Germacarboxylic acid: An organic-acid analogue based on a heavier group 14 element

Article abstract of DOI:10.1002/anie.200460872

First impressions: An oxidative addition between [LGeOH] and elemental sulfur leads to the isolation of the first germacarboxylic acid [LGe(S)OH] (L=HC{(CMe)(2,6-iPr₂C₆H₃N)}₂; see picture). In the solid state [LGe(S)OH] displays preferential of the thiono-form and formation of hydrogen-bond arrays generates dimers. This germacarboxylic acid shows how the heavier congeners of Group 14 can mimic well know organic functional groups.

Full text of DOI:10.1002/anie.200460872

Communications
Germanium Chemistry
Germacarboxylic Acid: An Organic-Acid
Analogue Based on a Heavier Group 14
Element**
Leslie W. Pineda, Vojtech Jancik, Herbert W. Roesky,*
and Regine Herbst-Irmer
Dedicated to Professor Jean-Marie Lehn
on the occasion ofhis 65th birthday
Carbon multiple-bonded species, especially those containing
carbonyl groups (aldehydes, amide esters, ketones) are widely
known and useful systems in organic chemistry.[1] As far as the
heavier congeners of Group 14 are concerned, a steady and
remarkable development has been experienced, which
includes the synthesis of unsaturated species. Additionally a
myriad of mixed unsaturated compounds has been prepared
containing elements of Groups 14–16.[2] However, owing to
the high reactivity and tendency to polymerize these species
have to be thermodynamically and kinetically stabilized.
In the case of germanium–chalcogen double-bonded
species, a few thio-, seleno-, and telluroketones were pre-
pared.[3] We have already reported the synthesis and structure
of [HC{(CMe)(2,6-iPr2C6H3N)}2Ge(S)X][4] (X = Cl, F,
HC{(CMe)(2,6-iPr2C6H3N)}2 = 2,6-iPr2C6H3NC(CH3)CH-
C(CH3)NC6H3-2,6-iPr2) with Group 14 and 16 elements
[*] Dipl.-Chem. L. W. Pineda, Dipl.-Chem. V. Jancik,
Prof. Dr. H. W. Roesky, Dr. R. Herbst-Irmer
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,
the Göttinger Akademie der Wissenschaften, and the Fonds der
Chemischen Industrie. L.W.P. thanks the Deutscher Akademischer
Austauschdienst (DAAD) for a predoctoral fellowship.
5534
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200460872
Angew. Chem. Int. Ed. 2004, 43, 5534 –5536

Angewandte
Chemie
bearing a halide. Furthermore, the synthesis and structures of
the selenium analogue [HC{(CMe)(2,6-iPr2C6H3N)}2Ge-
(Se)X] (X = Cl, F), as well as the functionalized derivative
[HC{(CMe)(2,6-iPr2C6H3N)}2Ge(E)R] (E = S, Se; R = Me
nBu) were reported.[5] Recently, we succeeded in the isolation
and structural characterization of the first terminal hydroxide
based on germanium(ii) [HC{(CMe)(2,6-iPr2C6H3N)}2GeOH]
(1).[6] As a stable precursor compound 1 is quite intriguing for
the generation of new functional groups. To our knowledge
the co-existence and fast tautomeric equilibrium for thiolo-
carboxylic acid 2 and thionocarboxylic acid 3 is known, but
the latter group does not exist in the free state (Scheme 1).[7]
Herein we report the first successful isolation and full
characterization of a germanium thionoacid [HC{(CMe)-
(2,6-iPr2C6H3N)}2Ge(S)OH] (4), which has no isolated prece-
dent in the carbon system (see Scheme 2).
shift. Thus, this resonance shift indicates a fairly acidic nature
of the terminal OH proton. Furthermore no evidence was
found for any tautomeric equilibrium of 4. The most abundant
ion peak in the EI mass spectrum appeared at m/z 525
[MÀMe]+, and the signal at m/z 540 (40%) was assigned to
the molecular ion [M]+ (correct isotopic pattern).
Maintaining a toluene solution of 4 for two weeks at
À208C, resulted in colorless single crystals suitable for X-ray
structural analysis.[8] Compound 4 crystallizes in the mono-
clinic space group C2/c, with one monomer and one molecule
of toluene in the asymmetric unit. Intermolecular interaction
of the hydroxy group with the sulfur atom results in the
À
formation of the hydrogen-bonding array (O H···S) leading
to dimers (Figure 1). The hydrogen bonded donor–acceptor
Scheme 1. Tautomeric equilibrium for the thiolo- and thionocarboxylic
acid.
The reaction of 1 in the presence of equivalent amounts of
elemental sulfur at room temperature in toluene leads after
three days to the white compound 4 in moderate yield.
(Scheme 2).
Figure 1. Thermal ellipsoid plot of 4 (thermal ellipsoids set at 50%
probability). H atoms, except for the OH group, and interstitial toluene
molecules, are omitted for clarity. Selected bond lengths [Š] and
angles [8]: Ge(1)-O(1) 1.751(2), Ge(1)-N(2) 1.911(2), Ge(1)-N(1)
1.916(2), Ge(1)-S(1) 2.077(1); O(1)-Ge(1)-N(2) 99.6(1), O(1)-Ge(1)-
N(1) 102.2(1), N(2)-Ge(1)-N(1) 95.6(1), O(1)-Ge(1)-S(1) 121.4(1),
N(2)-Ge(1)-S(1) 118.8(1), N(1)-Ge(1)-S(1) 114.9(1).
separations (H···S, 2.537 Š and O···S 3.234 Š) follow the same
trend as those reported in literature.[9] The coordination
environment around the germanium atom comprises two
nitrogen atoms from the supporting ligand, one hydroxy
group, and one sulfur atom, and has a distorted tetrahedral
geometry.
Scheme 2. Ar=2,6-iPr2C6H3.
Compound 4 is soluble in benzene, THF, and hexane, but
insoluble in pentane and shows no decomposition on expo-
sure to air. Compound 4 was fully characterized by IR, H,
1
À
The Ge O bond length (1.751(2) Š) in 4 is significantly
and 13C NMR spectroscopy, EI mass spectrometry, elemental
analysis, and X-ray structural analysis. By comparison of the
IR spectrum of 1, which exhibits a sharp OH stretching
vibration at 3571 cmÀ1[6] with the corresponding frequency of
4 (3238 cmÀ1) a significant shift to lower wave numbers is
observed. Such behavior may be due to the formation of
shorter than that in 1 (1.828(1) Š), as a result of the smaller
atomic radius of GeIV compared with that of GeII. Indeed,
IV
À
similar Ge O bond lengths for Ge species have been
described, (tBu2Ge(OH)2 (1.781(4) and 1.779(2) Š)[10] and
1.779(5) Š in [(FcN)3GeOH] (Fc = CpFe(h5-C5H4)).[11]
A
À
shorter Ge N bond length and wider N-Ge-N angle are
1
hydrogen bonds. Interestingly, the H NMR spectrum of 4
expected (av. 1.914(2) Š and 95.6(1)8) than in 1. A compar-
3
À
exhibits a resonance signal at d = 2.30 ppm for the hydroxy
hydrogen, which by comparison with that of 1 (d = 1.54 ppm)
clearly shows a downfield shift. Again intermolecular hydro-
gen interaction and a change of the oxidation state of the
germanium atom are plausible explanations for the observed
ison of the Ge S bond length in [{h -[(m-tBuN)2(SiMet-
Bu)2]}GeS][12] (2.063(3) Š), and in [HC{(CMe)(2,6-
iPr2C6H3N)}2Ge(S)X][4]
(X = Cl,
F),
(2.053(6)
and
2.050(9) Š), with that in 4 (2.077(1) Š) shows a good agree-
À
ment. Likewise, the Ge O bond length in [(dppe)Pd(m-S)(m-
Angew. Chem. Int. Ed. 2004, 43, 5534 –5536
www.angewandte.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5535

Communications
[4] Y. Ding, Q. Ma, H. W. Roesky, R. Herbst-Irmer, I. Usón, M.
Noltemeyer, H.-G. Schmidt, Organometallics 2002, 21, 5216 –
5220.
[5] Y. Ding, Q. Ma, H. W. Roesky, I. Usón, M. Noltemeyer, H.-G.
Schmidt, J. Chem. Soc. Dalton Trans. 2003, 1094 – 1098.
[6] L. W. Pineda, V. Jancik, H. W. Roesky, D. Neculai, A. M.
Neculai, Angew. Chem. 2004, 116, 1443 – 1445; Angew. Chem.
Int. Ed. 2004, 43, 1419 – 1421.
CH2O)Ge{N(SiMe3)2}2]
(dppe = bis(diphenylphosphanyl)-
ethene)[13] (1.785(6) Š), a compound which has almost the
same coordination environment and geometry at the germa-
nium center as 4, correlates well with that in 4.
In summary the reaction of 1 and elemental sulfur
resulted in the formation of the title compound 4 which
represents a new class of “carbon-free” carbonic acid
analogues based on germanium. The stability of 4 against
oxygen and water at room temperature makes these systems
quite interesting for biological investigations.
[7] a) F. Duus in Comprehensive Organic Chemistry, Vol. 3 (Eds.: D.
Barton, W. D. Ollis), Pergamon, Oxford, 1979, pp. 420 – 421; b) J.
Hine, Physical Organic Chemistry, McGraw-Hill, 1962, p. 238.
[8] Crystal data for 4·toluene: C36H50GeN2OS, Mr = 631.43, mono-
clinic, space group C2/c, a = 26.021(1), b = 16.045(1), c =
18.006(2) Š, b = 114.79(1)8, V= 6825(1) Š3, Z = 8, 1calcd
1.229 gcmÀ3
F(000) = 2688, l = 1.54178 Š, T= 100(2) K,
=
Experimental Section
,
m(CuKa) = 2.002 mmÀ1. Data for the structure were collected on
a Bruker three-circle diffractometer equipped with a SMART
6000 CCD detector. Intensity measurements were performed on
a rapidly cooled crystal (0.20 ” 0.10 ” 0.10 mm3) in the range
6.66 ꢀ 2q ꢀ 118.088. Of the 21505 measured reflections, 4748
were independent [R(int) = 0.0363]. The structure was solved by
direct methods (SHELXS-97)[14] and refined with all data by full-
All manipulations were performed under a dry and oxygen-free
atmosphere (N2 or Ar) by using Schlenk-line and glove-box
techniques. Solvents were purified prior to use by distillation over
appropriate drying agents in a nitrogen atmosphere.
4: A solution of 1 (1.56 g, 3.07 mmol) in toluene (30 mL) was
slowly added to a suspension of elemental sulfur (0.09 g, 3.07 mmol)
in toluene (15 mL) by cannula at room temperature. After 3 days
under constant stirring at ambient temperature the yellow solution
turned slightly green. After removal of all volatiles the remaining
crude product was rinsed with pentane (3 ” 10 mL) and dried under
reduced pressure to yield pure 4. Yield: 1.10 g (66%); m.p. 3008C
(decomp); IR (KBr): n˜ = 3238, 3063, 2965, 2867, 1638, 1539, 1442,
matrix least squares on F2.[15] The hydrogen atoms of C H bonds
À
were placed in idealized positions, whereas the hydrogen atom
from the OH moiety was localized from the difference electron-
density map and refined isotropically. The final refinements
converged at R1 = 0.0283 for I > 2s(I), wR2 = 0.0730 for all data.
The final difference Fourier synthesis gave a min/max residual
electron density À0.279/ + 0.355 eŠÀ3. CCDC-240065 (4) con-
tains the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.cam.a-
c.uk/conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB21EZ, UK;
fax: (+ 44)1223-336-033; or deposit@ccdc.cam.ac.uk).
[9] a) N. N. Greenwood, A. Earnshaw, Chemistry ofthe Elements ,
Butterworth-Heinemann, Oxford, 1997, p. 60; b) A. F. Wells,
Structural Inorganic Chemistry, Clarendon, Oxford, 1984, p. 357.
[10] H. Puff, S. Franken, W. Schuh, W. Schwab, J. Organomet. Chem.
1983, 254, 33 – 41.
1388, 1322, 1257, 1175, 1102, 1023, 933, 875, 797, 712, 501 cmÀ1
;
1H NMR (500 MHz, C6D6, 258C, TMS): d = 7.09–7.16 (m, 6H, m-, p-
Ar-H), 4.83 (s, 1H, g-CH), 3.62 (sept, 3J(H,H) = 6.8 Hz, 2H,
CH(CH3)2), 3.35 (sept, 3J(H,H) = 6.8 Hz, 2H, CH(CH3)2), 2.30 (s,
1H, OH), 1.57 (d, 3J(H,H) = 6.8 Hz, 6H, CH(CH3)2), 1.47 (s, 6H,
3
3
CH3), 1.26 (d, J(H,H) = 6.8 Hz, 6H, CH(CH3)2), 1.16 (d, J(H,H) =
6.8 Hz, 6H, CH(CH3)2), 1.05 ppm (d, 3J(H,H) = 6.8 Hz, 6H,
CH(CH3)2); 13C NMR (125.8 MHz, C6D6, 258C, TMS): d = 169.9
=
(C N), 145.9, 144.9, 137.2, 128.9, 124.8, 124,6 (i-, o-, m-, p-, Ar), 98.5
(g-CH), 29.5 (CH3), 27.9 (CH(CH3)2), 26.3 (CH(CH3)2), 24.7
(CH(CH3)2), 24.6 (CH(CH3)2), 23.8 (CH(CH3)2), 23.7 ppm
(CH(CH3)2); EI-MS (70 eV): m/z (%): 540 (40) [M]+, 525 (100)
[MÀCH3]+; elemental analysis (%) calcd for C29H42GeN2OS (539.32):
C 64.59, H 7.85, N 5.19; found: C 64.20, H 7.57, N 5.12.
[11] A. Fischer, K. Jacob, F. T. Edelmann, Z. Anorg. Allg. Chem.
2003, 629, 963 – 967.
[12] M. Veith, S. Becker, V. Huch, Angew. Chem. 1989, 101, 1287 –
1289; Angew. Chem. Int. Ed. Engl. 1989, 28, 1237 – 1238. For
comparison, see also M. C. Kuchta, G. Parkin, J. Chem. Soc.
Chem. Commun. 1994, 1351 – 1352; M. Veith, A. Rammo, Z.
Anorg. Allg. Chem. 1997, 623, 861 – 872; I. Saur, G. Rima, H.
Gornitzka, K. Miqueu, J. Barrau, Organometallics 2003, 22,
1106 – 1109.
Received: June 4, 2004
Keywords: acids · germanium · hydrogen bonds · oxidative
.
addition · sulfur
[13] Z. T. Cygan, J. W. Kampf, M. M. Banaszak Holl, Organometal-
lics 2004, 23, 2370 – 2375.
[1] J. McMurry, Organic Chemistry, Brooks-Cole, CA, 1992,
pp. 695 – 705.
[14] “SHELXS-97, Program for Structure Solution”: G. M. Shel-
drick, Acta Crystallogr. Sect. A 1990, 46, 467 – 473.
[15] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Gꢀttingen, Gꢀttingen (Germany),
1997.
[2] P. P. Power, Chem. Rev. 1999, 99, 3463 – 3504.
[3] a) N. Tokitoh, R. Okazaki, Adv. Organomet. Chem. 2001, 47,
121 – 166; b) N. Tokitoh, T. Matsumoto, R. Okazaki, Bull. Chem.
Soc. Jpn. 1999, 72, 1665 – 1684; c) T. Matsumoto, N. Tokitoh, R.
Okazaki, J. Am. Chem. Soc. 1999, 121, 8811 – 8824.
5536
ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2004, 43, 5534 –5536