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Chemiluminescence Oscillations Driven by a Flow-through Reactor in the [Ru(bpy)3]2+ Catalyzed BelousovЦZhabotinskii Reaction.

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the tetramer this effect is reduced through cage bonding.[']
For [rBuSiAl] an almost identical Si-A1 distance (ca.
260 pm) was found in the monomer and tetramer, which can
be seen as a result of a low steric repulsion between the
rBu,Si groups in the tetramer. The Si-A1 bond has a relatively small force constant[' and therefore reacts sensitively
to disturbances.
The reaction energy AE,,,, for the tetramerization of
rBu,SiAl is obtained from the SCF approximation as shown
in (a). For H,SiAI and Me,SiAl, the very similar values
AE,,,,([tBu,SiAl],)
=
E([rBu,SiAl],)
-
4 E(tBu,SiAl)
= - 430 kJmol-'
(a)
-397 and - 427 kJ mol- respectively, were obtained. The
SCF approximation underestimates the tetramerization energy. This is shown by MP2 calculations, which for H,SiAI
showed an addditional contribution of -207 kJmol-I and
for Me,SiAl of -228 kJmol-', which is in agreement with
the results for the tetramerization of AIR (R = H, F, Cl,),
A A E z - 200 kJ mol- '.['I If a similar effect is assumed also
for tBu,SiAl, then a tetramerization energy of ca. -600 kJ
mol- ' can be expected."'] This value corresponds to a bond
energy of 150 kJmol-' per electron pair or tetrahedral face
or 100 kJmol-' per AI-A1 pair or tetrahedral edge.
The comparison of [tBu,SiAI], with AI,R, (R = H, CI, F,
C P ) [ ~shows
]
a consistent picture. Since no K delocalization
n(tBu,Si) --t z(A1) is expected for tBu,SiAl, the the metal
atoms of the tetramer are as strongly bound as in AI,H,
( - 571 kJmol-'[91), in agreement with the calculated distances.
In particular, the bonds in Cp4AI, are significantly weaker
than those in [tBu,SiAl],: in the Cp compound, the A1-AI
distance of 276.9 pm (exp.;13' calc. 279.6 pm[']) is relatively
long, and the tetramerization energy (- 160 kJmol-', with
MP2) is relatively low. These results are in agreement with
those found experimentally: [tBu,SiAl], can be sublimed at
180 "C, whereas Cp,*AI, in the solid form decomposes at
70 0C.f201
The compound [tBu,SiAl], (see Fig. 1 , bottom) is a molecule with a completely nonpolar (hydrophobic) surface.
Therefore, it is to be expected that crystals are highly disordered or even show plastic phases. This could be an explanation for the above mentioned difficulties for the structure
determination.
According to our calculations. [tBu,SiAl], holds a special
position among the Al' compounds: the Al, tetrahedron
shows optimal stabilization (lacking competition of an: delocalization in the monomer) and is shielded without larger
steric hindrance or strains by the substituents.
Received: October 24, 1991 [Z4986IE]
German version: Anzrw. Chcm. 1992, 104, 327
CAS Registry numbers:
H,SiAI. 138540-84-8; [H,SiAI],,
138540-85-9; Me,SiAl. 138540-86-0:
[M~,SIAI],. 138540-87-1: tBu,SiAI, 138540-88-2; [tBu,SiAlj,. 13x540-89-3.
[ l ] M . Tacke. H. Schnockel, Inorg. Chem. 1989, 28. 2895.
[Z] P. Paetzold, Angeii'. Chem. 1991. 103. 559; Angew. Chem. Int. €d Engl.
1991, 30. 544.
[3] C . Dohmeier, C. Robl, M. Tacke, H. Schnockel. Angel{,. Chem. 1991, 103.
594: Angew. CAfwn.Int. €d. Engl. 1991, 30. 564.
[4J J. Aihara. BUN. C/zen?. SOC.Jpn. 1983. 56. 335.
[51 D. J. Swanton. R. Ahlrichs, T/7ror. Chin?. Acru 1989, 75, 163.
[6l N . Wiberg in Frontiers of'Orgunosilicon Chemistr~(Eds.: A. R. Bassindale,
P P. Gaspar). The Royal Society of Chemistry, C~imbndge,1991, p. 263270.
[71 P. R. LeBreton, S. Urano, M. Shahbaz, S. L. Emery, J. A. Morrison, J.
Am. Chern. SOC.1986, 108. 3937; T. Davan. J. A. Morrison. Inotg. Chmn7.
1986, 3.
2366.
A n g w Chein. Int. Ed. Engl. 31 (1992) No. 3
C
[S] D. J. Swanton, R. Ahlrichs, M. Hiser. Chem. Phgs. Lett. 1989. 155. 329.
[9] R. Ahlrichs, M. Ehrig, H. Horn, Chem. Phgs. Lett. 1991. 183. 227.
[lo] A. F. Wells, Structural Inorganic Chemistry. Oxford University Press, Oxford, 1984, p. 1060.
[ l l ] K. Wade, Chem. Cornmun. 1971,792; Ade. Inorg. Chr~m.RadiochcAm. 1976,
18. 1.
[I21 The following basis sets were nsed: Al, Si: [lls7pld/6s4pld], q(d) = 0.3
and 0.4 repectively; C in R = Me and Si bound in R = tBu: [Xs4p:4s2p],
primary C in R = tBu: [9s3p/2slp]; H in R = H : [4s/2s], in R = Me and
R = rBu: [3s/ls]. The basis sets for C and H were energy optimized using
neopentane as model compound. For the Si bound C, a double-zeta basis
set was used to have sufficient flexibility for the description of the Si-C
bond.
1131 R. Ahlrichs. M. Bir, M. Hiser, H. Horn, C. Kolmel, Chrm. Phgs. Lerr.
1989, 162, 165.
[14] C. Moller, M. S. Plesset, Phys. Rev. 1934,46. 618; MP2 denotes the treatment of electron correlation in the second order of perturbation theory,
starting from the Hartree-Fock ground state. In o u r calculations. we only
included the correlation of the valence electrons.
[15] Examples of investigations of AIH and AI,H, with more precise methods
(MP?-gradient, coupled cluster (CCSD(T))) showed that correlation effects reduce the AI-A1 distance only by 2 pm. The bond energy of the
tetramer is underestimated in the MP2 approximation by approximately
50 kJ mol-I. Analogous relationships are also to be expected for the compounds examined here (J. Gauss, personal communication).
[16] IBu,SIAI does not have the highest possible symmetry C , , because in this
case imaginary wave numbers of 99 i c m - ' and 27 icm-' were obtained
for two normal modes. The lowering of symmetry from C,. to C , . which
is caused by steric hindrance of the wt-butyl groups, leads to an energy
reduction of 20 kJmol-'. For [Me,SiAl], and [lBu,SiAl],, for which force
field calculations were not possible, T, and T symmetry respectively were
assumed on the basis of these results.
1171 W. Uhl. 2. Nuturfiirsch. B 1987. 42, 557.
[I81 In the framework of the SCF approximation the force constant of the
AI-Si bond is 100 N m - ' in rBu,SiAl, 94 N m - ' in H,SiAI, 133 N m - ' in
[H,SiAI],.
[I91 A MP2 calculation for [tBu,SiAl], was unfortunately not possible.
(201 On the basis of its low decomposition temperature ( around - 6 0 T ) .
Cp,AI, could not be investigated i n a crystalline form; C. Dohmcier. H.
Schnockel, unpublished.
Chemiluminescence Oscillations Driven
by a Flow-through Reactor in the [R~(bpy)~]''
Catalyzed Belousov-Zhabotinskii Reaction
By Harry R. Weigt*
The Belousov-Zhabotinskii (BZ) reaction["-in the strict
sense the metal-ion-catalyzed oxidation of malonic acid by
bromate/sulfuric acid--is already considered a classical
model system for the formation of dissipative structures.[21
On exceeding certain critical parameters and for suitable
reaction procedures far from the equilibrium, sustained concentration oscillations occur, for example, or even spatially
and spatial/temporally organized reaction states.[,] The extremely complicated underlying mechanism has not nearly
been elucidated .I4]
An interesting extension of conventional methods is the
involvement of electronically excited species on the basis of
oscillating chemiluminescence (OCL) arising spontaneously
in many BZ systems.[51The measurement of the OCL has
proved to be a convenient, very sensitive technique, which
appears to be most highly developed for [Ru(bpy),]'+ catalyzed BZ systems (bpy = 2,2'-bipyridine).L61Some of the reaSORS for this are the remarkable photophysical and photochemical properties of the metal complex,['^ including its CL
potential through the excited charge-transfer state.['] In the
[*I
Dr. H. R. Weigt
Fachbereich Physik der Universitat
Am Neuen Palais 20, D-0-1571 Potsdam (FRG)
VCH VerlugrgesmllslhaJi mhH, W-6940 Wemheim, 1992
0570-0R33/92IO303-0355$3.50+ .25:0
355
past without exception, however, batch experiments were
conducted. As this process is limited fundamentally to transient states and structures, the interpretation in particular of
the sometimes very complicated temporal CL behavior appeared problematic. For instance, for a system with the concentrations given in the legend of Figure 1 under batch conditions (i.e., on the way to equilibrium), we found an
oscillator lifetime of only 30 min which had a extremely variable oscillation form almost impossible to interpret.
tFig. 2. Dependence of OCL structure on the total volume flow V. Operating
parameters: p[mLmin-l] = 4.0 (A): 3.0 (B); 2.5 (C); 2.0 (D); 1.5 (E); 1.0 (F);
0.3 ( C ) ;remaining conditions and C L measurement as in Figure 1.
-f
Fig. I. CSTR-stabilized OCL in [ R ~ ( b p y ) , ] ~catalyzed
+
BZ system. Operating
parameters: initial concentrations [mol L- '1 = 0.053(Br03-); 0.35 (CH,.
([Ru(bpy),lz'); 1.0 (H,SO,); reactor volume = 26cm3:
(COOH),): 1 x
T = 299K; V = 2.2 m l m i n - l . C L measurement: A,, = 610 nm; redox potential (dotted line): potential difference (peak-to-peak) = 40 mV.
Stabilization of the various, only momentarily existing
system states over a longer period was achieved with a
(stirred) flow-through reactor (CSTR = Continuous-flow
Stirred Tank Reactor).''] This provides a thermodynamically
open system through a constant flux of starting materials
and simultaneous removal of products. Among the freely
variable operating parameters are the flux concentrations,
the average residence time of the reactive material (as quotient of the reactor volume and total flow rate) and the reactor temperature. Figure 1 shows the behavior of the system
for the chosen set of parameters under flow conditions. Represented are the time-resolved CL intensity['0a1 and the
simultaneously recorded redox potential.['0b1 The OCL is
characterized by significantly more features in its oscillogram than in that of the potential. For each oscillation three
clearly distinguishable emission peaks are reproduced in a
basic pattern. The periodic steep onset of the luminescence
corresponds to the beginning of the autocatalytic part of the
process (recognized by the drop in the redox potential). The
signal shape of the electrode's (integrated) display does,
however, not correspond to the characteristic CL peak pattern for this set of parameters.
Even on variation of only the total flow rate P, a number
of O C L modes can be generated. As example Figure 2 shows
the behavior for a stepwise decrease of P. The essential part
of a cycle for each V is represented. Between the individual
stabilized cycles (corresponding to the limit cycle behavior)
in this experiment is a period of nonstationary transition
behavior lasting of the order of 1 h. The oscillation pictures
resulting from the chosen P a r e obtained independent of the
operating mode of the reactor and the direction of V change.
Hysteresis effects, which are conceivable, were not observed.
At high flow rates (above 12 mLmin-') the time-resolved
CL structure is characterized by a pronounced side peak
(similar to that found for batch experiments a short time
after the startr6]),which is deformed to a shoulder as P
decreases. At = 3.0 mLmin- a second side peak following the first in time is seen, which becomes a needlelike signal. Concomitant with this change is a decrease of the major
peak. Below V = 1.O mLmin-' the curve shape is markedly
'
356
;7
VCH Verlugsyesellsi.liufifnhH, W-6940 W<,inheim, 1992
smoothed; at 0.3 mLmin-' (corresponding to a relatively
large average residence time for the reactants) only a weak
kink may be seen in the relatively weak CL signal.
In contrast to the hardly changing curve shape of the
potential (for redox as well as Br--sensitive electrodes), the
OCL is apparently a selective indicator representing specific
but still coded responses of the system to the variation of the
operating parameters. The controlled development of the
C L structure will thus be able to contribute supplementary
information to that obtained from conventional methods in
the discussion on relevant elementary processes.
The CSTR-stabilized OCL also appears interesting in connection with newer investigations on the oxygen effect on BZ
oscillator^.['^^' 31 We could confirm the results of Saigusa" 31&xtrapolated to flow conditions-to a large extent.
When the reaction mixture is enriched with additional oxygen, a transition to an "0,-induced state"['3J is observed
(Fig. 3).[14]This transition is characterized by a noticeably
02
tFig. 3. Oxygen-induced OCL regime in flow experiment [14]. Operating
parameters: V = 2.0 m l m i n - ' ; 0, flow rate = 0.12 Lmin-'; remaining conditions and C L measurement as in Figure 1.
different period, CL-amplitude, and oscillation shape. The
OCL here undoubtedly points to a phase change. In contrast
to Saigusa" 31 our system returned to the original undisturbed state after switching off the oxygen flow. This reversibility naturally occurs only in the flow experiment.
Received: October 17, 1991 (24974 IE]
German version: Angew. Chem. 1992, 104, 358
CAS Registry numbers:
[Ru(bpy),]'+, 15158-62-0; malonic acid, 141-82-2; 0,, 7782-44-7.
[l] a) B. P. Belousov, Sb. Ref. Radars. Med. 1959, 145; b) A. M. Zhabotinskij, Selbsrerregte Konrentrutionsschningungen (Russ.), Nauka, Moskau.
1974.
[2] G. Nicolis. 1. Prigogine. Self~Orgumsarlonin Non-Eyuillhrium systems,
Wilev. New York, 1977.
0570-0;Y33/92/0303-0356B 3.50+.25;0
Anyen,. Chen?. Int. Ed. Engl. 31 (1992) No. 3
[3] a ) U. F. Franck, Anxeir.. Chem. 1978, 90, 1; Angeir.. Chem. I n t . Ed. En&'/.
1978, 17. 1 ; b) R. J. Field in Oscillations and Travelling Wuves in Chemical
.?vxiems (Eds.: R. J. Field, M. Burger), Wiley, New York, 1985. Chapter 2.
[4] L. Gyorgi. T. Turanyi. R. J. Field, 1 Phvs. Chem. 1990, 94, 7162.
[5] A. D. Kardvaev, G. S. Pdrshin, 1
'
. P. Kazakov, I;ve.~t.Akad. Nark SSSR,
Sw. Khirn. 1980, 221.
[6] a) F. Bolletta. V. Balrani. 1 Am. Chem. Sor. 1982, 104, 4250; b) H. R.
Weigt. H. Ritschel. G . Junghdhnel. Z . Ch1.m. 1983. 23. 152; H. R. Weigt,
G . Junghihnel, ;bid. 1985, 25. 382; c) A. D. Karavaev, V. P. Kazakov.
G. A . Tolstikov, Teor. Eksp. Khirn. 1986, 65.
17) R. J. Watts. J. Chem. Educ. 1983, 60. 834.
[XI a) F. E. Lytle, D. M. Hercules, Pholorhem. Photohiol. 1971, 13, 123; b) I.
Rubinstein, A. J. Bard. J. Am. Chem. Sor. 1981, 103, 512.
[9] A. Pacault. P. Hanusse, P. De Kepper. C. Vidal, J. Boissonade, Arc. Chem.
Rrs. 1976. 9. 43s.
[lo] a) The chernilumi~~escence
was registered with a photomultiplier after including a high-intensity monochromator (Bausch & Lomb) in the circuit.
Measurements were performed a t an OCL wavelength maximum of
610 nm (spectral width: 10 nm). The OCL spectrum agrees both with the
stationary photoluminescence (see [6a,b] and H. R. Weigt. Dbserfufion.
Phdagogische Hochschule Potsdam, 1984) and the oscillating photoluminescence (H. R. Weigt, unpublished); b) the potential was recorded at a
platinum redox electrode (MC 20, Meinsberg) relative to a silver chloride
electrode (SE 20. Meinsberg).
[ I l l A. D. Karavaev. V. P. Kazakov, Teor. Eksp. Khim. 1990, 566.
112) P. Ruoff. R. M. Noyes, 1 Phps. Chem. 1989, 93, 7394.
1131 H . Saigusa, C k m . Phps. Lerf. 1989. 157, 251.
1141 Oxygen (technical quality) was introduced into the lower part of the redctor through a capillary. The gas flow was determined with a flow meler
(TG 400, Medingen).
Dimerization of Thiophene to Give a Linear
S(CH),S Fragment with [(C,Me,)Rh(C,H,),]
**
The 'H NMR spectrum shows eight distinct multiplets for
the eight methine groups; a COSY spectrum (COSY =
correlated spectroscopy) indicates that these groups are attached in a linear array. Two distinct C,Me, resonances are
also observed. The 13C NMR spectrum shows two downfield singlet and six upfield doublet resonances, suggesting
that six carbons in the chain are attached to metal centers. A
3C/1H HETCOR spectrum (HECTOR = heteronuclear
correlation) shows that these six carbons are adjacent to each
other at an end of the (CH), chain. These data led to the
formulation of 1 as indicated in Equation (b). Use of a-deu-
'
b)
1
-+-
teriothiophene in the reaction leads to a product in which the
resonances at 6 = 6.503, 6.009,4.165, and 3.245 are diminished in intensity by half, indicating that the S(CH),S fragment arises by the coupling of two a thiophene carbons after
C-S cleavage.
Confirmation of the structure deduced from NMR results
was obtained from a single-crystal X-ray diffraction study."]
Since the compound proved difficult to crystallize, a preliminary data set was obtained on a small crystal (Fig. 1). A
By Robert M . Chin and Wiiiiam D . Jones*
Reactions of thiophenes with transition metals as models
for studying the hydrodesulfurization of petroleum have
aroused increased interest over the past few years."' A variety of coordination modes of thiophene have been found,[*]
and reactions in which the ring has been cleaved have been
The simple insertion of an unsaturated rhodiurnt4]or iridium"] metal center into the thiophene C-S bond
has also been examined [Eq. (a)], and we report here an
example in which C-C bond formation occurs concomitant
with the C-S cleavage.
c17
t2
c2e
Heating a solution of [(C,Me,)Rh(C,H,),] with a 20-fold
excess of thiophene in benzene solution at 90 "C for 15 h was
followed by removal of solvent and extraction of the residue
with hexane. Upon cooling a red-black precipitate forms.
The product is identified as 1 on the basis of NMR and
analytical
Fig. 1. PLUTO drawing of the structure of 1 in the solid state. Selected distances. Rh(1)-S(l), 2.38(2); Rh(1)-C(l), 2.1 1(7); Rh(l)-C(2). 2.15(7); Rh(1)C(3), 2.30(7); Rh(2)-S(2), 2.36(2); Rh(2)-C(4), 2.19(6); Rh(2)-C(5), 2.12(7);
Rh(2)-C(6), 2.31(7); %I)-C(l), 1.65(8); S(2)-C(S), 1.80(7); C(I)-C(2). lS(1);
C(2)-C(3), 1.54(9); C(3)-C(4), 1.5(1); C(4)-C(5), 1.33(8); C(5)-C(6), 1.4(1);
C(6)-C(7), 1.5(1); C(7)-C(8), 1.4(1)
[(CsMe,)Rh],(~~2-1,2,3,4,~~-5,6,7,10-~4-S(CH)~S]
1
[*] Prof. W D. Jones, R. M. Chin
Department of Chemistry University of Rochester, Rochester,
NY 14627 (USA)
[**I This work was supported by the National Science Foundation grant CHE9102318.
Angew C h w . h i . Ed. EngI. 31 (1992) No. 3
0 VCH
more symmetric molecule with the S(CH),S unit bound in a
1 ,2,3,4-q4-7,8,9,10-q4 fashion is not observed, despite the
fact that [ (C,Me,)Rh(polyolefin)] complexes are expected to
be labile at 200 T , [ ' l leading to the conclusion that the structure observed for 1 is thermodynamically preferred.
Verlugsgi~seilschuftmbH, W-6940 Weinheim, 1992
0570-0833iSZj0303-0357 $3.50+ .25/0
357
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