Crystal and molecular structure of the trans-hyponitrite compounds Ph 3E(μ-ONNO)EPh3 (E = Ge, Pb)

Article abstract of DOI:10.1002/zaac.201100543

The synthesis of the trans-hyponitrite compounds Ph₃E(μ-ONNO) EPh₃ [E = Ge (1), Pb (2)] as well as their crystal and molecular structure are reported. Compound 1 crystallized from toluene/pentane in the trigonal space group Rβar{3}$ with a = 29.7969(18), b = 29.7969(18), c = 11.8465(6) A= 120°; V = 9108.8(9) A³; Z = 12, I = 1.461 gA·cm^-3,T = 173(2) K. Compound 2 crystallized from toluene/iso-hexane in the triclinic space group Pβar{3}$ with a = 10.0330(2), b = 11.0615(2), c = 24.2080(4) A; α = 97.3730(10), β = 95.8550(10), = 115.3940(10)°; V = 2369.69(7) A³; Z = 3, I = 1.970 ·cm^-3, T = 173(2) K.The crystal structure determination revealed that two conformational isomers exist in the row of related group 14 element compounds. Whereas the species of tin and lead exhibit a S-shaped arrangement of the hyponitrite group between the two EPh₃ fragments, the corresponding germanium compound shows instead of a N-shape within the hyponitrite group. DFT calculations revealed that S-shaped conformers should be in all three cases the more stable ones. This stands in contrast to the observed N conformation of 1 in the crystal.

Full text of DOI:10.1002/zaac.201100543

SHORT COMMUNICATION
DOI: 10.1002/zaac.201100543
Crystal and Molecular Structure of the trans-Hyponitrite Compounds
Ph3E(μ-ONNO)EPh3 (E = Ge, Pb)
Tobias Mayer[a] and Hans-Christian Böttcher*[a]
Dedicated to Professor Wolfgang Beck on the Occasion of His 80th Birthday
Keywords: Hyponitrite; Germanium; Lead; Crystal Structure; DFT calculations
Abstract. The synthesis of the trans-hyponitrite compounds Ph3E(μ- structure determination revealed that two conformational isomers exist
ONNO)EPh3 [E = Ge (1), Pb (2)] as well as their crystal and molecular
in the row of related group 14 element compounds. Whereas the spe-
structure are reported. Compound 1 crystallized from toluene/pentane cies of tin and lead exhibit a S-shaped arrangement of the hyponitrite
¯
in the trigonal space group R3 with a = 29.7969(18), b = 29.7969(18), group between the two EPh3 fragments, the corresponding germanium
c = 11.8465(6) Å; γ = 120°; V = 9108.8(9) Å3; Z = 12, ρ = 1.461 g·cm–3,
compound shows instead of a N-shape within the hyponitrite group.
DFT calculations revealed that S-shaped conformers should be in all
three cases the more stable ones. This stands in contrast to the observed
N conformation of 1 in the crystal.
T = 173(2) K. Compound 2 crystallized from toluene/iso-hexane in the
¯
triclinic space group P1 with a = 10.0330(2), b = 11.0615(2), c =
24.2080(4) Å; α = 97.3730(10), β = 95.8550(10), γ = 115.3940(10)°;
V = 2369.69(7) Å3; Z = 3, ρ = 1.970 g·cm–3, T = 173(2) K.The crystal
tures of some organic hyponitrites were reported.[12] In this
paper we describe the synthesis and the crystal and molecular
structures of the title compounds Ph3E(μ-ONNO)EPh3 [E =
Ge (1), Pb (2)].
Introduction
Recently we reported the crystal and molecular structure of
the hyponitrite compound Ph3Sn(μ-ONNO)SnPh3.[1] During
the last years compounds containing hyponitrite groups got
more and more in the focus of bioinorganic investigation be-
cause they offer the possibility to serve as model compounds
of active intermediates in enzymatic processes of nitric oxide
reductases (NORs).[2–7] In the field of transition metal hyponi-
trito complexes we reported recently[8] the synthesis and the
X-ray crystal structures of some new compounds [Ru2(CO)4-
(μ-H)(μ-PtBu)2(μ-L2)(μ-η2-ONNO)] (L2 = bisphosphane or
aminobisphosphane). In contrast to the synthesis of the title
species reported therein, the latter compounds were formed by
a direct reaction of nitric oxide with the corresponding coordi-
natively unsaturated precursor complexes. Very recently the
chemistry of reductive N–N coupling of NO on transition
metal complexes affording nitrous oxide was reviewed.[9] In
the field of main group element compounds containing hypo-
nitrite groups only few species were described in the literature.
In 1968, Beck et al. reported compounds of the formula
Ph3E(μ-ONNO)EPh3 (E = Sn, Pb), which were characterized
by IR spectroscopy and elemental analysis.[10] A second report
in this area was represented by the synthesis and characteriza-
tion of the bis(trimethylsilyl) hyponitrite, Me3Si(μ-ONNO)
SiMe3, by Wiberg et al.[11] Furthermore the X-ray crystal struc-
Results and Discussion
As described by Beck et al.,[10] the compound Ph3Pb(μ-
ONNO)PbPh3 (2) was prepared by the reaction of tri-
phenylplumbyl iodide with silver hyponitrite (molar ratio 2:1)
in toluene by stirring at room temperature overnight. Com-
pound 2 was obtained by this way in satisfactory yields as a
colorless microcrystalline powder. Beside the known spectro-
scopic data,[10] compound 2 was additionally characterized by
1
NMR spectroscopy (1H and 13C). Thus the H NMR spectrum
of 2 in [D8]toluene showed the expected signals for the phenyl
protons in the range of δ = 7.68–7.33 ppm. In a similar manner
we used also the above mentioned synthesis for the preparation
of the new compound Ph3Ge(μ-ONNO)GePh3 (1). Thus the
reaction of triphenylgermyl bromide with Ag2N2O2 (2:1) in
toluene by stirring overnight at room temperature afforded the
latter species as colorless crystals in yields of about 53%. The
1
new compound 1 was characterized by elemental analysis, H
and 13C NMR spectroscopy, and an X-ray crystal structure
analysis. In the 1H NMR spectrum of 1 ([D8]toluene) the
phenyl protons resonate at δ = 7.67–7.51 ppm. The IR spec-
trum of 1 (as solid) showed a band at 964 cm–1 corresponding
to the hyponitrite group ν(NO).
* Prof. Dr. H.-C. Böttcher
E-Mail: hans.boettcher@cup.uni-muenchen.de
[a] Department Chemie
Ludwig-Maximilians-Universität
Butenandtstr. 5–13
81377 München, Germany
Suitable crystals for an X-ray diffraction study of 1 were
obtained by slow diffusion of pentane into a toluene solution
Z. Anorg. Allg. Chem. 2012, 638, (᭿), 1–5
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

T. Mayer, H.-C. Böttcher
SHORT COMMUNICATION
of the compound at room temperature. The crystal structure
determination revealed that crystals of 1 belong to the trigonal
¯
space group R3 with two crystallographically independent mo-
lecules in the asymmetric unit. The second molecule of 1 is
disordered in the crystal resulting in a high value wR2. The
molecular structure of 1 as a selected ORTEP view of one
molecule is shown in Figure 1. The molecule consists of two
Ph3Ge units bridged by a trans-hyponitrite group. The mole-
cule of 1 is related to that of the trans-hyponitrite compound
Ph3Sn(μ-ONNO)SnPh3 (3).[1] In both molecules the hyponitr-
ite group was found in the more stable trans configuration
and the following bonding characteristics were observed for
3: d(Sn–O) = 2.062(2)–2.069(2), d(N–N) = 1.231(6)–1.240(5),
d(N–O)
= 1.365(3)–1.372(3) Å, and angles N–N–O =
110.8(3)–111.6(3), N–O–Sn = 115.6(3)–117.0(2)°[1] (the corre-
sponding data for 1 see caption in Figure 1).
Figure 2. Molecular structure of Ph3Pb(μ-ONNO)PbPh3 (2) in the
crystal (ORTEP drawing with 50% probabilityl ellipsoids). For clarity
only one molecule of the asymmetric unit is shown, whereby the asym-
metric unit contains one and a half molecule. Selected distances /Å
and angles /°: Pb1–O1 2.198(4), Pb2–O2 2.188(5), N1–O1 1.368(8),
N2–O2 1.355(8), N1–N2 1.246(9); Pb1–O1–N1 114.0(4), Pb1–O1–N1
114.0(4), O1–N1–N2 111.2(5), O2–N2–N1 112.4(5).
33.4 and 44.5 kJ·mol–1, respectively), for 1 only a small ΔE of
5.8 kJ·mol–1 was calculated. We assume that reasons of the
crystal package could be responsible for the observation of the
less stable N-shaped conformation in solid 1. Moreover, DFT
calculations on the hitherto unknown compounds Ph3E(μ-
ONNO)EPh3 [E = C (4), Si (5] were performed. For the latter
two species energy differences between ES and EN afforded
negative values (ΔE = –37.2 and –6.7 kJ·mol–1 respectively),
therefore the N-shaped conformers should be the more stable
ones in these cases. Unfortunately, the synthesis of the species
4 and 5, respectively, failed till now in our hands to confirm
these theoretical predictions. However, on the other hand, the
crystal structure investigations of some organic hyponitrites
confirmed the N-shaped conformation.[12]
Figure 1. Molecular structure of Ph3Ge(μ-ONNO)GePh3 (1) in the
crystal (ORTEP drawing with 50% probabilityl ellipsoids) For clarity
only one molecule of the asymmetric unit is shown, whereby the asym-
metric unit contains only a half of the molecule of 1. Selected dis-
tances /Å and angles /°: Ge–O 1.824(5), N–O 1.388(8), N–Ni 1.225(8);
Ge–O–N 110.6(4), Ni–N–O 108.5(6). Atoms are generated by sym-
metry operation i: 1/3–x, 2/3–y, 2/3–z.
The crystal structure determination of compound 2 afforded
¯
that crystals of 2 belong to the triclinic space group P1 crys-
Conclusions
tallizing with three molecules in the unit cell. As observed for
1 and 3, respectively, also in 2 the hyponitrite group is found
in the more stable trans configuration. A selected ORTEP view
of one molecule of 2 is shown in Figure 2, important bond
lengths and angles are given in the caption. The molecular
structure of 2 is closely related to that of 1 and 3, respectively.
However a remarkable difference with respect to the confor-
mation of these molecules in the solid was found and should
be briefly discussed.
In crystals of 1 the trans-hyponitrite group connects the both
GePh3 fragments “horizontal” (N-shape), whereas in solid 2
and 3, respectively, a “vertical” arrangement of this group be-
tween the EPh3 (E = Sn, Pb) fragments (S-shape) was found.
In this light DFT calculations were carried out affording that
the S-shaped conformers should be the more stable ones in all
three cases. However, whereas for 2 and 3, respectively, the
The crystal and molecular structures of the trans-hyponitrite
compounds Ph3E(μ-ONNO)EPh3 [E = Ge (1), Pb (2)] were
determined by single-crystal X-ray diffraction studies. The
bonding characteristics of 1 and 2, respectively, correspond
well with the previous reported ones for the closely related
compound Ph3Sn(μ-ONNO)SnPh3. DFT calculations afforded
that the compounds with E = C and Si should be arranged in
the more stable N-shaped conformation, whereas the related
analogues of germanium, tin, and lead should exhibit a S-
shaped conformation. Interestingly for the germanium com-
pound also the N-shaped arrangement was found, which could
be presumably caused by reasons of the package in the crystal.
Experimental Section
General: All synthetic work was carried out under argon using stan-
energy differences between ES and EN are significant (ΔE = dard Schlenk techniques. All chemicals were purchased from Sigma.
2
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trans-Hyponitrite Compounds Ph3E(μ-ONNO)EPh3 (E = Ge, Pb)
Ag2N2O2 was synthesized according to the known procedure.[13] NMR
spectra were recorded with a Jeol Eclipse 400 instrument operating at
400 MHz (1H) and at 100 MHz (13C). Chemical shifts are given in
ppm relative to TMS (1H, 13C). Infrared spectra were recorded from
solids with a JASCO FT/IR-460 plus spectrometer.
Table 1. Experimental details of the crystal structure determination of
1 and 2.
1
2
M
T /°C
Space group
667.80
–100
R3
937.00
–100
P1
¯
¯
Synthesis of Ph3Ge(μ-ONNO)GePh3 (1): Ph3GeBr (364 mg,
0.95 mmol) was dissolved in toluene (10 mL). Ag2N2O2 (154 mg,
0.56 mmol) was added and the resulting slurry was stirred for 20 h
under exclusion of light. After filtration from the precipitated silver
halide, the solvent was removed under reduced pressure. The remain-
ing residue was recrystallized three times from toluene/iso-hexane
(1:2) affording a colorless microcrystalline powder. Yield 168 mg
(53%). Mp 113 °C (dec.). C36H30Ge2N2O2 (667.83): C 64.08 (calcd.
a /Å
b /Å
c /Å
α /°
29.7969(18)
29.7969(18)
11.8465(6)
90
90
120
9108.8(9)
12
1.461
10.0330(2)
11.0615(2)
24.2080(4)
97.3730(10)
95.8550(10)
115.3940(10)
2369.69(7)
3
β /°
γ /°
V /Å3
Z
1
64.47); H 4.53 (4.51); N 4.45 (4.18)%. IR: ν(NO): 964 vs. cm–1. H
Density /g·cm–3
1.970
10.677
μ /mm–1
2.015
NMR ([D8]toluene): δ = 7.67–7.51 (m, 30 H, C6H5). 13C{1H} NMR
([D8]toluene): δ = 137.1, 135.2, 130.4, 128.7 (C6H5).
2 θmax /°
55
55
Reflections, collected
Reflections, independent
Refined parameters
wR2 (all data)
R1
52392
4732
266
0.1980
0.0881
18837
10864
568
0.0809
Synthesis of Ph3Pb(μ-ONNO)PbPh3 (2): Ph3PbI (540 mg,
0.96 mmol) was dissolved in toluene (20 mL). Ag2N2O2 (396 mg,
1.72 mmol) was added and the resulting slurry was stirred for 20 h
under exclusion of light. After filtration from the precipitated silver
halide, the solvent was removed under reduced pressure. The remain-
ing residue was recrystallized once from toluene/iso-hexane (1:2) af-
fording a colorless microcrystalline powder. Yield 184 mg (41%). Mp
131 °C (dec.). C36H30N2O2Pb2 (938.18): C 46.38 (calcd. 46.05); H
3.53 (3.22); N 2.85 (2.99)%. IR: ν(NO): 1015 vs. cm–1. 1H NMR
([D8]toluene): δ = 7.68–7.33 (m, 30 H, C6H5). 13C{1H} NMR ([D8]tol-
uene): δ = 137.9, 137.1, 130.5, 129.9 (C6H5).
0.0373
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Acknowledgement
The authors are grateful to the Department of Chemistry of the Ludwig
Maximilian University Munich for supporting these investigations. T.
M. thanks Prof. P. Klüfers for financial support. A. Gallien we thank
for collecting the X-ray crystal data.
Z. Anorg. Allg. Chem. 2012, 1–5
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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T. Mayer, H.-C. Böttcher
SHORT COMMUNICATION
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Received: December 19, 2011
Published Online: ᭿
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 1–5

trans-Hyponitrite Compounds Ph3E(μ-ONNO)EPh3 (E = Ge, Pb)
T. Mayer, H.-C. Böttcher* ................................................ 1–5
Crystal and Molecular Structure of the trans-Hyponitrite Com-
pounds Ph3E(μ-ONNO)EPh3 (E = Ge, Pb)
Z. Anorg. Allg. Chem. 2012, 1–5
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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