Synthesis and first x-ray structural analysis of monomeric imino-λ5-stibanes

Article abstract of DOI:10.1021/ic991120e

Triaryl (trifluoromethylsulfonylimino)-λ⁵-stibanes (Ar₃-Sb=NSO₂CF₃) were prepared by the Kirsanov-type reaction of triarylantimony dichlorides with CF₃SO₂NH₂ in the presence of K

Full text of DOI:10.1021/ic991120e

1340
Inorg. Chem. 2000, 39, 1340-1341
Synthesis and First X-ray Structural Analysis of Monomeric Imino-λ5-stibanes
Yoshihiro Matano,* Hazumi Nomura, and Hitomi Suzuki†
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
ReceiVed September 20, 1999
Iminopnictoranes of the general formula R3MdNR′ (M ) P,
As, Sb, Bi)1 are useful reagents in organic synthesis.2 They are
also versatile nitrene sources for transition-metal imido com-
plexes.3 The interesting structural feature of this class of
compounds would be the formal double-bond character of the
pnictogen-nitrogen bond. Recently, Koketsu et al. examined the
structures of a series of imaginary iminopnictoranes, H3MdNH
(M ) P, As, Sb, Bi), by means of ab initio calculations (MP2-
DZ-d level) and predicted that the double-bond character in the
MdN bond would decrease in the order P > As > Sb > Bi.4
Although the literature contains many reports for the crystal
structures of lighter iminopnictoranes, very little information is
available for imino-λ5-stibanes (R3SbdNR′). In 1995, Wright et
al. reported the X-ray crystal structure of [Ph3Sb(µ-NCH2CH2-
Ph)]2 (1), which possesses the four-membered Sb2N2 core with
two distorted trigonal bipyramidal antimony centers and, therefore,
may be regarded as an imino-λ5-stibane dimer.5 To the best of
our knowledge, however, there has been no report on the X-ray
crystal structure of imino-λ5-stibanes that exist in the monomeric
form. Here we report the synthesis and first crystal structure
determination of novel monomeric triaryl(imino)-λ5-stibanes.
As shown in Scheme 1, triaryl(trifluoromethylsulfonylimino)-
λ5-stibanes 3a,b (Ar3SbdNSO2CF3: a, Ar ) 2-MeC6H4; b, Ar
) 2-MeOC6H4) were prepared in good yield by the Kirsanov-
type reaction6 of triarylantimony dichlorides 2a,b with CF3SO2-
NH2 in the presence of KO-t-Bu and by the redox condensation7
of triarylstibines 4a,b with CF3SO2NH2 in the presence of diethyl
azodicarboxylate. These methods failed for the synthesis of 3c.8
Thus, ortho substituents are important for the stabilization of the
SbdN bond (see below).
Scheme 1a
a Reagents and conditions: A, H2NSO2CF3, KO-t-Bu (2.2 equiv),
CH2Cl2, -50 °C to rt; B, H2NSO2CF3, EtO2CNdNCO2Et, Et2O, 0 °C to
rt.
Figure 1. ORTEP diagram of 3a (30% ellipsoids). Bond lengths (Å):
Sb-C1, 2.112(4); Sb-C8, 2.103(4); Sb-C15, 2.107(4); Sb-N, 1.958-
(4); N-S, 1.536(4); S-O1, 1.441(3); S-O2, 1.428(4). Bond angles
(deg): C1-Sb-C8, 113.2(2); C1-Sb-C15, 106.3(2); C8-Sb-C15,
108.9(2); C1-Sb-N, 109.5(2); C8-Sb-N, 117.2(2); C15-Sb-N, 100.5-
(2); C1-C2-C7, 123.9(4); C8-C9-C14, 123.2(4); C15-C16-C21,
123.0(4).
The ortho substituted imino-λ5-stibanes 3a,b were characterized
by 1H NMR and IR spectroscopies as well as by X-ray diffraction
* Author to whom correspondence should be addressed. E-mail: matano@
kuchem.kyoto-u.ac.jp. Fax: +81-75-753-4000. Phone: +81-75-753-4042.
† Current address: Department of Chemistry, School of Science, Kwansei
Gakuin University, Uegahara, Nishinomiya 662-0891, Japan.
(1) Regardless of the degree of double-bond character, the pnictogen-
nitrogen bonds in iminopnictoranes are described as MdN for clarity.
(2) See, e.g.: (a) Johnson, A. W. Ylides and Imines of Phosphorus; Wiley:
New York, 1993. (b) Lloyd, D.; Gosney, I. In The Chemistry of Organic
Arsenic, Antimony and Bismuth Compounds; Patai, S., Ed.; Wiley: New
York, 1994; Chapter 16, pp 657-693. (c) Matano, Y.; Suzuki, H. Bull.
Chem. Soc. Jpn. 1996, 69, 2673.
(3) See, e.g.: (a) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1988. (b) Harlan, E. W.; Holm, R. H. J. Am. Chem.
Soc. 1990, 112, 186. (c) Chong, A. O.; Oshima, K.; Sharpless, K. B. J.
Am. Chem. Soc. 1977, 99, 3420.
(4) Koketsu, J.; Ninomiya, Y.; Suzuki, Y.; Koga, N. Inorg. Chem. 1997,
36, 694. The predicted bond length and bond order of the MdN bond
in H3MdNH: P, 1.601 Å, 1.667; As, 1.715 Å, 1.537; Sb, 1.899 Å, 1.492;
Bi, 1.977 Å, 1.315. The Sb-N bond length of H2Sb-NH2 was predicted
to be 2.049 Å.
analysis. Figures 1 and 2 show the ORTEP diagrams of 3a and
3b, respectively, with selected bond lengths and bond angles.9
Both 3a and 3b have been found to exist in the monomeric form,
and each antimony center possesses a distorted tetrahedral
geometry. The SbdN bond lengths, 1.958(4) and 1.962(2) Å, are
shorter than the Sb-N bond lengths of compound 15 [1.990(3)-
2.122(3) Å] as well as those of antimony(III) amides10 [2.041-
(6)-2.064(6) Å for Sb(NHC6H2-t-Bu3)3 and 2.074(7)-2.081(7)
Å for Sb(NdCPh2)3]. However, the SbdN bond lengths of 3a,b
are longer than the estimated value (1.91 Å) for the SbdN double
bond.11 It is in contrast that the PdN bond length [1.579(4) Å]
observed for Ph3PdNSO2Tol12 is close to the estimated value
(9) See Supporting Information.
(5) Edwards, A. J.; Paver, M. A.; Pearson, P.; Raithby, P. R.; Rennie, M.-
A.; Russell, C. A.; Wright, D. S. J. Organomet. Chem. 1995, 503, C29.
(6) Kirsanov, A. V.; Makitra, R. G. Zh. Obshch. Khim. 1956, 26, 907.
(7) Bittner, S.; Assaf, Y.; Krief, P.; Pomerantz, M.; Ziemnicka, B. T.; Smith,
C. G. J. Org. Chem. 1985, 50, 1712.
(8) Radchenko et al. prepared Ph3SbdNSO2CF3 from Ph3Sb and N3SO2-
CF3. Radchenko, O. A.; Nazaretyan, V. P.; Yagupol’skii, L. M. Zh.
Obshch. Khim. 1976, 46, 565.
(10) (a) Burford, N.; Macdonald, C. L. B.; Robertson, K. N.; Cameron, T. S.
Inorg. Chem. 1996, 35, 4013. (b) Edwards, A. J.; Paver, M. A.; Raithby,
P. R.; Russell, C. A.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1993,
2257.
(11) Dean, J. A. Lange’s Handbook of Chemistry, 11th ed.; McGraw-Hill:
New York, 1973; Tables 3-9.
(12) Cameron, A. F.; Hair, N. J.; Morris, D. G. Acta Crystallogr. 1974, B30,
221.
10.1021/ic991120e CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/11/2000

Communications
Inorganic Chemistry, Vol. 39, No. 7, 2000 1341
considerably to the actual bond state in 3.16 This is also consistent
with the low-frequency appearance of an asymmetric SO2
stretching band of 3a,b (1287 cm-1 for 3a; 1279 cm-1 for 3b)
compared with that of CF3SO2NH2 (1360 cm-1) in the IR spectra.
One of the sulfonyl oxygen atoms, O1, was found to coordinate
weakly to the antimony center with Sb‚‚‚O1 distances of 3.261-
(3) and 3.110(2) Å, which are shorter than the sum of their van
der Waals radii (ca. 3.6 Å).11 Due to the intramolecular coordina-
tion, the Sb, N, S, and O1 atoms in 3a,b are almost in the same
plane with a small torsion angle (10.0(4)° for 3a; 9.5(2)° for 3b).
The ortho substituents are likely to contribute to kinetic and
thermodynamic stabilization17 of the SbdN bond. The o-methyl
groups in 3a lean ca. 3° away from the antimony center, indicating
the steric congestion around the SbdN bond. On the other hand,
the o-methoxy groups in 3b lean ca. 5° closer toward the
antimony, indicating the attractive interaction between the meth-
oxy oxygen and antimony atoms.18 Thus, the SbdN bond may
be sterically protected in 3a, while it may be stabilized both
electronically and sterically in 3b.
Figure 2. ORTEP diagram of 3b (30% ellipsoids). Bond lengths (Å):
Sb-C1, 2.096(2); Sb-C8, 2.089(2); Sb-C15, 2.096(2); Sb-N, 1.962-
(2); N-S, 1.536(2); S-O1, 1.444(2); S-O2, 1.434(2). Bond angles
(deg): C1-Sb-C8, 110.45(10); C1-Sb-C15, 106.58(9); C8-Sb-C15,
113.23(9); C1-Sb-N, 107.58(9); C8-Sb-N, 111.42(8); C15-Sb-N,
107.29(9); C1-C2-O3, 114.8(2); C8-C9-O4, 114.8(2); C15-C16-
O5, 115.1(2).
The reason why compound 1 exists in the dimeric form and
compounds 3 exist in the monomeric form may be largely
attributed to the electronic and steric influences from the N- as
well as Sb-substituents. When we consider the monomeric form
(1.60 Å) for the PdN double bond.11 Thus, the Sb(V)dN bond
of monomeric imino-λ5-stibanes 3a,b possesses moderate single-
bond character, whereas the P(V)dN bond of Ph3PdNSO2Tol
has a significant double-bond character. On the other hand, the
N-S bond lengths [1.536(4) and 1.536(2) Å] are much shorter
than the N-S single-bond length (1.76 Å) of sulfamic acid13 and
fall in the range of the NdS double bonds.11 Moreover, the Sd
O bond lengths [1.428(4)-1.444(2) Å] are longer than a typical
SdO double-bond length (1.40 Å).14 The observed N-S and Sd
O bond lengths of 3a,b are close to those of chloramine-T hydrate
[1.590(2) and 1.439(2)-1.455(2) Å], which are considered to
possess an NdS double bond as well as an S-O single bond.15
It appears therefore that the canonical forms 3Y and 3Z contribute
of 1, the negative charge arising from the bond polarization Sbδ+
-
Nδ- should be mostly localized on the nitrogen and the steric
environment around the SbdN bond seems to be less congested.
By contrast, the negative charge in 3 can be delocalized through
the sulfonyl group, and the steric congestion around the SbdN
bond should be much larger. As a result, the SbdN bond in
monomeric 1 would readily dimerize, whereas that in 3 would
remain unchanged.
In summary, we have determined the crystal structure of the
monomeric imino-λ5-stibanes 3a,b for the first time and revealed
that the SbdN bond possesses moderate single-bond character
owing to the resonance hybridization with the electron-withdraw-
ing N-sulfonyl group. It appears that the ortho substituents as well
as the N-sulfonyl group stabilize the SbdN bond and prevent it
from dimerization.
(13) Sass, R. L. Acta Crystallogr. 1960, 13, 320.
(14) Gillespie, R. J.; Robinson, E. A. Can. J. Chem. 1963, 41, 2074.
(15) Olmstead, M. M.; Power, P. P. Inorg. Chem. 1986, 25, 4057.
(16) The relatively short SbdN bond lengths compared with the known Sb-N
single-bond distances may suggest that 3X contributes, to some extent,
to the actual bond state. However, the electrostatic attraction force
between the polarized Sbδ+ and Nδ- atoms in 3Y would also cause the
Sb-N bond shortening.
(17) (a) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J.
Am. Chem. Soc. 1981, 103, 4587. (b) West, R.; Fink, M. J.; Michl, J.
Science 1981, 214, 1343. (c) Cowley, A. H.; Kilduff, J. E.; Newman, T.
H.; Pakulski, M. J. Am. Chem. Soc. 1982, 104, 5820. (d) Tokitoh, N.;
Arai, Y.; Okazaki, R.; Nagase, S. Science 1997, 277, 78. (e) McEwen,
W. E.; Lau, K. W. J. Org. Chem. 1982, 47, 3595. (f) Wada, M.; Kanzaki,
M.; Fujiwara, M.; Kajihara, K.; Erabi, T. Bull. Chem. Soc. Jpn. 1991,
64, 1782.
Acknowledgment. This work was supported by a Grant-in-
Aid (No. 11120224) from the Ministry of Education, Science,
Sports and Culture of Japan.
Supporting Information Available: Experimental procedures for the
synthesis of 3 and spectroscopic, analytical, and X-ray diffraction data
for 3a,b. This material is available free of charge via the Internet at
http://pubs.acs.org.
(18) The Sb‚‚‚O(methoxy) distances in 3b are 2.951(2)-3.018(2) Å.
IC991120E