Novel heteroleptic germanium(II) compounds from [2,4-Di-tert-butyl-6-((dimethylamino)methyl)phenyl]germanium chloride: Synthesis, structure, and derivatization

Article abstract of DOI:10.1021/om990557r

The synthesis of novel heteroleptic germanium(II) compounds starting from [2,4-di-tert-butyl-6-((dimethylamino)methyl)phenyl]germanium chloride, MamxGeCl (1), is reported. 1 reacts with potassium alkoxides to give the alkoxy-substituted compounds MamxGeO-

Full text of DOI:10.1021/om990557r

4778
Organometallics 1999, 18, 4778-4784
Novel Heter olep tic Ger m a n iu m (II) Com p ou n d s fr om
[2,4-Di-ter t-bu tyl-6-((d im eth yla m in o)m eth yl)p h en yl]ger m a n iu m
Ch lor id e: Syn th esis, Str u ctu r e, a n d Der iva tiza tion
Peter J utzi,* Silke Keitemeyer, Beate Neumann, and Hans-Georg Stammler
Faculty of Chemistry, University of Bielefeld, Universita¨tsstrasse, 33615 Bielefeld, Germany
Received J uly 19, 1999
The synthesis of novel heteroleptic germanium(II) compounds starting from [2,4-di-tert-
butyl-6-((dimethylamino)methyl)phenyl]germanium chloride, MamxGeCl (1), is reported. 1
reacts with potassium alkoxides to give the alkoxy-substituted compounds MamxGeO-t-Bu
(2), MamxGeO-i-Pr (3), MamxGeOEt (4), and MamxGeOMe (5). The ethynyl-substituted
species MamxGe(CtCPh) (6) and MamxGe(CtCH) (7) are obtained by the reaction of 1
with LiCtCPh and NaCtCH, respectively. The alkyl-substituted germanium(II) species
MamxGeR (R ) t-Bu (8), n-Bu (9), Me (10)) are formed by the reaction of 1 with the
corresponding alkyllithium compounds. Derivatization of 8-10 with MeI leads to the
formation of compounds containing the germyl cations [MamxGe(t-Bu)(Me)]+ (11a ), [Mamx-
Ge(n-Bu)(Me)]+ (12a ), and [MamxGe(Me)2]+ (13a ), respectively. All new species have been
characterized by NMR, MS, and microanalytical data. X-ray crystal structure determinations
are presented for 3, 4, 6, 7, and 11.
In tr od u ction
workers in 1994.4 This ligand combines the steric
features of a supermesityl group2c,e and the electronic
properties of the 2-((dimethylamino)methyl)phenyl sys-
tem.5 In 1998 we reported the first results concerning
the application of this ligand in germanium chemistry.6
The synthesis of the monomeric MamxGeCl (1) from
GeCl2‚(dioxane) and 1 equiv of MamxLi as well as the
treatment of 1 with various nucleophiles, leading to the
formation of novel diarylgermanium(II) compounds, was
described.
Here we report the synthesis and structural charac-
terization of heteroleptic germanium(II) species contain-
ing the Mamx substituent and sterically unpretentious
ligands, which are so far nearly unknown in the
chemistry of monomeric germanium(II) compounds. We
present the alkoxy-substituted compounds MamxGeO-
t-Bu (2), MamxGeO-i-Pr (3), MamxGeOEt (4), and
MamxGeOMe (5) as well as the ethynyl-substituted
species MamxGe(CtCPh) (6) and MamxGeCtCH (7).
Furthermore, we report on the synthesis of the alkyl-
substituted germanium(II) compounds MamxGe-t-Bu
(8), MamxGe-n-Bu (9), and MamxGeMe (10) and their
derivatization with MeI under formation of the ionic
compounds [MamxGe(t-Bu)(Me)]+I- (11), [MamxGe(n-
Bu)(Me)]+I- (12), and [MamxGe(Me)2]+I- (13).
The synthesis of stable germylenessthe germanium
analogues of the carbenesshas attracted much attention
over the last 20 years.1 Germylenes having small
substituents are unstable toward oligomerization. They
can be stabilized kinetically by the use of bulky ligands
and/or thermodynamically by donor substituents, which
reduce the electron deficiency at the germanium(II)
center. Up to now a rather large number of germanium-
(II) compounds has been isolated using these concepts.2,3
The 2,4-di-tert-butyl-6-((dimethylamino)methyl)phen-
yl ligand, abbreviated Mamx (Mamx ) m ethyla mino-
m ethyl-m-xylyl), was introduced by Yoshifuji and co-
(1) See for example: (a) Rivie`re, P.; Rivie`re-Baudet, M.; Satge´, J .
In Comprehensive Organometalic Chemistry; Pergamon: Oxford, U.K.,
1982; Vol. 2, Chapter 10. (b) Neumann, W. P. Chem. Rev. 1991, 91,
311. (c) Barrau, J .; Rima, G. Coord. Chem. Rev. 1998, 178, 593.
(2) (a) Davidson, P. J .; Harris, D. H.; Lappert, M. F. J . Chem. Soc.,
Dalton Trans. 1976, 2268. (b) J utzi, P.; Becker, A.; Stammler, H. G.;
Neumann, B. Organometallics 1991, 10, 1647. (c) J utzi, P.; Leue, C.
Organometallics 1994, 13, 2898. (d) Lange, L; Meyer, B.; du Mont, W.-
W. J . Organomet. Chem. 1987, 329, C17. (e) J uti, P.; Schmidt, H.;
Neumann, B.; Stammler, H.-G. Organometallics 1996, 15, 741. (f)
Tokitoh, N.; Manmaru, K.; Okazaki, R. Organometallics 1994, 13, 167.
(g) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics
1997, 16, 1920. (h) Pu, L.; Olmstead, M. M.; Power, P. P. Organome-
tallics 1998, 17, 5602.
(3) (a) Scibelli, J . V.; Curtis, M. D. J . Am. Chem. Soc. 1973, 95, 924.
(b) J utzi, P.; Kohl, F.; Hofmann, P.; Kru¨ger, C. Tsay, Y.-H. Chem. Ber.
1980, 113, 757. (c) Karsch, H. H. Russ. Chem. Bull. (Engl. Transl.)
1993, 42, 1937 and references cited therein. (d) J utzi, P. Schmidt, H.;
Neumann, B.; Stammler, H.-G. J . Organomet. Chem. 1995, 499, 7. (e)
Dias, H. V. R.; Wang, Z. J . Am. Chem. Soc. 1997, 119, 4650. (f) Foley,
S. R.; Bensimon, C.; Richeson, D. S. J . Am. Chem. Soc. 1997, 119,
10359. (g) Ossig, G.; Meller, A.; Bro¨nneke, C.; Mu¨ller, O.; Scha¨fer, M.;
Herbst-Irmer, R. Organometallics 1997, 16, 2116. (h) Leung, W.-P.;
Kwok, W.-H.; Weng, L.-H.; Law, L. T. C.; Zhou, Z. Y.; Mak, T. C. W. J .
Chem. Soc., Dalton Trans. 1997, 4301. (i) Drohst, C.; Hitchcock, P. B.;
Lappert, M. F.; Pierssens, L. J .-M. J . Chem. Soc., Chem. Commun.
1997, 1141. (j) Karsch, H. H.; Schlu¨ter, P. A.; Reisky, M. Eur. J . Inorg.
Chem. 1998, 433. (k) Benet, S.; Cardin, C. J .; Cardin, D. J .; Constan-
tine, S. P., Heath, P.; Rashid, H.; Teixeira, S.; Thorpe, J . H.; Todd, A.
K. Organometallics 1999, 18, 389.
Resu lts a n d Discu ssion
1. Ger m an iu m (II) Com pou n ds with Sm all Alkoxy
Su bstitu en ts (Ma m xGeOR). Stabilization of alkoxy-
(4) Yoshifuji, M.; Kamijo, K.; Toyota, K. Tetrahedron Lett. 1994, 35,
3971.
(5) (a) Corriu, P.; Lanneau, G.; Priou, C.; Soulairol, F.; Auner, N.;
Probst, R.; Conlin, R.; Tan, C. J . Organomet. Chem. 1994, 466, 55. (b)
Belzner, J .; Scha¨r, D.; Kneisel, B. O.; Herbst-Irmer, R. Organometallics
1995, 14, 1840.
(6) Schmidt, H.; Keitemeyer, S.; Neumann, B.; Stammler, H.-G.;
Schoeller, W. W.; J utzi, P. Organometallics 1998, 17, 2149.
10.1021/om990557r CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/22/1999

Novel Heteroleptic Germanium(II) Compounds
Organometallics, Vol. 18, No. 23, 1999 4779
Sch em e 1
and aryloxygermylenes in a monomeric form has proved
to be difficult, because the formation of dimers or
polymers is favored.7 Therefore, only a few monomeric
alkoxy- and aryloxygermylenes have been reported in
the literature,8 and even fewer have been completely
characterized. The first structurally characterized mono-
meric diaryloxygermylene, Ge{O(2,6-(t-Bu)2-4-Me-
C6H2}2,9 and dialkoxygermylene, Ge{OC(t-Bu)3}2, were
reported by Lappert et al.10 The synthesis of intramo-
lecularly base stabilized aryloxygermylenes has been
reported by Barrau et al. only recently.1c,11
F igu r e 1. Molecular structure of 3.
Treatment of MamxGeCl (1) with an excess of the
respective potassium alkoxide (1:4) in the presence of
15-crown-5 in toluene at ambient temperature led to the
formation of the germanium(II) compounds MamxGeO-
t-Bu (2), MamxGeO-i-Pr (3), MamxGeOEt (4), and
MamxGeOMe (5) (Scheme 1).
After removal of the solvent and of the crown ether
by distillation, the remaining compounds 2-5 were
purified by sublimation in vacuo. They could be isolated
in good yields as colorless powders, which are soluble
in common organic aprotic solvents. In the absence of
15-crown-5, no reaction was observed. The high thermal
stability of 2-5 is noteworthy. For example, the poten-
tially most unstable germanium(II) compound 5 can be
treated either in solution or as a solid at 80-100 °C for
hours without decomposition.
Crystals suitable for an X-ray structure analysis of 3
and 4 were obtained from a n-hexane solution. The
molecular structures of 3 and 4 are shown in Figures 1
and 2. Crystallographic data are given in Table 1;
selected bond lengths and angles are presented in
Table 2.
In the structures of 3 and 4, the germanium atom is
three-coordinate, forming one σ-bond to each substituent
and an additional NfGe donor bond. The Ge-Caryl bond
length is 2.039(3) Å for 3 and 2.037(4) Å for 4; typical
GeII-Cσ bond distances vary between 1.98 and 2.14 Å.12
The Ge-O bond length is 1.856(2) Å in 3 and 1.844(3)
Å in 4; these values are in the same range as those
observed in Ge[OC(t-Bu)3]2 (1.896(6) and 1.832(11) Å)10
or in the aryloxygermylene Ge[O(2,6-(t-Bu)2-4-Me-
(C6H2)]2 (1.802(8) and 1.812(7) Å).9 The Ge-N bond
length is 2.149(2) Å for 3 and 2.123(3) Å for 4, which is
slightly elongated in comparison to that for 1 (2.093(6)
F igu r e 2. Molecular structure of 4.
Å)6 but shortened compared to the distances found for
other base-stabilized germylenes such as Cp∧GeCl (2.29
Å)3d and Ge[2-{(Me3Si)2C}-C5H4N)]2 (2.27 Å).3h In 3 and
4, the geometry at the germanium atom is worth
mentioning. In both compounds the bond angles at the
metal center are in the same range: The angle R (Caryl
Ge-N) is 81.3° in 3 and 82.4° in 4; the angles â (Caryl
-
-
Ge-OR) and γ (RO-Ge-N) are nearly rectangular (â
= 93°, γ = 92°). The degree of hybridization of the
germanium atom can be inferred from these data; hence,
it follows that the germanium atom in 3 and 4 is almost
not hybridized. The lone pair occupies an orbital with
high s character, and the σ-bonds to the ligands are
formed by using p orbitals at the germanium center.
The nitrogen atom of the coordinating amino side chain
is oriented nearly perpendicular to the Caryl-Ge-O-
plane, allowing ideal interaction with the vacant Ge(p)
orbital.
The solution NMR data of 3 and 4 are in accord with
the solid-state structures. The benzylic as well as the
methyl protons of the (dimethylamino)methyl side chain
are diastereotopic due to the chirality of the germanium
center (Chart 1); thus, the 1H NMR spectra show
doublets for the methylene protons and two singlets for
the N(CH3)2 groups. A permanent coordination of the
amino group is observed even at high temperatures,
indicating a very strong NfGe interaction.
2. Ger m an iu m (II) Com pou n ds with Eth yn yl Su b-
stitu en ts (Ma m xGeCtCR). Species with ethynyl sub-
stituents constitute a novel class of heteroleptic germa-
nium compounds. In silicon chemistry, various ethynylsi-
(7) (a) Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Smith, S. J .;
Thorne, A. J . J . Chem. Soc., Chem. Commun. 1983, 1438. (b) Veith,
M. To¨llner, F. J . Organomet. Chem. 1983, 246, 219. (c) Veith, M.;
Hobein, P.; Ro¨sler, R. Z. Naturforsch. 1989, 44B, 1067.
(8) (a) Meller, A.; Gra¨be, C.-P. Chem. Ber. 1985, 118, 2020. (b)
Roesky, H.W.; Scholz, M.; Noltemeyer, M. Chem. Ber. 1990, 123, 2303.
(9) Cetinkaya, B.; Gu¨mru¨kcu¨, I.; Lappert, M. F.; Atwood, J . L.;
Rogers, R. D.; Zaworotko, M. J . J . Am. Chem. Soc. 1980, 102, 2088.
(10) Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Smith, S. J .;
Thorne, A. J . J . Chem. Soc., Chem. Commun. 1985, 939.
(11) (a) Barrau, J .; Rima, G.; El Amraoui, T. Inorg. Chim. Acta 1996,
241, 9. (b) Barrau, J .; Rima, G.; El Amraoui, T. J . Organomet. Chem.
1998, 561, 167. (c) Barrau, J .; Rima, G.; El Amraoui, T. J . Organomet.
Chem. 1998, 570, 163.
(12) J utzi, P.; Becker, A.; Leue, C.; Stammler, H.-G.; Neumann, B.
Organometallics 1991, 10, 3838.

4780 Organometallics, Vol. 18, No. 23, 1999
Ta ble 1. Cr ysta llogr a p h ic Da ta for 3, 4, 6, 7, a n d 11
J utzi et al.
3
4
6
7
11
empirical formula
fw
C
20H35GeNO
C19H33GeNO
364.05
C25H33GeN
420.11
C19H29GeN
344.02
C26H48NOI
590.14
378.08
cryst color, habit
cryst size, mm3
temp, K
colorless, plates
0.7 × 0.5 × 0.15
colorless, plates
0.80 × 0.40 × 0.20
colorless, needles
0.8 × 0.3 × 0.1
173(2)
colorless, rhombic
0.4 × 0.4 × 0.1
colorless, plates
0.4 × 0.3 × 0.02
radiation (λ, Å)
space group
unit cell dimens
a, Å
b, Å
c, Å
Mo KR (0.71073 Å), graphite monochromator
P21/c
P21/c
P21/c
P21/c
P21/c
11.237(3)
15.818(4)
11.864(3)
90
99.49(2)
90
17.215(5)
9.551(2)
12.006(3)
90
15.248(8)
13.836(7)
11.133(7)
90
9.820(2)
15.818(3)
12.165(3)
90
16.230(3)
12.357(2)
14.941(3)
90
105.12(2)
90
R, deg
â, deg
91.01(2)
90
99.60(5)
90
102.63(2)
90
γ, deg
V, Å3
2079.9(9)
4
1973.7(9)
4
2516(2)
4
1843.9(7)
4
2892.7(9)
4
Z
density (calcd),
1.207
1.225
1.205
1.239
1.355
Mg/m3
θ range for data
collecn, deg
no. of rflns collected
no. of indep rflns
1.84-27.49
2.37-27.50
2.37-27.03
2.13-27.06
2.10-28.5
5017
4759
5314
4279
7615
7339 (Rint
0.0531)
4781 (Rint
0.0323)
)
4535 (Rint
0.0333)
none
)
5047 (Rint
0.0425)
)
4047 (Rint
0.0745)
)
)
abs cor
empirical
empirical
empirical
empirical
final R indices (I > 2σ(I))
RF
0.0451
0.0918
3408
0.0548
0.1216
3048
0.0595
0.1152
3342
0.0652
0.1231
2429
0.0666
0.1440
4507
2
RF
no. of rflns used
for R indices
no. of params
largest diff peak
and hole, e/Å3
diffractometer used
programs used
structure
218
0.418, -0.423
221
0.965, -0.891
252
0.884, -0.709
198
0.796, -0.659
271
0.915, -1.185
Siemens R3m/V
Siemens P2(1)
Siemens P2(1)
Siemens P2(1)
Siemens P2(1)
Siemens SHELXTL plus SHELXL-97
full-matrix least squares on F2
refinement
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3 a n d 4
3
4
Ge(1)-O(1)
Ge(1)-C(1)
Ge(1)-N(1)
1.856(2)
2.039(3)
2.149(2)
1.844(3)
2.037(4)
2.123(3)
O(1)-Ge(1)-C(1)
O(1)-Ge(1)-N(1)
C(1)-Ge(1)-N(1)
92.94(10)
91.32(9)
81.26(10)
92.56(13)
91.62(13)
82.26(13)
Ch a r t 1
F igu r e 3. Molecular structure of 6.
Sch em e 2
lylenes have been prepared in matrixes,13 but compa-
rable germanium compounds are unknown.
Reaction of 1 with Li(CtCPh) in THF at -60 °C
furnished the heteroleptic germanium(II) compound
MamxGe(CtCPh) (6), whereas the ethynyl-substituted
species MamxGe(CtCH) (7) was synthesized by stirring
a suspension of 1 and Na(CtCH) in THF at ambient
temperature for 3 days (Scheme 2).
Crystals suitable for an X-ray structure analysis were
obtained from a toluene solution. The molecular struc-
tures of 6 and 7 are depicted in Figures 3 and 4. Crystal
structure parameters are given in Table 1, and selected
bond lengths and angles are collected in Table 3.
In compounds 6 and 7 the structural features at the
germanium center are quite similar to those found for
3 and 4; again, the Mamx ligand is coordinated in a
bidentate fashion. The Caryl-Ge-Cethynyl and the
Caryl/ethynyl-Ge-N angles are nearly rectangular (Table
3). The Ge-Caryl bond length is 2.035(4) Å for 6 and
2.026(5) Å for 7. The Ge-N bond distances are almost
identical and are again elongated in comparison to 1
(2.126(4) Å (6) and 2.124(4) Å (7)). The Ge-Cethynyl bond
(13) Apeloig, Y.; Karni, M.; West, R.; Welsh, K. J . Am. Chem. Soc.
1994, 116, 9719.

Novel Heteroleptic Germanium(II) Compounds
Organometallics, Vol. 18, No. 23, 1999 4781
Sch em e 3
Sch em e 4
F igu r e 4. Molecular structure of 7.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 6 a n d 7
6
7
Ge(1)-Cethynyl
Ge(1)-C(1)
2.001(4)
2.035(4)
2.126(2)
1.209(6)
1.989(6)
2.026(5)
2.124(4)
1.191(8)
Ge(1)-N(1)
Cethynyl-Cethynyl
Cethynyl-Ge(1)-C(1)
Cethynyl-Ge(1)-N(1)
C(1)-Ge(1)-N(1)
97.90(16)
91.97(16)
82.70(15)
165.6(4)
95.4(2)
92.9(2)
82.04(18)
171.1(5)
Cethynyl-Cethynyl-Ge(1)
length is 2.001(4) Å for 6 and 1.989(6) Å for 7. The CC
triple-bond distance is 1.209(6) Å in 6 and 1.191(8) Å
in 7. The C-C bond length in acetylene is 1.204 Å,1414
which is slightly elongated compared to that in 6 and
shortened in comparison with that in 7. The Ge-C-C
angle is 165.6(4)° in 6 and 171.1(5)° in 7, respectively.
The structures of 6 and 7 found in the solid state are
also present in solution; the permanent coordination of
the amino group to the germanium(II) center is observed
even at high temperatures (80 °C). Thus, again doublets
for the methylene protons and two singlets for the
dimethylamino protons are detected in the 1H NMR
spectra of 6 and 7. In the 13C NMR spectra the signals
for the acetylenic carbon atoms are observed at 109.6
and 111.2 ppm for 6 and 97.8 and 103.6 ppm for 7,
respectively; this means a low-field shift of approxi-
mately 30 ppm in comparison with phenylacetylene
(78.6, 84.6 ppm) and acetylene (71.9 ppm).15
decomposition is observed in solution at 80 °C. The NMR
data of 8-10 are in accordance with those of all other
germanium(II) compounds containing the Mamx ligand;
a permanent coordination of the amino side chain is
observed. Compounds 8-10 were characterized by
standard CI-MS techniques; the molecular ions were
observed, and no dimeric or other oligomeric species
were found.
Keeping in mind the fact that reaction of MeI with
diarylgermanium(II) compounds MamxGeAr (Ar )
Mamx, 2,4,6-(C3H7)3-C6H2) afforded ionic species con-
taining germyl cations,6 alkylation of 8-10 should
also be possible. Reaction of 8-10 with 1 equiv of MeI
in n-hexane led to the colorless compounds 11-13,
which contain the germyl cations [MamxGe(t-Bu)(Me)]+
(11a ), [MamxGe(n-Bu)(Me)]+ (12a ), and [MamxGe-
(Me)2]+ (13a ), respectively, and the counteranion I-
(Scheme 4).
3. Ger m a n iu m (II) Com p ou n d s w ith Alk yl Su b-
stitu en ts (Ma m xGeR) a n d Ger m yl Ca tion s. Up to
now several kinetically substituted stable dialkylger-
mylenes and arylalkylgermylenes have been reported
in the literature.1-3 The Mamx ligand is able to stabilize
germanium(II) species containing nonbulky alkyl ligands,
as demonstrated by the synthesis of MamxGe-t-Bu (8),
MamxGe-n-Bu (9), and MamxGeMe (10). Compounds
8-10 were obtained by reaction of 1 with 1 equiv of the
corresponding alkyllithium reagent in n-hexane at -60
°C. After filtration and removal of all volatiles in vacuo,
8-10 were isolated as yellow solids (8, 9) and as a yellow
viscous oil (10), respectively (Scheme 3).16
Crystals of 11, suitable for an X-ray structure analy-
sis, were obtained from THF solution. The molecular
structure of 11a is shown in Figure 5. Crystallographic
data for 11 are given in Table 1, and selected bond
lengths and angles are collected in Table 4.
In compound 11, the closest Ge-I distance is 4.887
Å, which excludes any bonding interactions. In 11a , the
germanium atom is surrounded by the three carbon
atoms (Caryl, Ct-Bu, CMe) in a nearly perfect trigonal-
planar fashion; the angle sum is 351.5°. The Ge-C bond
lengths do not vary significantly. The Ge-CMe bond
length (1.938(6) Å) is in accordance with the distances
Compounds 8-10 are stable at room temperature in
n-hexane solution and in the solid state, but slow
(15) Hesse, M.; Meier, H.; Zeeh, B. Spectroscopic Methods in Organic
Chemistry; Thieme Verlag: Stuttgart, Germany, 1984.
(16) Purification of the alkylgermylenes by crystallization, sublima-
tion, or distillation was not successful; therefore, no elemental analyses
could be performed.
(14) CRC Handbook of Chemistry and Physics, 60th ed.; CRC
Press: Boca Raton, FL, 1979.

4782 Organometallics, Vol. 18, No. 23, 1999
J utzi et al.
nium(II) center; due to the strong NfGe bond, alkyla-
tion takes place at the germanium and not at the
nitrogen atom. (iii) By coordination of the amino side
chain a five-membered ring (GeNC3) with low ring
strain is formed. The Caryl-Ge-N angle in all com-
pounds is almost rectangular (=83°). For this reason
nearly ideal interaction between the nitrogen atom and
the vacant Ge(p) orbital is observed.
A characteristic feature of a germylene (singlet ground
state) is the presence of an electron lone pair and of a
vacant p orbital at the germanium center. In the
compounds mentioned above the p(Ge) orbital is not
vacant and, as shown, interaction takes place between
the nitrogen and the germanium atom. Therefore, we
wish to describe the species presented in this work and
in general germanium compounds containing the Mamx
ligand not as germylenes, but as monomeric germa-
nium(II) compounds.
F igu r e 5. Molecular structure of 11a .
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 11
Ge(1)-C(22)
Ge(1)-C(1)
Ge(1)-C(18)
1.938(6)
1.962(6)
1.983(7)
Ge(1)-N(1)
Ge(1)-I(1)
2.014(6)
4.887
Exp er im en ta l Section
Gen er a l Da ta . All manipulations were carried out under
a purified argon atmosphere using standard vacuum tech-
niques. The solvents were commercially available, purified by
conventional means, and distilled immediately prior to use.
15-Crown-5, t-BuLi (1.6 M solution in pentane), n-BuLi (1.6
M solution in hexane), MeLi (1.6 M solution in Et2O), MeI,
phenylacetylene, and potassium acetylide were commercially
available. MamxGeCl,6 NaO-t-Bu, NaO-i-Pr, NaOEt, and
NaOMe were prepared according to the literature. Elemental
analyses were performed by the Microanalytical Laboratory
of Universita¨t Bielefeld. The NMR spectra were recorded using
a Bruker Avance DRX 500 spectrometer (1H, 500.1 MHz; 13C-
{1H}, 125.8 MHz). Chemical shifts are reported in ppm and
are referenced to the solvent as an internal standard. Mass
spectrometry was performed using a VG Autospec spectro-
meter. Only characteristic fragments and isotopes of the
highest abundance are listed.
C(22)-Ge(1)-C(1)
126.3(3) C(22)-Ge(1)-N(1) 102.8(3)
86.9(2)
113.4(3) C(18)-Ge(1)-N(1) 110.7(3)
C(22)-Ge(1)-C(18) 111.8(3) C(1)-Ge(1)-N(1)
C(1)-Ge(1)-C(18)
found for germyl cations presented in our previous
work.6 The CarylCt-BuCMe plane and the Ge-N bond
vector form an angle of 75.7°; the Ge-N bond length is
shortened compared to that of other germylenes with
the Mamx ligand.
The 1H NMR spectra of 11-13 demonstrate the large
effect the alkylation has on the germanium center.
Thus, the spectra show an enormous low-field shift of
up to 2 ppm of the NCH3 as well as of the CH2 protons
in comparison with 8 and 9; hence, it follows that the
NfGe interaction is strengthened in the germyl cations.
In 13 the germanium center is no longer chiral, and as
a result the methyl and methylene protons of the amino
side chain are not diastereotopic, as indicated by one
singlet for the NCH3 and one singlet for the CH2
protons.
Gen er a l P r oced u r e for th e P r ep a r a tion of th e Alk oxy-
ger m a n iu m (II) Com p ou n d s 2-5. The sodium alkoxide (16
mmol) NaOR (2, R ) t-Bu; 3, R ) i-Pr; 4, R ) Et; 5, R ) Me)
was added to a solution of 3.95 mmol (1.40 g) of 1 and 3.95
mmol of 15-crown-5 (0.87 g, 0.78 mL) in toluene (25 mL) at
ambient temperature. The reaction mixture was stirred for 24
h at that temperature. After filtration and removal of the
solvent and of the crown ether by distillation (93 °C, 0.05
mbar), the germanium(II) species 2-5 were purified by
sublimation in vacuo.
Con clu sion s
It has been demonstrated that the chloro species
MamxGeCl (1) is a useful precursor for novel hetero-
leptic germanium(II) compounds. Starting from 1, we
have prepared and structurally characterized several
alkoxy-substituted germanium(II) compounds (2-5) as
well as the ethynyl species 6 and 7. Additionally we
synthesized the alkyl-substituted species MamxGeR (R
) t-Bu (8), n-Bu (9), Me (10)). The nucleophilic character
of the germanium center has been pointed out by
reaction of 8-10 with MeI leading to ionic compounds
containing germyl cations. All these compounds show
a high stability, which can be referred to the unique
characteristics of the Mamx ligand. (i) Due to the fact
that the tert-butyl group in the ortho position of the Caryl
atom shields the germanium atom, nucleophilic attack
on the metal center is rendered to be more difficult;
therefore, further nucleophilic substitution at these
germanium(II) species only takes place with strong
nucleophiles. (ii) A permanent coordination of the amino
side chain is observed even at high temperatures. This
leads to a thermodynamic stabilization of the germa-
Ma m xGeO-t-Bu (2): Yield: 1.05 g (2.67 mmol, 68%). 1H
NMR (C6D6): δ 1.32, 1.50, 1.68 (3s, 9H, t-Bu), 1.85, 2.15 (2s,
2
3H, N(CH3)2), 2.96, 4.28 (2d, 1H, -CH2-, J ) 13 Hz), 6.95,
7.49 (2s, 1H, aryl H). 13C NMR (C6D6): δ 31.7, 34.0 (C(CH3)3),
34.7 (C(CH3)3), 35.0 (OC(CH3)3), 38.1 (C(CH3)3), 43.6, 45.2
(N(CH3)2), 66.6 (OC(CH3)3), 67.2 (-CH2-), 118.5, 121.0 (ter-
tiary aryl C), 144.4, 149.5, 150.7, 157.0 (quaternary aryl-C).
MS (CI; m/z (Irel)): 393 (100, M+), 320 (15, MamxGe+). Anal.
Calcd for C21H37GeNO (Mr ) 392.17): C, 64.31; H, 9.50; N,
3.57. Found: C, 64.10; H, 9.30; N, 3.59.
Ma m xGeO-i-P r (3). Recrystallization of the sublimate from
n-hexane yielded 0.97 g (2.56 mmol, 65%) of 3 as colorless
1
crystals. H NMR (C6D6): δ 1.34 (s, 9H, t-Bu), 1.36, 1.41 (2d,
3
3H, OCH(CH3)2, J ) 6 Hz), 1.66 (s, 9H, t-Bu), 1.82, 2.17 (2s,
3H, N(CH3)2), 2.92, 4.32 (2d, 1H, -CH2-, 2J ) 13 Hz), 4.41
(pseudo-septet), 1H, OCH(CH3)2), 6.95, 7.49 (2s, 1H, aryl H).
13C NMR (C6D6): δ 27.6, 27.9 (OCH(CH3)2), 31.7, 33.8 (C(CH3)3),
34.8, 37.9 (C(CH3)3), 43.4, 44.6 (N(CH3)2), 67.3 (-CH2-), 68.0
(OCH(CH3)2), 118.4, 120.9 (tertiary aryl C), 144.8, 150.0, 156.5,
156.9 (quaternary aryl C). MS (CI; m/z (Irel)): 379 (48, M+),
364 (23, M+ - CH3), 320 (87, MamxGe+). Anal. Calcd for

Novel Heteroleptic Germanium(II) Compounds
Organometallics, Vol. 18, No. 23, 1999 4783
C20H35GeNO (Mr ) 378.14): C, 63.52; H, 9.32; N, 3.70.
Found: C, 63.30; H, 9.18; N, 3.41.
Ma m xGe-t-Bu (8). Reaction of 1 (0.39 g, 1.10 mmol) in
n-hexane (20 mL) with t-BuLi (1.7 M solution in pentane, 0.65
mL, 1.10 mmol) at -60 °C afforded 6 as a yellow solid. 1H NMR
(C6D6): δ 1.21, 1.35, 1.62 (3s, 9H, t-Bu), 2.00, 2.05 (2s, 3H,
Ma m xGeOEt (4). Recrystallization of the sublimate from
n-hexane yielded 0.96 g (2.63 mmol, 67%) of 4 as colorless
crystals. 1H NMR (C6D6): δ 1.35 (s, 9H, t-Bu), 1.41 (t, 3H,
CH2CH3, 3J ) 7 Hz), 1.67 (s, 9H, t-Bu), 1.81, 2.14 (2s, 3H,
N(CH3)2), 2.92 (d, 1H, -CH2-, 2J ) 13 Hz), 4.17 (m, 2H, CH2-
CH3), 4.30 (d, 1H, -CH2-, 2J ) 13 Hz), 6.97, 7.51 (2s, 1H,
aryl H). 13C NMR (C6D6): δ 20.9 (OCH2CH3), 31.7, 33.7
(C(CH3)3), 34.8, 38.0 (C(CH3)3), 43.5, 44.7 (N(CH3)2), 62.9
(OCH2CH3), 67.5 (-CH2-), 118.3, 123.6 (tertiary aryl C), 144.9,
149.9, 156.3, 157.0 (quaternary aryl C). MS (CI; m/z (Irel)): 365
(60, M+), 350 (12, M+ - CH3), 320 (64, MamxGe+). Anal. Calcd
for C19H33GeNO (Mr) 364.12): C, 62.67; H, 9.13; N, 3.84.
Found: C, 62.40; H, 9.39; N, 3.83.
2
N(CH3)2), 2.95, 4.13 (2d, 1H, -CH2-, J ) 14 Hz), 6.99, 7.55
(2s, 1H, aryl H). 13C NMR (C6D6): δ 31.7, 31.8, 34.5 (C(CH3)3),
33.1, 34.6, 38.1 (C(CH3)3), 45.5, 49.2 (N(CH3)2), 69.4 (-CH2-),
117.8, 122.1 (tertiary aryl C), 143.5, 148.5, 157.0, 157.6
(quaternary aryl C). MS (CI; m/z (Irel)): 378 (87, M+ + H), 320
(100, MamxGe+).
Ma m xGe-n -Bu (9). Reaction of 1 (0.69 g, 1.96 mmol) in
n-hexane (30 mL) with n-BuLi (1.6 M solution in hexane, 1.23
mL, 1.96 mmol) at -60 °C afforded 7 as a yellow solid. 1H NMR
3
(C6D6): δ 1.03 (t, 3H, n-Bu CH3, J ) 7 Hz), 1.07-1.61 (broad
m, 6H, -(CH2)3-), 1.37, 1.59 (2s, 9H, t-Bu), 1.95, 2.01 (2s, 3H,
2
Ma m xGeOMe (5). Yield: 0.73 g (2.08 mmol, 53%). 1H NMR
(C6D6): δ 1.35, 1.65 (2s, 9H, t-Bu), 1.81, 2.13 (2s, 3H, N(CH3)2),
N(CH3)2), 2.95, 3.96 (2d, 1H, -CH2-, J ) 14 Hz), 6.99, 7.52
(2s, 1H, aryl H). 13C NMR (C6D6): δ 14.36 (-CH3), 26.1, 27.4,
31.4 (-(CH2)3-), 31.4, 33.2 (C(CH3)3), 34.7, 37.9 (C(CH3)3), 44.4,
48.1 (N(CH3)2), 68.5 (-CH2-), 117.8, 121.0 (tertiary aryl C),
142.2, 148.5, 156.3, 158.9 (quaternary aryl C). MS (CI; m/z
(Irel)): 377 (95, M+), 335 (18, M+ - CH3), 320 (100, MamxGe+).
Ma m xGeMe (10). Reaction of 1 (0.32 g, 0.91 mmol) in
n-hexane (30 mL) with MeLi (1.6 M in diethyl ether, 0.57 mL,
0.91 mmol) at -60 °C afforded 8 as a yellow oil. 1H NMR
(C6D6): δ 0.68 (s, 3H, GeCH3), 1.38, 1.60 (2s, 9H, t-Bu), 1.89,
1.98 (2s, 3H, N(CH3)2), 2.97, 3.95 (2d, 1H, -CH2-, 2J ) 14
Hz), 7.00, 7.52 (2s, 1H, aryl-H). 13C NMR (C6D6): δ 9.4 (-CH3),
31.4, 33.2 (C(CH3)3), 34.6, 38.2 (C(CH3)3), 44.1, 45.5 (N(CH3)2),
65.4 (-CH2-), 120.9, 123.9 (tertiary aryl C), 136.5, 144.3,
150.7, 158.7. MS (CI; m/z (Irel)): 335 (100, M+), 320 (52,
MamxGe+).
2
2.95 (d, 1H, -CH2-, J ) 13 Hz), 3.95 (s, 3H, OCH3), 4.27 (d,
1H, -CH2-, 2J ) 13 Hz), 6.97, 7.50 (2s, 1H, aryl H). 13C NMR
(C6D6): δ 31.7, 33.6 (C(CH3)3), 34.8, 37.9 (C(CH3)3), 43.5, 44.6
(N(CH3)2), 55.4 (OCH3), 67.6 (-CH2-), 118.2, 120.9 (tertiary
aryl C), 144.9, 150.1, 156.1, 157.1 (quaternaryaryl-C). MS (CI;
m/z (Irel)): 351 (80, M+), 336 (22, MamxGeO+), 320 (100,
MamxGe+). Anal. Calcd for C18H31GeNO (Mr ) 350.09): C,
61.75; H, 8.92; N, 4.00. Found: C, 61.31; H, 9.14; N, 3.92.
P r ep a r a tion of Ma m xGe(CtCP h ) (6). Within 3 min 1.25
mL of a 1.6 M solution of n-BuLi in n-hexane was added to a
stirred solution of phenylacetylene (0.20 g, 2.00 mmol) in THF
(10 mL) at -60 °C. After the mixture was warmed to room
temperature within 3 h, it was added to a solution of 1 (0.71
g, 2.00 mmol) in THF (15 mL) at -60 °C. The reaction mixture
turned immediately yellow, and the solution was warmed to
room temperature. The solvent was removed in vacuo, and the
residue was extracted with toluene. Cooling the liquid yielded
0.64 g (76%) of 6 as colorless crystals.1H NMR (C6D6): δ 1.35,
1.66 (2s, 9H, t-Bu), 1.83, 2.40 (2s, 3H, N(CH3)2), 3.05, 4.52 (2d,
1H, -CH2-, 2J ) 13 Hz), 6.92 (m, 3H, m,p-Ph), 7.01 (s, 1H,
Gen er a l P r oced u r e for th e P r ep a r a tion of th e Ion ic
Com p ou n d s 11-13. One equivalent of MeI was added to a
freshly prepared solution of the alkylgermanium(II) species
(8-10) in n-hexane at -50 °C. The reaction mixture was
warmed to room temperature, giving a colorless suspension.
Evaporation of the solvent and recrystallization of the residue
from THF yielded the ionic compounds 11-13 as colorless
crystals.
3
aryl H Mamx), 7.41 (d, 2H, o-Ph, J ) 7 Hz), 7.54 (s, 1H, aryl
H Mamx). 13C NMR (THF-d8): δ 31.9, 33.0 (C(CH3)3), 35.2,
37.9 (C(CH3)3), 46.1, 46.8 (N(CH3)2), 70.6 (-CH2-), 109.6, 111.2
(-CCPh), 118.8, 121.4 (tertiary aryl C, Mamx), 126.6, 127.4,
128.6, 131.8 (aryl C, Ph) 144.4, 149.8, 154.2, 156.5 (quaternary
aryl C, Mamx). MS (CI; m/z (Irel)): 422 (8, M+ + H), 320 (16,
MamxGe+). Anal. Calcd for C25H33GeN (Mr ) 420.18): C,
71.46; H, 7.92; N, 3.33. Found: C, 70.26; H, 7.78; N, 3.18.
P r ep a r a tion of Ma m xGe(CtCH) (8). To a suspension of
sodium acetylide (0.11 g, 2.29 mmol, purified by washing three
times with pentane) in THF (30 mL) was added a solution of
1 (0.81 g, 2.29 mmol) in THF (15 mL) at ambient temperature
within 5 min. The reaction mixture was stirred at that
temperature for 3 days. The solvent was removed in vacuo,
and the residue was dissolved in toluene. Cooling the solution
to -30 °C after filtration and concentration yielded 0.47 g
[Ma m xGe(t-Bu )(Me)]+I- (11). Reaction of 8 (0.86 mmol)
in n-hexane (15 mL) with MeI (0.12 g, 0.05 mL, 0.86 mmol)
1
yielded 0.25 g (57%) of colorless crystals. H NMR (THF-d8):
δ 1.29, 1.34, 1.39 (3s, 9H, t-Bu), 1.50 (s, 3H, Ge-CH3), 3.18,
3.69 (2s, 3H, N(CH3)2), 4.67, 5.27 (2d, 1H, -CH2-, 2J ) 16
Hz), 7.42, 7.64 (2s, 1H, aryl H). 13C NMR (THF-d8): δ 1.8 (Ge-
CH3), 28.4, 31.4 (C(CH3)3), 32.2 (C(CH3)3), 33.0 (C(CH3)3), 35.6,
37.4 (C(CH3)3), 48.9, 49.1 (N(CH3)2), 67.6 (-CH2-), 121.9, 124.4
(tertiary aryl C), 126.2, 142.8, 154.9, 158.0 (quaternary aryl
C). MS (CI, M+ ) MamxGe(t-Bu)(Me)+; m/z (Irel)): 392 (5, M+),
378 (100, M+ + H - CH3), 320 (71, MamxGe+). Anal. Calcd
for C22H40GeNI (Mr ) 518.06): C, 51.00; H, 7.78; N, 2.70.
Found: C, 50.80; H, 7.99; N, 2.59.
[Ma m xGe(n -Bu )(Me)]+I- (12). Reaction of 9 (1.18 mmol)
in n-hexane (20 mL) with MeI (0.17 g, 0.07 mL, 1.18 mmol)
1
(60%) of 8 as colorless crystals. H NMR (C6D6): δ 1.34, 1.62
1
(2s, 9H, t-Bu), 1.77, 2.33 (2s, 3H, N(CH3)2), 2.64 (s, 1H, -CCH),
2.99, 4.47 (2d, 1H, -CH2-, 2J ) 13 Hz), 6.98, 7.51 (2s, 1H,
aryl H).13C NMR (C6D6): δ 31.7, 32.9 (C(CH3)3), 34.7, 37.6
(C(CH3)3), 45.4, 46.0 (N(CH3)2), 69.7 (-CH2-), 97.8 (-CCH),
103.6 (-CCH), 118.2, 121.3 (tertiary aryl C), 143.5, 149.5,
153.6, 156.6 (quaternary aryl C). MS (CI; m/z (Irel)): 346 (100,
M+ + H), 320 (38, MamxGe+). Anal. Calcd for C19H29GeN (Mr
) 344.09): C, 66.32; H, 8.49; N, 4.07. Found: C, 66.02; H, 8.85;
N, 3.80.
Gen er a l P r oced u r e for th e P r ep a r a tion of th e Alk yl-
ger m a n iu m (II) Com p ou n d s 8-10. A solution of an equimo-
lar amount of the alkyllithium reagent (t-BuLi (8), n-BuLi (9),
MeLi (10)) was added slowly to a suspension of 1 in n-hexane
at -60 °C. The mixture was stirred at that temperature for 4
h and then warmed to room temperature. After the mixture
was stirred for another 12 h at that temperature, the LiCl was
filtered off and the solvent was removed in vacuo.
yielded 0.30 g (49%) of a colorless powder. H NMR (C6D6): δ
3
0.93 (t, 3H, -CH3, J ) 7 Hz), 1.07, 1.19 (2s, 9H, t-Bu), 1.32
(s, 3H, Ge-CH3), 1.50-2.00 (broad multipletts, 6H, -(CH2)3-
2
), 3.61, 3.87 (2s, 3H, N(CH3)2), 5.11, 5.53 (2d, 1H, -CH2-, J
) 15 Hz), 7.41, 7.47 (2s, 1H, aryl H). 13C NMR (C6D6): δ 1.9
(Ge-CH3), 13.8 (-CH3), 18.6, 26.0, 26.8 (-(CH2)3)-), 31.2, 32.2
(C(CH3)3), 35.1, 36.3 (C(CH3)3), 47.8, 48.0 (N(CH3)2), 66.4
(-CH2-), 121.4, 123.6 (tertiary aryl C), 126.1, 142.2, 154.7,
156.3 (quaternary aryl C). MS (CI, M+ ) MamxGe(n-Bu)(Me)+;
m/z (Irel)): 392 (17, M+), 376 (38, M+ - CH4), 320 (20,
MamxGe+). Anal. Calcd for C22H40GeNI (Mr ) 518.06): C,
51.00; H, 7.78; N, 2.70. Found: C, 50.40; H, 7.33; N, 2.43.
[Ma m xGe(Me)2]+I- (13). Reaction of 10 (1.40 mmol) in
n-hexane (40 mL) with MeI (0.20 g, 0.09 mL, 1.40 mmol)
yielded 0.38 g (58%) of colorless needles.1H NMR (CD3CN): δ
1.10 (s, 6H, Ge(CH3)2), 1.31, 1.34 (2s, 9H, t-Bu), 2.85 (s, 6H,
N(CH3)2), 4.36 (s, 2H, -CH2-), 7.29, 7.61 (2s, 1H, aryl H). 13
C

4784 Organometallics, Vol. 18, No. 23, 1999
J utzi et al.
NMR (DMSO-d6): δ 1.12 (Ge(CH3)2), 30.9, 32.0 (C(CH3)3), 34.8,
36.3 (C(CH3)3), 46.3 (N(CH3)2), 65.6 (-CH2-), 120.0, 123.7
(tertiary aryl C), 125.6, 140.9, 154.0, 156.2 (quaternary aryl-
C). MS (CI, M+ ) MamxGe(Me)2+;m/z (Irel)): 350 (4, M+), Anal.
Calcd for C19H34GeNI (Mr ) 476.03): C, 47.94; H, 7.19; N, 2.94.
Found: C, 47.92; H, 7.20; N, 2.90.
Chemischen Industrie” as well as a gift of germanium
from Chemetall GmbH, Frankfurt/Main, Germany, is
gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and selected bond
lengths and angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. The financial support of the
“Deutsche Forschungsgemeinschaft” and the “Fonds der
OM990557R