Synthesis and structure of N-heterocyclic carbene complexes of germanium(II)

Article abstract of DOI:10.1021/om800368d

The synthesis and structural characterization of a series of N-heterocyclic carbene (NHC) complexes of GeR₁R₂ are reported, where R₁ = R₂ = Mes (Mes = 2,4,6-trimethylphenyl) (1), R ₁ = R₂ = F (5), R₁ = R₂ = Br (6), R₁ = Cl, R₂ = OTf (OTf = O₃SCF₃) (7), R₁ = R₂ = O^tBu (10), and R₁ = R₂ = NCS (11). The bond length between the carbenic carbon and the germanium is observed to vary in accordance with the π-donating ability of the substituent on Ge. Efforts to synthesize stable complexes with small alkyl or aryl substituents were not successful; evidence for oligomerization of the GeR₂ fragment is presented. The reaction between 1 and 3 (R ₁ = R₂ = Cl) resulted in the formation of an NHC-coordinated germylgermylene (13). The ¹H NMR spectra of 3-7,10, and 11 display broad signals at room temperature. To rationalize the ¹H NMR spectra, mechanisms for conformational interchange, as well as intermolecular exchanges, are discussed.

Full text of DOI:10.1021/om800368d

Organometallics 2008, 27, 5043–5051
5043
Synthesis and Structure of N-Heterocyclic Carbene Complexes of
Germanium(II)
Paul A. Rupar, Michael C. Jennings, and Kim M. Baines*
Department of Chemistry, The UniVersity of Western Ontario, London, Ontario, N6A 5B7, Canada
ReceiVed April 27, 2008
The synthesis and structural characterization of a series of N-heterocyclic carbene (NHC) complexes
of GeR1R2 are reported, where R1 ) R2 ) Mes (Mes ) 2,4,6-trimethylphenyl) (1), R1 ) R2 ) F (5), R1
) R2 ) Br (6), R1 ) Cl, R2 ) OTf (OTf ) O3SCF3) (7), R1 ) R2 ) OtBu (10), and R1 ) R2 ) NCS
(11). The bond length between the carbenic carbon and the germanium is observed to vary in accordance
with the π-donating ability of the substituent on Ge. Efforts to synthesize stable complexes with small
alkyl or aryl substituents were not successful; evidence for oligomerization of the GeR2 fragment is
presented. The reaction between 1 and 3 (R1 ) R2 ) Cl) resulted in the formation of an NHC-coordinated
germylgermylene (13). The 1H NMR spectra of 3-7, 10, and 11 display broad signals at room temperature.
To rationalize the 1H NMR spectra, mechanisms for conformational interchange, as well as intermolecular
exchanges, are discussed.
Scheme 1
Introduction
GeCl2 · dioxane, first synthesized in the mid 1960s by Nefedov
and co-workers,1 is a rare example of an intermolecularly
stabilized germylene. Since the solid can be briefly handled
under aerobic conditions and the ligand is readily displaced,
this complex has proven to be extremely useful for the synthesis
of a variety of germanium(II) and germanium(IV) compounds.2,3
Stabilization of the dichlorogermylene is achieved by the
intermolecular donation of electron density from the Lewis base,
* Corresponding author. E-mail: kbaines2@uwo.ca.
(1) Kolesnikov, S. P.; Shiryaev, V. I.; Nefedov, O. M. IzV. Akad. Nauk
SSSR, Ser. Khim. 1966, 584.
(2) (a) Neumann, W. P. Chem. ReV. 1991, 91, 311. (b) Barrau, J.; Rima,
G. Coord. Chem. ReV. 1998, 178-180, 593. (c) Weidenbruch, M. Eur.
J. Inorg. Chem. 1999, 373. (d) Satge´, J. Chem. Heterocycl. Compd. 1999,
35, 1013. (e) Boganov, S. E.; Faustov, V. I.; Egorov, M. P.; Nefedov, O. M.
Russ. Chem. Bull., Int. Ed. 2004, 53, 960. (f) Zemlyanskii, N. N.; Borisova,
I. V.; Nechaev, M. S.; Khrustalev, V. N.; Lunin, V. V.; Antipin, M. Y.;
Ustynyuk, Y. A. Russ. Chem. Bull., Int. Ed. 2004, 53, 980. (g) Ku¨hl, O.
Coord. Chem. ReV. 2004, 248, 411. (h) Leung, W. P.; Kan, K. W.; Chong,
K. H. Coord. Chem. ReV. 2007, 251, 2253. (i) Weinert, C. S. In
ComprehensiVe Organometallic Chemistry III Vol. 3; Mingos, D. M. P.,
Crabtree, R. H., Housecroft, C. E., Eds.; Elsevier: Oxford, 2007; pp 699-
808. (j) Saur, I.; Alonso, S. G.; Barrau, J. Appl. Organomet. Chem. 2005,
19, 414. (k) Nagendran, S.; Roesky, H. Organometallics 2008, 27, 457.
(3) (a) Cissell, J. A.; Vaid, T. P.; DiPasquale, A. G.; Rheingold, A. L.
Inorg. Chem. 2007, 46, 7713. (b) Cissell, J. A.; Vaid, T. P.; DiPasquale,
A. G.; Rheingold, A. L. J. Am. Chem. Soc. 2007, 129, 7841. (c) Lee, V. Y.;
Takanashi, K.; Kato, R.; Matsuno, T.; Ichinohe, M.; Sekiguchi, A. J.
Organomet. Chem. 2007, 692, 2800. (d) Segmueller, T.; Schlueter, P. A.;
Drees, M.; Schier, A.; Nogai, S.; Mitzel, N. W.; Strassner, T.; Karsch, H. H.
J. Organomet. Chem. 2007, 692, 2789. (e) Zabula, A. V.; Hahn, F. E.;
Pape, T.; Hepp, A. Organometallics 2007, 26, 1972. (f) Hahn, F. E.; Zabula,
A. V.; Pape, T.; Hepp, A. Eur. J. Inorg. Chem. 2007, 2405. (g) Gushwa,
A. F.; Richards, A. F. J. Chem. Cryst. 2006, 36, 851. (h) Fedushkin, I. L.;
Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2006, 3266. (i) Eichler,
J. F.; Just, O.; Rees, W. S., Jr. Inorg. Chem. 2006, 45, 6706. (j) Pampuch,
B.; Saak, W.; Weidenbruch, M. J. Organomet. Chem. 2006, 691, 3540. (k)
Fedushkin, I. L.; Khvoinova, N. M.; Baurin, A. Yu.; Chudakova, V. A.;
Skatova, A. A.; Cherkasov, V. K.; Fukin, G. K.; Baranov, E. V. Russ. Chem.
Bull. 2006, 55, 74. (l) West, R.; Moser, D. F.; Guzei, I. A.; Lee, G.; Naka,
A.; Li, W.; Zabula, A.; Bukalov, S.; Leites, L. Organometallics 2006, 25,
2709. (m) Leung, W.; Wong, K.; Wang, Z.; Mak, T. C. W. Organometallics
2006, 25, 2037. (n) Schoepper, A.; Saak, W.; Weidenbruch, M. J.
Organomet. Chem. 2006, 691, 809. (o) Stanciu, C.; Richards, A. F.; Stender,
M.; Olmstead, M. M.; Power, P. P. Polyhedron 2006, 25, 477.
1,4-dioxane, into the empty p-orbital on germanium. Evidently,
a relatively weak donor is sufficient to produce a stable complex
because of the inherent stability of the dichlorogermylene.2
Despite the obvious usefulness of GeCl2 · dioxane, it is some-
what surprising that the chemistry of stable intermolecular
complexes of transient Ge(II) compounds is relatively unexplored.
Recently we reported the synthesis of 1 from the reaction of
tetramesityldigermene4 with carbene 25 (Scheme 1); 1 was the
first example of a transient diorganogermylene stabilized
intermolecularly by an N-heterocyclic carbene (NHC).6-8 The
use of a strong σ-donor was key for stabilization as, in general,
intermolecular complexes of simple diarylgermylenes exist only
as transient intermediates.9 Although occupation of the p-orbital
(4) Hurni, K. L.; Rupar, P. A.; Payne, N. C.; Baines, K. M. Organo-
metallics 2007, 26, 5569.
(5) Kuhn, N.; Kratz, T. Synthesis 1993, 561.
(6) Rupar, P. A.; Jennings, M. C.; Ragogna, P. J.; Baines, K. M.
Organometallics 2007, 26, 4109.
(7) For a recent review on main group carbene complexes, see: Kuhn,
N.; Al-Sheikh, A. Coord. Chem. ReV. 2005, 249, 829.
(8) Rupar, P. A.; Jennings, M. C.; Baines, K. M. Can. J. Chem. 2007,
85, 141.
(9) (a) Leigh, W. J.; Lollmahomed, F.; Harrington, C. R.; McDonald,
J. M. Organometallics 2006, 25, 5424. (b) Huck, L. A.; Leigh, W. J.
Organometallics 2007, 26, 1339.
10.1021/om800368d CCC: $40.75
2008 American Chemical Society
Publication on Web 09/11/2008

5044 Organometallics, Vol. 27, No. 19, 2008
Rupar et al.
Chart 1
Scheme 2
on Ge by the carbene lone pair is clearly necessary for the
stabilization of 1, steric shielding provided by the mesityl groups
most likely also plays a role. Compound 1 is stable indefinitely
under an inert atmosphere at room temperature. However, by
reaction with a strong nucleophile, such as MeLi, at room
temperature or by heating 1 in the presence of a good germylene
trap, such as dimethylbutadiene, the ability of compound 1 to
act as a masked germylene was demonstrated (Scheme 1).
We have also synthesized the NHC-complexed dichloro- and
diiodogermylenes 3 and 4 (Chart 1) with the expectation that
these compounds could be utilized as precursors for the synthesis
of other base-stabilized germanium(II) compounds and related
species. Indeed, we were able to synthesize a germanium-
centered dication by reaction of the diiodo derivative 4 with 2
equiv of an N-heterocyclic carbene.10
In this paper, we now describe the synthesis and structural
characterization of a number of NHC-stabilized Ge(II) com-
pounds derived from the dichloro derivative 3. Our goal is to
produce versatile reagents for the facile delivery of synthetically
useful germylenes. In a subsequent paper, we will report on
the reactivity of the complexes described herein and their ability
to act as germylene equivalents.
manium atoms of opposing molecules in the unit cell of 6 are
within the sum of their van der Waals radii (4.30 Å)13 at 3.67
Å. This value greatly exceeds the bond length of a Ge-Ge single
bond (typical range 2.41-2.46 Å)14 and is, most likely, a
consequence of crystal packing rather than any meaningful
bonding interaction.
Since a triflate-germanium bond (triflate ) OTf ) O3SCF3)
is expected to ionize quite readily, and thus, be synthetically
useful, we attempted to make the ditriflate derivative. Addition
of Me3SiOTf to 3, followed by removal of the solvent, yielded
1
Results and Discussion
a white powder (Scheme 2, eq 3). The H NMR spectrum of
the white powder was, predictably, similar to that of 3, while
the 19F NMR spectrum of the solid showed a signal whose
chemical shift was consistent with a triflate moiety. Surprisingly,
a signal attributable to a Ge-Cl bond stretch at 315 cm-1 was
apparent in the FT-Raman spectrum of the powder. Crystals of
the product were obtained; single-crystal X-ray diffraction
confirmed the formation of 7, an NHC-germylene complex with
both a chloride and a triflate substituent present on the
The dichloro (3) and diiodo (4) N-heterocyclic carbene-
germylene derivatives have been previously synthesized and
characterized.10 To complete the halogen series, the difluoro
and dibromo analogues were also synthesized. Reaction of 3
with excess potassium fluoride and a catalytic amount of 18-
crown-6 resulted in the formation of the difluoro-substituted
derivative 5, while the addition of excess Me3SiBr to 3 resulted
in the formation of the dibromo analogue 6 (Scheme 2, eqs 1
and 2). The chemical shifts of the signals in the 1H NMR spectra
of the halogen derivatives 3-6 are very similar and, thus, are
not very diagnostic. However, the four compounds, 3-6, can
be easily differentiated on the basis of the wavenumber for the
Ge-X stretching vibration observed by FT-Raman spectroscopy
(F ) 530 cm-1, Cl ) 316 cm-1, Br ) 232 cm-1, I ) 205
cm-1).11
The structures of 5 and 6 were verified by single-crystal X-ray
diffraction. The compounds are isomorphous to one another and
to 3 and 4.10 Only the structure of 6 is presented (Figure 1).
One other NHC dihalogermylene complex has been structurally
characterized, a diiodo derivative with a bulkier NHC (mesityl
groups on nitrogen and unsubstituted at the alkenyl carbons);
this complex was found to have similar metrics.12 In general,
the halide derivatives are monomeric in the solid state, showing
no significant intermolecular interactions. However, the ger-
Figure 1. Thermal ellipsoid plot (50% probability surface) of 6.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg) for compound 6: C(1)-Ge ) 2.089(5), Ge-Br(1)
) 2.4514(9), Ge-Br(2) ) 2.4572(8), Br(1)-Ge-Br(2) ) 99.67(3),
Br(1)-Ge-C(1) ) 94.78(14), Br(2)-Ge-C(1) ) 95.73(14).
Selected bond lengths (Å) and angles (deg) for compound 5:
C(1)-Ge ) 2.117(7), Ge-F(1) ) 1.829(5), Ge-F(2) ) 1.829(5),
F(1)-Ge-F(2) ) 95.1(3), F(1)-Ge-C(1) ) 91.2(3), F(2)-Ge-C(1)
) 94.6(3).
(10) Rupar, P. A.; Staroverov, V. N.; Ragogna, P. J.; Baines, K. M.
J. Am. Chem. Soc. 2007, 129, 15138.
(11) Boganov, S. E.; Egorov, M. P.; Faustov, V. I.; Nefedov, O. M. In
The Chemistry of Organic Germanium, Tin and Lead Compounds, Vol. 2;
Rappoport, Z., Ed.; John Wiley & Sons Ltd.: West Sussex, England, 2002;
pp 749-841.
(12) Arduengo, A. J., III; Dias, H. V. R.; Calabrese, J. C.; Davidson, F.
Inorg. Chem. 1993, 32, 1541.

N-Heterocyclic Carbene Complexes of Germanium(II)
Organometallics, Vol. 27, No. 19, 2008 5045
interaction between the two fragments was observed both in
solution and in the solid state.16 The substituents on the nitrogen
atoms of the N-heterocyclic germylene are N-neopentyl rather
than N-tert-butyl, as in 9. The difference in the extent of
complexation with an NHC between the two germylenes is
likely due to a combination of the ring annulation, which
increases Lewis acidity of the germanium,17 and the increased
flexibility of the neopentyl group, which reduces steric bulk in
comparison to the tert-butyl group.
In general, Ge(OR)2 compounds rapidly oligomerize, which
makes isolation and characterization of such germylenes dif-
ficult.2 Even the sterically encumbered Ge(ODipp)2 (Dipp )
2,6-diisopropylphenyl) derivative forms a dimer in the solid
state.18 However, a few discrete dialkoxy19 and diaryloxy18,20-24
germylenes have been structurally characterized. An NHC could
potentially stabilize the reactive dialkoxygermylenes through
occupation of the p-orbital on the germanium and allow isolation
of monomeric molecular complexes.25 Nucleophilic substitution
of the chlorides in 3 using 2 equiv of potassium tert-butoxide
proceeded cleanly (Scheme 3, eq 5). The 1H NMR spectrum of
the white powder isolated from the reaction was consistent with
the di(tert-butoxy)-substituted carbene-germylene complex
10. The structure of the product was confirmed by X-ray
crystallography (Figure 3). Two monomeric molecules of 10
were present in the asymmetric unit. Both molecules have
identical connectivity and orientation, but differ significantly
in the carbenic carbon-Ge bond length (2.120(9) Å vs 2.224(14)
Å).
Ge(NCS)2 has been studied previously; the germylene is
stable in dilute solution but polymerizes rapidly upon isolation.26
Again, coordination of the NHC should allow isolation of a
monomeric base-stabilized Ge(NCS)2. Two equivalents of
KSCN underwent a reaction with 3 to form complex 11 as
determined by FT-Raman and X-ray crystallography (Scheme
3, eq 6). Four chemically identical but crystallographically
unique molecules of 11 are found in the asymmetric unit. Each
molecule shows the same connectivity with two N-bonded
thiocyanates attached to the germanium center (Figure 4). The
central C(1)-Ge bond lengths vary (2.105(9), 2.072(9), 2.075(10),
and 2.062(9) Å) with an average value of 2.078 Å. There are
also short intermolecular contacts between the sulfur atoms and
neighboring germanium atoms. The closest S-Ge approach is
3.61 Å, which is much longer than the length of a typical S-Ge
single bond (the average S-Ge single bond length is 2.21-2.29
Å).14 In contrast to Ge(NCS)2,26 11 is stable under an inert
Figure 2. Thermal ellipsoid plot (50% probability surface) of 7.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): C(1)-Ge ) 2.068(2), Ge-Cl ) 2.2680(6),
Ge-O(14) ) 2.0342(16), S-O(14) ) 1.4914(16), S-O(15) )
1.4273(19), S-O(16) ) 1.4914(16), C(1)-Ge-Cl ) 95.51,
C(1)-Ge-O(14) ) 89.81(8), Cl-Ge-O(14) ) 92.69(6).
germanium center (Figure 2). The triflate is covalently bound
to the germanium with a Ge-O bond length of 2.0342(16) Å
(cf. 1.75-1.85 Å for a typical Ge-O bond).14 The carbenic
carbon-germanium bond is reduced in length to 2.068(2) Å
(from 2.106(3) Å in 3), and the chlorine-germanium bond
length has decreased to 2.2680(6) Å (from an average of 2.294
Å in 3). These observations are consistent with a δ+ charge on
germanium due to the electron-withdrawing triflate group. As
observed in the solid state structure of 6, the germanium atoms
in opposing molecules of 7 are within the sum of their van der
Waals radii at 3.75 Å but, once again, far outside the distance
expected of a Ge-Ge bond (typical range 2.41-2.46 Å).14
Efforts to replace both chlorides on 3 using a large excess of
Me3SiOTf were not successful; only 7 was isolated. Attempts
to use AgOTf to facilitate chloride/triflate metathesis also failed;
complex mixtures were formed and no single compound could
be identified.
Unlike most Ge(II) compounds, many N-heterocyclic ger-
mylenes are indefinitely stable due to partial occupation of the
empty p-orbital on germanium by the nitrogen lone pair of
electrons.2g,3e,f This partial occupation makes N-heterocyclic
germylenes less Lewis acidic, and as a result, it was expected
that the strength of a coordination complex with 2 would be
weakened. Indeed, the addition of the dilithium salt 8 to a
solution of 3 resulted in the formation of two compounds: free
carbene 2 and N-heterocyclic germylene 915 (Scheme 3, eq 4).
Complete dissociation of the carbene was confirmed by NMR
spectroscopy: the 1H NMR chemical shifts of the signals in the
reaction mixture are identical to an independently prepared
solution of 3 and 9 and to the chemical shifts of the signals in
(16) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Dalton
Trans. 2000, 3094.
(17) Ku¨hl, O.; Lifson, K.; Langel, W. Eur. J. Org. Chem. 2006, 2336.
(18) Weinert, C. S.; Fenwick, A. E.; Fanwick, P. E.; Rothwell, I. P.
J. Chem. Soc., Dalton Trans. 2003, 532.
(19) Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Smith, S. J.; Thorne,
A. J. J. Chem. Soc., Chem. Commun. 1985, 939.
(20) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. J. Chem. Soc., Dalton
Trans. 2002, 2948.
(21) 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.
(22) Barrau, J.; Rima, G.; El Amraoui, T. Organometallics 1998, 17,
607.
(23) Barrau, J.; Rima, G.; El Amraoui, T. J. Organomet. Chem. 1998,
570, 163.
(24) Gerung, H.; Boyle, T. J.; Tribby, L. J.; Bunge, S. D.; Brinker, C. J.;
Han, S. M. J. Am. Chem. Soc. 2006, 128, 5244.
(25) Using an intermolecular coordinating donor to stabilize a Ge(OR)2
species has been previously reported. For example, Ge(OMes)2 forms a
monomer when coordinated by an amine. See: Bonnefille, E.; Mazie`res,
S.; El Hawi, N.; Gornitzka, H.; Couret, C. J. Organomet. Chem. 2006, 691,
5619.
(26) Onyszchuk, M.; Castel, A.; Rivie`re, P.; Satge´, J. J. Organomet.
Chem. 1986, 317, C35.
1
the H NMR spectra of the isolated compounds. In addition,
the 13C NMR spectrum of the reaction mixture showed a signal
at 207 ppm, attributed to the carbenic carbon, which is identical
to the 13C chemical shift of the carbenic carbon in a pure sample
of 2.5 The reaction between an annulated NHC with an annulated
N-heterocyclic germylene has been examined; a weak bonding
(13) Chauvin, R. J. Phys. Chem. 1992, 96, 9194.
(14) Baines, K. M.; Stibbs, W. G. Coord. Chem. ReV. 1995, 145, 157.
(15) N-heterocyclic germylene 9 has been reported previously. See:
Hermann, W. A.; Denk, M.; Behm, J.; Scherer, W.; Klingan, F.; Bock, H.;
Solouki, B.; Wagner, M. Angew. Chem., Int. Ed. Engl. 1992, 31, 1485.

5046 Organometallics, Vol. 27, No. 19, 2008
Rupar et al.
Scheme 3
atmosphere both in the solid state or in solution. Both Ge(NCS)2
and 11 show Ge-N connectivity rather than Ge-S connectivity,
which indicates that Ge(II) has a preference for the harder
nitrogen atom over the softer sulfur atom. Only one other
structurally characterized thiocyanato germanium compound, a
tetraazacyclotetradecine Ge(IV) complex, is known; this com-
pound also shows a preference for Ge-N bonding.27
Simple dialkylgermylenes are extremely reactive intermedi-
ates and cannot be isolated under standard conditions.2 Experi-
mental evidence suggests that transient dialkylgermylenes form
reversible donor-acceptor complexes with Lewis bases in
Figure 4. Thermal ellipsoid plot (50% probability surface) of 11.
Only one of the four molecules from the asymmetric unit is shown.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): C(1)-Ge ) 2.105(9), Ge(1)-N(14) ) 1.983(8),
Ge(1)-N(17) ) 1.998(9), N(14)-C(15) ) 1.146(11), N(17)-C(18)
) 1.207(13), N(14)-Ge(1)-N(17) ) 89.7(4), N(14)-Ge(1)-C(1)
) 93.1(4), N(17)-Ge(1)-C(1) ) 90.0(4).
Figure 3. Thermal ellipsoid plot (50% probability surface) of 10.
Only one of the two molecules in the asymmetric unit is shown.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): C(1)-Ge ) 2.120(9), O(1)-Ge(1) ) 1.874(5),
O(1)-Ge(1)-O(1a) ) 95.4(4), O(1)-Ge(1)-C(1) ) 89.5(2).

N-Heterocyclic Carbene Complexes of Germanium(II)
Organometallics, Vol. 27, No. 19, 2008 5047
A carbene-germanium(II) complex with both a mesityl and
a chloro substituent would be useful in the synthesis of NHC-
coordinated heteroleptic germylenes. Intermolecular ligand
redistributions between germanium(II) compounds are known
to occur between aryl and chloro substituents,31 and therefore,
compounds 1 and 3 were dissolved in THF to determine if
1
exchange would occur (Scheme 4). The H NMR spectrum of
the mixture was complex. Signals attributable to unreacted 1
were observed in addition to signals consistent with several
compounds containing mesityl and carbene fragments. The
formation of a thin metallic film, presumably elemental ger-
manium, on the wall of the reaction vessel was also observed.
A white powder precipitated upon addition of pentane to a C6H6
1
solution of the crude products. The H NMR spectrum of the
precipitate showed signals consistent with two nonequivalent
mesityl groups in a 1:1 ratio and a carbene moiety. Crystals
were grown and the structure was determined by X-ray
crystallography to be germylgermylene 13 (Figure 6). The
compound contains two germanium atoms: a three-coordinate
Ge with a vacant coordination site that is presumably occupied
by a lone pair of electrons, and a coordinately saturated Ge.
Compound 13 is a rare example of a donor-stabilized ger-
mylgermylene; such compounds are important intermediates in
a number of reactions involving germanium. Few have been
directly observed and structurally characterized.32,33
In the reaction producing 13, compounds 1 and 3 are
combined in an equal molar ratio; however, the 1H NMR
spectrum of the crude reaction mixture showed signals attribut-
able to unreacted 1. The low isolated yield of 13 (25%) and the
complex product mixture indicates that other products are
formed under the reaction conditions. The formation of a
metallic film implies that redox chemistry is occurring. Unfor-
tunately, efforts to identify other reaction products were
unsuccessful. The reduction of main group compounds by NHCs
has been reported. The reduction appears to be driven by the
formal elimination of X2 (X ) halogen) from the main group
element.34
Figure 5. Thermal ellipsoid plot (50% probability surface) of 12.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ge(1)-Ge(1A) ) 2.4587(7), Ge(1)-Ge(2) )
2.4632(5), Ge(2)-Ge(2A) ) 2.4555(7), Ge(1A)-Ge(1)-Ge(2) )
88.987(11), Ge(2A)-Ge(2)-Ge(1) ) 89.061(11).
solution.2 NHCs are among the strongest known neutral Lewis
bases and, therefore, should form strong coordination complexes
with dialkylgermylenes. Indeed, the isolation of 1 demonstrated
that an unstable diarylgermylene can be isolated using NHC
complexation. We attempted to form NHC complexes of GeR2
(where R ) small alkyl) by the reaction of 3 with alkyl Grignard
or lithium reagents. Invariably, and independent of reaction
conditions, only complex mixtures were formed.28 Broad signals
in the 1H NMR spectra of the crude reaction mixture suggested
that some polymeric material may be formed.
In addition to dialkyl complexes, the synthesis of other
diaryl systems was also attempted. The reaction of Tol2Mg
with 3 gave 12 as the only isolated tolyl-containing product
(Scheme 3, eq 7). The cyclotetragermane likely results from
the oligomerization of four Ge(Tol)2 fragments. Broad signals
1
attributable to tolyl groups in the H NMR spectra of the
crude reaction mixture suggest that larger oligomers are also
formed. The identity of 12 was confirmed by 1H NMR
spectroscopy and X-ray crystallography (Figure 5).29 The
Grignard reagent Mes2Mg,30 reacted with 3 to produce
complex 1 and, thus, provides an alternate route to 1 that
does not require the use of tetramesityldigermene4 as a
starting material (Scheme 3, eq 8). The reaction proceeds
slowly, taking three days at room temperature to complete.
The results from the attempted substitution reactions with
organometallic reagents demonstrate that nucleophilic displace-
ment of the chlorides from 3 is possible, but the NHC-
diorganogermylene products are apparently unstable under the
reaction conditions. In addition to coordination of a strong Lewis
base, steric protection of the germanium center must be
necessary for the isolation of complexed diorganogermylenes.
By virtue of its isolation and characterization, compound 1 meets
these requirements.
The formation of 13 was unexpected and arises, presumably,
by the insertion of a molecule of 1 into the Ge-Cl bond of a
molecule of 3, with concomitant loss of a carbene. Germylenes
are known to readily insert into many different types of bonds.2
The formation of 12 and 13 provides some insight into why
our attempts to synthesize carbene-germylene complexes with
smaller aryl or alkyl groups on germanium failed. Presumably,
the insertion reactions are more facile with smaller R groups
on Ge, and thus, oligomerization occurs during the attempted
syntheses of carbene-stabilized GeR2 complexes.
Secondary insertion reactions do not appear to be taking place
during the synthesis of compounds 4-7, 10, and 11, all of which
(31) Richards, A. F.; Brynda, M.; Power, P. P. J. Chem. Soc., Chem.
Commun. 2004, 1592.
(32) Power, P. P. In Modern Aspects of Main Group Chemistry; Lattman,
M., Kemp, R. A., Eds.; American Chemical Society: Washington, DC, 2006;
pp 179-191.
(33) (a) Richards, A. F.; Phillips, A. D.; Olmstead, M. M.; Power, P. P.
J. Am. Chem. Soc. 2003, 125, 3204. (b) Fukaya, N.; Sekiyama, H.; Ichinohe,
M.; Sekiguchi, A. Chem. Lett. 2002, 802. (c) Fukaya, N.; Ichinohe, M.;
Kabe, Y.; Sekiguchi, A. Organometallics 2001, 20, 3364. (d) Setaka, W.;
Sakamoto, K.; Kira, M.; Power, P. P. Organometallics 2001, 20, 4460. (e)
Baines, K. M.; Cooke, J. A.; Vittal, J. J. J. Chem. Soc., Chem. Commun.
1992, 1484. (f) Fujdala, K. L.; Gracey, D. W. K.; Wong, E. F.; Baines,
K. M. Can. J. Chem. 2002, 80, 1387. (g) Dixon, C. E.; Netherton, M. R.;
Baines, K. M. J. Am. Chem. Soc. 1998, 120, 10365. (h) Dixon, C. E.; Liu,
H. W.; VanderKant, C. M.; Baines, K. M. Organometallics 1996, 15, 5701.
(34) (a) Ellis, B. D.; Dyker, C. A.; Decken, A.; Macdonald, C. L. B.
Chem. Commun. 2005, 1965. (b) Dutton, J. L.; Tabeshi, R.; Jennings, M. C.;
Lough, A. J.; Ragogna, P. J. Inorg. Chem. 2007, 46, 8594.
(27) Shen, X.; Sakata, K.; Hashimoto, M. Polyhedron 2002, 21, 969.
(28) Substitution reactions with all of the dihalo derivatives 3-6 were
attempted and gave similar results.
(29) For examples of other R8Ge4 ring systems, see: Ando, W.;
Tsumuraya, T. J. Chem. Soc., Chem. Commun. 1987, 1514.
(30) For the preparation of the mesityl Grignard reagent, the Schlenk
equilibrium was driven toward Mes2Mg by the precipitation of
MgBr2 · dioxane. The addition of this Grignard reagent to 3 resulted in a
higher yield for the formation of 1 in comparison to the addition of
MesMgBr. See: Cannon, K. C.; Krow, G. R. In Handbook of Grignard
Reagents; Silverman, G. S., Rakita, P. E., Eds; Marcel Dekker: New York,
1996.

5048 Organometallics, Vol. 27, No. 19, 2008
Rupar et al.
Scheme 4
Table 1. Comparison of the Structural Parameters of NHC-GeR2 Complexes
NHC-Ge-R angle
(deg)a
compound
substitution
bond length (Å)
R-Ge-R angle (deg)
ref
9
10
diazabutadiene
(OtBu)2
n/a
n/a
n/a
89.5, 94.3
av 91.9
15, this work
this work
2.120(9), 2.224(14)
av 2.172
95.4(4), 89.4(3)
av 92.4
5
3
F2
Cl2
2.117(7)
2.106(3)
95.1(3)
97.82(3)
92.9
94.7
this work
10
6
4
11
Br2
I2
(NCS)2
2.089(5)
2.086(3)
99.67(3)
95.1
97.5
this work
10
this work
99.865(17)
89.7(4), 91.6(3), 90.6(3), 90.6(3)
av 90.6
112.61(9)
92.69(5)
2.105(9), 2.062(9), 2.075(10), 2.072(9)
91.6, 92.7, 91.4, 91.3
av 2.079
2.078(3)
2.068(2)
av 91.8
102.6
92.7
1
7
Mes2
Cl, OTf
6
this work
a Each entry is the average of two NHC-Ge-R angles on a given germanium atom.
have electron-withdrawing substituents bonded to germanium.
Electron-withdrawing groups, which stabilize the germanium
electron lone pair, appear to inhibit further reaction chemistry.
Structural Comparisons. The NHC-germylene complexes
described in this work have similar solid state structures with
metrics consistent with Ge(II) donor/acceptor complexes. The
R-Ge-R bond angles are approximately 90°; the planes of the
carbenic rings are orthogonal to the R-Ge-R planes and bisect
the other substituents on the germanium atoms (Table 1). The
metrics of compound 1 differ slightly from the metrics of the
other complexes: the angles around germanium are more obtuse,
which is likely due to the steric bulk of the mesityl substituents.
Ola´h et al. have recently examined the nature of Lewis
acid-base interactions of silicon(II) or germanium(II) com-
pounds with the neutral donors NH3, PH3, and AsH3.35 In
general, π-donating substituents on the heavy group 14 element
reduce the interaction energy between the substituted germylene
and a donor presumably by transferring electron density into
the empty p-orbital. For germanium, interaction energies
decrease in the following order: (forms energetically most
favorable complex) GeH2, > GeHCH3 > GeCl2 ≈ GeF2 >
Ge(OH)2 > Ge(NH2)2 (forms least energetically favorable
complex).35
A trend in the variation of the carbenic C-Ge bond length
with respect to the π-donating ability of atoms located on
germanium was observed in compounds 1, 3-7, 11, and 12.
This is best illustrated by comparing the metrics of 1 (Mes-
substituted) with 5 (F-substituted). On the basis of steric
arguments and the electronegativity of the substituents, 5 may
be expected to have the shortest C(1)-Ge bond length since
fluorine has a very small atomic radius and is more electron-
withdrawing than mesityl. Instead, 5 was observed to have one
of the longest carbenic C(1)-Ge bond lengths, while 1 has one
of the shortest (Table 1). This observation is consistent with
Ola´h et al.’s findings:35 the lone pairs of electrons on fluorine
donate electron density into the σ*-orbital of the carbenic
carbon-germanium bond, and consequently, the bond length
between C(1) and Ge is elongated compared to the other
compounds. In contrast, the π-electrons of the mesityl substit-
uents are relatively poor electron donors and the carbenic
carbon-germanium bond is one of the shortest in the series.
Further evidence for the weakening of the carbene C(1)-Ge
bond by competing π-donation is apparent in the formation of
9, where the strong electron-donating ability of the two nitrogen
substituents on germanium provides enough electron density
to the p-orbital to completely dislodge the carbene.
Figure 6. Thermal ellipsoid plot (50% probability surface) of 13.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ge(1)-Ge(2) ) 2.5355(19), C(1)-Ge(1) )
2.147(12), Ge(2)-C(21) ) 2.017(5), Ge(2)-C(31) ) 2.013(5),
Ge(1)-Cl(1) ) 2.147(12), Ge(2)-Cl(2) ) 2.230(3), C(1)-Ge(1)-
Cl(1))101.8(3),Cl(1)-Ge(1)-Ge(2))88.6(4),Cl(2)-Ge(2)-Ge(1)
) 108.30(10), Cl(2)-Ge(2)-C(21) ) 110.8(2), Cl(2)-Ge(2)-C(31)
) 98.6(2), C(21)-Ge(2)-C(31) ) 107.4(3).
The short carbene C(1)-Ge bond in 7 can be attributed to
the electron-withdrawing triflate group. Although the germanium

N-Heterocyclic Carbene Complexes of Germanium(II)
Organometallics, Vol. 27, No. 19, 2008 5049
Figure 7. 1H NMR spectra of compound 3 focusing on the isopropyl methyne region (4.5-6.2 ppm) at 26 °C (top) and at -90 °C (bottom)
in THF-d8.
Chart 2
Intermolecular exchange between the carbene and germylene
moieties on the NMR time scale is an alternative explanation
for the line broadening of the signals in the 1H NMR spectra of
3-7, 10, and 11 at room temperature. Either dissociative or
associative exchange is possible. No reaction was observed at
room temperature when 2,3-dimethylbutadiene (DMB), a well-
known germylene trap, was added to solutions of 3-7, 10, and
11 in C6H6. Thus, the formation of free germylene in solution
is unlikely at room temperature, and the dissociative mechanism
was discarded. The possibility of associative exchange is more
atom has a potential π-donor (the chlorine), the effect of the
triflate appears to dominate.
1
Variable-Temperature 1H NMR Spectroscopy. The signals
difficult to rule out. In the H NMR spectra of 1 and 13, with
1
the bulkiest substituents at germanium, the signals are sharp,
whereas the signals in the 1H NMR spectra of compounds with
small substituents at germanium (3-7, 10, and 11) are broad.
Possibly, the compounds with small substituents undergo
associative exchange of the ligands on the NMR time scale.
However, compounds with bulky substituents are unable to
approach each other and, thus, do not undergo exchange.
observed in the room-temperature H NMR spectra of com-
pounds 3-7, 10, and 11 are broad. As expected, the signal
assigned to the vinylic methyls of the carbene is a singlet and
the signal assigned to the methyls of the isopropyl moiety is a
broadened doublet. However, the signal assigned to the methyne
1H is not the expected septet; instead, it is very broad, often
disappearing into the baseline of the spectrum.
Variable-temperature 1H NMR spectroscopy was performed
on compounds 3-7, 10, and 11; the results obtained were
similar, and thus, only the results for compound 3 will be
discussed. At -90 °C, the broad signal assigned to the methyne
1H resolved into three septets, which integrated in a 1:2:1 ratio
(Figure 7). To explain this observation, the following model is
proposed: at 26 °C, hindered rotation about the CH-N bond
Conclusions
In summary, 3 is a versatile reagent that we have used to
synthesize a series of stable N-heterocyclic carbene complexes
of germanium(II) via substitution chemistry. The goal of
stabilizing transient germylenes with an NHC was partially
successful: complexes 1, 10, 11, and 13 are all stable derivatives
of otherwise transient germylenes. NHC 2 appears to be
unsuitable for the stabilization of simple diorganogermylenes;
perhaps a more basic36 or sterically encumbered37 carbene would
allow the formation of stable Ge(II) complexes. An attempted
ligand exchange between 1 and 3 to form a complexed
heteroleptic germylene resulted in the unexpected formation of
germylgermylene 13.
The structural characterization of the carbene-germylene
complexes 3-7, 10, and 11 showed that the length of the
carbenic carbon-germanium bond is significantly influenced
by the nature of the substituents on germanium. Substituents
with an available lone pair of electrons lengthen the C(1)-Ge
bond by competing with the carbene for occupancy of the
p-orbital on germanium.
1
results in line broadening in the H NMR spectrum. At -90
°C, this rotation halts, along with rotation about the C(1)-Ge
bond, and two conformations predominate. In one conformation,
1
depicted as rotamer A in Chart 2, the methyne H’s are not
equivalent because of the orientation of the GeCl2 moiety. The
second conformation, rotamer B in Chart 2, occurs with the
GeCl2 moiety in such an orientation that the methyne 1H’s are
equivalent. The upfield region of the 1H NMR spectrum of 3 at
-90 °C showed numerous, overlapping signals consistent with
the reduced symmetry of the rotamers. All of the remaining
halogenated complexes (4, 5, and 6) showed the same behavior
1
as 3. Compound 10 also displayed three different methyne H
1
signals at low temperature in the H NMR spectrum, although
complete resolution of the septets was not achieved. For
compounds 7 and 11, the broad signals did not completely
resolve into different signals at low temperatures. Presumably,
resolution of the signals would be achieved at temperatures
lower than -90 °C. Finally, for compounds 1 and 13, rotation
about the CH-N bond appears to be have stopped at room
temperature (the methyne signal is sharp); however, rotation
about the C(1)-Ge bond has not (only one methyne signal is
observed).
Compounds 3-7, 10, and 11 display broad signals in their
room-temperature H NMR spectra. Two explanations were
1
(35) Ola´h, J.; Proft, F. D.; Veszpre´mi, T.; Geerlings, P. J. Phys. Chem.
A. 2005, 109, 1608.
(36) Nakafuji, S.; Kobayashi, J.; Kawashima, T. Angew. Chem., Int. Ed.
2008, 47, 1141.
(37) Jafarpour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet. Chem.
2000, 606, 49.

5050 Organometallics, Vol. 27, No. 19, 2008
Rupar et al.
Table 2. Crystallographic Data
6
5
7
10
empirical formula
fw
C11H20N2GeF2
290.88
C11H20N2GeBr2
412.70
C12H20N2GeClF3O3S
574.46
C19H38GeN2O2
399.10
cryst syst
space group
monoclinic
Cc
orthorhombic
Pccn
triclinic
P1
monoclinic
Pm
j
a (Å)
b (Å)
c (Å)
12.124(2)
9.830(2)
11.487(2)
90
103.38(3)
90
14.3290(4)
17.6782(3)
12.3781(5)
90
90
90
8.9383(3)
9.2138(3)
11.3287(5)
95.712(2)
105.712(2)
96.726(6)
883.50(6)
2
8.7579(6)
14.0465(11)
9.2646(6)
90
102.212(4)
90
R (deg)
ꢀ (deg)
γ (deg)
volume (Å3)
1331.8(5)
4
3135.51(16)
8
1113.92(14)
2
Z
no. of data/restraints/params
goodness-of-fit
R [I > 2σ(I)]
1877/2/152
1.068
0.0578
0.1501
0.754, -0.905
3644/0/151
1.049
0.0569
0.1668
1.420, -1.237
4047/0/214
1.070
0.0396
0.0914
0.594, -1.058
4752/2/261
1.046
0.0709
0.1997
2.725, -0.707
wR2 (all data)
largest diff peak and hole (e Å-3
)
11
12
C56H56Ge4
1019.37
monoclinic
C2/c
13
C29H42Cl2Ge2N2
634.73
monoclinic
P21/c
empirical formula
fw
cryst syst
space group
C13H20GeN4S2
369.04
triclinic
j
P1
a (Å)
b (Å)
c (Å)
10.3332(4)
19.2660(7)
19.3942(9)
105.353(2)
104.885(2)
104.763(2)
3375.2(2)
8
21.5323(8)
10.8763(3)
20.9354(5)
90
97.4440(16)
90
20.4418(6)
9.6341(2)
15.6432(4)
90
93.422(2)
90
R (deg)
ꢀ (deg)
γ (deg)
volume (Å3)
4861(3)
4
3075.25(14)
4
Z
no. of data/restraints/params
goodness-of-fit
R [I > 2σ(I)]
15 215/0/746
1.121
0.0742
0.2476
3.00, -1.842
5577/0/275
1.058
0.0424
0.1218
0.853, -1.046
5363/0/305
1.040
0.1090
0.2846
3.534, -2.359
wR2 (all data)
largest diff peak and hole (e Å-3
)
days at room temperature. After this time, a white precipitate
(presumed to be KCl) was removed by centrifugation and was
discarded. The solvent was removed under high vacuum to yield a
white powder, which was triturated with Et2O (2 mL × 2). The
white powder was dried under high vacuum to give 5 (0.15 g, 67%).
Crystals suitable for single-crystal X-ray diffraction analysis were
obtained by slow diffusion of pentane into a saturated C6H6 solution.
Mp: 103-108 °C (dec). 1H NMR (C6D6): δ 1.15 (d, 3JHH ) 7 Hz,
12 H), 1.42 (s, 6 H), 5.46 (broad, 2 H). 19F NMR: δ -112. FT-
Raman: 209 (s), 530 (m), 888 (m), 1084 (w), 1142 (w), 1286 (w),
1324 (w), 1352 (w), 1399 (m), 1458 (m), 1637 (m), 2941 (s), 2985
(s).
Synthesis of 6. To a colorless solution of 3 (1.0 mmol, 0.32 g)
in C6H6 (5 mL) was added Me3SiBr (0.52 mL, 4.0 mmol, 0.12 g).
The reaction mixture was stirred for 24 h, and then hexanes (10
mL) were added. A white precipitate was collected, triturated with
hexanes (2 mL × 2), and dried under high vacuum to give 6 (0.29
g, 71%). Crystals suitable for single-crystal X-ray diffraction
analysis were obtained by slow diffusion of pentane into a saturated
C6H6 solution. Mp: 150 °C (dec). 1H NMR (C6D6): δ 1.09 (d, 3JHH
) 7 Hz, 12 H), 1.37 (s, 6 H), 5.52 (broad, 2 H). FT-Raman (cm-1):
106 (m), 133 (w), 213 (m), 232 (s), 886 (w), 1284 (m), 1414 (m),
1443 (m), 1624 (m), 2940 (s), 2982 (m). Anal. Calcd for
C11H20N2GeBr2: C, 32.01; N, 6.79; H, 4.88. Found: C, 32.08; N,
6.42; H, 5.24.
provided for these observations: hindered rotation or an as-
sociative exchange of ligands. However, further experiments
are required to determine the basis for the line broadening in
1
the room-temperature H NMR spectra of 3-7, 10, and 11.
We are currently investigating the reactivity of these com-
plexes and their ability to act as germylene equivalents and will
report on this in due course.
Experimental Section
Reactions were performed under an inert atmosphere of nitrogen
using standard techniques. Solvents were purified according to
literature procedures38 and stored over 4 Å molecular sieves under
N2. All NMR spectra were acquired using C6D6 or THF-d8 as the
solvent. 1H NMR spectra were referenced to residual C6D5H (7.15
ppm) or the upfield THF-d7 transition (3.58 ppm). 13C spectra were
referenced to the 13C central transition (128.0 ppm) of C6D6. 19F
spectra were referenced externally to C6H5F (-113.1 ppm relative
to CFCl3). The signals in the 13C NMR spectra of the complexes
were broad at both room temperature and -90 °C, and thus, the
data are not listed. Melting points were determined under an N2
atmosphere and are uncorrected. FT-Raman spectra were acquired
on bulk samples sealed in a melting point tube under nitrogen.
Compounds 3,10 4,10 and 815 were synthesized according to
literature procedures. Mes2Mg and Tol2Mg were prepared using
modified literature procedures.30 Elemental analyses were performed
at Guelph Chemical Laboratories, Guelph, Ontario, Canada.
Synthesis of 5. To a colorless solution of 3 (0.77 mmol, 0.25 g)
in THF (4 mL) were added KF (2.0 mmol, 0.12 g) and 18-crown-
16 (0.03 mmol, 0.01 g). The reaction mixture was stirred for 2
Synthesis of 7. To a colorless solution of 3 (1.0 mmol, 0.32 g)
in C6H6 (6 mL) was added Me3SiOTf (2 mmol, 0.36 mL). The
reaction mixture was allowed to stir for 2 h, after which time the
solvent was removed under high vacuum to yield a white powder.
The powder was triturated with hexanes (3 mL × 2) and was dried
under high vacuum. The white powder was identified as 7 (0.36 g,
62%). Crystals suitable for single-crystal X-ray diffraction analysis
were grown by slow diffusion of pentane into a saturated C6H6
(38) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

N-Heterocyclic Carbene Complexes of Germanium(II)
Organometallics, Vol. 27, No. 19, 2008 5051
solution. Mp: 101-103 °C (dec). 1H NMR (C6D6): δ 1.08 (d, 3JHH
) 7 Hz, 12 H), 1.30 (s, 6 H), 5.18 (broad, 2H). 19F NMR (C6D6):
-78. FT-Raman (cm-1): 100 (m), 315 (s), 585 (w), 764 (m), 888
(m), 973 (m), 1235 (w) 1287 (m), 1447 (m), 1623 (m), 2949 (s),
2994 (m). Anal. Calcd for C12H20N2GeClF3O3S: C, 32.95; N, 6.40;
H, 4.61. Found: C, 33.05; N, 6.42; H, 4.91.
C6H6 solution resulted in the formation of crystals of 12. Crystals
suitable for single-crystal X-ray diffraction analysis were grown
1
by slow diffusion of pentane into a saturated C6H6 solution. H
3
NMR (C6D6): δ 2.00 (s, 24 H), 6.92 (d, JHH ) 7 Hz, 16 H), (d,
3JHH ) 7 Hz, 16 H).
Synthesis of 13. To a deep yellow solution of 1 (0.32 mmol)
dissolved in THF (10 mL) was added 3 (0.10 g, 0.32 mmol). The
reaction mixture was stirred for 2 days, after which time it became
orange in color. The solvent was removed under vacuum to yield
an orange-yellow residue, which was then resuspended in C6H6 (2
mL). The orange solution was turbid; the fine particulates were
removed by centrifugation and discarded. Pentane (4 mL) was added
to the C6H6 solution, and a pale yellow solid precipitated. The pale
yellow solid was collected, triturated with pentane (2 × 2 mL),
and dried under high vacuum to give 13 (0.06 g, 25%). Crystals
suitable for single-crystal X-ray diffraction analysis were grown
by slow diffusion of pentane into a saturated C6H6 solution. Mp:
Addition of 8 to 3. A solution of 8 (1 mmol) dissolved in THF
(3 mL) was added dropwise to a stirring solution of 3 (0.36 g, 1.1
mmol) dissolved in THF (10 mL), which was cooled in a dry ice/
acetone bath. The reaction mixture was stirred for 18 h, during
which time it was allowed to warm to room temperature. After
this time, the reaction mixture was orange in color. The solvent
was evaporated under high vacuum, leaving behind an orange
residue. The residue was taken up in C6D6. Insoluble salts (presumed
to be LiCl) suspended in the C6D6 solution were removed by
centrifugation. 1H and 13C NMR spectra of the solution were
consistent with the formation of 25 and 9.15
t
1
3
Synthesis of 10. BuOK (1.8 mmol, 0.20 g) was added to a
180-183 °C (dec). H NMR (C6H6): δ 0.79 (d, JHH ) 7 Hz, 6
3
colorless solution of 3 (0.93 mmol, 0.30 g) dissolved in THF
(3 mL). The reaction mixture was allowed to stir for 18 h at room
temperature, after which time a white precipitate (presumed to be
KCl) was collected by centrifugation and discarded. The solvent
was removed under vacuum, yielding 10 (0.32 g, 89%). Crystals
suitable for single-crystal X-ray diffraction were grown by placing
a saturated Et2O solution in a freezer at -20 °C for 1 week. Mp:
H), 1.23 (d, JHH ) 7 Hz, 6 H), 1.47 (s, 6 H), 2.07 (s, 3 H), 2.09
(s, 3 H), 2.62 (s, 6 H), 2.84 (s, 6 H), 5.61 (sept, 3JHH ) 7 Hz, 2 H),
6.66 (s, 2 H), 6.71 (s, 2 H). FT-Raman (cm-1): 102 (s), 276 (w),
324 (w), 354 (w), 534 (w), 561 (m), 584 (w), 760 (w), 887 (w),
992 (w), 1284 (s), 1344 (m), 1380 (m), 1442 (m), 1601 (m), 1628
(m), 2730 (w), 2916 (m), 2978 (w). Anal. Calcd for C29H42N2GeCl2:
C, 54.87; N, 4.41; H, 6.67. Found: C, 54.58; N, 4.06; H, 6.75.
Single-Crystal X-ray Diffraction. Data were collected at low
temperature (-123 °C) on a Nonius Kappa-CCD area detector
diffractometer with COLLECT. The unit cell parameters were
calculated and refined from the full data set. Crystal cell refinement
and data reduction were carried out using HKL2000 DENZO-
SMN.39 Absorption corrections were applied using HKL2000
DENZO-SMN (SCALEPACK).
1
3
94-102 °C (dec). H NMR (C6H6): δ 1.28 (d, JHH ) 7 Hz, 12
H), 1.53 (s, 6 H), 1.67 (s, 18 H), 6.07 (broad, 2H). FT-Raman
(cm-1): 84 (m), 120 (m), 295 (w), 464 (w), 531 (w), 608 (w), 765
(m), 887 (w), 1233 (w), 1295 (w), 1451 (s), 1628 (w), 2912 (s),
2937 (s), 2970 (s). Anal. Calcd for C19H38GeN2O2: C, 57.17; N,
7.02; H, 9.60. Found: C, 56.88; N, 6.84; H, 9.68.
Synthesis of 11. To a colorless solution of 3 (0.93 mmol, 0.3 g)
in THF (5 mL) was added KSCN (1.86 mmol, 0.18 g). The reaction
mixture was allowed to stir for 2 days at room temperature, after
which time the solvent was removed under vacuum to yield a white
residue. The residue was suspended in C6H6 (6 mL); a white solid
(presumed to be KCl) was removed by centrifugation and then
discarded. Hexanes was added to the C6H6 solution; the white
precipitate was collected. The solid was dried under vacuum to
give 11 (82%, 0.28 g). Crystals suitable for single-crystal X-ray
diffraction analysis were grown by slow diffusion of pentane into
a saturated C6H6 solution. Mp: 122-124 °C (dec). 1H NMR (C6D6):
The SHELXTL/PC V6.14 suite of programs was used to solve
the structures by direct methods.40 Subsequent difference Fourier
syntheses allowed the remaining atoms to be located. All of the
non-hydrogen atoms were refined with anisotropic thermal param-
eters. The hydrogen atom positions were calculated geometrically
and were included as riding on their respective carbon atoms.
Both compounds 12 and 13 showed signs of nonmerohedral
twinning in the E-statistics, and the Fobs values were consistently
higher than the Fcalcs. WinGX41 was used to “detwin” the data.
ROTAX42 found the twin law. “Make HKLF5” was used to
generate the detwinned file used in further refinement.
3
δ 0.94 (d, JHH ) 7 Hz, 12 H), 1.27 (s, 6 H), 4.94 (broad, 2H).
FT-Raman (cm-1): 152 (w), 191 (w), 226 (w), 290 (m), 457(w),
486 (w), 584 (w), 863 (m), 887 (m), 1287 (m), 1359 (w), 1442
(m), 1623 (m), 2046 (s), 2059 (s), 2936 (s), 2973 (m). Anal. Calcd
for C13H20N4GeS2: C, 42.30; N,15.18; H, 5.46. Found: C, 42.33;
N, 14.82; H, 6.49.
Acknowledgment. We thank the NSERC (Canada), the
Ontario Photonics Consortium (OPC), and the University of
Western Ontario for funding. We thank Dr. P. J. Ragogna
and members of the Ragogna group for helpful discussions.
We also thank Teck Cominco Ltd. for a generous gift of
GeCl4.
Synthesis of 1 via 3. Compound 3 (0.13 g, 0.4 mmol) was added
to a stirring solution of Mes2Mg (0.4 mmol) in THF/dioxane (4
mL of THF, 1 mL of dioxane). The solution became yellow in
color and was allowed to stir for 3 days at room temperature. A
white precipitate (presumed to be MgCl2 · dioxane) was removed
by centrifugation. The 1H NMR spectrum of the bright yellow
solution was consistent with quantitative formation of 1.6
Reaction of Tol2Mg with 3. To a solution of 3 (0.16 g, 0.5
mmol) dissolved in THF (4 mL) was added Tol2Mg (0.5 mmol)
dissolved in THF/dioxane (4 mL of THF, 2 mL of dioxane). The
color of the solution became yellow and was allowed to stir for
18 h at room temperature. After 18 h, the white precipitate
(presumed to be MgCl2 · dioxane) was removed by centrifugation.
The solvent was removed to yield a pale yellow residue. The residue
was dissolved in C6H6 (3 mL). Vapor diffusion of Et2O into the
Supporting Information Available: Crystallographic data in
.cif format. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM800368D
(39) Otwinowski, Z.; Minor, W. In Methods in Enzymology. Vol. 276:
Macromolecular Crystallography Part A; Carter, C. W., Jr., Sweet, R. M.,
Eds.; Academic Press: New York, 1997; p 307.
(40) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(41) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(42) Cooper, R. I.; Gould, R. O.; Parsons, S.; Watkin, D. J. J. Appl.
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