Synthesis, Structure, and Reactivity of Ga-Substituted Distibenes and Sb-Analogues of Bicyclo[1.1.0]butane

Article abstract of DOI:10.1002/chem.201701248

Monovalent gallanediyl LGa {L=HC[C(Me)N(2,6-iPr₂C₆H₃)]₂} reacts with SbX₃ to form the Ga-substituted distibenes [(LGaX)₂Sb₂] (X=NMeEt 1, Cl 2). Upon heating, 2 reacts to the bicyclo[1.1.0]butane analogue [(LGaCl)₂(μ,η^1:1-Sb₄)] 3 containing a [Sb₄]^2? dianion. Moreover, 2 reacts with Li amides LiNR₂ in salt elimination reactions that form the corresponding amido-substituted compounds 1 and [(LGaNMe₂)₂Sb₂] 4, whereas reactions of 4 and [(LGaNMe₂)₂(μ,η^1:1-Sb₄)] 5 with two equivalents of GaCl₃ resulted in the formation of 2 and 3, respectively. 1, 2 and 3 were characterized by ¹H and ¹³C NMR spectroscopy, elemental analysis, and single crystal X-ray diffraction. In addition, their bonding situation was analyzed by quantum chemical calculations.

Full text of DOI:10.1002/chem.201701248

A Journal of
Accepted Article
Title: Synthesis, structure and reactivity of Ga-substituted distibenes
and Sb-analogues of bicyclo[1.1.0]butane
Authors: Lars Tuscher, Christoph Helling, Chelladurai Ganesamoorthy,
Julia Krüger, Christoph Wölper, Walter Frank, Anton
Nizovtsev, and Stephan Schulz
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10.1002/chem.201701248
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Synthesis, structure and reactivity of Ga-substituted distibenes
and Sb-analogues of bicyclo[1.1.0]butane
Lars Tuscher,[a] Christoph Helling,[a] Chelladurai Ganesamoorthy,[a] Julia Krüger,[a] Christoph Wölper,[a]
Walter Frank,[b] Anton S. Nizovtsev,[c,d] and Stephan Schulz*[a]
Dedication to Prof. D. Naumann on the occasion of his 75th birthday.
Abstract: Monovalent gallanediyl LGa {L
=
HC[C(Me)N(2,6-i-
Sb polyanions are rare and the most likely reason for this finding
is that they cannot be synthesized by activation reactions of the
neutral Sb4 tetrahedron, which is not a stable species under
ambient conditions. To the best of our knowledge, an intact Sb4
tetrahedron was only reported in vapor phase deposited Sb thin
films and identified by scanning tunneling microscopy (STM).[6]
Therefore, the development of bottom-up strategies for the
synthesis of Sb polyanions using molecular precursors is of high
interest.[7] Wright et al. reported on the synthesis of the Zintl
compound [Sb7Li3∙6HNMe2] by controlled thermolysis reaction of
{[Sb(PCy)3]2Li6∙6HNMe2} in toluene at low temperature
(40 °C),[7a] while in recent years Kloo, Burford and Weigand et. al.
established reductive catenation reactions for the synthesis of
group 15 polycations.[8]
Pr2C6H3)]2} reacts with SbX3 with formation of the Ga-substituted
distibenes [(LGaX)2Sb2] (X = NMeEt 1, Cl 2). Upon heating, 2 reacts
to the bicyclo[1.1.0]butane analogue [(LGaCl)2(,1:1-Sb4)]
3
containing a [Sb4]2- dianion. Moreover, 2 reacts with Li amides LiNR2
in salt elimination reactions with formation of the corresponding
amido-substituted compounds 1 and [(LGaNMe2)2Sb2] 4, whereas
reactions of 4 and [(LGaNMe2)2(,1:1-Sb4)] 5 with two equivalents of
GaCl3 resulted in the formation of 2 and 3, respectively. 1, 2 and 3
were characterized by 1H and 13C NMR spectroscopy, elemental
analysis and single crystal X-ray diffraction. In addition, their bonding
situation was analyzed by quantum chemical calculations.
Our long term general interest in the reactivity of low-valent main
group metal complexes and in group 15 metal chemistry recently
resulted in the synthesis of several polyatomic antimony clusters.
They were synthesized by controlled reduction reactions of
molecular Sb complexes, in which the Sb atoms are either
bonded to different heteroatoms X with different Sb-X bonding
energies (X = C, N) or adopt different formal oxidation states (+I,
Introduction
Polyanionic Zintl-type anions [Ey]x- of group 15 elements have
been intensively studied since their first discovery in the early
years of the last century.[1] They are typically prepared by
reactions of the elements with alkaline metals in liquid NH3 or
other amines or by solid state reactions of the elements.
Moreover, reduction reactions of P4 and As4 with organometallic
complexes also give access to a large variety of such polyanions
including realgar-type P8 tetraanions [(Cp*2Sm)4P8] (Cp* =
[9]
+II, +III). While antimony trialkyls SbR3 in contrast to BiEt3
failed to react with gallanediyl LGa {L = HC[C(Me)N(2,6-i-
Pr2C6H3)]2}, the reaction between Sb(NMe2)3 and LGa
proceeded under mild reaction conditions with formation of the
Ga-substituted distibene [(LGaNMe2)2Sb2] 4, which contains a
central Sb=Sb double bond and formally a [Sb2]2- dianion.[10]
Upon heating, 4 was converted into [(LGaNMe2)2(,1:1-Sb4)] 5,
the first Sb analogue of bicyclo[1.1.0]butane, which formally
contains a [Sb4]2- dianion.[10] In addition, reduction reactions of
distibines R4Sb2 (R = Me, Et) with LM (M = Al, Ga) proceeded
with insertion of LM into the weak Sb-Sb bond and subsequent
formation of LM(SbEt2)2,[11] whereas analogous reactions with
stronger reducing Mg(I) reagents occurred with formation of the
C5Me5), [{(NNfc)Sc}4P8] (NNfc
= =
1,1'-fc(NSitBuMe2)2, fc
ferrocenylene),[2] transition metal-coordinated E4-8 cages,[3] and
Lewis acid/base-stabilized P4 and P8 polyanions.[4] In addition,
transition metal complexes containing neutral E4 (E = P, As)
tetrahedra have been synthesized.[5]
In remarkable contrast, analogous metal complexes containing
[a]
M. Sc. L. Tuscher, B. Sc. C. Helling, Dr. C. Ganesamoorthy, B. Sc.
J. Krüger, Dr. C. Wölper, Prof. Dr. S. Schulz
Faculty of Chemistry and Center for NanoIntegration (CENIDE),
University of Duisburg-Essen, Universitätsstr. 5-7, S07 S03 C30, D-
45117 Essen, Germany
Zintl-type
[Sb8]4-
anions
[(LMg)4(4,2:2:2:2-Sb8)]
and
[(L'Mg)4(4,2:2:2:2-Sb8)] {L' = HC[C(Me)N(2,4,6-Me3C6H2)]2},[12]
respectively. Very recently, we showed that reduction reactions
of cyclo-tetrastibine [Cp*Sb]4, in which the central Sb atoms
adopt the formal oxidation state +I, with LGa and [L''Mg]2 (L'' = i-
Pr2NC[N(2,6-i-Pr2C6H3)]2) yielded [(LGa)2(,2:2-Sb4)] and
[(L''Mg)4(4,1:2:2:2-Sb4)].[13] Even though both compounds
formally contain [Sb4]4- tetraanions as central structural motif,
their connectivity and bonding nature strongly differ.
Fax: (+) 201-183 3830; E-mail: stephan.schulz@uni-due.de
https://www.uni-due.de/ak_schulz/index_en.php
Prof. Dr. W. Frank
Institute for Inorganic Chemistry and Structural Chemistry,
University of Düsseldorf
[b]
[c]
Dr. A. S. Nizovtsev
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the
Russian Academy of Sciences, Academician Lavrentiev Avenue 3,
630090, Novosibirsk, Russian Federation
We now systematically expanded our studies and report herein
on the synthesis, solid state structures, thermal stability and
chemical reactivity of several new complexes containing [Sb2]2-
and [Sb4]2- dianions. In addition, their bonding situation was
analyzed in detail by quantum chemical calculations.
[d]
Novosibirsk State University, Pirogova Street 2, 630090,
Novosibirsk, Russian Federation
Supporting information for this article (experimental details including
1H, 13C NMR, IR spectra and computational details) is available on
the WWW under http://dx.doi.org/xxx</.
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Results and Discussion
by reduction of a NHC-SbCl3 adduct failed.[14a,b] However, the
three-electron reduction of the adduct CAAC-SbCl3 (CAAC =
cyclic alkyl(amino)carbene) with 3 eq. of KC8 yielded the CAAC-
stabilized diatomic Sb2 species [{(CAAC)Sb}2], whereas one-
and two-electron reduction reactions proceeded with formation
of the CAAC-stabilized neutral antimony-centered radical
(CAAC)SbCl2 and the chloro-stibinidene (CAAC)SbCl,
respectively.[14c]
In order to prove if the reduction reaction of Sb(NR2)3 with LGa
opens up a general route for the synthesis of Ga-coordinated
distibenes, we investigated this reaction in more detail.
Unfortunately, only the reaction of LGa with Sb(NMeEt)3
proceeded with formation of the distibene [(LGaNMeEt)2Sb2] 1,
whereas those with sterically more hindered Sb trisamides
including Sb(NEt2)3, Sb[N(i-Pr)2]3 and Sb[N(SiMe3)2]3 completely
failed, even at elevated temperatures (up to 100 °C) and
elongated reaction times (up to 7d). These findings show the
subtle influence of small changes of the steric size of the organic
substituents R on the reactivity of Sb(NR2)3. This is further
underlined by the observation, that the reaction of LGa with
Sb(NMe2)3 proceeded already slowly at room temperature with
the formation of [(LGaNMe2)2Sb2] 4, while that with Sb(NMeEt)3
occurred only under neat reaction condition in the absence of
any solvents at temperatures of at least + 60 °C (Scheme 1).
Scheme 3. Synthesis of 3.
1 and 2 dissolve moderately in benzene, toluene and hexane
whereas 3 dissolves poorly in benzene and toluene and is
insoluble in hexane. Crystals of 1 – 3 can be stored in a glove
box under Ar atmosphere for several months. The 1H NMR
spectrum of 1 in toluene-d8 shows broad and overlapping signals
for the organic substituents. It consists of broad multiplets (from
3.95 to 3.43 ppm) and two doublets (1.29, 1.02 ppm) for the i-Pr
groups of the -diketiminate ligand, while the γ-CH and two
methyl groups of the C3N2M ring exhibit only single resonances
(4.78, 1.61 ppm). Furthermore, the amide ligand (NMeEt) shows
two singlets (3.10, 2.67 ppm, Me) and rather broad multiplets
(2.91, 1.34 ppm, Et). Unfortunately, no satisfying 13C NMR
Scheme 1. Synthesis of 1.
We further interested reactions of LGa with other Sb(III)
reagents to evaluate the reduction potential of LGa in detail. The
reaction with SbCl3 in 2:1 molar ratio in toluene at ambient
temperature proceeded with formation of a yellow-greenish
solution, from which yellow-green crystals of [(LGaCl)2Sb2] 2
were isolated upon storage at room temperature (Scheme 2).
1
spectrum was obtained from 1 due to its poor solubility. The H
NMR spectra of 2 and 3 are similar and show two septets (2,
3.91, 3.05; 3, 3.63, 3.05 ppm) and four doublets (2, 1.38, 1.20,
1.11, 1.01; 3, 1.52, 1.41, 1.17, 0.97 ppm) for the magnetically
inequivalent i-Pr groups of the β-diketiminate ligand, while the γ-
CH and two methyl groups of the C3N2M ring exhibit only single
resonances (2, 4.97, 1.63; 3, 4.79, 1.52 ppm). The 13C NMR
spectra of 2 and 3 each show 14 signals of the -diketiminate
groups and the data are consistent with the molecular structures
as determined by X-ray diffraction.
1 – 5 are promising starting reagents for salt elimination and
substitution reactions due to the presence of reactive Ga-Cl and
Ga-N groups. We therefore studied NMR-scale reactions of 2
and 3 with Li amides (LiNMe2, LiNMeEt) as well as reactions of 4
and 5 with GaCl3 (Scheme 4). 2 reacts at room temperature with
two eq. of LiNMe2 and LiNMeEt in toluene-d8 with LiCl
elimination and formation of the corresponding amide-
substituted complexes [(LGaNR2)2Sb2] (NR2 = NMeEt 1, NMe2 4),
which were unambiguously identified by their 1H NMR spectra
(Fig S12 and S13). In contrast, the reaction of 3 with two eq. of
LiNMe2 only showed the formation of LGa and LGa(NMe2)2 and
a so far unidentified product, whereas resonances due to the
formation of 5 were not observed (Fig. S14). Interestingly, the
Scheme 2. Synthesis of 2.
The thermal stability of 1, 2 and [(LGaNMe2)2Sb2] 4 significantly
differed. Heating a toluene solution of 4 to 120 °C for 24 h
yielded [(LGaNMe2)2(,1:1-Sb4)] 5,[10] whereas 2 required 7 days
of heating at 130 °C for the formation of [(LGaCl)2(,1:1-Sb4)] 3
(Scheme 3) and thermolysis of a toluene solution of 1 at 120 °C
for 3 days yielded several products according to 1H NMR studies.
Unfortunately, any attempts to separate the different species via
fractional crystallization failed. However, our studies clearly
demonstrate the high synthetic potential of the insertion–
reduction method using LGa compared to the coordination
reduction approach by use of N-heterocyclic carbenes (NHCs),
since the attempted synthesis of an NHC-stabilized Sb4 complex
previously
reported
NMe2-substituted
complexes
[(LGaNMe2)2Sb2] 4 and [(LGaNMe2)2(,1:1-Sb4)] 5 underwent
Cl/amide exchange reactions in reactions with GaCl3 at room
temperature and afforded 2 and 3, respectively (Figs. S15, S16).
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Use of an excess of GaCl3 in the reaction with 4 resulted in the
formation of LGaCl2 and a grey precipitate, respectively.
NMeEt 1, Cl 2), resulting in a trans-bent orientation of the planar
Ga–Sb=Sb–Ga units (figures 1, 2). The Ga atoms, which
typically adopt distorted tetrahedral coordination spheres, are
slightly displaced from the best plane of the C3N2 units of the
ligand [1: 0.679(4) Å, 2: 0.6121(14) Å] as was previously
observed for LGa as well as [(LGaNMe2)2Sb2]
4 and
[(LGaNMe2)2(,1:1-Sb4] 5, respectively. The Sb-Sb bond lengths
in 1 [2.6433(6) Å] and 2 [2.6461(2) Å] are almost identical and
comparable to those observed in 4 [2.6477(3) Å][10] and other
distibenes of the general type RSb=SbR, which were found to
range from 2.64 to 2.70 Å,[16] whereas they are substantially
shorter compared to Sb-Sb bond lengths in distibines of the type
L2Sb-SbL2, which rather contain Sb-Sb single bonds.[17]
Scheme 4. Reactivity studies of Sb22- and Sb42- ions with Li-amides and GaCl3.
Solid state structures. The molecular structures of 1, 2 and 3
were determined by single crystal X-ray diffraction. The reaction
of LGa with Sb(NMeEt)3 yielded crystalline materials, from which
suitable red crystals of
1 were hand-picked under the
microscope. Single crystals of 2∙C7H8 and 3∙0.5C6H6 were
obtained from saturated solutions in toluene (2) and benzene (3),
respectively, upon storage at room temperature for 2 days.
Figure 2. Molecular structure of [(LGaCl)2Sb2] in the crystal of 2. H-atoms
have been omitted for clarity. Displacement ellipsoids are drawn at the 50%
probability level and the symmetry generated part of the molecule is depicted
in pale colors.
The Ga-Sb bond length in 1 [2.6169(5) Å] and 4 (2.6200(4) Å)[10]
are comparable, while that of 2 [2.5818(19) Å] is slightly shorter
(Table 1). This finding most likely results from the electron-
withdrawing effect of the Cl-substituent, which enhances the
Lewis acidity of the Ga atom. The Ga-Sb bond lengths are
significantly shorter than Ga-Sb single bonds as-observed in
Lewis acid-base adducts of the general type R3Sb-GaR'3,[18] the
base-stabilized monomer dmap-Ga(Et)2Sb(SiMe3)2 (dmap = 4-
NMe2-pyridine; 2.648(1) Å)[19] and in heterocyclic compounds
such as [R2GaSbR'2]x, in which the Ga-Sb bond lengths were
found to range from 2.666 Å to 2.772 Å.[20] They are also slightly
shorter than the sum of the covalent radii (Ga = 1.24 Å; Sb =
1.40 Å).[21] The Sb-Sb-Ga bond angle (94.71(1)°) agrees with the
Sb-Sb-H angle calculated for HSb=SbH (93.0°)[22] and those
reported for ArSb=SbAr.[23]
Figure 1. Molecular structure of [(LGaNMeEt)2Sb2] 1. H-atoms and minor
components of the disordered NMeEt residues have been omitted for clarity.
Displacement ellipsoids are drawn at the 50% probability level and the
symmetry generated part of the molecule is depicted in pale colors.
1 and 3 crystallize in the monoclinic system with space group
P21/n and P21/c, respectively, while 2 crystallizes in the triclinic
space group P-1 (Figures 1 - 3). The molecules of 1 and 2 are
located on centers of inversion. The asymmetric unit of 2
contains an additional toluene molecule. In 3, the molecule
occupies a general position, while a benzene molecule is placed
on a center of inversion.[15] The centrosymmetric distibene (Sb2)
units within 1 and 2 are coordinated by two LGaX groups (X =
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Table 1. Comparison of bond lengths (Å) and angles (°) in Ga-substituted
distibenes 1, 2, and [(LGaNMe2)2Sb2] 4.[10]
Table 2. Comparison of bond lengths (Å) and angles (°) in the Ga2Sb4
cores of [(L'Ga)2(,2:2-Sb4)],[13] [(LGaNMe2)2(,1:1-Sb4)] 5[10] and
[(LGaCl)2(,1:1-Sb4)] 3.[a]
1
2
4
[(L'Ga)2(,2:2-Sb4)]
5
3
Sb1-Sb1a
Ga1-Sb1
2.6433(6)
2.6169(5)
-
2.6461(2)
2.58178(19)
2.2319(4)
1.9439(11)
1.9564(10)
-
2.6477(3)
2.6200(4)
-
Ga1-Sb1
Ga1-Sb2
Ga2-Sb3
Ga2-Sb4
Sb1-Sb2
Sb1-Sb3
Sb1-Sb4
Sb2-Sb3
Sb2-Sb4
Sb3-Sb4
2.6637(11)
2.6748(11)
2.6676(11)
2.6779(11)
-
2.5975(5)
2.6008(13)
-
-
Ga1-Cl1
-
-
Ga1-N1
2.005(3)
1.991(3)
1.864(3)
95.839(16)
93.28(12)
-
1.9894(13)
1.9826(13)
1.8558(13)
94.710(8)
93.16(5)
-
-
2.6044(14)
2.8368(11)
2.8480(11)
3.6277(10)
2.7850(11)
2.8215(11)
2.8434(11)
Ga1-N2
2.8298(4)
2.8139(4)
-
Ga1-N3
2.8500(9)
2.8675(7)
2.8683(8)
2.8722(8)
-
Ga1-Sb1-Sb1a
N1-Ga1-N2
Cl1-Ga1-Sb1
N3-Ga1-Sb1
89.476(6)
96.40(5)
117.383(13)
-
2.7920(5)
2.8299(4)[b]
2.8139(4)[b]
115.28(11)
116.37(4)
80.30(3)
(Ga1-Sb1-Sb4)
Ga1-Sb1-Sb2
101.704(14)
89.86(4)
The central Sb4 unit in 3 adopts a "butterfly-type" conformation
and is coordinated by two LGaCl fragments as was observed for
[(LGaNMe2)2(,1:1-Sb4)] 5.[10] Within the Sb4 core, two
approximately equilateral Sb3 triangles share a mutual edge
(Sb2–Sb3) and the angle between the planes of the Sb3
triangles is 94.39°. The endocyclic Sb-Sb-Sb bond angles within
the triangles are close to the ideal value of 60°, while the extra-
triangular ones are enlarged (~80°) as was previously observed
in 5 (75°).[10] Alternatively, the Sb4 unit can be described as
tetrahedron with one missing edge. The shortest Sb-Sb bond in
3 and 5 occurs between Sb2 and Sb3, while those to Sb1 and
Sb4, which are each further coordinated to one Ga atom, are
slightly elongated (Table 2).
Ga1-Sb1-Sb3
Ga1-Sb2-Sb3
Ga1-Sb2-Sb4
Ga2-Sb4-Sb2
79.08(3)
78.57(3)
80.03(3)
80.33(3)
105.770(14)
96.40(4)
-
-
-
-
-
91.80(4)
79.35(3)
(Ga2-Sb4-Sb2)
Ga2-Sb4-Sb3
-
93.58(4)
Ga2-Sb3-Sb1
Ga2-Sb3-Sb2
79.84(3)
80.58(3)
-
-
-
-
81.19(2)
(Sb3-Sb1-Sb4)
Sb2-Sb1-Sb3
59.300(13)
58.67(3)
Sb1-Sb2-Sb3
Sb1-Sb3-Sb2
-
60.065(11)
60.635(11)
60.87(3)
60.47(3)
81.86(2)
81.49(2)
(Sb1-Sb4-Sb2)
Sb1-Sb3-Sb4
75.585(14)[b]
79.20(3)
Sb2-Sb3-Sb4
Sb3-Sb2-Sb4
Sb2-Sb4-Sb3
Sb1-Sb2-Sb4
-
60.636(11)[b]
60.065(11)[b]
59.300(13)[b]
75.084(14)[b]
60.16(3)
60.95(3)
58.89(3)
79.75(3)
80.79(2)
-
-
[a] Ideal Sb4 tetrahedron: Sb-Sb 2.80 Å, Sb-Sb-Sb 60°.[21] [b] Sb4 = Sb1a.
Figure 3. Molecular structure of [(LGaCl)2(,1:1-Sb4)] in the crystal of 3. H-
atoms have been omitted for clarity. Displacement ellipsoids are drawn at the
50% probability level.
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Comparable Sb-Sb bond lengths were observed in phosphine-
stabilized, cationic Sb4 rings of the type [(R3P)4Sb4][OTf]4 [R =
Me 2.8354(6)-2.8797(5) Å;
R = Et 2.838(2)-2.884(2) Å],
[(Me3P)3Sb4R2] [2.8209(5)-2.8612(5) Å][8d,g] and in the
2-
3-
homoatomic Sb4 (av. 2.750 Å) and Sb7 polyanions (av. 2.797
Å).[24] The Sb1···Sb4 distance of 3.6277(10) Å is far too large to
be considered as a covalent bond. The Ga atoms in 3 adopt
distorted tetrahedral geometries. The Sb–Ga bonds are
comparable to those of 1, 3, 5[10] and [(L'Ga)2(,2:2-Sb4)]
[2.6637(11)-2.6779(11) Å],[13] but slightly shorter than the sum of
the covalent radii. The offsets from the best plane of the C3N2
units of the ligands are 0.60(2) Å (Ga1) and 0.51(2) Å (Ga2).
Quantum chemical calculations. The bonding situations in 1, 2,
and 3 were analyzed by using a number of quantum chemical
techniques to gain further insight into the chemical bonding
within the Ga2Sb2 and Ga2Sb4 skeletons and the results were
also compared to those observed in [(LGaNMe2)2(,1:1-Sb4)] 5
and [(L'Ga)2(,2:2-Sb4)],[13] respectively. All calculated bond
lengths within the Ga2Sb2 (1, 2) and Ga2Sb4 (3) cores (BP86-
D3/def2-SVP level of theory,[25–29] Tables S2 - S4) agree well
with the corresponding experimental values (Δr=0.02–0.08 Å).
As predicted by AIM, ELF, and NBO analyses,[30–33] all Sb–Sb
bonds in 1, 2, and 3 are covalent in nature (Tables S2 - S4,
Figures 4 - 6), in accordance to recently reported computational
data for these types of complexes.[12,13,34]
Figure 6. (a) Atomic labeling for the Ga2Sb4 skeleton and ELF distribution in
[(LGaCl)2(,1:1-Sb4)] 3 in the (b) Sb1–Sb2–Sb3, (c) Sb2–Sb3–Sb4, (d) Ga1–
Sb1–Sb3, and (e) Ga2–Sb4–Sb3 planes. V(Ga,Sb), V(Sb), and V(Sb,Sb)
basins are indicated by white, yellow, and black arrows, respectively.
However, the Sb–Sb bond in 1 (2.677 Å) and 2 (2.682 Å) are
considerably shorter compared to those in 3 (2.845 - 2.906 Å),
clearly indicating multiple bonding character between the Sb
atoms. Indeed, NBO analysis finds two-center two-electron σSb–
and πSb–Sb bonds with occupation numbers (ON) ranging
Sb
between 1.89 and 1.95 |e| (Tables S2, S3) in 1 and 2, while 3 is
characterized by only σSb–Sb bonds (ON = 1.95–1.97 |e|, Table
S4). ELF distribution reveals one V(Sb,Sb) valence disynaptic
basin populated by 1.2 - 1.3 e between each pair of connected
Sb atoms in 3 (Figure 6), and two V(Sb,Sb) basins in 1 and 2
[V(Sb,Sb)]=1.1 - 1.3; Figures 4, 5). Thus, 3 contains five Sb–
Sb single bonds, whereas 1 and 2 possess Sb=Sb double bonds.
In addition, each Sb atom from 1, 2, and 3 has one lone pair
(N
Figure 4. (a) Atomic labeling for the Ga2Sb2 skeleton and (b) ELF distribution
in [(LGaNMeEt)2Sb2] 1 in the Ga1–Sb1–Sb2 plane. V(Ga,Sb), V(Sb), and
V(Sb,Sb) basins are indicated by white, yellow, and black arrows, respectively.
(Tables S2 - S4), as calculated by NBO analysis (ON = 1.9 -
(N
2.0 |e|) and ELF
[V(Sb)] = 2.8 - 3.2 e; Figures 4 - 6).The Ga–
Sb bonds are also covalent, which is supported by the presence
of σGa–Sb bonds (ON = 1.96 - 1.97 |e|) with notable values of
polarization coefficients (|cGa|2 = 41 - 45%), the high contribution
of the electrons of Ga into the V(Ga,Sb) basins according to
(N
ELF/AIM intersection procedure
[V(Ga,Sb)|Ga] = 1.2 -
ꢀ
1.3 e),[35] and shared–type Ga–Sb interactions (  ꢁ ꢃꢄ <0;
ꢂ
ꢅ
|
|
ꢆꢂꢃꢄꢅ /ꢇꢂꢃꢄꢅ>2, ꢈꢂꢃꢄꢅ<0). Substitution of NMeEt group by Cl
atom leads to decreasing of NPA partial charges on Ga from
+1.23/+1.26 |e| (1) to +1.03/+1.07 |e| (2) and +1.06 |e| (3).
The chemical bonding pattern in the Ga2Sb4 core of 3 is very
similar to that of 5. Despite the slightly shorter Ga–Sb distances
(2.633/2.634 Å) compared to 5 (2.647/2.652 Å), the calculated
parameters of the bonds within the cores are almost the
same.[13]
Figure 5. (a) Atomic labeling for the Ga2Sb2 skeleton and (b) ELF distribution
in [(LGaCl)2Sb2] 2 in the Ga1–Sb1–Sb2 plane. V(Ga,Sb), V(Sb), and V(Sb,Sb)
basins are indicated by white, yellow, and black arrows, respectively.
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10.1002/chem.201701248
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and 2.67 (br s, 3 H, NMeEt), 2.91 (br m, 2 H, NMeCH2CH3), 1.61 (s, 6 H,
Conclusions
3
ArNCCH3), 1.34 (br m, 3 H, NMeCH2CH3), 1.29 (br d, 12 H, JH-H = 6.6
3
Hz, CH(CH3)2), 1.02 (br d, 6 H, JH-H = 6.6 Hz, CH(CH3)2). 13C NMR
In summary, Ga-substituted distibenes of the general type
[(LGaX)2Sb2] (X = NMeEt 1, Cl 2, NMe2 4) were obtained from
reactions of LGa with SbX3 [X = Cl, NMeEt, NMe2]. Upon
(toluene-d8, 75 MHz, 25 °C): No clear data because of poor solubility of 1.
Synthesis of [(LGaCl)2Sb2] 2. Method A: LGa (100 mg, 0.205 mmol)
and SbCl3 (23.4 mg, 0.103 mmol) were dissolved in 0.5 mL of toluene-d8
in a J-Young NMR tube and stirred at room temperature for 2 days. The
solution was kept at room temperature for further 2 days to yield green
crystals of 2. Crystals were separated from the solution and recrystallized
again from toluene to afford pure form of 2. Method B: In a J-Young
NMR tube, [(LGaNMe2)2Sb2] 4 (30 mg, 0.023 mmol) and GaCl3 (8.1 mg,
0.046 mmol) were dissolved in 0.5 mL of toluene-d8 and the reaction
progress was monitored periodically using 1H NMR spectroscopy. The
color changed from deep red into a greenish solution. After 24 hours at
ambient temperature, all resonances corresponding to [(LGaNMe2)2Sb2]
4 were vanished and 2 was isolated as green crystalline solids after
removal of the solvent in vacuum. M. p. 240 °C (dec.). Yield 15.2 mg
(51.3 %). Anal. Calcd. for C58H82N4Cl2Ga2Sb2: C, 54.04; H, 6.41; N, 4.35.
Found: C, 54.50; H, 6.43; N, 4.28 %. IR (neat):  3059, 2960, 2925, 2867,
1551, 1520, 1463, 1436, 1385, 1314, 1261, 1176, 1099, 1017, 939, 863,
793, 770, 711, 637, 525 cm-1. 1H NMR (C6D6, 300 MHz, 25 °C):  7.11-
thermal treatment, only
2
and
4
rearranged into the
corresponding tetrastibines [(LGaX)2(,1:1-Sb4)] (X = Cl 3, NMe2
5), demonstrating the subtle influence of the substituent X on the
reactivity of the distibenes. In addition, salt elimination reactions
of 2 with Li amides occurred with formation of amido-substituted
compounds 1 and 4, and 4 and 5 smoothly reacted with GaCl3 in
amide/Cl exchange reaction with subsequent formation of 2 and
3, respectively. 1 - 3 were structurally characterized by single
crystal X-ray diffraction and the bonding situation within these
new complexes was investigated by quantum chemical
calculations.
Experimental Section
3
6.91 (m, 6 H, C6H3-2,6-i-Pr2), 4.97 (s, 1 H, -CH), 3.91 (sept, JH-H = 6.7
General Procedures. Schlenk and glove-box techniques were chosen to
carry out all reactions and following work-up in purified argon atmosphere.
Toluene, hexane, pentane and diethyl ether were obtained after passing
these solvents through activated alumina columns on an MBraun Solvent
Purification System. Deuterated NMR solvents were stored over
activated molecular sieves (4 Å) and degassed prior to use. Karl Fischer
titration of the dry solvents show values less than 3 ppm. Exact molar
ratio of the reactions and the perfect reaction conditions were optimized
via 1H NMR by performing several minimum scale reactions in J-Young
NMR tubes using appropriate deuterated solvents under different
reaction conditions. LGa,[36] [(LGaNMe2)2Sb2] 4,[10] and Sb(NRR')3 (R,R' =
Me, Et)[37] were prepared according to literature methods, Li amides
Li(NRR') were synthesized by reaction of the corresponding amine with
n-BuLi in hexane and isolated as colorless crystalline solids, whereas
GaCl3 and solvents were obtained from commercial sources and purified
prior to use.
Hz, 2 H, CH(CH3)2), 3.05 (sept, 3JH-H = 6.7 Hz, 2 H, CH(CH3)2), 1.63 (s, 6
H, ArNCCH3), 1.38 (d, 6 H, 3JH-H = 6.7 Hz, CH(CH3)2), 1.20 (d, 6 H, 3JH-H
= 6.7 Hz, CH(CH3)2), 1.11 (d, 6 H, 3JH-H = 6.7 Hz, CH(CH3)2), 1.01 (d, 6 H,
3JH-H = 6.7 Hz, CH(CH3)2). 13C NMR (C6D6, 75 MHz, 25 °C):  169.46
(ArNCCH3), 146.52 (C6H3), 142.92 (C6H3), 141.58 (C6H3), 125.82 (C6H3),
124.49 (C6H3), 98.39 (-CH), 30.03 (CH(CH3)2), 28.40 (CH(CH3)2), 27.80
(CH(CH3)2), 25.17 (CH(CH3)2), 24.89 (CH(CH3)2), 24.84(CH(CH3)2),
24.28 (ArNCCH3).
Synthesis of [(LGaCl)2(,1:1-Sb4)] 3. A solution of 2 (30 mg, 0.0233
mmol) in 0.5 mL of toluene-d8 was heated at 130 °C for 7 days in a J-
Young NMR tube. The solution was slowly cooled to room temperature
and kept at this temperature for 1 day to afford yellow crystals of 3. The
crystals were separated from the mother liquor, washed with n-hexane
and dried in vacuum. Yield: 10 mg (0.0065 mmol, 56 %). M.pt: 194 C
(dec.). Anal. Calcd. for C58H82N4Cl2Ga2Sb4: C, 45.45; H, 5.39; N, 3.66.
Found: C, 45.40; H, 5.34; N, 3.71 %. IR (neat):  2958, 2917, 2860, 1521,
1441, 1383, 1320, 1257, 1171, 1096, 1021, 935, 866, 798, 757, 677, 631,
528, 441 cm-1. 1H NMR (C6D6, 500 MHz):  7.27-7.09 (m, 6 H, C6H3-2,6-i-
Pr2), 4.79 (s, 1 H, -CH), 3.63 (sept, 2 H, CH(CH3)2), 3.05 (sept, 2 H,
CH(CH3)2), 1.52 (s, 6 H, ArNCCH3), 1.52 (d, 6 H, J = 6.5 Hz, CH(CH3)2),
1.41 (d, 6 H, J = 6.5 Hz, CH(CH3)2), 1.17 (d, 6 H, J = 7 Hz, CH(CH3)2),
0.97 (d, 6 H, J = 7 Hz, CH(CH3)2). 13C NMR (C6D6, 150 MHz):  168.60
(ArNCCH3), 146.16 (C6H3), 142.92 (C6H3), 141.00 (C6H3), 126.00 (C6H3),
124.19 (C6H3), 97.39 (-CH-), 29.94 (CH(CH3)2), 28.05 (CH(CH3)2), 27.81
(CH(CH3)2), 24.76 (CH(CH3)2), 24.67 (CH(CH3)2), 24.63 (CH(CH3)2),
23.65 (ArNCCH3).
Instrumentation. The 1H (300 & 500 MHz) and 13C{1H} (75.5 & 150
MHz) NMR (δ in ppm) spectra were recorded using a Bruker Avance
DPX-300 or Bruker Avance III HD spectrometer and the spectra were
referenced to internal C6D5H (1H: δ = 7.154; 13C: δ = 128.39) and
C6D5CHD2 (1H: δ = 2.09; 13C: δ = 20.40). Microanalyses were performed
at the elemental analysis laboratory of the University of Duisburg-Essen.
IR spectra were measured in an ALPHA-T FT-IR spectrometer equipped
with a single reflection ATR sampling module. The melting points were
measured using a Thermo Scientific 9300 apparatus.
Synthesis of [(LGaNMeEt)2Sb2] 1. A solution of LGa (0.20 g, 0.40
mmol) and Sb(NMeEt)3 (0.12 g, 0.10 mL, 0.40 mmol) was heated at
60 °C without any solvent for 7 days in a J-Young NMR tube. During this
period of time, the color of the reaction solution changed from yellow to
red. The solution was then slowly cooled to room temperature to yield a
mixture of red and colorless crystals. The colorless crystals were washed
out with toluene (20.5 mL) to afford the pure form of 1 as insoluble
residue. M. p. 188 °C (dec.). Yield 0.063 g (47 %). Anal. Calcd. for
C64H98N6Ga2Sb2: C, 57.60; H, 7.40; N, 6.30. Found: C, 57.71; H, 7.43; N,
6.27 %. IR (neat):  3061, 2962, 2925, 2865, 2807, 2757, 1543, 1519,
1460, 1437, 1384, 1314, 1257, 1211, 1184, 1097, 1016, 992, 935, 880,
856, 792, 757, 720, 626, 565, 530, 440 cm-1. 1H NMR (toluene-d8,
300 MHz, 25 °C):  7.12-6.89 (m, 6 H, C6H3-2,6-i-Pr2), 4.78 (s, 1 H, -CH),
3.95 and 3.82 (br m, 2 H, CH(CH3)2), 3.43 (br m, 2 H, CH(CH3)2), 3.10
Computational details. The geometric parameters of the species under
study were fully optimized in the gas phase at the BP86-D3/def2-SVP
theoretical level[25–28] with a corresponding small-core relativistic effective
core potential for Sb[29] employing ultrafine grid. The stationary points
were characterized as minima on the potential energy surface by
vibrational analysis (the number of imaginary frequencies (NImag) was
equal to zero) and the structures obtained were used for the subsequent
calculations. Atoms in molecules (AIM)[30] and electron localization
function (ELF)[31,32] computations were performed with DGrid program[38]
using densities from the all-electron scalar relativistic (SR) ZORA-BP86-
D3/TZP computations.[25–27,39] ELF basin populations were calculated for
a rectangular parallelepipedic grid with a mesh size of 0.1 bohr. The
natural bond orbital analysis (NBO)[33] was performed at the BP86-
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10.1002/chem.201701248
Chemistry - A European Journal
FULL PAPER
D3/def2-SVP theoretical level as implemented in Gaussian09.[40] SR-
ZORA-BP86-D3/TZP computations were performed using ADF2013 suite
of programs (core potentials were not used, and quality of the Becke
numerical integration grid was set to the keyword good),[41–43] while the
remaining computations were carried out in Gaussian09 code.[40]
Detailed information about AIM, ELF, and NBO can be found
elsewhere.[30–33]
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residues could only be refined anisotropically. Where possible ISOR and
RIGU restraints were necessary.
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[8]
Acknowledgements
Financial support by the Deutsche Forschungsgemeinschaft
(SCHU 1069/22-1) is acknowledged. A.S.N. is also thankful to
the Siberian Supercomputer Center SB RAS for providing
computational resources. We thank E. Hammes for technical
support.
Keywords: Main group elements • Polystibide • Cluster
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mm); monoclinic, space group P21/n;
a = 11.1860(16) Å, b =
13.8639(19) Å, c = 20.692(3) Å; α = 90°, β = 90.138(7)°, γ = 90°, V =
3209.0(8) Å3; Z = 2; μ = 1.705 mm-1; ρcalc = 1.381 g⋅cm-3; 75535
reflections (θmax
parameters; largest max./min in the final difference Fourier synthesis
1.768 e⋅Å-3/ -1.013 e⋅Å-3; max./min. transmission 0.75/0.60; R1
= 33.259°), 11702 unique (Rint = 0.0324); 366
=
0.0447 (I > 2σ(I)), wR2 = 0.1485 (all data). 2∙C7H8: [C72H98Cl2Ga2N4Sb2],
M = 1473.38, yellow green block, (0.498 × 0.251 × 0.224 mm); triclinic,
space group P-1; a = 10. 7920(4) Å, b = 13.3463(6) Å, c = 14.8284(7)
Å; α = 64.799(2)°, β = 75.432(2)°, γ = 79.932(2)°, V = 1741.60(14) Å3; Z
[5]
= 1; μ = 1.652 mm-1; ρcalc = 1.405 g⋅cm-3; 99689 reflections (θmax
=
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10.1002/chem.201701248
Chemistry - A European Journal
FULL PAPER
33.283°), 13056 unique (Rint
=
0.0257); 381 parameters; largest
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0.0616 (all data). 3∙0.5C6H6: [C61H85Cl2Ga2N4Sb4], M = 1571.66, yellow
prism, (0.100 × 0.030 × 0.030 mm); monoclinic, space group P21c; a =
19.2808(4) Å, b = 16.6624(5) Å, c = 20.8408(5) Å; α = 90°, β =
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102.133(2)°, γ = 90°, V = 6545.9(3) Å3; Z = 4; μ = 2.558 mm-1; ρcalc
1.595 g⋅cm-3; 50152 reflections (θmax = 24.999°), 11512 unique (Rint
=
=
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0.1493); 678 parameters; largest max./min in the final difference
Fourier synthesis 0.837 e⋅Å-3/ -0.964 e⋅Å-3; R1 = 0.0918 (I > 2σ(I)), wR2
=
0.1341 (all data). The crystallographic data of 1, 2∙C7H8 and
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1523607 (3∙0.5C6H6). Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge, CB21EZ (fax:
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10.1002/chem.201701248
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
FULL PAPER
LGa reacts with SbX3 with formation of
Ga-substituted distibenes [(LGaX)2Sb2]
(NMeEt 1, Cl 2, NMe2 4). 2 and 4 were
thermally converted into the
L. Tuscher, C. Helling, C.
Ganesamoorthy, J. Krüger, C. Wölper,
W. Frank, A. S. Nizovtsev,and S. Schulz*
Page No. – Page No.
corresponding tetrastibines
[(LGaX)2(,1:1-Sb4)] (Cl 3, NMe2 5).
Salt elimination reactions of 2 with Li
amides yielded amido-substituted
compounds 1 and 4, while
Synthesis, structure and reactivity of
Ga-substituted distibenes and Sb-
analogues of bicyclo[1.1.0]butane
amide/chloride exchange reactions of
4 and 5 react with GaCl3 yielded 2 and
3. Quantum chemical calculations
revealed the bonding situation within
the complexes.
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