Cp3(*)Al5I6: An intermediate in reactions leading to elemental aluminum and Al(III) species?

Article abstract of DOI:10.1002/(SICI)1521-3773(19980918)37:17<2397::AID-ANIE2397>3.0.CO;2-K

A first indication of the reaction mechanism for the disproportionation of an Al(I) species to an Al(III) compound and metallic aluminum is provided by the isolation of [Cp₃(*)Al₅I₆], an intermediate that is formed in the ready disproportionation of [Cp(°)Al] in the presence of Al₂I₆ (see reaction sequence). This potentially key role of Al(I) compounds could be of great significance for large-scale industrial processes. X = I, Cl.

Full text of DOI:10.1002/(SICI)1521-3773(19980918)37:17<2397::AID-ANIE2397>3.0.CO;2-K

COMMUNICATIONS
�
1
� 1
bishomotropylium cation 9 (16.6 kcalmol more stable than
), was confirmed to be bishomoaromatic by Cremer based on
[9] The most stable triplet species (C
s
) is 20.7 kcalmol higher in energy
than 4 (UB3LYP/6-31G*): V. Gogonea, unpublished results.
10] a) For the application of geometric aromaticity criteria, see P. von R.
Schleyer, P. Freeman, H. Jiao, B. Goldfuss, Angew. Chem. 1995, 107,
4
[
[
[
15]
geometric and magnetic criteria. The NICS at the geometric
center of 9 ( � 11.8) and L ˆ� 18.5 ppm cgs (i.e., similar to
3
32; Angew. Chem. Int. Ed. Engl. 1995, 34, 337; b) V. I. Minkin, M. N.
Glukhovtsev, B. Y. Simkin, Aromaticity and Antiaromaticity, Wiley,
New York, 1994.
[
16]
that of 4 ), corroborate this conclusion. This cation reacts to
[4,5]
give the observed cis-8,9-dihydroindenes 3 (X ˆ OH or Cl).
11] a) P. von R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. v. E.
Hommes, J. Am. Chem. Soc. 1996, 118, 6317; b) P. von R. Schleyer, H.
Jiao, N. J. R. van E. Hommes, V. G. Malkin, O. Malkin, J. Am. Chem.
Soc. 1997, 119, 12669.
[12] a) For the use of diamagnetic susceptibility exaltations as aromaticity
criteria, see H. J. Dauben, J. D. Wilson, J. L. Laity in Nonbenzoid
Aromaticity, Vol. II (Ed.: J. P. Snyder), Academic Press, New York,
971, pp. 166 ± 206; b) P. von R. Schleyer, H. Jiao, Pure Appl. Chem.
996, 68, 209; c) see also reference [10a].
[13] The Aces II program system: J. F. Stanton, J. Gauss, J. D. Watts, W. J.
In summary, the geometric and magnetic criteria (NICS and
L) exhibited by 4 now reveal this species to be the first
Möbius aromatic system in the Heilbronner sense, for which
[
4,5]
there is experimental evidence. Without such evidence, the
nature of 4 was not recognized originally. Furthermore, early
speculations were incorrect: While conformation 6 is avoided,
transition state 7 is not high in energy.
scrambling of the deuterium label, observed for 3 even at
668C, is consistent with the low barrier computed for 7,
permitting rapid interconversion of the helical 4 enantiomers.
Ninefold repetition of the enantiomerization results in
complete distribution of a deuterium label in 4. In conclusion,
the experimental findings reported nearly three decades
1
1
[
5b]
The complete
Lauderdale, R. Bartlett, Int. J. Quantum Chem. 1992, S26, 879.
14] a) M. S. J. Dewar, Angew. Chem. 1971, 83, 859; Angew. Chem. Int. Ed.
�
[
Engl. 1971, 10, 761; b) H. Jiao, P. von R. Schleyer, J. Phys. Org. Chem.
1
998, in press.
[15] D. Cremer, P. Svensson, E. Kraka, Z. Konkoli, P. Ahlberg, J. Am.
Chem. Soc. 1993, 115, 7457.
[16] Magnetic susceptibilities depend on the area of the delocalized
system. This complicates comparisons among molecules with different
sizes and shapese: B. Maoche, J. Gayoso, O. Ouamerali, Rev. Roum.
Chem. 1984, 26, 613.
[
4,5]
‡
ago
are explained by assuming that the (CH)9 intermedi-
ates were 4n-electron Möbius aromatic systems. Our predic-
tion that 4 is the most stable monocyclic (CH)9 cation might
‡
be verified by applying modern experimental techniques such
as laser flash photolysis, which has been employed to observe
short-lived carbocations.
[17] a) F. L. Cozens, R. A. McClelland, S. Steenken, J. Am. Chem. Soc.
1
993, 115, 5050; b) M. Patz, H. Mayr, J. Bartl, S. Steenken, Angew.
[
17]
Chem. 1995, 107, 519; Angew. Chem Int. Ed. Engl. 1995, 34, 490; c)
R. A. McClelland, F. L. Cozens, J. Li, S. Steenken, J. Chem. Soc.
Perkin Trans. 2 1996, 1531.
Received: March 16, 1998 [Z11593IE]
German version: Angew. Chem. 1998, 110, 2515 ± 2517
Keywords: aromaticity ´ carbocations ´ density functional
calculations ´ magnetic properties ´ Möbius strips
Cp*Al I : An Intermediate in Reactions
3
5 6
III
Leading to Elemental Aluminum and Al
Species?**
[
[
1] E. Heilbronner, Tetrahedron Lett. 1964, 1923.
2] a) H. E. Zimmerman, J. Am. Chem. Soc. 1966, 88, 1564; b) H. E.
Zimmerman, Acc. Chem. Res. 1971, 4, 272; c) H. Jiao, P. von R.
Schleyer, Angew. Chem. 1993, 105, 1833; Angew. Chem. Int. Ed. Engl.
Christoph Üffing, Elke Baum, Ralf Köppe, and
Hansgeorg Schnöckel*
1993, 32, 1763; d) H. Jiao, P. von R. Schleyer, J. Chem. Soc. Perkin
Dedicated to Professor Heinrich Nöth
on the occasion of his 70th birthday
Trans. 2 1994, 407.
[
[
3] D. P. Craig, J. Chem. Soc. 1959, 997.
4] J. C. Barborak, T. M. Su, P. von R. Schleyer, G. Boche, G. Schneider, J.
Am. Chem. Soc. 1971, 93, 279.
I
As we have demonstrated in earlier work, Al species are
[
5] a) A. G. Anastassiou, E. Yakali, J. Chem. Soc. Chem. Commun. 1972,
reactive both in solid noble gases and under preparative
synthetic conditions,[ and often react to give thermodynami-
92; b) ªThe Cyclononatetraenyl Cationº: A. G. Anastassiou, Topics in
1]
Nonbenzoid Aromatic Chemistry, Vol. 1, Wiley, New York, 1973, p. 18;
c) E. Yakali, Dissertation, Syracuse University, NY, 1973.
III
cally more stable Al products and metallic aluminum.
[
6] A. G. Anastassiou, E. Yakali, J. Am. Chem. Soc. 1971, 93, 3803.
Cp*Al] [Cp*AlCl ] is thus formed as the final product
‡
�
[
2
3
[
7] We learned only recently that Anastassiou and Yakali actually
from Cp*Al and AlCl3 with simultaneous deposition of
aluminum. This isomer of the sesquichloride [Cp*Al Cl ]
‡
considered the possibility of a Möbius cation (CH)
9
in 1969, and this
3
2
3
anticipation might have been also the incentive to carry out the early
investigations outlined here: A. G. Anastassiou, E. Yakali, private
communication (see also reference [5c]).
‡
contains the aluminocenium ion [Cp*Al] as a structural
2
peculiarity.[ To understand this reaction mechanism and to
find out how Al species can react in general, we carried out
2]
[
8] a) Geometries were optimized at the B3LYP/6-311 ‡ G** level.
I
Frequencies and ZPE corrections are computed at the B3LYP/6 ±
investigations with the aim of capturing intermediate products
of the disproportionation.
31G* level with Gaussian 94. The NICS and magnetic susceptibilities
were calculated with GIAO and CSGT methods, respectively (as
implemented in G94); b) GAUSSIAN 94, Revision C.3: M. J. Frisch,
G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb,
J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K.
Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B.
Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challa-
combe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres,
E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J.
Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, J. A.
Pople, Gaussian, Inc., Pittsburgh, PA, 1995.
[
*] Prof. Dr. H. Schnöckel, Dr. C. Üffing, Dr. E. Baum, Dr. R. Köppe
Institut für Anorganische Chemie der Universität
Engesserstrasse, Geb. 30.45, D-76128 Karlsruhe (Germany)
Fax : (‡ 49)721-608-4854
E-mail: hg@achpc9.chemie.uni-karlsruhe.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
Angew. Chem. Int. Ed. 1998, 37, No. 17
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3717-2397 $ 17.50+.50/0
2397

COMMUNICATIONS
To prepare as stable an intermediate as possible, we
selected AlI instead of AlCl and treated the iodide with
substance and very sensitive to hydrolysis. Crystals of 1 thus
obtained contain toluene such that the formula may be
3
3
[5]
[
{Cp*Al} ] under the exclusion of donors; that is, we provided
written as 1 ´ 0.5C H . The X-ray structure analysis at
4
7 8
soft substituents that have a proven capability for stabilizing
elements in low oxidation states. It became apparent that the
presence of Al2I6 dramatically increased the tendency of
� 738C shows that 1 has a cagelike framework comprising
five Al and two I atoms, in which the aluminum atom Al(1) is
coordinated in a tetrahedral fashion by two iodine atoms
(Al(1) ± I(1) 257, Al(1) ± I(2) 254 pm) and two Cp*-substitut-
ed aluminum atoms (Al(2), Al(3); Al ± Al 252 ± 253, Al ± C
214 ± 224 pm) (Figure 1a). The iodine atoms I(3) and I(4) lie
at a considerably larger distance from Al(1) (Al(1) ± I(3) 398,
Al(1) ± I(4) 388 pm) and form a plane with I(1) and I(2); Al(1)
also lies in this plane.
[
Cp*Al] to disproportionate: Whereas pure [Cp*Al] can be
heated in solution to almost 908C without visible decom-
position, it disproportionates in the presence of Al I even
2
6
below room temperature. This means that even a relatively
I
stable Al compound such as [Cp*Al] reacts so rapidly at
room temperature that intermediate products cannot nor-
[
3]
mally be intercepted. In view of this, proof of the partic-
An Al unit (Al(4), Al(5); Al ± Al 254 pm) is arranged
2
I
0
ipation of other Al species in the reaction between Al and
almost perpendicular to the Al group. One of the metal
3
III
Al should be even more difficult if not altogether impossible
atoms of this Al unit is coordinated by three iodine atoms
2
to obtain. Therefore, the structurally characterized intermedi-
(Al(5) ± I(3) 260, Al(5) ± I(5) 254, Al(5) ± I(6) 257 pm), and
the other by one iodine atom and a Cp* substituent (Al(4) ±
I(4) 281, Al(4) ± C 215 ± 234 pm). The iodine atoms I(3) and
I(4) occupy an eclipsed conformation with respect to the Al2
unit. In addition, there are interactions between these iodine
ate product presented hereÐ[Cp*Al I ] (1), which could be
3
5 6
isolated at � 208CÐis of particular significance (Figure 1a).
Compound 1 is formed from a suspension of [{Cp*Al} ] and
4
Al I (molar ratio 1:2) in toluene at � 208C. It is a colorless
2
6
atoms and the Al atoms Al(2) and Al(3) of the Al unit. The
3
atomic distances are shown in Figure 1b.[ In agreement with
the average oxidation number 1.8 for aluminum, the Al ± Al
and Al ± I distances in 1 resemble those in donor-stabilized
aluminum(ii) diiodides.[ The structure of 1 provides a first
indication of the reaction mechanism for the reaction of
6]
10]
[
Cp*Al] with Al I (Scheme 1).
2 6
Scheme 1. Reaction of three molecules of [Cp*Al] with one molecule of
Al . Schematic representation (top) and reaction equation (bottom).
2 6
I
It is apparent that monomeric [Cp*Al] has a tendency to
undergo insertion reactions. Even at � 208CÐthat is, at very
low [Cp*Al] concentrations[ Ðthree [Cp*Al] molecules are
inserted into bridging Al ± I bonds. At the same time, three
bridging Al ± I bonds of Al I are expanded so much that only
11]
2
6
the weak Al-I-Al bridging interactions mentioned above
remain.
To decide whether the experimentally observed species
‡
should be described as separated ions [Cp*Al I ] -
2
3 2
�
[
Cp*Al I ] , as an ion pair, or as a donor± acceptor complex,
2 4
[9]
we carried out extensive quantum-chemical calculations.
Figure 1. a) Structure of 1 in the crystal (SCHAKAL[4]). Hydrogen atoms
are not shown. b) Schematic representation of the structure of 1 with
several distances [pm]. Further distances [pm] and angles [8]: Al(2) ± Al(3)
These show that the calculated geometry parameters (e.g.,
several Al ± I distances and the angle AlCp*-Al-AlCp*) for
isolated ions do not agree with the observed structural data.
Additional calculations were therefore carried out for the
model compounds [Cp Al I ] (1a), Br Al I (1b), and H Al I
5 6
407(1), Al(2)/Al(3) ± CCp* 214.4(6) ± 224.4(7), Al(4) ± C(21) 233.6(6),
Al(4) ± C(22) 227.1(6), Al(4) ± C(23) 215.2(5), Al(4) ± C(24) 215.6(6),
Al(4) ± C(25) 225.3(7), Al(1) ± Al(5) 597(2), Al(1) ± Al(4) 608(2); Al(2)-
Al(1)-Al(3) 107.23(7), I(1)-Al(1)-I(2) 111.73(9), CCp*-Al-Al(1) 117.3(2) ±
3
5
6
3
5
6
3
1c).[ It became clear that the geometry is decisively
9]
(
176.9(2), Al(5)-Al(4)-I(4) 104.83(7), Al(4)-Al(5)-I(6) 111.10(8), Al(4)-
Al(5)-I(3) 111.27(7), I(6)-Al(5)-I(3) 108.04(13).
influenced by the Cp* groups, because both the hydrogen-
2
398
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3717-2398 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1998, 37, No. 17

COMMUNICATIONS
and the bromine-substituted compounds have quite different
Al ± I distances in the bridges and very acute Al-Al-Al angles
[2] a) C. Dohmeier, H. Schnöckel, C. Robl, U. Schneider, R. Ahlrichs,
Angew. Chem. 1993, 105, 1714 ± 1716; Angew. Chem. Int. Ed. Engl.
1
1
993, 32, 1655; b) C. Dohmeier, Dissertation, Universität München,
994.
in the Al unit when compared with 1a. The compounds 1a ± c
3
also differ from one another considerably with regard to the
population analyses. Whereas the calculations for 1a result in
a clear charge separation between the Al3 and Al2 units
[
3] An example for an insertion of [Cp*Al] into a Si ± F bond is known,
however: S. Schulz, T. Schoop, H. W. Roesky, L. Häming, A. Steiner,
R. Herbst-Irmer, Angew. Chem. 1995, 107, 1015 ± 1016; Angew. Chem.
Int. Ed. Engl. 1995, 34, 919 ± 920.
(
(
Æ0.38) and negatively charged bridging iodine atoms
[4] E. Keller, SCHAKAL92, Universität Freiburg, 1992.
� 0.15), there are virtually no charge separations (Al :
3
[5] Crystal structure analysis of C H Al I ´ 0.5C H (1 ´ 0.5C H ): M ˆ
30
45
5
6
7
8
7
8
r
approx. � 0.04; Al : ca. ‡0.04). Furthermore, there are only
1348.09; crystal dimensions: 0.51  0.35  0.27 mm , Tˆ 200(2) K,
3
2
very weakly negatively polarized bridging iodine atoms (ca.
monoclinic, space group C2/c, a ˆ 21.974(5), b ˆ 27.730(70), c ˆ
3
[
9e]
17.107(4) Š, b ˆ 117.16(6)8, Vˆ 9274.6(236) Š , Z ˆ 8,
1
calcd
ˆ
�
0.04) in 1b and 1c.
The compounds 1a ± c also differ in their energy balance.
The insertion of three AlH units into a Al I molecule is, with
�
3
� 1
1.931 gcm
,
m ˆ 4.093 mm
,
F(000) ˆ 5064. Of 9952 reflections
measured on a four-circle diffractometer (STOE-STADI-4; MoKa
radiation, l ˆ 0.71073 Š; graphite monochromator), 8147 were inde-
pendent (R(int.) ˆ 0.0252); � 18 ꢀ h ꢀ 26; � 23 ꢀ h ꢀ 32; � 20 ꢀ l ꢀ 20;
3.98 ꢀ 2Vꢀ 49.968. The structure was solved by direct methods
2
6
�
1
4
38 kJmol , highly exothermic, whereas the insertion of the
�
1
CpAl units leads to an energy gain of just 199 kJmol . These
thermodynamic results are plausible in view of the calculated
charge separation in 1a. In conclusion, the quantum-chemical
calculations, which in the case of 1a produce results that are in
good agreement with the experimental structural data of 1,
permit the following bonding description for this intermedi-
ate. In contrast to the donor± acceptor complexes 1b and 1c, 1
and 1a are best described as contact ion pairs that dispropor-
tionate at room temperature to give elemental aluminum and
[
5a]
(
SHELXS-86),
and 6929 reflections (F > 4s(F)) were used for
full-matrix refinement of 402 parameters by the least-squares method
2
[5b]
against j F j (SHELXL-93). Hydrogen atoms were treated using a
rider model with fixed isotropic U values; weighting scheme: w� 1
ˆ
2
2
2
2
2
c
s F
o
‡ (0.0430P) ‡ 32.1956P, with P ˆ (F
o
‡ 2F
)/3; w scan (scan
width 0.82 ± 1.488); semi-empirical absorption correction (min./max.
transmission 0.2131/0.2579); R1 ˆ 0.0327 (F > 4s(F)); wR2 (all da-
�
3
ta) ˆ 0.0894; max./min. residual electron density 1.666/ � 1.202 eŠ
.
Further details on the crystal structure analysis may be obtained from
the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leo-
poldshafen, Germany (fax: (‡49)7247-808-666; e-mail: crysdata@fiz-
karlsruhe.de), on quoting the depository number CSD-408058.
a) SHELXS-86: G. M. Sheldrick, Acta Crystallogr. Sect. A 1990, 46,
III
[12]
Al species.
This type of insertion of Al species can also occur in
I
[
13]
technically relevant electrochemical reductions of organic
aluminum(iii) compounds. The resulting primary products can
insert themselves into the reagents and react in an analogous
manner to 1 to give species rich in aluminum. Unstable
intermediates such as these can then spontaneously dispro-
portionate to give elemental aluminum. The starting com-
4
67 ± 473; b) SHELXL-93: G. M. Sheldrick, Universität Göttingen,
1993.
[6] With respect to the Al ± I distances to the terminal I atoms in dimeric
[
7a]
[7b]
3
AlI (245 as well as 244.7 and 245.9 pm ), the distances from Al(1)
and Al(5) to their nearest neighboring iodine atoms are 9 ± 15 pm
longer. The Al ± I(4) and Al ± I(3) distances in the bridges are also
considerably elongated with respect to those in Al I . These results
2 6
III
pound (Al ) is also formed, which can then go through the
reaction cycle again. In a similar manner, Al species could
seem reasonable, however, when one considers that a) Al atoms in low
oxidation states have a much greater radius (the Al ± I distance in
I
[
8]
[
2
AlI ´ NEt
3 4
] is 264 pm; in a bridging bond an Al ± I distance of
also be important intermediates in the preparation of organic
aluminum compounds from aluminum and alkyl halides,
[
9]
83 pm has been calculated for Al I ) and b) higher coordination
2 2
numbers (in comparison to the examples listed under a)) lead to a
further increase in the interatomic distances in 1.
I
III
whereby the insertion of Al compounds into Al species
already formed could possibly lead to compounds analogous
[7] a) A. F. Wells, Structural Inorganic Chemistry, 5th ed., Clarendon,
Oxford, 1984; S. I. Troyanov, Zh. Neorgan. Khim. 1994, 39, 552 ± 555;
b) R. Kniep, P. Blees, W. Poll, Angew. Chem. 1982, 94, 370; Angew.
Chem. Int. Ed. Engl. 1982, 21, 386.
to 1.[14]
[
[
8] A. Ecker, H. Schnöckel, Z. Anorg. Allg. Chem. 1996, 622, 149 ± 152.
Experimental Section
[9a]
9] All ab initio calculations were carried out with the RI-DFT module
[
9b]
AlI
and toluene was added. The suspension was stored at � 208C. After a few
days clear, colorless crystals of 1 were formed along with solid [{Cp*Al} ].
3
(50 mg, 0.12 mmol) was combined with [{Cp*Al}
4
] (20 mg, 0.03 mmol),
(B ± P parametrization) of the program TURBOMOLE using SVP
[
9c]
basis sets. Population analyses were carried out with the method of
Mulliken. Atomic numbering for 1: see Figure 1; energies (E) [a.u.];
distances [pm]; angles [8]; partial charges (d): [Cp Al I ] (1a; C
3 5 6 1
4
Elemental aluminum was not deposited under these conditions. To transfer
the crystals quickly from the cold suspension onto the goniometer head,
they were warmed to room temperature in mineral oil (Aldrich) under an
argon stream. (The crystals decompose slowly in this oil; the color changes
from colorless to yellow and then to red.) In the cold N stream (200 K) on
2
the goniometer head, a glass-like protective coating is formed around the
crystal, thus preventing attack by air and moisture.
symmetry): E ˆ � 1861.284917; Al(1) ± Al(2) 257.0, Al(1) ± Al(3)
257.2, Al(2) ± I(3) 326.8, Al(2) ± I(4) 357.8, Al(3) ± I(3) 346.0, Al(3) ±
I(4) 332.1, Al(4) ± I(4) 278.4, Al(5) ± I(3) 268.0, Al(4) ± Al(5) 256.4,
Al(2) ± Al(3) 389.0; Al(2)-Al(1)-Al(3) 98.3, I(4)-Al(4)-Al(5) 109.9,
Al(4)-Al(5)-I(3) 108.5; d(CpAl(4)) ˆ 0.02, d(CpAl(2)) ˆ 0.10, d(CpAl(3)) ˆ
0.09, d(Al(1)) ˆ 0.30, d(Al(2)) ˆ 0.25, d(Al(3)) ˆ 0.25, d(Al(4)) ˆ
0
.29, d(Al(5)) ˆ 0.39, d(I(3)) ˆ � 0.17, d(I(4)) ˆ � 0.27, d(I(5)) ˆ
Received: December 11, 1997,
Revised version: May 4, 1998 [Z11252]
� 0.33, d(ªAl
considered as an ion pair due to the clear charge separation and the
strongly charged bridging iodine atoms (d(I) >� 0.15). Br Al (1b;
symmetry): E ˆ � 9003.663100; Al(1) ± Al(2) 260.2, Al(1) ± Al(3)
60.2, Al(2) ± I(3) 297.5, Al(3) ± I(3) 297.5, Al(2) ± I(4) 310.8, Al(3) ±
3
º) ˆ 0.38, d(ªAl
2
º) ˆ � 0.38; that is, 1a should be
German version: Angew. Chem. 1998, 110, 2488 ± 2491
3
5 6
I
C
2
1
Keywords: aluminum ´ disproportionations ´ insertions ´
intermediates ´ structure elucidation
I(4) 310.8, Al(4) ± I(4) 269.4, Al(5) ± I(3) 281.0, Al(4) ± Al(5) 257.1,
Al(2) ± Al(3) 335.3; Al(2)-Al(1)-Al(3) 80.2, I(4)-Al(4)-Al(5) 116.2,
Al(4)-Al(5)-I(3)
99.0;
d(BrAl(4)) ˆ � 0.18,
d(BrAl(2)) ˆ � 0.20,
d(BrAl(3)) ˆ � 0.20, d(Al(1)) ˆ 0.39, d(Al(2)) ˆ 0.23, d(Al(3)) ˆ 0.23,
[
1] C. Dohmeier, D. Loos, H. Schnöckel, Angew. Chem. 1996, 108, 141 ±
61; Angew. Chem. Int. Ed. Engl. 1996, 35, 129 ± 149.
d(Al(4)) ˆ 0.39, d(Al(5)) ˆ 0.37, d(I(3)) ˆ � 0.04, d(I(4)) ˆ � 0.05,
1
d(I(5)) ˆ � 0.23, d(ªAl
3
º) ˆ � 0.04, d(ªAl º) ˆ 0.04; that is, 1b should
2
Angew. Chem. Int. Ed. 1998, 37, No. 17
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3717-2399 $ 17.50+.50/0
2399

COMMUNICATIONS
be regarded as a donor± acceptor complex, as there is no charge
separation between the Al units and the bridging iodine atoms are
Average Octet Radical Polymer: A Stable
Polyphenoxyl with Star-Shaped
p Conjugation**
only weakly charged.[
9d]
[H
1282.817496; Al(1) ± Al(2) 259.7, Al(1) ± Al(3) 259.7, Al(2) ± I(3)
91.9, Al(2) ± I(4) 305.3, Al(3) ± I(3) 292.2, Al(3) ± I(4) 305.4, Al(4) ±
3
Al
5
I
6
]
(1c;
C
1
symmetry): E ˆ
�
2
Hiroyuki Nishide,* Makoto Miyasaka, and
Eishun Tsuchida
I(4) 268.4, Al(5) ± I(3) 282.0, Al(4) ± Al(5) 256.4, Al(2) ± Al(3) 333.0;
Al(2)-Al(1)-Al(3) 79.8, I(4)-Al(4)-Al(5) 114.2, Al(4)-Al(5)-I(3)
1
0
0
00.2; d(HAl(4)) ˆ � 0.02, d(HAl(2)) ˆ 0.09, d(HAl(3)) ˆ 0.09, d(Al(1)) ˆ
.40, d(Al(2)) ˆ 0.04, d(Al(3)) ˆ 0.04, d(Al(4)) ˆ 0.28, d(Al(5)) ˆ
The search for syntheses of organic molecules with very
high spin resulting from intramolecular through-bond mag-
netic ordering is driven by the desire to realize magnetism
.35, d(I(3)) ˆ � 0.03, d(I(4)) ˆ � 0.05, d(I(5)) ˆ � 0.24, d(ªAl º) ˆ
3
�
0.05, d(ªAl
2
º) ˆ 0.05; that is, 1c should be regarded as a donor±
acceptor complex, as there is no charge separation between the Al
[
9d]
[1]
units and the bridging iodine atoms are only weakly charged.
Al
based purely on organic components. High-spin alignment
�
1
2
I
6
‡ 3AlH !H
3
Al
5
I
6
:
DE ˆ � 438 kJmol
.
Al
2
I
6
‡ 3[CpAl] !
in the ground state has been demonstrated for cross-conju-
gated polyradicals or radical polymer main chains, such as
�
1
[Cp
3
Al
5
I
6
]: DE ˆ � 199 kJmol . a) K. Eichkorn, O. Treutler, H.
Öhm, M. Häser, R. Ahlrichs, Chem. Phys. Lett. 1995, 240, 283 ± 290;
Chem. Phys. Lett. 1995, 242, 652 ± 660; b) R. Ahlrichs, M. Bär, M.
Häser, H. Horn, C. Kölmel, Chem. Phys. Lett. 1989, 162, 165 ± 169;
c) A. Schäfer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97, 2571 ±
[
1b]
poly(1,3-phenylenecarbene)
and poly(1,3-phenylenephe-
nylmethine).[
1c]
Pseudo-two-dimensional branched, cyclic,
and ladder homologues have also been synthesized to increase
2577. d) A similar polarization was also calculated for Al
2
I
6
: donor-
[2]
the spin quantum number S at low temperature. The aim
acceptor complex; D2h symmetry; Al ± Ibridge 270.7, Al ± Iterminal 250.2,
Al ± Al 367.8; d(Ibridge) ˆ � 0.05, d(Iterminal) ˆ � 0.21; d(Al) ˆ 0.47.
10] a) A. Ecker, E. Baum, M. A. Friesen, M. A. Junker, C. Üffing, R.
Köppe, H. Schnöckel, Z. Anorg. Allg. Chem. 1998, 624, 513 ± 516; b) A.
Ecker, H. Schnöckel, Z. Anorg. Allg. Chem., in press.
was to diminish the damage of a radical or spin defect, which
is fatal for the cross-conjugated polyradicals. In addition,
these polyradicals lacked chemical stability at room temper-
ature.
[
[
[
11] In the 27Al NMR spectrum, monomeric [Cp*Al] can only be identified
There is another approach to the high-spin molecules that
makes use of p-conjugated linear polymers bearing pendant
radical groups on the polymer backbone which are p-
conjugated with the backbone to ensure the ferromagnetic
in equilibrium with [{Cp*Al}
for the tetramerization to [{Cp*Al}
12] The NMR spectrum of a mixture of [{Cp*Al}
4
] above about 608C, because the energy
�
1 [1]
4
] is around � 150 kJmol
.
4
] and Al
2
I
6
in deuterated
1
toluene shows signals at the following shifts: H NMR (Bruker AC-
2
d(C
50 spectrometer (250.134 MHz); room temperature; reference:
[1e]
connectivity of the radicals. In this type of polyradical, the
2
7
7
D
7
H)): d ˆ 2.09; Al NMR (Bruker AMX-300 spectrometer;
spin alignment between the pendant unpaired electrons is not
sensitive to a spin defects, which are unavoidable for radical
polymers of increasing molecular size because the magnetic
interaction is transmitted through the p-conjugated polymer
backbone. A further advantage is that the pendant, built-in
radical groups could be chosen from a series of chemically
stable organic radicals. We recently synthesized poly(1,2-
phenylenevinylene) containing di-tert-butylphenoxyl as the
pendant radical group (1) which has a through-conjugated
backbone bond and allows long-range ferromagnetic ex-
change interaction between the pendant unpaired electrons:
With a spin concentration of 0.7 per monomer unit, 1 displays
3
‡
room temperature; external reference: d([Al(H
2
O)
6
]
)): d ˆ 0. After
1
a reaction period of a few days at � 208C: H NMR: d (w1/2 [Hz]) ˆ
2
1
1
.07 (10), 2.03 (10) (both with low intensity), 1.93 (2), 1.85 (3), 1.78 (3),
.60 (3) (the latter in a ratio of about 3:3:2); 2 Al NMR: d (w1/2 [Hz]) ˆ
7
10 (br, weak), � 21 (550), � 83 (260). After about one month at
1
�
208C: H NMR: d (w1/2 [Hz]) ˆ 1.85 (2), 1.74 (2), 1.60 (2) (in a ratio
27
of about 2:3:4); Al NMR: d (w1/2 [Hz]) ˆ 110 (br, weak), � 21 (520),
�
82 (260). After about three months and intermediate tempering at
1
27
1
208C:
H
NMR:
d
(w1/2 [Hz]) ˆ 1.57 (sharp, s); Al-NMR:
d
(
w
1/2 [Hz]) ˆ � 19 (500, weak), � 81 (360), � 114 (very weak,
‡ [2a]
[
Cp*
complex reaction sequence than for the reaction between [{Cp*Al}
2
Al] ).
These NMR spectroscopic results indicate a more
4
]
[2a]
3
and AlCl .
III
[
13] See, for example, the electrochemical reduction of Al species to
elemental aluminum or the preparation of simple organic alum-
inum(iii) compounds from aluminum and alkyl halides: K. Ziegler, H.
Lehmkuhl, Z. Anorg. Allg. Chem. 1956, 283, 414 ± 424; W. Kautek, W.
Fromberg, J. A. de Hek, Metalloberfläche 1992, 46, 67 ± 74; J. Fischer,
Metalloberfläche 1996, 50, 183 ± 184; A. Ecker, H. Schnöckel, VDI-
Nachrichten 1996, 50, 22; H. Köhnlein, H. Schnöckel, Aluminum 1997,
[3]
values for S of 4/2 to 5/2. We report here our successful
improvement of both S and the stability of the polyradical by
extending 1 to the star-shaped homologue 2 (Scheme 1).
The precursor acetoxypolymer 2'' was synthesized in a one-
pot reaction by the Pd-catalyzed Heck reaction of styrene 3
with 1,3,5-triiodobenzene (4), the core of the star-shaped
polymer (see the Experimental Section). The molecular
weight and degree of polymerization (DP ˆ l ‡ m ‡ n ‡ 6 for
73, 766 ± 767.
III
[
14] Additional Al species are formed by their subsequent disproportio-
nation. This should lead to an increase in the reaction rate for the
formation of the desired end products.
2
) of the star-shaped polymer was controlled by the feed ratio
of 3 to 4 during the polymerization. The iodide groups had
completely reacted in every polymer. The DP measured by
[
*] Prof. H. Nishide, M. Miyasaka, Prof. E. Tsuchida
Department of Polymer Chemistry
Waseda University, Tokyo 169 ± 8555 (Japan)
Fax: (‡81)3-3209-5522
E-mail: nishide@mn.waseda.ac.jp
[
**] This work was partially supported by Grants-in-Aid for Scientific
Research (nos. 277/08246101 and 09305060) from the Ministry of
Education, Science and Culture, Japan, and by the NEDO R&D
Project on Precision Polycondensation. The authors thank Prof. A.
Rajca (University of Nebraska) for his productive comments on this
study.
2
400
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3717-2400 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1998, 37, No. 17