N-heterocyclic carbene copper(i) catalysed N-methylation of amines using CO2

Article abstract of DOI:10.1039/c5dt03506f

The N-methylation of amines using CO₂ and PhSiH₃ as source of CH₃ was efficiently performed using a N-heterocyclic carbene copper(i) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.

Full text of DOI:10.1039/c5dt03506f

Dalton
Transactions
View Article Online
View Journal
PAPER
N-heterocyclic carbene copper(I) catalysed
N-methylation of amines using CO2†
Cite this: DOI: 10.1039/c5dt03506f
a
a
b
b
Orlando Santoro, Faïma Lazreg, Yury Minenkov, Luigi Cavallo and
a
Catherine S. J. Cazin*
Received 8th September 2015,
Accepted 23rd September 2015
The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a
N-heterocyclic carbene copper(I) complex. The methodology was found compatible with aromatic and
aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to
support the proposed reaction mechanism for this transformation.
DOI: 10.1039/c5dt03506f
www.rsc.org/dalton
required as well as long reaction times (24 h to 48 h) and elev-
ated temperature (140 °C). Independently, Leitner and co-
Introduction
The simple methylation of amines is a well-known transform- workers reported that an alternative ruthenium based-system
6
ation in organic chemistry leading to compounds having appli- could enable this transformation. Recently, a nickel/phos-
cations in the synthesis of dyes, natural products and fine phine system able to promote this transformation was investi-
1
7
chemicals. Several synthetic protocols exist to achieve this gated. Organocatalysts have also been shown as efficient
8
transformation and include the nucleophilic substitution of promoters of this transformation. Finally, Beller and Cantat
electrophilic methylating reagents (e.g., methyl iodide) and the also showed that formic acid can be used as C source or as
1
9
,10
methylation with formaldehyde in the presence of reducing both C
reagents (e.g., formic acid and metal hydride). However, protocols suffer from the use of relatively expensive metals and
important drawbacks are associated with these procedures
1
and hydrogen source.
Despite their elegance, these
2
such as reagent toxicity or limitation in the substrate scope.
Recently, alternative methodologies have been reported based
on the use of CO as a methylating reagent. CO is an inexpen-
2
2
sive, non-toxic and the most abundant carbon source. It is
potentially the most attractive C feedstock to introduce
1
3
carbon into molecules. In 2013, Cantat and co-workers
reported an interesting methodology based on zinc using
[
Zn(Cl) (IPr)] (IPr = N,N′-bis-[2,6-(di-iso-propyl)phenyl] imida-
2
zol-2-ylidene) as catalyst. Phenylsilane was used as the redu-
4
cing reagent (Scheme 1). Almost concomitantly, Beller and co-
5
workers disclosed a ruthenium-based methodology. For the
latter, excess silane was required under 30 bar of carbon
dioxide. Shortly after, the same group reported a variant of this
transformation replacing the silane with hydrogen gas.
However, high pressure of H (60 bar) and CO (20 bar) were
2
2
a
EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST,
UK. E-mail: cc111@st-andrews.ac.uk
b
Physical Sciences and Engineering Division, King Abdullah University of Science and
Technology (KAUST), Kaust Catalysis Center, Thuwal 23955-6900, Saudi Arabia
†
Electronic supplementary information (ESI) available: Procedures for the syn-
thesis of the complexes, optimisation and protocol for catalysis, characterisation
of reaction products, DFT calculations, stoichiometric reactions assisting in sup-
porting mechanistic proposal. See DOI: 10.1039/c5dt03506f
2
Scheme 1 State-of-the-art for the methylation of amines with CO .
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
ligands and, in some cases, high pressures and temperatures.
In addition, mechanistic details for this reaction have not
been explored yet. Recently, it has been shown that economical
copper complexes can promote direct carboxylation of N–H
1
1,12
and C–H bonds using CO2.
Indeed, [Cu(OH)(IPr)] (1) as
catalyst allowed CO insertion into a C–H and N–H bonds
2
leading to the formation of carboxylic and carbamic acid
derivatives, respectively.
Moreover, copper-based complexes are well-established
1
3,14
catalysts for the hydrosilylation of CO
2
.
Based on these
observations, it was hypothesised that the reactivity of NHC–
copper complexes could be extended to the methylation of N–
H bonds. In particular, this could be performed in two steps: a Fig. 1 Catalysts studied in the N-methylation.
carboxylation followed by a reduction. Herein, we reported the
first Cu-catalysed methylation of amines with mechanistic
2
insight into the fixation of CO with amines.
Based on these promising results, the influence of the reac-
tion time was examined. After 2 hours all starting material was
converted into a mixture of amide (60%) and N-methylamine
Results and discussion
(
2
40%). This highlights that the CO insertion occurs in less
than 2 hours and that it is not the rate-limiting step in the
transformation. As a function of time, the amount of N-methyl-
ation increased. After 8 hours, 70% of the desired compound
was obtained. Finally, the optimal reaction conditions for the
In the initial optimisation studies, N-methylaniline 5a was
chosen as the benchmark substrate (Table 1).
The hydroxide complex 1 (Fig. 1) showed interesting reactiv-
ity in solvents such as toluene or benzene. However, no activity
was observed in alcohol solvents. By using its tert-butoxide
congener, 2, the conversion to the desired compound slightly
increased (Table 1, entries 5 and 6). The nature of the NHC
ligand was next examined. When the bulkier IPr* was used (3),
only 22% conversion to the methylated product was observed.
t
transformation were determined to be [Cu(O Bu)(IMes)]
(
10 mol%), phenylsilane at 100 °C under 2 bar of CO
2
for 20 h.
Using these conditions, the scope of the reaction was inves-
tigated, starting with secondary amines (Scheme 2).
N,N-Dimethylaniline 5b was obtained quantitatively and
selectively. Sterically congested N-methylanilines such as 6a
and 7a were efficiently converted into the desired compounds,
t
On the other hand, the IMes analogue complex [Cu(O Bu)-
(IMes)] 4 exhibits improved reactivity. Indeed, in the presence
of 4, full conversion into the desired product is observed in
toluene after 20 h.
a
Table 1 Optimisation of the catalyst, solvent and reaction time
b
b
Entry
[Cu]
Solvent
Time (h)
5b
5c
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
2
2
3
4
4
4
4
4
4
Toluene
Benzene
Isopropanol
THF
Toluene
THF
20
20
20
20
20
20
20
20
20
2
35%
40%
—
65%
60%
—
76%
50%
52%
78%
4%
24%
50%
48%
22%
96%
>99%
40%
45%
57%
70%
THF
THF
Toluene
Toluene
Toluene
Toluene
Toluene
0
1
2
3
60%
55%
43%
30%
4
6
8
Scheme 2 Cu-catalysed methylation of secondary amines using CO
as building block. Reaction conditions: amine (0.25 mmol),
4 (10 mol%), PhSiH (2 equiv.), toluene (2 mL), CO (2 bar), 100 °C, 20 h.
(2 bar), 100 °C. Conversion determined Conversions determined by GC, based on amine, minimum average of
2
C
1
a
Reaction conditions: amine (0.25 mmol), [Cu] (10 mol%), PhSiH
3
3
2
b
(
2 equiv.), solvent (2 mL), CO
2
by GC, based on amine, minimum average of two reactions.
a
b
t
3
two reactions. b : c ratio. KO Bu (10 mol%), PhSiH (4 equiv.).
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
Table 2 Influence of additives on the composition of the reaction
mixture
Reaction conditions
Entry
Substrate
8a
I
II
III
IV
1
2
3
4
b: 49%
c: 50%
b: 14%
c: 85%
b: 45%
c: 54%
b: 15%
c: 84%
b: 53%
c: 46%
b: 40%
c: 59%
b: 62%
c: 37%
b: 59%
c: 40%
b: 44%
c: 55%
b: 33%
c: 66%
b: 70%
c: 29%
b: 46%
c: 53%
b: 90%
c: 9%
9a
b: 64%
c: 35%
b: 75%
c: 24%
b: 72%
c: 27%
10a
11a
Scheme 3 Cu-catalysed methylation of anilines. Reaction conditions:
amine (0.25 mmol), 4 (10 mol%), PhSiH
3 2
(2 equiv.), toluene (2 mL), CO
Reaction conditions: amine (0.25 mmol), 4 (10 mol%), toluene (2 mL), (2 bar), 100 °C, 20 h. Conversions determined by GC, based on amine,
a
b
t
CO
2
(2 bar), 100 °C, 20 h. Conversions determined by GC, based on minimum average of two reactions. b : c : d : e ratio. KO Bu (10 mol%).
, no base.
, no base. IV: 4
amine, minimum average of two reactions. I: 2 equiv. PhSiH
II: 2 equiv. PhSiH
equiv. PhSiH , 10 mol% KO Bu.
3
t
3 3
, 10 mol% KO Bu. III: 4 equiv. PhSiH
t
3
the corresponding para-substituted product was isolated. Also
t
in this case, the addition of a catalytic amount of KO Bu
proved to have a positive effect on the reaction. In fact, the for-
mation of the monomethylated compound 13b was improved
while an increase in dimethylated product was observed for
substrates 12a and 14a.
the major product being the methylated compound (85% and
2%, respectively). In contrast, while full consumption of start-
ing materials was also observed with compounds 8–11, the
8
major product under these reaction conditions (2 equiv.
3
PhSiH , no base) was the amide intermediate. In order to over-
come this issue, the reaction conditions were further optimised,
Mechanistic studies
and the addition of additives was investigated (Table 2).
t
By adding a catalytic amount of KO Bu (10 mol% – II), an The proposed mechanism for the methylation of amines with
important increase in the formation of the methylated com- CO and silane is depicted in Scheme 4. The first steps of this
2
pound was observed for substates 9a–11a while only a slight pathway involve the formation of a hydride species followed by
improvement was observed for 8a. The same trend was the insertion of CO2 into the Cu–H bond affording a
observed by doubling the amount of silane. Finally, by com- Cu-formato species (I). The latter complex undergoes meta-
bining the two variations (4 equiv. of silane and 10 mol% thesis with the silane to afford the copper hydride species and
t
KO Bu), the conversion of all substrates towards the desired the siloxane II. The siloxane then reacts with the amine to
t
compounds was drastically improved. Although KO Bu may be form the amide derivative (III). The amide would further react
required to promote catalyst regeneration, by doubling its with the [Cu(H)(NHC)] to form species IV. This intermediate,
amount no further improvement was observed.
in the presence of silane, would regenerate the hydrido
It is interesting to note that, under our standard reaction complex and release the desired compound.
t
conditions, i.e. without adding 10 mol% of KO Bu, substrate
a leads to a 14% conversion of the methylated compound pathway described, we carried out DFT calculations with both
while the more hindered N,N-dicyclohexylamine (10a) is con- IMes- and IPr-based catalysts. The energetics of the transfor-
verted in 45%.
mation are reported in Scheme 4. Calculations indicate that
In order to obtain a more detailed understanding of the
9
Primary amines were next considered (Scheme 3). All sub- activation of the initial pre-catalyst to the [Cu(H)(NHC)]
strates investigated were completely converted into a mixture species, as well as the CO activation step by its insertion into
2
of mono- and di-methylated compounds and their corres- the Cu–H bond of [Cu(H)(NHC)], leading to the formato
ponding amide derivatives. Interestingly, the bulkiness of the species I, are relatively easy steps, with free energy barriers less
ortho substituents of substrates 12a and 13a did not affect the than 10 kcal mol− . The reactivity of I with the silane has a
1
−
1
outcome of the reaction; both led to the dimethylated product. relatively low energy barrier of 18–19 kcal mol . This step
No amide intermediate was observed with substrate 14a. In the regenerates [Cu(H)(NHC)], and liberates HC(O)OSiR3 (II),
case of methylthio-anilines, the position of the (S–CH ) substi- which can react with the amine to generate the amide inter-
3
tuent proved to be crucial. While 2-(methylthio)-aniline (15a) mediate III. Although this organic transformation is energeti-
was fully converted into the dimethylated product, only 10% of cally quite expensive, ca. 30 kcal mol− , it is consistent with
1
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Scheme 4 Pathways for methylation via CO
2
insertion. DFT calculated ΔG (kcal mol− ) are reported for NHC = IMes and IPr.
1
the harsh experimental conditions and previous compu-
1
5,16
tational work.
with [Cu(H)(NHC)] to generate [Cu(OCH
which can liberate R Si–O–CH –NR′ (V) through reaction with
R3SiH via fairly small activation barrier of 10–13 kcal mol
Once formed, the amide can easily react
2
NR′ )(NHC)] (IV),
2
3
2
2
−
1
.
The next step, reduction of V with hydrosilane, despite being
highly favorable thermodynamically, occurs via fairly high acti-
−
1
vation barriers of ∼35.0 kcal mol when the transformation is
1
5
not catalysed.
On the other hand, when catalysed by [Cu(H)(NHC)] the
barrier of this transformation is reduced to 26–28 kcal mol−
1 15
.
To support these computational findings, synthetic studies
were carried out. Phenylsilane was added to a solution of
1
[
Cu(OH)(IPr)] and the reaction was monitored by H NMR.
Scheme 5 Formation of [Cu{OC(O)H}(IPr)].
The data are in accordance with the in situ formation of
Cu(H)(IPr)] (18) (Scheme 5). The subsequent reaction of this
1
7
[
species with CO (2 bar) led to the formation of [Cu{OC(O)H}-
2
Finally, the reduction of 5c promoted by PhSiH in the pres-
ence of the copper catalyst was carried out. After 7 hours, the
reaction led to 64% conversion of the amide into the methyl-
3
1
3,18
(IPr)] (19).
The same outcome was obtained by reacting
[Cu(OH)(IPr)] with formic acid in benzene.
In order to corroborate the other steps of the proposed
ated product 5b confirming the methylation proceeds via
1
5
mechanism, stoichiometric NMR experiments were carried out
Scheme 6). By reacting 19 with N-methylaniline 5a in the pres-
ence of PhSiH , 50% conversion towards N-methylformanilide
N-formylamine intermediates.
(
3
5
c was observed. Noteworthy, the formation of the dimethylated
Conclusions
compound was not observed. This is probably due to the short
1
5
reaction time (7 hours rather than 20 hours). As highlighted In conclusion, the first NHC-copper-catalysed methylation of
in Scheme 6, the presence of silane is crucial for the formyla- N–H bonds using CO2 and silane as reagents was reported.
tion of N-methylaniline. In fact, the reaction solely promoted by The scope of this transformation showed that secondary
t
15
1
9 was unsuccessful in the presence or absence of KO Bu.
amines are converted under relatively mild conditions into the
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
4
5
3 2
CH ), 5.58 (s, 2H, H and H ), 5.60 (s, 4H, CHPh ), 6.97–7.01
1
3
(
{
m, 28H, CH ), 7.17 (m, 8H, CH ), 7.41 (m, 8H, CH ). C-
Ar
Ar
Ar
1
H} NMR (75 MHz, C
7
D
8
, 298 K): δ = 21.1 (s, CH
3
), 51.7 (s,
4
5
CHPh
2
), 123.2 (s, C and C ), 126.8 (s, CH Ar), 127.0 (s, CH Ar),
1
28.3 (s, CH Ar), 128.6 (s, CH Ar), 128.7 (s, CH Ar), 129.1 (s, CH
IV
IV
Ar), 129.9 (s, CH Ar), 130.3 (s, C Ar), 130.6 (s, C Ar), 141.7 (s,
C
IV
IV
IV
2
Ar), 143.5 (s, C Ar), 143.7 (s, C Ar). C has not been
observed. Elem. Anal.: Calcd for C H CuN O: C, 83.40; H,
2
5
33
2
5.78, N, 2.82. Found: C, 83.46, H, 5.65, N, 2.74.
General procedure for the methylation
Under an argon atmosphere, a 3 mL vial was charged with
t
t
[
Cu(O Bu)(IMes)] (4) (11 mg, 10 mol%), KO Bu (2.8 mg, 10 mol
%
1
) and toluene (2 mL). The amine substrate (0.25 mmol,
equiv.) and PhSiH (123 μL, 1.0 mol, 4 equiv.) were added
3
and the vial was sealed with a septum cap. The septum cap
was pierced with a syringe needle and placed into a six-slot
steal autoclave. The autoclave was sealed, purged twice with
CO
2 2
and heated at 100 °C (oil bath) under CO atmosphere
(
2 bar) for 20 hours. The reaction mixture was then allowed to
Scheme 6 NMR experiments.
cool and the gas was carefully released. The reaction mixture
was analysed by gas chromatography (GC). In the case of iso-
lated products, dichloromethane (5 mL) was added to the
crude and the mixture was extracted with HCl 1 M (3 × 10 mL).
The aqueous layer was neutralised by addition of K
1
desired methylated products while primary amines provide a
distribution of products depending on the nature of the sub-
strate. DFT calculations supported by experimental work were
carried out in order to elucidate the mechanism of this
transformation.
2 3
CO (pH =
2) and extracted with diethyl ether (3 × 10 mL). The ether
layer was dried over Na
the desired compounds.
,4,5-Trimethoxy-N,N-dimethylaniline,
400 MHz, CDCl , 298 K): δ = 2.93 (s, 6H, N–CH
O–CH ), 3.86 (s, 6H, O–CH ), 5.95 (s, 2H, CH phenyl) C-{ H}
NMR (75 MHz, CDCl , 298 K): δ = 41.3 (s, N–CH ), 56.13 (s,
2
SO
4
. Removal of the solvent afforded
1
3
17b.
H
NMR
(
3
3
), 3.78 (s, 3H,
1
3
1
Experimental
General information
3
3
3
3
IV
3 3
O–CH ), 61.2 (s, O–CH ), 91.0 (s, CH Ar), 130.0 (s, C Ar), 147.9
IV
IV
All reactions were carried out under argon atmosphere using (s, C Ar), 153.8 (s, C Ar). HMRS (APCI) m/z Calcd for
standard Schlenk and glovebox techniques. Chemicals were [C H O N + H] 212.1281. Found 212.1279.
+
1
1
17 3
used as received unless otherwise noted. Dry toluene was
Synthesis of [Cu{OC(O)H}(IPr)], (19)
obtained from a PureSolv SPS-400-5 solvent purification
1
13
1
system. H, and C-{ H} Nuclear Magnetic Resonance (NMR) Under an argon atmosphere, a vial was charged with [Cu(OH)
spectra were recorded on a Bruker-400 MHz or 300 MHz (IPr)] (1) (200 mg, 0.21 mmol, 1 equiv.), formic acid (16 μL,
spectrometers using the residual solvent peak as reference 0.21 mmol, 1 equiv.) and benzene (2 mL). The mixture was
(
CDCl : δ = 7.26 ppm, δ = 77.16 ppm, CD Cl : δ = 5.32 ppm, stirred at room temperature for 1 hour, the solution was then
3 H C 2 2 H
δ = 53.84 ppm, C D : δ = 2.08 ppm, δ = 20.4 ppm) at 298 K. concentrated under reduced pressure. The addition of pentane
C
7
8
H
C
Elemental analyses were performed at London Metropolitan Uni- (10 mL) afforded a colourless solid collected by filtration (Yield
1
3
versity. HMRS analyses were carried out by the EPSRC National = 82%). H NMR (400 MHz, CDCl , 298 K): δ = 1.22 (d, J
=
H–H
3
3
Mass Spectro,metry Service Centre at Swansea University.
6.8 Hz, 12H, CH–CH ), 1.29 (d, J
.56 (sept, JH–H = 7.0 Hz, 4H, CH–CH
H and H ), 7.29 (d, J
JH–H = 7.9 Hz, 2H, CH phenyl), 8.11 (s, 1H, C(O)H formyl)
H–H
= 6.8 Hz, 12H, CH–CH3),
isopropyl), 7.15 (s, 2H,
= 7.8 Hz, 4H, CH phenyl), 7.48 (t,
3
3
2
3
Synthesis of [Cu(OH)(IPr*)] (3)
4
5
3
H–H
3
In a glovebox, a round bottom flask was charged with [Cu(Cl)-
1
3
1
(
(
IPr*)] (250 mg, 0.25 mmol), CsOH (74 mg, 2 equiv.) and THF
3 3
C-{ H} NMR (75 MHz, CDCl , 298 K): δ = 24.0 (s, CH–CH ),
12.5 ml). The reaction mixture was stirred at room tempera- 24.8 (s, CH–CH ) 28.8 (s, CH–CH ), 123.3 (s, C Ar), 124.3 (s,
ture during 15 hours. The suspension was filtered through a CH Ar), 130.6 (s, C and C ), 134.5 (s, C Ar), 145.7 (s, CH Ar),
plug of celite. The solution was concentrated and pentane 167.9 (s, OC(O)H), 180.4 (s, C ).
IV
3
3
4
5
IV
2
(
10 mL) was added. The colourless precipitate was collected by
Computational details
filtration and washed with pentane (3 × 5 mL). The product
was obtained as a colourless solid in 89% yield (215 mg,
Geometry optimisations and calculations of thermochemical
1
0
.22 mmol). H NMR (300 MHz, C D , 298 K): δ = 1.74 (s, 6H, corrections. All geometry optimisations were performed using
7
8
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
1
9
the PBE GGA functional as implemented in PRIRODA 13
Y. Shi, Nat. Rev. Genet., 2012, 13, 343; (d) K. D. Meyer,
Y. Saletore, P. Zumbo, O. Elemento, C. E. Mason and
S. R. Jaffrey, Cell, 2012, 149, 1635; (e) Kirk-Othmer Encyclope-
dia of Chemical Technology, Wiley, New York, 4th edn, 1992,
p. 438.
2
0
21
DFT code. All electron basis sets (L1) comparable in quality
to the correlation consistent valence double-ζ plus polarisation
cc-PVDZ) basis sets of Dunning were used. All stationary geo-
metries were characterised by analytically calculated Hessian
(
matrix. Possible relativistic effects (for copper) were taken into
account via the Dyall Hamiltonian.
2 (a) H. T. Clarke, H. B. Gillespie and S. Z. Weisshaus, J. Am.
Chem. Soc., 1933, 55, 4571; (b) E. Farkas and C. J. Sunman,
J. Org. Chem., 1985, 50, 1110; (c) J. R. Harding, J. R. Jones,
S. Y. Lu and R. Wood, Tetrahedron Lett., 2002, 43, 9487;
(d) S. Kim, C. H. Oh, J. S. Ko, K. H. Ahn and Y. J. Kim,
J. Org. Chem., 1985, 50, 1927; (e) H. Alinezhad,
M. Tajbakhsh and R. Zamani, Synth. Commun., 2006, 36,
3609; (f) H. Alinezhad, M. Tajbakhsh, F. Salehian and
K. Fazli, Synth. Commun., 2010, 40, 2415; (g) M. Tanis and
G. Rauniyar, US Pat, 5105013, 1992; (h) M. Selva, P. Tundo
and A. Perosa, J. Org. Chem., 2002, 67, 9238; (i) P. Tundo
and M. Selva, Acc. Chem. Res., 2002, 35, 706; ( j) M. Selva,
P. Tundo and A. Perosa, J. Org. Chem., 2003, 68, 7374;
(k) M. Selva, P. Tundo and T. J. Foccardi, Org. Chem., 2005,
70, 2476; (l) M. Selva, A. Perosa, P. Tundo and D. Brunelli,
J. Org. Chem., 2006, 71, 5770; (m) M. Selva and A. Perosa,
Green Chem., 2008, 10, 457; (n) T. Oku, Y. Arita, H. Tsuneki
and T. Ikariya, J. Am. Chem. Soc., 2004, 126, 7368;
(o) Y. Zhao, S. W. Foo and S. Saito, Angew. Chem., Int. Ed.,
2011, 50, 3006.
3 (a) Carbon Dioxide as Chemical Feedstock, ed. M. Aresta,
Wiley-VCH, Wienheim, 2010; (b) M. Aresta, in Activation
of Small Molecules, ed. W. B. Tolman, Wiley-VCH, Wein-
heim, 2006, ch. 1; (c) D. H. Gibson, in Comprehensive
Coordination Chemistry-II, ed. J. A. McCleverty and
T. J. Meyer, Elsevier Ltd., Amsterdam, 2003, vol. 1,
section 1.30, p. 595.
4 O. Jacquet, X. Frogneux, C. D. N. Gomes and T. Cantat,
Chem. Sci., 2013, 4, 2127.
5 (a) Y. Li, X. Fang, K. Junge and M. Beller, Angew. Chem., Int.
Ed., 2013, 52, 9568; (b) Y. Li, I. Sorribes, T. Yan, K. Junge
and M. Beller, Angew. Chem., Int. Ed., 2013, 52, 12156.
2
2
The default, adaptively generated PRIRODA grid, corres-
ponding to an accuracy of the exchange–correlation energy per
atom (1 × 10− hartree) was decreased by a factor of 100 for
more accurate evaluation of the exchange–correlation energy.
Default values were used for the Self–Consistent–Field (SCF)
convergence and the maximum gradient for geometry optimi-
8
−
4
sation criterion (1 × 10 au), whereas the maximum displace-
ment geometry convergence criterion was decreased to 0.0018
au.
Translational, rotational, and vibrational partition func-
tions for thermal corrections to arrive at total Gibbs free ener-
gies were computed within the ideal-gas, rigid-rotor, and
harmonic oscillator approximations. The temperature used in
the calculations of thermochemical corrections was set to
2
98.15 K in all the cases.
Single-point (SP) energy evaluations. The energies were re-
evaluated at optimised geometries by means PBE GGA func-
2
3
tional as implemented in Gaussian 09 code. The effects from
2
4
dispersion were included via DFT-D3(BJ) correction term. All
electron def2-tzvpp basis sets of Ahlrichs groups were used
2
5
with corresponding density-fitting basis sets. The default
value for the SP SCF convergence was adopted. The “Integral
(
grid = ultrafine)” option was used for evaluation of the
exchange–correlation term.
Solvent effects. Electrostatic and non-electrostatic solvent
2
6
effects were estimated by means of SMD solvation model as
implemented in Gaussian 09 code. The internal program
values for toluene (dielectric constant, etc.) were adopted. A
standard state corresponding to 1 M ideal dilute solution was
used.
6
K. Beydoun, T. vom Stein, J. Klankermayer and W. Leitner,
Angew. Chem., Int. Ed., 2013, 52, 9554.
7
L. González-Sebastián, M. Flores-Alamo and J. J. García,
Organometallics, 2015, 34, 763.
Acknowledgements
The authors gratefully acknowledge the Royal Society (Univer-
sity Research Fellowship to C. S. J. C.), the EPSRC (DTG011 EP/
J500549/1) and the King Abdullah University of Science and
Technology for funding, and the EPSRC National Mass
Spectrometry Service Centre at Swansea University for HMRS
analyses.
8 (a) E. Blondiaux, J. Pouessel and T. Cantat, Angew. Chem.,
Int. Ed., 2014, 53, 12186; (b) S. Das, F. D. Bobbink,
G. Laurenczy and P. J. Dyson, Angew. Chem., Int. Ed., 2014,
53, 12876.
9 I. Sorribes, K. Junge and M. Beller, Chem. – Eur. J., 2014,
20, 7878.
10 S. Savourey, G. Lefèvre, J. Berthet and T. Cantat, Chem.
Commun., 2014, 50, 14033.
1
1 I. I. F. Boogaerts, G. C. Fortman, M. R. L. Furst,
C. S. J. Cazin and S. P. Nolan, Angew. Chem., Int. Ed., 2010,
49, 8674.
Notes and references
1
(a) J. M. Adams and S. Cory, Nature, 1975, 255, 28;
(
b) D. Dominissini, S. Moshitch-Moshkovitz, S. Schwartz, 12 G. C. Fortman, A. M. Z. Slawin and S. P. Nolan, Organo-
M. Salmon-Divon, L. Ungar, S. Osenberg, K. Cesarkas, metallics, 2010, 29, 3966.
J. Jacob-Hirsch, N. Amariglio, M. Kupiec, R. Sorek and 13 L. Zhang, J. Cheng and Z. Hou, Chem. Commun., 2013, 49,
G. Rechavi, Nature, 2012, 485, 201; (c) E. L. Greer and 4782.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
1
4 K. Motokura, D. Kashiwame, N. Takahashi, A. Miyaji and
T. Baba, Chem. – Eur. J., 2013, 19, 10030.
5 See ESI† for further information.
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
GAUSSIAN 09 (Revision D.01), Gaussian, Inc., Wallingford
CT, 2009.
1
1
6 S. Ilieva, B. Galabov, D. G. Musaev, K. Morokuma and
H. F. Schaefer, J. Org. Chem., 2003, 68, 1496.
1
7 (a) N. P. Mankad, D. S. Laitar and J. P. Sadighi, Organo-
metallics, 2004, 23, 3369; (b) M. R. Uehling, R. P. Rucker
and G. Lalic, J. Am. Chem. Soc., 2014, 136, 8799;
(c) A. M. Whittaker and G. Lalic, Org. Lett., 2013, 15,
1
112.
1
1
8 C. M. Wyss, B. K. Tate, J. Bacsa, T. G. Gray and J. P. Sadighi,
Angew. Chem., Int. Ed., 2013, 52, 12920.
9 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1
997, 78, 1396; J. P. Perdew, K. Burke and M. Ernzerhof,
Phys. Rev. Lett., 1996, 77, 3865.
0 D. N. Laikov and Y. A. Ustynyuk, Russ. Chem. Bull., 2005,
2
5
4, 820.
24 S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem.
Phys., 2010, 132, 224306.
2
2
2
1 D. N. Laikov, Chem. Phys. Lett., 2005, 416, 116.
2 K. G. Dyall, J. Chem. Phys., 1994, 100, 2118.
3 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
25 (a) F. Weigend and R. Ahlrichs, PCCP, 2005, 7, 3297;
(b) F. Weigend, PCCP, 2006, 8, 1057.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, 26 A. V. Marenich, C. J. Cramer and D. G. Truhlar, J. Phys.
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, Chem. B, 2009, 113, 6378.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.