Organometallics
COMMUNICATION
Scheme 2. Synthesis of SPh-Bridged Dinuclear Fe Complex
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: nakazawa@sci.osaka-cu.ac.jp.
’ ACKNOWLEDGMENT
This work was supported by a Challenging Exploratory
Research (No. 21655022) grant from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
(1) is in equilibrium with CpFe(CO){C(O)Me} (10). This 16e
species reacts with either Et3SiH or RSH existing in solution. In
the reaction with Et3SiH, the SiꢀH oxidative addition and
subsequent reductive elimination of MeC(O)H yield CpFe-
(CO)(SiEt3) (a), which then reacts with RSH to give b. Complex
b is alternatively produced in the reaction of 10 with RSH,
followed by MeC(O)H dissociation and SiꢀH oxidative addi-
tion of Et3SiH. As b has three different one-electron-donor
ligands, b may exhibit three kinds of couplings: coupling with
H and SR to give a, H and SiEt3 coupling to give a0, and coupling
with SR and SiEt3 to give c. The first two are reversible, but the
last one is presumably irreversible. Complex c thus formed reacts
with Et3SiH to give d, followed by H2 reductive elimination to
reproduce a (cycle A). Alternatively, c reacts with RSH to give d0,
followed by H2 reductive elimination to regenerate a0 (cycle B).
In order to obtain insight into the catalytic cycle, a stoichio-
metric reaction of CpFe(CO)(py)(SiEt3) (py= pyridine) (2) with
PhSH was examined. Complex 2 is considered to be a synthon of a,
because the py in 2 is known to dissociate readily to give a.11 The
products in this reaction were SPh-bridged dinuclear Fe complex
(3), free py, and Et3SiH (Scheme 2). Complex 3 is presumably
formed accordingto the reaction sequence of 2 f a f b f a0 f 3.
Next, a reaction of PhSH with Et3SiH in the presence of 3 as a
catalyst was examined under the same reaction conditions shown
in Table 1, and a TON of 0.4 was obtained (Table 1, entry 8). The
value is less than one-tenth of that when 1 is used as a catalyst. The
results suggest that the dehydrogenative coupling of thiol and
hydrosilane catalyzed by 1 does not proceed via a0; that is, cycle A
rather than cycle B is more plausible. Other results supporting cycle
A were obtained in a stoichiometric reaction of 1, Et3SiH, and
PhSH in a 1:1:1 ratio. In this reaction 12% of 3 based on 1 was
formed. The low yield suggests that 10 favorably reacts with Et3SiH
to give a. If 10 mainly reacts with PhSH, a0 would be formed and
then converted into 3, causing a higher yield of 3.
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In conclusion, we have established an unprecedented dehy-
drogenative coupling of thiol and hydrosilane catalyzed by an
iron complex to give silylthioether. It should be noted that (i) the
dehydrogenative coupling can be attained by a complex of a
readily available and environmentally friendly iron, (ii) the iron
complex serves as a catalyst, although sulfur-containing compounds
suchasthiol and silylthioetherexistinthereaction system, and (iii)
the iron catalyst produces only a hetero-dehydrogenative coupling
product (silylthioether) and no homo-dehydrogenative coupling
products such as disulfide or disilane. A plausible catalytic cycle is
proposed that involves a 16e species CpFe(CO)(SiR03) reacting
with RSH to give an Fe(IV) species CpFe(CO)(SR03)(SR)(H),
followed by reductive elimination to give RSSiR03.
’ ASSOCIATED CONTENT
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Supporting Information. Detailed experimental proce-
b
dures and the characterization of products. This material is
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dx.doi.org/10.1021/om200377e |Organometallics 2011, 30, 3461–3463