Ferrocenyl substituted chlorostilbenes and butadienes

Article abstract of DOI:10.1016/S0022-328X(01)00978-0

The readily accessible α-chlorophosphonates (OCH₂CMe₂CH₂O)P(O)CH(Cl)-C₆H₄-4-R [1: R=Me (a), OMe (b), Cl (c), H (d)] react with ferrocenecarboxaldehyde in the presence of NaH [Horner-Wadsworth-Emmons r

Full text of DOI:10.1016/S0022-328X(01)00978-0

Journal of Organometallic Chemistry 637–639 (2001) 616–620
www.elsevier.com/locate/jorganchem
Ferrocenyl substituted chlorostilbenes and butadienes
K. Senthil Kumar, K.C. Kumara Swamy *
School of Chemistry, Uni6ersity of Hyderabad, Hyderabad 500046, Andhra Pradesh, India
Received 10 April 2001; received in revised form 9 May 2001; accepted 10 May 2001
Abstract
The readily accessible a-chlorophosphonates (OCH2CMe2CH2O)P(O)CH(Cl)ꢀC6H4-4-R [1: R=Me (a), OMe (b), Cl (c), H (d)]
react with ferrocenecarboxaldehyde in the presence of NaH [Horner–Wadsworth–Emmons reaction] to give good yields of
ferrocenyl substituted chlorostilbenes. The novel bis ferrocenyl butadiene C5H5FeC5H4ꢀCHꢁCHꢀC(CN)CHC5H4FeC5H5 (9) as
well as the ferrocenyl 2-cyano-1,3-butadienes 4-RꢀC6H4ꢀCHꢁCHꢀC(CN)ꢁCHC5H4FeC5H5 [R=Me (10a), OMe (10b), Cl (10c)]
have been obtained by using the new allylphosphonate (OCH2CMe2CH2O)P(O)CH2C(CN)ꢁCHC5H4FeC5H5 (8); the latter
compound was prepared in good yields by the reaction of the Baylis–Hillman adduct, C5H5FeC5H4CH(OH)C(CN)ꢁCH2 (7), with
the chlorophosphite (OCH2CMe2CH2O)PCl. The electrochemical behavior of the ferrocenyl compounds thus synthesized has been
studied; two reversible one-electron processes are observed in the case of compound 9 suggesting a cooperative interaction
between the two ferrocenyl residues. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Ferrocenyl substituted olefins; Horner–Wadsworth–Emmons reaction; Baylis–Hillman adducts
H4)CH(OH)(CN)ꢁCH2. Thus, in this paper, we describe
the synthesis of: (a) ferrocenyl substituted stilbenes; and
(b) b-cyano substituted ferrocenyl butadienes.
1. Introduction
A convenient route to the a-chlorophosphonates of
the type (OCH2CMe2CH2O)P(O)CH(Cl)Ar (1) that are
useful precursors for the Horner–Wadsworth–Em-
mons (HWE) reaction has been reported earlier by us
[1,2]. Based on these phosphonates, we also developed a
simple route to ferrocenyl substituted acetylenes
C5H5FeC5H4CꢂCC6H4-4-Cl (2) [3] formed by HCl elim-
ination from the HWE products obtained by the reac-
tion of 1 with ferrocenecarboxaldehyde. In this context,
it was of interest to see (i) whether the precursor HWE
products of the type (C5H5FeC5H4)CHꢁC(Cl)(Ar) (3)
are stable or not and (ii) whether products in which
Ar=ferrocenyl could be obtained or not. It can be
noted that although a few reports are available on the
synthesis of ferrocenyl substituted olefins [4–7] a gen-
eral synthetic strategy for this class of compounds has
not been developed. In this connection we also consid-
ered the possibility of using phosphonates derived from
the reaction of a chlorophosphite (RO)2PCl with Bay-
lis–Hillman adducts [8] of the type (C5H5FeC5-
2. Results and discussion
Reaction of a-chlorophosphonates 1(a–d) [1–3] with
NaH followed by ferrocenecarboxaldehyde using THF
as the solvent gave the chloro substituted olefins 3(a–d)
as a (Z+E) isomeric mixture of products in good
yields (Scheme 1). The stoichiometry of NaH and the
solvent are important here; larger quantities of NaH
and the use of dimethylsulfoxide as a solvent lead to
acetylenes as reported before [3].
The 5-chlorofurfuryl phosphonate (4) [3] also reacts
readily with ferrocenecarboxaldehyde to give the olefin
5, but in this case, only the E-olefin is obtained
(Scheme 2).
* Corresponding author. Fax: +91-40-301-2460.
E-mail address: kckssc@uohyd.ernet.in (K.C. Kumara Swamy).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00978-0

K. Senthil Kumar, K.C. Kumara Swamy / Journal of Organometallic Chemistry 637–639 (2001) 616–620
617
for 3(a–d), 9, 10(a–c) as well as the acetylenes
(C5H5FeC5H4)CꢂCꢀC6H4-4-R [R=Cl, Me] to compare
the electrochemical behavior of these compounds with
that of ferrocene. In all the cases except 9, a reversible
redox couple with E1/2 in the range 0.42–0.54 V (Table
1) at a scan rate of 100 mV s−1 is observed. The equal
positive and negative peak heights and peak-to-peak
separation (DEp) suggest the characteristic one-electron
reversible process. For 9, two reversible one-electron
processes are observed (Fig. 1) with E1/2 values 0.38 and
0.58 V suggesting a cooperative interaction [15–17]
between the two ferrocenyl residues through the conju-
gated system.
Scheme 1.
In summary, new ferrocenyl substituted olefins that
include the bis (ferrocenyl) butadiene 8 have been syn-
thesized. Particularly, the use of phosphonates derived
from the Baylis–Hillman methodology may be devel-
oped further to incorporate ferrocenyl residues in com-
plex organic systems as these olefins have many reactive
centers.
Scheme 2.
As an alternative, we wanted to prepare the a-hy-
droxyphosphonate (6) by treating (OCH2CMe2-
CH2O)P(O)H with ferrocenecarboxaldehyde (it was
presumed that if 6 was obtained, it could be chlorinated
at the a-position using SOCl2). Unfortunately, this
reaction did not proceed in the expected manner, and
the only product that we could isolate was a phosphate
ester [l(P): −12.8], which was not analyzed further.
For the synthesis of ferrocenyl substituted butadienes
we first prepared the precursor allyl alcohol 7 by the
Baylis–Hillman methodology [8–11]. Treatment of 7
with the cyclic chlorophosphite (OCH2CMe2CH2O)PCl
[3] followed by thermal Arbuzov rearrangement gave
the phosphonate 8 (Scheme 3). Treatment of 8 with one
mole equivalent of ferrocenecarboxaldehyde in the pres-
ence of NaH readily formed the novel bis (ferrocenyl)
substituted butadiene 9 as a single isomer in high yields
(Scheme 4). Similar reactions with aromatic aldehydes
formed the monoferrocenyl substituted butadienes
10(a–c). Two points are to be noted in this synthesis: (i)
although other chlorophosphites [e.g. (EtO)2PCl] can
also be utilized to prepare phosphonates similar to 8,
they are expensive or inconvenient to handle; (ii) varia-
tions that are possible include the use of other vinylic
systems [e.g. CH2ꢁCH(COOMe)] in place of acryloni-
trile in the preparation of ferrocenyl substituted Baylis–
Hillman adducts (cf. Scheme 3).
Scheme 3.
As ferrocene and its derivatives are redox active
[12–14], we have recorded the cyclic voltammograms
Scheme 4.

618
K. Senthil Kumar, K.C. Kumara Swamy / Journal of Organometallic Chemistry 637–639 (2001) 616–620
Table 1
supporting electrolyte using glassy carbon working elec-
trode, Ag/AgCl reference electrode and platinum wire
as auxiliary electrode with ferrocene–ferrocenium cou-
ple as the redox standard [13].
Cyclic voltammetric data for compounds 3a–d, 9, 10a–c,
C5H5FeC5H4CꢀCC6H4-4-Cl and C5H5FeC5H4CꢀCC6H4-4-Me a
Compound
E1/2 (DEp)
3a
3b
3c
3d
+0.44 (97)
+0.42 (72)
+0.44 (86)
+0.47 (93)
3.1. Synthesis of the chloro substituted olefins
C5H5FeC5H4CHꢁC(Cl)ꢀC6H4-4-R [3: R=Me (a),
OMe (b), Cl (c), H (d)]
9
10a
+0.38 (73), +0.58 (59)
+0.53 (76)
3.1.1. Typical procedure for 3a
10b
+0.52 (63)
The phosphonate 1a (0.5 g, 1.73 mmol) in THF (10
ml) was added to a stirred suspension of NaH (washed
earlier with hexane) (0.16 g, 6.66 mmol) in THF (20 ml)
at 0 °C. After 0.5 h, ferrocenecarboxaldehyde (0.37 g,
1.73 mmol) in THF (10 ml) was added dropwise during
15 min and the mixture was stirred for 24 h. After
quenching with cold water (30 ml), the mixture was
extracted with ether (3×20 ml). The ether layer was
dried (Na2SO4) and the solvent was removed to obtain
a semi-solid which was purified by column chromatog-
raphy (silica gel, hexane) to obtain 3a (mixture of
isomers). Yield: 0.46 g (79%). M.p. (dec.): 100–102 °C.
10c
+0.54 (83)
+0.52 (76)
+0.49 (70)
C5H5FeC5H4CꢂCC6H4-4-Cl b
C5H5FeC5H4CꢂCC6H4-4-Me b
a E1/2 in V (with respect to Ag/AgCl) and DEp in mV; standardized
with respect to the ferrrocene–ferrocenium ion couple in acetonitrile,
TBAP [E1/2(DEp)=0.38 (85)].
b Prepared as outlined in Ref. [3].
1
IR (cm−1, major bands): w 1508, 1456, 1406. H-NMR:
l 2.41 (2 s merged, 3H, ArꢀCH3), 3.94, 4.13, 4.15, 4.21,
4.82 (m, together 9H, ferrocenyl-H), 6.62, 6.81 (2 s,
ratio 2:1, 1H, (Cl)CꢁCH), 7.19–7.60 (m, 4H, Ar-H).
13C-NMR: l 21.2, 21.4 (ArꢀCH3), 68.7, 69.2, 70.1
(ferrocenyl-C), 79.7, 80.4 (C(ferrocenyl)CHꢁCClꢀ),
123.9, 126.0, 126.6, 128.1, 129.0, 129.1, 135.5, 138.6,
(olefinic C+ArꢀC). MS: 338, 336 [M]+ 35,37Cl), 165,
(
152, 139.
Compounds 3b–d and 5 were prepared similarly
using the same molar quantities.
3b. Yield: 0.36 g (75%). M.p. (dec.): 68–70 °C. IR
1
Fig. 1. Cyclic voltammogram for compound 9 showing the two
reversible one-electron processes.
(cm−1, major bands): w 1599, 1508, 1458. H-NMR: l
3.85 (2 s merged, 3H, ArꢀOCH3), 3.93, 4.13, 4.15, 4.30,
4.75 (m, together 9H, ferrocenyl-H), 6.56, 6.70, (2 s,
ratio 1:1, 1H, (Cl)CꢁCH), 6.80–7.65 (m, 4H, ArꢀH).
13C-NMR: l 55.3 (ArꢀOCH3), 68.7, 69.1, 69.9 (ferro-
cenyl-C), 79.7, 80.4, (C(ferrocenyl)CHꢁCClꢀ), 113.7,
123.0, 126.3, 127.4, 130.4, (olefinic C+ArꢀC). MS:
3. Experimental
Solvents were dried and distilled prior to use [18].
Chemicals were purchased from Aldrich or local
352, 354 [M]+ 35,37Cl), 165, 152, 139.
(
sources.
Phosphonates
(OCH2CMe2CH2O)P(O)-
CH(Cl)ꢀC6H4-4-R [1: R=Me (a), OMe (b), Cl (c), H
(d)] and (OCH2CMe2CH2O)P(O)CH2-5-ClꢀC4H3O (4)
were prepared by using the methods outlined in the
literature [1–3]. The NMR spectra were recorded in
CDCl3 on a Bruker 200 MHz NMR spectrometer. IR
spectra were recorded on a JASCO FTIR 5300 spec-
trophotometer. Elemental analyses were obtained for
representative compounds and were carried out on a
Perkin–Elmer 240C CHN analyzer. Mass spectra were
recorded on a CEC-21-110B double focusing mass spec-
trometer. Cyclic voltammograms were recorded on a
Cypress systems model CS-1090/CS-1087 electroanalyt-
ical system; these measurements were made under dry
nitrogen in MeCN with 0.1 M [Bu4N][ClO4] as the
3c. Yield: 0.45 g (78%). M.p. (dec.): 88–90 °C. IR
1
(cm−1, major bands): w 1618, 1487, 1400. H-NMR: l
3.91, 4.13, 4.19, 4.36, 4.79 (m, together 9H, ferrocenyl-
H), 6.63, 6.81 (2 s, ratio 1:2, 1H, (Cl)CꢁCH), 7.26–7.57
(m, 4H, ArꢀH). 13C-NMR: l 68.8, 69.0, 69.3, 69.5, 70.2
(ferrocenyl-C), 79.2, 80.4, (C(ferrocenyl)CHꢁCClꢀ),
125.4, 127.2, 127.6, 128.5, 128.6, 130.5, 133.8 (olefinic
C+ArꢀC). Anal. Found: C, 60.45; H, 3.68. Calc. for
C18H14Cl2Fe: C, 60.52; H, 3.92%.
3d. Yield: 0.43 g (73%, liquid). IR (cm−1): w 1625,
1
1490, 1448, 1402. H-NMR: l 3.89, 4.11, 4.20, 4.36,
4.81 (m, together 9H, ferrocenyl-H), 6.62, 6.83 (2 s
ratio 1:1, 1H, (Cl)CꢁCH), 7.26–7.69 (m, 4H, ArꢀH).
13C-NMR: l 68.8, 69.2, 70.1 (ferrocenyl-C), 79.2, 80.1,

K. Senthil Kumar, K.C. Kumara Swamy / Journal of Organometallic Chemistry 637–639 (2001) 616–620
619
(C(ferrocenyl)CHꢁCClꢀ), 124.8, 126.1, 126.9, 128.0,
128.4, 128.6, 129.1 (olefinic C+ArꢀC).
57.08; H, 5.45; N, 3.32. Calc. for C19H22FeNO3P: C,
57.14; H, 5.51; N, 3.51%.
5. Yield: 0.30 g (52%). IR (cm−1): w 1710, 1670, 1639,
1
1570, 1504, 1450. H-NMR: 4.15, 4.30, 4.43 (3 s, 9H,
3.2. Synthesis of 2-cyano-1,3-butadienes containing
ferrocene C5H5FeC5H4CHꢁC(CN)CHꢁCHꢀR
[RꢁC5H5FeC5H4 (9), 4-MeꢀC6H4 (10a), 4-OMeꢀC6H4
(10b), 4-ClꢀC6H4 (10c)]
ferrocenyl-H), 6.15 (s, 2H, furfuryl-H), 6.36, 6.76 (AB
3
qrt, J(HꢀH)=16 Hz, 2H, CHꢁCH). 13C-NMR: 66.9,
69.7 (ferrocenyl-C), 82.0 (C(ferrocenyl)CHꢁCH), 108.0,
126.5, 136.0 (olefinic C+furfuryl C).
3.2.1. Typical procedure for 10a
3.1.2. Preparation of the Baylis–Hillman adduct
C5H5FeC5H4CH(OH)C(CN)ꢁCH2 [7]
Ferrocenyl allylphosphonate (8) (0.61 g, 1.53 mmol)
in THF (10 ml) was added to a stirred suspension of
NaH (0.15 g of 80% dispersion, 6.25 mmol) in THF (20
ml) at 0 °C. After 0.5 h, p-tolualdehyde (0.18 g, 1.49
mmol) in THF (10 ml) was added over a period of 5
min. The reaction mixture was stirred for 6 h, quenched
with cold water and then extracted with Et2O (3×20
ml). The ether layer was dried (Na2SO4) and the solvent
was removed to obtain a solid which was then purified
by column chromatography (silica gel, hexane) to ob-
tain 10a as a red solid (only one isomer). Yield: 0.5 g
(93%). M.p. 132–134 °C. IR (cm−1): 2214, 1583, 1512.
1H-NMR: l 2.35 (s, 3H, ArꢀCH3), 4.23, 4.51, 4.90 (m,
together 9H, ferrocenyl-H), 6.69 (d, 3J(HꢀH)=16.0
Hz, 1H, CHꢁCH), 6.92 (d, 3J(HꢀH)=15.8 Hz, 1H,
CHꢁCH), 6.94–7.37 (m, 4H, ArꢀH). 13C-NMR: l 21.4
(s, ArꢀCH3), 69.9, 71.5 (ferrocenyl-C), 107.2, 125.0,
126.5, 129.6, 130.7, 144.3 (olefinic C+CN+ArꢀC).
MS: 353 [M]+, 288, 212, 203, 190, 186, 121, 115, 107,
91.
A mixture of ferrocenecarboxaldehyde (0.5 g, 2.3
mmol), acrylonitrile (0.12 g, 2.3 mmol) and 1,4-diazabi-
cyclo[2.2.2]octane (DABCO, 0.05 g, 0.4 mmol) was
allowed to stand at room temperature (r.t.) for 3 days,
then taken up in Et2O (100 ml), washed with 10% dilute
HCl (50 ml). The ether phase was washed with water
(50 ml) and dried (Na2SO4). The solvent was removed
to obtain a solid which was purified by column chro-
matography (silica gel, hexane+EtOAc (99:1), yellow
band after ferrocenecarboxaldehyde) to obtain a yellow
solid. [There was also a second product (red) with a low
Rf value]. Yield: 0.36 g (57%). M.p. (dec.): 78 °C. IR
(cm−1): 3466, 2226, 1734. 1H-NMR: l 2.44 (2 d,
2J(HꢀH)=5.5 Hz, 1H, CH(OH)), 4.28 (s, 7H, ferro-
cenyl-H), 4.93 (m, 2H, ferrocenyl-H), 6.0 (AB qrt“2 s,
2H, CꢁCH2). 13C-NMR: l 65.8, 67.4, 68.8, 70.2, (ferro-
cenyl-C), 90.1 (CH(OH)), 117.3 (ꢀCꢂN), 125.9
(ꢀC(CN)ꢁCH2), 129.8 (ꢁCH2).
Compounds 9 and 10b and 10c were obtained by
using the same procedure with the same molar
quantities.
3.1.3. Preparation of 2-cyano-2-alkenylphosphonates
(OCH2CMe2CH2O)P(O)CH2C
(CN)ꢁC(H)C5H4FeC5H5 [8]
9. Yield: 0.24 g (88%). M.p. 198–200 °C. IR (cm−1):
1
To a stirred solution of the Baylis–Hillman adduct 7
(0.65 g, 2.45 mmol) and Et3N (0.24 g, 2.45 mmol) in
toluene (50 ml) (OCH2CMe2CH2O)PCl [3] (0.41 g, 2.45
mmol) was added dropwise at 0 °C under N2 and the
mixture was stirred for 6 h. The precipitate was filtered
off, washed with toluene (2×10 ml) and the washings
were added to the filtrate. The solvent from the com-
bined filtrate was removed and the residue was heated
at 80 °C under N2 for 4 h. The resultant product was
purified by column chromatography (silica gel, hex-
ane+EtOAc (1:1)) to obtain a dark-red solid. Yield:
0.85 g (86%). M.p. 148 °C. IR (cm−1): 2208, 1618,
2216, 1614, 1587. H-NMR: l 4.15, 4.22, 4.31, 4.41,
4.48, 4.86 (m, together 18H, 2C5H5FeC5H4), 6.33 (d,
3
3J(HꢀH)=15.7 Hz, 1H, CHꢁCH), 6.72 (d, J(HꢀH)=
15.7 Hz, 1H, CHꢁCHꢀ), 6.82 (s, 1H, CHꢁC(CN)).
13C-NMR: l 67 0, 69.3, 69.5, 69.5, 69.6, 69.8, 71.2
(ferrocenyl-C), 82.1 (C(ferrocenyl)ꢀCHꢁCH), 107.6,
117.7 (CꢂN), 123.3, 129.7, 141.8 (olefinic-C). MS: 447
[M]+, 382, 325, 305, 300, 260, 237, 224, 205, 186, 178,
172, 121.
10b. Yield: 0.35 g (88%). M.p. 102–104 °C. IR
1
(cm−1): 2216, 1684, 1602, 1510. H-NMR: l 3.83 (s,
3H, ArꢀOCH3), 4.22 (s), 4.51 (m), 4.89 (m) [together
9H, all ferrocenyl-H], 6.61 (d, 3J(HꢀH)=15.8 Hz,
CHꢁCH), 6.86–7.42 (m, 6H, olefinic H+
CHꢁC(CN)+ArꢀH). 13C-NMR: l 55.4 (ꢀOCH3), 69.8,
69.9, 70.9, 71.4 (ferrocenyl-C), 77.9 (C(ferrocenyl-
CHꢁCH)), 107.3, 114.3, 117.7, 120.9, 123.9, 127.9,
128.3, 129.2, 130.1, 143.7, 159.7 (olefinic C+CN+
ArꢀC).
1
1473, 1400, 1265. H-NMR: l 1.07, 1.15 (2 s, 6H, 2
2
CH3), 2.84 (d, J(PꢀH)=19.9 Hz, 2H, PꢀCH2), 3.88–
4.31 (m, 4H, 2 OCH2), 4.25 (s, 5H, C5H5FeC5H4), 4.46
(t, 3J(HꢀH)=2.0 Hz, 2 H, C5H5FeC5H4), 4.83 (t,
3J(HꢀH)=2.0 Hz,
2 H, C5H5FeC5H4), 7.04 (d,
4J(PꢀH)=4.9 Hz, ꢀC(CN)ꢁCH). 13C-NMR: l 21.5,
21.6 (2 CH3), 30.8 (d, 1J(PꢀC)=137.5 Hz, PꢀCH2) 32.7
(CMe2), 69.8, 71.3 (ferrocenyl-C), 75.7, 75.8 (d,
10c. Yield: 0.17 g (85%). M.p. 120–122 °C. IR: 2218,
3
1
2J(PꢀC)=6.0 Hz, ꢀOCH2), 94.6 (d, J(PꢀC)=5.0 Hz,
1579, 1489 cm−1. H-NMR: l 4.23 (s), 4.54 (m), 4.91
3
3
CHꢁC(CN), 118.2 (CꢂN), 149.6 (d, J(PꢀC)=10.0 Hz,
(m), [together 9H, ferrocenyl-H], 6.70 (d, J(HꢀH)=
C(H)ꢁC(CN). 31P-NMR: l 18.1. Anal. Found: C,
15.8 Hz, CHꢁCH), 6.85–7.43 (m, 6H, olefinic-H+

620
K. Senthil Kumar, K.C. Kumara Swamy / Journal of Organometallic Chemistry 637–639 (2001) 616–620
CHꢁC(CN), ArꢀH). 13C-NMR: 68.3, 69.9, 70.7, 71.7
(ferrocenyl-C), 106.6, 108.6, 119.0, 121.9, 126.6, 127.7,
128.0, 129.1, 130.8, 132.5, 134.2, 134.8, 141.8, 143.3,
145.6 (olefinic C+CꢂN+ArꢀC). Anal. Found: C,
67.35; H, 4.17; N, 3.56. Calc. for C21H16FeNCl: C,
67.48; H, 4.28; N, 3.75%.
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Acknowledgements
We thank the Council of Scientific and Industrial
Research (CSIR), New Delhi for the financial support.
We also thank Professor P.S. Zacharias for electro-
chemical data and Mr C. Muthiah for technical help.
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