Synthesis and structure of oligomeric dimesitylgermyl-substituted carbodiimides; characterization of higher oligomers

Article abstract of DOI:10.1021/om970604k

New cyclic oligomers of dimesitylgermylene carbodiimides (Mes₂GeNCN)_n (n = 3 (1) and 4 (2)) were synthesized by reactions of dimesityldichlorogermane with either cyanamide in the presence of triethylamine or lithium cyanamide. The re

Full text of DOI:10.1021/om970604k

Organometallics 1998, 17, 623-629
623
Syn th esis a n d Str u ctu r e of Oligom er ic
Dim esitylger m yl-Su bstitu ted Ca r bod iim id es;
Ch a r a cter iza tion of High er Oligom er s
Mohamed Dahrouch,† Monique Rivie`re-Baudet,*,† J acques Satge´,†
Monique Mauzac,‡ Christine J . Cardin,§ and J ames H. Thorpe§
He´te´rochimie Fondamentale et Applique´e, UPRES-A 5069 du CNRS and Laboratoire IMRCP,
Universite´ Paul Sabatier, 31062 Toulouse Cedex 4, France, and Chemistry Department,
University of Reading, Whiteknights, Reading RG4 9BB, U.K.
Received J uly 16, 1997
New cyclic oligomers of dimesitylgermylene carbodiimides (Mes2GeNCN)n (n ) 3 (1) and
4 (2)) were synthesized by reactions of dimesityldichlorogermane with either cyanamide in
the presence of triethylamine or lithium cyanamide. The reactions always gave 1, the trimer
of the hypothetical (Mes2GedN-CN), as the major compound. Higher oligomers 3 (n up to
20-30) also can be isolated, depending on the reaction conditions. In THF solution at room
temperature, 2 and 3 slowly isomerize to 1, which seems to be the most stable compound.
X-ray analysis of trimer 1 and tetramer 2 shows unstrained tetrahedral germanium atoms
and linear diimine linkers.
In tr od u ction
characterize the hypothetical monomer [Mes2GedN-
CtN].
A starting material for the formation of a germanium-
Although dimeric -[Me2GeNdCdN]-2 was postu-
lated once1 in an exchange reaction between Me2GeF2
and bis(trimethylsilyl)carbodiimide, such cyclic oligo-
mers have never been isolated nor characterized. Sili-
con analogues have been reported only recently;2-4 the
tetramer -(Me2Si-NdCdN)-4 has been thoroughly
studied. It is composed of planar 16-membered rings
with four SiMe2 groups connecting the four NCN
groups.4 In view of our interest in the synthesis of new
organometallic polymers and since oligomeric metal
carbodiimides are precursors for the pyrolytic synthesis
of M/C/N ceramics,2,3 we attempted to synthesize such
compounds and present our results within the germa-
nium series here.
nitrogen double bond is the corresponding chloro-
germylamine, which, depending on the nature of R, can
be unstable, decomposing as shown, Scheme 1.6,8-10
When cyanamide was used instead of a primary
amine in an equimolar ratio in a reaction with dimesit-
yldichlorogermane in the presence of Et3N, the corre-
sponding monochlorogermane could not be isolated and
the formation of any >N-H compounds was not ob-
served, in contrast to what was previously observed in
the case of trimesitylgermyl compounds.11 Instead, the
bis(dimesitylchlorogermyl)carbodiimide (Scheme 2, ii)
could be characterized in a mixture with the final
oligomeric compounds and some starting material.
When two or more equivalents of triethylamine were
used (Scheme 2, iii and iv), the only final product in
THF solution (or in the presence of an excess of
cyanamide) (Scheme 2, vi) was the cyclic trimer 1.
Thus, although 1 can be formed, in principle, through
the polymerization of the monomeric hypothetical [Mes2-
GedN-CN] (Scheme 2, v), it certainly is obtained
through intermolecular elimination between the dichlo-
rogermane and the cyanamide (Scheme 2, iv), as previ-
ously observed in the case of cyclogermazane forma-
tion.12
Resu lts a n d Discu ssion
As mesityl groups on germanium tend to stabilize
small molecules thought to be unstable or known only
as transient species,6,7 we began our study with mesityl
substituents on germanium in the hope of being able to
† He´te´rochimie Fondamentale et Applique´e, Universite´ Paul Sa-
batier. E-mail: riviere@ramses.ups-tlse.fr.
‡ Laboratoire IMRCP, Universite´ Paul Sabatier.
§ University of Reading. E-mail: C.J .Cardin@reading.ac.uk.
(1) Drake, J . E.; Glavincevski, B. M.; Henderson, H. E. Synth. React.
Inorg., Met. Org. Chem. 1978, 8, 7.
It was not possible to isolate a pure sample of bis-
(dimesitylchlorogermyl)carbodiimide from the reaction
(2) Seyferth, D.; Strohmann, C.; Dando, N. R.; Perrota, A. J .;
Gardner, J . P. Mater. Res. Soc. Sympos. Proc. 1994, 327, 191.
(3) Kienzle, A.; Obermeyer, A.; Riedel, R.; Aldinger, F.; Simon,
A. Chem. Ber. 1993, 126, 2569.
(4) Obermeyer, A.; Kienzle, A.; Weidlein, J .; Riedel, R.; Simon, A.
Z. Anorg. Allg. Chem. 1994, 620, 1357.
(5) Gordetsov, A. S.; Kozyukov, V. P.; Vostokov, I. A.; Sheludyakova,
S. V.; Dergunov, Yu. I.; Mironov, V. F. Russ. Chem. Rev. 1982, 51,
485; Usp. Khim. 1982, 51, 848.
(6) Rivie`re, P.; Rivie`re-Baudet, M.; Satge´, J . Comprehensive Orga-
nometallic Chemistry; Wilkinson, G., Gordon, F., Stone, F. G. A., Abel,
E. W., Eds.; Pergamon: New York, 1982; Vol. 2, Chapter 10; Ibid. Abel,
E. W., Gordon, F., Stone, F. G. A., Wilkinson, G., Davies, A., Eds.;
Pergamon: New York, 1995; Vol. 2, Chapter 5.
(7) Escudie´, J .; Couret, C.; Ranaivonjatovo H.; Satge´, J . Coord.
Chem. Rev. 1994, 130, 427.
(8) Rivie`re-Baudet, M. Main Group Met. Chem. 1995, 18, 353.
(9) Rivie`re-Baudet, M.; More`re, A.; Khallaayoun, A.; Satge´, J . Main
Group Met. Chem. 1992, 15, 255.
(10) Rivie`re-Baudet, M.; Khallaayoun, A.; Satge´, J .; Ahra, M. Synth.
React. Inorg. Met.sOrg. Chem. 1992, 22, 683.
(11) Dahrouch, M.; Rivie`re-Baudet, M.; Bertrand, G.; Gornitzka, H.
J . Organomet. Chem., submitted for publication.
(12) Rivie`re-Baudet, M.; El Baz, F.; Satge´, J .; Khallaayoun, A.; Ahra,
M. Phosphorus, Sulfur Silicon Relat. Elem. 1996, 112, 203.
S0276-7333(97)00604-3 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/30/1998

624 Organometallics, Vol. 17, No. 4, 1998
Dahrouch et al.
Sch em e 1
Sch em e 2
Sch em e 3
of dimesityldichlorogermane with either cyanamide or
lithium cyanamide in a 2:1 ratio (Scheme 3, i). Even
at low temperature, the reaction always afforded at least
small amounts of 1 (Scheme 3, i) in addition to the
expected bis(dimesithylchlorogermyl)carbodiimide. This
(dichlorogermyl)carbodiimide, as soon as formed, prob-
ably reacts with the cyanamide reagent in the reaction
mixture, as expected from Scheme 2, iv.
A 1:1 ratio of reagents at room temperature led to 1
(Scheme 3, ii), while at low temperature we were able
to characterize two higher cyclooligomers, the tetramer
2, and a higher oligomer 3 (Scheme 3, iii and iv). The
formation of 3 is favored by dilution in THF. Formation
of 2 and 3 is disfavored in the presence of an excess of
cyanamide, which probably induces a protic cleavage of
Ge-N bonds of higher polymers to give the more stable
trimer (Scheme 2, vi). NMR analysis of 3 showed only
one type of mesityl signal, with small amounts of 1 and
2 contaminants. Compounds 1, 2, and 3 were easily
identified by 1H NMR (Figure 1). Gel permeation
chromathography (GPC) experiments were performed
on 3 with toluene or tetrahydrofuran (THF) as the
eluant (see Figure 2). The chromatogram obtained in
toluene shows a small fraction of 1, 2, and a compound
of higher mass identified to n ) 5 by reference to the
calibration curve obtained from pure samples of 1, 2,
11
and Mes3GeNdCdNGeMes3 (accuracy of determina-
tion about M ) 50-100). We also observed a broad peak
due to species of higher molecular weight (n > 5) up to
10 000 g‚mol-1 (relative to polystyrene standards). The
number-average molecular weight (Mn) and weight-
average molecular weight (Mw) were, respectively, around
5000 g‚mol-1 and 7000 g‚mol-1 (versus polystyrene),
with a low dispersity (I) of 1.3. When GPC analysis was
performed using THF, the molecular weights of the
polymer were in the same range but the average
molecular weights appear to be slightly smaller: Mn )
3700, Mw ) 4700 relative to polystyrene standards, I )
1.4. Moreover, a large peak due to 1 appeared, confirm-
ing a cleavage of the polymer in THF leading to 1. The
other signals observed at high elution times correspond
to the dimesitylgermadiol Mes2Ge(OH)2 and dimesityl-

Characterization of Higher Oligomers
Organometallics, Vol. 17, No. 4, 1998 625
F igu r e 1. 1H NMR identification of 1, 2, and 3 in a
mixture (d) by comparison with recrystallized pure samples
of 1 (a) and 2 (b). The purest sample of 3 (c) is obtained
from Scheme 3, iii.
F igu r e 2. GPC traces of (Mes2GeNCN)n 3 in (a) toluene
solution and (b)THF solution. 1 (n ) 3), 2 (n ) 4), x ) Mes2-
Ge(OH)2, y ) (Mes2GeO)2, z ) (Mes2GeO)3.
digermoxane (Mes2GeO)2, formed by hydrolysis of the
moisture-sensitive Ge-N bonds.
Attempted recrystallization of 2 and 3 led to the
formation of 1, which is also the only compound obtained
after gentle heating or after a few days in THF solution
(Scheme 2, vi) (Figure 3). However, we were able to
partially recover thin white needles of tetramer 2 from
CHCl3 solution, which allowed an X-ray analysis of that
compound. 3 could not be recovered from CHCl3, and
from benzene a sticky product was obtained.
The fact that in THF 2 and 3 were converted to 1
(n)3) is possibly due to nucleophilic assistance by THF
at the metal, favoring the opening of Ge-N bonds
(Figure 4).
transamination from (dimesitylchlorogermyl)dimethyl-
amine (eq 1). Subsequent dehydrochlorination of the
dichloride gave 1 (eq 2). However, although bis(dimesit-
ylchlorogermyl)carbodiimide is the main product of the
reaction (eq 1), part of the dimethylamine formed acts
as a dehydrohalogenating agent and polymer 3 was also
obtained as a byproduct (cf. Experimental Section).
Bis(dimesitylchlorogermyl)carbodiimide cannot be iso-
lated by an exchange reaction (Scheme 4, i). Ge-N/
GeCl exchange, as in that reaction, requires heating
and, therefore, led to formation of 1 (Scheme 4, ii); one-
half of the starting dimesityldichorogermane remained
unchanged.
To prove the formation of poly(dimesitylgermylene)-
carbodiimide from N,N′-bis(dimesitylchlorogermyl)car-
X-r a y An a lysis of 1 a n d 2. X-ray analysis of trimer
1 gave the structure shown in Figure 5. The molecule
is twisted into a propeller-like conformation, but with
the overall structure possessing a center of symmetry,
showing that a racemic mixture of the novel macrocycles
had been formed. The diimine linkages are approxi-
mately linear as expected, with N-C bond lengths in
the range 1.192(5)-1.221(6) Å and angles in the range
171.1(5)-173.6(5)°. The germanium centers adopt an
unstrained tetrahedral geometry, with Ge-N bond
lengths in the range 1.834(4)-1.855(3) Å and Ge-C
distances in the range 1.942(4)-1.955(4) Å.
2Mes2Ge NMe2 + H2NCN
Cl
2Me2NH +
(1)
Mes2Ge
N
C
N
GeMes2
Cl
Cl
2Et3N
Mes2Ge
Cl
N
C
N
GeMes2 + H2NCN
-2Et3N, HCl
Cl
(2)
2/3 Mes2Ge
N C N
3
1
bodiimide (Scheme 2, iv, vi), we prepared the latter by

626 Organometallics, Vol. 17, No. 4, 1998
Dahrouch et al.
Sch em e 4
F igu r e 4.
F igu r e 5. A single molecule of the germanium trimer 1
showing the numbering scheme for the germanium and
nitrogen atoms. Thermal ellipsoids are shown at the 50%
probability level.
F igu r e 3. Example of the conversion of 2 to 1 at room
temperature in THF solution: (a) 2 recrystallized in CHCl3;
(b) after 2 days in THF; (c) after 5 days; (d) after 8 days.
F igu r e 6. A single molecule of the germanium tetramer
2 showing the numbering scheme for the germanium and
nitrogen atoms. Thermal ellipsoids are shown at the 50%
probability level.
X-ray analysis of tetramer 2 gave the overall structure
shown in Figure 6. This molecule crystallizes in the
unusual space group I4h, with the tetrameric molecule
possessing a 4h axis in the crystal. This high symmetry
may be related to the high rigidity associated with the
diimine and the mesityl groupings. The germanium
center again adopts an unstrained tetrahedral geometry
with Ge-N distances of 1.836(7) and 1.847(7) Å and
Ge-C distances of 1.956(7) and 1.970(8) Å. The N-C-N

Characterization of Higher Oligomers
Organometallics, Vol. 17, No. 4, 1998 627
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1
P r epar ation of Tr is(dim esitylger m ylen ecar bodiim ide)
(1). To cyanamide (0.31 g, 7.4 mmol) in solution in 10 mL
THF with Et3N (1.02 g, 10.09 mmol) was added dropwise with
stirring a solution of Mes2GeCl2 (0.91 g, 2.4 mmol) in 11 mL
of THF. After 18 h of stirring at room temperature, THF was
replaced by benzene (8 mL) and triethylamine hydrochloride
was filtered. Evaporation of the filtrate in vacuo gave a white
powder of crude 1. Recrystallization from benzene gave 0.62
g of pure 1, mp 168 °C (yield 74%; recrystallization can also
be performed from hexane or ether).
Ge(1)-N(6)
Ge(1)-N(1)
Ge(1)-C(13)
Ge(1)-C(4)
Ge(2)-N(3)
Ge(2)-N(2)
Ge(2)-C(22)
Ge(2)-C(31)
Ge(3)-N(5)
Ge(3)-N(4)
Ge(3)-C(49)
Ge(3)-C(40)
1.847(4)
1.855(3)
1.942(4)
1.945(4)
1.843(4)
1.843(4)
1.944(4)
1.955(4)
1.834(4)
1.848(4)
1.943(4)
1.949(4)
N(6)-Ge(1)-N(1)
N(6)-Ge(1)-C(13)
N(1)-Ge(1)-C(13)
N(6)-Ge(1)-C(4)
N(1)-Ge(1)-C(4)
C(13)-Ge(1)-C(4)
N(3)-Ge(2)-N(2)
N(3)-Ge(2)-C(22)
N(2)-Ge(2)-C(22)
N(3)-Ge(2)-C(31)
N(2)-Ge(2)-C(31)
C(22)-Ge(2)-C(31)
N(5)-Ge(3)-N(4)
N(5)-Ge(3)-C(49)
N(4)-Ge(3)-C(49)
N(5)-Ge(3)-C(40)
N(4)-Ge(3)-C(40)
C(49)-Ge(3)-C(40)
101.98(17)
108.90(16)
105.24(17)
108.98(17)
112.30(17)
118.18(16)
99.38(18)
110.35(18)
113.19(17)
111.91(17)
105.78(16)
115.09(16)
106.43(19)
103.5(2)
1H NMR (CDCl3): δ 2.22 (s, 18H, p-CH3), 2.30 (s, 36H,
o-CH3), 6.71 (s, 12H, CH). 13C NMR (CDCl3): δ 21.13 (p-CH3),
23.16 (o-CH3); 132.32 (C1), 142.96 (C2), 129.41 (C3), 139.60 (C4),
134.15 (NCN). IR: (CDCl3) (νas(NCN)): 2144 cm-1; (Nujol)
2133 cm-1
.
MS (DCi/CH4, m/z): 1053 (100, (M + 1)+), 1081
(12, (M + 29)+), and a small amount of tetramer 2 (1405 (10,
(M + 1)+)). Anal. Calcd for C57H66 N6Ge3: C, 65.02; H, 6.32;
N, 7.98. Found: C, 64.95; H, 6.23; N, 7.71.
114.43(17)
113.80(17)
104.38(19)
114.35(16)
Cr ysta l Da ta for 1, C57H66N6Ge3. M ) 1052.984. Tri-
clinic, P1h (No. 2). a ) 13.193(5) Å, b ) 15.729(5) Å, c ) 15.923-
(5) Å, R ) 107.32(6)°, â ) 112.61(5)°, γ )105.76(6)°. V ) 2617.6
Å,3 Z ) 2, Fc ) 1.265 Mg m-3, µ ) 2.308 mm-1. F(000) ) 1012.
T ) 293 K. λ (Mo KR) ) 0.710 73 Å.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2
Ge(1)-N(2)
Ge(1)-N(1)
Ge(1)-C(11)
Ge(1)-C(2)
1.836(7)
1.847(7)
1.956(7)
1.970(8)
N(2)-Ge(1)-N(1)
N(2)-Ge(1)-C(11)
N(1)-Ge(1)-C(11)
N(2)-Ge(1)-C(2)
N(1)-Ge(1)-C(2)
C(11)-Ge(1)-C(2)
C(7)-C(2)-C(3)
C(7)-C(2)-Ge(1)
C(3)-C(2)-Ge(1)
C(1)-N(1)-Ge(1)
103.4(3)
107.8(3)
113.1(3)
114.6(3)
105.1(3)
112.5(3)
119.8(8)
118.4(6)
121.7(6)
130.0(6)
The data were collected on a small Mar Research image
plate system using 3 kW sealed-tube molybdenum radiation
(T ) 293 K). Exposure time was 2 min per frame, and 95 2°
frames were collected. No correction for absorption was
applied, and decay was negligible. Data were processed with
the Mar Research version of Wolfgang Kabsch’s program XDS.
Cell constants were determined using the GLOREF routine
in XDS. The structure was solved using direct methods and
confirmed by Patterson methods refining on intensities to give
R1 ) 0.0561, wR2 ) 0.1673 for 7664 unique observed reflec-
tions. The refinement was based on F2. The programs
SHELXS96 and SHELXL96 were used for all calculations.
Hydrogen atoms were placed geometrically using the riding
model with thermal parameters set to 1.5 times that for the
atom to which the hydrogen is attached. The diagram was
drawn with PLATON. The data have been deposited with the
Cambridge Crystallographic Data Centre.
angle is 173.5(9)°, and the two C-N distances are
1.128(10) and 1.200(11) Å. Both molecules therefore
display a geometrical consistency. Selected bond lengths
and angles are shown in Table 1 for 1 and in Table 2
for 2.
Exp er im en ta l Section
Ch a r a cter iza tion of Bis(d im esitylch lor oger m yl)ca r -
bod iim id e. (1) Rea ction of Mes2GeCl2 w ith H2NCN
(Sch em es 2 a n d 3). To Mes2GeCl2 (0.90 g, 2.38 mmol) in 8
mL of THF was added dropwise at room temperature a
solution of H2NCN (0.05 g, 1.19 mmol) and Et3N (0.24 g, 2.38
mmol) in 5 mL of THF. After 2 h of stirring, THF was replaced
by benzene and [Et3NH]Cl was filtered. 1H NMR analysis of
the white residue obtained by evaporating the solvent in vacuo
showed the presence of Mes2GeCl2 (50%), 1 (25%), and Mes2-
(Cl)GeNdCdNGe(Cl)Mes2 (25%), the latter identified by com-
parison with a sample formed according to eq 1.
All syntheses were performed in dry solvents under a dry
nitrogen atmosphere using standard Schlenk techniques. The
compounds were characterized by the usual analytical tech-
1
niques: IR Perkin-Elmer 1600 FT; H NMR (80 MHz), AC 80
Bruker; 13C NMR (50.3 MHz), AC 200, δ ppm/TMS. For the
dimesitylgermylenecarbodiimides, the following numbering
system was adopted
(2) Rea ction of Lith iu m Cya n a m id e w ith Mes2GeCl2
(Sch em e 3). Lithium cyanamide was prepared by dropwise
addition of t-BuLi (1.7 M in pentane, 2.38 mmol, 1.4 mL) with
stirring to H2NCN (0.05 g, 1.19 mmol) in 3 mL of THF at -60
°C. The mixture was allowed to warm to room temperature
with stirring for 30 min. This solution was added with stirring
to Mes2GeCl2 (0.9 g, 2.38 mmol) in 7 mL of THF at -60 °C.
After 2 h at room temperature, THF was replaced by benzene
and LiCl was separated by centrifugation. Evaporation of the
Mass spectroscopy: Ribermag R1010 (DCi/CH4), Perkin-Elmer
SCIEX API 100 (APCI ) atmospheric-pressure chemical
ionization, eluant CH3CN, solvent benzene), and HP 5989 (Ei).
GPC analysis was performed on three Waters Styragel HR
columns (10-2, 10-1,1 µ), refractive index detection, with THF
or toluene as the eluant (1.2 mL/min) versus polystyrene
standards for high molecular weight compounds and versus
1
solvent gave a white residue whose H NMR analysis showed
the presence of Mes2GeCl2 (25%), 1 (9%), 2 (28%), and Mes2-
Ge(Cl)NdCdNGe(Cl)Mes2 (38%).
11
pure samples of Mes3GeNdCdNGeMes3 (M ) 900), 1 (M )
P r ep a r a tion of 1 by Tr a n sm eta la tion . To lithium
cyanamide (1.19 mmol in 5 mL of THF) prepared as before
was added Mes2GeCl2 (0.45 g, 1.17 mmol) in 6 mL of THF, at
room temperature with stirring. After replacement of THF
by benzene, centrifugation of LiCl, and evaporation of benzene,
0.32 g of 1 (yield 78%) was obtained.
1052), 2 (M ) 1404), and standards for low molecular weight
compounds. Elemental analysis was performed by the Mi-
croanalysis Center of Ecole Nationale Superieure de Chimie
de Toulouse. Dimesityldichlorogermane was prepared accord-
ing to literature.13 Other chemicals were purchased from
Aldrich Chemical Co.
P r ep a r a t ion of Tet r a k is(d im esit ylger m ylen eca r b o-
d iim id e) (2). A solution of H2NCN (0.10 g, 2.38 mmol) and
(13) Rivie`re, P.; Rivie`re-Baudet, M. Organomet. Synth. 1988, 4, 542.

628 Organometallics, Vol. 17, No. 4, 1998
Dahrouch et al.
Et3N (0.48 g, 4.76 mmol) in 7 mL of THF was added dropwise
with stirring to Mes2GeCl2 (0.90 g, 2.36 mmol) in 10 mL of
THF at -60 °C. The mixture was allowed to warm to room
temperature, THF was replaced by benzene and [Et3NH]Cl
was filtered. Evaporation of benzene gave 0.45 g (yield 54%)
of a white residue analyzed by 1H NMR to be composed of 1
(53%), 2 (38%), and 3 (9%). Slow recrystallization from
chloroform (10 mL) at room temperature afforded 0.08 g of
white needles of pure 2, mp 265 °C (yield 2%).
1H NMR (CDCl3): δ 2.22 (s, 72H, o, p-CH3), 6.66 (s, 16H,
CH). 13C NMR (CDCl3): δ 21.07 (p-CH3), 22.98 (o-CH3), 132.89
(C1), 142.94 (C2), 129.27 (C3), 139.26 (C4), 134.61 (NCN). IR:
(CDCl3) (νasNCN) 2122 cm-1; (Nujol) 2122 cm-1. MS (DCi/CH4,
m/z): 1405 (100, (M + 1)+). Anal. Calcd for C76 H88N8Ge4: C,
65.02; H, 6.32; N, 7.98. Found: C, 64.71; H, 5.96; N, 7.92.
The remaining solution contained only 1 (1H NMR analysis,
3 was converted to 1). Evaporation in vacuo gave 0.35 g of 1
(yield 43%).
of 2 at room temperature, percent of 1 formed after 1 day (5%),
2 days (17%), 5 days (53%), 8 days (92%) (Figure 3); conversion
of 3 at room temperature, percent of 1 formed after 1 day
(10%), 2 days (15%), 5 days (69%), 8 days (97%). (b) In benzene
solution: A solution of 3 in benzene either heated for 3 h at
90 °C or after 1 week at room temperature did not show any
change.
Con ver sion of 3 in th e P r esen ce of Excess Cya n a m id e.
A solution of 3 (0.2 mg/6 mL of THF) in the presence of an
excess of cyanamide (4 mol equiv) gave 10% of 1 after 18 h of
stirring at room temperature.
A solution of 3 (0.2 mg/6 mL of C6H6) in the presence of an
excess of cyanamide in suspension (4 mol equiv) after 18h of
stirring at room temperature gave 10% of 1.
Rea ction of Solu tion s of 2 a n d 3 w ith Air . The same
solution of 2 or 3 (in THF or benzene) kept at room temper-
ature in an open flask led slowly, by hydrolysis, to the
formation of Mes2Ge(OH)2 and (Mes2GeO)n (n ) 2, 3), char-
Cr ysta l Da ta for 2, (C19H22N2Ge)4. M ) 1323.36. Tet-
ragonal, I4h (No. 82). a ) 20.779(5) Å, b ) 20.779(5) Å, c )
8.615 (3) Å. V ) 3719.7 Å3. Z ) 2, Fc ) 1.738 Mg m-3, µ )
4.824 mm-1, F(000) ) 1908. T ) 293K, λ (Mo KR) ) 0.710 73
Å.
1
acterized by H NMR and GPC (Figure 2), by cleavage of the
moisture-sensitive Ge-N bonds.
P r ep a r a t ion of Bis(d im esit ylch lor oger m yl)ca r b o-
d iim id e by Tr a n sa m in a tion fr om Mes2Ge(Cl)NMe2 (eq
1). (1)P r ep a r a tion of Mes2Ge(Cl)NMe2. To Mes2GeCl2 (0.9
g, 2.36 mmol) in 7 mL of THF was added dropwise, at room
temperature with stirring, Me2NLi (2.36 mmol in THF). After
an additional 2 h of stirring at room temperature, THF was
replaced by benzene and LiCl separated by centrifugation.
Evaporation of benzene in vacuo led to a white, sticky
compound (0.68 g) identified by 1H and 13C NMR as pure Mes2-
Ge(Cl)NMe2. Yield: 74%.
1H NMR (CDCl3): δ 2.25 (s, 6H, p-CH3), 2.39 (s, 12H, o-CH3),
6.82 (s, 4H, CH), 2.61 (s, 6H, NMe2). 13C NMR (CDCl3): δ 21.07
(p-CH3), 23.16 (o-CH3), 133.73 (C1), 143.18 (C2), 129.66 (C3),
139.83 (C4), 39.72 (NMe2). MS (Ei, m/z): 391 (2, (M+•)), 356
(5, (M+• - Cl)), 346 (25, (M+• - Me2NH)).
(2) Tr a n sa m in a tion . To Mes2Ge(Cl)NMe2 (0.92 g, 2.36
mmol) in 4 mL of THF was added H2NCN (0.049 g, 1.18 mmol)
in 2 mL of THF dropwise at room temperature with stirring.
There was immediate evolution of dimethylamine. After a few
minutes, a light precipitate of [Me2NH2]Cl was formed. After
2 h of stirring, THF was replaced by benzene and dimethyl-
amine hydrochloride was removed by centrifugation. Evapo-
ration of solvents in vacuo gave a white, amorphous powder
(0.61 g) (mp 136 °C) of Mes2(Cl)GeNdCdNGe(Cl)Mes2 (con-
taining (Mes2GeNCN)n 3 (∼ 35%)), starting material for 1
thereafter.
The data were collected on a small Mar Research image
plate system using 3 kW sealed-tube molybdenum radiation
(T ) 293 K). Exposure time was 10 min per frame, and 95 2°
frames were collected. No correction for absorption was
applied, and decay was negligible. Data were processed with
the Mar Research version of Wolfgang Kabsch’s program XDS.
Cell constants were determined using the GLOREF routine
in XDS. The structure was solved using direct methods and
confirmed by Patterson methods refining on intensities to give
R1 ) 0.0606, wR2 ) 0.1724 for 1937 unique observed reflec-
tions. The refinement was based on F2. The programs
SHELXS96 and SHELXL96 were used for all calculations.
Hydrogen atoms were placed geometrically using the riding
model with thermal parameters set to 1.5 times that for the
atom to which the hydrogen is attached. The diagram was
drawn with PLATON. The data have been deposited with the
Cambridge Crystallographic Data Centre.
P r ep a r a tion of 3. To Mes2GeCl2 (0.90 g, 2.36 mmol) in
15 mL of THF was added dropwise over 30 min with stirring
at -70 °C lithium cyanamide (2.36 mmol) as a suspension in
10 mL of THF. The mixture was stirred at -70 °C for 1.5 h.
The THF was evaporated and immediately replaced by ben-
zene. Lithium chloride was separated by centrifugation. The
remaining solution was evaporated in a vacuum, leaving 0.71
g of a white amorphous residue of 3 (containing 10-15% of 1)
(yield 85%). 3 dissolved in benzene was reprecipitated by
addition of pentane. mp 100-110 °C (dec).
Spectral characteristics of Mes2(Cl)GeNdCdNGe(Cl)Mes2.
1H NMR (CDCl3): δ 2.22 (s, 36H, o-CH3-p-CH3), 6.72 (s, 8H,
CH). 13C NMR (CDCl3): δ 21.08 (p-CH3), 22.68 (o-CH3), 143.43
1H NMR (CDCl3): δ 2.17 (s, p-CH3), 2.10 (s, o-CH3), 6.58 (s,
CH). 13C NMR: (CDCl3) δ 21.12 (p-CH3), 22.93 (o-CH3), 132.87
(C1), 142.72 (C2), 129.26 (C3), 139.10 (C4), 132.00 (NCN); (C6D6)
δ 21.17 (p-CH3), 23.37 (o-CH3), 133.47 (C1), 143.14 (C2), 129.84
(C3), 139.37 (C4). IR (CDCl3): (νasNCN) 2108 cm-1. MS (DCi/
CH4, m/z): (Mes2GeNCN)5 1755 (5, (M + 1)+), (Mes2GeNCN)4
1405 (25, (M + 1)+), (Mes2GeNCN)3 1053 (100, (M + 1)+).
APCI: (Mes2GeNCN)6 2106 ((M + 1)+), (Mes2GeNCN)5 1755
((M + 1)+). Anal. Calcd for (C19H22N2Ge)n: C, 65.02; H, 6.32;
N, 7.98. Found: C, 64.67; H, 6.34; N, 7.53.
All attempts to recrystallize 3 from ether or chloroform gave
1; in benzene a sticky material was obtained. GPC analysis
in toluene: large, broad signal corresponding to a mass
distribution from 4 < n = 30 (polystyrene standard).
Con ver sion s of 2 a n d 3 in THF a n d Ben zen e Solu tion .
(a) Solutions of pure 2 or 3 in THF (=0.2 mg in 6 mL of THF)
were placed in sealed tubes. Each tube was either heated or
kept at room temperature before analysis. Then after opening
the tube, the THF was evaporated in vacuo and replaced by
CDCl3 for 1H NMR analysis. The results are as follows: 2 or
3 after 3 h at 80 °C were completely converted to 1; conversion
(C2), 129.16 (C3), 138.90 (C4). IR (CDCl3): (νasNCN) 2111 cm-1
MS (DCI/CH4, m/z): 733 (5, (M + 1)+).
.
F or m a tion of 1 fr om Bis(d im esitylch lor oger m yl)ca r -
bodiim ide (eq 2). The white powder of Mes2(Cl)GeNdCdNGe-
(Cl)Mes2 containing ∼35% of 3, prepared above, was dissolved
in 4 mL of THF and treated with an excess of cyanamide (0.1
g, 2.36 mmol) in 2 mL of THF. Et3N (0.48 g, 4.72 mmol) was
added, and the mixture was stirred for 1 h at room tempera-
ture. After replacement of THF with C6H6 to remove [Et3NH]-
Cl, evaporation of the solvent gave 0.38 g of 1 as a white
powder containing 18% of 3. Yield 81%.
F or m a tion of 1 by a n Exch a n ge Rea ction (Sch em e 4).
To Mes2GeCl2 (0.88 g, 2.32 mmol) in 5 mL of THF was added
Et3GeNdCdNGeEt311 (0.42 g, 1.16 mmol) in 5 mL of THF. Et3-
GeCl formation was monitored by gas chromatography and
required 16 h of heating at 80 °C for completion. After
evaporation of the solvent, triethylchlorogermane was distilled
in vacuo. 1H NMR analysis of the white residue (0.78 g)
showed the quantitative formation of 1. Higher oligomers 2
and 3 cannot be obtained in these experimental conditions.

Characterization of Higher Oligomers
Organometallics, Vol. 17, No. 4, 1998 629
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data and structure refinement details, positional and
thermal parameters, and bond distances and angles for 1 and
2 (18 pages). Ordering information is given on any current
masthead page.
Ack n ow led gm en t. We thank the European Com-
munity, Human and Capital Mobility Network program
for support (Grant No. CHRX930281), Prof. G. M.
Sheldrick and Prof. E. Keller for the use of their soft-
ware, and the University of Reading for support to
J .H.T.
OM970604K