Oxidative addition of thiols, and thiol/thiolate exchange reactions of low valent molybdenum and tungsten complexes. Synthetic, structural and calorimetric study of trigonal prismatic W(CO)2(1,10-phenanthroline)(3,4-toluenedithiolate)

Article abstract of DOI:10.1016/S0020-1693(02)01489-5

Reactions of W(CO)₃(phen)(EtCN) with butane thiols, thiophenol, 1,2-benzenedithiol, and 3,4-toluenedithiol have been investigated. Reaction of butanethiol results in simple ligand exchange to form the thiol complex W(CO)₃(phen)(

Full text of DOI:10.1016/S0020-1693(02)01489-5

Inorganica Chimica Acta 348 (2003) 157Á164
/
www.elsevier.com/locate/ica
Oxidative addition of thiols, and thiol/thiolate exchange reactions of
low valent molybdenum and tungsten complexes.
Synthetic, structural and calorimetric study of trigonal prismatic
W(CO)2(1,10-phenanthroline)(3,4-toluenedithiolate)
Russell F. Lang a, Telvin D. Ju b, Jeffrey C. Bryan c,d, Gregory J. Kubas d,*,
Carl D. Hoff b,*
a Kos Pharmaceuticals, Hollywood, FL 33324, USA
b Department of Chemistry, University of Miami, Coral Gables, FL 33126, USA
c Department of Chemistry, University of WisconsinÁ
LaCrosse, 1725 State Street, La Crosse, WI 54601, USA
/
d C-SIC, MS 514, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Received 12 September 2002; accepted 13 November 2002
Abstract
Reactions of W(CO)3(phen)(EtCN) with butane thiols, thiophenol, 1,2-benzenedithiol, and 3,4-toluenedithiol have been
investigated. Reaction of butanethiol results in simple ligand exchange to form the thiol complex W(CO)3(phen)(n or tBuSH).
Reaction with thiophenol results in oxidative addition to form the W(II) thiolate hydride complex W (CO)3(phen)(SPh)(H). The
lower reducing power of Mo compared to W is demonstrated in that simple ligand binding of PhSH to Mo(0) occurs forming
Mo(CO)3(phen)(PhSH). Reactions of arene dithiols with W(CO)3(phen)(EtCN) were found to proceed with initial oxidative
addition of one SÁ
and CO to form W(CO)2(phen)(arenedithiolate) complexes. The same complexes can be formed by thiol/thiolate exchange reactions:
W(CO)2(phen)(SR)2 (Rꢀt
Bu, Ph) react quantitatively with arene dithiol to yield W(CO)2(phen)(arenedithiolate). The crystal
structure of W(CO)2(phen)(3,4-toluenedithiolate) has been determined and is trigonal prismatic rather than octahedral. Values for
/
H bond of the chelating dithiols to form W(CO)3(phen)(H)[SÁarene(SH)]. These complexes slowly eliminate H2
/
/
DH8 (thiol/thiolate exchange) have been measured by solution calorimetry relative to W(CO)2(phen)(StBu)2ꢀ
/
0.0 kcal molꢁ1
;
(CO)2(phen)(SPh)2ꢀ
/
ꢁ
/
7.29
/
0.4 kcal molꢁ1 and W(CO)2(phen)(3,4-toluenedithiolate)ꢀ
/
ꢁ
/
12.59
/
0.6 kcal molꢁ1
.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Oxidative addition; Molybdenum complexes; Tungsten complexes
THF
Cr(CO)6 0 Cr(CO)5(THF) 0 Cr(CO)5(ButSH) (1)
ButSH
1. Introduction
ꢁCO
Thiols are important ligands in a number of metal
catalyzed processes [1]. They can bind to metals as well
No evidence for oxidative addition was found for the
Cr(0) complex with ButSH or even with thiophenol
as undergo oxidative addition of the RSÁH bond. Like
/
which has a weaker SÁ
indirect evidence for oxidative chemistry for the more
readily oxidizable heavier metal congener,
/H bond. However there was
thioethers, thiols are weak donor ligands to transition
metal complexes [2]. Darensbourg and coworkers [3]
reported the first crystal structure of a bound thiol
complex of a Group 6 metal based on reaction (1):
W(CO)5(PhSH). Thiol complexes can also be formed
by low temperature protonation of anionic thiolates,
exemplified by the iron carbonyl reactions (Eqs. (2) and
(3)) [4]. Spectroscopic evidence indicated that either
formation of unstable thiol complexes or oxidative
addition could occur depending on alkyl versus aryl
substituents on sulfur.
* Corresponding authors. Tel.: ꢂ
4571.
E-mail
choff@jaguar.ir.miami.edu (C.D. Hoff).
/
1-305-284-5843; fax: ꢂ
/
1-305-284-
addresses:
kubas@lanl.gov
(G.J.
Kubas),
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01489-5

158
R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á164
/
HBF4
Fe(RS)(CO)ꢁ4 0 Fe(CO)4(RSH) (RꢀMe; Et) (2)
Mo(diphos)2(H)(SR)ꢂRSH 0 Mo(diphos)2(H)2
 (SR)20 H2 ꢂMo(diphos)2(SR)2
Reaction of W(CO)3(phen)(EtCN) with disulfides was
shown earlier [7] by us to yield 16-electron W(II)
complexes as shown in Eq. (7).
(6)
HBF4
Fe(PhS)(CO)3[P(OEt)3)]ꢁ 0 FeH(PhS)(CO)3[P(OEt)3)]
(3)
Interestingly, there is also evidence for arrested oxida-
tive addition. Protonation of [Fe(SMe)(CO)3(PEt3)]ꢁ at
W(CO)3(phen)(EtCN)ꢂRSSR 0 W(CO)2(phen)(SR)2
ꢁ
/
80 8C gives a species with an abnormally high-field
NMR resonance for the SÁH proton near d ꢁ8 (Eq.
(4)) [4]. This resonance decays irreversibly on warming,
ꢂEtCN
(7)
/
/
In contrast, reaction of disulfides with the more
sterically crowded W(0) complex [8] W(PiPr3)2(CO)3
yielded 17-electron complexes of W(I) as shown in Eq.
(8):
and an isomeric mixture of hydridoÁ/thiolate complexes
results.
W(CO)3(PiPr3)2 ꢂ1=2RSÁSR 0 +W(SR)(CO)3(PiPr3)2
Reaction of W(CO)3(PiPr3)2 with thiols and hydrogen
sulfide, however, resulted in oxidative addition of the SÁ
(8)
/
ð4Þ
H bond producing seven coordinate W(II) complexes:
W(CO)3(PiPr3)2 ꢂRSÁH 0 WH(SR)(CO)3(PiPr3)2
(9)
The paper reports investigation of ligand binding and
oxidative addition of alkyl and aryl thiols and arene
dithiols to W(CO)3(phen)(EtCN). Calorimetric mea-
surements of thiol/thiolate exchange are also reported
as well as the crystal structure of W(CO)2(phen)(3,4-
toluenedithiolate).
Low temperature (ꢁ
/
57 8C) IR spectra of the initial
protonation product show a nCO band at 1870 cmꢁ1
consistent with an Fe(0) rather than an Fe(II) complex.
On warming, the band converts to bands that match
those observed for the hydrideÁ
mixture. Thus the kinetic product is proposed to
represent arrested oxidative addition of RSÁH. Thus
whether or not the RSÁH bond undergoes oxidative
/thiolate final product
/
2. Experimental
/
addition with a given metal complex will depend not
only on the specific metal complex (its oxidation state
and ancillary ligands) but also on the thiol. The
observed oxidative addition of thiophenol versus etha-
nethiol was attributed by Darensbourg [4] to the fact
All manipulations were performed in a glovebox or
using standard Schlenk techniques. Thiophenol (99ꢂ
/
%), t-butyl thiol (99%), n-butane thiol (99%) and the
dithiols, 3,4-toluenedithiol (90%) and 1,2-benzenedithiol
(96%), were obtained from Aldrich. They were used
without further purification other than degassing and
storage under argon in a glovebox. Organometallic
precursor complexes were prepared and purified by
standard procedures.
that the PhSÁ/H bond is about 10 kcal/mol weaker than
the EtSÁH bond [5].
/
Subsequent to oxidative addition or ligand binding of
thiols, elimination of hydrogen can occur to produce
metal thiolates. Richards and coworkers [6] have
reported preparation of stable thiolate hydrides as
shown in Eq. (5):
2.1. Reaction of W(CO)2(phen)(SPh)2 with 3,4-
toluenedithiol and 1, 2-benzenedithiol
Mo(diphos)2(N2)2 ꢂRSH 0 2N2 ꢂMoH(SR)(diphos)2
In a glove box, 0.6 g (1.2 equiv.) of 3,4-toluenedithiol
and 100 of ml CH2Cl2 were added to a 200 ml Schlenk
flask. To this 2.0 g (3.1 mmol) of W(CO)2(phen)(SPh)2
was added and the solution turned purple as the
complex dissolved. After 15 min the solution was
purple-red and an IR spectrum was obtained. Both
product and reactant have a band at 1847 cmꢁ1, and
little change in this area of the spectrum was observed,
however, the higher wavenumber band of the bis-
thiolate complex at 1944 cmꢁ1 decreased smoothly as
a new band grew in at 1930 cmꢁ1. After 5 h the reaction
was complete and an IR of the purple solution showed
(5)
In the case of thiols with bulky organic groups, the
thiolate hydride complexes were stable, and the crystal
structure of MoH(ArS)(diphos)2 was determined (Arꢀ
/
2,4,6-Pri3C6H2; diphosꢀ
/
Ph2PC2H4PPh2). For less steri-
cally demanding thiols, further reaction to yield dithio-
lates was observed and proposed to proceed by initial
formation of hydrido thiolate complexes as shown in
Eq. (5) which then undergo oxidative addition of a
second mole of thiol followed by reductive elimination
of hydrogen as shown in Eq. (6):

R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á
/164
159
only bands due to product at 1930 and 1847 cmꢁ1. To
this solution was added 75 ml of heptane and immedi-
ately a black precipitate formed. The solution was
filtered and 1.5 g of black powder was collected. A
sample of the collected solid was dissolved in THF and
an IR showed bands at 1928 and 1850 cmꢁ1 for
2.3. Reaction of W(CO)2(phen)(tdt) with CO
A solution of 0.40 g of W(CO)2(phen)(tdt) in 60 ml
THF was prepared in the glove box. Twenty-five
milliliters of this solution was immediately transferred
under an argon atmosphere to a 40 ml stainless steel
reactor fitted to a high pressure FTIR cell obtained from
Harrick Scientific. Initial bands in the FTIR spectrum of
the THF solution of W(CO)2(phen)(tdt) occurred at
W(CO)2(phen)(tdt) in this solvent (tdtꢀ3,4-toluene-
/
dithiolate). NMR data of W(CO)2(phen)(tdt) showed
the following resonances in CD2Cl2: phen protons (8H):
1928 and 1850 cmꢁ1. Addition of ꢀ
17 atm of CO
/
9.06 (d), 8.53 (d), 8.13 (d); phenꢂphenyl protons, 7.74
/
pressure to the solution resulted in disappearance of
these bands and appearance of new bands at 2012, 1929,
and 1892 cmꢁ1 assigned to the carbonyl addition
product W(CO)3(phen)(tdt). Release of pressure showed
disappearance of these bands and slow regeneration of
the original spectrum of W(CO)2(phen)(tdt).
(m); phenyl protons, 7.63 (s), 6.95 (d); methyl protons,
2.31 (s).
To confirm the stoichiometry of the reaction and
verify thiophenol as the other product, reaction of
W(CO)2(phen)(SPh)2 with 3,4-toluenedithiol was per-
formed in CD2Cl2 and evaluated by FT-IR and NMR.
To 3.0 ml of CD2Cl2 was added 5 ml (1 equiv.) of 3,4-
2.4. Calorimetric measurements of enthalpies of thiol/
thiolate exchange
toluenedithiol and 0.025
g
(0.039 mmol) of
W(CO)2(phen)(SPh)2. The solution remained in the
glovebox for 3 h at which time the IR and NMR
spectra of the purple solution were obtained. The IR
spectrum revealed the complex show only bands as-
signed to product in the CO region at 1930 and 1848
cmꢁ1. The NMR spectrum showed the expected reso-
nances due to W(CO)2(phen)(tdt). Resonances due to
unbound PhSH were as follows: phenyl protons (5H),
7.27 (m), 7.16 (m); thiol proton (1H), 3.52 (s). The ratio
of unbound PhSH to the product, W(CO)2(phen)(tdt)
was approximately two. No other resonances were
observed.
Calorimetric measurements were made in a Setaram
C-80 Calvet calorimeter. A typical procedure is de-
scribed for reaction of W(CO)2(phen)(StBu)2 and tolu-
ene dithiolate (tdt). In a glovebox the mixing cell of the
calorimeter was filled with 0.0302 g of recrystallized
W(CO)2(phen)(StBu)2 and 3.5 ml of a stock solution of
0.8053 g of tdt in 25 ml of freshly distilled THF. The cell
was sealed, taken from the glove box and loaded in the
calorimeter. Following temperature equilibration, reac-
tion was initiated by inverting the calorimeter and
followed to completion. The infrared spectrum taken
Reaction of W(CO)2(phen)(SPh)2 with 1,2-benzene-
dithiol occurred in a manner analogous to reaction with
3,4-dmt. IR bands for the black complex
W(CO)2(phen)(1,2-S2C6H4) in THF solution occur at
1929 and 1850 cmꢁ1 and are virtually identical in shape
and position to those for W(CO)2(phen)(tdt) (1928 and
1850 cmꢁ1). Attempts to grow crystals suitable for X-
following completion of the reaction (1Á2 h) confirmed
/
quantitative conversion of W(CO)2(phen)(StBu)2 to
W(CO)2(phen)(tdt). Reported enthalpies of reaction
for thiophenol (ꢁ
/
7.29
/
0.2 molꢁ1) and 3,4-dmt (ꢁ
/
12.59
/
0.5 kcal molꢁ1) have been adjusted for heats of
solution of the solid complexes.
2.5. Spectroscopic studies of reactions of
Mo(CO)3(phen)(THF) and W(CO)3(phen)(EtCN)
with thiols
ray
W(CO)2(phen)(1,2-S2C6H4) but succeeded for the ana-
diffraction
were
not
successful
for
logous methyl-substituted derivative.
2.5.1. Reaction of W(CO)3(phen)(EtCN) with PhSH
PhSH (4 ml, tenfold molar excess) was added to a
solution of 1.0 g of W(CO)3(phen)(EtCN) in 50 ml
CH2Cl2. The solution color changed from clear yellow
to dark brown. The IR spectrum of the solution showed
bands at 1997, 1913, and 1886 cmꢁ1. The shift to higher
wavenumber indicated oxidative addition to form
W(CO)3(phen)(H)(SPh) which was further characterized
by NMR spectroscopy as described below. The addition
of CO to an aliquot of this solution resulted in rapid
elimination of thiophenol and formation of
W(CO)4(phen). After 2 days under argon atmosphere
at room temperature (r.t.), a solid precipitated from
solution and was identified by IR and NMR spectro-
2.2. Crystal growth of W(CO)2(phen)(tdt)×
/
0.5THF
A solution of W(CO)2(phen)(tdt) was prepared in a
glovebox by adding 0.1 g of the solid to 10 ml of THF.
The purple solution was filtered through a syringe filter
into a 50-ml Erlenmeyer flask. The flask was sealed with
a septum and a syringe needle was inserted into the
septum to achieve very slow evaporation of the solid.
The solution was left undisturbed for 7 days at which
time black prism-like crystals were observed and used
for X-ray diffraction analysis. Solvent (0.5THF) was
present in the lattice.

160
R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á164
/
scopy to be the previously reported [6] complex
WCO)2(phen)(SPh)2.
of CH2Cl2. The solution rapidly turned purple, and the
IR spectrum showed bands at 1902 and 1787 cmꢁ1
attributed to W(CO)3(phen)(tBuSH). The addition of
excess EtCN to this solution regenerated the character-
istic bands of W(CO)3(phen)(EtCN) at 1898 and 1785
cmꢁ1, indicating reversible binding of BuSH. Similar
observations were made with butanethiol reaction,
which showed bands at 1901 and 1786 cmꢁ1 in
CH2Cl2 attributed to W(CO)3(phen)(BuSH). NMR
data for these reactions studied in CD2Cl2 showed large
peaks due to excess free thiol and also to EtCN. No sign
The reaction of W(CO)3(phen)(EtCN) and PhSH was
monitored by NMR in CD2Cl2. CD2Cl2 (2 ml) and 30 ml
(2.5 equiv.) of PhSH was added to 0.06 g of
W(CO)3(phen)(EtCN). The IR spectrum again showed
the bands attributed to W(CO)3(phen)(H)(SPh) at 1997,
1914 and 1888 cmꢁ1. In addition to signals due to free
thiophenol, NMR signals for the complex were found
at: phen (8H) 9.45 (d), 8.39 (d), 7.82 (dd), 7.75 (s); SÁ
C6H5 (5H), 6.34 (t), 6.11 (t), 5.83 (d); WÁH (1H) ꢁ3.22
(s). The expected 183W satellites (14.3% natural abun-
dance) for the hydride peak at Á3.22 ppm were not
/
/
/
of peaks in the range ꢁ
/
1 to ꢁ10 ppm (indicative of
/
/
metal hydride formation) were found for either complex.
clearly resolved because of a low signal/noise ratio.
2.5.4. Reaction of Mo(CO)3(phen)(THF) with PhSH
In a Schlenk tube, 0.05 g of Mo(CO)3(phen)(THF)
was stirred with 5 ml of CH2Cl2 under argon. An IR
spectrum of the blue solution showed bands at 1906 and
1779 cmꢁ1. Immediately following the addition of 60 ml
of PhSH (5 molar equiv.) the solution turned red and the
infrared bands shifted to 1915 and 1795 cmꢁ1 assigned
to Mo(CO)3(phen)(PhSH). These solutions were highly
air sensitive, and a stable product could not be isolated.
2.5.2. Reaction of W(CO)3(phen)(EtCN) with 3,4-
toluenedithiol
3,4-Toluenedithiol (0.3 g, 5 equiv.), 30 ml of THF,
and 0.2 g (0.40 mmol) of W(CO)3(phen)(EtCN) was
added into a 100-ml Schlenk flask in a glovebox. The
solution turned from deep blue to red. The IR spectrum
was assigned to the oxidative addition product
W(CO)3(phen)(H)[SC6H3(SH)(CH3)] with bands at
1998, 1916 and 1888 cmꢁ1 similar to those observed
for W(CO)3(phen)(H)(SPh) described above. The flask
was removed from the glovebox, evacuated, and placed
in a 40 8C water bath for 5 days. During that time the IR
bands at 1998, 1916 and 1888 cmꢁ1 decreased in
intensity, and new bands appeared at 1927and 1849
Resonances in the range ꢁ
/
1 to ꢁ10 ppm indicative of
/
metal hydride formation were not found.
3. Results and discussion
cmꢁ1
. These data were identical to those for
W(CO)2(phen)(tdt) prepared and characterized as de-
scribed earlier.
The thiol complexes reported here were labile and
readily decomposed, particularly in the absence of
excess thiol ligand that stabilizes them in solution
[9].1Attempts to isolate pure crystalline products suita-
ble for elemental analysis or for X-ray diffraction were
not successful. Reactions products were formulated
based on a combination of IR and NMR spectroscopic
data that readily establish whether or not oxidative
The reaction of W(CO)3(phen)(EtCN) with 3,4-tolue-
nedithiol was performed in CD2Cl2 to obtain an NMR
of the resulting reaction products. 3,4-Toluenedithiol
(0.02 g, 2.5 equiv.) was added to 2.5 ml of CD2Cl2 in a
small test tube followed by 0.03 g (0.06 mmol) of
W(CO)3(phen)(EtCN). The solution turned from deep
blue to yellowÁbrown within 5 min and no precipitate
/
addition of the RSÁH bond has occurred as well as
/
was observed. The solution was syringed into a NMR
tube and analyzed immediately. The NMR showed
resonances at 9.50 (d), 8.40 (d), and 7.78 (m) for the
eight phen protons. Two singlet resonances of approxi-
mately equal intensity were observed in the hydride
chemical conversion of proposed intermediate thiolate
hydrides to products of known or determined structure.
3.1. Reaction of W(CO)3(phen)(EtCN) with BuSH,
PhSH and arenedithiols
region at ꢁ
equal intensity were seen at 1.89 and 1.44 ppm that were
assigned to the ꢁCH3 group of bound 3,4-toluene-
/
3.35 and ꢁ
/
3.40 ppm, and two singlets of
/
Reaction of W(CO)3(phen)(EtCN) with excess buta-
n
t
dithiol. These two sets of peaks suggested the existence
of two isomers of the hydride thiolate complex. Reso-
nances attributed to unbound EtCN at 2.33 (q) and 1.27
(t) ppm as well as signals for unbound excess 3,4-
toluenedithiol were also observed.
nethiol (either the Bu or Bu isomer) resulted in simple
ligand substitution as shown in Eq. (10).
1
In the absence of stabilizing thiol ligand, for example under
vacuum or when redissolving a crude solid material for attempted
recrystallization the thiol complexes were observed to undergo a
reaction in which loss of one mole of thiol ligand from two moles of
complex yielded dinuclear mixed valent W(II)/W(0) complexes of the
form: [W(CO)3(phen)(m-SR)(H)][W(CO)3(phen)].
t
n
2.5.3. W(CO)3(phen)(EtCN) and BuSH and BuSH
tBuSH (40 ml, ꢀ
10 equiv.) was added to a solution
obtained from 0.0215 g of W(CO)3(phen)(EtCN) in 4 ml
/

R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á
/164
161
W(CO)3(phen)(EtCN)ꢂBuSH
0 W(CO)3(phen)(BuSH)ꢂEtCN
W(CO)3(phen)(H)(SPh)ꢂPhSH
(10)
0 W(CO)2(phen)(SPh)2 ꢂCOꢂH2
(14)
No evidence for oxidative addition was found for the
alkanethiols. This contrasted to the behavior of thio-
phenol as shown in Eq. (11):
A plausible mechanism would involve loss of CO as a
first step to generate a coordinatively unsaturated
dicarbonyl complex as shown in Eq. (15):
W(CO)3(phen)(H)(SPh)0 COꢂW(CO)2(phen)(H)
(SPh)
(15)
Binding a second mole of thiophenol would then lead to
elimination of H2 and CO in a manner analogous to that
reported for Mo(diphos)2(H)(SR) as shown in Eq. (6).
Carbon monoxide released in Eq. (14) is trapped as
shown in Eq. (16):
ð11Þ
An excess of thiophenol was used to study Reaction (11)
in order to displace EtCN which is a competitive ligand
and also to prevent formation of dinuclear products [9].
The observation that aryl but not alkyl thiols undergo
oxidative addition to the W(CO)3(phen) fragment is in
contrast to what was observed for W(CO)3(PiPr3)2
where both alkyl and aryl thiols underwent oxidative
additon [8]. This would indicate that the latter fragment
is more electron rich than the former. This close balance
regarding thiol/thiolate hydride binding is further illu-
strated by the observation that changing the metal from
W to Mo influences the equilibrium position such that
thiophenol does not undergo oxidative addition:
W(CO)3(phen)(H)(SPh)ꢂCO 0 W(CO)4(phen)
(16)
Spectroscopic study of reaction of 3,4-toluenedithiol
indicated oxidative addition of one thiol group as shown
in Eq. (17):
Mo(CO)3(phen)(THF)ꢂPhSH 0 Mo(CO)3(phen)
(17)
(PhSH)ꢂTHF
(12)
NMR data for in-situ formation indicate that two
isomers corresponding to oxidative addition of either
In this case the second row metal is less susceptible to
oxidative addition than the third row metal, as is
commonly observed. Spectroscopic evidence for oxida-
tive addition (versus simple ligand binding) of thiophe-
nol to molybdenum has been obtained at low levels of
PhSH where it is believed that dinuclear oxidative
addition occurs [9]. However, no evidence for a tauto-
meric monomeric thiolate hydride Mo(CO)3-
(phen)(H)(SPh) was obtained.
Strong ligands such as CO readily displace coordi-
thiols from W(CO)3(phen)(BuSH)
Mo(CO)3(phen)(PhSH). Displacement of thiophenol
by CO from W(CO)3(phen)(H)(SPh) is also facile and
presumably proceeds by initial formation of a tauto-
meric thiol complex W(CO)3(phen)(PhSH):
of the two SÁH groups are present in solution for
/
W(CO)3(phen)(H)[SC6H3(SH)(CH3)] (Eq. (17) only
shows one of the two possible isomers). Two resonances
of approximately equal intensity in the region of the
hydride proton (ꢁ
/
3.35, ꢁ3.40 ppm) and two singlets
/
attributed to methyl groups (1.89, 1.44 ppm) are present.
These observations suggest the existence of two isomeric
products corresponding to oxidative addition of either
of the two non-equivalent thiol groups.
The hydride thiolate complex formed by oxidative
addition of one of the SH groups undergoes slow
intramolecular reaction with the unbound thiol group.
Elimination of CO and H2 produces the chelated
nated
and
product, W(CO)2(phen)(tdt) (tdtꢀ
/
3,4-toluenedithio-
W(CO)3(phen)(H)(SPh)
late):
CO
l W(CO)3(phen)(PhSH) 0 W(CO)4(phen)
ꢂPhSH
(13)
Further reaction of thiolate hydride complexes to
ultimately form bis-thiolates is observed under anaero-
bic conditions. In the presence of excess thiophenol, the
hydride thiolate reacts over a period of days at room
temperature to produce the bis-thiolate complex, pre-
sumably with elimination of CO and H2 as shown in Eq.
(14):
(18)

162
R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á164
/
Eliminated CO reacts with remaining hydride thiolate
Table 1
Crystal data and structure refinement for W(CO)2(phen)(tdt)×
/0.5THF
complex in a manner analogous to that shown earlier in
Eq. (15) to produce W(CO)4(phen) as a side product. In
spite of the intramolecular nature of reaction (18) it
requires a period of days to occur in solution, as does
reaction (14).
Empirical formula
Temperature (K)
Radiation
C23H18N2O2.5S2W
293
graphite monochromatized Mo Ka
0.71073
triclinic
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
¯
P1
3.2. Reaction of W(CO)2(phen)(SPh)2 with 3,4-
toluenedithiol and 1,2-benzenedithiol
˚
a (A)
7.973(2)
9.702(2)
14.833(3)
83.06(2)
81.07(2)
73.27(2)
2
˚
b (A)
˚
c (A)
A more efficient preparation of W(CO)2(phen)(tdt) is
that obtained by thiol/thiolate exchange as shown in Eq.
(19):
a (8)
b (8)
g (8)
Z
Dcalc (g cmꢁ3
)
1.87
5.556
Nonius CAD4
Absorption coefficient (mmꢁ1
Diffractometer
)
Crystal size (mm3)
0.30ꢃ
2Á25
4056
/0.23ꢃ0.15
/
u Range for data collection (8)
Reflections collected
/
Independent reflections
Refinement method
3809 (F ꢁ4.0s(F))
/
full-matrix least-squares on F2
Data/restraints/parameters
Goodness-of-fit on F2
3368/0/266
0.97
ð19Þ
Final R indices [Iꢁ/2s(I)]
R1ꢀ
R1ꢀ
0.89/ꢁ
/
0.0243, wR2ꢀ
0.030, wR2ꢀ0.034
0.55
/0.0322
This reaction was monitored by NMR spectroscopy in
CD2Cl2 and confirmed the complete conversion to the
chelated dithiolate and the production of two molar
equivalents of PhSH per mole of W(CO)2(phen)(tdt)
formed. Reaction of W(CO)2(phen)(SPh)2 with 1,2-
benzenedithiol in THF forms the analogous benzene-
dithiolate complex W(CO)2(phen)(1,2-S2C6H4).
R indices (all data)
/
/
Max/min residual electron den-
sity
ꢂ
/
/
ꢁ3
˚
(e A
)
wꢀ
/
1/[s2(F)ꢂ0.0006F2].
/
3.3. Crystal structure of W(CO)2(phen)(tdt)
A crystal structure of W(CO)2(phen)(tdt) was ob-
tained, and the data are given in Table 1. ORTEP
drawings are shown in both Figs. 1 and 2 along with
selected bond distances and angles. As can be seen from
Fig. 2, the molecule possesses an almost perfect trigonal
prismatic coordination geometry, which is rare for metal
carbonyl complexes. Six-coordinate metal complexes are
typically octahedral [10]. LigandÁligand repulsion is
/
greater in trigonally distorted complexes relative to
octahedral geometry, and thus it is only in special cases
that trigonal prismatic geometry is observed, e.g. with
specific types of chelating ligands and a few metal
sulfides namely MoS2 and WS2. Several trisÁdithiolate
/
complexes are trigonal prismatic such as [Mo(S2C6H4)3]
[11] and [Re(S2C2Ph2)3] [12]. It has been proposed that
interligand SÁS bonding interactions may be responsible
/
Fig. 1. ORTEP drawing for W(CO)2(phen)(tdt). Selected bond dis-
˚
for the trigonal prismatic geometry in these complexes,
but this is still unresolved. The crystal structures of the
tances (A) and angles (8): WÁ
2.213, WÁN2ꢀ2.203, WÁC1ꢀ
83.6, N1ÁWÁN2ꢀ71.6, C1ÁWÁ
/
S1ꢀ
1.962, WÁ
C2ꢀ76.4. Complete crystallo-
/
2.414, WÁ
/
S2ꢀ
/
2.314, WÁ
/
N1ꢀ
/
/
/
/
/
/C2ꢀ
/
1.973; S1Á
/WÁ
/
S2ꢀ
/
complexes M(CO)2(SC6Hi2Pr3)(PMe2Ph)2 (Mꢀ
Mo, W)
/
/
/
/
/
/
/
graphic data and tables are available as supplementary information.
reported by Morris and Richards [6b] are rare examples
of complexes possessing trigonal prismatic geometry
that do not contain chelating ligands. It was suggested
that the severe steric demands imposed by the bulky
thiolate was responsible for the observed distorted
geometry. In other cases, where no rationale for the

R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á
/164
163
complex. Exposure to vacuum eliminates CO, regener-
ating the dicarbonyl quantitatively. Binding of a seventh
ligand to the electronically-unsaturated trigonal pris-
matic W(CO)2(phen)(tdt) is stronger than to octahedral
W(CO)2(phen)(SPh)2, which requires higher pressures of
CO to form W(CO)3(phen)(SPh)2 [7a].
3.5. Calorimetric measurements of thiol/thiolate
exchange
The quantitative nature of reaction (19) suggested its
possible use in calorimetric determination of relative
bond strengths for the two complexes involved. While
direct measurements of this reaction could be made, the
rate of reaction was somewhat slow and suggested use of
the more labile complex W(CO)2(phen)(StBu)2 as shown
in Eqs. (21) and (22) below:
Fig. 2. ORTEP drawing of W(CO)2(phen)(tdt) showing approximate
trigonal prismatic structure.
observed trigonal prismatic geometry is apparent, crys-
tal packing forces have been invoked [13]. The d4 16-
electron trigonal prismatic dicarbonyl complex
Mo(CO)2(S2CNiPr2)2 has been reported [14], and it
was suggested that the p-donor properties of the
dithiocarbamate ligands were at least partly responsible
for the trigonal prismatic geometry.
W(CO)2(phen)(StBu)2 ꢂ2PhSH 0 W(CO)2(phen)
(SPh)2 ꢂ2HStBu
(21)
DH ꢀꢁ7:290:2kcal molꢁ1
The WÁ
/
S(1) bond length in W(CO)2(phen)(tdt) is
W(CO)2(phen)(StBu)2 ꢂ3; 4-toluenedithiol 0 W(CO)2
˚
significantly longer (2.414 A) than for WÁ
/
S(2) (2.314
A). The average value (2.364 A) in this complex is
similar to the average values (2.361 A) for the WÁ
bond lengths in the octahedral complex [8]
W(CO)2(phen)(SPh)2 where the WÁS bond lengths for
˚
(phen)(tdt)ꢂ2HStBu
DH ꢀꢁ12:590:6kcal molꢁ1
(22)
/S
/
The enthalpies of reaction are reported in THF solution
because the rate of reaction is much faster in this
solvent. Subtracting Eq. (21) from Eq. (22) yields Eq.
˚
the two trans SPh groups are 2.354 and 2.368 A. Thus
while the average values are similar, there is a greater
difference between the two bond distances for the
trigonal prismatic structure. It is worth noting that the
recently reported [15] structure of W(NO)2(phen)(tdt)
shows it to be an octahedral complex and that while the
(19) and enables direct calculation of DHꢀ
kcal molꢁ1 for this reaction.
The observed enthalpies of reactions include changes
in HÁSR as well as MÁSR bond strengths. For example,
/
ꢁ
/
5.390.8
/
/
/
two WÁS bond distances are more nearly equal (2.423
/
the measured enthalpy of reaction (21) is analyzed in
terms of component bond strengths:
˚
and 2.461 A) their average length is about 0.08 A longer
˚
than for W(CO)2(phen)(tdt). It is tempting to ascribe the
DH ꢀꢁ7:2kcal molꢁ1
shorter WÁ
/
S2 distance in W(CO)2(phen)(tdt) to possible
ꢀꢁ2[fDWÁSPh ÁDWÁStBugꢂfDtBuSÁH ÁDPhSÁHg] (23)
additional WÁ
/
S p donation by this atom, but that
conclusion would require detailed theoretical analysis
beyond the scope of this paper. As discussed later, there
is an apparent thermochemical stability for the trigonal
prismatic structure as judged by enthalpies of thiol/
thiolate exchange.
Taking the value [5] of DtBuSÁH
molꢁ1 greater leads to the conclusion that DWÁStBu
DWÁSPh
6.4 kcal molꢁ1. Thus the driving force for
reaction (21) is primairly due to formation of the
stronger HÁ SPh bond, but this is
StBu versus HÁ
diminished by the fact that the WÁ
StBu bond is also
Á
/
DPhSÁH to be ꢀ
/
10 kcal
ꢀ
/
ꢂ
/
/
/
/
3.4. Reaction of W(CO)2(phen)(tdt) with CO
stronger, just by not as great an amount as the bond to
hydrogen. These data can be used to estimate relative
The
six-coordinate
16-electron
W(CO)2(phen)(tdt) readily binds CO in the reversible
complex
enthalpies of oxidative addition of HÁ
/
SPh and HÁ
/
StBu
in the tautomeric equilibrium shown in Eq. (24):
equilibrium shown in Eq. (20):
W(CO)3(phen)(RSH)l W(CO)3(phen)(SR)(H)
(24)
W(CO)2(phen)(tdt)ꢂCO l W(CO)3(phen)(tdt)
(20)
To a first approximation the WÁ
are considered to be similar for Rꢀ
more endothermic nature of breaking the HÁ
versus HÁSPh bond (ꢀ
10 kcal molꢁ1) is partially
compensated for by the more exothermic formation of
the WÁ SPh bond (ꢀ
StBu versus WÁ 6.4 kcal molꢁ1),
/
SRH and WÁ
/
H bonds
t
Binding of CO by W(CO)2(phen)(tdt) was found to be
quantitative at a pressure of 18 atm of CO. Lower
pressures (ca 3 atm) may only be needed to achieve this
since even under one atmosphere of CO the predomi-
nant species in solution at equilibrium is the tricarbonyl
/
Ph and Bu. The
/
StBu
/
/
/
/
/

164
R.F. Lang et al. / Inorganica Chimica Acta 348 (2003) 157Á164
/
leading to an estimate that oxidative addition of HÁ
StBu should be approximately 3.6 kcal molꢁ1 more
endothermic in this complex. In fact, the metalÁligand
bond for coordination of BuSH would be expected to
be somewhat stronger than the metalÁligand bond for
/
evidenced in the same complex. No evidence for this
was observed, but the close nature of this balance leaves
little doubt that further exploration could yield such
complexes. Kinetic study of these reactions aimed at
determining the barriers to oxidative addition of the
/
t
/
coordination of PhSH [2]. This would be expected to
slightly increase the gap between the two, further
disfavoring oxidative addition of the alkyl thiol due to
its (expected) more favorable complex formation. More
detailed thermochemical experiments on oxidative addi-
tion of thiols in this and related systems are in progress.
A second important point is the approximately 5 kcal
molꢁ1 greater relative stability of the trigonal prismatic
W(CO)2(phen)(tdt) versus the octahedral complex
W(CO)2(phen)(SPh)2. Thus while it was expected that
reaction (19) would occur because of the favorable
entropy of a reaction involving the ‘chelate effect’, it was
surprising to find that the trigonal prismatic structure
had a more favorable enthalpy of formation as well. In
spite of its increased thermodynamic stability, it appears
to be more reactive with regard to binding of an
additional ligand which would appear to imply a greater
degree of coordinative unsaturation. The relatively small
‘bite’ of the chelating dithiolate ligand may account for
both observations. Furthermore, electronic factors and
some dithiolene like character to the dianionic arene-
dithiolate ligand may also play a role. Additional
thermochemical studies on these and related metal
thiolate systems are in progress.
sulfurÁhydrogen bond are in progress and will be
reported later.
/
Acknowledgements
Support of this work by the Petroleum Research
Fund administered by the American Chemical Society
(C.D.H.) and the Department of Energy, Office of Basic
Energy Sciences, Division of Chemical Sciences (G.J.K.)
is gratefully acknowledged.
References
[1] E.I. Stiefel, K. Matsumoto (Eds.), Transition Metal Sulfur
Chemistry, ACS Symp. Ser. 6534, ACS, Columbus, OH, 1996,
p. 653.
[2] C.D. Hoff, Prog. Inorg. Chem. 40 (1992) 503.
[3] (a) M.Y. Darensbourg, E.M. Longridge, V. Payne, J. Reibenspies,
C.G. Riordan, J.J. Springs, J.C. Calabrese, Inorg. Chem. 29
(1990) 2721;
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(1990) 5789.
[4] M.Y. Darensbourg, W. Liaw, C.G. Riordan, J. Am. Chem. Soc.
111 (1989) 8051.
[5] S.W. Benson, Chem. Rev. 78 (1978) 23.
3.6. Conclusions
[6] (a) R.A. Henderson, D.L. Hughes, R.L. Richards, C. Shortman,
J. Chem. Soc., Dalton Trans. (1987) 1115.;
Preparation of W(CO)2(phen)(tdt) showed it to have a
near perfect trigonal prismatic structure compared to
the octahedral complex W(CO)2(phen)(SPh)2. Surpris-
ingly, the trigonal prismatic structure was also found to
be about 5 kcal molꢁ1 more stable with respect to the
thiol/thiolate exchange reactions shown in Eqs. (21) and
(22). In spite of this increased thermodynamic stability,
W(CO)2(phen)(tdt) was observed to more readily bind
CO than W(CO)2(phen)(SPh)2.
(b) T.E. Burrow, A.J. Lough, R.H. Morris, A. Hills, D.L.
Hughes, J.D. Lane, R.L. Richards. J. Chem. Soc., Dalton Trans.
(1991) 2519.
[7] (a) R.F. Lang, T.D. Ju, G. Kiss, C.D. Hoff, J.C. Bryan, G.J.
Kubas, Inorg. Chem. 33 (1994) 7917;
(b) T.D. Ju, K.B. Capps, G.C. Roper, R.F. Lang, C.D. Hoff,
Inorg. Chim. Acta 270 (1998) 488.
[8] (a) R.F. Lang, T.D. Ju, G. Kiss, C.D. Hoff, J.C. Bryan, G.J.
Kubas, J. Am. Chem. Soc. 116 (1994) 7917;
(b) R.F. Lang, T.D. Ju, G. Kiss, C.D. Hoff, J.C. Bryan, G.J.
Kubas, Inorg. Chim. Acta 259 (1997) 317.
The tautomeric equilibrium between simple ligand
binding of a thiol versus oxidative addition to form a
thiolate hydride complex is near the balance point for
[9] R.F. Lang, C.D. Hoff, Unpublished results.
[10] D.L. Kepert, Inorganic Stereochemistry, Springer-Verlag, Berlin,
1982.
the M(CO)3(phen) and M(CO)3(PR3)2 (MꢀMo,W)
/
[11] M.J. Bennett, M. Cowie, J.L. Martin, J.J. Takats, J. Am. Chem.
Soc. 95 (1973) 7504.
systems we have studied so far. As has been observed
by others, oxidative addition is more favorable for
thiophenol than alkyl thiols. It was hoped that an
example would be found in this system in which there
was a balance for the tautomeric equilibrium reaction in
[12] E.I. Stiefel, R. Eisenberg, R.C. Rosenberg, H.B. Gray, J. Am.
Chem. Soc. 88 (1966) 2856.
[13] D.L. Kepert, Prog. Inorg. Chem. 23 (1977) 1.
[14] J.L. Templeton, B.C. Ward, J. Am. Chem. Soc. 102 (1980) 6568.
[15] K.B. Capps, A. Bauer, K.A. Abboud, C.D. Hoff, Inorg. Chem. 38
(1999) 6212.
which bound thiol and thiolateÁhydride would be
/