Amidato complexes of ruthenium, rhodium and iridium from concise N-H bond activation: Exploration in catalysis

Article abstract of DOI:10.1016/j.tet.2015.03.028

Acceptor-substituted N-H groups as found in carbamides and sulfonamides are readily activated through suitable unsaturated metal complexes applying the concept of metal-ligand bifunctionality. This process constitutes the basis for an enantioselective int

Full text of DOI:10.1016/j.tet.2015.03.028

Tetrahedron 71 (2015) 4465e4472
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Amidato complexes of ruthenium, rhodium and iridium from
concise NeH bond activation: exploration in catalysis
R. Martín Romero a, Laura Fra a, Anton Lishchynskyi a, Claudio Martínez a, Jan Streuff b,
a,c,
*
~
Kilian Muniz
a Institut for Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona, Spain
b
€
€
Institut fur Organische Chemie, Albert-Ludwigs-Universitat Freiburg, Albertstr. 21, 79104 Freiburg, Germany
c Catalan Institution for Research and Advanced Studies (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Acceptor-substituted NeH groups as found in carbamides and sulfonamides are readily activated through
suitable unsaturated metal complexes applying the concept of metaleligand bifunctionality. This process
constitutes the basis for an enantioselective intramolecular addition of NeH groups onto activated al-
kenes. The resulting compounds can also be employed as catalyst precursors for transferhydrogenation.
Ó 2015 Published by Elsevier Ltd.
Received 2 February 2015
Received in revised form 5 March 2015
Accepted 6 March 2015
Available online 25 March 2015
Keywords:
Amination
Bond activation
Enantioselective catalysis
Metaleligand bifunctionality
Transition metals
1. Introduction
be competent centers to carry out the activation of NeH bonds.5 As
a result, such concepts are widely sought after and have been ex-
The transition metal catalyzed hydroamination of alkenes rep-
resents a versatile approach toward the synthesis of alkyl-nitrogen
bonds.1 In particular, the intramolecular version2 of this reaction
provides an efficient entry towards aminated cycloalkanes and
derivatives thereof, which are of interest as building blocks in the
synthesis of molecules with pharmaceutical, medicinal or bi-
ological interest.3
These reactions are also considered to be of perfect atom eco-
nomic nature,4 as the addition of an NeH bond across an alkene
essentially does not generate any by-products. In the best of all
cases, enantioselective catalytic hydroamination reactions do only
require the presence of the corresponding catalyst in the presence
of otherwise neutral conditions.4
plored to an impressive extent using engineered metal ligand
frameworks6 and related transition metal reactivity.7
One of the best activation-transfer systems known in literature
is the seminal transfer-hydrogenation system of Noyori.8 The
employed ruthenium catalyst simultaneously transfers a proton
and a hydride anion of secondary alcohols by formation of
a hydridic H-metal bond and a protic NeH bond at the ligand. The
formed species is then capable to enantioselectively and reversibly
transfer this activated ‘hydrogen’ to prochiral ketones, achieving
high ee and high turnover numbers at room temperature. Some
time ago, we reported on the application of this system for a se-
lective metaleligand bifunctional NeH bond activation making use
of the parent coordinatively unsaturated ruthenium complexes 1.9
The ruthenium center in 1 results to be Lewis-acidic enough to
accept the nucleophilic nitrogen while the activated nitrogen of the
ligand-backbone displays sufficient basicity to deprotonate the
NeH group of the substrate within the metal ligand coordination
sphere. The corresponding chiral-at-ruthenium complexes 2 were
formed as single diastereoisomers in good isolated yields and
within comparably short reaction times (Scheme 1).
Within the many concepts to activate NeH bonds in order to
generate the required reactivity for addition to an alkene, un-
saturated transition metal complexes have been demonstrated to
* Corresponding author. Tel./fax: þ34 977 920 813; e-mail address: kmuniz@iciq.
~
es (K. Muniz).
http://dx.doi.org/10.1016/j.tet.2015.03.028
0040-4020/Ó 2015 Published by Elsevier Ltd.

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R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
Scheme 1. Application of the metal ligand bifunctionality towards NeH activation.
Complexes of type 2 were then shown to be involved as suitable
catalyst states in new intramolecular CeN bond forming reactions.9
We here give a full account on the synthesis of additional amidato
metal complexes based on central rhodium and iridium atoms and
their exploration in aza-Michael addition reactions. In addition, we
discuss the application of amidato complexes of ruthenium, rho-
dium and iridium as catalyst precursors in the Noyori
transferhydrogenation.
2. Results and discussion
A logical extension of the use of pseudo-tetrahedral ruthenium
complexes consists in investigating the behavior of structurally
related rhodium and iridium complexes. These complexes could
indeed be accessed following a general two-step approach that
consists of a preformation of the coordinatively unsaturated com-
plexes 3, 5 and 7 containing rhodium and iridium as metal centers
and different monotosylated diamine ligands in order to demon-
strate the structural diversification that can be employed for
ligand-metal bifunctional NeH activation (Scheme 2).10 In contrast
to the facile synthesis of the parent ruthenium complexes 1,9 rho-
dium complexes 3 (green color) and 5 (yellow-red color) are less
stable both thermally and in the presence of air, respectively, and
should be submitted to reaction within short periods after their
synthesis. Unlike the rhodium precursors, iridium complex 7 (deep
purple color) can be handled with less care. All these activated
complexes are formally of unsaturated coordination and undergo
rapid and irreversible NeH bond activation in solution, which is
complete within seconds. No change in reactivity is observed and
the complexes 4aec, 6a and 8aec are isolated by simple evapora-
tion of solvent. Although in isolated form these products are stable
at room temperature over at least one week, the rhodium de-
rivatives 4aec and 6a are unstable in solution and sensitive to
column chromatography and need to be purified by crystallization
if impurities had formed over time.
It is noteworthy that all rhodium and iridium complexes are
formed as single diastereoisomers. As the step of NeH activation
within the metal ligand bifunctional motif results in the formation
of additional stereogenicity at the metal center, the present ap-
proach provides a unique entry into chiral-at-metal complexes
with defined absolute chirality.
To confirm the expected relative stereochemistry at the newly
created metal stereocentres, two of the product complexes were
submitted to X-ray analysis. As expected, both compounds 4a and
8a displayed an (S)-configuration in dependence of the (R,R)-eth-
ylene diamine ligand (Fig. 1).11 This outcome matches the one from
the NeH activation products of the corresponding ruthenium series
that had been reported earlier by our group. Obviously, these re-
sults are reminiscent of the seminal investigation of Noyori on the
stereochemical basis of chiral-at-ruthenium hydride complexes
that are the active catalysts in transferhydrogenation and hydro-
genation reactions.12 In addition, it confirms that the motif of un-
saturated compounds 1, 3, 5 and 7 does exercise efficient control
Scheme 2. Application of the metaleligand bifunctional NeH activation in the syn-
thesis of novel amidato complexes of rhodium and iridium.
within the activation of polar groups within the metaleligand bi-
functional activation.
The single stereoisomeric products are configurationally stable
within the common temperature range. To demonstrate this con-
text, variable temperature 1H NMR spectra were recorded for
iridium complex 8a. Fig. 2 displays representative spectra from
temperature range between T¼213e323 K. At all these tempera-
tures, only a single set of signals was observed, which is in agree-
ment with the expected stereochemical stability at the metal center
(Fig. 2).
In order to explore the capability of the new complexes as chiral
catalyst states in the previously described intramolecular aza-
Michael reaction,9 they were screened for the cyclization of the
standard substrate 9a to 10a. For this particular transformation, the
corresponding ruthenium complex 1a yielded 10a in 90% yield and
45% ee (Table 1, entry 1). The corresponding unsaturated rhodium
complexes 3 and 5 gave very good chemical yields, but comparably
low enantioselectivities (entries 2 and 3, respectively). Attempts to
employ the preformed amido complexes 4a and 6a, respectively,
did not result in any reactivity (entries 4,5). In contrast, the iridium
complex 7 catalyzed the formation of 10 in excellent yield and al-
ready 36% ee (entry 6). Interestingly, a similar result was obtained
when the reaction was started from the amido complex 8a (entry
7), which under the conditions obviously is capable of reverting
back to complex 7. This behavior is not observed for related

R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
4467
Fig. 2. Variable temperature 1H NMR spectra for iridium complex 8a (500 MHz, values
in ppm).
Table 1
Screening of catalytic efficiency of rhodium and iridium complexes in intramolecular
CeN bond forming reactions of 9a
Fig. 1. Solid state structures of rhodium complex 4a (top) and iridium complex 8a
(bottom).
ruthenium and rhodium complexes.9 Finally, at lower temperature
of ꢀ15 ꢁC, the iridium complex 7 catalyses the CeN bond formation
to 10a in a slightly higher enantioselectivity than the parent ru-
thenium complex 1a (entries 8,9).
As a result, complex 7 was screened in the catalytic aza-Michael
reaction of several substrates (Table 2). These reactions lead to very
good chemical yields and acceptable enantiomeric inductions. For
the acyclic substrate 11a, an enantiomeric excess of 32% was ob-
tained for the cyclized product 12a, which is significantly higher
than the 15% that are obtained with the corresponding ruthenium
complex 1a (entries 1,2). Still, this type of substrate appears to
contain too much flexibility in order to generate a defined stereo-
determining transition state for the CeN bond formation (vide in-
fra). To this end, arene derivatives 9bef performed better and led to
formation of the corresponding amination products 10bef with
enantiomeric excesses of 59e90%. As in the case of ruthenium
catalysts, para-substitution to the aniline nitrogen does not guar-
antee high enantiomeric induction (entries 3,4), while an alkyl
substituent in the remaining ortho-position influences a positive
effect (entries 5,6). A related effect is obtained for the naphthalene
core (entry 7). Product 10f is initially obtained in 84% ee, but can be
conveniently crystallized to enantiopurity upon crystallization
from methanol solution.
Entry
Catalyst
Yield [%]a
Ee [%]b
1
2
3
4
5
6
1a
3
5
4a
6a
7
8a
7
90
88
76
45
22
12
n.r.c
n.r.c
92
36
36
56
53
7
76
52
69
8d
9e
1a
a
Isolated yield after purification.
b
c
Ee values determined by analytical HPLC at a chiral stationary phase.
n.r.¼no reaction.
d
e
Reaction at ꢀ15 ꢁC with 96 h reaction time.
Reaction at ꢀ15 ꢁC.

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R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
Table 2
Screening of catalytic efficiency of iridium complex 7 in intramolecular CeN bond forming reactions
Entry
Substrate
Catalyst
Product
Yield [%]a
Ee [%]b
1
2
7
67
58
32
15
1a
3
4
7
7
61
61
67
59
5
6
7
7
65
76
90
85
7
7
68
84 (99)c
a
Isolated yield after purification.
Ee values determined by analytical HPLC at a chiral stationary phase.
After crystallization from MeOH.
b
c
These reactions are understood to follow the general catalytic
cycle that was previously postulated for catalyses with ruthenium
complexes generated from complex 1.9 Again, the present re-
actions are based on an efficient NeH activation reaction of sub-
strates 9 within the iridium-diamine framework of complex 7
(Fig. 3). The resulting amidato iridium complexes A should form as
a single chiral-at-iridium diastereoisomers as deduced from the
studies on formation of related complexes 8aec (Scheme 2). At the
stages A, the interaction between the amidate nitrogen and the
alkene will generate cyclic transition states B for the CeN bond
formation, which is possibly aided by a hydrogen bonding be-
tween the NH2-group of the ligand and the carbonyl group of the
ester. The present transition state B characterizes the hydro-
amination process as an aza-Michael reaction.15 A structurally
related mode of activation and transfer had been reported by
Ikariya for a metaleligand bifunctional Michael addition of mal-
onates to enones.16 It furthermore confirms the strategy of a dual
activation mode within the alkene amination process, which
combines classical approaches of metal-mediated hydroamination
through discrete [M]-N intermediates and carbonyl activation to
render the conjugated alkene more susceptible for conjugate
amination. CeN Bond formation at stages B lead to formation of
the indoline products 10 with concomitant regeneration of the
active catalyst state 7. As previously noted for the corresponding
ruthenium complexes, substitution at the 6-position of the aniline
R
NHTs
R
CO2Me
Ir
9
TsN
N
Ts
N
H
Ph
H
Ph
CO2Me
A
Ir
TsN
NH
R
Ph
Ph
7
Ts
Ir
TsN
N
H
N
Ph
H
R
H
Ts
O
N
Ph
H
OMe
CO2Me
B
10
Fig. 3. Catalytic cycle for the iridium-catalyzed aza-Michael addition.

R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
4469
ring of the substrate greatly enhances the enantioselectivity of the
reaction (cf., Table 2). This is the result of an effective steric re-
pulsion between the Cp* substituent of the chiral iridium catalyst
and the aryl substituent of the substrate. Consequential to the
stereogenic iridium center, these groups are placed in proximity at
stage B of the reaction, and their repulsion accelerates the enan-
tioselective product formation.
anion that is removed in the elimination reaction. As a result, the
transferhydrogenation contains the retro-N-H activation as the
initial step of the catalysis.
Table 3
Exploration of ruthenium, rhodium and iridum amidato complexes in the trans-
ferhydrogenation of acetophenone
One of the major disadvantages of the present approach may
be the irreversible loss of the catalysts during the work-up pro-
cess. To be able to recover and reuse the metal catalyst, we were
interested to introduce a heterogeneous version of the developed
bifunctional metaleligand catalyzed aza-Michael reaction by
attaching the corresponding catalyst to a resin surface. Pre-
ꢀ
viously, Pericas developed an efficient polystyrene-supported
version of the NoyorieIkariya catalyst,17 that could be success-
fully used for the highly enantioselective transfer hydrogenation
of alkyl aryl ketones with formic acid/triethylamine in the
presence of a small amount of dichloromethane. We applied the
described procedure for the preparation of the active 16eˉ amido-
ruthenium complex attached to the surface of the polystyrene
resin. Unfortunately, despite a number of reactions that were
performed in order to optimize the reaction, the heterogeneous
catalyst turned out to be less reactive and less chemoselective
(Scheme 3). An unexpected side reaction of alkene isomerisation
was observed, although the enantiomeric excess of the desired
cyclic product was relatively high (compare to the performance
of 1a in Table 1, entry 9).
Entry
Catalyst
Yield [%]a
Ee [%]b
1
2
3
4
5
6
2a
2b
2c
4c
6a
8a
90
89
95
90
50
33
97
97
96
93
95
90
a
Isolated yield after purification.
Ee values determined by analytical HPLC at a chiral stationary Chiralcel OD
b
phase (n-hexane/iPrOH, 98/2, v/v, 1 mL/min).
The same is observed for rhodium and iridium complexes. For
example, rhodium complexes 4c and 6a gave good, albeit lower
conversion of 14a to 15a (entries 4,5). For 4c, the observed ee value
of 93% is in good agreement with literature reports reporting on
the related chloride complex as catalyst precursor (90% ee).13 In
addition, 6a gives a slightly lower ee than reported in the literature
for the corresponding chloride complex (97% ee).14 This reaction
was terminated after 24 h to allow for comparison in relative rate,
when it had not reached full conversion. However, the reaction
remained of complete chemoselectivity at this stage as only
product 15a and unreacted starting material 14a were present.
Finally, the iridium complex 8a showed the common reduced re-
activity that is common in iridium hydrides.13 Despite the low
yield after 24 h, the enantioselectivity was high as expected (90%
ee, entry 6).
Scheme 3. Heterogeneous catalysis for the enantioselective aza-Michael reaction us-
ing a polystyrene (PS)-supported diamine ligand.
To fully confirm this context, the ruthenium complexes 2a and
2b were employed in additional transferhydrogenation reactions of
ketones (Table 4). Again, the obtained results compare well with
literature data on the related chloride precursor. It demonstrates
that the amido metal complexes obtained from NeH activation can
serve as bench-stable catalyst precursors for the present trans-
ferhydrogenation reactions.
As could be expected, rhodium and iridium complexes 4c, 6a
and 8a are versatile precatalysts for the standard metaleligand
bifunctional transferhydrogenation of ketones. In contrast to the
aza-Michael reactions from Table 2, where presence of any base
catalyses the undesired background reaction of a racemic CeN
bond formation, presence of base does not constitute a detrimental
effect in the case of transferhydrogenation with 2-propanol.
The capacity of various complexes to catalyse the trans-
ferhydrogenation of standard substrate acetophenone 14a to the
corresponding secondary alcohol (R)-1-phenyl ethanol 15a was
probed. Enantioselective alcohol formation was accomplished in
high yields and with high enantioselectivities (Table 3). In partic-
ular, our previously reported amido ruthenium complexes 2aec
gave conversions and enantiomeric excesses that are comparable to
the ones obtained with the corresponding chloride complexes in-
troduced by Noyori (entries 1e3). This observation can be ratio-
nalized by the assumption that the initial base-mediated formation
of the unsaturated complex 1 from Scheme 1 is independent of the
3. Conclusion
We have reported the synthesis of new chiral-at-metal amido
complexes of rhodium and iridium, which are formed through
a stereoselective NeH activation reaction making use of the met-
aleligand bifunctionality concept. The resulting complexes can be
employed as catalysts or catalyst precursors in enantioselective
transition metal catalysis as demonstrated for the case of an
intramolecular CeN bond forming reaction and for the case of
established transfer hydrogenation reactions for the synthesis of
enantioenriched secondary alcohols from ketones.

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R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
AreH), 7.05e7.10 (m, 3H, AreH), 7.17 (d, J¼8.3 Hz, 2H, AreH). 13C
Table 4
Exploration of ruthenium amidato complexes 2a,b in the transferhydrogenation of
ketones
NMR (75 MHz, CDCl3):
d
¼9.4 (CH3-Cp*), 21.0 (CH3-Ts), 45.8 (CH3-
Ms), 69.5 (CH), 72.1 (CH), 94.0 (Cp*), 94.1 (Cp*), 126.0, 127.1, 127.4,
127.9, 128.1, 128.5, 128.4, 138.9, 139.5, 139.6, 141.4. IR (KBr):
n
(cmꢀ1)¼3304, 3247, 068, 3027, 2966, 2935, 1603, 1506, 1465, 1337,
1270, 1163, 1127, 1112, 1086, 989, 917, 830, 718, 579. MS: m/z
(MALDI) calcd for C31H36N2O2SRh [Mꢀ NHSO2CH3]þ 618.2, found
618.2.
4.2. Tosylamidato rhodium complex (4b)
Synthesized according to general procedure A. Isolated as a red
solid. ½a 2D5
ꢂ
ꢀ12 (c¼0.448 g/100 mL, MeOH). 1H NMR (400 MHz,
CDCl3):
d
¼1.81 (s, 15H, CH3-Cp*), 2.14 (s, 3H, CH3-Ts), 2.41 (s, 3H,
CH3-Ts), 3.33 (s, 1H, NH), 3.46 (d, J¼9.3 Hz, 1H, CH), 3.65 (ddd,
J¼12.1, 11.1, 3.0 Hz, 1H, CH), 4.20 (d, J¼11.1 Hz, 1H, NH), 5.66 (t,
J¼12.1 Hz, 1H, NH), 6.55 (d, J¼8.1 Hz, 2H, AreH), 6.64e6.68 (m, 5H,
AreH), 6.74 (d, J¼8.6 Hz, 2H, AreH), 7.02e7.11 (m, 5H, AreH), 7.17
(d, J¼8.1 Hz, 2H, AreH), 7.26 (d, J¼8.6 Hz, 2H, AreH). 13C NMR
(100 MHz, CDCl3):
d¼9.5 (CH3-Cp*), 21.0 (CH3-Ts), 21.4 (CH3-Ts),
69.5 (CH), 72.1 (CH), 94.1 (Cp*), 94.2 (Cp*), 126.0, 126.1, 126.9, 126.9,
127.1, 127.4, 127.8, 128.1, 128.4,129.0, 139.0, 139.4, 139.4,141.4, 142.9,
144.6. IR (KBr):
n
(cmꢀ1)¼3350, 3304, 3242, 3068, 3032, 2966, 2919,
1603, 1511,1460,1337, 1271,1168, 1132,1086, 917, 820, 702, 579. MS:
m/z (MALDI) calcd for C31H36N2O2SRh [Mꢀ NHSO2C7H7]þ 618.2,
found 618.2.
4.3. Benzyl carbamidato rhodium complex (4c)
4. Experimental section
Synthesized according to general procedure A. Isolated as a red
solid. ½a 2D5
ꢂ
ꢀ26 (c¼0.116 g/100 mL, MeOH). 1H NMR (300 MHz,
All solvents, reagents and all deuterated solvents were pur-
chased from Aldrich and TCI commercial suppliers. Column chro-
matography was performed with silica gel (Merck, type 60,
0.063e0.2 mm). NMR spectra were recorded on a Bruker Avance
400 MHz or 500 MHz spectrometers, respectively. All chemical
shifts in NMR experiments were reported as parts per million
downfield from TMS. The following calibrations were used: CDCl3
CDCl3):
d
¼1.76 (s, 15H, CH3-Cp*), 2.16 (s, 3H, CH3-Ts), 3.08 (d,
J¼10.0 Hz, 1H, NH), 3.64 (ddd, J¼13.8, 10.8, 3.0 Hz, 1H, CH), 3.97 (s,
1H, NH), 3.97e3.98 (m, 1H, CH), 4.02 (d, J¼11.0 Hz, 1H, NH), 5.14 (d,
J¼3.0 Hz, 2H, CH2), 6.56 (d, J¼7.4 Hz, 2H, AreH), 6.65e7.41 (m, 15H,
AreH), 7.52 (d, J¼7.4 Hz, 2H, AreH). 13C NMR (75 MHz, CDCl3):
d
¼9.1 (CH3-Cp*), 21.1 (CH3-Ts), 66.8 (CH2), 69.8 (CH), 72.1 (CH), 93.2
d
¼7.26 and 77.0 ppm, CD2Cl2 ¼5.32 and 54.00 ppm. MS (ESI-
d
(Cp*), 93.3 (Cp*), 125.9, 126.9, 127.1, 127.3, 127.7, 128.0, 128.1, 128.1,
LCMS) experiments were performed using an Agilent 1100 HPLC
with a Bruker micro-TOF instrument (ESI). A Supelco C8 (5 cm x
128.2, 128.5, 128.6, 138.9, 139.5, 139.9, 142.0, 156.6, 163.4 (CO). IR
(KBr):
n
(cmꢀ1)¼3380, 3293, 3063, 3027, 2960, 2925, 1721, 1639,
4.6 mm, 5 mm particles) column was used with a linear elution
1460, 1404, 1352, 1271, 1132, 1086, 912, 825, 702, 584. MS: m/z
(MALDI) calcd for C31H36N2O2SRh [Mꢀ NHO2C8H7]þ 618.2, found
618.1.
gradient from 100% H2O (0.5% HCO2H) to 100% MeCN in 13 min at
a flow rate of 0.5 mL/min. MS (EI) and HRMS experiments were
performed on a Kratos MS 50 within the service centers at ICIQ. IR
spectra were taken in a Bruker Alpha instrument in the solid state.
Ruthenium complexes 2aec, amination precursors 9aef were
synthesized as described previously.10,12 Amination products
10aef10 and 12a18 are known compounds.
General procedure A for the NeH activation and resulting forma-
tion of the amidato metal complexes: A solution of 0.1 mmol of the
corresponding 16eꢀ-metal complex in 5 mL ab dichloromethane
was kept under an argon atmosphere and stirred at room tem-
perature. 1 equiv of a solution of the desired amide (0.1 mmol in
1 mL CH2Cl2) was added dropwise until the solution color change
remained permanently. The final complex was isolated by removal
of solvent under reduced pressure and isolated as crystalline
material.
4.4. Tosylamidato rhodium complex (6a)
Synthesized according to general procedure A. Isolated as a red
solid. ½a 2D5
ꢂ
ꢀ20.6 (c¼0.507 g/100 mL, MeOH). 1H NMR (300 MHz,
CDCl3):
d
¼0.67e1.18 (m, 4H, CH2), 1.35 (d, J¼12.5 Hz, 1H, CH2), 1.50
(d, J¼12.5 Hz, 1H, CH2), 1.70 (s, 15H, CH3-Cp*), 1.86e1.87 (m, 1H,
CH2), 1.94e1.95 (m, 1H, CH2), 2.35 (s, 6H, CH3-Ts), 2.38e2.39 (m, 1H,
CH), 2.48 (ddd, J¼14.0, 10.8, 3.2 Hz, 1H, CH), 2.72 (s, 1H, NH), 3.32 (d,
J¼11.3 Hz, 1H, NH), 4.37 (t, J¼11.3 Hz, 1H, NH), 7.12 (d, J¼8.3 Hz, 2H,
AreH), 7.19 (d, J¼8.3 Hz, 2H, AreH), 7.76 (d, J¼8.3 Hz, 2H, AreH),
7.81 (d, J¼8.3 Hz, 2H, AreH). 13C NMR (75 MHz, CDCl3):
¼9.4 (CH3-
d
Cp*), 21.3 (CH3-Ts), 24.4, 24.7, 34.6, 36.3, 63.4 (CH), 64.6 (CH), 93.7
(Cp*), 93.8 (Cp*), 126.0, 126.7, 128.7, 128.9, 140.2, 140.4, 144.8. IR
(KBr):
n
(cmꢀ1)¼3355, 3278, 3165, 3063, 3022, 2930, 2858, 1271,
4.1. Mesylamidato rhodium complex (4a)
1132, 1096, 902, 715, 671, 579, 554. MS: m/z (MALDI) calcd for
C
24H37N2O2SRh [Mꢀ NHSO2C7H7]þ 520.2, found 520.2.
Synthesized according to general procedure A. Isolated as a red
solid. ½a 2D5
ꢂ
ꢀ13 (c¼0.288 g/100 mL, MeOH). 1H NMR (300 MHz,
4.5. Mesylamidato iridium complex (8a)
CDCl3):
d
¼1.80 (s, 15H, CH3-Cp*), 2.14 (s, 3H, CH3-Ts), 3.16 (s, 3H,
CH3-Ms), 3.22 (s, 1H, NH), 3.50 (d, J¼11.0 Hz, 1H, CH), 3.63 (ddd,
J¼13.6, 10.6, 3.0 Hz, 1H, CH), 4.18 (d, J¼10.6 Hz, 1H, NH), 6.13 (t,
J¼11.7 Hz, 1H, NH), 6.52 (d, J¼8.3 Hz, 2H, AreH), 6.59e6.90 (m, 7H,
Synthesized according to general procedure A. Isolated as yel-
low solid in 97% yield. ½a D
ꢂ
25 50.3 (c¼0.16 g/100 mL, CH2Cl2). 1H NMR
(400 MHz, CDCl3):
d
¼1.81 (s, 15H, CH3-Cp*), 2.16 (s, 3H, CH3-Ts),

R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
4471
3.20 (s, 3H, CH3-Ms), 3.56 (ddd, J¼13.9, 11.0, 3.2 Hz, 1H, CH), 3.71 (s,
1H, NH), 3.95 (brd, 1H, NH), 4.44 (d, J¼11.0 Hz, 1H, CH), 6.54 (d,
J¼8.4 Hz, 2H, AreH), 6.65e6.78 (m, 6H, AreH), 6.85e6.91 (m, 2H,
AreH), 7.12e7.15 (m, 2H, AreH), 7.19 (d, J¼8.2 Hz, 2H, AreH). 13C
1416, 1330, 1288, 1258, 1196, 1168, 1159, 1074, 1029, 994, 964, 918,
890, 814, 780, 752, 735, 698, 657, 628, 569. HRMS: m/z (ESI) calcd
for C26H27NO4SNa [MþNa]þ 472.1559, found 472.1549.
NMR (100 MHz, CDCl3):
d
¼9.5 (CH3-Cp*), 21.1 (CH3-Ts), 45.6 (CH3-
Ms), 69.9 (CH), 74.8 (CH), 85.6 (Cp*), 126.3, 127.0, 127.2, 127.6, 128.0,
4.9. General procedure for intramolecular amination
128.4,128.7,138.1,138.8,139.7,140.9. IR:
n
(cmꢀ1)¼3277, 2960, 2921,
2853, 1493, 1454, 1378, 1260, 1228, 1185, 1116, 1082, 1029, 987, 903,
807, 794, 767, 749, 729, 697, 681, 652, 574. MS: m/z (MALDI) calcd
for C31H36N2O2SIr [Mꢀ NHSO2C2H6]þ 693.2, found 693.2.
The required 16ee-complexes 1a, 3, 5 and 7 were synthesized
by modified literature procedures:10,12 generally, 0.1 mmol of the
corresponding chloride-complex is dissolved in
2 mL of
dichloromethane. While the solution is stirred, an excess of po-
tassium hydroxide is added to cause the solution change its color
in the ways described in the text. Washing with water and quick
drying over CaH2 under argon atmosphere gives a solution of the
activated complex. The mixture is filtered under argon atmo-
sphere and washed with abs dichloromethane. This solution
containing the pure complex is concentrated to 5 mL and used
immediately. The colored solution of prepared catalyst with
known concentration (0.01 M) was subsequently used for cataly-
sis. To the solution of starting material (0.05 mmol) in toluene
(2 mL) at ꢀ15 ꢁC was added a solution with known concentration
of activated catalyst (0.5 mL of the solution per reaction,
0.005 mmol, 10 mol %). The reaction was stirred at this tempera-
ture for the periods reported in Tables 1 and 2, quenched with
a saturated aqueous solution of NH4Cl (5 mL) and extracted with
CHCl3 (15 mL). The organic layer was dried over MgSO4 and con-
centrated under reduced pressure to provide the crude product
mixture. Purification was carried out by column chromatography
as described previously.
4.6. Tosylamidato iridium complex (8b)
Synthesized according to general procedure A. Isolated as an
orange solid in 97% yield. ½a D25
ꢂ
44.7 (c¼0.500 g/100 mL, MeOH). 1H
NMR (300 MHz, CDCl3, MeOD):
d
¼1.70 (s, 15H, CH3-Cp*), 2.16 (s, 3H,
CH3-Ts), 2.42 (s, 3H, CH3-Ts), 3.52 (d, J¼11.0 Hz, 1H, CH), 4.16 (s, 2H,
NH2), 4.35 (d, J¼11.0 Hz, 1H, CH), 6.50 (d, J¼7.2 Hz, 2H, AreH),
6.63e6.83 (m, 7H, AreH), 7.02e7.17 (m, 5H, AreH), 7.30 (d,
J¼7.9 Hz, 2H, AreH), 7.90 (d, J¼8.3 Hz, 2H, AreH). 13C NMR (75 MHz,
CDCl3, MeOD):
d
¼9.5 (CH3-Cp*), 21.2 (CH3-Ts), 21.5 (CH3-Ts), 70.2
(CH), 74.9 (CH), 86.2 (Cp*), 125.9, 126.3, 126.7, 127.2, 127.5, 127.6,
128.4, 128.5, 128.7, 128.8, 129.4, 129.6, 138.2, 139.3, 140.5, 140.7,
141.7, 144.3. IR (KBr):
n
(cmꢀ1)¼3284, 3259, 3064, 3030, 2965, 2922,
2869, 1459, 1262, 1210, 1159, 1130, 1087, 909, 816, 702, 669, 569,
501. MS: m/z (MALDI) calcd for C32H39N2O2SIr [Mꢀ NHSO2C7H7]þ
708.2, found 708.2.
4.7. Benzyl carbamidato iridium complex (8c)
HPLC determination: 10a: Chiralpak-AD, 0.7 mL/min, 2-PrOH/
hexane, 10/90, v/v, tR1¼18.0 min (R-enantiomer), tR2¼24.2 min (S-
enantiomer); 10b: Chiralcel-OD, 0.5 mL/min, 2-PrOH/hexane, 10/
90, v/v, tR1¼27.5 min (R-enantiomer), tR2¼29.8 min (S-enantio-
mer). 10c: Chiralpak-AD, 0.7 mL/min, 2-PrOH/hexane, 10/90, v/v,
tR1¼12.6 min (S-enantiomer), tR2¼19.4 min (R-enantiomer). 10d:
Chiralpak-AD, 0.7 mL/min, 2-PrOH/hexane, 10/90, v/v, tR1¼9.5 min
(S-enantiomer), tR2¼11.0 min (R-enantiomer). 10e: Chiralpak-AD,
0.7 mL/min, 2-PrOH/hexane, 10/90, v/v, tR1¼8.9 min (S-enantio-
mer), tR2¼10.4 min (R-enantiomer). 10f: Chiralpak-AD, 0.7 mL/min,
2-PrOH/hexane, 10/90, v/v, tR1¼21.2 min (R-enantiomer),
tR2¼22.4 min (S-enantiomer). 12a: Chiralcel-OD, 1 mL/min, 2-
PrOH/hexane, 10/90, v/v, tR1¼19.3 min (R-enantiomer),
tR2¼22.4 min (S-enantiomer).
Synthesized according to general procedure A. Isolated as an
orange solid in 95% yield. ½a D25
ꢂ
ꢀ41 (c¼0.054 g/100 mL, MeOH). 1H
NMR (300 MHz, CDCl3):
d
¼1.67 (s, 15H, CH3-Cp*), 2.08 (s, 3H, CH3-
Ts), 3.49 (ddd, J¼13.6, 10.6, 3.2 Hz, 1H, CH), 4.18 (d, J¼10.9 Hz, 1H,
CH), 4.29 (s, 1H, NH), 4.99 (s, 2H, CH2), 5.05 (d, J¼4.0 Hz, 2H, NH2),
6.48 (dd, J¼7.0, 1.6 Hz, 2H, AreH), 6.61e6.72 (m, 7H, AreH),
6.97e7.22 (m, 8H, AreH), 7.42 (d, J¼7.7 Hz, 2H, AreH). 13C NMR
(75 MHz, CDCl3):
(CH), 75.4 (CH), 85.5 (Cp*), 126.7, 127.6, 127.6, 127.7, 127.8, 128.1,
d
¼9.7 (CH3-Cp*), 21.7 (CH3-Ts), 66.5 (CH2), 70.7
128.4, 128.6, 128.7, 128.8, 129.0, 129.1, 129.3, 139.4, 139.8, 139.9,
139.9, 141.9, 164.2 (CO). IR (KBr):
n
(cmꢀ1)¼3388, 3060, 3027, 2960,
2911,1718,1646,1456,1410,1261,1087,1028, 911, 799, 702, 581. MS:
m/z (MALDI) calcd for C32H39N2O2SIr [Mꢀ NHO2C8H7]þ 708.2,
found 708.2.
4.8. (E)-Methyl 6-(4-methylphenylsulfonamido)-5,5-
4.10. General procedure for transferhydrogenation
diphenylhex-2-enoate (11a)
In a Schlenk tube under an argon atmosphere, the correspond-
A
solution
of
N-(2,2-diphenylpent-4-en-1-yl)-4-
ing metal complex (0.5 or 5 mol %) is dissolved in 0.1 mL of iso-
methylbenzenesulfonamide19 (391 mg, 1.0 mmol) was dissolved
in 5 mL of freshly distilled dichloromethane. Grubbs-Hoveyda
catalyst (19 mg, 0.03 mmol) and methyl acrylate (0.8 mL,
9.0 mmol) were subsequently added in single portions and the
reaction was refluxed for 18 h at 50 ꢁC (external oil bath temper-
ature). The reaction mixture was then cooled to room temperature
and all volatile material was removed under reduce pressure. The
product was purified by column chromatography (silica gel, ethyl
acetate/n-hexane, 1/4, v/v) as a white solid (418 mg, 93%). Rf¼0.3.
Obtained as a white solid. Mp 131e132 ꢁC. 1H NMR (400 MHz,
propanol. A solution of KOH in iso-propanol (40 mL, 0.1 M) is then
added via syringe. An immediate color change occurs throughout
the addition, and a solution of acetophenone (0.2 mmol) in iso-
propanol (1.9 mL) is then added. The mixture is stirred at room
temperature overnight. The reaction is quenched by addition of an
aqueous solution of HCl (10%), and the mixture is extracted with
CH2Cl2 (3x). The combined organic phases are dried over Na2SO4,
filtrated over CeliteÒ and the solvent is removed under reduced
pressure. The crude mixture is purified by chromatography (silica
gel, n-hexane/ethyl acetate, 4/1, v/v) to obtain the desired sec-
ondary alcohol.
HPLC determination: 15a: Chiralcel-OD, 1.0 mL/min, 2-PrOH/
hexane, 2/98, v/v, tR1¼18.0 min (R-enantiomer), tR2¼25.0 min (S-
enantiomer); 15b: Chiralcel-OD, 0.5 mL/min, 2-PrOH/hexane, 2/98,
v/v, tR1¼15.5 min (R-enantiomer), tR2¼17.7 min (S-enantiomer).
15c: Chiralcel-OD, 1.0 mL/min, 2-PrOH/hexane, 2/98, v/v,
tR1¼22.6 min (R-enantiomer), tR2¼28.5 min (S-enantiomer); 15d:
CDCl3):
d
¼1.77e1.84 (m, 1H, CH2), 2.23e2.28 (m, 1H, CH2), 2.43 (s,
3H, CH3-Ts), 3.59 (d, J¼6.4 Hz, 2H, CH2), 3.70 (s, 3H, CO2CH3), 4.12 (t,
J¼6.4 Hz, 1H, NH), 5.68 (d, J¼15.8 Hz, 1H, CH), 6.75e6.83 (m, 1H,
CH), 7.06 (psd, J¼7.3 Hz, 4H, AreH), 7.18e7.31 (m, 8H, AreH), 7.65
(d, J¼8.2 Hz, 2H, AreH). 13C NMR (100 MHz, CDCl3):
¼21.7, 39.6,
d
49.7, 49.8, 51.5, 124.8, 127.2, 127.7, 128.8, 129.9, 136.3, 143.7, 143.8,
143.9, 166.4. IR:
n
(cmꢀ1)¼3216, 2865, 1718, 1650, 1597, 1493, 1445,

4472
R.M. Romero et al. / Tetrahedron 71 (2015) 4465e4472
40, 6785; (j) Salomon, M. A.; Jungton, A.-K.; Braun, T. Dalton Trans. 2009, 7669;
(k) Fafard, D.; Adhikari, C. M.; Foxman, B. M.; Mindiola, D. J.; Ozerov, O. V. J. Am.
Chem. Soc. 2007, 129, 10318; (l) Hillhouse, G. L.; Bercaw, J. E. J. Am. Chem. Soc.
1984, 106, 5472; (m) Zhao, J.; Goldman, A. S.; Hartwig, J. F. Science 2005, 307,
1080; (n) Sappa, E.; Milone, L. J. Organomet. Chem. 1973, 61, 383; (o) Hirano, M.;
Chiralcel-OD, 0.7 mL/min, 2-PrOH/hexane, 2/98, v/v, tR1¼11.5 min
(R-enantiomer), tR2¼14.3 min (S-enantiomer).
Acknowledgements
ꢁ
Onuki, K.; Kimura, Y.; Komiya, S. Inorg. Chim. Acta 2003, 352, 160; (p) Jimenez-
Tenorio, M.; Puerta, M. C.; Valerga, P. Eur. J. Inorg. Chem. 2005, 2631; (q) Tobisch,
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ꢁ
The authors thank Dr. E. Escudero-Adan and Dr. N. Cabello from
ICIQ Research Support Area for experimental assistance. Financial
support of this project was provided from the Cellex-ICIQ Pro-
gramme (postdoctoral contract to C. M.) and from the Spanish
Ministry for Economy and Competitiveness (CTQ2011-25027 and
CTQ2013-50105-EXP grants to K. M., and Severo Ochoa Excellence
Accreditation 2014-2018 to ICIQ, SEV-2013-0319).
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