Conformation and electrochemistry of some β-[alkyl-bridged biferrocenyl]-α,β-unsaturated ketones

Article abstract of DOI:10.1016/S0277-5387(98)00209-5

The geometrical and conformational isomerism of some β-[alkyl-bridged biferrocenyl]-α,β-unsaturated ketones was discussed on the basis of their IR and ¹HNMR spectra. They exist in s-cis conformation. The electrochemistry of the title compounds

Full text of DOI:10.1016/S0277-5387(98)00209-5

Polyhedron Vol[ 06\ No[ 12Ð13\ pp[ 3948Ð3953\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166Ð4276"87#99198Ð4
Conformation and electrochemistry of some b!
ðalkyl!bridged biferrocenylŁ!a\b!unsaturated
ketones
Yao!feng Yuan\a$Ling!yun Zhang\a Ai!guo Hu\a Ji!tao Wanga
and Wan!yi Liub
aNational Key Laboratory of Elemento!Organic Chemistry\ Department of Chemistry\ Nankai
University\ Tianjin 299960\ People|s Republic of China
bDepartment of Chemistry\ Ningxia University\ Yinchuan 649910\ People|s Republic of China
"Received 29 July 0886^ accepted 07 May 0887#
Abstract*The geometrical and conformational isomerism of some b!ðalkyl!bridged biferrocenylŁ!a\b!unsatu!
0
rated ketones was discussed on the basis of their IR and HNMR spectra[ They exist in s!cis conformation[
The electrochemistry of the title compounds was also studied using cyclic voltammetry[ Two distinct consecutive
pairs of one!electron reversible redox peaks centered on the two non!equivalent ferrocenyl fragments were
observed[ Þ 0887 Elsevier Science Ltd[ All rights reserved
Keywords] b!ðalkyl!bridged biferrocenylŁ!a\b!unsaturated ketones^ conformational study^ electrochemistry[
———————————————————————————————————————————————
INTRODUCTION
lytical grade[ The instruments used were the same as
those described in the literature ð5Ł[ Cyclic voltam!
metric experiments were performed on a BAS!099B
electrochemical analyzer equipped with a three elec!
trode assembly with 9[0 mol:l !n!Bu3NPF5 as support
electrolyte and CH1Cl1 as solvent[ The working elec!
trode was a platinum disk of 0[4 mm in diameter
embedded in a cobalt glass seal and was polished
consecutively with polishing alumina and diamond
suspensions between runs[ The reference electrode was
a KCl saturated calomel electrode[ A platinum _la!
ment was used as an auxiliary electrode[ The solutions
were saturated and blanketed with N1 before the _rst
scan[ Measurements were made at room temperature[
Binuclear ferrocene derivatives have aroused many
researches in recent years as redox active entities with
potential application in _elds such as materials for
molecular electronics and as biologically active com!
pounds ð0Ð2Ł[ Zanello|s group has done some work
on alkyl!bridged biferrocene compounds ð3\ 4Ł[ As a
continuation of our previous studies on alkyl!bridged
biferrocene ð5Ł\ we now report here the condensation
reactions of alkyl!bridged biferrocenyl formaldehyde
with aryl ketones\ which a}ord several b!ðalkyl!
bridged
biferrocenylŁ!a\b!unsaturated
"Scheme 0#[ Their conformational and electrochemical
properties are discussed as well[
ketones
Synthesis of b!ðalkyl!brid`ed biferrocenylŁ!a\b!unsatu!
rated ketones
EXPERIMENTAL
1\1!Diferrocenyl propane\ 1\1!diferrocenyl butane
and the corresponding formaldehyde derivatives were
prepared as before ð5Ł[ Other chemicals were of ana!
Taking compound 0 as an example] A solution of
1\1!propinyl!bridged
biferrocene
formaldehyde
"3[73 g\ 0[0 mmol# and p!aminopheylmethylketone
"1[86 g\ 1[1 mmol# in 84) EtOH "24 cm2# was stirred
at room temperature for 7Ð01 h in the presence of
KOH "9[057 g\ 2 mmol#[ The reaction mixture was
then extracted by CH1Cl1\ washed to neutral by water
$Author to whom correspondence should be addressed[
Tel[] ¦75!11!1249!8052^ Fax] ¦75!11!1249!3742^ E!mail]
yuanyfzÝpublic0[tpt[tj[cn
3948

3959
Yao!feng Yuan et al[
Scheme 0[ The preparation of the title compounds[
and dried with anhydrous Na1SO3[ After removal of may occur by the rotation around both C"0?#ÐC"b#
the solvent under reduced pressure\ the dark red resi! and C"a#ÐC"CO# bonds[ There are two favored
due was dissolved in a minimum amount of benzene coplanar forms\ s!cis "0# and s!trans "1#\ as illustrated
and chromatographed on alumina using C5H5 and in Scheme 1[ IR spectra is often used to study the
C5H5ÐEt1O "1]2# as eluents successively[ The resulting equilibrium between s!cis and s!trans ð7\ 8Ł[ Inves!
product was recrystallized by EtOHÐH1O[ 1Ð4 are tigation of many substituted monoferrocene ana!
synthesised analogously[ Yield ×89)[
logues have been reported ð09\ 00Ł[
The s!cis form is preferred because there may be
strong steric repulsion between H"b# and the ortho!
hydrogens on the phenyl group in s!trans confor!
mation[ There are sharp carbonyl bands and inten!
si_ed nC1CH bands in the IR spectra of their CCl3
solutions[ On the basis of the empirical rules suggested
by Shorter and Hayes et al[ ð7\ 8Ł\ the existence of
the equilibrium and the predominance of the s!cis
conformation in solution could be inferred[ This con!
clusion is also supported by their 0H NMR spectra[
RESULTS AND DISCUSSION
All the b!ðalkyl!bridged biferrocenylŁ!a\b!unsatu!
rated ketones are red solids stable in the air[ Their
analytical and melting points are listed in Table 0[
Their IR\ 0H NMR and UV spectra data are listed in
Tables 1Ð3\ respectively[
IR spectra
The KBr disk IR spectra of the b!ðalkyl!bridged 0H NMR spectra
biferrocenylŁ!a\b!unsaturated ketones show two
strong bands at about 0549 and 0489 cm−0\ due to the
0H NMR spectra of the new compounds are rec!
carbonyl and ethylenic stretching vibration respec! orded at room temperature[ As the cyclopentadienyl
tively[ The two peaks in the region 0999Ð0966 cm−0 protons are in almost the same chemical environment\
were allocated as dCH1CH of ole_n with a trans con! their signals overlap and form an multiplet[ In the
_guration ð6Ł[ While in CCl3 solution\ nC1O and nC1C 0H NMR spectra of the title compounds\ the ole_nic
bands split\ indicating the existence of an equilibrium protons give a doublet\ corresponding to an AB type
between s!cis and s!trans conformation[ Their IR spec! absorption[ The coupling constant is 04 Hz\ indicating
tral data in CCl3 solution were listed in Table 1[
they exist in trans!con_guration\ in which the bifer!
In compounds 0Ð4\ a conformational equilibrium rocenyl and the carbonyl groups take the opposite
Table 0[ Physical properties and elemental analyses data for the title compounds
Found "calcd# ")#
Compounds
M[p[ ">C#
C
H
N
0
1
2
3
4
079Ð070
72Ð73
24Ð26
39Ð30
71Ð72
58[9 "58[9#
69[8 "60[1#
58[9 "57[3#
60[9 "69[3#
55[6 "56[0#
4[5 "4[2#
4[5 "5[0#
5[2 "4[4#
5[1 "5[2#
4[7 "4[7#
1[8 "1[4#
−
1[3 "1[3#
−
−

Conformation and electrochemistry of some b!ðalkyl!bridged biferrocenylŁ!a\b!unsaturated ketones 3950
Table 1[ IR Data in CCl3 solution for the title compounds "cm−0
#
s!cis
s!trans
nC1C"1#
Compounds
nC1O"0#
nC1C"0#
nC1O"1#
dCH1CH
0
1
2
3
0565 "s#
0575 "s#
0548 "s#
0605 "s#
0537 "s#
0574
0441 "vs#
0447 "vs#
0438 "s#
0440 "vs#
0440 "s#
0599
0519 "s#
0550 "s#
0540 "vs#
0546 "vs#
0509 "vs#
0552
0474 "vs#
0482 "s#
0479 "s#
0485 "s#
0594 "s#
0506
0992 "s#
0991 "vs#
0903 "vs#
4
FcCH1CHC"O#Bu!na
FcCH1CHC"O#Ph
FcCH1CHC"O#C5H3!3!Mea
0550
0548
−
−
0524
0525
−
−
aFrom Ref[ð09Ł[
Table 2[ 0H NMR data for the title compounds "d\ ppm#
Ole_nic
Compounds
Bridged alkyl
0[8 "s\ 5H#
Cp
a
b
Ph
NH1
0
3[0Ð3[5 "m\ 06H#
6[9 "d\ 0H# 6[5 "d\ 0H#
6[1 "m\1H#\
6[8 "m\1H#
2[7 "s\ 1H#
1
2
0[2Ð0[5 "m\ 5H#
9[6 "m\ 2H#\
0[5 "s\ 2H#\
0[8 "m\ 1H#
9[7 "m\ 2H#\
0[5 "s\ 2H#\
0[8 "m\ 1H#
9[7 "m\ 2H#\
0[5 "s\ 2H#\
0[8 "m\ 1H#
2[8Ð3[5 "m\ 06H#
3[0Ð3[5 "m\ 06H#
6[9 "d\ 0H# 6[6 "d\ 0H#
6[9 "d\ 0H# 6[5 "d\ 0H#
6[1Ð6[8 "m\ 4H#
6[1Ð6[7 "m\ 3H#
2[7 "s\ 1H#
3
4
3[0Ð3[6 "m\ 06H#
3[0Ð3[3 "m\ 15H#
6[9 "d\ 0H# 6[5 "d\ 0H#
5[7 "d\ 0H# 6[5 "d\ 0H#
6[1 "m\1H#\
6[7 "m\2H#
Table 3[ UV absorptions of the title compounds and their related precursors "lmax\ nm#
Compounds pÐpꢀ"omax dÐd"omax
#
#
0
1
2
3
191 "77509#
193 "028799#
191 "75439#
193 "034599#
193 "193599#
193 "029099#
193 "017899#
138 "05649#
141 "52729#
144 "07199#
142 "48529#
256 "21689#
211 "33269#
258 "24659#
229 "35179#
221 "002419#
164 "51609#
171 "48569#
494 "3479#
371Ð430 "6469Ð6959#
493 "5809#
377Ð439 "6479Ð5039#
372Ð494 "3729Ð1589#
326Ð356 "6469Ð5449#
326Ð361 "6159Ð5579#
4
FcC"Me#1FcCHO
FcC"Me#"Et#CHO
position of the double bond[ This is in accordance so high[ Consequently\ the s!cis conformation is the
with their monoferrocenyl analogues reported in the favored conformation[
literature ð09Ł[ Both H"a# and H"b# signals are shifted
up_eld[ If the s!trans rotamer is favored\ H"a# is in the UV spectra
shielding area of the carbonyl group and H"b# is closer
to the aryl ring\ whose anisotropy would increase the
The UV spectra of the title compounds were rec!
shielding about H"b#[ Their d values could not be orded in 84) EtOH and are summarized in Table 3\

3951
Yao!feng Yuan et al[
Scheme 1[ Conformational equilibrium of the title compounds[
together with some related literature reported fer! 9[0 mol l−0 TBAFB"Bu3NBF3# as supporting elec!
rocene derivatives[ The strongest absorption bands at trolyte[ The measurements were carried out at 02>C[
211Ð258 nm can be assigned to the pÐpꢀ transition The scan rate was 099 mV s−0[ The Ep0 ðEp0ꢁ
of the a\b!unsaturated ketone conjugated with the 0:1"Epa0¦Epc0#Ł\ Ep1 ðEp1ꢁ0:1"Epa1¦Epc1#Ł and their
ferrocene nucleus[ The dÐd transition\ appears at a di}erences DEpꢁEp1−Ep0\ together with the Kcon and
longer wavelength in the region 371Ð430 nm as a RobinÐDay classi_cation ð01\ 02\ 03Ł are given in
broad peak[ The two ferrocenyl groups are indis! Table 4[ For comparison\ ferrocene\ 1\1!diferro!
tinguishable by UV spectra[ The large bathochromic cenylpropane "DFP#\ 1\1!diferrocenyl butane "DFB#\
shifts are ascribed to the extensive conjugation of a\b! diferrocenylketone "DFK# ð3Ł and bisferrocene "BF#
unsaturated ketone with the ferrocenyl moiety and the ð3Ł were also included in the measurements and the
interaction of the nonbonding d!orbital of iron with results are listed in Table 4[ The CV curves of 0 and 4
the substituents on the ferrocenyl group[ In addition\ are illustrated in Figs 0 and 1[
such large bathochromic shifts may also involve the
bridging alkyl group\ which play some role in elec!
tronic interactions[ This could be inferred from their
electrochemical behavior also[
The following could be inferred from Table 4[
0[ There are two pairs of redox peaks in the cyclic
voltammograms of all the compounds studied[
1[ The Ep0 values of the _rst redox peak are all lower
than that of ferrocene[ This is attributed to the
monosubstituted ferrocenyl group[ The bridging
alkyl and the other ferrocenyl group exert mainly
an electron!donating e}ect\ which makes it easier
to be oxidized[
Electrochemical studies
The cyclic voltammetric behaviours of the com!
pounds were studied using CH1Cl1 as solvent and
Table 4[ Electrochemical characteristics for the oxidation process of the title compounds and related molecules with the
RobinÐDay classi_cation of the relevant mix!valent species
Compounds
Ep0 "V#
Epc0−Epa0 "mV#
Ep1 "V#
Epc1−Epa1 "mV# DEp "V#
Kcon "×093# RobinÐDay class
0
1
2
3
9[244
9[248
9[275
9[278
9[265
9[244
9[217
9[44
78
092
61
79
52
9[437
9[442
9[560
9[565
9[517
9[440
9[440
9[63
64
60
67
62
64
65
62
9[082
9[083
9[174
9[170
9[151
9[085
9[112
9[08
9[07
9[08
5[5
6[9
1[6
9[19
9[48
9[09
79
II
II
IIÐIII
IIÐIII
IIÐIII
II
II
II
III
4
DFP
DFB
DFKa
BFa
70
63
9[33
9[68
9[24
Ferrocene
9[33
88
aFrom Ref[ð3Ł[

Conformation and electrochemistry of some b!ðalkyl!bridged biferrocenylŁ!a\b!unsaturated ketones 3952
Fig[ 0[ Cyclic voltammogram obtained in CH1Cl1 "9[0 mol:l Bu3NBF3# at room temperature at a potential sweep rate of
099 mV s−0 for 0[ The initial potential was set at 9[099 V and the switching potential was 0[999 V[
Fig[ 1[ Cyclic voltammogram obtained in CH1Cl1 "9[0 mol:l Bu3NBF3# at room temperature at a potential sweep rate of
099 mV s−0 for 4[ The initial potential was set at 9[099 V and the switching potential was 0[999 V[
2[ The Ep1 value of the second redox peak increases
in the order 0:1:4:2:3 and DEp increases in
the same order\ indicating the more deformation
from tetrahedral con_guration the parent com!
pounds ð04Ł is\ the more non!equivalent the two
Day classi_cation ð3\ 01\ 02Ł[ While in 2Ð4\ the
two subunits interact more\ thus causing extensive
delocalization[ They are classi_ed between the
weakly!interacting class II and strong!interacting
class III within the RobinÐDay classi_cation[
ferrocenyl groups are[ The amino group is an elec! 4[ For the redox of compounds with two or more
tron!donating group and\ as a result\ 0 and 2 are
oxidized slightly easier than 1 and 3[
3[ The DEp values of 0 and 1 reveal that the interaction
between the two Fe sub!units is slight\ the mon!
ocation is a slightly delocalized\ weakly interacting
class II mix valent species according to RobinÐ
ferrocenyl groups\ a number of factors a}ecting
the behavior of the ferrocenyl moieties concur[ In
the occurrence of two waves\ through!space and
through!bridge interactions and substituent e}ects
coexist[ The through!bridge interactions\ however\
seemed to be predominant[ The more deformation

3953
Yao!feng Yuan et al[
Malik\ K[ M[ A[\ Opromolla\ G[ and Zanello\ P[\
from regular tetrahedral con_guration caused by
J[ Or`anomet[ Chem[\ 0885\ 405\ 056[
5[ Yao!feng Yuan\ Ling!yun Zhang\ Wei!qing
Qian\ Ji!tao Wang\ Wan!yi Liu\ Trans[ Met[
Chem[0887\ 12"0#\ 10Ð13[
6[ Eglinton\ G[\ Physical Methods in Or`anic
Chemistry\ ed[ J[ C[ P[ Schwartz[ Oliver and Boyd\
Edinburgh\ 0853\ p[ 54[
7[ Shorter\ J[\ Quart[ Rev[\ 0869\ 13\ 322[
8[ Hayes\ W[ P[ and Timmons\ C[ J[\ Spectra Acta
A\ 0857\ 13\ 212[
09[ Kono\ H[\ Shiga\ M[\ Motoyama\ I[ and Hata\
K[\ Bull[ Chem[ Soc[ Jpn[\ 0869\ 32\ 0324[
00[ Nagy\ A[ G[ and Sohar\ P[\ J[ Or`anomet[ Chem[\
0889\ 289\ 106[
the bridging group\ the larger the di}erence in the
electrochemical behaviors of the ferrocenyl groups[
Acknowled`ements*This work was supported by the
National Natural Science Foundation of China and the
National Key Laboratory of Elemento!Organic Chemistry\
Nankai University[
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