cannula-transferred to a stirring acetone solution (5
mL) containing RuCl2(PPh3)3 (100 mg, 0.104 mmol) and P−N (32.0
mg, 0.104 mmol); the resulting yellow solution, after being stirred for
16 h, precipitated a solid, which was filtered off and dried in vacuo for
3 0 m i n . Y i e l d : 7 2 m g , 8 0 % . A n a l . C a l c d f o r
C39H39NCl2SP2Ru·acetone: C, 59.64; H, 5.36; N, 1.66. Found: C,
59.46; H, 5.53; N, 1.65. 31P{1H} NMR (CD2Cl2): δ 50.37 (d, PN, 2JPP
2
1
= 30.2 Hz), 41.33 (d, P, JPP = 30.2 Hz). H NMR (CD2Cl2): δ 7.9−
6.4 (29H, m, Ph), 3.35 (3H, s, NCH3), 3.10 (3H, s, NCH3), 2.10 (6H,
s, acetone), 0.70 (4H, m, overlap of SH(CH3) and SH(CH3)). IR: νSH
2533 s, νCO 1707 s (acetone). Yellow-brown, prism crystals of
3·acetone were obtained from a saturated acetone solution of the
complex left standing for 24 h.
cis-RuCl2(P−N)(PPh3)(EtSH) (4). The yellow complex was
prepared in the manner described for 3 but using excess EtSH (1
mL, 19.2 mmol) at 20 °C. Yield: 65 mg, 78%. Anal. Calcd for
C40H41NCl2SP2Ru·acetone: C, 58.62; H, 5.79; N, 1.52. Found: C,
59.08; H, 5.75; N, 1.46. 31P{1H} NMR (CD2Cl2): δ 52.43 (d, PN, 2JPP
2
1
= 30.2 Hz), 43.97 (d, P, JPP = 30.2 Hz). H NMR (CD2Cl2): δ 8.0−
6.4 (29H, m, Ph), 3.41 (3H, s, NCH3), 3.24 (3H, s, NCH3), 2.10 (6H,
s, acetone), 2.00 (1H, m, SHa(CHbHcCH3)), 0.88 (1H, m,
SH(CHbHcCH3)), 0.63 (1H, ddd, SHa(CHbHc)), 0.45 (3H, dd,
SH(CHaHbCH3)); free EtSH signals seen at δ 2.55 (2H, dq,
HSCH2CH3), 1.46 (1H, t, HSCH2CH3), 1.31 (3H, t, HSCH2CH3).
IR: νSH 2516 s, νCO 1707 s (acetone). Yellow, prism crystals of
4·1.5C6H6 were obtained from a saturated C6H6 solution of the
complex left in a sealed NMR tube for 24 h.
RuBr2(P−N)(PPh3) (1b). Yield: 185 mg, 51%. Anal. Calcd for
C38H35NBr2P2Ru: C, 55.09; H, 4.26; N, 1.69. Found: C, 54.57; H,
4.23; N, 1.64. 31P{1H} NMR (C6D6): δ 85.47 (d, PN, 2JPP = 36.3 Hz),
2
1
50.08 (d, P, JPP = 36.3 Hz). H NMR (C6D6): δ 7.8−6.7 (29H, m,
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In Situ Syntheses of cis-RuCl2(P−N)(PPh3)(R′SH) [R′ = nPr, iPr,
The NMR data for the H2S adducts (an AX 31P{1H} pattern
with 2J ∼ 26−30 Hz and two singlets in the 1H NMR spectrum
for inequivalent Me groups) are again close to those of the
previously reported analogues.5 An extension of the Karplus
relationship to vicinal coupling within the P−Ru−S−H system
was demonstrated previously for this type of complex,
specifically within the cis-RuX2(P−N)(PPh3)(SH2) complexes,
where X = Cl (2a) and Br (2b).5b Crystallographically
characterized metal−H2S complexes remain limited to just
five ruthenium(II) species.5,20
n
nPn (pentyl), Hx (hexyl), Bn (benzyl)]. These yellow species were
prepared in situ by the addition of ∼100-fold excess thiol to a CDCl3
or C6D6 solution of RuCl2(P−N)(PPh3). 31P{1H} NMR data are
summarized as follows. R = nPr. NMR (CDCl3): δ 51.22 (d, PN, 2JPP
=
30.1 Hz), 42.46 (d, P, 2JPP = 30.1 Hz). R = iPr. NMR (C6D6): δ 49.58
2
2
n
(d, PN, JPP = 30.2 Hz), 41.68 (d, P, JPP = 30.2 Hz). R = Pn. NMR
(C6D6): δ 51.30 (d, PN, 2JPP = 29.6 Hz), 42.84 (d, P, 2JPP = 29.6 Hz). R
n
2
= Hx. NMR (CDCl3): δ 51.15 (d, PN, JPP = 30.2 Hz), 42.57 (d, P,
2JPP = 30.2 Hz). R = Bn. NMR (CDCl3): δ 50.16 (d, PN, JPP = 30.4
2
2
Hz), 42.03 (d, P, JPP = 30.4 Hz).
[RuCl(P−N)]2(μ-O)(μ-Cl)2 (5). A suspension of RuCl2(P−N)-
(PPh3) (200 mg, 0.270 mmol) in acetone (10 mL) was stirred for
∼1 h under 1 atm of O2 to give a dark-green solution. Continued
stirring for ∼16 h generated a dark-green solid, which was filtered off,
washed with hexanes (2 × 10 mL), and dried in vacuo at 80 °C. Yield:
85 mg, 32%. Anal. Calcd for C40H40N2OCl4P2Ru2: C, 49.50; H, 4.15;
N, 2.89. Found: C, 49.50; H, 4.16; N, 2.75. 31P{1H} NMR (C6D6): δ
38.74 (d, PN, 4JPP = 10.4 Hz), 35.33 (d, PN, 4JPP = 10.4 Hz). 1H NMR
(C6D6): δ 8.4−6.6 (28H, m, Ph), 3.31 (3H, s, NCH3), 2.89 (3H, s,
NCH3), 2.11 (3H, s, NCH3), 2.02 (3H, s, NCH3). μeff = 0 μB (Gouy
method). Dark-green, platelet crystals of 5·acetone were obtained by
slow evaporation in air of an acetone solution of RuCl2(P−N)(PPh3)
over 24 h; the X-ray structure was reported in an earlier
communication from our group.4b
cis-RuCl2(P−N)(PPh3)(R′SH). These thiol complexes [R′ =
Me (3), Et (4)], like the H2S adducts, slowly precipitated
spontaneously out of solutions containing R′SH and excess
thiol. Both 3 and 4 were fully characterized and are isostructural
with the corresponding H2S adduct.5b The ORTEP plots
(Figures 1 and 2) show pseudooctahedral geometries with cis-
X-ray Crystallographic Analyses. Data for the structures of the
solvated complexes 3 and 4 were collected on a Rigaku/ADSC CCD
area detector with graphite-monochromated Mo Kα radiation (λ =
0.71069 Å) at 180 K and processed using the d*TREK area detector
program;16 the structures were solved by direct methods.17 All
refinements were performed using the SHELXL-97 program18 via the
WinGX interface.19 The non-H atoms were refined anisotropically; the
H atoms of the S−H moieties were refined isotropically, and the rest
of the H atoms were fixed in idealized, calculated positions.
Crystal data for C42H45Cl2NOP2RuS (3·acetone): M = 845.81;
yellow-brown prisms; crystal size 0.13 × 0.25 × 0.35 mm; monoclinic,
space group P21/n (No. 4); a = 14.207(1) Å, b = 16.275(2) Å, c =
16.712(3) Å; β = 92.667(1)°; V = 3860.1(9) Å3; Z = 4; Dc = 1.455 g
cm−3; F(000) = 1744; μ = 7.16 cm−1; 36449 total reflections; 9923
unique (Rint = 0.061); 8391 observed [I > 2σ(I)], R(F) = 0.055; Rw(F2,
all data) = 0.126; GOF = 1.18; residual density = −1.50 e/Å3.
Crystal data for C49H50Cl2NP2RuS (4·1.5C6H6): M = 918.92;
yellow prisms; crystal size 0.30 × 0.30 × 0.20 mm; monoclinic, space
group P21/n (No. 4); a = 16.6933(8) Å, b = 12.426(1) Å, c =
21.8288(6) Å; β = 106.331(1)°; V = 4345.3(5) Å3; Z = 4; Dc = 1.405 g
cm−3; F(000) = 1900; μ = 6.41 cm−1; 39270 total reflections; 11499
unique (Rint = 0.031); 8808 observed [I > 2σ(I)], R(F) = 0.033; Rw(F2,
all data) = 0.089; GOF = 1.06; residual density = −0.66 e/Å3.
Figure 1. ORTEP plot for 3 with thermal ellipsoids shown at the 33%
probability level. Some phenyl C atoms have been omitted for clarity.
Cl atoms and cis-P atoms, with the coordinated thiol trans to a
Cl atom and cis to both P atoms and the NMe2; selected bond
lengths and angles are shown Tables 1 and 2, respectively. A
search of the Cambridge Structural Database indicates that 3 is
the first structure of a transition metal−MeSH complex. The
S−H bond length of 1.06(4) Å is the shortest yet reported for
any transition metal−thiol complex; this bond length for 4 is
1.28(2) Å, intermediate between those of 1.20(3) and 1.30(3)
Å seen for the H2S analogue 2a;5b reported S−H bond lengths
of other ruthenium(II) thiol complexes are in the 1.18−1.38 Å
range.7a,e−g The Ru−S bond length in both 3 and 4 is 2.34 Å,
and for 2a, the length is 2.35 Å.5b These values are at the low
end of the 2.34−2.42 Å range reported for all other structurally
characterized ruthenium(II) thiols (see the Introduction
section), except one.7a,b,e−h,9 The exception is Ru(porp)-
(CPh2)(EtSH), where the value is 2.75 Å,9 and this could
result from steric interactions with the pentafluorophenyl
substituents of the porphyrin ligand and/or the trans influence
of the carbene ligand. The Ru−S−H angles of 102(2)° and
109.1(11)° for 3 and 4, respectively, are close to those observed
for the H2S adduct, 103(1)° and 111(1)°. Both the alkyl and H
of the R′SH ligand in 3 and 4 are situated below the S−P−Cl−
RESULTS AND DISCUSSION
■
RuX2(P−N)(PR3) Complexes and Their H2S Adducts.
Green, five-coordinate complexes of the type RuX2(P−
N)(PR3), where X = halogen and R = Ph or p-tolyl, and
some of their yellow H2S adducts (eq 1), have been reported
previously.4,5 The new analogues, RuI2(P−N)(PPh3) (1c),
RuX2(P−N)(P(p-tolyl)3) [X = Br (1b′), I (1c′)], and cis-
RuX2(P−N)(PR3)(SH2) [R = Ph, X = I (2c); R = p-tolyl; X =
Br (2b′), I (2c′)] were prepared by similar procedures. The
isolated 1c, 1b′, and 1c′ were made by reacting RuCl2(PR3)3
with the P−N ligand in the presence of NaX (X = Br, I) in
acetone. Reaction of the appropriate precursor with H2S in
solution gave the H2S adduct; 2b′ was isolated as an acetone-
solvated complex, while 2c and 2c′ were formed in situ in
CDCl3. The 31P{1H} and 1H NMR spectra of the five-
coordinate species are essentially the same as those reported
earlier for the chloro analogues:4a,5 an AX pattern with 2J ∼ 35
Hz for the cis-P atoms,4a and a singlet for NMe2, respectively.
5429
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the J values given in Figure 4 for the various HH couplings and
the 3JHP = 1.92 Hz coupling of the SHa proton to the PA atom.
This J value is reasonable based on a Karplus relationship
established within the P−Ru−S−H geometry of the isostruc-
tural cis-RuCl2(P−N)(PPh3)(SH2) species,5b noting in 4 the
small dihedral angle of 69.81° between the P1−Ru−S and Ru−
1
S−H1 planes. A H{31P}NMR spectrum (Figure S1 in the
Supporting Information) is thought to show that Ha is partially
coupled to P1 (labeled PA in Figure 3). The HH correlations
1
were confirmed by a 2D COSY H NMR experiment.
The solution, rt NMR spectra of 3, 4, and the isolated H2S
adducts (e.g., Figure 3) always show the presence of the
precursor five-coordinate species (see eq 1), implying
equilibrium reactions for these systems. The equilibrium
constants for these reversible reactions and the associated
thermodynamic data are considered later.
n
In Situ cis-RuCl2(P−N)(PPh3)(R′SH) Species (R′ = Pr,
iPr; nPn, nHx, Bn). Reactions of longer-chain thiols with
RuCl2(P−N)(PPh3) were also investigated, but attempts to
isolate the products were unsuccessful because of the facile loss
of R′SH and the O2 sensitivity of the systems. However, the
thiol species were readily detected in situ by 31P{1H} NMR
spectra in CDCl3 or C6D6; the addition of excess R′SH to the
green solution of the precursor generated a yellow solution
containing the product. The 1H NMR spectra were
uninformative because the product signals were obscured by
those of excess thiol. The 31P{1H}-AX patterns are like those of
the H2S, MeSH, and EtSH complexes and depend little on the
nature of the thiol: all of the R′SH and H2S species have δ(PN)
and δ(P) values in the respective ranges of 49−52 and 41−46
Figure 2. ORTEP plot for 4 with thermal ellipsoids shown at the 33%
probability level. Some phenyl C atoms have been omitted for clarity.
Cl plane, and there is no hydrogen bonding between SH and
the cis-Cl atom. The thiol H atom points toward the planes of
the Ph groups: the H···C15 and H···C22 distances in 3 (2.84
and 2.49 Å, respectively), and the H···C11 and H···C24
distances in 4 (2.83 and 2.30 Å, respectively), indicate possible
SH/π (phenyl rings) interactions,5b,21 which may play a role in
stabilizing the coordinated thiol.
2
ppm, with JPP values of 29.5−30.5 Hz. The 31P{1H} NMR
i
n
spectra of the R′ = Pr and Pn systems also revealed a further
2
AX pattern in the same regions but with higher JPP values of
The 31P{1H} NMR spectra of 3 and 4 in CD2Cl2 are
consistent with the solid-state structures and are very similar to
those of the H2S adducts (see above). The spectra show an AX
pattern for the cis-P atoms at δ ∼51 and ∼42 (2JPP ∼ 30 Hz),
respectively, for the P−N and PPh3 ligands. Of note, the
binding of RSH and H2S (eq 1) results in an initial vacant site
trans to PN becoming occupied by Cl, whereas the PR3 ligand
remains trans to the N atom, and this is reflected in an upfield
shift of ∼30 ppm for the PN resonance, whereas that of the PR3
ligand changes by <5 ppm. The 1H NMR spectra of 3 (δ 3.35,
3.10) and 4 (δ 3.41, 3.24) reveal the expected inequivalence of
the NMe groups. For 3, the S(CH3) and SH resonances overlap
to give a multiplet at δ 0.70, but at −50 °C, these signals resolve
into a doublet for S(CH3) at δ 0.65 (2JHH = 6.97) and a broad
multiplet for SH at δ 0.60. For 4, the coordinated S atom is
chiral and the methylene CHbHc protons are diastereotopic,
and hence anisochronous.22 The 1H NMR spectrum (Figure 3)
shows multiplets at δ 2.00 and 0.88 for these protons, and the
spectrum for the coordinated EtSH is nicely simulated using
36.6 and 36.1 Hz, respectively; these spectra are tentatively
assigned to the trans isomers, based on data for the trans-
RuCl2(P−N)(PPh3)(L) complexes, where L = H2O, MeOH,
2
and EtOH, which have JPP values of 36−38 Hz within the AX
pattern.6b As seen qualitatively in the 31P{1H} NMR spectra,
formation of the thiol species (eq 1) becomes less favorable
with increasing bulk of the R′ group, and no reactions were
observed with excess PhSH or thiophene.
IR and UV−vis Spectra. The vibration modes ν3, ν1, and ν2
of gaseous H2S (Scheme 1) are seen at 2629, 2615, and 1180
cm−1, respectively.23 For the Ru-SH2 adducts 2a,5a 2a′,5a 2b,
and 2b′ (see the Experimental Section), the ν3 and ν1 bands are
observed at lower wavenumbers (in the 2506−2495 and 2476−
2449 cm−1 regions), likely indicating a lengthening of the S−H
bonds upon coordination, while ν2 is obscured by other bands.
For MeSH and EtSH, only the ν1 stretch is observed (at 2580
and 2573 cm−1, respectively),24 and again this is lowered within
the cis-RuCl2(P−N)(PPh3)(R′SH) complexes 3 and 4 by ∼47
cm−1 (R′ = Me) and ∼57 cm−1 (R′ = Et). Limited data5,6,7b,e
Table 1. Selected Bond Lengths (Å) for 3 and 4 with Estimated Standard Deviations in Parentheses
3
4
3
4
Ru1−S1
Ru1−P1
Ru1−P2
Ru1−N1
2.3393(8)
2.2802(8)
2.3109(8)
2.335(2)
2.3397(5)
2.2743(4)
2.3110(5)
2.3646(15)
Ru1−Cl1
Ru1−Cl2
S1−H1
S1−C39
S1−C1
2.4238(8)
2.4470(8)
1.06(4)
2.4210(5)
2.4678(5)
1.28(2)
1.802(3)
1.8243(19)
1.510(3)
C1−C2
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Table 2. Selected Bond Angles (deg) for 3 and 4 with Estimated Standard Deviations in Parentheses
3
4
3
4
H1−S1−C39
H1−S1−C1
99(2)
S1−Ru1−P1
S1−Ru1−P2
S1−Ru1−N1
Cl2−Ru1−P1
Cl2−Ru1−P2
Cl2−Ru1−N1
P1−Ru1−N1
P2−Ru1−N1
S1−C1−C2
86.14(3)
94.85(3)
87.08(7)
169.27(3)
86.70(3)
86.52(6)
83.26(6)
172.96(7)
87.383(17)
97.191(16)
85.34(4)
94.4(11)
Ru1−S1−H1
Ru1−S1−C39
Ru1−S1−C1
Cl1−Ru1−S1
Cl1−Ru1−P1
Cl1−Ru1−P2
Cl1−Ru1−N1
Cl1−Ru1−Cl2
102(2)
109.1(11)
116.50(12)
167.859(17)
91.766(16)
86.30(4)
115.85(8)
174.610(16)
96.246(17)
86.154(17)
91.17(4)
176.60(3)
92.51(3)
88.50(3)
89.67(7)
90.68(3)
82.48(4)
176.74(4)
109.49(17)
88.584(17)
suggest that coordination of R′SH or H2S to RuII always results
in a lowering of the νSH values. In Ru(SH2)(PPh3)(“S4”)·THF,
where “S4” is the dianion 1,2-bis[(2-mercaptophenyl)thio]-
ethane, the decrease in the ν values by 200−350 cm−1 seems
exceptional and is likely due to the presence of S−H···S and S−
H···O hydrogen bridges.25 Surprisingly, the ν1 and ν3 values for
2a and 2b are the same (2506 and 2476 cm−1, respectively), as
are the values for 2a′ and 2b′ (2495 and 2449 cm−1), showing
that the substitution of Cl− by Br− has no effect on the S−H
stretching modes, whereas the replacement of PPh3 by P(p-
tolyl)3 within the chloro species decreases these bands by ∼10
and ∼25 cm−1, respectively,5,6 possibly because of increased
SH/π interactions within the ring system of the p-tolyl group.
Unfortunately, a direct comparison between the two structures5
cannot be made because only one H atom of the H2S ligand
was located in the P(p-tolyl)3 complex.5a
1
Figure 3. H NMR spectrum (500 MHz) of 4 in CD2Cl2 at 20 °C.
Note: 4 is in equilibrium with 1a (δ 3.13, s, NMe2) and free EtSH (*)
(δ 2.55 dq, HSCH2CH3; δ 1.46, t, HSCH2; δ 1.31, t, (CH2CH3);
●
acetone ( ) (δ 2.1, s).
The green RuX2(P−N)(PR3) complexes in CH2Cl2 have
visible absorption bands in the ranges 452−512 nm (λ1; ε1 ∼
780−1170 M−1 cm−1) and 672−780 nm (λ2; ε2 ∼ 435−615
M−1 cm−1; Table S and Figure S2 in the Supporting
Information). The binding of R′SH (R′ = H, Me, Et) gives
yellow products that show a blue shift of λ1 by up to ∼30 nm
(with ε1 values decreased by ∼25%), while λ2 is no longer seen
in the 530−820 nm region. The ε values and observed trend for
both λ1 and λ2, where the band energies decrease in the
sequence Cl > Br > I (Table S in the Supporting Information),
indicate that the bands likely result from RuII-to-P-ligand
charge-transfer transitions aided by π donation from the halide
ligands. Coordination of the S ligands perhaps shifts the λ2
band to lower energy. Attempts to investigate kinetics via the
UV−vis spectral changes were unsuccessful because of the
“instantaneous” reactions even at −10 °C; data obtained by
stopped-flow experiments, even with attempted rigorous
exclusion of air, were irreproducible because of decomposition
of the reactant and/or products. Equilibrium constants were,
however, readily measured under Ar via NMR data acquired in
J. Young NMR tubes.
1
Figure 4. H NMR spectra of coordinated EtSH of complex 4 (500
MHz, CD2Cl2): (a) simulated spectrum, J values in Hz; (b) expanded
regions of the actual spectrum (Figure 3).
Thermodynamics for Reversible Formation of the H2S
and Thiol Complexes. The equilibrium constants (K) were
determined for the reversible binding of H2S and R′SH (eq 2;
1
R′ = H, Me, Et) using H NMR integration data for each
Scheme 1
species in C6D6; better resolved peaks were seen in this solvent
trans‐RuCl2(P−N)(PPh3) (1a) + R′SH
K
⇄ cis‐RuCl2(P−N)(PPh3)(R′SH)
(2)
(vs CD2Cl2 or CDCl3) over the temperature range used (13−
75 °C). The determination of K is illustrated by a consideration
of Figure 5, which shows data for dissociation of cis-RuCl2(P−
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this excludes consideration of energy changes in the trans-to-cis
halide rearrangement that accompanies the forward reaction
(see below). The relative K values at 25 °C show that the
MeSH complex 3 is the most stable, and qualitative visual
observations and UV−vis data confirm this: upon dissolution of
this complex, the color remains yellow, characteristic of 3,
whereas dissolution of the H2S and EtSH complexes gives a
green color due to the presence of 1a. The K values of the H2S
adducts 2a and 2b are also consistent with the usually observed
greater trans influence of Br− versus Cl−.26 Of note, within all of
the systems, increasing exothermicity is accompanied by
increasingly unfavorable entropic changes, yet a further example
of the commonly observed “compensation effect”;27 indeed, the
data of Table 3 give a good linear a plot of −ΔH° versus −ΔS°
(Figure S4 in the Supporting Information).
Enthalpy changes for the reverse reaction of eq 2 in the solid
state were obtained by DSC. Solid samples of the acetone-
solvated 2a, 3, and 4 complexes were heated in the DSC
chamber under N2, and the endothermic ΔH° values were
measured for the loss of H2S, MeSH, and EtSH, ignoring the
loss of acetone (Figure 6). The Ru−S bond strength in 4 is the
1
Figure 5. H NMR spectra in the region δ −0.5 to +4.5 (300 MHz,
C6D6) for the equilibrium established (by dissolution of the acetone
solvate of 2a) between 2a, 1a, and H2S at ∼20 °C. The acetone signal
in C6D6 is ∼0.5 ppm upfield from that in CDCl3 and CD2Cl2 (see 1H
NMR data for the isolated acetone solvates of 2b′, 3, and 4).
N)(PPh3)(SH2) (2a) to form some 1a, where K = [2a]/
[1a][H2S]. The samples for analysis were prepared by
dissolving the acetone solvate of 2a in C6D6 under Ar. As the
temperature is raised, the integrations of the 1H signals of 1a (δ
3.07, NMe2) and free H2S (δ 0.30) increase, while those of 2a
(δ 3.67, 2.97, NMe2) and RuSH2 (δ 1.02) decrease; this shows
qualitatively that the formation of 2a is exothermic. Because
[Ru]total is known (= [1a] + [2a]) and defining x as [2a]/[1a]
and y = 1a/[H2S]solution, K can be written as xy(1 + x)/[Ru]total
;
labeling the integrated peak areas in Figure 5 as α, β, ε, and ω
gives rise to the expressions shown in eq 3 from which x and y
(and, hence, K) can be calculated. Raw data for the equilibrium
α/3 (or ε/2)
(β − α)/6
(β − α)/6
ω/2
x =
;
y =
(3)
calculations involving three isolated H2S species and the
isolated MeSH and EtSH complexes (where similar calculations
apply) are given in the Appendix in the Supporting
Information. The K values and corresponding ΔH°, ΔS°, and
ΔG° values determined by van’t Hoff plots (Figure S3 in the
Supporting Information) are summarized in Table 3. We are
unaware of any other thermodynamic data reported upon
coordination of H2S or thiols to transition metals.
Figure 6. DSC curves for cis-RuCl2(P−N)(PPh3)(L) complexes.
Samples are heated in an N2 atmosphere (flow rate = 40 cm3 min−1) at
a rate of 5 °C min−1 to 200 °C.
weakest, possibly because of the larger EtSH ligand. Consistent
with this, the exothermicity for the formation of 4 in solution is
also the lowest value (Table 3), but the respective ΔH° values
determined in solution are up to 60% lower than those in the
solid state, and this is tentatively attributed to the enthalpy
change of a cis-to-trans dichloro isomerization process in
solution. When the yellow, solid samples of 2a, 3, and 4 are
heated under vacuum at 50 °C for over 2 h, the S ligands are
removed to give a green product, which upon exposure to air
rapidly decomposes to an uncharacterizable black powder. This
green product is different from the more aerobically stable 1a
and is thought to be mainly the cis isomer, as judged by far-IR
data: the trans isomer has its major band at 336 cm−1
(presumably νRuCl), whereas the presumed cis isomer shows
several bands in the 329−303 cm−1 region and no band at 336
cm−1. Dissolution of this cis isomer in CDCl3 results in the
rapid formation of the trans isomer 1a, as observed by NMR
spectroscopy. A comparison of the solution and solid-state
enthalpy values (ignoring any solvation effects in the solution
equilibria) gives, for conversion of the cis isomer to the more
thermodynamically stable trans isomer 1a, ΔH° values of −39
to −66 kJ mol−1 within the five-coordinate species. These
The negative ΔS° values are consistent with the binding of a
small molecule to a metal site, while the low-value
exothermicities imply relatively weak Ru−S bond energies;
Table 3. Thermodynamic Data at 25 °C for the Formation of
cis-RuX2(P−N)(PR3)(L) Complexes in C6D6 (eq 2)
b
b
RuX2(P−N)
ΔG°
ΔH°
(kJ mol−1
ΔS°
a
(PR3)(L)
K (M−1
)
(kJ mol−1
)
)
(J mol−1 K−1
)
X = Cl, R = Ph, 153
5
−12.5 0.1
−9.7 0.2
−11.9 0.3
−46
−33
−54
4
−112 14
L = H2S (2a)
X = Br, R = Ph,
L = H2S (2b)
51
4
4
9
−77 13
X = Cl, R = p-
tolyl, L = H2S
(2a′)
120 15
−140 35
X = Cl, R = Ph, 296 20
−14.1 0.2
−12.5 0.1
−28
−22
3
4
−48 10
−32 14
L = MeSH (3)
X = Cl, R = Ph, 154
8
L = EtSH (4)
a
b
Error values estimated from repeat experiments. Errors for ΔH° and
ΔS° estimated from maximum and minimum slopes and intercepts of
van’t Hoff plots, respectively.
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1
values are of the same order of magnitude as those reported for
the solid-phase isomerizations of the chloride ligands within the
six-coordinate RuCl2(CO)(PR)3 complexes (ΔH° = 15, 21,
and 48 kJ mol−1 for the R = Ph2Me, PhMe2, and Me3 species,
respectively).28
Compound 5. When green CH2Cl2 or C6H6 solutions of 1a
are exposed to O2, the color intensifies, and after ∼1 h of
reaction time, the addition of hexanes precipitates the dark-
blue-green complex 5, μ-dichloro-μ-oxobis[chloro(o-diphenyl-
phosphino-N,N′-dimethylaniline)ruthenium(III), which was
isolated in ∼30% yield; crystals of an acetone solvate were
obtained from acetone solutions. The X-ray structure of 5 was
briefly reported in a communication from our group that
described the formation of 5 via decomposition of cis-
RuCl2(P−N)(PPh3)(N2O).4b
(different from 5) that gives broad 31P{1H} and H NMR
signals. Evaporation of the solvents from the filtrate allowed for
isolation of a white solid, shown to be SPPh3, which was
characterized by elemental analysis and 31P{1H} data in CDCl3
(δ 44.8). Of interest, when a mixture of O2 and H2S (∼1:1 by
volume injection) is added to a CH2Cl2 solution of 2a and a 25-
fold excess of PPh3, the ruthenium complex before decom-
position catalytically converts in ∼20 min all of PPh3 to S
PPh3, with water as the coproduct. The reaction, shown in eq 4,
likely offers a new but impractical method for the synthesis of
phosphine sulfides!
Ru
1
2
H2S + PPh3 + O2 → SPPh3 + H2O
(4)
CONCLUSIONS
■
The reversible binding of thiols to a five-coordinate ruthenium-
(II) complex is described, as well as further examples of H2S
complexes of a type previously reported by our group. Crystal
structures of the MeSH and EtSH complexes are presented; the
former is the first example of a structurally characterized
transition metal−MeSH complex, which (to the best of our
knowledge) has the shortest S−H bond length yet reported for
any metal−thiol complex. The NMR, IR, and UV−vis spectra
of the adducts are consistent with their formulations, and
thermodynamic data of their formation reveal ΔH° values in
the range of −30 to −55 kJ mol−1 for H2S bonding and −20 to
−30 kJ mol−1 for the thiols, implying relatively weak Ru−S
bond energies; the ΔS° values are negative, as expected.
Whereas trans-RuCl2(P−N)(PPh3) decomposes in air to the
known complex 5 and OPPh3, cis-RuCl2(P−N)(PPh3)(SH2)
can catalyze the O2 oxidation of a mixture of H2S and PPh3 to
H2O and SPPh3.
The ORTEP plot and key geometric parameters have been
published,4b but no discussion of the structure was presented.
Each Ru has pseudooctahedral geometry, being coordinated to
one P−N ligand, one terminal Cl, two μ-Cl ligands, and one μ-
O ligand. The Ru−Ru distance (2.92 Å) is typical of a Ru−Ru
single bond (2.632−3.034 Å),29 implying the presence of a
RuIII−O−RuIII moiety. The metal−metal bond results in
reduced bond angles at the μ-Cl (71.25 and 71.92°) and μ-O
(98.6°) ligands; in complexes with longer Ru−Ru distances,
such angles are significantly larger (e.g., a RuIII−O−RuIII angle
of 122.3° is seen in a complex with a Ru−Ru distance of 3.266
Å).30 The Ru−O bond lengths (both 1.92 Å) are up to ∼0.1 Å
longer than those of other reported (μ-O)RuIII2 species (1.80−
1.90 Å)30,31 and are ∼0.1 Å shorter than those in RuIII2-μ-OH
and RuIII2-μ-OH2 complexes.32,33 The O atom is centered
equally between the Ru atoms, but the Ru−μ-Cl lengths reveal
the trans influence of the P atom in that the Ru1−Cl1 and
Ru2−Cl2 distances, where the Cl atoms are trans to the P
atoms, are ∼0.2 Å longer than the Ru1−Cl2 and Ru2−Cl1
bonds, where the Cl atoms are trans to the N atoms. This same
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic data for the structures of 3 and 4 (CIF
files), UV−vis data for the MeSH, EtSH, and H2S adducts, H
NMR signal for the S−Ha proton in 4, detailed data for the K
equilibria and van’t Hoff plots, and the compensation effect
plot. This material is available free of charge via the Internet at
http://pubs.acs.org.
1
effect has also been seen in RuII (μ-Cl)2 species.34 Complex 5 is
2
diamagnetic, as evidenced by a magnetic susceptibility
measurement; the spin coupling may result from a Ru−Ru
interaction, but strong electronic coupling between the low-
spin d5 RuIII ions through the oxo bridge and the relatively
small Ru−O−Ru angle cannot be ruled out.31a,35
AUTHOR INFORMATION
Corresponding Author
*E-mail: brj@chem.ubc.ca.
Notes
■
Solution NMR data in C6D6 for 5 show an AB pattern for the
P atoms with coupling through four bonds (4JPP = 10.4 Hz) and
four singlets for inequivalent NMe groups. The UV−vis
spectrum in dimethyl sulfoxide shows intense LMCT bands
at 348 (ε = 15300 M−1 cm−1) and 652 nm (ε = 11200 M−1
The authors declare no competing financial interest.
†Deceased October 27, 1998.
ACKNOWLEDGMENTS
■
We thank the Natural Sciences and Engineering Council of
Canada for financial support and Colonial Metals Inc. for a loan
of RuCl3·xH2O.
cm−1); the data resemble those for other RuIII species with
2
bridging ligands.31a,b,35
O2 (and not trace water) is needed for the formation of 5. An
in situ reaction of 1a and O2 in C6D6 at rt to form 5 also
generates OPPh3 (δP 25.41), and indeed 1a will catalyze the
O2 oxidation of added PPh3 to the oxide before any 5 is
detected.
The H2S complexes are also very O2-sensitive in solution.
When O2 is added to a yellow CDCl3 solution of 2a under 1
atm of H2S at rt, a dark-green solution is again formed rapidly,
but the addition of hexanes now results in a green-brown solid
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