Hydride-rhodium(III)-N-heterocyclic carbene catalysts for vinyl-selective h/d exchange: A structure-activity study

Article abstract of DOI:10.1002/chem.201402499

A series of neutral and cationic Rh^III-hydride and Rh ^III-ethyl complexes bearing a NHC ligand has been synthesized and evaluated as catalyst precursors for H/D exchange of styrene using CD ₃OD as a deuterium source. Various ligands have been examined in order to understand how the stereoelectronic properties can modulate the catalytic activity. Most of these complexes proved to be very active and selective in the vinylic H/D exchange, without deuteration at the aromatic positions, displaying very high selectivity toward the positions. In particular, the cationic complex [RhClH(CH₃CN)₃(IPr)]CF ₃SO₃ showed excellent catalytic activity, reaching the maximum attainable degree of vinylic deuteration in only 20 min. By modulation of the catalyst structure, we obtained improved α/β selectivity. Thus, the catalyst [RhClH(κ²-O,N-C₉H ₆NO)(SIPr)], bearing an 8-quinolinolate ligand and a bulky and strongly electron-donating SIPr as the NHC, showed total selectivity for the β-vinylic positions. This systematic study has shown that increased electron density and steric demand at the metal center can improve both the catalytic activity and selectivity. Complexes bearing ligands with very high steric hindrance, however, proved to be inactive.

Full text of DOI:10.1002/chem.201402499

DOI: 10.1002/chem.201402499
Full Paper
&
Carbene Catalysis
Hydride-Rhodium(III)-N-Heterocyclic Carbene Catalysts for Vinyl-
Selective H/D Exchange: A Structure–Activity Study
[
a]
[a, b]
[a]
Andrea Di Giuseppe,* Ricardo Castarlenas,*
Jesffls J. PØrez-Torrente,
[a]
[a, c]
Fernando J. Lahoz, and Luis A. Oro*
Dedicated in memory of Marꢀa Pilar Garcꢀa Clemente
III
Abstract: A series of neutral and cationic Rh -hydride and
ty, reaching the maximum attainable degree of b-vinylic
deuteration in only 20 min. By modulation of the catalyst
structure, we obtained improved a/b selectivity. Thus, the
III
Rh -ethyl complexes bearing a NHC ligand has been synthe-
sized and evaluated as catalyst precursors for H/D exchange
2
of styrene using CD OD as a deuterium source. Various li-
catalyst [RhClH(k -O,N-C H NO)(SIPr)], bearing an 8-quinoli-
3
9
6
gands have been examined in order to understand how the
stereoelectronic properties can modulate the catalytic activi-
ty. Most of these complexes proved to be very active and se-
lective in the vinylic H/D exchange, without deuteration at
the aromatic positions, displaying very high selectivity
toward the b-positions. In particular, the cationic complex
nolate ligand and a bulky and strongly electron-donating
SIPr as the NHC, showed total selectivity for the b-vinylic po-
sitions. This systematic study has shown that increased elec-
tron density and steric demand at the metal center can im-
prove both the catalytic activity and selectivity. Complexes
bearing ligands with very high steric hindrance, however,
proved to be inactive.
[
RhClH(CH CN) (IPr)]CF SO showed excellent catalytic activi-
3 3 3 3
Introduction
harsh reaction conditions, which constitutes a major draw-
[3]
back. For this reason, the development of new catalysts with
high activity and selectivity represents a very important and
Deuterium-labeled compounds are nowadays used as essential
tools in a wide range of fields, whether it be for fundamental
research or practical applications, for example, drug metabo-
lism, structural study of biological macromolecules, reaction
mechanisms and kinetics, quantification of environmental pol-
lutants and residual pesticides, synthesis of heavy drugs, pro-
duction of innovative optical materials, or markers in diesel
[2b]
challenging task. Transition-metal-based homogeneous and
heterogeneous catalytic systems allow H/D exchange reactions
to be performed under mild conditions, preventing substrate
decomposition, with high tolerance toward the main function-
al groups. Moreover, such catalytic systems open the way for
greater choice of the deuterium source, such as D , D O, or or-
2
2
[
1]
oil. Straightforward H/D exchange in the target molecule is
a more efficient and cost-effective preparative method than
the classical multistep synthesis from deuterated starting mate-
ganic deuterated solvents, according to the most compatible
conditions for the substrate.
[4]
[5]
Since the pioneering works of Garnett and Shilov in the
1960s, a plethora of transition-metal-based homogeneous cata-
lytic systems for H/D exchange have been developed, includ-
[
2]
rials. However, direct substrate deuteration generally requires
[
4c,6]
[4d,6g,t,7]
[7h,8]
ing those based on iridium,
rhodium,
palladium,
and osmiu-
[
a] Dr. A. Di Giuseppe, Dr. R. Castarlenas, Prof. Dr. J. J. Pꢁrez-Torrente,
Prof. Dr. F. J. Lahoz, Prof. Dr. L. A. Oro
Departamento de Quꢀmica Inorgꢂnica
Instituto de Sꢀntesis Quꢀmica y Catꢂlisis Homogꢁnea
Universidad de Zaragoza - CSIC
[4a,b,5,7h,8a,c,9]
[7i,10]
[11]
platinum,
ruthenium,
cobalt,
[7i,10h,12]
m.
shown by their ability to deuterate different CꢀH groups of ali-
phatic, aromatic, and vi-
nylic substrates. However, the control of regio- and
The versatility of these organometallic catalysts is
[2b,6k,m,7b,f,10b,e,i]
[2b,4a,6k,m,o,s–u,7b,g,k,9d,10e,h,j,12]
C/Pedro Cerbuna 12, 50009 Zaragoza (Spain)
E-mail: dgandrea@unizar.es
[6a,n,7a,d,e,i,10g]
stereoselectivity still remains an important challenge, especially
for the deuteration of olefins in the presence of aromatic
groups.
rcastar@unizar.es
oro@unizar.es
[
b] Dr. R. Castarlenas
ARAID Foundation Researcher
In this context, a key issue to take into account is that most
transformations mediated by transition-metal-based catalytic
systems proceed according to a CꢀH activation mechanism
[
c] Prof. Dr. L. A. Oro
Center of Research Excellence in Refining & Petrochemicals
King Fahd University of Petroleum & Minerals
Dhahran, 31261 Saudi Arabia
[6,7f,g,k,8b,c,9d,10a–f,h,12,13]
(
Scheme 1a).
The selectivity of the reaction
depends on the activation energies of the relevant CꢀH moiet-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402499.
ies, which are related to their dissociation energies. Thus, the
Chem. Eur. J. 2014, 20, 1 – 14
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&
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diisopropylphenyl)imidazol-2-car-
bene (IPr), 1,3-bis(2,6-diisopro-
pylphenyl)imidazolidin-2-carbene
(
SIPr), 1,3-bis(2,4,6-trimethylphe-
nyl)imidazol-2-carbene (IMes),
,3-dicyclohexylimidazol-2-car-
1
bene (ICy), and 1,3-bis(2,6-dime-
thylphenyl)tetrahydropyrimidin-
2-carbene (SPXyl), the syntheses
of which have been reported in
[18]
the literature (Scheme 2).
The dinuclear [Rh(m-Cl)(NHC)-
2
(
h -coe)]2 complexes (coe=cy-
clooctene) were synthesized as
described by James and co-
[
16b]
workers.
Thus, reactions of
Scheme 1. Possible mechanism for H/D exchange reaction of olefins: CꢀH activation (top) and insertion/b-elimina-
2
[
Rh(m-Cl)(h -coe) ] (1) with the
2
2
tion pathway (bottom).
observed reactivity order is generally: C ꢀH>C ꢀH>C ꢀH.
sp
sp2
sp3
In particular, in the case of substrates with both aromatic and
olefinic groups, for which the CꢀH bond dissociation energies
are comparable, selective activation of the vinylic protons is
[
6m,14]
problematic.
An efficient strategy for selective deuterium-
labeling of alkenes is to use a metal hydride species that gives
rise to an alternative insertion–elimination mechanism, which
[
4d,6g,7a,e,i,j,11]
is not operative for aromatic protons (Scheme 1b).
In addition, a high oxidation state of the metal center may
reduce the competitive olefin CꢀH activation pathway and
thereby prevent hydrogenation of the double bond of the
target olefin. Moreover, a bulky and strongly electron-donating
ancillary ligand should provide additional stability to the hy-
dride-metal species in a high oxidation state, while exerting
a significant steric effect in the vicinity of the coordination site,
which may dramatically influence the selectivity of the reac-
Scheme 2. NHC ligands used in this work.
corresponding free NHC ligands gave the dinuclear complexes
III
[7d,i]
2
2
tion. With this in mind, we envisaged Rh complexes
bear-
[Rh(m-Cl)(IPr)(h -coe)] (2a) and [Rh(m-Cl)(IMes)(h -coe)] (3). Fol-
2 2
[
15]
[7j]
ing a N-heterocyclic carbene ligand (NHC) as potential cata-
lysts for facilitating the H/D exchange of olefins in an active
and selective manner. Thus, in this work, we report the synthe-
lowing the previously reported synthetic scheme, treatment
of the dimers 2a and 3 with 8-hydroxyquinoline in toluene at
room temperature led to the diastereoselective synthesis of
III
2
sis of a set of hydride-Rh -NHC catalysts and a systematic
the 16-electron complexes [RhClH(k -O,N-C H NO)(NHC)] (4,
9
6
study of their catalytic activities in the deuterium labeling of
styrene. The results of this study have allowed us to disclose
highly efficient catalysts and to establish a relationship be-
tween the structure of the complex and its catalytic activity. A
IPr; 5, IMes; Scheme 3). Complexes 4 and 5 were isolated as
[7j]
orange solids in yields of 76 and 79%, respectively. The relat-
ed mononuclear hydride/8-quinolinolate derivatives bearing
carbenes SIPr and SPXyl were synthesized according to a one-
pot procedure (Scheme 3). Thus, mixtures of [Rh(m-Cl)(coe) ] ,
[
7j]
part of this work has been previously communicated.
2
2
8-hydroxyquinoline, and NHC (SIPr or SPXyl) were stirred at
room temperature in THF for 2 h to give orange solutions of
2
2
Results and Discussion
the complexes [RhClH(k -O,N-C H NO)(SIPr)] (6) and [RhClH(k -
9 6
O,N-C H NO)(SPXyl)] (7), which were isolated as orange solids
III
9
6
Synthesis of neutral hydride-Rh -NHC complexes bearing an
in good yields. Unfortunately, this synthetic approach did not
work well for the ICy ligand. X-ray analysis of a crop of red
crystals collected from the reaction mixture revealed the for-
8-quinolinolate ligand
2
Dinuclear complexes of the type [Rh(m-Cl)(NHC)(h -olefin)] are
2
2
excellent starting materials since they are easy to prepare and
mation of the coordination ion pair [Rh(k -O,N-C H NO)(ICy) ]-
[RhCl (k -O,N-C H NO) ] . The formation of this species with
2 9 6 2 2
three ICy ligands is most probably a consequence of the lesser
steric demand of the ICy ligand (Figure S1, Supporting Infor-
mation).
9
6
3
[
16]
2
very reactive. With the aim of studying the effect of the NHC
ligand on the catalytic activity, we prepared several catalytic
precursors bearing a range of NHC ligands having different
[
17]
steric demands and electron-donating abilities: 1,3-bis(2,6-
&
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the Supporting Information). The
most noticeable signal in the
1
H NMR spectra of complexes 5,
6
, and 7 at 298 K is a shielded
doublet between d=ꢀ27.9 and
28.6 ppm (J =44–47 Hz),
ꢀ
Rh,H
corresponding to the hydride
ligand. Such a high-field-shifted
signal with a large Rh-H cou-
pling constant has also been ob-
served in related rhodium hy-
dride complexes, and is a diag-
nostic of a vacant site trans to
[7j,19]
the hydride ligand.
Interest-
ingly, complex 5 showed only
one signal for the two imidazole
Scheme 3. Synthesis of neutral hydride-Rh-NHC 8-quinolinolate complexes 1–9.
protons of IMes at d=6.39 ppm,
which, in addition to just three
2
An X-ray diffraction structural analysis of complex [RhClH(k -
signals at d=2.47, 2.44, and 1.90 ppm for the eighteen methyl
protons, indicates rapid rotation of the carbene ligand about
the RhꢀC axis at room temperature. A similar NMR pattern was
observed for 6, compatible with rapid rotation of the SIPr
ligand about the RhꢀC bond. However, the carbene ligand in 7
does not rotate, as demonstrated by the presence of four sig-
nals for the four methyl groups of the SPXyl ligand (d=2.64,
O,N-C H NO)(IPr)] (4; Figure 1) substantiates the suggested
9
6
strong trans influence of the hydride favoring the formation
a square-pyramidal structure with the hydride located in the
2.62, 2.56, and 2.55 ppm). This is in accordance with a reduction
in the C(carbene)-N-C(phenyl) angle in the six-membered tetra-
hydropyrimidine-type carbene, which causes the phenyl sub-
stituents to approach the metal center, thereby hampering ro-
[18b]
13
1
tation.
A salient feature of the C{ H}-APT spectra of 5–7 is
a deshielded doublet resonance corresponding to the Rh-CNHC
carbon atom. This signal appears at d=177.5 ppm for complex
5
, bearing a carbene with an unsaturated imidazole skeleton,
whereas it is shifted to 200.9 and 208.2 ppm for complexes 7
and 6, respectively, which implies that these saturated car-
benes are better electron-donor ligands than the unsaturated
[20]
carbenes.
To obtain more information about the influence of the 8-qui-
nolinolate ligand on the catalytic activity, complexes contain-
ing an electron-poor analogue, 5,7-dichloro-8-quinolinolate, or
the bulkier ligand 2-methyl-8-quinolinolate were prepared. A
synthetic route similar to that for 4 was followed for the syn-
Figure 1. Molecular diagram of 4. Selected bond lengths [Š] and angles [8]:
Rh–Cl 2.2993(7), Rh–O 1.9965(19), Rh–N(1) 2.062(2), Rh–C(10) 1.951(2), Rh–H
1
7
1
.43(4); Cl-Rh-O 174.70(5), Cl-Rh-C(10) 91.24(7), Cl-Rh-N(1) 95.53(7), Cl-Rh-H
8(2), O-Rh-N(1) 81.45(9), O-Rh-C(10) 92.13(8), O-Rh-H 107(2), N(1)-Rh-C(10)
71.92(9), N(1)-Rh-H 109(2), C(10)-Rh-H 68(2).
2
thesis of the 5,7-dichloro-8-quinolinolate complex, [RhClH(k -
O,N-C H NOCl )(IPr)] (8), which was obtained in 78% yield. On
9
4
2
the other hand, 2-methyl-8-quinolinol and 2a did not react at
room temperature, probably because the methyl group adja-
cent to the nitrogen atom hinders coordination to the metal.
Thus, the reaction was carried out at 808C for 2 h to give
apical position. The IPr ligand is located trans to the N-donor
atom of the bidentate 8-quinolinolate ligand (N(1)-Rh-C(10)=
171.92(9)8), with the chlorido ligand trans to the O-donor atom
2
[Cl-Rh-O=174.70(5)8]. The “wingtips” of the IPr adopt an out-
[RhClH(k -O,N-C H NOCH )(IPr)] (9) in 72% isolated yield
9
5
3
1
13
1
of-plane disposition from the square base of the pyramid, with
the aromatic rings pointing to the vacant site and the hydride
ligand. The rhodium-carbene separation [Rh-C(10)=1.951(2) Š]
agrees well with the expected value for an RhꢀC single
(Scheme 3). The H and C{ H} NMR spectra of 8 and 9 are in
accordance with their proposed structures. In both cases, the
1
high-field-shifted hydride resonance observed in the H NMR
spectrum at d=ꢀ27.81 ppm for 8 and at ꢀ28.43 ppm for 9
[
15c]
bond.
and the large J
are consistent with those of related unsatu-
Rh,H
NMR analysis of complexes 5–7 showed a pattern of reso-
nances comparable to that of complex 4 (for a summary of the
key characteristic NMR data of complexes 4–16, see Table S2 in
rated square-pyramidal complexes described previously. The
different electronic structure of 8 with respect to 4 is reflected
1
3
in the signals of the quinolinic ring, especially in the C NMR
Chem. Eur. J. 2014, 20, 1 – 14
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signal of the quaternary carbon atom directly bound to the
prepared. We synthesized complexes with different numbers
of chlorido ligands to obtain compounds with different charg-
es (dicationic, monocationic, and neutral) to better compare
this new family of complexes with those described previously.
In this case, a different source of hydride to 8-quinolinol was
used. One of the simplest species for hydride generation is
oxygen atom, which is shifted from d=170.9 ppm in 4 to d=
164.9 ppm in 8. In the case of complex 9, no interaction be-
tween the methyl group of the 2-methyl-8-quinolinolate ligand
and rhodium is observed.
[7a]
a strong acid. We selected two different acids to synthesize
complexes with different charges: triflic acid (CF SO H) and hy-
Synthesis of cationic complexes containing the hydride-Rh-
IPr skeleton
3
3
drochloric acid. The former was chosen for the relatively low
coordination ability of the triflate anion, thus producing cation-
Related cationic complexes containing the [RhH(IPr)] moiety
were synthesized in order to compare their catalytic properties
III
I
ic Rh hydride derivatives after reaction with Rh complexes. In
III
with those of the neutral complexes 4–9. The complex
contrast, reaction with HCl should lead to neutral Cl-Rh -H
2
[
RhH(k -O,N-C H NO)(IPr)(CH CN) ](PF ) (10) was prepared by
complexes due to the simultaneous coordination of a chlorido
ligand. Thus, two new complexes were prepared starting from
dimer 2a and the corresponding acid in acetonitrile at low
temperature: the cationic com-
9
6
3
2
6
removing the chlorido ligand in 4 by treatment with TlPF in
6
acetonitrile (Scheme 4). Complex 10 was isolated as an orange
plex [RhClH(CH CN) (IPr)]CF SO
3
3
3
3
(
11) by addition of CF SO H, and
3 3
the neutral complex [RhCl H-
2
(
CH CN) (IPr)] (12) by using
3 2
HCl(aq) (Scheme 4). Attempted
preparation of a dicationic com-
plex by treatment of complexes
1
1 or 12 with AgPF or TlPF was
6 6
unsuccessful. However, the addi-
tion of two equivalents of
CF SO H to a solution of the
3
3
chlorido-free dimer [Rh(m-OH)-
2
(
IPr)(h -coe)]2 (2-OH), recently
[21]
prepared in our laboratories,
in acetonitrile at ꢀ208C, led to
the formation of the dicationic
complex
[RhH(CH CN) (IPr)]-
3 4
(
CF SO ) (13) in 91% isolated
3
3 2
2
yield. The NMR spectra of 11–13
Scheme 4. Synthesis of complexes [RhH(k -O,N-C
9
H
6
NO)(IPr)(CH
3 2 6 3 3 3 3
CN) ]PF (10), [RhClH(CH CN) (IPr)]CF SO (11),
[RhCl
2
H(CH
3
CN)
2
(IPr)] (12), and [RhClH(CH
3
CN)
4
(IPr)](CF SO (13).
3
3
)
2
show the typical pattern for a sa-
III
turated Rh complex with an oc-
tahedral geometry. In particular,
1
solid in 68% yield. The H NMR spectrum of 10 in CD CN
the signal of the hydride ligand appears between d=ꢀ15.4
(7–8 Hz). Moreover, the
3
2
showed the same pattern as that of [RhClH(k -O,N-C H NO)-
IPr)(CH CN)] (4-CH CN) (the acetonitrile solvate of 4), with
and ꢀ18.7 ppm with a very small J
9
6
Rh,H
[7j]
(
signals of the imidazole protons in 11 and 13 also support this
geometry since they are downfield-shifted to d=7.44 and
7.65 ppm. In the case of 12, the =CH imidazole protons and
the carbon atoms of the IPr ligand are seen to be inequivalent,
3
3
a hydride signal at d=ꢀ17.52 ppm (J =21.1 Hz) and a down-
Rh,H
field-shifted signal at d=7.54 ppm corresponding to the imida-
zole ring protons. These spectroscopic features provide strong-
1
ly evidence that complex 10 in CH CN solution is octahedral
with a weakly coordinated acetonitrile ligand trans to the hy-
giving rise to two resonances in both the H NMR (d=7.26 and
3
13
1
7.25 ppm) and C{ H} NMR spectra (d=126.7 and 125.5 ppm).
This spectroscopic evidence points to a “frozen” structure pos-
sessing a mirror plane that contains the imidazole plane, with
a trans disposition of the two chlorido ligands, and rules out
a dinuclear structure (Scheme 4). Similarly to the behavior ob-
dride ligand. In fact, both acetonitrile molecules exchange with
13
1
the CD CN solvent. The C{ H} NMR spectrum displays a broad
3
signal at d=169.6 ppm corresponding to the carbene carbon
atom. This value is upfield-shifted compared to those of com-
plexes 4 and 4-CH CN (d=179.0 and 175.2 ppm, respectively),
served for 10, all acetonitrile ligands exchange with the CD CN
3
3
probably due to the positive charge on the cationic complex
solvent. The charges of the complexes seem to strongly influ-
ence the chemical shifts of the IPr resonances, especially those
of the carbene carbon atoms. Specifically, increasing charge
gives rise to a progressive shielding of this resonance: d=
167.0 ppm for the neutral complex 12, 161.2 ppm for the cat-
ionic species 11, and 153.8 ppm for the dicationic 13. The
10.
In order to assess the influence of the 8-quinolinolate li-
gands on the catalytic activity of complexes of this type, relat-
III
ed hydride-Rh -NHC systems in which the bidentate ligand is
replaced by weakly bonded ligands such as acetonitrile were
&
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latter proved to be the lowest chemical shift among all of the
complex 4. The ethyl ligand gives rise to a doublet at d=
III
prepared complexes of the type H-Rh -IPr.
21.0 ppm with JRh,C =28.4 Hz (>CH ) and a singlet at 20.6 ppm
2
(
CH ). The saturated complex 15 does not show remarkable
3
differences in its NMR spectra compared to the unsaturated
analogue 14, apart from a deshielding of the proton signal of
the imidazole at d=7.32 ppm, which is diagnostic of an octa-
III
Synthesis of Et-Rh -IPr complexes
Recently, our research group reported the synthesis and char-
I
2
III
acterization of a new Rh dinuclear complex [Rh(m-Cl)(IPr)(h -
hedral saturated Rh -IPr complex. It is important to remark
[
16e]
CH =CH )] (2b).
In our quest to find an alternative starting
that, even in this case, the coordination of CH CN does not
3
2
2 2
III
complex for the synthesis of Rh derivatives, we studied the re-
prevent free rotation of the carbene about the RhꢀC bond at
room temperature. In addition, coordination of an acetonitrile
ligand trans to the ethyl ligand does not significantly influence
activity of the ethylene dimer 2b. Interestingly, treatment of
2
b with 8-hydroxyquinoline or CF SO H resulted in the forma-
3 3
13
1
tion of Rh-ethyl compounds as a consequence of insertion of
the chemical shift of the >CH resonance in the C{ H} NMR
2
the coordinated ethylene into the RhꢀH bond of the inter-
spectrum (d=20.0 ppm, JRh,C =28.5 Hz).
III
[7a,22]
2
mediate Rh -hydride species.
It is worthy of note that
The reaction of [Rh(m-Cl)(IPr)(h -CH
=CH
2
)]
2
2
(2b) with
a similar reactivity was observed with styrene, although the in-
CF
plex [RhCl(CH
treating 2b with 1 equiv of acid in CH
mixture of 2b and the dicationic product [Rh(CH
(CH CN) ](CF SO (16). Treatment of this mixture with
a second equivalent of CF SO H gave a pale-yellow solution of
3 3 3
SO H in CH CN did not afford the monocationic ethyl com-
[7j]
+
sertion products could not be isolated in the solid state.
CH
2
)(CH
3
3
CN)
3
(IPr)] in analogy to 11. In fact,
CN gave an equimolar
CH )(IPr)-
However, the insertion of cyclooctene has never been ob-
served in any of the described RhꢀH complexes, probably be-
cause of the large size of this olefin.
3
2
3
)
3 2
3
4
3
2
Reaction of [Rh(m-Cl)(IPr)(h -CH =CH )] (2b) with 8-hydroxy-
3
3
2
2 2
quinoline in toluene gave an orange solution of the unsaturat-
16, which was isolated as a white solid in 79% yield
(Scheme 6). Surprisingly, treatment of the hydride species 11
2
ed complex [RhCl(CH CH )(k -O,N-C H NO)(IPr)] (14), which was
2
3
9
6
isolated as an orange solid in 86% yield. Similarly to what was
with an excess of CF SO H did not result in formation of the di-
3 3
observed for complex 4, coordination of an acetonitrile mole-
cationic complex 13 (analogous to 16). It is therefore evident
that the ethyl ligand provides a special stereoelectronic envi-
ronment that increases the reactivity of the monocationic spe-
cies.
ꢀ
cule at the vacant site resulted in the formation of an 18 e
2
complex,
Scheme 5).
[RhCl(CH CH )(k -O,N-C H NO)(IPr)(CH CN)]
(15)
2
3
9
6
3
(
Single crystals of 16 suitable
for X-ray analysis were obtained
by slow diffusion of diethyl ether
layered on a saturated solution
of 16 in CH Cl . The complex
2
2
shows a slightly distorted octa-
hedral geometry around the
metal center, with the IPr and
ethyl ligands in a mutually cis
Scheme 5. Synthesis of Rh-ethyl species 14 and 15.
The spectroscopic properties
of complex 14 closely resemble
those of 4. The ethyl group does
not seem to affect the rotation
of the carbene moiety and at
room temperature only one
signal for the imidazole protons
was observed at d=6.71 ppm.
Scheme 6. Preparation of the dicationic complex 16.
As already stated, this upfield-
shifted signal is indicative of
a
pentacoordinated structure.
This consideration, together with the strong trans influence of
the ethyl group, leads us to propose a square-pyramidal geom-
etry for complex 14, with the ethyl group in the apical posi-
tion. As expected, the methylene protons of the ethyl ligand
are diastereotopic, thus showing two doublet of doublet quad-
disposition (Figure 2). The Rh-C(11) distance of 2.026(7) Š is
[15c]
typical of an RhꢀC single bond.
A similar distance is ob-
served between the Rh and the ethyl ligand (2.065(7) Š), with
the methyl group pointing down from the IPr ligand with a tor-
sion angle C(11)(IPr)-Rh-C1-C2 of 162.2(7)8. The two acetonitrile
molecules oriented mutually trans exhibit similar distances to
the Rh center, RhꢀN(1) 1.994(7) Š and RhꢀN(3) 1.998(6) Š.
However, the acetonitrile ligand trans to the ethyl ligand
13
1
ruplets with JRh,H =3.2 Hz. In the C{ H} NMR spectrum, the
signal of the carbene carbon atom appears as a doublet at d=
174.5 ppm with JRh,C =51.8 Hz, similar to the value observed for
Chem. Eur. J. 2014, 20, 1 – 14
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5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
Catalytic activity studies
The synthesized complexes were evaluated as catalysts for H/D
exchange in olefins using CD OD as a deuterium source. Sty-
3
rene was chosen as a model olefin for the evaluation of cata-
lytic activity and selectivity (Scheme 7). The reactions were per-
Scheme 7. Selective H/D exchange reaction.
Figure 2. Molecular diagram of the cation of 16. Selected bond lengths [Š]
and angles [8]: Rh–C(1) 2.065(7), Rh–N(1) 1.994(7), Rh–N(2) 2.197(7), Rh–N(3)
formed in NMR tubes sealed under argon containing 0.5 mL of
1
.998(6), Rh–N(4) 2.092(7), Rh–C(11) 2.026(7); C(1)-Rh-N(1) 88.7(3), C(1)-Rh-
CD OD with a 2 mol% catalyst loading at 258C, and were
3
N(2) 177.1(3), C(1)-Rh-N(3) 90.1(3), C(1)-Rh-N(4) 93.7(3), C(1)-Rh-C(11) 86.8(3),
N(1)-Rh-N(2) 92.9(3), N(1)-Rh-N(3) 168.0(2), N(1)-Rh-N(4) 82.6(3), N(1)-Rh-C(11)
monitored by NMR spectroscopy. Vinylic deuteration was ex-
clusively observed for all of the catalysts, with a very high se-
lectivity in favor of the b-position (Figure 3, Table 1).
96.3(3), N(2)-Rh-N(3) 87.9(3), N(2)-Rh-N(4) 84.1(3), N(2)-Rh-C(11) 95.4(3), N(3)-
Rh-N(4) 85.6(3), N(3)-Rh-C(11) 95.6(3), N(4)-Rh-C(11) 178.8(3).
shows a longer RhꢀN(2) separation of 2.197(7) Š, which is in
agreement with the high trans influence of the ethyl ligand.
The acetonitrile ligand trans to the IPr ligand shows an inter-
mediate RhꢀN bond distance of 2.092(7) Š. It is remarkable
that the acetonitrile ligands cis to IPr are bonded in a bent
fashion, presenting a deviation of about 148, with angles of
Rh-N(1)-C(3) 165.5(6)8, Rh-N(2)-C(5) 166.3(6)8, and Rh-N(3)-C(7)
166.9(7)8. This deviation most probably results from the high
steric demand of the carbene ligand in combination with the
weakness of the rhodium–acetonitrile bonds. In fact, the aceto-
nitrile ligand disposed trans to the IPr ligand is also deformed,
but only by 88 (Rh-N(4)-C(9) 172.0(7)8).
1
13
1
The H and C{ H} NMR spectra of 16 are in accordance with
the proposed structure. In this case, the symmetry of the com-
plex, in combination with the rapid rotation of the carbene,
Figure 3. H/D exchange in styrene catalyzed by 4, 5, 6, 11, and 12.
1
leads to only one H NMR signal for the four isopropyl protons
and two signals for the eight methyl groups. As expected for
[
a]
III
Table 1. Styrene H/D exchange promoted by different catalysts.
a saturated hydride-Rh -NHC complex, the signal of the imida-
zole protons appears downfield-shifted (d=7.46 ppm) with re-
Entry
Catalyst
t
[h]
a-D
[%]
b-D
[%]
TOF1/2
[h ]
[
b]
[b]
ꢀ1 [c]
spect to the analogous unsaturated complex. The >CH pro-
2
tons of the ethyl ligands give rise to a single resonance at d=
1
2
3
4
5
6
7
8
9
4
5
6
7
8
3
5
1
24
6
7
24
0.3
2.2
24
4
3
8
92
92
92
trace
91
86
8
92
91
trace
92
192
178
306
–
90
39
2
.76 ppm, which is in agreement with the C symmetry of the
s
complex. Only one signal corresponding to free acetonitrile is
trace
trace
12
13
2
10
16
trace
6
[
d]
observed due to fast exchange with the CD CN solvent. The
3
13
1
C{ H} NMR spectrum displays a doublet at d=150.3 ppm,
[d]
9
[
[
[
d]
d]
d]
with JRh,C =52.2 Hz, corresponding to the carbene carbon
atom, which is the most shielded of such centers within all of
the complexes described in this work, probably due to the di-
cationic nature of the complex. The signal of the methylene
carbon atom bonded to rhodium appears at d=18.4 ppm,
similarly to those of 14 and 15, but the JRh,C of 17.6 Hz is signif-
icantly lower.
10
11
12
13
14
15
16
–
3110
171
–
139
139
–
10
1
1
12
13
4
24
6
92
trace
trace
[
3
a] Reaction conditions: [Styrene]=1m in 0.5 mL of CD OD with 2 mol%
of catalyst at 258C. [b] % of deuterium incorporation at the specified po-
sition (a or b). [c] H/D exchange at the b-position, TOF calculated at 50%
conversion. [d] Reaction performed at 808C.
&
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The catalytic performances of the complexes varied greatly,
with modification of the ancillary ligands having the expected
dramatic effect thereon. In particular, the results obtained for 6
and 11 stand out among all of the reported data. The cationic
+
acetonitrile-solvated Rh hydride complex [RhClH(CH CN) (IPr)]
3
3
(
11) displayed excellent activity in the deuteration of the b-
ꢀ
1
vinyl positions of styrene (TOF1/2 =3110 h ), giving 92% deu-
terium incorporation in less than 20 min (entry 8). This com-
plex proved to be the most active catalyst among all of those
synthesized, giving a tenfold faster reaction rate than the pre-
2
viously reported complex [RhClH(k -O,N-C H NO)(IPr)] (4)
9
6
(entry 1). In addition, it is worthy of note that the value of 92%
b-deuteration attained with 11 is very close to the maximum
theoretical level of b-deuteration attainable under the reaction
conditions (92.5%), thus representing a deuteration efficiency
[
23]
of >99%. However, this exceptional increase in catalytic ac-
tivity was accompanied by a loss of selectivity, as 10% deutera-
tion at the a-vinyl position was also observed. Although the
activity of a catalyst is highly important, for practical applica-
tions the selectivity is fundamental. In this respect, complex
2
[
RhClH(k -O,N-C H NO)(SIPr)] (6) is certainly the catalyst precur-
9
6
sor with the best catalytic performance. In fact, as can be ob-
served from Table 1 (entry 3), in addition to its excellent cata-
III
Scheme 8. Mechanism of H/D exchange of olefins mediated by Rh -H cata-
lyst.
ꢀ
1
lytic activity (TOF1/2 =306 h ), outstandingly high selectivity in
the deuteration at the b-vinyl positions (also in this case
>
99% of the maximum theoretical b-deuteration) was ach-
ieved, with deuterium incorporation at the a-vinyl position
only at trace levels. As regards the other synthesized com-
plexes, good results in terms of catalytic performance were ob-
tained for 5, 8, 12, 14, and 15 (entries 2, 5, 9, 11, and 12, re-
spectively), with TOF1/2 values between 90 and 179 h , and
good selectivity towards deuteration at the b-vinyl positions of
the olefin. On the other hand, complex 9 showed moderate ac-
tivity at 808C (entry 6), and complexes 7, 10, 13, and 16 were
practically inactive even at 808C (entries 4, 7, 10, and 13, re-
spectively).
can enter the benzyl position, the hydrogen atom cannot
easily leave. On the contrary, in the case of complex e, the ter-
minal methyl group can easily rotate to form complex f, from
which the b-deuterated olefin is obtained after b-H elimina-
tion.
ꢀ
1
The NHC ligand has a strong influence on the catalytic per-
formance. Substituting IPr by IMes in complex 5 (entry 2) leads
to decreases in both activity and selectivity. This is probably
due to the lower electron-donating ability and bulkiness of
[15b,20]
IMes with respect to IPr.
Complex 6, bearing the ligand
In order to analyze these results in more detail, taking into
account the different natures of the catalyst precursors, it was
deemed important to focus on the mechanism by which these
SIPr, proved to be the most selective of the studied catalysts
and the most active among those bearing the 8-quinolinolate
ligand (entry 3). SIPr, the saturated analogue of IPr, is slightly
[
7j]
[15b]
catalysts operate. As previously proposed, the first step of
more electron-donating and bulky,
which may account for
III
the process is the exchange of the hydride ligand Rh -H (a) by
the observed improvement in catalytic performance. In view of
the trend that an increase in steric hindrance imposed by the
NHC ligand improves the selectivity, we envisaged that the in-
troduction of a bulky tetrahydropyrimidine-based NHC ligand
(SPXyl) in complex 7 could improve the catalytic outcome.
Somewhat surprisingly, however, complex 7 proved to be com-
pletely ineffective (entry 4). It has been found that the hydride
deuterium from the deuterated solvent (CD OD) to generate
3
III
[24]
an Rh -D species (b) (Scheme 8). Then, after coordination of
the olefin to complex b to give an intermediate species with
[
25]
2
the ligands in a cis disposition, the orientation of the h -co-
ordinated olefin determines the insertion pathway. A 1,2-inser-
tion into the RhꢀD bond gives rise to the linear product c,
whereas a 2,1-insertion provides the branched product e. At
this point, rotation about the C -C alkyl axis is essential for ef-
ligand of 7 does not undergo H/D exchange in CD OD even at
3
808C, thus explaining its inactivity as a deuterium labeling cat-
alyst. The high steric hindrance of the SPXyl ligand most prob-
1
2
[
26]
fective H/D exchange (c!d; e!f). Subsequent b-H elimina-
tion from d leads to a-deuteration, whereas that from f yields
the b-deuterated olefin. The critical step determining the selec-
tivity is thus the rotation about the C -C alkyl axis. In the case
ably prevents hydride-CD OD interaction. Thus, it becomes evi-
3
dent that bigger is better but without overshooting.
The steric and electronic properties of the 8-quinolinolate
ligand also have an impact on the catalytic performance. Modi-
fication of the bidentate O,N ligand led to a complex with
lower electronic density (complex 8) and to another complex
with greater steric hindrance close to the metal center (com-
1
2
of c, the steric hindrance imposed by the ligands in the com-
plex restricts this rotation (and the formation of d) due to re-
pulsion between the R group of the alkyl ligand and the sub-
stituents of the NHC. As a result, although a deuterium atom
Chem. Eur. J. 2014, 20, 1 – 14
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plex 9). Catalyst 8 bears two chloro substituents on the quino-
linolate skeleton, which decrease the electron density at the
metal center and thereby reduce the catalytic activity (entry 5),
yielding results comparable to those obtained with complex 5
Conclusions
III
III
A series of new hydride-Rh -NHC and ethyl-Rh -NHC com-
plexes containing different substituted quinolinolate or aceto-
nitrile donor ligands has been synthesized and fully character-
(entry 2). The case of complex 9, bearing a 2-methyl-8-quinoli-
III
nolate ligand, is slightly different. Catalyst 9 showed no catalyt-
ic activity at room temperature, and only moderate activity
and selectivity at 808C (entry 6). In this case, contrary to 7, the
ized. Both types of Rh -NHC complexes have been used as cat-
alysts for the H/D exchange of olefins using CD OD as a deute-
3
rium source. Most of these complexes proved to be very active
and selective in the vinylic H/D exchange of styrene, without
concomitant deuteration of the aromatic ring. Moreover, they
were able to catalyze deuteration at the vinylic b-positions
with very high selectivity.
hydride ligand in 9 was smoothly exchanged with CD OD.
3
Thus, the steric hindrance imposed by the quinolinolate ligand
apparently hampers olefin coordination.
The charge on each complex also influences its catalytic per-
2
formance. In fact, the catalyst precursor [RhH(k -O,N-C H NO)-
It has been observed that the NHC ligand plays an impor-
tant role in the catalytic activity and selectivity. In fact, among
9
6
(
IPr)(CH CN) ](PF ) (10), the cationic derivative of complex 4 ob-
3 2 6
2
tained by elimination of the chlorido ligand, showed no cata-
lytic activity at all (entry 7). In sharp contrast, the cationic
chlorido complex [RhClH(CH CN) (IPr)]CF SO (11) proved to be
the series [RhClH(k -O,N-C H NO)(NHC)], taking the IPr complex
9
6
as a reference, the complex bearing the most electron-donat-
ing carbene, SIPr, proved to be the most active catalyst, show-
ing outstanding selectivity for the b-vinylic positions, whereas
the introduction of a less electron-donating and less bulky car-
bene such as IMes decreased the catalytic activity and selectivi-
ty. On the other hand, complexes bearing carbenes with good
electron-donating properties but with large steric hindrance,
such as SPXyl, did not show any catalytic activity. The remain-
ing ligands also played an important role in determining the
catalytic properties. In fact, complexes without a chlorido
ligand were found to be inactive, and the introduction of an 8-
quinolinolate ligand with either an electron-withdrawing sub-
stituent or a bulky group near to the Rh reduced or completely
suppressed the catalytic activity, respectively. Replacement of
the chelating quinolinolate ligand by weakly bonded acetoni-
trile ligands increased the catalytic activity but decreased the
selectivity of the catalyst. In fact, the cationic complex [RhClH-
3
3
3
3
the most active catalyst precursor among all of those synthe-
sized (entry 8). This result suggests that the presence of a chlor-
ido ligand is essential for the activity of the catalyst. The role
III
of the chlorido ligand is most probably to stabilize the key Rh
catalytic species. In fact, it was observed that complex 10 de-
composed rapidly under the reaction conditions, leading to an
unidentified mixture of complexes incapable of catalyzing the
H/D exchange of styrene. This chlorido effect can also be ap-
preciated in the case of the complexes lacking an 8-quinolino-
late ligand and bearing more labile acetonitrile ligands. The ex-
cellent catalytic activity of 11 could also be related to the pres-
ence of labile acetonitrile ligands, which facilitates the olefin
coordination and insertion processes. However, this effect also
leads to a loss of selectivity (10% a-deuteration). The presence
of two chlorido ligands in the neutral complex [RhCl H-
2
+
(
(
CH CN) (IPr)] (12) resulted in a decrease in the catalytic activity
entry 9). Finally, the dicationic complex lacking a chloride
(CH CN) (IPr)] showed excellent catalytic activity, reaching the
3
2
3
3
maximum attainable degree of b-vinylic deuteration in only
III
ligand [RhH(CH CN) (IPr)](CF SO ) (13) was totally inactive
20 min. On the other hand, among the ethyl-Rh -IPr series,
3
4
3
3 2
(entry 10). As shown in Scheme 8, the insertion–elimination
complex [RhCl(CH CH )(8-quinolinolate)(IPr)] also showed good
2
3
mechanism operative for H/D exchange in olefins requires the
participation of active hydride species. On this basis, ethyl
catalytic activity, which can be rationalized by assuming an
equilibrium with a hydride-olefin species. In conclusion, this
work represents an in-depth study for developing improved
catalytic systems by ligand modification, which, along with the
understanding of the catalytic mechanism, should allow for
the design of better performing catalysts.
complexes 14–16 should be inactive. However, complex [RhCl-
2
(
CH CH )(k -O,N-C H NO)(IPr)] (14) was found to be only slight-
2
3
9
6
ly less active than its hydride counterpart 4 (entry 11). This can
be explained by assuming that such a species could be in
[
22]
equilibrium with a hydride-olefin species (Scheme 9).
Experimental Section
General information
All reactions were carried out with rigorous exclusion of air using
Schlenk-tube techniques. Organic solvents were obtained oxygen-
and water-free from a Solvent Purification System (Innovative Tech-
nologies), except for THF, which was dried over sodium and dis-
Scheme 9. Equilibrium between Rh-ethyl and Rh-H/ethylene species.
2
tilled under argon prior to use. The starting materials [Rh(m-Cl)(h -
As expected, the catalytic performance of the acetonitrile
complex 15 (entry 12) was identical to that of 14, since dissoci-
ation of the labile acetonitrile ligand produces the same active
species. Moreover, the dicationic catalyst precursor [Rh-
[
27]
2
[16b]
2
coe)2]2 (1),
[Rh(m-Cl)(IPr)(h -coe)] (2a),
[Rh(m-Cl)(IPr)(h -CH =
2
2
[16e]
2
[21]
2
CH )] (2b),
[Rh(m-OH)(IPr)(h -coe)] (2-OH), [Rh(m-Cl)(IMes)(h -
2
2
2
[16b]
2
[7j]
[18a]
[18a]
coe)]2 (3),
[RhClH(k -O,N-C H NO)(IPr)] (4),
IPr,
IMes,
9
6
[18c]
[18b]
[18d]
ICy,
SPXyl,
and SIPr
were prepared following the proce-
1
31
1
19
13
1
(
CH CH )(IPr)(CH CN) ](CF SO ) (16), which does not contain
dures described in the literature. H, P{ H}, F, and C{ H} NMR
spectra were recorded on either a Varian Gemini 2000, a Bruker
2
3
3
4
3
3 2
a chlorido ligand, proved to be completely inactive (entry 13).
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ARX 300, or a Bruker Avance 500 or 400 MHz instrument. Chemical
shifts (expressed in parts per million) are referenced to residual sol-
125.1 (all s; CHPh-SIPr), 129.6 (s; C6-Quin), 120.9 (s; C3-Quin), 114.3 (s; C7-
Quin), 111.1 (s; C5-Quin), 54.4 (s; CH2-SIPr), 29.5 and 29.4 (both s;
CHMeSIPr), 27.1, 27.0, 24.6, and 24.5 ppm (all s; CHMeSIPr).
1
13
1
31
1
19
vent peaks ( H, C{ H}) or external H PO ( P{ H}) or CFCl ( F).
3
4
3
1
1
Spectral assignments were achieved by a combination of H- H
1
3
1
1
13
COSY, C{ H}-APT, and H- C HSQC/HMBC experiments. C, H, and
N analyses were carried out with a Perkin–Elmer 2400 CHNS/O ana-
lyzer.
2
Preparation of [RhClH(k -O,N-C H NO)(SPXyl)] (7)
9
6
The complex was prepared as described for 6 starting from
(300 mg, 0.418 mmol), SPXyl (245 mg, 0.836 mmol), and 8-hy-
1
droxyquinoline (121 mg, 0.836 mmol), and was obtained as an
orange solid. Yield: 327 mg (68%); elemental analysis calcd (%) for
C H N ClORh: C 60.48, H 5.43, N 7.30; found: C 60.86, H 5.53, N
Catalytic H/D exchange
The appropriate catalyst (0.01 mmol) was dissolved in CD OD
3
29 31
3
1
(
0.5 mL) in an NMR tube and then the olefin (0.5 mmol) was
6.95; H NMR (500 MHz, [D ]toluene, 298 K): d=8.89 (dd, J =4.8,
8 H,H
1
added; the reaction course was monitored by H NMR spectrosco-
py. The H/D exchange was quantified on the basis of the decrease
in the integral of the olefin resonances compared to those of the
internal standard hexamethyldisiloxane (2 mL, 10 mmol). Successful
1.3 Hz, 1H; H2-Quin), 7.24 (dd, JH,H =8.3, 1.3 Hz, 1H; H4-Quin), 7.21 (dd,
JH,H =7.9, 7.8 Hz, 1H; H6-Quin), 6.9–6.6 (m, 6H; HPh-SPXyl), 7.05 (dd,
JH,H =7.8, 1.0 Hz, 1H; H7-Quin), 6.53 (dd, JH,H =7.9, 1.0 Hz, 1H; H5-Quin),
6.35 (dd, JH,H =8.3, JH,H =4.8 Hz, 1H; H3-Quin), 3.0–2.9 (m, 4H;
2
deuteration of the olefin was confirmed by H NMR spectroscopy.
CH NSPXyl), 2.64, 2.62, 2.55, and 2.56 (all s, 12H; Me6-Xyl), 1.76 and
2
1
.65 (both m, 2H; CH
), ꢀ27.94 ppm (d, 1H, J =44.4 Hz; H-
2-SPXyl
Rh,H
13
1
2
Rh); C{ H}-APT NMR (100.6 MHz, [D ]toluene, 298 K): d=200.9 (d,
8
Preparation of [RhClH(k -O,N-C H NO)(IMes)] (5)
9
6
JC,Rh =44.5 Hz; Rh-CSPXyl), 170.6 (s; C8-Quin), 147.2 and 139.0 (both s;
A yellow solution of 3 (300 mg, 0.271 mmol) in toluene (10 mL)
was treated with 8-hydroxyquinoline (79 mg, 0.542 mmol) and the
mixture was stirred at room temperature for 45 min. It was then
concentrated to a volume of about 1 mL, whereupon n-hexane
C N), 146.2 (s; C2-Quin), 145.1 (s; C8a-Quin), 137.0 (s; C4-Quin), 139.6,
q
139.4, 137.5, and 137.2 (all s; Cq-SPXyl), 129.8, 129.5, 129.3, 129.2,
128.9, and 128.5 (s; CHPh-SPXyl), 130.9 (s; C4a-Quin), 129.5 (s; C6-Quin),
120.8 (s; C3-Quin), 113.9 (s; C7-Quin), 110.7 (s; C5-Quin), 47.3 and 46.7
(
3 mL) was added to induce the precipitation of an orange solid,
(both s; CH NSPXyl), 21.9 (s; CH2-SPXyl), 19.8, 19.6, 18.8, and 18.7 ppm
2
which was washed with hexane (3”3 mL) and dried in vacuo.
Yield: 252 mg (79%); elemental analysis calcd (%) for
C H N ClORh: C 61.28, H 5.31, N 7.15; found: C 61.54, H 5.39, N
(all s; MeSPXyl).
3
0
31
3
2
Preparation of [RhClH(k -O,N-C H NOCl )(IPr)] (8)
1
9
4
2
7
4
7
1
6
1
.11; H NMR (400 MHz, [D ]toluene, 298 K): d=8.92 (d, J
.6 Hz, 1H; H2-Quin), 7.17 (d, JH,H =8.1 Hz, 1H; H4-Quin), 7.14 (dd, JH,H
=
=
8
H,H
The complex was prepared as described for 5 starting from 2a
(300 mg, 0.235 mmol) and 5,7-dichloro-8-hydroxyquinoline
(100 mg, 0.470 mmol), and was isolated as an orange solid. Yield:
272 mg (78%); elemental analysis calcd (%) for C H N Cl ORh: C
.8, 7.7 Hz, 1H; H6-Quin), 6.68 (br, 4H; HPh-IMes), 7.04 (d, JH,H =7.7 Hz,
H; H7-Quin), 6.39 (s, 2H; =CHN), 6.48 (d, JH,H =7.8 Hz, 1H; H5-Quin),
.29 (dd, JH,H =8.1, 4.6 Hz, 1H; H3-Quin), 2.47, 2.44, and 1.90 (all s,
36
41
3
3
1
13
1
8H; MeIMes), ꢀ28.49 ppm (d, 1H, J =46.0 Hz; H-Rh); C{ H}-APT
58.35, H 5.58, N 5.67; found: C 58.74, H 5.40, N 5.59; H NMR
Rh,H
NMR (100.6 MHz, [D ]toluene, 298 K): d=177.5 (d, J =49.7 Hz;
(300 MHz, C D , 298 K): d=8.85 (d, J =4.4 Hz, 1H; H2-Quin), 7.65 (s,
8
C,Rh
6
6
H,H
Rh-C ), 171.1 (s; C8-Quin), 146.5 (s; C2-Quin), 145.5 (s; C8a-Quin), 139.6,
1H; H6-Quin), 7.65 (d, JH,H =8.1 Hz, 1H; H4-Quin), 7.2–7.0 (m, 6H; HPh-IPr),
6.75 (s, 2H; =CHN), 6.18 (dd, JH,H =8.1, JH,H =4.4 Hz, 1H; H3-Quin),
IPr
1
37.8, and 137.5 (all s; Cq-IMes), 137.6 (s; C N), 137.1 (s; C4-Quin), 130.9
q
(
(
1
s; C4a-Quin), 129.9 and 129.8 (both s; CHPh-IMes), 129.5 (s; C6-Quin), 123.4
s; =CHN), 120.8 (s; C3-Quin), 114.4 (s; C7-Quin), 111.3 (s; C5-Quin), 21.3,
8.9, and 18.8 ppm (all s; MeIMes).
3.42 and 3.40 (both sept, JH,H =6.8 Hz, 4H; CHMe ), 1.58, 1.56, 1.16,
IPr
and 1.15 (all d, JH,H =6.8 Hz, 24H; CHMe ), ꢀ27.81 ppm (d, 1H,
IPr
13
1
JRh,H =43.6 Hz; H-Rh); C{ H}-APT NMR (75.4 MHz, C D , 298 K): d=
6 6
1
76.7 (d, JC,Rh =49.2 Hz; Rh-C ), 164.9 (s; C8-Quin), 147.6 and 147.5
IPr
2
(both s; Cq-IPr), 147.4 (s; C2-Quin), 145.5 (s; C8a-Quin), 137.9 (s; C
N),
q
Preparation of [RhClH(k -O,N-C H NO)(SIPr)] (6)
9
6
1
33.9 (s; C4-Quin), 130.8, 125.7, and 124.5 (s; CHPh-IPr), 129.6 (s; C6-Quin),
A yellow suspension of 1 (300 mg, 0.418 mmol) in THF (10 mL) was
125.1 (s; =CHN), 121.2 (s; C3-Quin), 117.6 (s; C7-Quin), 112.9 (s; C5-Quin),
treated with SIPr (327 mg, 0.838 mmol) and 8-hydroxyquinoline
126.6 (s; C4a-Quin), 29.0 and 28.9 (both s; CHMe ), 26.3, 26.2, 23.6,
IPr
(
121 mg, 0.836 mmol) and the mixture was stirred at room temper-
and 23.4 ppm (all s; CHMeIPr).
ature for 30 min. The resulting orange solution was then concen-
trated to dryness, the residue was redissolved in toluene (10 mL),
and the solution was filtered through a bed of Celite. The filtrate
was concentrated to a volume of about 1 mL and then n-hexane
2
Preparation of [RhClH(k -O,N-C H NOCH )(IPr)] (9)
9
5
3
A yellow solution of 2a (300 mg, 0.235 mmol) in toluene (10 mL)
was treated with 2-methyl-8-hydroxyquinoline (75 mg, 0.470 mmol)
and the mixture was stirred at 808C for 2 h. It was then concentrat-
ed to a volume of about 1 mL, whereupon n-hexane (3 mL) was
added to induce the precipitation of an orange solid, which was
washed with hexane (3”3 mL) and dried in vacuo. Yield: 229 mg
(71%); elemental analysis calcd (%) for C H N ClORh: C 64.77, H
(
3 mL) was added to induce the precipitation of an orange solid,
which was washed with hexane (3”3 mL) and dried in vacuo.
Yield: 231 mg (73%); elemental analysis calcd (%) for
C H N ClORh: C 64.14, H 6.73, N 6.23; found: C 64.56, H 6.85, N
3
6
45
1
3
6
.15; H NMR (300 MHz, C D , 298 K): d=8.97 (d, J =4.3 Hz, 1H;
6 6 H,H
H2-Quin), 7.19 (dd, JH,H =7.7, 7.4 Hz, 1H; H6-Quin), 7.12 (d, JH,H =8.1 Hz,
37
45
3
1
1
6
H; H4-Quin), 7.10 (m, 6H; HPh-SIPr), 7.07 (d, JH,H =7.4 Hz, 1H; H7-Quin),
.50 (d, JH,H =7.7 Hz, 1H; H5-Quin), 6.24 (dd, JH,H =8.1, 4.3 Hz, 1H; H3-
6.61, N 6.12; found: C 65.04, H 6.93, N 6.12; H NMR (300 MHz,
C D , 298 K): d=7.23 (dd, J =7.9, 7.8 Hz, 1H; H6-Quin), 7.17 (d,
6
6
H,H
Quin), 3.90 and 3.87 (both sept, JH,H =6.6 Hz, 4H; CHMeSIPr), 3.83 (m,
H; CH2-SIPr), 1.64, 1.62, 1.25, and 1.22 (all d, JH,H =6.6 Hz, 24H;
JH,H =8.4 Hz, 1H; H4-Quin), 7.2–7.0 (m, 6H; HPh-IPr), 7.08 (dd, JH,H =7.9,
1.0 Hz, 1H; H7-Quin), 6.75 (s, 2H; =CHN), 6.60 (dd, JH,H =7.8, 1.0 Hz,
1H; H5-Quin), 6.15 (d, JH,H =8.4 Hz, 1H; H3-Quin), 3.57 and 3.51 (both br,
4
13
1
CHMeSIPr), ꢀ28.61 ppm (d, 1H, J =47.3 Hz; H-Rh); C{ H}-APT
Rh,H
NMR (75.4 MHz, C D , 298 K): d=208.2 (d, J =44.7 Hz; Rh-CSIPr),
4H; CHMe ), 2.78 (s, 1H; CH3-Quin), 1.56, 1.54, 1.15, and 1.14 (all d,
6
6
C,Rh
IPr
1
1
70.9 (s; C8-Quin), 148.9 (s; Cq-SIPr), 146.5 (s; C2-Quin), 145.2 (s; C8a-Quin),
JH,H =6.8 Hz, 24H; CHMe ), ꢀ28.43 ppm (d, 1H, J =45.2 Hz; H-
IPr
Rh,H
13
1
37.2 (s; C4-Quin), 136.1 (s; C N), 130.8 (s; C4a-Quin), 130.3, 125.2, and
Rh); C{ H}-APT NMR (75.4 MHz, C D , 298 K): d=175.7 (d, J
=
q
6
6
C,Rh
Chem. Eur. J. 2014, 20, 1 – 14
www.chemeurj.org
9
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
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These are not the final page numbers! ÞÞ

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13
1
5
1.6 Hz; Rh-C ), 170.5 (s; C8-Quin), 162.3 (s; C2-Quin), 148.1 and 148.0
8.5 Hz, 1H; H-Rh); C{ H}-APT NMR (100.6 MHz, CD CN, 253 K): d=
IPr
3
(
both s; Cq-IPr), 144.4 (s; C8a-Quin), 137.5 (s; C4-Quin), 137.2 (s; C N),
167.0 (d, JC,Rh =49.9 Hz; Rh-C ), 147.6 and 147.3 (both s; Cq-IPr),
q
IPr
1
31.0, 124.8, and 124.7 (s; CHPh-IPr), 129.1 (s; C4a-Quin), 128.3 (s; C6-
138.1 and 137.0 (both s; C N), 130.4 and 129.7 (both s; Cp-Ph-IPr),
q
Quin), 125.1 (s; =CHN), 124.4 (s; C3-Quin), 115.1 (s; C7-Quin), 111.4 (s; C5-
126.7 and 125.5 (both s; =CHN), 123.7 and 125.5 (both s; Cm-Ph-IPr),
Quin), 29.4 and 29.3 (both s; CHMe ), 27.3 (s; CH3-Quin), 26.9, 26.8,
28.3 and 28.2 (both s; CHMe ), 25.3, 25.2, 22.4, and 22.3 ppm (all
IPr
IPr
2
3.9, and 23.8 ppm (all s; CHMeIPr).
s; CHMeIPr).
2
Preparation of [RhH(k -O,N-C H NO)(IPr)(CH CN) ]PF (10)
Preparation of [RhH(CH
A yellow suspension of 2-OH (300 mg, 0.242 mmol) in CH CN
3
3 4 2
CN) (IPr)](OTf) (13)
9
6
3
2
6
An orange solution of 4 (150 mg, 0.223 mmol) in CH CN (5 mL)
3
was treated with TlPF (78 mg, 0.223 mmol) and the mixture was
(10 mL) at ꢀ208C was treated with HOTf (175 mL, 1.455 mmol) and
the mixture was stirred at low temperature for 15 min. The result-
ing pale-yellow solution was concentrated to a volume of about
1 mL, whereupon cold (ꢀ208C) diethyl ether was added to induce
the precipitation of a white solid, which was washed with diethyl
ether (3”4 mL) and dried in vacuo. Yield: 508 mg (91%); elemental
6
stirred at room temperature for 15 min. The resulting suspension
was then filtered through a Celite bed. The filtrate was concentrat-
ed to dryness and the residue was triturated with diethyl ether to
give an orange solid, which was washed with diethyl ether (3”
2
mL) and dried in vacuo. Yield: 131 mg (68%); elemental analysis
calcd (%) for C H N ORhPF : C 55.62, H 5.72, N 8.11; found: C
analysis calcd (%) for C37
6.72; found: C 46.19, H 4.98, N 8.72, S 6.92; H NMR (400 MHz,
CD CN, 298 K): d=7.68 (t, JH,H =7.5 Hz, 2H; Hp-Ph-IPr), 7.52 (t, JH,H =
H N F O S Rh: C 46.54, H 5.17, N 8.80, S
49 6 6 6 2
4
0
49
5
1
6
1
5
5.86, H 5.88, N 8.05; H NMR (400 MHz, CD CN, 298 K): d=8.40 (d,
3
JH,H =4.7 Hz, 1H; H2-Quin), 8.20 (d, JH,H =8.4 Hz, 1H; H4-Quin), 7.54 (s,
3
2
8
1
2
H; =CHN), 7.36 (dd, JH,H =8.4, 4.7 Hz, 1H; H3-Quin), 7.24 (dd, JH,H
.1, 8.0 Hz, 1H; H6-Quin), 7.5–7.3 (m, 6H; HPh-IPr), 6.87 (dd, JH,H =8.1,
.0 Hz, 1H; H5-Quin), 6.69 (dd, JH,H =8.0, 1.0 Hz, 1H; H7-Quin), 2.85 and
=
7.5 Hz, 4H; Hm-Ph-IPr), 7.65 (s, 2H; =CHN), 2.38 (sept, JH,H =6.8 Hz,
4H; CHMeIPr), 1.32 and 1.14 (both d, JH,H =6.8 Hz, 24H; CHMeIPr),
13
1
ꢀ15.38 ppm (d,
(100.6 MHz, CD CN, 298 K): d=153.8 (d, JC,Rh =46.7 Hz; Rh-CIPr),
147.1 (s; C ), 136.4 (s; C N), 132.7 (s; Cp-Ph-IPr), 128.9 (s; =CHN), 125.6
(s; Cm-Ph-IPr), 122.0 (q, JC,F =321.0 Hz; CF ), 29.8 (s; CHMeIPr), 26.0 and
J
Rh,H =7.3 Hz, 1H; H-Rh);
C{ H}-APT NMR
.84 (both sept, JH,H =6.8 Hz, 4H; CHMe ), 1.30, 1.23, 1.19, and 1.17
3
IPr
(
all d, JH,H =6.8 Hz, 24H; CHMe ), ꢀ17.52 ppm (d, 1H, J
=
Rh,H
q
q
IPr
1
3
1
2
1
1
1
1.1 Hz; H-Rh); C{ H}-APT NMR (100.6 MHz, CD CN, 298 K): d=
3
3
19
71.3 (s; C8-Quin), 169.6 (br; Rh-C ), 148.1 and 148.0 (both s; Cq-IPr),
22.7 ppm (both s; CHMeIPr); F NMR (376 MHz, CD
ꢀ79.2 ppm (s; OTf).
CN, 298 K): d=
3
IPr
46.8 (s; C2-Quin), 144.4 (s; C8a-Quin), 138.8 (s; C4-Quin), 138.3 (s; C N),
q
31.7, 125.5, and 125.4 (s; CHPh-IPr), 131.4 (s; C4a-Quin), 130.7 (s; C6-
Quin), 127.4 (s; =CHN), 125.0 (s; C3-Quin), 115.3 (s; C7-Quin), 112.0 (s; C5-
2
Preparation of [RhCl(CH CH )(k -O,N-C H NO)(IPr)] (14)
2
3
9
6
Quin), 29.7 and 29.6 (both s; CHMe ), 26.1, 26.0, 23.5, and 23.4 ppm
IPr
1
3
(
all s; CHMeIPr);
P NMR (121.5 MHz, CD CN, 298 K): d=
The complex was prepared as described for 5 starting from 2b
(300 mg, 0.270 mmol) and 8-hydroxyquinoline (78 mg,
.540 mmol), and was obtained as an orange solid. Yield: 325 mg
86%); elemental analysis calcd (%) for C H N ClORh: C 65.19, H
.77, N 6.00; found: C 65.56, H 6.32, N 6.24; H NMR (400 MHz,
, 298 K): d=9.17 (d, JH,H =4.7 Hz, 1H; H2-Quin), 7.31 (d, JH,H =
3
ꢀ
144.6 ppm (sept, JP,F =706.6 Hz; PF6).
0
(
6
38
47
3
1
Preparation of [RhClH(CH CN) (IPr)]OTf (11)
3
3
A yellow suspension of 2a (300 mg, 0.270 mmol) in CH CN (10 mL)
C
6
D
6
3
at 253 K was treated with HOTf (48 mL, 0.540 mmol) and the mix-
ture was stirred at low temperature for 15 min. The resulting solu-
tion was concentrated to a volume of about 1 mL, whereupon
cold (ꢀ208C) diethyl ether was added to induce the precipitation
of a white solid, which was washed with diethyl ether (3”4 mL)
and dried in vacuo. Yield: 315 mg (73%); elemental analysis calcd
8.5 Hz, 1H; H4-Quin), 7.29 (dd, JH,H =7.9, 7.8 Hz, 1H; H6-Quin), 7.06 (m,
6H; HPh-IPr), 7.13 (dd, JH,H =7.8, 1.0 Hz, 1H; H7-Quin), 6.71 (s, 2H; =
CHN), 6.61 (dd, JH,H =7.9, 1.0 Hz, 1H; H5-Quin), 6.39 (dd, JH,H =8.5,
4.7 Hz, 1H; H3-Quin), 3.62 and 3.09 (both ddq, JH,H =7.3, 7.1 Hz, JRh,H
=
3.2 Hz, 2H; CH2-Ethyl), 3.50 and 3.49 (both sept, JH,H =6.6 Hz, 4H;
CHMeIPr), 1.65, 1.41, 1.15, and 1.08 (all d, JH,H =6.6 Hz, 24H; CHMeIPr),
13
1
(
%) for C H N F ClO SRh: C 51.03, H 5.79, N 8.75, S 4.00; found: C
ꢀ0.27 ppm (dvt, JRh,H =1.5 Hz, N=14.6 Hz, 3H; CH3-Ethyl); C{ H}-APT
NMR (100.6 MHz, C , 298 K): d=174.5 (d, JC,Rh =51.8 Hz; Rh-CIPr),
171.5 (s; C8-Quin), 147.8 and 147.5 (both s; Cq-IPr), 146.6 (s; C2-Quin),
145.2 (s; C8a-Quin), 137.1 (s; C4-Quin), 136.2 (s; C N), 131.0 (s; C4a-Quin),
3
4
46
5
3
3
1
5
7
7
1.30, H 6.04, N 8.43, S 4.12; H NMR (400 MHz, CD CN, 298 K): d=
D
6 6
3
.59 (t, JH,H =7.8 Hz, 2H; Hp-Ph-IPr), 7.46 (d, JH,H =7.8 Hz, 4H; Hm-Ph-IPr),
.44 (s, 2H; =CHN), 2.69 and 2.68 (both sept, JH,H =6.8 Hz, 4H;
q
CHMe ), 1.30, 1.29, 1.11, and 1.08 (all d, J =6.8 Hz, 24H; CHMe ),
130.9, 124.5, and 124.2 (all s; CHPh-IPr), 129.9 (s; C6-Quin), 125.7 (s; =
CHN), 120.1 (s; C3-Quin), 115.1 (s; C7-Quin), 110.8 (s; C5-Quin), 29.5 and
29.4 (both s; CHMeIPr), 27.1, 26.8, 23.6, and 23.5 (all s; CHMeIPr), 21.0
(d, JRh,C =28.4 Hz; CH2-Ethyl), 20.6 ppm (s; CH3-Ethyl).
IPr
H,H
IPr
13
1
ꢀ
17.05 ppm (d, JRh,H =8.4 Hz, 1H; H-Rh);
C{ H}-APT NMR
(
100.6 MHz, CD CN, 298 K): d=161.2 (d, J =49.1 Hz; Rh-CIPr),
3
C,Rh
1
47.2 (both s; Cq-IPr), 137.4 (s; C N), 131.7 (s; Cp-Ph-IPr), 127.5 (s; =
q
CHN), 125.0 (s; Cm-Ph-IPr), 122.1 (q, JC,F =321.2 Hz; CF ), 29.5 and 29.4
3
(
both s; CHMe ), 26.2, 25.9, 23.0, and 22.3 ppm (all s; CHMe );
2
IPr
IPr
Preparation of [RhCl(CH CH )(k -O,N-C H NO)(IPr)(CH CN)]
2
3
9
6
3
1
9
F NMR (376 MHz, CD CN, 298 K): d=ꢀ78.2 ppm (s; OTf).
3
(
15)
An orange solution of 14 (100 mg, 0.143 mmol) in toluene/CH CN
3
Preparation of [RhCl H(CH CN) (IPr)] (12)
2
3
2
(1:1, v/v; 5 mL) was stirred at room temperature for 30 min. It was
The complex was prepared as described for 11 starting from 2a
300 mg, 0.270 mmol) and 37% aqueous HCl (44 mL, 0.540 mmol).
then concentrated to dryness and subsequent trituration of the
residue with hexane induced the precipitation of an orange solid,
which was washed with hexane (3”2 mL) and dried in vacuo.
Yield: 84 mg (80%); elemental analysis calcd (%) for C H N ClORh:
(
A white solid was obtained. Yield: 223 mg (64%); elemental analy-
sis calcd (%) for C H N Cl Rh: C 57.68, H 6.71, N 8.68; found: C
3
1
43
1
4
2
40 50
4
1
5
2
3
8.06, H 6.88, N 8.61; H NMR (400 MHz, CD CN, 253 K): d=7.52 (m,
H; Hp-Ph-IPr), 7.39 (m, 4H; Hm-Ph-IPr), 7.26 and 7.25 (br, 2H; =CHN),
C 64.33, H 6.45, N 7.25; found: C 64.82, H 6.80, N 7.56; H NMR
3
(400 MHz, C D /CD CN, 4:1, 298 K): d=9.08 (d, J =4.2 Hz, 1H; H2-
6
6
3
H,H
.14 and 2.85 (both sept, JH,H =6.6 Hz, 4H; CHMe ), 1.27, 1.26, 1.05,
Quin), 7.76 (d, JH,H =8.1 Hz, 1H; H4-Quin), 7.32 (s, 2H; =CHN), 7.30 (dd,
JH,H =7.9, 7.8 Hz, 1H; H6-Quin), 7.2–7.1 (m, 6H; HPh-IPr), 7.04 (d, JH,H =
IPr
and 1.02 (all d, JH,H =6.6 Hz, 24H; CHMe ), ꢀ18.63 ppm (d, J
=
Rh,H
IPr
&
&
Chem. Eur. J. 2014, 20, 1 – 14
www.chemeurj.org
10
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
7
.9 Hz, 1H; H7-Quin), 6.90 (dd, JH,H =8.1, 4.2 Hz, 1H; H3-Quin), 6.78 (d,
JH,H =7.8 Hz, 1H; H5-Quin), 3.35 and 2.98 (both m, 2H; CH2-Ethyl), 3.44
br, 4H; CHMe ), 1.60, 1.34, 1.24, and 1.16 (all d, J =6.5 Hz, 24H;
Crystal data for complex 16
C H F N O RhS ·CH Cl ; M =1067.83; colorless block; 0.162”
39
53
6
6
6
2
2
2
r
(
IPr
H,H
3
0
.070”0.057 mm ; triclinic; P 1¯ ; a=12.134(7), b=12.587(7), c=
CHMe ), 1.43 (s; CH CN), ꢀ0.44 ppm (dvt, J =1.5 Hz, N=
IPr
3
1
Rh,H
3
1
16.471(9) Š; a=87.112(10), b=78.900(9), g=83.677(10)8; Z=2; V=
1
4
1
1
1
4.0 Hz, 3H; CH
); C{ H}-APT NMR (100.6 MHz, C D /CD CN,
-Ethyl 6 6 3
3
3
ꢀ3
ꢀ1
2
452(2) Š ; 1 =1.446 gcm ; m=0.614 mm , min. and max.
calcd
:1, 298 K): d=172.4 (d, JC,Rh =50.2 Hz; Rh-C ), 170.9 (s; C8-Quin),
IPr
transmission factors: 0.907 and 0.956; 2qmax =50.008; 24575 reflec-
tions collected, 8587 unique [Rint =0.1047]; numbers of data/re-
47.5 and 147.1 (both s; Cq-IPr), 145.9 (s; C2-Quin), 144.6 (s; C8a-Quin),
37.1 (s; C4-Quin), 135.8 (s; C N), 130.6 (s; C4a-Quin), 130.5, 124.1, and
q
straints/parameters: 8587/0/577; final GoF: 1.074, R =0.0851 [5841
1
23.7 (all s; CHPh-IPr), 129.6 (s; C6-Quin), 126.0 (s; =CHN), 121.0 (s; C3-
reflections, I>2s(I)], wR =0.1863 for all data; largest difference
2
Quin), 116.9 (s; CH CN), 114.7 (s; C -Quin), 110.4 (s; C -Quin), 29.1 and
2
3
7
5
3
peak: 1.162 eŠ . The fluorine atoms of the triflate anions showed
9.1 (both s; CHMe ), 26.4, 26.1, 23.0, and 22.9 (all s; CHMe ), 20.0
IPr IPr
high thermal parameters; static disorder was included for one of
these anions. A dichloromethane solvent molecule was also ob-
served in the crystal structure; both chlorine atoms were also in-
cluded in a disordered model with complementary occupancy fac-
tors (0.674/0.326(19)). All of the relevant highest residual density
peaks were found close to the metal atom, with no chemical
sense.
(
d, JRh,C =28.5 Hz; CH2-Ethyl), 19.9 (s; CH3-Ethyl), 0.28 ppm (s; CH CN).
3
Preparation of [Rh(C H )(CH CN) (IPr)](OTf) (16)
2
5
3
3
2
A yellow suspension of 3 (300 mg, 0.270 mmol) in CH CN (10 mL)
3
at ꢀ208C was treated with trifluoromethanesulfonic acid (96 mL,
1
1
.080 mmol) and the mixture was stirred at low temperature for
5 min. The resulting pale-yellow solution was concentrated to
CCDC-989941 (4) and 989942 (16) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
a volume of about 1 mL, whereupon cold (ꢀ208C) diethyl ether
was added to induce the precipitation of a white solid, which was
washed with diethyl ether (3”4 mL) and dried in vacuo. Yield:
4
17 mg (79%); elemental analysis calcd (%) for C H N F O S Rh: C
39 53 6 6 6 2
4
7.66, H 5.44, N 8.55, S 6.52; found: C 47.99, H 5.51, N 8.60, S 6.75;
1
H NMR (400 MHz, CD CN, 298 K): d=7.56 (t, JH,H =7.7 Hz, 2H; Hp-Ph-
3
Acknowledgements
IPr), 7.46 (t, JH,H =7.7 Hz, 4H; Hm-Ph-IPr), 7.33 (s, 2H; =CHN), 2.76 (dq,
JRh,H =2.2 Hz, JH,H =7.4 Hz, 2H; CH2-Ethyl), 2.67 (sept, JH,H =6.8 Hz, 4H;
CHMe ), 1.40 and 1.13 (both d, J =6.5 Hz, 24H; CHMe ),
Financial support from the Spanish Ministerio de Economía y
Competitividad (MEC/FEDER) under the Project CTQ2010–
15221, the Diputación General de Aragón (E07) and Fondo
Social Europeo, the ARAID Foundation, and the CONSOLIDER
INGENIO-2010 under the Project MULTICAT (CSD2009–00050) is
gratefully acknowledged.
IPr
H,H
IPr
13
1
0
.95 ppm (t, JH,H =7.4 Hz, 3H; CH3-Ethyl);
C{ H}-APT NMR
(
100.6 MHz, CD CN, 298 K): d=150.3 (d, J =52.2 Hz; Rh-CIPr),
3
C,Rh
1
47.2 (both s; Cq-IPr), 137.3 (s; C N), 133.1 (s; Cp-Ph-IPr), 129.0 (s; =
q
CHN), 125.6 (s; Cm-Ph-IPr), 122.1 (q, JC,F =321.2 Hz; CF ), 29.9 (s;
3
CHMeIPr), 26.0 and 23.0 (both s; CHMeIPr), 19.8 (s; CH3-Ethyl), 18.4 ppm
19
(
d, JRh,C =17.6 Hz; CH2-Ethyl); F NMR (376 MHz, CD CN, 298 K): d=
3
ꢀ
78.2 ppm (s; OTf).
Keywords: alkenes
· deuteration · H/D exchange · N-
heterocyclic carbenes · rhodium
Crystal structure determination for complexes 4 and 16
X-ray diffraction data were collected at 100(2) K on a Bruker SMART
APEX CCD (complex 16) or a Bruker APEX II (complex 4) area de-
tector diffractometer using graphite-monochromated MoKa radia-
tion (l=0.71073 Š) and narrow w rotations (0.38). Intensities were
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C H ClN ORh·C H ; M =764.23; orange prism; 0.167”0.136”
3
6
43
3
3
7
8
r
0
2
1
0
.130 mm ; monoclinic; P2 /n; a=13.1379(10), b=13.8002(11), c=
1
3
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=
ꢀ3
ꢀ1
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9
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Chem. Eur. J. 2014, 20, 1 – 14
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11
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&
&
These are not the final page numbers! ÞÞ

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D and 12.3 mmol of D are present. For this reason, the maximum grade
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Received: March 6, 2014
Published online on && &&, 0000
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FULL PAPER
&
Carbene Catalysis
A. Di Giuseppe,* R. Castarlenas,*
J. J. Pꢁrez-Torrente, F. J. Lahoz, L. A. Oro*
&& – &&
Hydride-Rhodium(III)-N-Heterocyclic
Carbene Catalysts for Vinyl-Selective
H/D Exchange: A Structure–Activity
Study
III
A series of H-Rh -NHC complexes with
tween steric hindrance and electron
donation provides a catalytic system
with outstanding activity and total se-
lectivity for deuteration at b-vinyl posi-
tions.
different ancillary ligands has been syn-
thesized and evaluated as catalyst pre-
cursors in H/D exchange of a-olefins
(
see figure). An adequate balance be-
&
&
Chem. Eur. J. 2014, 20, 1 – 14
www.chemeurj.org
14
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!