Iridium-catalyzed allylic substitutions with cyclometalated phosphoramidite complexes bearing a dibenzocyclooctatetraene ligand: Preparation of (π-Allyl)Ir complexes and computational and NMR spectroscopic studies

Article abstract of DOI:10.1002/chem.201201772

(π-Allyl)Ir complexes derived from dibenzocyclooctatetraene and phosphoramidites by cyclometalation are effective catalysts for allylic substitution reactions of linear monosubstituted allylic carbonates. These catalysts provide exceptionally high degrees

Full text of DOI:10.1002/chem.201201772

FULL PAPER
DOI: 10.1002/chem.201201772
Iridium-Catalyzed Allylic Substitutions with Cyclometalated
Phosphoramidite Complexes Bearing a Dibenzocyclooctatetraene Ligand:
Preparation of (p-Allyl)Ir Complexes and Computational and NMR
Spectroscopic Studies
Jevgenij A. Raskatov, Mascha Jꢀkel, Bernd F. Straub, Frank Rominger, and
Gꢁnter Helmchen*[a]
Abstract:
(p-Allyl)Ir complexes de-
ditions. A series of (p-allyl)Ir com-
plexes were prepared and character-
ized by X-ray crystal structure analyses.
An allylic amination with aniline dis-
played different resting states depend-
ing on the presence of a strong base.
DFT calculations were carried out on
the mechanistic aspects of these reac-
tions. The results suggest that for the
(p-allyl)Ir complexes, the formation
and reactions with nucleophiles pro-
ceed with comparable rates.
rived from dibenzocyclooctatetraene
and phosphoramidites by cyclometala-
tion are effective catalysts for allylic
substitution reactions of linear mono-
substituted allylic carbonates. These
catalysts provide exceptionally high de-
grees of regioselectivity and allow the
reactions to be run under aerobic con-
Keywords: allylic substitution
asymmetric catalysis iridium
·
·
·
phosphoramidites · reaction mecha-
nisms
Introduction
From 1997[1] onwards, the Ir-catalyzed allylic substitution re-
action has been developed into a useful tool for organic syn-
thesis. The reaction allows branched allylic derivatives 2 to
be prepared from readily available linear allylic derivatives,
most often allylic carbonates 1 (Scheme 1).[2] Catalysts for
ꢀ
this reaction are usually prepared by base-induced C H ac-
tivation from [{Ir
A
The scope of the reaction with respect to the nucleophile is
very broad; C-, N-, O-, and S-nucleophiles having been used
successfully, and enantioselectivities are usually high.[5] In-
tramolecular reactions are facile and can be carried out at
concentrations of 1m and higher without noticeable compet-
ing polymerization.[3,6]
Scheme 1. Ir-catalyzed allylic substitution reactions and the most com-
monly used ligands.
Regioselectivities 2:3 are high with sp2 substituents R, but
can be as low as about 70:30 with aliphatic substituents R.
We have introduced catalysts derived from [{Ir
ACHTUNGTRENNUNG
(dbcot=dibenzocyclooctatetraene),[7]
which
reported.[9] The unusual properties of these new catalysts
have induced us to study the mechanistic aspects of their re-
actions. Herein, we report these results, including DFT cal-
culations and catalyst optimization studies.
induce superior regioselectivity and, in addition, allow the
substitution reactions to be run under aerobic conditions.
Dbcot can be conveniently prepared on a multigram scale.[8]
Several successful applications of these catalysts have been
Current views on catalyst activation and the catalytic
cycle of the reaction are shown in Scheme 2.[4,10,11] In the
first step, mixing [{IrACTHNUGRTNE(NUG diene)Cl}2] with a phosphoramidite (L)
yields complexes of the well-known type C1. Treatment of
[a] Dr. J. A. Raskatov, M. Jꢀkel, Prof. Dr. B. F. Straub, Dr. F. Rominger,
Prof. Dr. G. Helmchen
Organisch-Chemisches Institut
ꢀ
C1 with base effects C H activation to give iridacycles of
type C2, which have been characterized previously.[4] Entry
into the catalytic cycle likely proceeds via a 16 valence elec-
tron (VE) complex of type C3, which has so far not been
isolated. Next, coordination of the substrate to form C4 and
oxidative addition to give the crucial p-allyl complexes C5
Ruprecht-Karls-Universitꢀt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
Fax : (+49)6221-544205
E-mail: g.helmchen@oci.uni-heidelberg.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201772.
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plexes.[10] Their complete deter-
mination of the kinetic data
shows that the formation of the
p-allyl intermediate determines
the steric course of the substitu-
tion reaction. Recently, DFT
calculations on the cyclometala-
tion step of cod complexes have
been published by You and co-
workers.[5]
Results and Discussion
Preparation
of
(p-allyl)-
AHCTUNGTRENNUNG
The (p-allyl)Ir complexes were
prepared according to a method
developed recently by us for
complexes C5 with cod as diene
ligand.[11] This very convenient
method also allowed a variety
of dbcot complexes to be pre-
Scheme 2. Catalytic cycle of an allylic substitution reaction using a catalyst prepared in situ from compound
C1 by treatment with an amine base (B).
occurs. A wide variety of complexes C5 with cod as diene
ligand have been prepared (see below) and are active cata-
lysts. Based on investigation of the reaction kinetics of allyl-
ic amination reactions, Hartwig and co-workers have postu-
lated that the formation of the p-allyl complexes C5, in
which the diene=cod, is reversible and endergonic,[10] while
we have identified a p-complex as the resting state of an al-
lylic alkylation reaction.[11] The reaction of C5 with a nucleo-
phile produces the olefin complexes C6. Such complexes
have been observed by NMR spectroscopy. Depending
mainly on the nucleophile, the p-allyl complex C5 or the
product complex C6 have been observed as resting states of
the reaction.
The steric course of the reaction, that is, the relationship
between the configuration of the product and that of the
catalyst, has previously been assessed for the step C5!C6,
that is, the addition of the nucleophile at the p-allyl com-
plex,[10,11] by DFT calculations. The correct configuration of
the product was derived by using the simple argument that
the nucleophile would preferentially add at the terminal
carbon atom of the observed p-allyl complex, which was
also found in the DFT calculations to be the most stable[11]
and displayed the longer bond with Ir.
pared in excellent yields of 84–98% [Eq. (1)]. The method
involves the simple treatment of solution of [{Ir-
AHCTUNGTRE(GNNUN dbcot)Cl}2], L, and allylic carbonate 1 in THF with a solu-
ble silver salt, usually AgOTf, followed by the removal of
AgCl by filtration:
a
½fIrðdbcotÞClg2ꢁþLþ1þAgOTf ! C5þAgClþCO2þCH3OH
ð1Þ
These complexes (Figure 1) are stable against water and air,
can be purified by column chromatography on silica gel, and
can be stored for extended periods of time. Several com-
plexes were characterized by X-ray crystal-structure analysis
(see below).
This argument is a problematic one in the case of Ir catal-
ysis, because IrIII complexes are kinetically inert and, thus,
the fast equilibration of p-allyl complexes, which is typical
for PdII complexes, is usually not valid for Ir complexes. It is
necessary, therefore, to also investigate the formation of p-
(allyl)Ir complexes, that is, the steps C3!C4!C5. This has
now been carried out for a dbcot complex with the help of
DFT calculations. The necessity to investigate the full set of
steps is underlined by a very recent report by Madrahimov
and Hartwig on the corresponding reactions with cod com-
Figure 1. Atom numbering in complexes C5.
The dbcot complexes prepared in the course of our inves-
tigation, as well as the previously elucidated mechanism for
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
Scheme 3. Synthesis of (p-allyl)Ir complexes C5a–C5e (X=OTf) from
simple components.
Figure 2. Preparation of compound C5c. 31P{1H} NMR spectra: A) [{Ir-
ACHUTNGERN(NUG dbcot)Cl}2] (0.02 mmol)+AHCUTTGNREN(NUNG R,R,aR)-L2 (0.04 mmol) in [D8]THF (0.5 mL)
after 30 min at RT; B) addition of AgOTf (0.04 mmol) to solution (A) at
RT; C) mixture (B) measured at 238 K; D) addition of cinnamyl methyl
carbonate (0.04 mmol) to solution (B), recorded after 3 h at RT.
the formation of the corresponding cod complexes,[11] are
shown in Scheme 3. The formation of complex C5c was
monitored by 31P NMR spectroscopy (Figure 2). Initially,
complex C1 (Ar=o-(MeO)C6H4) was prepared by mixing
[{Ir
A
with cinnamyl methyl carbonate (1a). Within 3 h, the
31P NMR resonances of the hydrides vanished and a singlet
that corresponded to complex C5c remained (Figure 2D).
AgOTf was added, which caused a precipitation of AgCl.
The resultant solution displayed an asymmetric signal at
d31P =125 ppm at room temperature (Figure 2B). Upon
cooling, this signal split into two peaks with an intensity
Allylic substitution reactions with complexes C5 as catalysts
1
ratio of 9:1 (Figure 2C). The corresponding H NMR spec-
ꢀ
trum (not shown) displayed Ir H resonances at d=
These new allyl complexes were probed as catalysts under
salt-free conditions[12] with a set of representative substrates,
and the results were compared with those achieved with cat-
alysts formed in situ (Table 1). The configurational relation-
ships given in Scheme 1 were found to be valid for all of the
reactions. As a rule, isolated complexes C5 induced slightly
ꢀ21.1 ppm and d=ꢀ18.5 ppm with an intensity ratio of
10:1. Accordingly, lines in Figure 2B and 2C were assigned
to the diastereomers of the complex C3H (Ar=o-
(MeO)C6H4). Solution B (Figure 2), which contained [{Ir-
ACHTUNGTRENNUNG(dbcot)Cl}2], ligand L2, and AgOTf in THF, was treated
Table 1. Allylic substitution reactions (according to Scheme 1) with isolated or in-situ-generated complexes C5 as catalysts (solvent: THF, base: TBD=
1,5,7-triazabicyclo
[4.4.0]dec-5-ene).[a]
ACHTUNGTRENNUNG
Entry
R
Pronucleophile/nucleophile
CH2A(CO2CH3)2
2A(CO2CH3)2
2A(CO2CH3)2
(Boc)2
(Boc)2
(Boc)2
Catalyst
t [h]
Yield 2+3 [%][b]
2/3[c]
ee [%][d]
1
2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
G
in situ[e]
C5c[e]
C5c
2
1
4
18
2
3
18
3.5
1
3.5
3.5
19
1
96
91
91
63
70
93
88
73
79[f]
90
91
64
80
83
73
99:1
99:1
98:2
95:5
93:7
94:6
92:8
92:8
99
99
96
99
98
98
98
95
–
94
94
93
93
93
93
CH
CH
HN
HN
HN
CHTUNGTRENNUNG
3[g]
4
E
G
in situ[e]
C5b[e]
C5b
5
ACHTUNGTRENNUNG
6[g]
7
E
PhNH2
PhNH2
PhNH2
in situ[e]
C5b[e]
C5b[f]
in situ
C5b[e]
C5b
8
9
0:100
10[h]
11[h]
12[g]
13[h]
14[h]
15[g,h]
nPr
nPr
nPr
CH2OCPh3
CH2OCPh3
CH2OCPh3
CH
CH
CH
CH
CH
CH
G
97:3
97:3
97:3
92:8
93:7
96:4
in situ[e]
C5c[e]
C5b
1
3
[a] Reactions were carried out under “salt-free conditions” (see ref. [12]). Catalyst in situ: a solution of [{IrACTHNUTRGNEN(UG dbcot)Cl}2] (2 mol%), ligand L2 (4 mol%),
and dry TBD (8 mol%) was stirred in dry THF (0.5 mL) at RT for 10 min. Isolated complex as the catalyst: compound C5 (4 mol%) was dissolved in
dry THF (0.5 mL). Allylic substitution reaction: a solution of the catalyst was treated with carbonate 1 (0.5 mmol), the nucleophile or pronucleophile
1
(0.6 mmol), and, when compound C5 was used as the catalyst, TBD (8 mol%). [b] Yield of isolated product. [c] Determined by H NMR spectroscopy of
the crude products. [d] Determined by chiral HPLC (see the Experimental Section). [e] The reaction was carried out with a catalyst that was derived
from ent-L2. [f] The reaction was carried out without additional base. Besides compound 3a, 13% of linear N,N-dicinnamylaniline was isolated. [g] The
reaction was carried out under aerobic conditions. [h] The reaction was carried out at 508C. Boc=tert-butoxycarbonyl.
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G. Helmchen et al.
Table 3. Allylic amination reactions with an allylic trimethylammonium
salt as the substrate.[a]
faster reactions than the in-situ-generated catalysts, and the
regioselectivities (1H NMR spectroscopy) and enantioselec-
tivities (HPLC) were the same within the range of precision
of the measurements. We had earlier noted that reactions
that were catalyzed by dbcot complexes could be run under
aerobic conditions (Table 1, entries 3, 6, 12, and 15), which
is not possible with the corresponding cod complexes.
Entry
Catalyst
Diene
t
Yield
2/3[c]
ee
[h]
2+3 [%][b]
[%][d]
Allylic substitution reactions catalyzed by cod complexes
are usually run in THF as solvent, because more polar sol-
vents are detrimental with respect to enantioselectivity.[13]
The generally enhanced robustness of the dbcot complexes
allows the reactions to be run in a very broad range of sol-
vents, as is apparent from the results for an alkylation reac-
tion (Table 2). Regioselectivity is practically independent of
1
2
3
4
5
6
7
in situ
in situ[e]
C5f[f]
in situ
in situ
C5b
cod
cod
cod
dbcot
dbcot
dbcot
dbcot
6
24
6
6
24
6
43
69
57
37
52
58
62
93:7
80:20
95:5
70:30
30:70
91:9
94
94
94
89
80
92
85
C5b
24
82:18
[a] Reaction conditions: At RT, either
a solution of [{IrCATHNUTGENRUGN(diene)Cl}2]
(2 mol%), ligand L2 (4 mol%), and dry TBD (8 mol%) in dry THF
(1.25 mL) (in situ procedure) or a solution of compound C5 (4 mol%)
and dry TBD (8 mol%) was prepared in dry THF (1.25 mL); then, am-
Table 2. Influence of the solvent on the alkylation reaction (according to
Scheme 1, carbonate 1c, dimethyl malonate as the pronucleophile) by
using complexes C5b and C5d as the catalyst.[a]
monium salt
4 (0.25 mmol) and BnNH2 (0.75 mmol) were added.
1
[b] Yield of isolated product. [c] Determined by H NMR spectroscopy of
the crude products. [d] Determined by chiral HPLC (see the Experimen-
tal Section). [e] The reaction was carried out with ent-L2. [f] C5 f=[Ir-
Entry Solvent
Catalyst
t
Yield
2/3[c] ee
[%][d]
[h] 2+3 [%][b]
1
2
3
4
5
6
7
8
CH3CN
CH3CN
DMF
C5b
C5d
C5b
C5d
C5b[e]
C5d
C5b
C5d
1
86
1.5 74
88
1.5 74
94:6
94:6
92:8
n.d. 90
92:8
92:8
93:7
94:6
95:5
96:4
94:6
94:6
94:6
96
95
94
AHCTUNGTREUN(GNN cod)ACHTNURTGEG(NNUN C,P-L2)ACHTNGURTEN(NUGN crotyl)]OTf; for its preparation, see ref. [11].
1
DMF
ever, the reversibility of the reaction was apparent by the
formation of linear product 3 upon extending the reaction
time to 24 h. From a practical point of view, ammonium
salts are clearly inferior to carbonates as substrates.
DMSO
DMSO
iPrOH
iPrOH
1,2-dichloroethane C5b
1,2-dichloroethane C5d
toluene
toluene
1,4-dioxane
3
5
77
78
92
88
90
93
95
95
96
96
94
1.5 74
80
1.5 74
82
1.5 75
85
1.5 73
2
9
10
11
12
13
2
Resting state of an allylic amination reaction upon the use
of a (p-allyl)ACTHNUTRGNE(NUG dbcot)Ir complex as a catalyst
C5b[e]
C5d
C5b
7
The resting state of allylic substitution reactions catalyzed
by cod complexes has been investigated by the Hartwig
group[10] and by our group.[11] For the allylic amination reac-
tion with aniline, complex C6 (diene=cod) was observed as
the resting state, which led Hartwig and co-workers to con-
clude that the formation of the (p-allyl)Ir complexes is en-
dergonic and reversible. For that work, in situ catalysts were
used. However, for an alkylation reaction with dimethyl
malonate that was catalyzed with an isolated allyl complex
(C5, diene=cod), we observed the allyl complex to be the
resting state. Herein, we have investigated the reaction of
aniline with cinnamyl methyl carbonate (1a) using the dbcot
complex C5b as the catalyst; we found that both scenarios
were observable for a given set of substrates, depending on
the presence/absence of a strong base.[15]
[a] Reactions were carried out at 508C: Complex C5 (4 mol%) was dis-
solved in absolute solvent (0.5 mL) and carbonate 1c (0.25 mmol), CH2-
ACHTUNGTRENNUNG(CO2CH3)2 (0.3 mmol), and dry TBD (8 mol%) were added. [b] Yield of
isolated product. [c] Determined by 1H NMR spectroscopy of the crude
products. [d] Determined by chiral HPLC (see the Experimental Sec-
tion). [e] The reaction was carried out with ent-C5b.
the solvent, whereas enantioselectivity is eroded in DMF
and, notably, in DMSO, but not in MeCN. Low selectivity
with DMSO was also observed by us for a hydroxylation re-
action,[9c] whereas a beneficial effect of this solvent has been
reported for allylic amination reactions run under aerobic
conditions.[9b]
As described below, DFT calculations were carried out on
the course of the allylic substitution reaction with allylic tri-
methylammonium ions as reaction partners. Metal-catalyzed
allylic substitution reactions with allylic ammonium salts
have been reported with Pd but not with Ir catalysts;[14]
therefore, we have investigated the allylic amination of the
ammonium salt 4, as an example (Table 3), to assess whether
the results are similar to those achieved with the typically
used allylic carbonates. Catalysts containing a cod or dbcot
ancillary ligand were probed. Under kinetically controlled
conditions and short reaction times (6 h), the regio- and
enantioselectivities, as well as the steric course of the reac-
tions, were similar to those obtained with carbonates. How-
Thus, when the reaction was run with catalyst C5b without
an additional base, the linear product 3a was formed. Initial-
ly, up to 10% of branched product 2a was observed (by
1H NMR spectroscopy), which vanished during the course of
the reaction, that is, compound 3a is the product under ther-
modynamic control. Clearly, the intermediary branched am-
monium salt and/or the corresponding Ir complex undergoes
a
further amination reaction (Scheme 4). 31P NMR
(Figure 3), as well as 1H NMR spectra were measured
during the reaction and after the amination step had been
completed. Addition of carbonate 1a and aniline to the sol-
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
Scheme 4. Influence of base on the reaction of aniline with carbonate 1a.
Figure 4. Allylic amination according to Scheme 4 with an additional cat-
alytic amount of TBD; 31P{1H} NMR spectra: A) compound C5b
(0.02 mmol) in [D8]THF (0.5 mL); B) addition of carbonate 1a
(0.5 mmol), PhNH2 (0.6 mmol), and TBD (0.04 mmol) to solution (A),
recorded after 10 min at RT; C) recorded after 2 h at RT, the reaction
1
was complete (by H NMR spectroscopy) after 1.5 h.
a catalytic amount of TBD led to the formation of a species
displaying a signal at d31P =141.0 ppm, which persisted
throughout the reaction. In analogy to the corresponding re-
action of the cod complexes, this new species is presumably
olefin complex C6 (diene=dbcot, R=Ph; Scheme 2). Quite
clearly, fast deprotonation of the intermediary branched am-
monium salt leads to a stable olefin complex (C6) under ki-
netic control.
Figure 3. Allylic amination without additional base, according to
Scheme 4; 31P{1H} NMR spectra: A) compound C5b (0.02 mmol) in
[D8]THF (0.5 mL); B) addition of carbonate 1a (0.5 mmol) and PhNH2
(0.6 mmol) to solution (A), recorded after 10 min at RT; C) recorded
after 1.5 h at RT, the reaction was complete (by 1H NMR spectroscopy)
after 30 min.
X-ray crystal structures of the (p-allyl)Ir complexes
High-resolution crystal structures were obtained for com-
ution of the crotyl complex C5b (Figure 3A) caused the for-
mation of cinnamyl complex C5c (d31P =112.4 ppm, Fig-
ure 3B). This intermediate persisted throughout the amina-
tion reaction. A small signal at d31P =141.0 ppm likely be-
longs to the Ir complex C6 of the branched product (see
below). A signal corresponding to the olefin complex of the
linear product was not observed.
Next, the course of the reaction was investigated with the
addition of a catalytic amount of base. Weak bases, such as
triethylamine, had no significant effect; however, strong
plexes [Ir
(crotyl)]+ (C5b), [Ir
(dbcot)(C,P-L1)
(crotyl)]+ (C5d), and [Ir
(cinnamyl)]+ (C5e); the counterion was triflate in all cases
(Scheme 3). Selected geometric parameters are listed in
Table 4.
The five-membered iridacycle adopts envelope conforma-
tion A (Figure 5) in all of the crystal structures (Figure 6).
This parallels well with the previous results obtained for a
broad range of cod analogues.[10,11] For complexes C5a and
C5b, a second rotamer (A’) was observed, in which the aryl
ring a was flipped (Figure 5, conformer A’). DFT calcula-
tions for complex C5a suggest that the conformer A’ is disfa-
vored by 2.1 kcalmolꢀ1 with respect to conformer A (see the
Supporting Information). Therefore, the subsequent discus-
sion of crystallographic parameters and the Computational
G
E
E
U
ACHTUNGTRENN(UNG C,P-L2)-
G
E
E
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
bases TBD (1,5,7-triazabicyclo
ACHTUNGERTN[NUNG 4.4.0]dec-5-ene) and DBU
(1,8-diazabicyclo[5.4.0]undec-7-ene) completely changed the
ACHTUNGTRENNUNG
course of the reaction in that the branched product 2a was
predominantly formed (Table 1). A representative set of
31P NMR spectra is shown in Figure 4. Addition of aniline to
a mixture of complex C5b, cinnamyl methyl carbonate, and
Table 4. Selected bond lengths [ꢂ] and bond angles [8] in (p-allyl)Ir complexes C5a–C5e.
Complex[a] Ir C1A
C1A C2A C2A C3A C1A-C2A-C3A P-Ir-CH2 Sum of bond t(C8’-C7’-N-C7) t(Ir-C8-C7-C1)
ꢀ
ꢀ
Ir C2A
ꢀ
Ir C3A
ꢀ
ꢀ
angles at N
C5a
C5b
C5c
2.245(6) 2.190(5) 2.221(6) 1.420(10) 1.399(10) 120.6(6)
76.6(2)
76.1(1)
74.3(1)
76.9(1)
75.6(2)
76.0(2)
359.8
359.7
356.1
357.5
357.2
356.1
115.9
115.6
150.8
153.2
139.9
141.8
ꢀ149.0
ꢀ152.2
ꢀ167.2
ꢀ164.4
ꢀ167.0
ꢀ169.5
2.346(4) 2.211(3) 2.190(3) 1.397(6)
2.397(4) 2.233(4) 2.204(4) 1.409(6)
2.359(3) 2.230(3) 2.204(4) 1.393(5)
1.417(6)
1.424(6)
1.434(5)
120.9(3)
122.4(4)
122.2(3)
C5d
C5e/1[a]
C5e/2[a]
2.394(8) 2.223(7) 2.174(8) 1.385(11) 1.408(11) 121.4(8)
2.408(7) 2.211(7) 2.174(8) 1.386(12) 1.415(11) 122.2(8)
[a] The designations “/1” and “/2” refer to independent molecules within the unit cell.
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G. Helmchen et al.
Figure 7. Crystal structure of complex C5c represented as ball-and-stick
(left) and CPK models (right).
Given that this is a rotation about a single bond (Figure 5,
conformers C and D), this variation is not likely to be asso-
ciated with significant energetic differences and is possibly
rooted in different crystal packing forces between the crys-
tals.
The crotyl complexes C5b (L2) and C5d (L1) display a
slightly less pronounced (but still significant) distortion;
Figure 5. Conformations of the C,P-chelate ligand in complexes C5 (Ar=
o-(MeO)C6H4 or Ph).
ꢀ
ꢀ
again, Ir C1A is longer than Ir C3A. On the other hand, the
unsubstituted allyl moiety in complex C5a was essentially
ꢀ
symmetric with respect to its bonding to iridium (Ir C1A =
ꢀ
2.245, Ir C3A =2.221 ꢂ). The torsional angle C8’-C7’-N-C7
spans a rather broad range between 115.68 (C5b) and 153.28
(C5d; Figure 6).
The distances between the iridium atom and the allyl
moiety in complexes C5b and C5c were compared with
those of their cod analogues (Figure 8). For both complexes
C5b and C5c, the bond lengths in the dbcot structures and
their corresponding cod structures are similar (Table 5).
Some variation in the orientation of the free a- and b-aryl
rings is again apparent.
Figure 6. Superposition of segments of the crystal structures of (p-allyl)Ir
complexes C5; the allylic fragment, dbcot, and BINOL are omitted for
clarity. For a color Figure, see the Supporting Information.
Section are based exclusively on conformer A. The (b)ary-
lethyl group was found in the conformation D (Figure 5) for
all structures (Figure 6), again paralleling nicely the observa-
tions made for the cod complexes.
Concerning the allylic moiety, the crystal structure of cin-
namyl complex C5c is discussed as an example (Figure 7)
and subsequently compared with its analogues. The bonding
of the cinnamyl moiety to iridium in complex C5c is distort-
Figure 8. Comparison of the structures of analogous cod and dbcot com-
plexes. Left: superposition of the structures of crotyl complex C5b with
its cod analogue (two crystallographically independent structures);[11b]
right: an analogous superposition of complex C5c and its cod analogue
(two crystallographically independent structures).[11b] For a color Figure,
see the Supporting Information.
ꢀ
ed in that the Ir C1A distance is substantially longer than
ꢀ
ꢀ
the Ir C3A distance (2.397 vs. 2.204 ꢂ). The Ir C2A distance
ꢀ
(2.233 ꢂ) is very similar to that of Ir C3A. The allylic bonds
ꢀ
ꢀ
C1A C2A and C2A C3A are not significantly different from
each other. The structure possesses strong resemblance to
the analogue C5e derived from ligand L1. A substantial dif-
ference between complexes C5c and C5e was only found
with the 1-phenylethyl substituent, for which the torsional
angles were 150.88 (C5c), 139.98 (C5e/1), and 141.88 (C5e/2).
DFT calculations
Computations were carried out on various structures with
reference to the catalytic cycle shown in Scheme 2 (R=
CH3, diene=dbcot, and Ar=o-(MeO)C6H4).
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
Table 5. Comparison of the iridium–allyl distances [ꢂ] for complexes
C5b and C5c with their cod analogues (C5f and C5g, respectively).
CH3; Scheme 3) and then the oxidative addition step by cal-
culating the energies of all of the transition states (TSOx
,
Complex[a]
ꢀ
Ir C1A
ꢀ
Ir C2A
ꢀ
Ir C3A
Scheme 2 and Scheme 5) leading to them. Then, the two
pathways with the lowest values of the transition state ener-
gies were explored in full.
C5b (dbcot)
C5f/1[b]
2.346(4)
2.32(2)
2.38(2)
2.211(3)
2.17(2)
2.21(2)
2.190(3)
2.21(2)
2.20(2)
C5f/2[b]
C5c (dbcot)
2.397(4)
2.413(8)
2.452(9)
2.233(4)
2.226(8)
2.228(8)
2.204(4)
2.168(8)
2.173(8)
C5g/1[b]
C5g/2[b]
[a] The designations “/1” and “/2” refer to independent molecules within
the unit cell. [b] C5f=[Ir(cod)(C,P-L2)(crotyl)]OTf, C5g=[Ir(cod)(C,P-
L2)(cinnamyl)]SbF6; for structural data, see ref. [11].
A
E
E
N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Survey: The formation of (p-allyl)Ir complexes C5 from
complex C3: In our previous computational investigation of
the Ir-catalyzed allylic substitution reaction, we showed that
the most stable p-allyl complex would give rise to the exper-
imentally observed enantiomer of the product. Only a part
of the catalytic cycle, the reaction of the (p-allyl)Ir species
with NH3 as a model nucleophile, was addressed. However,
equilibration within the (p-allyl)Ir manifold is slow, which
typically manifests itself in substantial memory effects.[16]
This suggests that the enantioselectivity of the reaction is
pre-determined at the early stage of the formation of the al-
lylic intermediate. In this scenario, the reaction of the 16 VE
species C3 with a chosen allylic substrate would result in the
formation of the most stable, experimentally observed allylic
complex. Accordingly, we computationally explored this
pathway. Even if direct interconversion within the allylic
manifold is slow, an indirect equilibration is possible if their
formation by nucleophilic displacement is fast, reversible,
and endergonic, as assumed by Hartwig and co-workers for
allylic amination reactions. In that case, a Curtin–Hammett
scenario would apply and the
Scheme 5. Schematic representation of the key steps leading to the for-
mation of complexes C5 (R=CH3).
AHCTUNGRTEGNUN(N p-Allyl)Ir complexes C5 (R=CH3, diene=dbcot, Ar=o-
(H3CO)C6H4): As we have shown previously for cod com-
plexes, there are eight fundamental configurations (R=H)
of the (p-allyl)Ir complexes of type C5;[11] these are sche-
matically described in Figure 9. Our previous computations
that covered all of these possible configurations were carried
out for the simplified system described in Figure 10, which
contained a cyclooctatetraene moiety and a chiral P,C ligand
derived from 2,2’-dihydroxybiphenyl rather than BINOL.
For this system, the P-series was favored over the C-series.
This was mainly attributed to the fact that in the C-series
the two ligands with the strongest trans influence, that is, the
allyl ligand and the C8 atom of the chiral ligand (for atom
numbering, see Figure 1), were located trans to each other.
energy of the transition state of
the reaction C5!C6 would be
the essential factor.
An N,N,N-trimethylcrotylam-
monium ion was chosen as the
substrate that leads to the allyl-
ic manifold with the generation
of a neutral leaving group to
avoid complications associated
with charge separation in the
transition state, as would arise
with commonly used anionic
leaving groups. Experiments
demonstrated that enantioselec-
tivities comparable to those ob-
served with the most commonly
employed allylic carbonate sub-
strates can be achieved (see
above), thus justifying the
choice of the model substrate.
First, we investigated the rel-
ative stability of all of the possi-
Figure 9. Schematic representations of the configurations of (p-allyl)Ir complexes C5; g=dbcot; P and C
series: one of the allylic carbon atoms is located trans to the P atom and to the CH2 group of the C,P ligand,
ꢀ
respectively; exo and endo: the C2A H bond of the allyl ligand points towards dbcot and away from dbcot, re-
ble p-allyl complexes (C5, R= spectively.
Chem. Eur. J. 2012, 00, 0 – 0
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G. Helmchen et al.
these isomers are followed by L-P-endo-C5 (R1 =CH3, R2 =
H; 5.1 kcalmolꢀ1). The difference between these dbcot com-
plexes and the model system studied previously is most
likely rooted in the higher steric requirement of the former
system, so that the electronic effects are no longer domi-
nant.
The crystallographically determined characteristic distan-
ces and angles were well reproduced by the calculations
(Table 6, entry 1). The most pronounced deviation is ob-
ꢀ
served for the Ir C1A bond, which is substantially overesti-
Figure 10. Previously used model for comparison of the relative energies
of (p-allyl)Ir complexes (cot=cyclooctatetraene; see ref. [11a]).
mated in the DFT calculations (2.44 ꢂ vs. crystallographical-
ly determined 2.35 ꢂ). For all structures with R1 =H and
R2 =CH3, a more substantial distortion of the (p-allyl)Ir
moiety into the direction of a h1 structure is observed for
the exo structures than for the endo structures (Table 6).
The origin of this difference is likely the higher repulsion
between the dbcot ligand and proton 2A, which is oriented
towards the dbcot ligand in the exo structures but not in the
endo structures. However for R1 =H and R2 =CH3, both the
D-P-endo- and D-P-exo isomers exhibit a weak tendency to-
wards this distortion. As noted previously for the model
system, the distortion is more pronounced in the C-series
than in the P-series. Interestingly, within the C-series, the
distortion is stronger for the endo complexes than for the
exo complexes, which is opposite to the trend found in the
P-series. In all cases, there is a preference for the isomer
with R1 =CH3, R2 =H over the counterpart (R1 =H, R2 =
CH3).
No calculations had been done for complexes derived from
the combination dbcot/L2. It was necessary to calculate the
16 nonsimplified allylic complexes C5 (R=CH3) in their
lowest energy conformations (A/C, Figure 5) prior to inves-
tigating their formation. All of these calculations were done
on conformer A, in which the two OCH3 substituents adopt-
ꢀ
ed a syn disposition relative to the NC H bonds (Figure 5).
The crystallographically observed allylic complex D-P-endo-
C5 (R1 =H, R2 =CH3) was computed to be the most stable
isomer (Table 6). The corresponding complex was the most
stable for the model system of Figure 10.
The experimentally observed isomer is energetically well
separated from other structures. The next best calculated
isomers, D-C-endo-C5 (R1 =CH3, R2 =H) and D-P-endo-C5
(R1 =H, R2 =CH3) were destabilized by 4 kcalmolꢀ1
(Table 6, entries 5 and 9). The endo isomers are energetical-
ly preferred over their exo counterparts in the P-series,
whereas, in the C-series, the difference is less pronounced.
Other than previously found for the simplified model
system, there is no clear energetic distinction between the
P- and the C-series of the dbcot complexes. Although the
lowest energy isomer has the P-configuration, the two next-
best isomers (R1 =CH3 and R2 =H) possess D-C-endo-
(4.3 kcalmolꢀ1) and D-C-exo configurations (4.9 kcalmolꢀ1);
Oxidative addition to afford allylic complexes C5 (R=CH3,
Ar=o-(H3CO)C6H4): All of the transition states of oxidative
addition leading to the 16 p-allyl complexes C5 (R=CH3)
were located (Figure 11); the results are presented in
Table 7. A graphical representation of the lowest energy
transition state is shown in Figure 14. The crystallographical-
ly observed and energetically favored (computation) allyl
complex D-P-endo-C5 (R1 =CH3, R2 =H) was calculated to
Table 6. Relative energies [kcalmolꢀ1] and selected bond lengths [ꢂ] and bond angles [8] of (p-allyl)Ir complexes C5; R=CH3, diene=dbcot, Ar=o-
(H3CO)C6H4 (conformational isomers A, C; Figure 5).[a]
[b]
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Entry
C5
Configuration
EC5
Ir C1A
Ir C2A
Ir C3A
C1A C2A
C2A C3A
C1A-C2A-C3A
P-Ir-CH2
1
2
3
4
5
6
7
8
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =CH3, R2 =H
R1 =H, R2 =CH3
R1 =H, R2 =CH3
R1 =H, R2 =CH3
R1 =H, R2 =CH3
R1 =H, R2 =CH3
R1 =H, R2 =CH3
R1 =H, R2 =CH3
R1 =H, R2 =CH3
D-P-endo
D-P-exo
0
2.44
2.51
2.44
2.57
2.71
2.65
2.67
2.60
2.25
2.28
2.23
2.31
2.36
2.40
2.32
2.36
2.27
2.32
2.27
2.33
2.36
2.36
2.34
2.35
2.26
2.28
2.30
2.30
2.30
2.31
2.30
2.31
2.22
2.21
2.22
2.18
2.15
2.16
2.16
2.17
2.37
2.35
2.48
2.33
2.32
2.27
2.36
2.29
1.41
1.39
1.41
1.39
1.38
1.38
1.39
1.38
1.42
1.42
1.43
1.41
1.41
1.40
1.42
1.40
1.43
1.43
1.42
1.44
1.45
1.45
1.45
1.45
1.41
1.41
1.40
1.41
1.42
1.43
1.41
1.43
122.5
123.1
123.1
123.1
124.5
124.5
123.6
123.1
121.8
123.1
122.9
123.3
123.3
122.7
122.4
123.8
74.8
75.8
72.4
74.4
73.4
74.4
73.1
73.0
75.4
76.1
72.7
73.3
72.9
73.7
74.8
73.9
5.3
5.1
7.3
4.3
4.9
7.5
7.9
4.1
6.1
8.5
9.2
5.8
6.8
8.9
9.7
L-P-endo
L-P-exo
D-C-endo
D-C-exo
L-C-endo
L-C-exo
D-P-endo
D-P-exo
L-P-endo
L-P-exo
D-C-endo
D-C-exo
L-C-endo
L-C-exo
9
10
11
12
13
14
15
16
[a] All energies are normalized to the lowest energy allylic isomer C5, D-P-endo (R1 =CH3, R2 =H). [b] Energies were obtained from solvent-corrected
geometry optimizations (scrf-pcm, THF) with subsequent zero-point corrections.
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
entry 3), followed by five transition states with energies be-
tween 2.5 and 3.5 kcalmolꢀ1, all of which contained the sub-
stitution pattern R1 =H, R2 =CH3. The next-best kinetic
channel for an isomer with the substitution pattern R1 =
CH3, R2 =H was calculated to be D-P-exo-C5. The transi-
tion-state energy was 2.7 kcalmolꢀ1 higher than that com-
puted for L-P-endo-C5 (R1 =CH3, R2 =H). Thus, these com-
putational results are compatible with the view that the ob-
served p-allyl complex is the most stable and also the kineti-
cally preferred one.
The typical structural features of the transition states in
the oxidative addition reaction can be summarized as fol-
ꢀ
lows: The length of the breaking C N bond lies between
2.15 and 2.37 ꢂ, thus spanning a rather broad range. The
distance between iridium and the reacting carbon center
adopts typical values between 2.70 and 2.98 ꢂ.
Structure
of
complex
C3
(diene=dbcot,
Ar=o-
(H3CO)C6H4) and the possibilities for substrate coordination:
Having located the 16 transition states in the oxidative addi-
tion reaction, we proceeded to model the complete path-
ways for the formation of the two kinetically most viable
isomers, D-P-endo- and L-P-endo-C5 (R1 =CH3, R2 =H),
starting from the 16 VE complex C3 (Figure 11).
Figure 11. Pathways for the formation of the isomers of complex C4 and
isomers D-P-endo- and L-P-endo-C5, which are associated with the
lowest and second lowest transition state energies (TSOx), respectively;
R1 =CH3, R2 =H, diene=dbcot, Ar=o-(H3CO)C6H4.
A model of the d8 16 VE complex C3 was generated by
removing the allylic moiety from the energetically lowest
lying allylic complex, D-P-endo-C5 (R1 =H, R2 =CH3;
Figure 9), followed by energy minimization of the residual
fragment. As a control calculation, the same procedure was
performed starting from L-P-endo-C5 and D-C-endo-C5
(both R1 =H, R2 =CH3), which produced the same structure
of complex C3. Complex C3 was found to possess square-
planar geometry with respect to the iridium center.
be associated with the lowest energy transition state for the
oxidative addition step (Table 7, entry 1). In the following
section, all other transition states (TSOx) in the oxidative ad-
dition reaction are normalized to the lowest energy transi-
tion state.
The next-best reaction channel was determined computa-
tionally to be that of L-P-endo-C5 (R1 =CH3, R2 =H), with
a relative transition-state energy of 2.1 kcalmolꢀ1 (Table 7,
Table 7. Energies [kcalmolꢀ1] and selected bond lengths [ꢂ] and torsion angles [8] of the transition states for the oxidative addition step (TSOx
,
Scheme 5).
[a]
ꢀ
ꢀ
ꢀ
ꢀ
Entry
Descriptor
ETSox
N C3A
Ir C1A
Ir C2A
Ir C3A
C8-Ir-C2A-C1A
C8-Ir-C2A-H2A
Ir-C1A-C2A-C3A
R1 =CH3, R2 =H
1
2
3
4
5
6
7
8
D-P-endo
D-P-exo
0
2.20
2.31
2.30
2.37
2.20
2.22
2.26
2.27
2.27
2.28
2.26
2.27
2.28
2.28
2.27
2.26
2.28
2.30
2.28
2.34
2.30
2.32
2.32
2.30
2.74
2.77
2.70
2.79
2.75
2.79
2.77
2.83
ꢀ99.0
ꢀ70.0
94.6
14.8
176.3
ꢀ19.5
178.2
ꢀ66.6
100.9
67.5
79.5
ꢀ80.5
ꢀ77.9
79.4
4.8
2.1
6.5
8.2
9.3
13.4
12.8
L-P-endo
L-P-exo
D-C-endo
D-C-exo
L-C-endo
L-C-exo
65.0
179.9
ꢀ146.6
ꢀ179.1
155.4
79.1
ꢀ78.7
ꢀ79.5
84.2
ꢀ90.2
ꢀ
ꢀ
ꢀ
ꢀ
Entry
Descriptor
ETSox
N C1A
Ir C1A
Ir C2A
Ir C3A
C8-Ir-C2A-C3A
C8-Ir-C2A-H2A
Ir-C3A-C2A-C1A
R1 =H, R2 =CH3
9
D-P-endo
D-P-exo
3.0
2.5
7.0
2.9
3.5
3.0
8.2
8.8
2.19
2.27
2.26
2.37
2.16
2.24
2.15
2.21
2.78
2.78
2.77
2.76
2.89
2.98
2.94
2.98
2.28
2.30
2.28
2.31
2.31
2.33
2.31
2.33
2.25
2.21
2.25
2.21
2.20
2.17
2.19
2.18
123.0
79.7
ꢀ118.6
ꢀ84.4
42.3
10.6
ꢀ168.2
ꢀ6.3
ꢀ81.6
78.5
80.6
ꢀ76.5
ꢀ84.5
88.7
10
11
12
13
14
15
16
L-P-endo
L-P-exo
D-C-endo
D-C-exo
L-C-endo
L-C-exo
163.4
ꢀ69.3
1.2
114.2
ꢀ39.2
71.2
ꢀ115.0
86.9
ꢀ90.2
ꢀ0.8
[a] The atom numbering of the allylic moiety depends on the way in which it is coordinated to the iridium atom. For the isomers with R1 =H and R2 =
ꢀ
CH3, the relevant distance is N C1A. The same is true for dihedral angles C8-Ir-C2A-C1A and Ir-C1A-C2A-C3A.
Chem. Eur. J. 2012, 00, 0 – 0
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G. Helmchen et al.
Table 8. Energies [kcalmolꢀ1] of the species described in Figure 14.
Upon coordination of the olefinic substrate, the dbcot
ligand has to rotate out of the plane to accommodate the
steric bulk of the incoming allylic substrate and to enable
constructive orbital overlap between the LUMO of the
alkene (p*) and the HOMO of complex C3 (mainly dz2 at
the iridium atom). The relevant orbitals are shown in
Figure 12. Notably, the substrate cannot approach complex
Entry
Descriptor
ERel
1
2
3
4
5
6
7
8
9
C3
TSCoord
C4
TSOx
C5
TSCoord
C4
0.0
13.0
5.3
14.5
2.8
9.8
4.3
16.6
7.9
D-P-endo
R1 =CH3, R2 =H
L-P-endo
R1 =CH3, R2 =H
TSOx
C5
Figure 14. All of the stationary points are normalized to
complex C3/substrate/NH3. Starting from the isolated allylic
substrate and complex C3 (0.0 kcalmolꢀ1), olefin complexes
C4 are formed in an endergonic reaction (5.3 and 4.3 kcal
molꢀ1 for configurations D-P-endo and L-P-endo (R1 =CH3,
R2 =H), respectively). The corresponding transition states
(TSCoord) possess energies of 13.0 kcalmolꢀ1 (D-P-endo) and
9.8 kcalmolꢀ1 (L-P-endo), which are substantially lower
than the subsequent barriers (TSOx) of oxidative addition
(14.5 and 16.6 kcalmolꢀ1, respectively). This identifies TSOx
computationally as the rate-determining step for the forma-
tion of the allylic species, that is, the enantioselectivity of
the reaction might be determined by the relative rates of
formation of the allylic manifold. The geometric aspects of
the formation of the allylic complexes are discussed in the
Supporting Information.
Figure 12. HOMO of complex C3 (left) and LUMO of the allylic sub-
strate (right); diene=dbcot, Ar=o-(H3CO)C6H4.
C3 from above because this would not lead to constructive
overlap between the HOMO of complex C3 and the LUMO
of the substrate. The possible trajectories of the substrate
that do not violate orbital symmetry are shown in Figure 13.
Reaction of D-P-endo-C5 (R1 =CH3, R2 =H, Ar=o-
(MeO)C6H4) with NH3 as the model nucleophile to yield
complex C6: The reactivity of D-P-endo-C5 in the allylic
substitution reaction was assessed by conducting calculations
with ammonia as the model nucleophile. The activation bar-
riers were computed as 11.6 kcalmolꢀ1 and 16.0 kcalmolꢀ1
for the reactions at the C1A and C3A positions, respectively,
thereby producing the corresponding olefin complexes C6.
This mirrors well the experimentally observed regioselectivi-
ty of the reaction and agrees with our previous computation-
al investigations. For the corresponding olefin complexes
C6, energies of 0.5 kcalmolꢀ1 (branched) and 2.6 kcalmolꢀ1
(linear) were found relative to the state allyl complex/isolat-
ed NH3.
The difference in activation energies for amination at the
C1A (branched) versus C3A positions (linear) is 4.4 kcal
molꢀ1, which is essentially identical to the energetic differ-
ence for the analogous unsimplified cyclooctadiene-based
system (4.3 kcalmolꢀ1), as previously reported by our
group.[11a] However, whereas the relative order of stability of
product complexes C6 is marked for the dbcot complexes, it
was small for the cod complexes (0.4 kcalmolꢀ1) and favored
the linear product.
Figure 13. Possible structural adaptations of complex C3. The descriptors
trans-C and trans-P designate the direction of the incoming substrate,
whereas the curved arrows indicate the sense of rotation of dbcot, there-
by generating the D or L chirality. For a color Figure see, the Supporting
Information.
The L/D chirality at the iridium center, as well as the P/C
configuration, are determined during the substrate coordina-
tion step, which gives rise to a total of the four possible co-
ordination isomers (D-P, L-P, D-C, and L-C). The exo/endo
configuration and the position of the methyl group relative
to the rest of the coordination sphere of the iridium center
(C1A or C3A) are determined by the rotational state of the
olefin within each of the coordination isomers.
Conclusion
The results for the reaction that proceeds from complex
C3 to allyl complexes C5 are described in Table 8 and
A very convenient one-pot procedure for the preparation of
phosphoramidite-derived cyclometalated (p-allyl)Ir com-
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
Figure 14. Relevant stationary points for the formation of allylic complex D-P-endo-C5 from compound C3; R1 =CH3, R2 =H, diene=dbcot, Ar=o-
(H3CO)C6H4.
tion states in the amination reactions possessed one imaginary frequency,
plexes containing the ligand dbcot is described; the struc-
ꢀ
which represented the vector of the C N bond formation in all cases.
tures of the complexes were determined by X-ray crystal
structure analysis. Allylic substitution reactions with dbcot
complexes as single-species catalysts were found to generally
proceed with a high degree of both regio- and enantioselec-
tivity; a wide variety of solvents as well as aerobic condi-
tions are tolerated. For an allylic amination reaction with
aniline, the resting states were different for the reactions
run with and without the presence of a strong base.
DFT calculations on nonsimplified models satisfactorily
reproduced the structural and energetic features of the new
(p-allyl)Ir complexes. The computational investigation also
considered several steps in the putative catalytic cycle.
These results are consistent with the view that the preferen-
tially formed p-allyl complexes are both the most stable and
the kinetically preferred complexes.
Zero-point energy corrections were carried out for all computed energies.
Furthermore, the influence of the solvent was taken into account by em-
ploying the polarized continuum model (PCM-SCRF) in all calcula-
tions[23] with THF (e=7.6) as the solvent.[24]
General methods: 1H NMR spectroscopy: Bruker AC-300 (300.13 MHz),
Bruker Avance 500 (500.13 MHz) or Bruker Avance 600 (600.13 MHz);
RT; CD2Cl2, CDCl3, or [D8]THF; chemical shifts (d) are reported relative
to TMS or to residual undeuterated solvent (CHCl3 in CDCl3 at dH =
7.26 ppm);[25] signal multiplicity: s (singlet), d (doublet), t (triplet), q
(quartet), m (multiplet), dd (doublet of doublets), dt (doublet of triplets),
1
ddd (doublet of doublet of doublets), bs (broad signal). H NMR spectra
of all new compounds are given in the Supporting Information. 13C NMR
spectroscopy: Bruker AC-300 (75.48 MHz), Bruker Avance 500
(125.76 MHz) or Bruker Avance 600 (150.90 MHz); RT; CD2Cl2, CDCl3,
or [D8]THF; chemical shifts (d) are reported relative to residual undeu-
terated solvent CHCl3 (dC =77.16 ppm, central line of the triplet);[25] des-
ignation of the multiplicity for {1H} spectra:
s (singlet, quaternary
C atom), d (doublet, CH group), t (triplet, CH2 group), q (quartet, CH3
group). 31P NMR spectroscopy: Bruker DRX-250 (101.26 MHz), Bruker
AC-300 (121.50 MHz), Bruker Avance 500 (202.46 MHz), or Bruker
Avance 600 (242.94 MHz); RT; CD2Cl2, CDCl3, or [D8]THF; chemical
shifts (d) are reported relative to TMS in the 1H NMR spectrum.[26] For
compounds C5a–C5e, assignments were confirmed by H,H COSY,
H,C COSY, TOCSY, HMBC, NOESY, and DEPT spectra; for atom
numbering, see Figure 1. HRMS (ESI+): Bruker ApexQe FT-ICR mass
spectrometer.
Experimental Section
Computational details: For all of the computations, the hybrid Becke
functional (B3)[17] for electron exchange and the correlation functional of
Lee, Yang, and Parr (LYP),[18] as implemented in the GAUSSIAN 09
software package, was used.[19] The SDD basis set with the associated Ef-
fective Core Potential was employed for iridium.[20] For other atoms, the
6-31G(d) level of theory was used.[21]
Flash column chromatography: silica gel (0.032–0.062) from Macherey,
Nagel and Co. Dry THF was obtained from MBraun, MB SPS-800 sol-
vent purification system. The hygroscopic base 1,5,7-triazabicyclo-
Transition states were located by using restricted geometry optimizations
as follows: The distance between the nitrogen nucleophile and the react-
ing carbon atom was fixed at 2.0 ꢂ for the reactions at atoms C1A or
C3A. The geometries were then fully optimized as saddle points of first
order by employing the Berny algorithm.[22] To confirm the nature of the
stationary points, frequency calculations were undertaken, which yielded
zero imaginary frequencies for all allyl and olefin complexes. The transi-
AHCTUNGERTG[NNUN 4.4.0]dec-5-ene (TBD) was stored in a desiccator over KOH and weigh-
ing was carried out quickly. Unless otherwise stated, reactions were car-
ried out under an argon atmosphere in anhydrous conditions. IUPAC
names were generated by the ACD/Labs 6.0 programm from Advanced
Chemistry Development, Inc.
Chem. Eur. J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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G. Helmchen et al.
The syntheses, spectroscopic data, and the determination of the enantio-
meric excess of the following compounds have already been reported:
128.70, 128.48, 128.27 (d; 4ꢃPh), 128.10, 128.01 (d; BINOL), 127.80,
127.25, 127.08 (d; 3ꢃArdbcot), 126.97 (d; BINOL), 126.70 (d; Ph), 126.70
(d; Ardbcot), 126.70, 126.59, 126.36 (d; 3ꢃBINOL), 126.11 (d; Ardbcot),
125.93, 125.58 (d; 2ꢃBINOL), 125.58, 124.81 (d; 2ꢃArdbcot), 123.94 (d;
Ph), 121.36, 121.21 (s; 2ꢃBINOL), 120.83 (d; BINOL), 120.53, 120.07 (d;
2ꢃPh), 119.86 (d; BINOL), 110.36 (d; Ph), 110.05 (d; Ardbcot), 106.80 (d;
1a;[9b] 1b;[28] 1c;[27] 2a, Nu=CH(CO2CH3)2;[28] 2a, Nu=N
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
Nu=NHPh;[4] 2a, Nu=NHBn;[4] 2b, Nu=CH
CH
(CO2CH3)2.[28,11a]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
General procedure for the preparation of (p-allyl)Ir complexes (GP1): In
a flame-dried Schlenk tube under an argon atmosphere, complex C1 was
prepared by stirring a solution of [{IrACHTUNRGTNEUNG(dbcot)Cl}2] (8.6 mg, 10 mmol) and
C2A), 104.64 (d; C1C), 93.62 (d; C2C), 88.84 (d, J
75.51 (d, J(C,P)=5.8 Hz; C4C), 60.88 (t, J(C,P)=29.3 Hz; C1A), 59.45 (d,
(C,P)=33.0 Hz; C7), 55.89 (t; C3A), 55.98, 54.44 (q; 2ꢃOCH3), 51.98 (d,
ACHTUNGTREN(NUNG C,P)=4.4 Hz; C3C),
A
ACHTUNGTRENNUNG
J
J
ACHTUNGTRENNUNG
ligand L* (20 mmol) in dry THF (0.5 mL, <30 mg water per mL THF,
Karl–Fischer titration) at room temperature for 30 min. Then, allylic car-
bonate (40 mmol) and AgX (20 mmol) were added to the orange solution,
thereby causing the formation of a white precipitate. The mixture was
stirred at room temperature for the stated time. The white precipitate
was removed by filtration through a pad of Celite and excess carbonate
was removed by flash column chromatography on silica gel (CH2Cl2 then
CH2Cl2/isopropanol, 97:3).
ACHUTNGRENU(NG C,P)=5.3 Hz; C7’), 22.15 (t, JACHUTNGTREN(NNGU C,P)=6.5 Hz; C8), 18.50 ppm (q; C8’);
31P{1H} NMR (242.94 MHz, CD2Cl2): d=111.61 ppm; HRMS (ESI+): m/
z calcd for C57H50IrNO4P+: 1036.31057; found: 1036.30991 [M]+.
C5b: According to GP1, [{IrACHTNUGRTNE(NUG dbcot)Cl}2] (167 mg, 193 mmol) and ligand
(S,S,aS)-L2 (234 mg, 396 mmol) were stirred in dry THF (10 mL) at room
temperature for 30 min. Then, crotyl methyl carbonate (104 mg,
800 mmol) and AgOTf (103 mg, 400 mmol) were added. After 18 h, the re-
sultant white precipitate was removed by filtration and the crude product
was subjected to flash column chromatography on silica gel (CH2Cl2 then
CH2Cl2/isopropanol, 97:3) to yield compound C5b (457 mg, 98%) as a
light yellow powder. 1H NMR (500.13 MHz, CD2Cl2): d=8.28 (d, J=
8.7 Hz, 1H; BINOL), 8.19 (d, J=8.8 Hz, 1H; BINOL), 8.13 (d, J=
8.2 Hz, 1H; BINOL), 8.01 (d, J=8.1 Hz, 1H; BINOL), 7.59–7.66 (m,
3H; 3ꢃBINOL), 7.46–7.55 (m, 3H; 2ꢃPh, BINOL), 7.26–40 (m, 4H; 2ꢃ
Ph, 2ꢃBINOL), 7.157.23 (m, 2H; Ph, BINOL), 6.88–7.07 (m, 7H; 3ꢃPh,
BINOL, 3ꢃArdbcot), 6.78 (d, J=7.5 Hz, 1H; Ardbcot), 6.75 (d, J=7.4 Hz,
1H; Ardbcot), 6.47 (dd, J=7.2, 7.2 Hz, 1H; Ardbcot), 5.99 (dd, J=7.6,
7.6 Hz, 1H; dbcotol-H), 5.67 (dd, J=7.3, 7.3 Hz, 1H; Ardbcot), 5.12 (d, J=
7.4 Hz, 1H; Ardbcot), 4.71 (dd, J=6.8, 6.8 Hz, 1H; dbcotol-H), 4.42–4.59
(m, 4H; 7-H, 7’-H, 1A-H, 2A-H), 4.19–4.24 (m, 1H; dbcotol-H), 4.13 (d,
J=9.1 Hz, 1H; dbcotol-H), 3.8 (s, 3H; OCH3), 3.54 (s, 3H; OCH3), 3.02
(m, 1H; 3A,syn-H), 2.36 (dd, J=11.6, 4.6 Hz, 1H; 8b-H), 2.09–2.16 (m,
1H; 3A,anti-H), 1.70–1.76 (m, 3H; CH3), 0.80 (dd, J=11.9, 11.9 Hz, 1H;
General procedure for the allylic substitution reactions (GP2, Scheme 1):
In a dry Schlenk flask under an argon atmosphere, a solution of [{Ir-
ACHTUNGTRENNUNG(dbcot)Cl}2] (2 mol%), ligand L2 (4 mol%), and TBD (8 mol%; in situ
procedure) or compound C5 (4 mol%) in absolute THF (0.5 mL) was
prepared and stirred at room temperature for 10 min; then, carbonate 1
(0.5 mmol), a pronucleophile (0.6 mmol), and, possibly, a base (8 mol%)
were added and the conversion was monitored by TLC.
(2E)-N,N,N-Trimethyl-3-phenylprop-2-en-1-aminium trifluoromethane-
sulfonate (4): Trimethylamine (4.2m in EtOH, 1.19 mL, 5.0 mmol) and
cinnamyl bromide (985 mg, 5.00 mmol) were added to a solution of
sodium triflate (860 mg, 5.00 mmol) in acetone (15 mL). The mixture was
stirred at room temperature for 30 min, and the resultant precipitate was
removed by filtration through a pad of Celite. The crude product was
subjected to flash column chromatography on silica gel (CH2Cl2/CH3OH,
9:1) to yield compound 4 (1.372 g, 84%) as a yellowish oil. 1H NMR
(300.19 MHz, CD3OD): d=7.59–7.54 (m, 2H; 2ꢃPh), 7.42–7.32 (m, 3H;
3ꢃPh), 7.00 (d, J=15.7 Hz, 1H; CHPh), 6.44 (dt, J=15.7, 7.7 Hz, 1H;
CHCH2), 4.11 (d, J=7.6 Hz, 2H; CH2), 3.15 ppm (s, 9H; CH3); 13C NMR
(75.48 MHz, CD3OD): d=144.47 (d; CHPh), 136.49 (s; Ph), 130.39 (d;
Ph), 129.86 (d; 2ꢃPh), 128.37 (d; 2ꢃPh), 116.12 (d; CHCH2), 69.46 (t;
CH2), 53.07 ppm (q; 3ꢃCH3); HRMS (ESI+): m/z calcd for
C25H36F3N2O3S+: 501.23932; found: 501.23967 [2M+CF3SO3]+.
ACTHNUTRGNEUNG
8a-H), 0.56 ppm (d, J=7.3 Hz, 3H; 8’-H); 13C{1 H,31P} NMR
(125.76 MHz, CD2Cl2): d=156.53, 156.46 (s; 2ꢃAr), 147.83, 146.15 (s; 2ꢃ
BINOL), 142.62, 141.32, 139.24, 136.66 (s; 4ꢃArdbcot), 132.9, 132.25,
131.75 (s; 3ꢃBINOL), 131.44 (d; BINOL), 131.26 (s; BINOL), 130.97 (d;
BINOL), 129.60 (s; Ar), 129.10 (d; Ar), 128.71 (d; Ar), 128.51 (s; Ar),
128.20 (d; Ar), 128.15 (d; BINOL), 128.03 (d; BINOL), 127.57 (d;
Ardbcot), 127.11, 127.07, 126.98, 126.93, 126.87, 126.75, 126.71, 126.66,
126.39 (d; 9ꢃAr), 125.99 (d; BINOL), 125.64 (d; Ardbcot), 125.49 (d;
BINOL), 124.81 (d; Ardbcot), 123.62 (d; Ar), 121.44, 120.86 (s; 2ꢃ
BINOL), 120.67, 120.15, 119.97 (d; 3ꢃAr), 110.36 (d; Ardbcot), 110.10 (d;
Ar), 107.00 (d; C2A), 103.81 (d; CH-dbcotol), 93.82 (d; CH-dbcotol), 91.27
(d; CH-dbcotol), 84.46 (d; C1A), 81.67 (d; CH-dbcotol), 59.10 (d; C7),
54.99, 54.43 (q; 2ꢃOCH3), 51.77 (d; C7’), 47.97 (t; C3A), 18.44 (q; C8’),
18.08 (t; C8), 14.61 ppm (q; CH3); 31P{1H} NMR (202.47 MHz, CD2Cl2):
d=112.92 ppm; HRMS (ESI+): m/z calcd for C58H52IrNO4P+:
1050.32623; found: 1050.32467 [M]+.
C5a: According to GP1, [{IrACHTUNTRGNEUNG(dbcot)Cl}2] (86 mg, 100 mmol) and ligand
(R,R,aR)-L2 (120 mg, 200 mmol) were stirred in dry THF (5 mL) at room
temperature for 30 min. Allyl methyl carbonate (46.4 mg, 400 mmol) and
AgOTf (51 mg, 200 mmol) were added. After 24 h, the resultant white
precipitate was removed by filtration and the crude product was subject-
ed to flash column chromatography on silica gel (CH2Cl2 then CH2Cl2/
isopropanol, 97:3) to yield compound C5a (228 mg, 96%) as a light
yellow powder. 1H NMR (600.13 MHz, CD2Cl2): d=8.31 (d, J=8.7 Hz,
1H; BINOL), 8.20 (d, J=8.8 Hz, 1H; BINOL), 8.13 (d, J=8.1 Hz, 1H;
BINOL), 8.01 (d, J=8.1 Hz, 1H; BINOL), 7.67 (d, J=8.8 Hz, 1H;
BINOL), 7.64 (d, J=8.8 Hz, 1H; BINOL), 7.61 (dd, J=7.4, 7.4 Hz, 1H;
BINOL), 7.48–7.54 (m, 2H; BINOL, Ph), 7.41 (d, J=7.4 Hz, 1H; Ph),
7.37 (dd, J=7.7, 7.7 Hz, 1H; Ph), 7.33 (dd, J=7.5, 7.5 Hz, 1H; Ph), 7.29
(dd, J=7.3, 7.3 Hz, 1H; BINOL), 7.27 (dd, J=7.3, 7.3 Hz; 1H; BINOL),
7.18–7.24 (m, 2H; BINOL, Ph), 7.03 (d, J=7.6 Hz, 1H; Ardbcot), 6.96–
7.01 (m, 3H; 2ꢃPh, Ardbcot), 6.89–6.94 (m, 3H; Ph, Ardbcot, BINOL), 6.82
(d, J=7.5 Hz, 1H; Ardbcot), 6.77 (d, J=7.7 Hz, 1H; Ardbcot), 6.48 (dd, J=
7.3, 7.3 Hz, 1H; Ardbcot), 6.04 (dd, J=7.8, 7.8 Hz, 1H; 2C-H), 5.68 (dd, J=
7.3, 7.3 Hz, 1H; Ardbcot), 5.13 (d, J=8.2 Hz, 1H; 4C-H), 5.10 (d, J=
7.5 Hz, 1H; Ardbcot), 4.76 (dd, J=7.5, 7.5 Hz, 1H; 3C-H), 4.68–4.73 (m,
1H; 7-H), 4.63–4.68 (m, 1H; 2A-H), 4.51–4.56 (m, 1H; 1A,syn-H), 4.44–
4.51 (m, 1H; 7’-H), 4.31 (d, J=9.2 Hz, 1H; 1C-H), 3.86 (s, 3H; OCH3),
3.76 (dd, J=10.3, 10.3 Hz, 1H; 1A,anti-H), 3.58 (s, 3H; OCH3), 3.49 (dd,
J=7.9, 7.9 Hz, 1H; 3A,syn-H), 2.61 (d, J=11.9 Hz, 1H; 3A,anti-H), 2.00 (dd,
J=11.6, 5.6 Hz, 1H; 8b-H), 0.90 (dd, J=11.3, 11.3 Hz, 1H; 8a-H),
0.55 ppm (d, J=7.4 Hz, 3H; 8’-H); 13C{1H} NMR (150.90 MHz, CD2Cl2):
C5c: According to GP1, [{IrACHTNUGRTNE(NUG dbcot)Cl}2] (173 mg, 200 mmol) and ligand
(R,R,aR)-L2 (240 mg, 400 mmol) were stirred in dry THF (10 mL) at
room temperature for 30 min. Then, cinnamyl methyl carbonate 1a
(154 mg, 800 mmol) and AgOTf (103 mg, 400 mmol) were added. After
18 h, the resultant white precipitate was removed by filtration and the
crude product was subjected to flash column chromatography on silica
gel (CH2Cl2 then CH2Cl2/isopropanol, 97:3) to yield compound C5c
1
(478 mg, 95%) as a light yellow powder. H NMR (600.13 MHz, CD2Cl2):
d=8.33 (d, J=8.8 Hz, 1H; BINOL), 8.20 (d, J=8.9 Hz, 1H; BINOL),
8.15 (d, J=8.2 Hz, 1H; BINOL), 8.01 (d, J=8.4 Hz, 1H; BINOL), 7.71
(d, J=8.8 Hz, 1H; BINOL), 7.60–7.66 (m, 2H; 2ꢃBINOL), 7.57 (d, J=
7.9 Hz, 1H; Ph), 7.48–7.53 (m, 2H; Ph, BINOL), 7.35–7.41 (m, 3H;
PhAllyl, 2ꢃPh), 7.20–7.32 (m, 5H; 2ꢃPhAllyl, 3ꢃBINOL), 7.18 (dd, J=7.3,
7.3 Hz, 1H; Ph), 7.04–7.10 (m, 3H; Ardbcot, 2ꢃPh), 6.98 (ddd, J=7.6, 7.6,
1.1 Hz, 1H; Ardbcot), 6.95 (d, J=8.0 Hz, 1H; Ph), 6.91 (d, J=8.5 Hz, 1H;
BINOL), 6.89 (d, J=7.7 Hz, 1H; Ardbcot), 6.76–6.83 (m, 2H; 2ꢃPhAllyl),
6.69 (d, J=7.6 Hz, 1H; Ardbcot), 6.67 (d, J=7.7 Hz, 1H; Ardbcot), 6.45 (dd,
J=7.3, 7.3 Hz, 1H; Ardbcot), 6.10 (dd, J=9.0, 6.5 Hz, 1H; dbcotol-H), 5.65
(dd, J=7.4, 7.4 Hz, 1H; Ardbcot), 5.43–5.50 (m, 1H; 1A-H), 5.23–5.30 (m,
1H; 2A-H), 5.18 (d, J=7.7 Hz, 1H; Ardbcot), 4.71 (dd, J=11.8, 5.3 Hz,
1H; 7-H), 4.53–4.64 (m, 2H; 7’-H, dbcotol-H), 4.47 (d, J=9.1 Hz, 1H;
d=156.50, 156.39 (s; 2ꢃPh), 147.87 (s, J
(s, J(C,P)=7.6 Hz; BINOL), 142.99, 140.66, 138.98, 136.71 (s; 4ꢃArdbcot),
132.83, 132.18, 131.71 (s; 3ꢃBINOL), 131.47 (d; BINOL), 131.15 (s;
BINOL), 130.96 (d; BINOL), 129.44 (s, J(C,P)=11.6 Hz; Ph), 128.97,
ACHTUNGTNER(NUNG C,P)=16.5 Hz; BINOL), 146.12
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
dbcotol-H), 4.10 (s, 3H; OCH3), 3.59 (s, 3H; OCH3), 3.46 (dd, J=8.7,
3.2 Hz, 1H; dbcotol), 3.05 (dd, J=7.5, 7.5 Hz, 1H; 3A,syn-H), 2.27–2.34 (m,
2H; 8b-H, 3A,anti-H), 0.80 (dd, J=11.7, 11.7 Hz, 1H; 8a-H), 0.59 (d, J=
7.5 Hz, 3H; 8’-H); 13C{1H} NMR (150.90 MHz, CD2Cl2): d=156.55,
then CH2Cl2/isopropanol, 97:3) to yield compound C5e (229 mg, 95%) as
a light yellow powder. 1H NMR (500.13 MHz, CD2Cl2): d=8.37 (d, J=
8.8 Hz 1H; BINOL), 8.15–8.21 (m, 2H; 2ꢃBINOL), 7.99 (d, J=8.2 Hz,
1H; BINOL), 7.84 (d, J=8.8 Hz, 1H; BINOL), 7.62–7.67 (m, 2H; 2ꢃ
156.29 (s; 2ꢃPh), 147.72 (s, J
(C,P)=8.5 Hz; BINOL), 141.49, 141.45, 139.36, 137.14 (s; 4ꢃArdbcot),
132.85, 132.23 (s; 2ꢃBINOL), 132.07 (s, J(C,P)=6.0 Hz; PhAllyl), 131.79
(s; BINOL), 131.52 (d; BINOL), 131.27 (s; BINOL), 131.00 (d; BINOL),
129.63 (d; Ardbcot), 129.52 (s, J(C,P)=12.8 Hz; Ph), 129.36, 129.26, 128.82
(d; 3ꢃPh), 128.40, 128.39 (d; 2ꢃPhAllyl), 128.35 (s; Ph), 128.21 (d; Ph),
128.14, 128.05 (d; 2ꢃBINOL), 127.21 (2d; 2ꢃPhAllyl), 127.10 (d; Ardbcot),
127.08 (d; Ph), 126.94 (d; BINOL), 126.83 (d; Ardbcot), 126.83, 126.71 (d;
2ꢃBINOL), 126.71 (d; Ardbcot), 126.42 (d; Ph), 126.32 (d; Ardbcot), 126.06
(d; BINOL), 125.71 (d; Ar), 125.51, 124.89 (d; 2ꢃArdbcot), 123.40 (d; Ph),
121.45, 121.42 (s; 2ꢃBINOL), 120.83 (d; BINOL), 120.83, 120.28 (d; 2ꢃ
Ph), 119.82 (d; BINOL), 110.21 (d; Ardbcot), 110.16 (d; Ph), 102.95 (d;
ACHTUNGTRNE(NUNG C,P)=16.6 Hz; BINOL), 146.05 (s, J-
BINOL), 7.48–7.57 (m, 3H; BINOL, 2ꢃPh), 7.27–7.47 (m, 9H; PhAllyl
,
ACHTUNGTRENNUNG
2ꢃBINOL, 6ꢃPh), 7.20–7.27 (m, 5H; BINOL, 2ꢃPhAllyl, 2ꢃPh), 7.06
(dd, J=7.3, 7.3 Hz, 1H; Ardbcot), 6.98 (dd, J=7.2, 7.2 Hz, 1H; Ardbcot),
6.94 (d, J=8.4 Hz, 1H; BINOL), 6.91 (d, J=7.7 Hz, 1H; Ardbcot), 6.81 (d,
J=7.7 Hz, 1H; Ardbcot), 6.68–6.75 (m, 3H; Ardbcot, 2ꢃPhAllyl), 6.54 (dd, J=
7.4, 7.4 Hz, 1H; Ardbcot), 5.99 (d, J=9.3 Hz, 1H; dbcotol-H), 5.80 (dd, J=
7.5, 7.5 Hz, 1H; Aryldbcot), 5.55 (d, J=13.0 Hz, 1H; 1A-H), 5.14–5.23 (m,
1H; 2A-H), 5.06 (d, J=7.7 Hz, 1H; Ardbcot), 4.79 (d, J=8.7 Hz, 1H; dbco-
tol-H), 4.64 (d, J=9.3 Hz, 1H; dbcotol-H), 3.91–4.07 (m, 2H; 7-H, 7’-H),
3.51 (d, J=8.7 Hz, 1H; dbcotol-H), 3.27 (d, J=6.8 Hz, 1H; 3A,syn-H), 2.60
(d, J=11.2 Hz, 1H; 3A,anti-H), 2.07 (dd, J=12.4, 5.4 Hz, 1H; 8b-H), 1.04
(dd, J=12.0 Hz, 1H; 8a-H), 0.69 ppm (d, J=7.4 Hz, 3H; 8’-H); 13C NMR
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
CH-dbcotol), 97.66 (d, J
CH-dbcotol), 93.15 (d; CH-dbcotol), 90.26 (d, J
84.77 (d, J(C,P)=6.6 Hz; CH-dbcotol), 59.17 (d, J
54.90, 54.51 (q; 2ꢃOCH3), 51.77 (d, J(C,P)=4.8 Hz; C7’),46.01 (t; C3A),
A
ACHTUNGTREN(NUNG C,P)=4.6 Hz;
(125.76 MHz, CD2Cl2): 147.82 (s, J
ACHTUNGTRNE(NUNG C,P)=17.0 Hz; BINOL), 146.34 (s, J-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
137.19 (s; PhAllyl,, 2ꢃPh, 4ꢃArdbcot), 132.96, 132.22, 131.86 (s; 3ꢃBINOL),
131.81 (d; BINOL), 131.24 (s; BINOL), 131.17 (d; BINOL), 129.52,
129.66 (d; 2ꢃPhAllyl), 129.10 (d; 2ꢃPh), 128.57 (d; 2ꢃPhAllyl), 128.29 (d;
2ꢃPh), 128.15, 128.13 (d; BINOL), 127.87, 127.94, 127.79 (d; 4ꢃPh),
127.07, 127.09, 127.12, 127.18, 127.19 (d, BINOL; 3ꢃArdbcot, PhAllyl),
126.90, 126.81 (d; Ardbcot,), 126.77, 126.75, 126.41 (d; 3ꢃBINOL), 126.35
(d; Ardbcot,), 126.11 (d; BINOL), 125.85 (d; 2ꢃPh), 125.74 (d; BINOL),
AHCTUNGTRENNUNG
21.55 (t, JACHTUNGTRENNUNG
(C,P)=7.7 Hz; C8), 18.40 (q; C8’); 31P{1H} NMR (242.94 MHz,
CD2Cl2): d=110.81 ppm; HRMS (ESI+): m/z calcd for C63H54IrNO4P+:
1112.34195; found: 1112.34094 [M]+.
C5d: According to GP1, [{IrACHTNUGRTNE(NUG dbcot)Cl}2] (173 mg, 201 mmol) and ligand
(S,S,aS)-L1 (217 mg, 402 mmol) were stirred in dry THF (10 mL) at room
temperature for 60 min. Then, crotyl methyl carbonate (104 mg,
798 mmol) and AgOTf (104 mg, 406 mmol) were added. After 21 h, the re-
sultant white precipitate was removed by filtration and the crude product
was subjected to flash column chromatography on silica gel (CH2Cl2 then
CH2Cl2/isopropanol, 97:3) to yield compound C5d (385 mg, 84%) as a
light-yellow powder. 1H NMR (500.13 MHz, CD2Cl2): d=8.35 (d, J=
8.8 Hz, 1H; BINOL), 8.16 (2d, J=8.7 Hz, 2H; 2ꢃBINOL), 7.98 (d, J=
8.2 Hz, 1H; BINOL), 7.76 (d, J=8.8 Hz, 1H; BINOL), 7.61–7.66 (m 2H;
2ꢃBINOL), 7.47–7.53 (m, 3H; BINOL, 2ꢃPh), 7.26–7.43 (m 8H; 2ꢃ
BINOL, 6ꢃPh), 7.17–7.23 (m, 3H; BINOL, 2ꢃPh), 7.06 (d, J=7.5 Hz,
1H; Ardbcot), 6.92–7.01 (m, 3H; BINOL, 2ꢃArdbcot), 6.89 (d, J=7.6 Hz,
1H; Ardbcot), 6.76 (d, J=7.0 Hz, 1H; Ardbcot), 6.57 (dd, J=7.2, 7.2 Hz,
1H; Ardbcot), 5.87 (dd, J=8.9, 6.8 Hz, 1H; dbcotol-H), 5.82 (dd, J=7.2,
7.2 Hz, 1H; Ardbcot), 4.97 (d, J=7.6 Hz, 1H; Ardbcot), 4.85 (dd, J=8.5,
6.3 Hz, 1H; dbcotol-H), 4.38–4.52 (m, 2H; 2A-H, 1A-H), 4.27 (d, J=
9.2 Hz, 1H; dbcotol-H), 4.22 (dd, J=8.6, 3.0 Hz, 1H; dbcotol-H), 3.89–
3.98 (m, 1H; 7’-H), 3.81 (dd, J=11.5, 5.4 Hz, 1H; 7-H), 3.17–3.23 (m,
1H; 3A,syn-H), 2.38 (d, J=11.0 Hz, 1H; 3A,anti-H), 2.13 (dd, J=11.7,
5.6 Hz, 1H; 8b-H), 1.67 (dd, J=8.5, 5.3 Hz, 3H; CH3), 1.04 (dd, J=
11.6 Hz, 1H; 8a-H), 0.66 ppm (d, J=7.4 Hz, 3H; 8’-H); 13C NMR
125.69, 125.12 (d; 2ꢃArdbcot), 121.46 (s; BINOL), 121.18 (s, J
3.1 Hz; BINOL), 121.02 (d, (C,P)=3.1 Hz; BINOL), 119.69 (d;
BINOL), 104.14 (d; CH-dbcotol), 98.05 (d, J(C,P)=4.1 Hz; C2A), 93.01
(d, J(C,P)=4.5 Hz; CH-dbcotol), 91.00 (d, J(C,P)=22.1 Hz; C1A), 84.58
(d, J(C,P)=6.7 Hz; CH-dbcotol), 65.43 (d, J(C,P)=31.0 Hz; C7), 59.79 (d,
(C,P)=5.3 Hz; C7’),46.43 (t; C3A), 24.18 (t, (C,P)=6.4 Hz; C8),
ACHTUNGTRENNUNG(C,P)=
JACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
J
N
JACHTUNGTRENNUNG
18.37 ppm (q; C8’); 31P{1H} NMR (202.46 MHz, CD2Cl2): d=110.57 ppm;
HRMS (ESI+): m/z calcd for C61H50IrNO2P+: 1052.32079; found
1052.31884 [M]+.
X-ray crystal structure analysis: Data sets were collected on a Bruker
Smart CCD (C5c, C5d) or a Bruker APEX (C5a, C5b, C5e) diffractome-
ter with MoKa radiation (l=0.71073 ꢂ, graphite monochromator) at
200 K. A complete sphere in reciprocal space was covered by 0.38 w-
scans in all cases. For all datasets, the intensities were corrected for Lor-
entz and polarization effects; an empirical absorption correction, based
on the Laue symmetry of the reciprocal space, was applied by using
SADABS.[30] All structures were solved by using direct methods and re-
fined against F2 with
a full-matrix least-squares algorithm and the
SHELXTL software package.[31] Hydrogen atoms were treated by using
appropriate riding models.
(125.76 MHz, CD2Cl2): d=147.89 (s, J
ACHTUNGTRENNUNG
J
N
For compounds C5a, C5b, C5c, and C5e, the diffusion-controlled crystalli-
zation of racemates, which were obtained by mixing enantiomers, was
performed as follows: In a shortened NMR tube (length 10 cm), a solu-
tion of racemic complex C5 in CH2Cl2 was carefully covered with a layer
of Et2O. This procedure furnished crystals that were suitable for X-ray
analysis. In the case of compound C5d, single crystals were obtained
from a solution of the enantiopure compound, which was derived from
ligand (S,S,aS)-L1, in [D8]THF.
Ph), 141.16 (s; Ardbcot), 139.73 (s; Ph), 139.05, 136.50 (s; 2ꢃArdbcot),
133.02, 132.22, 131.76 (s; 3ꢃBINOL), 131.70 (d; BINOL), 131.21 (s;
BINOL), 131.13 (d; BINOL), 129.07 (d; 2ꢃPh), 128.00, 128.06, 128.12,
128.14, 128.26, 128.26 (d; 2ꢃBINOL, 4ꢃPh), 127.69 (d; 2ꢃPh), 127.51,
127.20 (d; 2ꢃArdbcot), 126.88, 126.94, 126.99, 127.12, 127.15 (d; BINOL,
4ꢃArdbcot), 126.78, 126.77, 126.42, 126.13 (d; 4ꢃBINOL), 125.97 (d; 2ꢃ
Ph), 125.78 (d; Ardbcot), 125.68 (d; BINOL), 125.04 (d; Ardbcot), 121.54 (s,
J
ACHTUNGTREN(NUNG C,P)=3.3 Hz;
C5a: Brownish crystals (polyhedra); 0.28ꢃ0.14ꢃ0.10 mm3; monoclinic;
space group C2/c; Z=8; a=25.955(3), b=19.1317(19), c=21.760(2) ꢂ;
b=102.424(2)8; V=10552.2(18) ꢂ3; 1=1.546 gcmꢀ3; qmax =28.338; total
reflns 55471; unique reflns 13134 (Rint =0.0454); observed reflns 11057
[I>2s(I)]; m=2.72 mmꢀ1; Tmin =0.52, Tmax =0.77; 709 parameters refined;
GOF 1.17 for observed reflections; final residual values R1(F)=0.056,
wR(F2)=0.137 for observed reflections; residual electron density ꢀ2.12
AHCTUNGTRENNUNG
J
JACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(C,P)=4.2 Hz; CH3); 31P{1H} NMR (202.47 MHz, CD2Cl2): d=
112.68 ppm; HRMS (ESI+): m/z calcd for C56H48IrNO2P+: 990.30507;
found 990.30502 [M]+.
to 1.69 eꢂꢀ3
.
C5b: Brownish crystals (polyhedra); 0.22ꢃ0.22ꢃ0.14 mm3; monoclinic;
space group C2/c; Z=8; a=25.955(4), b=19.068(3), c=21.794(3) ꢂ; b=
102.170(3)8; V=10544(2) ꢂ3; 1=1.564 gcmꢀ3; qmax =28.398; total reflns
55579; unique reflns 13169 (Rint =0.0352); observed reflns 11403 [I>
2s(I)]; m=2.72 mmꢀ1; Tmin =0.59, Tmax =0.70; 698 parameters refined;
GOF 1.08 for observed reflections; final residual values R1(F)=0.037,
C5e: According to GP1, [{IrACHTUNTRGNEUNG(dbcot)Cl}2] (86 mg, 100 mmol) and ligand
(S,S,aS)-L1 (108 mg, 200 mmol) were stirred in dry THF (5 mL) at room
temperature for 60 min. Cinnamyl methyl carbonate 1a (77 mg,
400 mmol) and AgOTf (51.4 mg, 200 mmol) were added. After 24 h, the
resultant white precipitate was removed by filtration and the crude prod-
uct was subjected to flash column chromatography on silica gel (CH2Cl2
Chem. Eur. J. 2012, 00, 0 – 0
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G. Helmchen et al.
wR(F2)=0.091 for observed reflections; residual electron density ꢀ0.66
[7] S. Spiess, C. Welter, G. Franck, J.-P. Taquet, G. Helmchen, Angew.
Chem. 2008, 120, 7764; Angew. Chem. Int. Ed. 2008, 47, 7652.
[8] G. Franck, M. Brill, G. Helmchen, Org. Synth. 2012, 89, 55.
[9] a) G. Franck, K. Brçdner, G. Helmchen, Org. Lett. 2010, 12, 3886;
b) P. Tosatti, J. Horn, A. J. Canpbell, D. House, A. Nelson, S. P.
Marsden, Adv. Synth. Catal. 2010, 352, 3153; c) M. Gꢀrtner, S.
Mader, K. Seehafer, G. Helmchen, J. Am. Chem. Soc. 2011, 133,
2072; d) K.-Y. Ye, H. He, W.-B. Liu, L.-X. Dai, G. Helmchen, S.-L.
You, J. Am. Chem. Soc. 2011, 133, 19006; e) K.-Y. Ye, L.-X. Dai, S.-
L. You, Org. Biol. Chem. 2012, 10, 5932.
to 1.92 eꢂꢀ3
.
C5c: Brownish crystals (polyhedra); 0.34ꢃ0.22ꢃ0.14 mm3; triclinic; space
¯
group P1; Z=2; a=12.1337(1), b=14.9512(1), c=18.4822(1) ꢂ; a=
85.5960(10)8, b=80.7790(10)8, g=75.0460(10)8; V=3195.30(4) ꢂ3; 1=
1.488 gcmꢀ3; qmax =27.478; total reflns 32222; unique reflns 14474 (Rint
=
0.0406); observed reflns 13031 [I>2s(I)]; m=2.38 mmꢀ1
max =0.73; 853 parameters refined; GOF 1.08 for observed reflections;
; Tmin =0.50,
T
final residual values R1(F)=0.040, wR(F2)=0.105 for observed reflec-
tions; residual electron density ꢀ1.39 to 1.64 eꢂꢀ3
.
´
[10] a) S. T. Madrahimov, D. Markovic, J. F. Hartwig, J. Am. Chem. Soc.
C5d: Colorless crystals (polyhedra); 0.34ꢃ0.27ꢃ0.18 mm3; monoclinic;
´
2009, 131, 7228; b) D. Markovic, J. F. Hartwig, J. Am. Chem. Soc.
space group P21; Z=2; a=13.8110(1), b=11.5716(1), c=17.0108(1) ꢂ;
2007, 129, 11680; c) S. T. Madrahimov, J. F. Hartwig, J. Am. Chem.
Soc. 2012, 134, 8136.
b=95.170(1)8; V=2707.53(3) ꢂ3; 1=1.471 gcmꢀ3
; qmax =27.438; total
reflns 27177; unique reflns 12047 (Rint =0.0324); observed reflns 11251
[I>2s(I)]; m=2.59 mmꢀ1; Tmin =0.47, Tmax =0.65; 655 parameters refined;
GOF 1.07 for observed reflections; final residual values R1(F)=0.024,
wR(F2)=0.059 for observed reflections; residual electron density ꢀ0.49
[11] a) J. A. Raskatov, S. Spiess, C. Gnamm, K. Brçdner, F. Rominger, G.
Helmchen, Chem. Eur. J. 2010, 16, 6601; b) S. Spiess, J. A. Raskatov,
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[13] T. Ohmura, J. F. Hartwig, J. Am. Chem. Soc. 2002, 124, 15164.
[14] T. Doi, A. Yanagisawa, M. Miyazawa, K. Yamamoto, Tetrahedron:
Asymmetry 1995, 6, 389.
[15] Corresponding experiments with an analogous cod complex gave
analogous results, see: S. Spiess, Dissertation, Universitꢀt Heidel-
berg, 2009. Furthermore, the resting state of the alkylation with di-
methyl malonate as a pronucleophile was also investigated with a
dbcot complex as the catalyst. The (p-allyl)Ir complex was found as
a resting state, as in the case of the cod complexes (see ref. [11a]).
[16] a) K. D. John, K. V. Salazar, B. L. Scott, R. T. Baker, A. P. Sattel-
berger, Organometallics 2001, 20, 296; b) B. Bartels, C. Garcia-
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c) C. Garcꢅa-Yebra, J. P. Janssen, F. Rominger, G. Helmchen, Orga-
nometallics 2004, 23, 5459.
to 0.62 eꢂꢀ3
.
C5e: Brownish crystals (plates); 0.27ꢃ0.24ꢃ0.07 mm3; triclinic; space
¯
group P1; Z=4; a=16.0194(17), b=16.9075(18), c=23.284(3) ꢂ; a=
74.654(2)8, b=73.921(2)8, g=68.160(2)8; V=5531.6(10) ꢂ3; 1=
1.538 gcmꢀ3; qmax =28.498; total reflns 74653; unique reflns 27190 (Rint
=
0.0416); observed reflns 32494 [I>2s(I)]; m=2.59 mmꢀ1
max =0.84; 1432 parameters refined; GOF 1.09 for observed reflections;
; Tmin =0.54,
T
final residual values R1(F)=0.052, wR(F2)=0.116 for observed reflec-
tions; residual electron density ꢀ1.41 to 2.12 eꢂꢀ3
.
CCDC-883814 (C5a), CCDC-883815 (C5b), CCDC-883816 (C5c),
CCDC-883817 (C5d), and CCDC-883818 (C5e) contain the supplementa-
ry crystallographic 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.
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Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 623). We thank Kerstin Brçdner and Olena Tverskoy for experi-
mental assistance, and Prof. Dr. Klaus Ditrich, BASF SE, for providing
enantiopure arylethylamines.
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Iridium-Catalyzed Allylic Substitutions with Phosphoramidites
FULL PAPER
[27] C. Gnamm, G. Franck, N. Miller, T. Stork, K. Brçdner, G. Helm-
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[30] G. M. Sheldrick, SADABS 2008/1, Bruker Analytical X-ray Divi-
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Received: May 19, 2012
Published online: && &&, 0000
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G. Helmchen et al.
Bigger is better: The replacement of
cod by dibenzo-cot is worth the effort
because (allyl)Ir complexes of the
latter compound are catalysts that give
rise to improved regioselectivity and
stability in iridium-catalyzed allylic
aminations and alkylations.
Reaction Mechanisms
J. A. Raskatov, M. Jꢀkel, B. F. Straub,
F. Rominger, G. Helmchen* &&&& — &&&&
Iridium-Catalyzed Allylic Substitutions
with Cyclometalated Phosphoramidite
Complexes Bearing a Dibenzocyclooc-
tatetraene Ligand: Preparation of (p-
Allyl)Ir Complexes and Computational
and NMR Spectroscopic Studies
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www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
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