Preparation and structure of the first germanium(II) hydroxide: The congener of an unknown low-valent carbon analogue

Article abstract of DOI:10.1002/anie.200353205

Trapping HCl with an Arduengo-type carbene was the key to preparing and isolating the first germanium(II) hydroxide [LGeOH] (L = HC{(CMe)(2,6-iPr ₂C₆H₃N)}₂) by hydrolysis of the corresponding chloride. In the so

Full text of DOI:10.1002/anie.200353205

Angewandte
Chemie
A Germanium(ii) Hydroxide
Preparation and Structure of the First
Germanium(ii) Hydroxide: The Congener of an
Unknown Low-Valent Carbon Analogue**
Leslie W. Pineda, Vojtech Jancik, Herbert W. Roesky,*
Dante Neculai, and Ana M. Neculai
Dedicated to Professor Pedro Aymonino
on the occasion ofhis 75th birthday
In 1984 it was noted that the picture of the structural
chemistry of hydroxides is far from complete,[1] and 20 years
later this is still the case. In recent years, we have been
interested in organometallic hydroxides. We reported on the
preparation and structural characterization of unusual com-
pounds such as [LAl(OH)2][2] (L = HC{(CMe)(2,6-
iPr2C6H3N)}2), [(Me3Si)3CSnO(OH)]3,[3] and [(CpZr)6(m4-
O)(m-O)4(m-OH)8],[4] and a series of experiments concerning
the so-called water effect in organometallic chemistry.[5]
Interestingly, only a few examples of well-characterized
germanium(iv) hydroxides are known: Ph3GeOH,
(C10H7)3GeOH, (C6H11)3GeOH,[6] 2tBu2Ge(OH)2·(tBu2GeO-
H)2O·H2O,[7] and [Fc(tBu)(OH)Ge]2O [Fc = CpFe(h5-
C5H4)],[8] and no such compounds based on germanium(ii)
have been reported. The most common route to organo-
germanium hydroxides is through the hydrolysis of organo-
halogermanes, but they can be only isolated when the
supporting ligand is bulky enough.[9]
Here we report on the hydrolysis of the stable german-
ium(ii) chloride [HC{(CMe)(2,6-iPr2C6H3N)}2GeCl] (1),[10]
with a slight excess of water and one equivalent of 1,3-
dimesitylimidazol-2-ylidene[11] (2; Mes = 2,4,6-Me3C6H2) in
toluene at room temperature, which led to the formation of
[HC{(CMe)(2,6-iPr2C6H3N)}2GeOH] (3) in good yield
(Scheme 1). In contrast, conventional hydrolysis of 1 in the
presence of an amine or in liquid ammonia was unsuccessful
Scheme 1. Ar=2,6-iPr2C6H3, Mes=2,4,6-Me3C6H2.
[*] Dipl.-Chem. L. W. Pineda, Dipl.-Chem. V. Jancik,
Prof. Dr. H. W. Roesky, Dr. D. Neculai, Dr. A. M. Neculai
Institut für Anorganische Chemie
Universität Göttingen
Tammannstrasse 4, 37077 Göttingen (Germany)
Fax: (+49)551-39-3373
E-mail: hroesky@gwdg.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. L.W.P thanks the
Deutscher Akademischer Austauschdienst (DAAD) for a predoc-
toral fellowship.
Angew. Chem. Int. Ed. 2004, 43, 1419 –1421
DOI: 10.1002/anie.200353205
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1419

Communications
due to the formation of several side products. Moreover, the
separation of 3 from the amine·HCl adduct was not possible.
Addition of HCl to the N-heterocyclic carbene 2 is clearly a
key step in this reaction. The easy formation of 4 and its low
solubility allow the separation of 3 from 4.
Compound 3 is a yellow solid that is soluble in pentane,
THF, dichloromethane, benzene, and diethyl ether, but
insoluble in hexane. It was characterized by IR, 1H, and
13C NMR spectroscopy, EI mass spectrometry, elemental
analysis, and X-ray single-crystal analysis. In the IR spectrum
a sharp absorption around 3571 cmÀ1 can be attributed to the
À
O H stretching frequency. Theoretical calculations on
Ge(OH)2 showed that two vibrational frequencies could be
expected at 3675 and 3735 cmÀ1 [12]
These values are in good
.
agreement with that of 3 when it is taken into account that
some symmetry constraints are involved. In addition, the
monoanionic ligand in 3 might affect the vibrational fre-
quency by means of its steric demand and bonding mode. The
1H NMR spectrum shows the expected pattern for the b-
diketiminato ligand[10] and a resonance for the hydroxide
proton at high field (d = 1.54 ppm), which is in accordance
with the chemical shift observed for the OH group in
tBu2Ge(OH)2 (d = 1.49 ppm).[13] Surprisingly, the resonance
for the corresponding group of (FcN)3GeOH (FcN =
CpFe{h5-C5H3(CH2NMe2)-2}) was found at d = 8.98 ppm.[14]
The most intense peak in the EI mass spectrum appeared at
m/z = 403 [MÀMeÀGeÀOH]+, and the signal at m/z = 508
(25%) was assigned to the molecular ion [M]+.
Figure 1. Thermal-ellipsoid plot of 3 at the 50% probability level.
H atoms, except for the OH group, are omitted for clarity. Selected
À
À
bond lengths [Š] and angles [8]: Ge1 O 1.828(1), Ge1 N1 2.008(1),
À
Ge1 N1’ 2.008(1); O1-Ge1-N1 93.9(6), O1-Ge1-N1’ 94.8(6), N1-Ge1-
N1’ 89.5(1).
nate carbon analogue of composition RC(OH) has so far not
been reported. An RC(OH) species should be extremely
unstable and rearrange to the corresponding aldehyde.
Single crystals of 3[15] suitable for X-ray structural analysis
were grown by maintaining the reaction mixture in toluene/ Experimental Section
All manipulations were performed under a dry and oxygen-free
atmosphere (N2 or Ar) by using Schlenk-line and glove-box
techniques.
hexane (2.5:1) at À208C for three weeks. Complex 3 crystal-
lizes in the monoclinic space group C12/c1, with two half
dimers in the asymmetric unit. In 3 a germanium atom is
attached to two nitrogen atoms from the backbone of the
chelating ligand and a hydroxyl group, and a lone pair
presumably occupies the fourth coordination site, an assump-
tion that is supported by the presence of an intermolecular
interaction between the H atom of the OH group, which was
3: 1 (1.28 g, 2.43 mmol) and 2 (0.74 g, 2.43 mmol) were dissolved
in toluene (20 mL) at room temperature, then water (87.5 mL,
2.0 mmol) was slowly added, and the mixture was stirred. A white
precipitate immediately formed. The reaction mixture was stirred for
about 15 min, then the white precipitate was separated by filtration
in vacuo. The remaining colorless solution was evaporated, and the
resulting yellow solid of 3 was rinsed with hexane (2 ” 10 mL) and
dried in vacuo. Yield: 1.04 g (84%); m.p. 1408C; IR (KBr): n˜ = 3571,
2964, 2867, 1623, 1554, 1383, 1320, 1174, 1100, 1018, 918, 853, 795, 758,
À
located and refined, and another germanium atom (O H···Ge
3.064(26) Š). The coordination geometry about germanium is
À
derived from a distorted tetrahedron (Figure 1). The Ge N
1
588, 521, 366 cmÀ1; H NMR (200 MHz, C6D6): d = 7.15 (m, 6H, 2,6-
bond lengths and N-Ge-N angle are 2.008(1) Š and 89.5(1)8,
iPr2C6H3), 4.91 (s, 1H, g-CH), 3.60–3.80 (sept, 2H, (CH3)2), 3.20–3.40
(sept, 2H, (CH3)2), 1.60 (s, 6H, CH3), 1.54 (s, 1H, OH), 1.33 (d, 6H,
CH(CH3)2), 1.29 (d, 6H, CH(CH3)2), 1.21 (d, 6H, CH(CH3)2),
1.12 ppm (d, 6H, CH(CH3)2); 13C NMR (50.327 MHz, THF): d =
163.31 (NC), 146.37 (NC), 143.62 (ArC), 141.00 (ArC), 124.87
(ArC), 124.06 (ArC), 96.98 (g-C), 29.16 (CH(CH3)2), 28.02
(CH(CH3)2), 26.69 (CH(CH3)2), 24.73 (CH(CH3)2), 24.57
(CH(CH3)2), 24.08 (CH(CH3)2), 23.25 ppm (NC(CH3)); MS (EI):
m/z (%): 508 (25) [M]+, 403 (100) [MÀMeÀGeÀOH]+; elemental
analysis (%) calcd for C29H42GeN2O (507.24): C 68.67, H 8.35, N 5.52;
found: C 69.20, H 8.48, N 5.52.
respectively. These data can be compared with the slightly
À
shorter Ge N bond lengths in 1 (1.988(2) and 1.997(3) Š) and
[LGeF] (1.977(19) and 1.978(18) Š; L = HC{(CMe)(2,6-
iPr2C6H3N)}2).[16] Conversely, the Ge N bond lengths are
À
slightly longer in [HB(3,5-Me2pz)3Ge]I,[17] (av 2.03(2) Š; pz =
pyrazole ring) and [LGeMe] (2.008(2) and 2.038(2) Š).[16]
A noteworthy feature of compound 3 is the GeOH moiety
À
À
À
(Ge O 1.828(1), O H 0.795(7) Š); the Ge O bond length is
in good agreement with those predicted for Ge(OH)2 (av
1.804 Š).[12] Moreover, the O H distance of 3 is somewhat
shorter than that of water (0.96 Š). Interestingly, and as might
À
Received: October 31, 2003 [Z53205]
À
be expected, shorter Ge OH bond lengths are found in
germanium(iv) compounds due to the smaller radius of GeIV
Keywords: carbenes · germanium · hydrolysis · hydroxides
.
relative to GeII (e.g., Ge O 1.781(4) and 1.779(2) Š in
À
tBu2Ge(OH)2,[13] and 1.779(5) Š in (FcN)3GeOH).[14]
In summary, compound 3 is the first example of the
hitherto unknown germanium(ii) hydroxides. A low-coordi-
[1] a) A. F. Wells, Structural Inorganic Chemistry, Clarendon,
Oxford, 1984, p. 627; b) A. F. Holleman, E. Wiberg, Lehrbuch
1420
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www.angewandte.org
Angew. Chem. Int. Ed. 2004, 43, 1419 –1421

Angewandte
Chemie
der Anorganischen Chemie, Walter de Gruyter, Berlin, 1995,
p. 960; c) N. N. Greenwood, A. Earnshaw, Chemistry ofthe
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[2] G. Bai, Y. Peng, H. W. Roesky, J. Li, H.-G. Schmidt, M.
Noltemeyer, Angew. Chem. 2003, 115, 1164 – 1167; Angew.
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[3] J. Janssen, J. Magull, H. W. Roesky, Angew. Chem. 2002, 114,
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[4] G. Bai, H. W. Roesky, J. Li, T. Labahn, F. Cimpoesu, J. Magull,
Organometallics 2003, 22, 3034 – 3038.
[5] H. W. Roesky, M. G. Walawalkar, R. Murugavel, Acc. Chem.
Res. 2001, 34, 201 – 211, and references therein.
[6] M. Lesbre, P. Mazerolles, J. SatgØ, The Organic Compounds of
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[7] J. Beckmann, K. Jurkschart, M. Schürmann, Eur. J. Inorg. Chem.
2000, 939 – 941.
[8] Y. Zhang, F. Cervantes-Lee, K. H. Pannell, Organometallics
2003, 22, 510 – 515.
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Organometallic Chemistry, Vol. 2 (Eds.: G. Wilkinson, F. G. A.
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[11] a) A. J. Arduengo III, H. V. R. Dias, R. L. Harlow, M. Kline, J.
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[12] J. R. T. Johnson, I. Panas, Chem. Phys. 1999, 249, 273 – 303.
[13] H. Puff, S. Franken, W. Schuh, W. Schwab, J. Organomet. Chem.
1983, 254, 33 – 41.
[15] Crystal data for 3: C29H42GeN2O, Mr = 507.24, monoclinic, space
group C12/c1, a = 24.765(3), b = 15.155(2), c = 14.700(2) Š, b =
94.56(2)8,
V= 5499.6(12) Š3, Z = 8, 1calcd = 2.251 gcmÀ3
F(000) = 2160, l = 1.54178 Š, T= 100(2) K, m(CuKa) =
1.66 mmÀ1
Data were collected on Bruker three-circle
,
.
a
diffractometer equipped with a SMART 6000 CCD detector.
Intensity measurements were performed on a rapidly cooled
crystal (dimensions 0.20 ” 0.10 ” 0.10 mm) in the range 3.42 ꢀ
2q ꢀ 59.608. Of the 3752 measured reflections, 3635 were
independent. The structure was solved by direct methods
(SHELXS-97)[18] and refined for all data by full-matrix least-
2
À
squares methods on F . The hydrogen atoms of C H bonds were
placed in idealized positions. The final refinements converged at
R1 = 0.0247 for I > 2s(I) and wR2 = 0.0650 for all data. The final
difference Fourier synthesis gave min./max. residual electron
density of À0.338/0.318 eŠÀ3. CCDC 222748 (3) contains the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB21EZ, UK; fax:
(+ 44)1223-336-033; or deposit@ccdc.cam.ac.uk).
[16] Y. Ding, H. Hao, H. W. Roesky, M. Noltemeyer, H.-G. Schmidt,
Organometallics 2001, 20, 4806 – 4811. For comparison, see also
a) Y. Ding, Q. Ma, H. W. Roesky, R. Herbst-Irmer, I. Usꢀn, M.
Noltemeyer, H.-G. Schmidt, Organometallics 2002, 21, 5216 –
5220; b) M. Stender, A. D. Phillips, P. P. Power, Inorg. Chem.
2001, 40, 5314 – 5315.
[17] D. L. Reger, P. S. Coan, Inorg. Chem. 1996, 35, 258 – 260.
[18] G. M. Sheldrick, SHELXS-97, Program for crystal structure
refinement, University of Gꢁttingen, Gꢁttingen, Germany, 1997.
[14] A. Fischer, K. Jacob, F. T. Edelmann, Z. Anorg. Allg. Chem.
2003, 629, 963 – 967.
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1421