Reduction vs. metathesis in the reactions of bismuth trihromide with a bulky lithium silanide - An experimental and theoretical study

Article abstract of DOI:10.1002/ejic.200900773

On reaction of BiBr₃ with Li(thf)₃SiPh₂fBu (1) in the corresponding ratios redox/metathesis reactions were observed, yielding dibismuthane (tBuPh₂Si)₄Bi₂ (2) and disilylbismuth halide (tBuPh₂Si)₂BiBr (3). The latter is a reaction intermediate in the formation of the dark-red 2. The X-ray crystal structures of 1-3 were determined by low-temperature X-ray diffraction. The Si₂Bi-BiSi₂ core of 2 is in the semi-eclipsed conformation. No oligomerization of nonthermochromic 2 was observed. Compound 3 is a mixed substituted monomer with a pyramidal environment around the bismuth center. On the basis of quantum chemical calculations, the formation of tertiary bismuthane (tBuPh₂Si)₃Bi is not expected for steric reasons. According to DFT-optimized geometries of the simplified model systems n[(H₃Si)₂Bi]₂ (n = 1-3), the closed-shell attraction between intermolecular Bi centers in the chain provides a moderate elongation of the intramolecular Bi-Bi bond in the dibismuthane unit and a shortening of the intermolecular Bi-Bi contacts. According to MP4(SDQ) computations, such oligomerization is carried out by intermolecular interaction of s lone pairs that are bound together and p-type orbitais of the Bi-Bi bonds in the bismuth chain. An increase in the number of [(H₃Si) ₂Bi]₂ molecules per chain results in a decrease in the HOMO-LUMO gap and leads to a bathochromic shift. TD-PBEO computations suggest that the lowest energy electron transition in 2 is metal-metal charge transfer. In addition, the attractive contributions in the chain [(H₃A) ₂Bi]₂ ... [Bi(AH₃)₂]₂ with silyl groups (A = Si) outweigh the repulsion of the Bi...Bi centers, whereas for the alkyl-substituted bismuth chain (A = C) the repulsive van der Waals force dominates. This fact makes the rectangle oligomerization model more preferred for n[(H₃A)₂Bi]₂ (A = C; n = 2), while for A. = Si chain formation is favored in the gas phase.

Full text of DOI:10.1002/ejic.200900773

FULL PAPER
DOI: 10.1002/ejic.200900773
Reduction vs. Metathesis in the Reactions of Bismuth Tribromide with a Bulky
Lithium Silanide – An Experimental and Theoretical Study
Kirill Yu. Monakhov,[a] Thomas Zessin,[a] and Gerald Linti*[a]
Keywords: Bismuth / Silicon / Lithium / Crystal structure analysis / Density functional calculations
On reaction of BiBr3 with Li(thf)3SiPh2tBu (1) in the corre- bond in the dibismuthane unit and a shortening of the inter-
sponding ratios redox/metathesis reactions were observed,
yielding dibismuthane (tBuPh2Si)4Bi2 (2) and disilylbismuth
halide (tBuPh2Si)2BiBr (3). The latter is a reaction intermedi-
ate in the formation of the dark-red 2. The X-ray crystal
structures of 1–3 were determined by low-temperature X-ray
diffraction. The Si2Bi–BiSi2 core of 2 is in the semi-eclipsed
conformation. No oligomerization of “nonthermochromic” 2
was observed. Compound 3 is a mixed substituted monomer
with a pyramidal environment around the bismuth center.
On the basis of quantum chemical calculations, the formation
of tertiary bismuthane (tBuPh2Si)3Bi is not expected for steric
reasons. According to DFT-optimized geometries of the sim-
plified model systems n[(H3Si)2Bi]2 (n = 1–3), the closed-shell
attraction between intermolecular Bi centers in the chain
provides a moderate elongation of the intramolecular Bi–Bi
molecular Bi···Bi contacts. According to MP4(SDQ) computa-
tions, such oligomerization is carried out by intermolecular
interaction of s lone pairs that are bound together and p-type
orbitals of the Bi–Bi bonds in the bismuth chain. An increase
in the number of [(H3Si)2Bi]2 molecules per chain results in
a decrease in the HOMO–LUMO gap and leads to a bathoch-
romic shift. TD-PBE0 computations suggest that the lowest
energy electron transition in 2 is metal–metal charge transfer.
In addition, the attractive contributions in the chain [(H3A)2-
Bi]2···[Bi(AH3)2]2 with silyl groups (A = Si) outweigh the re-
pulsion of the Bi···Bi centers, whereas for the alkyl-substi-
tuted bismuth chain (A = C) the repulsive van der Waals force
dominates. This fact makes the rectangle oligomerization
model more preferred for n[(H3A)2Bi]2 (A = C; n = 2), while
for A = Si chain formation is favored in the gas phase.
phanides[4] {the formation of the silyl-substituted bismuth
complexes from the reactions of ArЈBiCl2 [ArЈ = 2,6-(2,6-
iPr2–C6H3)2-C6H3] with potassium silanides was not
observed},[12] (e) dehydrosilylation of group 13 diorganohy-
drides with trisilylbismuthane,[5,6,9] (f) heterometallic ad-
dition of trisilylbismuthane to group 13 trialkyl com-
pounds,[6–8] (g) conversion of trisilylbismuthane with cop-
per(I) tert-butoxide and trialkylphosphanes,[10] and (h) me-
tathesis reaction of a heterometallic aluminum–bismuth ad-
duct with a trialkyl indium–pyridine adduct.[11]
We report here on the redox and metathesis conversions
of bismuth tribromide with the lithium silanide Li(thf)3-
SiPh2tBu[13] in various ratios, resulting in a stable silyl-sub-
stituted dibismuthane and a disilylbismuth halide. We also
use quantum chemical calculations on simplified model
compounds of silyl- and alkyl-substituted bismuthanes to
obtain an insight into the possibility of forming (R3Si)3Bi
structures, the stability of the silyl-substituted (H3Si)2E·
radicals against dimerization as well as the instability of
[(H3Si)2E]2 molecules towards dissociation in the series of
pnicogens E = P, As, Sb, Bi. In addition, the oligomeriza-
tion of n(H3A)2Bi· radicals (A = C, Si; n = 2–4), the bond-
ing and orbital situations as well as the electronic exci-
tations in the dibismuthane and its oligomerized forms were
studied with use of density functional (DFT), time-depend-
ent density functional (TD-DFT), and conventional ab ini-
Introduction
The chemistry of silyl-substituted bismuth compounds is
an object of intensive study in the last years, because of
the interesting behavior of these compounds in synthetic
reactions and the following applications and the ability of
these compounds to form interesting structural motives.
Only seventeen examples of such species, whose structures
have been determined by X-ray diffraction, are well-known
up to now. Primarily, these are homonuclear[1–3] (four exam-
ples) and heteronuclear[1,3,5–11] complexes (thirteen exam-
ples) containing silyl groups of various steric requirements
[SiMe3, SitBu3, Si(SiMe3)3], which play a stabilizing role
here. In these compounds, bismuth displays the oxidation
states +1, +2 and +3. Homo- and heteronuclear silyl-substi-
tuted bismuth complexes could be obtained by different
synthetic strategies: (a) metalation of trisilylbismuthane
with alkyllithium,[1] (b) conversion of lithium bis(trisilylbis-
muthane) with 1,2-dibromoethane,[1] (c) conversion of so-
dium potassium bismuthide with 1,2-dichlorotetramethyl-
disilane,[2] (d) reduction of bismuth halides with alkali
metal silanides[3] and with silyl-substituted lithium phos-
[a] Anorganisch-Chemisches Institut, Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-546617
E-mail: gerald.linti@aci.uni-heidelberg.de
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Reactions of Bismuth Tribromide with a Bulky Lithium Silanide
tio theory to obtain an insight into the nature of Bi–Bi and 2, which forms here predominantly (ratio ca. 2.5:1 accord-
Bi···Bi interactions, which could be observed in the fluid ing to 29Si NMR signals). Interestingly, the dark-green solu-
and crystalline phase.
tion is more stable than that of red color, which decomposes
with formation of elemental bismuth after short periods of
time at low temperature (–20 °C) or much faster at room
temperature. In our opinion, the dark-green oily solution
should contain a form of 3 oligomerized via weak Br–
Bi···Br intermolecular contacts (like Mes2BiBr,[14] for exam-
ple), which are broken on dissolution of the oligomer to
give 3. However, no crystals could be isolated from this
solution.
Results and Discussion
Synthesis
The reactions of BiBr3 with Li(thf)3SiPh2tBu (1) in the
corresponding ratios in the solvent toluene yield the silyl-
substituted bismuthanes 2 and 3 (Scheme 1). Thus, the in-
tended salt metathesis reaction of BiBr3 with three equiva-
lents of 1 leads to a redox process under the applied condi-
tions (warming from –78 °C to room temp. during the reac-
tion), resulting in the dibismuthane (tBuPh2Si)4Bi2 (2) and
X-ray Crystal Structures
Single crystals of 1–3 suitable for X-ray structure deter-
the disilane (tBuPh2Si)2. During the reaction the color of mination were isolated from the corresponding solutions at
the solution changes from green to red-brown. Workup al- –20 °C.
lows isolation of 2 as dark-red crystals soluble in toluene.
Tris(tetrahydrofuran)lithium(tert-butyldiphenylsilanide)-
The 29Si NMR spectrum of the dark-red solution contains lithium [Li(thf)3SiPh2tBu (1)] was synthesized by starting
two signals: singlets for the silicon atoms of dibismuthane from the reaction of chloro-tert-butyldiphenylsilane,
(δ = 15.9 ppm) and disilane (δ = –2.16 ppm).
tBuPh2SiCl, with lithium granulate in tetrahydrofuran solu-
The formation of (tBuPh2Si)3Bi was not observed. This tion according to the literature procedure.[13] The com-
is probably due to steric reasons, which will be discussed pound was crystallized from a n-hexane/thf mixture at
later.
–20 °C. Compound 1 crystallizes in the monoclinic crystal
Heating of 2 under reflux at 100 °C for 3 h did not lead system, space group P21/n (Table 3). Figure 1 shows the
to disproportionation into elemental bismuth and molecular structure of 1 in the solid state. The asymmetric
(tBuPh2Si)3Bi or to dissociation of 2 into corresponding unit contains three independent molecules of 1. The crystal
radicals. As a result, 2 could be observed in the reaction structure displays monomer silanide units, where the lith-
solution again as a thermodynamically stable compound. ium ions are surrounded by three thf molecules and a sili-
This high thermostability may be related to the relatively con atom in a tetrahedral geometry. They differ only in the
short Bi–Bi distance in 2.
slight disorder of coordinated thf molecules and in the rota-
The reaction of BiBr3 with 1 in a 1:2 and 1:1 ratio gives tional conformation of the (thf)3Li and the SiPh2tBu units.
the disilylbismuth halide (tBuPh2Si)2BiBr (3) together with For the CBuSiLiO, torsional angle values of 37°, 39°, and
2. Here, after workup of the reaction mixture, red crystals 49° are observed. The Si–Li bond lengths in the three inde-
of 3 could be isolated from the dark-green hexane solution pendent molecules [266.0(5), 267.5(5), 269.0(5) pm] are
as well as from the red toluene solution only. The 29Si NMR fairly similar. This is in the typical range, as compared to
spectra of the solutions show singlets at δ = –4.19 and other thf adducts of monomeric lithium silanides {262.7 pm
–6.10 ppm, respectively. In addition, both solutions contain in Li(thf)3SiPh(NEt2)2,[15] 266.9 pm in Li(thf)3Si-
Scheme 1. Reaction pathways I and II leading to the formation of bismuthanes 2 and 3.
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K. Yu. Monakhov, T. Zessin, G. Linti
FULL PAPER
(SiMe3)3,[16] 267.2 pm in Li(thf)3SiPh3,[16] 267.8 and
268.2 pm in Li(thf)3SiPh2(NEt2),[15] 271.7 pm in Li(thf)3-
SitBu3,[17,18] 273.2 pm in Li(thf)3SiPh2(NPh2),[19] and
276.0 pm in Li(thf)3Si(SiMe2SiMe3)3[20]}.
Figure 2. Molecular structure of 2 (crystal; the thermal ellipsoids
are given at the 30% probability level; hydrogen atoms are omitted
for clarity). Selected bond lengths [pm] and angles [°]: Bi1–Bi2
300.6(8), Bi1–Si2 268.9(2), Bi1–Si1 270.8(2), Bi2–Si4 268.6(3), Bi2–
Si3 268.7(3), Si1–C11 187.8(9), Si1–C1 190.2(9), Si1–C5 191.4(9),
Si2–C21 186.4(8), Si2–C27 187.1(9), Si2–C17 190.7(8), Si3–C43
187.5(8), Si3–C37 189.6(8), Si3–C33 191.3(10), Si4–C53 187.5(9),
Si4–C59 188.3(8), Si4–C49 192.3(9), Si2–Bi1–Si1 101.63(7), Si2–
Bi1–Bi2 93.87(6), Si1–Bi1–Bi2 124.58(6), Si4–Bi2–Si3 101.77(8),
Si4–Bi2–Bi1 94.98(6), Si3–Bi2–Bi1 124.28(5), C11–Si1–C1 113.6(4),
C11–Si1–C5 108.4(4), C1–Si1–C5 106.3(4), C11–Si1–Bi1 118.4(2),
C1–Si1–Bi1 107.5(3), C5–Si1–Bi1 101.3(3), C21–Si2–C27 106.5(4),
C21–Si2–C17 113.3(4), C27–Si2–C17 106.6(4), C21–Si2–Bi1
115.7(3), C27–Si2–Bi1 107.4(2), C17–Si2–Bi1 106.9(3), C43–Si3–
C37 106.9(4), C43–Si3–C33 113.2(4), C37–Si3–C33 106.5(4), C43–
Si3–Bi2 117.7(3), C37–Si3–Bi2 102.6(3), C33–Si3–Bi2 108.8(3),
C53–Si4–C59 106.9(4), C53–Si4–C49 106.7(4), C59–Si4–C49
113.4(4), C53–Si4–Bi2 107.9(3), C59–Si4–Bi2 115.0(3), C49–Si4–
Bi2 106.6(3), Si1–Bi1–Bi2–Si3 4.62(9), Si2–Bi1–Bi2–Si3 –102.36(8),
Si1–Bi1–Bi2–Si4 –103.26(8), Si2–Bi1–Bi2–Si4 149.76(8).
Figure 1. Molecular structure of lithium silanide 1 (crystal; the
thermal ellipsoids are given at the 30% probability level; hydrogen
atoms are omitted for clarity). Only one of the three independent
molecules is shown. Selected bond lengths [pm] and angles [°]: Si1–
Li1 267.5(5), Si1–C5 192.0(4), Si1–C11 192.7(4), Si1–C1 195.8(5),
O1–Li1 198.1(8), O2–Li1 196.1(8), O3–Li1 192.4(8), C5–Si1–C11
99.8(2), C5–Si1–C1 106.3(2), C11–Si1–C1 102.2(2), O3–Li1–O2
105.1(3), O3–Li1–O1 99.1(4), O2–Li1–O1 106.8(3).
Compound 2 crystallizes in the triclinic crystal system,
¯
space group P1, Z = 2 (Table 3, Figure 2). The solid-state
molecular structure shows a dibismuthane with a Bi–Bi
bond length of 300.6 pm. The Si2Bi–BiSi2 core is in the
semi-eclipsed conformation, where each bismuth atom is
surrounded by two tert-butyldiphenylsilyl (tBuPh2Si)
groups. Two silyl-containing dibismuthanes of similar struc-
tural type, but with less bulky silyl (Me3Si) or alkyl [(Me3Si)2-
CH] groups, have been reported up to now.[1,21] The Bi–Bi
distance in 2 is shorter by 2.9 pm and 4.7 pm than in anti-
periplanar molecules (Me3Si)4Bi2 (dBi–Bi = 303.5 pm)[1] and
[(Me3Si)2CH]4Bi2 (dBi–Bi = 305.3 pm),[21] respectively. Fi-
nally, it is 3.4 pm shorter than the sum of the covalent radii
Bi–Bi bond. Such effective steric protection of the bismuth
centers in 2 can be regarded as one of the main reasons of
the stability of this compound.
(∆Σrcov = 304 pm). The Bi–Si bond lengths in 2 are dBi–Si
268.6–270.8 pm, which is expected from the covalent radii
of bismuth and silicon [rcov(Si) = 0.5r(Si–Si), r(Si–Si)
=
=
238.6 pm in (tBuPh2Si)2]. The molecules of 2 can be re-
garded as isolated ones with a shortest intermolecular
Bi···Bi distance of 1000 pm. In (Me3Si)4Bi2, aggregation via
Figure 3. Space-filling models of silyl-substituted dibismuthanes 2
Bi···Bi contacts (380.4 pm) was observed.[1,22] This leads to (left) and [(Me3Si)2Bi]2 (right).
a moderate elongation of the Bi–Bi bond in the dibis-
muthane unit. The quantum chemical calculations, which
will be discussed later, provide evidence for this.
The bond angles around bismuth lie in the wide range of
94–125°, resulting in a sum of angles at the bismuth centers
The space-filling representations of the silyl-substituted (Bisum) of 320.1° (Bi1) and 321.0° (Bi2). The dihedral angle
molecules 2 and [(Me3Si)2Bi]2 in Figure 3 show that bulky τ between Si–Bi–Si planes is 84.1° (Figure 4). Thus, all of
tBuPh2Si groups of 2 more effectively surround the reactive these angles are evidence of steric strain in 2.
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Reactions of Bismuth Tribromide with a Bulky Lithium Silanide
Figure 6. Space-filling models of disilylbismuth bromide 3.
Figure 4. The core of dibismuthane 2. Views along the Bi–Bi bond.
Quantum Chemical Calculations
Compound 3 crystallizes in the orthorhombic crystal sys-
tem, space group P212121. Its solid-state structure (Table 3,
Figure 5) is similar to [(Me3Si)2CH]2BiCl,[23] which is de-
scribed as a mixed-substituted monomeric diorganobis-
muth halide with a pyramidal environment around the bis-
muth center. The Bi–Si bond lengths in 3 are 267.8 pm and
269.6 pm, which are similar to the Bi–Si distances in 2. The
Bi–Br distance is 266.7 pm. The Si–Bi–Si angle is 100.22°.
As in [(Me3Si)2CH]2BiCl, we observed a slight dissimilarity
of the R–Bi–X angles (Si–Bi–Br = 96.97° and 98.70°). Such
slight distortions in the Bi–Si bond lengths and Si–Bi–Br
angles may be related to steric strain in 3. In addition, the
total sum of angles at the bismuth center (Bisum) is 295.9°.
This is a smaller deviation than that in 2 from the expected
structure of R3Bi with bond angles of 90° each.
Pyramidal (R3Si)3Bi Structures
The possibility of forming (R3Si)3Bi structures may be
related to a “hybridization sp valence orbitals effect” of the
metal, to the presence of the lone pair on the metal atom
and its type, an orientation of the lone pair, and as a conse-
quence the repulsive interactions of the R3Si groups around
metal center. Thus, according to the natural localized mo-
lecular orbitals (NLMO) analysis at the MP2(full) level on
the DFT-optimized geometry of the simplified electrostatic
model (H3Si)3Bi, the bismuth atom uses 9.3% s and 90.4%
p orbitals for bonding with silyl groups [s8.3%p91.4% accord-
ing to the natural bond orbital (NBO)]. The lone pair of
electrons on Bi possesses 74.6% s and 25.4% p character
(according to the NLMO). As a result, the (H3Si)3Bi struc-
ture shows a pyramidal environment around Bi (Figure 7),
where the Si–Bi–Si angles are 89°. In NBO evaluations, the
Bi–Si bonds are more weakly polarized toward Si atoms
(ca. 50.7%). In this manner, the valence sp hybrid orbitals
at Bi are adapted for a nucleophilic attack of only moder-
ately bulky alkyl or silyl anions like [(Me3Si2)AH]– (A = C)
or [AMe3]– (A = Si) to form (R3A)3Bi.[24] Increased steric
bulk of substituents leads to an increase in the Bi–Si bond
lengths [267.0 pm for (H3Si)3Bi; 267.8 pm for (Me3Si)3Bi;
273.2–275.9 pm for (iPr3Si)3Bi] and the Si–Bi–Si angles
[89.0° for (H3Si)3Bi, 96.8° for (Me3Si)3Bi, 107.1–109.7° for
(iPr3Si)3Bi], and, consequently, to more steric strain in the
molecule. Here, (tBuPh2Si)3Bi is a good example. Thus, ac-
cording to the DFT-optimized geometry of the tertiary bis-
muthane (tBuPh2Si)3Bi, the Bi–Si bond lengths and the Si–
Bi–Si angles lie between 273.3 and 275.1 pm, and 99.6 and
109.8°, respectively. Such relatively large deviations in the
Bi–Si distances and the Si–Bi–Si angles may be related to
repulsive interactions of the silyl substituents in (tBuPh2Si)3-
Bi. Therefore, three bulky tBuPh2Si ligands may be hardly
coordinated to the bismuth centre on the way of experimen-
tally described reactions here, whereas for indium (for ex-
ample), displaying a planar structural motive in the solid
state, this is accessible {see [(tBuPh2Si)3In]}.[25]
Figure 5. Molecular structure of 3 (crystal; the thermal ellipsoids
are given at the 30% probability level; hydrogen atoms are omitted
for clarity). Selected bond lengths [pm] and angles [°]: Br1–Bi1
266.7(7), Bi1–Si1 267.8(1), Bi1–Si2 269.6(1), Si1–C11 186.8(5), Si1–
C5 187.4(4), Si1–C1 191.0(5), Si2–C27 186.3(4), Si2–C21 186.9(4),
Si2–C17 189.8(5), Br1–Bi1–Si1 98.70(3), Br1–Bi1–Si2 96.97(3),
Si1–Bi1–Si2 100.22(3), C11–Si1–C5 111.69(2), C11–Si1–C1
107.7(2), C5–Si1–C1 112.9(2), C11–Si1–Bi1 117.2(1), C5–Si1–Bi1
98.4(1), C1–Si1–Bi1 108.8(2), C27–Si2–C21 110.8(2), C27–Si2–C17
113.2(2), C21–Si2–C17 108.0(2), C27–Si2–Bi1 114.4(1), C21–Si2–
Bi1 103.1(1), C17–Si2–Bi1 106.7(2).
As can be seen from the space-filling model of 3 (Fig-
ure 6), there is a vacant site on the bismuth atom, which is
assigned to the lone pair (LP) on the bismuth atom.
Through this LP, intermolecular interactions like Br–Bi···Br
in the oligomerized form are enabled.
Figure 7. DFT-optimized structure for (R3Si)3Bi (R = H, Me, iPr,
tBuPh2) molecules and view of sp valence orbitals of metal.
Eur. J. Inorg. Chem. 2010, 322–332
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K. Yu. Monakhov, T. Zessin, G. Linti
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Pnicogen Radicals (H3Si)2E· and Their Dimers
Table 1. Intramolecular properties. Computed structural and bond
strength parameters, and calculated charges and energies for mole-
cules [(H3Si)2E]2 (E = P, As, Sb, Bi) of C2h symmetry.
Formation of persistent radicals (RЈ)2E· (RЈ = alkyl or
amide) of group 15 elements is well known. Thus, the phos-
phanyl and arsinyl radicals,[26,27] generated in solution by
reaction of the dialkyl- or diamidophosphorus(III) or -arsen-
ic(III) monochlorides with an electron-rich olefin, or un-
der photolytic conditions by melting or vaporizing of the
dipnicogens [here, (PRЈ2)2], could be observed in solution
as well as in the gas phase and characterized by ESR spec-
troscopy, gas-phase electron diffraction (GED), and X-ray
crystal analysis. In addition, the participation of the group
15 p elements in the formation of the silyl radicals is estab-
lished. For example, homolysis of tris(triethylsilyl)antimony
led to antimony and free triethylsilyl radicals.[28] In case of
bismuth, the formation of its (RЈ)2Bi· radicals was observed
in the gas phase. Thus, the signals for (RЈ)2Bi+ ions [RЈ =
Parameter
(H3Si)2E–E(SiH3)2
E = P
E = As
E = Sb
E = Bi
d(E–E)[a]
225.7
247.6
285.6
301.4
[b]
QNPA
–0.3990
–0.350
+0.350
0.995
0.761
–215.4
215.4
–0.2568
–0.320
+0.320
0.980
0.722
–188.8
188.8
+0.0002
–0.283
+0.283
0.974
0.719
–155.8
155.8
+0.0741
–0.234
+0.234
0.970
0.658
–141.3
141.3
∆Qct(as)[c]
∆Qct(dis)[c]
WBI[c]
OOv[d]
[e]
∆Eas
[e]
∆Edis
[a] E–E bond lengths [pm] were computed at the PBE0/BS-I level
of theory. [b] The NPA pnicogen charges e were computed at the
MP2(full)/BS-II//PBE0/BS-I level. [c] Total charge transfers (∆Qct)
e upon association (as) and dissociation (dis) and the Wiberg bond
index (WBI) for E–E were calculated at the MP2(full)/BS-II//PBE0/
BS-I level. [d] Order of overlapping (OOv) of the valence sp orbitals
(Me3Si2)CH or 2,6-(Me2NCH2)2C6H3] could be detected by of the pnicogens was computed at the MP2(full)/BS-II//PBE0/BS-I
EI mass spectrometry.[21,29] The probable formation of the
bismuth radicals in liquid ammonia was reported by Gil-
man.[30] Di-p-tolylbismuth halide and sodium reacted to
yield an intensely green colored solution. The homolytic
cleavage of the Bi–Bi single bond should depend on the
steric bulk of the ligands. In our case, we could observe a
bismuth cation [(tBuPh2Si)2Bi]+ in toluene solution by
LIFDI mass spectrometry, indicating homolytic dissoci-
ation of the dibismuthane and subsequent ionization.
Herein, we discuss the stability of the silyl-substituted
(H3Si)2E· radicals towards dimerization, and thus, the insta-
bility of [(H3Si)2E]2 molecules towards dissociation in the
series of pnicogens E = P, As, Sb, Bi on the basis of the
bond association and dissociation energies, respectively, as
well as on the basis of the total charge transfer on the pnic-
ogen atoms during both of these processes.
level. [e] E–E bond association (∆Eas) and bond dissociation (∆Edis
energies [kJ/mol] were calculated at the MP4(SDQ)/BS-II//PBE0/
BS-I level.
)
Upon traveling downward within group E, the bond
length E–E in the [(H3Si)2E]2 compounds becomes longer
and the natural population analysis (NPA) pnicogen charge
becomes more positive (Table 1, Figure 8). This is in line
with the increasing covalent radii and decreasing electrone-
gativity of the homologous elements. The relatively small
increase in the Bi–Bi bond length compared to that in the
Sb–Sb bond length may be related to “relativistic effects”,
which result in a decrease in the atom sizes and a shortening
of the E–E bond. Upon dimerization of the pnicogen radi-
cals, the association energies for [(H3Si)2E]2 decrease within
the group (Table 1, Figure 9). In addition, the total intra-
molecular charge transfer for the lighter elements becomes
more negative; this corresponds to a better stabilization of
the molecules by the formation of E–E bonds. As a conse-
quence, the instability of the E–E bond increases within the
group, which is expressed in a decrease in the bond dissoci-
ation energies of [(H3Si)2E]2 molecules. Here, as expected,
the longer the bond length, the less is the bond energy. The
total charge transfer also indicates that the Bi–Bi bond is
the most flexible among the E–E bonds of other pnicogens.
The E–E bond strengths for [(H3Si)2E]2 molecules (P–P Ͼ
As–As Ͼ Sb–Sb Ͼ Bi–Bi), on the basis of the Wiberg bond
Figure 8. Calculated bond lengths and NPA pnicogen charges for
[(H3Si)2E]2 (A = P, As, Sb, Bi).
Figure 9. Calculated E–E bond association energies for (H3Si)2E·
and E–E bond dissociation energies for [(H3Si)2E]2 (E = P, As, Sb,
Bi) and corresponding total charge transfers on the pnicogen
indexes (WBIs) and the effective overlapping of orbitals, atoms.
326
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Reactions of Bismuth Tribromide with a Bulky Lithium Silanide
provide evidence for results described above (Table 1). As a here, as well as two highly positive charges on neighboring
result, the [(H3Si)2Bi]2 dimers possess the lowest stability Bi atoms should lead to an elongation of the intermolecular
among these compounds of pnicogens. An increase in sta- Bi+Q···+QBi bond. As a result, the repulsive van der Waals
bility of the bismuth species might be achieved by the steric force between two alkyl-substituted dimers (A = C) domi-
bulk of the silyl substituents. For example, dibismuthanes nates (Table 2). All in all, this is well expressed for the chain
R4Bi2 with little and moderate steric protection [R = Me, oligomerization. However, the distorted rectangle oligomer-
Et, SiMe3, CH(SiMe3)2] are thermolabile and have a ten- ization reveals an inverse situation: here, the intermolecular
dency toward disproportionation into elemental bismuth Bi···Bi distances between alkyl-substituted dimers are
and tertiary bismuthanes (R3A)3Bi. In contrast to this, bis- slightly shorter than those between the silyl-substituted di-
muthane molecules RyBix (x, y = 2–4) with bulky groups mers. This phenomenon will be discussed later.
[R = Ph, Mes, SitBu, Si(SiMe3)3; in our case R = tBuPh2]
are stabilized with respect to thermal decomposition.[1,3,4,31]
N-merization of n(H3A)2Bi· Radicals and Oligomerization
of Dimers
The n-merization of (H3A)2Bi· radicals into [(H3A)2Bi]n
(A = C, Si; n = 2–3) and the oligomerization associated
with the formation of the systems n[(H3A)2Bi]2 (A = C, Si;
n = 2) via intermolecular Bi···Bi contacts here were evalu-
ated by means of structure, charge, and energy calculations
(Table 2, Figure 10). According to DFT computations the
intramolecular Bi–Bi bond lengths in n[(H3A)2Bi]2 elongate
upon oligomerization. In [(H3A)2Bi]3 a 3c3e bond is to be
formulated. The tetramers n[(H3A)2Bi]2 (n = 2) are a model
for the oligomerization observed for R4Bi2 compounds in
the liquid and crystalline phase. Here, rectangle and chain
oligomerization has to be distinguished. Thus, the Bi2 unit
is retained and only weak intermolecular Bi···Bi contacts
Figure 10. General view of DFT-optimized structures of [(H3A)2-
Bi]n (A = C, Si) molecules (hydrogen atoms are omitted for clarity).
appear. The intermolecular Bi···Bi distances in n[(H3A)2-
Bi]2 are shorter than the sum of van der Waals radii of Bi
in the chain oligomerization and longer in case of the dis-
The increase in the energy gain (En) per radical (H3A)2-
torted rectangle oligomerization. As can be seen, the NPA Bi· unit for [(H3A)2Bi]n and n[(H3A)2Bi] (A = C, Si) mole-
bismuth charges in the silyl-substituted molecules are much cules listed in Table 2 indicates increased stabilization of the
lower than those in the alkyl-substituted molecules. This corresponding systems. Therefore, the silyl-substituted
corresponds to better donor properties of the silyl substitu- molecules spend more energy per radical unit than alkyl-
ents and leads to a shrinking of the covalent radius of bis- substituted ones gain. The energies of the intermolecular
muth in the alkyl derivatives. The different electronegativity Bi···Bi contacts (∆Einter) in the tetramers n[(H3A)2Bi]2 (n =
of C and Si atoms, better polarization of the Bi–C bonds, 2) show that for A = C the distorted rectangle oligomeriza-
which are highly polarized toward carbon atoms (ca. 70%) tion is more preferred (about 1.4 times more in the exother-
Table 2. Intermolecular properties. Computed structural parameters and calculated charges and energies for molecules [(H3A)2E]2 (E =
P, As, Sb, Bi; A = C, Si).
Parameter
[(H3A)2Bi]n
n = 2
n[(H3A)2Bi]2
n = 2 (rectangle)
n = 3
n = 2 (chain)
A = C
A = Si
A = C
A = Si
A = C
A = Si
A = C
A = Si
Bi1–Bi2[a]
Bi2–Bi3
Bi3–Bi4
Bi1–Bi3
Bi2–Bi4
299.9
–
–
–
301.4
–
–
–
319.4
319.3
–
–
–
+0.849
+0.773[d]
–130.4
–
320.2
319.5
–
–
–
+0.127
–0.019[d]
–153.2
–
301.4
–
302.5
–
300.8
392.2
300.7
–
302.6
379.9
302.5
–
301.4
424.2
425.3
+0.799av
+0.799av
–277.2
–16.2
–69.3
302.5
429.5
431.5
+0.044av
+0.041av
–301.7
–19.1
–75.4
–
–
–
–
[b]
QNPA
+0.814
+0.074
+0.828
+0.793[e]
–272.4
–11.5
–68.1
+0.099
+0.028[e]
–303.1
–20.6
–75.8
[c]
∆Emer
–130.5
–
–65.2
–141.3
–
–70.6
[c]
∆Einter
[c]
En
–43.5
–51.1
[a] Bi–Bi bond lengths and intermolecular Bi···Bi contacts [pm] were computed at the PBE0/BS-I level of theory. [b] The NPA charges e
at Bi were computed at the MP2(full)/BS-II//PBE0/BS-I level. [c] Energies of n-merization of (H3A)2Bi· radicals and energies of intermo-
lecular contacts (∆Emer and ∆Einter, respectively) [kJ/mol], as well as energy gains per radical unit (En) were calculated at the MP4(SDQ)/
BS-II//PBE0/BS-I level. [d] NPA charge on the central Bi atom in the trimer. [e] NPA charges on intermolecular interaction centers of
bismuth.
Eur. J. Inorg. Chem. 2010, 322–332
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327

K. Yu. Monakhov, T. Zessin, G. Linti
FULL PAPER
mic energy) over chain formation, whilst for A = Si the In this manner, an increase in steric strain and rigidity of
chain oligomerization is slightly more preferred. As one of the substituents on the metal atoms should lead to a moder-
the reasons, this inversion barrier at bismuth may be related ate shift into chain formation or no oligomerization. As a
to better delocalization of two high charges on Bi for A = result, the types of oligomerization represented above are
C via the distorted rectangle, even though the Bi···Bi dis- not expected for the molecules with effectively protecting
tances in the rectangle formation are longer than the sum silyl (like tBuPh2Si) or alkyl ligands (see Figure 3, too).
of van der Waals radii of Bi. Such an effect is more weakly
NBO Analysis
expressed for A = Si. An appreciable increase in the exo-
thermic energies ∆Einter with the increase in the number of
n[(H3A)2Bi]2 molecules per chain (n = 3) was not observed.
In our opinion, the exchange of H atoms for Me groups in
anti-periplanar [(H3Si)2Bi]2 should lead to a stronger shift
to chain formation on the basis of an increase in the steric
strain in the molecule. Thus, the forms of the oligomeriza-
tion, described above for the gas phase, could be experimen-
The charges (QNPA) on the bismuth atoms (natural elec-
tron configuration 6s1.786p3.13) in [(H3Si)2Bi]2, obtained by
natural population analysis (NPA) at the MP2(full) level,
are slightly positive (+0.074 e). The NPA bismuth charge in
(H3Si)2BiBr is much more positive than in [(H3Si)2Bi]2,
QNPA = +0.521 e. The results of the NBO evaluations for
[(H3Si)2Bi]2 show that the bonding between bismuth centers
(Bi–Bi; WBI = 0.97) is mainly carried out by p–p orbital
overlap (s5.0%p94.5%d0.5%), (Figure 11). This overlap corre-
sponds to the HOMO, which indicates a σ bond between
the bismuth atoms (50%) (Figure 12). As a result, the
[(H3Si)2Bi]2 molecule is apolar with a dipole moment of
0 Debye. The hybrid HOMO–1, HOMO–2, HOMO–3, and
HOMO–4 contain the main contributions from the Bi–Si
interactions, whereas the HOMO–5 and HOMO–6 are
metal lone pairs of mainly s character (s78.5%p21.5%; NLMO
analysis provides the same result). In the polar molecule
(H3Si)2BiBr (dipole moment ca. 4 Debye), the lone pair
NHO at Bi is of type s (s80.1%p19.9%), too.
tally observed for (R2Bi)2 [R = Me, SiMe3; R2 = (CMe =
[21]
CH)2; chain][1,32] and {[(Me3Si)2CH]2Bi}2
(rectangle).
Here, it is necessary to remark that rectangle formation for
the {[(Me3Si)2CH]2Bi}2 molecule was established in the li-
quid phase by NMR spectroscopy as a dynamic process of
an exchange of the [(Me3Si)2CH]2Bi units between associ-
ated molecules, whereas in the crystalline phase, only chain
formation for alkyl- and silyl-substituted dibismuthanes is
well-known.[1,32] While the results obtained in the gas phase
for the silyl-substituted dibismuthane molecules are in line
with their experimental behavior in the crystalline phase
{see [(Me3Si)2Bi]2[1]}, the alkyl-substituted derivatives re-
veal various behavior. In addition, in the gas phase the in-
tramolecular Bi–Bi bond length and the intermolecular
Bi···Bi distance in the chained molecule n[(H3A)2Bi]2 (A =
C; n = 2) are 300.8 and 392.2 pm, respectively, whereas in
the crystalline phase experimentally observed Bi–Bi bond
length and Bi···Bi distance are 312 and 358 pm, respectively.
Interestingly, the lengthening of the intramolecular Bi···Bi
distance in the chained R4Bi2···Bi2R4 (R = H) system to a
value of 312 pm (in accordance with experimentally ob-
served Bi–Bi bond lengths for R = Me in the crystalline
phase) leads to a shortening in the intermolecular Bi···Bi
distance, and as consequence, to an increase of about 11%
in energy of intermolecular contacts.[33] All in all, such a
difference in structure and energy behavior in the gas, li-
quid, and crystalline phases may be related to the tempera-
ture factor, phase transitions, as well as to an influence of
the solvent molecules. All of these possible reasons demand
Figure 11. Graphical representation of the NBO hybrid HOMO of
the model (H3Si)2Bi–Bi(SiH3)2.
Results from MO Theory
Figure 12 presents the frontier molecular orbitals of
additional investigations on such factor-dependent systems. [(H3Si)2Bi]2 obtained by means of canonical MO theory,
In addition, the chain and rectangle oligomerization should which were computed at the MP4(SDQ)/BS-II//PBE0/BS-I
strongly depend on steric strain and rigidity of the ligands. level. Thus, according to the atomic orbital population of
Figure 12. Graphical representation of the frontier canonical molecular orbitals of (H3Si)2Bi–Bi(SiH3)2 (Ϯ 0.02 isosurface value).
328
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Reactions of Bismuth Tribromide with a Bulky Lithium Silanide
MOs, the components of HOMO–1 and LUMO come [(H3Si)2Bi]2···[Bi(SiH3)2]2 intermolecular interaction, the
mainly from p orbitals of bismuth, while the HOMO con- charges on the bismuth interacting centers are reduced from
tains the large s lone pair orbital parts of bismuth.
+0.074 e in dimer [(H3Si)2Bi]2 to + 0.028 e in oligomer
According to results of MO theory, the s LPs on Bi in [(H3Si)2Bi]2···[Bi(SiH3)2]2, whereas the charges on the non-
model compound [(H3Si)2Bi]2 with non-overloaded silyl interacting bismuth centers become slightly more positive +
substituents correspond to the HOMO. Interactions 0.099 e, accordingly. This induced dipole causes an electro-
through these LPs are known and were observed in the re- static attraction between these two nonpolar molecules.
actions of tBu3M with Bi2Et4, resulting in Lewis acid–base Thus, the dipole moment of [(H3Si)2Bi]2 is 0 Debye, whereas
adducts [Et4Bi2][MtBu3]2 (where M = Al, Ga).[34] An in- that of [(H3Si)2Bi]2···[Bi(SiH3)2]2 becomes more positive,
crease in steric protection of the substituents should lead to 0.46 Debye. In addition, such Bi···Bi intermolecular attrac-
a decrease in activity of the s LPs, and accordingly to an tion is very weak (0.04) according to the WBI. This fact
increase in stereochemical inert character. Therefore, the and the small charges involved here, as well as the absence
stereochemically active role of the LPs of bismuth in 2 is of other intermolecular contacts, point to the London dis-
expressed very weakly. The s LP of 3 corresponds to the persion force.
HOMO, too.
Interestingly, the HOMO–LUMO ∆E gap for [(H3Si)2-
Bi]n decreases upon oligomerization (Figure 13). Thus, de-
localization of p electrons of (H3Si)2Bi· radicals (∆E =
9.43 eV) in the Bi–Bi bond (the Bi–Bi stretching frequency
is 127 cm–1) leads to the reduction of ∆E toward 8.73 eV (n
= 2). The Bi–Bi chain-oligomerized forms, n[(H3Si)2Bi]2,
have gaps of 7.75 eV (n = 2) and 7.24 eV (n = 3), accord-
ingly. The values of the first ionization potentials (IP =
EHOMO; on the basis of the Koopman’s theorem) and the
energy values of the lowest occupied molecular orbitals de-
crease, accordingly. According to DFT-optimized geome-
tries of the n[(H3Si)2Bi]2 systems (n = 1–3), the interaction
between intermolecular Bi centers in the chain provides a
moderate elongation of the intramolecular Bi–Bi bond in
the dibismuthane unit from 301.4 pm for n = 1 through
302.5/302.6 pm for n = 2 toward 302.6/302.7 and 303.9 pm
(central unit) for n = 3. In addition, this leads to a shorting
of the intermolecular Bi···Bi contacts from 379.9 pm for n
= 2 toward 378.2 pm (average) for n = 3.
Figure 14. Graphical representation of the frontier canonical mo-
lecular orbitals of [(H3Si)2Bi]2···[Bi(SiH3)2]2 upon oligomerization
(Ϯ 0.02 isosurface value).
TD-DFT Computations
According to time-dependent (TD) DFT computations
of vertical electronic transitions in [(H3Si)2Bi]2, the lowest
energy S0 Ǟ S1 electronic transition corresponds to the
HOMO Ǟ LUMO and HOMO–1 Ǟ LUMO excitations
Figure 13. Changes in the HOMO–LUMO energy gap for n(H3Si)2-
with a predominantly nBi(s,p) Ǟ n*Bi(p) character. The tran-
Bi· (n = 1–2) and n[(H3Si)2Bi]2 (n = 2–3) systems upon n-merization
sitions are in the near UV region (301 nm, 4.12 eV, 33
and chain oligomerization, respectively.
223 cm–1). Such electron transfer can be described as metal–
As can be seen in Figure 14, the intermolecular interac- metal charge transfer (MMCT excitation). Intermolecular
tions in the chained [(H3Si)2Bi]2···[Bi(SiH3)2]2 molecule interaction of s LPs of the Bi–Bi bond in the bismuth chain-
correspond to the bonding HOMO-1 (s LP orbitals that oligomerized form (Figures 13, 14) leads to a bathochromic
are bound together) and HOMO-3 (p-type orbitals that are shift toward lower frequencies. Thus, the lowest energy elec-
bound together) and the LUMO with overlapping intermo- tronic transitions for n[(H3Si)2Bi]2 are 301 (n = 1), 347 (n =
lecular p* orbitals, whereas the HOMO and the HOMO-2 2), and 391 nm (n = 3). This fits well with the results de-
are intermolecular antibonding in nature and correspond scribed above (Figure 13). Experimentally, a change in color
[1]
to the intramolecular interactions in each dimer molecule is observed for [(Me3Si)2Bi]2 upon transition between the
[(H3Si)2Bi]2 (as described in Figure 12). As a result of the fluid phase {red [(Me3Si)2Bi]2} and the crystalline phase
Eur. J. Inorg. Chem. 2010, 322–332
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329

K. Yu. Monakhov, T. Zessin, G. Linti
FULL PAPER
ture procedure.[13] Elemental analysis was performed in the micro-
analytical laboratory of Ruprecht-Karls-University of Heidelberg.
1H, 13C, and 29Si NMR spectra were recorded with a Bruker Ad-
vance-400 (399.89, 100.55, and 79.44 MHz for 1H, 13C, and 29Si
analyses, respectively) instrument. Chemical shifts are reported in
δ units (ppm) and are referenced to an external standard of tet-
ramethylsilane (TMS) SiMe4 (δ = 0.00 ppm) and benzene C6D6 (δ
= 7.13 ppm). Electronic spectra were measured at room temp. un-
der an argon atmosphere with a Tidas II J&M spectrophotometer,
using toluene as solvent. The LIFDI-MS was recorded with a
{green n[(Me3Si)2Bi]2, where n is the number of molecules
in the Bi chain}. These results are in contrast to those ob-
tained for 2, which is “nonthermochromic” dibismuthane.
In addition, a maximum absorption band for the com-
pounds with more bulky silyl ligands should be shifted to
lower energy, too. The absorption spectrum of 2 in toluene
provides evidence for this. Thus, the observed lowest energy
absorption maximum lies at 465 nm (2.67 eV, 21 505 cm–1)
in the visible spectral region and is close to the value of the
S0 Ǟ S1 electronic transition (the HOMO Ǟ LUMO and JEOL JMS-700 operating in the positive ion mode with full scan-
ning in the range 200–1800; compound 2 was supplied as dilute
HOMO–2 Ǟ LUMO excitations) determined computation-
ally by using the fixed structure of 2 from X-ray crystal-
lography (418 nm, 2.97 eV, 23 923 cm–1).
solutions at about 0.2 mgmL–1 in toluene.
Crystal Structure Determination: X-ray data for single crystals of
1–3 were collected with a STOE IPDS I diffractometer equipped
with an image plate area detector, using a graphite monochromator
(Mo-Kα) (λ = 71.073 pm). The structure was refined against all F2
data by full-matrix least-squares techniques (SHELXT 5.01; PC
Version, Siemens, Bruker AXS).[35] All non-hydrogen atoms were
refined with anisotropic thermal parameters. All H atoms were
placed in calculated positions and refined by using a riding model.
A summary of crystal data and structure refinements for the com-
pounds are listed in Table 3. CCDC-742475 (1), -742476
(2·2C6H5Me), -742477 (3), and -742909 (tBuPh2Si) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Conclusions
By the reactions of BiBr3 with various amounts of the
bulky lithium silanide 1, the formation of Bi–Bi bonded
product 2 could be observed. However, 2 was isolated only
from the redox reaction in 1:3 ratio, as a main product. The
formation of tertiary bismuthane (tBuPh2Si)3Bi was not ob-
served. This is probably due to steric reasons. Accordingly,
no oligomerization of 2 is observed. This is in contrast to
the observation that Bi2(SiMe3)4 is “thermochromic”,[1]
where oligomerization via Bi···Bi contacts is observed. In
all reactions, both metathesis and redox processes were ob-
served. These led to the formation of Bi–Br bonded product
3 simultaneously with 2.
Compound 2: A suspension of (2.93 g, 6.34 mmol) Li(thf)3SitBuPh2
(1) in toluene (20 mL) was added dropwise to a stirred solution of
(0.95 g, 2.11 mmol) BiBr3 in toluene (40 mL) at –78 °C. The dark-
colored reaction mixture was stirred for an additional 3 h at low
The bulky SiPh2tBu ligand is a valuable source, which
should promote the radicalization processes in the reactions temperature and was then slowly warmed to ambient temperature.
Initially, a green solution was observed. After stirring for 16 h, all
volatile reaction components were removed with an oil vacuum
pump. The residue was extracted with hexane (60 mL) and then
with toluene (60 mL). After filtration, dark-red solutions were ob-
tained. The hexane and toluene fractions show similar 29Si NMR
signals. The toluene and solutions were reduced to a volume of
15 mL and cooled to –20 °C, resulting in the formation of dark-red
crystals of 2; yield: 1.88 g (64%; with reference to Bi). Compound 2
is soluble in organic solvents and stable in the range –30–100 °C.
C64H76Bi2Si4 (1374.46): calcd. C 55.88, H 5.57; found C 55.69, H
of trigonal pyramidal structural units (like EX3) of the
group 15 elements (E = P, As, Sb, Bi) with alkali metal
silanide M(sol)nSiPh2tBu (M = Li, Na, K; n = 0–3) on the
basis of the shape of the silyl substituents (steric factor) and
“hybridization sp valence orbital effect” of the correspond-
ing element E (electronic factor).
Dibismuthanes such as 2 are potentially useful and im-
portant starting reagents for further synthetic applications.
On one hand, these may react via the s LPs of Bi as σ-
donor, to form Lewis acid–base adducts;[34] on the other 6.05. 1H NMR (400 MHz, C6D6, iTMS): δ = 1.12 (s, CMe3, 1),
7.58 (m, o-Ph), 7.67 (m, p-Ph), 7.79 (m, m-Ph) ppm. 13C NMR
hand, the more sterically demanding alkyl or silyl groups
(like those in 2) are, the less stereochemically active these
orbitals are. This is due to the increasing protection of the
metal center in the molecules. Finally, such compounds
(100.55 MHz, C6D6, iTMS): δ = 26.8 (s, CMe3), 30.4 (s, CMe3),
129.7 (m-Ph), 132.6 (p-Ph), 136.0 (o-Ph), 138.2 (i-Ph) ppm. 29Si
NMR (79.44 MHz, C6D6, eTMS): δ = 15.9 (s, SiPh2tBu) ppm. UV/
Vis (toluene): λmax (ε, Lmol–1 cm–1) = 465 (2132) nm. LIFDI-MS
with Bi–Bi bonds open a way to ring systems or to bismuth
(toluene): m/z (%) = 1374.6 (100) [M]+, 1135.4 (13) [M+
SiPh2tBu], 687.3 (18) [(tBuPh2Si)2Bi]+, 447.3 (5) [(tBuPh2Si)Bi]+.
–
species in its +1 oxidation state, for example.[31b] Sterically
protecting ligands should play a key role and determine all
probabilities of reaction of the complexes.
Compound 3: A suspension of (3.06 g, 6.63 mmol) (1) in toluene
(20 mL) was added dropwise to a stirred solution of (1.49 g
3.31 mmol) BiBr3 in toluene (40 mL) at –78 °C. The dark-colored
reaction mixture was stirred for an additional 3 h at low tempera-
ture and was then slowly warmed to ambient temperature. After
stirring for 16 h, all volatile reaction components were removed
with an oil vacuum pump, and the residue was extracted first with
hexane (60 mL) and then with toluene (60 mL). After filtration of
the hexane and toluene fractions, the dark-green (denoted “DGS”)
and red (denoted “RS”) solutions were obtained, respectively. Hex-
ane and toluene solutions were reduced to a volume 15 mL and
Experimental Section
General: All manipulations were carried out with the use of stan-
dard Schlenk techniques under an oxygen-free and water-free argon
atmosphere and in vacuo. All organic solvents were distilled, dried,
and degassed according to standard procedures. Hexane and tolu-
ene were dried with sodium/benzophenone and freshly distilled un-
der argon. Li(thf)3SiPh2tBu (1), was prepared according to a litera-
330
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Reactions of Bismuth Tribromide with a Bulky Lithium Silanide
Table 3. Crystal data and structure refinement details for 1–3.
1
2·2C6H5Me
3
Empirical formula
Formula weight [g/mol]
Temperature [K]
Crystal color
Crystal size [mm]3
Crystal system
Space group
a [pm]
C28H43LiO3Si
462.32
200
pale green
0.37ϫ0.35ϫ0.24
monoclinic
P21/n
1018.6(2)
1711.3(3)
4808(1)
C78H92Bi2Si4
1559.84
200
C32H38BiBrSi2
767.69
200
dark red
0.3ϫ0.16ϫ0.07
triclinic
red
0.41ϫ0.14ϫ0.06
orthorhombic
P21 21 21
1044.1(2)
1150.9(2)
2526.2(5)
¯
P1
1368.8(3)
1421.5(3)
1848.0(4)
96.01(3)
b [pm]
c [pm]
α [°]
β [°]
90.08(3)
92.84(3)
101.42(3)
3496(1)
γ [°]
V [Å3]
8381(3)
3035(1)
4
1.680
7.223
Z
12
1.099
0.109
3020
2
Dcalc [Mg/m3]
µ (Mo-Kα) [mm–1]
F(000)
1.482
5.137
1564
1504
2θ-range [°]
Abs. corr.
Min/max transm.
Index ranges
2.04–26.13
numerical
0.9618/0.9832
–12 Յ h Յ 12
–21 Յ k Յ 21
–59 Յ l Յ 59
36694
2.52–30.63
numerical
0.255/0.674
–19 Յ h Յ 19
–20 Յ k Յ 19
–26 Յ l Յ 26
42336
2.11–28.15
numerical
0.1945/0.5230
–13 Յ h Յ 13
–15 Յ k Յ 14
–33 Յ l Յ 33
29770
Reflections collected
Independent reflections
Observed refl. [IϾ2σ(I)]
Data/restraints/parameters
Goodness-of-fit (S) on F2
Final R indices [IϾ2σ(I)]
14556
6160
19419
9297
7354
6592
14556/0/912
0.842
R1 = 0.0630
wR2 = 0.1291
R1 = 0.1463
wR2 = 0.1553
19419/0/757
0.774
R1 = 0.0515,
wR2 = 0.1055
R1 = 0.1249,
wR2 = 0.1235
2578/–3067
7354/0/326
0.923
R1 = 0.0248,
wR2 = 0.0509
R1 = 0.0307,
wR2 = 0.0521
1121/–548
R indices (all data)
Largest diff. peak/hole [enm–3] 214/–192
cooled to –20 °C, resulting in the formation of only red crystals of
3. 29Si NMR spectra for both solutions contain the silicon signals
of 2 and disilane, too. Yield of DGS: 0.91 g (35.7%; with reference
to Bi). Yield of RS: 0.48 g (19.0%; with reference to Bi). After
short periods of time at –20 °C or at room temp., both solutions
decompose with formation of elemental bismuth. The crystals of 2
(which form predominantly) also were obtained by this reaction in
a 1:1 ratio (29Si NMR signals of 2 and disilane were observed, too).
DGS: The signals of 2 and disilane are omitted. 1H NMR
(400 MHz, C6D6, iTMS): δ = 7.87 (m, m-Ph), 7.71 (m, p-Ph), 7.49
(m, o-Ph), 1.21 (s, CMe3) ppm. 13C NMR (100.55 MHz, C6D6,
iTMS): δ = 138.5 (i-Ph), 137.1 (o-Ph), 133.3 (p-Ph), 130.0 (m-Ph),
31.2 (s, CMe3), 27.0 (s, CMe3) ppm. 29Si NMR (79.44 MHz, C6D6,
eTMS): δ = –4.2 (s, SiPh2tBu) ppm.
I). All other computations were carried out on PBE0 optimized
geometries with the Gaussian 03 program package.[39] We used Los
Alamos National Laboratory 2 (LANL2) relativistic effective core
potentials (RECPs) to describe the core electrons of In, P, As, Sb,
Bi, and Br atoms and employed split-valence (double-ζ) quality
basis sets to describe their s and p valence electrons. For P, As, Sb,
Bi, and Br atoms, the LANL2DZ basis set was augmented by add-
ing one set of polarization and one set of diffuse functions.[40] For
Si, C, and H atoms, all-electron split-valence 6-311+G(d,p) basis
sets supplemented with a single set of diffuse functions on carbon
and silicon atoms were employed.[41] The combination of
LANL2DZdp and 6-311+G(d,p) is denoted Basis Set System II
(BS-II). The vibrational frequencies were evaluated on all DFT-
optimized geometries by using the HF method to verify their status
as true local minima on the potential energy surface and to obtain
zero-point corrections to the energies (ZPE) without scaling. The
nature of the chemical bonding was analyzed by means of the NBO
approach with the second-order Møller–Plesset perturbation
theory, including all valence electrons in the configuration space
[MP2(full)]. The atomic charges were computed within the natural
population analysis (NPA). Wiberg indexes were evaluated and
used as bond strength indicators. NBO analyses were performed
with NBO Version 3.1[42] incorporated in the Gaussian 03 program.
To gain insight into the vertical singlet electronic states, time-de-
pendent functional theory[43] (TD-PBE0 method) calculations were
performed. Energies reported herein were evaluated by using the
fourth-order Møller–Plesset perturbation theory [MP4(SDQ)] in
combination with PBE0 parameterization.
RS: The signals of 2, disilane, and DGS are omitted. 1H NMR
(400 MHz, C6D6, iTMS): δ = 7.74 (m, m-Ph), 7.63 (m, p-Ph), 7.29
(m, o-Ph), 1.14 (s, CMe3) ppm. 13C NMR (100.55 MHz, C6D6,
iTMS): δ = 138.3 (i-Ph), 136.3 (o-Ph), 132.7 (p-Ph), 129.9 (m-Ph),
31.1 (s, CMe3), 27.6 (s, CMe3) ppm. 29Si NMR (79.44 MHz, C6D6,
eTMS): δ = –6.1 (s, SiPh2tBu) ppm.
Computational Methods: DFT structure optimizations were per-
formed with the Turbomole program,[36] adopting the multiple
“M3” grid size for the density fitting and a SCF convergence crite-
rion of 1ϫ10–7 Eh. The initial geometries were fully optimized with
the hybrid exchange-correlation functional PBE0.[37] As Gaussian
AO basis for all atoms, all-electron split valence SV(P) sets of def2-
type[38] were employed (Basis Set System I, which is denoted BS-
Eur. J. Inorg. Chem. 2010, 322–332
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
331

K. Yu. Monakhov, T. Zessin, G. Linti
FULL PAPER
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Received: August 6, 2009
Published Online: November 27, 2009
332
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