Synthesis and ligand properties of 1-phosphaethenyl-2-phosphanylferrocenes

Article abstract of DOI:10.1021/om8008316

(S)-1-Phosphaemenyl-2-diarylphosphanylferrocenes with planar chirality (Fc(CH=PMes*)PAr₂: PAr₂ = PPh₂ (3a), P(1-naphmyl)Ph (3b)) are prepared in high yields from optically active 2-phosphanylferrocenecarboxaldehydes by the phospha-Peterson reactions with Mes*P(Li)SiMe₃ in THF. The stereo-chemistry of 3b is determined by X-ray diffraction analysis. Compounds 3a and 3b readily react with [PtMe₂(μ-SMe₂)]₂ in Et₂O to afford dimethyl complexes with bidentate coordination of these ligands (PtMe₂(L): L = 3a (4a), 3b (4b)). The X-ray structure of 4b reveals almost identical trans-influence of the phosphaethenyl and phosphanyl groups, snowing comparable cr-donating abilities of those components. Treatment of 3a and 3b with [Pd(η³-allyl)(μ-Cl)]₂ in CH ₂Cl₂ in the presence of AgOTf forms the corresponding π-allyl complexes [Pd(η³-allyl)(L)]OTf (L = 3a (5a), 3b (5b)), respectively, which are mixtures of diastereomers with endo- and exo-oriented π-allyl ligands. Complex 5a catalyzes hydroamination of 1,3-cyclohexadiene with aniline in toluene in the presence of 5 A molecular sieves at room temperature, giving N-cyclohexen-3-ylaniline in 84% yield.

Full text of DOI:10.1021/om8008316

Organometallics 2008, 27, 6279–6285
6279
Synthesis and Ligand Properties of
1-Phosphaethenyl-2-phosphanylferrocenes
Ryo Takita, Yuko Takada, Rader S. Jensen, Masaaki Okazaki, and Fumiyuki Ozawa*
International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto
UniVersity, Uji, Kyoto 611-0011, Japan
ReceiVed August 26, 2008
(S)-1-Phosphaethenyl-2-diarylphosphanylferrocenes with planar chirality (Fc(CHdPMes*)PAr2: PAr2
) PPh2 (3a), P(1-naphthyl)Ph (3b)) are prepared in high yields from optically active 2-phosphanylfer-
rocenecarboxaldehydes by the phospha-Peterson reactions with Mes*P(Li)SiMe3 in THF. The stereo-
chemistry of 3b is determined by X-ray diffraction analysis. Compounds 3a and 3b readily react with
[PtMe2(µ-SMe2)]2 in Et2O to afford dimethyl complexes with bidentate coordination of these ligands
(PtMe2(L): L ) 3a (4a), 3b (4b)). The X-ray structure of 4b reveals almost identical trans-influence of
the phosphaethenyl and phosphanyl groups, showing comparable σ-donating abilities of those components.
Treatment of 3a and 3b with [Pd(η3-allyl)(µ-Cl)]2 in CH2Cl2 in the presence of AgOTf forms the
corresponding π-allyl complexes [Pd(η3-allyl)(L)]OTf (L ) 3a (5a), 3b (5b)), respectively, which are
mixtures of diastereomers with endo- and exo-oriented π-allyl ligands. Complex 5a catalyzes hydroami-
nation of 1,3-cyclohexadiene with aniline in toluene in the presence of 5 Å molecular sieves at room
temperature, giving N-cyclohexen-3-ylaniline in 84% yield.
Chart 1
Introduction
Recent advances in transition metal catalysis have been
largely dependent on the development of supporting ligands,
because ligand properties dominate the catalytic performance
of transition metal complexes. While phosphanes, imines, and
pyridine derivatives are most widely used, new types of ligands
with unique electronic properties have recently emerged. For
example, N-heterocyclic carbenes (NHCs) are extremely strong
σ-donors, which have enabled versatile transformations of aryl
chlorides in palladium-catalyzed reactions.1 NHCs have led to
notable improvements in the Grubbs-type olefin metathesis
catalysts as well.2 More recently, phosphaalkenes with a PdC
double bond have been examined as new entries of supporting
ligands.3 We have reported highly efficient catalyses using 1,2-
diaryl-3,4-diphosphinidenecyclobutenes as bidentate phosphaalk-
ene ligands (DPCB-Y, Chart 1).4 Representative examples
include dehydrative allylation with allylic alcohols (Pd),5
cyclodehydration of cis-2-butene-1,4-diol with active methylene
compounds (Pd),6 hydroamination of 1,3-dienes with aniline
(Pd),7 conjugate addition of benzyl carbamate to R,ꢀ-unsaturated
ketones (Pd),8 and Z-selective hydrosilylation of alkynes (Ru).9
This paper reports the synthesis and coordination chemistry of
1-phosphaethenyl-2-phosphanylferrocenes with planar chirality
(3a, b), which have been prepared aiming at the following
points: (1) direct comparison of the ligand properties of
phosphaalkene and phosphane, (2) application of phosphaalkene
ligands to catalytic asymmetric reactions.
Phosphaalkenes adopt end-on coordination with transition
metals via two types of orbital interactions, σ-donation and
π-back-donation.3 The most remarkable feature of phosphaalk-
enes is the extremely low-lying π* orbital of the PdC bond,
which induces strong π-back-donation. We recently documented
that DPCB-Y forms extended π-conjugated systems with
platinum via highly efficient dπ-pπ interactions (i.e., π-back-
donation).10 The π-conjugation stabilizes DPCB-Y complexes
especially in low-valent oxidation states to a great extent, and
this unique ligand property is a key to the high catalytic activities
* To whom correspondence should be addressed. E-mail: ozawa@
scl.kyoto-u.ac.jp.
(1) (a) N-Heterocyclic Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley-
VCH: Weinheim, 2006. (b) Enders, D.; Niemeier, O.; Henseler, A. Chem.
ReV. 2007, 107, 5606.
(2) Handbook of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim,
2003.
(3) (a) Le Floch, P. Coord. Chem. ReV. 2006, 250, 627. (b) Mathey, F.
Angew. Chem., Int. Ed. 2003, 42, 1578. (c) Mathey, F. J. Organomet. Chem.
2002, 646, 15. (d) Weber, L. Angew. Chem., Int. Ed. 2002, 41, 563.
(4) (a) Ozawa, F.; Yoshifuji, M. Dalton Trans. 2006, 4987. (b) Ozawa,
F.; Yoshifuji, M. C. R. Chimie 2004, 7, 747.
(7) Minami, T.; Okamoto, H.; Ikeda, S.; Tanaka, R.; Ozawa, F.;
Yoshifuji, M. Angew. Chem., Int. Ed. 2001, 40, 4501.
(5) (a) Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami,
T.; Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968. (b) Ozawa, F.;
Ishiyama, T.; Yamamoto, S.; Kawagishi, S.; Murakami, H.; Yoshifuji, M.
Organometallics 2004, 23, 1698. (c) Murakami, H.; Minami, T.; Ozawa,
F. J. Org. Chem. 2004, 69, 4482.
(6) Murakami, H.; Matsui, Y.; Ozawa, F.; Yoshifuji, M. J. Organomet.
Chem. 2006, 691, 3151.
(8) Jensen, R. S.; Umeda, K.; Okazaki, M.; Ozawa, F.; Yoshifuji, M. J.
Organomet. Chem. 2007, 692, 286.
(9) (a) Nagao, M.; Asano, K.; Umeda, K.; Katayama, H.; Ozawa, F. J.
Org. Chem. 2005, 70, 10511. (b) Hayashi, A.; Yoshitomi, T.; Umeda, K.;
Okazaki, M.; Ozawa, F. Organometallics 2008, 27, 2321.
(10) (a) Hayashi, K.; Nakatani, M.; Hayashi, A.; Takano, M.; Okazaki,
M.; Toyota, K.; Yoshifuji, M.; Ozawa, F. Organometallics 2008, 27, 1970.
10.1021/om8008316 CCC: $40.75
2008 American Chemical Society
Publication on Web 10/29/2008

6280 Organometallics, Vol. 27, No. 23, 2008
Scheme 1. Synthetic Routes to Chiral 1-Phosphaethenyl-2-phosphanylferrocenes
Takita et al.
of DPCB-Y complexes.4 On the other hand, although the
σ-donating ability is another important ligand property, this
information for phosphaalkenes has been limited. Phosphaethene
(H2CdPH) bears lone-pair electrons at an orbital level close to
phosphane (PH3).11 However, since the 3s orbital is predominant
in the lone-pair orbital,3a phosphaalkenes are generally regarded
as moderate σ-donors, considerably weaker than phosphanes.
We previously tried to estimate the σ-donating ability of
DPCB-Y ligands by comparison of the structural data of
PtMe2(DPCB-Y) with diphosphane analogues.12 In this study,
we prepared new bidentate ligands 3a and 3b, having both
phosphaalkene and phosphane moieties as coordination sites,
to compare the σ-donating abilities of those components more
precisely in the same molecule. For constructing such molecules,
the phosphaalkene moiety should be attached to an unsaturated
hydrocarbon system to secure the thermodynamic stability of
the PdC bond via π-conjugation.3a We therefore employed a
2-phosphanylferrocenyl group as the counterpart of the phos-
phaethenyl group for taking advantage of accessibility of the
ferrocene-based precursors 2a and 2b (Scheme 1).13,14 Since
the asymmetric synthesis of these precursors has recently been
established, we were able to successfully prepare the desired
compounds 3a and 3b in enantiomerically pure forms.
ecarboxaldehyde 2b. The enantioselective synthesis of 2b was
accomplished by a method reported by Chen et al.14
Compounds 3a and 3b were identified by NMR spectroscopy,
mass spectrometry, and elemental analysis. Each compound
showed one set of NMR signals assignable to a single
stereoisomer. The 31P{1H} NMR signals were observed as two
sets of doublets in typical regions of ferrocenylphosphanes (δ
-22.8 (3a), -30.0 (3b)) and phosphaalkenes (δ 247.8 (3a),
1
248.5 (3b)). In the H NMR spectra, a vinylic proton signal
arising from the phosphaethenyl group appeared at δ 8.18 with
2
a JPH coupling of 24 Hz for both compounds; the chemical
shift and coupling constant are consistent with the E-configu-
ration of the phosphaethenyl group.16
The stereochemistry of 3b (SFc,RP) was uniquely determined
by X-ray diffraction analysis (space group P212121). Figure 1
shows the crystal structure, which consists of two rotamers
around the phosphaethenyl-ferrocene bond (C1-C2 (A),
C46-C47 (B)). The Mes* group is bonded to the PdC bond
in vertical orientation. The 1-naphthyl and phenyl groups in the
phosphanyl group are situated in axial and equatorial positions,
respectively. Since the two ortho t-Bu groups of the Mes* group
1
are observed equivalently at δ 1.25 in the H NMR spectrum
measured at room temperature, these rotamers are interconverted
in an NMR time scale by bond rotation in solution.
Preparation and Structures of Dimethylplatinum(II)
Complexes. Compounds 3a and 3b readily reacted with
[PtMe2(µ-SMe2)]2 in Et2O at room temperature to give dimethyl
complexes 4a and 4b, respectively (eq 1), which were isolated
as red crystals, fairly stable to air and moisture. While the free
ligand 3a decomposed upon electrochemical oxidation, complex
Results and Discussion
Preparation of 1-Phosphaethenyl-2-phosphanylferrocenes.
Scheme 1 outlines the synthetic routes to 3a and 3b. Compound
2a (SFc) as the precursor of 3a was prepared from the chiral
acetal 1 according to a procedure developed by Kagan et al.13
Treatment of 2a with Mes*P(Li)SiMe3 in THF at room
temperature led to the phospha-Peterson reaction,15 giving 3a,
which was isolated in 78% yield as a red solid. Similarly,
compound 3b, having a P-chiral 1-naphthyl(phenyl)phosphanyl
group, was prepared in 94% yield from corresponding ferrocen-
4a exhibited a reversible one-electron oxidation wave (E1/2
)
0.34 V vs Fc+/Fc, ∆E ) 0.13 V) in the cyclic voltammogram
recorded in CH2Cl2 in the presence of Bu4NBF4 (0.1 M) at room
temperature.
(11) (a) Lacombe, S.; Gonbeau, D.; Cabioch, J.-L.; Pellerin, B.; Denis,
J.-M.; Pfister-Guillouzo, G. J. Am. Chem. Soc. 1988, 110, 6964. (b) Bock,
H.; Bankmann, M. Angew. Chem., Int. Ed. 1986, 25, 265.
(12) Ozawa, F.; Kawagishi, S.; Ishiyama, T.; Yoshifuji, M. Organome-
tallics 2004, 23, 1325.
(13) Riant, O.; Samuel, O.; Flessner, T.; Taudiene, S.; Kagan, H. B. J.
Org. Chem. 1997, 62, 6733.
(14) (a) Chen, W.; Roberts, S. M.; Whittall, J.; Steiner, A. Chem.
Commun. 2006, 2916. See also:(b) Chen, W.; Mbafor, W.; Roberts, S. M.;
Whittall, J. J. Am. Chem. Soc. 2006, 128, 3922. (c) Chen, W.; McCormack,
P. J.; Mohammed, K.; Mbafor, W.; Roberts, S. M. Angew. Chem., Int. Ed.
2007, 46, 4141.
(15) Yam, M.; Chong, J. H.; Tsang, C.-W.; Patrick, B. O.; Lam, A. E.;
Gates, D. P. Inorg. Chem. 2006, 45, 5225, and references therein.
Complex 4b adopts a square-planar configuration around the
platinum (Figure 2).17a The six-membered chelate ring com-
prised of Pt, P1, C3, C4, C5, and P2 atoms also has planarity,17b
while the ferrocene unit inclines slightly from the chelate ring
(ca. 11°). The P1-Pt-P2 angle is 94.31(3)°, the value of which

1-Phosphaethenyl-2-phosphanylferrocenes
Organometallics, Vol. 27, No. 23, 2008 6281
Figure 1. Molecular structures of two rotamers of 3b. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg)
are as follows: [A] P1-C1 ) 1.668(5), P1-C12 ) 1.871(4), C1-C2 ) 1.471(6), P2-C3 ) 1.811(4), P2-C30 ) 1.862(4), P2-C36 )
1.839(4), C1-P1-C12 ) 103.5(2), P1-C1-C2) 125.2(3), C12-P1-C1-C2 ) -178.1(4), C1-C2-C3-P2 ) -3.1(7). [B] P3-C46 )
1.673(5), P3-C57 ) 1.854(4), C46-C47 ) 1.457(6), P4-C48 ) 1.810(4), P4-C75 ) 1.853(4), P4-C81 ) 1.845(4), C46-P3-C57 )
105.0(2), P3-C46-C47 ) 121.7(4), C57-P3-C46-C47 ) 178.4(3), C46-C47-C48-P4 ) -1.6(6).
ethenyl and phosphanyl groups. Considering the minimal
π-bonding character of the Pt-Me bond, it is convincing that
the trans-influence mainly reflects the σ-donating abilities of
trans ligands.19 Accordingly, it is concluded that the CdPMes*
group has almost identical σ-donating ability to the P(Np)Ph
group. This conclusion is consistent with the 13C{1H} NMR
data of 4a and 4b, showing two methyl-carbon signals with
comparable chemical shifts and 1JPtC couplings: (4a) δ 2.2 (666
Hz), 6.0 (626 Hz); (4b) δ 3.4 (670 Hz), 6.1 (629 Hz).
Table 1 lists the structural data of 4b and the related DPCB-Y
and diphosphane complexes. While the Pt-Me lengths range
from 2.074(3) to 2.113(3) Å, the average deviation from the
mean bond distance (2.099 Å) is very small (0.009 Å).
Accordingly, it is likely that the σ-donating ability of phos-
phaalkene is essentially comparable to that of phosphane, and
the slightly shorter Pt-Me distances of DPCB-Y complexes
Figure 2. Molecular structure of 4b · Et2O. Hydrogen atoms and
Et2O molecule are omitted for clarity. Selected bond distances (Å)
and angles (deg): Pt-C1 ) 2.105(4), Pt-C2 ) 2.102(4), Pt-P1
) 2.2358(9), Pt-P2 ) 2.2706(9), P1-C3 ) 1.668(4), P1-C14 )
1.842(4), C3-C4 ) 1.456(5), P2-C5 ) 1.819(4), P2-C32 )
1.836(4), P2-C38 ) 1.847(4), C1-Pt-C2 ) 84.01(16), P1-Pt-P2
) 94.31(3), C1-Pt-P1 ) 176.29(11), C2-Pt-P2 ) 172.95(11),
C3-P1-C14)108.23(18),C4-C3-P1)125.2(3),C14-P1-C3-C4
) 179.7(3), C3-C4-C5-P2 ) 9.0(6), P1-C3-C4-C8 ) 169.4(3),
Pt1-P2-C5-C6 ) -167.9(3), C3-P1-C14-C15 ) -92.0(3),
C3-P1-C14-C19 ) 92.2(3).
are ascribed mainly to substituent effects.
Preparation and Catalytic Properties of (π-Allyl)palla-
dium(II) Complexes. As a preliminary attempt at finding the
utility of chiral phosphaalkene ligands in catalytic asymmetric
reactions, 3a and 3b were introduced to (π-allyl)palladium
complexes (eq 2). However, the resulting 5a and 5b were
mixtures of diastereomers with the π-allyl ligands in endo and
exo orientations toward the ferrocene unit (endo/exo ) 1/1 (5a),
1/0.8 (5b)). Thus, no stereoselectivity was observed for the
complexation of 3a and 3b with the Pd(η3-allyl) entity. For
example, the 31P{1H} NMR spectrum of 5a exhibited two pairs
of doublets at δ 13.3 and 178.1 (2JPP ) 74 Hz) and 13.2 and
180.0 (2JPP ) 72 Hz) in almost the same intensities. Further
is notably larger than those of PtMe2(DPCB) (82.85(4)°) and
PtMe2(DPCB-OMe) (83.33(3)°),12 but almost identical to that
of PtMe2(dppp) (94.30(3)°), having a six-membered chelate
structure.18 The Mes* group is perpendicular to the coordination
plane. Unlike the free ligand 3b, no bond-rotation causing the
exchange of ortho t-Bu signals (δ 1.49 and 1.80) was observed
1
structure assignment was performed by H NMR analysis.
1
in the H NMR spectrum.
Interestingly, the two Pt-Me bonds of 4b are almost identical
in length, showing very similar trans-influence of the phospha-
(16) (a) Yoshifuji, M.; Toyota, K.; Inamoto, N. Tetrahedron Lett. 1985,
26, 1727. (b) Yoshifuji, M.; Toyota, K.; Inamoto, N. Tetrahedron Lett. 1985,
26, 6443. (c) Yoshifuji, M.; Toyota, K.; Matsuda, I.; Niitsu, T.; Inamoto,
N.; Hirotsu, K.; Higuchi, T. Tetrahedron 1988, 44, 1363. (d) Appel, R.;
Menzel, J.; Knoch, F.; Volz, P. Z. Anorg. Allg. Chem. 1986, 534, 100. (e)
Gudimetla, V. B.; Rheingold, A. L.; Payton, J. L.; Peng, H.; Simpson, M. C.;
Protasiewicz, J. D. Inorg. Chem. 2006, 45, 4895.
(17) (a) The sum of the four angles around platinum is 360.0°. (b) The
sum of the six vertical angles of the chelate ring is 718.8°.
(18) Thomas, J. C.; Peters, J. C. J. Am. Chem. Soc. 2003, 125, 8870.
Table 2 summarizes the NMR data of 5a together with the
NOE correlations observed by NOESY. Because of the restricted
(19) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738, and
references therein.
(20) Smith, D. C., Jr.; Haar, C. M.; Stevens, E. D.; Nolan, S. P.; Marshall,
W. J.; Moloy, K. G. Organometallics 2000, 19, 1427.

6282 Organometallics, Vol. 27, No. 23, 2008
Takita et al.
Table 1. Bond Distances and Angles (deg) of Dimethylplatinum(II) Complexes
bond distance (Å)
bond angle (deg)
C-Pt-C
compound
Pt-C
Pt-P
P-Pt-C
P-Pt-P
4b
2.105(4)
2.102(4)
2.093(3)
2.089(4)
2.074(3)
2.102(3)
2.113(3)
2.109(5)
2.106(6)
2.2358(9)
2.2706(9)
2.2909(8)
2.2948(7)
2.2878(8)
2.2714(8)
2.2724(8)
2.261(1)
176.3(1)
173.0(1)
178.5(1)
177.8(1)
177.8(1)
174.94(9)
175.99(10)
174.8(2)
174.7(2)
84.0(2)
94.31(3)
PtMe2(DPCB)a
85.1(2)
85.9(2)
82.85(4)
83.33(3)
PtMe2(DPCB-OMe)a
PtMe2(dppp)b
86.0(1)
94.30(3)
95.39(5)
PtMe2(dpmcp)c
d
2.265(1)
a DPCB ) 1,2-diphenyl-3,4-bis{(2,4,6-tri-tert-butylphenyl)phosphinidene}cyclobutene: ref 12. b Ref 18. c dpmcp ) 1,1-bis(diphenylphosphanyl-
methyl)cyclopropane: ref 20. d Not reported.
Table 2. 1H NMR Chemical Shifts and NOE Correlations for 5aa
a The data were accumulated at room temperature in CD2Cl2 on a 400 MHz NMR instrument. The NOE correlations were examined by NOESY.
rotation of the Mes* group, all t-Bu signals appeared as
independent singlet peaks well separated from one another.
Among them, the signals at δ 1.72 and 1.80 showed cross-peaks
with the signals of the nonsubstituted Cp at δ 4.07 and 4.26,
respectively, and therefore they were assigned to t-Bu3 groups
in each isomer. The t-Bu3 signal at δ 1.72 had an NOE
correlation with the central proton signal of the allyl ligand (Hc)
at δ 6.01, indicating the endo orientation of the allyl ligand.
On the other hand, the other isomer showed no NOE correlation
between t-Bu3 (δ 1.80) and Hc (δ 5.54) signals. Instead, the Hc
proton (δ 5.54) was correlated with the t-Bu1 group (δ 1.04)
on the opposite side of the nonsubstituted Cp ring. Consequently,
this isomer was assigned to the exo form.
this reaction has been examined using diphosphane-coordinated
palladium complexes, the catalytic activity is modest, and the
reaction generally takes several days for completion at room
temperature.21,22 On the other hand, we have already reported
that the DPCB-OMe complex [Pd(η3-allyl)(DPCB-OMe)]OTf
exhibits an exceptionally high catalytic activity, affording the
(21) (a) Johns, A. M.; Utsunomiya, M.; Incarvito, C. D.; Hartwig, J. F.
J. Am. Chem. Soc. 2006, 128, 1828. (b) Lober, O.; Kawatsura, M.; Hartwig,
J. F. J. Am. Chem. Soc. 2001, 123, 4367. (c) Hartwig, J. F. Pure Appl.
Chem. 2004, 76, 507.
(22) (a) Taube, R. In Applied Homogenerous Catalysis with Organo-
metallic Compounds, Vol. 1; Cornils, B., Herrmann, W. A., Eds.; VCH:
Weinheim, 1996; p 507. (b) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998,
98, 675.
Next, the catalytic performance of 5a and 5b was investigated
in hydroamination of 1,3-cyclohexadiene with aniline. While

1-Phosphaethenyl-2-phosphanylferrocenes
Organometallics, Vol. 27, No. 23, 2008 6283
Table 3. Hydroamination of 1,3-Cyclohexadiene with Aniline
Catalyzed by 5a and 5ba
improved by addition of molecular sieves to the system (entries
5-8 in Table 2). Particularly, the reaction using 5a and MS5A
led to 84% yield of the product, while no remarkable asymmetric
induction was observed as expected from the nonselective
formation of the endo and exo isomers of (π-allyl)palladium
complexes.
time
(h)
yield
(%)c
ee
entry
catalyst
solvent
additiveb
(%)d
1
2
3
4
5
6
7
8
5a
5a
5a
5a
5a
5a
5a
5b
toluene
Et2O
THF
CH2Cl2
toluene
toluene
toluene
toluene
43
96
100
126
49
44
49
53
45
31
55
0
72
76
84
61
8
21
0
Conclusion
Using the newly prepared, ferrocene-based ligands bearing
both phosphaalkene and phosphane moieties as coordination
sites (3a and 3b), we confirmed that the phosphaethenyl and
diarylphosphanyl groups exhibit almost identical trans-influence
toward Pt-Me bonds. This finding is consistent with the
comparable lone-pair orbital levels of phosphaethene and
phosphane, previously estimated by ab initio MO calculations.12
On the other hand, it was also observed that the ferrocene-based
phosphaalkene ligands are rather unstable in palladium-catalyzed
hydroamination of 1,3-cyclohexadiene with aniline and readily
undergo addition of a nucleophile to give a pallada-phospha-
cyclopropane as a catalytically inactive species. Although this
undesirable process could be restrained to a considerable extent
by addition of molecular sieves to the catalytic system, the
observed catalytic performance was still far from the DPCB-
OMe catalyst. Through the previous studies, we were convinced
that the occurrence of extended π-conjugation over the 1,2-
diaryl-3,4-diphosphinidenecyclobutene skeleton is crucial not
only for the chemical stability but also for the high catalytic
activity of DPCB-Y complexes. In this sense, the ferrocene unit
was unfit as the counterpart of the phosphaalkene moiety.
Further development of new phosphaalkene ligands especially
for asymmetric catalysis is underway in this research group.
MS3A
MS4A
MS5A
MS5A
1
0
3
0
a The reactions were performed with 1,3-cyclohexadiene (0.5 mmol),
aniline (1.0 mmol), catalyst (0.01 mmol, 2 mol %), and solvent (1 mL)
at room temperature. b 100 mg/mL of activated molecular sieves was
added. c Determined by GLC using tridecane as an internal standard.
d Determined by HPLC using a chiral stationary phase column (Daicel
Chiralpak AD-H).
hydroamination product in nearly quantitative yield within 3-5 h
under the same reaction conditions.7
Table 3 summarizes the results for 5a and 5b. Unlike the
DPCB-OMe catalyst, the catalytic activity of 5a was modest,
and the reaction did not reach completion in several kinds of
solvents (entries 1-4). Follow-up experiments using 31P NMR
revealed the occurrence of degradation of palladium species
under catalytic conditions. Thus, when 5a was treated with
aniline (40 equiv) in toluene in the presence of 1,3-cyclohexa-
diene (20 equiv) at room temperature, the signals of 5a
disappeared within 1 h, and instead two sets of signals assignable
to the endo and exo isomers of (η3-cyclohexenyl)palladium
intermediate appeared at δ 12.3 and 178.8 (each doublet, JPP
)
74 Hz) and δ 11.7 and 181.5 (each doublet, JPP ) 70 Hz),
respectively, in a 1:2 ratio. Subsequently, these signals gradually
decreased for 2 days to be replaced by new singlets at δ 13.4
and 72.0 with the same intensities. Based on the similarity of
the chemical shift to analogous compounds previously re-
ported,23 the signal at δ 72.0 is assignable to a pallada-phospha-
cyclopropane (A, see the possible structure shown below)
formed by addition of a nucleophile (Nu), very probably aniline
or water. Therefore, we added molecular sieves to the catalytic
solution and examined palladium complexes. As a result, it was
found that the degradation of (η3-cyclohexenyl)palladium species
could be prevented to a considerable extent. Thus, a mixture of
5a, 1,3-cyclohexadiene (20 equiv), and aniline (40 equiv) was
stirred for 2 days at room temperature in the presence of MS5A
(100 mg/mL). The 31P{1H} NMR spectrum revealed that 49%
of the (η3-cyclohexenyl)palladium complex remains together
with A.
Experimental Section
General Considerations. All manipulations of air- and/or
moisture-sensitive compounds were carried out under a nitrogen
or argon atmosphere using standard Schlenk techniques. Toluene
and hexane were distilled from sodium benzophenone ketyl and
stored over activated molecular sieves (MS4A). CDCl3 was purified
by passing through an alumina column, degassed by freeze-pump-
thaw cycles, and stored over MS4A. CD2Cl2 was dried over calcium
hydride, transferred under vacuum, and stored over MS4A.
Dehydrated Et2O, THF, and CH2Cl2 were purchased (Wako) and
used as received. 1,3-Cyclohexadiene and aniline were distilled prior
to use. [PtMe2(µ-SMe2)]2 and [Pd(η3-C3H5)(µ-Cl)]2 were prepared
according to the literature.24,25
NMR spectra were recorded on a Bruker Avance 400 spectrom-
eter. Chemical shifts are reported in δ, referenced to 1H (of residual
protons) and 13C signals of deuterated solvents as internal standards
or to the 31P signal of 85% H3PO4 as an external standard. Cyclic
voltammetry was performed with a BAS ALS600C electrochemical
analyzer. Optical rotation was measured on a SEPA-200 polarim-
eter. Enantiomer excess of hydroamination product was determined
by HPLC using a Daicel Chiralpak AD-H column and hexane as
an eluting solvent. HRMS and elemental analysis were performed
by the ICR Analytical Laboratory, Kyoto University.
Preparation of 2-Phosphanyl-1-phosphaethenylferrocenes
(3a,b). A typical procedure is reported for 3a. To a solution of
Mes*PH2 (2,4,6-tri-tert-butylphenylphosphane) (0.209 g, 0.75
mmol) in THF (20 mL) was added n-BuLi (1.58 M in hexane, 0.47
mL, 0.75 mmol) at -78 °C. The mixture was stirred for 15 min,
warmed to room temperature, and stirred further for 30 min.
In accordance with the NMR observations described above,
the yield of catalytic hydroamination product was clearly
(23) (a) Liang, H.; Nishide, K.; Ito, S.; Yoshifuji, M. Tetrahedron Lett.
2003, 44, 8297. (b) Jouaiti, A.; Geoffrey, M.; Bernardinelli, G. Chem.
Commun. 1996, 437. (c) van der Sluis, M.; Beverwijk, V.; Termaten, A.;
Gavrilova, E.; Bickelhaupt, F.; Kooijman, H.; Veldman, N.; Spek, A. L.
Organometallics 1997, 16, 1144.
(24) Scott, J. D.; Puddephatt, R. J. Organometallics 1983, 2, 1643.
(25) Tatsuno, Y.; Yoshida, T.; Otsuka, S. Inorg. Synth. 1990, 28, 343.

6284 Organometallics, Vol. 27, No. 23, 2008
Takita et al.
Me3SiCl (0.095 mL, 0.75 mmol) was added, and after 30 min,
n-BuLi (1.58 M in hexane, 0.47 mL, 0.75 mmol) was slowly added.
The mixture was stirred for 30 min at room temperature and then
cooled to -78 °C. To this solution, a solution of 2-diphenylphos-
phanylferrocenecarboxaldehyde (2a, 0.199 g, 0.50 mmol) in THF
(10 mL) was added dropwise. The solution was gradually warmed
to room temperature and stirred until no trace of 2a was detected
by TLC. Me3SiCl (0.095 mL, 0.75 mmol) was added, and the
reaction mixture was stirred for 15 min and concentrated to dryness
under vacuum. The resulting residue was subjected to flash column
chromatography (SiO2, hexane/CH2Cl2 ) 90/10) to give 3a as a
red solid in 78% yield (0.258 g, 0.39 mmol). Similarly, compound
3b was obtained as a red solid from (SFe,RP)-2-(1-naphthylphe-
nylphosphanyl)ferrocenecarboxaldehyde (2b) in 94% yield.
3a. Mp: 83-85 °C. [R]D20 ) +636 (c 0.182, CHCl3). 1H NMR
(CDCl3, 20 °C): δ 1.34 (s, 9H), 1.38 (br, 18H), 3.90 (s, 1H), 4.06
(s, 5H), 4.50 (virtual triplet, Japp ) 2.5 Hz, 1H), 5.06 (s, 1H),
7.03-7.10 (m, 2H), 7.15-7.21 (m, 3H), 7.33-7.40 (m, 5H),
7.48-7.55 (m, 2H), 8.18 (dd, JPH ) 24.2 Hz, JPH ) 2.7 Hz, 1H).
13C{1H} NMR (CDCl3, 20 °C): δ 31.4 (s), 33.7 (s), 33.8 (s), 34.9
(s), 38.2 (s), 67.4 (dd, JPC ) 17 and 3 Hz), 70.0 (s), 70.8 (s), 72.6
(d, JPC ) 3 Hz), 75.6 (dd, JPC ) 9 and 7 Hz), 92.4 (dd, JPC ) 25
and 23 Hz), 121.7 (s), 127.7 (s), 127.9 (d, JPC ) 6 Hz), 128.1 (d,
JPC ) 8 Hz), 129.2 (s), 132.2 (d, JPC ) 18 Hz), 135.2 (d, JPC ) 21
Hz), 137.2 (d, JPC ) 8 Hz), 138.8 (dd, JPC ) 55 and 1 Hz), 139.6
(d, JPC ) 9 Hz), 149.2 (s), 153.7 (s), 171.4 (dd, JPC ) 35 and 9
Hz). 31P{1H} NMR (CDCl3, 20 °C): δ -22.8 (d, JPP ) 15 Hz),
247.8 (d, JPP ) 15 Hz). HRMS (EI), m/z: calcd for C41H48FeP2
658.2580 [M]+; found 658.2564. Anal. Calcd for C41H48 FeP2: C,
74.77; H, 7.35. Found: C, 75.10; H, 7.75.
JPC ) 4 Hz), 71.0 (s), 73.9 (dd, JPC ) 74 and 16 Hz), 74.5 (virtual
triplet, Japp ) 5 Hz), 91.2 (dd, JPC ) 18 and 4 Hz), 123.7 (dd, JPC
) 39 and 7 Hz), 128.3 (dd, JPC ) 10 and 9 Hz), 129.5 (d, JPC
)
2 Hz), 130.9 (d, JPC ) 2 Hz), 132.4 (d, JPC ) 11 Hz, JPtC ) 11
Hz), 136.1 (d, JPC ) 12 Hz, JPtC ) 20 Hz), 137.8 (d, JPC ) 46 Hz,
JPtC ) 14 Hz), 145.8 (dd, JPC ) 51 and 4 Hz, JPtC ) 30 Hz), 152.0
(s), 155.1 (d, JPC ) 2 Hz), 155.6 (s). 31P{1H} NMR (CD2Cl2, 20
°C): δ 4.6 (d, JPP ) 19 Hz, JPtP ) 1714 Hz), 210.2 (d, JPP ) 19
Hz, JPtP ) 1953 Hz). HRMS (FAB), m/z: calcd for C43H54FeP2195Pt
883.270 [M + H]+, found 883.269. Anal. Calcd for C43H54FeP2Pt:
C, 58.44; H, 6.16. Found: C, 58.12; H, 6.22.
4b. Mp: >300 °C. 1H NMR (CD2Cl2, 20 °C): δ 0.45 (m, JPtH
)
72.2 Hz, 6H), 1.34 (s, 9H), 1.49 (s, 9H), 1.80 (s, 9H), 3.81 (s, 5H),
4.18 (s, 1H), 4.36 (virtual triplet, Japp ) 2.5 Hz, 1H), 4.48 (s, 1H),
7.19 (t, JHH ) 7.8 Hz, 1H), 7.34-7.49 (m, 3H), 7.55-7.70 (m,
5H), 7.78-7.91 (m, 3H), 8.15-8.30 (m, 3H). 13C{1H} NMR
(CD2Cl2, 20 °C): δ 3.4 (dd, JPC ) 117 and 6 Hz, JPtC ) 670 Hz),
6.1 (dd, JPC ) 96 and 6 Hz, JPtC ) 629 Hz), 31.5 (s), 34.2 (s), 35.4
(s, JPtC ) 12 Hz), 35.6 (s), 39.5 (s), 40.0 (s), 67.9 (dd, JPC ) 47
and 10 Hz), 70.4 (d, JPC ) 5 Hz), 71.0 (s), 72.1 (dd, JPC ) 16 and
7 Hz), 75.4 (virtual triplet, Japp ) 5 Hz), 91.4 (dd, JPC ) 20 and 6
Hz), 123.7 (d, JPC ) 7 Hz), 123.9 (d, JPC ) 7 Hz), 124.5 (d, JPC
)
9 Hz), 125.7 (s), 126.2 (s), 127.8 (d, JPC ) 11 Hz), 128.5 (d, JPC
) 10 Hz), 129.0 (dd, JPC ) 6 and 4 Hz), 129.2 (s), 130.8 (s), 131.3
(s), 131.6 (d, JPC ) 5 Hz, JPtC ) 9 Hz), 132.7 (d, JPC ) 45 Hz),
133.5 (d, JPC ) 12 Hz), 134.7 (d, JPC ) 7 Hz), 134.8 (d, JPC ) 48
Hz), 137.3 (d, JPC ) 13 Hz, JPtC ) 26 Hz), 146.1 (dd, JPC ) 49
and 3 Hz, JPtC ) 30 Hz), 152.1 (s), 155.5 (d, JPC ) 28 Hz). 31P{1H}
NMR (CD2Cl2, 20 °C): δ 1.8 (d, JPP ) 18 Hz, JPtP ) 1685 Hz),
209.5 (d, JPP ) 18 Hz, JPtP ) 1964 Hz). HRMS (FAB), m/z: calcd
for C47H56FeP2195Pt 933.285 [M]+; found 933.284. Anal. Calcd for
C47H56FeP2Pt · C4H10O: C, 60.77; H, 6.60. Found: C, 60.74; H, 6.62.
Preparation of (π-Allyl)palladium(II) Complexes (5a,b). A
typical procedure is reported for 5a. [Pd(η3-allyl)(µ-Cl)]2 (18.9 mg,
0.050 mmol) and 3a (65.9 mg, 0.10 mmol) were dissolved in
CH2Cl2 (2 mL) at room temperature. The solution was cooled to 0
°C, and AgOTf (30.8 mg, 0.12 mmol) was added. The mixture
was stirred at room temperature for 2 h. A white precipitate of
AgCl formed in the system was removed by filtration through a
Celite pad. The filtrate was concentrated to dryness, and the resultant
residue was washed with hexane (3 mL × 3) and dried under
vacuum to afford [Pd(η3-allyl)(3a)]OTf (5a) in 94% yield (89.9
mg, 0.094 mmol) as a purple solid, which was analytically pure.
Similarly, complex 5b was obtained as a purple solid in 87% yield.
3b. Mp: 165-168 °C. [R]D20 ) +778 (c 0.184, CHCl3). 1H NMR
(CDCl3, 20 °C): δ 1.25 (br, 18H), 1.28 (s, 9H), 3.86 (s, 1H), 4.14
(s, 5H), 4.54 (virtual triplet, Japp ) 2.4 Hz, 1H), 5.09 (s, 1H), 7.02
(dd, J ) 6.2 and 5.7 Hz, 1H), 7.25-7.41 (m, 8H), 7.50-7.58 (m,
2H), 7.74 (d, J ) 8.1 Hz, 1H), 7.78 (d, J ) 8.1 Hz, 1H), 8.11 (d,
J ) 3.3 Hz, 1H), 8.18 (dd, J ) 24.0 and 2.9 Hz, 1H). 13C{1H}
NMR (CD2Cl2, 20 °C): δ 31.6 (s), 34.0 (s), 34.1 (s), 35.3 (s), 38.6
(s), 68.5 (dd, JPC ) 16 and 3 Hz), 70.7 (s), 71.6 (s), 73.8 (d, JPC
)
4 Hz), 76.1 (dd, JPC ) 9 and 6 Hz), 93.0 (dd, JPC ) 25 and 23 Hz),
122.2 (s), 126.0 (d, JPC ) 7 Hz), 126.1 (s), 126.2 (d, JPC ) 2 Hz),
126.3 (s), 128.7 (d, JPC ) 8 Hz), 129.0 (d, JPC ) 1 Hz), 129.2 (s),
129.8 (s), 131.6 (s), 133.9 (d, JPC ) 4 Hz), 134.8 (d, JPC ) 21 Hz),
135.5 (d, JPC ) 21 Hz), 136.9 (d, JPC ) 8 Hz), 137.3 (d, JPC ) 14
Hz), 139.7 (dd, JPC ) 55 and 2 Hz), 149.9 (s), 154.4 (s), 172.0
(dd, JPC ) 35 and 9 Hz). 31P{1H} NMR (CDCl3, 20 °C): δ -30.0
(d, JPP ) 18 Hz), 248.5 (d, JPP ) 18 Hz). HRMS (FAB), m/z: calcd
for C45H50FeP2 709.2815 [M + H]+; found 709.2820. Anal. Calcd
for C45H50FeP2: C, 76.27; H, 7.11. Found: C, 76.16; H, 7.17.
Preparation of Dimethylplatinum(II) Complexes (4a,b). A
typical procedure is reported for 4a. To a suspension of [PtMe2(µ-
SMe2)]2 (28.7 mg, 0.050 mmol) in Et2O (5 mL) was added 3a (65.8
mg, 0.10 mmol). The mixture was stirred at room temperature
overnight. Volatile materials were removed under reduced pressure
to afford a red solid, which was dissolved in a minimum amount
of CH2Cl2, layered with pentane, and allowed to stand at 0 °C to
form red crystals of 4a in 84% yield (70 mg, 0.42 mmol). Complex
4b was similarly prepared using 3b instead of 3a. Recrystallization
from Et2O gave red crystals with the composition of 4b · Et2O,
suitable for X-ray structure analysis.
5a (1:1 mixture of endo and exo isomers). Mp: 231-234 °C
(dec). HRMS (FAB), m/z: calcd for C45H54O3F3P2SFe106Pd 955.161
[M + H]+; found 955.161. Anal. Calcd for C45H53F3FeO3P2PdS:
C, 56.59; H, 5.59. Found: C, 56.19; H, 5.77. The NMR data of
each isomer are as follows.
Endo isomer. 1H NMR (CD2Cl2, 20 °C): δ 1.27 (s, 9H), 1.35 (s,
9H), 1.72 (s, 9H), 3.21 (t, J ) 11.9 Hz, 1H), 3.85 (t, J ) 12.8 Hz,
1H), 4.07 (s, 5H), 4.55 (2H), 4.66 (t, J ) 6.2 Hz, 1H), 4.78 (s,
1H), 4.89 (q, J ) 2.4 Hz, 1H), 6.01 (septet, J ) 6.9 Hz, 1H), 7.20
(dd, J ) 12.1 and 7.7 Hz, 2H), 7.36-7.86 (m, 10H), 7.91 (d, J )
25.8 Hz, 1H). 31P{1H} NMR (CD2Cl2, 20 °C): 13.3 (d, JPP ) 74
Hz), 178.1 (d, JPP ) 74 Hz).
1
Exo isomer. H NMR (CD2Cl2, 20 °C): 1.04 (s, 9H), 1.37 (s,
9H), 1.80 (s, 9H), 3.23 (t, J ) 12.0 Hz, 1H), 3.68 (t, J ) 11.7 Hz,
1H), 4.26 (s, 5H), 4.44 (s, 1H), 4.49 (t, J ) 6.7 Hz, 1H), 4.55
(1H), 4.76 (s, 1H), 4.92 (q, J ) 2.4 Hz, 1H), 5.54 (septet, J ) 6.7
Hz, 1H), 7.12 (dd, J ) 12.2 and 7.8 Hz), 7.36-7.86 (m, 10H),
7.87 (d, J ) 26.1 Hz, 1H). 31P{1H} NMR (CD2Cl2, 20 °C): δ 13.2
(d, JPP ) 72 Hz), 180.0 (d, JPP ) 72 Hz).
1
4a. Mp: 245-248 °C (dec). H NMR (CD2Cl2, 20 °C): δ 0.46
(m, JPtH ) 70.6 Hz, 3H), 0.75 (m, JPtH ) 74.6 Hz, 3H), 1.31 (s,
9H), 1.35 (s, 9H), 1.76 (s, 9H), 4.00 (s, 5H), 4.15 (s, 1H), 4.45-4.52
(m, 2H), 7.21-7.63 (m, 9H), 7.72 (d, JPH ) 22.8 Hz, 1H),
7.83-7.94 (m, 2H). 13C{1H} NMR (CD2Cl2, 20 °C): δ 2.2 (dd, JPC
) 117 and 7 Hz, JPtC ) 666 Hz), 6.0 (dd, JPC ) 97 and 6 Hz, JPtC
) 626 Hz), 31.6 (s), 34.4 (s, JPtC ) 4 Hz), 35.1 (s, JPtC ) 5 Hz),
35.5 (s), 39.2 (s), 40.1 (s), 63.9 (dd, JPC ) 49 and 11 Hz), 70.3 (d,
5b (1:0.8 mixture of endo and exo isomers). Mp: 164-167 °C
(dec). HRMS (FAB), m/z: calcd for C48H55FeP2106Pd 855.216 [M
+ H]+; found 855.217. Anal. Calcd for C49H55F3FeO3P2PdS: C,

1-Phosphaethenyl-2-phosphanylferrocenes
Organometallics, Vol. 27, No. 23, 2008 6285
Table 4. Crystallographic Data for 3b and 4b · Et2O
Catalytic Hydroamination. To a Schlenk tube containing
catalyst 5a (9.5 mg, 0.01 mmol) were added successively 1,3-
cyclohexadiene (48 µL, 0.50 mmol), toluene (1.0 mL), tridecane
(20 µL, GLC standard), and aniline (0.091 mL, 1.0 mmol). The
mixture was stirred at room temperature and examined by GLC.
The reaction solution was concentrated and subjected to flash
column chromatography (SiO2, 70/1 ) hexane/AcOEt), affording
N-cyclohexen-3-ylaniline as colorless oil. The enantiomer excess
of the product was determined by chiral HPLC (Daicel Chiralpak
AD-H, hexane, flow rate ) 0.17 mL/min, tR ) 71.8 (major) and
78.7 min (minor)).
X-ray Diffraction Analysis of 3b and 4b · Et2O. The X-ray
diffraction studies were performed on a Rigaku Mercury CCD
diffractometer with graphite-monochromated Mo KR radiation (λ
) 0.71070 Å). The intensity data were collected at 173 K (3b) or
113 K (4b · Et2O) and corrected for Lorentz and polarization effects
and absorption (numerical). The structure was solved by direct
methods (SHELXS-97) and refined on F2 against all reflections
(SHELXL-97).26 Further information has been deposited with the
Cambridge Crystallographic Data Centre (CCDC-699610 and
-699611). A summary of the data is given in Table 4.
3b
4b · Et2O
formula
fw
C45H50FeP2
708.64
C51H66FeOP2Pt
1007.92
cryst size, mm
cryst syst
space group
a (Å)
0.50 × 0.10 × 0.04
orthorhombic
P212121 (#19)
14.550(3)
15.300(3)
34.447(7)
7669(3)
0.30 × 0.20 × 0.04
orthorhombic
P212121 (#19)
10.46390(10)
17.2101(2)
25.5495(3)
4601.08(9)
4
b (Å)
c (Å)
V (Å3)
Z
8
dcalcd (g cm-3
)
1.228
0.507
173(2)
1.455
3.457
113(2)
µ(Mo KR) (mm-1
temp (K)
)
θ range (deg)
3.49-27.48
2.28-28.54
49 777
no. of reflns collected 62 571
no. of unique reflns
transmn factor
17494 (Rint ) 0.0790) 11538 (Rint ) 0.0504)
0.7857-0.9800
0.4236-0.8741
no. of reflections
with I > 2σ(I)
13 618
10 485
no. of variables
891
522
goodness-of-fit on F2 1.049
1.003
final R indices (I >
R1 ) 0.0659,
R1 ) 0.0287,
wR2 ) 0.0665
R1 ) 0.0348,
wR2 ) 0.0688
2σ(I))
wR2 ) 0.1383
R1 ) 0.0905,
wR2 ) 0.1531
R indices (all data)
Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research on Priority Areas (No.
18064010, “Synergy of Elements”) from the Ministry of
Education, Science, Sports, and Culture, Japan. R.T. is
grateful for a Grant-in-Aid for Young Scientists (Start-up,
No. 19890103) from Japan Society for the Promotion of
Science, and for financial support from The Uehara Memorial
Foundation.
58.55; H, 5.51. Found: C, 58.33; H, 5.69. The NMR data of each
isomer are as follows.
Endo isomer. 1H NMR (CD2Cl2, 20 °C): δ 1.20 (s, 9H), 1.35 (s,
9H), 1.70 (s, 9H), 3.07 (t, J ) 11.7 Hz, 1H), 4.07 (s, 5H), 4.12 (t,
J ) 12.8 Hz, 1H), 4.45 (s, 1H), 4.51 (br, 1H), 4.69 (br, 1H), 4.79
(s, 1H), 4.88 (m, 1H), 5.95 (septet, J ) 6.7 Hz, 1H), 7.24 (dd, J )
13.3 and 7.2 Hz, 1H), 7.30-7.58 (m, 8H), 7.60-8.20 (m, 18H).
31P{1H} NMR (CD2Cl2, 20 °C): δ 7.7 (d, JPP ) 72 Hz), 180.2 (d,
JPP ) 72 Hz).
Supporting Information Available: Crystallographic data for
3b and 4b · Et2O in cif format. This material is available free of
charge via the Internet://pus.acs.org.
1
Exo isomer. H NMR (CD2Cl2, 20 °C): δ 0.79 (s, 9H), 1.32 (s,
9H), 1.78 (s, 9H), 2.99 (t, J ) 12.7 Hz, 1H), 3.50 (t, JPH ) 11.7
Hz, 1H), 4.29 (s, 5H), 4.30 (s, 1H), 4.33 (br, 1H), 4.59 (br, 1H),
4.79 (s, 1H), 4.88 (m, 1H), 5.39 (septet, J ) 6.8 Hz, 1H), 7.03 (dd,
J ) 12.8 and 7.2 Hz, 1H), 7.30-7.58 (m, 8H), 7.60-8.20 (m, 18H).
31P{1H} NMR (CD2Cl2, 20 °C): δ 8.9 (d, JPP ) 73 Hz), 182.7 (d,
JPP ) 73 Hz).
OM8008316
(26) Sheldrick, G. M. SHELX-97; University of Go¨ttingen: Germany,
1997.