Synthesis and tunable reactivity of N-heterocyclic germylene

Article abstract of DOI:10.1002/asia.201200379

Modifying the β-diketimine ligand LH 1 (LH=[ArN=C(Me)-CH=C(Me)-NHAr], Ar=2,6-iPr₂C₆H₃) through replacement of the proton in 3-position by a benzyl group (Bz) leads to the new ^BzLH ligand 2, which could be isolated in 77 % yield. According to ¹H NMR spectroscopy, 2 is a mixture of the bis(imino) form [(ArN=C(Me)] ₂CH(Bz) 2a and its tautomer [ArN=C(Me)-C(Bz)=C(Me)NHAr] 2b. Nevertheless, lithiation of the mixture of 2a and 2b affords solely the N-lithiated β-diketiminate [ArN=C(Me)-C(Bz)=C(Me)-NLiAr], ^BzLLi 3. The latter reacts readily with GeCl_2·dioxane to form the chlorogermylene ^BzLGeCl 4, which serves as a precursor for a new zwitterionic germylene by dehydrochlorination with LiN(SiMe₃) ₂. This reaction leads to the zwitterionic germylene ^BzL'Ge: 5 (^BzL'=ArNC(=CH₂)C(Bz)=C(Me)NAr) which could be isolated in 83 % yield. The benzyl group has a distinct influence on the reactivity of zwitterionic 5 in comparison to its benzyl-free analogue, as shown by the reaction of 5 with phenylacetylene, which yields solely the 1,4-addition product 6, that is, the alkynyl germylene ^BzLGeCCPh. Compounds 2-6 have been fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single-crystal X-ray diffraction analyses. Copyright

Full text of DOI:10.1002/asia.201200379

DOI: 10.1002/asia.201200379
Synthesis and Tunable Reactivity of N-Heterocyclic Germylene
Yun Xiong, Shenglai Yao, and Matthias Driess*[a]
À
Abstract: Modifying the b-diketimine
C(Bz)=C(Me) NLiAr], BzLLi 3. The
be isolated in 83% yield. The benzyl
group has a distinct influence on the
reactivity of zwitterionic 5 in compari-
son to its benzyl-free analogue, as
shown by the reaction of 5 with phenyl-
acetylene, which yields solely the 1,4-
addition product 6, that is, the alkynyl
germylene BzLGeCCPh. Compounds 2–
6 have been fully characterized by mul-
tinuclear NMR spectroscopy, mass
spectrometry, elemental analyses, and
single-crystal X-ray diffraction analy-
ses.
À
ligand LH 1 (LH=[ArN=C(Me) CH=
latter reacts readily with GeCl2·dioxane
to form the chlorogermylene BzLGeCl
4, which serves as a precursor for
a new zwitterionic germylene by dehy-
À
C(Me) NHAr],
Ar=2,6-iPr2C6H3)
through replacement of the proton in
3-position by a benzyl group (Bz) leads
to the new BzLH ligand 2, which could
be isolated in 77% yield. According to
1H NMR spectroscopy, 2 is a mixture
drochlorination with LiN
reaction leads to the zwitterionic ger-
mylene BzL’Ge: (BzL’=ArNC
(=
ACHTUNGTRNEN(UNG SiMe3)2. This
5
ACHTUNGTRENNUNG
of the bis
N
CH2)C(Bz)=C(Me)NAr) which could
C(Me)]2CH(Bz) 2a and its tautomer
À
[ArN=C(Me) C(Bz)=C(Me)NHAr]
Keywords: 1,4-addition · bond acti-
vation · carbene homologues · dike-
timinates · germanium
2b. Nevertheless, lithiation of the mix-
ture of 2a and 2b affords solely the N-
À
lithiated b-diketiminate [ArN=C(Me)
Introduction
Heavier carbene analogues are very reactive and thus indis-
pensable building blocks in synthetic chemistry.[1] In general,
kinetic or thermodynamic stabilization (or both) is needed
for the successful preparation of isolable heavier carbene
analogues, especially for the synthesis of silylenes and ger-
mylenes.
It has been shown that b-diketiminate (nacnac) chelate li-
gands bearing bulky ortho-substituted aryl groups at the ni-
trogen atoms can be applied to the synthesis of a variety of
low-valent transition-metal and main-group-element com-
plexes, including silicon(II) and germanium(II) species.[1–4]
Among the nacnac ligand systems, LH (Scheme 1, R1 =Ar=
2,6-iPr2C6H3, R2 =Me, R3 =H) represents one of the most
suitable ligands used to date for the synthesis of isolable
complexes with mono- and divalent heavier Group 14 ele-
ments.[5] Meanwhile, it has been demonstrated that the
subtle changes of steric demand in the ortho-substituted
group R1 as well as in the groups R2 and R3 at the C3N2 unit
(Scheme 1) can lead to significantly different chemistry. For
instance, starting from LH a zwitterionic silylene L’Si:[5a]
and its analogous germylene L’Ge:[5b] are easily accessible.
However, when smaller groups such as R1 =2,6-Et2C6H3 or
Scheme 1. N,N-bidentate ligands derived from the b-diketiminate
(nacnac) system. Bz=benzyl.
2,6-Me2C6H3 were employed as substituents at the nitrogen
atom under the same reaction conditions, no corresponding
silylene could be obtained.[5c] Moreover, using the modified
nacnac ligand with tert-butyl group at nitrogen (R1 position),
merely a dimerized silylene could be isolated.[6] It is note-
worthy that the influence of different substituents at the R2
and especially at the R3 positions on the reactivity of nacnac
complexes bearing divalent Si and Ge is far less explored in
comparison to that of position R1, presumably owing to the
rather limited access to such modified nacnac ligands. Most
recently, the altered ligand LA with different R2 and R3
groups (Scheme 1) was synthesized, from which the corre-
[a] Y. Xiong, S. Yao, M. Driess
Technische Universitꢀt Berlin
Department of Chemistry: Metalorganics and Inorganic Materials,
Sekr. C2
Strasse des 17. Juni 135, 10623 Berlin (Germany)
Fax : (+49)30-314-29732
E-mail: matthias.driess@tu-berlin.de
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FULL PAPER
sponding zwitterionic N-heterocyclic germylene LA’Ge:
could be produced.[7] In order to understand the influence of
substituents at the ring carbon atoms of the C3N2 framework
of the b-diketimine ligand in more detail, we synthesized
the new ligand BzLH bearing a benzyl group in the 3-posi-
tion of the C3N2 skeleton (Scheme 1). Herein we report the
synthesis of the new zwitterionic germylene BzL’Ge: (BzL’=
ArNCACHTUNGTRENNUNG(=CH2)C(Bz)=C(Me)NAr, Ar=2,6-iPr2C6H3) based
Scheme 3. Synthesis of BzLH 2a and 2b.
on the benzyl-modified ligand BzLH and its markedly differ-
ent reactivity towards phenylacetylene in comparison to that
of L’Ge:.
Owing to the facile tautomerization in solutions, BzLH can
be formed as a mixture of isomers 2a and 2b. This result is
evident in the 1H NMR spectrum of the isolated product
BzLH in C6D6, which shows two sets of signals corresponding
to the tautomers 2a and 2b (Scheme 3 and Experimental
Section). The CH(Bz) moiety in 2a (Scheme 3) exhibits
a triplet at d=4.20 ppm for the methine proton and a dou-
blet at d=3.46 ppm for the methylene protons of the Bz
group. In contrast, the isomer 2b with a cyclic structure sim-
ilar to 1 exhibits a singlet at d=3.70 ppm for the CH2Ph
protons and a characteristic downfield singlet resonance at
d=14.0 ppm for the NH proton. From n-hexane solutions
the isomer 2a could be isolated by crystallization as color-
less plates at À208C; its structure has been confirmed by
single-crystal X-ray diffraction analysis (Figure 1).
Results and Discussion
Synthesis of BzLH 2a,b and BzLLi 3
According to previous reports, attempts to synthesize the
benzyl-modified b-diketimine BzLH by stepwise lithiation
and subsequent benzylation of LH 1 in n-hexane as solvent
failed but led merely to small amounts of 3,3-dibenzylated
b-diketimine Bz2L and unreacted LH (1; Scheme2)[8]
Figure 1. Molecular structure of the tautomer 2a. Thermal ellipsoids are
drawn at 50% probability level. H atoms (except the H at C3) are omit-
ted for clarity. Selected bond lengths (ꢂ) and angles (8): C1–C2 1.490(2),
C2–C3 1.524(2), C3–C4 1.525(2), C4–C5 1.501(2), C2–N1 1.275(2), N2–
C4 1.276(2), C3–C6 1.535(2), C6–C7 1.507(2); C1-C2-N1 126.3(2), N2-C4-
C5 125.6(1), C5-C4-C3 117.9(1), C1-C2-C3 115.4(1), C2-C3-C4 111.2(1),
C2-C3-C6 111.4(1), C4-C3-C6 112.9(1), C3-C6-C7 112.9(1).
Scheme 2. Introduction of benzyl groups (Bz) at the nacnac ligand L by
reaction of LLi with PhCH2Br (BzBr). Ar=2,6-iPr2C6H3.
¯
We learned that choosing a more polar aprotic solvent is
key to synthesize the desired monobenzylated b-diketimine
BzLH. Since LLi has a higher solubility in diethyl ether than
in n-hexane, BzLH is now accessible because the unwanted
translithiation of BzLH by LLi and thus the second benzyla-
tion of BzLH can be suppressed in diethyl ether. Therefore,
the reaction using a slightly molar excess of BzBr (2%) in
diethyl ether furnishes the desired monobenzylated b-diketi-
mine BzLH in 77% yield (Scheme 3).
Compound 2a crystallizes in the triclinic space group P1.
The molecule possesses an acyclic structure with the C3
atom being tetrahedrally surrounded by three carbon atoms
and a hydrogen atom. As expected, the relatively short C2–
N1 (1.275(2) ꢂ) and N2–C4 distances (1.276(2) ꢂ) indicate
C N double bonds, while the C1–C2 (1.490(2) ꢂ), C2–C3
(1.524(2) ꢂ), C3–C4 (1.525(2) ꢂ), C4–C5 (1.501(2) ꢂ), C3–
C6, (1.535(2) ꢂ), and C6–C7 distances (1.507(2) ꢂ) reflect
À
À
C C single bonds.
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N-Heterocyclic Germylene
Lithiation of both isomers 2a and 2b with MeLi is
straightforward and gives the desired b-diketiminate lithium
salt 3 in quantitative yield (Scheme 4), which can be unam-
served for the analogous N-heterocyclic chlorogermylene
LGeCl.[9]
The dehydrochlorination of 4 with LiNACHTUNTGRNEUNG(SiMe3)2 in THF
1
biguously identified by H and 13C NMR spectroscopy. Ac-
led to the quantitative formation (as determined by
1H NMR spectroscopy) of the expected germylene BzL’Ge: 5
(Scheme 4), which could be isolated in 83% yield. The
1H NMR spectrum of 5 exhibits two singlets at d=3.49 and
4.09 ppm, respectively, for the diastereotopic exocyclic CH2
protons and a singlet at d=3.77 ppm for the methylene pro-
tons of the benzyl group. Compound 5 crystallized in n-
hexane as red single crystals that were suitable for an X-ray
diffraction analysis. In contrast to the molecular structure of
4, the six-membered C3N2Ge ring in 5 is almost planar
(Figure 3). The phenyl ring of the benzyl group is perpendic-
1
cordingly, the H NMR spectrum of 3 shows only a down-
field-shifted singlet for the PhCH2 protons at d=4.04 ppm.
Scheme 4. Synthesis of BzLLi (3),BzLGeCl (4), and BzL’Ge: (5).
Synthesis of BzLGeCl (4) and BzL’Ge: (5)
Compound 3 reacts readily with GeCl2·dioxane in diethyl
ether to form the chlorogermylene 4, which could be isolat-
ed as a yellow powder in 81% yield (Scheme 4). The latter
is insoluble in n-hexane, sparingly soluble in diethyl ether,
but well soluble in THF. Its composition has been confirmed
Figure 3. Molecular structure of BzL’Ge: (5). Thermal ellipsoids are
drawn at 50% probability level. H atoms (except those at C1) are omit-
ted for clarity. Selected bond lengths (ꢂ) and angles (8): Ge1–N1
1.847(2), Ge1–N2 1.851(2), C1–C2 1.425(4), C2–C3 1.422(4), C3–C4
1.400(4), C4–C5 1.444(4), C3–C6 1.515(4), C6–C7 1.517(4), C2–N1
1.406(3), C4–N2 1.410(3); N2-Ge1-N1 94.98(9), C2-N1-Ge1 128.5(2), C4-
N2-Ge1 128.1(2), C2-C3-C6 116.3(2), C4-C3-C6 117.0(2), C3-C6-C7
116.2(2), C1-C2-C3 122.1(2), C3-C4-C5 122.2(3).
1
by H and 13C NMR spectroscopy, EI-MS spectrometry and
elemental analysis. Compound 4 crystallized from diethyl
¯
ether at room temperature in the triclinic space group P1.
Its molecular structure consists of a six-membered, puckered
C3N2Ge ring with a pyramidally coordinated GeII atom
(Figure 2). The bond lengths are very similar to those ob-
À
ular to the C3N2Ge ring plane. The Ge N bonds (average
1.849 ꢂ) become shorter than those in its precursor 4
À
(1.963 ꢂ), and the same is true for the C1 C2 distance. De-
spite the benzyl group at the 4-postion in 5, the geometric
parameters are quite similar to those observed in germylene
L’Ge:.[5b] For instance, the C2 C3 and C3 C4 bond lengths
in the C3N2Ge ring in 5 (1.422(4), 1.400(4) ꢂ) are compara-
ble to the corresponding values in L’Ge: (1.402(3),
À
À
À
1.392(3) ꢂ). The Ge N distances in 5 (1.847(2), 1.851(2) ꢂ)
are also close to those observed in L’Ge: (1.866(2),
1.865(2) ꢂ).
Figure 2. Molecular structure of BzLGeCl (4). Thermal ellipsoids are
drawn at 50% probability level. H atoms are omitted for clarity. Selected
bond lengths (ꢂ) and angles (8): Ge1–N1 1.964(2), Ge1–N2 1.962(2),
Ge1–Cl1 2.329(1), C1–C2 1.502(3), C2–C3 1.420(3), C3–C4 1.404(3), C4–
C5 1.513(3), C3–C6 1.511(3), C6–C7 1.523(3), N2–C4 1.343(3), N1–C2
1.338(2); N2-Ge1-N1 89.93(7), N2-Ge1-Cl1 94.22(5), N1-Ge1-Cl1
94.06(5), C2-N1-Ge1 123.6(1), C4-N2-Ge1 122.8(1), C3-C6-C7 117.0(2),
C2-C3-C6 118.1(2), C4-C3-C6 117.8(2).
Reaction of BzL’Ge: (5) with Phenylacetylene
In our previous work we showed that germylene L’Ge: can
react with phenylacetylene to yield two products, namely
À
a [4+2] cycloaddition product in 67% yield and a C H acti-
vation product (1,4-addition) in 16% yield (Scheme 5).[10]
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Matthias Driess et al.
FULL PAPER
À
The preferred C H activation of phenylacetylene by 5 to
yield the 1,4-addition product 6 indicates that the benzyl
group in 4-position of the C3N2Ge ring facilitates an ylide-
like reactivity as suggested for L’Ge: by DFT calculations
and disfavors a [4+2] cycloaddition for steric reasons.[5b,10]
Conclusions
In summary, the newly benzyl-modified nacnac ligand in
BzLH (2) could be synthesized, which is easily accessible by
stepwise lithiation of LH (1) with nBuLi in diethyl ether
and single benzylation with BzBr, to afford a tautomeric
mixture of BzLH (2a/2b); subsequent lithiation of the mix-
ture with MeLi furnished 3. Reaction of
3
with
Scheme 5. Different reactivity of the new germylene 5 versus L’Ge:[10]
GeCl2·dioxane led to the N-heterocyclic chlorogermylene 4,
which could be converted by dehydrochlorination into the
zwitterionic germylene 5 in quantitative yield. Remarkably,
the benzyl group at the C3N2Ge ring facilitates an ylide-like
reactivity towards phenylacetylene to yield exclusively the
The latter ambivalent reactivity of the zwitterionic L’Ge: is
strikingly different from that of the analogous silylene L’Si:.
To examine the change of reactivity for the benzyl-modified
germylene 5, phenylacetylene was employed under the same
reaction conditions. Interestingly, the conversion afforded
1,4-addition product (alkynylgermylene, BzLGe
ACTHUNTGRENNG(U CCPh)) 6.
À
exclusively the C H activation product 6, as indicated by
Experimental Section
the disappearance of the two characteristic singlets for the
exocyclic CH2 protons in 5 in the 1H NMR spectrum
(Scheme 5).
General Considerations
All experiments and manipulations were carried out under dry oxygen-
free nitrogen using standard Schlenk techniques or in an MBraun inert
atmosphere dry-box containing an atmosphere of purified nitrogen. Sol-
vents were dried by standard methods and freshly distilled prior to use.
The NMR spectra were recorded with Bruker spectrometers ARX200,
AV400 and with residual solvent signals as internal references (1H and
13C{H}) or with an external reference (SiMe4 for 29Si). Abbreviations: s=
singlet; d=doublet; t=triplet; sept=septet; m=multiplet; br=broad.
Elemental analyses were performed on a FlashEA 1112 CHNS Analyzer.
Compound 6 crystallized as yellowish plates in n-hexane.
The structure of 6, which is quite similar to that of 4, was
confirmed by X-ray diffraction analysis (Figure 4). The six-
membered C3N2Ge ring again exhibits a puckered confor-
mation. The alkynyl moiety at the three-coordinate GeII
atom and the benzyl group are oriented away from each
other. Due to statistical disorder of the GeCCPh moiety,
a discussion of structural parameters is not meaningful.
Single-Crystal X-ray Structure Determination
Crystals were each mounted on a glass capillary in perfluorinated oil and
measured in a cold N2 flow. The data of 2a, 4, 5, and 6 were collected on
an Oxford Diffraction Xcalibur S Sapphire at 150 K (MoKa-radiation, l=
0.71073 ꢂ). The structures were solved by direct methods and refined on
11
F2 with the SHELX-97 software package. The positions of the H atoms
were calculated and considered isotropically according to a riding model.
CCDC 878533 (2a), CCDC 878534 (4), CCDC 878535 (5), and
CCDC 878536 (6) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre at www.ccdc.cam.ac.uk./data_re-
quest/cif.
BzLH (2a)
¯
Triclinic, space group P1, a=11.0830(5), b=12.2132(8), c=13.7190(9) ꢂ,
a=67.998(6), b=67.580(5), g=89.060(4)8, V=1574.18(16) ꢂ3, Z=2,
ACTHNUTRGNEUNG
1calcd =1.073 MgmÀ3, m(MoKa)=0.061 mmÀ1, 15264 collected reflections,
5536 crystallographically independent reflections [Rint =0.0389], 3395 re-
2
flections with I>2s(l), qmax =258, R(Fo)=0.0426 (I>2s(l)), wRACHTUNGTRENNUNG(Fo )=
0.0941 (all data), 353 refined parameters.
Figure 4. Molecular structure of BzLGe
ACTHNUTRGNEU(GN CCPh) (6). Thermal ellipsoids are
drawn at 50% probability level. H atoms and the disordered part of the
ꢀ
C CPh moiety are omitted for clarity. Selected bond lengths (ꢂ): N1–
BzLGeCl (4)
Ge1a 1.815(5), N1–Ge1b 2.132(5), Ge1a–C37a 1.94(3), G1b–C37b
1.97(2), Ge1a–N2 2.002(5), Ge1b–N2 2.033(5), N1–C2 1.344(5), N2–C4
1.330(6), C1–C2 1.507(6), C2–C3 1.400(6), C3–C4 1.415(6), C4–C5
1.520(6), C3–C6 1.522(6), C6–C7 1.511(8).
¯
Triclinic, space group P1, a=12.1310(8), b=12.3090(9), c=
12.7248(10) ꢂ, a=90.016(6), b=108.196(6), g=113.830(7)8, V=
1633.6(2) ꢂ3, Z=2, 1calcd =1.252 MgmÀ3 (MoKa)=1.046 mmÀ1
, mACHTUNRTEGNNUNG , 12347
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N-Heterocyclic Germylene
collected reflections, 5732 crystallographically independent reflections
suitable for X-ray analysis were obtained from diethyl ether. M.p. 1728C
(decomposed); 1H NMR (200.13 MHz, C6D6, 258C): d=1.05 (d, 3J-
[Rint =0.03391], 5201 reflections with I>2s(l), qmax =258, R(Fo)=0.0319
2
(I>2s(l)), wR
N
(H,H)=7.0 Hz, 6H; CHMe2), 1.12 (d, 3J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
1.24 (d, 3J
N
ACHTUNGTRENNUNG
BzL’Ge: (5)
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
Monoclinic, space group P21/n, a=12.5423(17), b=19.345(2), c=
13.9173(19) ꢂ, b=102.880(15)8, V=3291.8(7) ꢂ3, Z=4, 1calcd
1.169 MgmÀ3, m(MoKa)=0.955 mmÀ1, 26068 collected reflections, 5791
crystallographically independent reflections [Rint =0.0677], 4855 reflec-
tions with I>2s(l), qmax =258, R(Fo)=0.0455 (I>2s(l)), wRACHTNUGTRENUNG(Fo )=0.1107
(all data), 361 refined parameters.
CHMe2), 7.00–7.31 ppm (m, 11H, Ph); 13C{1H} NMR (100.61 MHz, C6D6,
258C): d=21.5 (NCMe), 24.2, 24.3, 24.8, 27.5, 28.4, 29.4 (CHMe2), 36.9
(CH2Ph), 107.0 (g-C), 124.1, 125.8, 126.4, 127.8, 128.1, 128.3, 128.9, 140.7,
141.0, 143.7, 147.3, 165.5 ppm (NCMe, Ph); EI-MS: m/z (%): 615
[MÀH]+; elemental analysis calcd (%) for C36H47N2GeCl: C 70.21, H
7.69, N 4.55; found: C 69.95, H 7.53, N 4.64.
=
ACHTUNGTRENNUNG
2
Bz
ꢀ
LGeC CPh (6)
Compound 5: To a solution of 4 (0.97 g, 1.58 mmol) in THF (20 mL) was
added LiNACTHUNGTRENNG(U SiMe3)2ACHTUNGTREN(NGUN Et2O) (0.38 g, 1.58 mmol) at room temperature under
stirring. The solution was stirred for one hour. The precipitate was fil-
tered away and the solvent was changed to n-hexane. From n-hexane
compound 5 crystallized as red plates with yield of 0.76 g (1.31 mmol,
83%). M.p. 1408C (decomposed); 1H NMR (200.13 MHz, C6D6, 258C):
Monoclinic, space group C2/c, a=33.690(2), b=13.655(1), c=
22.091(1) ꢂ, b=117.869(7)8, V=8984.1(1) ꢂ3, Z=4, 1calcd =1.008 MgmÀ3
(MoKa)=0.709 mmÀ1, 29622 collected reflections, 7890 crystallographi-
cally independent reflections [Rint =0.0414], 5313 reflections with I>
,
mACHTUNGTRENNUNG
2
2s(l), qmax =258, R(Fo)=0.0856 (I>2s(l)), wRACHTNUTRGNE(NUG Fo )=0.2897 (all data),
d=1.17 (d, 3J
6H; CHMe2), 1.28 (d, 3J
G
ACHTUNGTRENNUNG
516 refined parameters.
G
ACHTUNGTRENNUNG
7.0 Hz, 6H; CHMe2), 1.58 (s, 3H; NCMe), 3.49 (s, 1H, NCCH2), 3,52–
3,77 (m, 4H; CHMe2), 3.77 (s, 2H; CH2Ph), 4.09 (s, 1H; NCCH2), 7.03–
7.35 ppm (m, br, 11H; Ph); 13C{1H} NMR (100.61 MHz, C6D6, 258C): d=
18.6 (NCMe), 23.4, 24.5, 25.6, 25.8 (CHMe2), 28.4, 28.5 (CHMe2), 38.1
(CH2Ph), 84.6 (NCCH2), 111.1 (g-C), 124.2, 125.6, 126.0, 127.9, 128.3,
128.7, 140.0, 140.2, 141.2, 141.3, 147.1, 147.3, 151.4 ppm (NCMe, NCCH2,
CH2Ph 2,6-iPr2C6H3); HR-ESI: m/z (%): 581.29548 [M+H]+, calcd
581.29455; elemental analysis calcd (%) for C36H46N2Ge: C 74.63, H 8.00,
N 4.84, found: C 74.81, H 8.05, N 4.84.
Syntheses
Compounds 2a and 2b
To a solution of compound 1 (7.08 g, 16.9 mmol) in diethyl ether (50 mL)
was added n-butyllithium (6.76 mL, 2.5m solution in n-hexane) at À208C
under stirring. The reaction solution was allowed to warm to room tem-
perature. After 2 h the reaction was finished. Benzylbromide (2.10 mL,
98%, 17.2 mmol) was added to the yellow solution in situ at room tem-
perature. The reaction mixture was stirred for three days. The solution
was dried under vacuum. The product was extracted with n-hexane. From
the concentrated solution compound 2a crystallized as colorless plates at
À208C. The remaining solution was dried under vacuum and the residue
was dissolved in methanol (5 mL), which yielded colorless crystals of
a mixture of 2a and 2b. The first and second crops of 2a and 2b amount-
ed 6.62 g, 13.0 mmol (77% yield). M.p. 828C; 1H NMR (200.13 MHz,
Compound 6: To a solution of 5 (0.65 g, 1.12 mmol) in diethyl ether
(10 mL) was added phenylacetylene (0.13 mL, d=0.92 gmLÀ1
,
1.12 mmol) at room temperature. The reaction mixture was left to stand
for 2 h. The color changed from deep red to orange. From n-hexane com-
pound 6 crystallized as colorless plates at 48C with yield of 0.59 g
(0.87 mmol, 78%). M.p. 518C (decomposed); 1H NMR (200.13 MHz,
C6D6, 258C): d=1.16 (d, 3J
(H,H)=7.0 Hz, 6H; CHMe)2, 1.34 (d, 3J
1.50 (d, 3J
(H,H)=7.0 Hz, 6H; CHMe)2, 1.71 (s, 6H; NCMe), 3.51 (sept.,
3J(H,H)=7.0 Hz, 2H; CHMe2), 3.68 (s, 2H; PhCH2), 4.06 (sept., 3J-
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
C6D6, 258C): for 2a: d=1.06 (d, 3J
(H,H)=7 Hz, 6H; CHMe2), 1.12 (d, 3J
(d, 3J(H,H)=7 Hz, 6H; CHMe2), 1.68 (s, 6H; NCMe), 2.51 (sept, 3J-
(H,H)=7.0 Hz, 2H; CHMe2), 2.75 (sept, J
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTREG(NNNU H,H)=7.0 Hz, 2H; CHMe2), 6.90–7.19 (m, br, 12H; Ph), 7.48–7.62 ppm
3
A
ACHTUNGTREN(UNGN H,H)=7.0 Hz, 2H; CHMe2),
(m, 4H; Ph); 13C{1H} NMR (100.61 MHz, C6D6, 258C): d=21.4 (NCMe),
3
3
3.46 (d, J
7.03–7.21 ppm (m, br, 11H; Ph); for 2b: 1.18 (d, 3J
CHMe2), 1.19 (d, 3J
(H,H)=7 Hz, 12H; CHMe2), 1.69 (s, 6H; NCMe),
3.36 (sept, 3J
(H,H)=7 Hz, 4H; CHMe2), 3.70 (s, 2H, PhCH2), 7.04–7.32
ACHTUNGTRENNUNG(H,H)=7 Hz, 2H, CH2Ph), 4.20 (t, JCAHTUNGTRENNNUG
ꢀ
24.3, 24.6, 24.8, 27.7, 28.6, 29.2 (CHMe2), 37.1 (CH2Ph), 104.0, 106.4 (C
CPh), 113.7 (g-C), 124.2, 125.2, 126.2, 126.4, 127.2, 128.1 128.4, 128.9,
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
131.9, 141.9, 142.5, 143.6, 147.0, 166.9 ppm (NCMe, CH2Ph 2,6-iPr2C6H3,
A
+
ꢀ
C CPh); HR-ESI: m/z (%): 683.33953 [M+H] , calcd 683.34150; ele-
(m, br, 11H; Ph), 14.0 ppm (s, 1H, NH); HR-ESI: m/z (%): 509.38848
[M+H]+, calcd 509.38120; elemental analysis calcd (%) for C36H48N2: C
84.99, H 9.51, N 5.51; found: C 84.74, H 9.32, N 5.41.
mental analysis calcd (%) for C44H52N2Ge: C 77.55, H 7.69, N 4.11,
found: C 77.55, H 7.87, N 3.98.
Compound 3: To a solution of 2a and 2b (2.90 g, 5.70 mmol) in diethyl
ether (50 mL) was added n-butyllithium (2.5m in diethyl ether, 2.28 mL,
5.70 mmol) at À108C under stirring. The reaction was completed in 2 h
and the solvent was changed to THF. From THF compound 3 was ob-
tained at À208C as yellow crystals with yield of 2.70 g (5.24 mmol, 92%).
M.p. 1308C (decomposed); 1H NMR (200.13 MHz, C6D6, 258C): d=1.21
Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie for financial support.
(d, 3J
CHMe2), 1.90 (s, 6H; NCMe), 3.38 (sept, J
4.04 (s, 2H; CH2Ph), 6.99–7.10 (m, br, 7H; Ph), 7.30 (t, J
2H, Ph), 7.48 ppm (d, 3J(H,H)=7.3 Hz, 2H; Ph); 13C{1H} NMR
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=7.0 Hz, 12H; CHMe2), 1.23 (d, 3J
3
AHCTUNGTRENNUNG
3
AHCTUNGTREGUN(NN H,H)=7.3 Hz,
[1] Recent reviews of the chemistry of heavier carbene homologues:
a) N. Tokitoh, R. Okazaki, Coord. Chem. Rev. 2000, 210, 251;
b) “Recent Advances in structural chemistry of organic germanium,
tin and lead compounds”: K. W. Klinkhammer in The Chemistry of
Organic Germanium, Tin and Lead Compounds, Vol. 2 (Ed.: Z.
Rappoport), Wiley, New York, 2002, chap. 4, pp. 284–332; c) O.
Kꢄhl, Coord. Chem. Rev. 2004, 248, 411; d) N. J. Hill, R. West, J. Or-
ganomet. Chem. 2004, 689, 4165; e) M. Kira, J. Organomet. Chem.
2004, 689, 4475; f) I. Saur, S. G. Alonso, J. Barrau, Appl. Organomet.
Chem. 2005, 19, 414; g) W. P. Leung, K. W. Kan, K. H. Chong,
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Eur. J. Inorg. Chem. 2008, 5165; i) S. Nagendran, H. W. Roesky, Or-
ganometallics 2008, 27, 457; j) Y. Mizuhata, T. Sasamori, N. Tokitoh,
AHCTUNGTRENNUNG
(100.61 MHz, C6D6, 258C): d=21.1 (NCMe), 23.9, 24.1 (CHMe2), 28.2
(CHMe2), 38.1 (CH2Ph), 96.6 (g-C), 122.8, 123.4, 125.6, 127.9, 128.3,
140.9, 145.2, 150.2, 164.5 ppm (NCMe, Ph); HR-ESI: m/z (%): 509.38793
[MÀLi+H]+, calcd 509.38120 elemental analysis calcd (%) for
C36H47N2Li·THF: C 81.87, H 9.45, N 4.77, found: C 81.86, H 9.48, N 4.73.
Compound 4: GeCl2··dioxane (0.66 g, 2.85 mmol) was added to a yellow
solution of 3 (1.47 g, 2.85 mmol) in toluene (80 mL) at room temperature.
From the solution colorless precipitate formed immediately. After six
hours the salt LiCl was filtered away, and the solution was dried in
vacuum and washed with n-hexane (2ꢃ8 mL), which yielded yellowish
powder of 5 with yield of 1.42 g (2.30 mmol, 81%). Single crystals of 4
Chem. Asian J. 2012, 00, 0 – 0
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Matthias Driess et al.
FULL PAPER
Chem. Rev. 2009, 109, 3479; k) S. M. Mandal, H. W. Roesky, Chem.
Commun. 2010, 46, 6016; l) M. Asay, C. Jones, M. Driess, Chem.
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[8] D. T. Carey, E. K. Cope-Eatough, E. Vilaplana-Mafe, F. S. Mair,
R. G. Pritchard, J. E. Warren, R. J. Woods, Dalton Trans. 2003, 1083.
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5314.
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[11] G. M. Sheldrick, SHELX-97 Program for Crystal Structure Determi-
nation, Universitꢀt Gçttingen (Germany) 1997.
[2] J. Feldman, S. J. McLain, A. Parthasarathy, W. J. Marshall, J. C. Cal-
abrese, S. D. Arthur, Organometallics 1997, 16, 1514.
[3] W. Clegg, E. K. Cope, A. J. Edwards, F. S. Mair, Inorg. Chem. 1998,
37, 2317.
[4] a) L. Bourget-Merle, M. F. Lappert, J. R. Severn, Chem. Rev. 2002,
102, 3031; b) S. Yao, M. Driess, Acc. Chem. Res. 2012, 45, 276.
[5] a) M. Driess, S. Yao, M. Brym, C. Van Wꢄllen, D. Lenz, J. Am.
Chem. Soc. 2006, 128, 9628; b) M. Driess, S. Yao, M. Brym, C. van
Wꢄllen, Angew. Chem. 2006, 118, 4455; Angew. Chem. Int. Ed. 2006,
45, 4349; c) Y. Xiong, S. Yao, M. Driess, unpublished results;
d) W. D. Woodul, E. Carter, R. Mꢄller, A. F. Richards, A. Stasch, M.
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133, 10074.
Received: April 26, 2012
Published online: && &&, 0000
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FULL PAPER
Germanium Chemistry
Yun Xiong, Shenglai Yao,
Matthias Driess*
&&&& — &&&&
Synthesis and Tunable Reactivity of N-
Heterocyclic Germylene
Good germs: Lithiation and monoben-
zylation of b-diketimine LH afforded
the new benzyl-modified b-diketimine
1a and its tautomer 1b (not shown).
Lithiation and subsequent reaction
with GeCl2·dioxane furnished the
chlorogermylene 2, which could be
transformed quantitatively into the
new zwitterionic germylene 3.
Remarkably, 3 reacts with phenylace-
tylene exclusively under 1,4-addition
to give the alkynyl germylene 4 owing
to the s-donating benzyl group.
Chem. Asian J. 2012, 00, 0 – 0
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