Synthesis, characterization and the crystal structures of novel achiral and chiral α-ferrocenyl α-aminophosphine oxides

Article abstract of DOI:10.1016/j.inoche.2006.02.027

Novel achiral α-ferrocenyl α-aminophosphine oxides (2a-2e) have been prepared by the reaction of ferrocenylaldimines (1a-1e) with Ph₂PLi at room temperature in 63-92% yield. Similarly, starting from l-phenylalaninol derived ferrocenylaldimine (

Full text of DOI:10.1016/j.inoche.2006.02.027

Inorganic Chemistry Communications 9 (2006) 529–532
www.elsevier.com/locate/inoche
Synthesis, characterization and the crystal structures of novel
achiral and chiral a-ferrocenyl a-aminophosphine oxides
*
*
Ling-Zhi Du, Jun-Fang Gong , Yu Zhu, Yang-Jie Wu, Mao-Ping Song
Department of Chemistry, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Zhengzhou University,
Daxue Road 75, Zhengzhou, Henan Province 450052, PR China
Received 2 December 2005; accepted 22 February 2006
Available online 3 March 2006
Abstract
Novel achiral a-ferrocenyl a-aminophosphine oxides (2a–2e) have been prepared by the reaction of ferrocenylaldimines (1a–1e) with
Ph2PLi at room temperature in 63–92% yield. Similarly, starting from L-phenylalaninol derived ferrocenylaldimine (3), the corresponding
(S,S)-phosphine oxide (4) and its (R,S)-diastereomer (5) were isolated by fractional crystallization in 41% and 16% yield, respectively. All
the achiral and chiral a-aminophosphine oxides were air-stable and easily accessible. They were fully characterized by elemental analysis,
1H NMR, 31P NMR and IR spectra. In addition, structures of 2e and 4 have been determined by X-ray single-crystal analysis.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: a-Aminophosphine oxides; Chiral; Ferrocenyl; Crystal structures; Synthesis
Ligands which contain multiple mixed donors, such as
hard and soft donors (often called hybrid ligands) find
increasing use in chemistry due to the new properties and
reactivities introduced in the hybrid ligand–metal interac-
tions. Aminophosphine oxides are a class of hybrid ligand
possessing two potential donor atoms – the amino group
nitrogen and the oxygen from the phosphine oxide group.
Studies on this type of ligand are relatively small. Dodoff
et al. reported that certain Pt(II) and Pd(II) complexes with
aminophosphine oxides were important biologically active
compounds [1]. Starting from a-aminoacids, some
a-aminophosphine oxides were also synthesized as poten-
tial HIV-Protease Inhibitors [2]. Recently, Balakrishna
et al. found that reactions of Ph2PN(H)Ph with parafor-
maldehyde or aromatic aldehydes led to the insertion of
‘RCH’ into the P(III)AN bond to give a-aminophosphine
oxides Ph2P(O)CH(R)N(H)Ph (R=H, Ar) and they studied
the coordination properties of Ph2P(O)CH2N(H)Ph with
Zn, Cd, Hg and U [3–5]. In addition, aminophosphine oxi-
des are found to be useful ligands in some catalytic reac-
tions. For example, in the hydroformylation of olefins,
some aminophosphine oxides were reported to be remark-
ably more active than their corresponding aminophos-
phines in combination with rhodium [6–8]. The mixed
donor aminophosphine oxide ligands also gave good
results in the ruthenium-catalyzed asymmetric transfer
hydrogenation reactions (up to 93% ee) [9,10]. We are
interested in the design and synthesis of new hybrid ligands
and their applications. In this aspect, the ferrocene-
containing ligands are especially attractive because of the
specific and unique geometries as well as electronic proper-
ties that the ferrocene provides [11–16]. In this communica-
tion, we present the synthesis, characterization and the
crystal structures of novel achiral and chiral a-ferrocenyl
a-aminophosphine oxides obtained from the reaction of
ferrocenylaldimines with Ph2PLi.
The ferrocenylaldimines (1a–1e) were readily prepared
by condensation of formylferrocene with arylamines
according to the published procedure [17]. Reaction of
ferrocenylaldimines (1) with Ph2PLi was carried out in
THF at room temperature for 10 h. After hydrolysis and
*
Corresponding authors. Tel.: +86 371 67763207; fax: +86 371
67766667.
E-mail addresses: gongjf@zzu.edu.cn (J.-F. Gong), mpsong9350@zzu.
edu.cn (M.-P. Song).
1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.02.027

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L.-Z. Du et al. / Inorganic Chemistry Communications 9 (2006) 529–532
purification, the products 2 were obtained in 63–92%
yield. It was found that the isolated products 2 were
a-aminophosphine oxides instead of the corresponding
a-aminophosphines. The results showed that an oxidation
process took place during the work up (Scheme 1). These
new achiral a-ferrocenyl a-aminophosphine oxides were
1
characterized by elemental analysis, H NMR, 31P NMR
and IR spectra [18]. The IR spectra show the mNH of 2e
at 3321 cmꢀ1 and that of the others in the range of 3399–
3443 cmꢀ1
.
The strong absorption around 1175–
1188 cmꢀ1 is assigned to mP@O. In addition, absorptions
at approximately 1000 and 1100 cmꢀ1 indicate the
existence of an unsubstituted Cp ring [19]. The 31P NMR
spectra of 2a and 2c show single resonances at 29.7 and
1
29.8 ppm, respectively. The H NMR spectra of 2 show
an irregular triplet at 4.92–5.02 ppm for the CH protons.
For 2a and 2c the signals of NH appear at 4.26 and
4.40 ppm, respectively as an irregular doublet, while for
2b, 2d and 2e the corresponding signals shift to upfield
and overlap with the signals of the substituted Cp ring.
The molecular structure of 2e has been determined by sin-
gle-crystal X-ray analysis [20]. Fig. 1 shows that compound
2e exists as a dimer in the crystal due to intermolecular
NAH. . .O@P hydrogen bonds between H (from NH) of
one molecule and O (from P@O) of an adjacent molecule
Fig. 1. Dimer of 2e showing intermolecular NAH. . .O@P H-bonding.
Selected bond lengths (A) and bond angles (°): P(1)AO(1) 1.486(2),
P(1)AC(11) 1.849(3), P(1)AC(20) 1.796(3), P(1)AC(26) 1.812(3),
N(1)AC(11) 1.459(3), N(1)AC(12) 1.391(4), N(1)AH(1E) 0.79(3);
˚
O(1)AP(1)AC(11)
O(1)AP(1)AC(26)
C(20)AP(1)AC(11)
N(1)AC(11)AP(1)
111.54(13),
111.93(14),
108.17(14),
106.0(2),
O(1)AP(1)AC(20)
C(20)AP(1)AC(26)
C(26)AP(1)AC(11)
C(12)AN(1)AC(11)
113.24(13),
105.13(14),
106.38(14),
123.9(2),
˚
˚
C(12)AN(1)AH(1E) 115(2), C(11)AN(1)AH(1E) 116(2).
(d(N. . .O) = 3.171(3) A, d(H. . .O) = 2.39(3) A, NAH. . .O
bond angle is 168(3)°). In 2e, the PAO bond distance is
˚
1.486(2) A and the PAC bond distances are in the range
˚
of 1.796(3)–1.849(3) A. The data are comparable to those
ceeded smoothly and the corresponding phosphine oxides
were obtained as a mixture of diastereomers after prepara-
tive TLC on silica gel plates eluting with CH2Cl2:acetone
(10:1) (Scheme 2). The two diastereomers were separated
successfully by fractional crystallization from dichloro-
methane–petroleum ether at r.t., giving 4 in 41% yield
and its diastereomer 5 in 16% yield [18].
found in the literature [3,5]. The geometry around the
nitrogen is nearly planar and the sum of the angles is 355°.
Based on the above results, we used an optically active
ferrocenylaldimine (3) obtained from the reaction of form-
ylferrocene with L-phenylalaninol. We hope to be able to
induce chirality at the C atom of imino group and get a sin-
gle diastereomer or two diastereomers that can be easily
separated. As expected, the reaction of 3 with Ph2PLi pro-
The (S,S) configuration of the chiral carbon atoms in 4
is confirmed by X-ray structural analysis [20]. Fig. 2 shows
that in the lattice of 4 there also exist intermolecular hydro-
gen bonds. However, this time the hydrogen bonds
between H (from OH not NH) in one molecule and O
H
H
H
N
R
C
N
R
˚
(from P@O) in an adjacent molecule (d(O. . .O) = 2.708(3) A,
Ph2PLi
P
O
Fe
˚
Fe
Ph
d(H. . .O) = 1.80(4) A, OAH. . .O bond angle is 168(4)°) form
THF, r.t.
Ph
a one dimensional chain structure of 4. In 4, the PAO bond
˚
distance is 1.493(2) A and the PAC bond distances are in
2
1
˚
the range of 1.807(3)–1.862(3) A, which resemble the values
R = H(a), CH3(b), Cl(c), OCH3(d), OC2H5(e)
found in 2e. Unlike 2e, the geometry around the nitrogen is
trigonal pyramidal with an angle sum of 335°.
Scheme 1.
O
H
Ph
Ph
O
H
CH Ph
Ph
Ph
2
P
P
CH Ph
CH Ph
2
2
H
C
C
N
OH
N
N
Ph PLi
2
OH
OH
H
H
+
Fe
Fe
Fe
THF, r.t.
3
5
4
Scheme 2.

L.-Z. Du et al. / Inorganic Chemistry Communications 9 (2006) 529–532
531
˚
Fig. 2. 1D chain structure of 4 showing intermolecular OAH. . .O@P H-bonding. Selected bond lengths (A) and bond angles (°): P(1)AO(1) 1.493(2),
P(1)AC(11) 1.862(3), P(1)AC(12) 1.817(3), P(1)AC(18) 1.807(3), N(1)AC(11) 1.475(3), N(1)AC(24) 1.475(4), N(1)AH(1E) 0.84(3); O(1)AP(1)AC(11)
110.24(13), O(1)AP(1)AC(12) 110.58(14), O(1)AP(1)AC(18) 110.78(14), C(12)AP(1)AC(11) 109.05(14), C(18)AP(1)AC(11) 107.31(12),
C(18)AP(1)AC(12) 108.80(15), N(1)AC(11)AP(1) 104.96(18), C(24)AN(1)AC(11) 115.6(2), C(24)AN(1)AH(1E) 109.2(19), C(11)AN(1)AH(1E) 110(2).
[3] S. Priya, M.S. Balakrishna, J.T. Mague, Inorg. Chem. Commun. 4
In conclusion, the new achiral a-ferrocenyl a-amino-
phosphine oxides were prepared in good to excellent yields
in one simple synthetic step from the reaction of ferrocenyl-
aldimines with Ph2PLi. Furthermore, starting from L-phe-
(2001) 437–440.
[4] S. Priya, M.S. Balakrishna, J.T. Mague, S.M. Mobin, Inorg. Chem.
42 (2003) 1272–1281.
[5] S. Priya, M.S. Balakrishna, S.M. Mobin, Polyhedron 24 (2005) 1641–
nylalaninol derived ferrocenylaldimine, the corresponding
(S,S)-phosphine oxide and its (R,S)-diastereomer were
obtained by a similar procedure. Since amino alcohols
are inexpensive and easily available, structural variations
will be convenient to introduce. Applications of these novel
ferrocene-containing a-aminophosphine oxides in catalysis
and asymmetric synthesis are currently under investigation
in our laboratory. The results will be reported in due
course.
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Acknowledgements
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We thank the National Natural Science Foundation of
China (Project 20472074) and Specialized Research Fund
for the Doctoral Program of Higher Education (SRFDP)
(20040459008) for financial support of this work.
Appendix A. Supplementary data
[18] Synthesis of compound 2e: Small lithium sticks (0.023 g, 3.3 mmol)
were added quickly to a stirred solution of triphenylphosphine
(0.395 g, 1.5 mmol) in 10 mL THF at room temperature under
nitrogen and stirred for 5 h. Then the reaction mixture was transferred
to a Schlenk flask by syringe and tert-butyl chloride (0.16 mL,
1.5 mmol) was added at 0 °C. After stirring at room temperature for
1 h to get rid of PhLi, 1e (0.25 g, 0.75 mmol) was added and stirred for
10 h. The reaction mixture was quenched with water and extracted
with dichloromethane. The combined organic layers were washed with
brine, dried over Na2SO4 and concentrated under reduced pressure.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.
2006.02.027.
References
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L.-Z. Du et al. / Inorganic Chemistry Communications 9 (2006) 529–532
The residue was purified by preparative TLC on silica gel plates using
CH2Cl2-acetone (10:1) as eluent, to produce 0.253 g (63%) of 2e as
yellow solids. m.p. 199–200 °C. IR (KBr Pellet): 3321, 1609, 1514,
[20] Crystals of 2e and 4 were obtained by recrystallization from
dichloromethane- petroleum ether at r.t.. A single crystal of 2e or 4
suitable for X-ray analysis was mounted on a glass fiber. All
measurements were made on a Rigaku-IV imaging plate area detector
1436, 1220, 1182, 1116, 1002, 831, 727, 696, 496 cmꢀ1 1H NMR
.
˚
(400 MHz, CDCl3): d 7.75 (m, 4H, Ph-H), 7.46 (m, 2H, Ph-H), 7.37 (m,
4H, Ph-H), 6.76 (d, J = 8.8 Hz, 2H, Ar-H), 6.65 (d, J = 8.8 Hz, 2H,
Ar-H), 4.92 (m, 1H, CH), 4.10 (s, 1H, C5H4), 4.07 (s, 1H, C5H4), 4.02
(s, 1H, C5H4), 3.94 (m, 4H, C5H4 + NH + CH2), 3.86 (s, 5H, C5H5),
1.36 (t, J = 7.0 Hz, 3H, CH3). Anal. Calc. for C31H30FeNO2P: C,
69.54; H, 5.65; N, 2.62. Found: C, 69.12; H, 5.62; N, 2.61%.
Compounds 2a–2d were prepared by a similar procedure. 2a: 92%,
Anal. Calc. for C29H26FeNOP: C, 70.89; H, 5.33; N, 2.85. Found: C,
70.46; H, 5.32; N, 2.89%. 2b: 68%, Anal. Calc. for C30H28FeNOP: C,
71.30; H, 5.58; N, 2.77. Found: C, 71.15; H, 5.66; N, 2.71%. 2c: 78%,
Anal. Calc. for C29H25ClFeNOP: C, 66.25; H, 4.79; N, 2.66. Found: C,
66.11; H, 4.78; N, 2.61%. 2d: 65%, Anal. Calc. for C30H28FeNO2P: C,
69.11; H, 5.41; N, 2.69. Found: C, 69.08; H, 5.45; N, 2.57%. The chiral
compound 4 and 5 were prepared by a similar procedure. 4: 41%,
with graphite monochromated Mo Ka radiation (k = 0.71073 A). The
data were corrected for Lorentz and polarization factors. The
structures were solved by direct methods [21] and expanded using
Fourier techniques and refined by full-matrix least-squares methods.
The non-hydrogen atoms were refined anisotropically, and the
hydrogen atoms were included but not refined. All calculations were
performed using the teXsan [22] crystallographic software package of
Molecular Structure corporation. Crystal data for 2e: M = 535.38,
˚
˚
Orthorhombic, space group Pbca, a = 12.346(3) A, b = 20.343(4) A,
3
˚
˚
c = 21.411(4) A, a = 90°, b = 90°, c = 90°, V = 5377.9(19) A , Z = 8,
l = 0.649 mmꢀ1, Dc = 1.322 Mg/m3, F(000) = 2240, h 2.15–25.00°,
14,094 reflections collected, 4346 reflections unique (R(int) = 0.0398),
The final R indices [I > 2r(I)]: R1 = 0.0493, wR2 = 0.1054, R indices
(all data): R1 = 0.0823, wR2 = 0.1154. CCDC No. 287661. Crystal
data for 4: M = 549.41, Orthorhombic, space group P2(1)2(1)2(1),
20
½aꢁD ¼ ꢀ106 (c = 0.095, CH2Cl2). m.p. 165 °C. IR (KBr Pellet): 3341,
3250, 3057, 1596, 1562, 1436 1114, 1003, 839, 741, 698, 492 cmꢀ1. 1H
NMR (400 MHz, DMSO): d 7.74 (m, 4H, Ph-H), 7.56 (m, 2H, Ph-H),
7.47 (m, 4H, Ph-H), 7.20 (m, 3H, Ph-H), 7.14 (d, J = 7.0 Hz, 2H, Ph-
H), 4.74 (d, J = 9.4 Hz, 1H, CH), 4.11 (s, 5H, C5H5), 3.98 (s, 1H,
C5H4), 3.92 (s, 1H, C5H4), 3.88 (s, 1H, C5H4), 3.41 (s, 1H, C5H4), 3.29
(dd, J = 10.6, 3.8 Hz, 1H, CH2OH), 3.20 (dd, J = 10.6, 4.6 Hz, 1H,
CH2OH), 3.12 (m, 1H, NHCH), 2.80 (dd, J = 12.8, 6.8 Hz, 1H,
CH2Ph), 2.70 (dd, J = 12.8, 6.6 Hz, 1H, CH2Ph). 31P{1H}NMR
(162 MHz, DMSO): d 29.5. Anal. Calc. for C32H32FeNO2P: C, 69.95;
H, 5.87; N, 2.55. Found: C, 69.48; H, 5.83; N, 2.56%. 5: 16%, Anal.
Calc. for C32H32FeNO2P: C, 69.95; H, 5.87; N, 2.55. Found: C, 69.56;
H, 5.84; N, 2.54%.
a = 8.8686(18) A, b = 12.526(3) A, c = 24.481(4) A, a = 90°, b = 90°,
˚
˚
˚
c = 90°, V = 2719.6(9) A , Z = 4, l = 0.643 mmꢀ1, Dc = 1.342 Mg/
3
˚
m3, F(000) = 1152, h 1.66–25.50°, 9079 reflections collected, 4952
reflections unique (R(int) = 0.0329), The final R indices [I > 2r(I)]:
R1 = 0.0381, wR2 = 0.0918,
R indices (all data): R1 = 0.0434,
wR2 = 0.0936. CCDC No. 287660. Copies of the data may be obtained
free of charge from The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44 1223 336 033, e-mail:deposit@ccdc.cam.ac.uk
or on the web www: http://www. ccdc.cam.ac.uk).
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Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994) 435–
436.
[19] M. Rosenblum, R.B. Woodward, J. Am. Chem. Soc. 80 (1958) 5443–
5449.
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tion, 1985 and 1992.