Tetrylenes chelated by hybrid amido-amino ligand: Derivatives of 2-[(N, N -dimethylamino)methyl]aniline

Article abstract of DOI:10.1021/ic2011056

Reaction of 2-[(dimethylamino)methyl]aniline with butyllithium, followed by conversion with trimethylsilyl, triphenylsilyl, triphenylgermyl, trimethylstannyl, or tri-n-butylstannyl chloride, gives the corresponding substituted aniline. These compounds wer

Full text of DOI:10.1021/ic2011056

ARTICLE
pubs.acs.org/IC
Tetrylenes Chelated by Hybrid AmidoꢀAmino Ligand: Derivatives of
2-[(N,N-Dimethylamino)methyl]aniline
Hana Vaꢀnkꢁatovꢁa,† Lies Broeckaert,‡ Frank De Proft,‡ Roman Olejník,† Jan Turek,† Zdeꢀnka Padꢀelkovꢁa,† and
ꢁ
Aleꢀs Ruꢀziꢀcka*,†
†Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Pardubice 53210,
Czech Republic
‡Department of General Chemistry (ALGC), Vrije Universiteit Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium
S Supporting Information
b
ABSTRACT: Reaction of 2-[(dimethylamino)methyl]aniline
with butyllithium, followed by conversion with trimethylsilyl,
triphenylsilyl, triphenylgermyl, trimethylstannyl, or tri-n-butyl-
stannyl chloride, gives the corresponding substituted aniline.
These compounds were further deprotonated by butyllithium
and reacted with germanium, tin, and lead dichlorides, respec-
tively, in both stoichiometric ratios 2:1 and 1:1, providing the
target homo- ([2-(Me2NCH2)C6H4(YR3)N]2M) and het-
eroleptic ([2-(Me2NCH2)C6H4(YR3)N]MCl) germylenes and
stannylenes, where M = Ge, Sn, Y = Si, Ge, and R = Me, Ph.
Unlike all of these cases, the heteroleptic plumbylene can only
be obtained with this reaction when the amide is substituted by a trimethylsilyl moiety. Anilines substituted by trimethyltin or tri-n-
butyltin moieties gave transmetalation products after the second deprotonation by butyllithium. The trimethyltin-substituted
stannylenes could likewise not be obtained by hexamethyldisilazane elimination of (trimethylstannyl)-2-[(dimethylamino)-
methyl]aniline with 0.5 mol equiv of either bis[bis(trimethylsilyl)amido]tin or {bis[bis(trimethylsilyl)amido]tin chloride}.
Products of these reactions are heterocubanes with compositions {[2-(Me2NCH2)C6H4N]Sn}4 and [2-(Me2NCH2)C6H4N]2-
(μ2-SnMe2)2, respectively, and Me4Sn or Me3SnCl. The structures of trimethylsilyl- and triphenylgermyl-substituted germylenes,
stannylenes, and plumbylenes, as well as a number of their precursors, in the crystalline state, were investigated by X-ray diffraction
and NMR spectroscopy in solution. Density functional theory methods were used for evaluation of the structures of several
compounds.
’ INTRODUCTION
Tetrylenes, low-valent group 14 compounds including car-
benes, silylenes, germylenes, stannylenes, and plumbylenes, are a
subject of growing research interest.1 In particular, metal amides
are among the most studied and used compounds in catalysis and
new materials preparation.2 The heavier elements of group 14
metal amides with the metal atom in a lower oxidation state are
widely accepted as carbene3 [M(NR2)], radical4 [M(NR2)3], or
alkyne5 analogues. Special attention has been paid to the reac-
tivity of M(NR2)2 compounds in oxidative addition reactions,6 in
the activation of small molecules,7 in the use as carbene analogues
for complexation8 of transition-metal complexes, and in reduc-
tions to metal clusters.9 Even though the first work on these
groups of metal amides was reported by Lappert in 19743a and
many compounds were prepared and structurally characterized,
amides containing both group 14 metals and an amino function-
ality remain rather uncommon (Figure 1).10
Figure 1. Examples of amino-group-chelated amidotetrylenes (M = Ge,
Sn, Pb).
Figure 2. C,N- and N,N-chelated homoleptic tetrylenes.
Such compounds are nearly restricted to pyridine derivatives
with the intramolecular donor interaction from the amino nitro-
gen atom to the metal (Figure 1B). The successful stabilization of
Received: May 25, 2011
Published: September 08, 2011
r
2011 American Chemical Society
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Table 1. Selected Crystallographic Data for 30, 8a, 8b, 12, and 14ꢀ18
30 1.5C4H8O2
8a
8b
12
14 3.5C6D12
3
3
formula
cell setting
space group
a (Å)
C36H66Li2N4O6Si2
monoclinic
P 21/c
C24H42GeN4Si2
triclinic
C24H42GeN4Si2
monoclinic
Cc
C24H42N4Si2Sn
monoclinic
P 21/c
C54H54Ge2N4Sn
triclinic
P 1
P1
9.6670(5)
14.0810(5)
16.6901(14)
90
9.8378(9)
10.6822(8)
14.9001(8)
77.456(5)
86.819(6)
86.819(6)
2
17.7691(9)
10.0000(8)
15.4009(6)
90
13.7200(11)
14.4010(12)
18.5601(7)
90
10.5760(7)
14.4601(14)
23.856(2)
80.329(7)
86.883(7)
70.892(7)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
Z
115.567(7)
90
92.782(12)
90
129.951(5)
90
2
4
4
V (Å3)
2049.4(2)
4593 (0.067)
0.460/ꢀ0.321
1.160
1404.1(2)
6379 (0.0673)
0.478/ꢀ0.472
1.091
2733.4(3)
5721 (0.0673)
2.099/ꢀ1.451
1.132
2811.2(3)
6440 (0.0632)
0.420/ꢀ0.692
1.105
3398.3(5)
15458 (0.0826)
5.342/ꢀ1.042
1.123
a
total (Rint
)
max/min τ (e/Å3)
GOFb
Rc/wR c
0.0669/0.1142
0.0373/0.0844
0.0690/0.1617
0.0306/0.0563
0.0883/0.2050
15
16
17
18
formula
cell setting
space group
a (Å)
C27H27ClGeN2Sn
C24H42Cl2N4Pb2Si2
monoclinic
P 21/c
C36H48N8Sn4
C22H36N4Sn2
triclinic
monoclinic
C 2/c
tetragonal
I4
P1
34.1866(9)
8.4024(11)
19.1884(7)
90
6.8431(4)
12.7100(7)
19.6427(12)
90
14.0430(9)
14.0430(8)
9.6569(7)
90
7.6861(4)
8.8950(3)
9.0669(3)
105.140(3)
91.336(3)
99.662(4)
1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
Z
111.428(11)
90
110.055(5)
90
90
90
8
2
2
V (Å3)
5130.9(8)
5738 (0.0496)
0.498/ꢀ0.497
1.105
1604.85(17)
3567 (0.0622)
1.735/ꢀ2.166
1.145
1904.4(4)
2164 (0.0298)
0.284/ꢀ0.307
1.079
588.41(4)
2682 (0.0198)
0.395/ꢀ0.640
1.129
a
total (Rint
max/min τ (e/Å3)
GOFb
)
Rc/wRc
0.0314/0.0544
0.0409/0.0819
0.0224/0.0427
0.0161/0.0394
a Rint = ∑|Fo ꢀ Fo,mean2|/∑Fo . GOF = [∑(w(Fo ꢀ Fc2)2)/(Ndiffrs ꢀ Nparams)]1/2 for all data. c R(F) = ∑||Fo| ꢀ |Fc||/∑|Fo| for observed data; wR(F2) =
2
2 b
2
[∑(w(Fo ꢀ Fc2)2)/(∑w(Fo ) )]1/2 for all data.
2
2 2
low-valent group 14 metals and the special chemical behavior of
compounds containing a [2-(dimethylamino)methyl]phenyl ligand
(Figure 2A)11 prompted us to explore the chemistry of lower-
valent complexes of heavier group 14 metals with [2-(dimethy-
lamino)methyl]aniline as a ligand (Figure 2B). Thus, this ligand
contains both the amido functionality, prone to strong nitrogen-
to-metal covalent bonds, and the pendant amino group for the
formation of a weaker intramolecular donorꢀacceptor interac-
tion, which together give rise to a six-membered diazametalla
ring, similar to related β-diketiminato ligand-substituted
tetrylenes.12 The steric protection at the amido functionality is
expected to be very variable and, together with the hemilabile
coordination of the amino group, would give rise to structure
fine-tuning, which is the main goal of this paper.
operating at 500.13 MHz for 1H and 186.50 MHz for 119Sn nuclei and on
a Bruker Avance II 400 spectrometer operating at 400.13 MHz for 1H
and 81.49 MHz for 207Pb nuclei. All deuterated solvents were degassed
and then stored over a potassium or sodium mirror under an argon
atmosphere. Solutions were obtained by dissolving approximately 40 mg
1
of each compound in 0.5 mL of a deuterated solvent. Values of H
chemical shifts were calibrated to internal standard tetramethylsilane
[δ(1H) = 0.00] or to residual signals of benzene [δ(1H) = 7.16] and
THF [δ(1H) = 3.58 or 1.73]. The 119Sn and 207Pb chemical shifts are
referred to external neat tetramethylstannane (δ = 0.0) and tetraethyl-
lead (δ = 0.0), respectively, and measured using the inverse-gated
proton broad-band decoupling mode.
Crystallography. The X-ray diffraction data (Tables 1 and S1ꢀS3
in the Supporting Information) obtained from colorless crystals of
compounds 1, 30, 4, 5, 8a, 8b, 12, and 14ꢀ18 and 1-(chloromethyl)-
2-nitrobenzene were obtained at 150 K using an Oxford Cryostream
low-temperature device on a Nonius Kappa CCD diffractometer with
Mo Kα radiation (λ = 0.710 73 Å), a graphite monochromator, and the
ϕ- and χ-scan mode. Data reductions were performed with DENZO-
SMN.13 The absorption was corrected by integration methods.14
Structures were solved by direct methods (SIR92)15 and refined by
’ EXPERIMENTAL SECTION
NMR Spectroscopy. NMR spectra were recorded at 295 K from
solutions in benzene-d6 and/or tetrahydrofuran (THF)-d8 on a Bruker
Avance 500 spectrometer, equipped with a z-gradient 5-mm probe,
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full-matrix least squares based on F2 (SHELXL97).16 Hydrogen atoms
were mostly located on a difference Fourier map; however, to ensure
uniformity of the treatment of the crystal, all hydrogen atoms were
recalculated into idealized positions (riding model) and assigned
temperature factors Hiso(H) = 1.2Ueq(pivot atom) or 1.5Ueq for the
methyl moiety, using CꢀH bond distances of 0.96, 0.97, and 0.93 Å for
methyl, methylene, and aromatic hydrogen atoms, respectively, and 0.86 Å
for NꢀH bonds.
(s, 9H, Si(CH3)3). 13C{1H} NMR (125 MHz, C6D6, ppm): δ 149.09
(C10), 128.56 (C20), 129.77 (C60), 129.56 (C50), 126.00 (C40), 120.46
(C30), 61.21 (C70), 46.58 (NMe2), 2.28 (SiMe3). Anal. Calcd for
C12H21ClGeN2Si: C, 43.75; H, 6.43; N, 8.50. Found: C, 43.8; H, 6.5; N, 8.5.
Preparation of {{2-[(CH3)2NCH2]C6H4}(GePh3)N}2Ge (10).
n-Butyllithium (1.6 M solution in hexanes, 0.29 mL, 0.46 mmol) was
added dropwise to a stirred solution of 5 (210 mg, 0.46 mmol) in 15 mL
of hexane at room temperature, causing the immediate precipitation of a
white powder, which was washed with 10 mL of hexane. Afterward, the
solvent was evaporated and the resulting product was dissolved in 15 mL
of diethyl ether and added dropwise to a suspension of the 1:1
germanium(II) chlorideꢀdioxane complex (54 mg, 0.23 mmol) in
15 mL of diethyl ether. The reaction mixture was stirred overnight
and filtered away from lithium chloride. The solution was reduced to half
of its volume in vacuo (118 mg, yield 52%). 1H NMR (500 MHz, C6D6,
Crystallographic data for structural analysis have been deposited
with the Cambridge Crystallographic Data Centre (825147ꢀ825159).
Copies of this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EY, U.K. (fax +44-
1223-336033; e-mail deposit@ccdc.cam.ac.uk, or www http://www.
ccdc.cam.ac.uk).
Synthetic Procedures. Standard Schlenk techniques were used
for all manipulations under argon. n-Butyllithium (1.6 M in hexanes,
Sigma-Aldrich), trimethylsilyl chloride (98%, Sigma-Aldrich), triphe-
nylsilyl chloride (96% Sigma-Aldrich), triphenylgermyl chloride (99%,
Sigma-Aldrich), trimethylstannyl chloride (97%, Sigma-Aldrich), tribu-
tyltin chloride (97%, Fluka), tin(II) chloride (99.9%, anhydrous, Strem
Chemicals), a 1:1 germanium(II) chlorideꢀdioxane complex (Sigma-
Aldrich), and lead(II) chloride (p.a., Lachema) were used without
further purification. Diethyl ether and n-hexane were dried over and
distilled from a potassiumꢀsodium alloy, degassed, and stored under
argon over a potassium mirror. High-purity deuterated solvents were
distilled from a potassium mirror, degassed, and stored over a sodium
mirror. Compounds 1, bis[bis(trimethylsilyl)amido]tin(II), bis[bis-
(trimethylsilyl)amido]lead(II), and bis[bis(trimethylsilyl)amidotin(II)
chloride] were obtained by published methods.17,18 For the preparation
of 3ꢀ7, see the Supporting Information.
3
ppm): δ 7.61ꢀ7.59 (m, 18H, Ph), 7.50 (d, J = 6.4 Hz, 2H, H60),
7.13ꢀ7.06 (m, 24H, Ph, H30, H40, H50), 3.73, 2.92 (AX spin system Δδ =
0.81 ppm = 405.1 Hz, 13.4 Hz, 4H, CH2), 1.83 (broad signal, 12H,
13
N(CH3)2). C{1H} NMR (125 MHz, C6D6, ppm): δ 150.88 (C10),
139.16 (Ph), 136.98 (C20), 136.76 (Ph), 135.80 (C60), 135.28 (Ph),
130.84 (C50), 129.50 (C40), 128.59 (Ph), 128.55 (C30), 65.01 (C70),
44.83 (NMe2). Anal. Calcd for C54H54Ge3N4: C, 66.40; H, 5.57; N,
5.74. Found: C, 66.5; H, 5.6; N, 5.8.
Preparation of {2-[(CH3)2NCH2]C6H4}(GePh3)NGeCl (11).
A workup similar to that for 10 was used except that the stoichiometric
ratio of the starting compounds was 1:1 (210 mg, 0.46 mmol of 5
corresponds to 108 mg, 0.46 mmol of the 1:1germanium(II) chloride
1
dioxane complex; 151 mg, yield 58%). H NMR (500 MHz, C6D6,
3
ppm): δ 7.14ꢀ7.10 (m, 15H, Ph), 6.80 (d, J = 7.4 Hz, 1H, H60),
6.61ꢀ6.57 (m, 2H, H40, H50), 6.32 (d, 3J = 8.0 Hz, 1H, H30), 3.26, 3.11
(AB spin system Δδ = 0.15 ppm = 75.0 Hz, 12.1 Hz, 2H, C70), 1.91
(broad signal, 6H, NMe2). 13C{1H} NMR (125 MHz, C6D6, ppm):
δ 150.16 (C10), 136.26 (Ph), 135.41 (Ph), 134.90 (C20), 134.51 (C60),
134.10 (Ph), 130.13 (C50), 129.76 (C40), 129.43 (C30), 128.57 (Ph),
61.39 (C70), 44.11 (NMe2). Anal. Calcd for C27H27Ge2N2Cl: C, 57.89;
H, 4.86; N, 5.00. found: C, 58.0; H, 4.9; N, 5.0.
Compositional analyses were determined under an inert atmosphere
of argon on an EA 1108 automatic analyzer by Fisons Instruments.
Preparation of {{2-[(CH3)2NCH2]C6H4}(SiMe3)N}2Ge (8).
n-Butyllithium (1.6 M solution in hexanes, 0.74 mL, 1.19 mmol) was
added dropwise to a stirred solution of 3 (272 mg, 1.19 mmol) in 20 mL
of hexane at room temperature, causing the immediate precipitation of a
white powder, which was washed with 10 mL of hexane. Afterward, the
solvent was evaporated and the resulting product was dissolved in 20 mL
of diethyl ether and added dropwise to a suspension of the 1:1
germanium(II) chlorideꢀdioxane complex (138 mg, 0.595 mmol) in
15 mL of diethyl ether. The reaction mixture was stirred overnight and
filtered away from lithium chloride. The solution was reduced to a half of
the volume in vacuo. Single crystals of 8b were obtained from diethyl
ether at ꢀ28 °C (211 mg, yield 67%) and those of polymorph 8a from
Preparation of {{2-[(CH3)2NCH2]C6H4}(SiMe3)N}2Sn (12).
n-Butyllithium (1.6 M solution in hexanes, 8.96 mL, 14.34 mmol) was
added dropwise to a stirred solution of 3 (3.19 g, 14.34 mmol) in 40 mL
of hexane at room temperature, causing the immediate precipitation of a
white powder, which was washed with 10 mL of hexane. Afterward, the
solvent was evaporated and the resulting product was dissolved in 35 mL
of diethyl ether and added dropwise to a suspension of tin(II) chloride
(1.36 g, 7.17 mmol) in 40 mL of diethyl ether. The reaction mixture was
stirred overnight and filtered away from lithium chloride. The solution
was reduced to a half of its volume in vacuo. Single crystals of 12 were
obtained from diethyl ether at ꢀ28 °C (2.98 g, yield 74%). Mp: 113 °C
1
toluene at ꢀ28 °C. Mp: 132 °C (dec). H NMR (500 MHz, C6D6,
ppm): δ 7.31 (d, 3J = 7.0 Hz, 2H, H60), 6.83 (t, 3J = 7.4 Hz, 2H, H50),
6.66 (t, 3J = 7.6 Hz, 2H, H40), 6.00 (d, 3J = 7.9 Hz, 2H, H30), 3.71, 3.11
(AX spin system Δδ = 0.60 ppm = 300.1 Hz, 13.2 Hz, 4H, C70), 2.18 (s,
12H, NMe2), 0.25 (s, 18H, SiMe3). 13C{1H} NMR (125 MHz, C6D6,
ppm): δ 149.75 (C10), 133.64 (C20), 129.02 (C60), 128.93 (C50),
128.00 (C40), 121.76 (C30), 62.05 (C70), 46.36 (NMe2), 3.22 (SiMe3).
Anal. Calcd for C24H42Ge2N4Si2: C, 55.93; H, 8.21; N, 10.87. Found: C,
55.8; H, 8.1; N, 10.8.
1
3
(dec). H NMR (500 MHz, C6D6, ppm): δ 7.29 (t, J = 7.7 Hz, 1H,
H50), 7.16 (d, 3J = 7.1 Hz, 2H, H60), 6.83 (d, 3J = 7.9 Hz, 2H, H30), 6.78
(t, 3J = 7.4 Hz, 2H, H40), 3.72, 2.52 (AX spin system Δδ = 1.20 ppm =
599.4 Hz, 11.2 Hz, 4H, CH2), 2.00 (s, 12H, N(CH3)2), 0.32 (s, 18H,
13
Si(CH3)3). C{1H} NMR (100 MHz, C6D6, ppm): δ 152.38 (C10),
133.90 (C20), 130.84 (C60), 130.63 (C50), 129.47 (C40), 120.87 (C30),
63.74 (C70), 46.12 (NMe2), 2.72 (SiMe3). 119Sn{1H} NMR (500 MHz,
C6D6, ppm): δ ꢀ115.6. 119Sn{1H} NMR (500 MHz, THF-d8, ppm):
δ ꢀ118.0. Anal. Calcd for C24H42Si2N4Sn: C, 51.34; H, 7.54; N, 9.98.
Found: C, 51.4; H, 7.6; N, 9.9.
The compound {{2-[(CH3)2NCH2]C6H4}(SiMe3)NLi(C4H8O2)}2-
(C4H8O2) (30) was obtained as a minor product from the second crop of
crystallization.
Preparation of {2-[(CH3)2NCH2]C6H4}(SiMe3)NGeCl (9). A
workup similar to that for 8 was used except that the stoichiometric ratio
of the starting compounds was 1:1 (272 mg, 1.19 mmol of 3 corresponds
to 276 mg, 1.19 mmol of the 1:1 germanium(II) chlorideꢀdioxane
complex; 227 mg, yield 60%). 1H NMR (500 MHz, C6D6, ppm): δ 7.14
(t, 3J = 7.7 Hz, 1H, H50), 6.95 (d, 3J = 7.3 Hz, 1H, H60), 6.87 (d, 3J =
8.0 Hz, 1H, H30), 6.72 (d, 3J = 7.4 Hz, 1H, H40), 3.00, 2.51 (AX spin
system 248.9 Hz, 11.8 Hz, 2H, CH2), 1.96 (s, 6H, N(CH3)2), 0.26
Preparation of {2-[(CH3)2NCH2]C6H4}(SiMe3)NSnCl (13). A
workup similar to that for 12 was used except that the stoichiometric
ratio of the starting compounds was 1:1 (3.19 g, 14.34 mmol of 3
corresponds to 2.72 g, 14.34 mmol of tin(II) chloride; 4.47 g, yield 83%).
1H NMR (500 MHz, C6D6, ppm): δ 7.26 (t, 3J = 7.6 Hz, 1H, H50), 7.06
(d, 3J = 8.0 Hz, 1H, H60), 6.99 (d, 3J = 7.3 Hz, 1H, H30), 6.83 (t, 3J = 7.3
Hz, 1H, H40), 3.12, 2.54 (AX spin system Δδ = 0.58 ppm = 288.2 Hz,
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2H, C70), 2.06 (s, 6H, NMe2), 0.37 (s, 9H, SiMe3). 13C{1H} NMR (125
MHz, C6D6, ppm): δ 151.56 (C10), 131.49 (C20), 130.32 (C60), 128.83
(C50), 127.62 (C40), 120.52 (C30), 62.07 (C70), 45.49 (NMe2), 3.59
(SiMe3). 119Sn{1H} NMR (500 MHz, C6D6, ppm): δ ꢀ51.2. 119Sn-
{1H} NMR (500 MHz, THF-d8, ppm): δ ꢀ64.6. Anal. Calcd for C12Cl
H21SiSnN2: C, 38.38; H, 5.64; N, 7.46. Found: C, 38.5; H, 5.7; N, 7.4.
Preparation of {{2-[(CH3)2NCH2]C6H4}(GePh3)N}2Sn (14).
n-Butyllithium (1.6 M solution in hexanes, 2.59 mL, 4.15 mmol) was
added dropwise to a stirred solution of 5 (1.88 g, 4.15 mmol) in 35 mL of
hexane at room temperature, causing the immediate precipitation of a
white powder, which was washed with 10 mL of hexane. Afterward, the
solvent was evaporated and the resulting product was dissolved in 35 mL
of diethyl ether and added dropwise to a suspension of tin(II) chloride
(393 mg, 2.075 mmol) in 25 mL of diethyl ether. The reaction mixture
was stirred overnight and filtered away from lithium chloride. The
solution was reduced to half of its volume in vacuo. Compound 14 was
crystallized from toluene at ꢀ28 °C (1.29 g, yield 61%). Single crystals of
14 were obtained from deuterated cyclohexane in a vacuum-sealed
NMR tube. 1H NMR (500 MHz, C6D6, ppm): δ 7.72ꢀ7.56 (m, 12H,
Ph), 7.14ꢀ7.08 (m, 20H, H40 + Ph), 6.94 (d, 3J = 7.4 Hz, 2H, H60), 6.72
(t, 3J = 7.4 Hz, 2H, H50), 6.43 (d, 3J = 7.8 Hz, 2H, H30), 3.54, 2.12 (AX
spin system 503.3 Hz, 10.2 Hz, 4H, C70), 1.93 (s, 12H, NMe2). 13C{1H}
NMR (125 MHz, C6D6, ppm): δ 154.38 (C10), 139.65 (Ph), 136.47
(Ph), 135.71 (C20), 134.43 (C60), 131.47 (C50), 129.35 (Ph), 128.86
(C40), 128.68 (Ph), 121.43 (C30), 64.98 (C70), 44.82 (NMe2). 119Sn-
{1H} NMR (500 MHz, C6D6, ppm): δ ꢀ124.5. 119Sn{1H} NMR (500
MHz, THF-d8, ppm): δ ꢀ128.6. Anal. Calcd for C54H54Ge2N4Sn: C,
63.40; H, 5.32; N, 5.48. Found: C, 63.5; H, 5.3; N, 5.5.
Chart 1
δ 1816.3. Anal. Calcd for C12H21ClN2PbSi: C, 31.06; H, 4.56; N,
6.04. Found: C, 31.2; H, 4.6; N, 6.0.
Preparation of {{2-[(CH3)2NCH2]C6H4}NSn}4 (17). A solu-
tion of 6 (232 mg, 0.37 mmol) in diethyl ether (15 mL) was added to a
suspension of bis[bis(trimethylsilyl)amido]tin(II) (163 mg, 0.19 mmol)
in diethyl ether (10 mL), and the reaction mixture was stirred overnight
and then filtered. Single crystals of the unexpected product 17 were
obtained from a diethyl ether solution at room temperature (91 mg,
yield 46%). Mp: >330 °C. 13C CP/MAS NMR: δ 142, 133, 130, 127,
125, 124, 61, 45, 44. 119Sn MAS NMR (ppm): δ ꢀ139.9. Anal. Calcd: C,
40.50; H, 4.53; N, 10.50. Found: C, 40.6; H, 4.6; N, 10.5. Me4Sn was
identified in the mother liquors by 1H, 13C, and 119Sn NMR spectros-
copy [δ(119Sn) = ꢀ1.4 ppm].19
Preparation of {2-[(CH3)2NCH2]C6H4}(GePh3)NSnCl (15).
The solution of 5 (186 mg, 0.41 mmol) in diethyl ether (15 mL) was added
to a suspension of bis{bis[bis(trimethylsilyl)amido]tin(II) chloride}
(129 mg, 0.21 mmol) in diethyl ether (10 mL), and the reaction mixture
was stirred overnight and then filtered. Single crystals of 15 were
obtained from diethyl ether at room temperature (139 mg, yield
Alternative Preparation of 17. A solution of 6 (226 mg,
0.72 mmol) in diethyl ether (15 mL) was added to a suspension of
bis{bis[bis(trimethylsilyl)amido]tin(II) chloride} (227 mg, 0.36 mmol)
in diethyl ether (10 mL), and the reaction mixture was stirred overnight
and then filtered. Single crystals of 17 were obtained from diethyl ether
at room temperature (62 mg, yield 32%). Me3SnCl was identified in the
mother liquors by 1H, 13C, and 119Sn NMR spectroscopy [δ(119Sn) =
ꢀ156.0 ppm].19
1
56%). Mp: 79 °C. H NMR (400 MHz, C6D6, ppm): δ 7.81ꢀ7.80
(m, 5H, Ph), 7.29 (d, 3J = 8.1 Hz, 1H, H60), 7.16ꢀ7.10 (m, 10H, Ph),
6.88 (t, 3J = 7.6 Hz, 1H, H40), 6.59 (d, 3J = 7.4 Hz, 1H, H30), 6.88 (t, 3J =
7.3 Hz, 1H, H50), 3.36, 2.57 (AX spin system Δδ = 0.79 ppm = 314.6 Hz,
11.6 Hz, 2H, CH2), 1.79 (s, 3H, N(CH3)2), 1.52 (s, 3H, N(CH3)2).
13C{1H} NMR (125 MHz, THF-d8, ppm): δ 153.42 (C10), 137.78
(Ph), 135.08 (Ph), 130.91 (C60), 129.43 (Ph), 128.84 (C50), 128.22
(Ph), 127.24 (C20), 124.73 (C40), 115.89 (C30), 67.37 (C70), 43.94
(NMe2). 119Sn{1H} NMR (500 MHz, C6D6, ppm): δ ꢀ85.8. 119Sn-
{1H} NMR (500 MHz, THF-d8, ppm): δ ꢀ89.7. Anal. Calcd for
C27H27ClGe2N2Sn: C, 53.48; H, 4.49; N, 4.62. Found: C, 53.5; H,
4.5; N, 4.7.
Preparation of{{2-[(CH3)2NCH2]C6H4}NSnMe2}2 (18). Com-
pound 18 was obtained from the reaction of bis[bis(trimethylsilyl)-
amido]tin(II) and 6 as a minor product. Single crystals of 18 were
obtained from hexane extraction at room temperature (31 mg, yield 7%).
Mp: 165 °C (dec). 1H NMR (500 MHz, THF-d8, ppm): δ 6.82 (t, 3J =
7.2 Hz, 1H, H40), 6.70 (d, 3J = 7.6.6 Hz, 1H, H30), 6.30 (d, 3J = 8.2 Hz, 1H,
H60), 6.14 (t, 3J = 7.2 Hz, 1H, H50), 4.18 (broad signal, 1H, C70), 2.89
(broad signal, 1H, C70), 2.18 (broad signal, 6H, NMe2), 0.62 (broad
signal, 6H, SnMe2). 119Sn{1H} NMR (500 MHz, THF-d8, ppm):
δ ꢀ123.8. Anal. Calcd for C12H21ClN2PbSi: C, 44.49; H, 6.11; N, 9.43.
Found: C, 44.5; H, 6.2; N, 9.4.
Preparation of{{2-[(CH3)2NCH2]C6H4}(SiMe3)NPbCl}2 (16).
n-Butyllithium (1.6 M solution in hexanes, 0.70 mL, 1.12 mmol) was
added dropwise to a stirredsolution of3 (249 mg, 1.12 mmol) in 15 mLof
hexane at room temperature, causing the immediate precipitation of a
white powder, which was washed with 10 mL of hexane. Afterward, the
solvent was evaporated and the resulting product was dissolved in 20 mL
of diethyl ether and added dropwise to a suspension of lead(II) chloride
(311 mg, 1.12 mmol) in 20 mL of diethyl ether. The reaction mixture was
stirredovernightand filteredawayfrom lithiumchloride. The solution was
reduced to half of its volume in vacuo. Single crystals of 16 were obtained
from diethyl ether at room temperature. (379 mg, yield 73%). Mp: 128 °C
(dec). 1H NMR (500 MHz, C6D6, ppm): δ 7.09 (t, 3J = 7.0 Hz, 1H, H40),
7.02 (d, 3J = 7.1 Hz, 1H, H60), 6.72 (t, 3J = 7.3 Hz, 1H, H50), 6.06 (broad
signal., 1H, H30), 3.85 (broad signal, 1H, C70), 2.59 (broad signal, 1H,
C70), 2.11(s, 6H, NMe2), 0.09(s, 9H, SiMe3). 13C{1H} NMR(125 MHz,
C6D6, ppm): δ 153.40 (C10 broad), 134.12 (C60), 132.41 (C20),
131.13 (C50), 129.42 (C40), 120.63 (C30), 63.59 (C70), 45.95
(NMe2), 3.33 (SiMe3). 207Pb{1H} NMR (81 MHz, C6D6, ppm):
’ COMPUTATIONAL DETAILS
All calculations were performed with the Gaussian 09 program.20
Density functional theory (DFT)21 geometry optimizations of the mole-
cules were done using a hybrid B3LYP functional22 and a Pople 6-311+
+g(d,p) basis set23 on all atoms, with a LANL2DZ ECP pseudopotential24
for tin and lead atoms. The cubane 16 was optimized with the Dunning-
type basis set cc-pVDZ25 on carbon, hydrogen, and nitrogen and the cc-
pVDZ-PP26 basis set on tin. Frequency calculations were carried out to
confirm that the obtained structures correspond to minima on the
potential energy surface.
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Scheme 1. Preparation of Target Compoundsa
Figure 4. Molecular structure of 8a in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Ge1ꢀN1 1.9166(19), Ge1ꢀN3 1.9137(18),
Ge1ꢀN2 2.290(2), Ge1ꢀN4 4.996(2), Si1ꢀN1 1.733(2); N1ꢀGe1ꢀ
N2 89.95(8), N1ꢀGe1ꢀN3 101.08(8), N3ꢀGe1ꢀN4 59.08(7),
Si1ꢀN1ꢀGe1 121.39(11), C1ꢀC2ꢀC7ꢀN2 66.5(3), C13ꢀC14ꢀ
C19ꢀN4 157.5(2).
a Reagents and conditions: (i) n-BuLi; (ii) YR3Cl, where Y = Si, Ge, Sn
and R = Me, n-Bu, Ph; (iii) 1/2MCl2, where M = Ge, Sn, Pb; (iv) MCl2,
where M = Ge, Sn, Pb.
Figure 5. Molecular structure of 8b in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Ge1ꢀN1 1.979(6), Ge1ꢀN3 1.975(6), Ge1ꢀN2
2.176(5), Ge1ꢀN4 2.178(5), Si1ꢀN1 1.713(6), N1ꢀGe1ꢀN2 95.3(2);
N1ꢀGe1ꢀN3 147.3(2), N2ꢀGe1ꢀN4 113.9(2), Si1ꢀN1ꢀGe1 127.1(3),
C1ꢀC2ꢀC7ꢀN2 73.5(8).
Figure 3. Molecular structure of 30 ({[ArN(SiMe3)Li(diox)]2-μ2-diox]})
in a PLUTON representation. Hydrogen atoms are omitted for clarity.
Selected interatomic distances (Å) and angles (deg): O1ꢀLi1 2.023(5),
O3ꢀLi1 1.994(5), N2ꢀLi1 2.140(5), N1ꢀLi1 1.993(5); N1ꢀLi1ꢀO3
112.2(2), N1ꢀLi1ꢀO1 125.5(3), O3ꢀLi1ꢀO1 99.0(2), N1ꢀLi1ꢀN2
101.1(2), O3ꢀLi1ꢀN2 112.5(2), O1ꢀLi1ꢀN2 106.6(2), C1ꢀC2ꢀC7ꢀ
N2 71.6(3).
which is probably caused by the high steric hindrance of the Ph3Si
group on the NH one.
The trimethylsilyl-substituted lithium amide 30 was obtained
as a minor byproduct of the reaction of lithiated (trimethylsilyl)-
’ RESULTS AND DISCUSSION
Synthesis. The ligand ArNNH2 (1; Chart 1) was prepared
according to the literature,17 where it was used for amidoxime
ligand preparation. In our present work, it is used for the first time
as such.
Compound 1 can be converted with 1 mol equiv of
n-butyllithium for single deprotonation to lithium anilide, in
which, in turn, lithium gets electrophilically substituted by
an YR3 moiety, with Y a group 14 element in the oxidation
state IV+ [YR3 = SiMe3, SiPh3, GePh3, SnMe3, and Sn(n-Bu)3;
see Scheme 1, compounds 1 and 3ꢀ7]. Descriptions of the
preparation, structures, and properties of 1ꢀ7 are located in
the Supporting Information.
amide 3 with GeCl2 diox. The yellow, extremely air-sensitive
3
crystals were suitable for X-ray diffraction. The crystal structure
of 30 (Figure 3) is composed by two trimethylsilyl-substituted
lithium amides, which are connected by one dioxane molecule,
while each lithium atom is coordinated by one additional dioxane
molecule. The second oxygen donor atom of these two dioxane
molecules remains uncoordinated (Figures 3 and S5 in the
Supporting Information). The lithium atom centers are four-
coordinated with a tetrahedral vicinity configuration and can
be compared directly to the monomeric species [(pmdeta)-
LiN(SiMe3)2]27 or lithium amidinate coordinated by two THF
molecules.28
All the compounds substituted with a YR3 moiety (3ꢀ7) can
be deprotonated by butyllithium to produce the corresponding
lithium salt, except the triphenylsilyl-substituted compound 4,
Homoleptic Tetrylenes. The conversion of lithium salts with
trimethylsilyl and triphenylgermyl substituents with 0.5 mol equiv
of GeCl2 diox or SnCl2 provides the corresponding homoleptic
3
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Table 2. Selected Interatomic Measured/Calculated Distances (Å) and Angles (deg) of a Selection of Compounds
8a
8b
12
14
15
16
d[MꢀN(YR3)]
d[MꢀN(Me2)]
1.9166(19)/ 1.9513
1.9137(18)/ 1.9409
2.290(2)/ 2.4641
4.996(2)/ 5.071
101.08(8)
1.979(6)/ 2.235
1.975(6)/ 2.235
2.176(5)/ 2.386
2.178(5)/ 2.386
147.3(2)
2.131(2)/ 2.144
2.134(2)/ 2.144
2.640(2)/ 2.828
2.668(2)/ 2.8281
103.41(8)
2.151(6)
2.145(6)
2.638(8)
2.497(8)
93.3(2)
2.107(2)
2.221(6)
2.349(2)
2.509(6)
NamidoꢀMꢀNamido
NaminoꢀMꢀNamino
113.9(2)
160.98(7)
172.7(2)
germylenes (8 and 10) and stannylenes (12 and 14), respec-
tively. Attempts to prepare related homoleptic plumbylenes were
undertaken, but all experiments reveal almost the same results:
(i) the trimethylsilyl-substituted plumbylene 18 was the only
isolated product to be soluble, independent of the molar ratio of
the starting lithium salt and PbCl2, and (ii) in all experiments
with triphenylgermyl-substituted lithium amide and lead dichlor-
ide, the starting triphenylgermyl-substituted aniline 5 was iso-
lated after the reaction. The reaction of 2 mol equiv of [bis-
(trimethylsilyl)amido]lead(II) with substituted anilines 3 and 5
did not lead to the desired products under standard conditions
(overnight stirring at room temperature).
The typical pattern of 1H NMR spectra is one set of signals,
except for the diastereotopic benzylic protons, which give rise to
AX spin systems for all prepared homoleptic tetrylenes (∼400
Hz for germylenes and ∼550 Hz for stannylenes). The 119Sn
chemical shift in C6D6 at room temperature is ꢀ115.6 and
ꢀ124.5 ppm for 12 and 14, respectively. Nearly the same values
(ꢀ118.0 and ꢀ128.6 ppm) were found in THF-d8, clearly
indicating coordination hampering of THF units toward the
tin atom.
Single crystals of homoleptic germylene 8 and stannylenes 12
and 14 suitable for structure determination by X-ray methods
were obtained.
In the case of 8, single crystals of two different polymorphs, 8a
and 8b, were found to be suitable for X-ray diffraction: 8a
crystallized from toluene and 8b from diethyl ether.
The germanium atom in the first polymorph, 8a (Figure 4),
reveals the coordination geometry of the trigonal pyramid with
two amido nitrogen atoms and a single of the chelating amino
nitrogen atoms in the basement of the pyramid. With the lone
pair at its top, the electron domain structure of 8a is that of a
strongly distorted tetrahedron. The second amino group is even
expelled from the primary coordination sphere of the germanium
atom. On the other hand, the germanium atom is four-coordi-
nated in 8b (Figure 5) with pseudo-trigonal-bipyramidal struc-
ture deviation from the ideal tetrahedral geometry (Ψ-trigonal
bipyramid), where the amido nitrogen atoms (N1 and N3)
occupy axial positions and the coordinating amino groups (N2
and N4) and the lone electron pair equatorial positions. This
coordination geometry is reflected in a strongly reduced
N1ꢀGe1ꢀN3 angle of 147.3(2)° compared to the axial bond
angle of 180° of an ideal trigonal bipyramid and a N2ꢀGe1ꢀN4
angle of 113.9(2)° compared to the ideal 120° equatorial bond.
The GeꢀN bonds are significantly shorter for the amido
nitrogen atoms, 1.979(6) and 1.975(6) Å, than for the amino
ones, 2.176(5) and 2.178(5) Å. This is confirmed by DFT
calculations. Thus, Table 2 reveals that the calculated Geꢀamido
N bond distance (2.235 Å) is again shorter than the Geꢀamino
N one (2.386 Å). Nevertheless, the latter bond length indicates a
Figure 6. Molecular structure of 12 in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Sn1ꢀN1 2.131(2), Sn1ꢀN3 2.134(2), Sn1ꢀN2
2.640(2), Sn1ꢀN4 2.668(2), Si1ꢀN1 1.723(2); N1ꢀSn1ꢀN2 80.39(9),
N1ꢀSn1ꢀN3 103.41(8), N2ꢀSn1ꢀN4 160.98(7), Si1ꢀN1ꢀSn1
121.74(11), C1ꢀC2ꢀC7ꢀN2 68.2(5).
strong coordination of the amino group to the germanium atom
and, hence, a high stabilization of the germylene 8b.
The bonds between the germanium atom and amido nitrogen
atoms are shorter by ca. 0.06 Å (DFT calculated: 0.28 Å) than
those in the first polymorph 8a, but the amino NꢀGe distance
increased by ca. 0.12 Å (DFT calculated: 0.08 Å). The calculated
energy difference between 8a and 8b is 24.4 kcal/mol, with
compound 8a being the low-energy isomer, which is in agree-
ment with the shorter (calculated) GeꢀN amido distances in 8a
(see values in Table 2).
The coordination polyhedra around the tin atoms in tri-
methylsilyl- (12) and triphenylgermyl-substituted (14) homo-
leptic stannylenes (Figures 6 and 7) are distorted Ψ-trigonal
bipyramids similar to that of the germylene 8b. The main
difference between these structures is that in stannylenes the
amido nitrogen atoms occupy the equatorial positions, together
with the lone electron pair. The weakly coordinated amino
groups are located in the axial positions. The amino NꢀSnꢀN
interatomic angles are 160.98(7) and 172.7(2)° (for 12 and 14);
in germylene 8b, these atoms are in pseudoequatorial positions
(Scheme 2).
The bond distances between the amido nitrogen atoms and
the tin atoms are slightly larger by 0.01ꢀ0.02 Å in 14 than in 12
and by ca. 0.04 Å compared to, for example, bis[N-(trimethylsilyl)-
N-(2,6-diisopropylphenyl)amido]tin(II)29 [2.095(3)Å]. The cal-
culated Snꢀamido N distances of stannylene 12 (Table 2) are in
very good agreement with the experimental values. The intramo-
lecularly coordinating amino groups in 12 and 14 display only quite
weak coordination to the tin atom compared to the similar
germylene 8b. On the other hand, the SnꢀN distances are similar
to the corresponding distances in the C,N-chelated stannylene.11b
Structures of 12 and 14 also differ in the orientation of the ligands,
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Figure 7. Molecular structure of 14 3.5C6D12 in a PLUTON repre-
3
sentation. Hydrogen atoms and solvent molecules are omitted for clarity.
Selected interatomic distances (Å) and angles (deg): Sn1ꢀN1 2.151(6),
Sn1ꢀN3 2.145(6), Sn1ꢀN2 2.638(8), Sn1ꢀN4 2.597(8), Ge1ꢀN1
1.836(6); N1ꢀSn1ꢀN3 93.3(2), N2ꢀSn1ꢀN4 172.7(2), N1ꢀSn1ꢀ
N2 83.8(2), N1ꢀSn1ꢀN4 101.8(2), Ge1ꢀN1ꢀSn1 128.6(3), C1ꢀ
C2ꢀC7ꢀN2 77.2(8).
Figure 8. Molecular structure of 15 in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Sn1ꢀN1 2.107(2), Sn1ꢀCl1 2.4642(8), Sn1ꢀN2
2.349(2), Ge1ꢀN1 1.835(2); N1ꢀSn1ꢀN2 86.71(9), N1ꢀSn1ꢀCl1
92.89(7), Ge1ꢀN1ꢀSn1 118.29(12), C1ꢀC2ꢀC7ꢀN2 71.1(4), Sn1
3 3 3
Cl1a 4.053(2).
Scheme 2. Structural Differences within the Group of Com-
number at the lead atom higher than 2.30 For comparison,
the 207Pb chemical shift of the C,N-chelated plumbylene
[2-(Me2NCH2)C6H4]2Pb,31 with the coordination geometry
of Ψ-trigonal bipyramid at 2624 ppm.
pounds Studieda
The structure determination of the triphenylgermyl-substi-
tuted heteroleptic stannylene 15 by X-ray diffraction reveals its
monomeric structure in the crystalline state (Figure 8). Thus, the
chlorine atom of the adjacent molecule is too remote from the
primary coordination sphere of the tin central atom [4.053(2)Å]
to consider a dimeric structure. The monomeric nature of 15
is further reflected by the short bond distance Sn1ꢀCl1 of
2.4642(8) Å, shorter by about 0.1 Å than that in typical dimeric
amides like, for example, [{Sn(N(C6H3iPr2-2,6)(SiMe3))-
(μ-Cl)}2]9a having no extra coordination. Similar monomeric
stannylenes containing bidentate ligands were described in the
literature14bꢀe,f,34 for β-diketiminates, amidinates, guanidinates,
or bidentate amides. The nearly pyramidal configuration of the
tin atom consists of the chlorine atom, the amino nitrogen atom,
which is much more strongly coordinated [2.349(2)Å] than that
in the homoleptic species 12 and 14, and the amido nitrogen
atom, with almost the same SnꢀN distance as that in 12 or 14.
The structure of 16 is dimeric, with the lead atoms being
connected by nonsymmetrical chlorine bridges (Figure 9),
similar to that in three lead amidinates and guanidinates33 and
pyridyl-substituted34 ones; on the other hand, the β-diketimi-
nate-substituted plumbylene is virtually monomeric.12g The lead
atom in 16 is virtually five-coordinated with the coordination
geometry of a Ψ-trigonal bipyramid, in which the trimethylsilyl-
substituted amido nitrogen and one of the chlorine atoms
occupy, together with the lone electron pair, the three equatorial
positions. The adjacent chlorine and nitrogen atoms from the
coordinated amino group are located in the axial positions. The
amido group N1ꢀPb1 bond distance of 2.221(6) Å (DFT calcu-
lated: 2.194 Å) is comparable to the corresponding bond distance
in another trimethylsilyl-substituted amide, [(2,6-iPr2C6H3)-
N(SiMe3)]2Pb [2.204(3) Å].31 The Pb1ꢀN2 atom bond dis-
tance of 2.509(6) Å (DFT calculated: 2.626 Å) is shorter than
that in [2-(Me2NCH2)C6H4]2Pb,31 ca. 2.7 Å. The strong con-
trast between the PbꢀCl contact distances, 2.620(2) Å (DFT
calculated: 2.647 Å) for the Pb1ꢀCl1 distance and 3.167(2) Å
a An elliptical arc means a ligand, N1 an amido nitrogen atom, and N2 an
amino nitrogen atom.
with 12 displaying a πꢀπ-stacking interaction between the aro-
matic rings. The aromatic rings of the ligand in 14 are also coplanar,
but one of them is twisted away, as a likely consequence of sterical
strain.
Heteroleptic Tetrylenes. Heteroleptic germylenes (9 and 11),
stannylenes (13 and 15), and plumbylene (18) were prepared by a
method similar to that of the homoleptic analogues using the molar
ratio of reactants 1:1.
The resonance patterns in the 1H NMR spectra of all germylenes
and stannylenes are quite similar to those of the homoleptic
tetrylenes, with the AX (or AB) spin pattern characteristic for the
diastereotopic benzylic protons with separations of ∼300 Hz in
all spectra except the case of the triphenylgermyl-substituted
germylene 11 with a strongly coupled AB system and a separa-
tion of only 75 Hz.
In the 119Sn NMR spectra of stannylenes 13 and 15, the
chemical shifts of ꢀ51.2 and ꢀ85.8 ppm were found in C6D6 at
room temperature. Similar values of ꢀ64.6 and ꢀ89.7 ppm were
detected in THF-d8, revealing further that these species are
monomeric with no additional coordination in solutions of both
coordinating and noncoordinating solvents.
The 207Pb chemical shift in the NMR spectrum of 18 is 1816
ppm, which corresponds to plumbylenes with a coordination
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Scheme 3. Preparation of Compounds 17 and 18a
a Reagents and conditions: (i) bis[bis(trimethylsilyl)amido]tin(II),
in Et2O, at RT; (ii) bis[bis(trimethylsilyl)amidotin(II) chloride], in
Et2O, at RT.
Figure 9. Molecular structure of 16 in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Pb1ꢀN1 2.221(6), Pb1ꢀCl1 2.620(2), Pb1ꢀ
Cl1a 3.167(2), Pb1ꢀN2 2.509(6), N1ꢀC1 1.415(8), Si1ꢀN1 1.718(6);
N1ꢀPb1ꢀN2 84.11(19), Pb1ꢀCl1ꢀPb1a 99.34(6), N2ꢀPb1ꢀCl1a
168.96(15), N1ꢀPb1ꢀCl1 92.82(16), Si1ꢀN1ꢀPb1 119.1(3), C1ꢀ
C2ꢀC7ꢀN2 74.8(8).
(theory: 3.205 Å) for the Pb1ꢀCl1a distance, is comparable to
the findings of Junk et al.33 and could be explained by the sterical
strain induced by the ligand. A direct comparison of the hetero-
leptic stannylene 15 and plumbylene 16 reveals mainly structural
similarities at the level of the MꢀCl and Mꢀamido N bond
distances, the higher values of which in 16 are caused by either
the higher covalent radius of the lead atom or the bridging nature of
the chlorine atoms. The axial angle N2ꢀPb1ꢀCl1a of 168.96(15)°
is close to the 180° ideal value, in spite of the equatorial lone-pair
repulsion (Scheme 2).
Figure 10. Molecular structure of 17 in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Sn1ꢀN1a 2.162(2), Sn1ꢀN1 2.179(3),
Sn1ꢀN1b 2.466(3), Sn1ꢀN2a 2.527(3); N1ꢀSn1ꢀN1b 83.42(12),
N1aꢀSn1ꢀN1b 76.93(11), N1ꢀSn1ꢀN1a 82.50(12), N1aꢀSn1ꢀN2a
82.35(11), N1ꢀSn1ꢀN2a 93.95(12), N1bꢀSn1ꢀN2a 159.24(10),
Sn1ꢀN1ꢀSn1c 103.82(12), Sn1bꢀN1ꢀSn1c 94.94(11), Sn1ꢀN1ꢀ
Sn1b 96.28(11).
The possible monomerꢀdimer equilibrium of plumbylene 16
was investigated by DFT computations. The complexation or
dimerization energy of two monomer molecules amounts to
ꢀ11.6 kcal/mol, indicating a stabilizing interaction. The Gibbs
free energy difference ΔG is found to be 0.09 kcal/mol. The
calculated equilibrium constant for this monomerꢀdimer equi-
librium, estimated using Boltzmann's statistical thermodynamics,
is 0.61. More details are given in the Supporting Information.
Quest for a Stannyl-Substituted Amido Stannylene. Be-
cause of the general interest in compounds containing two metals
of the same element, but with different oxidation states in the
same molecule, attempts to prepare trimethyltin- or tributyltin-
substituted stannylenes were undertaken. A plethora of synthetic
attempts, including the inorganic salt elimination as in the
preparation of stannylenes 12ꢀ15 discussed above, invariably
resulted in inseparable mixtures of unknown composition,
similar to previously reported attempts using tributyltin- or
triphenyltin-substituted 2,6-diisopropylaniline.35 On the other
hand, reactions of 6 with bis[bis(trimethylsilyl)amido]tin(II) or
bis{bis[bis(trimethylsilyl)amido]tin(II) chloride} gave the
unexpected heterocubane structure (Scheme 2), together with
[2-(Me2NCH2)C6H4N]2(μ2-SnMe2)2 and Me4Sn, in the case of
reaction with [bis(trimethylsilyl)amido]tin(II), or Me3SnCl, in
the second reaction, as the main products. All compounds
and 119Sn CP/MAS NMR spectroscopy. The chemical shift
values of the signals in the 13C CP MAS NMR spectrum are
found in the expected chemical shift ranges (see the Experi-
mental Section); two distinct signals were found for the diaster-
eotopic methyl carbon atoms. The heterocubane geometry
(Figure 10) reveals a strongly distorted cube structure, with
the distances of faces’ centroids being 2.143(2) Å, while the
deviation of the fourth atom of each face defined by three other
atoms is about 0.47 Å. The cube is composed of four tin atoms
and four imido nitrogen atoms with distances of 3.417(3) Å
(DFT calculated: 3.488 Å) between the tin atoms of each face.
The coordination sphere configuration of each tin atom is that of
a strongly distorted Ψ-trigonal bipyramid with the lone electron
pair and two imido nitrogen atoms in equatorial positions, while a
third imido nitrogen atom and the coordinated amino group are
located in axial positions. The contact distance between the
amino group nitrogen and the tin atoms [2.527(3) Å)] (DFT
calculated: 2.752 Å) lies in the range defined by the correspond-
ing distance in the heteroleptic [2.349(2) Å in 15] and the
homoleptic stannylene [2.640(2) and 2.668(2) for 12 and
2.638(8) Å for 14]. The bond distances between each tin atom
and the imido nitrogen atoms are similar for both equatorial
substituents [2.162(2) and 2.179(3) Å] (DFT calculated: 2.227
and 2.254 Å) but are quite different for the axial imido nitrogen
1
generated were identified by H and 119Sn NMR, and the
structures of 17 and 18 were determined by X-ray diffraction
(Scheme 3).
The heterocubane 17 is, in fact, the tetramer of the tin imide of
composition [2-(Me2NCH2)C6H4N]Sn (Figure 9). Its crystal
structure was determined by X-ray diffraction as well as by 13C
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ARTICLE
[Sn1ꢀN2 2.4921(15) Å]. The tin coordination spheres display
distorted trigonal-bipyramidal configurations with almost perfect
equatorial bond angles. Also, the axial angle [162.79(5)°] is
closer to the ideal value than that in the cubane 17. Interestingly,
the N1ꢀSn1ꢀN1a angle 78.91(6)° is much smaller than the
Sn1ꢀN1ꢀSn1a angle [101.09(6)°].
’ CONCLUSIONS
The group 14 metal anilinates containing groups with a broad
variety of steric strain were prepared and characterized in
solution and in the crystalline state. Some of these compounds
can be further deprotonated and substituted by low-valent group
14 organometallic substituents. All germylenes and stannylenes
are monomeric in solutions of coordinating and noncoordinating
solvents as well as in the crystalline state. Main structural
differences were observed for homoleptic germylenes and stan-
nylene, where three motifs were found (see Scheme 2). The
amido nitrogen atoms can be present in both the equatorial and
axial positions of the Ψ-trigonal bipyramid. The distances
between metal and amino nitrogen atoms, delimiting the in-
tramolecular interaction strength responsible for stabilization of
compounds, are found in a large range of values from the very
strong ones, such as, for example, in the case of monomeric
heteroleptic stannylene 15, to uncoordinated ones, such as those
for one of the amino nitrogen atoms in 8a. For plumbylenes, only
the heteroleptic compound containing the smallest ligand, the
trimethylsilyl-substituted one, could be obtained and was char-
acterized as a dimer in the crystalline state. Attempts to prepare
stannylenes substituted by tin(IV) moieties afforded a hetero-
cubane and dimethyltin(IV) derivative, both containing an
imido ligand.
Figure 11. Molecular structure of 18 in a PLUTON representation.
Hydrogen atoms are omitted for clarity. Selected interatomic distances
(Å) and angles (deg): Sn1ꢀN1 2.0428(15), Sn1ꢀN1a 2.1339(15),
Sn1ꢀC10 2.1366(19), Sn1ꢀC11 2.1393(19), Sn1ꢀN2 2.4921(15),
Sn1ꢀSn1a 3.2255(2); N1ꢀSn1ꢀN1a 78.91(6), N1ꢀSn1ꢀN2 84.39(5),
Sn1ꢀN1ꢀSn1a 101.09(6), C10ꢀSn1ꢀC11 118.70(8), C10ꢀSn1ꢀN1
121.52(7), N1ꢀSn1ꢀC11 121.52(7), N1aꢀSn1ꢀN2 162.79(5), C1ꢀ
C2ꢀC7ꢀN2 58.7(2).
atom [2.466(3) Å] (DFT calculated: 2.431 Å). The NꢀSnꢀN
angles between the core atoms of the distorted cube are smaller
than the angles of the ideal cube, and, accordingly, the SnꢀNꢀSn
angles are larger, with an extreme value for the Sn1ꢀN1ꢀSn1c
angle of 103.82(12)° (DFT calculated: 101.6°). The angles
between the imido nitrogen atom, the tin one, and the coordi-
nated amino nitrogen one in axial positions of the distorted Ψ-
trigonal bipyramid of each tin atom differ significantly from the
ideal value of 180° [for example, N1bꢀSn1ꢀN2a 159.24(10)°].
A DFT optimization of the heterocubane 17 geometry has
been performed in order to assess the structure distortion.
Virtually identical structures were found in silico and in the
crystalline state. The coordinates are given in the Supporting
Information.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic data in CIF
b
format, extensive figures of compounds 3ꢀ16 (Figures S1ꢀS12),
experimental details as well as discussion, Tables S1ꢀS10 with
all of the crystallographically related data and DFT optimiza-
tions. This material is available free of charge via the Internet
at http://pubs.acs.org.
Compound 18 is rather unique, with two similar structures
having been obtained by Roesky and Schuh for bis(μ2-2,
6-diisopropylamidophenyl)tetramethylditin(IV) and 1,1,2,3,3,
4-hexa-tert-butyl-1,3-distanna-2,4-diazacyclobutane.36 The forma-
tion of this compound through the metathetical exchange mecha-
nism from a trimethylstannyl-substituted amide is obviously
’ AUTHOR INFORMATION
1
taking place. The H NMR spectrum of 18 in THF-d8 reveals
a pair of broad resonances for the NCH2 moiety and single,
likewise broad resonances for the NCH3 as well as the Sn(CH3)2
groups. By contrast, the aromatic resonances are sharp and
display the usual homonuclear coupling splittings. In the 119Sn
NMR spectrum, a broad signal was found at ꢀ123.0 ppm,
indicating that in solution the tin atom is pentacoordinated,
similar to 17 or [2-[(N,N-dimethylamino)methyl]phenyl]-
dimethyltin(IV) chloride and its hydrolysis products.37
The structure of 18 (Figure 11) is probably the result of
dimerization of the dimethyltin(IV) imide, 2-(Me2NCH2)-
C6H4NdSnMe2, displaying a nearly perfect planar arrangement
of all heteroatoms and also the carbon atoms C1 and C1a. The
core four-membered Sn2N2 ring reveals rather different SnꢀN
distances, with Sn1ꢀN1 being 2.0428(15) Å and Sn1ꢀN1a
being 2.1339(15) Å, while the smaller one is comparable to those
found in [(t-Bu2Sn)-μ2-N(t-Bu)2]2 (2.059 and 2.055 Å) and
[(t-Bu2Sn)-μ2-(N-2,6-i-Pr2C6H3)]2 (2.047 and 2.059 Å).
The longer Sn1ꢀN1a bond is caused by the trans effect of the
rather strong intramolecular coordination of the amino group
Corresponding Author
*E-mail: ales.ruzicka@upce.cz.
’ ACKNOWLEDGMENT
Financial support of the Science Foundation of the Czech
Republic is greatly acknowledged (Grant P203/10/P092). L.B.
and F.D.P. acknowledge the Research Foundation Flanders and
VUB for continuous support. Helpful comments and suggestions
by Prof. R. Willem, Department of Materials and Chemistry,
VUB, are acknowledged.
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