P-stereogenic ferrocene-based (Trifluoromethyl)phosphanes: Synthesis, structure, coordination properties and catalysis

Article abstract of DOI:10.1002/ejoc.201001162

Diastereoselective ortho-hydroxymethylation of (R)-(1-ferrocenylethyl) dimethylamine and Bronsted-acid-mediatednucleophilic substitution with phenyl(trifluoromethyl)phosphane affords an epimeric mixture of P-stereogenic amine-phosphanes 4a and 4b, which a

Full text of DOI:10.1002/ejoc.201001162

FULL PAPER
DOI: 10.1002/ejoc.201001162
P-Stereogenic Ferrocene-Based (Trifluoromethyl)phosphanes: Synthesis,
Structure, Coordination Properties and Catalysis
[a]
[a][‡]
ˇ [a]
Aline Sondenecker, Ján Cvengros, Raphael Aardoom,
and Antonio Togni*[a]
Keywords: Ferrocene / Chiral auxiliaries / Asymmetric catalysis / Electrophilic trifluoromethylation / Phosphanes / Ligand
design
Diastereoselective ortho-hydroxymethylation of (R)-(1-ferro- These bis(phosphanes) combine three elements of chirality
cenylethyl)dimethylamine
and
Brønsted-acid-mediated
(C-central, P-central and planar) and bear a trifluoromethyl
group at a stereogenic phosphorus atom. Their complexes
with transition metals (Pd, Rh, Ir) were studied and charac-
terized by means of NMR techniques and X-ray crystallo-
graphic analyses, and the bidentate ligands proved efficient
in stereoselective catalysis.
nucleophilic substitution with phenyl(trifluoromethyl)phos-
phane affords an epimeric mixture of P-stereogenic amine–
phosphanes 4a and 4b, which are readily separated by
crystallization from methanol. Subsequent substitution of the
dimethylamino group with diphenylphosphane occurs with-
out epimerization, yielding novel bis(phosphanes) 1a and 1b.
has disclosed the synthesis of [Fe{η5-C5H4P(CF3)2}2]
(dfmpf) by treating [Fe{η5-C5H4P(OPh)2}2] with 4 equiv. of
CF3SiMe3 and CsF in diethyl ether.[5]
Introduction
Over the years, a plethora of chiral bidentate ferrocenyl
ligands has been fine-tuned in terms of steric and electronic
properties for efficient applications in a broad spectrum of
transition-metal-catalyzed reactions.[1] The Josiphos ligand
family developed by Togni and Spindler stands out as one
of the most potent ferrocenediylbis(phosphanes).[2] Their
modular synthesis, which relies upon sequential substitu-
tion of two phosphanyl groups in the last two steps, allows
for a convenient and facile modification of their perform-
ance in catalysis, which is often difficult with other bis-
(phosphanes).[3] However, the introduction of some uncom-
mon substituents remains a challenging task. For example,
the installation of small groups with strong electron-with-
drawing properties at one of the phosphorus atoms would
represent an intriguing approach for the alteration of the
bonding behavior between the P-donor and the transition
metal in a complex. The trifluoromethyl fragment, which is
the smallest member of the perfluoroalkyl series, appears to
be the most obvious candidate for the synthesis of phos-
phane ligands with altered σ-donating and π-accepting
properties. Reports on ferrocene-based trifluoromethylated
phosphanes are scarce. This paucity likely stems from the
lack of established protocols for the trifluoromethylation of
phosphanes.[4] To the best of our knowledge, only Caffyn
We have recently succeeded in accessing secondary and
tertiary (trifluoromethyl)phosphanes with a new class of
electrophilic trifluoromethylating reagents based on hyper-
valent λ3-organoiodine compounds.[6,7] In our ongoing ef-
forts in the field of both electrophilic trifluoromethylation
and synthesis and applications of ferrocenylphosphane li-
gands, we wished to demonstrate that both areas of interest
could be effectively merged. Herein, we present the synthe-
sis of new enantiomerically pure (trifluoromethyl)phos-
phane ligands 1a and 1b, which combine three elements of
chirality, as well as an initial demonstration of their possible
utility in asymmetric hydrogenation.
Results and Discussion
Ligand Synthesis
[a] Department of Chemistry and Applied Biosciences, Swiss
Federal Institute of Technology, ETH Zürich,
8093 Zürich, Switzerland
In order to render the synthetic approach highly modu-
lar, we intended to introduce the phosphanyl substituents in
the last two steps of the synthesis by sequential nucleophilic
substitutions. Retrosynthetic disconnection thus leads to
the primary alcohol 7, which is easily accessible from the
(R)-Ugi amine 8, as depicted in Scheme 1. Because the de-
Fax: +41-44-632-1310
E-mail: togni@inorg.chem.ethz.ch
[‡] X-ray crystallographic measurements
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201001162.
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P-Stereogenic Ferrocene-Based (Trifluoromethyl)phosphanes
tailed comparison of the stereoelectronic effects of the sub- phosphane 4 in good yields as a mixture of diastereoisomers
stituents was one of our objectives, we also considered the (Scheme 3). Attempts to separate the two epimers of 4 by
synthesis of the methyl and phenyl analogues 2 and 3.
means of preparative HPLC with a chiral stationary phase
(Chiralcel OJ column) happened to be successful. Amine–
phosphane (R,SFc,RP)-4a (the absolute configuration at the
phosphorus atom was determined by X-ray analysis, vide in-
fra) was isolated as the major product in 45% yield as an
orange crystalline solid, whereas the second epimer
(R,SFc,SP)-4b turned out to be an orange oil (23%). This
striking difference in physicochemical properties prompted
us to seek a more convenient method of separation. To our
delight, a simple crystallization from hot methanol yielded
the enantiomerically pure amine–phosphane (R,SFc,RP)-4a
(crystals) and (R,SFc,SP)-4b (mother liquor) in a highly ef-
ficient manner.
Scheme 1. Retrosynthetic analysis.
Primarily, we focused our attention on the preparation
of the prerequisite phosphanes 10 and 11 (Scheme 2). Ac-
cording to the protocol established in our laboratories, com-
mercially available phenylphosphane (9) was treated with an
equimolar amount of hypervalent λ3-organoiodine reagent
12, affording the desired phenyl(trifluoromethyl)phosphane
(10). The complete consumption of 12 was verified by 19F
NMR spectroscopy. Since 10 proved rather unstable and
difficult to handle, and the by-products from the electro-
philic trifluoromethylation (2-iodobenzoic acid and un-
identified phosphorus-containing species) did not interfere
in the subsequent transformation, the reaction mixture was
used immediately without any further purification (vide in-
fra). The corresponding methyl(phenyl)phosphane (11) was
also synthesized by starting from 9.[8] Deprotonation with
sodium in Et2O, followed by the addition of 1 equiv. of
iodomethane, furnished compound 11 in 87% yield after
distillation.
Scheme 3. Modular preparation of chiral ferrocene-based (trifluoro-
methyl)phosphanes by starting from the (R)-Ugi amine 8. Reagents
and conditions: (a) (1) tBuLi, Et2O, –78 °C, 30 min, then 0 °C, 2 h,
(2) DMF, 0 °C to room temp. 16 h; (b) LiAlH4, THF, 0 °C to room
temp. 16 h; (c) HBF4·Et2O, 10 (crude mixture), DCM, –78 °C to
room temp. 16 h; (d) crystallization from hot methanol; (e) HPPh2,
AcOH, 90 °C, 5 h. [a] Diastereomeric ratio was determined by 31P
NMR spectroscopy.
Scheme 2. Synthesis of phosphanes 10 and 11. Reagents and condi-
tions: (a) 12, DCM, room temp., 1 h; (b) (1) Na, Et2O, 35 °C, 1 h,
(2) MeI, r.t. to 35 °C, 30 min.
Standard nucleophilic substitution of the dimethylamino
The actual ligand synthesis commenced with formylation group by a diphenylphosphanyl substituent was then per-
of the (R)-Ugi amine 8 by a well-established diastereoselec- formed in acetic acid at 90 °C for 5 h, affording the desired
tive ortho-lithiation followed by the addition of DMF.[9] The bis(phosphane) 1 in good yield (89%). Also in this case, the
corresponding aldehyde (R,SFc)-13 was then reduced by Li- separation of the epimeric mixture by crystallization from
AlH4 to the desired alcohol (R,SFc)-7 in an overall yield of methanol occurred with comparable effectiveness. Interest-
86% over two steps. The hydroxy group was subsequently ingly, the reaction starting from enantiomerically pure
replaced by the phosphane 10 in the presence of HBF4·Et2O (R,SFc,RP)-4a or (R,SFc,SP)-4b, gave (R,RFc,RP)-1a or
according to the protocols described by Fukuzawa[10] and (R,RFc,SP)-1b in slightly better yields (93% and 92%,
Weissensteiner,[11] yielding the ferrocenyl-derived amine– respectively). Furthermore, the transformation proceeded
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79

A. Sondenecker, J. Cvengrosˇ, R. Aardoom, A. Togni
FULL PAPER
without epimerization at the stereogenic phosphorus atom, of the Cambridge Structure Database) of a chiral ferrocenyl
thus indicating the high configurational stability of these ligand containing a (trifluoromethyl)phosphane moiety.
compounds. In fact, ligand 1a did not show any detectable The absolute configuration at the stereogenic phosphorus
epimerization even when it was heated in [D8]toluene at atom was unambiguously assigned in both cases to be (R).
100 °C for 3 d, as monitored by 31P NMR spectroscopy. As is usually observed in compounds derived from Ugi’s
This is in good agreement with a general observation that amine, the nitrogen atom (N1 in 4a) or the phosphorus
an electron-withdrawing group increases the epimerization atom (P2 in 1a) attached to C11 are in a pseudo-axial posi-
barrier.[12] It is also noteworthy that the amine–phosphanes tion with respect to the ferrocene core as indicated by the
4a and 4b and the bis(phosphanes) 1a and 1b were stable torsion angles C1–C2–C15–P1 80.29(12)° and C2–C1–C11–
under the conditions of an aqueous workup and column N1 –64.36(13)° for 1a and C2–C1–C11–P2 –99.4(5)° for
chromatography.
4a.[13]
For the sake of comparing the stereoelectronic effects of
The crystallization of both (R,RFc,RP)-1a and
(R,SFc,RP)-4a from methanol provided crystals suitable for the substituent, we have also attempted to synthesize some
an X-ray diffraction study (Figure 1). These structures rep- other bis(phosphane) ligands analogous to 1. Our efforts
resent the first crystallographic analyses (based on a search are summarized in Scheme 4. By applying the same proto-
col established for the synthesis of ligand 1, alcohol (R,SFc)-
7 was treated with HBF4·Et2O followed by the addition of
methyl(phenyl)phosphane (11) or commercially available di-
phenylphosphane. The amine–phosphane 5, which has a
stereogenic phosphorus atom, was isolated as an epimeric
mixture in 81% yield (dr = 51:49). All attempts to separate
the diastereoisomers, even by means of HPLC proved fruit-
less. Diphenylphosphane analogue 6 was obtained in a
moderate yield of 68%, and was transformed into the
known bis(phosphane) 3 upon treatment with diphenyl-
phosphane in acetic acid at elevated temperature (72%).[14]
However, no formation of the methyl analogue 2 was ob-
served under these conditions. Variation of reaction condi-
tions revealed 90% conversion of 5 at 90 °C after 3 h when
trifluoroacetic acid (TFA) was used as solvent instead of
the traditional acetic acid. The bis(phosphane) 2 turned out
to be rather air-sensitive, and it was isolated after workup
and purification by flash chromatography under inert con-
ditions using degassed solvents in 65% yield as a mixture of
two epimeric isomers, which in our hands, despite numerous
efforts, remained inseparable. These facts emphasize the ad-
vantage of trifluoromethylated phosphanes as being less
prone towards oxidation and configurationally more stable.
Scheme 4. Synthesis of bis(phosphane) ligands analogous to 1.
Figure 1. ORTEP drawing of the molecular structure of ligands
Reagents and conditions: (a) HBF4·Et2O, 11 or HPPh2, DCM,
(R,SFc,RP)-4a and (R,RFc,RP)-1a. Thermal ellipsoids are set at 50%
–78 °C to room temp. 16 h; (b) for 5: HPPh2, TFA, 90 °C, 3 h;
probability for 4a and 30% for 1a. Hydrogen atoms are omitted
(c) for 6: HPPh2, AcOH, 90 °C, 5 h. [a] Diastereomeric ratio was
for clarity. Selected bond lengths [Å] and angles [°]: (R,RFc,RP)-1a:
determined by 31P NMR spectroscopy.
P1–C16 1.8809(13), P1–C17 1.8262(12), C16–F1 1.3444(15), C16–
F2 1.3513(14), C16–F3 1.3540(14), C15–P1–C16 96.34(5); C15–P1–
C17 106.26(5), C16–P1–C17 95.71(5), C1–C11–N1 108.34(9), C1–
C11–C12 112.19(10), N1–C11–C12 115.44(10). (R,SFc,RP)-4a: P1–
C14 1.866(5), P1–C15 1.830(4), C14–F1 1.341(6), C14–F2 1.361(6),
C14–F3 1.347(5); C13–P1–C14 96.0(2), C13–P1–C15 103.7(2),
C14–P1–C15 97.9(2), C1–C11–P2 106.7(4), C1–C11–C12 113.5(4),
P2–C11–C12 106.8(3).
Coordination Chemical Properties
The coordination chemistry of bis(phosphane) 1a was in-
vestigated by analyses of three different transition-metal
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P-Stereogenic Ferrocene-Based (Trifluoromethyl)phosphanes
complexes. [Rh(cod)(S,SFc,SP)-1a]BF4 (14) was synthesized
by reaction of [Rh(cod)2]BF4 with (S,SFc,SP)-1a in CH2Cl2
solution. [Ir(cod)(R,RFc,RP)-1a]BF4 (15) was prepared by
reaction of [Ir2Cl2(cod)2] with (R,RFc,RP)-1a in THF fol-
lowed by anion metathesis with AgBF4. [PdCl2(R,RFc,RP)-
1a] (16) was synthesized by reaction of [PdCl2(cod)] with
(R,RFc,RP)-1a in CH2Cl2 solution (Scheme 5).
Scheme 5. Synthesis of complexes 14, 15 and 16. Reagents and con-
ditions: (a) [Rh(cod)2]BF4, DCM, room temp., 1 h; (b) AgBF4,
[Ir2Cl2(cod)2], THF, room temp., 45 min, then (R,RFc,RP)-1a, room
temp., 15 h; (c) [PdCl2(cod)], DCM, room temp., 2 h.
X-ray crystal-structure analysis established the molecular
structures of 14, 15 and 16, as shown in Figure 2. The 16-
valence-electron rhodium and iridium monocationic species
are somewhat distorted square-planar complexes, with the
vertices of the square plane being occupied by the phospho-
rus atoms and by the two η2-bonded double bonds of 1,5-
cyclooctadiene (Table 1). Similarly, the geometry around
the palladium atom is distorted square-planar, as indicated
by the P–Pd–P bite angle [102.69(3)° and 101.81(3)° for two
crystallographically independent molecules in the unit cell]
and the Cl–Pd–Cl angle [89.18(3)° and 88.96(3)°].
Table 1. Structural data concerning the coordination sphere around
the rhodium and iridium atoms in the crystal structures of
[Rh(cod)(S,SFc,SP)-1a]BF4 (14) and [Ir(cod)(R,RFc,RP)-1a]BF4
(15).
[Rh(cod)(S,SFc,SP)-1a]BF4 [Ir(cod)(S,SFc,SP)-1a]BF4
M–P1
M–P2[b]
2.3100(5)[a]
2.2679(4)
2.280(2)
2.191(2)
2.225(2)
2.277(2)
1.386(3)
1.378(3)
99.21(2)
2.3162(6)
2.2731(6)
2.257(3)
2.157(3)
2.198(3)
2.251(2)
1.402(4)
1.390(4)
100.58(2)
M–CP11
M–CP12
M–CP21
M–CP22
CP11–CP12
CP21–CP22
P1–M–P2
[a] Distances are given in Å and angles in °. Standard deviations
are given in parentheses. [b] P2 is the phosphorus atom bearing the
trifluoromethyl group.
In each of these complexes, the bond between the metal
atom and the phosphorus atom bearing the electron-with-
drawing CF3 group is shorter than the one involving the
second phosphorus atom [e.g. in 15: Ir–P1(Ph)2 2.3162(6) Å
Figure 2. ORTEP drawing of the molecular structures of complexes
14, 15 and one of the two molecules in the asymmetric unit of 16.
Thermal ellipsoids are set at 50% probability. Hydrogen atoms are
omitted for clarity.
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81

A. Sondenecker, J. Cvengrosˇ, R. Aardoom, A. Togni
FULL PAPER
Figure 3. 31P{1H} NMR spectrum (121 MHz, CDCl3) of the Rh complex [Rh(cod)1a]BF4 (14) showing chemical shift and coupling
parameters of both phosphanes.
vs. Ir–P2(CF3)(Ph) 2.2731(6) Å]. This is because of the Table 2. Asymmetric hydrogenation of dimethyl itaconate.
stronger s-character of the phosphorus lone-pair of the P–
CF3 unit, as predicted by Bent’s rule.[15] This difference is
also reflected in the bonds between the metal atom and the
olefinic carbon atoms of cyclooctadiene as the longest M–
Ccod bond is trans to the shortest M–P bond.
Entry
Ligand
Solvent
t
[h]
Conv.
[%]
ee
[%]
The modification of the phosphorus atom by an electro-
negative group results in an increased coupling constant be-
tween the phosphorus and rhodium atoms as observed in
the 31P NMR spectrum of 14. The 1JP,Rh coupling constant
for the phenyl(trifluoromethyl)phosphanyl substituent is
24 Hz larger than that for the diphenylphosphanyl substitu-
ent (Figure 3). Interestingly, the coupling constant between
the two phosphane substituents in the Rh complex is 8
times larger than the one in the free ligand (36.7 Hz vs.
4.4 Hz).
1
2
3
4
5
6
7
8
9
10
11
12
13
(R,SFc,RP)-4a
(R,SFc,SP)-4b
(R,RFc,RP)-1a
(R,RFc,SP)-1b
(R,RFc,RP)-1a CF3CH2OH
(R,RFc,SP)-1b (CF3)2CHOH
(R,RFc,RP)-1a
(R,RFc,SP)-1b
(R,RFc,SP)-1b
(R,RFc,SP)-1b
(R,RFc)-3
(R,RFc,RP)-1a
(R,RFc,SP)-1b
DCM
DCM
MeOH
MeOH
24
24
24
24
24
20
36
0
0
0
0
0
–
–
–
24
0
–
DCM
DCM
DCM
DCM
DCM
CHCl3
CHCl3
0.5
0.5
2[a]
0.5[b]\
0.5
0.5
0.5
100
100
100
100
100
100
100
13 (R)
72 (R)
66 (R)
76 (R)
68 (S)
37 (S)
69 (R)
Catalysis
[a] 0.1 mol-% catalyst. [b] At 0 °C.
We tested the catalytic performance of the novel ligands
in the RhI-catalyzed asymmetric hydrogenation, with di-
methyl itaconate as a model substrate. Typically, the experi-
Interestingly, the stereogenic phosphorus atom proved
ments were carried out with 1 mol-% of [Rh(cod)2]SbF6 crucial for the stereoselective outcome of the reaction.
and 1.1 mol-% of the ligand. The results are summarized in Whereas the use of (R,RFc,RP)-1a in DCM yielded the (R)-
Table 2. Whereas the initial screening revealed that the configured hydrogenation product with only 13% ee, the
amine–phosphanes 4a and 4b were generally inefficient (En- epimeric ligand (R,RFc,SP)-1b led to the same enantiomer
tries 1 and 2), an interesting tendency was observed with in 72% ee (Entries 7 and 8). This effect is even more pro-
the bis(phosphanes) 1a and 1b. In protic solvents (meth- nounced in chloroform, as a switch in the absolute configu-
anol, trifluoroethanol or hexafluoroisopropyl alcohol) no ration of the major enantiomer of the product was observed
hydrogenation occurred even after 24 h (Entries 3–6). How- (Entries 12 and 13). Although the value obtained with
ever, the use of chlorinated solvents (dichloromethane or (R,RFc,SP)-1b is comparable to the one obtained with
chloroform) led to complete conversion at 25 °C within (R,RFc)-3 (ligand possessing no stereogenic phosphorus
30 min. The achieved enantioselectivities are only modest, atom; Entry 11), the absolute configuration of the major
suggesting that the methylene bridge between the ferrocene product enantiomer was opposite. It was also shown that
unit and the phenyl(trifluoromethyl)phosphanyl group may the loading of the catalyst could be lowered to 0.1 mol-%,
provide undesired conformational freedom.
but the reaction time had to be extended to 2 h, and a slight
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P-Stereogenic Ferrocene-Based (Trifluoromethyl)phosphanes
-775647 [(R,RFc,RP)-1a], -775648 (14), -775649 (16) and -775650
(15) contain the supplementary 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.
decrease of enantioselectivity was observed (Entry 9). On
the other hand, the reaction proceeds at a similar rate at
0 °C, and a somewhat higher ee was obtained (Entry 10).
Compounds: Reagents were purchased from common vendors and
used as received. [PdCl2(cod)],[16] [Ir2Cl2(cod)2],[17] 1-(trifluoro-
methyl)-1,2-benziodoxol-3-(1H)-one,[6a] 1-[(R)-1-(dimethylamino)-
ethyl]-2-(SFc)-formylferrocene[10] and 1-[(R)-1-(dimethylamino)-
ethyl]-2-(SFc)-(hydroxymethyl)ferrocene[10] were prepared accord-
ing to literature procedures.
Conclusions
We have developed a facile synthesis of novel ferrocene-
derived bis(phosphane) ligands bearing a trifluoromethyl
group at a stereogenic phosphorus atom. To the best of our
knowledge, these are the first examples of ligands of this
kind reported in the literature. The enantiomerically pure
ligands were prepared in a concise manner consisting of 4
steps yielding 36% and 18% of two diastereoisomers, which
were separated by simple crystallization from methanol.
The coordination properties with transition metals (Rh, Ir,
Pd) were studied by means of NMR and X-ray analysis.
The influence of the trifluoromethyl group on the structure
of these complexes was demonstrated.
The potential of these ligands was investigated in asym-
metric catalysis. A strong influence of the solvent on the
ligands’ performance was revealed, and the importance of
the stereogenic phosphorus atom was demonstrated. The
enantiomeric excesses obtained in asymmetric hydrogena-
tion of dimethyl itaconate are far from those obtained with
other privileged ligands, but the reaction rates in chlori-
nated solvents account for their catalytic potential. Further-
more, our results represent the first proof of principle that
the replacement of a phenyl group by a trifluoromethyl
fragment in a “classical” chiral phosphane can lead to an
improved ligand performance.
Phenyl(trifluoromethyl)phosphane (10): Phenylphosphane (22.0 μL,
0.2 mmol) was added to a solution of 1-(trifluoromethyl)-1,2-benz-
iodoxol-3-(1H)-one (12) (63 mg, 0.2 mmol) in DCM (0.5 mL) in a
glovebox. The reaction mixture was stirred at room temp. After
1 h, the starting materials were found to be consumed, based on
the 19F and 31P{1H} NMR spectra, and the conversion to product
10 was estimated to be 84% based on the comparison of the ratio
of the integrals of the product signal to the signal of the internal
standard PhCF3 in the 19F NMR spectrum. The crude mixture was
used without any purification. 19F NMR (188 MHz, CD2Cl2): δ =
2
3
–52.15 (dd, JF,P = 57.5, JF,H = 11.5 Hz, PCF3) ppm. 31P{1H}
2
NMR (80 MHz, CD2Cl2): δ = –40.38 (q, JP,F = 57.5 Hz, PCF3)
ppm.
Methyl(phenyl)phosphane (11): To a suspension of Na (1.05 g,
45.50 mmol) in Et2O (25 mL), H2PPh (5 mL, 45.5 mmol) was
added through cannula to give a yellow suspension, which was
heated at reflux (35 °C) for 1 h. After cooling to room temp., MeI
(2.83 mL, 45.46 mmol) was added, giving a white suspension in an
exothermic reaction. After heating at reflux for another 30 min, the
white suspension was filtered through a cannula filter and then
distilled under vacuum, affording 11 as a colorless liquid (4.90 g,
87%). 1H NMR (250 MHz, CDCl3): δ = 7.57–7.51 (m, 2 H, Ph-
Because the synthetic strategy presented herein is highly
modular, we are currently focusing our attention on fine-
tuning of the catalytic properties of these ligands by mod-
ifying the phosphane units. The new ligands are being ex-
tensively screened in other asymmetric catalytic reactions
where the effect of the strong electron-withdrawing group
at the phosphorus atom might be more pronounced.
2
H), 7.39–7.29 (m, 3 H, Ph-H), 1.44 (d, JP,H = 2.9 Hz, 3 H, CH3)
ppm. 31P{1H} NMR (101 MHz, CDCl3): δ = –70.54 (s) ppm.
1
13C{1H} NMR (75 MHz, CDCl3): δ = 136.99 (d, JP,C = 9.9 Hz,
2
Ph-C ipso), 132.79 (d, JP,C = 16.0 Hz, Ph-CH ortho), 128.46 (d,
4
3JP,C = 5.9 Hz, Ph-CH meta), 128.07 (d, JP,C = 1.3 Hz, Ph-CH
1
para), 6.29 (d, JP,C = 11.7 Hz, CH3) ppm.
(SFc)-1-[(R)-1-(Dimethylamino)ethyl]-2-{[(RP/SP)-phenyl(trifluoro-
methyl)phosphanyl]methyl}ferrocene (4): A solution of fluoroboric
acid (1.7 mL, 12.5 mmol, 51–57% in diethyl ether) was added drop-
wise to a cooled (–78 °C) solution of (R,SFc)-7 (230 mg, 0.8 mmol)
in DCM (2.5 mL). The red reaction mixture was stirred at –78 °C
for 10 min, and phenyl(trifluoromethyl)phosphane (10) (crude mix-
ture, ca. 100 mg, 0.8 mmol) was added dropwise at the same tem-
perature. The temperature was raised to room temp., and the mix-
ture was stirred for 16 h. The reaction was quenched with aq.
Na2CO3 (satd., 50 mL), and DCM was added. The phases were
separated, and the aqueous phase was extracted 3 times with DCM
(30 mL). The combined organic phases were washed with brine
(50 mL) and dried (MgSO4). Evaporation of the solvent gave the
crude product, which was purified by PTLC on basic Alox with
hexane/TBME (10:1) as eluent, affording pure 4 as an orange oil.
(243 mg, 68%) This oil was a mixture of diastereoisomers. The dia-
stereoisomeric ratio based on31P NMR spectroscopy was
(R,SFc,RP)-4a/(R,SFc,SP)-4b = 0.34:0.66. Separation of the two epi-
mers was performed by preparative HPLC using a Chiralcel OJ
column, eluting with hexane/iPrOH (98:2), 15 mL/min, on a 10–
Experimental Section
General: The reactions were carried out in dried glassware under
argon by using Schlenk techniques. All solvents were freshly dis-
tilled under argon from an appropriate drying agent before use.
DCM was also degassed by three freeze-pump-thaw cycles. Flash
chromatography was performed with Fluka silica gel 60. NMR
spectra were measured with Bruker Avance 300, 400, 500 or 700
spectrometers. Chemical shifts are referenced to residual solvent
signals (1H, 13C, 19F, 31P). High-resolution mass spectra were
measured by the MS-Service of the Laboratorium für Organische
Chemie der ETH. Elemental analyses were carried out by the Labo-
ratory of Microelemental Analysis (ETH Zürich). HPLC analyses
were measured with an Agilent Series 1100 instrument. X-ray struc-
tures were measured with a Bruker CCD diffractometer, solved
either by Patterson or direct methods and successive interpretation
of the difference Fourier maps, followed by full-matrix least-
squares refinement (against F2). CCDC-775646 [(R,SFc,RP)-4a], 50 mg scale, or by crystallization from hot methanol affording pure
Eur. J. Org. Chem. 2011, 78–87
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
83

A. Sondenecker, J. Cvengrosˇ, R. Aardoom, A. Togni
FULL PAPER
(R,SFc,RP)-4a as an orange solid (161 mg, 45 %) and pure
4.04 (m, 0.51 H, Cp-H4 B), 4.02 (s, 3.04 H, CpЈ-HЈ B, Cp-H4 A),
3.95 (br. s, 0.49 H, Cp-H3 A), 3.87–3.83 (m, 1.0 H, CHCH3 A,
CHCH3 B), 3.01 (d, J = 15.0 Hz, 0.49 H, CH2 A), 2.93 (d, J =
(R,SFc,SP)-4b as an orange oil (82 mg, 23%). [α]2D5 = –22 (c = 1,
1
CHCl3). H NMR (300 MHz, CDCl3): δ = 7.76–7.71 (m, 2 H, Ph-
2
H), 7.48–7.46 (m, 3 H, Ph-H), 4.15 (br. s, 2 H, Cp-H), 4.11 (s, 5
14.3 Hz, 0.51 H, CH2 B), 2.84 (dd, J = 14.1, JP,H = 3.4 Hz, 0.51
2
H, CpЈ-HЈ), 4.07 (m, 1 H, Cp-H), 3.89 (q, J = 6.7 Hz, 1 H, H, CH2 B), 2.78 (dd, J = 14.1, JP,H = 1.6 Hz, 0.49 H, CH2 A),
2
CHCH3), 3.32 (dd, J = 14.7, JP,H = 4.0 Hz, 1 H, CH2), 3.22 (dd,
2.17 [s, 3.06 H, N(CH3)2 B], 2.16 [s, 2.94 H, N(CH3)2 A], 1.41 (d,
2
J = 14.7, JP,H = 5.3 Hz, 1 H, CH2), 1.89 [s, 6 H, N(CH3)2], 1.28 J = 6.7 Hz, 1.47 H, CHCH3 A), 1.39 (d, J = 6.7 Hz, 1.53 H,
(d, J = 6.7 Hz, 3 H, CHCH3) ppm. 19F NMR (188 MHz, CDCl3): δ CHCH3 B), 1.36 (d, JP,H = 3.9 Hz, 1.47 H, PCH3 A), 1.34 (d,
1
= –59.40 (d, 2JP,F = 60.5 Hz, CF3) ppm. 31P{1H} NMR (122 MHz,
1JP,H = 3.7 Hz, 1.53 H, PCH3 B) ppm. 31P{1H} NMR (283 MHz,
CDCl3): δ = –31.95 (s, PCH3 B), –32.43 (s, PCH3 A) ppm. 13C{1H}
2
CDCl3): δ = –7.70 (q, JF,P = 60.5 Hz,) ppm. 13C{1H} NMR
2
1
(76 MHz, CDCl3): δ = 133.93 (d, JP,C = 21.6 Hz, Ph-CH ortho),
NMR (176 MHz, CDCl3): δ = 141.88 (d, JP,C = 32.9 Hz, Ph-C
1
1
1
1
2
132.40 (dq, JF,C = 322.4, JP,C = 40.6 Hz, CF3), 131.13 (dd, JP,C
ipso A), 141.79 (d, JP,C = 31.6 Hz, Ph-C ipso B), 131.83 (d, JP,C
3
4
2
= 16.2, JF,C = 3.8 Hz, Ph-C ipso), 130.50 (d, JP,C = 1.0 Hz, Ph-
= 19.1 Hz, Ph-CH ortho B), 131.24 (d, JP,C = 17.9 Hz, Ph-CH
ortho A), 128.56 (s, Ph-CH para B), 128.33 (d, JP,C = 6.7 Hz, Ph-
CH meta B), 128.29 (d, JP,C = 5.9 Hz, Ph-CH meta A), 128.06 (s,
3
3
3
CH para), 128.52 (d, JP,C = 7.9 Hz, Ph-CH meta), 88.83 (d, JP,C
= 2.8 Hz, Cp-C1), 84.07 (d, 2JP,C = 24.6 Hz, Cp-C2), 69.48 (s, CpЈ-
3
3
3
3
CHЈ), 68.90 (d, JP,C = 5.0 Hz, Cp-CH), 66.77 (s, Cp-CH), 65.50
Ph-CH para A), 89.29 (d, JP,C = 2.8 Hz, Cp-C1 B), 89.24 (d, JP,C
(s, Cp-CH), 57.24 (s, CHCH3), 39.44 [d, JP,C = 1.5 Hz, N(CH3)2],
= 1.9 Hz, Cp-C1 A), 85.06 (d, 2JP,C = 15.0 Hz, Cp-C2 B), 84.83 (d,
1
3
21.93 (qd, JP,C = 11.5, JC,F = 3.5 Hz, CH2), 8.42 (s, CHCH3) 2JP,C = 11.0 Hz, Cp-C2 A), 69.54 (d, JP,C = 0.5 Hz, CpЈ-CHЈ B),
ppm. MS (EI): m/z (%) = 447.10 (38) [M]+, 402.04 (93) [M – 69.51 (d, JP,C = 0.8 Hz, CpЈ-CHЈ A), 68.58 (d, JP,C = 9.2 Hz, Cp-
3
3
N(CH3)2], 333.05 (100). C22H25F3FeNP (447.26): calcd. C 59.08, H C3H B), 68.41 (d, JP,C = 6.5 Hz, Cp-C3H A), 66.38 (s, Cp-C5H
5.63, N 3.13, F 12.74; found C 58.8, H 5.67, N 3.05, F 12.47.
A), 66.28 (s, Cp-C5H B), 65.40 (s, Cp-C4H B), 65.34 (s, Cp-C4H
A), 56.75 (s, CHCH3 A), 56.63 (s, CHCH3 B), 40.41 [d, JP,C
(R,SFc,SP)-4b: [α]2D5 = +87 (c = 1, CHCl3). 1H NMR (300 MHz,
=
CDCl3): δ = 7.79–7.74 (m, 2 H, Ph-H), 7.52–7.46 (m, 3 H, Ph-H), 1.0 Hz, N(CH3)2 A], 40.24 [s, N(CH3)2 B], 30.55 (d, 1JP,C = 13.2 Hz,
1
1
4.09 (s, 1 H, Cp-H), 4.01 (s, 5 H, CpЈ-HЈ), 3.97–3.01 (m, 2 H, Cp- CH2 B), 30.52 (d, JP,C = 15.0 Hz, CH2 A), 12.14 (d, JP, C
=
2
1
H and CHCH3), 3.80 (s, 1 H, Cp-H), 3.38 (dd, J = 14.5, JP,H
=
15.3 Hz, PCH3 A), 12.07 (d, JP,C = 15.0 Hz, PCH3 B), 11.57 (s,
6.6 Hz, 1 H, CH2), 3.20 (d, J = 14.5 Hz, 1 H, CH2), 2.13 [s, 6 CHCH3 A), 10.83 (s, CHCH3 B) ppm. HRMS (EI): calcd. for
H, N(CH3)2], 1.34 (d, J = 6.7 Hz, 3 H, CHCH3) ppm. 19F NMR C22H28NPFe [M]+ 393.3012; found (%) 393.1300 (56) [M]+,
2
(188 MHz, CDCl3): δ = –58.83 (d, JP,F = 61.9 Hz, CF3) ppm. 348.0789 (100) [M – N(CH3 )2 ]+ , 224.9915 (100) [M –
2
31P{1H} NMR (122 MHz, CDCl3): δ = –10.69 (q, JF,P = 61.9 Hz) PPh2CH3N(CH3)2]+.
2
ppm. 13C{1H} NMR (76 MHz, CDCl3): δ = 134.65 (dq, JP,C
=
4
4
(SFc)-1-[(R)-1-(Dimethylamino)ethyl]-2-[(diphenylphosphanyl)meth-
yl]ferrocene (6): A solution of fluoroboric acid (4.4 mL, 32.3 mmol,
51–57% in diethyl ether) was added dropwise to a cooled (–78 °C)
solution of (R,SFc)-7 (591 mg, 2.1 mmol) in DCM (6 mL). The red
reaction mixture was stirred at –78 °C for 10 min, and diphenyl-
phosphane (0.43 mL, 2.5 mmol) was added dropwise at the same
temperature. The temperature was raised to room temp., and the
mixture was stirred for 16 h. The reaction was quenched with aq.
Na2CO3 (satd., 50 mL) and DCM was added. The phases were
separated, and the aqueous phase was extracted 3 times with DCM
(30 mL). The combined organic phases were washed with brine
(50 mL) and dried (MgSO4). Evaporation of the solvent gave the
22.5, JF,C = 0.7 Hz, Ph-CH ortho), 130.90 (d, JP,C = 1.0 Hz, Ph-
CH para), 130.19 (d, JP,C = 19.4 Hz, Ph-C ipso), 131.61 (dq, JF,C
= 321.6, JP,C = 39.3 Hz, CF3), 128.60 (d, JP,C = 8.2 Hz, Ph-CH
1
1
1
3
3
2
meta), 89.33 (d, JP,C = 3.1 Hz, Cp-C), 82.31 (d, JP,C = 19.7 Hz,
Cp-C), 69.46 (s, CpЈ-CHЈ), 68.93 (d, 3JP,C = 6.1 Hz, Cp-CH), 66.67
(s, Cp-CH), 65.50 (s, Cp-CH), 57.02 (s, CHCH3), 39.81 [d, JP,C
=
1
3
1.6 Hz, N(CH3)2], 22.35 (qd, JP,C = 13.8, JF,C = 3.6 Hz, CH2),
9.98 (s, CHCH3) ppm. MS (EI): m/z (%) = 447.10 (38) [M]+, 402.04
(93) [M – N(CH3)2], 333.05 (100). C22H25F3FeNP (447.26): calcd.
C 59.08, H 5.63, F 12.74, N 3.13; found C 59.12, H 5.64, F 12.59,
N 3.13.
(SFc)-1-[(R)-1-(Dimethylamino)ethyl]-2-{[(RP/SP)-methyl(phenyl)- crude product, which was purified by PTLC on basic Alox with
phosphanyl]methyl}ferrocene (5): A solution of fluoroboric acid
(2.6 mL, 19.1 mmol, 51–57% in diethyl ether) was added dropwise
hexane/TBME (10:1) as eluent, affording pure 6 as an orange oil
(720 mg, 77%). H NMR (300 MHz, CDCl3): δ = 7.54–7.44 (m, 4
1
to a cooled (–78 °C) solution of (R,SFc)-7 (350 mg, 1.2 mmol) in H, Ph-H), 7.39–7.30 (m, 6 H, Ph-H), 4.09–4.07 (m, 1 H, Cp-H5),
CH2Cl2 (4 mL). The red reaction mixture was stirred at –78 °C for
10 min, and methyl(phenyl)phosphane (11) (180 mg, 1.45 mmol)
was added dropwise at the same temperature. The temperature was
raised to room temp., and the mixture was stirred for 16 h. The
reaction was quenched with aq. Na2CO3 (satd., 70 mL), and
CH2Cl2 was added. The phases were separated, and the aqueous
phase was extracted 3 times with CH2Cl2 (50 mL). The combined
organic phases were washed with brine (70 mL) and dried
(MgSO4). Evaporation of the solvent gave the crude product, which
was purified by flash chromatography (FC) with hexane/EtOAc/
Et3N (10:2:0.2) as eluent, affording pure 5 as an orange oil (370 mg,
81%) as a mixture of diastereoisomers. The diastereoisomeric ratio
based on 31P NMR spectroscopy was 0.49:0.51. 1H NMR
(700 MHz, CDCl3): δ = 7.64–7.62 (m, 1.02 H, Ph-H ortho B), 7.57–
4.05 (s, 5 H, CpЈ-HЈ), 3.96 (t, J = 2.3 Hz, 1 H, Cp-H4), 3.90–3.83
(m overlapping with q, 3J = 6.7 Hz, 2 H, Cp-H3, CHCH3), 3.31
2
2
(dd, J = 14.9, JP,H = 2.3 Hz, 1 H, CH2), 3.20 (dd, J = 14.9, JP,H
= 1.3 Hz, 1 H, CH2), 2.13 [s, 6 H, N(CH3)2], 1.40 (d, J = 6.7 Hz,
3 H, CHCH3) ppm. 31P{1H} NMR (101 MHz, CDCl3): δ = –15.15
(s, PPh2) ppm. 13C{1H} NMR (63 MHz, CDCl3): δ = 140.11 (d,
1JP,C = 15.8 Hz, Ph-C ipso), 139.86 (d, JP,C = 16.5 Hz, Ph-C ipso),
133.43 (d, JP,C = 20.0 Hz, Ph-CH ortho), 132.44 (d, JP, C
18.2 Hz, Ph-CH ortho), 128.76 (s, Ph-CH para), 128.46 (d, JP,C
12.2 Hz, Ph-CH meta), 128.45 (s, Ph-CH para), 128.32 (d, JP,C
1
2
2
=
=
=
3
3
3
15.8 Hz, Ph-CH meta), 89.13 (d, JP,C = 4.0 Hz, Cp-C1), 84.80 (d,
2JP,C = 16.3 Hz, Cp-C2), 69.64 (d, JP,C = 0.9 Hz, CpЈ-CHЈ), 69.10
3
4
(d, JP,C = 9.0 Hz, Cp-C3H), 66.39 (d, JP,C = 0.8 Hz, Cp-C5H),
65.43 (s, Cp-C4H), 56.87 (s, CHCH3), 40.57 [d, JP,C = 1.1 Hz,
7.55 (m, 0.98 H, Ph-H ortho A), 7.45–7.42 (m, 1.02 H, Ph-H meta N(CH3)2], 28.42 (d, 1JP,C = 14.7 Hz, C2H), 12.02 (s, CHCH3) ppm.
B), 7.41–7.39 (m, 1.49 H, Ph-H meta A, Ph-H para B), 7.36–7.34
(m, 0.49 H, Ph-H para A), 4.14 (br. s, 0.51 H, Cp-H3 B), 4.10 (br.
s, 1.0 H, Cp-H5 A, Cp-H5 B), 4.06 (s, 2.45 H, CpЈ-HЈ A), 4.05–
HRMS (EI): calcd. for C27H30FeNP [M]+ 455.1460; found (%)
455.1459 (22) [M]+, 410.0892 (100) [M – N(CH3)2]+, 225.0359 (50)
[M – PPh2 – N(CH3)2]+.
84
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 78–87

P-Stereogenic Ferrocene-Based (Trifluoromethyl)phosphanes
1
3
(RFc)-1-[(R)-1-(Diphenylphosphanyl)ethyl]-2-{[(RP/SP)-phenyl(tri- 1.1 Hz, Ph-CH para), 130.50 (qd, JP,C = 13.9, JF,C = 3.4 Hz,
PPhCF3-C ipso), 129.69 (s, Ph-CH para), 129.25 (d, 3JP,C = 8.4 Hz,
fluoromethyl)phosphanyl]methyl}ferrocene (1): (R,SFc,RP/SP)-4
3
Ph-CH meta), 128.95 (s, Ph-CH para), 128.89 (d, JP,C = 7.1 Hz,
(78 mg, 0.17 mmol, epimeric ratio 0.34:0.66) was dissolved in de-
gassed AcOH (0.7 mL), resulting in an orange-red homogeneous
solution. After the addition of diphenylphosphane (39 μL,
0.22 mmol) at room temp., the reaction mixture was stirred in a
preheated oil bath at 90 °C for 5 h. The resulting dark orange mix-
ture was quenched with aq. Na2CO3 (satd., 10 mL), and CH2Cl2
was added. The phases were separated, and the aqueous phase was
extracted 3 times with CH2Cl2 (5 mL). The combined organic
phases were washed with brine (10 mL) and dried (MgSO4). Evapo-
ration of the solvent gave the crude product, which was purified by
FC with hexane/TBME (10:1) as eluent, affording pure 1 as an
orange oil (89.5 mg, 89%) as an epimeric mixture. The diastereoiso-
meric ratio based on 31P NMR spectroscopy was (R,RFc,RP)-1a/
(R,RFc,SP)-1b = 0.66:0.34. Separation of the two epimers was
performed by crystallization from hot MeOH, affording pure
(R,RFc,RP)-1a as an orange solid (60 mg, 60 %) and pure
(R,RFc,SP)-1b as an orange oil (29 mg, 29%). Reaction with enan-
tiomerically pure (R,SFc,RP)-4a or (R,SFc,SP)-4b afforded enantio-
merically pure (R,RFc,RP)-1a or (R,RFc,SP)-1b in 93% and 92%
3
Ph-CH meta), 128.27 (d, JP,C = 6.1 Hz, Ph-CH meta), 91.79 (dd,
3
2
3
2JP,C = 16.5, JP,C = 6.2 Hz, Cp-C1), 82.81 (dd, JP,C = 17.8, JP,C
= 1.8 Hz, Cp-C2), 69.41 (d, JP,C = 1.6 Hz, CpЈ-CHЈ), 68.28 (d, 3JP,C
= 12.1 Hz, Cp-C3), 66.85 (dd, JP,C = 6.1, JP,C = 1.8 Hz, Cp-C5),
66.60 (s, Cp-C4), 30.39 (d, JP,C = 14.8 Hz, CHCH3), 21.51 (qd,
1JP,C = 11.6, JF,C = 3.2 Hz, CH2), 19.67 (d, JP,C = 18.7 Hz,
CHCH3) ppm. HRMS (EI): calcd. for C32H29F3P2Fe [M]+
588.3680; found (%) 588.1043 (11) [M]+, 519.1074 (13) [M – CF3],
403.0460 (100) [M – PPh2]. C32H29F3FeP2 (588.37): calcd. C 65.32,
H 4.97; found C 65.04, H 5.12.
3
4
1
3
2
(RFc)-1-[(R)-1-(Diphenylphosphanyl)ethyl]-2-{[(RP/SP)-methyl(phen-
yl)phosphanyl]methyl}ferrocene (2): (R,SFc,RP/SP)-5 (440 mg,
1.12 mmol, epimeric ratio 0.51:0.49) was dissolved in TFA (0.7 mL)
resulting in an orange-red homogeneous solution. After the ad-
dition of diphenylphosphane (253 μL, 1.46 mmol) at room temp.,
the reaction mixture was stirred in a preheated oil bath at 90 °C
for 5 h. The resulting dark orange mixture was concentrated to give
the crude product, which was purified by FC with hexane/EtOAc/
Et3N (20:0.3:0.3) as eluent, affording pure 2 as an orange oil
(468 mg, 79%) as an epimeric mixture. The diastereoisomeric ratio
based on 31P NMR spectroscopy was 0.48:0.52. 1H NMR
(250 MHz, CDCl3): δ = 7.61–7.51 (m, 3 H, Ph-H), 7.45–7.36 (m, 7
H, Ph-H), 7.29–7.15 (m, 3 H, Ph-H), 7.12–7.06 (m, 1 H, Ph-H),
7.04–6.97 (m, 1 H, Ph-H), 4.18 (s, 2.40 H, CpЈ-HЈ A), 4.16–4.13
(m, 0.80 H, Cp-H), 4.10 (t, J = 2.6 Hz, 0.70 H, Cp-H), 4.06 (s, 2.60
H, CpЈ-HЈ B), 4.03–4.01 (m, 1.0 H, Cp-H), 3.86–3.84 (m, 0.50 H,
yield, respectively. (R,RFc,RP)-1a: [α]2D5 = –182 (c = 1, CHCl3). H
1
NMR (300 MHz, CDCl3): δ = 7.65–7.61 (m, 2 H, Ph-H), 7.54–7.41
(m, 8 H, Ph-H), 7.30–7.25 (m, 1 H, Ph-H), 7.19–7.13 (m, 2 H, Ph-
H), 7.02–6.97 (m, 2 H, Ph-H), 4.18 (s, 5 H, CpЈ-HЈ), 4.15 (s, 1 H,
Cp-H5), 4.03–3.99 (m, 1 H, Cp-H4), 3.50 (s, 1 H, Cp-H3), 3.35
3
(qd, J = 14.6, 2JP,H = 6.3 Hz, 1 H, CHCH3), 2.48 (d, J = 15.6 Hz,
2
1 H, CH2), 1.96 (dd, J = 15.6, JP,H = 6.6 Hz, 1 H, CH2), 1.60 (dd,
J = 14.6, 3JP,H = 6.6 Hz, 3 H, CHCH3) ppm. 19F NMR (188 MHz,
2
2
CDCl3): δ = –59.01 (d, JP,F = 64.3 Hz, CF3) ppm. 31P{1H} NMR
Cp-H), 3.41 (qd, J = 6.8, JP,H = 4.1 Hz, 0.48 H, CHCH3 A), 3.30
(qd, J = 7.0, 2JP,H = 4.7 Hz, 0.52 H, CHCH3 B), 2.49 (dd, J = 15.3,
(122 MHz, CDCl3): δ = 6.45 (d, JP,P = 4.4 Hz, PPh2), –11.63 (qd,
2
2JP,H = 0.9 Hz, 0.48 H, CH2 A), 2.36 (dd, J = 15.3, JP,H = 0.8 Hz,
2JF,P = 64.3, JP,P = 4.4 Hz, PPhCF3). 13C{1H} NMR (101 MHz,
1
0.52 H, CH2 B), 2.01 (d, J = 2.5 Hz, 0.52 H, CH2 B), 1.95 (d, J =
CDCl3): δ = 137.56 (d, JP,C = 17.5 Hz, PPh2-C ipso), 135.79 (d,
3
1JP,C = 16.7 Hz, PPh2-C ipso), 134.55 (d, 2JP,C = 20.1 Hz, PPh2-CH
2.5 Hz, 0.48 H, CH2 A), 1.59 (dd, J = 6.8, JP,H = 3.5 Hz, 1.44 H,
3
2
CHCH3 A), 1.53 (dd, J = 7.0, JP,H = 4.3 Hz, 1.56 H, CHCH3 B),
ortho), 133.95 (d, JP,C = 17.6 Hz, PPhCF3-CH ortho), 131.84 (qd,
2
2
1JF,C = 321.1, 1JP,C = 33.1 Hz, CF3), 131.38 (s, Ph-CH para), 129.75
1.28 (d, JP,H = 4.0 Hz, 1.56 H, PCH3 B), 1.20 (d, JP,H = 3.8 Hz,
1.44 H, PCH3 A) ppm. 31P{1H} NMR (101 MHz, CDCl3): δ = 5.76
(d, JP,P = 9.6 Hz, PPh2 B), 5.74, (d, JP,P = 4.6 Hz, PPh2 A), –36.90
(d, JP,P = 9.6 Hz, PCH3 B), –38.33 (d, JP,P = 4.6 Hz, PCH3 A)
ppm. HRMS (EI): calcd. for C32H32P2Fe [M]+ 534.1287; found (%)
534.1326 (15) [M]+, 349.0823 (100) [M – PPh2]+, 226.0446 (5) [M –
PPh2PPhMe]+.
1
3
(s, Ph-CH para), 129.57 (qd, JP,C = 15.1, JF,C = 3.4 Hz, PPhCF3-
3
C ipso), 129.00 (d, JP,C = 6.4 Hz, Ph-CH meta), 128.81 (s, Ph-CH
3
2
para), 128.24 (d, JP,C = 6.2 Hz, Ph-CH meta), 91.92 (dd, JP,C
=
15.5, 3JP,C = 6.6 Hz, Cp-C1), 81.78 (dd, 2JP,C = 13.9, 3JP,C = 1.6 Hz,
Cp-C2), 69.58 (d, JP,C = 2.5 Hz, CpЈ-CHЈ), 67.96 (d, 3JP,C = 8.0 Hz,
3
4
Cp-C3), 66.55 (dd, JP,C = 5.7, JP,C = 1.8 Hz, Cp-C5), 66.46 (s,
Cp-C4), 30.25 (d, 1JP,C = 13.9 Hz, CHCH3), 20.00 (qd, 1JP,C = 11.2,
(RFc)-1-[(R)-1-(Diphenylphosphanyl)ethyl]-2-[(diphenylphosphanyl)-
methyl]ferrocene (3): (R,SFc)-6 (720 mg, 1.58 mmol) was dissolved
in degassed AcOH (3.0 mL), resulting in an orange-red homogen-
eous solution. After the addition of diphenylphosphane (358 μL,
2.06 mmol) at room temp., the reaction mixture was stirred in a
preheated oil bath at 110 °C for 3 h. The resulting dark orange
mixture was quenched with aq. Na2CO3 (satd., 70 mL), and DCM
was added. The phases were separated, and the aqueous phase was
extracted 3 times with DCM (50 mL). The combined organic
phases were washed with brine (50 mL) and dried (MgSO4). Evapo-
ration of the solvent gave the crude product, which was purified by
FC with hexane/EtOAc/NEt3 (20:0.3:0.3) as eluent, affording pure
3JF,C = 3.4 Hz, CH2), 19.72 (d, JP,C = 20.3 Hz, CHCH3) ppm.
2
HRMS (EI): calcd. for C32H29F3P2Fe [M]+ 588.3680; found (%)
588.1043 (11) [M]+, 519.1074 (13) [M – CF3], 403.0460 (100) [M –
PPh2]. C32H29F3P2Fe (588.37): calcd. C 65.32, H 4.97, found C
65.08, H 5.24. (R,RFc,SP)-1b: [α]2D5 = +109 (c = 0.74, CHCl3). H
1
NMR (400 MHz, CDCl3): δ = 7.75–7.72 (m, 2 H, Ph-H), 7.60–7.51
(m, 5 H, Ph-H), 7.47–7.46 (m, 3 H, Ph-H), 7.31–7.28 (m, 1 H, Ph-
H), 7.23–7.19 (m, 2 H, Ph-H), 7.03–7.00 (m, 2 H, Ph-H), 4.16–4.15
(m, 2 H, Cp-H), 4.11 (s, 1 H, Cp-H), 4.02 (s, 5 H, CpЈ-HЈ), 3.22
3
2
(qd, J = 14.1, JP,H = 6.7 Hz, 1 H, CHCH3), 2.72 (dd, J = 15.9,
2JP,H = 5.3 Hz, 1 H, CH2), 1.95 (d, J = 15.9 Hz, 1 H, CH2), 1.56
(dd, J = 14.1, JP,H = 7.0 Hz, 3 H, CHCH3) ppm. 19F NMR
(188 MHz, CDCl3): δ = –58.23 (d, JP,F = 64.6 Hz, CF3) ppm.
31P{1H} NMR (122 MHz, CDCl3):δ = 6.27 (d, JP,P = 8.3 Hz,
PPh2), –10.34 (qd, JF,P = 64.6, JP,P = 8.3 Hz, PPhCF3) ppm.
13C{1H} NMR (101 MHz, CDCl3): δ = 137.43 (d, JP,C = 16.7 Hz,
PPh2-C ipso), 135.82 (d, JP,C = 16.7 Hz, PPh2-C ipso), 135.06 (d,
2JP,C = 22.6 Hz, PPhCF3-CH ortho), 134.74 (d, JP,C = 19.9 Hz,
3
1
3 as an orange foamy solid (679.2 mg, 72%). H NMR (300 MHz,
2
CDCl3): δ = 7.58–7.52 (m, 3 H, Ph-H), 7.43–7.12 (m, 14 H, Ph-H),
7.07–7.01 (m, 3 H, Ph-H), 4.13 (s, 5 H, CpЈ-HЈ), 4.05 (s, 1 H, Cp-
H5), 4.00 (t, J = 2.7 Hz, 1 H, Cp-H4), 3.80 (s, 1 H, Cp-H3), 3.37
2
1
2
(qd, J = 14.0, JP,H = 6.9 Hz, 1 H, CHCH3), 2.61 (d, J = 15.4 Hz,
1
2
1 H, CH2), 2.11 (dd, J = 15.4, JP,H = 4.3 Hz, 1 H, CH2), 1.56
2
3
(dd, J = 14.0, JP,H = 7.0 Hz, 3 H, CHCH3) ppm. 31P{1H} NMR
2
PPh2-CH ortho), 133.50 (d, JP,C = 17.1 Hz, PPh2-CH ortho), (121 MHz, CDCl3): δ = 5.79 (d, JP,P = 4.1 Hz, CHCH3PPh2),
1
1
4
131.66 (qd, JF,C = 321.2, JP,C = 34.9 Hz, CF3), 131.65 (d, JP,C
=
–18.21 (d, JP,P = 4.1 Hz, CH2PPh2) ppm. 13C{1H} NMR (75 MHz,
Eur. J. Org. Chem. 2011, 78–87
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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85

A. Sondenecker, J. Cvengrosˇ, R. Aardoom, A. Togni
FULL PAPER
CDCl3): δ = 140.40 (d, 1JP,C = 14.8 Hz, Ph-C ipso), 139.23 (d, 1JP,C (dd, JP,C = 8.7, JP,C = 1.4 Hz, Cp-C1), 78.67 (dd, JP,C = 8.9, JP,C
=
1.8 Hz, Cp-C2), 70.87 (s, Cp-CH), 69.80 (s, 5 CpЈ-CHЈ), 67.26 (d,
JP,C = 1.4 Hz, Cp-CH), 66.26 (s, Cp-CH), 64.77 (dd, JP,C = 14.6,
JP,C = 1.6 Hz, cod-CH), 64.07 (dd, JP,C = 14.2, JP,C = 0.7 Hz, cod-
1
= 15.5 Hz, Ph-C ipso), 137.69 (d, JP,C = 17.7 Hz, Ph-C ipso),
1
2
135.87 (d, JP,C = 16.9 Hz, Ph-C ipso), 134.36 (d, JP,C = 20.0 Hz,
Ph-CH ortho), 133.31 (d, 2JP,C = 17.4 Hz, Ph-CH ortho), 133.08 (d,
2JP,C = 20.1 Hz, Ph-CH ortho), 132.55 (d, JP,C = 18.6 Hz, Ph-CH CH), 36.55 (d, JP,C = 6.2 Hz, cod-CH2), 29.91 (dd, JP,C = 4.1, JP,C
2
4
4
ortho), 129.11 (d, JP,C = 0.6 Hz, Ph-CH para), 128.60 (d, JP,C
=
= 1.1 Hz, cod-CH2), 29.19 (dd, JP,C = 14.9, JP,C = 1.8 Hz, CHCH3),
0.5 Hz, Ph-CH para), 128.36 (d, JP,C = 7.0 Hz, Ph-CH meta), 26.00 (d, JP,C = 16.2 Hz, CH2), 16.24 (d, JP,C = 6.2 Hz, CHCH3)
128.26 (s, Ph-CH meta), 128.19 (d, JP,C = 6.4 Hz, Ph-CH meta), ppm.
3
3
3
2
127.82 (d, JP,C = 6.1 Hz, Ph-CH meta), 91.29 (dd, JP,C = 16.8,
[PdCl2(R,RFc,RP)-1a] (16): [PdCl2(cod)] (31 mg, 0.11 mmol) was
added in one portion to a solution of (R,RFc,RP)-1a (70 mg,
0.12 mmol) in CH2Cl2 (2 mL), and the resulting red mixture was
stirred at room temp. for 2 h. The precipitated complex was filtered
off in air, washed with cold hexane and dried in vacuo, affording
pure 16 as an orange microcrystalline solid (82 mg, 94%). 1H NMR
(400 MHz, CD2Cl2): δ = 8.08–8.03 (m, 2 H, PPhCF3-H ortho),
7.90–7.85 (m, 2 H, PPh2-H ortho), 7.73–7.69 (m, 1 H, PPhCF3-H
para), 7.67–7.57 (m, 8 H, 2 PPhCF3-H meta, 2 PPh2-H meta, 2
PPh2-H ortho, 2 PPh2-H para), 7.49–7.44 (m, 2 H, PPh2-H meta),
4.51 (s, 1 H, Cp-H3), 4.10 (s, 5 H, CpЈ-HЈ), 4.09–4.08 (m, 1 H, Cp-
3JP,C = 5.8 Hz, Cp-C1), 83.90 (dd, 2JP,C = 13.6, JP,C = 1.9 Hz, Cp-
3
3
C2), 69.16 (d, JP,C = 2.1 Hz, CpЈ-CHЈ), 68.32 (d, JP,C = 9.9 Hz,
Cp-CH3), 66.01 (dd, JP,C = 6.2, JP,C = 1.5 Hz, Cp-CH5), 65.61
(s, Cp-CH4), 29.73 (d, JP,C = 14.5 Hz, CHCH3), 27.05 (dd, JP,C
3
4
1
1
2
= 13.7, JP,C = 1.5 Hz, CH2), 19.28 (d, JP,C = 18.6 Hz, CHCH3)
ppm. HRMS (EI): calcd. for C37H34P2Fe [M]+ 596.1502; found (%)
596.1478 (7) [M]+, 411.0978 (47), 183.0381 (100).
[Rh(cod)(S,SFc,SP)-1a]BF4 (14): A solution of (S,SFc,SP)-1a (61 mg,
0.10 mmol) and [Rh(cod)2]BF4 (40 mg, 0.09 mmol) in CH2Cl2
(2 mL) was stirred at room temp. for 1 h. One third of the solvent
was evaporated, and hexane was added. The microcrystalline solid
thus formed was filtered off, washed with cold hexane, and dried
in vacuo, affording pure 14 as a red microcrystalline, air-sensitive
material (64 mg, 75%). 1H NMR (300 MHz, CDCl3): δ = 8.04–
7.98 (m, 2 H, Ph-H), 7.85–7.79 (m, 2 H, Ph-H), 7.74–7.43 (m, 11
H, Ph-H), 5.15 (br. s, 2 H, cod-CH), 4.65 (br. s, 2 H, cod-CH),
4.30–4.25 (m, 3 H, cod-CH and Cp-H), 4.13 (s, 5 H, CpЈ-HЈ), 4.09–
4.04 (m, 2 H, cod-CH), 3.89 (s, 1 H, Cp-H), 3.64–3.54 (m, 1 H,
CHCH3), 3.27 (s, 1 H, Cp-H), 2.18–1.92 (m, 10 H, cod-CH2 and 2
CH2), 1.39–1.33 (dd, J = 12.7, JP,H = 6.7 Hz, 3 H, CHCH3) ppm.
19F NMR (188 MHz, CDCl3): δ = –53.43 (d, 2JP,F = 53.0 Hz, CF3),
–154.04 (s, BF4) ppm. 31P{1H} NMR (122 MHz, CDCl3): δ = 32.91
2
2
H4), 4.00 (td, 1 H, J = 15.7, JP,H = 2.2 Hz, CH2), 3.75 (qd, 1 H,
3J = 13.5, JP,H = 6.8 Hz, CHCH3), 3.48 (d, 1 H, 2J = 15.7 Hz,
2
CH2), 3.20 (s, 1 H, Cp-H5), 1.34 (dd, 3 H, 3J = 13.5, 3JP,H = 6.9 Hz,
CHCH3). 19F NMR (377 MHz, CD2Cl2): δ = –50.45 (d, JP,F
=
2
66.6 Hz, CF3). 31P{1H} NMR (122 MHz, CD2Cl2): δ = 36.95 (qd,
2JF,P = 66.6, JP,P = 2.2 Hz, PPhCF3), 32.83 (d, JP,P = 2.2 Hz, PPh2).
13C{1H} NMR (101 MHz, CD2Cl2, 2 PPh2-C ipso, C1, and C2
could not be seen): δ = 136.51 (d, 2JP,C = 10.5 Hz, PPh2-CH ortho),
134.33 (qd, 2JP,C = 12.8, 4JF,C = 1.0 Hz, PPhCF3-CH ortho), 133.35
4
2
(d, JP,C = 3.0 Hz, PPhCF3-CH para), 132.73 (d, JP,C = 8.5 Hz,
4
PPh2-CH ortho), 132.03 (d, JP,C = 2.7 Hz, PPh2-CH para), 131.62
4
3
(d, JP,C = 3.0 Hz, PPh2-CH para), 129.61 (d, JP,C = 11.6 Hz,
1
2
3
(qdd, JRh,P = 161.1, JF,P = 53.0, JP,P = 36.7 Hz, PPhCF3), 24.02
PPhCF3-CH meta), 129.23 (d, JP,C = 10.5 Hz, PPh2-CH meta),
127.88 (d, JP,C = 11.6 Hz, PPh2-CH meta), 125.90 (d, JP,C
68.5 Hz, PPhCF3-C ipso), 124.44 (qd, JF,C = 321.5, JP,C = 72.9,
CF3), 70.07 (s, CpЈ-CHЈ), 69.83 (s, Cp-C3), 68.15 (d, 3JP,C = 1.8 Hz,
Cp-C5), 67.50 (s, Cp-C4), 33.72 (ddd, J = 21.5, 4.1, 0.5 Hz,
1
3
1
(dd, JRh,P
=
135.9, JP,P
=
36.7 Hz, PPh2) ppm. MS
=
(HiResMALDI): calcd. for C32H29F3P2Fe [M+] 886.26, 799.10 [M –
BF4]+; found 799.1048 [M – BF4]+.
1
1
[Ir(cod) (R,RFc,RP)-1a]BF4 (15): AgBF4 (17 mg, 0.09 mmol) was
added in one portion to a solution of [Ir2Cl2(cod)2] (28 mg,
0.04 mmol) in THF (0.7 mL), and the resulting orange mixture was
stirred at room temp. in a glove-box for 45 min. The mixture was
then filtered through Celite (removal of AgCl) yielding an orange
solution, which turned black upon addition of (R,RFc,RP)-1a
(50 mg, 0.09 mmol). The reaction mixture was stirred overnight.
Evaporation of the solvent gave the crude product, which was fil-
tered through Alox with CH2Cl2 as eluent, affording pure 15 as a
yellow microcrystalline solid (97 mg, 24%). 1H NMR (400 MHz,
CDCl3): δ = 8.14–8.10 (m, 2 H, Ph-H), 7.85–7.80 (m, 2 H, Ph-H),
7.58–7.51 (m, 3 H, Ph-H), 7.49–7.44 (m, 2 H, Ph-H), 7.42–7.35 (m,
2 H, Ph-H), 7.24–7.20 (m, 2 H, Ph-H), 7.16–7.12 (m, 2 H, Ph-H),
1
CHCH3), 29.82 (d, JP,C = 18.3 Hz, CH2), 16.50 (dd, J = 5.0,
0.5 Hz, CHCH3). MS (HiResMALDI): calcd. for C32H29Cl2-
F3FeP2Pd [M+] 765.94; found (%) 832.02 (22), 788.45 (8) [M +
Na]+, 759.27 (100), 729.51 (12) [M – Cl]+, 694.38 (12) [M – Cl2]+.
Supporting Information (see footnote on the first page of this arti-
cle): NMR spectra (1H, 13C, 31P, 19F) of selected new compounds.
Acknowledgments
Financial support from the ETH Zürich is gratefully acknowl-
edged. Acknowledgments are also made to the late Heinz Rüegger
and Aitor Moreno for valuable NMR assistance.
2
4.76 (qd, J = 7.2, JP,H = 4.0 Hz, 1 H, CHCH3), 4.35 (d, J =
13.7 Hz, 1 H, CH2), 4.23 (s, 1 H, Cp-H), 4.04 (s, 5 H, CpЈ-HЈ),
3.95 (t, J = 13.7 Hz, 1 H, CH2), 3.60 (t, J = 2.5 Hz, 1 H, Cp-H),
3.17–3.13 (m, 2 H, cod-CH), 3.08–3.02 (m, 2 H, cod-CH), 2.88 (s,
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2
(d, JP,P = 12.4 Hz, PPh2), –4.26 (qd, JF,P = 39.7, JP,P = 12.4 Hz,
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Ph-CH), 127.96 (s, Ph-CH), 127.72 (d, JP,C = 9.4 Hz, Ph-CH), 90.04
86
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Eur. J. Org. Chem. 2011, 78–87

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Received: August 17, 2010
Published Online: November 12, 2010
Eur. J. Org. Chem. 2011, 78–87
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
87