Antimony imido and imido-amido compounds: A new route to an imidoantimony macrocycle

Article abstract of DOI:10.1039/b007020n

The syntheses of the antimony imido-amido and imido compounds Sb₂(NH-2,6-Me₂C₆H₃) ₂(n-N-2,6-Me₂C₆H₃)₂ and Sb₁₂(NPh)₁₈ are described. T

Full text of DOI:10.1039/b007020n

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Antimony imido and imido–amido compounds: a new route to an
imidoantimony macrocycle
Richard Bryant, Siân C. James, John C. Jeffery, Nicholas C. Norman,* A. Guy Orpen and
Ulrike Weckenmann
The University of Bristol, School of Chemistry, Bristol, UK BS8 1TS.
E-mail: N. C. Norman@Bristol.ac.uk
Received 30th August 2000, Accepted 18th October 2000
First published as an Advance Article on the web 30th October 2000
The syntheses of the antimony imido–amido and imido
compounds
Sb2(NH-2,6-Me2C6H3)2(ꢀ-N-2,6-Me2C6H3)2
and Sb12(NPh)18 are described.
Compounds of antimony and bismuth incorporating amido
and/or imido substituents are important both in terms of the
fundamental chemistry of these elements1 and as starting
materials for further synthesis.2 Well characterised examples
in which the antimony and bismuth centres are bonded only
to nitrogen are still few in number, however. For antimony
these include the tris-amido species Sb(NR2)3 (R = Me,3,4 Et,4
Pr,4 Bu,4 SiMe3 1c) and Sb(NH-2,4,6-But3C6H2)3,5 dinuclear
imido–amido compounds Sb2(NMe2)2(µ-NR)2 [R = 4-methyl-
pyridin-2-yl 1,6 3,4,5-(MeO)3C6H2 2,6 2,6-Pri2C6H3 32] and
Sb2[N(SiMe3)2]2(µ-NBut)2,7 and a range of species based on
the anions [Sb(NR)3]3Ϫ (R = PhCH2CH2,8 cyclohexyl9), [Sb2-
(NCy)2(µ-NCy)2]2Ϫ
(Cy = cyclohexyl),9b,10
[Sb3(NMe2)2(µ-
NCy)4]Ϫ 8,10c and [Sb3(NHCy)2(µ-NCy)4]Ϫ.9b,10c † Of particular
interest (see below) is the twenty four-membered imido-
antimony metallacycle Sb12[N-2-(MeO)C6H4]18 4.11 Bismuth
compounds include the tris-amido derivatives Bi(NR2)3 (R =
Me,12–14 SiMe3,13,14 Ph15) and Bi(NH-2,4,6-But3C6H2)3,5 the
imido–amido compounds Bi2(NHR)2(µ-NR)2 (R = 2,6-Pri2-
C6H3) 516 and Bi3(NHR)(µ-NR)4 (R = 2,6-Me2C6H3)17 and the
dianion [Bi2(NBut)2(µ-NBut)2]2Ϫ.18 We note also the structure
of Bi2[Me2Si(NBut)2]2[µ-Me2Si(NBut)2].19 Herein we describe
the synthesis and structure of the dinuclear imido–amido
compound Sb2(NH-2,6-Me2C6H3)2(µ-N-2,6-Me2C6H3)2 6 and
the imido metallacycle Sb12(NPh)18 7.
The reaction between SbCl3 and three equivalents of the
primary amide salt Li[NH-2,6-Me2C6H3] in thf/Et2O (thf =
tetrahydrofuran) afforded, after work-up, yellow crystals of
the imido–amido compound Sb2(NH-2,6-Me2C6H3)2(µ-N-2,6-
Me2C6H3)2 6‡ the structure of which was established by X-ray
crystallography (Fig. 1).§ Compound 6, which resides on a
crystallographic centre of inversion, comprises two trigonal
pyramidal antimony centres each carrying a terminal primary
amido group and bridged by two imido units. The disposition
of the amido groups with respect to the central Sb2N2 unit is
trans (A) (required by the crystallographic inversion centre) as
Fig. 1 A view of the molecular structure of 6 showing the atom
numbering scheme. Atoms are drawn as spheres of arbitrary radius.
Ellipsoids are drawn at the 40% level. Selected bond lengths (Å) and
angles (Њ) include: Sb(1)–N(1) 2.042(4), Sb(1)–N(2) 2.033(4), Sb(1)–
N(2A) 2.057(4), N(1)–C(11) 1.403(6), N(2)–C(21) 1.427(6); N(1)–
Sb(1)–N(2) 92.2(2), N(1)–Sb(1)–N(2A) 98.8(2), N(2)–Sb(1)–N(2A)
77.5(2), Sb(1)–N(1)–C(11) 136.2(4), Sb(1)–N(2)–Sb(1A) 102.5(2),
Sb(1)–N(2)–C(21) 129.7(3), Sb(1A)–N(2)–C(21) 126.2(3). Symmetry
transformations used to generate equivalent atoms: A, Ϫx, Ϫy, Ϫz.
examples the nitrogen atoms are very close to trigonal planar
and the antimony atoms are highly pyramidal. The orientation
of the imido aryl groups with respect to the Sb2N2 units range
from almost perpendicular in 6 to nearly coplanar in 1; in both
1 and 2, however, these orientations are influenced by signifi-
cant intermolecular interactions6 which are absent in the solid
state structure of 6. Further metric data for 6 is given in the
caption to Fig. 1.
The reaction between SbCl3 and three equivalents of lithium
anilide Li[NHPh] also afforded a yellow crystalline material||
which was identified by X-ray crystallography as the twenty
four-membered imidoantimony metallacycle Sb12(NPh)18
7
analogous to the previously characterised species Sb12[N-2-
(MeO)C6H4]18 4.11 Crystals of 7 were of very poor quality,
however, and no metric or crystallographic data is given here
but the structure determination** was sufficient to establish the
atom connectivities beyond reasonable doubt. The structure
is illustrated below. Molecules of 7 have approximate C6h sym-
metry with antimony centres alternating between being on
the outside and inside of the twenty four-membered ring and
alternately bridged by (µ-NPh)2 and (µ-NPh) units. The struc-
ture may also be described as containing linked trans-related
(NPh)Sb(µ-NPh)2Sb(NPh) moieties (i.e. type A above) of
similar form to 6 but having the terminal amido hydrogens
replaced by the next antimony in the macrocycle. Thus, the
gross structure of 7 is the same as found in 4 although the
molecular symmetry of 4 is reduced to S6 due to the presence
found in the related structures of 1, 2 and 5 although in contrast
to the cis (B) configuration observed for 3.¶ The Sb–N bond
distances (terminal and bridging) are all similar [Sb(1)–N(1)
2.042(4), Sb(1)–N(2) 2.033(4), Sb(1)–N(2A) 2.057(4) Å] and are
comparable to those observed in 1 and 2 although the Sb–
amide bond lengths in 1 and 2 [2.019(5) and 2.013(5) Å respect-
ively] are shorter than the Sb–imido nitrogen distances in these
structures [1, 2.052(5), 2.068(5); 2, 2.048(4), 2.060(4) Å].6 In all
DOI: 10.1039/b007020n
J. Chem. Soc., Dalton Trans., 2000, 4007–4009
This journal is © The Royal Society of Chemistry 2000
4007

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Hydrogen atoms were attached in idealised positions. CCDC reference
number 186/2229. See http://www.rsc.org/suppdata/dt/b0/b007020n/ for
crystallographic files in .cif format.
¶ The factors affecting whether a trans or cis geometry is observed
in the solid state for imido–amido compounds of the type E2(NR2)2-
(µ-NR)2 (E = Sb, Bi) have been discussed by Wright and Beswick2
although it is likely that both isomers of such species are present in
1
solution. In the case of 6, the H NMR spectrum reveals four methyl
signals of equal intensity consistent with the presence of equal amounts
of both isomers in C6D6 solution.
|| A solution of SbCl3 (0.050 g, 2.19 mmol) dissolved in thf (10 cm3) was
added to a stirred solution of Li[NHPh], prepared from PhNH2 (0.59
cm3, 6.57 mmol) and BunLi (4.1 cm3 of a 1.6 M solution in hexanes), in
Et2O (10 cm3) at 0 ЊC which resulted in an immediate colour change
from colourless to yellow-orange and formation of a white precipitate.
After warming to room temperature, filtration afforded a clear yellow
filtrate which yielded yellow feather-like crystals of 7 (85% recrystal-
lised yield) on cooling to 4 ЊC. One of these was used for X-ray diffrac-
tion although it was of poor quality. Repeated attempts to grow better
quality crystals from this and other (e.g. CH2Cl2/hexane) solvent
systems met with no success. C108H90Sb12N18 requires C, 41.85; H, 2.95;
N, 8.15. Found C, 41.60; H, 2.70; N, 9.00%. Mass spectrum (EI): the
following antimony–imido fragments were observed, m/z 943 [Sb4-
(NPh)5], 820 [Sb3(NPh)5], 729 [Sb3(NPh)4], 638 [Sb3(NPh)3], 426
[Sb2(NPh)2].
and disposition of the imido OMe groups. Clearly the intra-
molecular O ؒ ؒ ؒ Sb interactions present in 4 are not found in 7
which is interesting in light of the conjecture in ref. 11 indi-
cating that such intramolecular interactions might favour the
observed metallacyclic structure over alternative polymeric
forms. The basic Sb12N18 cyclic structure found in 4 and 7 may
now be seen as a more general structural type not critically
dependent on the nature of the R group and any associated
secondary bonding interactions.
** Despite repeated attempts, good quality crystals of 7 could not be
obtained and only a weak and poor quality data set was collected. The
data is not of sufficient quality to warrant deposition although the unit
The formation of 6 and 7 may be thought to occur formally
according to eqns. (1)–(3) as discussed for related examples by
Burford et al.5 and Roesky et al.16
¯
cell dimensions are given here; triclinic, space group P1, a = 17.538(5),
b = 17.596(5), c = 27.431(7) Å, α = 84.085(16), β = 79.647(19), γ =
61.340(17)Њ, U = 2566(2) Å3. The possibility of the presence of solvent
of crystallisation in 7 cannot be ruled out although the microanalytical
data on bulk samples|| are consistent with unsolvated crystals.
SbCl3 ϩ 3 Li[NHR] → Sb(NHR)3 ϩ 3 LiCl (1)
2 Sb(NHR)3 → Sb2(NHR)2(µ-NR)2 ϩ 2 NH2R (2)
1 (a) M. A. Paver, C. A. Russell and D. S. Wright, Angew. Chem.,
Int. Ed. Engl., 1995, 34, 1545; (b) M. A. Beswick, M. E. G.
Mosquera and D. S. Wright, J. Chem. Soc., Dalton Trans., 1998,
2437; (c) M. F. Lappert, A. R. Sanger, R. C. Srivastava and P. P.
Power, Metal and Metalloid Amides, Ellis Horwood, Chichester,
1979.
2 M. A. Beswick and D. S. Wright, Coord. Chem. Rev., 1998, 176,
373.
3 K. Moedritzer, Inorg. Chem., 1964, 3, 609.
4 A. Kiennemann, G. Levy, F. Schué and C. Taniélian, J. Organomet.
Chem., 1972, 35, 143.
5 N. Burford, C. L. B. Macdonald, K. N. Robertson and T. S.
Cameron, Inorg. Chem., 1996, 35, 4013.
6 A. J. Edwards, M. A. Paver, M.-A. Rennie, P. R. Raithby, C. A.
Russell and D. S. Wright, J. Chem. Soc., Dalton Trans., 1994,
2963.
12 Sb(NHR)3 → Sb12(µ-NR)18 ϩ 18 NH2R
(3)
In conclusion, these results show that the structure of
the product obtained from reactions between SbCl3 and
lithium primary amides is strongly dependent on the amido
R group but that formation of the twenty four-membered
imidoantimony macrocycles is not dependent on intra-
molecular secondary bonding interactions. The high yield
synthesis of macrocyclic 7 will also enable a study of its host–
guest chemistry, the potential for which was also discussed
for 4.11
7 B. Ross, J. Belz and M. Nieger, Chem. Ber., 1990, 123, 975.
8 A. J. Edwards, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A.
Russell and D. S. Wright, Angew. Chem., Int. Ed. Engl., 1994, 33,
1277.
9 (a) D. Barr, A. J. Edwards, M. A. Paver, P. R. Raithby, M.-A.
Rennie, C. A. Russell and D. S. Wright, Angew. Chem., Int. Ed.
Engl., 1995, 34, 1012; (b) M. A. Beswick, N. L. Cromhout, C. N.
Harmer, M. A. Paver, P. R. Raithby, M.-A. Rennie, A. Steiner and
D. S. Wright, Inorg. Chem., 1997, 36, 1740; (c) A. Bashall, M. A.
Beswick, C. N. Harmer, M. McPartlin, M. A. Paver and D. S.
Wright, J. Chem. Soc., Dalton Trans., 1998, 517.
10 (a) D. Barr, A. J. Edwards, S. Pullen, M. A. Paver, P. R. Raithby,
M.-A. Rennie, C. A. Russell and D. S. Wright, Angew. Chem.,
Int. Ed. Engl., 1994, 33, 1875; (b) R. A. Alton, D. Barr, A. J.
Edwards, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A. Russell
and D. S. Wright, J. Chem. Soc., Chem. Commun., 1994, 1481;
(c) A. Bashall, M. A. Beswick, C. N. Harmer, A. D. Hopkins,
M. McPartlin, M. A. Paver, P. R. Raithby and D. S. Wright,
J. Chem. Soc., Dalton Trans., 1998, 1389; (d) A. Bashall, M. A.
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Acknowledgements
We thank the EPSRC for support and Laporte plc and The
Royal Society for additional supporting funds.
Notes and references
† For a more detailed discussion of the anionic imido and imido–amido
compounds of antimony, see refs. 1a,b and 2.
‡ A solution of SbCl3 (0.050 g, 2.19 mmol) dissolved in thf (10 cm3) was
added to a stirred solution of Li[NH-2,6-Me2C6H3], prepared from
1-NH2-2,6-Me2C6H3 (0.81 cm3, 6.57 mmol) and BunLi (4.1 cm3 of a 1.6
M solution in hexanes), in Et2O (10 cm3) at 0 ЊC which resulted in an
immediate colour change from colourless to yellow-orange and form-
ation of a white precipitate. After warming to room temperature, all
volatiles were removed by vacuum and the remaining solid redissolved
in CH2Cl2 (30 cm3). Filtration afforded a clear yellow filtrate which was
reduced in volume by vacuum to about 5 cm3. Addition of an overlayer
of hexane (20 cm3) followed by solvent diffusion at Ϫ30 ЊC over a
period of days afforded yellow needle-like crystals of 6 (25% recrystal-
lised yield) one of which was used for X-ray diffraction. 1H NMR
(C6D6) δ 7.20–6.55 (m, Ph), 2.85 (s, Me), 2.80 (s, Me), 2.30 (s, Me), 2.25
(s, Me). C32H38Sb2N4 requires C, 53.20; H, 5.30; N, 7.75. Found C,
50.35; H, 5.00; N, 7.10%.
11 M. A. Beswick, M. K. Davies, M. A. Paver, P. R. Raithby, A. Steiner
and D. S. Wright, Angew. Chem., Int. Ed. Engl., 1996, 35,
1508.
§ Crystal data for Sb2(NH-2,6-Me2C6H3)2(µ-N-2,6-C6H3)2 6: M =
12 F. Ando, T. Hayashi, K. Ohashi and J. Koketsu, J. Inorg. Nucl.
Chem., 1975, 37, 2011.
¯
722.16, triclinic, space group P1 (no. 2), a = 7.929(2), b = 10.012(3),
c = 11.075(4) Å, α = 101.00(2), β = 110.705(14), γ = 107.892(14)Њ,
U = 736.9(4) Å3, T = 173(2) K, Z = 1, µ(Mo-Kα) = 1.860 mmϪ1, 3491
reflections measured, 2479 unique (Rint = 0.0297), final R1 = 0.0417 (all
data). Data for 6 were collected on a Bruker SMART-CCD detector
and the structure was solved and refined against F2 using SHELXL97.20
13 W. Clegg, N. A. Compton, R. J. Errington, G. A. Fisher, M. E.
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14 C. J. Carmalt, N. A. Compton, R. J. Errington, G. A. Fisher,
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4008
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