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Copper-catalysed reductive amination of nitriles
and organic-group reductions using dimethylamine
Cite this: RSC Adv., 2014, 4, 51845
borane†
a
Dominic van der Waals, Alan Pettmanb and Jonathan M. J. Williamsa
Received 25th September 2014
Accepted 8th October 2014
*
DOI: 10.1039/c4ra11193a
A heterogeneous copper catalyst, formed in situ, has been shown to bonds are broken in the rate determining step.5 Alternatively,
dehydrocouple commercially available amine boranes whilst trans- heterogeneous methods have also been reported focussing on
ferring hydrogen for the reduction of selected organic functional the use of copper nano-particles and copper oxides6 and this
groups in an aqueous medium. The catalytic system has also been was extended to investigate the bis-chloride salts of copper,
shown to promote the reductive amination of aryl nitriles.
nickel and cobalt for dehydrogenation.7 The amino-borane
polymeric product was seen to stabilise the nano-particles
formed, a feature that has also been used in other reductively
formed nano-particles such as gold and silver.8
The use of stoichiometric metallic reagents for the reduction
and interconversion of organic functional groups is a common
approach in organic synthesis. Well known literature
surrounding the use of hydride reagents, such as LiAlH4 and
NaBH4, has long been established. Their use however involves
intrinsic detriments including stoichiometric metallic waste
and hazardous reactivity which suggests a need for an alterna-
tive and ideally catalytic method for organic functional group
reductions.
Amine boranes have attracted a lot of wide spread interest
due to their high hydrogen to molecular mass ratios, affording a
light weight but dense energy source, the intrinsic stability of
the amine boranes however means that catalytic methods to
facilitate the release of hydrogen have been required. Pioneer-
ing investigations focused initially on group IV metallocenes as
catalysts.1,2 These however were superseded by the use of plat-
inum group metals which showed greater rates of hydrogen
release. Particular emphasis of investigation was given to
heterogeneous Rh catalysts3 as well as homogeneous Ir based
catalysts; this included an interesting report by Stevens et al.
investigating the use of an Ir(III) compound alongside compu-
tational studies.4 A rare example of a non-precious metal in the
catalysis of amine borane dehydrocoupling was reported where
the combined use of Ni(cod)2 along with a range of NHCs with
kinetic experiments showing that both the B–H and the N–H
Amine boranes are less reported for their use in organic
synthesis than as a source of hydrogen. Notable exceptions to
this is the application of Au/TiO2 nano-particles for the catalytic
reduction of nitro-aromatics, this proceeds via the very rapid
production of the aryl hydroxylamine which is then slowly
reduced to the aniline product.9 There are also several reports of
the use of precious metals such as that by Burke et al. regarding
the reduction of olens with a variety of Re catalysts. These
catalysed the hydrogen transfer from dimethylamine borane to
reduce a range of alkenes via a homogeneous mechanism.10 The
use of Rh colloids for the reduction of alkenes and nitro-aryl
compounds has also been reported.11
Within our own group, the catalytic reduction of a wide
scope of organic functional groups using a ruthenium catalyst
has been reported. The introduction of enantiomerically pure
ligands to the ruthenium centre was shown to enable the ster-
eoselective reduction of aromatic ketones with moderate
enantiomeric excesses.12 Further work to expand this method-
ology to enable the reductive amination of nitriles was consid-
ered interesting, as nitriles are widely available yet there is very
little literature concerning their reductive amination. Rare
examples include our own report of the heterogeneous reduc-
tive amination of nitriles, focussing on the use of a Pt/C13
catalyst. A Pd/C system was also reported by Rylander et al.,
alongside the use of a Rh/C catalyst.14 Recently the use of Pt
nanowires has been reported which showed rapid amine–nitrile
addition followed by slow reduction of the intermediate.15
Following from these publications, a methodology for the
reductive amination of nitriles with amines or amine
aDepartment of Chemistry, University of Bath, Claverton Down, BA2 7AY, Bath, UK.
E-mail: dvdw20@bath.ac.uk; J.M.J.Williams@bath.ac.uk
bChemical R & D, Pzer Global Research & Development, Sandwich, Kent CT13 9NJ,
UK. E-mail: alan.pettman@pzer.com
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra11193a
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 51845–51849 | 51845