Thermal reactions of titanium thiolates: Terminal titanium sulfides in C-S bond cleavage reactions

Article abstract of DOI:10.1021/om9804428

The thermolysis of monocyclopentadienyltitanium thiolate complexes leads to ligand redistributions and C-S bond cleavage reactions. Kinetic study of the C-S bond thermolysis reaction of CpTi(OC₆H₃-2,6-i-Pr₂)(SBn)₂ (2) to the sulfide-bridged dimer [CpTi(OC₆H₃-2,6-i-Pr₂)(μ-S)]₂ (1) is shown to be first order in 2, consistent with an intramolecular process proceeding via a terminal sulfide intermediate and rapid dimerization (k = 2.8 × 10^-6 s^-1). The related species CpTi(OC₆H₃-2,6-i-Pr₂)(SBn)Cl (3), CpTi(OC₆H₃-2,6-i-Pr₂)(SMe)₂ (4), and CpTi(OC₆H₃-2,6-i-Pr₂)(SPh)₂ (5) are thermally stable, although compounds 4 and 5 undergo thermally induced ligand redistribution reactions. These redistribution reactions are thought to occur via a dimeric intermediate in which bridging thiolate ligands are exchanged between two metal centers. A dimeric intermediate is supported by the characterization of the species [CpTi(SR)₂(μ-SR)]₂ (R = Et (7), Bn (8)) which are dimeric in solution at low temperature and in the solid state. In contrast, Cp*Ti(SBn)₃ (9) is monomeric. Efforts to intercept a terminal sulfide intermediate in the formation of 1 were unsuccessful, although reaction of CpTiCl₂Me with LiSBn in the presence of PMe₃ gives [CpTiCl(μ-S)]₂[PMe₃Bn] (10) in low yield. The analogue of 2, Cp*Ti(OC₆H₃-2,6-i-Pr₂)(SBn)₂, 12, is thermally stable; however, thermolysis of Cp*TiCl(SBn)₂ gave [Cp*TiCl(μ-S)]₂ (13). Ultimately, the LiCl adduct of a terminal sulfide species Cp*Ti(OC₆H₃-2,6-i-Pr ₂)(μ-S)(μ-Cl)Li(THF)₂ (14) was isolated from the reaction of Cp*Ti(OC₆H₃-2,6-i-Pr₂)Cl₂ (11) with Li₂S. Treatment of (14) with PMe₃ generates the monomeric terminal sulfide complex species Cp*Ti(OC₆H₃-2,6-i-Pr₂)(S)(PMe ₃) (15), which is unstable, slowly evolving PMe₃ affording [Cp*Ti(OC₆H₃-2,6-i-Pr₂)(μ-S)] ₂ (16). Compound 16 is also obtained directly by heating solutions of 14. Crystallographic studies of 8,10,12,13,14, and 16 are reported herein. The intermediacy of terminal metal sulfides in C-S processes are discussed.

Full text of DOI:10.1021/om9804428

3716
Organometallics 1998, 17, 3716-3722
Th er m a l Rea ction s of Tita n iu m Th iola tes: Ter m in a l
Tita n iu m Su lfid es in CsS Bon d Clea va ge Rea ction s
Andrea V. Firth, Eva Witt, and Douglas W. Stephan*
Department of Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4
Received J une 1, 1998
The thermolysis of monocyclopentadienyltitanium thiolate complexes leads to ligand
redistributions and C-S bond cleavage reactions. Kinetic study of the C-S bond thermolysis
reaction of CpTi(OC6H3-2,6-i-Pr2)(SBn)2 (2) to the sulfide-bridged dimer [CpTi(OC6H3-2,6-
i-Pr2)(µ-S)]2 (1) is shown to be first order in 2, consistent with an intramolecular process
proceeding via a terminal sulfide intermediate and rapid dimerization (k ) 2.8 × 10-6 s-1).
The related species CpTi(OC6H3-2,6-i-Pr2)(SBn)Cl (3), CpTi(OC6H3-2,6-i-Pr2)(SMe)2 (4), and
CpTi(OC6H3-2,6-i-Pr2)(SPh)2 (5) are thermally stable, although compounds 4 and 5 undergo
thermally induced ligand redistribution reactions. These redistribution reactions are thought
to occur via a dimeric intermediate in which bridging thiolate ligands are exchanged between
two metal centers. A dimeric intermediate is supported by the characterization of the species
[CpTi(SR)2(µ-SR)]2 (R ) Et (7), Bn (8)) which are dimeric in solution at low temperature
and in the solid state. In contrast, Cp*Ti(SBn)3 (9) is monomeric. Efforts to intercept a
terminal sulfide intermediate in the formation of 1 were unsuccessful, although reaction of
CpTiCl2Me with LiSBn in the presence of PMe3 gives [CpTiCl(µ-S)]2[PMe3Bn] (10) in low
yield. The analogue of 2, Cp*Ti(OC6H3-2,6-i-Pr2)(SBn)2, 12, is thermally stable; however,
thermolysis of Cp*TiCl(SBn)2 gave [Cp*TiCl(µ-S)]2 (13). Ultimately, the LiCl adduct of a
terminal sulfide species Cp*Ti(OC6H3-2,6-i-Pr2)(µ-S)(µ-Cl)Li(THF)2 (14) was isolated from
the reaction of Cp*Ti(OC6H3-2,6-i-Pr2)Cl2 (11) with Li2S. Treatment of (14) with PMe3
generates the monomeric terminal sulfide complex species Cp*Ti(OC6H3-2,6-i-Pr2)(S)(PMe3)
(15), which is unstable, slowly evolving PMe3 affording [Cp*Ti(OC6H3-2,6-i-Pr2)(µ-S)]2 (16).
Compound 16 is also obtained directly by heating solutions of 14. Crystallographic studies
of 8, 10, 12, 13, 14, and 16 are reported herein. The intermediacy of terminal metal sulfides
in C-S processes are discussed.
Sch em e 1. Ea r ly Tr a n sition Meta l Su lfu r
Aggr ega tes
In tr od u ction
Transition-metal sulfide aggregates are of well-
documented importance in biological systems1-3 and
industrial processes such as dehydrosulfurization and
catalysis.4 Complexes containing terminal sulfide ligands
are much less common, and in fact, it has only been
recently that such species have been reported for group
4 metals. The anionic terminal sulfide complex
[Ti(S)Cl4]2- was the first such species described.5 Sub-
sequently, the research groups of Bergman6 and
Parkin7-9 reported the synthesis and chemistry of the
complexes Cp*2M(S)py (M ) Ti, Zr). More recently,
(1) Robson, R. L.; Eady, R. R.; Richardson, T. H.; Miller, R. W.;
Hawkins, M.; Postgate, J . R. Nature 1986, 322, 388.
(2) Hales, B. J .; Case, E. E.; Morningstar, J . E.; Dzeda, M. F.;
Mauterer, L. A. Biochemistry 1986, 25, 7251.
(3) Kustin, K.; Macara, I. G. Comm. Inorg. Chem. 1982, 2, 1.
(4) Steifel, E. I.; Matasumoto, K. Transition Metal Sufur Chemistry,
Biological and Industrial Significance; American Chemical Society:
Washington, DC, 1996.
(5) Muller, U.; Krug, V. Angew. Chem., Int. Ed. Engl. 1988, 27, 293.
(6) Sweeney, Z. K.; Polse, J . L.; Andersen, R. A.; Bergman, R. G.;
Kubinec, M. G. J . Am. Chem. Soc. 1997, 119, 4543.
(7) Howard, W. A.; Parkin, G.; Rheingold, A. Polyhedron 1995, 14,
25.
Kubas et al.10 has described the dimeric species [CpTi-
(µ-S)(S)]2 while Hagadorn and Arnold11 reported the
2-
species (PhC(NSiMe3)2))2Ti(S)py (Scheme 2). With the
exception of the two salts, synthetic pathways to these
(8) Trnka, T. M.; Parkin, G. Polyhedron 1997, 16, 1031.
(9) Howard, W. A.; Trnka, T. M.; Waters, M.; Parkin, G. J .
Organomet. Chem. 1997, 528, 95-121.
(10) Lundmark, P. J .; Kubas, G. L.; Scott, B. L. Organometallics
1996, 15, 3631.
(11) Hagadorn, J . R.; Arnold, J . Inorg. Chem. 1997, 36, 2928.
S0276-7333(98)00442-7 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/28/1998

Thermal Reactions of Titanium Thiolates
Organometallics, Vol. 17, No. 17, 1998 3717
Syn th esis of Cp Ti(OC6H3-2,6-i-P r 2)(SR)2 (R ) Me (4),
P h (5)). These compounds were prepared in a similar manner,
and thus, one such preparation is presented. To CpTi(OC6H3-
2,6-i-Pr2)Cl2 (100 mg, 0.26 mmol) dissolved in 2 mL of THF
was added NaSMe (35 mg, 0.51 mmol). The reaction mixture
was stirred for 12 h and filtered, and the solvent was removed,
affording the red solid 4 in 54% yield. 4: 1H NMR (C6D6, 25
°C) δ 1.22 (d, 12H, |J H-H| ) 7 Hz), 2.99 (s, 6H), 3.57 (sept, 2H,
|J H-H| ) 7 Hz), 6.04 (s, 5H), 7.01 (m, 3H); 13C{1H} NMR (C6D6,
25 °C) δ 12.5, 24.0, 26.7, 123.4, 123.8, 131.8, 139.4, 159.5.
HRMS calcd for C19H28TiOS2 384.1061, found 384.1059. 5:
Sch em e 2. Gr ou p IV Meta l Ter m in a l Su lfid es
terminal sulfide complexes involve oxidation of a M(II)
species by sulfur. C-S bond cleavage is an alternative
route to M-S bond formation. The research groups of
Winter12 and Bochmann13 have produced TiS and TiS2
films from titanium thiolate precursors. In an analo-
gous manner, M-S aggregates as Zr3S3(t-BuS)2(BH4)4-
(THF)2 and Zr6S6(t-BuS)4(BH4)8(THF)2,14 Zr3S(S-t-Bu)10,15
(CpTi)4(µ3-S)3(µ2-S)(µ2-SEt)2, (CpTi)6(µ3-S)4(µ3-O)4,16 and
[(CpTi(OC6H3-2,6-i-Pr2)(µ3-S)]3TiCp17 have been pre-
pared via C-S bond thermolysis reactions. Some of the
more recent examples are depicted in Scheme 1. More
recently, we have described the high-yield thermolysis
of CpTi(OC6H3-2,6-i-Pr2)(SBn)2 (2) to the sulfide-bridged
dimer [CpTi(OC6H3-2,6-i-Pr2)(µ-S)]2 (1).17
Unlike the complex reactions affording larger M-S
aggregates, the reactions of discrete monocyclopenta-
dienyltitanium thiolate complexes, a class of compounds
that has drawn little attention, are ammenable to
detailed study. To that end, we address herein, the
nature and thermal stability of such compounds. These
species undergo thermally induced ligand redistribution
reactions and C-S bond thermolyses. Kinetic study and
synthetic efforts affirm that C-S bond thermolysis
proceeds through terminal titanium sulfide intermedi-
ates in these cases. The implications of these results
for the formation of M-S aggregates via C-S bond
activation are considered.
1
Yield 56%; H NMR (C6D6, 25 °C) δ 1.18 (s, 12H, |J H-H| ) 7
Hz), 3.61 (sept, 2H, |J H-H| ) 7 Hz), 6.04 (s, 5H), 6.84 (br m,
9H), 7.70 (d, 4H, |J H-H| ) 7 Hz); 13C{1H} NMR (C6D6, 25 °C)
δ 24.4, 26.3, 117.1, 123.9, 125.2, 127.8, 128.2, 131.1, 138.2,
143.6, 162.5. HRMS calcd for C29H32TiOS2 508.1374, found
508.1374.
Gen er a tion of 2, 4, a n d Cp Ti(OC6H3-2,6-i-P r 2)(SMe)-
(SBn ) (6). (i) To 4 (18 mg, 0.04 mmol) dissolved in 1 mL of
C6D6 was added 2 (25 mg, 0.04 mmol). The mixture was
allowed to stand for 10 min. (ii) To 3 (100 mg, 0.21 mmol)
dissolved in 2 mL of benzene was added NaSMe (15 mg, 0.21
mmol). The reaction mixture was stirred for 12 h and filtered,
and the solvent was removed. In either case, a mixture of 2,
4, and 6 was obtained. 6: 1H NMR (C6D6, 25 °C) δ 7.4-6.9
(m, 8H), 6.05 (s, 5H), 4.80 (d, 2H), 3.61 (sept, 2H), 2.96 (s, 3H),
1.22 (m, 12H).
Syn th esis of [Cp Ti(SR)2(µ-SR)]2 (R ) Et (7), Bn (8)).
These compounds were prepared in a similar manner, and
thus, only one representative preparation is described. To
CpTiCl3 (50 mg, 0.23 mmol) dissolved in 5 mL of benzene was
added LiSEt (46.8 mg, 0.69 mmol). The reaction mixture was
stirred for 2 h and filtered, and the solvent was removed in
vacuuo. The residue was extracted into hexane, filtered, and
allowed to stand. Dark red crystals of 7 were obtained in 71%
yield. 7: 1H NMR (C7D8, 70 °C) δ 1.30 (t, 9H, |J H-H| ) 7 Hz),
3.64 (q, 6H, |J H-H| ) 7 Hz), 6.13 (s, 5H); 13C{1H} NMR (C7D8,
70 °C) δ 12.4, 28.9, 108.2; 1H NMR (C7D8, -40 °C) δ 1.26 (d of
t, 6H, |J H-H| ) 13, 7 Hz), 1.37 (d of t, 12H, |J H-H| ) 13, 7 Hz),
2.98 (d of q, 4H, |J H-H| ) 7, 13 Hz), 3.17(d of q, 4H, |J H-H| )
7, 13 Hz), 3.32 (d of q, 8H, |J H-H| ) 7, 13 Hz), 3.37(d of q, 8H,
|J H-H| ) 7, 13 Hz), 6.38 (s, 10H); 13C{1H} NMR (C7D8, -40 °C)
δ 21.9, 23.1, 45.6, 47.0, 118.1. HRMS calcd for C11H20TiS3
Exp er im en ta l Section
Gen er a l Da ta . All preparations were done under an
atmosphere of dry, O2-free N2 employing either Schlenk-line
techniques or a Vacuum Atmospheres inert atmosphere glove-
box. Solvents were reagent grade, distilled from the appropri-
ate drying agents under N2, and degassed by the freeze-thaw
method at least 3 times prior to use. All organic reagents were
purified by conventional methods. 1H and 13C{1H} NMR
spectra were recorded on Bruker Avance 300 and 500 MHz
instruments. Trace amounts of protonated solvents were used
as references, and chemical shifts are reported relative to
SiMe4. Low- and high-resolution EI mass spectra were
obtained employing a Kratos Profile mass spectrometer outfit-
ted with a N2 glovebag enclosure for the inlet port. Combus-
tion analyses were performed by Galbraith Laboratories Inc.,
Knoxville, TN, or E + R Microanalytical Laboratory, Corona,
NY. CpTiCl2Me,18 [CpTi(OC6H3-2,6-i-Pr2)(µ-S)]2 (1), CpTi-
(OC6H3-2,6-i-Pr2)(SBn)2 (2), CpTi(OC6H3-2,6-i-Pr2)(SEt)2, CpTi-
(OC6H3-2,6-i-Pr2)(SBn)Cl (3), and CpTi(OC6H3-2,6-i-Pr2)Cl2
were prepared via published methods.17
1
296.0207, found 296.0215. 8: Yield 62%, H NMR (C7D8, 60
°C) δ 4.78 (s, 6H), 5.97 (s, 5H), 7.01 (br m, 9H), 7.18 (d, 6H,
|J H-H| ) 7 Hz); 1H NMR (C7D8, -25 °C) δ 4.03(d, 2H, |J H-H| )
13 Hz), 4.47 (d, 2H, |J H-H| ) 13 Hz), 4.58 (d, 4H, |J H-H| ) 13
Hz), 4.76 (d, 4H, |J H-H| ) 13 Hz), 6.05 (s, 10H), 7.1-7.2 (m,
br, 18H), 7.42 (d, 8H, |J H-H| ) 7 Hz), 7.53 (d, 4H, |J H-H| ) 7
Hz); 13C{1H} NMR (C7D8, -25 °C) δ 50.3, 52.0, 114.8, 125.3,
126.9, 128.6, 128.7, 129.1, 130.1, 140.6, 142.9. HRMS calcd
for C26H26TiS3 482.0675, found 482.0676. Anal. Calcd: C,
64.71; H, 5.43. Found: C, 64.55; H, 5.29.
Syn th esis of Cp *Ti(SBn )3 (9). To Cp*TiCl3 (100 mg, 0.34
mmol) suspended in 5 mL of pentane was added HSBn (128
mg, 1.04 mmol), followed by NEt3 (110 mg, 1.09 mmol). The
reaction mixture was stirred for 24 h, then filtered, after which
the solvent was reduced to 0.5 mL. Red-orange crystals were
obtained in 54% yield. 1H NMR (C6D6, 25 °C) δ: 2.05 (s, 15H),
5.09 (s, 6H), 7.03 (m, 6H), 7.1 (m, 3H), 7.40 (d, 6H, |J H-H| ) 7
Hz). 13C{1H} NMR (C6D6, 25 °C) δ: 13.3, 43.2, 126.7, 128.5,
128.1, 128.8, 142.4. HRMS calcd for C31H36TiS3 552.1459,
found 552.1455.
(12) Winter, C. H.; Sheridan, P. H.; Lewkebandara, T. S.; Heeg, M.
J .; Proscia, J . W. J . Am. Chem. Soc. 1992, 114, 1095.
(13) Bochmann, M.; Hawkins, I.; Wilson, L. M. J . Chem. Soc., Chem.
Commun. 1988, 344.
(14) Coucouvanis, D.; Lester, R. K.; Kanatzidis, M. G.; Kessissoglou,
D. P. J . Am. Chem. Soc. 1985, 107, 8279.
(15) Coucouvanis, D.; Hadjikyriacou, A.; Kanatzidis, M. G. J . Chem.
Soc., Chem. Commun. 1985, 1224.
(16) Firth, A. V.; Stephan, D. W. Inorg. Chem. 1997, 36, 1260.
(17) Firth, A. V.; Stephan, D. W. Organometallics 1997, 16, 2183.
(18) Erskine, G. J .; Hurst, G. J . B.; Weinberg, E. L.; Hunter, B. K.;
McCowan, J . D. J . Organomet. Chem. 1984, 267, 265.
Isola tion of [Cp TiCl(µ-S)]2[P Me3Bn ] (10). To CpTiCl2-
Me (100 mg, 0.5 mmol) dissolved in 5 mL of benzene was added
LiSBn (65 mg, 0.5 mmol), followed by excess PMe3. The
reaction mixture was stirred for 12 h filtered, and allowed to
stand several days. Dark red crystalline solid crystallized from
benzene in low (<5%) yield.
Syn th esis of Cp*Ti(OC6H3-2,6-i-P r 2)Cl2 (11). To Cp*TiCl3
(100 mg, 0.34 mmol) dissolved in 5 mL of benzene was added

3718 Organometallics, Vol. 17, No. 17, 1998
Firth et al.
HOC6H3-2,6-i-Pr2 (62µL, 0.34 mmol), followed by NEt3 (46.8µL,
0.34 mmol). The reaction mixture was stirred for 12 h and
filtered, and the solvent volume was reduced to 0.5 mL.
Yellow-orange crystals were obtained in 50% yield. 1H NMR
(C6D6, 25 °C) δ: 1.26 (d, 12H, |J H-H| ) 7 Hz), 1.89 (s, 15H),
3.38 (sept, 2H, |J H-H| ) 7 Hz), 7.04 (m, 3H). 13C{1H} NMR
(C6D6, 25 °C) δ: 12.5, 24.0, 26.7, 123.4, 123.8, 131.8, 139.4,
159.5. HRMS calcd for C22H32TiOCl2 430.1310, found 430.1298.
Anal. Calcd: C, 61.27; H, 7.48. Found: C, 61.14; H, 7.28.
Syn th esis of Cp *Ti(OC6H3-2,6-i-P r 2)(SBn )2 (12). To 11
(50 mg, 0.11 mmol) dissolved in 5 mL of benzene was added
HSBn (26.3 µL, 0.22 mmol), followed by NEt3 (31.3 µL, 0.22
mmol). The reaction mixture was stirred for 12 h and filtered,
and the solvent volume was reduced to 0.5 mL. Yellow-orange
crystals were obtained in 62% yield. 1H NMR (C6D6, 25 °C) δ:
1.30 (d, 12H, |J H-H| ) 7 Hz), 1.99 (s, 15H), 3.78 (sept, 2H, |J H-H
|
) 7 Hz), 4.91 (s, 4H), 7.07 (m, 9H, Ar), 7.35 (d, 4H, |J H-H| ) 7
Hz). 13C{1H} NMR (C6D6, 25 °C) δ: 12.8, 26.1, 30.3, 40.5,
111.0, 123.2, 124.2, 126.8, 127.0, 128.7, 129.1, 139.7, 143.0,
158.5. HRMS calcd for C36H46TiOS2 606.2470, found 606.2445.
Anal. Calcd: C, 71.26; H, 7.64. Found: C, 71.10; H, 7.33.
F igu r e 1. Plot of the rate of formation of 1 as a function
of the concentration of 2.
constant of 2.8 × 10-6 s-1 at 133 °C with a goodness of fit of
0.99, confirming first-order kinetics.
Syn th esis of [Cp *TiCl(µ-S)]2 (13). To Cp*TiCl3 (100 mg,
0.34 mmol) dissolved in 5 mL of benzene was added HSBn
(81.0 µL, 0.68 mmol), followed by NEt3 (96.5 µL, 0.68 mmol).
The reaction mixture was stirred for 12 h and filtered, and
the reaction mixture was heated for 12-16 h. Upon cooling,
dark red crystals formed and were subsequently isolated in
25% yield. 1H NMR (C6D6, 25 °C) δ: 2.14 (s, 15H). 13C{1H}
X-r a y Da ta Collection a n d Red u ction . X-ray quality
crystals of 8, 10, 12, 13, 14, and 16 were obtained directly from
the preparations as described above. The crystals were
manipulated and mounted in capillaries in a glovebox, thus
maintaining a dry, O2-free environment for each crystal.
Diffraction experiments were performed on a Rigaku AFC6
diffractometer equipped with graphite-monochromatized Mo
KR radiation or on a Siemens SMART system CCD diffracto-
meter. Employing the Rigaku diffractometer, the initial
orientation matrixes were obtained from 20 machine-centered
reflections selected by an automated peak search routine.
These data were used to determine the crystal systems.
Automated Laue system check routines around each axis were
consistent with the crystal system. Ultimately, 25 reflections
(20° < 2θ < 25°) were used to obtain the final lattice
parameters and orientation matrixes. Crystal data are sum-
marized in Table 1. The observed extinctions were consistent
with the space groups in each case. The data sets were
collected in three shells (4.5° < 2θ < 45-50.0°), and three
standard reflections were recorded every 197 reflections. Fixed
scan rates were employed. Up to four repetitive scans of each
reflection at the respective scan rates were averaged to ensure
meaningful statistics. The number of scans of each reflection
was determined by the intensity. The intensities of the
standards showed no statistically significant change over the
duration of the data collections. The data were processed
using the TEXSAN crystal solution package operating on a
SGI Challenger mainframe with remote X-terminals. The
reflections with Fo > 3σFo were used in the refinements.
Diffraction experiments performed on a Siemens SMART
System CCD diffractometer involved collecting a hemisphere
of data in 1329 frames with 10 s exposure times. A measure
of decay was obtained by re-collecting the first 50 frames of
each data set. The intensities of reflections within these
frames showed no statistically significant change over the
duration of the data collections. The data were processed
using the SAINT and XPREP processing package. An empiri-
cal absorption correction based on redundant data was applied
to each data set. Subsequent solution and refinement was
performed using the SHELXTL solution package operating on
a SGI computer.
NMR (C6D6, 25 °C) δ: 13.8, 131.9. HRMS calcd for C20H30
-
Ti2S2Cl2 500.0125, found 500.0120. Anal. Calcd: C, 47.92;
H, 6.03. Found: C, 47.79; H, 5.99.
Syn th esis of Cp *Ti(OC6H3-2,6-i-P r 2)(µ-S)(µ-Cl)Li(THF )2
(14). To a solution of Cp*Ti(OC6H3-2,6-i-Pr2)Cl2 (100 mg, 0.22
mmol) dissolved in 5 mL of THF was added Li2S (11.7 mg, 0.3
mmol). The reaction mixture was stirred for 12 h and filtered,
and the solvent was reduced to 0.5 mL. Yellow-orange crystals
were obtained in 62% yield. 1H NMR (C6D6, 25 °C) δ: 1.34
(m, 8H), 1.41 (d, 6H, |J H-H| ) 7 Hz), 1.45 (d, br, 6H, |J H-H| )
7 Hz), 2.26 (s, 15H), 3.53 (m, 8H), 4.00 (br, 2H), 6.97 (t, 1H,
|J H-H| ) 7 Hz), 7.18 (d, 2H, |J H-H| ) 7 Hz). 13C{1H} NMR
(C6D6, 25 °C) δ: 13.1, 24.6, 25.5, 25.9, 68.3, 119.8, 123.2, 123.8,
137.6,152.4. Anal. Calcd for C30H48ClLiO3STi: C, 62.23; H,
8.36. Found: C, 62.13; H, 8.19.
Gen er a tion of Cp *Ti(OC6H3-2,6-i-P r 2)(S)(P Me3) (15).
To 14 (25 mg, 0.043 mmol) in 0.5 mL of C6D6 was added PMe3
(10.4 µL, 0.1 mmol). The mixture was filtered. NMR data
indicated the formation of 15 in 42% NMR yield. 1H NMR
(C6D6, 25 °C) δ: 1.06 (d, 6H, |J H-H| ) 7 Hz), 1.16 (d, 6H, |J H-H
|
) 7 Hz), 2.05 (s, 15H), 3.38 (sept, 2H), 7.00 (t, 1H, |J H-H| ) 7
Hz), 7.25 (d, 2H, |J H-H| ) 7 Hz). 13C{1H} NMR (C6D6, 25 °C)
δ: 13.5, 24.5, 25.0, 26.7, 121.3, 123.8, 126.8, 138.6, 161.5. 31P
NMR (C6D6, 25 °C) δ: -8.30.
2
2
Syn th esis of [Cp *Ti(OC6H3-2,6-i-P r 2)(µ-S)]2 (16). A solu-
tion of 15 (100 mg) in toluene (2 mL) was heated for 1 h and
filtered, and the solvent was reduced to 0.5 mL. Dark crystals
of 16 formed in 54% yield. 1H NMR (C6D6, 25 °C) δ: 1.29 (d,
6H, |J H-H| ) 7 Hz), 1.60 (d, 6H, |J H-H| ) 7 Hz), 2.01 (s, 15H),
3.55 (sept, 2H, |J H-H| ) 7 Hz), 7.08 (t, 1H, |J H-H| ) 7 Hz), 7.25
(d, 2H, |J H-H| ) 7 Hz). 13C{1H} NMR (C6D6, 25 °C) δ: 13.6,
24.7, 25.8, 26.5, 121.6, 124.0, 131.8, 138.6, 161.0. HRMS calcd
for C44H64O2S2Ti2 784.3306, found 784.3305. Anal. Calcd C,
67.33; H, 8.22. Found: C, 67.21; H, 8.13.
Str u ctu r e Solu tion a n d Refin em en t. Non-hydrogen
atomic scattering factors were taken from the literature
tabulations.19,20 The Ti atom positions were determined using
direct methods employing either the SHELXTL or Mithril
Kin etic Stu d ies of th e Th er m olysis of 2. The reactions
performed at five concentrations of 2 in xylene-d11 were
maintained at 133 °C, and the ratio of 2 to 1 was monitored
every 30 min over a 12-16 h period by 1H NMR spectroscopy.
Plots of the concentration of product versus time were prepared
to ascertain the rate for each concentration, and subsequently,
a plot of the rates versus concentration of 2 was obtained
(Figure 1). A least-squares fit of these data afforded a rate
(19) Cromer, D. T.; Mann, J . B. Acta Crystallogr., Sect. A 1968, A24,
324.
(20) Cromer, D. T.; Mann, J . B. Acta Crystallogr., Sect. A 1968, A24,
390.

Thermal Reactions of Titanium Thiolates
Organometallics, Vol. 17, No. 17, 1998 3719
Ta ble 1. Cr ysta llogr a p h ic P a r a m eter s
8
10
12
13
14
16
formula
fw
C
52H52Ti2S6
C26H32PTi2S2Cl2
606.34
C39H49OTiS2
645.84
C30H30Ti2S2Cl2
250.64
C30H48ClLiO3STi
579.06
C44H64O2S2Ti2
784.88
965.14
cryst size
a (Å)
b (Å)
0.23 × 0.19 × 0.21 0.22 × 0.22 × 0.35 0.25 × 0.24 × 0.22 0.31 × 0.24 × 0.19 0.22 × 0.20 × 0.15 0.12 × 0.26 × 0.15
13.319(4)
17.232(6)
11.142(3)
102.61(3)
100.13(2)
97.82(3)
triclinic
P1h
15.850(5)
11.806(3)
16.730(4)
12.226(9)
15.793(3)
10.028(3)
93.98(3)
103.91(3)
86.06(4)
triclinic
P1h
8.92(1)
11.782(5)
16.300(3)
9.574(6)
106.82(3)
110.54(5)
84.39(3)
triclinic
P1h
9.828(2)
10.017(3)
12.224(5)
82.130(15)
69.83(3)
71.45(2)
triclinic
P1h
12.98(1)
11.112(8)
c (Å)
R (deg)
â (deg)
γ (deg)
cryst syst
space group
vol (Å3)
Dcalcd (g cm-1
Z
106.73(2)
112.91(6)
monoclinic
P21/a
2997(1)
1.34
monoclinic
C2/m
1184(2)
1.40
2415(1)
1.32
1872(1)
1.15
1648(1)
1.17
1070.4(6)
1.22
)
2
4
2
2
2
2
abs coeff, µ, cm-1
no. of data collected
no. of data Fo > 3σ(Fo
6.24
8504
2551
9.16
5577
787
3.67
6598
2471
10.78
1180
714
4.30
5801
1412
5.04
5015
3220
2
2
)
no. of variables
trans. factors
R (%)
281
130
373
66
217
226
0.9248-1.0000
7.6
0.9010-1.000
9.1
na
8.4
0.738-1.000
5.5
0.745-1.000
7.3
0.290-1.000
8.2
Rw (%)a
5.1
7.9
7.5
4.5
8.6
13.9*
goodness of fit
2.00
2.15
2.37
2.45
2.20
0.75
a
Weighted R based on all data.
direct-methods routines. The remaining non-hydrogen atoms
were located from successive difference Fourier map calcula-
tions. The refinements were carried out by using full-matrix
least-squares techniques on F, minimizing the function ω(|Fo|
- |Fc|)2 where the weight ω is defined as 4Fo2/2σ(Fo2) and Fo
and Fc are the observed and calculated structure factor
amplitudes. In the final cycles of each refinement, the number
of non-hydrogen atoms assigned anisotropic temperature
factors was determined so as to maintain a reasonable data:
variable ratio. The remaining atoms were assigned isotropic
temperature factors. Empirical absorption corrections were
applied to the data sets based on either ψ-scan data or a
DIFABS calculation and employing the software resident in
the TEXSAN or SHELXTL packages. Hydrogen atom posi-
tions were calculated and allowed to ride on the carbon to
which they are bonded, assuming a C-H bond length of 0.95
Å. Hydrogen atom temperature factors were fixed at 1.10
times the isotropic temperature factor of the carbon atom to
which they are bonded. The hydrogen atom contributions were
calculated but not refined. The final values of R, Rw, and the
goodness of fit in the final cycles of the refinements are given
in Table 1. The locations of the largest peaks in the final
difference Fourier map calculation as well as the magnitude
of the residual electron densities in each case were of no
chemical significance. Tables of crystallographic data have
been deposited as Supporting Information.
was performed in o-xylene-d11. For each sample, the
NMR tube containing the reaction was maintained at
133 °C and the ratio of 2 to 1 monitored every 30 min
over a 12-16 h period. A plot of the rate of the
formation of 1 as a function of the concentration of 2
affirms that the reaction is first order in 2 (Figure 1).
This is consistent with a rate-determining step involving
the intramolecular formation of a terminal sulfide
intermediate followed by rapid dimerization. The pseudo-
first-order rate constant was determined to be 2.8 ×
10-6 s-1
.
In an effort to broaden the scope of S-C bond cleavage
with a view to potentially isolating an intermediate, the
related species CpTi(OC6H3-2,6-i-Pr2)(SBn)Cl (3), CpTi-
(OC6H3-2,6-i-Pr2)(SMe)2 (4), and CpTi(OC6H3-2,6-i-Pr2)-
(SPh)2 (5) were prepared via reactions of CpTi(OC6H3-
2,6-i-Pr2)Cl2 with the appropriate thiolate. Compound
3, like CpTi(OC6H3-2,6-i-Pr2)(SEt)2 and CpTi(OC6H3-
2,6-i-Pr2)(S-t-Bu)Cl,17 was found to be thermally stable
upon heating to 80 °C for 12 h, whereas compounds 4
and 5 underwent thermally induced ligand redistribu-
tion reactions. Thus, for example, heating 5 at 80 °C
for a few hours resulted in the formation of a mixture
containing 5, the known species CpTi(SPh)3,21 and the
new, structurally characterized species CpTi(OC6H3-2,6-
i-Pr2)2(SPh).22 In a similar sense, complex 4 reacts
rapidly with 2 to effect thiolate ligand scrambling, thus
resulting in a statistical mixture of 2, 4, and CpTi-
(OC6H3-2,6-i-Pr2)(SMe)(SBn) (6). This same mixture of
compounds is obtained in reaction of 3 and NaSMe.
Spectroscopic monitoring of the thermolysis of the
statistical mixture of 2, 4, and 6 revealed the clean
formation of 1 and the sulfide byproducts SBn2 and
S(Bn)Me. It is clear from these results that both ligand
redistribution and C-S bond cleavage reactions are
markedly dependent on the electronic environment at
the metal center and C-S bond strength.
Resu lts a n d Discu ssion
We have previously described the thermolysis of CpTi-
(OC6H3-2,6-i-Pr2)(SBn)2 (2) to the sulfide-bridged dimer
[CpTi(OC6H3-2,6-i-Pr2)(µ-S)]2 (1) with the concurrent
formation of SBn2.17 Possible mechanisms considered
for this thermolysis include inter- and intramolecular
processes (Scheme 3). A bimetallic process could involve
dimerization where ligand proximity prompts benzyl
group transfer and elimination of dialkylsulfide. An
alternative mechanism involves a unimolecular process
in which benzyl group transfer to an adjacent thiolate
ligand is the rate-determining step. This latter mech-
anism infers a terminal sulfide (TidS) intermediate
which rapidly dimerizes. The later proposition of a
terminal sulfide intermediate is supported, in principle,
by the recent isolation of terminal titanium sulfide
complexes.5-11 A kinetic study of the reaction of 2 to 1
Ligand redistribution reactions are thought to occur
via a dimeric intermediate in which bridging thiolate
(21) Klapoetke, T.; Laskowski, R.; Kopf, H. Z. Naturforsch., B:
Chem. Sci. 1987, 42, 777.
(22) Firth, A. V.; Stephan, D. W. Unpublished results.

3720 Organometallics, Vol. 17, No. 17, 1998
Firth et al.
Sch em e 3. P r op osed P a th w a ys for C-S Bon d
Clea va ge
F igu r e 2. ORTEP drawing of [CpTi(SBn)2(µ-SBn)]2 (8);
30% thermal ellipsoids are shown. Ti(1)-S(1) 2.526(4) Å;
Ti(1)-S(2) 2.484(4) Å; Ti(1)-S(3) 2.361(4) Å; Ti(1)-S(4)
2.355(4) Å; Ti(2)-S(1) 2.448(4) Å; Ti(2)-S(2) 2.610(4) Å;
Ti(2)-S(5) 2.358(4) Å; Ti(2)-S(6) 2.351(4) Å; S(1)-Ti(1)-
S(2) 66.0(1)°; S(1)-Ti(1)-S(3) 78.9(1)°; S(1)-Ti(1)-S(4)
137.4(1)°; S(2)-Ti(1)-S(3) 126.6(1)°; S(2)-Ti(1)-S(4) 88.2-
(1)°; S(3)-Ti(1)-S(4) 92.3(1)°; S(1)-Ti(2)-S(2) 65.2(1)°;
S(1)-Ti(2)-S(5) 88.3(1)°; S(1)-Ti(2)-S(6) 114.9(1)°; S(2)-
Ti(2)-S(5) 147.5(1)°; S(2)-Ti(2)-S(6) 82.6(1)°; S(5)-Ti(2)-
S(6) 92.9(1)°; Ti(1)-S(1)-Ti(2) 111.7(1)°; Ti(1)-S(2)-Ti(2)
107.8(1)°.
Sch em e 4. P r op osed Mech a n ism for Liga n d
Red istr ibu tion Rea ction s
Sch em e 5. P ossible Isom er s of [Cp Ti(SBn )3]2
ligands are exchanged between the two metal centers
(Scheme 4). The notion of a dimeric intermediate is
conceptually supported by the structural data for the
23
related trithiolate compound [Cp*Zr(SR)2(µ-SR)]2 as
well as the thiolate-bridged titanium compound [CpTi-
(µ2-SCH2CH2S)Cl]2.24 While these species are dynamic
in solution, their dimeric nature in the solid state has
been confirmed. Differing thermodynamic stabilities
cannot drive analogous ligand redistribution reactions
in the compounds [CpTi(SR)2(µ-SR)]2 (R ) Et (7), Bn
(8)) and Cp*Ti(SBn)3 (9). These species are extremely
air sensitive yet are readily prepared by reaction of the
respective thiol and base on CpTiCl3 or Cp*TiCl3. 1H
NMR spectra for 7 at 30 °C show broad resonances
attributable to the cyclopentadienyl, methylene, and
methyl protons. Upon cooling to -40 °C, these signals
sharpen, giving a sharp single resonance attributable
to the cyclopentadienyl protons, two triplets for the
methyl groups, and three ABX3 multiplets for the
methylene protons. These data infer a symmetric
dimeric formulation, in which two thiolate groups bridge
the two metal centers. In the case of the related
complex [Cp*Zr(SEt)2(µ-SEt)]2, three isomers were de-
tected by NMR.23 In contrast, only a single isomer of 7
is observed, although four structural isomers are con-
ceivable. The NMR data infer the dominant isomer of
7 is the one in which the cyclopentadienyl and bridging
thiolate ligands adopt a transoid disposition with re-
spect to the Ti2S2 core (Scheme 5). Compound 8 displays
a similar temperature-dependent behavior, with three
methylene resonances at -40 °C. Again, the low-
temperature solution NMR data suggest a symmetric
dimeric formulation for 8. This interpretation has been
confirmed crystallographically. The dissociation of 8 in
solution at elevated temperatures is further evidence
that thermal induction of C-S bond cleavage is likely
to involve a unimolecular process.
Compound 8 is a dissymmetric dimer (Figure 2) in
which a thiolate ligand from each of the two CpTi(SBn)3
units bridge the two metal centers. Both the cyclopen-
tadienyl groups as well as the benzyl substituents on
the bridging sulfur atoms adopt a transoid disposition
with respect to the Ti2S2 core. The Ti2S2 core is not
planar as the interplanar angle between the adjoining
TiS2 planes is 153.5(1)°. In addition, the bridging Ti-S
distances in 8 reflect a dissymmetry in the core with
two longer (2.526(4), 2.610(4) Å) and two shorter dis-
tances (2.484(4), 2.448(4) Å). Within the Ti2S2 core, the
S-Ti-S angles are 111.7(1)° and 107.8(1)° at S(1) and
S(2), respectively. While the transoid disposition of the
substituents is similar to that reported for [Cp*Zr(SEt)2-
(µ-SEt)]2,23 the distortions of the core is in marked
contrast to the Zr analogue. The observed core distor-
tions are attributed to steric crowding about the Ti
centers.
The related complex Cp*Ti(SBn)3 (9) was also pre-
pared in a manner similar to that employed for 8;
however, this species is monomeric in solution to -90
°C. The absence of association in this case is attributed
to the steric demands of the pentamethylcyclopentadi-
(23) Heyn, R. H.; Stephan, D. W. Inorg. Chem. 1995, 34, 2804.
(24) Huang, Y.; Nadasdi, T. T.; Drake, R. J .; Stephan, D. W. Inorg.
Chem. 1993, 32, 3022.

Thermal Reactions of Titanium Thiolates
Organometallics, Vol. 17, No. 17, 1998 3721
F igu r e 3. ORTEP drawing of [CpTiCl(µ-S)]2[PMe3Bn] (10);
30% thermal ellipsoids are shown. Ti(1)-Ti(2) 3.016(8) Å;
Ti(1)-Cl(1) 2.35(1) Å; Ti(1)-S(1) 2.29(1) Å; Ti(1)-S(2) 2.30-
(1) Å; Ti(2)-Cl(2) 2.32(1) Å; Ti(2)-S(1) 2.31(1) Å; Ti(2)-
S(2) 2.27(1) Å; P(1)-C(11) 1.76(4) Å; P(1)-C(12) 1.84(3) Å;
P(1)-C(13) 1.74(4) Å; P(1)-C(14) 1.84(4) Å; Cl(1)-Ti(1)-
S(1) 103.9(4)°; Cl(1)-Ti(1)-S(2) 102.6(4)°; S(1)-Ti(1)-S(2)
97.6(4)°; S(2)-Ti(2)-S(1) 97.9(4)°; Cl(2)-Ti(2)-S(2) 103.7-
(5)°; Ti(1)-S(1)-Ti(2) 81.9(4)°; Ti(1)-S(2)-Ti(2) 82.5(4)°;
C(11)-P(1)-C(12) 108(2)°; C(11)-P(1)-C(13) 114(2)°; C(11)-
P(1)-C(14) 106(2)°; C(12)-P(1)-C(13) 107(2)°.
F igu r e 4. ORTEP drawing of Cp*Ti(OC6H3-2,6-i-Pr2)-
(SBn)2 (12); 30% thermal ellipsoids are shown. Ti(1)-S(1)
2.342(4) Å; Ti(1)-S(2) 2.329(3) Å; Ti(1)-O(1) 1.823(7) Å;
S(1)-Ti(1)-S(2) 104.9(1)°; S(1)-Ti(1)-O(1) 104.0(3)°; S(2)-
Ti(1)-O(1) 103.4(2)°; Ti(1)-O(1)-C(11) 167.8(7)°; Ti(1)-
S(1)-C(23) 103.5(4)°; Ti(1)-S(2)-C(30) 100.1(4)°.
enyl ligand and the resulting diminished Lewis acidity
at the metal center.
The results of the kinetic study described above
implicate a terminal sulfide intermediate Cp(OR)Ti(S)
in the formation of 1. This prompted efforts to isolate
or synthesize such a sulfide derivative (or a close
relative). Donor ligands such as phosphine or pyridine
have recently been used to stabilize the terminal sulfide
complexes, while acetylenes have been shown to un-
dergo cycloaddition reactions with terminal chalco-
genides6 and phosphinidenes.25,26 Thermolyses of 2 in
the presence of such reagents gave rise to complex
mixtures of uncharacterized products. In no case was
there evidence for trapped sulfide products. However,
for the reaction of CpTiCl2Me with LiSBn in the
presence of PMe3, the crystalline product [CpTiCl(µ-
S)]2[PMe3Bn] (10) was isolated in low yield. The
crystallographic study of 10 (Figure 3) confirmed the
formulation of this salt as formally containing a mixed-
valent Ti(III)/Ti(IV) sulfide-bridged anion and the phos-
phonium salt cation. Structurally similar to 1, the
presence of the charge in the anion of 10 gives rise to
Ti-S (2.29(1) and 2.30(1) Å), S-Ti-Sav (97.8(3)°), and
Ti-S-Tiav (82.2(4)°) that reflect a closer approach of the
two metal centers. The resulting Ti-Ti distance in 10
(3.016(8) Å) compares with that of 3.141(3) Å seen in 1.
As 10 is formed in low yield, general conclusions
regarding its mechanism of formation are not appropri-
ate; however, it is clear that phosphine intervenes to
permit transfer of a benzyl substituent to phosphorus.
In an alternative strategy to isolate a related terminal
sulfide complex, the pentamethylcyclopentadienyl ana-
logue of 1, Cp*Ti(OC6H3-2,6-i-Pr2)(SBn)2 (12), was also
prepared in a straightforward manner via treatment of
Cp*Ti(OC6H3-2,6-i-Pr2)Cl2 (11) with thiol and base.
Spectroscopic and crystallographic data (Figure 4) con-
firmed the expected three-legged piano-stool geometry
of compound 12. The greater electron-donor ability of
the pentamethylcyclopentadienyl ligand is reflected in
the slightly longer Ti-O (12, 1.823(7) Å; 1, 1.796(3) Å)9
and Ti-Sav (12, 2.336(4) Å; 1, 2.329(3) Å)9 bonds. The
F igu r e 5. ORTEP drawing of [Cp*TiCl(µ-S)]2 (13); 30%
thermal ellipsoids are shown. Ti(1)-Ti(1) 3.127(3) Å; Ti-
(1)-Cl(1) 2.266(4) Å; Ti(1)-S(1) 2.277(2) Å; Ti(1)-S(1)′
2.277(2) Å; Cl(1)-Ti(1)-S(1) 105.00(6)°; Ti(1)-S(1)-Ti(1)
86.8(1)°; S(1)-Ti(1)-S(1)′ 93.2(1)°.
Ti-O-C angle of 167.8(7)° is typical of those reported
for other complexes containing the CpTi(OR) fragment
and is consistent with some degree of π-donation
between O and Ti.
In contrast to 2, compound 12 is thermally stable,
even when kept at 120 °C for 18 h. This thermal
stability was attributed to the enhanced electron density
at Ti, although steric inhibition of the C-S bond
activation could not be ruled out. In a related effort, a
mixture of Cp*TiCl(SBn)2 and a lesser amount of
Cp*TiCl2(SBn) was formed in the reaction of Cp*TiCl3
with 2 equiv of benzylthiol. While the former product
is the major species, attempts to isolate this species were
frustrated, presumably by ligand redistribution reac-
tions. Nonetheless, thermolysis of this reaction mixture
at 80 °C for 12 h lead to the generation of SBn2 and the
sulfide-bridged dimer [Cp*TiCl(µ-S)]2 (13). Formulation
of 13 as a symmetric dimer is supported by the absence
of the benzyl signals in the NMR data and has been
confirmed by a crystallographic study (Figure 5). Two
crystallographically imposed perpendicular mirror planes
-
pass through the Ti and Cl atoms and bisect the C5Me5
ligand, dictating a transoid disposition of the chloride
and C5Me5- ligands with respect to the Ti2S2 core. The
Ti-Cl distance of 2.266(4) Å is typical, while the Ti-S
distance of 2.277(2) Å is shorter than that seen in 1
(2.314(4), 2.302(4) Å).17 The planar Ti2S2 core is similar
in geometry to that seen in 1 with S-Ti-S and Ti-S-
Ti angles of 93.2(1)° and 86.8(1)°.
(25) Breen, T. L.; Stephan, D. W. J . Am. Chem. Soc. 1995, 117,
11914.
(26) Breen, T. L.; Stephan, D. W. J . Am. Chem. Soc. 1996, 118, 4204.

3722 Organometallics, Vol. 17, No. 17, 1998
Firth et al.
F igu r e 7. ORTEP drawing of [Cp*Ti(OC6H3-2,6-i-Pr2)(µ-
S)]2 (16); 30% thermal ellipsoids are shown. Ti(1)-O(1)
1.827(5) Å; Ti(1)-S(1) 2.301(2) Å; Ti(1)-S(1) 2.305(3) Å;
Ti(1)-Ti(1)′ 3.155(3) Å; S(1)-Ti(1)′ 2.305(3) Å; O(1)-Ti-
(1)-S(1) 105.1(2)°; O(1)-Ti(1)-S(1) 105.0(2)°; S(1)-Ti(1)-
S(1) 93.51(9)°; Ti(1)-S(1)-Ti(1) 86.49(9)°.
F igu r e 6. ORTEP drawing of Cp*Ti(OC6H3-2,6-i-Pr2)(µ-
S)(µ-Cl)Li(THF)2 (14); 30% thermal ellipsoids are shown.
Ti(1)-Cl(1) 2.287(4) Å; Ti(1)-S(1) 2.263(4) Å; Ti(1)-O(1)
1.853(9) Å; Cl(1)-Li(1) 2.43(3) Å; S(1)-Li(1) 2.42(3) Å;
O(2)-Li(1) 1.91(3) Å; O(3)-Li(1) 1.93(2) Å; Cl(1)-Ti(1)-
S(1) 100.2(1)°; Cl(1)-Ti(1)-O(1) 104.4(3)°; S(1)-Ti(1)-O(1)
104.3(3)°; Ti(1)-Cl(1)-Li(1) 82.8(6)°; Ti(1)-S(1)-Li(1) 83.6-
(7)°; Cl(1)-Li(1)-S(1) 92(1)°.
PMe3 at room temperature in solution and affording
[Cp*Ti(OC6H3-2,6-i-Pr2)(µ-S)]2 (16). Compound 16 is
also obtained directly by heating a solution of 14 to 80
°C for 12 h. The dimeric nature of 16 was confirmed
crystallographically (Figure 7). Structural details were
similar to those seen for 1 with a Ti-S distance of 2.305-
(3) Å and a Ti-Ti′ separation of 3.155(3) Å.
Sch em e 6. Syn th esis/Rea ctivity of Ter m in a l
Su lfid e Ad d u ct 14
The isolation of 16 from 14 is consistent with the
mechanism proposed for the formation of 1. Of course
in that case the intermediate could not be intercepted.
The steric bulk of the ancillary ligands in 14 and 15
has been crafted to permit isolation of the terminal
sulfide. In a broader sense, these results prompt
speculation regarding the possibility that larger ag-
gregates assemble from sterically unprotected sulfide
intermediates generated via similar C-S bond activa-
tion processes.
Although attempts to isolate or trap a terminal sulfide
intermediate via C-S bond cleavage were unsuccessful,
an alternative strategy has been developed which does
afford a terminal sulfide derivative. Reaction of 11 with
Li2S at 25 °C yields a new orange product 14. NMR
data confirms the presence of Cp* and aryloxide ancil-
lary ligands as well as suggests the presence of coordi-
nated THF. An X-ray study of 14 confirmed the
formulation as Cp*Ti(OC6H3-2,6-i-Pr2)(µ-S)(µ-Cl)Li-
(THF)2 (Figure 6). The Ti-S distance of 2.263(4) Å is
somewhat longer than that seen in [PhC(NSiMe3)2)]2-
Ti(S)Py (2.139(1) Å),11 Cp*2Ti(S)Py (2.217(1) Å),6 Na2-
[CpTi(µ-S)(S)]2 (2.202(1), 2.187(1) Å),10 and (NEt2)2[Ti-
(S)Cl4] (2.111(1) Å)5 but shorter that the Ti-S distances
seen in 8, 10, and 12. Thus, species 14 is best viewed
as a LiCl adduct of the terminal sulfide fragment in
which the S acts as a donor to Li and the Cl as a donor
to Ti.
Treatment of 14 with PMe3 affords the species Cp*Ti-
(OC6H3-2,6-i-Pr2)(S)(PMe3) (15), Scheme 6. Spectro-
scopic characterization of this donor adduct of the
terminal sulfide was consistent with the formulations.
For example, compound 15 gives rise to a 31P NMR
chemical shift at -8.3 ppm, reminiscent of the shift
attributed to coordinated PMe3 in Cp2Zr(PC6H4-t-Bu3)-
(PMe3).27 Compounds 15 is unstable, slowly evolving
Su m m a r y
The thermolysis of S-C bonds in 2 proceeds via a
process first order in dithiolate complex, consistent with
a unimolecular process and terminal-Ti-sulfide inter-
mediate. In contrast, ligand redistribution reactions
proceed via a bimolecular associative process. Attempts
to intervene in C-S bond cleavage failed to access the
terminal sulfide intermediate. Nonetheless, the termi-
nal sulfide adducts are isolable employing an alternative
synthetic strategy. Dimerization of these terminal
sulfide species proceeds in a facile manner. While a
number of other reports describe complex aggregates
derived from C-S bond cleavage reactions, this report
implicates monometallic terminal sulfides as intermedi-
ates in these processes. Current efforts are targeting
the reactivity of terminal sulfide complexes generated
in situ via C-S bond cleavage reactions as well as the
use of such reactions in desulfurization chemistry.
Ack n ow led gm en t . Financial support from the
NSERC of Canada is gratefully acknowledged. The DFG
(Germany) is thanked for the award of a postdoctoral
fellowship to E.W.
Su p p or tin g In for m a tion Ava ila ble: Spectroscopic data
and tables of crystallographic parameters, hydrogen atom
parameters, and thermal parameters (41 pages). Ordering
information is given on any current masthead page.
(27) Hou, Z.; Breen, T. L.; Stephan, D. W. Organometallics 1993,
12, 3158.
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