Germanium-containing heterobicyclic 10-π-electron ring systems. Synthesis and characterization of neutral and cationic germanium(II) derivatives of aminotroponiminates

Article abstract of DOI:10.1021/ja970196b

The neutral and cationic aminotroponiminate derivatives of germanium(II) have been investigated. The treatment of GeCl₂·(1,4-dioxane) with [(i- Pr)₂ATI]Li or [(Me)₂ATI]Li in a 1:1 molar ratio gave the corresponding monochl

Full text of DOI:10.1021/ja970196b

4650
J. Am. Chem. Soc. 1997, 119, 4650-4655
Germanium-Containing Heterobicyclic 10-π-Electron Ring
Systems. Synthesis and Characterization of Neutral and
Cationic Germanium(II) Derivatives of Aminotroponiminates
H. V. Rasika Dias* and Ziyun Wang
Contribution from the Department of Chemistry and Biochemistry, The UniVersity of Texas
at Arlington, Arlington, Texas 76019-0065
ReceiVed January 21, 1997X
Abstract: The neutral and cationic aminotroponiminate derivatives of germanium(II) have been investigated. The
treatment of GeCl2‚(1,4-dioxane) with [(i-Pr)2ATI]Li or [(Me)2ATI]Li in a 1:1 molar ratio gave the corresponding
monochloro germanium(II) complex. Substitution of the chloride ion of [(i-Pr)2ATI]GeCl with weakly coordinating
anions [CF3SO3]- and [(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)]- led to cationic germanium(II) species containing
{[(i-Pr)2ATI]Ge}+ ion. Although NMR data of the cationic species show notable differences relative to their neutral
analog, the solid state data show only minor changes in the C7N2Ge moiety. The Ge-N bond distances of the
cations are not indicative of significant Ge-N π-bonding. These compounds feature some of the smallest N-Ge-N
angles known for Ge(II) compounds. Attempted synthesis of the tetraphenylborate salt of {[(Me)2ATI]Ge}+ led to
1
a phenyl group transfer product [(Me)2ATI]GePh‚BPh3 with a Ge(II)-B bond. Details of the H, 13C NMR
spectroscopy and X-ray crystal structures of all these compounds are described.
Introduction
serve as good precursors (e.g., 3) for the chemical vapor
deposition of germanium11,13 or as starting material (e.g., 1) for
the synthesis of various germanium derivatives.7,8,20-23
In the last two decades the chemistry of thermally stable
bivalent compounds of germanium has developed into an active
area of research.1-8 Ligands with nitrogen donors have
particularly been useful in the synthesis of these systems.
Compounds 1-4 represent a group of monomeric germylenes
(germanium analogs of carbene) with good thermal stability.9-12
They display two-coordinate, V-shaped geometry at the ger-
manium center. Sterically demanding substituents are necessary
to prevent the aggregation of these species. For example, the
N-isopropyl analog of 3 forms dimers in the solid state.13
Compound 2 is significantly more stable than the closely related
3.11 This and the results from several other studies suggest that
the conjugated ligand backbones may also play an important
role in improving the stability.2,14,15 In fact, it is even possible
to isolate carbon16-18 and silicon19 analogs of 2 (carbenes and
silylenes) in stable crystalline form.2 Some of the germylenes
X Abstract published in AdVance ACS Abstracts, May 1, 1997.
(1) Harrison, P. G. In ComprehensiVe Coordination Chemistry; Wilkin-
son, G., Gillard, D., McCleverty, J. A., Eds.; Pergamon: Oxford, 1987;
Vol. 3, p 183.
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828.
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King, R. B., Ed.; Wiley: New York, 1994; Vol. 3, p 1292.
(4) Neumann, W. P. Chem. ReV. 1991, 91, 311.
In contrast to the neutral germylenes (e.g., 1-4), related
cationic germanium(II) complexes are rare.1 A small number
of such species having cyclopentadienyl ligands (e.g., {[η5-
C5Me5]Ge}X, where X ) [BF4], [CF3SO3], and [AlCl4];24,25
(5) Barrau, J.; Escudie´, J.; Satge´, J. Chem. ReV. 1990, 90, 283.
(6) Satge´, J. J. Organomet. Chem. 1990, 400, 121.
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(8) Lappert, M. F. Main Group Met. Chem. 1994, 17, 183.
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P. P.; Olmstead, M. M. Inorg. Chim. Acta 1992, 198-200, 203.
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P.; Rivie´re-Baudet, M. J. Chem. Soc., Dalton Trans. 1977, 2004.
(11) Herrmann, W. A.; Denk, M.; Behm, J.; Scherer, W.; Klingan, F.
R.; Bock, H.; Solouki, B.; Wagner, M. Angew. Chem., Int. Ed. Engl. 1992,
31, 1485.
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(17) Dias, H. V. R.; Jin, W. Tetrahedron Lett. 1994, 35, 1365.
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Am. Chem. Soc. 1992, 114, 5530.
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Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. J. Am. Chem. Soc.
1994, 116, 2691.
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J.-M. Angew. Chem., Int. Ed. Engl. 1994, 33, 1156.
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10912.
(22) Bartlett, R. A.; Power, P. P. J. Am. Chem. Soc. 1990, 112, 3660.
(23) Chen, H.; Bartlett, R. A.; Dias, H. V. R.; Olmstead, M. M.; Power,
P. P. Inorg. Chem. 1991, 30, 3390.
(12) Pfeiffer, J.; Maringgele, W.; Noltemeyer, M.; Meiler, A. Chem. Ber.
1989, 122, 245.
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Herrmann, W. A. Chem. Mater. 1996, 8, 825.
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1994, 475, 73.
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S0002-7863(97)00196-0 CCC: $14.00 © 1997 American Chemical Society

Ge-Containing Heterobicyclic 10-π-Electron Ring Systems
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4651
spectra were run with 1H decoupling and the chemical shifts are reported
in ppm vs Me4Si. Melting points were obtained on a Mel-Temp II
apparatus and were not corrected. Elemental analyses were performed
at The University of Texas at Arlington on a Perkin Elmer 2400 CHN
analyzer.
{[η2-Me4C5H]Me2Si[η5-Me4C5]Ge}[GeCl3]),26,27 arenes (e.g.,
[(p-C6H4CH2CH2)3GeCl]2[Al4O2Cl10]),28 and nitrogen donors
(e.g., [Ge2(3,5-(CH3)2Pz)3][GeCl3]29 and {[HB(3,5-(CH3)2Pz)3]-
Ge}I)30 have been reported in the literature.
One area of focus in our laboratory is the chemistry of
N-alkyl-2-(alkylamino)troponiminate ([(R)2ATI]-) derivatives
of main group elements.31-33 This ligand [(R)2ATI]-, which
features a delocalized 10-π-electron ligand backbone, has not
been used widely in the main group chemistry.31-35 Considering
the current level of interest in the main group heterocyclic
π-systems,2,11,12,14-16,18,19,36-43 and the importance of germyl-
enes1-8 and the germanium centered cations,1,24,44-46 we have
decided to investigate the neutral and cationic [(R)2ATI]-
derivatives of germanium(II). We were particularly interested
in investigating the role the two nitrogen donors and the cyclic
π-system in [(R)2ATI]- may play in stabilizing species such as
{[(R)2ATI]Ge}+ in the monomeric form.
Synthesis of [(i-Pr)2ATI]GeCl (5). A diethyl ether solution (20
mL) of [(i-Pr)2ATI]H (500 mg, 2.45 mmol) was treated with n-BuLi
(1.53 mL, 1.6 M hexane solution) at 0 °C. This mixture was then
stirred for 0.5 h and slowly added to GeCl2‚(1,4-dioxane) (570 mg,
2.45 mmol) in diethyl ether (15 mL) at -78 °C. The mixture
immediately became cloudy. After an hour, the mixture was allowed
to warm to room temperature and stirred overnight. The resulting
reddish solution was filtered through a bed of Celite, and the volatile
materials were removed from the filtrate under reduced pressure to
obtain the product as an orange red solid (92% yield, 0.70 mg).
Recrystallization from toluene-hexane at -20 °C gave orange crystals
1
of [(i-Pr)2ATI]GeCl. Mp 108-110 °C; H NMR (C6D6) δ 1.32 (d,
6H, J ) 6.2 Hz, CH3), 1.52 (d, 6H, J ) 6.2 Hz, CH3), 3.67 (septet,
2H, J ) 6.2 Hz, CH(CH3)2), 6.29 (t, 1H, J ) 9.4 Hz, H5), 6.34 (d, 2H,
J ) 11.4 Hz, H3,7), 6.76 (t, 2H, J ) 10.2 Hz, H4,6); 13C{1H} NMR
(C6D6) δ 22.7 (CH3), 23.7 (CH3), 49.3 (CH(CH3)2), 115.5 (C5), 122.0
(C3,7), 136.6 (C4,6), 160.6 (C2,8); 1H NMR (CDCl3) δ 1.63 (d, 12H, J )
6.3 Hz, CH3), 4.26 (septet, 2H, J ) 6.3 Hz, CH(CH3)2), 6.74 (t, 1H, J
) 9.3 Hz, H5), 6.92 (d, 2H, J ) 11.2 Hz, H3,7), 7.33 (t, 2H, J ) 10.4
Hz, H4,6); 13C{1H} NMR (CDCl3) δ 23.8 (br s, CH3), 49.3 (CH(CH3)2),
115.7 (C5), 123.0 (C3,7), 136.8 (C4,6), 160.5 (C2,8). Anal. Calcd for
C13H19N2ClGe: C, 50.15; H, 6.15; N, 9.0. Found: C, 50.18; H, 6.26;
N, 8.73.
In this paper we report the synthesis and characterization
of germanium(II) derivatives of aminotroponiminate ligands
[(i-Pr)2ATI]- and [(Me)2ATI]-. They include a novel cationic
species {[(i-Pr)2ATI]Ge}[(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)]
and a triphenylboron adduct [(Me)2ATI]GePh‚BPh3. Synthesis
of [(Me)2ATI]GePh‚BPh3 involves a phenyl group transfer from
-
a BPh4 anion.
Experimental Section
Synthesis of {[(i-Pr)2ATI]Ge}[CF3SO3] (6). [(i-Pr)2ATI]GeCl (100
mg, 0.32 mmol) and CF3SO3Ag (80 mg, 0.32 mmol) were mixed in
dichloromethane (10 mL) at room temperature. The mixture im-
mediately became cloudy yellow and was then stirred overnight and
filtered through a bed of Celite. The filtrate was concentrated and kept
at -20 °C to obtain 6 as a yellow solid in 86% yield. X-ray quality
crystals were obtained from a dichloromethane-hexane solution. Mp
111-113 °C; 1H NMR (CDCl3) δ 1.68 (d, 6H, J ) 6.2 Hz, CH3), 4.40
(septet, 2H, J ) 6.2 Hz, CH(CH3)2), 7.15 (t, 1H, J ) 9.5 Hz, H5), 7.29
(d, 2H, J ) 11.3 Hz, H3,7), 7.64 (dd, 2H, J ) 11.2, 11.8 Hz, H4,6);
13C{1H} NMR (CDCl3) δ 23.9 (CH3), 49.4 (CH(CH3)2), 117.6 (C5),
119.5 (q, CF3, J(C,F) ) 320 Hz), 127.3 (C3,7), 137.4 (C4,6), 160.2 (C2,8);
1H NMR (C6D6) δ 1.39 (d, 6H, J ) 6.6 Hz, CH3), 3.66 (septet, 2H, J
) 6.6 Hz, CH(CH3)2), 6.46 (t, 1H, J ) 9.5 Hz, H5), 6.52 (d, 2H, J )
11.6 Hz, H3,7), 6.68 (dd, 2H, J ) 11.0, 9.0 Hz, H4,6); 13C{1H} NMR
(C6D6) δ 23.5 (CH3), 49.3 (CH(CH3)2), 117.2 (C5), 120.7 (q, CF3, J(C,F)
) 318 Hz), 126.1 (C3,7), 137.1 (C4,6), 160.1 (C2,8). Anal. Calcd for
C14H19F3N2O3SGe: C, 39.57; H, 4.51; N, 6.59. Found: C, 39.11; H,
4.51; N, 6.59.
All manipulations were carried out under an atmosphere of purified
nitrogen with standard Schlenk techniques or in a Vacuum Atmospheres
single station drybox equipped with a -25 °C refrigerator. Solvents
were distilled from conventional drying agents and degassed twice prior
to use. Glassware was ovendried at 150 °C overnight. [(i-Pr)2ATI]H,31
[(Me)2ATI]H,33 and GeCl2‚(1,4-dioxane) were prepared according to
the previously reported methods. n-BuLi (1.6 M solution in hexane),
(η5-C5H5)ZrCl3, CF3SO3Ag, and NaBPh4 were obtained from com-
1
mercial sources and used as received. The H and 13C NMR spectra
were recorded at room temperature on a Bruker MSL-300 spectrometer
(1H, 300.13 MHz; 13C, 75.47 MHz) or a Nicolet NT-200 spectrometer
(1H, 200.07 MHz; 13C, 50.31 MHz), unless otherwise noted. Chemical
shifts for 1H NMR spectra are relative to internal Me4Si. The 13C NMR
(26) Kohl, F. X.; Dickbreder, R.; Jutzi, P.; Mu¨ller, G.; Huber, B. J.
Organomet. Chem. 1986, 309, C43.
(27) Kohl, F. X.; Dickbreder, R.; Jutzi, P.; Mu¨ller, G.; Huber, B. Chem.
Ber. 1989, 122, 871.
(28) Probst, T.; Steigelmann, O.; Riede, J.; Schmidbaur, H. Angew.
Chem., Int. Ed. Engl. 1990, 29, 1397.
(29) Steiner, A.; Stalke, D. Inorg. Chem. 1995, 34, 4846.
(30) Reger, D. L.; Coan, P. S. Inorg. Chem. 1996, 35, 258.
(31) Dias, H. V. R.; Jin, W.; Ratcliff, R. E. Inorg. Chem. 1995, 34, 6100.
(32) Dias, H. V. R.; Jin, W. J. Am. Chem. Soc. 1996, 118, 9123.
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(35) Eaton, D. R.; McClellan, W. R. Inorg. Chem. 1967, 6, 2134.
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117, 5421.
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L. J. Am. Chem. Soc. 1996, 118, 10457.
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Soc. 1996, 118, 2023.
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Klooster, W. T.; Koetzle, T. F. J. Am. Chem. Soc. 1994, 116, 6812.
(41) Arduengo, A. J., III; Bock, H.; Chen, H.; Denk, M.; Dixon, D. A.;
Green, J. C.; Herrmann, W. A.; Jones, N. L.; Wagner, M.; West, R. J. Am.
Chem. Soc. 1994, 116, 6641.
(42) Colomer, E.; Corriu, R. J. P.; Lheureux, M. Chem. ReV. 1990, 90,
265.
(43) Blakeman, P.; Gehrhus, B.; Green, J. C.; Heinicke, J.; Lappert, M.
F.; Kindermann, M.; Veszpre´mi, T. J. Chem. Soc., Dalton Trans. 1996,
1475.
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499, 49.
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(46) Sekiguchi, A.; Tsukamoto, M.; Ichinohe, M. Science 1997, 275,
60.
Synthesis of {[(i-Pr)2ATI]Ge}[(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-
C5H5)] (7). [(i-Pr)2ATI]GeCl (100 mg, 0.32 mmol) and (η5-C5H5)ZrCl3
(169 mg, 0.64 mmol) were mixed in dichloromethane (15 mL) at room
temperature. This mixture was then stirred overnight and filtered
through a bed of Celite. The filtrate was collected and the volatile
materials were removed under reduced pressure to obtain a yellow solid.
Recrystallization from dichloromethane-hexanes at -20 °C gave
1
yellow crystals of 7. Mp 187-189 °C; H NMR (CDCl3) δ 1.67 (d,
12H, J ) 6.6 Hz, CH3), 4.46 (septet, 2H, J ) 6.6 Hz, CH(CH3)2), 6.55
(s, 5H, CH), 7.30 (t, 1H, J ) 9.4 Hz, H5), 7.42 (d, 2H, J ) 11.3 Hz,
H
3,7), 7.73 (t, 2H, J ) 10.3 Hz, H4,6); 13C{1H} NMR (CDCl3) δ 24.2
(CH3), 50.6 (CH(CH3)2), 118.5 (C5), 120.5, 124.7, 137.4 (C4,6), 160.2
(C2,8). Anal. Calcd for C23H29N2Cl7GeZr‚1.1CH2Cl2: C, 31.12; H, 3.38;
N, 3.01. Found: C, 31.52; H, 3.54; N, 2.41.
Synthesis of [(Me)2ATI]GeCl (8). A THF solution (20 mL) of
[(Me)2ATI]H (500 mg, 3.37 mmol) was treated with n-BuLi (2.11 mL,
3.37 mmol, 1.6 M hexane solution) at 0 °C. This mixture was then
stirred for 0.5 h and slowly added to GeCl2‚(1,4-dioxane) (780 mg,
3.37 mmol) in THF (20 mL) at 0 °C. After being stirred for an
additional 1 h, the mixture was allowed to warm to room temperature
and stirred overnight. The volatiles were removed under vacuum, and
the solid residue was extracted into toluene. The solution was filtered
through a bed of Celite, and the filtrate was concentrated and cooled
to -25 °C to obtain 8 in 65% yield. X-ray quality crystals were
obtained from a mixture of toluene-dichloromethane at -20 °C. Mp

4652 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Dias and Wang
Table 1. Crystal Data and Summary of Data Collection and Refinement
5
6
7
8
9
formula
fw
C13H19ClN2Ge
311.34
C14H19F3GeN2O3S
424.96
C23H29Cl7GeN2Zr2
836.66
C9H11ClN2Ge
255.24
C33H31BN2Ge
539.00
space group
a, Å
b, Å
c, Å
P21/c
P21/n
P21/c
P21/c
P21/c
16.398(2)
9.745(2)
36.510(5)
90
99.496(10)
90
7.8359(14)
13.562(2)
16.994(2)
90
97.04(1)
90
10.043(1)
21.372(3)
14.888(2)
90
104.084(13)
90
9.825(3)
11.664(2)
10.110(2)
90
118.22(2)
90
8.378(1)
16.677(1)
19.026(2)
90
90.76(1)
90
R, deg
â, deg
γ, deg
vol, Å3
5754.6(14)
16
1792.3(5)
4
3099.4(8)
4
1020.9(4)
4
2657.9(5)
4
Z
T, K
183(2)
0.71073
1.437
2.296
0.0389, 0.0719
0.0693, 0.0853
183(2)
0.71073
1.575
1.869
0.0274, 0.0668
0.0344, 0.0710
183(2)
0.71073
1.793
2.244
0.0390, 0.0998
0.0551, 0.1099
183(2)
0.71073
1.661
3.216
0.0253, 0.0545
0.0335, 0.0575
183(2)
0.71073
1.346
1.177
0.0315, 0.0706
0.0456, 0.0763
λ(Mo KR), Å
density (calc), g/cm3
absorpn coeff, mm-1
R1, wR2 [I > 2σ(I)]a
R1, wR2 [all data]a
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
Table 2. Selected Bond Distances (Å) and Angles (deg) (L ) [(i-Pr)2ATI]; M ) Ge or Sn; X ) Cl or O)
LGeCla
LSnCl
[(Me)2ATI]GeCl
LGeOTf
{LGe}+
{LSn}+
M-N
1.956(4)
2.164(5)
2.164(5)
2.542(2)
1.332(7)
1.331(7)
73.9(2)
1.937(3)
1.938(3)
2.377(1)
1.342(4)
1.342(4)
80.1(1)
1.910(2)
1.916(2)
2.255(2)
1.354(3)
1.352(3)
81.79(8)
89.63(8)
88.74(8)
1.901(5)
1.917(5)
2.153(3)
2.142(3)
M-X
N-Cring
2.368(2)
1.341(6)
1.347(8)
1.346(8)
81.7(2)
1.335(5)
1.341(5)
74.48(12)
N-M-N
N-M-X
80.3(2)
96.6(1)
92.43(13)
94.13(12)
96.28(8)
97.30(8)
a Averages of four independent molecules in the asymmetric unit.
1
145-148 °C; H NMR (CDCl3) δ 3.30 (s, 6H, CH3), 6.82 (m, 3H),
version 5 based on SHELXL-93) software package48 provided by the
Siemens Analytical X-ray Instruments, Inc. Some details of data
collection and refinements are given in Table 1. Selected bond distances
and angles are given in Table 2. Further details of the crystal structures
are presented in the Supporting Information.
7.39 (t, 2H, J ) 9 Hz); 13C{1H} NMR (CDCl3) δ 32.2 (CH3), 115.8
(C5), 123.6 (C3,7), 137.3 (C4,6), 160.8 (C2,8). Anal. Calcd for
C9H11N2GeCl: C, 42.35; H, 4.34; N, 10.98. Found: C, 41.59; H, 4.28;
N, 9.70.
Synthesis of [(Me)2ATI]GePh‚BPh3 (9). [(Me)2ATI]GeCl (150 mg,
0.59 mmol) and NaBPh4 (201 mg, 0.59 mmol) were mixed in
dichloromethane (15 mL) at room temperature. The mixture gradually
turned bright red and was then stirred overnight and filtered through a
bed of Celite. The filtrate was concentrated and kept at -20 °C. Dark
red-orange crystals of 9 were obtained from dichloromethane-hexane
in 84% yield. Mp 210-215 °C; 1H NMR (CDCl3) δ 2.37 (s, 6H, CH3),
6.30 (d, J ) 11.2 Hz), 6.52 (t, J ) 9.4 Hz), 7.11-7.30 (m, br); 13C{1H}
NMR (CDCl3) δ 32.8 (CH3), 114.5, 122.0, 125.7 (br), 127.1, 130.0,
135.0, 136.4, 138.9, 142.2, 161.2. Anal. Calcd for C33H31BN2Ge: C,
73.53; H, 5.80; N, 5.20. Found: C, 73.23; H, 5.56; N, 4.56.
X-ray Structure Determination. A suitable crystal covered with
a layer of hydrocarbon oil was selected and attached to a glass fiber
and immediately placed in the low-temperature nitrogen stream.47 Data
collections were carried out at -90 °C on a Siemens P4 diffractometer
equipped with a LT-2A device for low-temperature work and graphite
monochromated Mo KR radiation (λ ) 0.710 73 Å). The unit cell
parameters of 5, 6, 7, 8, and 9 were determined by least-squares
refinement of 33, 30, 30, 30, and 66 reflections, respectively. Three
standard reflections were measured at every 97 data points to check
for crystal deterioration and/or misalignment. No significant deteriora-
tion in intensity was observed. Data were corrected for Lorentz,
polarization, and absorption (using ψ scans) effects. Structures were
solved by direct methods followed by successive cycles of full-matrix
least-squares refinement on F2 and difference Fourier analysis. All
the non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were included at calculated positions. They were treated as riding
atoms with isotropic displacement parameters fixed 1.2 or 1.5 times
the value refined for the respective host atom. Software programs and
the sources of scattering factors are contained in the SHELXTL (PC
Results and Discussion
Synthesis of the germanium(II) chlorides [(i-Pr)2ATI]GeCl
(5) and [(Me)2ATI]GeCl (8) was achieved by the treatment of
GeCl2‚(1,4-dioxane) with [(i-Pr)2ATI]Li or [(Me)2ATI]Li in a
1:1 molar ratio in Et2O or THF. The products were isolated as
orange solids in excellent yields (Schemes 1 and 2) and
1
characterized by H and 13C NMR spectroscopy and by X-ray
diffraction. The 1H NMR spectrum of 5 taken in CDCl3 shows
three well-separated multiplets which correspond to H(5),
H(3,7), and H(4,6). The 13C NMR spectrum displayed four
resonances for the ring carbons. A nearly identical four-signal
pattern was observed for 8 in the aromatic region of the 13C
NMR spectrum. Interestingly, methyls of the isopropyl sub-
1
stituents of 5 appear as two sets of doublets in the H NMR
spectrum recorded in C6D6, suggesting two different environ-
ments for the -CH3 moieties. This is perhaps due to the
asymmetry caused by the Cl group on the germanium center.
Likewise, they appear as two signals in the 13C NMR spectrum.
However, in CDCl3, methyl groups appear only as a doublet in
the 1H NMR spectrum and as a broad singlet in the 13C
spectrum. A similar solvent effect was observed in the tin
analog [(i-Pr)2ATI]SnCl.
The X-ray crystal structure of 5 and the atom numbering
scheme are shown in Figure 1. The asymmetric unit contains
four chemically similar but crystallographically different mol-
ecules of 5. One of them is notably different from the rest due
to the orientation of methyls of the isopropyl groups as illustrated
(47) Hope, H. In Experimental Organometallic Chemistry; ACS Sym-
posium Series, No. 357; Wayda, A. L., Darensbourg, M. Y., Eds.; American
Chemical Society: Washington, DC, 1987; p 257.
(48) SHELXTL (PC Version 5.0); Siemens Industrial Automation, Inc.:
Madison, WI, 1994.

Ge-Containing Heterobicyclic 10-π-Electron Ring Systems
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4653
Scheme 1
Figure 1. Structures and atom numbering schemes of two crystallo-
graphically different molecules of [(i-Pr)2ATI]GeCl (5).
Scheme 2
Figure 2. Structure and atom numbering scheme for [(Me)2ATI]GeCl
(8).
1
in good yield. The room temperature H and 13C NMR data
indicate the presence of magnetically equivalent methyl groups.
For example, -CH3 groups of 6 give rise to a doublet in the
1H NMR spectrum taken in C6D6. Note that in 5 two sets of
doublets were observed for the corresponding protons. These
data agree with the removal of chloride from the germanium
center leading to a relatively less crowded environment around
germanium. The 1H NMR resonances of the ring protons of 6
(δ 7.15, 7.29, and 7.64 in CDCl3) show a downfield shift relative
to those of 5 (δ 6.74, 6.92, and 7.33). This may be an indication
of the increased positive charge on the ligand backbone.
The X-ray crystallographic data of 6 do not show complete
anion/cation separation (Figure 3). The CF3SO3- group binds
weakly to the germanium center with a Ge-O distance of
2.255(2) Å (cf. sum of the covalent radii of Ge and O ) 1.95
Å). In addition, the packing diagram shows that there is a very
long intermolecular contact between germanium and oxygen
atoms (Ge‚‚‚O, 3.87 Å; O-Ge‚‚‚O, 152°) forming a chain
structure. The Ge-N distances are slightly shorter than those
of the chloro analogs 5 and 8 (Table 2).
in Figure 1. The germanium center adopts a pyramidal
geometry that is fairly common in Ge(II) chemistry. The
average Ge-Cl and Ge-N distances are 2.368(2) and 1.956(4)
Å, respectively. The X-ray crystal structure of 8, which contains
a sterically less demanding [(Me)2ATI]- ligand, is illustrated
in Figure 2. The Ge-Cl (2.3774(10) Å) and Ge-N (1.937(3)
and 1.938(3) Å) bond distances are essentially similar to those
of 5. As evident from the data presented in Table 2, the Ge-N
distances are significantly shorter and the N-Ge-N angles are
several degrees larger than the corresponding structural param-
eter in [(i-Pr)2ATI]SnCl. These germanium compounds do not
show intermolecular Ge‚‚‚Cl contacts whereas the tin complex
displays weak Sn‚‚‚Cl interactions.32
In order to generate cationic {[(R)2ATI]Ge}+ species, we have
attempted the substitution of the chloride group of 5 or 8 with
various weakly coordinating anions. The treatment of [(i-Pr)2-
ATI]GeCl with CF3SO3Ag led to {[(i-Pr)2ATI]Ge}[CF3SO3] (6)

4654 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Dias and Wang
Figure 4. Structure and atom numbering scheme for {[(i-Pr)2ATI]-
Ge}[(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)] (7).
Figure 3. Structure and atom numbering scheme for {[(i-Pr)2ATI]-
Ge}[CF3SO3] (6).
We have reported earlier the synthesis of a cationic Sn(II)
species using the [(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)]- an-
ion.32 It is also possible to prepare the analogous Ge(II)
complex {[(i-Pr)2ATI]Ge}[(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)]
(7). This was obtained by treating 5 with 2 equiv of (η5-
C5H5)ZrCl3 in CH2Cl2 (Scheme 1). The (η5-C5H5)ZrCl3 serves
1
as a chloride abstracting agent in this reaction. The H and
13C NMR spectroscopic data of the crude mixture indicate the
formation of 7 with some unidentified impurities. Compound
7 can be crystallized from CH2Cl2-hexane. It is an air- and
moisture-sensitive yellow solid that shows moderate solubility
in CHCl3 or CH2Cl2. The solubility of 7 is very poor in hydro-
carbon solvents such as toluene.
Both the 1H and 13C NMR data corresponding to the
{[(i-Pr)2ATI]Ge}+ unit are very similar between 6 and 7. The
ring protons of 7 show a small downfield shift compared to the
1
corresponding H resonances of {[(i-Pr)2ATI]Sn}[(η5-C5H5)-
ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)]. Apart from that, the 1H and 13
C
Figure 5. Diagram of 7 showing weak Ge‚‚‚Cl interactions.
NMR spectra of 7 are similar to those of the tin analog. The
119Sn NMR spectroscopic data of {[(i-Pr)2ATI]Sn}[(η5-C5H5)-
ZrCl2(µ-Cl)3ZrCl2(η5-C5H5)] suggested the presence of two
coordinate Sn(II) species.32 Therefore, it is reasonable to expect
that the Ge(II) species 7 (and 6) would also show similar ion
separation in solution. The NMR data of 7 can also be
compared to those of the free ligand [(i-Pr)2ATI]H.31 Compared
to [(i-Pr)2ATI]H, all the corresponding resonances due to protons
of 7 appear at significantly downfield positions. Some of the
13C NMR chemical shifts are also notably different. For
example, the peak due to C(2,8) of 7 appears around δ 160
whereas in the free ligand it was observed at 151 ppm.
The solid state structure of 7 is depicted in Figure 4.
Compound 7 consists of the cationic {[(i-Pr)2ATI]Ge}+ moiety
and the chloride bridged [(η5-C5H5)ZrCl2(µ-Cl)3ZrCl2(η5-
C5H5)]- anion. Features of the anionic [(η5-C5H5)ZrCl2(µ-
Cl)3ZrCl2(η5-C5H5)]- unit are described elsewhere.32 The
germanium center adopts a V-shaped geometry with a N-Ge-N
angle of 81.7(2)°. The C7N2Ge moiety is essentially planer.
The Ge-N bond distances in the cation are 1.901(5) and
1.917(5) Å. In addition to these two bonds, there are two weak
interactions between the germanium ion of the cation and
terminal chloride atoms (Cl6 and Cl1A) of the [(η5-C5H5)ZrCl2(µ-
Cl)3ZrCl2(η5-C5H5)]- anions. This gives rise to a zigzag chain
structure shown in Figure 5. Similar interactions in the Sn(II)
cation lead to centrosymmetric dimers.32 These Ge‚‚‚Cl separa-
tions of 3.123 and 3.115 Å are considerably long compared to
the typical Ge-Cl single-bond distances. They can be compared
to covalently bound Ge-Cl distances of 5 (av. 2.368(2)Å) and
8 (2.377(1)Å) or to the weak Ge‚‚‚Cl contacts (3.235(6) and
3.394(6) Å) of {[η2-Me4C5H]Me2Si[η5-Me4C5]Ge}[GeCl3].26
The Cl6‚‚‚Ge‚‚‚Cl1A angle is 169.8°. It is also noteworthy that
the Ge‚‚‚Cl contacts of 7 are even longer than the Sn‚‚‚Cl
separations of the tin analog (2.979 and 3.070 Å).
Interestingly, the key structural parameters of the cationic
{[(i-Pr)2ATI]Ge}+ moiety are only slightly different from neutral
germanium complexes such as 5 or 8 (see Table 2). The Ge-N
bond lengths are marginally smaller and the N-Ge-N angles
are >2° wider in the cationic species. The Ge-N distances
and N-Ge-N angles of 7 can also be compared to those of 1
(Ge-N, 1.878(5), 1.873(5) Å; N-Ge-N, 107.1(2)°),9 2 (Ge-
N, 1.856(1) Å; N-Ge-N, 84.8(1)°),11 3 (Ge-N, 1.833(2) Å;
N-Ge-N, 88.0(1)°),11 4 (Ge-N, 1.861(8), 1.866(9) Å; N-Ge-
N, 87.2(4)°),12 and the interesting cyclic species [Ge(NC6H2But3-
2,4,6)]2 (Ge-N, 1.844(3), 1.855(3) Å; N-Ge-N, 86.3(1)°),49
and [Ge(NC6H3Pri2-2,6)]3 (Ge-N, av 1.859(2) Å; N-Ge-N,
av 101.8(1)°).22,23 A typical GedN bond is about 1.691-1.703
Å long.1 In general, these Ge-N distances are shorter than
the corresponding interatomic distances of 6 and 7. This is
perhaps due to the difference between diamido donors (e.g., in
2) and the amido/imido donor combination (e.g., in 7). As
mentioned earlier, a few structurally characterized cationic ger-
manium compounds are also known, e.g., [Ge2(3,5-(CH3)2Pz)3]-
[GeCl3]29 and {[HB(3,5-(CH3)2Pz)3]Ge}I.30 The Ge-N dis-
(49) Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J. J. Chem. Soc., Chem.
Commun. 1990, 1587.

Ge-Containing Heterobicyclic 10-π-Electron Ring Systems
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4655
ecules containing Ge-B bonds are mostly limited to the carbo-
rane family.51 Nevertheless, the Ge-B distance of 2.156(4) Å
can be compared to GeII-B (2.265(6), 2.243(6), and 2.250(6)
Å) and GeIV-B (1.995(6) distances of closo-1-GeII-2,3-(Me3Si)2-
5-(GeIVCl3)-2,3-C2B4H3.52 The N-Ge-N angle of 81.69(10)°
is similar to that observed in the cationic derivatives.
One of the interesting features of aminotroponiminato deriva-
tives of germanium(II) is the planar, bicyclic 10-π-electron ring
system. In contrast to the neutral adducts such as 5 or 8, the
germanium center of the {[(i-Pr)2ATI]Ge}+ cation has an empty
out-of-plane p-orbital that is capable of interacting with the
ligand π-electron system. Such π-interaction would lead to a
somewhat shorter Ge-N bond distance. Theoretical studies
predict that in Ge(NH2)2 the pπ-pπ delocalization would shorten
the Ge-N distance by about 0.06-0.07 Å.14 A comparison of
structural data between [(i-Pr)2ATI]GeCl and {[(i-Pr)2ATI]Ge}+
indeed shows a reduction (about 0.047 Å). However, the
magnitude of shortening, particularly when considered along
with possible steric effects and experimental uncertainties, is
not indicative of a significant change in the Ge-N bond order.
The presence of non-bonded contacts between the cationic
germanium center and anions also points to the relatively weak
nature of this pπ-pπ bonding.
In summary, neutral and cationic germanium(II) derivatives
of aminotroponiminate ligand can be isolated in stable, crystal-
line form. These compounds feature heterobicyclic C7N2Ge ring
systems. The NMR data of the cationic species suggest the
delocalization of positive charge over the C7N2Ge ring. How-
ever, this does not accompany a significant increase in the
Ge-N π-bonding. Attempted synthesis of the tetraphenylborate
salt of {[(Me)2ATI]Ge}+ led to a novel phenyl group transfer
product with a GeII-B bond.
Figure 6. Structure and atom numbering scheme for [(Me)2ATI]-
GePh‚BPh3 (9).
tances and N-Ge-N angles of these three coordinate germa-
nium(II) species are 1.971 Å, 90.5° and 2.03 Å, 86.9°, respec-
tively. They are significantly larger than the corresponding
structural parameters of 6 and 7. Overall, compounds 5-8
feature some of the smallest N-Ge-N angles observed in Ge(II)
chemistry.2
In order to isolate a two-coordinate Ge(II) cation free of even
weak cation/anion interactions, we have attempted to replace
-
Cl- of 5 with BPh4 anions. Unfortunately, the reaction
between 5 and NaBPh4 resulted in a complicated mixture of
products. The analogous reaction between NaBPh4 and 8 was
much cleaner and afforded a red solid. The NMR data of this
product, however, did not point to the formation of expected
{[(Me)2ATI]Ge}[BPh4]. For example, the aromatic region of
the 13C NMR spectrum showed eleven well-separated signals.
Fortunately, this compound produced excellent X-ray quality
crystals, and the finding of the X-ray diffraction study is
illustrated in Figure 6 and indicates the formation of [(Me)2-
ATI]GePh‚BPh3 (9) rather than the cationic Ge(II) species.
Although the exact mechanism is uncertain, the formation of
[(Me)2ATI]GePh‚BPh3 may involve a phenyl group migration
from BPh4- anion to the cationic germanium(II) center followed
by the association of the two resulting fragments BPh3 and
Acknowledgment. We thank the donors of The Petroleum
Research Fund, administered by the American Chemical Society,
and The Robert A. Welch Foundation for support of this work.
The authors also wish to acknowledge The University of Texas
at Arlington for providing funds to purchase the Siemens P4
single-crystal X-ray diffractometer.
Supporting Information Available: Tables of crystallo-
graphic data, atomic coordinates, thermal parameters, and com-
plete bond distances and angles for 5, 6, 7, 8, and 9 (28 pages).
See any current masthead page for ordering and Internet access
instructions.
-
[(Me)2ATI]GePh. The phenyl group transfer from BPh4 to
metal centers is well-known.50 However, we are unaware of
such instances involving germanium(II) cations.
The germanium atom of 9 adopts a tetrahedral geometry with
Ge-N bond lengths of 1.913(2) and 1.920(2) Å. These
distances are not very different when compared to the corre-
sponding bond lengths of 8. Structurally authenticated mol-
JA970196B
(51) Cambridge Structural Database; Cambridge, England, January,
1996.
(52) Siriwardane, U.; Islam, M. S.; Maguire, J. A.; Hosmane, N. S.
Organometallics 1988, 7, 1893.
(50) Strauss, S. H. Chem. ReV. 1993, 93, 927 and the references therein.