Synthesis and characterization of β-diketiminate germanium(II) compounds

Article abstract of DOI:10.1021/ic202388d

Reactions of LGeCl (L = CH[C(Me)N(Ar)]₂; Ar = 2,6-iPr ₂C₆H₃)with KOtBu or LiR (R = 2-thienyl, N(H)Ar, PPh₂)yielded the germanium(II)compounds LGeR [R = OtBu (1), 2-thienyl (2), N(H)Ar (3), PPh₂

Full text of DOI:10.1021/ic202388d

Article
pubs.acs.org/IC
Synthesis and Characterization of β-Diketiminate Germanium(II)
Compounds
Ying Yang,†,‡ Na Zhao,† Yile Wu,† Hongping Zhu,*,† and Herbert W. Roesky*,§
†State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University,
361005 Xiamen, People's Republic of China
‡School of Chemistry and Chemical Engineering, Central South University, 410083 Changsha, People's Republic of China
§Institut fur Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Reactions of LGeCl (L = CH[C(Me)N(Ar)]2; Ar = 2,6-iPr2C6H3) with KOtBu or LiR (R = 2-thienyl, N(H)Ar,
PPh2) yielded the germanium(II) compounds LGeR [R = OtBu (1), 2-thienyl (2), N(H)Ar (3), PPh2 (4)]. The reduction of (2-
thienyl)2PCl with lithium afforded the diphosphane [(2-thienyl)2P]2 (5). The treatment of (2-thienyl)2PCl with LiAlH4 or
KHBtBu3 led to the formation of (2-thienyl)2PH (6). The NHC-assisted reaction of LGeCl and 6 resulted in the isolation of
LGeP(2-thienyl)2 (7). This is the first example where NHC is used for eliminating HCl from compounds with P−H and Ge−Cl
bonds. All solid products were characterized by elemental analysis, NMR and IR spectroscopy, and single-crystal X-ray structure
determination.
(Ar)]2; Ar = 2,6-iPr2C6H3; R = OtBu (1), 2-thienyl (2), N(H)
Ar (3), PPh2 (4), and P(2-thienyl)2 (7)].
INTRODUCTION
■
Germylenes are heavier divalent carbene analogues1 and
contain a singlet lone pair capable of binding to transition
metals in a coordinate fashion.2 Transition metal−germylene
chemistry has attracted special attention because of the
increased propensity of addition reactions across the M−GeII
bond for the activation of a variety of small molecules and
functional groups.3,4 Typically, group 10 metal germylene
complexes have shown the feasibility to interact with H2, CO2,5
O2,4,6 and COS.7 However, the synthesis of M−GeII
compounds by using the heteroleptic germylene LGeR (L =
monovalent ligand) with tunable substituents R is still limited
in its variety. It will be of interest to incorporate additional
donor functionalities adjacent to the GeII center to provide
further bonding sites for different metal fragments. The latter
may compete or collaborate with each other and turn out to be
efficient catalysts. In this approach, we have obtained some
results by using π-donor derivatives of composition LGeC
CR′ to generate their metal complexes with CuI and AgI
acceptors.8 To extend this work, we adopt a different strategy
by preparing germylenes containing adjacent σ-donor function-
alities as precursors. Therefore, we describe herein the
syntheses and characterization of LGeR [L = CH[C(Me)N-
RESULTS AND DISCUSSION
■
The metathesis reaction of LGeCl (L = HC[C(Me)N(Ar)]2, Ar
= 2,6-iPr2C6H3) with 1 equiv of KOtBu was carried out in Et2O
to give the targeted complex LGeOtBu (1, Scheme 1) in
Scheme 1. Formation of Compound 1 (Ar = 2,6-iPr2C6H3)
moderate yield. The 1H NMR resonances for the β-
diketiminate ligand are similar to those observed for related
germanium(II) compounds,9 with typical isopropyl patterns of
Received: November 4, 2011
Published: February 9, 2012
© 2012 American Chemical Society
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Article
two septets for CH groups and four doublets for methyl groups.
A high-field singlet (0.82 ppm) indicates the presence of the
tBu group. This method (elimination of alkali-metal chloride) is
found to be also applicable to the synthesis of LGeOC6F5,
which was alternatively accessible by the nucleophilic addition
of L′Ge (L′ = HC[{C(CH2)N(Ar)}C(Me)N(Ar)]) to
C6F5OH.10 In contrast, an attempt to react LGeCl with
LiOAr* (Ar* = 2,6-tBu2-4-MeC6H2) under the same conditions
or even at elevated temperatures was not successful, which is
presumably due to the increased steric hindrance around the
LiO moiety.
ppm).16 The β-diketiminato ligand plays an important role in
stabilizing compounds like 4. Reference reactions of
GeCl2·dioxane with 2 equiv of LiPPh2·2THF in the absence
or presence of NHC gave a mixture of products consisting of
17
diphosphane (Ph2P)2 as the major side product.
However, unlike the facile formation of 4, no reaction was
observed between LGeCl and the lithium-treated (2-
thienyl)2PCl. Therefore, we focused on this lithiation process.
The treatment of (2-thienyl)2PCl in THF with lithium chips
was accompanied by a color change of the solution from
colorless to bright yellow. After filtration, a crystalline solid of
[(2-thienyl)2P]2 (5; Scheme 3) was obtained in good yield
Analogously, the reaction of LGeCl with the in situ formed 2-
thienyl−Li from 2-thienyl bromide and nBuLi allowed isolation
1
of LGe(2-thienyl) (2; Scheme 2). In the H NMR spectrum,
Scheme 3. Formation of Compounds 5 and 6
Scheme 2. Formation of Compounds 2−4 and L′Ge (Ar =
2,6-iPr2C6H3)
from the concentrated filtrate. The 31P NMR chemical shift of 5
(−38.64 ppm) is significantly upfield-shifted when compared
with that of the precursor (2-thienyl)2PCl (53.23 ppm). In the
1H and 13C NMR spectra, the thienyl groups are unequivocally
identified. The resulting product was 5,18 which was further
characterized by single-crystal X-ray structural analysis.
Therefore, we switched to secondary phosphine as the
precursor19 for preparing (2-thienyl)2PLi. The treatment of (2-
thienyl)2PCl with LiAlH4 (or KHBtBu3) in OEt2 provided a
colorless liquid [(2-thienyl)2PH (6)] in low yield (Scheme 3).
In the IR spectrum of 6, the characteristic band (2285 cm−1)
indicates the presence of a PH group, which is in the expected
range (Mes2PH, 2361 and 2338 cm−1, where Mes = 2,4,6-
three characteristic multiplets (7.35, 7.33, and 6.82 ppm)
indicate the presence of a thienyl group with correct integration
ratios relative to those of the β-diketiminato ligand backbone.
The treatment of LGeCl with LiNEt2 or LiNiPr2 led to an
immediate color change of the reaction solution from bright
yellow to brown red and finally resulted in the formation of
L′Ge instead of the expected LGeNEt2 or LGeNiPr2 (Scheme
2). The syntheses of LGeNH2 and LGeNMe2 have been
previously demonstrated.11 The result obtained through the
elimination of LiCl and secondary amine is exactly the same as
that from the reaction of LGeCl with LiN(SiMe3)2.12 It has also
been demonstrated that L″GeN(SiMe3)2 could be isolated with
the support of a smaller β-diketiminato ligand (L″ =
HC[{C(CH2)N(Ar)}C(Me)N(Ph)]).13 On the contrary, the
treatment of LGeCl with LiN(H)Ar smoothly afforded
LGeN(H)Ar (3) in good yield (Scheme 2), in spite of the
increased steric bulk around the N center of the lithium amide
precursor. In another route, 3 was obtained by reducing LGeCl
with K.14 Consequently, we assume that LGeNR′2 derivatives
are only stable when R′ substituents are small enough, while
LGeN(H)R′ compounds may be obtained with larger R′
groups.
Me3C6H2).19 The H NMR spectrum shows a doublet (5.49
1
1
ppm) with a JPH coupling constant of 294.1 Hz, which is
consistent with the observation of a singlet (−90.06 ppm) in
the 31P NMR spectrum. These data are highly comparable to
1
those for Mes2PH (1H, 5.36 ppm, JPH = 235 Hz; 31P, −92.4
ppm).19 However, further reaction of 6 with nBuLi gave a
mixture of products according to NMR monitoring.
Also the treatment of LGeCl with lithium chips was not
successful. The isolated product was LLi. Subsequently, 6 was
treated with LGeCl in the presence of N-heterocyclic carbene
(NHC), where NHC functions as a HCl scavenger (Scheme 4).
Scheme 4. Formation of Compound 7 (NHC =
[C(Me)N(iPr)]2C)
A toluene solution of LGeCl was treated with the filtrate of
the reaction solution of Ph2PCl and lithium chips in
tetrahydrofuran (THF). After the addition of the chips, the
color of the mixture changed rapidly into a dark red. After
workup, a crystalline solid of LGePPh2 (4) was obtained from
an n-hexane extract (Scheme 2). The 31P NMR spectrum of 4
displays a low-field singlet (−14.91 ppm), which is close to that
in [{(Me3Si)2CH}(C6H4-2-CH2NMe2)P]2Ge (−45.8 ppm)15
and distinct from that found in LGeP(SiMe3)2 (−192.7
The same NHC-involved strategy was before successfully
applied to synthesize germanium(II) hydroxide LGeOH by
hydrolysis of LGeCl.20 To a mixture of LGeCl and NHC in
toluene was added a THF solution of 6. A color change from
yellow to dark red occurred almost instantly. A crystalline solid
of LGeP(2-thienyl)2 (7) was obtained from the n-hexane
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1, 2, 4, and 7
LGeOtBu (1), X = O(1)
LGe(2-thienyl) (2), X = C(16)
LGePPh2 (4), X = P(1)
LGeP(2-thienyl)2 (7), X = P(1)
Ge(1)−X
1.8272(14)
2.0312(14)
2.0159(14)
1.431(2)
1.966(9)
1.993(4)
1.993(4)
2.4746(11)
2.003(3)
2.029(3)
2.4453(15)
2.031(3)
2.025(4)
Ge(1)−N(1)
Ge(1)−N(2)
O(1)−C(30)
N(1)−Ge(1)−N(2)
N(1)−Ge(1)−X
N(2)−Ge(1)−X
87.68(5)
95.97(5)
91.7(2)
99.5(3)
99.5(3)
88.20(11)
99.24(8)
99.29(8)
88.65(14)
101.39(11)
97.88(11)
94.46(6)
C(30)−O(1)−Ge(1)
C(30)−P(1)−C
C(30)−P(1)−Ge(1)
C−P(1)−Ge(1)
121.60(11)
99.14(16)
100.25(10)
100.69(12)
104.3(2)
94.26(17)
100.04(16)
Table 2. Crystal Data, Data Collection Parameters, and Structure Refinement Details for Compounds 1, 2, 4, 5, and 7
LGeOtBu (1)
851949
LGe(2-thienyl) (2)
851950
LGePPh2 (4)
851951
[(2-thienyl)2P]2 (5)
851952
LGeP(2-thienyl)2 (7)
851953
CCDC
empirical formula
fw
C33H50GeN2O
563.34
C33H44GeN2S
573.35
C41H51GeN2P
675.40
C16H12P2S4
394.44
C37H47GeN2PS2
687.45
temp, K
cryst syst
space group
a, Å
173(2)
173(2)
173(2)
173(2)
173(2)
monoclinic
P21/n
orthorhombic
Cmca
monoclinic
P21/c
monoclinic
P21/c
monoclinic
P21/n
13.341(3)
16.611(3)
15.085(3)
90
22.3720 (13)
9.3145 (7)
28.869 (3)
90
17.202(3)
12.099(2)
18.032(4)
90
8.8941(18)
8.5353(17)
11.821(2)
90
10.3778(8)
15.2472(16)
22.2675(18)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
107.07(3)
90
90
99.31(3)
90
104.99(3)
90
93.784(8)
90
90
V, Å3
3195.7(11)
4
6015.8 (8)
8
3703.6(13)
4
866.9(3)
2
3515.8(5)
4
Z
D
calcd, g/cm3
1.171
1.266
1.211
1.511
1.299
μ, mm−1
0.984
1.112
0.900
0.724
1.064
F(000)
1208
2432
1432
404
1448
cryst size, mm
θ range, deg
index range
0.60 × 0.45 × 0.22
3.04−27.48
−17 ≤ h ≤ 17
−21 ≤ k ≤ 21
−19 ≤ l ≤ 19
0.50 × 0.40 × 0.05
2.76−25.00
−26 ≤ h ≤ 24
−6 ≤ k ≤ 11
−14 ≤ l ≤ 34
0.10 × 0.10 × 0.10
3.00−25.00
−20 ≤ h ≤ 20
−14 ≤ k ≤ 14
−19 ≤ l ≤ 21
0.27 × 0.20 × 0.07
3.36−25.00
−10 ≤ h ≤ 10
−10 ≤ k ≤ 10
−14 ≤ l ≤ 14
0.10 × 0.10 × 0.02
2.67−25.00
−11 ≤ h ≤ 12
−18 ≤ k ≤ 17
−26 ≤ l ≤ 15
reflns collected/unique 30657/7307 [R(int) =
8440/2709 [R(int) =
0.0591]
28277/6499 [R(int) =
0.0645]
6461/1514 [R(int) =
0.0417]
16594/6158 [R(int) =
0.0970]
0.0379]
data/restraints/param
GOF on F2
7307/4/364
1.081
2709/19/192
1.080
6499/0/417
1.165
1514/0/100
1.234
6158/4/399
1.027
final R indices [I >
2σ(I)]
R1 = 0.0319, wR2 =
0.0771
R1 = 0.0895, wR2 =
0.1778
R1 = 0.0406, wR2 =
0.0870
R1 = 0.0964, wR2 =
0.2997
R1 = 0.0732, wR2 =
0.0882
R indices (all data)
R1 = 0.0451, wR2 =
0.0823
R1 = 0.1205, wR2 =
0.1924
R1 = 0.0717, wR2 =
0.1189
R1 = 0.1151, wR2 =
0.3419
R1 = 0.1275, wR2 =
0.1005
largest diff peak/hole, 0.357/−0.299
0.867/−1.627
0.741/−0.985
2.193/−0.760
0.529/−0.499
e/Å3
extract in moderate yield. The 31P NMR spectrum displays a
singlet (−74.87 ppm), which is markedly low-field-shifted
relative to that of 6 (−90.06 ppm). In the 1H NMR spectrum of
7, the distinct doublet for PH proton resonance of secondary
phosphine disappears and three multiplets (6.85, 6.52, and 6.50
ppm) are assignable to proton resonances of the thienyl groups.
In contrast, the reaction of LGeH and (2-thienyl)2PCl in the
presence of NHC does not yield 7. For comparison reasons, the
above-mentioned LGeOC6F5 could also not be obtained using
the NHC-assisted metathesis reaction of LGeCl and
C6F5OH.21
bond lengths and angles are reported in Table 1 (except for
compound 5), and crystal data and collection parameters are
listed in Table 2. The Ge and P centers are all three-coordinate,
and each adopts a pyramidal geometry. Pyramidalization was
measured by calculating the angle (θ) at the center of the
pyramid.22 The obtained θGe angles [123.3° (1), 120.1° (2),
121.1° (4), 120.8° (7)] indicate an evident deviation from
planarity (θ = 90°) and are more or less close to the ideal case
with three mutually perpendicular Ge 4p atomic orbitals (θ ≈
125.3°). It is suggested that the germanium σ orbital owns a
high 4p character in the Ge−X (X = O, C, P) bond, while a
lone pair of electrons occupies the germanium vertex with high
4s character.16,23 The θP angles [117.8° (4), 117.6° (5), 118.1°
The composition of compounds 1, 2, 4, 5, and 7 was further
confirmed by single-crystal X-ray structural analysis. Selected
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(7)] are found in a narrow range and suggest a situation for P
vertexes similar to those for Ge sites. Compounds 1, 2, 4, and 7
each consist of a puckered C3N2Ge six-membered ring in boat
conformation. Compound 2 shows the structural features of the
parent LGeCl in terms of the orientation of substituents at the
Ge center as well as the comparable folding angle between
N(1)−C(2)−C(4)−N(2) (denoted as N2C2) and N2Ge planes
[19.18° (2), 21.18° (LGeCl)]. In contrast, the folding angles
for compounds 1, 4, and 7 are much wider [34.34° (1), 36.59°
(4), 39.19° (7)], and the corresponding substituents are all
bent down relative to the prow atom.
Compound 1 crystallizes from n-hexane in the monoclinic
space group P21/n (Table 2). The molecular structure of 1
(Figure 1) features a nearly right angle of N−Ge−O (95.21°
Figure 2. Molecular structure of 2. Thermal ellipsoids are drawn at the
50% level, and all H atoms, except those of the thienyl group, are
omitted for clarity.
Compound 4 (Figure 3) crystallizes as bright-yellow crystals
in the monoclinic space group P21/c. The N−Ge−P (99.26°
Figure 1. Molecular structure of 1. Thermal ellipsoids are drawn at the
50% level, and all H atoms are omitted for clarity.
av) and a bent Ge−O−C linkage [121.60(11)°]. These data are
marginally larger but still comparable to those of the phenyl
analogue LGeOPh [93.88 and 117.5(4)°].10 It is noted that the
Ge−O bond length [1.8272(14) Å] is evidently shorter than
those observed for (C5H5)Sn(μ-OtBu)2GeOtBu [1.839(10)
Å],24 NHC·Ge(OtBu)2 [1.874(5) Å],25 and aryl-substituted
analogues LGeOPh [1.860(4) Å] and LGeOC6F5 [1.9515(14)
Å].10 Comparable Ge−O distances are found in LGeOH
[1.828(1) Å]20 and Ge(OAr′)2 [1.826(1) and 1.827(1) Å; Ar′ =
2,3,5,6-Ph4C6H].26 In addition, the O−C bond separation of 1
[1.431(2) Å] is longer than those of terminal alkoxyl groups in
compounds mentioned above (1.319−1.424 Å).10,24,25
Compound 2 represents the first structurally characterized
complex with a thienyl group bound directly to the GeII center.
The crystal structure of 2 (Figure 2) is of higher symmetry
(orthorhombic, Cmca) than that of 1. A mirror plane passes
through C(3), Ge(1), and the thienyl group. The imposed
symmetry implies that the thienyl ring is exactly planar and
perpendicular to the N2C2 plane. The S atom is directed
opposite to the lone pair of electrons on the Ge center. The
N−Ge−C angle [99.5(3)°] is a little wider than the N−Ge−O
angle in 1 (95.25° av), and the Ge−C bond length [1.966(9)
Å] is slightly longer than those found in germanium(IV) thienyl
compounds (1.94−1.95 Å).27
Figure 3. Molecular structure of 4. Thermal ellipsoids are drawn at the
50% level, and all H atoms are omitted for clarity.
av), Ge−P−C (100.47° av), and C−P−C [99.14(16)°] angles
are very close to each other. The chemically active lone pairs at
the respective Ge and P apexes are located in a trans
arrangement along the Ge−P vector. Two phenyl planes are
almost mutually perpendicular (87.55°), while their angles
relative to the N2C2 quasi-plane are quite different (48.61 vs
69.27°). Although some other compounds containing the
−GePPh2 moiety have been previously structurally charac-
terized, none of them has a three-coordinate P atom bound to
the GeII center.28 The Ge−P bond length [2.4746(11) Å] of 4
is substantially longer than those found in related germanium-
(II) compounds [2.333(1)−2.4300(11) Å]15,16,29 and slightly
shorter than those in dimeric (tBu2PGeCl)2 [2.4876(8) Å]30 as
well as in the adduct Ph3P·GeCl2 [2.5084(7) Å].31 The product
of the reaction of (2-thienyl)2 PCl and Li is [( 2-thienyl)2P]2
(5). The single-crystal X-ray structural analysis of 5 is shown in
Figure 4. The P(1)−P(1A) bond length of 2.241(3) Å falls in
the expected range of compounds with P−P single bonds.
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Ar (3), PPh2 (4)] were obtained from the reaction of LGeCl
with the corresponding alkali-metal precursors. The preparation
of the (2-thienyl)2PLi precursor was not successful by the
treatment of (2-thienyl)2PCl with lithium. Instead, the
diphosphane 5 was formed in this reduction. 7 was successfully
prepared from the NHC-assisted reaction of LGeCl and 6. This
is the first example where NHC is used for eliminating HCl
from compounds with P−H and Ge−Cl functionalities. The Ge
as well as the P centers exhibit pyramidal geometry and
accommodate a lone pair of electrons with high 4s character. 1
represents an interesting example with short Ge−O and long
O−C bond lengths. Germanium(II) compounds with 2-thienyl
(2), PPh2 (4), and P(2-thienyl)2 (7) substituents are interesting
precursors for coordination compounds.
EXPERIMENTAL SECTION
■
Figure 4. Molecular structure of 5. Thermal ellipsoids are drawn at the
50%. Selected bond lengths (Å) and angles (deg): P(1)−P(1A)
2.241(3), P(1)−C(1) 1.822(7), P(1)−C(5) 1.822(6); C(1)−P(1)−
C(5) 104.6(3), C(1)−P(1)−P(1A) 97.5(2), C(5)−P(1)−P(1A)
98.7(2).
Materials and Methods. All manipulations were carried out
under nitrogen using Schlenk techniques or inside a Mbraun glovebox
filled with argon, in which the calibrated values of O2 and H2O were
controlled below 1.2 ppm. Organic solvents including toluene, n-
hexane, THF, and Et2O were predried with sodium wire and then
heated with sodium/potassium benzophenone under nitrogen prior to
use. C6D6 was degassed, dried with a sodium/potassium alloy, and
filtered before use. NMR spectra were recorded on a Bruker AV 500
spectrometer. Melting points were measured in a sealed glass tube
Compound 7 (Figure 5) crystallizes in the monoclinic space
group P21/n. The C−P−C angle of 7 [104.3(2)°] is a little
using a Buchi B-540 instrument without correction. IR spectra were
̈
recorded on a Nicolet 380 (Thermo Fisher Scientific) spectrometer.
Elemental analysis was performed with a Thermo Quest Italia SPA EA
1110 instrument. Chemicals commercially available were purchased
from Aldrich and used as received. GeCl2·dioxane,33 LGeCl (L =
HC[C(Me)N(Ar)]2, Ar = 2,6-iPr2C6H3),9 LGeH,34 L′Ge (L′ =
HC[{C(CH2)N(Ar)}C(Me)N(Ar)]),12 LiPPh2·2THF,35 (2-thie-
nyl)2PCl,36 LiOAr* (Ar* = 2,6-tBu2-4-MeC6H2),37 LiOC6F5, LiNEt2,
LiNiPr2, LiN(H)Ar,38 and 1,3-diisopropyl-4,5-dimethylimidazol-2-
ylidene (abbreviated as NHC)39 were prepared as described in the
literature or by modified methods.
LGeOtBu (1). At −18 °C, a suspension of KOtBu (0.12 g, 1 mmol)
in Et2O (20 mL) was added drop by drop to a solution of LGeCl (0.53
g, 1 mmol) in Et2O (30 mL). The mixture was stirred and warmed to
room temperature. After stirring for additional 12 h, the solvent was
removed under vacuum and the residue was extracted with n-hexane
(8 mL). The extract was stored at −18 °C in a freezer for 2 days, and
X-ray-quality pale-yellow block crystals of 1 were obtained (0.41 g,
73%). Mp: 216 °C. 1H NMR (500.13 MHz, C6D6, ppm): δ 7.05−7.20
(m, Ar), 4.64 (s, 1 H, γ-CH), 3.86 (sept, 3JHH = 6.9 Hz, 2 H, CHMe2),
3.37 (sept, 3JHH = 7.0 Hz, 2 H, CHMe2), 1.54 (d, 3JHH = 6.8 Hz, 6 H,
Figure 5. Molecular structure of 7. Thermal ellipsoids are drawn at the
50% level, and all H atoms, except those of the thienyl groups, are
omitted for clarity.
3
CHMe2), 1.54 (s, 6 H, β-Me), 1.37 (d, JHH = 6.8 Hz, 6 H, CHMe2),
3
3
1.19 (d, JHH = 6.9 Hz, 6 H, CHMe2), 1.13 (d, JHH = 6.8 Hz, 6 H,
CHMe2), 0.82 (s, 9 H, CMe3). 13C NMR (126 MHz, C6D6, ppm): δ
163.66 (CN), 145.20, 144.23, 139.69, 126.50, 124.02, 123.73 (Ar),
94.73 (γ-CH), 69.74 (CMe3), 33.24 (CMe3), 28.50, 28.33 (CHMe2),
25.87, 24.60, 24.37, 24.08 (CHMe2), 22.47 (β-Me). IR (Nujol mull,
wider than that of 4 [99.03(19)°], while the angle between the
two thienyl planes (135.98°) is much broader than that for
their phenyl counterparts in 4 (87.93°). The two thienyl planes
show similar angles of 78.15° and 79.71° relative to the N2C2
quasi-plane, respectively. The Ge−P bond length [2.4453(15)
Å] of 7 is a little shorter than that in 4 [2.4746(11) Å]. In line
with 4, the lone pairs of electrons at Ge and P sites are directed
to the opposite direction. As such, the S atoms on thienyl
groups gain the chance of being aligned with the Ge center,32
creating a bowl-like environment with potential chelating
ability.
cm−1): ν
̃
1658.52 (vw), 1621.28 (vw), 1562.66 (w), 1554.89 (w),
1520.4 (w), 1322.76 (m), 1173.01 (w), 1099.79 (vw), 1057.79 (vw),
1019.26 (w), 935.43 (w), 891.32 (vw), 850.2 (vw), 793.87 (w), 765.43
(w), 608.33 (vw). Anal. Calcd for C33H50GeN2O (563.4): C, 70.35; H,
8.95; N, 4.97. Found: C, 68.78; H, 8.73; N, 4.94.
LGe(2-thienyl) (2). At −50 °C, nBuLi (0.52 mL, 2.4 M, 1.25 mmol)
was added drop by drop to a solution of 2-bromothiophene (0.20 g,
1.25 mmol) in Et2O (30 mL). The mixture was stirred and warmed to
room temperature. Additional stirring for 12 h ensured the complete
formation of 2-thienyllithium. The light-brown suspension of 2-
thienyllithium obtained was added to a solution of LGeCl (0.53 g, 1
mmol) in Et2O (30 mL) at −18 °C. After stirring for 12 h, the solvent
was removed under vacuum and the residue was treated upon quick
washing with cold n-hexane (2 × 2 mL) and then extracted with n-
hexane (10 mL). The extract was kept at −18 °C for 2 days, and X-ray-
quality pale-yellow crystals of 2 were obtained (0.37 g, 65%). Mp: 191
CONCLUSION
■
Germanium(II) compounds of composition LGeR (L =
CH[C(Me)N(Ar)]2; Ar = 2,6-iPr2C6H3) containing adjacent
σ-donating functionalities [R = OtBu (1), 2-thienyl (2), N(H)
2429
dx.doi.org/10.1021/ic202388d | Inorg. Chem. 2012, 51, 2425−2431

Inorganic Chemistry
Article
1
°C. H NMR (500.13 MHz, C6D6, ppm): δ 7.35 (m, 1H, HC5), 7.33
C6D6, ppm): δ −90.06. IR (Nujol mull, cm−1): ν
̃
2284.96 (w, PH),
(m, 1H, HC3), 6.83−7.20 (m, Ar), 6.82 (m, 1H, HC4), 5.10 (s, 1 H, γ-
1408.22 (m), 1334.8 (w), 1219.34 (s), 1083.91 (m), 1053.9 (vw),
1002.94 (s), 895.61 (w), 851.56 (m), 831.97 (w), 796.56 (m), 742.06
(w), 703.81 (vs), 501.39 (w), 424.22 (m).
3
3
CH), 3.64 (sept, JHH = 7.0 Hz, 2 H, CHMe2), 2.98 (sept, JHH = 7.0
Hz, 2 H, CHMe2), 1.63 (d, 3JHH = 6.6 Hz, 6 H, CHMe2), 1.41 (s, 6 H,
β-Me), 1.17 (d, 3JHH = 6.6 Hz, 6 H, CHMe2), 1.07 (d, 3JHH = 6.6 Hz, 6
LGeP(2-thienyl)2 (7). At −18 °C, KBHtBu3 (1 mL, 1 M in Et2O, 1
mmol) was added to a solution of (2-thienyl)2PCl (0.23 g, 1 mmol) in
Et2O (30 mL). This mixture was stirred and warmed to room
temperature. After additional stirring for 12 h, the complete formation
of 6 was observed, and the suspension obtained was added to a
mixture of LGeCl (0.53 g, 1 mmol) and NHC (0.18 g, 1 mmol) in
Et2O (40 mL) at −18 °C. The mixture was vigorously stirred and
warmed to room temperature. After additional stirring for 12 h, all
volatiles were removed under vacuum to give an oily paste. A small
portion of n-hexane (3 mL) was layered on this paste. By storing the
oily paste at room temperature for 1 week, dark-red crystals of 7 were
H, CHMe2), 0.69 (d, JHH = 6.6 Hz, 6 H, CHMe2). 13C NMR (126
3
MHz, C6D6, ppm): δ 165.93 (CN), 146.67, 143.33, 141.24 (Ar),
137.16 (C5), 130.02 (C3), 127.09 (Ar), 125.53 (C4), 124.59, 123.94
(Ar), 98.93 (γ-CH), 29.01, 28.10 (CHMe2), 25.54, 24.50, 24.34, 23.80
(CHMe2), 23.22 (β-Me). IR (Nujol mull, cm−1): ν
̃
1658.3 (vw),
1621.73 (vw), 1551.76 (w), 1529.15 (w), 1316.22 (m), 1256.18 (w),
1170.76 (w), 1098.75 (w), 1056.95 (w), 1019.84 (w), 968.25 (w),
934.97 (w), 852.04 (w), 794.37 (w), 757.06 (w), 636.56 (vw), 520.32
(vw). Anal. Calcd for C33H44GeN2S (573.42): C, 69.12; H, 7.73; N,
4.89. Found: C, 68.57; H, 7.58; N, 4.91.
1
obtained (0.26 g, 38%). Mp: 198 °C. H NMR (500.13 MHz, C6D6,
LGeN(H)Ar (3). The preparation of 3 is similar to that of 2 using
ArHNLi (2.4 mmol), which is in situ formed from the reaction of
ArNH2 (0.5 mL, 2.4 mmol), nBuLi (1 mL, 2.4 M in n-hexane, 2.4
mmol), and LGeCl (1.26 g, 2.4 mmol) as starting materials.
Compound 3 was obtained as colorless crystals (1.1 g, 69%).
Spectroscopic data are identical with those previously reported.14
LGePPh2 (4). Finely divided lithium chips (0.07 g, 10 mmol)) were
added to a solution of Ph2PCl (0.44 g, 2 mmol) in THF (30 mL) at
room temperature. The mixture was vigorously stirred for 6 h, and
Ph2PLi was formed and added via filtration to a solution of LGeCl
(1.05 g, 2 mmol) in Et2O (40 mL) at −18 °C. The mixture was stirred
and warmed to room temperature. After additional stirring for 12 h, all
volatiles were removed under vacuum and the residue was extracted
with n-hexane (15 mL). The solution was concentrated (ca. 5 mL) and
then stored at −18 °C in a freezer. After 2 days, dark-red crystals of 4
ppm): δ 6.83−7.20 (m, Ar), 6.85 (m, 1H, HC5), 6.52 (m, 1H, HC3),
6.50 (m, 1H, HC4), 4.70 (s, 1 H, γ-CH), 4.03 (m, 2 H, CHMe2), 3.25
3
3
(sept, JHH = 6.8 Hz, 2 H, CHMe2), 1.78 (d, JHH = 6.8 Hz, 6 H,
3
CHMe2), 1.42 (s, 6 H, β-Me), 1.20 (d, JHH = 6.8 Hz, 6 H, CHMe2),
3
3
1.09 (d, JHH = 6.6 Hz, 6 H, CHMe2), 1.06 (d, JHH = 6.8 Hz, 6 H,
CHMe2). 13C NMR (126 MHz, C6D6, ppm): δ 166.42 (CN), 144.90,
143.07, 140.48 (Ar), 140.11 (d, JPC = 42.2 Hz, C2), 136.40 (C5),
133.35 (d, JPC = 19.7 Hz, C4), 128.93 (C3), 127.03, 124.78, 124.25
(Ar), 96.63 (γ-CH), 28.70, 28.70 (CHMe2), 25.06, 24.95, 24.51, 24.27
(CHMe2), 22.48 (β-Me). 31P NMR (202 MHz, C6D6, ppm): δ −74.87.
IR (Nujol mull, cm−1): ν
̃
2669 (m), 1709.76 (vw), 1691.65 (vw),
1658.99 (vw), 1641.71 (vw), 1620.57 (vw), 1553.48 (w), 1513.75 (w),
1316.64 (s), 1215.64 (w), 1170.14 (m), 1096.55 (w), 1079.23 (w),
1055.53 (w), 1014.84 (w), 966.33 (w), 934.14 (w), 890.97 (w), 845.03
(w), 822.71 (w), 792.62 (w), 704.01 (w), 692.71 (w), 570.22 (vw),
516.23 (vw), 498.9 (vw), 428.11 (vw). Anal. Calcd for
C37H47GeN2PS2 (687.53): C, 64.64; H, 6.89; N, 4.07. Found: C,
64.01; H, 6.73; N, 4.11.
1
were obtained (0.96 g, 71%). Mp: 202 °C. H NMR (500.13 MHz,
C6D6, ppm): δ 6.75−7.02 (m, Ar), 4.73 (s, 1 H, γ-CH), 4.14 (m, 2 H,
CHMe2), 3.23 (sept, 3JHH = 7.0 Hz, 2 H, CHMe2), 1.69 (d, 3JHH = 7.0
3
Hz, 6 H, CHMe2), 1.44 (s, 6 H, β-Me), 1.20 (d, JHH = 7.0 Hz, 6 H,
CHMe2), 1.07 (d, 3JHH = 7.0 Hz, 6 H, CHMe2), 0.98 (d, 3JHH = 7.0 Hz,
6 H, CHMe2). 13C NMR (126 MHz, C6D6, ppm): δ 166.42 (CN),
144.98, 143.16, 141.25 (Ar), 140.75 (d, JPC = 27.9 Hz, Ph), 135.38 (d,
JPC = 16.9 Hz, Ph), 134.50 (d, JPC = 13.0 Hz, Ph), 134.40 (d, JPC = 12.8
Hz, Ph), 127.00, 125.70, 124.92 (Ar), 124.22 (Ph), 96.97 (γ-CH),
29.00, 28.93, 28.40 (CHMe2), 25.18, 24.90, 24.46, 24.07, 23.99
(CHMe2), 22.58 (β-Me). 31P NMR (202 MHz, C6D6, ppm): δ −14.91.
Structure Determination. Data were collected on a Rigaku R-
AXIS RAPID Image Plate single-crystal diffractometer for 1, 4, and 5
and an Oxford Gemini S Ultra system for 2 and 7. In all cases,
graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å) was used
in ω-scan mode. Absorption corrections were applied using the
spherical harmonics program (multiscan type). The structures were
solved by direct methods (SHELXS-97)40 and were refined by full-
matrix least squares on F2 with the program SHELXL-97.41 In general,
the non-H atoms were located by difference Fourier synthesis and
refined anisotropically, and H atoms were included using the riding
model with Uiso tied to Uiso of the parent atoms unless otherwise
specified. A summary of cell parameters, data collection, and structure
solution and refinement is given in Table 2.
IR (Nujol mull, cm−1): ν
̃
2668.8 (w), 1555.19 (w), 1513.4 (w),
1319.14 (m), 1257.2 (m), 1174.6 (w), 1096.81 (w), 1058.43 (w),
1017.62 (w), 965.87 (w), 933.92 (w), 853.24 (w), 792.56 (w), 758.11
(w), 736.9 (m), 694.79 (m), 519.4 (vw), 498.68 (vw), 475.86 (vw),
445.02 (vw). Anal. Calcd for C41H51GeN2P (675.47): C, 72.9; H, 7.61;
N, 4.15. Found: C, 71.81; H, 7.56; N, 4.19.
[(2-Thienyl)2P]2 (5). Finely divided lithium chips (0.04 g, 5 mmol))
were added to a solution of (2-thienyl)2PCl (0.23 g, 1 mmol) in THF
(20 mL) at room temperature. The mixture was vigorously stirred for
6 h. All volatiles were removed under vacuum, and the residue was
extracted with n-hexane (10 mL). The extract was concentrated (ca. 5
mL) and stored at −18 °C in a freezer. After 2 days, pale-yellow
ASSOCIATED CONTENT
* Supporting Information
Crystal data (CIF) for compounds 1, 2, 4, 5, and 7. This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
1
crystals of 5 were obtained (0.34 g, 87%). Mp: 136 °C. H NMR
(500.13 MHz, C6D6, ppm): δ 7.24 (m, 1H, HC5), 6.59 (m, 1H, HC3),
6.58 (m, 1H, HC4). 13C NMR (126 MHz, C6D6, ppm): δ 136.41 (t,
JPC = 15.7 Hz, C5), 132.13 (C3), 128.95 (C2), 128.18 (C4). 31P NMR
AUTHOR INFORMATION
Corresponding Author
*E-mail: hpzhu@xmu.edu.cn (H.Z.), hroesky@gwdg.de
(H.W.R.). Fax: (+86) 592-2181912 (H.Z.), (+49) 551-393-
373 (H.W.R.).
■
(202 MHz, C6D6, ppm): δ −38.64. IR (Nujol mull, cm−1): ν
̃
1623.14
(m), 1552.6 (s), 1321.57 (s), 1276.05 (m), 1259.37 (m), 1220.93 (w),
1174.31 (m), 1100.4 (m), 1057.63 (m), 1021.81 (m), 974.83 (w),
935.12 (w), 889.51 (vw), 854.09 (w), 796.32 (m), 758.35 (m), 596.15
(vw), 524.52 (vw). Anal. Calcd for C16H12P2S4 (394.47): C, 48.72; H,
3.07. Found: C, 48.35; H, 3.13.
Notes
The authors declare no competing financial interest.
(2-Thienyl)2PH (6). The preparation of 6 was accomplished like that
of Mes2PH19 from (2-thienyl)2PCl (0.47 g, 2 mmol) and LiAlH4 (0.08
ACKNOWLEDGMENTS
1
■
g, 2 mmol) to give a colorless liquid. Yield: 0.09 g (23%). H NMR
This work was supported by the NSFC (Grants 20902112,
20972129, and 20423002), the China Postdoctoral Science
Foundation (Grant 20090460748), and the Deutsche For-
schungsgemeinschaft.
(500.13 MHz, C6D6, ppm): δ 7.12−7.14 (m, 1 H, HC5), 6.98 (m, 1 H,
HC3), 6.63 (m, 1 H, HC4), 5.49 (d, 1JPH = 294.11 Hz, 1 H). 13C NMR
(126 MHz, C6D6, ppm): δ 136.27 (d, JPC = 27.8 Hz, C5), 133.03 (d,
JPC = 24.1 Hz, C2), 131.97 (C3), 127.98 (C4). 31P NMR (202 MHz,
2430
dx.doi.org/10.1021/ic202388d | Inorg. Chem. 2012, 51, 2425−2431

Inorganic Chemistry
Article
(28) (a) Bruncks, N.; du Mont, W.-W.; Pickardt, J.; Rudolph, G.
Chem. Ber. 1981, 114, 3572−3580. (b) Veith, M.; Zimmer, M. Z.
Anorg. Allg. Chem. 1996, 622, 1471−1477. (c) Fedotova, Y. V.;
Kornev, A. N.; Sushev, V. V.; Kursky, Y. A.; Mushtina, T. G.;
Makarenko, N. P.; Fukin, G. K.; Abakumov, G. A.; Zakharov, L. N.;
Rheingold, A. L. J. Organomet. Chem. 2004, 689, 3060−3074.
(d) Davis, M. F.; Levason, W.; Reid, G.; Webster, M. Dalton Trans.
2008, 2261−2269.
(29) (a) Izod, K.; Stewart, J.; Clark, E. R.; McFarlane, W.; Allen, B.;
Clegg, W.; Harrington, R. W. Organometallics 2009, 28, 3327−3337.
(b) Reddy, N. D.; Jana, A.; Roesky, H. W.; Samuel, P. P.; Schulzke, C.
Dalton Trans. 2010, 39, 234−238. (c) Izod, K.; Stewart, J.; Clark, E. R.;
Clegg, W.; Harrington, R. W. Inorg. Chem. 2010, 49, 4698−4707.
(30) Druckenbrodt, C.; du Mont, W. W.; Ruthe, F.; Jones, P. G. Z.
Anorg. Allg. Chem. 1998, 624, 590−594.
(31) Leites, L. A.; Zabula, A. V.; Bukalov, S. S.; Korlyukov, A. A.;
Koroteev, P. S.; Maslennikova, O. S.; Egorov, M. P.; Nefedov, O. M. J.
Mol. Struct. 2005, 750, 116−122.
REFERENCES
■
(1) (a) Nagendran, S.; Roesky, H. W. Organometallics 2008, 27, 457−
492. (b) Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Chem. Rev. 2009, 109,
3479−3511.
(2) (a) Petz, W. Chem. Rev. 1986, 86, 1019−1047. (b) Lappert, M.
F.; Rowe, R. S. Coord. Chem. Rev. 1990, 100, 267−292. (c) Neumann,
W. P. Chem. Rev. 1991, 91, 311−334. (d) Tokitoh, N.; Okazaki, R.
Coord. Chem. Rev. 2000, 210, 251−277.
(3) (a) Castel, A.; Riviere, P.; Satge, J.; Moreau, J. J. E.; Corriu, R. J.
P. Organometallics 1983, 2, 1498−1502. (b) Banaszak Holl, M. M.;
Peck, D. R. Germanimum: Organometallic Chemistry; John Wiley &
Sons, Ltd.: New York, 2006. (c) Leung, W. P.; So, C. W.; Chong, K.
H.; Kan, K. W.; Chan, H. S.; Mak, T. C. W. Organometallics 2006, 25,
2851−2858. (d) Arii, H.; Nakadate, F.; Mochida, K. Organometallics
2009, 28, 4909−4911.
(4) York, J. T.; Young, V. G.; Tolman, W. B. Inorg. Chem. 2006, 45,
4191−4198.
(5) Litz, K. E.; Henderson, K.; Gourley, R. W.; Holl, M. M. B.
Organometallics 1995, 14, 5008−5010.
(6) Cygan, Z. T.; Bender, J. E.; Litz, K. E.; Kampf, J. W.; Banaszak
Holl, M. M. Organometallics 2002, 21, 5373−5381.
(7) Cygan, Z. T.; Kampf, J. W.; Banaszak Holl, M. M. Inorg. Chem.
2003, 42, 7219−7226.
(8) Zhao, N.; Yang, Y.; Tan, G. W.; Li, Y.; Zhu, H. P.; Roesky, H. W.
Unpublished results.
(32) One of the thienyl rings exhibits disorder at the S(2) and C(35)
sites because the same crystallographic position of them is settled by
C(35′) and S(2′), respectively. This disorder could not be removed by
reducing the symmetry of the space group. Thus, the structure of 7 is
best described with the help of the occupation factors 0.64 and 0.36.
(33) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.;
Thorne, A. J. J. Chem. Soc., Dalton Trans. 1986, 1551−1556.
(34) (a) Pineda, L. W.; Jancik, V.; Starke, K.; Oswald, R. B.; Roesky,
H. W. Angew. Chem., Int. Ed. 2006, 45, 2602−2605. (b) Jana, A.;
Ghoshal, D.; Roesky, H. W.; Objartel, I.; Schwab, G.; Stalke, D. J. Am.
Chem. Soc. 2009, 131, 1288−1293.
(9) (a) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.;
Power, P. P. Organometallics 2001, 20, 1190−1194. (b) During the
revision of this manuscript, Ferro et al. (dx.doi.org/10.1021/
ic201841m) reported the synthesis and characterization of compound
1.
(35) Bartlett, R. A.; Olmstead, M. M.; Power, P. P. Inorg. Chem. 1986,
25, 1243−1247.
(10) Jana, A.; Nekoueishahraki, B.; Roesky, H. W.; Schulzke, C.
Organometallics 2009, 28, 3763−3766.
(36) Derrien, N.; Dousson, C. B.; Roberts, S. M.; Berens, U.; Burk,
M. J.; Ohff, M. Tetrahedron: Asym. 1999, 10, 3341−3352.
(37) Healy, M. D.; Barron, A. R. Angew. Chem., Int. Ed. 1992, 31,
921−922.
(11) (a) Jana, A.; Objartel, I.; Roesky, H. W.; Stalke, D. Inorg. Chem.
2009, 48, 798−800. (b) Jana, A.; Roesky, H. W.; Schulzke, C.; Samuel,
P. P.; Doring, A. Inorg. Chem. 2010, 49, 5554−5559.
̈
(38) Patton, J. T.; Feng, S. G.; Abboud, K. A. Organometallics 2001,
20, 3399−3405.
(12) Driess, M.; Yao, S. L.; Brym, M.; van Wullen, C. Angew. Chem.,
̈
Int. Ed. 2006, 45, 4349−4352.
(39) Kuhn, N.; Kratz, T. Synthesis 1993, 561−562.
(13) Akkari, A.; Byrne, J. J.; Saur, I.; Rima, G.; Gornitzka, H.; Barrau,
J. J. Organomet. Chem. 2001, 622, 190−198.
(40) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467−473.
(41) Sheldrick, G. M. SHELX-97, Programs for the Solution and
(14) Wang, W.; Yao, S.; van Wullen, C.; Driess, M. J. Am. Chem. Soc.
̈
Refinement of Crystal Structures; Universitat Gottingen: Gottingen,
̈
̈
̈
2008, 130, 9640−9641.
Germany, 1997.
(15) Izod, K.; McFarlane, W.; Allen, B.; Clegg, W.; Harrington, R. W.
Organometallics 2005, 24, 2157−2167.
(16) Yao, S. L.; Brym, M.; Merz, K.; Driess, M. Organometallics 2008,
27, 3601−3607.
(17) Dashti-Mommertz, A.; Neumuller, B. Z. Anorg. Allg. Chem.
̈
1999, 625, 954−960.
(18) Burck, S.; Gudat, D.; Nieger, M. Angew. Chem., Int. Ed. 2004, 43,
4801−4804.
(19) Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Sigel, G. A. Inorg.
Chem. 1987, 26, 1941−1946.
(20) Pineda, L. W.; Jancik, V.; Roesky, H. W.; Neculai, D.; Neculai,
A. M. Angew. Chem., Int. Ed. 2004, 43, 1419−1421.
(21) Kuhn, N.; Mallah, E.; Maichle-Moßmer, C.; Steimann, M. Z.
̈
Naturforsch., B: Chem. Sci. 2009, 64, 835−839.
(22) Haddon, R. C. J. Am. Chem. Soc. 1987, 109, 1676−1685.
(23) Maksic,
2623−2629.
́ ̌ ́
Z. B.; Kovacevic, B. J. Chem. Soc., Perkin Trans. 2 1999,
(24) Veith, M.; Mathur, C.; Mathur, S.; Huch, V. Organometallics
1997, 16, 1292−1299.
(25) Rupar, P. A.; Jennings, M. C.; Baines, K. M. Organometallics
2008, 27, 5043−5051.
(26) Weinert, C. S.; Fenwick, A. E.; Fanwick, P. E.; Rothwell, I. P.
Dalton Trans. 2003, 532−539.
(27) (a) Lukevics, E.; Belyakov, S.; Pudova, O. J. Organomet. Chem.
1996, 523, 41−45. (b) Karipides, A.; Reed, A. T.; Haller, D. A.; Hayes,
F. Acta Crystallogr., Sect. B 1977, 33, 950−951. (c) Lukevics, E.;
Ignatovich, L.; Belyakov, S. Chem. Heterocycl. Compd. 2007, 43, 243−
249.
2431
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