Dihydrogen activation by titanium sulfide complexes

Article abstract of DOI:10.1021/om9907876

The titanocene sulfido complex Cp*₂Ti(S)py (1, Cp* = pentamethylcyclopentadienyl; py = pyridine) is synthesized by addition of a suspension of S₈ to a toluene solution of Cp*₂Ti-(CH₂CH₂) (2) and py. The rate of rotation of the pyridine ligand in solution was determined by ¹H NMR spectroscopy, and the structure of 1 was determined by X-ray crystallography. Complex 1 reacts reversibly with dihydrogen to give Cp*₂Ti(H)SH (6) and py. Reaction of 1 with HD gives an equilibrium mixture of Cp*₂Ti(D)SH and Cp*₂Ti(H)SD; H₂ and D₂ are not formed in this reaction. ID ¹H NMR magnetization transfer spectra and 2D EXSY ¹H NMR spectra of 6 in the presence of H₂ show that in solution the H₂, hydride, and hydrosulfido hydrogen atoms exchange. A four-center mechanism for this exchange is proposed. The EXSY studies show that the Ti-H and S-H hydrogens exchange with each other more rapidly than either of those hydrogens exchanges with external H₂. A transient dihydrogen complex intermediate is proposed to explain this observation. The infrared spectrum of 6 shows an absorption assigned to the Ti-H stretching mode at 1591 cm^-1 that shifts upon deuteration to 1154 cm^-1. Reaction of 1 with trimethylsilane, diethylsilane, or dimethylsilane gives Cp*₂-Ti(H)SSiMe₃ (7), Cp*₂Ti(H)SSiHEt₂ (8), or Cp*₂Ti(H)SSiHMe₂ (9), respectively. The isotope effect for the reaction producing 7 has been measured, and a mechanism is proposed. Treatment of 1 with an additional equivalent of S₈ results in the formation of the disulfide Cp*₂Ti(S₂) (4). Acetylene inserts into the Ti-S bond of 4 to produce the vinyl disulfide complex 5. The structures of 4 and 5 have been determined by X-ray diffraction. Compound 4 reacts with 2 in the presence of py to produce 1. Phosphines react with 4 in the presence of H₂ to provide 6 and the corresponding phosphine sulfide. Reaction of hydrogen with 4 gives Cp*₂-Ti(SH)₂ (3). The reactions of 1 and 4 with dihydrogen provide a model for possible mechanisms of H₂ activation by metal-sulfide hydrodesulfurization catalysts.

Full text of DOI:10.1021/om9907876

5502
Organometallics 1999, 18, 5502-5510
Dih yd r ogen Activa tion by Tita n iu m Su lfid e Com p lexes
Zachary K. Sweeney, J ennifer L. Polse, Robert G. Bergman,* and
Richard A. Andersen*
Department of Chemistry, University of California, Berkeley, California 94720
Received October 4, 1999
The titanocene sulfido complex Cp*2Ti(S)py (1, Cp* ) pentamethylcyclopentadienyl; py )
pyridine) is synthesized by addition of a suspension of S8 to a toluene solution of Cp*2Ti-
(CH2CH2) (2) and py. The rate of rotation of the pyridine ligand in solution was determined
1
by H NMR spectroscopy, and the structure of 1 was determined by X-ray crystallography.
Complex 1 reacts reversibly with dihydrogen to give Cp*2Ti(H)SH (6) and py. Reaction of 1
with HD gives an equilibrium mixture of Cp*2Ti(D)SH and Cp*2Ti(H)SD; H2 and D2 are not
1
formed in this reaction. 1D H NMR magnetization transfer spectra and 2D EXSY 1H NMR
spectra of 6 in the presence of H2 show that in solution the H2, hydride, and hydrosulfido
hydrogen atoms exchange. A four-center mechanism for this exchange is proposed. The EXSY
studies show that the Ti-H and S-H hydrogens exchange with each other more rapidly
than either of those hydrogens exchanges with external H2. A transient dihydrogen complex
intermediate is proposed to explain this observation. The infrared spectrum of 6 shows an
absorption assigned to the Ti-H stretching mode at 1591 cm-1 that shifts upon deuteration
to 1154 cm-1. Reaction of 1 with trimethylsilane, diethylsilane, or dimethylsilane gives Cp*2-
Ti(H)SSiMe3 (7), Cp*2Ti(H)SSiHEt2 (8), or Cp*2Ti(H)SSiHMe2 (9), respectively. The isotope
effect for the reaction producing 7 has been measured, and a mechanism is proposed.
Treatment of 1 with an additional equivalent of S8 results in the formation of the disulfide
Cp*2Ti(S2) (4). Acetylene inserts into the Ti-S bond of 4 to produce the vinyl disulfide complex
5. The structures of 4 and 5 have been determined by X-ray diffraction. Compound 4 reacts
with 2 in the presence of py to produce 1. Phosphines react with 4 in the presence of H2 to
provide 6 and the corresponding phosphine sulfide. Reaction of hydrogen with 4 gives Cp*2-
Ti(SH)2 (3). The reactions of 1 and 4 with dihydrogen provide a model for possible mechanisms
of H2 activation by metal-sulfide hydrodesulfurization catalysts.
In tr od u ction
Although the reactions of dihydrogen with metal-
sulfide surfaces have been explored theoretically and
experimentally, the process by which H2 is activated on
hydrodesulfurization catalysts is still unclear.1-5
A
number of different mechanisms have been proposed for
this step, including reaction of H2 with a metal-sulfide
bond (eq 1a)6,7 and H2 addition across the disulfide bond
of a metal-disulfide complex (eq 1b).8,9
electron spectroscopic13 investigations. Some of these
studies indicate that there are both bridging and non-
bridging disulfide groups on the catalyst surface.14
There is less evidence for the existence of nonbridging
sulfide (S2-) groups, although these species have been
observed as intermediates during the sulfiding of metal
oxide surfaces and could arise from oxidation of the
reduced metal surface during the desulfurization pro-
cess.15 The original suggestion for the presence of MdS
groups on the catalyst surface was based on the produc-
tion of butadiene during the desulfurization of thiophene
and by an apparent requirement for metal “anion
vacancies” for catalytic activity (Scheme 1).6
Evidence for surface disulfide (S22-) groups comes
from infrared emission,10 Raman,11,12 and X-ray photo-
(1) Clausen, B. S.; Topsoe, H.; Massoth, F. E. Hydrotreating
Catalysis; Anderson, J ., Boudart, M., Eds.; Springer: Berlin, 1996; Vol.
11.
(2) Sa´nchez-Delgado, R. A. J . Mol. Catal. 1994, 86, 287.
(3) Prins, R.; De Beer, V. H. J .; Somorjai, G. A. Catal. Rev.-Sci. Eng.
1989, 31, 1.
(4) Anderson, A. B.; Al-Saigh, Z. Y.; Hall, W. K. J . Phys. Chem. 1988,
92 (2), 803.
(5) Lacroix, M.; Yuan, S.; Breysse, M.; Doremieux-Morin, C.; Frais-
sard, J . J . Catalysis 1992, 138, 409.
(6) Lipsch, J . M. J . G.; Schuit, G. C. A. J . Catal. 1969, 15, 179.
(7) Angelici, R. J . Acc. Chem. Res. 1988, 21, 387.
(8) Polz, J .; Zeilinger, H.; Mu¨ller, B.; Kno¨zinger, H. J . Catal. 1989,
120, 22.
(9) Startsev, A. N. Catal. Rev.-Sci. Eng. 1995, 37, 353.
(10) Weber, T.; Muijsers, J . C.; van Wolput, J . H. M. C.; Verhagen,
C. P. J .; Niemantsverdriet, J . W. J . Phys. Chem. 1996, 100, 14144.
(11) Payen, E.; Kasztelan, S.; Grimblot, J . J . Mol. Struct. 1988, 174,
71.
Mechanistic insight into the activation and hydroge-
nation of organosulfur species on surfaces has increas-
(13) Nagai, M.; Irisawa, A.; Omi, S. J . Phys. Chem. B 1998, 102,
7619.
(14) Muijsers, J . C.; Weber, T.; van Hardeveld, R. M.; Zandbergen,
H. W.; Niemantsverdriet, J . W. J . Catal. 1995, 157, 698.
(15) X-ray photoelectron spectroscopic studies are consistent with
the presence of S2- ligands, although most of these probably bridge
metal atoms.
(12) Schrader, G. L.; Cheng, C. P. J . Catal. 1983, 80, 369.
10.1021/om9907876 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/23/1999

Dihydrogen Activation
Organometallics, Vol. 18, No. 26, 1999 5503
Sch em e 1
ingly come from investigations of the solution phase
reactions of thiophenes with soluble monomeric metal
compounds.16-18 However, little is known as yet about
the processes by which hydrogen could be activated on
the catalyst surface. There is no direct evidence for the
processes illustrated in eq 1a and eq 1b, as neither the
activation of dihydrogen by a terminal metal sulfide
complex nor the reaction of dihydrogen with a mono-
meric metal disulfide complex has been observed in a
homogeneous system.19 In this report, we describe the
synthesis of monomeric titanocene sulfide and disulfide
complexes that react with dihydrogen and other small
molecules.20
F igu r e 1. ORTEP diagram of Cp*2Ti(S)py (1). Selected
distances (Å) and angles (deg): Ti-S 2.217(1), Ti-N
2.245(3), N-Ti-S 93.9(7), Cp*-Ti-Cp* 136.1(3).
Elemental sulfur has been used as a sulfur atom
source in the synthesis of early metal-sulfide complexes
by several workers. Westphal and Steudel treated the
titanium(II) complex Cp2Ti(CO)2 with elemental sulfur
in their syntheses of various titanocene polysulfides.23
Parkin and co-workers have also reported that Cp*2Zr-
(S)py24 and Cp*2Hf(S)py can be synthesized by treat-
ment of Cp*2Zr(CO)2 or Cp*2Hf(CO)2 with S8 in the
presence of py.25,26 Similarly, 1 is formed quantitatively
when a toluene solution of 2, py, and S8 is stirred
overnight (eq 3). When this reaction was monitored by
1H NMR spectroscopy, an intermediate was observed
in the reaction mixture. Mass spectral analysis indi-
cated that this intermediate was the disulfide complex
Cp*2Ti(η2-S2) (4).
Resu lts
Syn th esis of Cp *2Ti(S)p y (1). Previous work in our
laboratory had shown that the terminal titanocene oxo
complex Cp*2Ti(O)py (py ) pyridine, Cp* ) penta-
methylcyclopentadienyl) can be synthesized by the
careful addition of 1 equiv of H2O to THF solutions of
Cp*2Ti(C2H4) (2) and py.21 Our initial efforts toward the
synthesis of Cp*2Ti(S)py (1) therefore focused on using
H2S as a sulfur atom source. Condensation of 1 equiv
of H2S onto THF solutions of 2 and py does provide
complex 1 in low yield. However, inspection of the crude
reaction mixture by 1H NMR spectroscopy indicated that
significant amounts of Cp*2Ti(SH)2 (3)22 also formed
during the reaction. When this procedure was performed
on a small scale in a sealed tube, 1H NMR spectroscopic
analysis showed that 1, 2, and 3 were present in the
product mixture along with ethane and a small amount
of ethylene (eq 2). We therefore sought an improved
method for sulfur atom transfer.
The structure of 1 was determined by an X-ray
diffraction study. An ORTEP diagram and selected bond
lengths and angles are shown in Figure 1. The general
structure of 1 is similar to that of other Cp*2M(E)py
complexes (M ) Ti, Zr, Hf; E ) chalcogen), where the
pyridine ligand lies in the plane bisecting the Cp rings.27
The Ti-S bond distance of 2.216(1) Å is consistent with
1
the presence of a Ti-S multiple bond.28 The H NMR
spectrum of 1 at 25 °C in toluene-d8 shows only a single
resonance for the meta protons of the pyridine ligand,
while the ortho protons are broadened into the baseline.
Cooling this solution to 243 K results in the appearance
of five inequivalent pyridine resonances. From the
coalescence temperature of the meta protons of the
pyridine ring (267 K) and the difference in chemical shift
of these resonances at the slow exchange limit (34 ( 5
Hz) an exchange rate of 75 ( 11 s-1 at 267 K was
(16) Bianchini, C.; Meli, A. Acc. Chem. Res. 1998, 31, 109.
(17) Angelici, R. J . Coord. Chem. Rev. 1990, 105, 61.
(18) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259.
(19) Rakowski Dubois, M.; J agirdar, B.; Noll, B.; Dietz, S. Syntheses,
Structures, and Reactions of Cyclopentadienyl Metal Complexes with
Bridging Sulfur Ligands; Stiefel, E. I., Matsumoto, K., Eds.; American
Chemical Society: Washington D.C., 1996.
(20) Some of these results have been communicated: Sweeney, Z.
K.; Polse, J . L.; Andersen, R. A.; Bergman, R. G.; Kubinec, M. G. J .
Am. Chem. Soc. 1997, 119, 4543.
(23) Westphal, U.; Steudel, R. Phosphorus, Sulfur, Silicon 1992, 65,
151.
(24) Carney, M. J .; Walsh, P. J .; Bergman, R. G. J . Am. Chem. Soc.
1990, 112, 6426.
(21) Smith, M. R.; Matsunaga, P. T.; Andersen, R. A. J . Am. Chem.
Soc. 1993, 115, 7049.
(22) Bottomley, F.; Drummond, D. F.; Egharevba, G. O.; White, P.
S. Organometallics 1986, 5, 1620.
(25) Howard, W. A.; Parkin, G. J . Am. Chem. Soc. 1994, 116, 606.
(26) Howard, W. A.; Parkin, G. J . Organomet. Chem. 1994, 472, C1.
(27) Parkin, G. Prog. Inorg. Chem. 1998, 47, 1.
(28) Hagadorn, J . R.; Arnold, J . Inorg. Chem. 1997, 36, 2928.

5504 Organometallics, Vol. 18, No. 26, 1999
Sweeney et al.
Sch em e 2
disulfide complexes.34-36 The S-S bond distance of
2-
2.069(3) Å is intermediate between that found for S2
-
and S2 and is indicative of a considerable amount of
electron density localized on the disulfide ligand.37
As expected, 4 reacts with ethylene complex 2 in the
presence of pyridine to provide 1 (Scheme 2). This
transformation confirms that 4 is a viable intermediate
in the synthesis of 1 from 2. Other sulfur atom transfer
reactions were also attempted. While 4 did not react
with mercury at 25 °C, treatment of benzene solutions
of 4 and pyridine with either trimethylphosphine or
triphenylphosphine produces 1 and the corresponding
phosphine sulfide. The disulfide can also serve as a
precursor for larger titanocene-sulfur rings. For ex-
ample, addition of several equivalents of sulfur to
benzene solutions of 4 provides the trisulfide metalla-
cycle Cp*2Ti(η2-S3).
Vinyl disulfide 5 is formed upon treatment of solu-
tions of 4 with acetylene (Scheme 2). The 1H NMR
spectrum of 5 in benzene-d6 shows coupled proton
resonances at 6.78 and 5.71 ppm (J ) 9.0 Hz), and the
13C NMR spectrum features a downfield methine reso-
nance at 201.5 ppm that is characteristic of vinylic
carbon bound to titanium.31,38 The connectivity of 5 was
confirmed by X-ray diffraction. Although there is dis-
order in the metallacyle, the structure was solved by
modeling two different ligand orientations such that the
sum of the occupancies is 1 and the minority compo-
nents were refined with isotropic thermal parameters.
This analysis resulted in a reasonable least-squares
refinement. As shown in Figure 3, the thiametallacycle
is nonplanar. The Cp* ligands are staggered with
respect to each other, and the sulfur ligand is bent away
from the Cp* methyl group located between the ligating
S and C atoms. This appears to be purely a result of
internal steric interaction, as there are no apparent
short intermolecular contacts. Only a single Cp* reso-
nance is observed by 1H NMR spectroscopy in solutions
of 5 at 25 °C, suggesting that rapid ring flipping of the
vinyl disulfide ligand must be occurring in solution.
Rauchfuss has shown that similar vinyl disulfide com-
plexes are highly fluxional.39
F igu r e 2. ORTEP diagram of Cp*2Ti(S2) (4). Selected
distances (Å) and angles (deg): Ti-S 2.413(2), S-S 2.069(3),
S-Ti-S 50.8(1), Ti-S-S 64.6(1).
determined.29,30 We have previously found that the rate
of dissociation of pyridine from 1 at 293 K is ap-
proximately 2.2 × 10-2 s-1 31
.
Apparently, there are two
exchange processes involving the pyridine ligand of 1:
fast rotation about the Ti-N bond and relatively slow
dissociation of pyridine from the metal center.
Syn t h esis a n d R ea ct ivit y of Cp *2Ti(η2-S2) (4).
Parkin and co-workers have speculated that dichalco-
genides may function as intermediates in the synthesis
of terminal zirconocene chalcogenide complexes, and the
identification of disulfide complex 4 during the synthesis
of 1 (vide supra) prompted us to synthesize this com-
pound and explore its reactivity.32 Although we found
that 4 can be prepared simply by addition of 2 equiv of
elemental sulfur to toluene solutions of 2, this synthetic
route results in the formation of small amounts of Cp*2-
Ti(η2-S3),33 which is difficult to separate from the
disulfide by crystallization. Therefore, 4 is best prepared
by the reaction of 1 equiv of ethylene sulfide or elemen-
tal sulfur with 1 (eq 4).
The structure of 4 was confirmed by X-ray crystal-
lography. An ORTEP diagram and selected bond lengths
and angles are shown in Figure 2. The molecule crystal-
lizes in the space group Fdd2 and lies on a crystal-
lographic 2-fold axis. The Ti-S bond length (2.413(2)
Å) is 0.2 Å longer than the Ti-S distance in 1 and is
similar to the Ti-S bond lengths in other titanium
The known bis(hydrosulfido) complex 3 is gradually
produced when solutions of 4 are heated to 70 °C under
(29) Binsch, G. Dynamic Nuclear Magnetic Resonance Spectroscopy;
(34) Verma, A. K.; Chou, J .-H.; Rauchfuss, T. B. Inorg. Chem. 1998,
37, 5960.
(35) Hagadorn, J . R.; Arnold, J . Organometallics 1998, 17, 1355.
(36) Guilard, R.; Ratti, C.; Tabard, A.; Richard, P.; Dubois, D.;
Kadish, K. M. Inorg. Chem. 1990, 29, 2532.
(37) Mu¨ller, A.; J aegermann, W.; Enemark, J . H. Coord. Chem. Rev.
1982, 46, 245.
J ackman, L. M., Cotton, F. A., Eds.; Academic Press: New York, 1975.
(30) The corresponding free energy of activation is ∆Gq
) 13.3
267
kcal mol-1. This value is close to the ∆Gq267 of 12.2 kcal mol-1 measured
by Mountford et al. for pyridine rotation in [TpMe2Ti(NBut)Cl(py-But)]:
Dunn, S. C.; Mountford, P.; Shishkin, O. V. Inorg. Chem. 1996, 35,
1006.
(31) Sweeney, Z. K.; Polse, J . L.; Andersen, R. A.; Bergman, R. G.
J . Am. Chem. Soc. 1998, 120, 7825.
(32) Howard, W. A.; Parkin, G. Polyhedron 1995, 14, 25.
(33) Shaver, A.; McCall, J . M. Organometallics 1984, 3, 1823.
(38) Polse, J . L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem. Soc.
1995, 117, 5393.
(39) Giolando, D. M.; Rauchfuss, T. B.; Rheingold, A. L.; Wilson, S.
R. Organometallics 1987, 6, 667.

Dihydrogen Activation
Organometallics, Vol. 18, No. 26, 1999 5505
F igu r e 3. ORTEP diagram of Cp*2Ti(η2-SSC(H)dC(H))
(5). See the Supporting Information for details of structure
solution and tables of bond lengths and angles.
1 atm of H2. After crystallization from a toluene/pentane
mixture, 3 can be isolated in 80% yield. The identity of
3 was confirmed by 1H NMR spectroscopy and elemental
analysis of the recrystallized product. No intermediates
F igu r e 4. 1H NMR spectra (500 MHz, 233 K) of 6 showing
results of spin saturation transfer experiments: (a) control
spectrum, (b) spectrum with saturation of TiH resonance,
(c) difference spectrum (b - a).
1
were observed when the reaction was monitored by H
NMR spectroscopy, although a small amount of Cp*2-
Ti(η2-S3) formed during the course of the reaction. When
3 was heated to 105 °C in benzene-d6 under 1 atm of
D2 for several days, no deuterium was incorporated into
3 (as judged by 1H and 2H NMR spectroscopy). This
suggests that the reduction of 4 with dihydrogen is not
reversible.
bound to the metal center. As the temperature of the
solution is lowered to -30 °C, the pyridine resonances
sharpen and peaks assigned to free H2 and the Ti-H
and S-H protons of the hydrosulfido-hydride 6 become
well resolved (eq 6).42
We also attempted to use atom transfer chemistry to
produce oxygen- and sulfur-containing heterocycles such
as Cp*2Ti(η2-SO). Sulfur-oxygen heterocycles of titano-
cene have been synthesized previously; however, to our
knowledge there are no reported examples of three-
membered metallacycles of this type.40 Upon treatment
of 1 with several equivalents of N2O, equal amounts of
Cp*2Ti(O)py and disulfide 4 are formed (eq 5).41 No
intermediates were identified when this reaction was
The variation of the 1H NMR spectrum of 6 with
temperature suggests that the dihydrogen, hydrosulfido,
and metal-hydride protons are exchanging with one
another, and the exchange process was initially inves-
tigated by spin saturation transfer experiments. Upon
irradiation of the H2 resonance at -50 °C, the intensities
of both the Ti-H and S-H resonances decreased. The
intensities of the S-H and H2 resonances also decreased
upon irradiation of the Ti-H resonance. Interestingly,
upon irradiation of the Ti-H resonance we observed
considerable magnetization transfer to the hydrosulfido
proton but only a relatively small amount of magnetiza-
tion transfer to H2 (Figure 4).
1
monitored at 193 K by H NMR spectroscopy.
This exchange process was also investigated using 1H
EXSY NMR spectroscopy,43 which provides quantitative
information regarding the rate of proton transfer in
Rea ction s of 1 w ith H2. An immediate color change
from red to yellow is observed upon addition of 1 atm
1
1
multisite exchange systems. The 2D H EXSY spectrum
of H2 to a degassed toluene solution of 1. The H NMR
(mixing time ) 100 ms) of the solution at -30 °C is
shown in Figure 5. The spectrum confirms that ex-
change is occurring between all three proton sites (H2,
Ti-H, and SH), and the first-order rate constants for
each exchange process were calculated from a kinetic
spectrum of the yellow solution at 25 °C shows only a
single Cp* resonance and slightly broadened pyridine
resonances. The chemical shifts of the pyridine reso-
nances indicate that the pyridine ligand is no longer
(40) Steudel, R.; Prenzel, A.; Pickardt, J . Angew. Chem., Int. Ed.
Engl. 1991, 30, 552.
(41) Parkin et al. have observed that treatment of Cp*2Zr(Te)py with
N2O results in formation of Cp*2Zr(O)py and elemental Te. See:
Howard, W. A.; Trnka, T. M.; Parkin, G. J . Organomet. Chem. 1997,
528, 95.
(42) The resonances for the hydride and hydrosulfido protons in 1H
NMR spectra of 6 were assigned on the basis of the shifts of the hydride
resonances in 7-9 and the shifts of the hydrosulfido resonance in 3
and related compounds.
(43) Perrin, C.; Dwyer, T. J . Chem. Rev. 1990, 90, 935.

5506 Organometallics, Vol. 18, No. 26, 1999
Sweeney et al.
We have made several attempts to isolate 6 from the
reaction of 1 with H2. Unfortunately, only sulfide 1 is
isolated following removal of the volatile materials
under reduced pressure from a solution containing 6 and
py. Addition of pentane to concentrated toluene solu-
tions of 6 and py results only in the precipitation of 1,
which is apparently less soluble than hydrosulfido-
hydride 6, with which it is in equilibrium. Compound 6
can be prepared by other synthetic routes, however.
Addition of 1 equiv of H2S or disulfide 4 to Cp*2TiH2
under an atmosphere of H2 provides 6 along with
varying amounts of the bis(hydrosulfido) species 3.
Complex 6 is also produced quantitatively from the
reactions of phosphines with 4 in the presence of H2 (eq
8). When the products of the phosphine reaction are
1
F igu r e 5. 2D H EXSY spectrum of 6.
exposed to dynamic vacuum, the color of the solution
changes from yellow to dark red and a number of Cp*-
1
containing compounds are observed by H NMR spec-
troscopy. Attempts to obtain 6 as a solid from this
synthetic route therefore avoided exposure to vacuum.
Treatment of disulfide 4 with 1 equiv of triphenylphoso-
phine followed by removal of the solvent under a stream
of argon and dihydrogen provides a reddish solid that
can be redissolved in benzene-d6 under H2 and can be
1
shown by H NMR spectroscopy to be a mixture of 6
and SdPPh3. The IR spectrum of this solid shows a
strong absorption at 1591 cm-1 assigned to the Ti-H
stretching mode that shifts to 1154 cm-1 when the
complex is prepared using D2. A weak band at 2609
cm-1 is assigned to the SH stretching mode of the
material prepared using H2. This absorption is absent
in the deuterated analogue; however, the SD absorption
is obscured by aryl overtone bands in the 2000-1800
cm-1 region, preventing conclusive assignment of this
feature.46 Other workers have observed similar frequen-
cies for hydride and hydrosulfido stretching modes in
F igu r e 6. 1H NMR spectrum of 6-HD (400 MHz, 243 K)
showing SH and TiH resonances of unequal intensity.
matrix analysis of the peak volumes.44 The rate con-
stants for TiH/H2 and SH/H2 exchange are both 0.2 (
0.2 s-1, and the rate constant for TiH/SH exchange is
1.2 ( 0.2 s-1
.
Reaction of HD with 1 does not result in the formation
of H2 or D2.45 The fact that H/D exchange is not
catalyzed by 1 or 6 indicates that the addition and
elimination of H2 from the metal center proceeds strictly
in a pairwise fashion and that potential metathesis
processes such as reaction of dihydrogen with the
hydride ligand of 6 are not operative. The 1H NMR
spectrum of 6-HD is identical to the spectrum of 6-H2
except that integration of the hydride and hydrosulfido
resonances is no longer equal (Figure 6). Instead, the
relative intensities of the SH:TiH resonances is 1.7:1.
This ratio is essentially constant between 213 and 270
K and appears to be the result of an equilibrium isotope
effect (EIE) in which the deuterium atom prefers to
occupy the metal-hydride site of 6-HD (eq 7).
early metal metallocene complexes. For example, the
47
Ti-H stretching frequency in Cp*2TiH2 is 1560 cm-1
,
and the SH stretching frequency in 3 was determined
to be 2580 cm-1 22
.
The intramolecular EIE in 6-HD (eq
7) is unexpected in light of the observed stretching
frequencies for the hydrosulfido and hydride protons in
6. Due to the large contribution of the zero-point energy
difference in determining the EIE, the position with the
higher stretching frequency is usually the preferred
binding site for the heavier isotope.48 Intermolecular
EIEs that are not predicted by stretching force constants
are usually attributed to metal-hydride bending
modes.49,50 It is possible that bending modes are respon-
(46) A weak stretch was observed at 1885 cm-1 (calculated for Ti-
S-D: 1872 cm-1).
(47) Bercaw, J . E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J .
Am. Chem. Soc. 1972, 94, 1219.
(48) Ritchie, C. D. Physical Organic Chemistry. The Fundamental
Concepts, 2nd ed.; Marcel Dekker: New York, 1990.
(49) Bender, B. R.; Kubas, G. J .; J ones, L. H.; Swanson, B. I.; Eckert,
J .; Capps, K. B.; Hoff, C. D. J . Am. Chem. Soc. 1997, 119, 9179.
(50) Rabinovich, D.; Parkin, G. J . Am. Chem. Soc. 1993, 115, 353.
(44) Abel, E. W.; Coston, T. P. J .; Orrell, K. G.; Sik, V.; Stephenson,
D. J . J . Magn. Reson. 1986, 70, 34.
(45) If 1 was recrystallized only once, rapid formation of an equi-
librium mixture of H2, HD, and D2 is observed. This exchange is
probably catalyzed by traces of 2, which is converted to Cp*2TiH2 and
Cp*2TiH upon reaction with dihydrogen. See ref 89.

Dihydrogen Activation
Organometallics, Vol. 18, No. 26, 1999 5507
sible for the EIE in 6-HD; however, further analysis of
this effect is precluded by our inability to unambigu-
ously assign bending modes associated with the hydride
or hydrosulfido protons.
important step in the activation of dihydrogen by
hydrogenases and hydrodesulfurization catalysts.59 How-
ever, since the sulfur atom has a tendency to bridge two
metal centers, most complexes containing sulfur ligands
are either coordinatively or electronically saturated, and
potential reaction partners cannot be activated by
coordination to the metal center. Transformations in-
volving sulfide complexes are therefore often limited to
reactions that take advantage of the localization of
electron density on the sulfide ligand (i.e., ligand
oxidation, adduct formation with Lewis acids).60
Rea ction of 1 w ith Sila n es. We have also found
that 1 reacts cleanly with silanes. An immediate color
change from red to orange and the production of a single
compound in nearly quantitative yield are observed
upon addition of trimethylsilane to a benzene solution
1
of 1. The H NMR spectrum of the product in benzene-
d6 shows a singlet at δ 4.13 assigned to the Ti-H proton
of 7 (eq 9). This resonance is not present in the 1H NMR
Terminal titanium sulfide complexes have been re-
ported, and reactivity studies of some of these com-
pounds have been performed. Geoffroy et al. found that
the macrocycle-supported complex [η4-Me4taa]TidS re-
acted with strong electrophiles such as hexafluoroace-
tone.61,62 The syntheses and structures of the salts
[NR4]2[Ti(S)Cl4] (R ) Ph, Et)63 and Na2[CpTi(µ-S)(S)]2
64
have also been described. More recently, Hagadorn and
Arnold prepared and structurally characterized the
benzamidinate complex (PhC(NSiMe3)2)2Ti(S)py.28,35
These compounds are all apparently unreactive toward
nonpolar substrates such as dihydrogen and silanes.65
spectrum when the monodeuterated analogue (7-D) is
prepared from the reaction of 1 with trimethylsilane-
d1. To confirm the connectivity of the complex, 7 was
independently synthesized from the reaction of Cp*2Ti-
(H)Cl with NaSSi(CH3)3. An X-ray diffraction study has
also confirmed the structure of 8.51
Silane addition to the TidS bond is reversible. For
example, thermolysis of 7 at 75 °C in the presence of 3
equiv of H2SiMe2 gave a mixture of HSiMe3, H2SiMe2,
7, and 9. To establish that this exchange involved the
intramolecular 1,2-elimination of silane, a benzene-d6
solution of Cp*2Ti(D)SSiMe3 and H2SiMe2 was heated
to 75 °C for 2 days. Inspection of the reaction mixture
by 1H and 2H NMR spectroscopy showed only the
reactants, 9, and DSiMe3 (eq 10). This result demon-
Several unsaturated group IV imido complexes have
been shown to react with dihydrogen to produce ani-
lide-hydride complexes.66,67 In some cases, these reac-
tions have been found to be reversible. For example,
Smith et al. showed that Cp*2TidN(C6H5) reacts revers-
ibly with H2 to form Cp*2Ti(H)N(H)C6H5 (10).68,69 Zir-
conocene oxo and titanocene oxo complexes also react
with dihydrogen, although these reactions do not cleanly
produce products resulting from simple addition of H2
across the metal-oxygen bond. Instead, treatment of
Cp*2Ti(O)py with 1 atm of H2 provides a mixture of
products including Cp*2Ti(OH)2 and Cp*2Ti(H)(OH),
and heating Cp*2Zr(O)py to 80 °C in the presence of
dihydrogen forms dinuclear [Cp*2Zr(H)](µ-O)[Cp*2Zr-
(OH)].70
The production of 6 by treatment of 1 with dihydrogen
(eq 6) constitutes the first direct observation of the
activation of dihydrogen by a terminal sulfide species,
and the labeling experiments and kinetic studies that
strates that, as in the reaction of 1 with H2, addition
and elimination of the Si-H bond occur strictly in a
pairwise fashion. To gain further insight into the
transition state for these processes, the kinetic isotope
effect for the reaction of 1 with HSiMe3 was measured.
The kH/kD was determined to be 1.3 ( 0.1 at 298 K.
(58) Schlaf, M.; Lough, A. J .; Morris, R. H. Organometallics 1996,
15, 4423.
(59) Stiefel, E. I.; Matsumoto, K. Transition Metal Sulfur Chemis-
try: Biological and Industrial Significance; American Chemical Soci-
ety: Washington, D.C., 1996.
(60) For a recent exception see: Vicic, D. A.; J ones, W. D. J . Am.
Chem. Soc. 1999, 121, 4070.
(61) Me4taa ) dianion of 7,16-dihydro-6,8,15,17-tetramethyldibenzo-
[1,4,8,11]tetraazacyclotetradecine. Goedken, V. L.; Ladd, J . A. Chem.
Commun. 1982, 142.
Discu ssion
Processes in which a sulfur ligand functions as a
proton acceptor in the heterolytic cleavage of dihydrogen
are of interest,19,52-58 as this is thought to be an
(62) Housmekerides, C. E.; Ramage, D. L.; Kretz, C. M.; Shontz, J .
T.; Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S. Inorg.
Chem. 1992, 31, 4453.
(63) Mu¨ller, U.; Krug, V. Angew. Chem., Int. Ed. Engl. 1988, 27,
293.
(64) Lundmark, P. J .; Kubas, G. J .; Scott, B. L. Organometallics
1996, 15, 3631.
(65) The zirconium analogue of 1, Cp*2Zr(S)py, also does not react
with dihydrogen. See: Howard, W. A.; Trnka, T. M.; Parkin, G. J .
Organomet. Chem. 1997, 528, 95.
(51) In the crystal, the molecule possesses a crystallographic 2-fold
axis that passes through the Ti atom and the Si atom, disordering the
sulfur and the methylene carbons. While this disorder reduces the
accuracy of the bond distances and angles, it does confirm the
structural assignment of the product. See the Supporting Information
for details.
(52) Bianchini, C.; Meli, A.; Oberhauser, W.; Vizza, F. Chem.
Commun. 1999, 671.
(53) Bianchini, C.; Meli, A. Inorg. Chem. 1987, 26, 4268.
(54) Sellmann, D.; Rackelmann, G. H.; Heinemann, F. W. Chem.
Eur. J . 1997, 3, 2071.
(55) Sellmann, D.; Ka¨ppler, J .; Moll, M. J . Am. Chem. Soc. 1993,
115, 1830.
(66) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J . Am. Chem.
Soc. 1988, 110, 8731.
(67) Bennett, J . L.; Wolczanski, P. T. J . Am. Chem. Soc. 1997, 119,
10696.
(68) Smith, M. R.; Ball, G. E.; Andersen, R. A. To be submitted.
(69) Polse, J . L.; Andersen, R. A.; Bergman, R. G. J . Am. Chem. Soc.
1998, 120, 13405.
(56) Rakowski Dubois, M. Chem. Rev. 1989, 89, 1.
(57) J essop, P. G.; Morris, R. H. Inorg. Chem. 1993, 32, 2236.
(70) Howard, W. A.; Waters, M.; Parkin, G. J . Am. Chem. Soc. 1993,
115, 4917.

5508 Organometallics, Vol. 18, No. 26, 1999
Sweeney et al.
Sch em e 3
Sch em e 4
gested that a dihydrogen complex is an intermediate in
the heterolytic activation of H2 by an unsaturated
rhodium thiolate complex.54,55 Schlaf and Morris have
also reported an osmium system in which a hydrido-
thiolate complex is in equilibrium with a dihydrogen
complex (eq 11).58,77
were performed provide a detailed picture of the mech-
anism of this reaction. Given the fact that 1 is an 18-
electron complex and contains a labile pyridine ligand,
it is reasonable to assume that the initial stage of the
reaction of 1 with H2 involves dissociation of pyridine
from the metal center and formation of the 16-electron
complex [Cp*2TidS]. Addition of H2 to the metal-sulfur
bond could then proceed via a polarized four-membered
transition state, as is commonly postulated for σ-bond
metathesis reactions.71 The principle of microscopic
reversibility dictates that the 1,2-elimination of H2 from
6 should also occur via a four-centered transition state.
This mechanistic hypothesis is consistent with the result
from the reaction of 1 with HD, which demonstrates
that addition and elimination of H2 occur strictly in a
pairwise fashion. It is also supported by the 2D 1H
EXSY studies of 1, which show that the rates of
exchange of H2 with the Ti-H and SH protons are
identical.
Since the discovery of stable molecular hydrogen
complexes, it has been widely recognized that such
species can function as intermediates along the pathway
to homolytic or heterolytic dihydrogen activation.72
Although d0 metal complexes are formally incapable of
stabilizing molecular hydrogen adducts by “back dona-
tion”, calculations have nevertheless suggested that d0
metal-dihydrogen complexes can be intermediates in
hydride exchange reactions.73-75 Schwartz et al. have
also proposed that dihydrogen complexes are intermedi-
ates in the activation of H2 by d0 zirconocene alkyl
complexes.76 The 1D and 2D NMR studies of solutions
of 1 and H2 that we have performed are consistent with
the intermediacy of a molecular dihydrogen complex in
the hydrogen exchange reactions of 6 (Scheme 3). In
particular, the observation that intramolecular proton
exchange is faster than intermolecular proton exchange
indicates the transient [Cp*2Ti(S)‚(H2)] is formed and
undergoes rotation and readdition of H2 significantly
faster than the H2 molecule leaves the coordination
sphere.
The reactions of 1 with silanes provide a model for
the reaction of 1 with dihydrogen. Given the expected
nucleophilicity of the [Cp*2TidS] species,31 we have
considered two possible mechanisms for the addition of
silanes to 1. The first mechanism involves attack of the
sulfide ligand on the silane to form a pentacoordinate
silicon center followed by rapid transfer of the hydride
to the metal center (Scheme 4, path A).78 The second
mechanistic postulate involves a single four-centered
transition state similar to the transition states proposed
for silane metathesis reactions (Scheme 4, path B).79
Rate-determining formation of a pentacoordinate silicon
intermediate as shown in path A should result in an
inverse isotope effect.78 Conversely, a normal isotope
effect would be expected for the process shown for path
B, since the Si-H bond should be considerably weak-
ened in the transition state.80 Our observation of a
normal isotope effect in the reaction of 1 with HSiMe3
suggests that the rate-determining step involves a
concerted [2+2] addition as shown in path B.
Rea ctivity of Disu lfid e 4. The chemistry of ti-
tanocene polysulfides has been explored extensively
because these complexes participate in atom transfer
reactions and serve as precursors for a variety of
interesting carbon- and heteroatom-containing metal-
lacycles.81 Monomeric titanocene disulfides have not
been prepared however, since compounds of the stoi-
chiometry (C5H4R)2TiS2 form the sulfur-bridged dimers
1,4-[(C5H4R)2Ti]2S4.39 The atom transfer reactions of 4
and the presumed intermediate [Cp2Ti(η2-SO)] are
characteristic of the kinetic lability of chalcogen me-
tallacycles.82 The atom transfer reaction between 4 and
2 in the presence of pyridine has precedent both in Woo’s
studies of the reactions of titanium porphyrin complexes
The intermediacy of a dihydrogen complex has also
been postulated for a number of other heterolytic
activations of H2 where a proton is transferred to a
sulfur ligand. For example, Sellmann et al. have sug-
(71) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203.
(72) J essop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155.
(73) Ziegler, T.; Folga, E.; Berces, A. J . Am. Chem. Soc. 1993, 115,
636.
(74) Brintzinger, H. H. J . Organomet. Chem. 1979, 171, 337.
(75) Neuhaus, A. H.; Glendening, E. D.; Streitwieser, A. Organo-
metallics 1996, 15, 3688.
(76) Gell, K. I.; Posin, B.; Schwartz, J .; Williams, G. M. J . Am. Chem.
Soc. 1982, 104, 1846.
(77) Schlaf, M.; Morris, R. H. Chem. Commun. 1995, 625.
(78) Gountchev, T. I.; Tilley, T. D. J . Am. Chem. Soc. 1997, 119,
12831.
(79) Tilley, T. D. Comments Inorg. Chem. 1990, 10, 37.
(80) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in
Organic Chemistry, 3rd ed.; HarperCollins: New York, 1987.
(81) Kustos, M.; Steudel, R. J . Org. Chem. 1995, 60, 8056.
(82) Fischer, J . M.; Piers, W. E.; Ziegler, T.; Macgillivray, L. R.;
Zaworotko, M. J . Chem. Eur. J . 1996, 2, 1221.

Dihydrogen Activation
Organometallics, Vol. 18, No. 26, 1999 5509
243 K in phase-sensitive mode using the Bruker pulse program
noesytp (see Supporting Information for further details). Mass
spectrometric (MS) analyses were obtained at the University
of California, Berkeley Mass Spectrometry Facility. Elemental
analyses were performed at the University of California,
Berkeley Microanalytical Facility. Reactions with gases and
low-boiling liquids involved condensation of a calculated
pressure of gas from a bulb of known volume into the reaction
vessel at -196 °C. These vacuum transfers were accomplished
with a digital MKS Baratron gauge attached to a high-vacuum
line.
Ma ter ia ls. Unless otherwise noted, reagents were pur-
chased from commercial suppliers and used without further
purification. All nondeuterated solvents (Fisher) were either
distilled from sodium metal under N2 or passed through a
column of activated alumina under nitrogen pressure and
sparged with N2 prior to use. Deuterated solvents (Cambridge
Isotope Laboratories) were purified by vacuum transfer from
sodium prior to use. Pyridine was distilled from sodium under
dinitrogen. Elemental sulfur was purified by recrystallization
from dry benzene. Acetylene was purified by passing the gas
through two cold (-78 °C) traps separated by a trap containing
concentrated sulfuric acid. H2 (Matheson) and HD (99%,
Cambridge Isotope Laboratories) were used as received. (Cp*2-
Ti(H)Cl,87 NaSSiMe3,88 and 131 were prepared by literature
methods. Cp*2Ti(C2H4) (2)89 was prepared by the literature
method except that Cp*2TiCl90 was used instead of Cp*2TiCl2.
Cp *2Ti(SH)2 (3) fr om 4. This compound has been previ-
ously reported by Bottomley et al. from reaction of Cp*2Ti-
(CO)2 with H2S.22 Hydrogen (1 atm) was added to a frozen
benzene (5 mL) solution of 4 (80 mg, 0.21 mmol) at -196 °C.
The solution was thawed and heated to 70 °C for 4 days, during
which time the solution color changed from deep red to red-
orange. The solvent was removed in vacuo, and the remaining
solid was crystallized from toluene/pentane to yield 64 mg
(80%) of 3. 1H NMR (C6D6): δ 2.85 (2Η), 1.83 (30Η) ppm. Αnal.
Calcd for C20H32S2Ti: C, 62.48; H, 8.40. Found: C, 62.29; H,
8.47.
and in the reactivity of CO complexes of bis(permeth-
ylcyclopentadienyl)zirconocene dichalcogenides.32,83 Ab-
straction of a sulfur atom by tertiary phosphines is not
unexpected in light of the strength of the resulting
phosphorus-sulfur bond.84,85 This transformation is
synthetically useful however, since it provides a way to
generate [Cp*2TidS] in the absence of pyridine.
The reaction of 4 with dihydrogen to produce Cp*2-
Ti(SH)2 is relevant to proposed mechanisms for hydro-
gen activation on metal sulfide surfaces. As the metal
center in 4 is electronically unsaturated and undergoes
insertion of acetylene into the metal-sulfur bond (vide
supra), it seems reasonable to propose that formation
of Cp*2Ti(SH)2 from the reaction between 4 and H2
occurs via initial addition of H2 across a metal-sulfur
bond as shown in eq 12. This mechanism has precedent
in the formation of hydrosulfido ligands by sulfur atom
transfer into metal-hydride bonds,86 and it is consistent
with the ability of titanocene disulfide complexes to
rapidly rearrange.39 Previous studies have shown that
bridging disulfide ligands activate H2,56 and this work
suggests that the nonbridging disulfide moieties present
on catalyst surfaces may also be capable of reacting with
dihydrogen.
Con clu sion
We have synthesized and crystallographically char-
acterized monomeric titanium sulfide and disulfide
complexes. The reactions of these model compounds
with dihydrogen support the postulate that dihydrogen
could be activated by nonbridging disulfide or sulfide
groups on hydrodesulfurization catalysts. The reaction
of the sulfide complex with dihydrogen is reversible, and
NMR studies suggest that this transformation proceeds
via an η2-H2 intermediate. The titanocene disulfide
complex Cp*2Ti(η2-S2) also participates in atom transfer
reactions and reacts with acetylene to form an unusual
vinyl disulfide complex. We are currently attempting
to synthesize early metal sulfido complexes that do not
require stabilization by donor ligands such as pyridine.
Cp *2Ti(η2-S2) (4). A suspension of elemental sulfur (18.1
mg, 0.56 mmol) in toluene (5 mL) was added dropwise to a
stirred solution of 1 (243 mg, 0.56 mmol) in toluene (10 mL).
The solution immediately turned red and was stirred for 2 days
at 25 °C. The volatile materials were removed in vacuo, and
residue was recrystallized from toluene to yield purple crystals
1
of 4 (145 mg, 67%). H NMR (C6D6): δ 1.80 (s) ppm. 13C{1H}
NMR: δ 124.8 (C-CH3), 12.3 (C-CH3) ppm. IR (KBr): 2903
(s), 1489 (w), 1435 (m), 1375 (s), 1141 (m), 1019 (w), 737 (s)
cm-1. MS (EI): m/z 382 (M+). Anal. Calcd for C20H30S2Ti: C,
62.81; H, 7.91. Found: C, 62.68; H, 7.78.
Cp *2Ti(SSC(H)CH) (5). Compound 4 (55 mg, 0.14 mmol)
was dissolved in benzene (5 mL) and placed in a resealable
glass ampule fitted with a septum. Acetylene was bubbled
through the solution for 5 min, and the ampule was resealed.
After 1 week, the volatile materials were removed to give a
solid that was crystallized from toluene/pentane to give orange
Exp er im en ta l Section
1
crystals of 5 (33 mg, 56%). H NMR (C6D6): δ 6.78 (d, J ) 9.0
Hz, 1H), 5.77 (d, J ) 9.0 Hz, H), 1.82 (s, 30H) ppm. 13C{1H}
NMR: δ 201.5 (CH), 136.5 (CH), 123.6 (C-CH3), 12.3 (C-CH3)
ppm. IR (KBr): 2907 (s), 2715 (w), 1490 (w), 1432 (m), 1377
(s), 1260 (w), 1019 (s), 803 (w) cm-1. MS (EI): m/z 408 (M+).
Anal. Calcd for C22H32S2Ti: C, 64.69; H, 7.90. Found: C, 64.49;
H, 7.92.
Gen er a l P r oced u r es. Unless otherwise noted, reactions
and manipulations were performed in an inert atmosphere (N2)
glovebox or using standard Schlenk and high vacuum line
techniques. Glassware was dried overnight at 150 °C before
use. Except where noted, all NMR spectra were acquired at
25 °C. In cases where assignment of 13C{1H} NMR resonances
from the initial 13C{1H} NMR spectrum was ambiguous,
resonances were assigned using standard DEPT 45, 90, and/
Cp *2Ti(H)(SH) (6). Method A: An NMR tube containing a
solution of 1 (4.0 mg, 0.093 mmol) in toluene-d8 (0.5 mL) was
degassed and charged with approximately 1 atm of H2 at -196
1
or 135 pulse sequences. 2D H EXSY spectra were aquired at
(83) Woo, L. K. Chem. Rev. 1993, 93, 1125.
(84) Capps, K. B.; Wixmerten, B.; Bauer, A.; Hoff, C. D. Inorg. Chem.
1998, 37, 2861.
(85) Proulx, G.; Bergman, R. G. Organometallics 1996, 15, 133.
(86) For leading references see: Bauer, A.; Capps, K. B.; Wixmerten,
B.; Abboud, K. A.; Hoff, C. D. Inorg. Chem. 1999, 38, 2136.
(87) Luinstra, G. A.; Teuben, J . H. Chem. Commun. 1990, 1470.
(88) Do, Y.; Simhon, E. D.; Holm, R. H. Inorg. Chem. 1983, 22, 3809.
(89) Cohen, S. A.; Auburn, P. R.; Bercaw, J . E. J . Am. Chem. Soc.
1983, 105, 1136.
(90) Pattiasiana, J . W.; Heeres, H. J .; van Bolhuis, F.; Meetsma,
A.; Teuben, J . H.; Spek, A. L. Organometallics 1987, 6, 1004.

5510 Organometallics, Vol. 18, No. 26, 1999
Sweeney et al.
°C. Upon thawing, the color of the solution immediately
changed from red to yellow. Method B: An ampule was
charged with 74 mg (0.19 mmol) of 4 and 51 mg (0.19 mmol)
of triphenylphosphine. Et2O (5 mL) was condensed onto the
solids at -196 °C, and 1 atm of H2 was added. The solution
was thawed and stirred at 25 °C for 4 h and then transferred
by cannula (under a H2/Ar mixture) to a Schlenk tube. Storing
this solution at -80 °C overnight resulted in the precipitation
of 38 mg (0.13 mmol) of white triphenylphosphine sulfide
(identified by IR spectroscopy). The supernatant was filtered
at -78 °C to another Schlenk flask, and the solvent was
removed under a H2/Ar stream at 25 °C. Analysis of this solid
10.8 (CH3), 8.5 (CH2) ppm. IR (cyclohexane): 2994 (s), 2750
(w), 2036 (s), 1604 (s), 1463 (m), 1326 (s), 1020 (m), 927 (s),
848 (s), 708 (m), 590 (m) cm-1. MS (EI): m/z 437 (M+). Anal.
Calcd for C24H42SSiTi: C, 65.87; H, 9.44. Found: C, 65.92; H,
9.62.
Cp *2Ti(H)(SSiHMe2) (9). Dimethylsilane (0.187 mmol) was
condensed into an evacuated resealable ampule containing a
frozen solution of 1 (80 mg, 0.187 mmol) in benzene (5 mL) at
-196 °C. The solution was thawed and allowed to stand for
30 min. The solvent was removed in vacuo, and 9 (70 mg, 92%)
was collected as an analytically pure orange solid. 1H NMR
(C6D6): δ 5.30 (m, 1H), 4.01 (s, 1H), 1.92 (s, 30H), 0.44 (d, 6H)
ppm. 13C{1H} NMR: δ 122.0 (C-CH3), 13.1 (C-CH3), 5.2 (Si-
CH3) ppm. IR (Nujol): 2723 (w), 2096 (s), 1600 (m), 1234 (m),
1022 (m), 877 (s), 831 (m) cm-1. MS (EI): m/z 409 (M - H+).
Anal. Calcd for C22H38SSiTi: C, 64.36; H, 9.34. Found: C,
64.44; H, 9.33.
1
by H NMR spectroscopy under H2 showed it to be a mixture
of triphenylphosphine sulfide and 6. Spectroscopic data for 6:
1H NMR, 252 K, (C7D8): δ 3.96 (s, 1H), 2.62 (s, 1H), 1.86 (s,
30H) ppm. 13C{1H} NMR, 252 K, (C7H8): δ 118.4 (C-CH3),
12.6 (C-CH3) ppm. IR (Nujol): 1591 cm-1 (Ti-H).
Cp *2Ti(H)(SSiMe3) (7). Trimethylsilane (0.36 mmol) was
condensed into an evacuated resealable ampule containing a
frozen solution of 1 (79 mg, 0.18 mmol) in benzene (5 mL).
The solution was thawed and allowed to stand for several
hours. The solvent was then removed in vacuo to yield 7 as
an analytically pure orange solid (68 mg, 94%). 1H NMR
(C6D6): δ 4.13 (s, 1H), 1.90 (s, 30H), 0.51 (s, 9H) ppm. 13C{1H}
NMR: δ 121.9 (C-CH3), 13.3 (C-CH3), 8.2 (Si-CH3) ppm. IR
(Nujol): 2721 (w), 1679 (w), 1606 (m), 1238 (s), 1022 (m), 952
(w), 825 (s) 746 (m), 676 (m), 636 (s) cm-1. MS (EI): m/z 423
(M - H+). Anal. Calcd for C23H40SSiTi: C, 65.06; H, 9.50.
Found: C, 64.99; H, 9.51.
Ack n ow led gm en t. We thank the National Insti-
tutes of Health for generous financial support (Grant
No. GM-25459 to R.B.) and Dr. F. J . Hollander
(CHEXRAY, UCB) for solving the crystal structures of
1, 4, 5, and 8. We also thank Professor K. Orrell (Exeter)
for providing us with a copy of the D2DNMR program.
Dr. R. Morris Bullock (Brookhaven) and Dr. Roberto
Sanchez-Delgado (IVIC, Caracas; Guggenheim Fellow
at UCB) are acknowledged for helpful discussions. Z.S.
is grateful for a graduate fellowship from the Chevron
Corporation.
Cp *2Ti(H)(SSiHEt 2) (8). A resealable glass ampule was
charged with a solution of 1 (192 mg, 0.45 mmol) in benzene
(5 mL). The solution was frozen, and diethylsilane (0.67 mmol)
was condensed into the ampule. The solution was thawed and
allowed to stand at 25 °C for 1 h. The volatile materials were
removed in vacuo, and the resulting solid was recrystallized
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
tails of the data collection, data reduction and structure
solution and refinement, positional and thermal parameters,
bond lengths, bond angles, and torsion angles for 1, 4, 5, and
8 and details of the 2D EXSY NMR study of 6.
1
from pentane to yield 8 (105 mg, 53%) as orange crystals. H
NMR (C6D6): δ 5.11 (m, 1H), 1.92 (s, 30H), 1.20 (t, 6H), 0.89
(m, 4H) ppm. 13C{1H} NMR: δ 121.6 (C-CH3), 12.9 (C-CH3),
OM9907876