The enthalpy of insertion of sulfur into the metal-hydrogen bond. Synthetic, structural, and calorimetric study of the complexes HS-M(CO)3C5R5 [M = Cr, Mo, W; R = H, Me]

Article abstract of DOI:10.1021/ic981221x

Synthetic and calorimetric studies of the sulfhydryl complexes HS-M(CO)₃C₅R₅ (M = Cr, R = Me; M = Mo, W, R = H, Me) are reported. The Mo and W complexes can be obtained in high yield by reaction of the hydrido complexes H-M(CO)₃C₅R₅ with Ph₃Sb=S, which readily undergoes single S atom transfer to the metal-hydrogen bond yielding the metal-sulfhydryl complex. Direct reaction between the metal hydrides and a limited amount of sulfur also yields the sulfhydryl complexes as the dominant organometallic product. At sulfur atom/metal hydride ratios higher than 1/1, additional products formulated as HS_n-M(CO)₃C₅R₅ are detected. The enthalpies of insertion of sulfur from Ph₃Sb=S and S₈ into the metal-hydrogen bond have been determined by solution calorimetry. The HS-M(CO)₃C₅R₅ complexes (M= Mo, W) are readily desulfurized by PCy₃ for R = H, but not for R = Me. The M-SH bond strength estimates for the complexes HS-M(CO)₃C₅Me₅ increases in the order Cr (46) < Mo (55) < W (63) (kcal/mol). The HS-Mo(CO)₃C₅Me₅ group has a pK_a value at least 4 pK_a units less acidic than that of H-Mo(CO)₃C₅Me₅. The crystal structure of HS-Mo(CO)₃C₅Me₅ is reported.

Full text of DOI:10.1021/ic981221x

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2136
Inorg. Chem. 1999, 38, 2136-2142
The Enthalpy of Insertion of Sulfur into the Metal-Hydrogen Bond. Synthetic, Structural,
and Calorimetric Study of the Complexes HS-M(CO)3C5R5 [M ) Cr, Mo, W; R ) H, Me]
Andreas Bauer,† Kenneth B. Capps,† Bodo Wixmerten,† Khalil A. Abboud,*,‡ and
Carl D. Hoff*,†
Departments of Chemistry, University of Miami, Coral Gables, Florida 33124, and University of Florida,
Gainesville, Florida 32611
ReceiVed October 19, 1998
Synthetic and calorimetric studies of the sulfhydryl complexes HS-M(CO)3C5R5 (M ) Cr, R ) Me; M ) Mo,
W, R ) H, Me) are reported. The Mo and W complexes can be obtained in high yield by reaction of the hydrido
complexes H-M(CO)3C5R5 with Ph3SbdS, which readily undergoes single S atom transfer to the metal-hydrogen
bond yielding the metal-sulfhydryl complex. Direct reaction between the metal hydrides and a limited amount
of sulfur also yields the sulfhydryl complexes as the dominant organometallic product. At sulfur atom/metal
hydride ratios higher than 1/1, additional products formulated as HSn-M(CO)3C5R5 are detected. The enthalpies
of insertion of sulfur from Ph3SbdS and S8 into the metal-hydrogen bond have been determined by solution
calorimetry. The HS-M(CO)3C5R5 complexes (M ) Mo, W) are readily desulfurized by PCy3 for R ) H, but
not for R ) Me. The M-SH bond strength estimates for the complexes HS-M(CO)3C5Me5 increases in the
order Cr (46) < Mo (55) < W (63) (kcal/mol). The HS-Mo(CO)3C5Me5 group has a pKa value at least 4 pKa
units less acidic than that of H-Mo(CO)3C5Me5. The crystal structure of HS-W(CO)3C5Me5 is reported.
Introduction
corresponding M-SR bond but also to allow either measurement
or calculation of reactions such as the formal desulfurization
shown in eq 4 and H atom transfer in eq 5. Determining the
The chemistry of metal/sulfur/hydrogen systems is both
complex and important. Coordinated thiols and sulfhydryls no
doubt play an important role in catalytic processes such as
hydrodesulfurization1 and also in biochemical systems such as
nitrogen fixation.2 Despite that, there is very little physical data
on the nature of the M-SH bond.3 We have recently reported
thermochemical studies which led to M-SR bond strength
estimates for chromium,4 molybdenum,5 and tungsten6 thiolate
complexes. These studies were based on reactions of disulfides
as shown in eqs 1-3.
LnM-SH f LnM-H + “S”
LnM-SH f LnM)S + “H”
(4)
(5)
thermochemical driving force for reactions in eqs 4 and 5
depends on knowing the relative (or absolute) M-SH as well
as M-H and M)S bond strengths.
The greater kinetic reactivity of metal sulfhydryl versus metal
thiolate is well-known.3 A practical consequence is that while
a wide range of complexes LnM-(SR)x have been prepared,
there are fewer corresponding compounds of the formula LnM-
(SH)x. Insertion of sulfur into the Pt-H bond has recently been
reported7 by Jones and co-workers. Of relevance to this paper
is the report that the complex HS-W(CO)3C5H5 can be
prepared8a from the corresponding tungsten hydride and ethylene
sulfide according to eq 6. The sulfhydryl complex has been
H-Mo(CO)3C5R5 + RSSR f RS-Mo(CO)3C5R5 + RSH
(1)
•Cr(CO)3C5Me5 + 1/2RSSR f RS-Cr(CO)3C5Me5 (2)
W(CO)3(PCy3)2 + 1/2RSSR f RS-W(CO)3(PCy3)2 (3)
To the authors’ knowledge, there is no information about the
enthalpy of formation of sulfhydryl complexes LnM-SH. This
is of interest not only to compare the M-SH bond to the
H-W(CO)3C5H5 + C2H4S f HS-W(CO)3C5H5 + C2H4
(6)
† University of Miami.
‡ University of Florida.
reported8b,c to react with organic N-polysulfido phthalimide
derivatives as shown in eq 7. The organometallic polysulfido
complexes were reported to decompose to thiolate complexes
by desulfurization, although the fate of the extruded sulfur is
not described.
(1) Transition Metal-Sulfur Chemistry. ACS Symp. Ser. 1996, 653.
(2) Molybdenum Enzymes, Cofactors, and Model Systems; Stiefel, E. I.,
Coucouvanis, D., Newton, W. E., Eds.; ACS Symposium Series 535;
American Chemical Society: Washington, D.C., 1993.
(3) To our knowledge there are no reports of the M-SH bond strength.
For report of M-SR bond strengths in a related system, see: Dias,
A. R.; Simoes, J. A. M. Polyhedron 1988, 7, 1531.
(4) (a) Ju, T. D.; Capps, K. B.; Lang, R. F.; Roper, G. C.; Hoff, C. D.
Inorg. Chem. 1997, 36, 614. (b) Ju, T. D.; Lang, R. F.; Roper, G. C.;
Hoff, C. D. J. Am. Chem. Soc. 1996, 118, 5328.
(5) Mukerjee, S. L.; Gonzalez, A. A.; Nolan, S. P.; Ju, T. D.; Lang, R.
L.; Hoff, C. D. Inorg. Chim. Acta 1995, 240, 175.
(6) Lang, R. F.; Ju, T. D.; Kiss, G.; Hoff, C. D.; Byran, C. J.; Kubas, G.
J. J. Am. Chem. Soc. 1994, 116, 7917.
(7) Morton, M. S.; Lachicotte, R. J.; Vicic, D. A.; Jones, W. D.
Organometallics 1999, 18, 227.
(8) (a) Beck, W.; Danzer, W.; Thiel, G. Angew. Chem., Int. Ed. Engl.
1973, 12, 582. (b) Shaver, A.; Hartgerink, J.; Lai, R. D.; Bird, P.;
Ansari, N. Organometallics 1983, 2, 938. (c) Shaver, A.; McCall, J.
M.; Bird, P. H.; Ansari, N. Organometallics 1983, 2, 1894. (d) Shaver,
A.; Hartgerink, J. Can. J. Chem. 1997, 65, 1190.
10.1021/ic981221x CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/08/1999

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The Enthalpy of Insertion of Sulfur into the M-H Bond
Inorganic Chemistry, Vol. 38, No. 9, 1999 2137
Table 1. Crystal Data and Structure Refinement for
HS-W(CO)3C5Me5
empirical formula
fw
temp
C13H16O3SW
436.17
173(2) °C
wavelength
cryst syst
space group
unit cell dimens
0.710 73 Å
monoclinic
P2(1)/c
The capability of compounds to store and release sulfur by
sulfur atom transfer (SAT) reactions is controlled by both
thermodynamic and kinetic factors that are not fully understood.
Not long ago, Jason9 showed the ability of Ph3AsdS and Ph3-
SbdS to efficiently serve as S atom transfer reagents. We have
recently reported the enthalpies of sulfurization of a series of
tertiary phosphines, arsines, and stibines forming the corre-
sponding sulfides10 (eq 8). This provided a range of sulfur atom
a ) 7.3394(1) Å
b ) 8.5719(2) Å
c ) 23.0617(5) Å
R ) 90°
â ) 96.466(1)°
γ ) 90°
vol
Z
1441.64(5) Å3
4
2.010 g/cm3
R3E + 1/8S8 f R3EdS
(E ) P, As, Sb)
(8)
density (calcd)
abs coeff
81.54 cm-1
F(000)
cryst size
θ range for data collection
index ranges
832
0.36 × 0.18 × 0.16 mm3
transfer enthalpies which we are currently extending to other
main group and transition metal systems capable of formal sulfur
atom insertion. In that regard, the metal-hydride functional
group represents a good target, and we discuss here our studies
of sulfurization and desulfurization to metal hydrides
H-M(CO)3C5R5.
1.78-27.50°
-8 e h e 9, -11 e k e 8,
-25 e l e 29
10 279
reflns collected
indept reflns
completeness to θ ) 27.50°
abs corr
min and max abs
refinement meth
data/restraints/params
goodness of fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
extinction coeff
3310 [R(int) ) 0.0242]
99.8%
integration by crystal faces
0.109, 0.343
Experimental Section
full-matrix least squares on F2
3310/4/185
General Procedure. All manipulations were carried out using
standard Schlenk techniques under an atmosphere of argon or in a
Vacuum Atmospheres glovebox. Solvents were purified by distillation
from sodium/benzophenone under argon into flame-dried glassware.
H2S (99.5%) from Matheson Gas was used as obtained. Ph3SbdS and
PCy3 were commercially available and used without further purification.
Orthorhombic sulfur (99.9995%), obtained from Johnson Mathey,
was further recrystallized from carbon disulfide. The complexes
H-M(CO)3C5R5 (M ) Cr, R ) Me; M ) Mo, W, R ) H, Me),11
Na+[Mo(CO)3C5Me5]-11, PhS-M(CO)3C5Me5 (M ) Cr,4 Mo5), and
MeS-Cr(CO)3C5Me54 were prepared and purified by standard literature
procedures. Kinetic studies and infrared measurements were made on
a Perkin-Elmer 2000 FT-IR equipped with an i-series microscope. NMR
data was recorded on a Varian VXR 400 spectrometer. Calorimetric
measurements were made using techniques described in detail else-
where.4,6 The crystal structure of HS-W(CO)3C5Me5 was determined
on a Siemens SMART diffractometer.
Preparation of the Complexes HS-M(CO)3C5R5 (M ) Cr, R )
H; M ) Mo, W, R ) H, Me). From H-M(CO)3C5R5 and Ph3Sbd
S. In the glovebox a solution of 0.4 mmol H-M(CO)3C5R5 in 10 mL
of tetrahydrofuran was transferred onto 0.4 mmol of solid Ph3SbdS
with stirring. After 1 h, the reaction was complete as determined by
FT-IR spectroscopy. Spectroscopic data, IR and NMR, for the
complexes are summarized in Table 2. Concentration of the solution
to about 2-3 mL followed by addition of heptane and cooling to -20
°C afforded the crystalline complexes in 70-90% yield, except for
HS-Cr(CO)3C5Me5 and HS-Mo(CO)3C5H5, which are unstable at
ambient temperature.
1.233
R1 ) 0.0261, wR2 ) 0.0522 [2987]
R1 ) 0.0323, wR2 ) 0.0534
0.0085(3)
largest diff peak and hole
1.386 and -0.603 e Å-3
a R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. wR2 ) [∑[w(Fo2 - Fc )2]/
2
∑[w(Fo )2]]1/2. S ) [∑[w(Fo - Fc2)2]/(n - p)]1/2. w ) 1/[s2(Fo ) +
2
2
2
(0.0370p)2 + 0.31p], p ) [max(Fo ,0) + 2Fc2]/3.
2
Table 2. Spectroscopic Data for the Complexes HS-M(CO)3C5R5
1H NMR (ppm)
(C6D6; 25 °C)
IR (cm-1
)
(25 °C)
HS-Cr(CO)3C5Me5
HS-Mo(CO)3C5H5
1.37 (C5H5), -3.23 (SH)
4.53 (C5H5), -2.93 (SH)
2008, 1949 (toluene)
2034, 1954 (toluene)
2033, 1950 (THF)
HS-Mo(CO)3C5Me5 1.48 (C5Me5), -2.21 (SH) 2021, 1941 (toluene)
2021, 1938 (THF)
2029, 1940 (toluene)
2028, 1936 (THF)
HS-W(CO)3C5H5
HS-W(CO)3C5Me5
4.52 (C5H5), -2.48 (SH)
1.54 (C5Me5), -1.95 (SH) 2017, 1928 (toluene)
2016, 1925 (THF)
this solution was removed to obtain a spectrum of the stock solution
prior to beginning the reaction. To this solution was added 4.5 mL of
a 0.05588 M Ph3SbdS solution, yielding a solution with [H-Mo-
(CO)3C5Me5] and [Ph3SbdS] ) 0.00880 M. This procedure was
repeated in tetrahydrofuran. The reaction obeyed second-order kinet-
ics: rate ) kobs[H-Mo(CO)3C5Me5][Ph3SbdS] in both toluene and THF
with values for kobs at 15 °C of 0.15 M-1 s-1 in THF and 0.0079 M-1
s-1 in toluene.
Reactions. Reaction of H-W(CO)3C5H5 with Excess S8. A
solution of S8 (58.3 mg, 0.23 mmol) in 10 mL of toluene was syringed
on top of H-W(CO)3C5H5 (54.0 mg, 0.16 mmol). FT-IR peaks at 2031
and 1940 cm-1 were consistent with the formulation HSn-W(CO)3C5H5.
Further, 1H NMR showed peaks at 4.96, 4.90, and 4.84 ppm (C5H5) in
C6D6 also consistent with the formulation HSn-W(CO)3C5H5, as well
as peaks at 4.52 ppm (C5H5) and -2.48 ppm (SH) due to HS-
W(CO)3C5H5.
From H-M(CO)3C5R5 and S8. To a solution of 0.4 mmol of
H-M(CO)3C5R5 in 10 mL of tetrahydrofuran was added a solution of
0.05 mmol of S8 in 1 mL of tetrahydrofuran with stirring. After 1 h,
the reaction was complete as determined by FT-IR. Removal of the
solvent in vacuo gave the crude complexes HS-M(CO)3C5R5 in yields
greater than 80% except for the unstable HS-Cr(CO)3C5Me5 and HS-
Mo(CO)3C5H5.
Kinetics. H-Mo(CO)3C5Me5 and Ph3SbdS. Under an atmosphere
of CO, 25 mL of a 0.01059 M toluene solution of H-Mo(CO)3C5Me5
was allowed to equilibrate to a temperature of 15 °C. One milliliter of
Reaction of HSn-W(CO)3C5H5 with n Equiv of PCy3. Four
milliliters of the HSn-W(CO)3C5H5 solution (2031 and 1940 cm-1
)
(9) Jason, M. E. Inorg. Chem. 1997, 36, 2641.
(10) Capps, K. B.; Wixmerten, B.; Bauer, A.; Hoff, C. D. Inorg. Chem.
1998, 37, 2861.
(11) Davis, R.; Kane-Maguire, L. A. P. In ComprehensiVe Organometallic
Chemistry, Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Vol. 3,
pp 1191-1195.
from above was syringed on top of solid PCy3 (207.8 mg, 0.74 mmol)
with a rapid conversion (seconds) to HS-W(CO)3C5H5 (2029 and 1940
cm-1) and a much slower conversion (hours) to H-W(CO)3C5H5 (2020
and 1926 cm-1) as seen by FT-IR.

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2138 Inorganic Chemistry, Vol. 38, No. 9, 1999
Bauer et al.
Reaction of HSn-W(CO)3C5H5 with n Equiv of H-W(CO)3C5H5.
A solution of H-W(CO)3C5H5 (114.2 mg, 0.34 mmol) in 15 mL of
THF was syringed on top of solid S8 (20.7 mg, 0.08 mmol). A rapid
reaction occurred as confirmed by the presence of FT-IR peaks at 2029
and 1937 cm-1 consistent with the formulation HSn-W(CO)3C5H5. This
solution was then syringed on top of solid H-W(CO)3C5H5 (100.0 mg,
0.30 mmol) with a slow conversion to HS-W(CO)3C5H5 (2028 and
1936 cm-1) as seen by FT-IR.
Reaction of R′-Mo(CO)3C5R5 [R ) H, R′ ) Bz; R ) Me, R′ )
Me] with Ph3SbdS. A solution of R′-Mo(CO)3C5R5 (0.16 mmol) in
10 mL of tetrahydrofuran was transferred onto solid Ph3SbdS (0.16
mmol) and stirred for about 9 h. FT-IR confirmed no reaction.
Reaction of MeS-Cr(CO)3C5Me5 and PhS-Mo(CO)3C5Me5 with
H2S. Typically, a solution of RS-M(CO)3C5Me5 (0.1 mmol) in 12 mL
of tetrahydrofuran was treated with H2S gas (25 mL, 1.1 mmol). The
reaction was complete after 3 h. The formation of HS-M(CO)3C5Me5
(M ) Cr, 2007 and 1946 cm-1; M ) Mo, 2010 and 1921 cm-1) was
confirmed by its FT-IR spectrum with decrease in bands due to RS-
M(CO)3C5Me5 (M ) Cr, R ) Me, 1997, 1938, and 1915 cm-1; M )
Mo, R ) Ph, 2020, 1943, and 1927 cm-1).
Reaction of HS-W(CO)3C5H5 with PCy3. To HS-W(CO)3C5H5
(104 mg, 0.3 mmol) dissolved in 10 mL of tetrahydrofuran was added
a solution of PCy3 (84 mg, 0.3 mmol) in 5 mL of tetrahydrofuran with
stirring. The reaction was complete after 3 h, and the product
H-W(CO)3C5H5 (2018 and 1924 cm-1) was identified by its FT-IR
spectrum. Formation of SdPCy3 was confirmed by 1H NMR by
comparison with an authentic sample.
Figure 1. Molecular structure of HS-W(CO)3C5Me5 [ORTEP, 50%
probability ellipsoids: the minor part of the disorder (S1′, C1′, and
O1′) was omitted for clarity]. Selected bond distances (Å) and angles
(deg): W-S1 2.522(2), S1-H1 1.04(7), W-S1-H1 108(4).
Results
Reaction of H-M(CO)3C5R5 with Ph3SbdS. Reaction of
triphenylantimony sulfide and metal hydrides was rapid and
quantitative as shown in eq 9. Stable crystalline products could
Reaction of HS-Mo(CO)3C5Me5 with 10 Equiv of Na+[Mo-
(CO)3C5Me5]-. A mixture of solid HS-Mo(CO)3C5Me5 (7 mg, 0.02
mmol) and Na+[Mo(CO)3C5Me5]- (68 mg, 0.2 mmol) was dissolved
in 15 mL of tetrahydrofuran. No formation of H-Mo(CO)3C5Me5 was
observed by FT-IR.
H-M(CO)3C5R5(soln) + Ph3SbdS(solid) f
HS-M(CO)3C5R5(soln) + Ph3Sb(soln) (9)
Reaction of HS-Mo(CO)3C5H5 with Na+[Mo(CO)3C5Me5]-. HS-
Mo(CO)3C5H5 was prepared in situ from H-Mo(CO)3C5H5 (74 mg,
0.3 mmol) and S8 (10 mg, 0.038 mmol) in 10 mL of tetrahydrofuran.
The conversion to the sulfhydryl complex was confirmed by FT-IR
(2033 and 1950 cm-1). With stirring, 10 mL of a tetrahydrofuran
solution of Na+[Mo(CO)3C5Me5]- (101 mg, 0.3 mmol) was added with
FT-IR peaks at 1887, 1785, and 1731 cm-1. The exchange reaction
was complete within minutes, as seen by FT-IR, to yield Na+[Mo-
(CO)3C5H5]- (1900, 1798, and 1732 cm-1) and HS-Mo(CO)3C5Me5
(2021 and 1938 cm-1).
be isolated for M ) Mo, R ) Me, and for M ) W, R ) H,
Me. The complexes HS-Mo(CO)3C5H5 and HS-Cr(CO)3C5-
Me5 could be detected spectroscopically, but decomposed in
solution or during attempted workup. Reaction of solid Ph3-
SbdS is recommended, since a solution of Ph3SbdS slowly
decomposes to Ph3Sb and elemental sulfur.9 Spectroscopic data
for the complexes prepared according to eq 9 are summarized
in Table 2. Kinetic studies of reaction involving H-Mo(CO)3C5-
Me5 and Ph3SbdS showed that the reaction obeyed second-
order kinetics: rate ) kobs[H-Mo(CO)3C5Me5][Ph3SbdS] in
Crystal Structure of HS-W(CO)3C5Me5. Crystal growth was
achieved by slow cooling of a toluene solution of the complex to - 20
°C. An orange, blocklike single crystal, 0.36 × 0.18 × 0.16 mm, of
HS-W(CO)3C5Me5 was selected. Data were collected on a Siemens
SMART PLATFORM equipped with a CCD area detector and a
graphite monochromator utilizing Mo KR radiation. Cell parameters
were refined using up to 7761 reflections. A hemisphere of data (1381
frames) was collected using the ω-scan method (0.3° frame width).
The first 50 frames were remeasured at the end of data collection to
monitor instrument and crystal stability (maximum correction on I was
<1%). The structure was solved by the direct methods in SHELXTL5
and refined using full-matrix least squares. Non-H atoms were treated
anisotropically, whereas the methyl hydrogen atoms were calculated
in ideal positions and were riding on their respective carbon atoms.
The geometry around the W atom can be described as a four-legged
piano stool with the three CO and the HS ligands occupying the square
base. The HS and one CO group diagonally located from it are
disordered and were refined in two parts. Their site occupation factors
were dependently refined to 0.69(1) for the major part, and consequently
0.31(1) for the minor part. The major and minor parts of the CO and
HS groups were constrained to be respectively equivalent. Only the
proton on the S atom of the major part was located from a difference
Fourier map and refined freely but with an isotropic thermal parameter
of 1.5 times that of the S atom. Refinement was done using F2. Crystal
and experimental data are summarized in Table 1, and an ORTEP
representation is depicted in Figure 1.
both toluene and THF. The values of kobs at 15 °C were kobs
)
0.15 M-1 s-1 (THF) and kobs ) 0.0079 M-1 s-1 (toluene).
Reaction of H-M(CO)3C5R5 with S8. Reaction of the metal
hydrides and purified S8 in tetrahydrofuran solution yielded the
metal sulfhydryl complexes as well as varying amounts of
polysulfido hydride complexes as summarized in eq 10 for
tungsten. The nature of the products formed in eq 10 depended
H-W(CO)3C5H5 + S8 f
HS-W(CO)3C5H5 + HSn-W(CO)3C5H5 (10)
on the metal/sulfur ratio, the specific metal complex, and the
solvent and temperature. If a deficiency of sulfur was used such
that the molar M/S ratio . 1, conversion to the metal sulfhydryl
complex based on sulfur as the limiting reagent was quantitative
as determined by both IR and NMR spectroscopy. A similar
pattern of stability for the sulfhydryl complexes prepared in this
way with those obtained from Ph3SbdS was observed. The
complexes HS-Mo(CO)3C5H5 and HS-Cr(CO)3C5Me5 could
again be characterized spectroscopically, but decomposed in
solution. In the case of HS-Cr(CO)3C5Me5, the principal
products of decomposition could be identified as the known
complexes [C5Me5(CO)2CrdSdCr(CO)2C5Me5], [C5Me5(CO)2-
Cr(µ-S2)Cr(CO)3C5Me5], and [C5Me5(CO)2Cr-(µ-S2)Cr(CO)2C5-

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The Enthalpy of Insertion of Sulfur into the M-H Bond
Inorganic Chemistry, Vol. 38, No. 9, 1999 2139
Table 3. Calorimetric Dataa for “S” Insertion into the H-M Bond
of H-M(CO)3C5R5
Me5].12 In the case of HS-Mo(CO)3C5H5, insoluble precipitates
were formed and not characterized.
Reaction of sulfur with the metal hydrides at metal hydride/
sulfur ratios higher than 1/1 provided evidence for formation
of polysulfide complexes HSnM(CO)3C5R5 analogous to the
alkyl polysulfides reported earlier8 as shown in eq 7. For the
polysulfide hydrides the carbonyl IR bands were shifted to
higher wavenumbers (2-3 cm-1) and the NMR signals of the
C5H5 ring were shifted downfield. Chemical evidence for this
formulation was generated by the fact that addition of excess
hydride to the already formed polysulfide complexes resulted
in smooth reaction to produce the metal sulfhydryl complex
(eq 11). Furthermore, addition of excess PCy3 to HSn-
-∆H, sulfur soln
-∆H, solid SdSbPh3
THF
C5Me5(CO)3Mo-SH 12.8 ( 0.4 12.4 ( 0.4
C5H5(CO)3W-SH 11.2 ( 0.3
C5Me5(CO)3W-SH 12.8 ( 0.2 12.2 ( 0.6
C5Me5(CO)3Cr-SH
5.0 ( 0.2b
toluene
toluene
11.3 ( 0.2
11.7 ( 0.5
12.6 ( 0.8
a ∆H in kcal/mol for all species in solution at 30 °C. b Calculated
on the basis of enthalpy of reaction of PhS-Cr(CO)3C5Me5 and H2S
as discussed in text.
hours in solution under H2S and CO, but upon evacuation during
workup decomposed and could not be isolated as solids.
Solution Calorimetric Studies. Enthalpies of reaction of the
metal hydrides with triphenylantimony sulfide were measured
as shown in eq 9. We have previously determined that the
enthalpy of reaction 16 is + 5.2 ( 0.5 kcal/mol.10 Subtraction
HSn-W(CO)3C5H5 + nH-W(CO)3C5H5 f
(n+1) HS-W(CO)3C5H5 (11)
W(CO)3C5H5 resulted in rapid conversion (seconds) to HS-
W(CO)3C5H5 and SdPCy3 followed by a much slower con-
version (hours) to H-W(CO)3C5H5 and SdPCy3 as shown in
eq 12. Attempts to separate the mixture of polysulfide complexes
Ph3SbdS(solid) f Ph3Sb(soln) + 1/8S8(soln) (16)
of reaction 16 from reaction 9 yields directly the reaction in eq
17. Calculated enthalpies of reaction (eq 17) based on experi-
H-M(CO)3C5R5(soln) + 1/8S8(soln) f
HS-M(CO)3C5R5(soln) (17)
mental determination of the enthalpies of reaction (eq 9) are
collected in Table 3. In addition, direct measurement of the
enthalpy of reaction 17 was also made with limiting sulfur as
a reagent. Reactions in THF were faster; however, there is
reasonable agreement between data for reaction in toluene and
THF indicating little solvent effect on the reaction energetics.
Desulfurization of HS-W(CO)3C5H5 by PCy3. The en-
thalpy of reaction in eq 18 was measured by solution calorimetry
in THF solution.
formed in eq 10 failed. In the presence of excess sulfur, insoluble
material, presumably consisting of dimeric and polymeric higher
oxidation state sulfides, was formed.13
Reaction of R′-Mo(CO)3C5R5 with Ph3SbdS. Reaction of
alkyl molybdenum complexes and triphenylantimony sulfide
was attempted to see if S atom insertion into the metal alkyl
bond forming thiolate complexes would occur. As shown in eq
13 in tetrahydrofuran over a period of 8 h, no reaction was
observed for R ) H, R′ ) Bz, and R ) Me, R′ ) Me.
HS-W(CO)3C5H5 + PCy3 f
H-W(CO)3C5H5 + SdPCy3 (18)
∆H ) -17.9 ( 3.0 kcal/mol
Reaction of MeS-Cr(CO)3C5Me5 and PhS-Mo(CO)3-
C5Me5 with H2S. A third route to the sulfhydryl complexes
investigated was thiol/hydrogen sulfide exchange as shown in
eqs 14 and 15. In the presence of excess hydrogen sulfide the
Previously we had reported10 the enthalpy of reaction in eq 19.
PCy3 + 1/8S8 f SdPCy3
(19)
MeS-Cr(CO)3C5Me5 + H2S f
∆H ) - 30.9 ( 1.9 kcal/mol
MeSH + HS-Cr(CO)3C5Me5 (14)
Subtraction of reaction 18 from reaction 19 yields a calculated
∆H ) - 13.0 ( 2.2 kcal/mol for sulfurization of H-W-
(CO)3C5H5. This is in reasonable agreement with other experi-
mental values in Table 3 and gives confidence to the measure-
ments. The enthalpy of reaction 14 was determined to be -0.5
( 0.3 kcal/mol in toluene solution. As discussed later, this value
can be used to estimate the Cr-SH bond strength as well as
the enthalpy of sulfurization of the chromium hydride.
Qualitative Studies of pKa of HS-M(CO)3C5R5 Com-
plexes. Several attempts were made to bracket the pKa of the
sulfhydryl complex. The first was attempted deprotonation by
a metal carbonyl anion according to eq 20. Even in the presence
PhS-Mo(CO)3C5Me5 + H2S f
PhSH + HS-Mo(CO)3C5Me5 (15)
reactions proceeded quantitatively as shown. The chromium
sulfhydryl complex obtained by this method had spectroscopic
properties identical to those of the complex, obtained in reactions
of the chromium hydride with triphenylantimony sulfide or
elemental sulfur as discussed above. Solutions of HS-Cr-
(CO)3C5Me5 prepared according to eq 14 were stable for several
(12) (a) Goh, L. Y.; Hambley, T. W.; Robertson, G. B. Organometallics
1987, 6, 1051. (b) Hermann, W. A.; Rohrmann, J.; Schafer, A. J.
Organomet. Chem. 1984, 265, C1.
(13) (a) DuBois, M. R.; DuBois, D. L.; VanDerveer, M. C.; Haltiwanger,
R. C. Inorg. Chem. 1981, 20, 3064. (b) DuBois, M. R.; VanDerveer,
M. C.; DuBois, D. L.; Haltiwanger, R. C.; Miller, W. K. J. Am. Chem.
Soc. 1980, 102, 7456. (c) DuBois, M. R.; Haltiwanger, R. C.; Miller,
D. J.; Glatzmaier, G. J. Am. Chem. Soc. 1979, 101, 5245.
Na+[Mo(CO)3C5Me5]- + HSMo(CO)3C5Me5 h HMo
(CO)3C5Me5 + Na+[SMo(CO)3C5Me5]- (20)
of a 10-fold molar excess of Na+[Mo(CO)3C5Me5]-, no