Spiroketal-based phosphorus ligands for highly regioselective hydroformylation of terminal and internal olefins

Article abstract of DOI:10.1002/chem.201203042

A new class of bidentate phosphoramidite ligands, based on a spiroketal backbone, has been developed for the rhodium-catalyzed hydroformylation reactions. A range of short- and long-chain olefins, were found amenable to the protocol, affording high catalytic activity and excellent regioselectivity for the linear aldehydes. Under the optimized reaction conditions, a turnover number (TON) of up to 2.3×10⁴ and linear to branched ratio (l/b) of up to 174.4 were obtained in the Rh^I-catalyzed hydroformylation of terminal olefins. Remarkably, the catalysts were also found to be efficient in the isomerization-hydroformylation of some internal olefins, to regioselectively afford the linear aldehydes with TON values of up to 2.0×10⁴ and l/b ratios in the range of 23.4-30.6. X-ray crystallographic analysis revealed the cis coordination of the ligand in the precatalyst [Rh(3 d)(acac)], whereas NMR and IR studies on the catalytically active hydride complex [HRh(CO)₂(3 d)] suggested an eq-eq coordination of the ligand in the species. Spiro-spine! The effect of a spiro backbone was observed in the rhodium-catalyzed hydroformylation of terminal and internal olefins. High activity and excellent regioselectivity for the formation of linear aldehydes was realized in the case of the matched stereochemistry of the ligand (see scheme). It was found that the spiroketal is superior to biphenyl as the backbone of the ligand in terms of the regioselectivity of hydroformylation. Copyright

Full text of DOI:10.1002/chem.201203042

DOI: 10.1002/chem.201203042
Spiroketal-Based Phosphorus Ligands for Highly Regioselective
Hydroformylation of Terminal and Internal Olefins
Xiaofei Jia,[a, b] Zheng Wang,[b] Chungu Xia,*[a] and Kuiling Ding*[b]
15288
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 15288 – 15295

FULL PAPER
Abstract: A new class of bidentate
phosphoramidite ligands, based on a
spiroketal backbone, has been devel-
oped for the rhodium-catalyzed hydro-
branched ratio (l/b) of up to 174.4 were
obtained in the RhI-catalyzed hydrofor-
mylation of terminal olefins. Remark-
hydes with TON values of up to 2.0ꢁ
104 and l/b ratios in the range of 23.4–
30.6. X-ray crystallographic analysis re-
vealed the cis coordination of the
AHCTUNGTRENNaGUN bly, the catalysts were also found to
formylation reactions.
A
range of
be efficient in the isomerization–hydro-
formylation of some internal olefins, to
regioselectively afford the linear alde-
ligand in the precatalyst [Rh
(acac)], whereas NMR and IR studies
on the catalytically active hydride com-
plex [HRh(CO)2A(3d)] suggested an eq–
eq coordination of the ligand in the
species.
ACHTUNGTRENNUNG(3d)-
short- and long-chain olefins, were
found amenable to the protocol, af-
fording high catalytic activity and ex-
cellent regioselectivity for the linear al-
dehydes. Under the optimized reaction
conditions, a turnover number (TON)
of up to 2.3ꢁ104 and linear to
ACHTUNGTRENNUNG
CTHUNGTRENNUNG
Keywords: homogeneous catalysis ·
hydroformylation · ligands · olefins ·
regioselectivity · rhodium
Introduction
Rhodium-catalyzed olefin hydroformylation is one of the
most important processes of homogeneous catalysis in in-
dustry.[1] Several million tons of various aldehydes and their
derivatives are produced worldwide per year. A key issue in
searching for efficient hydroformylation catalysts is the de-
velopment of new ligands. Monodentate phosphorus ligands
have been most commonly used in commercial hydroformy-
lation processes, but regioselectivity can become a concern
in some cases. Over the past several decades, a variety of
bisACHTUNGTRENNUNG
phosphorus ligands[2] have been successfully developed
for Rh-catalyzed hydroformylation of olefins (Scheme 1).
Despite these efforts, however, the catalytic systems that are
efficient and selective for hydroformylation of both terminal
olefins and the internal olefins still remain rare so far. Li-
gands that bear a biaryl scaffold with C2-symmetry, such as
Naphos,[3] Biphephos,[4] DuPont/DSM ligand,[5] pyrrole-
based bisphosphoramidite[6] and tetraphosphoramidite,[7]
have been reported to show excellent regioselectivities in
the hydroformylation of both terminal and internal olefins.
Xantphos, with a rigid xanthene structure initiated by van
Leeuwen, was shown to be a highly selective hydroformyla-
tion catalyst.[8] However, there was still room for improve-
ment in reactivity, regioselectivities, and/or substrate gener-
ality, particularly for the hydroformylation of internal ole-
fins. On the other hand, some spiro structures have been
Scheme 1. Selected examples of phosphine ligands for Rh-catalyzed hy-
droformylation of olefins.
recognized as being the privileged backbone for the con-
struction of chiral ligands in asymmetric catalysis,[9] which
have been rarely explored in the hydroformylation of ole-
fins.[10] In the present work, we report the development of a
new class of bisphosphorus ligands with a spiroketal back-
bone[11] and chelating units of N-pyrrolylphosphorus
(Scheme 2), whose high p-acidity has been disclosed as a
highly desirable attribute for hydroformylation of internal
olefins.[6–7] The rhodium complexes of these ligands were
shown to be highly efficient and regioselective in the catalyt-
ic hydroformylation of various terminal and internal olefins.
[a] X. Jia, Prof. Dr. C. Xia
State Key Laboratory of Oxo Synthesis and
Selective Oxidation, Lanzhou Institute of Chemical Physics
Chinese Academy of Sciences, 18 Tianshui Middle Road
Lanzhou 730000 (P.R. China)
Results and Discussion
The spiroketal-derived bisphosphoramidite ligands 3a–i
were readily synthesized by using a four-step reaction se-
quence (for details, see the Supporting Information). As
show in Scheme 2, the base-mediated condensation of 2,3-
dimethoxyarylaldehydes and alkyl ketones afforded the
bis(2,3-dimethoxybenzylidene)cyclopentanone derivatives 1
in good to excellent yields. Ni-catalyzed hydrogenation of 1,
followed by BBr3-mediated demethylation and acetalization
in one-pot, gave the key intermediate diphenols 2 as a cis/
trans isomeric mixture. The desired ligands 3 were finally
E-mail: cgxia@lzb.ac.cn
[b] X. Jia, Dr. Z. Wang, Prof. Dr. K. Ding
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences, 345 Lingling Road
Shanghai 200032 (P.R. China)
Fax : (+86)21-6416-6128
E-mail: kding@mail.sioc.ac.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203042.
Chem. Eur. J. 2012, 18, 15288 – 15295
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www.chemeurj.org
15289

K. Ding et al.
Table 1. Optimization of reaction conditions for the 3a/[RhACHTNUGTRENUNG(acac)(CO)2]-
catalyzed hydroformylation of 1-hexene.[a]
Entry
3a/
Rh
T
CO/H2
[bar]
l/b[b]
Linear[c]
[%]
Iso[d]
[%]
TON[e]
ACHTUNGTRENNUNG
[ꢁ103]
[8C]
U
1
2
3
4
5
6
7
8
9
1:1
2:1
3:1
4:1
2:1
2:1
2:1
2:1
2:1
100
100
100
100
90
110
140
100
100
20/20
20/20
20/20
20/20
20/20
20/20
20/20
10/10
30/30
21.9
146.1
160.3
146.1
177.6
103.2
50.0
95.6
99.3
99.4
99.3
99.4
99.0
98.0
99.4
99.1
17.9
16.0
18.3
17.6
12.7
18.9
23.7
27.1
11.1
6.9
7.5
7.5
7.5
6.3
6.9
7.5
6.3
7.8
157.7
113.9
[a] S/C=10000, [RhACHTNUTRGNEUNG(acac)(CO)2] (0.001 mmol), toluene (1.0 mL) as sol-
vent, decane as the internal standard, reaction time=3 h. [b] Linear/
branched ratio, determined by GC analysis. [c] Percentage of linear alde-
hyde in all aldehydes. [d] Isomerization to 2-hexenes. [e] Turnover
number, determined by GC analysis.
perature of 1408C (l/b=50.0, entry 7), attesting the thermal
robustness of the catalyst system, which is a valuable attrib-
ute for industrial high-temperature hydroformylation of
long-chained olefins.[12] The partial pressure of the syngas
was also found to be crucial for the reaction. Decreasing the
H2/CO pressure from 20/20 to10/10 bar resulted in a higher
percentage of alkene isomerization (Table 1, entry 8 vs. 2),
whereas increasing the H2/CO pressure to 30/30 bar led to
an enhancement of the rate and alleviated isomerization,
albeit at a cost of slightly lower regioselectivity (Table 1,
entry 9). Thus, the preliminary optimal conditions (toluene,
1008C, H2/CO=20/20 bar, substrate/L/Rh=10000:2:1) were
chosen for the ligand screening.
Subsequently, ligands 3b–j were tested for Rh-catalyzed
hydroformylation of 1-hexene under the reaction conditions
optimized above for ligand 3a. The results are shown in
Table 2. In comparison with 3a, ligand 3b with an ortho-
methyl substituent gave a substantially lower l/b ratio and a
declined reaction rate, whereas 3c with an ortho-chlorine on
Scheme 2. Synthesis of bisphosphoramidite ligands 3a–i.
prepared by treatment of diphenols 2 with chlorodipyroly-
phosphine in the presence of Et3N as a HCl scavenger.
These ligands are stable enough in the air, and were purified
by column chromatography on silica gel without special pre-
caution to water or air.
The RhI-catalyzed hydroformylation of terminal olefins
was first studied with spiroketal-based phosphorus ligand 3a
as the ligand and 1-hexene as the model substrate. The cata-
lyst was prepared in situ by mixing [RhACTHNUTRGNEN(UG acac)(CO)2] with
ligand 3a at the specified molar ratios, and the reactions
were carried out in toluene. For a preliminary screening of
reaction conditions, a substrate/catalyst (S/C) ratio of 10000
was used. The effects of the ligand/metal ratio, reaction tem-
perature, as well as the partial pressures of CO/H2 were ex-
amined, and the results are summarized in Table 1. Under
otherwise identical conditions, increasing the 3a/RhI ratio
from 1:1 to 2:1 resulted in a considerable enhancement of
the regioselectivity towards the linear aldehyde (l/b ratio
from 21.9 to 146.1, Table 1, entry 2 vs. 1), whereas further in-
crement of the ligand/metal ratio did not alter the regiose-
lectivity to a significant extent (Table 1, entries 3–4 vs. 2).
As expected, the reaction temperature also displayed a sig-
nificant effect on the hydroformylation. Although a higher
regioselectivity and a lower percentage of alkene isomeriza-
Table 2. Ligand screening for hydroformylation of 1-hexene.[a]
Entry
Ligand
l/b[b]
Linear[c]
[%]
Iso[d]
[%]
TON[e]
ACHTUNGTRENNUNG
[ꢁ103]
1
2
3
4
3a
3b
3c
3d
3d
3e
3 f
3g
3h
3i
146.1
4.9
99.3
83.1
99.3
99.4
99.5
99.2
83.8
84.6
85.8
68.5
98.9
16.0
2.4
19.6
18.0
17.7
8.2
8.5
3.3
16.3
9.2
8.7
7.5
3.3
6.6
7.8
5.7
7.2
3.6
3.9
6.6
7.8
9.0
146.1
174.4
207.3
122.5
5.2
5.5
6.1
2.2
86.7
5[f]
6
7
8
9
10
11
tion were observed at
a relatively lower temperature
3j
(908C), a higher temperature (1008C) was necessary to
afford a higher reaction rate (Table 1, entry 2 vs. 5). Notably,
a high regioselectivity was still achieved even under a tem-
[a] S/C=10000, [RhACHTNUTRGNEUNG(acac)(CO)2] (0.001 mmol), ligand/Rh ratio=2:1, T=
1008C, CO/H2 =20/20 bar, 3 h. toluene (1.0 mL) as solvent, decane as the
internal standard. [b–e] See Table 1. [f] Reaction time: 1 h.
15290
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Spiroketal-Based Phosphorus Ligands
FULL PAPER
Table 3. Hydroformylation of terminal olefins.[a]
the phenyl rings of the ligand backbone afforded
an overall similar catalytic performance. The use
of ligand 3d, bearing a chlorine substituent for R’
on the phenyl groups of the spiro backbone, result-
ed in an enhancement of the regioselectivity (l/b=
174.4, Table 2, entry 4). In the initial stage of the
reaction (1 h), the TON value for the catalysis
using this ligand was determined to be quite high
(5.7ꢁ103, Table 2, entry 5). Ligand 3e with bulky
tBu groups for R’ substituents resulted in a dimin-
ished percentage of isomerization (Table 2, entry 6
vs. 1). On the other hand, the cis-configured li-
gands 3 f, 3g, and 3i consistently afforded results
that were inferior to their trans-isomers in terms of
both activity and regioselectivity (Table 2, entries 7
vs. 1, 8 vs. 6, and entry 10, respectively), indicating
that a subtle modification of the ligand structure in
3 can lead to a drastic change in catalytic behavior.
Additionally, ligand 3h with an untethered 2,2’-
Entry
Substrate
L
CO/H2
[bar]
l/b[b]
Linear[c]
[%]
Iso.[d]
[%]
TON[e]
AHCTUNGTRENNUNG
1[f]
2[f]
3[f]
4[g]
5[g]
6[g]
7
propylene
propylene
propylene
1-butylene
1-butylene
1-butylene
1-hexene
1-hexene
1-hexene
1-octene
1-octene
1-octene
styrene
3a
3d
3j
3a
3d
3j
3a
3d
3j
3a
3d
3j
10/10
10/10
10/10
10/10
10/10
10/10
20/20
20/20
20/20
20/20
20/20
20/20
5/5
53.6
58.2
23.3
97.0
106.5
53.3
146.1
174.4
86.7
59.2
58.2
39.8
3.4
98.2
98.3
95.9
99.0
99.1
98.2
99.3
99.4
98.9
98.3
98.3
97.6
77.5
78.0
–
–
–
–
–
1.4ꢁ104
2.1ꢁ104
4.8ꢁ104
1.6ꢁ104
2.3ꢁ104
4.5ꢁ104
7.5ꢁ103
7.8ꢁ103
9.0ꢁ103
6.9ꢁ103
7.5ꢁ103
8.7ꢁ103
6.0ꢁ103
6.9ꢁ103
–
16.0
18.0
8.7
19.9
22.6
12.9
–
8
9
10
11
12
13
14
3d
3j
styrene
5/5
3.5
–
[a] S/C=10000, [RhACTHUNRGTNEUNG(acac)(CO)2] (0.001 mmol), ligand/Rh ratio=2:1, T=1008C, 3 h.
toluene (1.0 mL) as solvent, decane as internal standard. [b–e] See Table 1. [f] S/C=
50000, toluene (2.0 mL) as solvent. [g] S/C=50000.
spirobisACHTUNGTRENNUNG[chroman] backbone also afforded a con-
siderably lower l/b ratio relative to that of 3a
(Table 2, entry 9 vs. 1), albeit with comparable cat-
alytic activity, presumably as a result of increased conforma-
tional freedom in transition states when using the Rh/3h
catalyst. For comparison, a known ligand 3j[6] with a biphen-
yl backbone was also tested in this reaction under the condi-
tions optimized for 3a; the ligand 3j afforded a somewhat
lower l/b ratio than that of the latter, albeit with a slightly
higher activity (Table 2, entry 11 vs. 1). These results sug-
gested that both the geometry and the rigidity of the back-
bone in ligand 3 are important in the Rh/3-catalyzed hydro-
formylation of 1-hexene. As a compromise between catalytic
selectivity and activity, ligands 3a, 3d, and 3j were used in
subsequent studies on hydroformylation of terminal olefins.
Under the optimized reaction conditions, a variety of ter-
minal olefins were investigated as substrates for Rh/3 cata-
lyzed hydroformylation. As shown in Table 3, the short-
chain olefins such as propylene and 1-butylene are readily
amenable to the hydroformylation procedure, affording ex-
cellent linear/branched ratios in the catalysis (l/b=53.3–
106.5, entries 1, 2, 4, and 5). Ligand 3d tends to be slightly
more active than 3a, and both attained a high regioselectivi-
ty in these reactions. In the cases of longer chain substrates
1-hexene and 1-octene, the regioselectivities towards the
linear aldehyde products were also high (l/b=58.2–174.4,
Table 3, entries 7, 8, 10, 11), though some isomerization
products could be found. For comparison, hydroformylation
of these terminal olefins were also conducted with 3j as the
ligand (Table 3, entries 3, 6, 9, and 12). Under the otherwise
identical conditions, ligands 3a and 3d consistently afforded
higher l/b values than 3j with a biphenyl backbone, thus at-
testing the advantages of spiroketal backbone in this type of
ligands. Remarkably, for the hydroformylation of styrene, an
olefin well-known to favor the formation of the branched al-
dehyde in many Rh-catalyzed hydroformylation studies,[13]
both 3d and 3j afforded preferentially the linear aldehyde
with a moderate selectivity (Table 3, entries 13–14).
Encouraged by these results, the isomerization–hydrofor-
mylation of more challenging internal olefins was then in-
vestigated using the industrially important (E)-2-butylene as
the standard substrate in the presence of 3/Rh (S/C=50000)
as the catalyst. The effects of ligand/metal ratio, tempera-
ture, and pressure on the regioselectivity and catalytic activi-
ty were evaluated, and the results are summarized in
Table 4. For the reactions involving ligand 3a, the regiose-
lectivity for the linear aldehyde increased with the incre-
ment of 3a/Rh ratio from 1:1 to 3:1 (Table 4, entries 1–3),
whereas further increasing the ratio to 4:1 resulted in a de-
cline in catalytic activity (entry 4). The CO/H2 partial pres-
sure was also found to influence the reaction (Table 4, en-
tries 5–7). Raising the H2 pressure led to an enhancement of
Table 4. Hydroformylation of (E)-2-butylene under different reaction
conditions.[a]
Entry
L
L/Rh
CO/H2
[bar]
T
ACHTUNGTNER[NUNG 8C]
l/b[b]
Linear[c]
[%]
TON[d]
N
1
2
3
4
5
6
7
8
3a
3a
3a
3a
3a
3a
3a
3a
3a
3c
3d
3e
3j
1:1
2:1
3:1
4:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
5/10
5/10
5/10
5/10
5/5
110
110
110
110
110
110
110
100
120
110
110
110
110
15.7
26.7
28.5
24.1
19.1
27.6
16.4
34.5
18.7
27.3
26.6
21.0
16.2
94.0
96.4
96.6
96.0
95.0
96.5
94.3
97.2
94.9
96.5
96.4
95.5
94.2
6.9ꢁ103
6.6ꢁ103
6.8ꢁ103
5.4ꢁ103
6.8ꢁ103
7.2ꢁ103
3.5ꢁ103
3.8ꢁ103
6.9ꢁ103
6.0ꢁ103
1.1ꢁ104
4.2ꢁ103
2.1ꢁ104
5/15
10/10
5/10
5/10
5/10
5/10
5/10
5/10
9
10
11
12
13
[a] S/C=50000, [RhACHTNUTRGNEUNG(acac)(CO)2] (0.001 mmol), 15 h, toluene (1.0 mL) as
solvent, decane as internal standard. [b–d] See Table 1.
Chem. Eur. J. 2012, 18, 15288 – 15295
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15291

K. Ding et al.
Table 5. Hydroformylation of internal olefins.[a]
both regioselectivity and activity (Table 4, entry 6 vs. 5),
whereas increasing the CO pressure resulted in a reverse
effect (Table 4, entry 7 vs. 3). With the temperature ranging
from 100 to 1208C, the regioselectivity increased with the
lowering of reaction temperature, but the reaction rate ex-
hibited a reverse trend (Table 4, entries 8, 9 vs. 3). As a com-
promise, the temperature of 1108C was thus chosen for sub-
sequent studies. Ligands 3c–3e were also examined in this
reaction under the conditions optimized for 3a, affording
generally high regioselectivities for the linear aldehyde
(l/b=21.0-27.3, Table 4, entries 10–12). As compared to the
ligand 3a, ligand 3c with a chlorine for R (o-Cl on the aryl
ring) delivered lower catalytic activity (Table 4, entry 10 vs.
3), whereas 3d with a chlorine for R’ (m-Cl on the aryl ring)
improved the TON value from 6.8ꢁ103 to 1.1ꢁ104 (Table 4,
entry 11 vs. 3). Ligand 3e with electron-donating tBu groups
for R’ also resulted in a significant degradation in catalytic
activity (Table 4, entry12 vs. 3). As a comparison, ligand 3j
was also tested in this reaction, affording an inferior regiose-
lectivity to that of 3a, albeit with a somewhat higher activity
(Table 4, entry 13 vs. 3).
Entry
Substrate
L
l/b[b]
Linear[c]
[%]
TON[d]
1
2
3
4
5
6
7
8
(Z)-2-butylene
(Z)-2-butylene
(Z)-2-butylene
(E)-2-butylene
(E)-2-butylene
(E)-2-butylene
2-butylene
2-butylene
2-butylene
2-octene
2-octene
3a
3d
3j
3a
3d
3j
3a
3d
3j
3a
3d
3j
31.8
30.6
18.2
28.5
26.6
16.2
29.4
27.8
20.0
23.4
24.0
19.2
97.0
96.8
94.8
96.6
96.4
94.2
96.7
96.5
95.2
95.9
96.0
95.1
1.2ꢁ104
2.0ꢁ104
2.7ꢁ104
6.8ꢁ103
1.1ꢁ104
2.1ꢁ104
8.9ꢁ103
1.5ꢁ104
2.1ꢁ104
3.8ꢁ103
4.5ꢁ103
6.6ꢁ103
9
10[e]
11[e]
12[e]
2-octene
[a] S/C=50000, [RhACHTNUTRGNEUNG(acac)(CO)2] (0.001 mmol), ligand/Rh ratio=3:1, T=
1108C, 15 h. toluene (1.0 mL) as solvent, decane as internal standard. [b–
d] See Table 1. [e] S/C=10000.
ed a lower regioselectivity than those of 3a and 3d, albeit
Finally, the isomerization–hydroformylation of some inter-
nal olefins, including (Z)-2-butylene, 2-butylene isomeric
mixture (E/Z=1/1), 2-octene (Z/E=4/1), was conducted
under the optimized reaction conditions (1108C, CO/H2 =
5/10 bar) using 3/Rh (L/Rh=3, S/C=50000) as the catalyst,
and the results are shown in Table 5. With either 3a or 3d
as the ligand, the reaction of (Z)-2-butylene proceeded
much faster than that of its (E)-isomer under the otherwise
identical conditions, and slightly higher regioselectivity was
achieved in the reaction of (Z)-2-butylene (Table 5, en-
tries 1, 2 vs. 4, 5, respectively). Such a difference in reactivi-
ty between (Z)- and (E)-2-butylene probably reflects their
steric interaction with the catalyst during the olefin coordi-
with a higher activity (Table 5, entries 3, 6, 9, and 12).
The precatalyst with the formula [RhACTHNUTRGNENGU(3d)CAHTUNGTRNE(NUGN acac)] has been
characterized by X-ray crystallography. As shown in Fig-
ure 1a, the Rh center of the complex adopts a square-planar
coordination with the chelating 3d and acac ligands, indicat-
ing that despite the steric bulkiness of the spiro-bisphos-
phoramidite ligand, cis coordination in the complex is still
À
feasible. The P-Rh-P bite angle (94.78) and Rh P bond
lengths (2.161 and 2.165 ꢂ) are similar to those found in
[RhACTHNUGRTENUNG(acac)] complexes containing bidentate phosphite li-
gands[14] or monodentate N-pyrrolylphosphines.[15] The spiro-
ketal backbone forms a twelve-membered heterometallocy-
clic ring with the Rh center, and thus enforcing sufficient
steric hindrance of the pyrrolyl rings around the rhodium
center. Additionally, the catalytically active hydride complex
À
nation and/or insertion into the Rh H bond, as a result of
the distinct geometrical arrangement of methyl groups
around the olefin double bond. A 1:1 (Z/E)-mixture of 2-bu-
tylene was also examined in the Rh-catalyzed isomeriza-
tion–hydroformylation reaction using either 3a or 3d as the
ligand, affording excellent l/b
[HRh(CO)2ACHTUNTRGNEUNG(3d)] was prepared in C6D6 under hydroformyla-
1
tion conditions and was characterized by H- and 31P NMR,
as well as IR spectroscopic analyses (for details, see the Sup-
ratios and high TON values
that are approximately a statis-
tical average of those obtained
using the two isolated isomers,
respectively
(Table 5,
en-
tries 7–8). In the case of
longer-chain substrate 2-octene
(Z/E=4/1), the regioselectivi-
ties towards the linear alde-
hyde were also high for both
Rh/3a and Rh/3d catalysts
(l/b=23.4 and 24.0, Table 5,
entries 10, 11). Under other-
wise identical conditions, hy-
droformylation of these inter-
nal olfins with the biphenol-
based ligand 3j always afford-
Figure 1. Crystal structure of a) [Rh
ACHUTGTNRENN(GU 3d)ACHTUGNTREN(NUGN acac)] and b) schematic representations of the bisequatorially coordi-
nated hydride complex [HRh(CO)2A(3d)].
CTHUNGTRENNUNG
15292
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 15288 – 15295

Spiroketal-Based Phosphorus Ligands
FULL PAPER
Table 6. Spectroscopic data of the [HRh(CO)23] complex.[a]
Chemical shifts (d values) were reported in ppm with internal TMS
(1H NMR), CDCl3 (13C NMR), or external 85% H3PO4 (31P NMR), re-
spectively. EI (70 eV) and ESI mass spectra were obtained on HP5989 A
and Mariner LC-TOF spectrometers, respectively. HRMS (EI) and
HRMS (ESI) were determined on Waters Micromass GCT Premier and
APEX III 7.0 TESLA FTMS spectrometers. Elemental analyses (C, H,
N) were performed with an Elemental VARIO EL apparatus. The IR
spectra were measured on a NICOLET AVATAR 330 or a Bruker
Tensor 27 spectrometer. GC analyses were measured on an Agilent
6890N or an Agilent 7820 A system.
Complex
[HRh(CO)
[HRh(CO)
d
G
d
E
JHP
[Hz]
JHRh
[Hz]
JRhP
[Hz]
vCO
[cmÀ1
]
A
A
G
G
N
À10.1
(br)
135
138
n.d.
n.d
220
2073,
2027
2078,
2026
E
À10.7
n.d.
n.d.
218
(br)
[a] Measured in [D6]benzene. [b] See ref. [6]. n.d=not determined.
A general procedure for preparation of ligand 3: A solution of diol
(0.32 mmol) in THF was added dropwise to a solution of 1,1’-(chloro-
phosphinediyl)bis(1H-pyrrole) (190.6 mg, 0.96 mmol) and triethylamine
(0.26 mL, 1.92 mmol) in THF (1 mL) at 08C. After stirring at room tem-
perature for 5 h, the precipitated Et3N·HCl salt was filtered off, and the
solvent of the filtrate was removed under vacuum. The residue was puri-
fied by flash column chromatography on silica gel (PE/EA=10/1) to
afford the product ligand 3.
porting Information). As shown in Table 6, the key spectral
data measured for the complex [HRh(CO)2A(3d)] are quite
similar to those for [HRh(CO)2ACHNUTGTREG(NNUN 3j)], which has been report-
CTHUNGTRENNUNG
ed by van Leeuwen[6] to adopt a trigonal bipyramidal struc-
ture wherein the bidentate ligand coordinates in a bis-
ACHTUNGTRENNUNG
equatorial (eq–eq) fashion to RhI (Figure 1b). The IR spec-
Ligand 3a: White solid, 94% yield. M.p. 1158C; 1H NMR (CDCl3,
400 MHz): d=6.92–6.84 (m, 4H), 6.77–6.76 (m, 6H), 6.68–6.66 (m, 4H),
6.17–6.15 (m, 8H), 2.89 (dd, J=16.0, 6.8 Hz, 2H), 2.53 (dd, J=16.0,
7.6 Hz, 2H), 2.33–2.29 (m, 2H), 1.91–1.88 (m, 2H), 1.44–1.41 (m,
2H) ppm. 13C NMR (CDCl3, 100 MHz): d=144.0 (d, J=2.2 Hz), 143.99
(d, J=1.5 Hz), 141.9 (d, J=5.2 Hz), 141.8 (d, J=5.2 Hz), 125.9, 124.5,
121.8, 121.3 (d, J=4.5 Hz), 121.2 (d, J=3.7 Hz), 121.1 (d, J=3.7 Hz),
119.4 (d, J=3.0 Hz), 119.3 (d, J=3.7 Hz), 111.97 (d, J=2.2 Hz), 111.95
(d, J=2.2 Hz), 111.82 (d, J=2.3 Hz), 111.80 (d, J=2.2 Hz), 109.5, 41.4,
27.8, 27.8 ppm; 31P NMR (161 MHz, CDCl3): d=111.4 ppm; FTIR
(neat): 2953, 2928, 2864, 1586, 1467, 1453, 1258, 1177, 1054, 1035,
trum of [HRh(CO)
for the carbonyl ligands around 2073 and 2027 cmÀ1, typical
for those eq–eq-coordinated [HRh(CO)2A(l-L)] complexes.
2ACHTUNGTRNE(NUNG 3d)] displayed two absorption bands
CTHUNGTRENNUNG
In view of these facts, it may be concluded that for the cata-
lytically active hydride complexes only the eq–eq-coordinat-
ed [HRh(CO)2ACHTUNGTRENNUNG(3d)] isomer is present in the present reac-
tion system (Figure 1b). Such a ligating pattern coupled
with the steric hindrance of the pyrrolyl rings around the
rhodium center, might account for the high regioselectivities
observed in Rh/3d catalysis.
726 cmÀ1
;
ESI-MS: m/z: 635; HRMS (ESI) m/z: calcd for
C35H32N4NaO4P2+: 657.1791 [M+Na+]; found: 657.1781.
Ligand 3b: White solid, 92% yield. M.p. 1428C; 1H NMR (CDCl3,
400 MHz): d=6.78–6.74 (m, 12H), 6.20 (t, J=2.4 Hz, 4H), 6.11 (t, J=
1.6 Hz, 4H), 2.75 (dd, J=15.6, 6.4 Hz, 2H), 2.45 (dd, J=15.6, 7.2 Hz,
2H), 2.25–2.17 (m, 2H), 1.93 (s, 6H), 1.85–1.84 (m, 2H), 1.39–1.38 (m,
2H) ppm; 13C NMR (CDCl3, 100 MHz): d=143.8 (d, J=2.3 Hz), 143.7
(d, J=2.2 Hz), 140.5 (d, J=4.4 Hz), 128.9 (d, J=1.5 Hz), 128.85, 123.8,
123.2, 122.7, 121.4, 121.37 (d, J=2.3 Hz), 121.29 (d, J=2.3 Hz), 121.2,
111.77 (d, J=2.3 Hz), 111.75 (d, J=2.2 Hz), 111.6 (d, J=2.2 Hz), 111.58
(d, J=2.2 Hz), 109.8, 41.2, 27.6, 27.5, 15.9 ppm. 31P NMR (161 MHz,
CDCl3): 112.0 ppm; FTIR (neat): 2964, 2930, 1576, 1494, 1454, 1177,
1069, 1052, 1034, 990, 728 cmÀ1; ESI-MS: m/z: 663 [M+H+]; HRMS
(ESI): m/z: calcd for C37H36N4NaO4P2+: 685.2104 [M+Na+]; found:
685.2099.
Conclusion
A new class of bidentate phosphoramidite ligands, based on
a spiroketal backbone, has been developed for the rhodium-
catalyzed hydroformylation reactions. A range of short- and
long-chain olefins, including both terminal and internal ole-
fins, were found amenable to the protocol, affording high
catalytic activity and excellent regioselectivity for the linear
aldehydes. A comparative study also indicated that the
spiroACHTUNGTRENNUNGketal is superior to the biphenyl as the backbone of the
ligand in terms of the regioselectivity of the hydroformyla-
tion reactions. X-ray crystallographic analysis revealed a cis
1
Ligand 3c: Colorless liquid, 67% yield. H NMR (CDCl3, 400 MHz): d=
6.96 (d, J=8.4 Hz, 2H), 6.78–6.66 (m, 10H), 6.21–6.20 (m, 8H), 3.03 (dd,
J=16.8, 6.8 Hz, 2H), 2.52 (dd, J=16.8, 7.2 Hz, 2H), 2.30–2.26 (m, 2H),
1.97–1.94 (m, 2H), 1.44–1.43 (m, 2H) ppm; 13C NMR (CDCl3, 100 MHz):
d=144.83 (d, J=2.0 Hz), 144.81 (d, J=2.1 Hz), 140.87 (d, J=5.3 Hz),
140.82 (d, J=4.1 Hz), 129.0, 124.1, 122.4, 121.2, 121.14, 121.07, 120.98,
119.76 (d, J=3.3 Hz), 119.73 (d, J=3.3 Hz), 112.26 (d, J=2.1 Hz), 112.24
(d, J=2.4 Hz), 112.11 (d, J=2.5 Hz), 112.08 (d, J=2.5 Hz), 109.0, 40.6,
28.0, 25.7 ppm; 31P NMR (161 MHz, CDCl3): d=108.8 ppm; FTIR
coordination of the ligand in the precatalyst [Rh
whereas NMR and IR studies on the catalytically active hy-
dride complex [HRh(CO)2A(3d)] suggested a eq–eq coordi-
ACHUTGTNREN(NUG 3d)AHCTUNGTRENN(UGN acac)],
CTHUNGTRENNUNG
nation of the ligand in the species. We believe that the facile
synthesis and excellent catalytic performance of the ligands
will stimulate further research on the application of spiro-
backbone-based ligands in industrially important hydrofor-
mylation reactions.
(neat): n˜ =1585, 1469, 1453, 1226, 1177, 1034, 886, 728 cmÀ1; ESI-MS:
+
m/z: 703 [M+H+]; HRMS (ESI): m/z: calcd for C35H31Cl2N4O4P2
703.1192 [M+H+]; found: 703.1177.
:
Ligand 3d: White solid, 50% yield. M.p. 908C; 1H NMR (CDCl3,
400 MHz): d=6.90 (d, J=2.0 Hz, 2H), 6.76–6.69 (m, 10H), 6.21–6.19 (m,
8H), 2.83 (dd, J=16.0, 6.4 Hz, 2H), 2.48 (dd, J=15.6, 7.2 Hz, 2H), 2.30–
2.26 (m, 2H), 1.93–1.90 (m, 2H), 1.42–1.39 (m, 2H) ppm; 13C NMR
(CDCl3, 75 MHz): d=142.61 (d, J=1.7 Hz), 142.58 (d, J=1.7 Hz), 142.3
(d, J=5.2 Hz), 142.2 (d, J=5.7 Hz), 127.1, 126.4, 124.3, 121.2 (d, J=
3.5 Hz), 121.1 (d, J=2.9 Hz), 121.0 (d, J=2.9 Hz), 119.7 (d, J=3.4 Hz),
119.6 (d, J=3.5 Hz), 112.32 (d, J=2.3 Hz), 112.30 (d, J=2.3 Hz), 112.19
(d, J=2.2 Hz), 112.16 (d, J=2.3 Hz), 109.8, 41.3, 27.8, 27.6 ppm;
31P NMR (161 MHz, CDCl3): d=111.8 ppm; FTIR (neat): n˜ =2962, 2941,
Experimental Section
General methods: Unless otherwise noted, all manipulations involving
air- or moisture-sensitive compounds were performed in a nitrogen-filled
glovebox or by using standard Schlenk techniques. Solvents were dried
according to standard procedures. Melting points were measured on a
RY-I apparatus and are uncorrected. 1H, 13C, and 31P NMR spectra were
recorded on a Varian Mercury 300 MHz or 400 MHz spectrometer.
2873, 1584, 1469, 1451, 1426, 1189, 1177, 1053, 1034, 1012, 999, 729 cmÀ1
;
Chem. Eur. J. 2012, 18, 15288 – 15295
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
15293

K. Ding et al.
ESI-MS: m/z: 703 [M+H+]; HRMS (ESI): m/z: calcd for
C35H31Cl2N4O4P2+: 703.1192 [M+H+]; found: 703.1178.
29.2, 27.0, 26.9, 24.4 ppm; 31P NMR (121 MHz, CDCl3): d=110.9,
110.2 ppm; FTIR (neat): n˜ =2921, 2854, 1586, 1462, 1450, 1258, 1177,
1049, 1036, 723 cmÀ1; ESI-MS: m/z: 649 [M+H+]; HRMS (ESI): m/z:
calcd for C36H34N4NaO4P2+: 671.1947 [M+Na+]; found: 671.1956.
Ligand 3j: White solid, 86% yield. 1H NMR (CDCl3, 400 MHz): d=
7.28–7.25 (m, 4H), 7.18–7.16 (m, 2H), 6.85 (d, J=8.0 Hz, 2H), 6.70 (s,
8H), 6.23 (s, 8H) ppm; 31P NMR (CDCl3, 161 MHz): d=108.3 ppm.
Ligand 3e: White solid, 95% yield. M.p. 1648C; 1H NMR (CDCl3,
400 MHz): d=6.92 (d, J=2.0 Hz, 2H), 6.80–6.78 (m, 4H), 6.74 (d, J=
2.4 Hz, 2H), 6.68–6.66 (m, 4H), 6.17 (dt, J=10.0, 2.0 Hz, 8H), 2.85 (dd,
J=16.0, 6.8 Hz, 2H), 2.51 (dd, J=15.6, 7.2 Hz, 2H), 2.28–2.24 (m, 2H),
1.89–1.86 (m, 2H), 1.44–1.40 (m, 2H), 1.27 (s, 18H) ppm; 13C NMR
(CDCl3, 100 MHz): d=145.0, 141.48 (d, J=2.2 Hz), 141.47 (d, J=
2.5 Hz), 141.25 (d, J=5.2 Hz), 141.2, 125.0, 121.4, 121.32 (d, J=3.0 Hz),
121.25, 121.2, 116.52 (d, J=3.7 Hz), 116.48 (d, J=3.0 Hz), 111.86 (d, J=
1.5 Hz), 111.84 (d, J=2.2 Hz), 111.63 (d, J=2.2 Hz), 111.61 (d, J=
2.3 Hz), 109.5, 41.4, 34.2, 31.4, 28.1, 27.8 ppm; 31P NMR (161 MHz,
CDCl3): 111.2 ppm; FTIR (neat): n˜ =2962, 2906, 2868, 1584, 1482, 1452,
Typical procedure for the hydroformylation of 1-hexene with ligand 3a:
In a glove box, a glass vial with a magnetic stirring bar was charged with
ligand 3a (1.27 mg, 0.002 mmol) and [RhACTHNUTRGNEG(NU acac)(CO)2] (0.26 mg,
0.001 mmol) in toluene (1.0 mL). The mixture was stirred for 5 min. 1-
Hexene (1.24 mL, 10 mmol) was then added, followed by decane (97 mL,
0.5 mmol) as the internal standard. The resulting mixture was transferred
to an autoclave, which was purged with nitrogen three times and subse-
quently charged with CO (20 bar) and H2 (20 bar). The autoclave was
then heated to 1008C (oil bath) for 3 h. The autoclave was cooled in ice
water, and the gas was carefully released in a well-ventilated hood. The
reaction mixture was immediately analyzed by GC to determine the turn-
over number (TON), percentage of isomerization, and regioselectivity
(l/b ratio).
1421, 1177, 1053, 1033, 726 cmÀ1. ESI-MS: m/z: 747 [M+H+]; HRMS
+
(ESI): m/z: calcd for C43H49N4O4P2
:
747.3224 [M+H+]; found:
747.3196.
Ligand 3 f: White solid, 77% yield, M.p. 1128C; 1H NMR (CDCl3,
300MHz): d=6.88–6.74 (m, 13H), 6.61 (d, J=8.1 Hz, 1H), 6.27–6.16 (m,
8H), 2.87 (dd, J=17.4, 6.6 Hz, 1H), 2.72–2.52 (m, 4H), 2.28–2.22 (m,
1H), 1.98–1.93 (m, 2H), 1.53–1.38 (m, 2H) ppm. 13C NMR (CDCl3,
75 MHz): d=144.6 (d, J=3.4 Hz), 143.0 (d, J=3.4 Hz), 142.1 (d, J=
9.8 Hz), 141.3 (d, J=9.1 Hz), 126.3 (d, J=2.2 Hz), 126.0 (d, J=2.3 Hz),
125.1(d, J=1.1 Hz), 122.3 (d, J=1.2 Hz), 121.5 (d, J=1.1 Hz), 121.3 (d,
J=2.3 Hz), 121.2 (d, J=1.7 Hz), 121.1 (d, J=1.7 Hz), 121.0 (d, J=
1.1 Hz), 120.9 (d, J=1.1 Hz), 119.4 (d, J=6.3 Hz), 119.0 (d, J=6.8 Hz),
112.1 (d, J=4.0 Hz), 111.9 (d, J=2.3 Hz), 111.8 (d, J=2.3 Hz), 101.8,
40.7, 37.0, 26.9, 25.5, 25.0, 23.8 ppm; 31P NMR (121 MHz, CDCl3): 112.3
(d, J=10.6 Hz), 110.4 (d, J=9.9 Hz) ppm; FTIR (neat): n˜ =2953, 2927,
1586, 1453, 1257, 1177, 1054, 1036, 726 cmÀ1; ESI-MS: m/z: 635 [M+H+];
HRMS (ESI): m/z: calcd for C35H32N4Na1O4P2+: 657.1791 [M+Na+];
found: 657.1775.
Typical procedure for the regioselective hydroformylation of (E)-2-
butene with ligand 3a: In a glove box, an autoclave with a magnetic stir-
ring bar was charged with ligand 3a (1.90 mg, 0.003 mmol), [Rh-
AHCTUNGTRE(GNNNU acac)(CO)2] (0.26 mg, 0.001 mmol), and decane (97 mL, 0.5 mmol) as in-
ternal standard in toluene (1.0 mL). The mixture was stirred for 5 min.
The autoclave was cooled to 08C, purged with nitrogen three times, and
then charged with (E)-2-butene (2.8 g, 50 mmol). The autoclave was
charged with CO (5 bar) and H2 (10 bar), and then heated to 1108C (oil
bath) for 15 h. The autoclave was cooled in ice water, and the gas was
carefully released in a well-ventilated hood. The reaction mixture was im-
mediately analyzed by GC to determine the turnover number (TON) and
regioselectivity (l/b ratio).
Ligand 3g: White solid, 95% yield. M.p. 1628C; 1H NMR (CDCl3,
400 MHz): d=6.86–6.74 (m, 11H), 6.56 (s, 1H), 6.26–6.23 (m, 8H), 2.81
(dd, J=17.2, 6.8 Hz, 1H), 2.70–2.49 (m, 4H), 2.26–2.24 (m, 1H), 1.97–
1.92 (m, 2H), 1.52–1.48 (m, 2H), 1.23 (s, 9H), 1.20 (s, 9H) ppm.
13C NMR (CDCl3, 100 MHz): d=144.2 (d, J=2.2 Hz), 144.11 (d, J=
1.5 Hz), 142.16 (d, J=1.5 Hz), 142.12 (dd, J=1.5 Hz), 141.5 (d, J=
9.6 Hz), 140.6 (d, J=8.1 Hz), 140.55, 124.1 (d, J=1.4 Hz), 122.8 (d, J=
1.5 Hz), 122.5 (d, J=1.5 Hz), 121.6, 121.5, 121.44 (d, J=1.5 Hz), 121.40,
121.37, 121.35, 121.33, 121.2 (d, J=2.9 Hz), 116.7 (d, J=6.0 Hz), 116.3 (d,
J=6.7 Hz), 112.0 (d, J=3.0 Hz), 111.97 (d, J=4.4 Hz), 111.80 (d, J=
3.7 Hz), 111.76 (d, J=4.5 Hz), 101.8, 40.9, 37.2, 34.1, 34.0, 31.4, 31.3, 27.2,
25.7, 25.0, 24.1 ppm; 31P NMR (161 MHz, CDCl3): d=111.2 (d, J=
14.0 Hz), 110.4 (d, J=14.5 Hz) ppm; FTIR (neat): n˜ =2962, 2869, 1584,
Acknowledgements
We thank the financial support of this work from the National Natural
Science Foundation of China (grant nos. 20821002, 20923005, 20972176),
the Major Basic Research Development Program of China (grant no.
2010CB833300), the Chinese Academy of Sciences, and the Science and
Technology Commission of Shanghai Municipality.
1481, 1452, 1422, 1177, 1053, 1033, 727 cmÀ1; ESI-MS (m/z): 747 [M+H+
[1] For reviews, see: a) Rhodium Catalyzed Hydroformylation, C.
Claver, P. W. N. M. van Leeuwen, Kluwer Academic Publishers, Dor-
drecht, The Netherlands, 2000; b) B. Breit, W. Seiche, Synthesis
2001, 1–36; c) P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H.
Reek, Acc. Chem. Res. 2001, 34, 895–904; d) M. L. Claver, Curr.
Org. Chem. 2005, 9, 701–718; e) F. Ungvꢃry, Coord. Chem. Rev.
2005, 249, 2946–2961.
[2] a) C. P. Casey, G. T. Whiteker, M. G. Melville, L. M. Petrovich,
J. A., Jr. Gavney, D. R. Powell, J. Am. Chem. Soc. 1992, 114, 5535–
5543; b) W. A. Herrmann, R. Schmid, C. W. Kohlpaintner, T. Prier-
meier, Organometallics 1995, 14, 1961–1968; c) C. P. Casey, E. L.
Paulsen, E. W. Beuttenmueller, B. R. Proft, L. M. Petrovich, B. A.
Matter, D. R. Powell, J. Am. Chem. Soc. 1997, 119, 11817–11825;
d) R. Paciello, L. Siggel, M. Rçer, Angew. Chem. 1999, 111, 2045–
2048; Angew. Chem. Int. Ed. 1999, 38, 1920–1923; e) V. F. Slagt,
J. N. H. Reek, P. C. J. Kamer, P. W. N. M. van Leeuwen, Angew.
Chem. 2001, 113, 4401–4404; Angew. Chem. Int. Ed. 2001, 40, 4271–
4274; f) B. Breit, W. Seiche, J. Am. Chem. Soc. 2003, 125, 6608–
6609; g) V. F. Slagt, P. W. N. M. van Leeuwen, J. N. H. Reek, Angew.
Chem. 2003, 115, 5777–5781; Angew. Chem. Int. Ed. 2003, 42, 5619–
5623; h) V. F. Slagt, P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H.
Reek, J. Am. Chem. Soc. 2004, 126, 1526–1536; i) B. Breit, W.
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+
]; HRMS (ESI): m/z: calcd for C43H49N4O4P2
:
747.3224 [M+H+],
found: 747.3194.
Ligand 3h: White solid, 64% yield, M.p. 1298C; 1H NMR (CDCl3,
400 MHz): d=6.88–6.76 (m, 12H), 6.61 (d, J=8.0 Hz, 2H), 6.29–6.26 (m,
8H), 2.92–2.85 (m, 2H), 2.66 (dd, J=17.6, 5.2 Hz, 2H), 2.24–2.18 (m,
2H), 2.01 (td, J=13.6, 6.8 Hz, 2H) ppm; 13C NMR (CDCl3, 100 MHz):
d=143.54 (d, J=0.8 Hz), 143.51 (d, J=1.6 Hz), 141.43 (d, J=0.8 Hz),
141.3, 125.5, 124.7, 121.5, 121.29 (d, J=3.0 Hz), 121.1, 120.8, 119.1, 119.0,
112.16 (d, J=0.8 Hz), 112.11 (d, J=0.7 Hz), 112.0 (d, J=0.8 Hz), 111.9
(d, J=1.1 Hz), 96.5, 30.7, 20.5 ppm. 31P NMR (161 MHz, CDCl3):
110.1 ppm; FTIR (neat): n˜ =2940, 1586, 1468, 1177, 1034, 975, 931, 856,
730 cmÀ1; ESI-MS: m/z: 609 [M+H+]; HRMS (ESI): m/z: calcd for
C33H30N4NaO4P2+: 631.1634 [M+Na+]; found: 631.1620.
Ligand 3i: White solid, 76% yield. M.p. 1178C; 1H NMR (CDCl3,
300 MHz): d=6.86–6.69 (m, 12H), 6.60–6.57 (m, 2H), 6.30–6.24 (m, 8H),
3.06 (dd, J=12.6, 4.8 Hz, 1H), 2.47–2.42 (m, 2H), 2.28 (d, J=12.6 Hz,
1H), 2.07–1.92 (m, 2H), 1.69–1.26 (m, 6H) ppm. 13C NMR (CDCl3,
75 MHz): d=143.34 (d, J=1.1 Hz), 143.31(d, J=1.1 Hz), 142.35 (d, J=
1.2 Hz), 142.31 (d, J=1.7 Hz), 141.31 (d, J=4.6 Hz), 141.2 (d, J=4.0 Hz),
126.0 (d, J=1.7 Hz), 125.4 (d, J=1.7 Hz), 125.3, 123.62 (d, J=1.7 Hz),
123.60 (d, J=1.2 Hz), 121.4 (d, J=2.3 Hz), 121.2, 121.16, 121.0, 120.9 (d,
J=1.1 Hz), 120.7 (d, J=1.1 Hz), 119.0 (d, J=6.2 Hz), 118.9 (d, J=
5.6 Hz), 112.1, 112.0, 111.9 (d, J=1.1 Hz), 111.86, 98.2, 38.3, 36.3, 29.3,
15294
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Chem. Eur. J. 2012, 18, 15288 – 15295

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Received: August 27, 2012
Published online: November 7, 2012
Chem. Eur. J. 2012, 18, 15288 – 15295
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
15295