Synthesis of molecular lead-pnictogen compounds including [Pb 4(SbSiiPr3)6], the first structurally characterised compound with a lead-antimony bond

Article abstract of DOI:10.1039/b921473a

The first structurally characterised lead(ii) antimony compound with a chemical bond between lead and antimony, [Pb₄(SbSiiPr ₃)₆] (3), was obtained by the reaction of iPr ₃SiSb-(SiMe₃)₂ with PbCl₂ in Et ₂O at 0 °C. The Pb₄Sb₆ cage structure can be described as a Pb₄Sb₄ heterocube where two SbSiiPr ₃ edges are replaced by (SbSiiPr₃)₂. The average Pb-Sb bond length is 297.7 pm. The heterocubane compounds [PbESi-tBu₂Ph]₄ (E = P, As) were obtained from the reactions of Pb{N(SiMe₃)₂}₂ with tBu ₂PhSiEH₂. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b921473a

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Synthesis of molecular lead–pnictogen compounds including
[Pb4(SbSiiPr3)6], the first structurally characterised compound
with a lead–antimony bondw
a
ab
¨
Stephan Traut and Carsten von Hanisch*
Received (in Cambridge, UK) 14th October 2009, Accepted 22nd December 2009
First published as an Advance Article on the web 22nd January 2010
DOI: 10.1039/b921473a
The first structurally characterised lead(II) antimony compound
with chemical bond between lead and antimony,
The 31P{1H} NMR spectrum shows a singlet signal with a
a
significant high field shift at ꢀ512.7 ppm. Similarly strong high
field shifts were observed for tin–phosphorus cage compounds
such as [SnPSiiPr3]6.5
[Pb4(SbSiiPr3)6] (3), was obtained by the reaction of iPr3SiSb-
(SiMe3)2 with PbCl2 in Et2O at 0 1C. The Pb4Sb6 cage structure
can be described as a Pb4Sb4 heterocube where two SbSiiPr3
edges are replaced by (SbSiiPr3)2. The average Pb–Sb
bond length is 297.7 pm. The heterocubane compounds
[PbESi-tBu2Ph]4 (E = P, As) were obtained from the reactions
of Pb{N(SiMe3)2}2 with tBu2PhSiEH2.
[PbAsSitBu2Ph]4ꢁ2THF (2) was obtained from the reaction
of
Pb{N(SiMe3)2}2
with
the
primary
silylarsine
ꢀ
tBu2PhSiAsH2.z It crystallises in the triclinic space group P1
with four THF molecules in the elementary cell.y The
molecular structure (Fig. 2) is almost identical to the
phosphorus compound 1, but with AsSitBu2Ph groups as
building blocks instead of the PSitBu2Ph fragments. The
average Pb–As–Pb angle is 98.921 and the average As–Pb–As
angle is 80.451. The As–Pb bond length are between 279.84
and 283.63 pm and comparable with the bond lengths in the
hexagonal prism [PbAsSiiPr3]6 (279.41–283.72 pm).2g
Molecular compounds of group 14/15 elements have been
investigated well by different research groups.1 However, the
systems Pb/E (E = P, As) are pretty scarce.2 Examples are
the cyclic compound [Pb{P(SiMe3)2}2]2 obtained from the
reaction of Pb{N(SiMe3)2}2 with HP(SiMe3)2 or the hexagonal
prism [PbAsSiiPr3]6 which was synthesised by the reaction of
iPr3SiAs(SiMe3)2 with PbCl2. Schumann described the lead(IV)
pnictogen compounds E(PbR3)3 (E = P, As, Sb; R = Me, Ph)
and Ph3PbEPh2 (E = As, Sb), but to the best of our
knowledge, no structure information of these compounds
has been made available so far. Moreover, the quaternary
phase K8PbNbAs5 containing Pb–As bonds is known.3
We succeeded in synthesising and structurally characterising
a lead–antimony compound produced by the reaction of
iPr3SiSb(SiMe3)2 with PbCl2 in Et2O at 0 1C. Black crystals
form during a period of three weeks at ꢀ35 1C. Crystal
structure analysis shows the formation of the cage compound
[Pb4(SbSiiPr3)6] (3).z Compound 3 crystallises in the mono-
clinic space group P21/c.y The Pb4Sb6 cage structure can be
described as a Pb4Sb4 heterocube where two SbSiiPr3 corners
are replaced by (SbSiiPr3)2 (Fig. 3). The two remaining
SbSiiPr3 corners (Sb(5) and Sb(6)) coordinate m3 to three Pb
Besides fundamental aspects of the formation and stability
of chemical bonds between heavy main group elements,
binary, ternary, and quaternary phases of these elements are
of considerable interest due to their potential use as thermo-
electrics. Cluster compounds of the element combination
Pb/As and Pb/Sb are potential precursors of such materials.4
The reaction of Pb{N(SiMe3)2}2 and tBu2PhSiPH2 at a
molar ratio of 1 : 1 leads to the formation of [PbPSitBu2Ph]4
(1) which can be isolated as orange crystals by cooling the
reaction mixture to 4 1C.z 1 crystallises in the triclinic space
ꢀ
group P1 and consists of a distorted Pb4P4 cube, the average
Pb–P–Pb angle is 98.021 and the average P–Pb–P angle is
81.591 (Fig. 1).y The deviation of these angles from 901
probably is a result of the large difference of the covalent radii
of Pb and P atoms. The P–Pb bond lengths are between
271.1(4) and 274.6(4) pm long. For comparison, the endocyclic
Pb–P bond lengths in the cyclic compound [Pb{P(SiMe3)2}2]2
are in the same range (274.7 and 279.6 pm).
a Institut fur Anorganische Chemie, KIT, Campus Sud,
Kaiserstr. 12 D-76131 Karlsruhe, Germany
¨
¨
Fig. 1 Molecular structure of 1; thermal ellipsoids represent a 40%
probability level, hydrogen atoms are not shown, selected bond lengths
(pm) and angles (1): P–Pb 271.1(4)–274.6(4), P–Si 223.1(5)–225.3(5);
Pb–P–Pb 97.34(1)–99.02(1), P–Pb–P 80.39(1)–82.61(1).
b Institut fur Nanotechnologie, KIT, Campus Nord, Postfach 3640
¨
D-76021 Karlsruhe, Germany. E-mail: carsten.vonhaenisch@kit.edu
w CCDC 751816–751818. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b921473a
ꢂc
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five-membered Pb2Sb3 rings. The formation of the antimony
barbells probably results from a redox process with the
formation of elemental lead as a by-product. The Pb–Sb bonds
are between 294.56(1) and 301.43(1) pm long and are in the
range expected for the Pb–Sb bond length (the sum of the
covalent radii is about 295 pm). The average Sb–Sb bond
length is 282.09 pm and, hence, exactly corresponds to the sum
of the covalent radii (Sb 141 pm). It is in the same range as in
other antimony compounds with Sb–Sb bonds such as
[Sb4(AsSiiPr3)4] (Sb–Sb 288–289 pm).6
To sum up, pnictogen compounds with large silyl groups
are possible precursors to achieve pnictogen bridged lead
compounds. It is proposed to carry out further studies to
achieve chemical bonds between bismuth and tin as well
as bismuth and lead. Such compounds are of fundamental
interest concerning the formation and stability of bonds
between these elements. Moreover, such compounds are
promising precursors for thermoelectric devices.
Fig. 2 Molecular structure of 2; thermal ellipsoids represent a 40%
probability level, hydrogen atoms are not shown, selected bond lengths
(pm) and angles (1); As–Pb 279.84(1)–283.63(1), As–Si 235.1(2)–235.8(2);
Pb–As–Pb 97.68(4)–100.16(4), As–Pb–As 79.40(3)–81.49(4).
Notes and references
z Experimental: All manipulations were performed under rigorous
exclusion of oxygen and moisture using
a Schlenk line and
nitrogen atmosphere. Solvents were dried and freshly distilled
before use. The starting materials were prepared according to litera-
ture: Pb{N(SiMe3)2}2,7 tBu2PhSiCl,8 [LiEH2(dme)] (E = P, As),9
iPr3SiSb(SiMe3)2.10 The NMR spectra were recorded with a Bruker
Ultrashield 300 spectrometer. MALDI-MS spectra were recorded on a
‘‘Applied Biosystems Voyager-DE Pro’’ with 1,8,9-anthracenetriol as
matrix.
atoms. In contrast to this, the (SbSiiPr3)2 units coordinate Z2
to three Pb atoms, such that one of the Sb atoms binds to two
lead atoms (Sb(1) and Sb(4), whereas the other Sb atom binds
to only one Pb atom (Sb(2) and Sb(3)). As a whole, the
cage consists of two four-membered Pb2Sb2 rings and four
tBu2PhSiPH2: A solution of 7.33 g tBu2PhSiCl (0.0287 mol) in
50 mL THF was added to a suspension of 3.72 g [LiPH2(dme)]
(0.0287 mol) in 75 mL THF at 0 1C. After stirring for 16 h at room
temperature, the THF was replaced by 100 mL of pentane. The
precipitated LiCl was subsequently removed by filtration. After
removal of the solvent, a vacuum distillation yielded a colourless oil
of 5.34 g (74%) tBu2PhSiPH2 (bp 83–84 1C at 10ꢀ3 mbar). H NMR
1
(C6D6): d 1.06 [s, 18H, CH3]; 1.44 [d, 1JP,H = 186 Hz, 2H, PH2]; 7.16
[m, 3H, Ph]; 7.69 [m, 2H, Ph]. 13C{1H} NMR (C6D6): d 21.9 [d,
2JC,P = 5.2 Hz, C(CH3)3]; 30.2 [d, 3JC,P = 1.9 Hz, CH3]; 128.7 [s, Ph];
130.1 [s, Ph]; 136.2 [d, JC,P = 7.1 Hz]; 136.7 [d, JC,P = 5.4 Hz, Ph].
29Si{1H} NMR (C6D6): d 17.9 [d; JSi,P = 30 Hz]. 31P NMR (C6D6):
1
d ꢀ265.4 [t with Si satellites, 1JP,H = 186 Hz, 1JSi,P = 30 Hz]. MS (EI,
70 eV) m/z (%): 252.1 [M+] (8). IR (KBr): 402 (w), 455 (s), 477 (s), 511
(s), 579 (s), 602 (s), 700 (s), 738 (s), 818 (s), 936 (m), 1012 (m), 1101 (s),
1195 (m) 1261 (w), 1364 (s), 1388 (s), 1426 (s), 1471 (s), 2303 (s), 2711
(w), 2858 (s), 2931 (vs), 3050 (m), 3071 (s).
tBu2PhSiAsH2: A solution of 9.43 g tBu2PhSiCl (0.0370 mol) in
25 mL DME was added to a suspension of 4.99 g [LiAsH2(dme)]
(0.0287 mol) in 150 mL DME at 0 1C. After stirring for 16 h at room
temperature, the DME was replaced by 100 mL of pentane. The
precipitated LiCl was subsequently removed by filtration. After
removal of the solvent, a vacuum distillation yielded a colourless oil
of 5.72 g (52%) tBu2PhSiAsH2 (bp 109–115 1C at 10ꢀ3 mbar). 1H
NMR (C6D6): d 0.94 [s, 2H, AsH2]; 1.08 [s, 18H, CH3]; 7.16 [m, 3H,
Ph]; 7.70 [m, 2H, Ph]. 13C{1H} NMR (C6D6): d 21.7 [s, C(CH3)]; 29.85
[s, CH3]; 128.1 [s, Ph]; 129.5 [s, Ph]; 136.4 [s, Ph]; 137.0 [s, Ph]. 29Si{1H}
NMR (C6D6): d 24.6 [s]. MS (EI, 70 eV) m/z (%): 296.1 [M+] (5) IR
(KBr): 402 (w), 453 (m), 477 (s), 493 (s), 571 (s), 621 (m), 642 (m),
700 (s), 737 (s), 819 (s), 935 (m), 955 (m), 1011 (s), 1099 (s), 1194 (m),
1260 (m), 1363 (s), 1388 (s), 1470 (s), 2098 (s), 2710 (w), 2858 (vs),
2931 (vs), 3071 (m).
[tBu2PhSiPPb]4 (1): At 0 1C, 0.45 mL Pb{N(SiMe3)2} (1 mmol) were
added to a solution of 0.25 mL tBu2PhSiPH2 (1 mmol) in 10 mL of
THF. The yellow solution was allowed to warm up to room tempera-
ture and was stirred for 16 h. After 1 d, orange crystals of 1 were
obtained at 4 1C, the yield being 0.128 g (28%).1H NMR (THF-D8):
d 1.28 [s, 18H, CH3]; 7.29–7.41 [m, 3H, Ph]; 7.75 [m, 2H, Ph]. 13C{1H}
NMR (THF-D8): d 30.5 [s, CH3]; 31.5 [s, C(CH3)3]; 129.0 [s, Ph]; 129.9
[s, Ph]; 136.3 [s, Ph]; 141.6 [s, Ph]. 29Si{1H} NMR (THF-D8): d ꢀ10.2 [s];
Fig. 3 Molecular structure of 3; thermal ellipsoids represent a 40%
probability level, hydrogen atoms are not shown, selected bond
lengths (pm) and angles (1): Sb(1)–Sb(2) 281.62(1), Sb(3)–Sb(4)
282.55(1), Sb(1)–Pb(1) 300.06(1), Sb(1)–Pb(2) 300.77(1), Sb(6)–Pb(1)
301.43(1), Sb(6)–Pb(2) 294.66(1), Sb(6)–Pb(3) 297.28(1), Sb(3)–Pb(3)
295.74(1), Sb(4)–Pb(4) 297.74(1), Sb(4)–Pb(2) 298.94(9), Sb(5)–Pb(1)
294.56(1), Sb(5)–Pb(3) 297.00(1), Sb(5)–Pb(4) 296.05(1), Sb(2)–Pb(4)
294.82(9), Sb–Si 256.3(3)–260.7(3); Sb(1)–Pb(1)–Sb(2) 82.06(3),
Pb(1)–Sb(6)–Pb(2) 97.89(3), Pb(1)–Sb(1)–Sb(6) 119.78(3), Sb(1)–
Sb(2)–Pb(4) 96.61(3), Sb(2)–Pb(4)–Sb(4) 88.37(3), Sb(4)–Sb(3)–Pb(3)
95.45(3), Sb(6)–Pb(3)–Sb(3) 100.64(3), Pb(2)–Sb(4)–Sb(3) 118.31(3).
ꢂc
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1
31P NMR (THF-D8): d ꢀ512.7 [s, Pb satellites, JP,Pb = 762 Hz].
The intensity data were collected on a STOE-IPDS2 (Mo-Ka
radiation, l = 0.71073 A). The structure was resolved by direct
methods and refined against F2 by the full-matrix least-squares
technique (Pb, P, As, Sb, Si, O, C refined anisotropically, all H atoms
calculated at ideal positions).
MALDI-MS: m/z: 1815.82 (M+ ꢀ Me); IR (KBr): 506 (vs), 575 (s),
700 (m), 814 (m), 1009 (w), 1095 (s), 1261 (w), 1382 (w), 1424 (m),
1467 (s), 2849 (s), 2922 (s), 3062 (w). Pb4P4Si4C56H92: Calc.: C 36.75,
H 5.07. Found: C 36.89, H 5.28%.
[(tBu2PhSiAsPb)4]ꢁ2THF (2): At 0 1C, 0.45 mL Pb{N(SiMe3)2}
(1 mmol) were added to a solution of 0.297 mL tBu2PhSiAsH2
(1 mmol) in 10 mL of THF. The yellow solution was allowed to warm
up to room temperature and was stirred for 16 h. After 1 d, orange
crystals of 2 were obtained at room temperature, the yield being
0.107 g (22%). 1H NMR (THF-D8): d 1.33 [s, 18H, CH3]; 7.45–7.49
[m, 3H, Ph]; 7.75 [dd, 2H, Ph]. 13C{1H} NMR (THF-D8): d 30.2
[s, CH3]; 31.9 [s, C(CH3)3]; 128.9 [s, Ph]; 129.8 [s, Ph]; 136.7 [s, Ph];
141.2 [s, Ph]. 29Si{1H} NMR (THF-D8): d ꢀ7.2 [s]. MALDI-MS: m/z:
1991.69 (M+ ꢀ Me); IR (KBr): 458 (m), 485 (vs), 572 (m), 613,3 (m),
700 (m), 736 (m), 813 (m), 1009 (m), 1094 (m), 1177 (w), 1260 (w),
1356 (w), 1382 (w), 1424 (m), 1467 (m), 2849 (s), 2922 (s), 3065 (w).
Pb4As4Si4C56H92: Calc.: C 33.53, H 4.62. Found: C 33.66, H 4.36%.
[iPr3SiSb)6Pb4] (3): At 0 1C, 0.424 mL iPr3SiSb(SiMe3)2 (1 mmol)
were added to a suspension of 0.278 g PbCl2 (1 mmol) in 10 mL of
Et2O. The solution was allowed to warm up slowly to room tempera-
ture and was stirred for 16 h. The dark precipitate was removed by
filtration and the solution was concentrated to approximately 5 mL.
After 3 weeks, a few black crystals of 3 were obtained reproducibly.
IR (KBr): 493 (m), 553 (w), 633 (m), 656 (m), 683 (m), 750 (m), 880
(vs), 1016 (s), 1097 (s), 1260 (s), 1461 (m), 2865 (vs), 2944 (vs).
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ꢀ
y Crystal data for 1: Pb4P4Si4C56H92 (180 K), triclinic, P1, a =
1418.7(3), b = 1549.1(3), c = 1599.8(3) pm, a = 73.32(3), b =
84.69(3), g = 80.68(3)1, V = 3319.6(11) A3, Z = 2, Dc = 1.831 g cmꢀ3
,
m = 10.313 mmꢀ1, F(000) = 1744, GOF = 1.063. A total of 15043
reflections were collected, 8256 of which were unique (Rint = 0.1194).
R1 (wR2) = 0.0789 (0.2033) for 613 parameters and 7323 reflections
(I 4 2s(I)).
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¨
1997, 36, 1894–1896.
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ꢀ
Crystal data for 2: Pb4As4Si4C64H108O2 (180 K), triclinic, P1, a =
378–382.
1432.4(3), b = 1640.4(3), c = 1863.0(4) pm, a = 66.81(3), b =
71.53(3), g = 81.69(3)1, V = 3815.5(13) A3, Z = 2, Dc = 1.872 g cmꢀ3
,
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Verlag, Stuttgart, Germany, 1996, vol. 3, pp. 189–193.
m = 10.619 mmꢀ1, F(000) = 2048, GOF = 0.869. A total of 22737
reflections were collected, 13420 of which were unique (Rint = 0.0557).
R1 (wR2) = 0.0430 (0.1208) for 653 parameters and 11090 reflections
(I 4 2s(I)).
¨
Crystal data for 3: Pb4Sb6Si6C54H122 (180 K), monoclinic, P21/c,
a = 2378.6(5), b = 1326.6(3), c = 2639.1(5) pm, b = 105.03(3)1, V =
8043(3) A3, Z = 4, Dc = 2.064 g cmꢀ3, m = 10.438 mmꢀ1, F(000) =
4656, GOF = 1.028. A total of 33876 reflections were collected, 14477
of which were unique (Rint = 0.0530). R1 (wR2) = 0.0458 (0.1181) for
630 parameters and 12169 reflections (I 4 2s(I)).
10 C. von Ha
nisch, P. Scheer and B. Rolli, Eur. J. Inorg. Chem., 2002,
¨
3268–3271.
ꢂc
This journal is The Royal Society of Chemistry 2010
1540 | Chem. Commun., 2010, 46, 1538–1540