Studies on the cyclomercuration of 1,1′-bis[(arylimino)phenylmethyl]ferrocenes

Article abstract of DOI:10.1016/S0277-5387(98)00388-X

The reaction of bisferrocenylimines with mercuric acetate and subsequent treatment with LiCl lead to formation of mono (9) and double (10) cyclomercurated derivatives. The ¹H NMR and ¹⁹⁹Hg NMR spectra of the double cyclomercurated bi

Full text of DOI:10.1016/S0277-5387(98)00388-X

Polyhedron 18 (1999) 1023–1027
Studies on the cyclomercuration of 1,19-
bis[(arylimino)phenylmethyl]ferrocenes
Xiu Ling Cuia, Yang Jie Wua, , Da Peng Zou , Cun Heng He , Ji Jie Chai
a
b
b
*
aDepartment of Chemistry, Key Laboratory of Applied Chemistry of Henan Province, Zhengzhou University, Zhengzhou 450052, PR China
bNational Research Center for Analysis of Drugs and Metabolites, The Chinese Academy of Medical Sciences, Beijing 100050, PR China
Received 22 June 1998; accepted 19 October 1998
Abstract
The reaction of bisferrocenylimines with mercuric acetate and subsequent treatment with LiCl lead to formation of mono (9) and
1
double (10) cyclomercurated derivatives. The H NMR and 199Hg NMR spectra of the double cyclomercurated bisferrocenylimines show
that compounds 10 exist as two isomers (meso and dl). The individual stereoisomers were isolated successfully by crystal picking. The
structures of these new compounds have been confirmed by elemental analysis, IR and 1H NMR spectroscopies, and further by X-ray
crystal structure determination of meso [hHgCl(h5-C5H3CPh5NAr)j2Fe] (Ar5m-CH3C6H4).
1999 Elsevier Science Ltd. All rights
reserved.
Keywords: Bisferrocenylimine; Mercury; Crystal structure
1. Introduction
the normal 1208 required for the sp2 hybridization state and
this facilitates the directing of mercury to the ortho-
position by the nitrogen. This study is now extended to
We have demonstrated that the mercuration of fer-
rocenylimines 1, 2 and 3 occur predominantly on the
ortho-position of the substituted Cp ring (cyclopentadienyl
ring), affording the cyclo-mercurated ferrocenylimines 4, 5
and 6 [1–3], respectively. Such reactions are of interest in
that they will provide a new route, after suitable functional
group modification, to inherently chiral 1,2-disubstituted
ferrocene. It has also been found that when R is a methyl
group and Ar contains electron-donating group such as
OCH3 or CH3 in the para-position, the yields of the
ortho-mercurated products are very low, and it appears that
the high electron density in the imino nitrogen is quite
unfavorable to the mercuration on the ortho-position [2].
Double cyclomercuration of 1,19-bis[1-(arylimino)ethyl]-
ferrocenes 7 mainly produced the mono-ortho-mercurated
products [4]. On the contrary, the acetoxymercuration
of 3 followed by the treatment of the resulting products
with lithium chloride produced ortho-chloromercurated
ferrocenylimines 6 in higher yields in comparison with
those of 1 and 2, indicating the important role played by
the C-phenyl. The effect of the phenyl can be due to the
steric repulsion between the C-phenyl and the ferrocenyl
moiety as well as the N-aryl leads to smaller angle u than
double
cyclomercuration
of
1,19-bis[(arylimino)-
phenylmethy]ferrocene, which can form both monocyclo-
mercurated and double cyclomercurated products, with two
isomers:meso-anddl-.Wesuccessfullyseparatedtheisomers
and determined the structure of meso isomer by X-ray
crystal analysis. This paper describes the experiment
designed to gain further insight into the substitution effect
and the relationship between the structure and property on
the double mercuration of bisferrocenylimines, related
stereochemistry and mechanism of the formation of stereo-
isomers of bis(mercury) complexes.
2. Results and discussion
*
Corresponding
wyj@mail.zzu.edu.cn
author.
Fax:
186-371-7979408;
e-mail:
The bisferrocenylimines [(h5-C5H4CPh5NAr)2Fe] des-
0277-5387/99/$ – see front matter
PII: S0277-5387(98)00388-X
1999 Elsevier Science Ltd. All rights reserved.

1024
X.L. Cui et al. / Polyhedron 18 (1999) 1023–1027
ignated as bis(FKB), were prepared by refluxing 1,19-
dibenzoylferrocene and the corresponding amines in the
presence of freshly activated Al2O3 [5] in toluene for 3 d.
Every day addition of small quantities of the amines and
activated Al2O3 was needed to complete the reaction.
Isolation of the pure bis(FKB) was achieved by chroma-
tography of the reaction mixture on silica gel under
reduced pressure; in each separation, the band possessing
the highest Rf values contained the compound 8.
no signals of the unsubstituted Cp ring. For example, the
1H NMR spectrum of 8a exhibited two signals at d 4.71
ppm and d 4.50 ppm integrating for protons 2 and 3
respectively, and the signals at d 6.33, d 6.46, d 6.65 and
d 6.91 ppm to the protons of N-phenyl ring. The multipet
at d 7.19 ppm was assigned to ten protons of the C-Ph
rings.
1
The H NMR spectra of compounds 9 indicated that the
starting material converted to the corresponding mono
mercurated products. The seven remaining protons in the
ferrocenyl moiety behaved as if in seven different mag-
netic environments. The signals of the protons of the Cp
ring can not be distinguished owing to the small chemical
shift difference between them.
1
What is most interesting is that the H NMR spectra of
10a, 10b exhibited two sets of signals and the 199Hg NMR
spectrum of 10a also exhibited two signals at d2760.96
and d2745.30 ppm. Every compound exists as two
isomers. We separated the different crystalline forms of
compound 10a by crystal picking. The major isomer was
meso-10a and minor isomer was dl-10a. The pair of the
proton signals for Cp ring for the individual stereoisomers,
meso-10a and dl-10a, occur at d 4.70, d 4.59, d 4.53 and
The cyclomercuration reaction was carried out with
bis(FKB) and two mole equivalents of mercuric acetate in
methylene dichloride and methanol at ambient temperature
for about 3.5 h, followed by the treatment with LiCl, gave
mono (9) and double (10) cyclomercurated fer-
rocenylketimines. The isolation of pure compounds 9 and
10 was carried out by chromatography of the reaction
mixture on silica gel, since the compound 10 exhibited
higher Rf values than that of the compound 9. The first
band is for compound of 10, second band is for compound
9 and third one is for the starting material. The yields of
mono- and double-mercuration products are higher than
those of 7 reported previously [4], indicating the important
role played by the C-phenyl. The C-phenyl may also
weaken the basicity of bisferrocenylimines 8, which is
favorable to the formation of the mercurated product. All
the new compounds were characterized by elemental
1
d 4.63, d 4.59, d 4.41 ppm, respectively. According to H
NMR study of the mercurated mono ferrocenylimines [3],
the signals at d 4.70, d 4.59 and d 4.53 ppm correspond to
protons 4, 3 and 5 in meso-form, respectively. The signals
at d 4.63, d 4.59 and d 4.41 ppm correspond to protons 4,
3 and 5 in dl-form, respectively. In the meso configuration,
the chemical shifts of the substituted Cp ring protons shift
to downfield significantly in comparison with d 4.57, d
4.53, d 4.40 ppm for the mono mercurated fer-
rocenylimines analogue compound 6.
1
analysis, IR and H NMR spectra.
The IR spectra of compounds 8–10 showed no absorp-
tion band at 1000 and 1100 cm21, which indicated the
presence of two substituted cyclopentadienyl rings [6]. In
addition, the C5N IR absorptions of the compounds 9 and
10 shifted to lower energy by 29–38 cm21 in comparison
with the frequency of compounds 8, which indicated that
the imino nitrogen coordinated with mercury [6] in com-
pounds 9 and 10.
The X-ray crystal structure of meso-10a was determined
and a perspective view of its molecular structure is shown
in Fig. 1, which has been supported by the spectral data.
Selected bond lengths and angles are listed in Tables 1 and
2, respectively. It confirms that in the compound the Fe
atom of the double mercurated bisferrocenylimine is
situated on a crystallographic center of symmetry. This
configuration is identified as the meso isomer. The com-
The 1H NMR spectra of bisferrocenylimines were
similar to those of mono ferrocenylimines [3], except for

X.L. Cui et al. / Polyhedron 18 (1999) 1023–1027
1025
Fig. 1. Structure of meso-10a.
bond angles Cl(4)-Hg(1)-C(13) and Cl(5)-Hg(2)-C(37)
are 172.98 and 178.08, close to the ideal value of 1808 in
organic derivatives of mercury [7]. The chelate cycles
Hg(1)-C(13)-C(20)-C(22)-N(9) and Hg(2)-C(37)-C(27)-
C(15)-N(12) are nearly planar. The dihedral angle between
the two substituted Cp rings and the two chelate cycles are
176.48 and 173.28, respectively. The interangles between
the two C-phenyl rings and the two substituted Cp rings
are 70.498 and 62.918 respectively, less than that in
compound 6 (81.988) [10]. As a result, the protons for the
Cp ring in meso-10a appear at downfield when compared
to those for compound 6. This can be interpreted in terms
of the interplanar angle u between the C-phenyl and
substituted Cp rings, since the anisotropy of the phenyl
ring varies as a cos2u function of the interplanar angle (the
larger u, the lower the deshielding) [11]. The Fe-C(Cp)
Table 1
Selected bond distances (A) for meso-10a
˚
Hg(1)-Cl(4)
Hg(1)-N(9)
Hg(1)-C(13)
Hg(2)-Cl(5)
Hg(2)-N(12)
Hg(2)-C(37)
Fe(3)-C(11)
Fe(3)-C(13)
Fe(3)-C(18)
Fe(3)-C(19)
2.31(1)
2.78(3)
2.06(3)
2.32(1)
2.84(1)
2.09(3)
2.04(3)
2.06(3)
2.07(3)
2.06(3)
Fe(3)-C(41)
Fe(3)-C(43)
N(9)-C(22)
N(9)-C(30)
N(12)-C(15)
N(12)-C(26)
Fe(3)-C(20)
Fe(3)-C(27)
Fe(3)-C(37)
Fe(3)-C(38)
2.11(4)
2.08(4)
1.26(4)
1.41(4)
1.28(4)
1.40(4)
2.06(3)
2.06(3)
2.06(3)
2.06(3)
pound meso-10a has two chloromercurio groups directly
linked to the 2-position of the two Cp rings. The N(9)-
˚
˚
Hg(1) and N(12)-Hg(2) distances are 2.78 A and 2.84 A
respectively, shorter than the sum of Van der Waals radii of
˚
˚
bond distance ranges from 2.04 A to 2.11 A. The average
˚
N and Hg (3.05–3.15 A) [7–9] and indicate the presence
˚
C-C bond length in the Cp ring is 1.435 A. The two Cp
of intramolecular coordination between N and Hg. The
rings are parallel with interplanar angle 1.728.
It was established that the mercuration involved the
initial coordination of the mercury to the imino nitrogen
and subsequent electrophilic attack at the 2-carbon atom
[1–3], which lead us to find proposed explanation for the
formation of stereoisomers in double cyclomercuration
(Scheme 1). Once one chelate ring is formed through the
cyclomercuration reaction, the orientation of the other Cp
ring during the second mercuration step determines the
stereochemistry. In case of formation of meso-product the
second electrophilic position is at C-59 whereas elec-
Table 2
Selected bond angles (8) for meso-10a
Cl(4)-Hg(1)-C(13)
Cl(4)-Hg(2)-C(37)
Hg(1)-C(13)-C(18)
Hg(1)-C(13)-C(20)
Hg(2)-C(37)-C(27)
Hg(2)-C(37)-C(38)
C(22)-N(9)-C(30)
N(12)-C(26)-C(36)
172.9(8)
178.0(8)
130.1(22)
117.2(21)
122.5(22)
125.9(21)
123.9(8)
118.0(7)
N(9)-C(22)-C(16)
C(14)-C(15)-N(12)
N(12)-C(15)-C(27)
N(9)-C(30)-C(25)
N(9)-C(30)-C(33)
N(12)-C(26)-C(8)
C(26)-N(12)-C(15)
N(9)-C(22)-C(20)
125.8(8)
124.8(8)
117.7(9)
122.3(8)
118.3(8)
122.7(8)
122.7(7)
117.1(9)

1026
X.L. Cui et al. / Polyhedron 18 (1999) 1023–1027
trophilic attack on the C-29 leads to the dl-form. After the
two chelate rings are formed, the interconversion of the
two stereoisomers is not possible without breaking the
Hg-C bond. The meso-isomer produced as the major
product is due to the difficult rotation about C-C bond
caused by the presence of C-phenyl ring.
3.4. 1,19-bis[(3-
bromophenylimino)phenylmethyl]ferrocene (8b)
Brown-red crystals, yields 16.7%, m.p. 180–180.58C, IR
KBr(pellet): 3021, 1617, 1586, 1553, 1455, 890, 791, 705
cm21, 1H NMR: 4.52 (t, 4H, J51.9 Hz, H-3); 4.69 (t, 4H,
J51.9 Hz, H-2); 6.45 (d, 2H, J57.6 Hz, N-Ph-H); 6.76 (s,
2H, N-Ph-H); 6.88 (d, 2H, J57.9 Hz, N-Ph-H); 6.96 (m,
2H, N-Ph-H); 7.17 m (10H, C-Ph-H). Found: C, 61.97; H,
3.65; N, 3.87. Calc. for C36H26Br2FeN2: C, 61.57; H,
3.73; N, 3.99%.
3. Experimental section
3.1. Materials and intruments
3.5. Mercuration of bisferrocenylimines
Melting points were measured on a WC-1 apparatus and
uncorrected. Elemental analyses were determined with a
Carlo Erba 1160 Elemental Analyzer. H NMR spectra
A solution of compound 8 (0.5 mmol) in methylene
dichloride (10 ml) was added into a 50 ml flask equipped
with a magnetic stirrer and an equilibrated addition funnel.
Meanwhile, 1 mmol of mercuric acetate was dissolved in a
sufficient amount of methanol. This solution was then
added dropwise to the flask over a period of 30 min.
Subsequently, 1.5 mmol of lithium chloride dissolved in
methanol was added, and then the mixture stirred for 30
min. The contents of the flask were transferred to a
separatory funnel, and an additional 20 ml of methylene
dichloride was added. The solution was washed with two
30 ml portions of water, and then dried over Na2SO4. The
resulting solution was evaporated in vacuo to a minimum
amount and subjected to a dry column of silica gel, eluted
with methylene dichloride. The first band is for compound
10, second band is for compound 9.
1
were recorded on a Bruker DPX-400, using CDCl3 as the
solvent and TMS as an internal standard. 199Hg NMR was
recorded on a Bruker DPX-400 spectrometer in CHCl3 at
258C. The operating frequency was 71.6 MHz. The routine
acquisition parameters used were as follows: pulse width
15.0 ms, acquisition time 1.1 s, spectral width 28571 Hz,
number of scans 28889. A solution of HgCl2 in DMSO-d6
was used as external reference. IR spectra were recorded
on a Perkin Elmer FTIR 1750 spectrophotometer. Chroma-
tography was carried out on a short column packed with
dry silica gel under reduced pressure.
3.2. Synthesis of the ferrocenylketimines
1,19-dibenzoylferrocene (1.0 g, 2.5 mmol) was dissolved
in toluene (30 ml) at room temperature. Once the starting
material had dissolved completely, the corresponding
amine (8.9 mmol) was added. The red solution was
refluxed for three days. Every day addition of small
quantities of the amines and activated Al2O3 was needed
to complete the reaction. The hot solution was carefully
filtered and the filtrate reduced to dryness on a rotary
evaporator. Isolation of the pure compound 8 was carried
out on silica gel under reduced pressure, the band posses-
sing the highest Rf values contained the compound 8. They
are new ferrocenylketimine and were characterized as
following:
3.6. 2-Chloromercurio-1,19-bis[(3-
methylphenylimino)phenylmethyl]ferrocene (9a)
Orange crystal, yields 19.8%. m.p. 145–1468C, IR
KBr(pellet): 3055, 2918, 1592, 1485, 1445, 783, 706
1
cm21. H NMR: 2.17 s, 2.15 s (6H, 2CH3); 4.49–4.76
(7H, Cp-H); 6.31–6.93 (8H, N-Ph-H); 7.14 m, 7.23 m
(10H, C-Ph-H). Found: C, 56.60; H, 5.67; N, 4.84. Calc.
for C38H31ClFeHgN2: C, 56.51; H, 5.59; N, 4.84%.
3.7. 2-chloromercurio-1,19-bis[(3-
bromophenylimino)phenylmethyl]ferrocene (9b)
Brown-red crystals, yields 48.1%, m.p. 144–1458C. IR
3.3. 1,19-bis[(3-
methylphenylimino)phenylmethyl]ferrocene (8a)
KBr(pellet): 3058, 1576, 1456, 1444, 894, 782, 709 cm21
.
1H NMR: 4.49–4.76 (7H, Cp-H); 6.32–6.95 (8H, N-Ph-
H); 7.11 m, 7.25 m (10H, C-Ph-H). Found: C, 45.78; H,
2.63; N, 3.04. Calc. for C36H25Br2ClFeHgN2: C, 46.05; H,
2.67; N, 2.99%.
Orange crystals, yields 55.9%, m.p. 164–164.58C, IR
KBr (pellet): 3020, 2919, 1618, 1596, 1578, 1456, 901,
793, 708 cm21. 1H NMR: 2.16 (s, 6H, CH3); 4.51 (t, 4H,
J51.9 Hz, H-3); 4.71 (t, 4H, J51.9 Hz, H-2); 6.33 (d,
2H, J57.8 Hz, N-Ph-H); 6.46 (s, 2H, N-Ph-H); 6.66 (d,
2H, J57.9 Hz, N-Ph-H); 6.91 (m, 2H, N-Ph-H); 7.19 m
(10H, C-Ph-H). Found: C, 79.82; H, 5.67; N, 4.84. Calc.
for C38H32FeN2: C, 79.69; H, 5.69; N, 4.84%.
3.8. 2,29-bis(chloromercurio)-1,19-bis[(3-
methylphenylimino)phenylmethylferrocene (10a)
Orange crystals, total yields 41.7%, m.p. .2508C (dec.).

X.L. Cui et al. / Polyhedron 18 (1999) 1023–1027
1027
IR KBr(pellet): 3057, 2920, 1589, 1486, 1426, 784, 706
cm21. 1H NMR: 2.15 s, 2.17 s (6H, 2CH3); (meso): 4.71 (t,
2H, J52.5 Hz, H-4), 4.59 m (2H, H-3); 4.53 (d, 2H,
J51.5 Hz, H-5); (dl): 4.63 (bs, 2H, H-4); 4.59 m (2H,
H-3); 4.42 (bs, 2H, H-5): 6.38–6.94 (8H, N-Ph-H); 7.18
m, 7.33 m (10H, C-Ph-H). Found: C, 44.05; H, 2.90; N,
2.91. Calc. for C38H30Cl2FeHgN2: C, 43.74; H, 2.88; N,
2.69%.
5385 reflections were measured, 3903 reflections were
considered with I .3s(I). The data were corrected for
Lorentz and polarization effects. The structure was solved
by using MAC Science CryatanG. Non-hydrogen atoms
were refined with anisotropic thermal parameters and
hydrogen atoms were refined isotropically, final R5
0.0740, Rw50.0856.
3.9. 2,29-bis(chloromercurio)-1,19-bis[(3-
Acknowledgements
bromophenylimino)phenylmethyl]ferrocene (10b)
We are grateful to the National Science Foundation of
China Project (29592066) and the Natural Science Founda-
tion of Henan Province for financial support of this work.
Brown-red crystals, total yields 34.9%. m.p. .2508C
(dec.). IR KBr(pellet): 3077, 1579, 1490, 1465, 901, 780,
706 cm21. 1H NMR: (meso): 4.73 t (2H, J52.5 Hz, H-4);
4.61 m (2H, H-3); 4.56 m (2H, H-5). (dl): 4.65 bs (2H,
H-4); 4.61 m (2H, H-3); 4.45 bs (2H, H-3). 6.36–7.06
(8H, N-Ph-H); 7.16 m, 7.33 m (10H, C-Ph-H). Found: C,
36.61; H, 2.05; N, 2.56. Calc. for C36H24Br2Cl2FeHgN2:
C, 36.85; H, 2.05; N, 2.39%.
References
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3.10. X-ray crystal structure determination for meso-10a
Crystal data: (C19H15NHgCl)2Fe, Mr51044.2, triclinic,
˚
˚
P-1, a57.745(3), b514.761(5), c515.657(5) A, a5
3
98.14(7), b597.16(8), g599.85(8)8, V51725.36 A , Z5
3
˚
2, Dc52.0086 g/cm , s50.71073 A.
An orange crystal of meso-10a measuring
0.80*0.20*0.10 mm3 was mounted on a MAC Science
DIP-2000. Data for crystal were collected with MoKa
radiation using the MAC Research Image Plate System.
The crystal was positioned at 90 mm from the Image Plate.
Forty five frames were measured at 48 intervals. Total of