Assembly of Mixed-Metal Cages Using Polyimido Antimony(III) Anions. Syntheses and Structures of [Sb3(NCy)4(HNCy)2]K·2(toluene), [Sb2(NCy)4]2M4 (M = Cu, Ag), and [Sb-(NCy)3]2Pb3 (Cy = Cyclohexyl, C6H11)

Article abstract of DOI:10.1021/ic961108b

Transmetalation reactions of the polyimido Sb(III) anions [Sb₃(NCy)₄(HNCy)₂]^-, [Sb₂(NCy)₄]^2-, and [Sb(NCy)₃]^3- with metal sources allows the logical assembly of cage compounds containing various mixed-metal stoichiometries. The breadth of this approach is illustrated by the syntheses of [Sb(NCy)₄(HNCy)₂]K·2(toluene) (1), containing an early main group metal, [Sb₂(NCy)₄]₂M₄ (M = Cu (2), Ag (3)), containing transition metals, and [Sb(NCy)₃Pb₃] (4), containing a p-block metal. The low-temperature X-ray structures of complexes 1-4 have been determined. Crystal data: 1, monoclinic, space group C2/c, a = 18.418(3) A?, b = 11.457(2) A?, c = 24.798(6) A?, β = 90.24-(2)°, Z = 4; 3, triclinic, space group P1, a = 11.501(2) A?, b = 13.752(3) A?, c = 22.868(5) A?, α = 103.50(3)°, β = 95.89(3)°, γ = 96.71(3)°, Z = 2; 4, triclinic, space group P1, a = 11.071(2) A?, b = 14.892(2) A?, c = 17.262(2) A?, α = 65.36(3)°, β = 74.21(3)°, γ = 70.70(3)°, Z = 2. The structure of 2 has been reported in preliminary form. The K⁺ ion of 1 is coordinated by four of the N centers of the [Sb₃(NCy)₄(HNCy)₂]^- ligand. In addition, β-C(-H)?K interactions involving four of the Cy groups and MeC(-H)?K interactions involving two toluene molecules give the K⁺ ion a 10-coordinate geometry. In 2 and 3, the N centers of two [Sb₂(NCy)₄]^2- dianions symmetrically coordinate a central M₄ square-planar core. The symmetrical complexation of three Pb-(II) centers by two [Sb(NCy)₃]^3- trianions produces an 11-membered polyhedral cage structure in 4.

Full text of DOI:10.1021/ic961108b

1740
Inorg. Chem. 1997, 36, 1740-1744
Ar ticles
Assembly of Mixed-Metal Cages Using Polyimido Antimony(III) Anions. Syntheses and
Structures of [Sb3(NCy)4(HNCy)2]K‚2(toluene), [Sb2(NCy)4]2M4 (M ) Cu, Ag), and [Sb-
(NCy)3]2Pb3 (Cy ) Cyclohexyl, C6H11)
Michael A. Beswick, Natalie L. Cromhout, Christopher N. Harmer, Michael A. Paver,
Paul R. Raithby, Moira-Ann Rennie, Alexander Steiner, and Dominic S. Wright*
Chemistry Department, Cambridge University, Lensfield Road, Cambridge CB2 1EW, U.K.
ReceiVed September 11, 1996X
Transmetalation reactions of the polyimido Sb(III) anions [Sb3(NCy)4(HNCy)2]-, [Sb2(NCy)4]2-, and [Sb(NCy)3]3-
with metal sources allows the logical assembly of cage compounds containing various mixed-metal stoichiometries.
The breadth of this approach is illustrated by the syntheses of [Sb(NCy)4(HNCy)2]K‚2(toluene) (1), containing
an early main group metal, [Sb2(NCy)4]2M4 (M ) Cu (2), Ag (3)), containing transition metals, and [Sb(NCy)3Pb3]
(4), containing a p-block metal. The low-temperature X-ray structures of complexes 1-4 have been determined.
Crystal data: 1, monoclinic, space group C2/c, a ) 18.418(3) Å, b ) 11.457(2) Å, c ) 24.798(6) Å, â ) 90.24-
(2)°, Z ) 4; 3, triclinic, space group P1h, a ) 11.501(2) Å, b ) 13.752(3) Å, c ) 22.868(5) Å, R ) 103.50(3)°,
â ) 95.89(3)°, γ ) 96.71(3)°, Z ) 2; 4, triclinic, space group P1h, a ) 11.071(2) Å, b ) 14.892(2) Å, c )
17.262(2) Å, R ) 65.36(3)°, â ) 74.21(3)°, γ ) 70.70(3)°, Z ) 2. The structure of 2 has been reported in
preliminary form. The K+ ion of 1 is coordinated by four of the N centers of the [Sb3(NCy)4(HNCy)2]- ligand.
In addition, â-C(-H)‚‚‚K interactions involving four of the Cy groups and MeC(-H)‚‚‚K interactions involving
two toluene molecules give the K+ ion a 10-coordinate geometry. In 2 and 3, the N centers of two [Sb2(NCy)4]2-
dianions symmetrically coordinate a central M4 square-planar core. The symmetrical complexation of three Pb-
(II) centers by two [Sb(NCy)3]3- trianions produces an 11-membered polyhedral cage structure in 4.
Introduction
Chart 1
We recently showed that highly reactive dimethylamido Sb-
(III) complexes1-3 can be employed in the syntheses of a family
of polyimido Sb(III) anions.4 The general synthetic strategy
(so called “mixed-metalation”) involves the stepwise deproto-
nation of primary amines (RNH2), using the Sb reagents to effect
the removal of the second proton. Thus, the reaction of the
[Sb(HNCy)4]- (Cy ) C6H11) anion with [Sb(NMe2)3] (1:2
equiv) gives [Sb3(NCy)4(NMe2)2]Li (containing the monoanion
I),4b the deprotonation of [CyNHLi] with the dimer [(Me2N)-
Sb2(µ-NCy)]2 (2:1 equiv) produces [Sb2(NCy)4]2Li4 (containing
the dianion II),4a and the reaction of [CyNHLi] with [Sb-
(NMe2)3] (3:1 equiv) gives [Sb(LiNCy)3]2Li6 (containing the
trianion III).4b
such polyimido Sb(III) anions can function as robust ligands
(not undergoing reduction and/or rearrangement upon ligand
transfer) and provided an enticing preliminary indication of the
potential coordination chemistry of this new class of ligands.5
We report here the further investigation of the transmetalation
reactions of polyimido anions with a range of metal salts. The
rigidity of these ligand systems and their application to the
preparation of mixed-metal cages is illustrated by the syntheses
and structures of the new cage complexes [Sb(NCy)4(HNCy)2]-
K‚2(toluene) (1), containing an early main group metal, [Sb2-
(NCy)4]2M4 (M ) Cu (2),5 Ag (3)), containing transition metals,
and [Sb(NCy)3]2Pb3 (4), containing a p-block metal.
The synthesis of [Sb2(NCy)4]2Cu4 (2), from the metal
exchange reaction of [Sb2(NCy)4]2Li4 with CuCl, illustrated that
X Abstract published in AdVance ACS Abstracts, March 15, 1997.
(1) (a) Moedritzer, K. Inorg. Chem. 1964, 3, 609. (b) Kiennemann, A.;
Levy, G.; Schue´, F.; Tanie´lian, J. J. Organomet. Chem. 1972, 35, 143.
(2) (a) Ando, F.; Hayashi, T.; Ohashi, K.; Koketsu, J. J. Inorg. Nucl. Chem.
1975, 37, 2011. (b) Clegg, W.; Compton, N. A.; Errington, R. J.;
Fischer, G. A.; Green, M. E.; Hockless, D. R.; Norman, N. C. Inorg.
Chem. 1991, 30, 4680.
(3) Edwards, A. J.; Paver, M. A.; Raithby, P. R.; Rennie, M.-A.; Russell,
C. A.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1994, 2963.
(4) (a) Alton, R. A.; Barr, D.; Edwards, A. J.; Paver, M. A.; Raithby, P.
R.; Rennie, M.-A.; Russell, C. A.; Wright, D. S. J. Chem. Soc., Chem.
Commun. 1994, 1481. (b) Edwards, A. J.; Paver, M. A.; Raithby, P.
R.; Rennie, M.-A.; Russell, C. A.; Wright, D. S. Angew. Chem. 1994,
106, 1334; Angew. Chem., Int. Ed. Engl. 1994, 33, 1277. (c) Barr, D.;
Beswick, M. A.; Edwards, A. J.; Galsworthy, J. R.; Paver, M. A.;
Rennie, M.-A.; Russell, C. A.; Raithby, P. R.; Verhorevoort K. L.;
Wright, D. S. Inorg. Chim. Acta 1996, 248, 9.
(5) Edwards, A. J.; Paver, M. A.; Rennie, M.-A.; Russell, C. A.; Raithby,
P. R.; Wright, D. S. Angew. Chem. 1994, 106, 1960; Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1875.
S0020-1669(96)01108-1 CCC: $14.00 © 1997 American Chemical Society

Mixed-Metal Cages
Inorganic Chemistry, Vol. 36, No. 9, 1997 1741
Table 1. Crystal Data for 1, 3, and 4
empirical fomula
C50H84KN6Sb3 1
1173.58
C52H96N8OSb4Ag4 3
C43H74N6Pb3Sb2 4
1540.15
fw
1767.85
crystal system
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
monoclinic
C2/c
18.418(3)
11.457(2)
24.798(6)
triclinic
triclinic
P1h
11.071(2)
14.892(3)
17.262(3)
65.36(3)
74.21(3)
70.70(3)
2411.3(8)
2
2.121
11.578
-120(2)
0.71073
R1 ) 0.091, wR2 ) 0.237
R1 ) 0.134, wR2 ) 0.296
P1h
11.501(2)
95.89(3)
22.868(5)
103.50(3)
95.89(3)
96.71(3)
3461.1(1)
2
2.679
2.679
90.24(2)
5233(2)
4
1.490
1.655
-120(2)
0.71073
R1 ) 0.026, wR2 ) 0.063
R1 ) 0.030, wR2 ) 0.066
F
calc (g cm-3
)
µ (mm-1
T (°C)
λ (Å)
)
-120(2)
0.71073
R1 ) 0.051, wR2 ) 0.174
R1 ) 0.079, wR2 ) 0.283
R indices for F > 4σ(F)a
R indices for all data
2
4
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑wFo ]0.5, w ) 1/[σ2(Fo ) + (xP)2 + yP], P ) (Fo + 2Fc2)/3.
Table 2. Selected Bond Lengths and Angles for
[(CyNH)2Sb3(NCy)4]K‚2(toluene) (1)
Scheme 1
Bond Lengths (Å)b
Sb(1)-N(3)
Sb(1)-N(2)
Sb(2)-N(1)
Sb(2)-N(2)
Sb(2)-N(3)
2.093(3)
2.220(3)
2.103(4)
2.004(3)
2.055(3)
K(1)-N(1)
2.803(4)
2.813(3)
range 2.77-2.95
3.05
K(1)-N(3)
â-C(Cy)-H‚‚‚K
CH2-H‚‚‚K
Bond Angles (deg)
87.9(1)
N(3)-Sb(1)-N(2a)
N(3)-Sb(1)-N(2)
N(2)-Sb(2)-N(3)
N(1)-Sb(1)-N(2)
N(1)-Sb(1)-N(3)
Sb(1)-N(3)-K(1)
Sb(2)-N(1)-K(1)
97.8(1)
98.7(1)
65.8(1)
69.9(1)
167.1(2)
74.4(1)
80.0(1)
96.0(1)
94.4(1)
94.6(1)
Sb(2)-N(3)-K(1)
N(1)-K(1)-N(3)
N(3)-K(1)-N(3a)a
N(1)-K(1)-N(1a)a
a Symmetry transformation used to generate equivalent atoms: (a)
3
-x + 1, y, z + /2.
Results and Discussion
-CH2- groups for the terminal and bridging NCy groups of 1
are not distinct at room temperature, there are two resonances
for the R-C(-H) groups for these ligand environments. The
1H and 13C NMR spectra of 1 also illustrate that the reaction
producing 1 involves metal exchange of Li for K rather than
producing a co-complex containing [KtBuO], as occurs in the
reaction of [Sb(NCy)3]Li6 with [KtBuO].6
The low-temperature (-120 °C) X-ray structures of com-
plexes 1-4 were obtained. Since the structure of 2 has already
been communicated,5 it will not be appropriate to discuss this
complex at length here, except by way of comparison. Details
of the structural refinements of complexes 1, 3, and 4 are shown
in Table 1. Tables 2-4 give selected bond lengths and angles
for 1, 3, and 4, respectively.
The low-temperature X-ray structure of 1 shows it to be the
heterobimetallic complex [(CyNH)2Sb3(NCy)4]K‚2(toluene).
The [(CyNH)2Sb(NCy)4]- anion and its mode of complexation
to the alkali metal cation are similar to those occurring in the
precursor [(Me2N)2Sb3(NCy)4]Li (Figure 1).4b Similar to that
of the latter, the alkali metal cation of 1 is complexed by two
of the µ-NCy groups of the anion [N(3)-K(1) 2.813(3) Å] and
by both of the terminal NHCy groups [N(1)-K(1) 2.803(4) Å].
The accommodation of the larger K+ cation into this framework
results in only minor distortions in the N-Sb-N angles in the
Sb3N6 unit of 1 compared to those in [(Me2N)2Sb3(NCy)4]Li.4b
The highly distorted square-based pyramidal geometry of the
K+ ion in 1 (average N-K-N 67.2°) leaves the cation open to
The polyimido Sb(III) anions I-III were prepared in the
manner described previously.4 [Sb(NCy)4(HNCy)2]K‚2(toluene)
(1) was prepared by the two-step in situ reaction of [Sb3(NCy)4-
(NMe2)2]Li with [CyNH2] (1:2 equiv, respectively), resulting
in the replacement of the terminal NMe2 groups for NHCy,
followed by metal exchange with [KtBuO] in toluene as the
solvent. [Sb2(NCy)4]2M4 [M ) Cu (2),5 Ag (3)] were synthe-
sized in good yields (60% for 2 and 52% for 3) by the
transmetalation reactions of [Sb2(NCy)4]2Li4 with CuCl and Ag-
(AcO) (AcO ) MeCO2-), respectively. These reactions occur
rapidly at room temperature in toluene with little or no
decomposition into the metals. However, attempts to prepare
3 using AgCl resulted in decomposition into Ag metal. The
preparation of 4 was accomplished by the transmetalation
reaction of [Sb(NCy)3]2Li6 with [Cp2Pb] (1:3 equiv) in toluene.
The reaction requires ca. 1 equiv of TMEDA [(Me2NCH2)2] to
dissolve the insoluble product initially formed (the complex then
being crystallized in 50% yield). (See Scheme 1)
Prior to their investigation by low-temperature X-ray crystal-
lography, complexes 1-4 were basically characterized by
obtaining their melting points and elemental analyses and by
1H NMR spectroscopy. All the complexes are surprisingly
thermally stable (up to ca. 200 °C for 1). Although satisfactory
elemental analyses (C, H, N) were obtained for 1-3, the C
content of 4 was found to be consistently slightly high. 1H NMR
studies of all the complexes were not particularly informative
due to the broadness of the Cy resonances found in the region
δ 0.5-2.5. 13C NMR studies were similarly uninformative for
complexes 3 and 4 (particularly for 3, where its low solubility
even in THF led to weak resonances). However, although the
(6) Edwards, A. J.; Paver, M. A.; Rennie, M.-A.; Russell, C. A.; Raithby,
P. R.; Wright, D. S. Angew. Chem. 1995, 107, 1088; Angew. Chem.,
Int. Ed. Engl. 1995, 34, 1012.

1742 Inorganic Chemistry, Vol. 36, No. 9, 1997
Beswick et al.
Table 3. Selected Bond Lengths and Angles for
[Sb2(NCy)4]Ag4‚THF (3)
Bond Lengths (Å)
Sb(1)-N(1)
Sb(1)-N(2)
Sb(2)-N(1)
Sb(2)-N(2)
Sb(3)-N(7)
Sb(3)-N(8)
Sb(4)-N(7)
Sb(4)-N(8)
2.07(1)
2.07(1)
2.07(1)
2.08(1)
2.07(1)
2.068(9)
2.10(1)
2.089(9)
Sb(1)-N(4)
2.04(1)
2.044(9)
2.94(1)
2.04(1)
2.81
2.154
3.158
Sb(2)-N(3)
Sb(3)-N(5)
Sb(4)-N(6)
av Ag‚‚‚Ag
av N(3-6)-Ag
av N(1,2,7,8)‚‚‚Ag
Bond Angles (deg)
Sb2N2 rings
av N-Sb-N
av Sb-N-Sb
av Ag‚‚‚Ag‚‚‚Ag
90.0
165.4
80.7
77.8
99.2
av N-Ag-N
av Ag-N-Ag
Table 4. Selected Bond Lengths and Angles for [Sb(NCy)3]2Pb3 (4)
Bond Lengths (Å)
Sb(1)-N(1)
Sb(1)-N(2)
Sb(1)-N(3)
Sb(2)-N(4)
Sb(2)-N(5)
Sb(2)-N(6)
Pb(1)-N(1)
Pb(1)-N(3)
Pb(1)-N(5)
Pb(1)-N(6)
Pb(2)-N(2)
2.06(3)
1.98(3)
2.05(3)
2.00(3)
2.08(3)
2.06(2)
2.43(3)
2.43(3)
2.36(3)
2.39(2)
2.40(2)
Pb(2)-N(3)
Pb(2)-N(4)
Pb(2)-N(6)
Pb(3)-N(1)
Pb(3)-N(2)
Pb(3)-N(4)
Pb(3)-N(5)
av Pb‚‚‚Pb
2.41(3)
2.39(3)
2.44(2)
2.36(3)
2.47(3)
2.46(3)
2.45(3)
3.69
av Pb‚‚‚Sb
3.46
Angles (deg)
85.7
av N-Sb-N
Sb(µ-N)2Pb rings
av Sb-N-Pb
av N-Pb-N
Pb(µ-N)2Pb rings
av Pb-N-Pb
av N-Pb-N
99.6
74.6
101.6
70.0
further coordination. This low coordination number leads to
further agostic C(-H)‚‚‚K+ interactions with four of the â-C-H
positions of the [(CyNH)2Sb(NCy)4]- anion (range 2.77-2.95
Å) and with the Me groups of two lattice-bound toluene
molecules (ca. 3.05 Å) (Figure 1b). Thus, the coordination
number of the K+ ion (including these loose interactions) is
10. Arene‚‚‚K+ π-interactions have been observed in the solid-
state structures of a number of metalloorganic derivatives (with
typical arene centroid‚‚‚K distances of 3.18-3.59 Å),7 and
agostic aliphatic C-H‚‚‚K+ interactions are now a well-
established feature in the structures of organopotassium com-
plexes (typically 3.0-3.4 Å).8 The nature of this bonding is
most likely to be electrostatic, rather than covalent.
The low-temperature X-ray structures of 25 and 3 show that
both complexes contain central M4 square planar cores (M )
Cu (2), Ag (3)) which are complexed by two [Sb2(NCy)4]2-
anions (the structure of 3 is shown in Figure 2). In 3, there is
one lattice-bound THF ligand per molecule in the unit cell which
is disordered over two sites.
Figure 1. (a) Structure of [(CyNH)2Sb3(NCy)4]K‚2(toluene) (1).
Toluene molecules are omitted for clarity, and thermal ellipsoids are
drawn at the 50% probability level. (b) Structure of 1 showing agostic
C-H‚‚‚K interactions with â-C-H and toluene CH3 groups. Thermal
ellipsoids are drawn at the 50% probability level.
found in other amido Sb complexes.9 The stabilizations of the
M4 cores in both complexes are also similar, with the pendant
CyN- arms of each of the terminal [Sb2(NCy)4]2- ligands
forming M-(µ-N)-M bridges at opposite edges of the M4 units
(average Cu-N 1.93 Å in 2, average Ag-N 2.15 Å in 3).
Presumably, the M4 fragments in 2 and 3 are largely held
together by these M-(µ-N)-M bridges, which result in roughly
linear geometries for the Cu or Ag centers in the cores (average
N-Cu-N 168.7° in 2, average N-Ag-N 165.4° in 3).
However, longer range M‚‚‚(µ-N)‚‚‚M interactions also occur
with the Sb-bridging Cy centers of the [Sb2(NCy)4]2- ligands
(average Cu‚‚‚N 2.75 Å in 2 and average Ag‚‚‚N 3.16 Å in 3).
As a result of these weak interactions, the [Sb(µ-NCy)]2 rings
of the dianions in both complexes are forced into distinctly
puckered conformations so as to bring the µ-N centers of each
into closer contact with opposite M‚‚‚M edges of the M4 core
(the µ-N wingtips of the butterfly-shaped Sb2N2 rings are
inclined at ca. 155.2° in 25 and 151.7° in 3 with respect to
Sb‚‚‚Sb contacts).
The geometries of the [Sb2(NCy)4]2- anions of 2 and 3 are
very similar, with the average Sb-N distances in both com-
plexes (2.05-2.08 Å in 2; cf. 2.07-2.09 Å in 3) and the angles
within the Sb2N2 rings (average Sb-N-Sb 99.6° and average
N-Sb-N 78.2° in 2; cf. average Sb-N-Sb 99.2° and average
N-Sb-N 77.8° in 3) falling in the same range. The Sb-N
distances within the [Sb2(NCy)4]2- dianions are typical of those
(7) For example, see: (a) Schavevien, C. J.; van Mechelen, J. B.
Organometallics 1991, 10, 1704. (b) Fuentes, G. R.; Coan, P. S.; Streih,
W. E.; Caulton, K. G. Polyhedron 1991, 10, 2371. (c) Geary, M. J.;
Cayton, R. H.; Folting, K.; Huffman, J. C.; Caulton, K. G. Polyhedron
1992, 11, 1369. (d) Hitchcock, P. B.; Lappert, M. F.; Lawless, G. A.;
Royo, B. J. Chem. Soc., Chem. Commun. 1993, 554.
The possibility of M‚‚‚M bonding in the M4 units of 2 and 3
cannot be discounted. The Cu‚‚‚Cu distances in the core of 2
(9) Bjo¨rgvisson, M.; Roesky, H. W.; Pauer, F.; Sheldrick, G. M. Chem.
Ber. 1992, 125, 767. Neubert, W.; Pritzkow, H.; Latscha, H. P. Angew.
Chem. 1988, 100, 298; Angew. Chem., Int. Ed. Engl. 1988, 27, 287.
(8) Schade, C.; Schleyer, P. v. R. AdV. Organomet. Chem. 1987, 27, 169
and references therein.

Mixed-Metal Cages
Inorganic Chemistry, Vol. 36, No. 9, 1997 1743
Figure 3. Structure of [Sb(NCy)3]2Pb3 (4). Thermal ellipsoids are
drawn at the 50% probability level.
metalloorganic Pb(II) complexes, e.g., average 2.33 Å in [Pb-
(µ-N)C(tBu)Ph)3Li‚THF],14 where the Pb(II) atom has a more
typical pyramidal, three-coordinate arrangement. This square-
based pyramidal geometry is symptomatic of the stereochemical
activity of the exo lone pairs on the Pb(II) atoms and has
precedent in the structures of [{X(‚‚NSiMe3)2}2Pb] [X )
Ph2P, C({4-F3C}C6H4)].15
Clearly the [Sb2N6Pb3] core of 4 is held together by N-Sb
and N-Pb bonding, rather than any significant metal‚‚‚metal
interactions (average Pb‚‚‚Sb 3.46 and average Pb‚‚‚Pb 3.69
Å; cf. Pb-Pb 3.00-3.24 Å in the trigonal bipyramidal cage
[Pb5]2- 16 and the estimated Pb-Sb covalent bond length of
ca. 2.80 Å11). However, it is nonetheless interesting to note
that the trigonal bipyramidal [Sb2Pb3] metal fragment of 4 is
(conceptually) an n + 1 (Wade’s rule) polyhedron. To our
knowledge, the cage arrangement and (group 14/15 metal)
stoichiometry of this complex are unprecedented structural
features.
A number of alkali metal complexes containing group 14
imido anions (related to those present in 1-4) have been
structurally characterized,17 and Veith has prepared several
mixed-metal compounds using the transmetalation reactions of
analogous imido silicon anions with main group metal salts.18
However, the coordination chemistry of the Sb(III) imido anions
has not been investigated until these current studies. The
formation of complexes 1-4 illustrates the application of
polyimido Sb(III) anions in the construction of heterometallic
cage compounds containing a variety of mixed-metal stoichi-
ometries. These polyimido anions are robust ligands which do
not rearrange upon reaction.
Figure 2. Structure of [Sb2(NCy)4]Ag4‚THF (3). THF lattice solvation
is omitted for clarity, and thermal ellipsoids are drawn at the 50%
probability level.
(average 2.57 Å),5 although somewhat longer than those
observed in [CuCH2SiMe3]4 (2.42 Å),10 are almost identical to
those present in Cu metal (2.56 Å).11 The Ag‚‚‚Ag distances
in 3 (average 2.81 Å) are similar both to those in Ag metal
(2.88 Å)11 and to those observed in the structures of a number
of Ag4 complexes (ca. 3.0-3.1 Å).12
A structural motif similar to that observed in 2 and 3 was
observed recently in [C6H4O2(Me2SiNtBu)2]2M4 (M ) Cu, Ag),
in which two essentially organic dianions stabilize M4 square
planar cores (M ) Cu, average Cu‚‚‚Cu 2.67 Å; M ) Ag,
average Ag‚‚‚Ag 3.0 Å).13 However, whereas in both 2 and 3
the four N donor centers of each [Sb2(NCy)4]2- dianion (two
pendant CyN, two µ-NCy) bridge all four sides of the M4 cores,
in [C6H4O2(Me2SiNtBu)2]2M4 the four donor centers of each
t
ligand (two pendant BuN, two O) bridge only two adjacent
sides of the M4 fragments.
The low-temperature X-ray structure of 4 shows that it is an
11-membered polyhedron in which two [Sb(NCy)3] units
symmetrically complex three Pb(II) centers at the equator of
the [Sb2N6Pb3] cage (Figure 3). The [Sb(NCy)3] units of 4 are
similar to those found in the cage structure of [Sb(NCH2CH2-
Ph)3]2Li6‚2THF3b However, although the Sb-N bond lengths
are similar to those found in [Sb(NCH2CH2Ph)3]2Li6‚2THF3b
(average 2.04 Å in 4; cf. 2.06 Å), there is a marked reduction
in the N-Sb-N angles of 4 (average N-Sb-N 85.7°; cf.
average N-Sb-N 94.5°). Each of the N centers of the [Sb-
(NCy)3] moieties µ2-bridge the Pb(II) atoms of the central Pb3
triangle of 4 (average Pb-N 2.42 Å, average Pb-(µ-N)-Pb
99.6°), resulting in similar square-based pyramidal geometries
for all of the Pb centers (average N-Pb-N 74.6°). Presumably
as a result of the relatively high coordination number of 4 for
the Pb(II) atoms, the Pb-N bonds connecting the [Sb(NCy)3]
and Pb3 units are slightly longer than those normally found in
Experimental Section
General Preparative Techniques. All the reactions were under-
taken under dry, O2-free argon using a vacuum line and standard inert-
(14) Edwards, A. J.; Paver, M. A.; Raithby, P. R.; Russell, C. A.; Wright,
D. S. J. Chem. Soc., Chem. Commun. 1993, 1086.
(15) Kiliman, U.; Noltemeyer, N.; Edelmann, F. T. J. Organomet. Chem.
1993, 35, 443.
(16) Edwards, P. A.; Corbett, J. D. Inorg. Chem. 1977, 16, 903.
(17) (a) Zsolnai, L.; Huttner G.; Driess, M. Angew. Chem. 1993, 105, 1549;
Angew. Chem., Int. Ed. Engl. 1993, 32, 1439. (b) Brauer, D. J.; Bu¨rger,
H.; Liewald, G. L.; Wilke, J. J. Organomet. Chem. 1985, 287, 305.
(c) Brauer, D. J.; Bu¨rger, H.; Liewald, G. L. J. Organomet. Chem.
1986, 308, 119. (d) Veith, M.; Spaniol, V.; Po¨hlmann, J.; Gross, F.;
Huch,V. Chem. Ber. 1993, 126, 2625. (e) Scherer, O. J.; Wolmer-
sha¨user, G.; Conrad, H. Angew. Chem. 1983, 95, 427; Angew. Chem.,
Int. Ed. Engl. 1983, 22, 404. (f) Neubert, W.; Pritkow, W.; Latscha,
H. P. Angew. Chem. 1988, 100, 298; Angew. Chem., Int. Ed. Engl.
1988, 27, 287. (g) Bjo¨rgvinsson, M.; Roesky, H. W.; Pauer, F.;
Sheldrick, G. M. Chem. Ber. 1992, 125, 767.
(10) Miele, P.; Foulen, J. D.; Hovnanian, N.; Durand, J.; Cot, L. J. Solid
State Inorg. Chem. 1992, 29, 573.
(11) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
Wiley: New York, 1988. Huheey, J. E. Inorganic Chemistry, 3rd
ed.: Harper and Row: New York, 1983.
(12) van Koten, G.; Noltes, J. G. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Pergamon:
London, 1982; p 709.
(13) Veith, M.; Woll, K. L. Chem. Ber. 1993, 126, 2383.
(18) Veith, M. Chem. ReV. 1990, 90, 3.

1744 Inorganic Chemistry, Vol. 36, No. 9, 1997
Beswick et al.
atmosphere techniques.19 THF and toluene were dried by distillation
over Na/benzophenone, and hexane was distilled over Na. TMEDA
was dried using molecular sieves (13X). The syntheses of the starting
materials [Sb3(NCy)4(NMe2)2]Li (containing the monoanion I),4a
[Sb2(NCy)4]2Li4 (containing the dianion II),4b and [Sb(LiNCy)3]2Li6
(containing the trianion III)4b were carried out using literature methods.
Complexes 1-4 were isolated and characterized with the aid of a N2-
filled glovebox (Miller-Howe; fitted with a Belle internal circulation
system). Melting points were determined by using a conventional
apparatus and sealing samples in capillaries under N2. Elemental
analyses (C, H, N) were performed by first sealing samples in airtight
aluminum boats (1-2 mg) prior to analysis using a Perkin-Elmer 240
elemental analyzer. 1H NMR spectra were recorded on a Bruker WH
250 MHz spectrometer, using the NMR solvents as internal reference
standards.
Synthesis of 1. CyNH2 (0.50 g, 5.0 mmol) was added to a solution
of [Sb3(NCy)4(NMe2)2]Li (1.77 g, 2.5 mmol) in toluene (10 mL). The
mixture was stirred at 20 °C (0.5 h) before a solution of K(tBuO) (0.28
g, 2.5 mmol) in toluene (10 mL) was added. Further stirring at 20 °C
(0.5 h) gave a cloudy, dark yellow solution. This was filtered (porosity
3, Celite) and reduced to ca. 5 mL under vacuum, and hexane (15 mL)
was added, giving a yellow precipitate. The precipitate was heated
back into solution, and storage at 20 °C (24 h) yielded light yellow
crystals of 1. The toluene solvent found in the solid-state structure of
the complex was liberated on isolating the complex and placing it under
vacuum (30 min, 0.1 atm). The following data were obtained for the
powder produced. Yield: 1.34 g (46%). Dec: 200 °C, finally at 240
°C. 1H NMR (+25 °C, 250 MHz, benzene-d6): δ 2.50 (mult), 1.00-
2.20 (overlapping mult) (Cy groups); the N-H could not be observed.
13C NMR (+25 °C, 250 MHz, THF-d8): δ 57.9 (d, C(R)-H, µ-NCy),
54.4 (d) [d, C(R)-H, terminal NCy], 46.0 (t), 43.3 (t), and 40.2 (t)
[-CH2-, NCy], 21.4 [q, -CH3, toluene]. Anal. Found: C, 42.8; H,
6.8; N, 8.4. Calcd: C, 43.7; H, 7.1; N, 8.5.
precipitate. The mixture was heated to reflux, and TMEDA ({Me2-
NCH2}2) was added dropwise until almost all of the solid had dissolved
(ca. 1 mL). The solution was filtered while hot (porosity 3, Celite)
and the filtrate reduced under vacuum to ca. 10 mL, producing a yellow
powder. The solid was heated into solution, and storage at 20 °C (2
days) gave large yellow cubic crystals of 4. Yield: 0.72 g (50%).
Dec: 195-200 °C. 1H NMR (+25 °C, 250 MHz, benzene-d6): δ 1.5-
2.5 (br overlapping mult, Cy groups). 13C NMR (+25 °C, 250 MHz,
benzene-d6): δ 51.4 (s) [C(R)-H, NCy], 46.2 (t), 42.1 (t), and 38.0 (t)
[-CH2-, NCy]. Anal. Found: C, 31.7; H, 4.5; N, 5.6. Calcd: C,
30.0; H, 4.2; N, 5.8.
X-ray Structure Determinations. Crystals were mounted directly
from solution under argon using a perfluorocarbon oil, which protected
them from atmospheric O2 and moisture.21 The oil froze at reduced
temperatures and held the crystal static in the X-ray beam. Data were
collected on a Stoe-Siemens AED four-circle diffractometer, and
semiempirical absorption corrections based on ψ scans were employed
for all complexes.22 For 1, distance and isotropic thermal parameter
restraints were employed for the disordered toluene molecules. All
the C atoms of the toluene were refined isotropically, with all other
non-hydrogen atoms being refined anistropically. For 3, distance
restraints were employed for the disordered lattice-bound THF molecule
(disordered over two sites with 50% occupancy in each), with only the
Ag and Sb atoms being refined anisotropically. For 4, all non-hydrogen
atoms were refined anisotropically. For all complexes, the H atoms
were fixed geometrically. All structures were solved by direct methods
(SHELXTL PLUS) and refined by full-matrix least-squares calculations
on F2 (SHELXL-9323). Details of the structure refinements for all
complexes are shown in Table 1. Atom coordinates, bond lengths and
angles, and thermal parameters have been deposited with the Cambridge
Crystallography Data Centre.
Acknowledgment. We gratefully acknowledge the EPSRC
(M.A.B., C.N.H., P.R.R., D.S.W.), The Royal Society (P.R.R.,
D.S.W.), the European Community (fellowship for A.S.), Jesus
College, Cambridge (fellowship for M.A.P.), the Cambridge
Crystallography Data Centre (M.-A.R.), and the ORS and
Commonwealth Trust (N.L.C.) for financial support.
Synthesis of 3. Ag(AcO) (4.0 g, 5.48 mmol) was added to a solution
of [Sb2(NCy)4]2Li2 (1.77 g, 1.37 mmol) in THF (20 mL). The mixture
was stirred at 20 °C (24 h). Filtration (porosity 3, Celite) removed the
decomposition products (principally Ag metal), giving a red-brown
solution. Reduction of the filtrate to ca. 5 mL under vacuum and
addition of hexane (15 mL) gave a precipitate of 3. Yield: 1.25 g
(52%). Dec: 115 °C. 1H NMR (+25 °C, 250 MHz, benzene-d6): δ
2.5-1.2 (br overlapping mult, Cy groups), 3.71 (mult), 1.38 (mult)
(THF); accurate integration could not be obtained due to the presence
of overlapping multiplets in the Cy region. 13C NMR (+25 °C, 250
MHz, THF-d8): δ 51.9 (d, C(R)-H, NCy), 47.0 (t), 42.2 (t) and 37.0
(t) [-CH2-, NCy]. Anal. Found: C, 35.4; H, 5.6; N, 6.0. Calcd:
C, 35.3; H, 5.4; N, 6.3. The elemental analysis confirms that the THF
lattice solvation is retained upon isolation of 3. Crystals suitable for
X-ray diffraction were grown from THF solution
Supporting Information Available: X-ray crystallographic files,
in CIF format, for compounds 1, 3, and 4 are available on the Internet
only. Access information is given on any current masthead page.
IC961108B
(20) Health and safety warning: Great care should be exercised in the
disposal of the black residue formed after sublimation of [Cp2Pb] for
a prolonged period. Sudden exposure can lead to a Very violent
exothermic reaction followed by explosion (do not attempt to fight
initial fire). Never add concentrated acids.
(21) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615.
(22) Sheldrick, G. M. XEMP, program for X-ray structure adsorption.
(23) Sheldrick, G. M., SHELXL-93, structure refinement package. Uni-
versity of Go¨ttingen, 1993.
Synthesis of 4. [Sb(NCy)3]2Li6 (0.712 g, 2.0 mmol) and [Cp2Pb]20
(1.01 g, 3.0 mmol) were dissolved in toluene (20 mL), giving a yellow
(19) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; Wiley: New York, 1986.