A unique crystalline-state reaction of an overcrowded distibene with molecular oxygen: The first example of a single crystal to a single crystal reaction with an external reagent

Full text of DOI:10.1021/ja973295y

J. Am. Chem. Soc. 1998, 120, 433-434
A Unique Crystalline-State Reaction of an
433
Overcrowded Distibene with Molecular Oxygen:
The First Example of a Single Crystal to a Single
Crystal Reaction with an External Reagent
Norihiro Tokitoh,*,† Yoshimitsu Arai,† Takahiro Sasamori,†
Renji Okazaki,*,† Shigeru Nagase,‡ Hidehiro Uekusa,§ and
Yuji Ohashi*§
Department of Chemistry, Graduate School of Science
The UniVersity of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
Department of Chemistry, Faculty of Science
Tokyo Metropolitan UniVersity
Minami-osawa, Hachioji, Tokyo 192-03, Japan
Department of Chemistry, Faculty of Science
Tokyo Institute of Technology
Figure 1. Perspective view of the crystal structure of distibene 2 along
the c axis. Selected bond lengths (Å) and angles (deg): Sb(1)-Sb(1)*
2.642(1), Sb(1)-C(1) 2.181(4), Sb(1)*-Sb(1)-C(1) 101.4(1).
2-12-1 O-okayama, Meguro-ku, Tokyo 152, Japan
Scheme 1
ReceiVed September 18, 1997
Since the first isolation of a stable diphosphene (ArPdPAr;
Ar ) 2,4,6-tri-tert-butylphenyl)1 several examples of stable
diphosphenes,2 aza-3a and phosphaarsenes3b,c (REdAsR; E ) N,
P), and diarsenes (RAsdAsR),3c,4 i.e., the heavier congeners of
an azo compound, have been synthesized by taking advantage of
steric protection with bulky substituents. Although theoretical
calculations predict that all the doubly bonded compounds
between heavier group 15 elements can be isolated as stable
species with appropriate steric protection groups,5 no stable
distibene (RSbdSbR) and dibismuthene (RBidBiR) have been
isolated so far. Very recently, however, we have succeeded in
the synthesis and characterization of the first stable dibismuthene
[TbtBidBiTbt (1)],6 i.e., the ultimate doubly bonded compound
consisting of the heaviest nonradioactive element, by utilizing
an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl (denoted as Tbt hereafter).7 The successful
isolation of 1 prompted us to challenge the synthesis and
characterization of the missing stable antimony-antimony double
bond compound. Here, we present the first isolation of a stable
distibene, TbtSbdSbTbt (2), and its unique reaction with mo-
lecular oxygen in the crystalline state.
with Li2Se in THF, with excess amount of hexamethylphospho-
rous triamide in toluene at 100 °C in a sealed tube (Scheme 1).
After heating for 12 h the solution turned green and the expected
distibene 2, which precipitated from the mixture on cooling, was
isolated in 94% yield by filtration in a glovebox filled with argon
as deep green single crystals.8
Distibene 2 is the first example of a stable antimony-antimony
double bond, and the green solution of 2 in hexane showed two
absorption maxima at λ1 ) 599 nm (ꢀ 170) and λ2 ) 466 nm (ꢀ
5200), which were assigned to the n f π* and π f π* transitions
of the SbdSb chromophore, respectively. The absorption maxima
thus obtained for 2 lie between those for the previously reported
stable diarsenes4 and those for the dibismuthene 1,6 and the
experimentally observed red shifts for the double-bond systems
of heavier group 15 elements on going from P to Bi agree with
the changes in the n, π, and π* orbital levels calculated for
HEdEH (E ) P, As, Sb, and Bi).9 Distibene 2 showed a strong
Raman line at 207 cm-1 (solid; excitation, He-Ne laser 632.8
nm) which is much higher than the frequencies observed for
distibines (e.g., Ph2Sb-SbPh2 141 cm-1).10
X-ray crystallographic analysis of the green crystal revealed
the molecular geometry of distibene 2 as shown in Figure 1, which
was found to be completely isomorphous with the dibismuthene
1. Considerable bond shortening (7%) of the Sb-Sb bond length
[2.642(1) Å] in 2 as compared with that reported for Ph2Sb-
SbPh2 [2.837 Å]10 clearly indicates its double-bond character,
while the observed Sb-Sb-C bond angle of 101.4(1)°, which
deviates greatly from the ideal sp2 hybridized bond angle (120°)
and approaches 90°, suggests that 2 has a nonhybridized Sb-Sb
double bond due to the 5s25p3 valence shell corelike nature of
the Sb atom as in the case of dibismuthene 1.
Distibene 2 was synthesized by the same method as in the case
of 1, i.e., deselenation reaction of the 1,3,5,2,4,6-triselenatristibane
3 (E ) Sb),8 which was prepared by the reaction of TbtSbCl2
8
† The University of Tokyo.
‡ Tokyo Metropolitan University.
§ Tokyo Institute of Technology.
(1) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J. Am.
Chem. Soc. 1981, 103, 4587.
(2) (a) For reviews, see: Weber, L. Chem. ReV. (Washington, D.C.) 1992,
92, 1839. (b) Yoshifuji, M. In Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Regitz, M., Scherer, O. J., Eds.; Thieme: Stuttgart,
Germany, 1990; pp 321-337. (c) Cowley, A. H.; Kilduff, J.; Pakulski, M.;
Stewart, C. J. Am. Chem. Soc. 1983, 105, 1655. (d) Yoshifuji, M.; Shibayama,
K.; Inamoto, N.; Matsushita, T.; Nishimoto, K. J. Am. Chem. Soc. 1983, 105,
2495. (e) Ranaivonjatovo, H.; Escudie´, J.; Couret, C.; Satge´, J. Phosphorus
Sulfur 1987, 31, 81.
(3) (a) Ahlemann, J.-T.; Ku¨nzel, A.; Roesky, H. W.; Noltemeyer, M.;
Markovskii, L.; Schmidt, H.-G. Inorg. Chem. 1996, 35, 6644. (b) Cowley, A.
H.; Kilduff, J.; Lasch, J. G.; Mehrotra, S.; Norman, N. C.; Pakulski, M.;
Whittlesey, B.; Atwood, J.; Hunter, W. Inorg. Chem. 1984, 23, 2582. (c)
Escudie´, J.; Couret, C.; Ranaivonjatovo, H.; Wolf, J.-G. Tetrahedron Lett.
1983, 24, 3625.
(4) Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem.
Soc. 1983, 105, 5506.
(5) Nagase, S.; Suzuki, S.; Kurakake, T. J. Chem. Soc., Chem. Commun.
1990, 1724.
(6) Tokitoh, N.; Arai, Y.; Okazaki, R.; Nagase, S. Science 1997, 277, 78.
(7) Okazaki, R.; Tokitoh, N.; Matsumoto, T. In Synthetic Methods of
Organometallic and Inorganic Chemistry; Auner, N., Klingebiel, U., Eds.;
Thieme: New York, 1996; Vol. 2, pp 260-269.
1
(8) 2: green crystals; mp > 300 °C; H NMR (CDCl3) δ 0.128 (s, 36H),
0.132 (s, 36H), 0.15 (s, 36H), 1.44 (s, 2H), 2.75 (s, 2H), 2.94 (s, 2H), 6.54 (s,
2H), 6.64 (s, 2H); UV (hexane) λmax 599 nm (ꢀ 170), 466 nm (ꢀ 5200); FT-
Raman (solid; excitation, He-Ne laser 632.8 nm) 207 cm-1 (νSbdSb). Anal.
Calcd for C54H118Sb2Si12: C, 48.11; H, 8.82. Found: C, 47.50; H, 8.70. All
the other new compounds here obtained showed satisfactory spectral and
analytical data, which are detailed in the Supporting Information together with
their synthetic procedures.
(9) Nagase, S. In The Chemistry of Organic Arsenic, Antimony and Bismuth
Compounds; Patai, S., Ed.; Wiley: New York, 1994; pp 1-24.
(10) Bu¨rger, H.; Eujen, R. J. Mol. Struct. 1983, 98, 265.
S0002-7863(97)03295-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/06/1998

434 J. Am. Chem. Soc., Vol. 120, No. 2, 1998
Communications to the Editor
Figure 3. Perspective view of the crystal structure of dioxadistibetane 8
along the c axis. Selected bond lengths (Å) and angles (deg): Sb(1)-
O(1) 2.004(7), Sb(1)-O(1)* 1.990(6), Sb(1)-Sb(1)* 3.039(1), Sb(1)-
C(1) 2.176(5), O(1)*-Sb(1)-O(1) 80.9(3), O(1)*-Sb(1)-C(1) 103.9(2),
O(1)-Sb(1)-C(1) 102.8(2), Sb(1)*-Sb(1)-C(1) 107.6(5).
In Figure 3 is shown the crystal structure of dioxadistibetane
8 viewed along the c axis together with selected intramolecular
parameters. The insertion of two oxygen atoms into the Sb-Sb
double bond effects only a slight change in the cell dimensions,
but leads to the elongation of the Sb-Sb distance (ca. 0.4 Å) in
8 [3.040(1) Å] as compared to that of the starting distibene 2.
One can reasonably imagine that the extremely bulky Tbt group
may provide molecular oxygen with enough space for the insertion
against the packing force. The presence of the relatively long
induction period is most likely interpreted in terms of a “domino”
type reaction caused by the oxidation of the molecules of 2 lying
on the exterior surface of the single crystal. The analysis of the
detailed mechanism is now in progress.
In summary, we have succeeded in the synthesis and charac-
terization of the first stable antimony-antimony double bond
compound, distibene 2, the structural and physical properties of
which will be of great importance for the systematic elucidation
of the intrinsic nature of the double bond systems between the
heavier group 15 elements. To our best knowledge, the unique
oxidation reaction of distibene 2 in the solid state is also the first
example of an intermolecular chemical reaction with an external
reagent in which the integrity of the crystal is fully preserved.13
Figure 2. Monitored changes of the cell parameters from 2 to 8: (a)
change of b axis length; (b) change of unit cell volume.
With the stable distibene 2 in hand, we have examined the
reactivity of the Sb-Sb double bond toward several reagents.
Treatment of 2 with bromine and iodine in carbon tetrachloride
at room temperature resulted in the cleavage of the Sb-Sb bond
to give the corresponding dihalostibines TbtSbBr2 (4) and TbtSbI2
(5) in quantitative yields, respectively,8 while the reaction of 2
with elemental selenium in tetrahydrofuran at 70 °C gave the
precursor 3 (E ) Sb; 23%) together with a triselenide TbtSe3Tbt
(16%).8 On the other hand, distibene 2 underwent a [2+3]-
cycloaddition reaction with bulky aryl-substituted nitrile oxides
ArCNO [Ar ) 2,4,6-trimethoxyphenyl (Tmp) or 2,4,6-trimeth-
ylphenyl (Mes)] to afford the corresponding adducts 6 and 7 in
59 and 58% yields, respectively.8
Acknowledgment. This work was partially supported by a Grant-
in-Aid for Scientific Research on Priority Areas (No. 09239208) from
the Ministry of Education, Science, Sports and Culture, Japan. We are
grateful to Professor Yukio Furukawa, the University of Tokyo, for the
measurement of FT-Raman spectra. We also thank Shin-etsu Chemical
Co., Ltd. and Tosoh Akzo Co., Ltd. for the generous gift of chlorosilanes
and alkyllithiums, respectively. Calculations were carried out with the
Gaussian 94 program.
Furthermore, during the course of our investigation of the
reactivity of 2 we have found a unique, interesting reactivity of
distibene 2 with oxygen. Although distibene 2 reacts with oxygen
in solution quite rapidly to give quantitatively the corresponding
colorless 1,3,2,4-dioxadistibetane derivative 8,8 2 is considerably
stable in the solid state in the open air. The crystals of 2 remained
dark green for several hours, but they slowly reacted with
atmospheric oxygen to give 8 quantitatively. Of particular note
is that in the crystalline state 2 reacts with molecular oxygen while
retaining its crystallinity. Thus, the reaction proceeds from single
crystals of 2 to single crystals of 8.
Supporting Information Available: Physical properties of com-
pounds 3-8, crystallographic data with complete tables of bond lengths,
bond angles, and thermal and positional parameters for 2 and 8, and
figures for the monitored changes of all the cell parameters from 2 to 8
(29 pages). See any current masthead page for ordering and Internet
access instructions.
JA973295Y
This unique oxidation process of 2 in the crystalline phase was
successfully monitored by repeated measurements of the cell
dimensions using an X-ray diffraction technique with an imaging
plate Weissenberg diffractometer.11 In Figure 2 are shown the
changes of the b axis length and unit cell volume. They clearly
indicate that the crystal dimensions of 2 abruptly changed to those
of 8 within 10 h after an induction period (ca. 30 h), and after
completion of the transformation of the unit cell dimensions three-
dimensional intensity data of 8 were collected using the identical
crystal initially used for the structural analysis of 2.12
(12) The crystal data of 2 and 8 are as follows: (2) C54H118Sb2Si12, M )
1348.06, a ) 12.863(2) Å, b ) 17.866(3) Å, c ) 9.2694(9) Å, R ) 96.469-
(9)°, â ) 107.036(11)°, γ ) 105.404(6)°, V ) 1921.3(5) Å3, triclinic, space
group P1h (no. 2), Z ) 1, final R1 ) 0.0697, wR2 ) 0.1982 for 7907 [I >
2σ(I)] observed reflections, GOF (on F2) ) 1.046; (8) C54H118O2Sb2Si12, M
) 1380.06, a ) 12.8965(13) Å, b ) 18.1927(19) Å, c ) 9.3392(11) Å, R )
93.964(7)°, â ) 108.630(6)°, γ ) 105.867(6)°, V ) 1967.6(4) Å3, triclinic,
space group P1h (no. 2), Z ) 1, final R1 ) 0.0842, wR2 ) 0.2556 for 7349 [I
> 2σ(I)] observed reflections, GOF (on F2) ) 1.086.
(13) West et al. have reported an interesting isomerization of a 1,2-
dioxadisiletane derivative to the corresponding 1,3-dioxadisiletane isomer in
the crystalline state, the process of which was partially monitored by X-ray
diffraction technique and solid-state NMR. McKillop, K. L.; Gillette, G. R.;
Powell, D. R.; West, R. J. Am. Chem. Soc. 1992, 114, 5203.
(11) Uekusa, H.; Ohashi, Y. Mol. Cryst. Liq. Cryst. 1996, 279, 285.