A new class of planar-chiral ferrocenes: Serendipitous formation of 1,2-ferrocenediylazaphosphinines

Article abstract of DOI:10.1021/om010603z

The reaction of 1-(α-aminoalkyl)-2-diphenyl-phosphinoferrocene (1) which glyoxals gave via an unusual heterocyclization 1,2-ferrocenediylazaphosphinines (3) as a new class of planar-chiral ferrocenes. The products were fully characterized by analytical and various spectroscopic techniques. In particular, a complete assignment of all protons and carbons was made by various NMR techniques. A substantial degree of π-electron delocalization extending over the fused heterocyclic ring can be evidenced by IR and UV/vis spectra and in the case of 3a by X-ray crystallographic data. Employment of rac-3a as ligand for Cu-catalyzed cyclo-propanation of styrene by ethyl diazoacetate revealed a complete diastereo-discrimination leading to the formation of trans-product in 100% yield.

Full text of DOI:10.1021/om010603z

5784
Organometallics 2001, 20, 5784-5787
A New Cla ss of P la n a r -Ch ir a l F er r ocen es: Ser en d ip itou s
F or m a tion of 1,2-F er r ocen ed iyla za p h osp h in in es
Geun-Ho Hwang, Eun-Sook Ryu, Dong-Kyu Park, Sang Chul Shim,
Chan Sik Cho, and Tae-J eong Kim*
Department of Industrial Chemistry, Kyungpook National University, Taegu, Korea 702-701
J ong Hwa J eong*
Department of Chemistry, Kyungpook National University, Taegu, Korea 701-702
Minserk Cheong
Research Institute for Basic Sciences and Department of Chemistry, Kyung Hee University,
Seoul, Korea 130-701
Received J uly 6, 2001
Ch a r t 1
Summary: The reaction of 1-(R-aminoalkyl)-2-diphenyl-
phosphinoferrocene (1) with glyoxals gave via an un-
usual heterocyclization 1,2-ferrocenediylazaphosphinines
(3) as a new class of planar-chiral ferrocenes. The
products were fully characterized by analytical and
various spectroscopic techniques. In particular, a com-
plete assignment of all protons and carbons was made
by various NMR techniques. A substantial degree of
π-electron delocalization extending over the fused het-
erocyclic ring can be evidenced by IR and UV/ vis spectra
and in the case of 3a by X-ray crystallographic data.
Employment of rac-3a as ligand for Cu-catalyzed cyclo-
propanation of styrene by ethyl diazoacetate revealed a
complete diastereo-discrimination leading to the forma-
tion of trans-product in 100% yield.
results. The R-diimine ligands are now well-known to
stablize organometallic complexes5 and have thus been
widely employed in a number of catalytic reactions.6
We now wish to put into entry a completely new class
of planar-chiral ferrocenes of the type (π-heteroaromatic
ring)FeCp (3) that have been formed via an unusual
cyclization from (S,R)-1-(R-aminoalkyl)-2-diphenylphos-
phinoferrocene (1) with glyoxals as illustrated in Scheme
1. Here the first (S) refers to the central chirality at the
asymmetric carbon center and the second (R) to the
planar chirality. In some cases, however, where R1 )
H, rac-1 was employed for the reaction.
In tr od u ction
The recent resurgence of interest in 1,2-disubstituted
planar-chiral ferrocenes has resulted in numerous in-
teresting compounds which are finding widespread
application in asymmetric catalysis.1 Among others,
those of the type (π-heterocycle)FeCp* developed by Fu
deserve special attention due to their successful ap-
plication not only as ligands but also as nucleophilic
catalysts in a number of asymmetric cataytic reac-
tions.2-3
Our recent success in the use of chiral C2-symmetric
bisferrocenyl diamine ligands such as 4 in asymmetric
catalysis4 has prompted us to examine the related
diimine analogues such as 5 as a potential source of
chiral ligand (Chart 1). Our rationale was straightfor-
ward: if the amino group can serve as an effective
ligand for high enantiomeric excess, then the diimine
derivatives could give better or at least comparable
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . In general, the
synthesis of diimines involves the condensation of a
diketone (or dialdehyde) with 2 equiv of an alkyl- or
arylamine, often catalyzed by a Lewis or Bronsted acid.
Surprisingly, however, the reaction between 1a and
glyoxal (R2 ) H) supposedly to give the bisferrocenyl-
diimine 5 proved futile. Instead, we ended up with
obtaining 3a as a single product regardless the reaction
conditions employed. For instance, any change in the
molar ratio between 1a and glyoxal would not alter the
result; neither would the change in the reaction tem-
peratures.
(1) For recent reviews, see: (a) Richards, C. J .; Locke, A. J .
Tetrahedron: Asymmetry 1998, 9, 2377. (b) Kagan, H. B.; Riant, O. In
Advances in Asymmetric Synthesis; Hassner, A., Ed.; J AI Press Inc.:
Greenwich, CT, 1997; Vol. 2, p 189.
(2) For a review, see: Fu, G. C. Acc. Chem. Res. 2000, 33, 412, and
references therin.
(3) Shintani, R.; Lo, M. M.-C.; Fu, G. C. Org. Lett. 2000, 2, 3695.
(4) (a) Song, J .-H.; Cho, D.-J .; J eon, S.-J .; Kim, Y.-H.; Kim, T.-J .
Inorg. Chem. 1999, 38, 893. (b) Cho, D.-J .; J eon, S.-J .; Kim, H.-S.; Cho,
C. S.; Shim, S. C.; Kim, T.-J . Tetrahedron: Asymmetry 1999, 10, 3833.
(c) Cho, D.-J .; J eon, S.-J .; Kim, H.-S.; Kim, T.-J . Synlett 1998, 617.
(5) Van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151.
(6) For some leading references on the use of diimine ligands, see:
(a) Fache, F.; Schulz, E.; Tommasino, M. L.; Lemaire, M. Chem. Rev.
2000, 100, 2159. (b) Ittel, S. D. L.; J ohnson, K.; Brookhart, M. Chem.
Rev. 2000, 100, 1169. (c) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F.
Angew. Chem., Int. Ed. 1999, 38, 428. (d) Togni, A.; Venanzi, L. M.
Angew. Chem., Int. Ed. Engl. 1994, 33, 497.
10.1021/om010603z CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/29/2001

Notes
Organometallics, Vol. 20, No. 26, 2001 5785
Sch em e 1
F igu r e 1. Crystal structure of (R)-3a .
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (R)-3a
P-C(2)
1.758(4)
1.806(4)
1.387(5)
1.406(5)
1.443(6)
P-C(6)
1.765(4)
1.811(3)
1.289(5)
1.240(5)
1.444(5)
P-C(15)
N-C(2)
P-C(21)
N-C(3)
C(1)-O
C(1)-C(2)
C(3)-C(5)
C(5)-C(6)
C(2)-P-C(6)
C(6)-P-C(15)
C(6)-P-C(21)
C(3)-N-C(2)
N-C(2)-P
N-C(3)-C(5)
C(5)-C(3)-C(4)
C(5)-C(6)-P
101.3(2)
111.0(2)
108.7(2)
124.6(3)
125.7(3)
123.8(3)
118.2(3)
120.5(3)
C(2)-P-C(15)
C(2)-P-C(21)
C(15)-P-C(21)
N-C(2)-C(1)
C(1)-C(2)-P
N-C(3)-C(4)
C(3)-C(5)-C(6)
O-C(1)-C(2)
114.6(2)
115.1(2)
106.2(2)
119.0(3)
115.3(3)
118.1(4)
124.1(3)
123.8(4)
One of the most striking features of this reaction is
the formation of a phosphorus ylide bond in a fused
heteroaromatic ring. Pedagogically, the reaction bears
some resemblance to the classical synthesis of phos-
phorus ylide compounds. One such example involves
initially the nucleophilic attack of phosphorus to an
alkyl halide to form a phosphonium salt followed by
deprotonation by a base (or nucleophile).7-8 The final
stage of heterocyclization which accompanies the loss
of the methine hydrogen may be the result of an
oxidative aromatization occurring under aerobic workup
conditions.9 An activation and functionalization of the
methine position in similar derivatives has recently
been reported and exploited by Knochel.10 In this
connection, it is worth noting that the retentive SN1 type
reaction generating a remarkably stable R-ferrocenyl-
alkyl carbocation is ubiquitous for this type of ferrocene
derivatives.11 A major driving force behind this reaction
is believed to be resonance stabilization by the formation
of a fused heteroaromatic ring through in situ genera-
tion of the aforementioned R-ferrocenylalkyl carbocation.
Finally, in connection with the stereochemical change
in the course of the reaction, the loss of the central
chirality at the asymmetric cabon atom can be noted,
while the planar chirality of the (R)-configuration
around the disubstituted Cp ring still remains as
confirmed by its X-ray crystal structure in Figure 1.
Selected bond lengths and angles are listed in Table 1.
respectively. Namely, the pair of P-C(2) and P-C(6)
in the six-membered ring have almost same bond
lengths of 1.758(4) and 1.765(4) Å, which are a little
longer than the traditional P-C (ylidic) bond distances
such as 1.674(3) Å in H2CdPPh2 and 1.629(3) Å in H2Cd
P(Fc)3 (Fc ) ferrocenyl).7,8 The bond distances in the
other pair of P-C(15) and P-C(21) with 1.806(4) and
1.811(3) Å fall within the range of typical P-C(sp3)
single bonds and are quite naturally longer than any of
the above values. The N-C(3) distance of 1.289(5) Å is
close to the normal CdN bond, and the N-C(2) distance
of 1.387(5) Å is a little shorter than the value for the
pure single N(sp3)-C(sp2).12
The IR and the UV-vis spectral data are quite
informative in regard to extended resonance in this
compound. For example, two IR stretching bands for Cd
N and CdO groups in 3a move to lower frequency
regions to appear at 1589 and 1543 cm-1, respectively.
The UV-vis spectrum of 3a exhibits the expected
bathochromic shift by showing two absorption maxima
(λmax, MLCT transition) at 325 and 375 nm, while the
same λmax value for 1a appears at 275 nm. Here it is
worth noting, for comparative purposes, that R-ferro-
cenylpolyenes of the type (C5H5)Fe[C5H4(CHdCHR)n]
reveal the progressive bathochromic shifts upon increas-
ing conjugation with n ) 1 to 3. With R ) 4′-NO2C6H4,
for instance, the absorption maxima appear at 354 nm
(n ) 1), 383 nm (n ) 2), and 396 nm (n ) 3).13 Various
techniques of 1H and 13C one- and two-dimensional
NMR spectroscopy provide additional insight and make
possible a complete assignment of every proton and
carbon in 3a .14
The structure shows that P, C(2), N, C(3), C(5), C(6),
C(7), C(8), and C(9) are coplanar within 0.041(4) Å
deviation. The bond angles in the six-membered het-
erocycle are in the range 101.3(2)-125.6(3)°. The two
heteroatoms, P and N, reveal two pairs of P-C(sp2) bond
distances and a pair of N-C(sp2) bond distances,
(7) Schmidbaur, H.; J eong, J .; Schier, A.; Graf, W.; Wilkinson, L.;
Muller, G. New J . Chem. 1989, 13, 341.
(8) Huang, Y. Z.; Shen, Y. C. Adv. Organomet. Chem. 1982, 21, 115.
(9) This reasoning was suggested by one of our referees, for which
we are grateful.
(10) Ireland, T.; Perea, J . J . A.; Knochel, P. Angew. Chem., Int. Ed.
1999, 38, 8, 1457.
(11) (a) Togni, A. In Ferrocenes: Homogeneous Catalysis, Organic
Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.; VCH:
Weinheim, Germany, 1995; p 175. (b) Allenmark, A. Tetrahedron Lett.
1974, 371.
(12) Gilli, G.; Bertolasi, V.; Bellucci, F.; Ferretti, V. J . Am. Chem.
Soc. 1986, 108, 2420.
(13) Naskar, D.; Das, S. K.; Giribabu, L.; Maiya, B. G.; Roy, S.
Organometallics 2000, 19, 1464.

5786 Organometallics, Vol. 20, No. 26, 2001
Notes
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Da ta for
Cu(3a )2 species, where 3a coordinates through nitrogen,
may be envisaged in the initial stage of the reaction.
In conclusion, the present work describes the synthe-
sis of a series of 1,2-ferrocendiylazaphosphinines as a
new family of planar-chiral ferrocenes formed seren-
dipitously from the reaction of 1-(R-aminoalkyl)-2-di-
phenylphosphinoferrocene (1) with various glyoxals.
Further work is underway to investigate the reaction
chemistry of 3 including potential application in asym-
metric nucleophilic catalysis as well as the asymmetric
version of the reaction described Table 3. The outcome
will appear elsewhere in due course.
(R)-3a
empirical formula
fw
C26H22FeNOP
451.27
cryst size
space group
0.35 × 0.40 × 0.50
P212121
a (Å)
b (Å)
8.6289(6)
13.4215(5)
18.5382(9)
2147.0(2)
4
c (Å)
V (Å3)
Z
T (K)
293(2)
radiation, λ(transmn range)
2θ range (deg)
data collected: h; k; l
no. of unique reflns
Mo KR 0.71073
3.74-50.94
-10, 0; 0, 16; 0, 22
2290
µ (mm-1
)
0.795
Exp er im en ta l Section
transmn range
refinement
goodness of fit
93-100
FMLS on F2
1.05
Gen er a l Rem a r k s. All reactions were carried out under
an atmosphere of nitrogen using standard Schlenk techniques.
Solvents were dried using standard procedures. The 1H and
13C NMR experiments were performed on a Bruker Advance
400 spectrometer. The 31P NMR spectra were recorded on a
Varian Unity Invova 300 WB spectrometer. Chemical shifts
were given as δ values with reference to tetramethylsilane
(TMS) as internal standard. GC-mass spectra were obtained
by using a Micromass QUATTRO II GC8000 series model with
electron energy of 20 or 70 eV. Optical rotations were meas-
ured on a J ASCO DIP-370 digital polarimeter at ambient
temperature. IR spectra were run on a Mattson FT-IR Galaxy
6030E spectrophotometer. UV-visible spectra were obtained
in CH2Cl2 on a Varian CARY 5G spectrophotometer. All
commercial reagents were purchased from Aldrich and used
as received. (S,R)-1a and rac-1d were prepared according to
the literature methods.16-17
R indices (I > 2σ(I))a
absolute structure param
max. residue density (e/Å3)
R1 ) 0.032; wR2 ) 0.79
0.02(3)
0.27
R1 )∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑wi(Fo - Fc2)/wi(Fo2)]1/2
.
a
2
Ta ble 3. Ca ta lytic Cyclop r op a n a tion of Styr en e:
Dia ster eoselectivity a s a F u n ction of r a c-3a a
L
trans:cis
yield (%)
blank
rac-3a
61:39
100:0
80
>99
P r ep a r a tion of (R)-3a . To a solution of (S,R)-1a (500 mg,
1.2 mmol) in MeOH (10 mL) was added an aqueous solution
(40%) of glyoxal (0.2 mL, 1.2 mmol). The mixture was stirred
for 5 h at room temperature, after which the solution was dried
over anhydrous MgSO4. Removal of any solids through filtra-
tion followed by concentration in vacuo gave the crude product.
Recrystallization from hexane/acetone (4:1) afforded the prod-
a
All data represent the average of two runs, and all yields are
GC yields.
Rea ction Scop e a n d Ca ta lytic Ap p lica tion . Struc-
tural modification with R1 and R2 has also allowed us
to obtain an array of the same type of products (3b-f).
The detailed procedure for NMR assignment for 3a
provides the basis for the structural confirmation for
all other compounds (3b-f) because of their spectral
similarities. Other spectroscopic (IR, UV-vis) features
of all these compounds are quite similar to those of 3a ,
and thus their structural confirmation can be readily
performed by comparison and by analogy.14 Although
the test for the reaction scope has so far been far from
being comprehensive, the reagent bearing R2 seems to
be limited to glyoxal derivatives (R2 ) H, Me, Ph) for
the product formation. Employment of simple aldehydes
and ketones such as 2-pyridinecarboxaldehyde, o-anis-
aldehyde, formaldehyde, 2,3-butadione, pyruvonitrile,
and formic hydrazide simply yielded corresponding
condensation imine products.
23
uct as orange crystals (540 mg, 90%). [R]D -1700 (c ) 0.1 in
CHCl3). The following numbering scheme for NMR character-
ization is based on Figure 1. 31P NMR (121 MHz, CDCl3,
1
H3PO4): δ -4.2 (s). H NMR (400 MHz, CDCl3): δ 9.6 (d, H1,
J PH ) 25.5), 2.36 (s, H4), 4.56 (m, H7), 4.63 (m, H8), 4.84 (m,
H9), 3.70 (s, H10-H14), 7.66-7.58 (m, H16/H20), 7.89-7.84
(m, H17/H19), 7.66-7.58 (m, H18), 7.35-7.30 (m, H22/H26),
7.54-7.47 (m, H23/H25), 7.45-7.39 (m, H24). 13C NMR (100.6
MHz, CDCl3): δ 185.0 (d, C1, J ) 22.3), 89.5 (d, C2, J ) 74.4),
136.3 (d, C3, J ) 12.6), 23.0 (s, C4), 83.6 (d, C5, J ) 4.8), 61.1
(d, C6, J ) 93.7), 70.8 (d, C7, J ) 6.8), 73.7 (d, C8, J ) 11.6),
67.5 (d, C9, J ) 4.8), 70.9 (s, C10-C14), 126.0 (d, C15, J )
93.7), 133.1 (d, C16/C20, J ) 10.6), 129.0 (d, C17/C19, J )
12.6), 132.6 (d, C18, J ) 2.9), 129.1 (d, C21, J ) 86.9), 128.3
(d, C22/C26, J ) 12.6), 133.5 (d, C23/C25, J ) 11.6), 131.9 (d,
C24, J ) 2.9). IR (KBr): 1589 cm-1 (vs), 1543 cm-1 (vs). UV/
vis (MeCN): λmax nm 375. EIMS m/z (rel intensity): 451 (M+,
100), 238 (30), 183 (22), 149 (38), 59 (53). Anal. Calcd for
Preliminary results on the use of rac-3a as ligand in
Cu-catalyzed cyclopropanation of styrene with ethyl
diazoacetate reveal that a perfect diastereo-discrimina-
tion in favor of trans product can be achieved (Table 3).
These results demonstrate that our ligand is far more
excellent in diastereoselectivity than the well-known C2-
symmetric diimines such as semicorrins, bisoxazolines,
and bisazaferrocene.15 Although the origin of diastereo-
control has yet to be illucidated, the formation of a
(15) (a) Lo, M. M.-C.; Fu, G. C. J . Am. Chem. Soc. 1998, 120, 10270.
(b) Fritschi, H.; Leutenegger, U.; Pfaltz, A. Angew. Chem., Int. Ed.
Engl. 1986, 25, 1005. Lowenthal, R. E.; Abiko, A.; Masamune, S.
Tetrahedron Lett 1990, 31, 6005. (c) Evans, D. A.; Woerpel, K. A.;
Hinman, M. A.; Faul, M. M. J . Am. Chem. Soc. 1991, 113, 726.
(16) (a) Hayashi, T.; Hayashi, C.; Uozumi, Y. Tetrahedron: Asym-
metry 1995, 6, 2503. (b) Hayashi, T.; Mise, T.; Fukushima, M.;
Kagotani, M.; Nagashima, N.; Hamada, Y.; Matsumoto, A.; Kawakami,
S.; Konishi, M.; Yamamoto, K.; Kumada, M. Bull. Chem. J pn. 1980,
53, 1138. (c) Marr, G.; Hunt, T. J . Chem. Soc. (C) 1969, 1070. (d)
Honeychuck, R. V.; Okoroafor, M. O.; Shen, L.-H.; Brubaker, C. H.,
J r.; Organometallics 1986, 5, 482.
(14) The detailed procedure for NMR assignment and relevant NMR
spectra of 3a -f are provided in the Supporting Information.
(17) Sheldrick, G. M. SHELXS-86; Universita¨t Go¨ttingen, 1986;
SHELXS-97, Universita¨t Go¨ttingen, 1997.

Notes
Organometallics, Vol. 20, No. 26, 2001 5787
C26H22NPOFe: C, 69.20; H, 4.88; N, 3.11. Found: C, 69.26;
H, 5.04; N, 2.98.
Ack n ow led gm en t. T.J .K. is grateful to KOSEF for
financial support (Grant No.: 2000-2-12200-001-3), to
Ms. Y. S. Park for the NMR experiments, and to Prof.
S.-O. Kang, Korea University, for the generous donation
of chlorodimethylphosphine.
X-r a y Str u ctu r e Deter m in a tion . Crystallogrphic data for
3a are collected in Table 2. An ORTEP drawing showing the
numbering scheme used in refinement is presented in Figure
1. Intensity data were collected at room temperature with a
CAD4 diffractometer using monochromated Mo KR radiation
(λ ) 0.71073 Å). Lorentz and polarization reflections were
applied and absorption corrections made with three Ψ scans.
The structures were solved by direct methods and refined by
full-matrix least-squares methods based on F2 using SHELXS-
97 and SHELXL-97.16 Non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were included in calcu-
lated positions. Additional crystallographic data are available
in the Supproting Information.
Su p p or tin g In for m a tion Ava ila ble: The detailed pro-
cedure for NMR assignment and relevant NMR spectra of 3a -
f, compound characterization data for 3b-f, and tables of
positional parameters and Biso/ Beq, H atom coordinates, aniso-
tropic displacement parameters, complete bond lengths and
angles, and least-squares planes for 3a . This material is
avaiable free of charge via the Internet at http://pubs.acs.org.
OM010603Z