β-diketiminate germylene-supported pentafluorophenylcopper(I) and -silver(I) complexes [LGe(Me)(CuC6F5)n] 2 (n = 1, 2), LGe[C(SiMe3)N2]AgC 6F5, and {LGe[C(SiMe3)N2](AgC 6F5)2}2

Article abstract of DOI:10.1021/ic300216m

Reactions of LGeMe (L = HC[C(Me)N-2,6-iPr₂C₆H ₃]₂) with 0.25 or 0.5 equiv of (CuC₆F ₅)₄ gave the products [LGe(Me)CuC₆F ₅]₂ (1) and [LGe(Me)(CuC₆F₅) ₂]₂ (2), respectively. In situ formed 1 reacted with 0.5 equiv of (CuC₆F₅)₄ to give 2 on the basis of NMR (¹H and ¹⁹F) spectral measurements. Conversely, 2 was converted into 1 by treatment with 2 equiv of LGeMe. Reactions of LGeC(SiMe ₃)N₂ with 1 or 2 equiv of AgC₆F ₅·MeCN produced the corresponding compounds LGe[C(SiMe ₃)N₂]AgC₆F₅ (3) and {LGe[C(SiMe ₃)N₂](AgC₆F₅)₂} ₂ (4). Similarly, 3 was converted into 4 by treatment with 1 equiv of AgC₆F₅·MeCN and 4 converted into 3 by reaction with 2 equiv of LGeC(SiMe₃)N₂. X-ray crystallographic studies showed that 1 contains a rhombically bridged (CuC₆F ₅)₂, while 2 has a chain-structurally aggregated (CuC ₆F₅)₄, both supported by LGeMe. Correspondingly, 3 showed a terminally bound AgC₆F₅ and 4 a chain-structurally aggregated (AgC₆F₅)₄, both supported by LGeC(SiMe₃)N₂. Photophysical studies proved that the Ge-Cu metal-metalloid donor-acceptor bonding persists in solutions of 1 and 2 and Ge-Ag donor-acceptor bonding in solutions of 3 and 4 as a result of the clear migration of their emission bands compared to those of the corresponding starting materials. Low-temperature (-50 °C) ¹⁹F NMR spectral measurements detected dissociation of 1, 2, and 4 by the aggregation part of the CuC₆F₅ or AgC₆F ₅ entities in solution. These results provide good support for pentafluorophenylcopper(I) or -silver(I) species having β-diketiminate germylene as a donor because of its remarkably electronic and steric character.

Full text of DOI:10.1021/ic300216m

Article
pubs.acs.org/IC
β‑Diketiminate Germylene-Supported Pentafluorophenylcopper(I)
and -silver(I) Complexes [LGe(Me)(CuC6F5)n]2 (n = 1, 2), LGe[C(SiMe3)
N2]AgC6F5, and {LGe[C(SiMe3)N2](AgC6F5)2}2 (L = HC[C(Me)N-
2,6‑iPr2C6H3]2): Synthesis and Structural Characterization
Na Zhao, Jinyuan Zhang, Ying Yang, Hongping Zhu,* Yan Li, and Gang Fu*
State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of
Alcohols−Ethers−Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China
S
* Supporting Information
ABSTRACT: Reactions of LGeMe (L = HC[C(Me)N-2,6-
iPr2C6H3]2) with 0.25 or 0.5 equiv of (CuC6F5)4 gave the
products [LGe(Me)CuC6F5]2 (1) and [LGe(Me)(CuC6F5)2]2
(2), respectively. In situ formed 1 reacted with 0.5 equiv of
(CuC6F5)4 to give 2 on the basis of NMR (1H and 19F)
spectral measurements. Conversely, 2 was converted into 1 by
treatment with 2 equiv of LGeMe. Reactions of LGeC-
(SiMe3)N2 with 1 or 2 equiv of AgC6F5·MeCN produced the
corresponding compounds LGe[C(SiMe3)N2]AgC6F5 (3) and
{LGe[C(SiMe3)N2](AgC6F5)2}2 (4). Similarly, 3 was con-
verted into 4 by treatment with 1 equiv of AgC6F5·MeCN and
4 converted into 3 by reaction with 2 equiv of LGeC(SiMe3)-
N2. X-ray crystallographic studies showed that 1 contains a rhombically bridged (CuC6F5)2, while 2 has a chain-structurally
aggregated (CuC6F5)4, both supported by LGeMe. Correspondingly, 3 showed a terminally bound AgC6F5 and 4 a chain-
structurally aggregated (AgC6F5)4, both supported by LGeC(SiMe3)N2. Photophysical studies proved that the Ge−Cu metal−
metalloid donor−acceptor bonding persists in solutions of 1 and 2 and Ge−Ag donor−acceptor bonding in solutions of 3 and 4
as a result of the clear migration of their emission bands compared to those of the corresponding starting materials. Low-
temperature (−50 °C) 19F NMR spectral measurements detected dissociation of 1, 2, and 4 by the aggregation part of the
CuC6F5 or AgC6F5 entities in solution. These results provide good support for pentafluorophenylcopper(I) or -silver(I) species
having β-diketiminate germylene as a donor because of its remarkably electronic and steric character.
= nPr, X = Cl or N3] were reported by Dias et al. in the early
2000s.10 The Ge−Cu complex [HC(Mes)N]2GeCuL′ (L′ =
HC[C(Me)N-2,6-Me2C6H3]2) was prepared by Tolman and
co-workers,11 and the Ge−Cu and Ge−Au complexes [R′(Cl)-
GeCuI]4 and R′(Cl)GeAuI [R′ = N(SiMe3)C(Ph)C(SiMe3)-
(C5H4N-2)] were synthesized by Leung and co-workers12 in
2006. In 2009, Mochida and co-workers reported complexes
L″(R″)GeCuL″ (L″ = HC[C(Me)NiPr]2; R″ = Cl, Me, or H)
and found that the Ge−Cu bonding could tolerate a further
metathesis reaction at the Ge center.13
We recently reported on the use of an NHC, imidazol-2-
ylidene, as the donor ligand not only to support the copper(I)
aryls in conjugate addition to the organic azide14a but also to
investigate stepwise the reaction of the NNP−ligand copper(I)
compound [o-NCH(C4H3N)PPh2C6H4]2Cu with elemen-
tal sulfur.14b We now show the use of NHGe as the donor
ligand to complex group 11 organometallic species. To our
knowledge, such compounds have not been reported
INTRODUCTION
■
N-Heterocyclic carbenes (NHCs) have been well developed
and used widely as strong donor ligands in organometallic and
catalytic chemistry in the past 20 years.1−3 The N-heterocyclic
germylenes (NHGes) have also been studied extensively.4
However, the reactivity of the NHGes as donors has been
described to a rather lesser extent.4h Some NHGes have been
reported to show the Lewis acidic reactivity5 as well as the
reductive activity of the singlet electron lone pair at the GeII
center.5b,6 As a donor ligand in incorporating the group 11
metal(I) species, Boehme and Frenking have calculated that the
metal−carbene bond dissociation energy of NHC → MCl (M
= Cu, Ag, Au) appears generally to be greater than that of a
metal−germylene NHGe → MCl.7 This suggests a distinctive
degree of interaction between NHC and NHGe with the group
11 metal(I) complexes as a result of their different electronic
properties.8 Nonetheless, a number of group 11 metal(I) NHC
complexes have been prepared,1j,9 and some related NHGe
complexes have also been synthesized. The Ge−Ag complexes
(R2ATI)(X)GeAg{HB[3,5-(CF3)2Pz]3} [R2ATI = N-alkyl-2-
(methylamino)troponiminate; R = Me, X = Cl or OSO2CF3; R
Received: January 30, 2012
Published: August 6, 2012
© 2012 American Chemical Society
8710
dx.doi.org/10.1021/ic300216m | Inorg. Chem. 2012, 51, 8710−8718

Inorganic Chemistry
Article
hitherto.15 An initial reaction was attempted between an N-
heterocyclic LGeMe (L = HC[C(Me)N-2,6-iPr2C6H3]2)6c and
(CuMes)4 (Mes = 2,4,6-Me3C6H2). Surprisingly, no reaction
was observed on the basis of the 1H NMR spectral
measurements.16 However, when the copper(I) species was
changed to (CuC6F5)4,17 the reaction occurred smoothly. Not
only [LGe(Me)CuC6F5]2 (1) but also [LGe(Me)(CuC6F5)2]2
(2) was isolated, depending on the molar ratio of the two
starting materials used. Further investigation of the reaction of
[LGe(Me)CuC6F5]2 (1). In a glovebox, a solution of (CuC6F5)4
(0.115 g, 0.125 mmol) in toluene (5 mL) was added to a solution of
LGeMe (0.253 g, 0.5 mmol) in toluene (5 mL). A quick color change
from orange red to light yellow was observed. The mixture was stirred
for 2 h and filtered, and the filtrate was kept at −20 °C. After 5 days,
X-ray-quality light-yellow crystals of 1·2toluene were collected by
filtration (0.34 g, 81%). Mp: 206 °C. 1H NMR (400 MHz, C6D6, 298
3
K, ppm): δ 0.35 (s, 6 H, GeMe), 1.01 (d, JHH = 6.8 Hz, 12 H), 1.13
(d, 3JHH = 6.8 Hz, 12 H), 1.20 (d, 3JHH = 6.8 Hz, 12 H), 1.45 (d, 3JHH
=
3
6.8 Hz, 12 H) (CHMe2), 1.36 (s, 12 H, CMe), 3.09 (sept, JHH = 6.8
18
LGeC(SiMe3)N2 with AgC6F5·MeCN19 in various molar
3
Hz, 4 H), 3.60 (sept, JHH = 6.8 Hz, 4 H) (CHMe2), 4.76 (s, 2 H, γ-
CH), 7.00−7.15 (m, 12 H, C6H3). 13C NMR (100 MHz, C6D6, 298 K,
ppm): δ 4.5 (br, GeMe), 21.2, 22.7, 24.29, 24.98, 25.94, 28.23, 29.58
(CMe and CHMe2), 98.5 (γ-C), 124.3, 125.1, 125.4, 129.1, 137.6,
137.9, 144.1, 145.1 (C6H3 and C6F5), 169.0 (CN). 19F NMR (376
MHz, C6D6, 298 K, ppm): δ −161.74 (br, 4 F, m-F), −159.17 (br, 2 F,
p-F), −111.01 (br, 4 F, o-F). Anal. Calcd for C72H88Cu2F10Ge2N4 (Mr
= 1471.85): C, 58.75; H, 6.03; N, 3.81. Found: C, 59.41; H, 6.62; N,
3.82.
ratios resulted in LGe[C(SiMe3)N2]AgC6F5 (3) and {LGe[C-
(SiMe3)N2](AgC6F5)2}2 (4), respectively. 1−4 have been
structurally characterized to show novel aggregation forms of
(MC6F5)n (M = Cu, n = 2, 4; M = Ag, n = 1, 4) supported by
the respective germylenes, which are different from those using
organic donor molecules.15b,19−24 Herein, we present the
synthesis and characterization of 1−4. Photophysical studies
are carried out to detect the Ge−Cu or Ge−Ag interactions,
[LGe(Me)(CuC6F5)2]2 (2). The preparation of 2 was performed
similarly to that for 1 using (CuC6F5)4 (0.231 g, 0.25 mmol) and
LGeMe (0.253 g, 0.5 mmol). X-ray-quality light-yellow crystals of
2·0.5toluene were obtained after the final solution was kept at −20 °C
1
and variable-temperature H and/or 19F NMR measurements
are performed to disclose the nature of the CuC6F5 or AgC6F5
aggregation under the germylene support.
1
for 5 days (0.44 g, 89%). Mp: 110 °C (dec). H NMR (400 MHz,
C6D6, 298 K, ppm): δ 0.38 (s, 6 H, GeMe), 0.96 (d, 3JHH = 6.8 Hz, 12
H), 1.07 (d, 3JHH = 6.8 Hz, 12 H), 1.16 (d, 3JHH = 6.8 Hz, 12H), 1.27
(d, 3JHH = 6.8 Hz, 12 H) (CHMe2), 1.28 (s, 12 H, CMe), 2.11 (s, 12 H,
EXPERIMENTAL SECTION
■
Materials and Methods. All syntheses and manipulations were
carried out on a Schlenk line or in an argon-filled MBraun glovebox
(typically oxygen and moisture were controlled at less than 1.2 ppm).
Toluene, n-hexane, tetrahydrofuran, and diethyl ether were predried
over fine sodium wires and then refluxed with sodium/potassium
benzophenone under a nitrogen atmosphere prior to use. CH2Cl2 and
CHCl3 were refluxed with CaH2 for 3 days before use. 1H (400 MHz),
13C (100 MHz), 19F (376 MHz), and 29Si (99 MHz) NMR spectra
were recorded on a Bruker Avance II 400 MHz spectrometer. Melting
points of compounds were measured in sealed glass tubes using a
3
3
PhMe), 2.90 (sept, JHH = 6.8 Hz, 4 H), 3.27 (sept, JHH = 6.8 Hz, 4
H) (CHMe2), 4.73 (s, 2 H, γ-CH), 6.90−7.16 (m, 32 H, C6H3 and
PhMe). 13C NMR (100 MHz, C6D6, 298 K, ppm): δ 4.28 (GeMe),
21.18, 22.64, 24.11, 24.19, 25.25, 25.58, 28.09, 29.65 (CMe, CHMe2,
and PhMe), 99.20 (γ-C), 124.58, 124.97, 125.45, 127.81, 128.31,
129.08, 137.43, 137.65, 144.39, 144.45 (C6H3, C6F5, and PhMe),
169.41 (CN). 19F NMR (376 MHz, C6D6, 298 K, ppm): δ −160.71
(br, 8 F, m-F), −153.60 (br, 4 F, p-F), −107.77 (br, 8 F, o-F). Anal.
Calcd for C87.5H92Cu4F20Ge2N4 (2·0.5toluene, Mr = 1979.13): C,
53.10; H, 4.69; N, 2.83. Found: C, 53.86; H, 4.77; N, 2.72.
Buchi 540 instrument. Elemental analyses were performed on a
̈
LGe[C(SiMe3)N2]AgC6F5 (3). In a glovebox, LGeC(SiMe3)N2
(0.121 g, 0.2 mmol) and AgC6F5·MeCN (0.063 g, 0.2 mmol) were
mixed in a brown vial and toluene (2.5 mL) was added. The mixture
was stirred for 0.5 h and then toluene (ca. 1 mL) added until all solids
had dissolved. After stirring for 0.5 h, the solution was filtered and the
filtrate was overlayered with n-hexane (1 mL) and then kept at −20
°C. After 2 days, light-yellow crystals of 3 were collected by filtration
Thermo Quest Italia SPA EA 1110 instrument. Commercial reagents
were purchased from Aldrich, Acros, Alfa-Assar, or Lvyin Chemical
Co. and used as received. LGeMe,6c (CuMes)4,16 (CuC6F5)4,17 and
AgC6F5·MeCN19 were prepared according to published procedures.
18
The synthesis of LGeC(SiMe3)N2 was modified using a one-pot
method as detailed.
Fluorescence spectra were measured on a Hitachi F-7000 FL
spectrophotometer and UV−vis spectra on a Shimadzu UV-2550
spectrophotometer with solution samples in CH2Cl2 (2 mL) at
concentrations of 1.0 × 10−3 mol L−1 for the former and of 1.0 × 10−5
mol L−1 for the latter. For fluorescence measurements, excitation
(xenon lamp)/emission slit widths of 10/10 nm were used with a scan
speed of 240 nm min−1. For UV measurements, a slit width (D2 lamp)
of 2.0 nm was used with a moderate scan speed.
LGeC(SiMe3)N2. nBuLi (1 mL, 2.5 mmol, 2.5 M solution in n-
hexane) was added to a solution of LH (1.045 g, 2.5 mmol) in toluene
(40 mL) at −30 °C. The mixture was allowed to warm to room
temperature and stirred for 12 h. The solution was cooled to −30 °C
and then slowly added to a precooled (−30 °C) suspension of
GeCl2·dioxane (0.580 g, 2.5 mmol) in toluene (20 mL) with stirring.
The mixture was warmed to room temperature and stirred for 12 h. An
orange-yellow suspension was formed and cooled to −30 °C before
the addition of LiC(SiMe3)N2, freshly prepared by the reaction of
N2CH(SiMe3) (2.5 mL, 2.5 mmol, 1.0 M solution in n-hexane) and
nBuLi (1 mL, 2.5 mmol, 2.5 M solution in n-hexane) in n-hexane (15
mL) at −30 °C to room temperature within 3 h. The mixture was
stirred for 20 h, all volatiles then removed under vacuum, and the
residue extracted into toluene. The extract was evaporated under
vacuum and further washed with cold n-hexane (2 × 1 mL) to give
LGeC(SiMe3)N2 as an orange-yellow crystalline solid (1.267 g, 84%).
The melting point (mp) and 1H NMR data identify the compound as
that prepared from the reaction of L′Ge (L′ = HC[C(CH2)N-2,6-
iPr2C6H3][C(Me)N-2,6-iPr2C6H3] with N2CHSiMe3.18
1
(0.125 g, 71%). Mp: 156 °C (dec). H NMR (400 MHz, CDCl3, 298
3
K, ppm): δ −0.07 (s, 9 H, SiMe3), 1.10 (d, JHH = 6.8 Hz, 6 H), 1.28
(d, 3JHH = 6.8 Hz, 6 H), 1.41 (d, 3JHH = 6.8 Hz, 6 H), 1.52 (d, 3JHH
=
6.8 Hz, 6 H) (CHMe2), 2.01 (s, 6 H, CMe), 3.15 (sept, 3JHH = 6.8 Hz,
2 H), 3.37 (sept, 3JHH = 6.8 Hz, 2 H) (CHMe2), 5.13 (s, 1 H, γ-CH),
7.23−7.35 (m, 6 H, C6H3). 13C NMR (100 MHz, CDCl3, 298 K,
ppm): δ 0.59 (SiMe3), 24.20, 24.50, 25.30, 25.40, 27.58, 30.45 (CMe
and CHMe2), 97.38 (γ-C), 125.05, 125.20, 128.81, 137.94, 143.36,
146.14 (C6H3 and C6F5), 169.54 (CN); the GeC carbon resonance was
not observed. 19F NMR (376 MHz, CDCl3, 298 K, ppm): δ −162.16
(m, 2 F, m-F), −159.68 (t, 1 F, p-F), −107.75 (m, 2 F, o-F). 29Si NMR
(99 MHz, CDCl3, ppm): δ 0.05 (s, SiMe3). Anal. Calcd for
C39H50AgF5GeN4Si (Mr = 878.38): C, 53.32; H, 5.74; N, 6.38.
Found: C, 53.57; H, 5.68; N, 6.45.
{LGe[C(SiMe3)N2](AgC6F5)2}2 (4). The preparation of 4 was
performed similarly to that for 3 using LGeC(SiMe3)N2 (0.091 g,
0.15 mmol) and AgC6F5·MeCN (0.095 g, 0.300 mmol). X-ray-quality
light-yellow crystals of 4 were obtained (0.095 g, 55%). Mp: 145 °C
1
(dec). H NMR (400 MHz, CDCl3, 298 K, ppm): δ −0.06 (s, 9 H,
3
SiMe3), 1.12 (d, 3JHH = 6.8 Hz, 12 H), 1.30 (d, JHH = 6.8 Hz, 12 H),
1.42 (d, 3JHH = 6.8 Hz, 12 H), 1.49 (d, 3JHH = 6.8 Hz, 12 H) (CHMe2),
2.04 (s, 12 H, CMe), 3.16 (sept, 3JHH = 6.8 Hz, 4 H), 3.29 (sept, 3JHH
= 6.8 Hz, 4 H) (CHMe2), 5.21 (s, 2 H, γ-CH), 7.18−7.34 (m, 12 H,
C6H3). 13C NMR (100 MHz, CDCl3, 298 K, ppm): δ 0.57 (SiMe3),
24.22, 24.48, 25.24, 25.38, 27.71, 30.27 (CHMe2 and CMe), 97.88 (γ-
C), 124.98, 125.28, 128.89, 137.39, 143.21, 146,12 (C6H3 and C6F5),
8711
dx.doi.org/10.1021/ic300216m | Inorg. Chem. 2012, 51, 8710−8718

Inorganic Chemistry
Article
a
Table 1. Summary of Crystal Data and Structure Refinement for 1·2toluene, 2·0.5toluene, 3, and 4
1·2 toluene
2·0.5 toluene
3
4
formula
fw
C86H104Cu2F10Ge2N4
1655.99
C87.5H92Cu4F20Ge2N4
1978.99
C39H50AgF5GeN4Si
878.38
C90H100Ag4F20Ge2N8Si2
2306.62
cryst syst
space group
a/Å
monoclinic
C2/c
monoclinic
P2(1)/c
monoclinic
P2(1)/c
monoclinic
P2(1)/n
21.0177(8)
16.8869(7)
22.5197(9)
13.638(3)
11.3442(3)
17.0271(5)
21.5490(5)
13.8783(6)
21.7083(7)
16.1356(8)
b/Å
21.394(4)
c/Å
16.103(3)
α/deg
β/deg
92.657(3)
105.49(3)
102.671(2)
102.470(4)
γ/deg
V/Å3
7984.2(6)
4527.7(16)
4061.01(19)
4
4746.6(3)
Ζ
4
2
2
ρcalcd/g cm−3
μ/mm−1
F(000)
cryst size/mm3
θ range/deg
index ranges
1.378
1.452
1.437
1.614
1.341
1.663
1.307
1.547
3440
2010
1800
2312
0.44 × 0.40 × 0.38
2.71−26.00
−25 ≤ h ≤ 22
−20 ≤ k ≤ 20
−27 ≤ l ≤ 27
31718
0.34 × 0.30 × 0.24
3.10−26.00
−16 ≤ h ≤ 16
−26 ≤ k ≤ 26
−19 ≤ l ≤ 19
53752
0.22 × 0.21 × 0.20
2.65−26.00
−13 ≤ h ≤ 13
−18 ≤ k ≤ 21
−26 ≤ l ≤ 26
31073
0.20 × 0.20 × 0.10
2.75−26.00
−14 ≤ h ≤ 17
−26 ≤ k ≤ 25
−19 ≤ l ≤ 19
28650
collected data
unique data
7817 (Rint = 0.0432)
99.6
8845 (Rint = 0.0462)
99.4
7953 (Rint = 0.0510)
99.9
9310 (Rint = 0.0921)
99.8
completeness to θ/%
data/restraints/param
GOF on F2
7817/0/452
1.118
8845/0/553
0.999
7953/0/473
0.795
9310/0/581
0.636
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak/hole (e Å−3
R1 = 0.0584, wR2 = 0.1490
R1 = 0.0743, wR2 = 0.1531
1.108/−0.921
R1 = 0.0410, wR2 = 0.1266
R1 = 0.0548, wR2 = 0.1350
1.004/−0.442
R1 = 0.0316, wR2 = 0.0519
R1 = 0.0626, wR2 = 0.0552
R1 = 0.0415, wR2 = 0.0339
R1 = 0 0.1102, wR2 = 0.0465
0.577/−0.404
)
0.333/−0.419
a
All data were collected at 173(2) K. R1 = ∑(||Fo| − |Fc||)/∑|Fo|, wR2 = [∑w(Fo2 − Fc2)2/∑w(Fo )]1/2, GOF = {∑[w(Fo2 − Fc2)2]/(No − Np)}1/2
.
2
169.87 (CN); the GeC carbon resonance was not observed. 19F NMR
(376 MHz, CDCl3, 298 K, ppm): δ −160.79 (br, 8 F, m-F), −152.66
(br, 4 F, p-F), −104.25 (br, 8 F, o-F). 29Si NMR (99 MHz, CDCl3, 298
K, ppm): δ 0.30 (s, SiMe3). Anal. Calcd for C97H108Ag4F20Ge2N8Si2
(4· toluene, Mr = 2398.84): C, 48.57; H, 4.54; N, 4.67. Found: C,
49.30; H, 4.74; N, 4.46.
in good yield (81%). Similarly, the reaction of LGeMe with 0.5
equiv of (CuC6F5)4 also yielded light-yellow crystals of
2·0.5toluene (89%; Scheme 1). Compounds 1 and 2 are both
Scheme 1. Synthesis of 1 and 2
X-ray Crystallographic Analyses of Complexes 1−4.
Crystallographic data of compounds 1·2toluene, 2·0.5toluene, 3, and
4 were collected on an Oxford Gemini S Ultra system. In all cases,
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) was used.
Absorption corrections were applied using the spherical harmonics
program (multiscan type). Structures were solved by direct methods
(SHELXS-96)25a and refined against F2 using SHELXL-97.25b In
general, 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. In 1·2toluene, 1 was disclosed as a half-moiety and toluene
molecules were found in disorder. Toluene was treated in a splitting
mode and refined isotropically. In 2·0.5toluene 2 was determined by a
half-moiety also, in which one of the iPr groups in the N-aryl
substituent of the L ligand was disordered, treated in a splitting mode,
and refined isotropically. The 0.5toluene was seriously disordered and
refined isotropically without the geometric hydrogen addition.
Compound 4 was determined as a half-moiety. The complete
molecules of 1, 2, and 4 were obtained by a symmetric operation.
Cell parameters, data collection, and structure solution and refinement
are given in Table 1.
air-sensitive and change color to dark green and finally to black
when exposed to air in the solid state or in solution. 1 is
thermally stable (mp 206 °C), whereas 2 is unstable and
decomposes at ca. 110 °C. Both of them have been fully
characterized by NMR (1H, 13C, and 19F), elemental, and
single-crystal X-ray structural analysis.
The 1H NMR spectrum of 1 recorded in C6D6 shows distinct
signals for the L ligand and the methyl group at the Ge center.
Two septets at δ 3.60 and 3.09 and four doublets at δ 1.45,
1.20, 1.13, and 1.01 correspond to the typical CHMe2 methine
and methyl protons in the ligand N-aryl substituents. A high-
field singlet at δ 0.35 is assigned to the GeMe protons. The 19F
RESULTS AND DISCUSSION
■
Synthesis and Characterization of 1 and 2. The
reaction of LGeMe (L = HC[C(Me)N-2,6-iPr2C6H3]2) with
0.25 equiv of (CuC6F5)4 proceeded smoothly in toluene at
room temperature and gave light-yellow crystals of 1·2toluene
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NMR spectrum shows resonances at δ −110.77, −159.17, and
−161.74 with an integral intensity ratio of 2:1:2, corresponding
to o-, p-, and m-F atoms, respectively. All of these fluorine
signals are broad, indicating that the CuC6F5 entities are
aggregated in 1, in which a fast equilibrium is established for the
C6F5 groups in solution at room temperature. 1H and 19F NMR
spectra of 2 show resonance patterns similar to those of 1 but
with different chemical shifts for the protons [δ 3.27 and 2.90
(CHMe2), 1.27, 1.16, 1.07, and 0.96 (CHMe2), and 0.38
of 2.127(5) and 2.130(5) Å, constituting a perfectly rhombic
Cu2C2 ring.
The Cu2C2 ring plane can be extended to the two Ge atoms
(mean deviation from the plane, ΔGe Cu C = 0.0574 Å), and
2
2 2
along the Ge2Cu2C2 plane, the two C6F5 groups at the Cu
atoms are orthogonally arranged, both locating well within the
L ligand N-aryls. The ipsilateral (C6F5)centriod···arylcentroid
distances are 3.794 and 3.821 Å with respective dihedral angles
of 18.2 and 20.9°, indicating π-stacking interactions between
the C6F5 groups and the L ligand aryls. Similar strong
interactions are observed in (CuC6F5)4·toluene2 by parallel
arrangement of the toluene molecules to the C6F5 groups at a
distance of 3.3 Å.20 In phenyl and pentafluorophenyl esters of
benzene-1,2-dicarboxylic acid and tetrafluorobenzene-1,2-dicar-
boxylic acid, such interactions are indicated by arene···arene
separations of 3.70−4.85 Å with corresponding dihedral angles
of 5−21°.27 It is reasonable that the steric and electronic
character of LGeMe leads to the lowest (CuC6F5)2 aggregate so
far observed among organocopper(I) complexes.28 Therefore,
the Cu(1)···Cu(1A) contact of 2.3819(11) Å appears to be the
shortest among the (CuC6F5)4 aggregates [2.4301(3)−
2.6779(8) Å],20,21 suggestive of a strong CuI···CuI d10−d10
interaction. Theoretical calculations have proved that such
interactions should be weakly attractive with respect to the
relative contraction of the 4s orbital by admixture with 3d
states. That effectively reduces the population of the 3d valence
shell,29 although there is a controversy as to the degree of such
interplays under the ligand support.30
(GeMe)] and fluorines [δ −107.77 (o-F), −153.60 (p-F), and
26
−160.71 (m-F)]. Δδ(19Fm,p
)
is δ 2.57 for 1 but δ 7.11 for 2,
suggesting different CuC6F5 aggregation forms in 1 and 2.
The X-ray structural analysis clearly shows for 1 and 2 the
1:0.25 and 1:0.5 molar ratio products of the two reactants. 1
contains a bridged (CuC6F5)2 and 2 a chain-structurally
aggregated (CuC6F5)4, both supported by LGeMe in general
centrosymmetry. Either (CuC6F5)2 or (CuC6F5)4 shows a new
type of aggregation significantly different from the known
20,22
square-ring one in (CuC6F5)4
and the puckered-ring ones
in [(CuC6F5)4·Dm]n (m = 2, n = 0, D = toluene,20 pyridine,21
naphthalene, and 2,2′-bithiophene;23 m = 1, n = ∞, D =
naphthalene and 2,2′-bithiophene22).
The structure of 1 (Figure 1) shows that the Ge center has
tetrahedral geometry due to formation of the Ge−CuC6F5
The structure of 2 (Figure 2) shows that a Ge−Cu bond
length, 2.2867(7) Å, is comparable to that in 1. However, the
Figure 1. Thermal ellipsoid (50%) drawing of 1. Selected bond lengths
[Å] and angles [deg]: Ge(1)−N(1) 1.973(4), Ge(1)−N(2) 1.968(4),
Ge(1)−C(6) 1.972(5), Ge(1)−Cu(1) 2.3228(7), Cu(1)−C(30)
2.127(5), Cu(1)−C(30A) 2.130(5), Cu(1)···Cu(1A) 2.3819(11);
N(1)−Ge(1)−N(2) 92.43(15), Cu(1)−Ge(1)−C(6) 120.98(17),
Ge(1)−Cu(1)···Cu(1A) 169.56(5), Cu(1)−C(30)−Cu(1A)
68.03(15), Ge(1)−Cu(1)−C(30) 122.58(13), Ge(1)−Cu(1)−C-
(30A) 124.19(13). Symmetry code: A, −x + 0.5, −y + 0.5, −z + 1.
Figure 2. Thermal ellipsoid (50%) drawing of 2. Selected bond lengths
[Å] and angles [deg]: Ge(1)−N(1) 1.955(3), Ge(1)−N(2) 1.943(2),
Ge(1)−C(7) 1.969(3), Ge(1)−Cu(1) 2.2867(7), Cu(1)−C(41)
2.039(3), Cu(2)−C(41) 2.005(3), Cu(2)−C(31) 1.953(3), Cu-
(2A)···C(31) 2.392(3), Cu(1)···Cu(2) 2.4157(7), Cu(2)···Cu(2A)
2.4919(8); N(1)−Ge(1)−N(2) 94.09(11), Cu(1)−Ge(1)−C(7)
124.82(12), Ge(1)−Cu(1)−C(41) 149.01(9), Cu(1)−C(41)−Cu(2)
73.35(11), C(31)−Cu(2)−C(41) 151.81(13), C(31)−Cu(2)−C-
(31A) 110.85(10), C(41)−Cu(2)−C(31A) 97.04(12), Ge(1)−
Cu(1)···Cu(2) 155.64(2), Cu(1)···Cu(2)···Cu(2A) 162.09(3). Sym-
metry code: A, −x + 1, −y, −z + 1.
bonding. The Ge−Cu bond length, 2.3228(7) Å, falls in the
range for those of Ge−Cu metal−metalloid donor−acceptor
bonding complexes [2.2138(4)−2.359(2) Å].11−13 The Ge−N
bond lengths, 1.968(4) and 1.973(4) Å, and the Ge−C
distance, 1.972(5) Å, are a little shorter than the corresponding
ones in the LGeMe precursor [Ge−N, 2.008(2) and 2.038(2)
Å; Ge−C, 2.002(4) Å].6c This can be interpreted as a result of a
σ donation of the s-orbital electron pair at the Ge center to
form the Ge−Cu bond, which increases the s character of the
bond between the Ge center and the adjacent coordinating
groups.10c The Cu center is three-coordinate in nearly
triangular geometry (periphery angle, 358.74°). Each C6F5
group bridges Cu(1) and Cu(1A) with Cu−CC F bond lengths
Cu(1) center is two-coordinate with the Ge(1)−Cu(1)−C(41)
bond angle of 149.01(9)°, significantly nonlinear, whereas the
Cu(2) atom appears three-coordinate in triangular geometry
(periphery angle, 359.70°). The (C6F5)C(41) group bridges
Cu(1) and Cu(2) with Cu(1)−C(41) and Cu(2)−C(41) bond
lengths of 2.039(3) and 2.005(3) Å. It vectorially splits the
6
5
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Cu(1)−C(41)−Cu(2) angle by unequal 45.6° and 27.8°
amounts. In sharp contrast, the (C6F5)C(31) group bonds to
Cu(2) and Cu(2A) with a shorter Cu(2)−C(31) bond length
of 1.953(3) Å versus a longer Cu(2A)−C(31) bond length of
2.392(3) Å. The Cu(2)(C6F5)C(31) moiety is planar (Δ =
0.0422 Å), while the Cu(2A) atom lies out of this plane
[Cu(2)−C(31)−Cu(2A), 69.15(10)°]. The Ge(1)Cu(1)-
Cu(2)Cu(2A)Cu(1A)Ge(1A)C(31)C(41)C(31A)C(41A)
core is observed to be closely planar (Δ = 0.0589 Å), while the
four C6F5 groups at the respective Cu atoms are arranged
orthogonally along the core, residing among the L ligand aryls
with ipsilateral (C6F5)centriod···arylcentroid distances of 3.881 and
4.014 Å and a (C6F5)centriod···(C6F5)centroid separation of 3.523
Å. This indicates that arene−arene π-stacking interactions are
present in 2 also. The Cu(2)···Cu(2A) separation [2.4919(8)
Å] is longer than the Cu(1)···Cu(2) distance [2.4157(7) Å].
Both of these two distances are longer than that for 1
[2.3819(11) Å].
Solution Interconversion of 1 and 2. The formation of
the dimeric (CuC6F5)2 aggregate in 1 and the tetrameric
(CuC6F5)4 in 2 is due to the use of different molar ratios of the
two starting materials. This suggests that production of these
two aggregates could be adjustable under the LGeMe support.
As shown in Figures 16s and 17s (see the Supporting
Information), monitoring of the reaction by 1H and 19F
NMR spectra showed the formation of 1 (see Figures 1s and 3s
in the Supporting Information) upon mixing LGeMe with 0.25
equiv of (CuC6F5)4 in C6D6. The further addition of 0.25 equiv
of (CuC6F5)4 into this reaction resulted in 2 (see Figures 4s
and 6s in the Supporting Information). Interestingly, the
addition of 1 equiv of LGeMe to this reaction system at room
temperature resulted in the re-formation of 1. Thus, 1 and 2
can be readily interconverted in solution as follows:
F); see Table 1s in the Supporting Information] whereas
another group of resonances at δ −106.37 (o-F), −153.07 (p-
F), and −160.14 (m-F) seemed close to the LGeMe-supported
CuC6F5 species rather than to the monomeric LGe(Me)-
CuC6F5 (Figure 22s in the Supporting Information). Mean-
while, the overall integral intensities for the former resonances
appeared much lower than those for the latter. All of these
results suggest a partial dissociation of the CuC6F5 entity from
2 to form free (CuC6F5)4. Similar results were also observed for
the 1:0.75, 1:1, and 1:2.5 molar ratio reactions (Figures 23s−
25s in the Supporting Information), in which the overall
integral resonance intensity for the free (CuC6F5)4 appeared to
increase compared to that for 2. Accordingly, the observation of
1
one set of the respective H and 19F resonances at room
temperature reasonably indicates a fast equilibrium on the
NMR time scale between the LGeMe-complexed CuC6F5 and
uncomplexed (CuC6F5)4 for 2 as well as for the 1:0.75, 1:1, and
1:2.5 molar ratio reactions. The formation of highly aggregated
(CuC6F5)n (n > 4) under the LGeMe support ought to be
impossible. Indeed, preparative-scale reactions of LGeMe with
(CuC6F5)4 in the molar ratio of 1:0.75 or 1:1 were carried out,
and only 2 was formed on the basis of NMR (1H and 19F)
spectra and X-ray diffraction analysis of the crystals isolated.
Synthesis and Characterization of 3 and 4. Encouraged
by the syntheses of 1 and 2, we investigated the reaction of the
germylene with pentafluorophenylsilver(I). The reaction of
LGeC(SiMe3)N2 with AgC6F5·MeCN was performed as before
but in the dark because of the photosensitivity of the silver
species. Compounds 3 (71% yield) and 4 (55% yield) were
obtained as light-yellow crystals according to the molar ratios of
1:1 and 1:2 of the two starting materials used (Scheme 2). A
Scheme 2. Synthesis of 3 and 4
The room temperature reactions of LGeMe with (CuC6F5)4
in molar ratios of 1:0.75, 1:1, and even 1:2.5 were continuously
monitored by NMR spectra to see if highly aggregated
(CuC6F5)n (n = 6, 8, or 20) could be formed under the
support of LGeMe, owing to its steric and electronic character.
The respective 1H and 19F NMR spectra displayed only one set
of resonances for each reaction, resembling those for the
respective 1:0.25 and 1:0.5 molar ratio reactions (see Figures
16s and 17s in the Supporting Information). The correspond-
ing proton and fluorine resonances showed a gradual migration
and then became more and more close, until the fluorine
chemical shifts appeared close to those of the starting material
(CuC6F5)4. Moreover, in all cases, broad fluorine resonances
were exhibited.
pentafluorophenylsilver(I) compound was prepared early in the
1970s.19a Probably because of the strong solvent dependence,
the solid-state structure of this compound has not yet been
disclosed, although it has been suggested to have a tetrameric,
square-ring structure similar to that of related arylsilver(I)
complexes.31 When treated with organic donors, infinitely long,
chainlike structure complexes AgC6F5·RCN (R = Me, Et) and
Au(C6F5)2Ag·SC4H8 were reported.19b,c Apparently, both 3 and
4 represent a new type of AgC6F5 aggregation supported by the
diketiminate germylene.
Low-temperature (−50 °C) 19F NMR spectral measurements
were performed on 1 and 2 as well as on the 1:0.75, 1:1, and
1:2.5 molar ratio reactions of LGeMe and (CuC6F5)4, all in
C7D8. First, one set of sharp resonances was seen for 1 (Figure
21s in the Supporting Information), which appeared similar to
those in the breakdown CuC6F5·D′ (D′ = pyridines or
substituted ones),21 implying that 1 dissociated to give
monomeric LGe(Me)CuC6F5 at low temperature. Second,
more than one set of broad resonances were observed for 2, in
which one group of the resonances at δ −105.06 (o-F),
−145.46 (p-F), and −158.72 (m-F) was assignable to free
(CuC6F5)4 [δ −104.65 (o-F), −145.71 (p-F), and −158.46 (m-
These two compounds are sensitive to air but only a little to
light. They are both thermally unstable. 3 decomposes at 156
1
°C and 4 at 145 °C. The H NMR spectra recorded in CDCl3
show one set of proton resonances for the L ligand and the
C(SiMe3)N2 group at Ge for 3 and 4. The 29Si NMR spectra
show the silicon resonance at δ 0.05 for 3 and at δ 0.30 for 4.
19F NMR spectra exhibit fluorine resonances for the C6F5
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group(s) with sharp signals present in 3 [δ −162.16 (m-F),
−159.68 (p-F), and −107.75 (o-F)] but much broader ones in
4 [δ −160.79 (m-F), −152.66 (p-F), −104.25 (o-F); Figures 9s
and 13s in the Supporting Information] compared to those in 1
and 2 (Figures 9s and 13s in the Supporting Information).
The X-ray structural analysis shows 3 as a monomeric
compound with AgC6F5 terminally bound to LGeC(SiMe3)N2
(Figure 3). The Ge−Ag bond length is 2.4480(3) Å,
Figure 4. Thermal ellipsoid (50%) drawing of 4. Selected bond lengths
[Å] and angles [deg]: Ge(1)−N(1) 1.953(3), Ge(1)−N(2) 1.924(4),
Ge(1)−C(6) 1.947(4), Ge(1)−Ag(1) 2.4258(5), Ag(1)−C(30)
2.264(4), Ag(2)−C(30) 2.155(5), Ag(2)−C(40) 2.091(5), Ag-
(2A)···C(40) 3.619, Ag(1)···Ag(2) 2.7264(5), Ag(2)···Ag(2A)
3.0627(7); N(1)−Ge(1)−N(2) 94.57(15), Ag(1)−Ge(1)−C(6)
114.70(12), Ge(1)−Ag(1)−C(30) 156.04(12), Ag(1)−C(30)−
Ag(2) 76.21(15), C(30)−Ag(2)−C(40) 167.32(15), Ge(1)−
Ag(1)···Ag(2) 149.41(2), Ag(1)···Ag(2)···Ag(2A) 153.19(2). Symme-
try code: A, −x − 1, −y, −z.
Figure 3. Thermal ellipsoid (50%) drawing of 3. Selected bond lengths
[Å] and angles [deg]: Ge(1)−N(1) 1.944(2), Ge(1)−N(2) 1.944(2),
Ge(1)−C(6) 1.945(3), Ge(1)−Ag(1) 2.4480(3), Ag(1)−C(30)
2.122(3); N(1)−Ge(1)−N(2) 94.19(9), Ag(1)−Ge(1)−C(6)
111.46(8), Ge(1)−Ag(1)−C(30) 173.16(10).
the (C6F5)C(40) group. Thus, the Ag(2)···Ag(2A) contact is
formed by 3.0627(7) Å on the basis of the centrosymmetric
operation. This distance is much longer than the Ag(1)···Ag(2)
one [2.7264(5) Å] but relates to those in ligand-unsustained
nonorganometallic silver(I) complexes [3.0228(5)−3.431(4)
Å].33 This indicates that the Ag(2)···Ag(2A) d10−d10
interaction is actually attractive but without ligand support.
Similar cases have only been found in silver(I)-involved infinite
chainlike complexes AuC6F5·SC4H8 [AuI···AuI, 3.128(2)−
3.306(1) Å]34a and Au(C6F5)2Ag·SC4H8 [AuI···AuI, 2.889(2)
Å; AuI···AgI, 2.717(2)−2.726(2) Å].34b It should therefore be
concluded that the adjacent Ag(1)···Ag(2) and Ag(1A)···Ag-
(2A) interplays are attractive because of the considerably
shorter distances, although they are supported by the C6F5
groups. The Cu···Cu distances in 1 and 2 are much shorter
than those of unsupported complexes [2.5790(4)−4.7230(5)
Å],33 similarly indicating that the CuI···CuI interactions are also
attractive. In addition, the four C6F5 groups locate among the L
ligand aryls with the ipsilateral (C6F5)centriod···arylcentroid of 4.043
and 5.221 Å and (C6F5)centriod···(C6F5)centroid of 3.548 Å, all
demonstrating arene−arene π-stacking interactions.
comparable to those in complexes (R2ATI)(X)GeAg{HB[3,5-
(CF3)2Pz]3} [2.4116(10)−2.4215(9) Å; R2ATI = N-alkyl-2-
(methylamino)troponiminate, R = Me, X = Cl or OSO2CF3; R
= nPr, X = Cl or N3],10 and fits well to the predicted one in
[HC(H)N]2GeAgCl (2.448 Å).7 The Ge−Ag metal−metalloid
donor−acceptor bonding also results in the shorter Ge−N and
Ge−C bond lengths around the Ge center compared with those
in LGeC(SiMe3)N2.18 The (C6F5)C(30) bonds to Ag(1) in a
perfect plane (Δ = 0.0143 Å) with a Ag(1)−C(30) bond
distance of 2.122(3) Å and a Ge−Ag−CC F angle of
6
5
173.16(10)°. This structural feature may suggest free rotation
of the C6F5 group in 3 in solution, therefore giving sharp
resonances in the 19F NMR spectrum.
The structure of 4 is very similar to that of 2 apart from the
C(SiMe3)N2 group replacing the Me and the Ag atom replacing
Cu both at the Ge atom (Figure 4). However, the (AgC6F5)4
array presents differences in the geometry compared to
(CuC6F5)4 in 2 due to the different metal centers. The
(C6F5)C(30) bridges Ag(1) and Ag(2) with a Ag(1)−C(30)
bond length of 2.264(4) Å and Ag(2)−C(30) of 2.155(5) Å
and a Ag(1)−C(30)−Ag(2) angle of 76.21(15)° [(C6F5)C(30)
vector bisection angles, 54.4° and 21.9°]. (C6F5)C(40) should be
considered terminally bound to Ag(2) because Ag(2)-
(C6F5)C(40) is almost planar (Δ = 0.0510 Å), while the
Ag(2)−C(40) bond length [2.091(5) Å] appears close to the
terminal bond in 3. Furthermore, the Ag(2A)···C(40)
separation is much greater (3.619 Å) and is even longer than
the corresponding van der Waals radii (3.42 Å).32 Such a
Ag(2)−(C6F5)C(40)···Ag(2A) bonding mode also is remarkably
different from those found in infinite chainlike complexes
AgC6F5·RCN [R = Me,19c 2.147(2) and 2.381(2) Å; R = Et,19b
2.128(5) and 2.387(5) Å]. All of these features suggest that
there is almost no interaction between the Ag(2A) atom and
The 1H and 19F NMR spectral-monitored reactions were also
carried out, revealing interconversion between 3 and 4 (Scheme
2 and Figures 18s−20s in the Supporting Information).
Although this appeared relatively complex compared to the
LGeMe/(CuC6F5)4 reaction system, a fast equilibrium on the
NMR time scale should be established between the LGeC-
(SiMe3)N2-complexed and uncomplexed AgC6F5 species for 4
as well as for the 1:3, 1:4, and 1:10 molar ratio reactions by the
1
related H and 19F NMR at room temperature as well as by
low-temperature (−50 °C) 19F NMR measurements (Figures
26s−30s in the Supporting Information). It is noteworthy that
the sharp fluorine resonance data pattern was maintained at
−50 °C for 3, which indirectly proves dissociation of 1 into its
monomeric form at low temperature.
Photoluminescence Studies of 1−4. We carried photo-
physical studies of 1−4 with starting materials LGeR [R = Me
and C(SiMe3)N2], (CuC6F5)4, and AgC6F5·MeCN for
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comparison. All samples were measured in a CH2Cl2 solution at
room temperature. The absorption, excitation, and emission
spectra of each compound are shown in Figures 31s−39s (see
the Supporting Information). The emission spectra for the
LGeMe/(Cu6F5)4 reaction system complexes are shown in
Figure 5(I) and for the LGeC(SiMe3)N2/AgC6F5·MeCN
pentafluorophenylcopper(I) and -silver(I) complexes 1−4.
These were clearly characterized by NMR (1H, 13C, 19F, and/
or 29Si) spectroscopy and X-ray crystallography. The reactions
were successful for germylene with (CuC6F5)4 rather than with
(CuMes)4.16 This implies a requirement of enhanced Lewis
acidity for the organocoinage metal(I) species in forming the
Ge−Cu metal−metalloid donor−acceptor bond. The formation
of (CuC6F5)n (n = 2, 4) or (AgC6F5)4 under germylene support
reflects the strong aggregation nature of the CuC6F5 or
(AgC6F5)4 entity, although these aggregations are affected by
the temperature in solution. However, the exhibition of the
weakly attractive CuI···CuI or AgI···AgI d10−d10 interactions
with or without ligand support as well as the arene−arene π
stackings among C6F5 and the L ligand aryls truly reveals the
electronic and steric properties of the N-heterocyclic β-
diketiminate germylene in character.36 In addition, structural
differences between 1 and 3 as well as between 2 and 4 clearly
show the disparity between the CuC6F5 and AgC6F5 species,
resulting from their different metal radii and the electronic
properties. Further work is in process on the use of the
germylene-supported CuC6F5 or AgC6F5 compounds for
organic molecule transformation reactions and synthesis of
the germylene-sustained organogold(I) complexes.
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF data, NMR spectra, and photophysical (absorption,
excitation, and emission) spectra for 1−4. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hpzhu@xmu.edu.cn (H.Z.), gfu@xmu.edu.cn (G.F.).
■
Figure 5. Luminescence spectra recorded in a CH2Cl2 solution at
room temperature by irradiation with a UV−vis lamp (λem, nm): (I)
LGeMe (404), (CuC6F5)4 (402), 1 (497), and 2 (458 and 558); (II)
LGeC(SiMe3)N2 (476), AgC6F5·MeCN (392), 3 (460), and 4 (526
and 648).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the 973 Program
(2012CB821704), the National Nature Science Foundation of
China (Grants 91027014 and 20972129), and the Innovative
Research Team Program (IRT1036 and J1030415). We thank
the reviewers and editors for their instructive suggestions on
this manuscript. We greatly thank Prof. G. Michael Blackburn
from the University of Sheffield for improvement of this
manuscript.
system compounds in Figure 5(II). Complex 1 displays green
luminescence (λem = 497 nm) upon excitation at λex = 336 nm
and 2 blue luminescence (λem = 458 nm) at λex = 340 nm.
These two emission bands are significantly red-shifted
compared to those of the starting materials LGeMe and
(CuC6F5)4 (both at λem = 404 nm) under the same conditions.
This is due to the strong Ge−Cu metal−metalloid donor−
acceptor bonding present in 1 and 2 in solution. Tolman and
co-workers have discussed the Cu → Ge[N(SiMe3)2]2/
Ge[(NMes)2(CH)2] charge-transfer (MLCT) transitions by
observation of the weaker shoulder bands in the UV−vis
spectra.11 The fact that coordination of metal ions by external
organic donor(s) often results in significant emission band
changes is well-known.35
Correspondingly, Figure 5(II) proves the persistence of the
Ge−Ag metal−metalloid donor−acceptor bonding in solution
from the presence of the blue luminescence band at 460 nm for
3 and the green one at 526 nm for 4 because these two bands
are both clearly shifted relative to those of LGeC(SiMe3)N2
(λem = 476 nm) and AgC6F5·MeCN (λem = 392 nm).
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CONCLUSIONS AND REMARKS
In summary, we have shown the use of the N-heterocyclic β-
diketiminate germylene in the formation of the
■
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