Photoreversible Zn2+ ion transportation across an interface using ion-chelating substituted photochromic 3,3′-indolospirobenzopyrans: Steric and electronic controlling effects

Article abstract of DOI:10.1002/ejic.200800614

The photoreversible transportation of Zn²⁺ ions across an interface using photochromic substituted-spirobenzopyrans has been demonstrated. The inclusion of strategically placed sterically influencing 3′-methyl-3b and 3-spirocyclohexyl-3c groupings is investigated and compared to the unsubstituted analogue 3a. Significant control over the spiropyran ringopening? closing reaction, and hence Zn²⁺ ion transportation has been realised. Additionally, the spiropyran ring-opening? closing reactions of two skeletally identical spirobenzo pyrans 4 and 5, but possessing "electronically-modifying" 5-trifluoromethyl-substitutents have been studied by ¹H NMR spectroscopy: this has enabled us to realise the additional biasing, on the ring-opening?closing process, excerpted on these systems through both selectively placed, inductively controlling functional-group substitution and/or, simultaneously, sterically influencing group substitution. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800614

FULL PAPER
DOI: 10.1002/ejic.200800614
Photoreversible Zn2+ Ion Transportation Across an Interface Using
Ion-Chelating Substituted Photochromic 3,3Ј-Indolospirobenzopyrans:
Steric and Electronic Controlling Effects
Craig J. Roxburgh,*[a][‡] Peter G. Sammes,[a] and Ayse Abdullah[b]
Keywords: Photochromism / Zinc ion transportation / Chelation / Photoreversibility / Spiro compounds
The photoreversible transportation of Zn2+ ions across an
interface using photochromic substituted-spirobenzopyrans
has been demonstrated. The inclusion of strategically placed
sterically influencing 3Ј-methyl-3b and 3-spirocyclohexyl-3c
groupings is investigated and compared to the unsubstituted
analogue 3a. Significant control over the spiropyran ring-
pyrans 4 and 5, but possessing “electronically-modifying” 5-
trifluoromethyl-substitutents have been studied by 1H NMR
spectroscopy: this has enabled us to realise the additional
biasing, on the ring-opening↔closing process, excerpted on
these systems through both selectively placed, inductively
controlling functional-group substitution and/or, simulta-
opening↔closing reaction, and hence Zn2+ ion transportation neously, sterically influencing group substitution.
has been realised. Additionally, the spiropyran ring-open-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ing↔closing reactions of two skeletally identical spirobenzo-
Germany, 2008)
Zinc is a vital element essential for all life forms. It is
present in all human body tissues and fluids, and stabilises
the molecular structure of cellular components and mem-
branes thus contributing to their maintenance and integrity.
It is found in over three hundred enzymes and participates
in the synthesis and degradation of carbohydrates, lipids,
proteins, and nucleic acids as well as in the metabolism of
other micronutrients: in particular it plays an essential role
in polynucleotide transcription and thus the process of ge-
netic expression. Consequently the development of a photo-
reversible zinc ion chelating system could, indirectly, poten-
tially offer the possibility of acting as a cellular probe; help
elucidate metabolic pathways, and ultimately lead to the de-
velopment of new drug candidates aimed at treatment of
ailments associated with abnormalities of the above classes
of structures. A system such as this could be utilised in the
presence of a specific and selective compound which modu-
lates the transportation of metal ions through cellular ion-
channels (i.e. when cell membranes are exposed to certain
molecular structures metal ions are expelled, commonly
through cellular ion-channels), the subsequent introduction
of the type of structures described here to the solution
could, thus, potentially act as a zinc ion probe. This could
potentially be achieved by the treatment of a cellular struc-
ture with a suitable ion-releasing compound. Subsequent
addition or, indeed, in vitro introduction of a solution con-
taining the spirobenzopyran, followed by photoirriatiation
would allow, by UV spectrophotometry, detection and mea-
surement of the zinc ion complexed merocyanine form. Al-
ternatively, cellular structures could be lysed and sub-
Introduction
There is ongoing interest in the development of reversible
metal-chelating agents in which chelation can be switched
on and off by exposure to light of different wavelengths.[1]
Several groups have made contributions to this area.[2]
A
popular substrate for such studies is the 6-nitrospi-
ro[chromene-2,2Ј-indole] system 1↔2 and its analogues
since these have well-documented photochemical proper-
ties.[3] Photoirradiation with UV light centred at λ = 380 nm
leads to the ring-opened zwitterionic (merocyanine or
quinonic) form 2, which can be converted back into the
ring-closed form, either by photoirradiation with visible
light, or thermally. This process may be repeated many
times and has formed the basis of light-induced ionic
switches. The photoreversible chelation of specific metal
ions has been reported in other systems.[4–7]
[a] Department of Chemistry, The Christopher Ingold Laborato-
ries, University College, The University of London,
London, WC1H OAJ, UK
[b] Department of Chemistry, Surrey University,
Guildford, GU2 7XH, UK
[‡] Current address: The Institute of Naval Medicine,
Alverstoke, Gosport, Hants, PO12 2DL, UK
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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C. J. Roxburgh P. G. Sammes, A. Abdullah
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sequently treated with the spirobenzopyran etc., as de-
scribed above.
Compounds possessing structural and functional groups
similar to those in structures 3a–c, 4 and 5 below are known
for their general ability to sequester metal ions; however, no
photoreversible Zn2+ ion chelating systems, in which Zn2+
ions have photoreversibly been transported across a solvent
interface have been reported. Further, no mention of steric
and electronically biasing substituent effects on photore-
versible Zn2+ ion transportation has been reported. We
were interested in developing this capability by devising
some new photochromic spirobenzopyrans since these
could be used to photoreversibly transport metal ions i.e.
Zn2+ ions across an interface; and thus, potentially, offer
the ultimate capability of through cellular membrane-trans-
portation.
In theory, a truly clean, on-off photoreversible system
would ideally extract zero Zn2+ ions from the aqueous layer
(or other medium) in the “dark”; on photoirradiation with
UV light it would extract, by chelation, 100% of the Zn2+
ions, and on photoirradiation with a different wavelength
light (in our case visible light) “un-chelate” the Zn2+ ions,
thus allowing them to return to the water layer: This is
practically extremely difficult to achieve, and in reality a
photoreversible ion-chelating system will probably lie some-
where in-between these two extremes.
Some qualitative experiments were conducted with the
compounds 3a–c, 4 and 5 in the presence of Li+, Na+, Ba2+
,
Mg2+ and Ca2+ ions to ascertain if these systems exhibited
a similar magnitude of interaction towards these metal ions,
as Zn2+; relatively little interaction, and hence selectivity, in
comparison to that with Zn2+ ions was observed.
Typical Syntheses of Spiro[chromene-2,2Ј-indoles] as
Exemplified for Compound 5
The syntheses of the spiro[chromene-2,2Ј-indoles] 3a–c,
4 and 5 were undertaken using standard methods, or slight
modifications thereof. Typically, the appropriately substi-
tuted hydrazines and ketones were condensed together to
yield the corresponding hydrazones; these were then
cyclised using variations on the Fischer indole synthesis.
Quaternisation of the indoles were affected using various
N-alkylating agents, from which the indolenines were ob-
tained, after treatment with aqueous sodium hydroxide. The
Discussion
We previously reported that the spirobenzopyran↔mero-
cyanine equilibrium position in crown-containing systems,
under photolysis, could be influenced by the use of appro-
priately placed “electronically-controlling” substituents;
specifically in the 5-position of the indole ring.[8a,8b]
Reported here are the syntheses of some new photore-
versible zinc ion chelating indolobenzospiropyrans, contain-
ing substituents that through specific and selective steric in-
teractions, inhibit, bias, and thus offer “steric-tuning” of
the photochromic ring-opening↔closing process: Specifi-
cally, 3b and 3c containing 3Ј-methyl (in the pyran ring)
and 3,3Ј-cyclohexyl (in the indole ring) groups, respectively;
these are compared and contrasted to the unsubstituted
parent structure 3a. Additionally, and importantly, demon-
stration that these structures photoreversibly transport
Zn2+ ions across an interface is made. Further, some new
compounds, 4 and 5, both possessing electronically-mod-
ifying substitutents, and in the case of 5, simultaneously, a
sterically influencing group, are reported; these have been
synthesised and photochemically evaluated. In detail, com-
pounds 4 and 5, possess a trifluoromethyl group in the 5-
position of the indole ring, and in the case of structure 5
an additional bulky sterically-biasing 3,3Ј-cyclohexyl group:
in the latter case the simultaneous effects of these two types
of functionalities, on the spirocyclic ring-opening↔closing
process, are tested, and compared and contrasted against
structure 4, not possessing such a bulky sterically modifying
group (cyclohexyl vs. geminal dimethyl substitution).
Scheme 1. Synthesis of the dispiro compound 5; typical synthetic
procedure for compounds 3a–c and 4.
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Photoreversible Zn2+ Ion Transportation
final spiro[chromene-2,2Ј-indoles] were obtained in good to UV spectroscopy for compounds 3a–c: (a) before adding
excellent yields – ranging from 59 to 91% – by condensation the metal salt (control); (b) after adding the metal salt in
between the appropriate indolenines and salicylaldehydes. the dark; (c) after photoirradiation of the solution with UV
A “typical” synthesis is exemplified in Scheme 1 for the new light, allowing remeasurement of the UV spectrum; and fi-
compound 5.
nally (d) on exposure to visible light, and remeasuring the
spectrum.
The experiments were repeated four times with 3 mL ali-
quots of the aqueous layers collected, for each of the com-
pounds 3a–c. The metal ion concentrations were quantified
using ICP-MS analysis, with the measurements (parts per
million, ppm) observed for each system given in Table 1,
with the corresponding percentages in Figure 2.
Demonstration of Zn2+ Ion Transportation in Compounds
3a–c Using Quantitative Inductively Coupled Plasma-Mass
Spectrometry
Inductively Coupled Plasma-Mass Spectrometry (ICP-
MS) is a reliable, widely used and accurate routine indus-
trial analysis technique for the quantification of metal spe-
cies. This was thus applied to quantify zinc ion concentra-
tions in the aqueous layers of the following test system, and
thus as a demonstration that photo-controlled metal ion
transport is taking place. The transport system (Test System Control (Std)
Table 1. Zinc ion concentrations (ppm) in the aqueous layer (start-
ing with a control solution of 2ϫ10–4 ).
3a
3b
3c
10.988
8.450
5.288
8.399
10.606
6.477
7.114
9.778
11.929
11.236
8.854
Dark
in Figure 1) previously devised and utilised by us was used
Irradiated (UV)
to test whether, for the above compounds 3a–c, Zn2+ ions
Visible light
10.266
were photoreversibly transported across a barrier (two im-
miscible layers of water and 1,2-dichloroethane).[9]
The bottom layer consisted of the compounds 3a–c
A decrease in the aqueous layer metal ion concentration
(2ϫ10–4 ) in 1,2-dichloroethane, and the top layer zinc is observed between the dark equilibrium state before and
perchlorate (2ϫ10–4 ) in water (1:1 ratio). The position of after photoirradiating it with UV light (migration of Zn2+
the spirocyclic↔merocyanine equilibrium was measured by ions into the organic layer), as indicated in Table 1. An in-
Figure 1. Metal ion transportation system.
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C. J. Roxburgh P. G. Sammes, A. Abdullah
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duction in the amount of open form, resulted in a reduction
of the extracted Zn2+ ions to 15%: this effect was photore-
versible. Thus compound 3c also possesses the ability to
photoreversibly chelate Zn2+ ions, albeit with a reduced
magnitude, compared to compound 3a. However, com-
pound 3a, under “dark” conditions yields significantly
more of the open-chelated form than structure 3c, but is
photodynamically more receptive, producing relatively
larger changes in the concentrations of extracted Zn2+ ions
under the “dark”↔UV↔visible irradiation sequence.
Overall, structure 3c therefore exhibits “cleaner” on↔off
photoreversible Zn2+ ion chelating properties than structure
3a, as there is significantly less metal ion extraction (5%
vs. 20%) under “dark” conditions; however, a far greater
enhancement of photo-induced Zn2+ ion transportation is
exhibited by structure 3a.
Figure 2. Compounds 3a–c: percentage Zn2+ ions left in the aque-
ous layer at 2ϫ10–4 .
crease in the aqueous layer zinc ion concentration was mea-
sured on exposure to visible light as the reverse – migration
of the zinc ions back into the water layer occurred (Table 1).
In conclusion, the above demonstrates that the consid-
ered placement of suitable sterically modifying substituents
can be used to “sterically tune” the photoreversible chelat-
ing properties of spirobenzopyrans: this, together with the
control that has been demonstrated to occur on substitution
with “purely” electronically modifying groups, enables one
to exert significant influences on the photoreversible chelat-
ing properties of these spirobenzopyrans.
Results
As can been seen from Figures 2 and 3, compounds 3a
and 3c produced the predicted trends, i.e. Zn2+ ions were
photoreversibly transported across a solvent interface using
two, appropriately different wavelength light sources (UV λ
≈ 365, Vis λ ≈ 550 nm): the degree of extraction, unsurpris-
ingly, varied with the structure of the compound. In the
“dark” compounds 3a and 3c extracted, by chelation, al-
most 23 and 5% Zn2+ ions respectively. The unsubstituted
compound 3a extracted 4.6 times the quantity of Zn2+ ions,
under “dark” conditions, as 3c, which is probably due to
the larger thermodynamic barrier to spirocyclic ring-open-
ing, due to incorporation of the sterically bulky spirocyclic-
cyclohexyl group. Subsequent phoroirradiation of 3a with
UV light increased the quantity of the open form and hence
the degree of Zn2+ ion chelation (23Ǟ55%), whilst irradia-
tion with visible light, caused a reduction in the amount of
open form, resulting in a concomitant loss of chelated Zn2+
ions (55Ǟ30%): this effect was photoreversible. Thus com-
pound 3a possess useable potential as a photoreversible
Zn2+ ion chelating agent.
The results for compound 3b initially suggest that almost
40% of the Zn2+ ions are extracted from the aqueous layer
under “dark” conditions; however, the UV spectroscopic
data did not support the presence of the expected trans-
zwitterionic open form (merocyanine) – i.e. there was no
UV absorption (λmax = 550 nm). We previously reported[8b]
that it was possible to study the ring-opening reaction of
spiro[chromene-2,2Ј-indoles] by treatment with deuteriotri-
fluoroacetic acid, and subsequently, the ring-closing reac-
1
tion, using sodium deuterioxide (we have found H NMR
spectroscopy to be clear and unambiguous with regard to
assigning the exact stereochemistry of the products, whereas
gross UV spectroscopy was less so). We therefore applied
this methodology to a range of compounds, including 3b;[9b]
1
the H NMR spectrum clearly indicated that solely the cis-
open form was generated (see Supporting Information for
spectra); in this cis-open form the geminal dimethyl group
possesses different absorbance shifts, whereas in the trans-
open form, due to the overall planar spatial stereochemical
orientation, they become equivalent. Further, treatment of
the acid-generated cis-open form, with sodium deuterioxide,
produces a yellow colourisation – consistent with lower
wavelength absorption – whereas the trans-open forms tend
to produce deep purple/red colourisations (higher wave-
length) when treated with sodium deuterioxide. It is pos-
sible that the 3-alkenic methyl group weakens the spirocy-
clic carbon–oxygen bond creating a more facile cleavage to
the cis-open form; however, by far, the relatively greatest,
Figure 3. Compounds 3a–c: percentage zinc ions extracted from the
aqueous layer (2ϫ10–4 ).
The spirocyclohexane-containing system 3c extracted and additional effects in this system, comes from the steric
only 5% (one-quarter of that extracted by 3a) of the Zn2+ interactions between the 3-alkenic methyl group and the
ions, as quantified by ICP-MS. Photoirradiation of 3c with 3,3Ј-geminal dimethyl groups: once the spirocyclic C–O
UV light resulted in the extraction of almost 25% of the bond has broken, rotation about the remnant single car-
Zn2+ ions from the water layer; subsequent photoirradia- bon–oxygen bond [C–C(Me)] must take place for isomeris-
tion with visible light, accompanied by a concomitant re- ation to the trans-open isomer to occur. In the cis-open
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Photoreversible Zn2+ Ion Transportation
form (Figure 4, b) the alkenic-methyl group sits above (or, to steric hindrance: the most stable isomer in this case was
equally, below) the 3,3Ј-geminal dimethyl groups; rotation assigned to the cis-open form (t1/2 = 3 s, λmax = 440 nm).
about the remnant spirocyclic carbon–carbon single bond,
It was summarised, that the introduction of a 3-alkenic
necessary for formation of the trans-open isomer (cf. 2), is methyl substituent into the benzospiropyran skeleton of
thus greatly restricted by steric hindrance. Therefore it is these molecules causes a major perturbation in their photo-
postulated that Zn2+ ion chelation is occurring within both chromic properties by creating a significant thermodynamic
the cis-closed form and, to a relatively far greater extent barrier to trans-merocyanine formation. The 3-alkenic
than the cis-closed form, the cis-open form. In both cases, methyl group sits above (or, equally, below) the geminal di-
however, chelation to the Zn2+ ions would be significantly methyl groups; rotation about the spirocyclic carbon–car-
lower than to the “possible” trans-open form. UV irradia- bon [C–C(Me)] bond (cf. Figure 4, b) is thus sterically in-
tion of the “dark equilibrium” state produces little change hibited: as a consequence little light-induced photochro-
in the quantity of Zn2+ ions extracted: indicating that a macity is observed.
near maximal Zn2+ ion chelation, for this state/system has
As mentioned earlier our aim was to design a totally
occurred. The above would tend to indicate a binding of “clean”, on/off photoreversible ion-chelating system. All
the Zn2+ ions to the cis-open form (cf. part b of Figure 4) three compounds 3a–c, to varying degrees, existed, under
with perhaps some, but relatively less, to the cis-closed “dark” conditions, in an “open” state; as our aim was to
form. The relatively small quantity of cis-closed isomer design a totally “clean”, on/off photoreversible chelating
would be expected to form the cis-open isomer when sub- system we thus attempted to inhibit “dark” ring-opening
jected to UV irradiation; this is perhaps why little increase such that Zn2+ ion chelation could be entirely controlled by
in Zn2+ ion chelation takes place. A relatively higher degree photoirradiations. In our previous reports for other sys-
of binding to the cis-open form, than the cis-closed form tems[8,9] we a found control i.e. significant limitation of
would be expected; however, as mentioned above, the de- ring-opening, could be achieved by the addition of selec-
gree of chelation to both of these two forms would be sig- tively placed electron-withdrawing substituents into the
nificantly less than to the trans-open form. Interestingly, the benzospiropyran skeleton – introduction of a 5-trifluoro-
UV spectroscopic data of structure 3b indicates, relatively, methyl substituent produced the most photo-responsive and
significant Zn2+ ion release on exposure to visible light (ap- controllable systems.[8,9] As 3a and 3c demonstrated the
proximately 40%Ǟ10%) indicating interaction of the che- greatest photoreversibility we synthesised and investigated
lated form with the “broad spectrum” visible light. This re- the two structures 4 and 5 below: these were identical in
sult would also suggest that the main “dark-structural iso- skeletal structure, and the nearest in overall structure, to 3a
mer” associated with compound 3b is the cis-open form, and 3c it was possible to readily synthesise, but possessed
which can interact with the “broad band” visible light, the required 5-trifluoromethyl substituent (5 is a new com-
whilst the pure cis-closed form, being far less conjugated, pound). In theory, addition of an electron-withdrawing sub-
would be less likely to do so. We believe the presence of the stituent would, as mentioned previously, potentially allow
Zn2+ ions, in this particular system, are promoting negative one to excerpt additional control over the Zn2+ ion seques-
photochromism. Thus, interaction of structure of 3b with tering process by inhibiting ring-opening (destabilisation of
Zn2+ ions produces, almost entirely, the cis-open form, the open-zwitterionic form). These structures were studied
which interacts to a small degree, and is sterically un- using 1H NMR spectroscopy, both, in the presence, and
changed, by photoirradiation with UV light. Therefore this absence, of Zn2+ ions [see Supporting Information for high
1
compound offers little potential as a truly photoreversible resolution H NMR spectra of compound 4 and 5 in both
Zn2+ ion chelating system: however, it offers potential as a the presence, and absence, of Zn2+ ions]: in the absence of
more “general” chelating system that can be, to a significant Zn2+ ions both systems existed entirely in the closed-spi-
degree, used to chelate, under “dark” conditions, and re- rocyclic form demonstrating the effectiveness of the 5-tri-
lease, on exposure to visible light, Zn2+ ions.
fluoromethyl substituent in “holding” the closed form. Ex-
periments involving the addition of one-equivalent, and
subsequently five-equivalents of Zn(ClO4)2 in CD3CN
caused the following effects: for compound 4 a new set of
aromatic signals appeared; the doublet associated with the
gem-dimethyl group broadened and a new singlet associated
with the N+–CH3 of the trans-open form appeared. In the
case of structure 5 the general 1H NMR spectra broadened;
the vinylic protons retained their cis coupling of 10 Hz; in
addition to the singlet associated with the N–CH3 grouping
at 2.7 ppm there appeared a second singlet due to the N+–
Figure 4. a) cis-closed form b) cis-open form.
The above findings are, in part, supported by the work CH3 of the open form. Thus, in the presence of zinc ions a
of Guglielmetti[10] and co-workers who elucidated these fin- simultaneous dynamic equilibrium mixture of both the cis-
dings on the closely related structure shown in part a of closed and trans-open forms exists – this observation in the
Figure 4. Guglielmetti confirmed the lack of the formation 1H NMR spectra can only be explained by interaction of
of the deeply coloured trans isomer, which he also ascribed the Zn2+ ions with the open-zwitterionic form. Thus for
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C. J. Roxburgh P. G. Sammes, A. Abdullah
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measurement of their UV/Vis absorption curves (“dark” curves).
The solutions were then irradiated for 1 min with UV light of λ =
365 nm generated from a steady power source. The UV light source
was a 200-W mercury/xenon lamp, focussed in a LOT-Oriel air-
cooled lamp housing, with solution filters (for details see below) to
eliminate light of 320 Ͻ λ Ͼ 400 nm (this allows maximal photo-
irradiation with a λmax centred at 365 nm, the absorption wave-
length of the spirobenzopyrans, and additionally avoids photoirra-
diation of the formed merocyanine, which has a λmax centred at
550 nm). The UV absorption spectra (UV curve) were measured;
this was followed by exposure of the cuvette to a visible-light source
(3 min: 100-W tungsten spotlight) and the UV absorption spectrum
remeasured.
compounds 4 and 5 the thermodyanamic binding of the
Zn2+ ion chelated species was strong enough to overcome
the powerful destabilising electron-withdrawing inductive
effect of the 5-trifluoromethyl substituent – which destabi-
lises the quaternary imminium ion present in the open-zwit-
terionic structure (cf. structure 2).
Solution filters used: A 1  cobalt and copper sulfate solution (1:1)
contained within a 2-mm walled Pyrex glass cuvette was prepared.
This combination of solution filter and Pyrex glass possesses an
irradiation window of between 450–650 nm with unwanted wave-
lengths outside this range effectively filtered out.
In both systems, even in the presence of five-equivalents
Zn2+ ions there was a predominance of the closed form.
In conclusion it can be deduced that the introduction of
electronically modifying (withdrawing) substituents allows
further biasing of the fluxional open↔closed equilibria in
these dynamic systems (in this case a biasing towards the
closed form). In the absence of the trifluoromethyl group
both systems existed, in the presence of Zn2+ ions, entirely
in the open form.
The equilibrium positions for the dynamic systems were measured
by UV and visible light spectroscopy according to the following
protocol:
(a) before adding the metal salt, in the “dark” for 1 h,
(b) after adding the metal salt, in the “dark” for 1 h,
In summary – we have synthesised, in good to excellent
yields, several new substituted-spiropyrans: demonstrated
Zn2+ ion chelation; photoreversible Zn2+ ion-transportation
across an interface, and the control and biasing of this
(c) exposure of the solution to UV light using a focused 200-W
high-pressure mercury/xenon light source, for 1 min, and remeasur-
ing the spectrum. Photoirradiations were carried out in the UV
range of 365 nm using a focussed LOT-Oriel air-cooled lamp hous-
transportation effect utilising both steric and electronic sub- ing,
stituents.
(d) in the visible region photoirradiations were carried out by ex-
posing the solution to a 100-W tungsten spotlight for 3 min and
remeasuring the UV spectrum,
Note: Whilst we have qualified and quantified the main
observations and results described here, we believe that the
metal ion binding interactions, and subsequent equilibrium
positions, in these systems are multifactorial and probably
involve an extremely complex set of interactions and theo-
retical parameters: The detailed discussion of which is out-
side the scope of this report being more applicable to indi-
vidual studies in theoretical journals. We believe that they
are comprised of, but not limited to, the following: 1) the
type and nature of the substituent in the 3-position of the
pyran ring, 2) the type and nature of the substituent in the
3,3Ј-position of the indole-ring, 3) the type and nature of
the substituent in the 5-position (through inductive effects,
when present), 4) the 8-benzo substituent or group, 5) the
size of the metal ion, 6) the charge density of the metal ion,
7) the distribution of charge throughout the zwitterionic
structure (in particular that of the phenoxide anion, 8) sol-
vent interactions (or non-interaction) and 9) the conforma-
tion of the overall system in solution.
(e) the reversibility of the examined systems was ascertained by
repetition of the above light cycles (at least three times).
1H NMR Spectroscopy: Studies were carried out with a JEOL
FX2000 spectrometer using deuteriochloroform of [D6]DMSO as
the solvent with tetramethylsilane (TMS) as the internal reference.
Multiplicities are reported as (s) singlet, (d) doublet, (t) triplet, (q)
quartet and (m) multiplet. Assignments of hydroxy and ammonium
protons were checked by deuterium exchange. Mass spectra were
recorded with a VG 7070H mass spectrometer interfaced with a
Finnigan Incos data system. Accurate mass measurements were
carried out at the EPSRC mass spectrometry service at the Univer-
sity of Wales, Swansea. UV spectroscopy was carried out using
Perkin–Elmer Lambda 5 and Lambda 9 spectrophotometers; both
instruments are double-beamed with thermostatically controlled
cell blocks. The Lambda 9 is also fitted with an digital RS232 port,
which allows remote control by PC. All UV measurements were
taken at 25 °C using 3-mL quartz cells with a 1-cm path length and
are referenced against air. IR spectra were recorded with a Perkin–
Elmer 983 spectrophotometer. Melting points were determined in
open capillary tubes with an Electrothermal melting point appara-
tus and are uncorrected. Elemental analyses were carried out by
MEDAC Ltd., Brunel Science Centre, Egham, Surrey, UK. Thin-
layer chromatography was performed over glass plates coated with
Merck silica gel 60 F254; flash chromatography was performed
using Merck 7734 silica gel (20–63 µm).
Experimental Section
Photoirradiation Studies: The photochromic properties of these
compounds
were
evaluated
by
preparing
solutions
(2ϫ10–5 moldm–3 unless otherwise stated), in the “dark”, in
freshly dried and redistilled solvents [generally tetrahydrofuran
(THF), acetonitrile, dichloroethane (DCE) or methanol]. Perchlo-
rate salts were dried with P2O5 for several days before use. Solu-
tions were placed in a stoppered 1-cm path length cuvette at room
temperature (20–25 °C) and allowed to equilibrate for 1 h before
Zinc ion concentrations were measured using Inductively Coupled
Plasma-Mass Spectrometry (ICP-MS).
Chemical intermediates were purchased from the Aldrich Chemical
Company unless otherwise stated.
4956
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4951–4960

Photoreversible Zn2+ Ion Transportation
8-Methoxy-1Ј,3Ј,3Ј-trimethyl-6-nitro-1Ј,3Ј-dihydrospiro[chromene-
hexyl). IR (CDCl , film): ν
= 3020, 2936 (satd. CH), 1604
max
˜
3
2,2Ј-indole] (3a): 2-Hydroxy-3-methoxy-5-nitrobenzaldehyde (0.4 g, (C=C), 1450, 1334 (NO2), 1216 (C–N), 1092 (C–C), 954 (C–O
2.03 mmol) and 1,3,3-trimethyl-2-methyleneindolenine (0.35 g, spiro), 771 cm–1 (ArH, 4 adj H). MS: m/z 393 [M+ + 1, 13.6], 392
2.02 mmol) were dissolved in ethanol (10 mL) and the resulting
solution heated under reflux for 8 h. Reduction of the solvent vol-
ume to approximately one-quarter of the original amount and cool-
ing in an ice box yielded a pink solid. One recrystallisation from
ethanol yielded the 3a as a pink powder (0.42 g, 59%), m.p. 166–
168 °C (ref.[11] 159–161 °C, 167 °C). 1H NMR (CDCl3): δ = 7.7 (d,
J = 3 Hz, 1 H, ArH), 7.63 (d, J = 3 Hz, 1 H, ArH), 7.19 (t, 1 H,
ArH), 7.07 (d, J = 7 Hz, 1 H, ArH), 6.87 (d, J = 10 Hz, 1 H,
CH=CH), 6.85 (t, 1 H, ArH), 6.55 (d, J = 7 Hz, 1 H, ArH), 5.83
(d, 1 H, J = 10, CH=CH), 3.81 (s, 3 H, OCH3), 2.75 (s, 3 H, N-
(M+, 54.4), 83 (100% base peak). C23H24N2O4 Acc (CI): calcd.
392.1736; found M+ = 392.1736.
8-Methoxy-1Ј,3Ј,3Ј-trimethyl-5Ј-(trifluoromethyl)-1Ј,3Ј-dihydrospiro-
[chromene-2,2Ј-indole] (4): 1,3,3-Trimethyl-2-methylene-5-(trifluoro-
methyl)indolenine (0.47 g, 0.20 mmol) was dissolved in ethanol
(10 mL), to which was added to 2-hydroxy-3-methoxybenzaldehyde
(0.30 g, 0.20 mmol) in ethanol (10 mL); and the resulting solution
heated under reflux for 24 h. Removal of the solvent under reduced
pressure produced a brown coloured solid which was recrystallised
from ethanol to yield 4 as a tan coloured crystalline solid (0.41 g,
68%), m.p. 126–128 °C (ref.[1] 125–127 °C). 1H NMR (CDCl3): δ =
7.49 (d, J = 7 Hz, 1 H, ArH), 7.36 (s, 1 H, ArH), 6.95 (d, J = 7 Hz,
1 H, ArH), 6.83–6.72 (m, 3 H, ArH), 6.62 (d, J = 7 Hz, 1 H, ArH),
5.71 (d, J = 10 Hz, 1 H, CH=CH), 3.72 (s, 3 H, OCH3), 2.8 (s, 3
H, CH3), 1.13, 1.06 ppm (6 H, gem dimethyl). IR (CDCl3, film):
CH ), 1.22, 1.18 ppm (6 H, gem dimethyl). IR (CDCl , film): ν
˜
max
3
3
= 3018, 2970 (satd. CH), 1606 (C=C), 1334 (NO2), 1216 (C–N),
1092 (C–C), 954 (C–O spiro), 771 cm–1 (4 adj. H). MS: m/z 354
[M+ + 2, 4.8], 253 [M+ + 1, 21.5], 352 [M+, 8.6], 351 [M+ – 1, 20.0],
158 (100% base peak). C20H20N2O4 (352.385): calcd. C 62.12, H
4.66, N 11.43; found C 62.19, H 4.58, N 11.22.
ν
= 3100 (satd. CH), 1600 (C=C), 1210 (C–N), 1400 (C–O),
˜
max
1100 (C–C), 954 (C–O spiro), 758 cm–1 (C–F). MS: m/z 376 [M+
+
8-Methoxy-1Ј,3Ј,3Ј,3-tetramethyl-6-nitro-1Ј,3Ј-dihydrospiro[chro-
mene-2,2Ј-indole] (3b): 2-Ethyl-1,3,3-trimethylindolium triflate
(1.00 g, 2.97 mmol) was dissolved in a 40% sodium hydroxide solu-
tion (10 mL) and the resulting mixture stirred for 5 min. Then di-
ethyl ether (10 mL) was added. The ether layer was separated from
the reaction mixture, dried (anhydrous sodium sulfate) and evapo-
rated under reduced pressure. The resulting yellow/orange oil ob-
tained was isolated (0.44 g, 2.34 mmol, 79%) and dissolved in etha-
nol (5 mL). 2-Hydroxy-3-methoxy-5-nitrobenzaldehyde (0.46 g,
2.43 mmol) in ethanol (5 mL) was added, and the resulting mixture
heated under reflux for 8 h. Partial removal of the ethanol under
reduced pressure produced a yellow/orange precipitate, which was
filtered off and recrystallised from chloroform/ethanol to yield 3b
as yellow/orange needles (0.57 g, 67%), m.p. 165–167 °C. 1H NMR
(CDCl3): δ = 7.59 (d, J = 7 Hz, 1 H, ArH), 7.57 (d, J = 7 Hz, 1 H,
ArH), 7.17 (t, J = 8, 1 Hz, 1 H, ArH), 7.0 (d, 1 H, ArH), 6.99 (d,
J = 7 Hz, 1 H, ArH), 6.55 (s, 1 H, CH=C), 3.7 (s, 3 H, OCH3),
2.83 (s, 3 H, NCH3), 1.96 (s, 3 H, CH3), 1.14 ppm (6 H, gem di-
1, 12], 375 [M+, 50], 374 [M+ – 1, 10], 360 (M+ – 15). C21H20NO2F3
Acc (EI): calcd. 375.1759; found M+ = 375.1759.
8-Methoxy-1Ј-methyl-5Ј-(trifluoromethyl)-1ЈH-dispiro[chromene-
2,2Ј-indole-3Ј,1ЈЈ-cyclohexane] (5): 1Ј,2Ј-Dimethyl-5Ј-(trifluorometh-
yl)spiro[cyclohexane-1,3Ј-indolium] triflate (0.61 g, 1.42 mmol) was
dissolved in a stirred 40% sodium hydroxide solution (15 mL) for
5 min, after which time diethyl ether (15 mL) was added. The ether
layer was separated from the reaction mixture, dried (anhydrous
sodium sulfate) and evaporated under reduced pressure to yield an
orange/yellow oil: The oil was isolated (0.19 g, 0.68 mmol), dis-
solved in ethanol (3 mL), and added to 2-hydroxy-3-methoxybenz-
aldehyde (0.10 g, 0.66 mmol) in ethanol (25 mL); and the resulting
solution heated under reflux for 24 h. Partial removal of the solvent
under reduced pressure yielded the title compound as a brown col-
oured solid. The solid was recrystallised from ethanol to yield 5 as
a beige/brown coloured precipitate (0.19 g, 70%). m.p. 129–131 °C.
1H NMR (CDCl3): δ = 7.57 (s, 1 H, ArH), 7.48 (d, J = 8 Hz, 1 H,
ArH), 6.9 (d, J = 10 Hz, 1 H, ArH), 6.83 (d, J = 8 Hz, 1 H, ArH),
6.80 (d, J = 8 Hz, 1 H, ArH), 6.74 (t, J = 7 Hz, 1 H, ArH), 6.51
(d, J = 8 Hz, 1 H, ArH), 5.77 (d, J = 10 Hz, 1 H, CH=CH), 3.72
(s, 3 H, OCH3), 2.80 (s, 3 H, NCH3), 2.1–1.3 ppm (m, 10 H, cyclo-
methyl). IR (CDCl , film): ν
= 3018 (satd. CH), 1533 (C=C),
˜
3
max
1210 (C–C), 1190, 1350 (NO2), 954 (C–O spiro), 771 cm–1 (4 adj
H’s). MS: m/z 368 [M+ + 2, 5.9], 367 [M+ + 1, 35.7], 366 (M+,
87.5), 351 (100 % base peak). C21H22N2O4 Acc (FAB): calcd.
366.1579; found M+ = 366.4103 (4.4 ppm), M+ + 1 = 366.4104
(3.5 ppm).
hexyl). IR (CDCl , film): ν
= 3150 (satd. CH), 1608 (C=C),
˜
3
max
1384 (C–O), 1210 (C–N), 1000 (C–C), 954 (C–O spiro), 755 cm–1
(C–F). MS: m/z 416 [M+ + 1, 20], 415 (M+, 100% base peak).
C24H24NO2F3 Acc (EI): calcd. 415.1759; found M+ = 415.1759.
8-Methoxy-1Ј-methyl-6-nitro-1ЈH-dispiro[chromene-2,2Ј-indole-
3Ј,1ЈЈ-cyclohexane] (3c): 1Ј,2Ј-Dimethyl-5Ј-(trifluoromethyl)spiro-
[cyclohexane-1,3Ј-indolium] triflate (1.45 g, 3.99 mmol) was dis-
solved in a 40% sodium hydroxide solution (10 mL). The resulting
solution was stirred for 5 min and diethyl ether (15 mL) was added.
The ether layer was separated from the reaction mixture, dried (an-
hydrous sodium sulfate) and evaporated under reduced pressure to
produce an yellow/orange oil. The oil that remained was isolated
(0.75 g, 3.50 mmol), dissolved in ethanol (3 mL), added to 2-hy-
droxy-3-methoxy-4-nitrobenzaldehyde (0.69 g, 3.50 mmol) in etha-
nol (25 mL); the resulting mixture was heated under reflux for 24 h.
Removal of the solvent under reduced pressure yielded a brown
coloured solid which was broken up and recrystallised from ethanol
to yield 3c as a dark beige/pale brown coloured precipitate (1.25 g,
Isopropyl Ethyl Ketone Phenylhydrazone: Phenylhydrazine (2.68 g,
24.81 mmol) was added to 2-methyl-3-pentanone (2.48 g,
24.80 mmol) in ethanol (10 mL) and the resulting solution heated
under reflux for 5 h. Removal of the ethanol under reduced pres-
sure yielded the title compound as a mobile, slightly red oil (3.20 g,
1
68%). H NMR (TCE): δ = 6.8–7.3 (m, J = 8 Hz, 5 H, ArH), 2.6
(q, 1 H, CH), 2.2–2.3 (q, 2 H, CH2CH3), 1.2 (t, 6 H, 2 ArCH3),
1.1 ppm (t, 3 H, CH CH ). IR (CDCl , film): ν = 3300–3500
˜
max
2
3
3
(C=N–H), 3100 (C–H), 1650 (C=C), 1530 cm–1 (C=N). MS: m/z
191 [M+ + 1, 16.7], 190 (M+, 100%, base peak), 175 (M+, – CH3,
3.6). C12H18N2 Acc (EI): calcd. 190.1470; found M+ = 190.1470.
1
91%), m.p. 196–198 °C. H NMR (CDCl3): δ = 7.68, 7.69 (d, J =
2-Ethyl-3,3-dimethyl-3H-indole: Isopropyl ethyl ketone phenylhy-
7 Hz, 1 H, ArH), 7.62, 7.61 (d, J = 7 Hz, 1 H, ArH), 7.41, 7.39 (d,
drazone (2.88 g, 15.16 mmol) was added to zinc chloride (0.50 g,
J = 7 Hz, 1 H, ArH), 7.21–7.17 (t, 1 H, ArH), 6.86, 6.83 (d, J = 3.66 mmol) in glacial acetic acid (50 mL) and the resulting mixture
10 Hz, 1 H, CH=CH), 6.85–6.81 (t, 1 H, ArH), 6.56, 6.54 (d, J =
7 Hz, 1 H, ArH), 5.88, 5.85 (d, J = 10 Hz, 1 H, CH=CH), 3.81 (s,
3 H, OCH3), 2.74 (s, 3 H, NCH3), 1.95–1.22 ppm (m, 10 H, cyclo-
heated on a steam bath, under nitrogen, for 4 h. The title com-
pound, obtained as a yellow/orange oil, after removal of the solvent
under reduced pressure, was purified over flash chromatography
Eur. J. Inorg. Chem. 2008, 4951–4960
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4957

C. J. Roxburgh P. G. Sammes, A. Abdullah
FULL PAPER
using chloroform as the elutant (2.29 g, 87%). H NMR (CDCl3):
δ = 6.90–7.30 (m, 4 H, ArH), 2.60 (q, 2 H, CH2CH3), 1.49 (t, 3 H,
CH2CH3), 1.47 ppm [s, 6 H, gem –C(CH3)2]. IR (CDCl3, film):
1
ture through a Vigreux column. Distillation under vacuum pro-
vided the title compound as a pale yellow liquid (8.85 g, 94%).
Cyclohexyl Ketone Phenylhydrazone:[12] Phenylhydrazine (3.00 g,
27.77 mmol) was added to cyclohexyl methyl ketone (3.50 g,
27.77 mmol) in ethanol (100 mL) and the resulting solution heated
under reflux for 0.5 h. Removal of the solvent under reduced pres-
sure yielded the title compound as a deep orange mobile oil (4.78 g,
79%). 1H NMR (CDCl3): δ = 11.0 (s, 1 H, NH, exchangeable D2O),
7.25 (t, 2 H, ArH), 7.03, 7.05 (dd, 2 H, ArH), 6.79, 6.83 (t, J =
8 Hz, 1 H, ArH), 1.90 [m, 1 H, (CH2)2CHC], 1.82 (s, 3 H, N=C–
CH3), 1.17–1.78 ppm (m, 10 H, cyclohexyl, 5 CH2). IR (CDCl3,
ν
= 3018 (satd. C–H), 1450 (C=N), 1533 (C=C), 1010 (C–C),
˜
max
1190 (C–N), 771 cm–1 (Ar-H, 4 adj. H). MS: m/z 174 [M+ + 1, 8.9],
173 (M+, 62.5), 158 (base peak, 100%). C12H15N Acc (EI): calcd.
173.1204; found 173.12040.
2-Ethyl-1,3,3-trimethylindolium Triflate: 2-Ethyl-3,3-dimethyl-3H-
indole (2.08 g, 12.02 mmol) was added to methyl trifluoromethane-
sulfonate (1.96 g, 12.02 mmol) in hexane (5 mL) and diethyl ether
(5 mL), the resulting solution was stirred at room temperature. In-
stantly, a yellow precipitate formed, which was filtered off and
recrystallized from ethanol to yield the title compound as deep
golden coloured crystals (3.81 g, 89%), m.p. 134–136 °C. 1H NMR
(CDCl3): δ = 7.20–7.69 (m, 4 H, ArH), 4.15 [s, 3 H, N+–CH3
(CF3SO3–)], 3.22–3.28 (q, 2 H, CH2CH3), 1.63 [s, 6 H, gem
ArC(CH3)2], 1.41–1.45 ppm (t, 3 H, CH2CH3). IR (CDCl3, film):
film): ν
= 3650 (N–H), 3020 (C–H), 1616 (C=C), 1520 (C–N),
˜
max
1020 (C–C), 760 cm–1 (ArH). MS: m/z 216 [M+, 6.6], 215 (M+ – 1,
8.1), 18 (base peak, 100%).
3-Cyclohexyl-2-methyl-3H-indole: Cyclohexyl methyl ketone phen-
ylhydrazone (4.65 g, 21.53 mmol) was added to zinc chloride
(1.00 g, 7.35 mmol) in glacial acetic acid (100 mL), and the re-
sulting solution heated on a steam bath, under nitrogen, for 3 h.
Filtration and removal of the glacial acetic acid under reduced
pressure yielded the title compound as an orange oil (3.25 g, 76%).
1H NMR (CDCl3): δ = 7.51–7.53 (d, J = 7 Hz, 1 H, ArH), 7.31 (d,
J = 7 Hz, 1 H, ArH), 7.15, 6.99 (m, 2 H, ArH), 2.7 (s, 3 H, CH3),
1.25–2.31 ppm (m, 10 H, cyclohexyl, 5 CH2). IR (CDCl3, film):
ν
= 2982 (satd. C–H), 1632 (C=C), 1630 (C=N), 1264 (C–F),
˜
max
1154 (SO2-O), 1032 (C–N), 736 cm–1 (Ar-H, 4 adj. H). MS: m/z
187 [M+ –149 (SO3CF3), 78.7], 173 (4.11), 172 (base peak 100%),
203 (M+ – SO3CF3 – 2 ϫ 15, 4.2). C14H18F3NO3S·0.75H2O
(350.87): calcd. C 49.84, H 5.38, N 4.15; found C 49.72, H 5.38, N
4.20].
ν
(CDCl3) 2932 (satd. C–H), 1688 (C=N), 1598 (C=C, Ar),
˜
(max)
1,3,3-Trimethyl-2-ethyleneindolene: 2-Ethyl-1,3,3-trimethylindolium
triflate (0.51 g, 1.51 mmol) was dissolved in a 40% sodium hydrox-
ide solution (5 mL). Diethyl ether (10 mL) was added and the re-
sultant solution vigorously stirred for 5 min. After this period the
ether layer was separated from the reaction mixture, dried (anhy-
drous sodium sulfate) and evaporated under reduced pressure to
yield the pure title compound as a pale yellow/orange oil (0.22 g,
79%). H NMR (CDCl3): δ = 6.38–7.09 (m, 4 H, ArH), 4.30–4.33
[q, 1 H, C=CH(CH3)], 2.93 (s, 3 H, NCH3), 1.88–1.92 (d, 3 H,
C=CHCH3), 1.13 ppm [s, 6 H, gem C(CH3)2]. IR (CDCl3, film):
1216 (C–N), 1026 cm–1 (C–C). MS: m/z 200 [M+ + 1, 27.6], 199
(M+, base peak, 100%), 198 [M+ – 1, 4.2]. C14H17N Acc (EI) calcd.
199.1361; found 199.1361.
1Ј,2Ј-Dimethylspiro[cyclohexane-1,3Ј-indolium] Triflate: 2Ј-Methyl-
spiro[cyclohexane-1,3Ј-indole] (3.22 g, 16.18 mmol) was added to
methyltrifluoromethane sulfonate (2.66 g, 16.22 mmol) in hexane
(20 mL) and diethyl ether (30 mL). Instantly a canary yellow pre-
cipitate formed which was filtered off and washed with diethyl ether
to yield the title compound as pale yellow coloured crystals (4.59 g,
1
1
78%), m.p. 126–128 °C. H NMR (CDCl3): δ = 7.91, 7.93 (d, 1 H,
ν
= 2982 (satd. C–H), 1632 (C=C), 1630 (C=N), 1032 (C–N),
˜
max
735 cm–1 (Ar-H, 4 adj. H). MS: m/z 188 [M+ + 1, 3.8], 175 (base
peak, 100%), 306 [M+ – 1, 15.8].
ArH), 7.66–7.68 (d, 1 H, ArH), 7.62 (t, J = 8 Hz, 1 H, ArH), 7.56
(t, J = 8 Hz, 1 H, ArH), 4.12 (s, 3 H, N+-CH3), 2.88 (s, 3 H, N+=C–
CH3), 1.54, 2.08 ppm (m, 10 H, cyclohexyl, 5 CH2). IR (CDCl3,
Cyclohexyl Methyl Ketone: A dry 100-mL three-necked round-bot-
tomed flask was fitted with a reflux condenser, a pressure-equalis-
ing dropping funnel, a mechanical stirrer, and an inlet tube to
maintain a static nitrogen atmosphere in the reaction vessel
throughout the reaction. In the flask were placed powdered lithium
hydride (0.69 g, 0.087 mol) and anhydrous predistilled 1,2-di-
methoxyethane (50 mL). While this solution was being stirred vig-
orously, a solution of cyclohexanecarboxylic acid (9.62 g,
0.075 mol) in anhydrous 1,2-dimethoxyethane (50 mL) was added
over a 10 min period. The resulting mixture was heated to reflux
while stirring for 2 h, at which time the hydrogen evolution and the
formation of lithium cyclohexanecarboxylate was complete. The re-
sulting suspension was cooled to approximately 10 °C with an ice-
bath and stirred vigorously while an ethereal solution containing
methyllithium (1.6 , 62 mL, 0.085 mol) was added dropwise over
30 min. After complete addition, the ice-bath was removed and the
resulting suspension was stirred at room temperature for 2 h. The
fine suspension in the reaction flask was agitated and siphoned
into a vigorously stirred solution of concentrated hydrochloric acid
(13.5 mL, 0.16 mol) and water (200 mL). The reaction flask was
rinsed with an additional amount of ether (60 mL), which was also
added to the aqueous solution. After the resulting mixture was sat-
urated with sodium chloride, the organic phase was separated and
the alkaline aqueous phase extracted with diethyl ether
(3ϫ100 mL). The organic solutions were combined and dried with
magnesium sulfate, the bulk of the ether was distilled from the mix-
film): νmax = 3020 (satd. C–H), 1590 (C=C), 1325 (C–C), 1210 (C–
˜
N), ArH (760), 758 cm–1 (C–F). MS: m/z 233 [M+ – (SO3CF3), 6.7],
323 (M+ – SO3CF3 – 1, 41.7), 218 (M+ – SO3CF3 – 15, 17.7), 217
( b a s e p e a k , 1 0 0 % ) 2 0 3 ( M+ – SO3 CF 3 – 2 ϫ 1 5 , 4 . 2 ) .
C16H20F3NO3S (363.397): calcd. C 52.88, H 5.55, N 3.86; found C
52.50, H 5.36, N 3.88.
1Ј-Methyl-2Ј-methylidene-5Ј-(trifluoromethyl)-1Ј,2Ј-dihydrospiro[cy-
clohexane-1,3Ј-indole]: 1Ј,2Ј-Dimethylspiro[cyclohexane-1,3Ј-indo-
lium] triflate (1.02 g, 2.81 mmol) was dissolved in a 40% sodium
hydroxide solution (10 mL) and stirred for ten minutes. Then di-
ethyl ether (10 mL) was added to the solution, stirring was contin-
ued for a further 5 min. The ether layer was separated from the
reaction mixture, dried (anhydrous sodium sulfate), filtered, and
removed under reduced pressure to yield the title compound as a
1
yellow/orange oil (0.45 g, 75%). H NMR (CDCl3): δ = 7.44 (d, J
= 7 Hz, 1 H, ArH), 7.14 (t, 1 H, ArH), 6.74 (t, 1 H, ArH), 6.56 (d,
J = 7 Hz, 1 H, ArH), 3.88 (dd, J = 10, 10 Hz, 2 H, C=CH2), 3.02
(s, 3 H, N-CH3), 1.83 ppm (m, 10 H, cyclohexyl, 5 CH2). IR
(CDCl , film): νmax = 2934 (satd. C–H), 1644 (C=N), 1604 (C=C),
˜
3
1908 (C–C), 908 (C–C), 775 cm–1 (Ar-H, 4 adj. H). MS: m/z 215
[M+ + 1, 18.5], 214 (M+, 46.9), 213 [M+ – 1, 80.0], 158 (base peak,
100%), 306 [M+ – 1, 15.8]. C15H19N Acc (EI): calcd. 213.1517;
found 213.1517.
Cyclohexyl Methyl Ketone [4-(Trifluoromethyl)phenyl]hydrazone (7):
[4-(Trifluoromethyl)phenyl]hydrazine (2.45 g, 13.92 mmol) was
4958
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4951–4960

Photoreversible Zn2+ Ion Transportation
added to cyclohexyl methyl ketone (1.75 g, 13.89 mmol) in ethanol
(50 mL) and the resulting solution heated under reflux for 7 h. Re-
moval of the solvent under reduced pressure yielded 7 as a bur-
gundy red mobile oil (2.45 g, 62%). H NMR (CDCl3): δ = 7.47,
7.44 (t, J = 7 Hz, 2 H, ArH), 7.09, 7.06 (d, J = 7 Hz, 2 H, ArH),
1.9 (m, 1 H, CH), 1.84 (s, 3 H, -CH3), 1.78–1.17 ppm (m, 10 H,
H, 9.2], 186 [M+ – CH3C(CH3)2H, 8.2], 172 [M+ – N=CCH3(CH3)2-
H, 4.5], 171 [–HN=CCH3(CH3)2H, 3.1], 145 (base peak, 100%), 69
(CF3 fragment, 17.4).
1
2,3,3-Trimethyl-5-(trifluoromethyl)-3H-indole: Isopropyl methyl
ketone [4-(trifluoromethyl)phenyl]hydrazone (2.68 g, 10.98 mmol)
and boron trifluoride–diethyl ether (1.56 g, 10.99 mmol), in acetic
acid (30 mL), were heated under reflux for 1 h prior to stirring at
room temperature for 3 h. After this period the resulting mixture
was filtered and the acetic acid removed under reduced pressure to
yield a light brown oil. Column chromatography of the oil was
carried out over silica, using ethyl acetate as the eluent, to yield the
CH , 5 cyclohexyl). IR (CDCl , film): ν = 3650 (N–H), 3020
˜
max
2
3
(satd. CH), 1616 (C=C), 1525 (C–N), 1020 (C–C), 785 (C–F), 760
cm–1 (ArH). MS: m/z 286 [M+ + 2, 4.6], 285 [M+ + 1, 4.7], 284
[M+, 5.4], 145 (100% base peak).
2Ј-Methyl-5Ј-(trifluoromethyl)spiro[cyclohexane-1,3Ј-indole] (8): Hy-
drazone 7 (3.30 g, 5.05 mmol) was added to zinc dichloride (0.25 g,
1.83 mmol) in acetic acid (100 mL), and the resulting solution
heated on a steam bath, under nitrogen, for 3 h. Filtration and
removal of the solvent under reduced pressure yielded 8 as an
orange oil (1.52 g, 70%). 1H NMR (CDCl3): δ = 7.92 (d, J = 7 Hz,
1 H, ArH), 7.62 (s, 1 H, ArH), 7.26 (d, J = 7 Hz, 1 H, ArH), 2.32
(s, 3 H, -CH3), 1.83–1.21 ppm (m, 10 H, CH2, 5 cyclohexyl). IR
1
title compound as a reddish oil (1.65 g, 54%). H NMR (CDCl3):
δ = 7.5–7.7 (m, 3 H, ArH), 2.3 (s, 3 H, N=CCH3), 1.3 ppm [s, 6
H, gem C(CH ) ]. IR (CDCl , film): ν = 2900–3000 (satd. C–
˜
max
3 2
3
H), 1600 (C=C), 1530 (C=N), 1250 cm–1 (C–F). MS: m/z 228 [M+
+ 1, 20.6], 227 (M+, 98.1), 226 [M+ – 1, 69.3], 212 (base peak,
100%).
Tetramethyl-5-(trifluoromethyl)indolium Iodide: 2,3,3-Trimethyl-5-
(trifluoromethyl)-3H-indole (1.60 g, 7.05 mmol) and methyl iodide
(0.96 g, 7.06 mmol) in diethyl ether (50 mL) were heated under re-
flux for 26 h. Removal of the solvent and excess methyl iodide un-
der reduced pressure yielded a white solid. The solid was recrystal-
lised from ethanol to yield the title compound as a white solid
(1.39 g, 51%), m.p. 206–208 °C. 1H NMR (CDCl3): δ = 8.1–8.4 (m,
3 H, ArH), 4.02 (s, 3 H, N+–CH3), 2.8 (s, 3 H, N+=C–CH3), 1.6
(CDCl , film): ν
= 2932 (satd. CH), 1688 (C=N), 1598 (C=C),
˜
3
max
1216, 1026 (C–C), 778 cm–1 (C–F). MS: m/z 268 [M+ + 1, 35.1],
267 (M+, 91.6), 266 [M+ – 1, 49.8], 252 (100 % base peak).
C15H16NF3 Acc (CI): calcd. 267.1235; found 267.1235.
1Ј,2Ј-Dimethyl-5Ј-(trifluoromethyl)spiro[cyclohexane-1,3Ј-indolium]
Triflate (9): Indole 8 (0.50 g, 1.86 mmol) was dissolved in diethyl
ether (15 mL) and hexane (10 mL); methyltrifluoromethane sulfon-
ate (0.32 g, 1.95 mmol) was added in one portion to the stirred
reaction mixture at room temperature. A tan coloured precipitate
instantly formed which was broken up and recrystallised from etha-
nol to yield 9 as pale yellow crystals (0.65 g, 80 %), m.p. 112–
ppm [s, 6 H, gem Ar-C(CH ) ]. IR (CDCl , film): ν = 1500–
˜
max
3 2
3
1450 (C=N), 1660, 1610 (C=C), 1400 (C–N), 1300–1150 (C–F),
1100 cm–1 (C–C). MS: m/z 242 (M+ – H1, 10.0), 18 (base peak,
100%). (M – HI) Acc EI C13H14NF3 calcd. 241.1078; found
241.1078.
1
114 °C. H NMR (CDCl3): δ = 8.12 (s, J = 7 Hz, 1 H, ArH), 7.91
(d, J = 7 Hz, 1 H, ArH), 7.84 (d, J = 7 Hz, 1 H, ArH), 4.17 (s, 3
H, N-CH3), 2.89 (s, 3 H, -CH3), 2.00–1.16 ppm (m, 10 H, CH2, 5
1,3,3-Trimethyl-2-methylene-5-(trifluoromethyl)indolenine: 1,2,3,3-
Tetramethyl-5-(trifluoromethyl)indolium iodide (1.15 g, 3.17
mmol) was dissolved in a 40% sodium hydroxide solution (25 mL)
and the resulting solution vigorously stirred, under a diethyl ether
layer, until the disappearance of the methiodide (24 h, detected by
TLC). A further quantity of diethyl ether (10 mL) was added, with
stirring continued for a further 4 h. The ether layer was separated,
dried (anhydrous sodium sulfate), and filtered to yield a yellow oil,
which quickly darkened on exposure to air (the extremely unstable
oil was stored under nitrogen at 0 °C, wrapped in silver foil). The
oil was triturated with cold diethyl ether (10 mL) to leave behind
the pure title compound as a yellow solid (0.26 g, 34%). 1H NMR:
No data available (the solid is not sufficiently soluble in any com-
cyclohexyl). IR (CDCl , film): νmax = 3020 (satd. CH), 1590 (C=C),
˜
3
1325 (C–C), 1210 (C–N), 760 (ArH), 758 cm–1 (C–F). MS: m/z 370
(M+ – CF3, 7.7), 282 (M+ – SO3CF3, 9.4) 83 (100% base peak),
203 (M+ – SO3CF3 – 2ϫ15, 4.2). C17H19F6NO3S·H2O: calcd. C
45.43, H 4.68, N 3.12; found C 45.12, H 4.68, N 3.12.
C17H19F6NO3S Acc FAB (M+ – SO3CF3) calcd. 282.146960; found
282.147906 (–3.4 ppm).
1Ј-Methyl-2Ј-methylidene-5Ј-(trifluoromethyl)-1Ј,2Ј-dihydrospiro[cy-
clohexane-1,3Ј-indole] (10): Triflate 9 (0.61 g, 1.42 mmol) was dis-
solved in a 40% sodium hydroxide solution (10 mL) suspended un-
der diethyl ether (10 mL), and vigorously stirred for 5 min. The
ether layer was separated, dried (anhydrous sodium sulfate), and
filtered to yield 10 as an yellow/orange oil (0.19 g, 48%). 1H NMR
(CDCl3): δ = 7.65 (s, 1 H, ArH), 7.55 (d, J = 7 Hz, 1 H, ArH), 6.83
(d, J = 7 Hz, 1 H, ArH), 3.88 (dd, J = 10, 10 Hz, 2 H, C=CH2), 2.8
(s, 3 H, N-CH3), 2.1–1.3 ppm (m, 10 H, CH2, 5 cyclohexyl). IR
mon solvent). IR (Nujol): ν
= 2750 (satd. C–H), 1650 (C=C),
˜
max
1240 (C–N), 720 cm–1 (C–F). MS: m/z 244 (M+ + 3, 27), 243 [M+
+ 2, 40], 242 [M+ + 1, 22], 241 [M+, 12], 183 (base peak, 100%).
Supporting Information (see also the footnote on the first page of
this article): Typical UV-Vis absorption spectra of 1 and 2, 1H
NMR spectra for compounds of type 3, 4 and 5.
(CDCl , film): ν
= 3100, 2935 (satd. CH), 1605 (C=C), 1210
˜
3
max
(C–N), 1400 (C–O), 1100 (C–C), 750 cm–1 (C–F). MS: m/z 282 [M+
+ 1, 12], 281 (M+, 100%, base peak).
Acknowledgments
Isopropyl Methyl Ketone [4-(Trifluoromethyl)phenyl]hydrazone: [4-
(Trifluoromethyl)phenyl]hydrazine (2.47 g, 14.03 mmol) was added
to 3-methylbutan-2-one (1.19 g, 14.00 mmol) in ethanol (20 mL)
and the resulting solution heated under reflux for 1.5 h. Removal
of solvent under reduced pressure yielded the title compound as a
mobile, slightly brown oil (3.09 g, 90%). 1H NMR (CDCl3): δ =
7.45 (br. d, J = 8, 2 H, ArH), 7.07 (br. d, J = 8, 2 H, ArH), 4.77
(br. s, 1 H, NH), 2.55 [hept, 1 H, (CH3)2CH], 1.91 (s, 3 H, N=C–
The authors thank the Science and Engineering Research Council
(SERC) for supporting this research.
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Eur. J. Inorg. Chem. 2008, 4951–4960
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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Received: June 17, 2008
Published Online: September 17, 2008
4960
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4951–4960