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Table 4 Coupling between thiols and boron reagentsa
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Entry
Borane (6)
R–SH (2)
Conversionb (%)
1
2
3
4
5
6
7
8
pinBH
pinBH
pinBH
pinBH
pinBH
catBH
catBH
catBH
Cy–SH (2a)
Cy–SH (2a)
C5H11–SH (2b)
Bn–SH (2d)
Ph–SH (2e)
Cy–SH (2a)
Bn–SH (2d)
Ph–SH (2e)
0c
7a; >99
7b; >99
7c; >99
7d; >99
7e; >76d
7f; >70d
7g; >89d
a
Reaction conditions: RSH (0.25 mmol), borane (0.55 mmol) and 1
(2.5 mol%) dissolved in toluene (0.5 mL). Determined by 1H NMR
spectroscopy. In the absence of catalyst (1). Desired coupled pro-
ducts (7e–7g) could not be isolated as pure compounds.
b
c
d
To further extend the generality and the activity of 1, boron-
containing substrates were subjected to the silicon coupling
optimised conditions (Table 4). Initially, the reaction in the
presence of pinacolborane (6a) was studied. It is noteworthy that,
again, the efficiency of the transformation is not dependent on the
nature of the thiol. Thus, reactions in the presence of alkyl, benzyl
and aryl thiols take place with full conversion and with a high
turnover number (TON: 200) (Table 4, entries 2–5). Catecholborane
(6b) successfully afforded the expected product in the presence of
thiophenol (2e) (Table 4, entry 8). However, the cyclohexyl- (2a) and
the benzylthiol (2d) did not lead to the desired coupled compound
with the same efficiency (Table 4, entry 8).
In summary, we have established a very general and simple
methodology for coupling reactions between thiols and other
heteroatom-containing substrates catalysed by [RuCl(PPh3)2-
(3-phenylindenyl)] (1). Disulfides can be obtained in good yields
under mild conditions. 1 shows the best activity to date (turnover
number up to 200) in the dehydrogenative coupling between
thiols and silanes to give the corresponding silylthioethers. We
have also demonstrated the utility of 1 in the first-reported
catalysed coupling reaction between thiols and boranes, repre-
senting a very efficient (turnover number up to 200) and simple
approach to the preparation of alkyl and aryl thiodioxaborolanes.
Further studies are ongoing in our laboratory to evaluate the
catalytic potential of 1 in related reactions.
¨
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´
´
The EPSRC and the ERC (FUNCAT) are gratefully acknowl-
edged for support of this work. SPN is a Royal Society Wolfson
Research Merit Award holder.
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19 The complex [RuCl(PPh3)2(3-phenylindenyl)] (1) is now commer-
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Notes and references
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23 An equimolecular amount of KOH was necessary to obtain high
conversions and yields.
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c
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