Homolytic C-S Bond Scission
J. Am. Chem. Soc., Vol. 119, No. 5, 1997 1035
Table 3. NMR Spectra of 1‚SC6H4Me- at Various Temperatures
temp (K)
249
bound thiolate
CpH
CpCH3
7.32 (m, 2H), 6.82 (m, 2H), 2.20 (s, 3 H)
5.70 (m, 1H), 5.51 (m, 2H), 5.31 (m, 1H), 5.22 (m, 1H),
5.18 (m, 1H), 5.01 (m, 1H), 4.86 (m, 1H)
5.70 (m, 1H), 5.51 (m, 2H), 5.31 (m, 1H), 5.23 (m, 1H),
5.19 (m, 1H), 5.03 (m, 1H), 4.88 (m, 1H)
5.70 (m, 1H), 5.51 (m, 2H), 5.31 (m, 1H), 5.26 (m, 1H),
5.21 (m, 1H), 5.03 (m, 1H), 4.89 (m, 1H)
2.01 (s, 3H), 1.99 (s, 3H)
2.01 (s, 3H), 2.00 (s, 3H)
2.02 (s, 6H)
263
273
283
7.32 (m, 2H), 6.82 (m, 2H), 2.20 (s, 3H)
7.32 (m, 2H), 6.82 (m, 2H), 2.20 (s, 3H)
7.32 (m, 2H), 6.82 (m, 2H), 2.20 (s, 3H)
5.70 (m, 1H), 5.51 (m, 2H), 5.31 (m, 1H), 5.26 (m, 1H),
2.03 (s, 6H)
5.21 (m, 1H), 5.04 (m, 1H), 4.91 (m, 1H)
Reaction of 1 with [(C6H5CH2)N(CH3)3][SC6H4CH3] ([BzNMe3]-
[SC6H4 CH3]). A 25-mL Erlenmeyer flask was charged with cluster 1
(50 mg, 0.074 mmol) and [BzNMe3][SC6H5CH3] (45 mg, 0.15 mmol).
Acetonitrile (4 mL) was added and the solution was stirred for 1 h.
The solution was filtered, then layered with diethyl ether to induce
crystallization. Dark green crystals (compound 3b) were obtained (32
mg). Anal. Calcd for C33H37Co2Mo2NO4S4: C, 41.70; H, 4.05; N,
1.52. Found: C, 42.51; H, 4.10; N, 1.46. IR (CH3CN) υ(CO): 1962
(approximately 10 µL) was added to the frozen solution. The tube
was then placed immediately into a precooled (213 K) NMR probe
and a proton spectrum was recorded. 1H-NMR (CD3CN, 213 K):
cluster 1, δ 5.83 (m, 4H), 5.49 (m, 4H), 2.13 (s, 6H); CH3C6H4SH, δ
7.40 (d, 2H), 7.20 (d, 2H), 2.33 (s, 3H). These products were identified
based on comparison with NMR spectra taken of authentic samples.
The proton resonance for the thiol group in compound CH3C6H4SH
was not observed in either the experimental or authentic sample.
Reaction of [NEt4][1‚SC(CH3)3] (5) with CF3SO3CH3. A 25-mL
Schlenk flask was charged with cluster 1 (21 mg, 0.031 mmol),
(NEt4)(S-tBu) (29 mg, 0.11 mmol), and (CD3)2CO (1 mL). The mixture
was stirred for 1 h, then transferred to a resealable NMR tube. The
tube was placed in an ethanol/N2 slush bath (T ) <-100 °C). CF3-
SO3CH3 (ca. 20 µL) was added to the frozen solution. The tube was
then placed immediately into a precooled (243 K) NMR probe and a
spectrum was recorded. 1H-NMR ((CD3)2CO, 243 K) compound 5a:
bound thiolate, δ 1.39 (s, 9H); bound CH3+, δ 2.38 (s, 3H); CpH, δ
5.82 (m, 1H), 5.66 (m, 1H), 5.62 (m, 1H), 5.58 (m, 1H), 5.28 (m, 1H),
5.22 (m, 1H), 5.13 (m, 2H); CpCH3: δ 2.11 (s, 3H), 2.08 (s, 3H);
CH3SC(CH3)3, δ 1.98 (s, 3H), 1.22 (s, 9H); cluster 1, δ 5.84 (m, 2H),
5.51 (m, 2H), 2.14 (s, 6H). Spectra were also recorded at 263, 283,
and 295 K. The intensity of the peaks associated with compound 5a
decreased as a function of temperature, while the intensity of the peaks
characteristic of cluster 1 increased.
Reaction of [NEt4][1•SC(CH3)3] with CH3I. A 50-mL Schlenk
flask was charged with cluster 1 (59 mg, 0.074 mmol), [NEt4][SC-
(CH3)3] (68 mg, 0.31 mmol), and THF (6 mL). After 5 min of stirring,
an aliquot of the reaction mixture was removed via syringe and injected
into a liquid IR cell. IR (THF) 1953 and 1898 cm-1. CH3I (≈30 µL)
was added to the reaction mixture. A white precipitate ([NEt4][I])
developed immediately. An aliquot of the reaction mixture was
removed for analysis by IR spectroscopy. IR (THF) of cluster 1: 2009,
1988, and 1955 cm-1. The identical result was obtained when [NEt4]-
[1‚SC(CH3)3] was allowed to react with (CH3)3CI. Cluster 1 was
recovered in a 75% yield. The organic product, ((CH3)3C)2S, was
detected by a GC-MS analysis of the reaction solution (m/e 146).
Reaction of 1 with (cyclo-C3H5)CH2SH. A resealable NMR tube
was charged with cluster 1 (22 mg, 0.033 mmol), (cyclo-C3H5)CH2SH
(4 mL, 0.045 mmol), and toluene-d8 (1 mL). The solution was heated
to reflux and the progress of the reaction was monitored periodically
by 1H-NMR spectroscopy. After approximately 4 h, the reaction was
complete. The cluster 2 was identified by comparison of the NMR
spectrum with those of authentic samples. The only organic product
that formed was 1-butene: 1H-NMR (C6D5CD3) of 1-butene: δ 0.85
(t, 3H), 1.91 (m, 2H), 4.96 (m, 1H), 5.01 (m, 1H), 5.77 (m, 1H). GC-
MS of NMR solution (m/e): 1-butene (56).
and 1913 cm-1 1H-NMR at 295 K (CD3CN): bound thiolate, δ 7.34
.
(d, 2H), 6.82 (d, 2H), 2.22 (s, 3H); cation, δ 7.54 (m, 5H), 4.37 (s,
2H), 2.98 (s, 9H); CpH: δ 5.50 (m, 2H) plus three additional broad
peaks between 4.9 and 6.0 ppm; CpCH3, δ 2.04 (s, 6H). Additionally,
1H-NMR spectra for compound 3b were collected at 249, 263, 273,
and 283 K. These spectra are summarized in Table 3.
Reaction of 1 with (NEt4)(SC6H4CH3). A resealable NMR tube
was charged with a solution of cluster 1 (17 mg, 0.025 mmol) in (CD3)2-
CO (0.5 mL). A solution of (NEt4)(SC6H4CH3) (13 mg, 0.051 mmol)
in (CD3)2CO (0.5 mL) was added to the frozen solution of cluster 1.
The tube was placed immediately into a cooled (213 K) NMR probe
1
and a spectrum was recorded. Compound 4a H-NMR ((CD3)2CO,
213 K): bound thiolate, δ 7.30 (d, 2H), 6.72 (d, 2H), 2.10 (s, 3H);
CpH, δ 5.29 (m, 2H), 5.21 (m, 2H), 5.07 (m, 2H), 4.92 (m, 2H);
CpCH3: δ 1.96 (s, 6H). At 266 K, resonances appeared in the proton
NMR spectrum that corresponded to a compound analogous to that of
compound 3b. Compound 4b 1H-NMR ((CD3)2CO, 263K): bound
thiolate, 7.39 (d, 2H), 6.68 (d, 2H), 2.19 (s, 3H); CpH, δ 5.72 (m, 1H),
5.48 (m, 2H), 5.34 (m, 1H), 5.28 (m, 1H), 5.24 (m, 1H), 4.97 (m, 1H),
4.89 (m, 1H); CpCH3: δ 2.03 (s, 3H), 2.00 (s, 3H).
Thermal Decomposition of Compound 3b. A resealable NMR
tube was charged with crystals of 3b (15 mg) and CD3CN (1 mL). An
oil bath was heated to 80 °C, then the tube was placed in the oil bath.
1
The progress of the reaction was monitored periodically by H-NMR
spectroscopy. After 1 h, all of compound 3b had reacted. The solvent
was removed in Vacuo and analyzed by GC-MS spectroscopy; three
organic products were detected (m/e): toluene-d1 (93), (C6H5-
CH2)N(CH3)2 (135), and CH3SC6H4CH3 (138). A dark solid remained
after the solvent was removed. The solid was identified as the
monoanion of 2. IR (CH3CN): υ(CO) 1898 and 1865 cm-1
.
t
Reaction of 1 with BuSNa. A resealable tube was charged with
cluster 1 (20 mg, 0.30 mmol), tBuSNa(4.0 mg, 0.30 mmol), and CH3-
CN (1.0 mL). The solution was heated to 80 °C for 2.5 h. GC-MS
analysis of the head gases revealed isobutane (m/e 58). No other
organic products were detected. The monoanion of 2 was detected by
IR analysis of the solution: υ(CO) 1898 and 1865 cm-1
.
Reaction of 1 with (cyclo-C3H5)CH2SLi. A resealable NMR tube
was charged with cluster 1 (20 mg, 0.07 mmol), (cyclo-C3H5)CH2SLi
(10 mg, 0.11 mmol), and CD3CN (0.7 mL). The solution was heated
to 80 °C. The progress of the reaction was monitored periodically by
1H-NMR spectroscopy. After 4 h, the tube was cooled to room
temperature. The head gases were analyzed by GC-MS. GC-MS (m/
e): 1-butene-d1 (57). The NMR solution was removed in Vacuo and
analyzed by GC-MS; no other organic products were detected. A dark
solid remained after removal of the solvent. IR (CH3CN): υ(CO) 1898
Kinetic Measurements of Thiol Desulfurization Reactions Medi-
ated by 1. Thiol kinetic experiments were conducted under pseudo-
first-order conditions with the concentration of the thiol in 10-fold
excess or more. Kinetic data for the desulfurization of aromatic and
aliphatic thiols were obtained by monitoring the disappearance of the
CO stretching band centered at 1959 cm-1 of cluster 1 (Figure 1). The
desulfurization reactions were performed in a 50-mL Schlenk flask
equipped with a reflux condenser. An oil bubbler was attached to the
reflux condenser. The flask was placed in an insulated oil bath and
constant temperature was maintained using a RFL model 76K-1
temperature controller. In a typical experiment, 5.0 mL of a 2 × 10-3
M solution of cluster 1 in decalin was syringed into the preheated
reaction flask followed by addition of 5.0 mL of thiol stock solution.
After 30 s, a syringe was used to remove an aliquot of the reaction
and 1865 cm-1
.
Reaction of (NEt4)(1‚SC6H4CH3) (4b) with CF3SO3H. A reseal-
able NMR tube was charged with cluster 1 (16 mg, 0.024 mmol),
(NEt4)(SC6H4CH3) (16 mg, 0.063 mmol), and CD3CN (1.0 mL). A
room temperature 1H-NMR spectrum revealed the thiolate complex
4bsanalogous to compound 3bswas formed. The tube was then
placed in an ethanol/N2 slush bath (T ) <-100 °C). Triflic acid