Less is more: Three-coordinate C,N-chelated distannynes and digermynes

Article abstract of DOI:10.1002/chem.201500695

We report here the synthesis of new C,N-chelated chlorostannylenes and germylenes L³MCl (M=Sn(1), Ge (2)) and L⁴MCl (M=Sn(3), Ge (4)) containing sterically demanding C,N-chelating ligands L^3,4 (L³=[2,4-di-tBu-6-

Full text of DOI:10.1002/chem.201500695

DOI: 10.1002/chem.201500695
Full Paper
&
Main-Group Chemistry
Less Is More: Three-Coordinate C,N-Chelated Distannynes and
Digermynes
[a]
[a]
[a]
[a]
[b]
ˇ
ˇ ˚ˇ ˇ
Miroslav Novµk, Marek Bouska, Libor Dostµl, Ales Ruzicka, Alexander Hoffmann,
Sonja Herres-Pawlis,*[b] and Roman Jambor*[a]
Abstract: We report here the synthesis of new C,N-chelated
chlorostannylenes and germylenes L3MCl (M=Sn(1), Ge (2))
and L4MCl (M=Sn(3), Ge (4)) containing sterically demand-
lene L5SnCl (9). Hence, we highlight the role of donor-driven
stabilization of tetrynes. Compounds 1–10 were character-
ized by means of elemental analysis, NMR spectroscopy, and
in the case of 1, 2, 5–7, and 10, also by single-crystal X-ray
diffraction analysis. The bonding situation in either three- or
four-coordinate distannynes 5, 7, and 10 was evaluated by
DFT calculations. DFT calculations were also used to compare
the nature of the metal–metal bond in three-coordinate C,N-
chelating distannyne [L3Sn]2 (5) and related digermyme
ing
C,N-chelating
ligands
L4 =[2,4-di-tBu-6-{(C6H3-2’,6’-iPr2)N=
L3,4
(L3 =[2,4-di-tBu-6-
(Et2NCH2)C6H2]À
;
CH}C6H2]À). Reductions of 1–4 yielded three-coordinate C,N-
chelated distannynes and digermynes [L3,4M]2 for the first
time (5: L3, M=Sn, 6: L3, M=Ge, 7: L4, M=Sn, 8: L4, M=Ge).
For comparison, the four-coordinate distannyne [L5Sn]2 (10)
stabilized by N,C,N-chelate L5 (L5 =[2,6-{(C6H3-2’,6’-Me2)N= [L3Ge]2 (6).
CH}2C6H3]À) was prepared by the reduction of chlorostanny-
Introduction
stabilized ditin compounds bearing bulky organic substituents
are characterized by the presence of a tin–tin multiple
bond.[4–7] In context with these studies and as part of a system-
atic study concerning the influence of different electronic and
steric properties of organic substituents on the character of
the tin–tin bond in discussed ditin complexes [RSn]2, we start-
ed to focus on sterically demanding C,N-chelating ligands that
could combine both kinetic and thermodynamic stabilizations
of the ditin compounds. All the above discussed compounds
are prepared by the reductive protocol of the starting hetero-
leptic stannylenes of the type RSnX (X=halide) and that is
why the stabilization of latter compounds is crucial for the syn-
thesis of the ditin compounds. In this context, we have shown
that the sterically demanding C,N-chelating ligand L1 is suitable
for the stabilization of homoleptic stannylenes, and despite
the steric bulk of ligand L1, the corresponding chlorostanny-
lene L1SnCl could not be isolated. In contrast, the use of C,N-
chelating ligand L2 (see below) provided the C,N-chelated
chlorostannylene L2SnCl. Despite the strong donor capacity of
an imine C=N moiety in the ligand L2, the latter ligand was in-
sufficient to stabilize the ditin compound [L2Sn]2 and we have
shown the latter compound underwent a disproportionation
reaction.[8] This could be also a reason of an insufficient pro-
tecting effect of the organic substituent in the ortho position
and that is why synthesis of ditin compounds containing relat-
ed C,N-chelating ligand bearing sterically demanding organic
groups in the ortho position towards tin atom was of current
interest. For this reason we have prepared the C,N-chelating li-
gands L3,4 containing a tBu group in the ortho position to-
wards a metal atom in the desired C,N-chelated chlorotetry-
lenes (Scheme 1).
Heavier Group 14 analogues of alkynes have been known
since the pioneering work of Power et al.[1] These compounds,
like the corresponding silicon,[2] germanium,[3] and tin[4] conge-
ners are of importance with the regard to their bonding situa-
tion. It was demonstrated that depending on the organic sub-
stituents, single-, double-, and triple-bonded structures have
been proposed.[5]
The design of a variety of rather bulky organic substituents
R was essential for the success in making distannynes [RSn]2
(R=C6H3-2,6-iPr2, C6H2-2,4,6-iPr3, C6H3-2,6-[C6H2-2,4,6-Me3]2,
Si(iPr)[CH(SiMe3)2]2).[6] It was also demonstrated that employ-
ment of intramolecularly coordinating ligands is an alternative
for the stabilization of organotin(I) species [RSn]2.[7] The ther-
modynamically stabilized ditin compounds are characterized
by the presence of a tin–tin single bond, whereas kinetically
ˇ
˚ˇ ˇ
[a] M. Novµk, M. Bouska, Dr. L. Dostµl, Dr. A. Ruzicka, Dr. R. Jambor
Department of General and Inorganic Chemistry
Faculty of Chemical Technology, University of Pardubice
Studentskµ 95, 53210, Pardubice (Czech Republic)
E-mail: roman.jambor@upce.cz
[b] Dr. A. Hoffmann, Prof. Dr. S. Herres-Pawlis
Institut für Anorganische Chemie
Rheinisch-Westfälische Technische Hochschule Aachen
Landoltweg 1,52074 Aachen (Germany)
E-mail: sonja.herres-pawlis@ac.rwth-aachen.de
Supporting information for this article (including crystallographic parame-
ters of compounds 1, 2, 5–7, and 10 (see Table S3) and the dependence of
MÀM (Ge, Sn) bond distances and CÀMÀM bond angles in structurally
characterized tetrynes (see Tables S1 and S2 and Figures S1 and S2)) is
available on the WWW under http://dx.doi.org/10.1002/chem.201500695.
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1
groups. The H NMR spectra of 3
and 4 revealed two signals for
the CH and four signals for the
CH3 protons of the iPr groups.
In addition, the 119Sn NMR spec-
tra of 1 and 3 display a sharp
signal at d=269.4 ppm (d=
154.7 ppm for 3), which is similar
to that of the related N!Sn co-
ordinated
[C6H3(CH2NMe2)2-2,6]SnCl
156 ppm),[9a]
[C6H3(NMe2)2-
organostannylenes
(d=
Scheme 1. C,N-chelating ligands used for the stabilization of distannynes and digermynes.
We report here the synthesis of new C,N-chelated chloros-
tannylenes and germylenes L3MCl (M=Sn(1), Ge (2)) and L4MCl
(M=Sn(3), Ge (4)) containing sterically demanding C,N-chelat-
ing ligands L3,4 (L3 =[2,4-di-tBu-6-(Et2NCH2)C6H2]À L4 =[2,4-di-
;
tBu-6-{(C6H3-2’,6’-iPr2)N=CH}C6H2]À). Attempts to convert 1–4
into the corresponding distannynes and digermynes provided
the first three-coordinate C,N-chelated distannynes and diger-
mynes [L3,4M]2 (5: L3, M=Sn, 6: L3, M=Ge, 7: L4, M=Sn, 8: L4,
M=Ge). For comparison, the four-coordinate distannyne
[L5Sn]2 (10) stabilized by the N,C,N-chelate ligand L5 (L5 =[2,6-
{(C6H3-2’,6’-Me2)N=CH}2C6H3]À) was prepared by the reduction
of chlorostannylene L5SnCl (9). Compounds 1–10 were charac-
terized by means of elemental analysis, NMR spectroscopy, and
in the case of 1, 2, 5–7, and 10, also by single-crystal X-ray dif-
fraction analysis. The bonding situation in either three-coordi-
nate or four-coordinate distannynes 5, 7, and 10 was evaluated
by DFT calculations. DFT calculations were also used to com-
Scheme 2. Synthesis of compounds 1–4.
pare the nature of the metal–metal bond in three-coordinate
C,N-chelated distannyne [L3Sn]2 (5) and related digermyme
[L3Ge]2 (6).
2,6]SnCl (d=380 ppm),[9b] and {C9H6N[CH(SiMe3)]-8}SnCl (d=
327 ppm),[9c] respectively.
Single crystals suitable for X-ray diffraction analysis of 1 and
2 were obtained from hexane solutions at À208C. The molecu-
lar structure of 1 and 2 together with selected geometric pa-
rameters are depicted in Figure 1.
Results and Discussion
Synthesis and characterization of C,N-chelated distannynes
and digermynes 5–8
Treatment of the corresponding organolithium com-
pounds L3,4Li with MCl2 (M=Sn, Ge) provided stable
C,N-chelated chlorostannylenes and germylenes
L3MCl (M=Sn(1), Ge (2)) and L4MCl (M=Sn(3), Ge (4))
(Scheme 2).
Compounds 1 and 2 are white crystalline materials
that are well soluble in organic solvents such as tolu-
ene, benzene, THF, Et2O or in n-hexane, whereas
compounds 3 and 4 are yellow crystalline material
that are well soluble in organic solvents such as tolu-
ene, benzene, THF, or Et2O. Compounds 1–4 were
characterized by using NMR spectroscopy. The 1H
and 119Sn NMR spectroscopy (for 1 and 3) proves the
existence of the intramolecular N!M coordination in
1
Figure 1. Molecular structures of compounds 1 (A) and 2 (B). There are two independent
molecules of 2 in the crystal structure. One molecule of 2 and the hydrogen atoms are
omitted for clarity. Selected bond lengths [Š] and angles [8]: For 1: Sn1ÀC1 2.1453(18),
Sn1ÀN1 2.345(3), Sn1ÀCl1 2.665(2); C1-Sn1-Cl1 119.67(6), C1-Sn1-N1 86.56(7). For 2: Ge1À
the solution of C6D6 of 1–4. Thus, the H NMR spectra
of 1 and 2 revealed AX spin system for the methyl-
ene CH2N protons and four signals for the CH2 to-
gether with two signals for the CH3 protons of Et C1 2.008(7), Ge1ÀN1 2.125(6), Ge1ÀCl1 2.324(3); C1-Ge1-Cl1 96.7(2), C1-Ge1-N1 83.1(3).
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The tin and germanium atoms, respectively, are three-coordi-
nated in 1 and 2 by C1 and N1 atoms of L3 ligand and one
chlorine atom Cl1. The nitrogen, carbon, and chlorine atoms
form a basal plane and define distorted trigonal pyramidal ge-
ometry of Sn and Ge atoms due the presence of stereochemi-
cally active electron lone pair. The N1-Sn1 and N1-Ge1 distan-
ces (2.345(3) Š in 1 and 2.125(6) Š in 2) are the result of strong
N!SnII and N!GeII interactions.
vealed a broad resonance at d=688.1 ppm for which, howev-
er, no 119Sn–117Sn coupling could be detected. This value is very
close to the value found for [Sn{(2,6-Me2NCH2)2C6H3}]2 (d=
612 ppm),[7b] in which the tin atom is stabilized by two N!Sn
coordination. The 119Sn NMR spectrum of 7 revealed a broad
resonance at d=264.1 ppm, which is upfield-shifted when
compared with that of 5 and [Sn{(2,6-Me2NCH2)2C6H3}]2.[7b,h] On
the other hand, the value of d 119Sn in 7 is shifted downfield
when compared with the related N!Sn coordinated distan-
nynes containing N,C,N-pincer ligands with C=N imine func-
tionality (d=79 for [Sn{(tBuN=CH)2C6H3}]2 and 115 and
134 ppm in [Sn{(2,6-iPr2C6H3N=C(CH3))2C6H3}]2, respectively).[7g,a]
The value of d 119Sn in 7 is thus similar to the value found in
tBuNC adduct of single-bonded amido-distannyne L†SnSnL†
(d=241 ppm, L† =ÀN(Ar†)(SiiPr3),
Treatment of 1 with K[BHEt3] and treatment of 2 with KC8 in
THF resulted in red solutions that provided, after the work up,
dark-red C,N-chelated distannyne [L3Sn]2 (5) and orange C,N-
chelated digermyne [L3Ge]2 (6), respectively (Scheme 3). In
a similar manner, the treatment of 3 with KC8 in THF yielded
a blue-green solution that provided, after the work up, the
Ar† =C6H2{C(H)Ph2}2iPr-2,4,6),[10]
in which the tin centrum is
three-coordinate, similar to 7.
Single crystals suitable for X-
ray diffraction analysis of 5–7
were obtained from hexane sol-
utions at À208C. The molecular
structures of 5–7 are shown in
Figures 2–4 and selected geo-
metrical parameters are given in
Table 1.
The Sn1ÀSn2 distances of
2.9692(17) Š in 5 and 2.9393(6) Š
in 7 lie between 2.668(1) and
3.066(1) Š of the parent com-
pounds Ar’SnSnAr’ and Ar*SnS-
nAr*, respectively, in which Ar’=
C6H3-2,6-(C6H3-2,6-iPr2)2
and
Ar*=C6H2-2,6-(C6H3-2,6-iPr2)2-4-
SiMe3.[1,6c] The SnÀSn bond
lengths are close to those found
in related intramolecularly coor-
dinated distannynes (range of
2.8981(1)–486(6) Š) stabilized by
Y,C,Y-chelating ligands (Y=N,
O),[7a,b,e,g] but they are shorter
Scheme 3. Synthesis of compounds 5–8.
dark-blue/green C,N-chelated distannyne [L4Sn]2 (7). In con-
trast, when compound 4 was reduced by KC8 in THF, the de-
composition was observed only. The digermyne [L4Ge]2 (8)
was, however, prepared by the treatment of 4 with potassium
in toluene at À788C as an air- and moisture-sensitive deep-
blue crystals (Scheme 3).
Compounds 5–8 were characterized by using NMR spectros-
1
copy. The H and 119Sn NMR spectroscopy (for 5 and 7) proves
the existence of the intramolecular N!M coordination in the
C6D6 solution of 5–8.
1
Thus, the H NMR spectra of 5 and 6 revealed an AX spin
system for the methylene CH2N protons and four signals for
the CH2 protons together with two signals for the CH3 protons
1
of the Et groups. The H NMR spectra of 7 and 8 revealed two
signals for the CH and four signals for the CH3 protons of iPr
groups. In addition, the 119Sn NMR spectrum (C6D6) of 5 re-
Figure 2. Molecular structure of 5. Hydrogen atoms are omitted for clarity.
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bonded amido-digermyne L*GeGeL* (2.7093(7) Š, L*=
ÀN(Ar*)(SiMe3), Ar*=C6H2{C(H)Ph2}2Me-2,4,6).[12] The intramo-
lecular GeÀN distances are 2.190(3) Š for Ge1ÀN1 and
2.184(3) Š for Ge2ÀN2 being somewhat longer than those
found in related N!Ge coordinated digermynes (range of
1.986(3)–36(3) Š).[11] The C1-Ge1-Ge2 and C20-Ge2-Ge1 angles
with values of 97.76(10) and 96.87(10)8, respectively, lie be-
tween 89.10(9) and 116.11(10)8 of the parent N!Ge coordinat-
ed digermynes.[11]
Prepared C,N-chelated distannynes 5 and 7 contain three-co-
ordinate tin atoms. As a result, the N!Sn interaction in 5 and
7 is stronger than the values found in single-bonded distan-
nynes containing N,C,N-ligands. In the C,N-chelated digermyne
6, the GeÀGe bond length is longer than in the related single-
bonded digermynes stabilized by N,C,N-pincer-type ligand
(Figure 4). This elongation of the GeÀGe bond cannot be result
of the stronger N!Ge interac-
Figure 3. Molecular structure of 7. Hydrogen atoms are omitted for clarity.
tion in 6, since the N!Ge coor-
Table 1. Selected bond lengths [Š] and angles [8] for 5–7 and 10 (Gaussian 09, M06-2X/def2-TZVP).
dination in 6 is weaker than in
related digermynes containing
N,C,N-pincer ligands.
Exptl
DFT
Exptl
DFT
Compound
5
7
Sn1ÀSn2
Sn1ÀN1
Sn2ÀN2
Sn1ÀC1
2.9692(17)
2.373(5)
2.371(5)
2.212(5)
93.45(15)
77.71(19)
3.005
2.425
2.420
2.234/2.231
94.3/99.7
77.0
2.9393(7)
2.228(4)
2.223(4)
2.193(5)
105.30(14)
76.99(17)
3.002
2.266
2.273
2.225/2.227
105.0/104.8
76.8
Synthesis and characterization
of N,C,N-chelated distannyne
[L5Sn]2 (10)
C1-Sn1-Sn2
C1-Sn1-N1
Compound
M1ÀM2
An intramolecularly coordinated
distannyne [L5Sn]2 (10) stabilized
by sterically demanding pincer
type ligand L5 was also synthe-
sized, with the aim of possible
comparison of the bonding sit-
uation in three-coordinate C,N-
chelated distannynes [L3Sn]2 (5)
and [L4Sn]2 (7). Treatment of the
6 (M=Ge)
10 (M=Sn)
2.68180(6)
2.190(3)
–
2.184(3)
–
2.631
2.210
–
2.212
–
–
2.303/2.033
97.8/100.1
81.2
2.9250(5)/2.9086(5)
2.482(3)/2.455(3)
2.526(3)/2.664(3)
2.983
2.531
2.567
M1ÀN1
M1ÀN2
M2ÀN2
M2ÀN3
2.492(3)/2.449(3)
2.613(3)/2.652(3)
2.146(3)/2.154(4)
108.27(9)/107.58(10)
71.43(10)/72.32(12)
2.532
2.525
2.170/2.164
108.5/102.9
70.7
M2ÀN4
–
M1ÀC1
2.020(3)
97.76(10)
80.48(13)
C1-M1-M2
C1-M1-N1
when compared with single-bonded amido-distannyne
L†SnSnL† (3.1429(7) Š, L† =-N(Ar†)(SiiPr3), Ar† =C6H2{C(H)Ph2}2iPr-
2,4,6).[10] The intramolecular SnÀN distances are 2.373(5) Š for
Sn1ÀN1 and 2.371(5) Š for Sn2ÀN2 in 5 (2.228(4) Š for Sn1ÀN1
and 2.223(4) Š for Sn2ÀN2 in 7). These are shorter than the
SnÀN distances found in related N!Sn coordinated distan-
nynes stabilized by N,C,N-pincer type ligands (the range of
2.4129(16)–2.6879(17) Š).[7a,b,g] The SnÀN interactions found in
5 and 7 represent one of the strongest coordination found in
N!Sn coordinated distannynes. The C1-Sn1-Sn2 and C20-Sn2-
Sn1 angles have values of 93.45(15) and 93.82(18)8 in 5,
whereas wider angles C1-Sn1-Sn2 (105.30(14)8) and C28-Sn2-
Sn1 (103.37(14)8) were found in 7. However, these bonding
angles lie between 96.63(5) and 121.26(4)8 of the parent Y,C,Y-
chelated distannynes (Y=N, O).[7a,b,e,g]
Figure 4. Molecular structure of 6. Hydrogen atoms are omitted for clarity.
The Ge1ÀGe2 distance of 2.6180(6) Š is longer than
2.5059(5) and 2.5685(5) Š of the parent N!Ge intramolecularly
coordinated digermynes [Ge{(2,6-iPr2C6H3N=CH)2C6H3}]2 and
[Ge{2-(2,6-iPr2C6H3N=C(CH3))C6H2(OCH2O)}]2.[11] The GeÀGe bond
length is, however, shorter when compared with single-
corresponding organolithium compound L5Li with SnCl2 pro-
vided the stable N,C,N-chelated chlorostannylene L5SnCl (9).
Treatment of 9 with KC8 in THF provided dark-blue N,C,N-che-
lated distannyne [L5Sn]2 (10) as air- and moisture-sensitive crys-
tals (Scheme 4).
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of the presence of N!Sn coor-
dination, both tin atoms of 10
are four-coordinated. Interesting-
ly, structurally related N!Sn co-
ordinated distannyne [Sn{(2,6-
iPr2C6H3N=C(CH3))2C6H3}]2, report-
ed by Roesky and co-workers,
contains one nitrogen donor
of the pincer ligand un-
coordinated,[7a]
atoms in distannynes [Sn{(2,6-
whereas
tin
Scheme 4. Synthesis of N,C,N-chelated distannyne 10.
[7b]
Me2NCH2)2C6H3}]2
and
[Sn{(tBuN=CH)2C6H3}]2,[7g] for ex-
ample, compounds containing sterically less-demanding pincer
substituents, are coordinated by both nitrogen atoms of
pincer ligands, in a similar manner as 10. It is evident that the
steric bulk of chelating ligands can affect the tin coordination
environment in intramolecularly coordinated distannynes.
The literature search thus indicates a wide range of SnÀSn
and GeÀGe bond lengths for structurally related distanynnes
and digermynes that mutually differ by the substituents. There-
fore, crystal structures of distannynes and digermynes of the
type arylÀMÀMÀaryl have been analyzed to find a correlation
between the MÀM bond length and the combination of C-M-
M angle. It can be generalized that the distanynnes with a SnÀ
Sn multiple bond have the SnÀSn bond lengths in the range
of 2.646–2.716 Š and the CÀSnÀSn moiety is in plane with the
aromatic system of the Sn-bound ligand with bond angles of
121.85–125.218 (see the Supporting Information, Figure S1 and
Table S1). In contrast, in the related compound with SnÀSn
single bond, that range of SnÀSn bond lengths is 2.898–
3.066 Š and the CÀSnÀSn moiety is basically perpendicular to
the aromatic system of the Sn-bound aromatic ring with the
bond angles 93.45–101.988 (see the Supporting Information,
Figure S1 and Table S1). From this point of view, complex 7
represents rare example of the single-bonded distannyne with
a wide CÀSnÀSn angle as the result of crystal packing effect of
ligand L4. This can be further demonstrated by the value of C-
Sn-Sn-C torsion angle that is 73.158. Similar trends have been
found in digermynes. The digermynes with GeÀGe multiple
bond have the GeÀGe bond lengths in the range of 2.212–
2.306 Š and the C-Ge-Ge moiety is in plane with the aromatic
system of the Ge-bound ligand with bond angles of 136.1–
121.98. In contrast, there are two compounds with GeÀGe
single bond having the GeÀGe bond lengths in the range of
2.506–2.569 Š and the narrow values of the C-Ge-Ge bond
angles at 89.1–98.28. Careful interpretation also suggests that
the GeÀGe bond length regularly decrease with the narrower
C-Ge-Ge angle. Nearly linear correlation of both mentioned
values (GeÀGe bond and C-Ge-Ge angle) has been found (see
the Supporting Information, Figure S2 and Table S2). The C,N-
chelated complex 6 is, however, out of this range and repre-
sents the single-bonded digermyne with an extra-long GeÀGe
bond.
Compound 10 was characterized by using NMR spectrosco-
1
py. The H and 119Sn NMR spectroscopy proves the existence of
the intramolecular N!Sn coordination in the solution of C6D6
1
of the N,C,N-chelated distannyne [L5Sn]2 (10). The H spectrum
of 10 revealed one signal for the CHÀN group and one signal
for the Me groups. In addition, the 119Sn NMR spectrum of 10
revealed a broad resonance at d=118 ppm, which is upfield-
shifted when compared with that of 5 (d=688.1 ppm), 7 (d=
264.1 ppm), and [Sn{(2,6-Me2NCH2)2C6H3}]2 (d=612 ppm).[7b]
The value of d 119Sn in 10 is close to the values found in struc-
turally related N!Sn coordinated distannyne [SnC6H3{2,6-
iPr2C6H3N=C(CH3)}2]2 (d=115 and 134, respectively)[7a] and
[{tBuN=CH}2]2 (d=79 ppm)[7g] containing N,C,N-pincer ligands
with a C=N imine functionality.
Single crystals suitable for X-ray diffraction analysis of 10
were obtained from hexane solutions at À208C. The molecular
structure of 10 consists of two independent molecules and is
shown in Figure 5. Selected geometrical parameters are given
in the Table 1.
Figure 5. Molecular structure of 10. Hydrogen atoms are omitted for clarity.
The Sn1ÀSn2 distance of 2.9250(5) Š (Sn3ÀSn4=2.9086(5) Š)
lie between 2.8981(1) and 3.0486(6) Š of the parent distan-
nynes stabilized by Y,C,Y-pincer ligands (Y=N, O),[7a,b,e,g] but
they are shorter when compared with that of single-bonded
amido-distannyne L†SnSnL† (3.1429(7) Š, L† =ÀN(Ar†)(SiiPr3),
Ar† =C6H2{C(H)Ph2}2iPr-2,4,6).[10] The intramolecular SnÀN dis-
tances vary between 2.449(3) Š for Sn4ÀN7 and 2.664(6) Š for
Sn3ÀN6 and they are within the range of 2.4129(16)–
2.6879(17) Š found in related N!Sn coordinated distannyn-
es,[7a,b,g] but longer than those found in 5 and 7. As the result
Chem. Eur. J. 2015, 21, 7820 – 7829
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
DFT calculations
donor of ligand L4 and the latter coordinates the metal center
through a stronger N!Sn interaction. This is reflected in
a Wiberg index of 0.23 for the N!Sn interaction for 5 and of
0.29 for 7. As result, the NBO charges increase for tin atom
going from 5 (0.49) to 7 (0.65). Simultaneously, the WBI de-
creases for the SnÀSn bond going from 5 (0.91) to 7 (0.79)
since the tin atoms obtain more stabilization from the imine
donors. Similarly to 7, the WBI for the SnÀSn bond is 0.77 in
compound 10, which indicates a similar character of the SnÀSn
bond in 7 and 10. In contrast, a weaker N!Sn interaction in 5
resulted in a large value of the WBI indicating a large SnÀSn
bond strength, that is, however, still a single bond, as the
length of the SnÀSn bond is in the range of a standard SnÀSn
single bond.[13] In comparison between the three-coordinate
distannyne 7 and the four-coordinate distannyne 10, it appears
that the imine-donors in 10 donate less each, since the tin
atom is four-coordinate here.
As the intramolecularly coordinated distannyne [L5Sn]2 (10) sta-
bilized by sterically demanding pincer type ligand L5 contains
four-coordinate tin atoms, whereas C,N-chelated distannynes
[L3Sn]2 (5) and [L4Sn]2 (7) contain three-coordinate tin atoms,
the bonding situation was evaluated by DFT calculations. DFT
calculations also enable the comparison of the nature of the
metal–metal bond in C,N-chelated distannyne [L3Sn]2 (5) and
related digermyme [L3Ge]2 (6). For these main group com-
plexes, M06-2X has proven to be a highly useful functional
with good predictive ability for molecular properties. Table 1
summarizes the key geometric data in comparison to the ex-
perimental data for 5, 6, 7, and 10 and shows a good accord-
ance between both data sets. In the next step, natural bond
orbitals and charges as well as Wiberg bond indices (WBI) have
been calculated (Tables 2 and 3 and Figure 6) for these four
complexes.
With regard to the molecular orbitals, natural bond orbitals
are helpful to visualize the lone pairs and the metal–metal
bonds because they are more localized than the canonical or-
bitals (Figure 6). In all four compounds, the lone pair possesses
a large p-contribution, which gives the lone pair a predominant
direction.
The Wiberg indices give an impression of the bond strength
of the regarded bonds. Compound 5 is stabilized by an amine
donor of ligand L3, whereas compound 7 possesses an imine
Table 2. NBO charges (in e-units) in 5–7 and 10 (M06-2X/def2-TZVP).
The different strength of N!Sn interaction again influences
the nature of the lone pair. The p-contribution of the lone pair
decreases slightly going from 5 (22%) to 7 and 10 (19%) since
the tin atoms obtain more stabilization from the imine donors.
Since the p-contribution is significant and giving a strong di-
rectionality, we interpret these data as a stereochemically
active lone pair.
5 (M=Sn)
6 (M=Ge)
7 (M=Sn)
10 (M=Sn)
M
N
C
0.49
À0.48
À0.45
0.36
À0.46
À0.41
0.65
À0.59
À0.43
0.72
À0.50
À0.43
DFT calculations were also used to compare the nature of
the metal–metal bond in three-coordinate distannyne 5 and
digermyme 6, stabilized by ligand L3. The NBO charges de-
creases for the central atom going from tin in 5 (0.49) to ger-
manium in 6 (0.36), whereas the WBI remains constant for the
metal–metal bond going from 5 (0.91) to 6 (0.93). The p-contri-
bution of the lone pair increases going from 5 (22%) to 6
(28%). This clearly demonstrates that ligand L3 is able
to stabilize strong metal–metal bonds in the dis-
cussed compounds. It is also evident that the
strength of N!Sn interaction may influence the
nature of the lone pair and the strength of metal–
metal bond.
Table 3. Wiberg bond indices in 5–7 and 10 (M06-2X/def2-TZVP).
5 (M=Sn)
6 (M=Ge)
7 (M=Sn)
10 (M=Sn)
MÀM
MÀN
MÀC
0.91
0.23
0.64
0.93
0.29
0.75
0.79
0.29
0.64
0.77
0.18
0.64
Conclusion
We have demonstrated that the application of C,N-
chelating ligands L3,4 containing a tBu group in the
ortho position towards metal atoms provided stable
C,N-chelated chlorostannylenes and germylenes 1–4.
Both ligands L3,4 have been also shown to be suffi-
cient for the stabilization of C,N-chelated distannynes
and digermynes 5–8 containing three-coordinate
metal centers. The tetrynes were so far stabilized by
either sterical bulky terphenyl ligands (two-coordi-
nate metal center), or by Y,C,Y-pincer ligands (four-co-
ordinate metal center). The design of new C,N-chelat-
Figure 6. Natural bond orbitals of the lone pairs (only one per compound shown) and
the metal–metal bonds of 5–7 and 10.
Chem. Eur. J. 2015, 21, 7820 – 7829
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Full Paper
ing ligands L3,4 thus provided a new type of tetrynes having
three-coordinate metal atoms. The values of SnÀSn bond
lengths found in distannynes 5 and 7 suggest that, despite the
three-coordinate tin center, these compounds are still single-
bonded species, similar to those stabilized by Y,C,Y-pincer-type
ligands. However, a wide C-Sn-Sn angle has been found in the
complex 7 as the result of crystal-packing effect of ligand L4. In
contrast, C,N-chelated digermyne 6 represents the example
with the longest GeÀGe bond length found in diaryldiger-
mynes.
149.1 ppm (Ar-C); elemental analysis calcd (%) for C19H32BrN
(354.38): C 64.4, H 9.1; found: C 64.6, H 9.0.
L4Br: 2,6-Diisopropylaniline (14.9 g, 84 mmol) was added to a solu-
tion of 2-bromo-3,5-di-tert-butylbenzaldehyde (25 g, 84 mmol) in
methanol (75 mL) at room temperature. After the addition of a few
drops of formic acid, the precipitation of yellow solid was ob-
served. The reaction mixture was stirred overnight. The yellow
solid was filtered off, washed with cold methanol, and dried under
vacuum to give L4Br. Yield: 28 g (73%). M.p. 129–1318C; 1H NMR
(C6D6, 400.13 MHz): d=1.21 (d, 12H, CH3, 3J(1H, 1H)=6.8 Hz), 1.25
3
1
(s, 9H, C(CH3)), 1.51 (s, 9H, C(CH3)), 3.21 (sept, 2H, CH, J(1H, H)=
4
1
6.8 Hz), 7.15–7.17 (m, 3H, ArH), 7.67 (d, 1H, ArH, J(1H, H)=2.4 Hz),
8.53 (d, 1H, ArH, 4J(1H, 1H)=2.4 Hz), 8.99 ppm (s, 1H, CH=N);
13C NMR (C6D6, 100.61 MHz): d=24.0 ((CH3)2CH), 28.8 ((CH3)2CH),
30.6 (C(CH3)3), 31.5 (C(CH3)3), 35.3 (C(CH3)3), 37.9 (C(CH3)3), 123.8,
124.1, 125.1, 125.2, 128.8, 137.5, 138.1, 148.7, 150.3, 150.8 (Ar-C),
164.1 ppm (CH=N); elemental analysis calcd (%) for C27H38BrN
(456.51): C 71.0, H 8.4; found: C 70.8, H 8.3.
DFT studies further showed that the strength of metal–metal
bond as well as the character of lone electron pair can be
tuned by the N!M (M=Sn, Ge) interaction. Compounds 5
and 6, which are stabilized by an amine donor of ligand L3,
have large values of the WBI for the metal–metal bonds,
whereas compounds 7 and 10, in which tin atoms obtain
more stabilization from the imine donors, showed weaker
metal–metal bonds with a lower WBI. All the data thus demon-
strated that both ligands L3,4 differ mutually. It has been further
demonstrated that p-contribution of the lone pair can be
tuned by the appropriate ligand system (L3 vs. L4) and the
higher p-character of lone pair can increase the bonding char-
acter of the MÀM bond. The DFT studies thus demonstrated
that in contrast to strictly single-bonded tetrynes that are sta-
bilized by Y,C,Y-chelating ligands, the use of C,N-chelating li-
gands may tune the nature of the metal–metal bond.
L3SnCl (1): A hexane solution of nBuLi (3.8 mL of 1.6m) was added
to a stirred solution of L3Br (2.05 g, 5.78 mmol) in Et2O (30 mL) at
08C. The mixture was allowed to warm up to room temperature
and stirred for 1 h. After that, the resulting yellow solution of L3Li
was cooled to À788C and added dropwise to the solution of SnCl2
(1.09 g, 5.78 mmol) in THF (15 mL) pre-cooled to À788C to give
pale-yellow solution. The reaction mixture was left to warm up to
room temperature and stirred for 4 h. Then, all volatiles were re-
moved under reduced pressure, the residue was suspended in
hexane (40 mL) and the insoluble material was filtered off. The fil-
trate was evaporated and the residue was extracted with hexane
(30 mL) once again. The hexane filtrate was concentrated and
cooled to À308C to afford colorless crystals of 1. Yield: 1.51 g
(61%); M.p. 114–1178C1H NMR (C6D6, 400.13 MHz): d=0.41 (t, 3H,
Experimental Section
3
1
3
1
CH3(Et), J(1H, H)=7.2 Hz), 0.75 (t, 3H, CH3(Et), J(1H, H)=6.8 Hz),
General procedures
1.35 (s, 9H, C(CH3)), 1.54 (s, 9H, C(CH3)), 2.12 (m, 1H, CH2(Et), J(1H,
3
1H)=7.2 Hz), 2.20 (m, 1H, CH2(Et), J(1H, H)=7.2 Hz), 2.65 (m, 1H,
3
1
All reactions were carried out under argon, using standard Schlenk
techniques. Solvents were dried by standard methods, and distilled
prior to use. Starting compounds L5Br was prepared according to
the literature[14] and SnCl2 and GeCl2*dioxane were purchased from
3
1
3
1
CH2(Et), J(1H, H)=6.8 Hz), 3.13 (m, 1H, CH2(Et), J(1H, H)=6.8 Hz),
3.46 and 4.42 (AX system, 2H, CH2N), 7.09 (s, 1H, ArH), 7.55 ppm (s,
1H, ArH); 13C NMR (C6D6, 100.61 MHz): d=7.9, 11.3 (CH3(Et)), 32.0
(C(CH3)), 34.5 (C(CH3)), 35.3 (C(CH3)), 38.3 (C(CH3)), 42.3, 46.3
(CH2(Et)), 63.3 (CH2N), 120.2, 121.9, 146.7, 150.9, 158.9, 167.4 (Ar-
C) ppm; 119Sn NMR (C6D6, 149.23 MHz): d=269.4 ppm; elemental
analysis calcd (%) for C19H32ClNSn (428.62): C 53.2, H 7.5; found: C
53.4, H 7.4.
1
Sigma Aldrich. The H, 13C, and 119Sn NMR spectra were recorded
1
on a Bruker Avance500 spectrometer at 300 K in C6D6. The H, 13C,
and 119Sn NMR chemical shifts (d) are given in ppm and referenced
to external Me4Si. Elemental analyses were performed on an LECO-
CHNS-932 analyzer.
L3GeCl (2): A hexane solution of nBuLi (1.92 mL of 1.6m) was
added to a stirred solution of L3Br (1.04 g, 2.94 mmol) in Et2O
(20 mL) at 08C. The mixture was allowed to warm up to room tem-
perature and stirred for 1 h. After that the resulting yellow solution
of L3Li was cooled to À788C and added dropwise to the solution
of GeCl2.dioxane (0.68 g, 2.94 mmol) in THF (15 mL) pre-cooled to
À788C to give pale-yellow solution. The reaction mixture was left
to warm up to room temperature and stirred overnight. Then, all
volatiles were removed under reduced pressure, the residue was
suspended in hexane (40 mL), and the insoluble material was fil-
tered off. The filtrate was evaporated and the residue was extract-
ed with hexane (30 mL) once again. The hexane filtrate was con-
centrated and cooled to À308C to afford colorless crystals of 2.
Yield: 0.44 g (39%). For 2: M.p. 99–1038C; 1H NMR (C6D6,
Syntheses
L3Br: Diethylamine (15.8 g, 216 mmol) was added to a solution of
2-bromo-1-bromomethyl-3,5-di-tert-butylbenzene[15]
(26.1 g,
72 mmol) in Et2O (150 mL) at room temperature and the reaction
mixture was stirred overnight. After that, the insoluble material
was filtered off and the filtrate was evaporated to give crude prod-
uct as yellow oil. The crude product was dissolved in Et2O (150 mL)
and HCl (aq) (1:2, 150 mL) was added. The organic phase was dis-
carded, to the aqueous phase KOH was added and the mixture
was extracted with Et2O (2”200 mL). The organic phase was dried
over MgSO4 and evaporated under reduced pressure to give L3Br
as white solid. Yield: 23.5 g (92%). M.p. 38–408C; 1H NMR (C6D6,
400.13 MHz): d=0.95 (t, 6H, CH3(Et), J(1H, H)=7.2 Hz), 1.32 (s, 9H,
C(CH3)), 1.61 (s, 9H, C(CH3)), 2.44 (q, 4H, CH2(Et), J(1H, H)=7.2 Hz),
3.77 (s, 2H, CH2N), 7.52 (d, 1H, ArH, J(1H, H)=2.4 Hz), 7.86 ppm
(d, 1H, ArH, 4J(1 H, 1 H)=2.4 Hz); 13C NMR (C6D6, 100.61 MHz): d=
12.4 (CH3(Et)), 30.2 (C(CH3)), 31.2 (C(CH3)), 34.7 (C(CH3)), 37.3
(C(CH3)), 47.6 (CH2(Et)), 59.6 (CH2N), 121.9, 123.4, 125.6, 141.1, 147.1,
400.13 MHz): d=0.55 (t, 3H, CH3(Et), J(1H, H)=7.2 Hz), 0.95 (t, 3H,
3
1
3
1
CH3(Et), J(1H, H)=6.8 Hz), 1.40 (s, 9H, C(CH3)), 1.68 (s, 9H, C(CH3)),
3
1
3
1
4
1
3
1
3
2.15 (m, 1H, CH2(Et), J(1H, H)=7.2 Hz), 2.32 (m, 1H, CH2(Et), J(1H,
1H)=7.2 Hz), 2.63 (m, 1H, CH2(Et), J(1H, H)=7.2 Hz), 3.23 (m, 1H,
CH2(Et), 3J(1H, 1H)=7.2 Hz), 3.35 and 4.35 (AX system, 2H, CH2N),
7.03 (s, 1H, ArH), 7.50 ppm (s, 1H, ArH); 13C NMR (C6D6,
3
1
Chem. Eur. J. 2015, 21, 7820 – 7829
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
100.61 MHz): d=7.2, 10.3 (CH3(Et)), 31.6 (C(CH3)), 33.7 (C(CH3)), 34.8
(C(CH3)), 37.7 (C(CH3)), 42.0, 46.2 (CH2(Et)), 61.9 (CH2N), 118.4, 121.1,
144.3, 150.9, 154.3, 156.6 ppm (Ar-C); elemental analysis calcd (%)
for C19H32ClNGe (382.56): C 59.7, H, 8.4; found: C 59.9, H 8.5.
1858C. 1H NMR (C6D6, 400.13 MHz): d=0.55 (t, 6H, CH3(Et), 3J(1H,
1H)=7.2 Hz), 1.00 (t, 6H, CH3(Et), 3J(1H, 1H)=7.2 Hz), 1.15 (s, 18H,
C(CH3)), 1.41 (s, 18H, C(CH3)), 2.66 (m, 2H, CH2(Et), 3J(1H, 1H)=
7.2 Hz), 2.80 (m, 2H, CH2(Et), 3J(1H, 1H)=7.2 Hz), 3.19 (m, 2H,
CH2(Et), J(1H, H)=7.2 Hz), 3.76 (m, 2H, CH2(Et), J(1H, H)=7.2 Hz),
3.83 and 4.15 (AX system, 4H, CH2N), 7.09 (s, 2H, ArH), 7.42 ppm (s,
2H, ArH); 13C NMR (C6D6, 100.61 MHz): d=9.2, 12.5 (CH3(Et)), 32.2
(C(CH3)), 32.3 (C(CH3)), 35.0 (C(CH3)), 37.7 (C(CH3)), 46.6, 48.2
(CH2(Et)), 67.5 (CH2N), 119.4, 121.3, 143.3, 147.6, 158.0, 166.7 ppm
(Ar-C); 119Sn NMR (C6D6, 149.23 MHz): d=688.4 ppm; elemental
analysis calcd (%) for C38H64N2Sn2 (786.33): C 58.1, H 8.2; found: C
58.4, H 8.5.
3
1
3
1
L4SnCl (3): A hexane solution of nBuLi (1.66 mL of 1.6m) was
added to a stirred solution of L4Br (1.01 g, 2.21 mmol) in THF
(20 mL) at À788C. The mixture was allowed to warm up to À408C
and stirred for 1 h at this temperature. After that the resulting red-
orange solution of L4Li was cooled to À788C and added dropwise
to the solution of SnCl2 (0.42 g, 2.21 mmol) in THF (15 mL) pre-
cooled to À788C to give orange solution. The reaction mixture
was left to warm up to room temperature and stirred 1 h. Then, all
volatiles were removed under reduced pressure, the residue was
suspended in toluene (40 mL), and the insoluble material was fil-
tered off. The toluene filtrate was evaporated and the solid was
washed with hexane to afford yellow powder material character-
ized as 3. Yield: 1.05 g (89%). M.p. 182–1858C; 1H NMR (C6D6,
L3GeGeL3 (6): A solution of 2 (0.44 g, 1.14 mmol) in THF (15 mL)
was added to freshly prepared KC8 (0.17 g, 1.25 mmol) at room
temperature and the color of the solution immediately changed
from pale yellow to dark-red/orange. The reaction mixture was
stirred overnight. The solvent was removed under reduced pres-
sure and the residue was extracted with hexane (30 mL). The
hexane filtrate was concentrated and cooled to À308C to afford
400.13 MHz): d=1.08 (d, 3H, CH3, J(1H, H)=8.0 Hz), 1.15 (d, 3H,
3
1
3
1
3
1
CH3, J(1H, H)=8.0 Hz), 1.30 (d, 3H, CH3, J(1H, H)=8.0 Hz), 1.38 (s,
9H, C(CH3)), 1.54 (d, 3H, CH3, 3J(1H, 1H)=8.0 Hz), 1.64 (s, 9H,
C(CH3)), 3.15 (sept, 1H, CH, J(1H, H)=8.0 Hz), 3.76 (sept, 1H, CH,
orange crystals of 6. Yield: 0.19 g (48%). M.p. 128–1318C. H NMR
1
3
1
3
1
(C6D6, 400.13 MHz): d=0.79 (t, 6H, CH3(Et), J(1H, H)=7.2 Hz), 0.91
3J(1H, H)=8.0 Hz), 7.18 (t, 1H, ArH, J(1H, H)=4.0 Hz), 7.30 (d, 1H,
ArH, 3J(1H, 1H)=4.0 Hz), 7.57 (s, 1H, ArH), 7.93 (s, 1H, ArH),
8.27 ppm (s, 1H, CH=N); 13C NMR (C6D6, 100.61 MHz): d=23.9, 24.5,
24.6, 25.9 ((CH3)2CH), 28.3, 29.6 ((CH3)2CH), 31.1 (C(CH3)3), 33.4
(C(CH3)3), 34.6 (C(CH3)3), 38.4 (C(CH3)3), 123.6, 125.0, 128.5, 129.5,
140.8, 142.4, 142.8, 143.2, 151.0, 159.8 (Ar-C), 177.5 ppm (CH=N);
119Sn NMR (C6D6, 149.23 MHz): d=154.7 ppm; elemental analysis
calcd (%) for C27H38ClSnN (530.76): C 61.1, H 7.2; found: C 61.3, H
7.4.
(t, 6H, CH3(Et), 3J(1H, 1H)=7.2 Hz), 1.18 (s, 18H, C(CH3)), 1.40 (s,
1
3
1
3
1
18H, C(CH3)), 2.44 (m, 2H, CH2(Et), J(1H, H)=7.2 Hz), 2.81 (m, 2H,
3
1
3
1
CH2(Et), J(1H, H)=7.2 Hz), 3.54 (m, 2H, CH2(Et), J(1H, H)=7.2 Hz),
3.69 (m, 2H, CH2(Et), J(1H, H)=7.2 Hz), 3.46 and 4.46 (AX system,
4H, CH2N), 7.00 (s, 2H, ArH), 7.35 ppm (s, 2H, ArH); 13C NMR (C6D6,
100.61 MHz): d=9.9, 10.1 (CH3(Et)), 32.1 (C(CH3)), 32.8 (C(CH3)), 34.9
(C(CH3)), 37.8 (C(CH3)), 46.7, 46.9 (CH2(Et)), 65.9 (CH2N), 118.3, 121.6,
141.2, 146.9, 154.8, 160.4 ppm (Ar-C); elemental analysis calcd (%)
for C38H64N2Ge2 (694.16): C 65.8, H 9.3; found: C 66.0, H 9.4
3
1
L4GeCl (4): A hexane solution of nBuLi (1.59 mL of 1.6m) was
added to a stirred solution of L4Br (0.97 g, 2.12 mmol) in THF
(20 mL) at À788C. The mixture was allowed to warm up to À408C
and stirred for 1 h at this temperature. After that the resulting red-
orange solution of L4Li was cooled to À788C and added dropwise
to the solution of GeCl2·dioxane (0.49 g, 2.12 mmol) in THF (15 mL)
pre-cooled to À788C to give orange solution. The reaction mixture
was left to warm up to room temperature and stirred 1 h. Then, all
volatiles were removed under reduced pressure, the residue was
suspended in hexane (30 mL) and the insoluble material was fil-
tered off. The hexane filtrate was concentrated and cooled to
À308C to afford orange crystals of 4. Yield: 0.65 g (63%). M.p.
L4SnSnL4 (7): A solution of 3 (0.62 g, 1.17 mmol) in THF (15 mL)
was added to freshly prepared KC8 (0.18 g, 1.29 mmol) at room
temperature and the color of the solution immediately changed
from yellow to dark-blue/green. The reaction mixture was stirred
overnight. The solvent was removed under reduced pressure and
the residue was extracted with hexane (30 mL). The hexane filtrate
was concentrated and cooled to 48C to afford dark-brown crystals
of 7. Yield: 0.34 g (58%). M.p. 139–1438C; 1H NMR (C6D6,
3
1
400.13 MHz): d=0.87 (d, 6H, CH3, J(1H, H)=6.8 Hz), 0.95 (s, 18H,
3
1
3
C(CH3)), 1.15 (d, 6H, CH3, J(1H, H)=6.8 Hz), 1.19 (d, 6H, CH3, J(1H,
1H)=6.8 Hz), 1.32 (s, 18H, C(CH3)), 1.53 (d, 6H, CH3, 3J(1H, 1H)=
6.8 Hz), 3.25 (sept, 2H, CH, J(1H, H)=6.8 Hz), 3.47 (sept, 2H, CH,
3
1
169–1738C; H NMR (C6D6, 400.13 MHz): d=0.94 (d, 3H, CH3, J(1H,
3J(1H, H)=6.8 Hz), 7.06 (d, 4H, ArH, J(1H, H)=5.0 Hz), 7.16 (t, 2H,
ArH, 3J(1H, 1H)=5.0 Hz), 7.34 (s, 2H, ArH), 7.69 (s, 2H, ArH),
8.29 ppm (s, 2H, CH=N); 13C NMR (C6D6, 100.61 MHz): d=24.0, 24.7,
25.0, 26.4 ((CH3)2CH), 28.4, 28.5 ((CH3)2CH), 31.1 (C(CH3)3), 31.2
(C(CH3)3), 34.1 (C(CH3)3), 36.8 (C(CH3)3), 123.7, 123.9, 124.6, 128.3,
141.4, 142.5, 145.0, 147.1, 158.7, 168.2 (Ar-C), 184.6 ppm (CH=N);
119Sn NMR (C6D6, 149.23 MHz): d=264.1; elemental analysis calcd
(%) for C54H76Sn2N2 (990.60): C 65.5, H 7.7; found: C 65.6, H 7.8.
1
3
1
3
1
1H)=7.0 Hz), 0.98 (d, 3H, CH3, J(1H, H)=8.0 Hz), 1.21 (d, 3H, CH3,
3
1
1
3
1
3J(1H, H)=7.0 Hz), 1.23 (s, 9H, C(CH3)), 1.33 (d, 3H, CH3, J(1H, H)=
8.0 Hz), 1.57 (s, 9H, C(CH3)), 3.15 (sept, 1H, CH, J(1H, H)=7.0 Hz),
3.44 (sept, 1H, CH, J(1H, H)=8.0 Hz), 7.03 (t, 1H, ArH, J(1H, H)=
3
1
3
1
3
1
5.0 Hz), 7.14 (d, 1H, ArH, J(1H, H)=5.0 Hz), 7.44 (s, 1H, ArH), 7.74
(s, 1H, ArH), 7.95 ppm (s, 1H, CH=N); 13C NMR (C6D6, 100.61 MHz):
d=24.6, 24.7, 25.2, 26.5 ((CH3)2CH), 28.8, 30.0 ((CH3)2CH), 31.6
(C(CH3)3), 33.5 (C(CH3)3), 35.1 (C(CH3)3), 38.9 (C(CH3)3), 124.2, 125.3,
127.1, 129.5, 141.1, 142.2, 143.9, 152.0, 158.3, 166.6 (Ar-C),
173.7 ppm (CH=N); elemental analysis calcd (%) for C27H38ClGeN
(484.69): C 66.9, H, 7.9; found: C 66.6, H 7.8.
3
1
L4GeGeL4 (8): A solution of 4 (0.21 g, 0.43 mmol) in toluene
(30 mL) was added to freshly deposited potassium mirror (18 mg,
0.47 mmol) at À788C. The reaction mixture was allowed to warm
up to room temperature and stirred 5 days. During this time the
color of the mixture changed from orange to dark blue and potas-
sium was consumed. The resulting suspension was filtered and tol-
uene filtrate was concentrated and cooled to 48C to afford dark-
blue crystals of 8. Yield: 60 mg (31%). M.p. 127–1308C. 1H NMR
L3SnSnL3 (5): A THF solution of K[(Et)3BH] (2.26 mL, 1m) was added
dropwise to a stirred solution of 1 (0.97 g, 2.26 mmol) in THF
(20 mL) at room temperature and the color of the solution
changed from pale yellow to dark red. The reaction mixture was
stirred for 2 h and then all volatiles were removed under reduced
pressure. The residue was suspended in toluene (20 mL) and the
insoluble material was filtered off. The toluene filtrate was evapo-
rated and washed with small amount of cold hexane to afford red
powder material characterized as 5. Yield: 0.55 g (62%). M.p. 182–
3
1
(C6D6, 400.13 MHz): d=0.90 (d, 6H, CH3, J(1H, H)=6.8 Hz), 0.97 (d,
3
1
6H, CH3, J(1H, H)=6.8 Hz), 1.10 (s, 18H, C(CH3)), 1.22 (d, 6H, CH3,
3J(1H, 1H)=6.8 Hz), 1.34 (s, 18H, C(CH3)), 1.52 (d, 6H, CH3, 3J(1H,
3
1
1H)=6.8 Hz), 3.23 (sept, 2H, CH, J(1H, H)=6.8 Hz), 3.37 (sept, 2H,
CH, 3J(1H, 1H)=6.8 Hz), 7.10–7.15 (m, 6H, ArH), 7.41 (s, 2H, ArH),
Chem. Eur. J. 2015, 21, 7820 – 7829
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Full Paper
7.72 (s, 2H, ArH), 8.24 ppm (s, 2H, CH=N); 13C NMR (C6D6,
100.61 MHz): d=23.5, 25.0, 25.1, 26.8 ((CH3)2CH), 28.1, 28.6
((CH3)2CH), 31.1 (C(CH3)3), 31.8 (C(CH3)3), 34.3 (C(CH3)3), 36.8
(C(CH3)3), 123.2, 123.6, 125.3, 127.1, 139.0, 142.4, 143.3, 146.9, 155.5,
159.6 (Ar-C), 174.8 ppm (CH=N); elemental analysis calcd (%) for
C54H76Ge2N2 (898.48): C 72.2, H 8.5; found: C 72.0, H 8.4.
methyl moiety with C-H=0.98, 0.97, and 0.93 Š for methyl, methyl-
ene and hydrogen atoms in aromatic rings, respectively. Crystallo-
graphic data for structural analysis have been deposited with the
Cambridge Crystallographic Data Centre. CCDC-1037996 (1), CCDC-
1037997 (5), CCDC-1037998 (6), CCDC-1037999 (2), CCDC-1038000
(10), and 1038001 (7) contain the supplementary 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.
L5SnCl (9): A hexane solution of nBuLi (0.84 mL of 1.6m) was
added to a stirred solution of L5Br (0.56 g, 1.34 mmol) in Et2O
(30 mL) at À708C and stirred for 3 h. The Et2O was filtrated and re-
maining solid was dissolved in toluene and the resulting solution
of L5Li was added dropwise to the toluene suspension of SnCl2
(0.26 g, 1.34 mmol) at À708C. The reaction mixture was left to
warm up to room temperature and stirred for 24 h. Then all vola-
tiles were removed under reduced pressure, the residue was sus-
pended in toluene/hexane (40 mL) and insoluble material was fil-
tered off. The filtrate was concentrated and cooled to À308C to
afford orange powder of 9. Yield: 0.51 g (77%). M.p. 168.1–
Acknowledgements
We are grateful to the Ministry of Education of the Czech Re-
public and to the Czech Science Foundation (project no. 15-
07091S) for supporting this work. Generous grants of comput-
ing time at the Paderborn Centre for Parallel Computing PC2
are gratefully acknowledged.
1
171.38C. H NMR (500.18 MHz, C6D6, 258C): d=2.43 (s, 12H, NCH3),
7.20–7.48 (m, 9H, ArH), 7.93 ppm (s, 2H, N=CH); 13C NMR
(125.77 MHz, C6D6, 258C): d=18.8 (CH3), 125.3, 128.2, 128.8, 128.9,
133.0, 142.2, 148.4, 169.1, 179.7 ppm; 119Sn NMR (186,49 MHz, C6D6,
258C): d=25.5 ppm; elemental analysis calcd (%) for C24H23N2ClSn
(493.6): C 58.4, H 4.7; found: C 58.6, H 4.9.
Keywords: coordination
modes
·
density
functional
calculations · germanium · main-group chemistry · NMR
spectroscopy · tin
L5SnSnL5 (10): A solution of 9 (0.51 g, 1.03 mmol) in THF (15 mL)
was added to freshly prepared KC8 (0.15 g, 1.11 mmol) at room
temperature and the color of the solution immediately changed
from orange to dark green. The reaction mixture was stirred for
4 h. The solvent was removed under reduced pressure and the res-
idue was extracted with hexane (30 mL). The hexane filtrate was
concentrated let to crystallize to afford black crystals of 10. Yield:
[1] A. D. Phillips, R. J. Wright, M. M. Olmstead, P. P. Power, J. Am. Chem. Soc.
2002, 124, 5930–5931.
[2] a) A. Sekiguchi, R. Kinjo, M. Ichinohe, Science 2004, 305, 1755–1757;
b) N. Wiberg, S. K. Vasisht, G. Fischer, P. Mayer, Z. Anorg. Allg. Chem.
2004, 630, 1823–1828; c) A. Sekiguchi, M. Ichinohe, R. Kinjo, Bull. Chem.
Soc. Jpn. 2006, 79, 825–832; d) A. Sekiguchi, Pure Appl. Chem. 2008, 80,
447–457; e) T. Sasamori, J. S. Han, K. Hironaka, N. Takagi, S. Nagase, N.
Tokitoh, Pure Appl. Chem. 2010, 82, 603–612; f) J. S. Han, T. Sasamori, Y.
Mizuhata, N. Tokitoh, J. Am. Chem. Soc. 2010, 132, 2546–2547; g) S. S.
Sen, A. Jana, H. W. Roesky, C. Schulzke, Angew. Chem. Int. Ed. 2009, 48,
8536–8538; Angew. Chem. 2009, 121, 8688–8690.
1
0.27 g (57%). M.p. 118 8C with decomp.; H NMR (500.18 MHz, C6D6,
258C): d=2.44 (s, 24H, NCH3), 7.22–7.44 (m, 18H, ArH), 7.92 ppm
(s, 4H, N=CH); 119Sn NMR (186.49 MHz, C6D6, 258C): d=118.0 ppm.
Computational details
The calculations were performed with Gaussian 09[16] by using the
hybrid functional M06–2X[17] with the Ahlrichs def2-TZVP basis
set,[18] which includes an effective core potential on tin. Tight con-
version criteria were applied. Both stationary points were charac-
terized by frequency analysis and show the correct number of neg-
ative eigenvalues (zero for a local minimum). Based on the geome-
try obtained by the M06–2X/def2-TZVP method, a NBO analysis
was performed by using this method with NBO 6.0.[19] The Wiberg
indices were used as implemented in Gaussian 09.
[3] a) M. Stender, A. D. Phillips, R. J. Wright, P. P. Power, Angew. Chem. Int.
Ed. 2002, 41, 1785–1787; Angew. Chem. 2002, 114, 1863–1865; b) Y. Su-
giyama, T. Sasamori, Y. Hosoi, Y. Furukawa, N. Takagi, S. Nagase, N. Toki-
toh, J. Am. Chem. Soc. 2006, 128, 1023–1031; c) W. Wang, S. Inoue, S.
Yao, M. Driess, Chem. Commun. 2009, 2661–2663; d) W.-P. Leung, W.-K.
Chiu, K.-H. Chong, T. C. W. Mak, Chem. Commun. 2009, 6822–6824; e) S.
Nagendran, S. S. Sen, H. W. Roesky, D. Koley, H. Grubmüller, A. Pal, R.
Herbst-Irmer, Organometallics 2008, 27, 5459–5463; f) S. P. Green, C.
Jones, P. C. Junk, K.-A. Lippert, A. Stasch, Chem. Commun. 2006, 3978–
3980. See also Ref. [12].
[4] a) O. T. Summerscales, X. Wang, P. P. Power, Angew. Chem. Int. Ed. 2010,
49, 4788–4790; Angew. Chem. 2010, 122, 4898–4900; b) O. T. Summer-
scales, J. C. Fettinger, P. P. Power, J. Am. Chem. Soc. 2011, 133, 11960–
11963; c) Y. Peng, B. D. Ellis, X. Wang, J. C. Fettinger, P. P. Power, Science
2009, 325, 1668–1670; d) Y. Peng, M. Brynda, B. D. Ellis, J. C. Fettinger,
E. Rivard, P. P. Power, Chem. Commun. 2008, 6042–6044; e) C. Cui, M. M.
Olmstead, J. C. Fettinger, G. H. Spikes, P. P. Power, J. Am. Chem. Soc.
2005, 127, 17530–17541; f) Y. Peng, X. Wang, J. C. Fettinger, P. P. Power,
Chem. Commun. 2010, 46, 943–945; g) O. T. Summerscales, M. M. Olm-
stead, P. P. Power, Organometallics 2011, 30, 3468–3471.
[5] a) P. P. Power, Nature 2010, 463, 171–177; b) P. P. Power, F. C. Gabbai,
Inorg. Chem. 2011, 50, 12221–12222; c) P. P. Power, Acc. Chem. Res.
2011, 44, 627–637; d) E. Rivard, P. P. Power, Inorg. Chem. 2007, 46,
10047–10064; e) P. P. Power, Organometallics 2007, 26, 4362–4372;
f) P. P. Power, Chem. Commun. 2003, 2091–2101.
Crystallography
The X-ray data (Table S1, see the Supporting Information) for color-
less (1 and 2), orange (5 and 6), dark brown (7), and black crystals
(10) were obtained at 150 K using Oxford Cryostream low-tempera-
ture device on a Nonius Kappa CCD diffractometer with MoKa radi-
ation (l=0.71073 Š), a graphite monochromator, and the f and
c scan mode. All attempts to get crystal structure of deep-blue
crystals of 8 provided structures with strongly disordered central
germanium atoms only and were not useful for further discussion.
Data reductions were performed with DENZO-SMN.[20] The absorp-
tion was corrected by integration methods.[21] Structures were
solved by direct methods (Sir92)[22] and refined by full matrix least-
square based on F2 (SHELXL97).[23] Hydrogen atoms were mostly lo-
calized on a difference Fourier map, however to ensure uniformity
of the treatment of the crystal, all hydrogen atoms were recalculat-
ed into idealized positions (riding model) and assigned tempera-
ture factors Hiso(H)=1.2 Ueq (pivot atom) or of 1.5 Ueq for the
[6] a) L. Pu, A. D. Phillips, A. F. Richards, M. Stender, R. S. Simons, M. M. Olm-
stead, P. P. Power, J. Am. Chem. Soc. 2003, 125, 11626–11636; b) Y. Peng,
R. C. Fischer, W. A. Merrill, J. Fischer, L. Pu, B. D. Ellis, J. C. Fettinger, R. H.
Herber, P. P. Power, Chem. Sci. 2010, 1, 461–468; c) R. C. Fischer, L. Pu,
J. C. Fettinger, M. A. Brynda, P. P. Power, J. Am. Chem. Soc. 2006, 128,
11366–11367.
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[7] a) S. Khan, R. Michel, J. M. Dieterich, R. A. Mata, H. W. Roesky, J.-P.
[15] S. Kimura, E. Bill, E. Bothe, T. Weyhermüller, K. J. Wieghardt, J. Am. Chem.
Soc. 2001, 123, 6025–6039.
Demers, A. Lange, D. Stalke, J. Am. Chem. Soc. 2011, 133, 17889–17894;
ˇ
[16] Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F.
Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith,
R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. Burant, S. S.
Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L.
Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dan-
nenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz,
J. Cioslowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2013.
b) R. Jambor, B. Kasnµ, K. Kirschner, M. Schürmann, K. Jurkschat, Angew.
Chem. Int. Ed. 2008, 47, 1650–1653; Angew. Chem. 2008, 120, 1674–
1677; c) C. Jones, S. J. Bonyhady, N. Holzmann, G. Frenking, A. Stasch,
Inorg. Chem. 2011, 50, 12315–12325; d) S. L. Choong, C. Schenk, A.
Stasch, D. Dange, C. Jones, Chem. Commun. 2012, 48, 2504–2506; e) M.
Wagner, Ch. Dietz, S. Krabbe, S. G. Koller, C. Strohmann, K. Jurkschat,
Inorg. Chem. 2012, 51, 6851–6859; f) S. P. Chia, H. W. Xi, Y. X. Li, K. H.
Lim, Ch. W. So, Angew. Chem. Int. Ed. 2013, 52, 6298; Angew. Chem.
2013, 125, 6418; g) S. P. Chia, R. Ganguly, Y. X. Li, Ch. W. So, Organome-
tallics 2012, 31, 6415. h) Compound 5 could exist in two diastereomeric
forms in solution. However, a low-temperature NMR spectroscopic ex-
periment did not allow the detection of two signals in 119Sn NMR spec-
trum of 5.
ˇ
˚ˇ ˇ
[8] M. Novµk, M. Bouska, L. Dostµl, A. Ruzicka, R. Jambor, Organometallics
[17] Y. Zhao, D. G. Truhlar, J. Chem. Phys. 2006, 125, 194101.
2014, 33, 6778–6784.
[18] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297.
[19] E. D. Glendening, C. R. Landis, F. J. Weinhold, Comput. Chem. 2013, 34,
1429.
[20] Z. Otwinowski, W. Minor Methods in Enzymology (Processing of X-ray
diffraction data collected in oscillation mode) 1997, 276, 307–326.
[21] P. Coppens, In: F. R. Ahmed, S. R. Hall, C. P. Huber, Editors, Crystallo-
graphic Computing, 1970, 255–270, Copenhagen, Munksgaard.
[22] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi Journal of Ap-
plied Crystallography (Early Finding of Preferred Orientation - a New
Method) 1994, 27, 1045–1050.
[9] a) J. T. B. H. Jastrzebski, P. A. van der Schaaf, J. Boersma, G. van Koten,
Organometallics 1989, 8, 1373–1375; b) C. Drost, P. B. Hitchcock, M. F.
Lappert, L. J.-M. Pierssens, Chem. Commun. 1997, 1141–1142; c) W.-P.
Leung, W.-H. Kwok, F. Xue, T. C. W. Mak, J. Am. Chem. Soc. 1997, 119,
1145–1146.
[10] T. J. Hadlington, C. Jones, Chem. Commun. 2014, 50, 2321–2323.
[11] S.-P. Chia, H.-X. Yeong, Ch. W. So, Inorg. Chem. 2012, 51, 1002–1010.
[12] J. Li, Ch. Schenk, C. Goedecke, G. Frenking, C. Jones, J. Am. Chem. Soc.
2011, 133, 18622–18625.
[13] P. Pyykkç, M. Atsumi, Chem. Eur. J. 2009, 15, 186; b) P. Pyykkç, M.
Atsumi, Chem. Eur. J. 2009, 15, 12770.
[23] G. M. Sheldrick SHELXL-97, University of Gçttingen: Gçttingen, 2008.
[14] M. Stol, D. J. M. Snelders, M. D. Godbole, R. W. A. Havenith, D. Haddle-
ton, G. Clarkson, M. Lutz, A. L. Spek, G. P. M. Van Klink, G. Van Koten, Or-
ganometallics 2007, 26, 3985–3994.
Received: February 17, 2015
Published online on April 15, 2015
Chem. Eur. J. 2015, 21, 7820 – 7829
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim