Synthesis of a germanium analogue of a dithiocarboxylic acid anhydride from the Ge(i) pyridyl-1-azaallyl dimer

Article abstract of DOI:10.1039/b916326c

The reaction of pyridyl-1-azaallyl germanium(ii) chloride RGeCl (1) [R = {N(SiMe₃)C(Ph)C(SiMe₃)(C₅H₄N-2)}] with lithium metal afforded the dimeric germanium(i) compound [(RGe) ₂] (2); compound 2 react

Full text of DOI:10.1039/b916326c

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Synthesis of a germanium analogue of a dithiocarboxylic acid anhydride
from the Ge(I) pyridyl-1-azaallyl dimerw
Wing-Por Leung,* Wang-Kin Chiu, Kim-Hung Chong and Thomas C. W. Mak
Received (in Cambridge, UK) 7th August 2009, Accepted 14th September 2009
First published as an Advance Article on the web 28th September 2009
DOI: 10.1039/b916326c
The reaction of pyridyl-1-azaallyl germanium(II) chloride
RGeCl (1) [R = {N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}] with
lithium metal afforded the dimeric germanium(I) compound
[(RGe)2] (2); compound 2 reacts with an excess of elemental
sulfur to afford the novel germanium analogue of a dithio-
carboxylic acid anhydride [{Ge(S)R}2S] (4) via the insertion of
elemental sulfur into the Ge(I)–Ge(I) bond followed by the
oxidative-addition of elemental sulfur to the germanium(II)
centres.
The coordination sites of the Ge(I) centres are each occupied
by the two N atoms of the azaallyl ligand and by the other
Ge(I) atom. The lone pair of the Ge(I) occupies the remaining
coordination site of the tetrahedron. The Ge–Ge bond
length in 2 is 2.6021(8) A, which is very close to the single
Ge–Ge interaction (2.61 A mean7), but significantly longer
than that for typical digermenes, R2GeGeR2 (2.21–2.51 A)7
and the two structurally characterized digermynes (2.2850(6)
and 2.2060(8) A).8,9 The Ge–Ge bond distance in 2 is in fact
comparable to that of the structurally characterized amidinato
Ge(I) dimer (2.6380(8) A)1 and that of the less bulky Ge(I)
dimer (2.569(5) A).2 Like the bulky amidinato Ge(I) dimer,1
compound 2 exhibits a trans-bent geometry. These obser-
vations suggest that Ge–Ge multiple bond is not present in 2.
We have investigated the reactivity of 2 in order to study the
bonding character between the Ge(I) centres in 2. Treatment
of 2 with an excess of sulfur afforded a yellowish-orange
mixture. Extraction of the crude product with CH2Cl2
followed by concentration of filtrate afforded yellow crystals
of [{Ge(S)[N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)]}2S] (4).
The reaction of 2 with an excess of sulfur (Scheme 2)
demonstrates that the Ge–Ge interaction in 2 is prone to
insertion and the Ge(I) dimers can undergo an oxidative-
addition reaction. The germanium compound 4 obtained is
the first example of a heavier group 14 element analogue of a
dithiocarboxylic acid anhydride. The germanium analogue of
dithiocarboxylic acid has been recently prepared by Roesky
and co-workers.10
The synthesis of novel dimeric Ge(I) compound was first
reported by Jones and co-workers in which the Ge(I) dimers
exhibit a trans-bent geometry.1 By using smaller substituents
on the amidinato ligand, Roesky reported the synthesis of a
germanium(I) dimer in a gauche-bent geometry.2 Recently,
Driess and co-workers have prepared a novel unsymmetrically
substituted digermylene with a Ge(I)–Ge(I) bond.3 One
common feature among these Ge(I) compounds is that they
show Ge–Ge interactions with a lone pair of electrons on each
germanium atom. Theoretical studies indicate that multiple
bond is not present in these Ge(I) dimers.
We have recently reported the synthesis and reactivities of
pyridyl-1-azaallyl germanium(II) chloride 1.4–6 Herein, we
report the synthesis of the germanium(I) pyridyl-1-azaallyl
dimer 2 from the reduction of 1. The reaction of 2 with an
excess of sulfur afforded the unprecedented germanium
analogue of a dithiocarboxylic acid anhydride 4.
Treatment of [Ge{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl]
(1) with 1 equiv. of lithium metal in THF for 12 h afforded
a dark green mixture. Dark green crystals of germanium(I)
dimer [{[N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)]Ge}2] (2) were
obtained by extraction of the crude product with Et2O
followed by concentration and cooling at 0 1C (Scheme 1).
Compound 2 showed good solubility in THF, toluene, Et2O
and CH2Cl2. It remains stable in solution or in the solid state
at room temperature in an inert atmosphere. Compound 2 has
been characterized by elemental analysis, NMR spectroscopyz
and X-ray structure analysis.y
The molecular structure of 4 is shown in Fig. 2. Each
germanium atom is bonded to a pyridyl-1-azaallyl ligand
in a N,N0-chelate fashion and to two sulfur atoms. The
single bond distances between the germanium atoms and the
central sulfur are 2.222(3) and 2.226(3) A, respectively.
The GeQS bond distances on each side are 2.070(3) and
2.062(4) A, which are similar to that of 2.056(2) A in
[Ge(S){N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl]6 and 2.053(6)
A in [{HC(CMeNAr)2}Ge(S)Cl] (Ar = 2,6-Pri2C6H3).11 The
bond distances are also close to the calculated GeQS bond
distance of 2.06 A,12 indicating the double bond nature
between germanium and sulfur on each side of the molecule.
The molecular structure of 2 is shown in Fig. 1. The
coordination environment of the Ge(I) atoms exhibits a
distorted tetrahedral geometry. The pyridyl-1-azaallyl ligand
is bonded to the germanium centre in a N,N0-chelate fashion.
Department of Chemistry, The Chinese University of Hong Kong,
Shatin, New Territories, Hong Kong, China.
E-mail: kevinleung@cuhk.edu.hk; Fax: +852 2603 5057
w Electronic supplementary information (ESI) available: Details of
experimental procedures, spectroscopic data for 2 and 4. CCDC
743825 and 743826. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b916326c
Scheme 1 Synthesis of compound 2.
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Fig.
1
ORTEP view (30% ellipsoid probability) of
Fig.
2
ORTEP view (30% ellipsoid probability) of
[{[N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)]Ge}2] (2). Hydrogen atoms are
omitted for clarity. Selected bond distances (A) and angles (1):
Ge(1)–Ge(2) 2.602(8), Ge(1)–N(1) 2.057(3), Ge(1)–N(2) 1.955(4),
Ge(2)–N(4) 1.957(3), Ge(2)–N(3) 2.054(4), Si(1)–C(6) 1.907(4), Si(2)–N(2)
1.746(4), N(1)–C(5) 1.366(5), N(2)–C(10) 1.381(5), N(1)–C(1) 1.352(5),
C(5)–C(6) 1.471(6), C(6)–C(10), 1.355(6); N(2)–Ge(1)–N(1) 86.9(2),
N(2)–Ge(1)–Ge(2) 102.7(1), N(1)–Ge(1)–Ge(2) 83.4(1), N(4)–Ge(2)–N(3)
87.1(1), N(4)–Ge(2)–Ge(1) 102.8(1), N(3)–Ge(2)–Ge(1) 85.1(1),
C(1)–N(1)–C(5) 120.3(4), C(1)–N(1)–Ge(1) 117.8(3), C(5)–N(1)–Ge(1)
121.8(3), C(10)–N(2)–Ge(1) 116.1(3).
[{Ge(S)[N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)]}2S] (4). Hydrogen atoms
are omitted for clarity. Selected bond distances (A) and angles (1):
S(3)–Ge(1) 2.222(3), S(3)–Ge(2) 2.226(3), Ge(1)–S(1) 2.070(3), Ge(2)–S(2)
2.062(4), Ge(1)–N(2) 1.842(8), Ge(1)–N(1) 1.947(8), Ge(2)–N(4) 1.846(7),
Ge(2)–N(3) 1.963(9), N(1)–C(5) 1.380(1), N(2)–C(10) 1.396(1),
C(5)–C(6) 1.476(1), C(6)–C(10) 1.370(1); Ge(1)–S(3)–Ge(2) 101.4(1),
N(2)–Ge(1)–S(1) 122.0(2), N(1)–Ge(1)–S(1) 113.0(2), N(2)–Ge(1)–S(3)
101.4(2), N(1)–Ge(1)–S(3) 101.9(2), S(1)–Ge(1)–S(3) 121.3(1),
N(2)–Ge(1)–N(1) 91.8(3), C(1)–N(1)–Ge(1) 121.1(7), C(5)–N(1)–Ge(1)
118.5(6), N(4)–Ge(2)–S(2) 121.5(3), N(3)–Ge(2)–S(2) 113.8(3),
N(4)–Ge(2)–S(3) 100.8(2), N(3)–Ge(2)–S(3) 102.7(2), S(2)–Ge(2)–S(3)
121.4(1).
We gratefully acknowledge financial support from The Chinese
University of Hong Kong (Direct Grant No. 2060324).
Notes and references
z Selected spectroscopic data for 2: 1H NMR (benzene-d6): d 0.24
(s, 9H, SiMe3), 0.26 (s, 9H, SiMe3), 6.06–6.12 (m, 1H, 5-py), 7.17–7.39
(m, 5H, Ph), 7.41–7.45 (m, 1H, 3-py), 7.78–7.82 (m, 1H, 4-py),
8.09–8.11 (d, 1H, 6-py). 13C{1H} NMR (benzene-d6): d 2.63, 3.74
(SiMe3), 114.215 (CSiMe3), 124.65, 130.01, 138.08, 142.23, 143.54,
145.94, 147.97, 156.45, 159.53 (Ph and Py), 164.60 (NCPh). 4: 1H
NMR (THF-d8): d ꢁ0.01 (s, 9H, SiMe3), 0.16 (s, 9H, SiMe3), 6.60–6.64
(t, 1H, 5-py), 7.02–7.28 (m, 5H, Ph), 7.36–7.40 (d, 1H, 3-py), 7.50–7.52
(t, 1H, 4-py), 7.81–7.83 (d, 1H, 6-py). 13C{1H} NMR (THF-d8): d 2.63,
3.31 (SiMe3), 118.66 (CSiMe3), 125.18, 128.08, 129.56, 131.50, 136.63,
137.37, 144.60, 146.18, 147.16 (Ph and Py), 159.18 (NCPh).
y Crystal data for 2: C38H54Ge2N4Si4, M = 824.39, crystal size =
0.50 ꢂ 0.40 ꢂ 0.30 mm, Flack parameter = ꢁ0.008(9), monoclinic,
space group P21, a = 13.346(3), b = 11.006(3), c = 15.589(4) A,
b = 108.301(4)1, V = 2173.8(9) A3, Z = 2, Dc = 1.259 g cmꢁ3, m =
1.523 mmꢁ1, l = 0.71073 A, T = 293(2) K, 2ymax = 25.001, F(000) =
860, 7263 independent reflections (Rint = 0.0342), R1 = 0.0397,
wR2 = 0.0913 (I 4 2s(I)), largest diff. peak and hole: 0.597 and
ꢁ0.281 e Aꢁ3. 4: C38H54Ge2N4S3Si4, M = 920.57, crystal size =
0.40 ꢂ 0.30 ꢂ 0.20 mm, Flack parameter = 0.027(17), orthorhombic,
space group Pna21, a = 24.360(6), b = 11.062(3), c = 17.424(5) A,
V = 4695(2) A3, Z = 4, Dc = 1.302 g cmꢁ3, m = 1.546 mmꢁ1, l =
0.71073 A, T = 293(2) K, 2ymax = 28.071, F(000) = 1912, 11252
independent reflections (Rint = 0.1514), R1 = 0.0694, wR2 = 0.1370
Scheme 2 Synthesis of compound 4.
(I 4 2s(I)), largest diff. peak and hole: 0.602 and ꢁ1.095 e Aꢁ3
.
In conclusion, we have prepared a germanium(I) dimer from
the reduction of pyridyl-1-azaallyl germanium (II) chloride
with lithium metal. Structural studies support that there are
no multiple bond characters in the Ge(I) dimer. The reaction
of the Ge(I) dimer with an excess of elemental sulfur afforded a
novel germanium analogue of a dithiocarboxylic acid anhydride.
1 S. P. Green, C. Jones, P. C. Junk, K.-A. Lippert and A. Stasch,
Chem. Commun., 2006, 3978.
2 S. Nagendran, S. S. Sen, H. W. Roesky, D. Koley, H. Grubmuller,
¨
A. Pal and R. Herbst-Irmer, Organometallics, 2008, 27, 5459.
3 W. Wang, S. Inoue, S. Yao and M. Driess, Chem. Commun., 2009, 2661.
4 W.-P. Leung, C.-W. So, Y. S. Wu, H.-W. Li and T. C. W. Mak,
Eur. J. Inorg. Chem., 2005, 513.
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5 W.-P. Leung, C.-W. So, K.-H. Chong, K.-W. Kan, H.-S. Chan and
T. C. W. Mak, Organometallics, 2006, 25, 2851.
6 W.-P. Leung, K.-H. Chong, Y.-S. Wu, C.-W. So, H.-S. Chan and
T. C. W. Mak, Eur. J. Inorg. Chem., 2006, 808.
7 As determined by the survey of the Cambridge Crystallographic
Database.
9 Y. Sugiyama, T. Sasamori, Y. Hosoi, Y. Furukawa, N. Takagi,
S. Nagase and N. Tokitoh, J. Am. Chem. Soc., 2006, 128, 1023.
10 A. Jana, D. Ghoshal, H. W. Roesky, I. Objartel, G. Schwab and
D. Stalke, J. Am. Chem. Soc., 2009, 131, 1288.
´
11 Y. Ding, Q. Ma, H. W. Roesky, I. Uson, M. Noltemeyer and
H. G. Schmidt, Dalton Trans., 2003, 1094.
8 M. Stender, A. D. Phillips, R. J. Wright and P. P. Power, Angew.
Chem., Int. Ed., 2002, 41, 1785.
12 L. Pauling, The Nature of The Chemical Bond, Cornell University
Press, Ithaca NY, 3rd edn, 1960, p. 224.
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6824 | Chem. Commun., 2009, 6822–6824