COMMUNICATION
DOI: 10.1002/chem.201202299
The Fluoride-Free Transmetalation of Organosilanes to Gold
Stꢀphanie Dupuy, Alexandra M. Z. Slawin, and Steven P. Nolan*[a]
During the last decade, homogenous gold catalysis has
been one of the most active research areas with new reactiv-
ities and methodologies being developed continuously. As a
soft p-acid, gold has been shown to be very efficient in the
partners. Unlike Grignard reagents, organozinc reagents are
more tolerant to functional groups but their sensitivity to
air, moisture and acidic hydrogen atoms[12] does not make
them a particularly attractive partner for the study we envis-
aged.[13] Although organostannanes are milder, more stable
and readily prepared reagents, the toxicity of the tin re-
agents and their by-products make them unattractive.[14] In
contrast, organosilanes are mild and stable and their price
make them very attractive. Additionally, a wide variety of
Hiyama-type couplings have recently been developed and
have led to a resurgence in the use of these reagents as cou-
pling partners.[15] A major disadvantage of the method is the
need for a fluoride source to act as an activator, forming a
hypervalent silicon species that facilitates the transfer of the
organic group onto the metal. Most organic-soluble fluoride
sources are very expensive, corrosive and incompatible with
silicon protecting groups.[16] Consequently, a number of fluo-
ride-free Hiyama-type couplings using base have recently
been developed.[17] Ball and co-workers recently reported a
facile and straightforward route to access arylcopper com-
plexes using arylsiloxanes with a copper fluoride species at
room temperature in THF (Scheme 1).[18] This method
proved to be very efficient but required the prior synthesis
activation of multiple bonds toward nucleophilic attack, thus
[1]
À
creating new C C bonds. In these reactions, a key step is
the formation of an organogold intermediate, which is fol-
lowed by its trapping with either an electrophile or a proton
to afford the desired product and regenerate the catalyst.
Very recently, the development of facile and straightforward
stoichiometric routes to access and isolate these intermedi-
ates has attracted significant interest in order to support
mechanistic proposals.[2] Very recently, they have been
shown to be very efficient in dual metal catalysis to trans-
ACHTUNGTRENNUNGmetACHTUNGTRENNUNG
alate to palladium,[3] rhodium,[4] nickel[5] or ruthenium
and iron centres.[6] Noteworthily, these isolated “intermedi-
ate” complexes display not only good stability toward air,
light and moisture, but also very interesting photolumines-
cent properties for possible uses in cancer therapy and imag-
ing.[7] Earlier syntheses of aryl gold(I) complexes have often
relied on organolithium or Grignard reagents, which pre-
clude the use of sensitive functional groups.[8]
Consequently, recent investigations have focused on the
use of stable arylboronic acids, in the presence of a base and
a gold species. The procedures allow the preparation of a
wide variety of arylgold compounds in good to high yields.
Moreover, this methodology has proven successful with
complexes bearing phosphines or N-heterocyclic carbenes.[9]
We have investigated very recently the role of the base in
this transmetalation of organoboron reagents using well-de-
of [CuACTHNURGTNE(NUG IPr)(F)].
Scheme 1. Synthesis of functionalised arylcopper by transmetalation of
arylsilanes.
fined basic complex [AuACTHNUGRTENUNG(IPr)(OH)] (1) [IPr=1,3-bis(diiso-
propyl)phenyl-imidazol-2-ylidene; pKaDMSO =30.5].[10,11] In
the initial report, mechanistic studies revealed that 1 was a
very active species in the transmetalation reaction and that
the transfer of the aryl moiety to gold readily occurred
within 10 min! Still intrigued by the efficiency of this gold
hydroxide complex as an organic moiety transfer promoter,
other organometallic partners, typically used in cross-cou-
pling reactions, were considered as potential transmetalation
The latter complex was prepared by a two-step synthesis,
starting from the copper chloride via the formation and iso-
lation of unstable and air-sensitive [Cu(NHC)(OtBu)].[19]
With these precedents in mind and taking advantage of the
recent and very promising reactivity of the Brønsted base 1
in transmetalation reactions, we examined whether the syn-
thesis of organogold complexes under fluoride-free condi-
tions could be achieved (Scheme 2).
[a] S. Dupuy, Prof. Dr. A. M. Z. Slawin, Prof. Dr. S. P. Nolan
EaStCHEM School of Chemistry
University of St. Andrews
Initial reactivity studies were performed by stirring phe-
nyltrimethoxysilane 2 with 1 in [D6]benzene at room tem-
perature for 30 min. Monitoring the reaction by 1H NMR
spectroscopy revealed that complete conversion had been
reached at this time. To our surprise, a different complex
than the expected NHC-gold-phenyl species was observed
St. Andrews, KY16 9ST (UK)
Supporting information for this article is available on the WWW
Chem. Eur. J. 2012, 18, 14923 – 14928
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14923