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Formation of an Oxalate-filled Cavity in a Reduced Cyclic Octanuclear Polyoxomolybdate [(n-C4H9)4N]2[Mo8O16(OCH3)8(C2O4)] formed from -[(n-C4H9)4N]4[Mo8O26] and Rhodizonic Acid.

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[lo] P. J. O'Malley, G. T. Babcock, R. C. Prince, Biochim. Biuphys. Acra 766
(1984) 283.
11 11 R. J. Debus, B. A. Barry, G. T. Backcock, L. McIntosh, Proc. Natl. Acad.
Sci. USA 85 (1988) 427.
[I21 B. A. Barry, C. T. Babcock, Proc. Natl. Acad. Sci. USA 84 (1987) 7099.
1131 H. B. Stegmann, H. J. Ruff, K. Scheffler, Angew. Chem. 97 (1985) 407;
Angew. Chem. Int. Ed. Engl. 24 (1985) 425.
1141 R. E. Blankenship, K. Sauer, Biochim. Biophys. Acra 3S7 (1974) 252.
[ I S ] M. Dunach, M. Seigneuret, J. Rigaud, E. Padros, Biochemistry 26 (1987)
[I61 Y. Siderer, R. Malkin, R. Poupko, 2. Luz, Arch. Brochem. Biophys. 179
(1977) 174.
[I71 H. 8. Stegmann, P. Schuler, H. J. Ruff, submitted for publication.
1181 W. Nebe, Arch. Forsrwes. 16 (1967) 109.
the generality of carbonyl insertion coupled with ligand
dissociation in polyoxomolybdate-carbonyl chemistry, we
have investigated the reaction of the molybdate 5 with
rhodizonic acid 7.
The product of the reaction of 5 with 7 is a light-green,
crystalline, diamagnetic species of analytical composition
The IR spectrum of 8 shows a band at 2930 c m - ' as-
sociated with the C-H stretching modes of the methoxy
groups, and strong bands at 1665 cm-' and 1543 cm-'
which are assigned to the carbonyl stretching vibrations
Formation of an Oxalate-filled Cavity in a
v(C=O) of non-equivalent carbonyl residues. The band at
Reduced Cyclic Octanuclear Polyoxomolybdate
[ ( ~ - C ~ H ~ ) ~ N I J M O ~ O ~ ~ ( O Cformed
H ~ ) ~ ( C Z ~ ~ ) I 972 cm-' is assigned to the v(Mo=O,) stretching vibration
(0,= terminal 0x0 group); furthermore, the position of the
from U - [ ( ~ - C ~ H ~ ) ~ N M M
O ~Rhodizonic
absorption suggests that the molybdenum centers of the
Mo"' starting compound have been reduced. The band at
By Qin Chen, Shuncheng Liu, and Jon Zubieta*
815 cm- ' establishes the presence of bridging 0x0 groups
Investigations of the interactions between polyoxometalate clusters and substrate organic molecules have been
prompted by the structural relationship of polyoxoanions
to solid
In the specific case of polyoxomolybdate-carbonyl interactions, carbonyl insertion into a molybdenum-oxygen bond provides the common feature of
The syntheses of organooxomolybdates
1 with acetyl-,Is1 2 with diacetyl-,161and 3 with diketalstructures?] depending upon the choice of organic substrate, have been discussed in terms of acid-base pair binding sites and models for substrate binding on solid oxide
surfaces.[81However, the products of such molybdate-car[ R C H M O ~ O ~ ~ H [] ~
H'C C H M O ~ O , ~ X ] ~ ~
bony1 reactions also depend intimately upon the nature of
the organic precursor, as demonstrated by the isolation of
the oxalatodimolybdate 4 from the reaction of the complex 5 with chloranilic acid 6 in methanol.[71This observation suggests that ligand dissociation will occur, subsequent to carbonyl insertion, with organic residues capable
of stabilizing a cationic leaving group. In order to examine
['I Prof. Dr. J. Zubieta, Q. Chen, S. Liu
Department of Chemistry
State University of New York at Albany
Albany, NY 12 222 (USA)
[**I This work was supported by the National Science Foundation (Grant
CHE 8514634 to J . Z.).
0 VCH Verlagsgesellschafi mbH. 0-6940 Weinheim. 1988
Fig. 1. Structure of the dlanion [ M O ~ O , ~ ( O C H , ) ~ ( C ~of
O ,8) ]in~ ~the crystal.
Selected bond lengths [A] and angles ["I: Mol-01, 2.367(7): Mo2-02,
2.377(7); Mo3-02, 2.385(8); Mo4-Ola. 2.367(7); Mo-0,, 1.678(11) (av); MoOb, 1.932(12) (av); Ma-O(methoxy), 2.106(11) (av); Mol-Mo2, 2.582(2);
Mo2-Mo3, 3.262(1); M03-Mo4, 2.574(2); Mo4-Mola, 3.312(1); CI-01,
1.25(2); CI-02, 1.37(2); CI-Cla, 1.43(2); 03-Mol-04, 71.4(3); 05-Mol0 6 , 94.3(3); 09-Mo3-010, 94.2(3); 03a-Mo4-04a, 71.2(3); 09-Mo4-010,
94.5(3); Mo-O,-Mo, 83.7(5) (av); Mo-O(methoxy)-Mo, 101.7(6) (av). Abbreviations: 0,.terminal 0x0 group; Oh,bridging 0x0 group; O(methoxy), bridging methoxy group oxygen donor.
The complex anion of compound 8 (Fig. 1)[lo1consists
of an octagonal array of Mo atoms, alternately bridged by
two methoxy groups o r two 0x0 groups producing a cyclic
"tiara" framework [ M O ~ O ~ ~ ( O C HThe
~ ) ~Mo-Mo
distances display a short-long alternation oaround the ring
(with average values of 2.578 and 3.287 A, resp.). Each of
the bonding Mo-Mo pairs is bridged by two 0x0 groups,
while two methoxy groups bridge each of the Mo-Mo
pairs with non-interacting distances. The methoxy groups
OS70-0833/88/1212-1724 $ 02 50/0
Angew. Chem Int. Ed. Engl. 27 (1988) No. 12
fold out from the ring, whereas the 0x0 groups fold into
the cavity formed by the ring. The Mo-Mo bonding distance of 2.578
is characteristic for Mo" d 1 centers in
bridged binuclear systems where a direct Mo-Mo interaction is present["' and it accounts for the observed diamagnetism of 8 as a consequence of strong magnetic coupling.
A remarkable feature of the structure of 8 is that the
cavity of the cyclic [Mo8016(OCH3)8]0unit is occupied by
an oxalate moiety, [C204]2Q.Each oxygen of the oxalate
group bridges two M o centers with non-bonding
Mo. . . M o distances. The oxalate unit, the eight M o centers and the eight terminal 0x0 groups form a planar
[ M o ~ O ~ ( C , O , ) ] 'unit
~ ~ (maximum deviation of 0.02 A from
the best plane through all atoms). The C - 0 distances of
the oxadate unit are dist!nctly non-equivalent (Cl-01,
1.25(2) A; C I - 0 2 , 1.37(2) A), suggesting that the multiple
bond character is localized in the C1-01 moieties.
\ /
/ \
0 +
Received: June 27, 1988 [Z 2828 IE]
German version: Angew. Chem. 100 (1988) 1792
[I] V. W. Day, W. G. Klemperer, Science (Washington, DC) 228 (1986)
121 M. T. Pope: Heleropoly and Isopoly Oxometalates. Springer, New York
[3] E. M. McCarron 111, R. L. Harlow, J . Am. Chem. SOC. 105 (1983)
141 T . X . Hsieh, S. N. Shaikh, J. Zubieta, Inorg. Chem. 26 (1987) 4079.
[5] R. D. Adams, M. F. Fredrich, W. GKlemperer, R.3. Liu, J . Am. Chem.
SOC.I01 (1979)491; R. D. Adams, W. G. Klemperer, R.3. Liu, J. Chem.
SOC.Chem Commun. 1979. 256.
161 V. W. Day, M. R. Thompson, W. G. Klemperer, R.-S. Liu, J . Am. Chem.
SOC.102 (1980) 5973.
[7] S. Liu, S. N. Shaikh, J. Zubieta, Inorg. Chem., in press.
[8] H. Knoziger, Adu. Catal. 25 (1976) 184.
[9] Rhodizonic acid 7 (0.766 g, 4.63 mmol) was added to a suspension of
the complex 5 (2.00 g, 0.93 mmol) in MeOH (50 mL). After stirring at
room temperature for six hours, the green solution was filtered and the
solvent removed under vacuum. The resultant green oil was dissolved in
methanol and carefully covered with a layer of ether. After standing for
8 days, light green crystals of 8 were collected in 25% yield.
[lo] Crystal Data: C42H96N202RM~R,
triclinic space group, Pi, a = 10.720(2),
b= 13.450(2), C = 13.476(2) A", a=73.28(1), 8=80.83(1), ~=79.92(1)",
V = 1819.8(6) A-3, Z= i . Structure solution and refinement based on
2215 reflections with F0>60(F0)(MoKa, A=0.71073 A); final discrepancy factor, 0.0486. Further details of the crystal structure investigation
are available on request from the Fachinformationszentrum Energie,
Physik, Mathematik GmbH, D-7514 Eggenstein-Leopoldshafen 2
(FRG), on quoting the depository number CSD-53330, the names of the
authors, and the journal citation.
[ I I] B. Spivack, 2. Dori, Coord Chem. Rev. 17 (1975) 99, and references
cited therein.
/ \
Scheme I .
The synthesis of a Mo"-oxalate cluster from polyoxomolybdate(v1) and rhodizonic acid precursors implies that in
this instance the well-documented carbonyl insertion reaction is coupled with ligand dissociation and redox processes. Although the mechanism of this chemical transformation is not yet known in detail, the process most likely
involves a succession of two-electron transfers and cationic intermediates of the type illustrated in Scheme 1.
Since multicenter Mo clusters are involved in the chemistry, the formally Mo'" sites produced in this sequence of
electron transfer steps are in proximity to oxidized Mo"'
sites and rapid disproportionation is to be expected:
Since the mechanism requires the formation of organic
cations, the isolation of the oxalate derivative is dependent
on the stability of the cationic species. Thus, whereas aglyoxal and phenanthrenequinone yield the simple insertion products 2 and 3,respectively, chloranilic acid 6 and
rhodizonic acid 7 undergo concomitant ligand dissociation to yield the oxalate derivatives 4 and 8, respectively.
As anticipated, effective stabilization of the cationic leaving group promotes the formation of oxalato complexes.
For example, di-tert-butylglyoxal (2,2,5,5-tetramethyl-3,4hexanedione) reacts with the molybdate 5 to give the complex 8 in 70% yield. We are currently investigating the
structural consequences of variations in the substituents of
Angew. Chem. Int. Ed. Engl. 27 (1988) No. I 2
such a-diketones upon the products of the carbonyl insertion into oxometalate cores.
Reductive Oligomerization of
The Tricyclo[]hexasilaneand
By Yoshio Kabe,* Mutsumi Kuroda, Yoshihiro Honda,
Osamu Yamashita, Takeshi Kawase, and
Satoru Masamme*
Numerous recent publications are concerned with both
the theoretical and synthetic aspects of strained polycycles,".21 for example, the bicyclo[l.I.O]tetrasilane sysThe successful construction of this particular ring
system suggests that trichlorosilanes (RSiC13) and 1,1,2,2tetrachlorodisilanes (RSiC12-SiC12R) could serve, with the
judicious selection of R, as precursors of hitherto unknown polycyclic systems including those represented by
the molecular formula (RS&". Summarizing our initial investigations along this line, we describe below that reductive oligomerization of 1,2-di-tert-butyl- 1,1,2,2-tetrachlorodisilane ( l y 3 ] proceeded in a unique and somewhat unexpected manner to provide tricycl0[2.2.0.O~~~]hexasilane
tetracyclo['.03~6]octasilane derivative^.'^' The following communication will then disclose an important aspect of 29Si-NMR spectroscopy displayed by these cyclic
[*] Dr. Y . Kabe, M. Kuroda, Dr.Y. Honda, Dr. 0. Yamashita
Institute for Fundamental Research and
Tochigi Research Laboratory, Kao Corporation
Ichikai-machi Haga-gun, Tochigi 321-34 (Japan)
Prof. Dr. S. Masamune, Dr. T. Kawase
Department of Chemistry, Massachusetts Institute of Technology
Cambridge, MA 02 139 (USA)
[**I The part of this work carried out at MIT was supported by the National
Science Foundation (USA).
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acid, cyclic, octanuclear, cavity, formation, och3, polyoxomolybdat, former, c4h9, reduced, mo8o16, c2o4, mo8o26, oxalate, rhodizonic, filled
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