Reactivity of α-germyl nitriles with acetonitrile: Synthesis, structures, and generation of Ph3Ge[NHC(CH3)CHCN] and 2,6-dimethyl-4-(triphenylgermylamino)pyrimidine from Ph3GeCH 2CN

Article abstract of DOI:10.1016/j.jorganchem.2011.08.029

The formation of 3-aminocrotononitrile and 4-amino-2,6- dimethylaminopyrimidine has been observed during the course of the hydrogermolysis reaction between a germanium amide and a germanium hydride, either as the free amines or bound to germanium as ligands consisting of their conjugate bases. These species arise from the dimerization or trimerization of acetonitrile, and have only been detected when germanium amides having substantial steric bulk at the germanium center are employed in the reaction. The isolation of germanium-bound 3-aminocrotononitrile compounds suggests that α-germyl nitrile species R₃GeCH₂CN that result from the reaction of the germanium amides R₃GeNMe₂ with CH ₃CN solvent also can further react with CH₃CN to generate the 3-aminocrotononitrile and 4-amido-2,6-dimethylaminopyrimidine species. The two germanes Ph₃Ge[NHC(CH₃)CHCN] and 2,6-dimethyl-4- (triphenylgermylamino)pyrimidine have been prepared and structurally characterized, and the conversion of Ph₃GeCH₂CN to Ph ₃Ge[NHC(CH₃)CHCN] and 2,6-dimethylamino-4- (triphenylgermylamino)pyrimidine as well as the conversion of Ph ₃Ge[NHC(CH₃)CHCN] to 2,6-dimethyl-4-(triphenylgermylamino) pyrimidine in acetonitrile solvent has been observed using ¹H NMR spectroscopy.

Full text of DOI:10.1016/j.jorganchem.2011.08.029

Journal of Organometallic Chemistry 696 (2011) 3721e3726
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactivity of
a
-germyl nitriles with acetonitrile: Synthesis,
structures, and generation of Ph3Ge[NHC(CH3)CHCN] and
2,6-dimethyl-4-(triphenylgermylamino)pyrimidine from Ph3GeCH2CN
,
Christian R. Samanamua, Arnold L. Rheingoldb, Charles S. Weinerta
*
a Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA
b Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093-0358, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The formation of 3-aminocrotononitrile and 4-amino-2,6-dimethylaminopyrimidine has been observed
during the course of the hydrogermolysis reaction between a germanium amide and a germanium
hydride, either as the free amines or bound to germanium as ligands consisting of their conjugate
bases. These species arise from the dimerization or trimerization of acetonitrile, and have only been
detected when germanium amides having substantial steric bulk at the germanium center are employed
in the reaction. The isolation of germanium-bound 3-aminocrotononitrile compounds suggests that
Received 29 June 2011
Received in revised form
18 August 2011
Accepted 22 August 2011
Keywords:
Germanium
a
-germyl nitrile species R3GeCH2CN that result from the reaction of the germanium amides R3GeNMe2
with CH3CN solvent also can further react with CH3CN to generate the 3-aminocrotononitrile and
4-amido-2,6-dimethylaminopyrimidine species. The two germanes Ph3Ge[NHC(CH3)]CHCN] and
2,6-dimethyl-4-(triphenylgermylamino)pyrimidine have been prepared and structurally characterized,
and the conversion of Ph3GeCH2CN to Ph3Ge[NHC(CH3)]CHCN] and 2,6-dimethylamino-4-(triphe-
nylgermylamino)pyrimidine as well as the conversion of Ph3Ge[NHC(CH3)]CHCN] to 2,6-dimethyl-4-
(triphenylgermylamino)pyrimidine in acetonitrile solvent has been observed using 1H NMR
spectroscopy.
Acetonitrile
Diacetonitrile
Triacetonitrile
Hydrogermolysis reaction
X-ray crystal structures
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
3-amidocrotononitrile-substituted germane But3Ge[NHC(CH3)]
CHCN] (3), where the free amine 1 is present as a nitrogen-bound
The hydrogermolysis reaction between a germanium amide and
a germanium hydride has proven to be a useful tool for the
formation of germaniumegermanium single bonds, and has been
shown to proceed via the in situ conversion of the germanium
ligand at germanium [1]. The free amines 1 and 2, as well as the
germaniumebound ligand in 3, result from the dimerization or
trimerization of acetonitrile that occurs via the Thorpe reaction
which is a general method for the base-catalyzed self-condensation
of aliphatic nitriles [12,13]. We have prepared the germanes Ph3Ge
[NHC(CH3)]CHCN] (4) and 2,6-dimethyl-4-(triphenylgermyla-
mino)pyrimidine (5) from the corresponding amines 1 and 2 and
Ph3GeCl, have determined their X-ray crystal structures, and have
investigated the in situ conversion of Ph3GeCH2CN to 4 and the
subsequent conversion of 4 to 5.
amide to an a-germyl nitrile that is the active species in the GeeGe
bond forming process [1e11]. Using this method, both linear and
branched oligogermane systems having up to seven germanium
atoms in the GeeGe backbone have been prepared. However, some
steric limitations to this process have been realized.
We have observed the formation of both 3-aminocrotononitrile
(1) and 4-amino-2,6-dimethylaminopyrimidine (2) during the
hydrogermolysis reaction when bulky germanium amides have
been employed as reactants. Specifically, the attempted synthesis of
(Ph3Ge)4Ge from (Ph3Ge)3GeNMe2 and Ph3GeH yielded a mixture
of products that included 1 and 2 [8,9], and the attempted synthesis
of Ph3GeGeBut3 from Ph3GeH and But3GeNMe2 generated the
2. Results and discussion
Compound 4 was prepared from a commercial sample of 3-
aminocrotononitrile which contained both the (E)- and (Z)-
isomers. The 1H NMR spectrum of the starting material indicated
that the two isomers were present in an approximate 2:1 (Z):(E)
ratio. Treatment 3-aminocrotononitrile with one equiv. of BunLi in
THF yielded the monolithium salt LiNHC(CH3)CHCN that was
* Corresponding author. Tel.: þ1 405 744 6543.
E-mail address: Weinert@chem.okstate.edu (C.S. Weinert).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.029

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C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 3721e3726
Scheme 1. Synthesis of Ph3Ge[NHC(CH3)¼CHCN (4).
subsequently added to Ph3GeCl in THF to yield the germanium
compound 4 in 80% yield (Scheme 1). After isolation and purifica-
tion of the product mixture the 1H NMR of 4 indicated that both
isomers of the 3-amidocrotononitrile ligand were present in an
approximate 1:1 isomeric ratio. Two sets of resonances for the
hydrogen atoms of the 3-amidocrotononitrile ligand were visible in
tetrahedral, and the average CipsoeGeeCipso bond angle is 111.14(7)ꢀ
and the average CipsoeGeeN bond angle is 107.7(7)ꢀ. The corre-
sponding angles in the tert-butyl-substituted compound 3 are
112.95(8) and 105.64(7)ꢀ indicating that the structure of 3 is slightly
more distorted from the ideal geometry than that of 4, as expected.
The nitrogen atoms of the 3-amidocrotononitrile ligand in both 3
and 4 are not pyramidal but rather adopt a distorted trigonal planar
geometry where the GeeNeC bond angles are 135.4(1) and
129.75(2)ꢀ for 3 and 4 (respectively). In both of these molecules, the
lone pair of electrons at nitrogen is conjugated with the CeC double
bond and the CeN triple bond in the ligand resulting in a planar
geometry at nitrogen. The distortion of the GeeNeC bond angle
from the idealized value of 120ꢀ results from the steric congestion
at the neighboring germanium atom, and the greater distortion in 3
versus 4 is attributable to the higher steric demands of the tert-
butyl groups present in 3. In addition, all of the carbon and nitrogen
atoms of the 3-amidocrotononitrile ligand are coplanar in both
structures.
the 1H NMR spectrum of 4 at
isomer and 3.76, 3.62, 1.42 ppm for the (Z)-isomer, where these
d 4.06, 3.49, 1.78 ppm for the (E)-
d
features correspond to the olefinic, amide, and methyl group
protons (respectively) in each case. The resonance for the olefinic
proton in the (Z)-isomer is expected to appear at higher field since
it is disposed trans- to the amino group due to the stronger trans-
interaction [14].
After heating the isolated material at 85 ꢀC in CH3CN for 7 days
the material had completely isomerized to the (E)-isomer and it has
been noted that this species is more stable than the (Z)-isomer [15].
The 1H NMR in benzene-d6 of the isolated material exhibited the
aforementioned three singlets at
nance for the amide proton appears upfield from that of the free
amine ( 4.69 (E) or 4.40 (Z) ppm) due to the attachment of the
d 4.06, 3.49, 1.78 ppm. The reso-
The 3-amidocrotononitrile ligand is present exclusively in the
(E)-configuration in the crystal structure of 4, which was also found
for the related tert-butyl substituted analogue (3) [1] as well as for
d
nitrogen atom to germanium, but this feature is shifted downfield
relative to that for 3 due to the presence of electron-withdrawing
phenyl substituents at germanium in 4 versus the tert-butyl
groups in 3.
Recrystallization of this material from hot benzene yielded X-
ray quality crystals, and an ORTEP diagram of 4 is shown in Fig. 1
and selected bond distances and angles are collected in Table 1.
The environment at germanium is distorted from idealized
the free amine 1 that was isolated from the reaction of (Ph3Ge)3
-
GeNMe2 with Ph3GeH [8,9]. The presence of the less sterically
demanding phenyl groups at the germanium center in 4 versus the
tert-butyl substituents in 3 has the most pronounced effect on the
structure of these molecules in the vicinity of the GeeN bond. The
GeeN distance in 4 is 1.866(1) Å and is shorter than that in 3
(1.895(2) Å) by 0.029 Å while the remaining bond distances and
angles in the 3-amidocrotononitrile ligand of 4 and those in 3 are
nearly identical. Similarly, the GeeNeCa bond angles in 4 and 3
also differ significantly, measuring 129.8(1) and 135.4(1)ꢀ (respec-
tively), but the remaining bond angles within the 3-
amidocrotononitrile ligands of these two species are nearly iden-
tical. In both compounds, the bond distances and angles between
the CaeCb atoms clearly indicate the presence of a C]C double
bond, and the CeCN bond angles in both compounds are nearly
linear, as expected.
The structure of free 3-aminocrotononitrile (1) has also been
reported [9], and closely resembles the ligands of 3 and 4 with the
exception of the environment about the NeC
a bond. The NeCa
bond in the free amine measures 1.346(1) Å and the NeCaeCb bond
Table 1
Bond distances (Å) and angles (ꢀ) for Ph3Ge[NHC(CH3)CHCN] (4).
Ge(1)eC(1)
Ge(1)eC(7)
Ge(1)eC(13)
Ge(1)eN(1)
N(1)eC(19)
C(19)eC(20)
C(19)eC(22)
C(20)eC(21)
C(21)eN(2)
1.940(2)
1.941(2)
1.939(2)
1.866(1)
1.359(2)
1.363(2)
1.505(2)
1.416(2)
1.153(2)
C(1)eGe(1)eC(7)
C(1)eGe(1)eC(13)
C(7)eGe(1)eC(13)
C(1)eGe(1)eN(1)
C(7)eGe(1)eN(1)
C(13)eGe(1)eN(1)
Ge(1)eN(1)eC(19)
N(1)eC(19)eC(20)
N(1)eC(19)eC(22)
C(19)eC(20)eC(21)
C(20)eC(21)eN(2)
C(20)eC(19)eC(22)
111.67(7)
110.75(7)
111.01(7)
104.97(6)
108.97(7)
109.26(7)
129.75(1)
123.5(2)
115.1(1)
121.6(2)
178.3(2)
121.4(2)
Fig. 1. ORTEP diagram of Ph3Ge[NHC(CH3)CHCN] (4). Thermal ellipsoids are drawn at
50% probability.

C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 3721e3726
3723
Scheme 2. Synthesis of 2,6-dimethyl-4-(triphenylgermylamino)pyrimidine (5).
angle is 121.6(1)ꢀ. Since the second substituent at the nitrogen
atom in 1 is a hydrogen rather than an R3Ge-group, it is expected
that the bond length would be shorter and the NeCaeCb bond
angle would be more acute in the free amine. However, the struc-
ture of the lithium salt [LiNHC(CH3)CHCN(NC5H5)2]2 (6) has been
determined, and this material is a dimer in the solid state that
adopts the (Z)-configuration about the C]C bond to allow the
formation of the dimeric structure [16]. Therefore, the metric
parameters within the 3-amidocrotononitrile group of this species
are significantly different from those in 3 and 4. Most notably, the
[9]. The average NeC and CeC bond distances within the pyrimi-
dine ring are 1.347(1) and 1.391(2) Å (respectively). The respective
single and double bond distances for a NeC bond are 1.46 and
1.27 Å, while the respective single and double bond distances for
a CeC bond are 1.50 and 1.35 Å [17] All of the carbon and nitrogen
atoms in the pyrimidine ring are coplanar, the NeC and CeC bond
distances in 5 are intermediate between the single and double bond
value, and the NeCeN, NeCeC, and CeCeC bond angles within the
pyrimidine ring in 5 range from 115.9(1) to 126.92(9)ꢀ. Therefore,
these metric parameters indicate that the pyrimidine ring in 5
maintains its aromaticity upon attachment to germanium.
We attempted to observe the conversion of Ph3GeCH2CN to 4 and
also 4 to 5 by NMR spectroscopy since both 3-aminocrotononitrile
and 4-amino-2,6-dimethylaminopyrimidine were isolated during
the attempted preparation of (Ph3Ge)4Ge from (Ph3Ge)3GeNMe2
and Ph3GeH after a reaction time of 72 h [8,9]. However, no reaction
was observed upon heating Ph3GeCH2CN in CD3CN solvent for one
week and heating 4 under the same conditions only resulted in the
isomerization of the mixture of (E)- and (Z)-isomers to the more
stable (E)-isomer while the generation of 5 was not detected. The
conversion of acetonitrile and 3-aminocrotononitrile to 4-amino-
2,6-dimethylaminopyrimidine in the presence of a catalytic amount
of [Me4N][OH]$5H2O has been reported and it has also been noted
that heating acetonitrile for long periods of time in the presence of
[Me4N][OH]$5H2O also generates small amounts of 4-amino-2,6-
dimethylaminopyrimidine [18].
NeC
a
bond distance in 6 is 1.249(5) Å and the NeC
aeCb bond angle
is 127.8(4)ꢀ. The NeC
a
bond distance in 6 is shorter than those in
both 3 and 4 as well as those in the free amine due to the formal
negative charge located at the nitrogen atom in 6 that is absent in
these three other covalently-bonded compounds.
Compound 5 was synthesized via treatment of 4-amino-2,6-
dimethylaminopyrimidine with one equiv. of BunLi followed by
reaction with Ph3GeCl and was isolated in 83% yield (Scheme 2).
The 1H NMR spectrum of 5 exhibits resonances at
d 5.56, 4.21, 2.36,
and 2.12 ppm corresponding to the ortho-aromatic proton, the
amide proton, the protons of the 6-methyl group, and the protons
of the 2-methyl group (respectively). The resonances for the
aromatic and amide protons are shifted significantly upfield from
those in the free ligand (d 6.10 and 5.29 ppm, respectively), once
again due to the attachment of the nitrogen atom to germanium.
An ORTEP diagram of 5 is shown in Fig. 2 and selected bond
distances and angles are collected in Table 2. The average GeeCipso
bond distance is 1.944(1) Å, the average CipsoeGeeCipso bond angle
is 111.15(5)ꢀ, and the average CipsoeGeeN bond angle is 107.66(5)ꢀ,
indicating a distorted tetrahedral environment at germanium that
is similar to that observed in 4. The GeeN bond distance in 5 is
1.861(1) Å and the GeeNeC bond angle is 121.79(7)ꢀ indicating that
the geometry at nitrogen is planar in 5 and is only slightly distorted
from the ideal value of 120ꢀ. The bond distances and angles within
the pyrimidine ring are nearly identical to those in the free amine 2
The presence of a base appears necessary for the interconver-
sion to take place in the case of both the free molecules and also
when these species are employed as ligands. In the aforementioned
reaction of (Ph3Ge)3GeNMe2 and Ph3GeH, the base present is
HNMe2 that is generated after the in situ conversion of (Ph3Ge)3
-
GeNMe2 to the a-germyl nitrile (Ph3Ge)3GeCH2CN [8,9]. The pKa of
dimethylamine is 10.64 [19] which is significantly less than that of
hydroxide, but it appears that HNMe2 is sufficiently basic enough to
Table 2
Selected bond distances (Å) and angles (ꢀ) for 2,6-dimethyl-4-(triphenylgermyla-
mino)pyrimidine (5).
Ge(1)eC(1)
Ge(1)eC(7)
Ge(1)eC(13)
Ge(1)eN(1)
N(1)eC(13)
N(2)eC(13)
N(2)eC(14)
N(3)eC(14)
N(3)eC(15)
C(13)eC(16)
C(14)eC(18)
C(15)eC(16)
C(15)eC(17)
1.945(1)
1.945(1)
1.943(1)
1.861(1)
1.357(1)
1.351(1)
1.336(1)
1.338(1)
1.362(1)
1.405(2)
1.505(2)
1.377(2)
1.498(2)
C(1)eGe(1)eC(7)
C(1)eGe(1)eC(19)
C(7)eGe(1)eC(19)
C(1) eGe(1)eN(1)
C(7)eGe(1)eN(1)
C(13)eGe(1)eN(1)
Ge(1)eN(1)eC(13)
N(1)eC(13)eC(16)
N(1)eC(13)eN(2)
N(2)eC(14)eN(3)
N(2)eC(13)eC(16)
N(2)eC(14)eC(18)
N(3)eC(14)eC(18)
N(3)eC(15)eC(16)
N(3)eC(15)eC(17)
C(13)eC(16)eC(15)
C(13)eN(2)eC(14)
C(14)eN(3)eC(15)
C(16)eC(15)eC(17)
113.49(5)
111.31(4)
108.66(5)
111.40(5)
102.75(4)
108.82(5)
121.79(7)
123.57(9)
115.8(1)
126.92(9)
120.66(9)
115.7(1)
117.36(9)
121.8(1)
116.5(1)
117.89(9)
116.81(9)
115.82(9)
121.7(1)
Fig. 2. ORTEP diagram of Ph3Ge[NHC4N2Me2-2,6] (5). Thermal ellipsoids are drawn at
50% probability.

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C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 3721e3726
promote the dimerization and trimerization of acetonitrile and/or
the conversion of the dimeric form to the trimeric one. In order to
investigate this postulate, we monitored the reactions of both
Ph3GeCH2CN [1] and 4 in CH3CN solvent in the presence of HNMe2
using 1H NMR spectroscopy.
group migrates such that it becomes attached to the nitrogen atom
that results from the incoming molecule of CH3CN. The conversion
of 4 to 5 is presumed to proceed via the deprotonation of the
nitrogen atom located alpha to germanium and this nucleophilic
nitrogen attacks the cyano carbon of a second CH3CN molecule.
Rearrangement of the resulting species, followed by a second attack
of nitrogen on the carbon atom of the cyano group originally
belonging to the 3-amidocrotononitrile ligand yields an imine that
undergoes a rearrangement to provide 5. This last rearrangement
also involves another migration of the Ph3Ge-group.
A sample of Ph3GeCH2CN was stirred in CH3CN solvent at 85 ꢀC
in the presence of HNMe2 and aliquots of this solution were
removed at regular intervals, the volatiles were removed in vacuo,
and the residue was taken up in C6D6. The 1H NMR spectrum of an
aliquot of Ph3GeCH2CN stirred in CH3CN solvent at 85 ꢀC for 18 h
indicated that the conversion of Ph3GeCH2CN to 4 had commenced.
Based on the integration of the signal at
sponding to the -protons of the eCH2CN ligand to that corre-
sponding to the methyl group of the 3-amidocrotononitrile ligand
of 4 at 1.78 ppm, ca. 20% of Ph3GeCH2CN had been converted to 4.
d 1.98 ppm [1] corre-
3. Conclusions
a
Previous investigations have suggested that the a-germyl nitrile
d
species R3GeCH2CN, which are generated in situ from the corre-
sponding germanium amides R3GeNMe2 in acetonitrile solvent,
can undergo further reaction with the CH3CN solvent to yield
germanes having ligands that consist of dimeric or trimeric
acetonitrile, particularly when steric crowding is present at
the active germanium site. The 3-amidocrotononitrile compound
But3Ge[NHC(CH3)]CHCN] (3) was isolated during the attempted
synthesis of But3GeGePh3 from But3GeNMe2 and Ph3GeH, [1] and
both 3-aminocrotononitrile and 2,6-dimethyl-4-aminopyrimidine
were generated during the reaction of (Ph3Ge)3GeNMe2 with
Ph3GeH [8,9]. Both of these reactions have significant steric bulk at
the amide-substituted germanium center involved in the reaction,
and presumably the presence of bulky substituents significantly
diminishes the rate of the hydrogermolysis reaction between the
germanium hydride and the
niumegermanium bond formation is not observed even after
prolonged reaction times. The -germyl nitrile is generated in situ
from the germanium amide starting material with concomitant
liberation of HNMe2, and the conversion of the germanium
bound eCH2CN ligand first to a 3-amidocrotononitrile ligand and
subsequently to the pyrimidine ligand is the only reaction that is
observed with sterically encumbered germanium reagents. The
presence of the base HNMe2 is required for this transformation to
take place.
Heating for an additional 48 h resulted in ca. 65% conversion to 4,
and after 5 days none of the Ph3GeCH2CN remained and only
signals corresponding to 4 and 5 were present. The formation of 5
was initially detected after a reaction time of 48 h, as singlets at
d
5.56, 2.36, and 2.12 ppm were clearly visible at this time in the 1H
NMR spectrum and after heating the reaction mixture at 85 ꢀC for
a total time of 9 days only the pyrimidine compound 5 was present.
In a separate experiment, compound 4 was stirred in CH3CN in
the presence of HNMe2 at 85 ꢀC and the reaction was monitored in
a similar fashion using 1H NMR spectroscopy. In this case, the initial
formation of 5 was detected after a reaction time of 6 h and
complete conversion of 4 to 5 had occurred after a reaction time of
4 days. Heating of the reaction mixture for a further 7 days did not
result in the detection of any additional reaction products indi-
cating that 5 is stable with respect to additional reaction with
CH3CN. The conversion of free CH3CN to its dimer and trimer has
been reported [18], and it also is evident that this transformation
can occur when the CH3CN is bound to a metal center, in this case
germanium, as the eCH2CN ligand.
a-germyl nitrile such that germa-
a
The proposed pathway for the conversion of Ph3GeCH2CN to 4
and the subsequent transformation of 4 to 5 is shown in Scheme 3,
which is consistent with the pathway that has been described for the
free amines and related species [20,21]. The transformation of
Ph3GeCH2CN to 4 involves an initial deprotonation at the a-carbon
of Ph3GeCH2CN, and the resulting nucleophilic site attacks the cyano
carbon of CH3CN and after rearrangement the triphenylgermyl
In light of these findings, the two germanes Ph3Ge[NHC(CH3)]
CHCN] (4) and 2,6-dimethyl-4-(triphenylgermylamino)pyrimidine
(5) have been prepared and structurally characterized, and their
Scheme 3. Proposed pathway for the formation of 4 and 5.

C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 3721e3726
3725
structures have been correlated with their NMR spectra. Using 1H
NMR spectroscopy, it has been determined that the -germyl nitrile
Melting points are uncorrected. Elemental analyses were con-
ducted by Galbraith Laboratories (Knoxville, TN).
a
Ph3GeCH2CN can be converted to both 4 and 5 in CH3CN solvent at
85 ꢀC in the presence of the base HNMe2. Furthermore, the
conversion of 4 to 5 was observed under the same reaction
conditions. These transformations are analogous to those which
have been reported for CH3CN and HNHC(CH3)]CHCN, and indi-
cate that the oligomerization of acetonitrile can also occur when
this material is bound to germanium as the eCH2CN ligand.
4.2. Synthesis of LiNHC(CH3)CHCN
To a solution of 3-aminocrotononitrile (2.00 g, 24.0 mmol) in
THF (50 mL) was added a solution of 2.8 M BunLi in hexane (4.3 mL,
12.0 mmol) via cannula. The resulting mixture was stirred at room
temperature for 2 h and the volatiles were removed in vacuo to
yield LiNHC(CH3)CHCN (1.90 g, 90%) as a dark brown oil.
4. Experimental section
4.3. Synthesis of Ph3GeNHC(CH3)CHCN (4)
4.1. General considerations
A solution of LiNHC(CH3)CHCN (0.26 g, 2.9 mmol) in THF
(20 mL) was added dropwise via cannula to a solution of Ph3GeCl
(1.00 g, 2.90 mmol) in THF (30 mL) and the resulting mixture was
stirred at room temperature for 2 h. The volatiles were subse-
quently removed in vacuo to yield a yellow solid that was dissolved
in benzene (15 mL) and filtered through Celite. The volatiles were
removed from the filtrate in vacuo to yield 4 (0.92 g, 80%) as
All manipulations of air-sensitive compounds were carried out
under an inert nitrogen atmosphere using standard Schenk,
syringe, and glovebox techniques [22]. The reagents 3-
aminocrotononitrile and 2,6-dimethyl-4-aminopyrimidine were
purchased from Acros Organics, Ph3GeCl was purchased from
Gelest, and BunLi (2.5 M in hexanes) was purchased from Aldrich.
The compound Ph3GeCH2CN was prepared according to the liter-
ature procedure [1]. The BunLi solution was titrated against
menthol using phenanthroline as an indicator prior to use and all
other reagents were used without further purification. Solvents
were dried using a Glass Contour solvent purification system. NMR
(1H and 13C) spectra were acquired using a Varian Gemini 2000
spectrometer and were referenced to residual protio solvent.
a yellow solid (m.p. 126 ꢀC). 1H NMR (C6D6, 25 ꢀC) (E)-Isomer:
d 7.55
(d, J ¼ 7.5 Hz, 6H o-C6H5), 7.27e7.15 (m, 9H, m-C6H5 and p-C6H5),
4.06 (s, 1H, C]CHCN), 3.49 (s, 1H, Ge-NH), 1.78 (s, 3H, CH3-C]C)
ppm. (Z)-Isomer:
d
7.72 (d, J ¼ 7.8 Hz, 6H o-C6H5), 7.27e7.15 (m, 9H,
m-C6H5 and p-C6H5), 3.76 (s, 1H, C]CHCN), 3.62 (s, 1H, GeeNH),
1.42 (s, 3H, CH3eC]C) ppm. 13C NMR (C6D6, 25 ꢀC) (E)-Isomer:
d
135.2 (-CN), 134.5 (ipso-C), 134.4 (o-C), 130.6 (NeC]C), 129.8
(NeC]C), 128.9 (p-C), 128.4 (m-C), 69.0 (eCH3) ppm. (Z)-Isomer:
Table 3
Crystallographic data for compounds Ph3Ge[NHC(CH3)CHCN] (4) and Ph3Ge[NHC4N2Me2-2,6] (5).
Compound
Ph3Ge[NHC(CH3)CHCN] (4)
C22H20GeN2
384.99
123(2)
0.71073
Monoclinic
P21/n
9.3073(5)
14.1217(7)
14.7323(8)
90
105.876(1)
90
1862.5(2)
4
2,6-dimethyl-4-(triphenylgermylamino)pyrimidine (5)
C24H23GeN3
426.04
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a, Å
123(2)
0.71073
Monoclinic
P21/c
9.3920(4)
17.6290(8)
12.8811(6)
90
92.118(2)
90
2131.3(2)
4
b, Å
c, Å
ꢀ
ꢀ
ꢀ
a
,
b
,
g
,
V, Å3
Z
r
(g cmꢁ1
)
1.373
1.650
792
1.328
1.451
880
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
0.40 ꢂ 0.35 ꢂ 0.20
0.38 ꢂ 0.30 ꢂ 0.20
Theta range for data collection
Index ranges
2.04e25.43ꢀ
1.96e33.53ꢀ
ꢁ10 ꢃ h ꢃ 11
ꢁ17 ꢃ k ꢃ 12
ꢁ17 ꢃ l ꢃ 17
12823
ꢁ14 ꢃ h ꢃ 14
ꢁ27 ꢃ k ꢃ 27
ꢁ19 ꢃ l ꢃ 20
54525
Reflections collected
Independent reflections
3432 (Rint ¼ 0.0294)
8344 (Rint ¼ 0.0443)
Completeness to
q
q
¼ 25.00 (100.0%)
q
¼ 25.00 (100.0%)
Absorption correction
Max. and Min. transmission
Refinement method
Multi-scan
Multi-scan
0.686 and 0.818
Full-matrix least-squares on F2
3432/0/231
0.7602 and 0.6087
Full-matrix least-squares on F2
8344/0/259
Data/restraints/parameters
Goodness-of-fit on F2
1.053
1.051
Final R indices (I < 2s(I))
R1
wR2
0.0230
0.0600
0.0279
0.0695
Final R indices (all data)
R1
0.0253
0.0349
wR2
0.0612
0.465 and e0.299
831179
0.0730
Largest diff. peak and hole (e Åꢁ3
CCDC Deposition Number
)
0.523 and ꢁ0.465
831180

3726
C.R. Samanamu et al. / Journal of Organometallic Chemistry 696 (2011) 3721e3726
d
134.8 (eCN), 134.5 (ipso-C), 134.4 (o-C), 130.4 (NeC]C), 129.1
4.8. X-ray crystal structure analysis
(NeC]C), 128.9 (p-C), 128.4 (m-C), 67.8 (-CH3) ppm. Anal. Calcd. for
C22H20GeN2: C, 68.61; H, 5.24. Found: C, 68.24; H, 4.90.
X-ray crystallographic measurements for 4 and 5 were made
using a Bruker APEX CCD system under a stream of nitrogen gas.
Data were corrected for absorption using SADABS and the struc-
tures were solved using direct methods (SIR-2004). All non-
hydrogen atoms were refined anisotropically by full-matrix least
squares (SHELXL-97). Data were corrected from absorption using
SADABS and all non-hydrogen atoms were refined using full-matrix
least squares (SHELXL-2008). Crystallographic data for 4 and 5 are
collected in Table 3. The CCDC deposition numbers shown in Table 3
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.ac.uk/data_request/cif
4.4. Synthesis of LiNHC4N2Me2-2,6
To
a solution of 2,6-dimethyl-4-aminopyrimidine (1.00 g,
9.20 mmol) in THF (50 mL) was added a solution of 2.8 M BunLi in
hexane (3.3 mL, 9.2 mmol) via cannula. A yellow precipitate
immediately formed which redissolved after vigorous stirring. The
solution was stirred at room temperature for 2 h and the volatiles
were removed in vacuo to yield LiNHC4N2Me2-2,6 (1.00 g, 95%) as
a yellow solid.
4.5. Synthesis of 2,6-dimethyl-4-(triphenylgermylamino)
pyrimidine (5)
Acknowledgment
A solution of LiNHC4N2Me2-2,6 (0.400 g, 3.5 mmol) inTHF (20 mL)
was added dropwise via cannula to a solution of Ph3GeCl (1.00 g,
2.9 mmol) in THF (30 mL). The solution was stirred at room
temperature for 2 h and the volatiles were removed in vacuo. The
resulting yellow solid was dissolved in benzene (15 mL) and filtered
through Celite. The volatiles were removed from the filtrate in vacuo
to yield Ph3Ge[NHC4N2Me2-2,6] (5) (1.20 g, 83%) as a yellow solid
Funding for this work was provided by a CAREER award from the
National Science Foundation (No. CHE-0844758) and is gratefully
acknowledged.
References
(m.p. 178 ꢀC). 1H NMR (C6D6, 25 ꢀC)
d
7.68 (d, J ¼ 7.7 Hz, 6H, o-C6H5),
7.15e7.12 (m, 9H, p-C6H5 and m-C6H5), 5.56 (s, 1H, C4N2H(CH3)2-2,6),
4.21 (s, 1H, Ge-NH), 2.36 (s, 3H, C4N2H(CH3)2-2,6), 2.11 (s, 3H,
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