NHC-induced conversion of a W–Ge double bond into the triple bond through formation of W–Ge single and double bonded intermediates

Article abstract of DOI:10.1016/j.jorganchem.2017.07.027

Reaction of hydrido(hydrogermylene) complex Cp*(CO)₂(H)W=Ge(H)(Tsi) (1, Tsi = C(SiMe₃)₃) with 1 equiv of ^MeIMe (^MeIMe = 1,3-dimethyl-4,5-dimethylimidazol-2-ylidene) immediately afforded NHC-stabilized germylene complex Cp*(CO)₂(H)WGe(H)(^MeIMe)(Tsi) (2) that has a zwitterionic, W–Ge single-bonded structure. Complex 2 was thermally unstable and intramolecular proton-transfer followed by hydride-transfer to the NHC-unit occurred slowly at room temperature to give anionic germylene complex [Cp*(CO)₂W=Ge(H)(Tsi)][H^MeIMe] ([3][H^MeIMe]) first and subsequently germylyne complex Cp*(CO)₂W≡Ge(Tsi) (4) and H₂^MeIMe. Although [3][H^MeIMe] was too unstable to be isolated, the salt of bulkier [H^MeIⁱPr]⁺, [Cp*(CO)₂W=Ge(H)(Tsi)][H^MeIⁱPr] ([3][H^MeIⁱPr]), was thermally more stable and was isolated and fully characterized.

Full text of DOI:10.1016/j.jorganchem.2017.07.027

Journal of Organometallic Chemistry 848 (2017) 89e94
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
NHC-induced conversion of a WeGe double bond into the triple bond
through formation of WeGe single and double bonded intermediates
Tetsuya Fukuda, Hisako Hashimoto*, Hiromi Tobita**
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai, 980-8578, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of hydrido(hydrogermylene) complex Cp*(CO)2(H)W¼Ge(H)(Tsi) (1, Tsi ¼ C(SiMe3)3) with 1
equiv of MeIMe (MeIMe ¼ 1,3-dimethyl-4,5-dimethylimidazol-2-ylidene) immediately afforded NHC-
stabilized germylene complex Cp*(CO)2(H)WGe(H)(MeIMe)(Tsi) (2) that has a zwitterionic, WeGe
single-bonded structure. Complex 2 was thermally unstable and intramolecular proton-transfer followed
by hydride-transfer to the NHC-unit occurred slowly at room temperature to give anionic germylene
complex [Cp*(CO)2W¼Ge(H)(Tsi)][HMeIMe] ([3][HMeIMe]) first and subsequently germylyne complex
Cp*(CO)2W≡Ge(Tsi) (4) and H2 MeIMe. Although [3][HMeIMe] was too unstable to be isolated, the salt of
bulkier [HMeIiPr]þ, [Cp*(CO)2W¼Ge(H)(Tsi)][HMeIiPr] ([3][HMeIiPr]), was thermally more stable and was
isolated and fully characterized.
Received 22 June 2017
Received in revised form
21 July 2017
Accepted 21 July 2017
Available online 23 July 2017
Keywords:
Germylene complex
Germylyne complex
NHC-carbene
© 2017 Elsevier B.V. All rights reserved.
Proton transfer
Hydride transfer
X-ray diffraction
1. Introduction
Cp(CO)2Mo≡Ge{2,6-Mes2-C6H3} by the reaction of anionic complex
Na[CpMo(CO)3] with chlorogermylene 2,6-Mes2-C6H3GeCl [2a].
Complexes having a triple bond between M (¼ transition metal)
and E (¼ Group 14 elements) are attracting considerable attention
in the fields of fundamental organometallic and coordination
chemistry. Thanks to recent outstanding advances in the synthesis
of suitable divalent precursors, the M≡E triple-bonded complexes
are now available for all Group 14 elements E [1e4]. However, the
number of their examples is still small, and study on their reactivity
at the M≡E bond is even rarer [1c,5]. To elucidate the detailed
chemical and physical properties of these M≡E triple-bonded
complexes, development of convenient synthetic methods for
them with a variety of substituents and metal fragments is
indispensable.
Some typical synthetic routes reported for these M≡E triple
bonded complexes are illustrated in Scheme 1. One is the direct
reaction of a stable divalent Group 14 element halide with an
anionic metal complex (Scheme 1, Type-I). Most of M≡E complexes
have been synthesized by this type of reaction. For example, Power
et al. synthesized the first example of germylyne complex
Abstraction of a substituent on a Group 14 element ligand in M¼E
double-bonded complexes can also afford M≡E complexes (Scheme
1, Type-II). According to this procedure, some silylyne complexes
[1a-d] have been synthesized. In all these reactions, stable divalent
Group 14 element halides, their-base-stabilized ones, or their
transition metal complexes were usually required as precursors.
We have previously reported a novel reaction of a hydrido(hy-
drogermylene) complex Cp*(CO)2(H)W¼Ge(H)(Tsi) (1, Tsi
¼
C(SiMe3)3), which was easily prepared from a trihydrogermane and
Cp*W(CO)2L(Me) (L ¼ CO, MeCN) [6], with ArNCO (Ar ¼ Ph, Mes)
giving a germylyne complex Cp*(CO)2W≡Ge(Tsi) (4) in high yield
via dehydrogenation [2h]. This type of reaction can be categorized
into the Type-III reaction (Scheme 1), in which an organic substrate
(Sub.) works as a hydrogen acceptor to convert an (H)M ¼ E(H)
double bond into an M≡E triple bond. We report here another
Type-III reaction in which germylene complex 1 is converted to
germylyne complex 4 by treatment with N-heterocyclic carbenes
(NHCs). This reaction was proved to proceed through stepwise
proton and hydride abstraction. Two types of intermediates were
successfully isolated and structurally characterized. One of them,
[Cp*(OC)2W¼Ge(H)(Tsi)][HMeIMe] ([3][HMeIMe]) (MeIMe ¼ 1,3-
dimethyl-4,5-dimethylimidazol-2-ylidene), is the first example of
anionic germylene complexes [7]. It should be mentioned that a
* Corresponding author.
** Corresponding author.
E-mail addresses: hhashimoto@m.tohoku.ac.jp (H. Hashimoto), tobita@m.
tohoku.ac.jp (H. Tobita).
http://dx.doi.org/10.1016/j.jorganchem.2017.07.027
0022-328X/© 2017 Elsevier B.V. All rights reserved.

90
T. Fukuda et al. / Journal of Organometallic Chemistry 848 (2017) 89e94
Scheme 1. Synthetic approaches to base-free M≡E triple-bonded complexes.
similar treatment of silylene complexes Cp*(CO)2(H)W¼Si(H)R
[R ¼ Tsi [8], Eind (1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) [9]]
with NHC gave analogous anionic silylene complexes
[Cp*(OC)2W¼Si(H)R][H-NHC], but the reaction did not proceed
further and their conversion into silylyne complexes
Cp*(CO)2W≡SiR (A: R ¼ Tsi [1e], B: Eind [1f]) required the addition
of a strong Lewis acid B(C6F5)3 to the anionic silylene complexes.
vacuum to measure a 1H NMR spectrum of 5a. 5a: 1H NMR
(400.1 MHz, C6D6, 300 K)
¼ 1.53 (s, CMe, 6H), 2.22 (s, NMe, 6H),
3.62 (s, NCH2N, 2H); 13C{1H} NMR (100.6 MHz, C6D6, 300 K):
¼ 9.9
(CMe), 37.9 (NMe), 81.3 (NCN), 123.8 (CMe). [3][HMeIMe]: 1H NMR
(400.1 MHz, C6D6, 300 K)
d
d
d
¼ 0.70 (s, 27H, SiMe), 0.93 (s, 6H,
C¼CMe), 2.46 (s, 15H, Cp*), 2.98 (s, 6H, NMe), 8.93 (s, 1H, NCHN),
2
13.28 (s, JWH ¼ 31.8 Hz, 1H, GeH).
Germylyne complex 4 was isolated in 52% yield (14 mg,
0.020 mmol) by a larger scale reaction using 2 (31 mg, 0.039 mmol)
in toluene (5 mL) and heating at 40 ꢂC for 5 days, followed by
recrystallization from hexane at ꢀ30 ꢂC. The NMR data of 4 ob-
tained from this experiment agreed well with the literature data
2. Experimental
Reaction of 1 with MeIMe: To a solution of 1 (42 mg,
0.062 mmol) in toluene (4 mL) was added MeIMe (9 mg, 0.07 mmol)
at room temperature. After 10 min, all volatiles were removed and
the residue was washed with cold hexane and ether to give
Cp*(CO)2(H)WGe(H)(MeIMe)(Tsi) (2) in 71% yield (35 mg,
0.043 mmol) as a light yellow powder. 2: 1H NMR (400.1 MHz, C6D6,
[2h]. 4: 1H NMR (400.1 MHz, C6D6, 300 K):
d
¼ 0.33 (s, 27H, SiMe),
2.08 (s, 15H, Cp*); 13C{1H} NMR (100.6 MHz, C6D6, 300 K):
d
¼ 4.4
(SiMe), 12.2 (C5Me5), 66.2 (C(SiMe)3), 100.8 (C5Me5), 224.8 (CO).
Reaction of 1 with MeIiPr: Isolation of anionic silylene com-
plex [3][HMeIiPr]: A solution of 1 (5 mg, 0.008 mmol) and a small
amount of C6Me6 in C6D6 (0.5 mL) was treated with MeIiPr (3 mg,
0.02 mmol) at room temperature to give [Cp*(CO)2W¼Ge(H)(Tsi)]
[HMeIiPr] ([3][HMeIiPr]) instantaneously in 91% NMR yield. Complex
[3][HMeIiPr] was isolated in 74% yield (20 mg, 0.023 mmol) as red
crystals in a larger scale reaction using 1 (21 mg, 0.031 mmol) and
MeIiPr (5.5 mg, 0.31 mmol) in C6D6 (0.5 mL) followed by recrystal-
lization from a THF solution layered with toluene at room tem-
300 K):
d
¼ ꢀ5.44 (s, 1H, 1JWH ¼ 48.6 Hz, WH), 0.47 (s, 27H, SiMe),
1.25, 1.27 (s, 3H ꢁ 2, MeC¼CMe of MeIMe), 2.02 (s, 15H, Cp*), 3.27,
3.56 (s, 3H ꢁ 2, NMe), 5.45 (s,1H, GeH); (400.1 MHz, THF-d8, 270 K):
d
¼ ꢀ6.16 (s, 1H, 1JWH ¼ 49.5 Hz, WH), 0.21 (s, 27H, SiMe), 1.91 (s,
15H, Cp*), 2.19, 2.22 (s, 3H ꢁ 2, MeC¼CMe of MeIMe), 3.84, 3.91 (s,
3H ꢁ 2, NMe), 5.41 (d, 1H, JHH ¼ 1.3 Hz, GeH); 13C{1H} NMR
3
(100.6 MHz, THF-d8, 270 K):
d
¼ 1.5 (C(SiMe)3), 5.8 (SiMe), 8.3, 8.7
(MeC¼CMe of MeIMe), 11.5 (C5Me5), 35.3, 38.4 (NMe), 98.9 (C5Me5),
perature. [3][HMeIiPr]: 1H NMR (400.1 MHz, C6D6, 300 K):
d
¼ 0.66
126.7, 127.0 (MeC¼CMe of MeIMe), 165.1 (NCN), 237.5, 247.2 (CO);
3
29Si{1H} NMR (79.5 MHz, THF-d8, 270 K):
d
¼ ꢀ0.2 (SiMe); IR (KBr
(s, 27H, SiMe), 1.26 (d, JHH ¼ 6.4 Hz, 12H, CHMe2), 1.44 (s, 6H,
3
pellet, cmꢀ1): 1971 (w, nGeH), 1880 (s, nCO), 1784 (s, nCO); Elemental
analysis: calcd. for C29H56GeN2O2Si3W; C: 43.24, H: 7.01, N: 3.48;
found C: 43.64, H: 6.89, N: 3.47.
C¼CMe), 2.47 (s, 15H, Cp*), 3.84 (sept, JHH ¼ 6.4 Hz, 2H, CHMe2),
8.84 (s, 1H, NCHN), 13.18 (s, 2JWH ¼ 32.7 Hz, 1H, GeH); (400.1 MHz,
THF-d8, 300 K):
d
¼ 0.19 (s, 27H, SiMe), 1.58 (d, 3JHH ¼ 6.4 Hz, 12H,
CHMe2), 2.13 (s, 15H, Cp*), 2.35 (s, 6H, C¼CMe), 4.64 (sept,
Thermal reaction of 2: Formation of germylyne complex 4
and H2 MeIMe (5a): A solution of 2 (4 mg, 0.005 mmol) in C6D6
(0.5 mL) containing a small amount of C6Me6 as an internal stan-
dard was kept at room temperature. After 6 days, formation of
Cp*(CO)2W≡GeTsi (4) and H2 MeIMe (5a) was observed in 73% and
58% conversion yields, respectively, at the conversion of 93% of 2.
3JHH
¼
6.4 Hz, 2H, CHMe2), 8.89 (s, 1H, NCHN), 12.54 (s,
2JWH ¼ 33.5 Hz,1H, GeH); 13C{1H} NMR (100.6 MHz, THF-d8, 300 K):
d
¼ 4.5 (SiMe), 8.3 (C¼CMe), 12.4 (C5Me5), 22.8 (CHMe2), 24.2
(C(SiMe)3), 51.5 (CHMe2), 98.2 (C5Me5), 127.6 (MeC¼CMe of H
MeIiPr), 130.9 (NCHN), 242.4 (CO); 29Si{1H} NMR (79.5 MHz, C6D6,
300 K):
d
¼ ꢀ5.1 (SiMe); IR (KBr pellet, cmꢀ1): 3178 (w, nNCHN), 1847
During
this
reaction,
formation
of
an
intermediate
[Cp*(CO)2W¼Ge(H)(Tsi)][HMeIMe] ([3][HMeIMe]) (in 20% NMR yield
after 4 h) was observed by 1H NMR. After 6 days, all volatiles were
transferred into an NMR tube by bulb-to-bulb distillation under
(w, nGeH), 1801 (s, nCO), 1720 (s, nCO); Elemental analysis: calcd. for
C33H64GeN2O2Si3W; C: 46.00, H: 7.49, N: 3.25; found C: 46.23, H:
7.35, N: 3.26.

T. Fukuda et al. / Journal of Organometallic Chemistry 848 (2017) 89e94
91
Thermal reaction of [3][H$MeIiPr]: A solution of [3][HMeIiPr]
(4 mg, 0.005 mmol) containing a small amount of C6Me6 in C6D6
(0.5 mL) was heated at 60 ꢂC. After 9 days, formation of 4 and H2
MeIiPr (5b) was observed in 71% and 43% NMR conversion yields,
respectively, at the conversion of 92% of [3][HMeIiPr]. Obtained 5b
was identified by comparing its chemical shifts dH and dC with those
of previously reported H2 MeIiPr [10]. H2 MeIiPr (5b): 1H NMR
3
(400.1 MHz, C6D6, 300 K)
d
¼ 0.97 (d, JHH ¼ 6.4 Hz, 12H, CHMe2),
1.59 (s, 6H, C¼CMe), 3.30 (sept, 3JHH ¼ 6.4 Hz, 2H, CHMe2), 4.20 (s,
2H, NCHN); 13C{1H} NMR (100.6 MHz, C6D6, 300 K):
d
¼ 10.4 (CMe),
18.4 (CHMe2), 47.1 (CHMe2), 61.6 (NCN), 121.2 (CMe).
Spectral data and X-ray crystal structure analysis data are
available as a Supplementary Material.
3. Results and discussion
Treatment of Cp*(CO)2(H)W¼Ge(H)(Tsi) (1) with 1 equiv. of
MeIMe at room temperature gave a base-stabilized germylene
complex Cp*(CO)2(H)WGe(H)(MeIMe)(Tsi) (2) via coordination of
MeIMe to the germanium atom (Scheme 2). Complex 2 was isolated
in 71% yield and characterized by various spectroscopic data and
elemental analysis. In the 1H NMR spectrum of 2, a singlet signal of
Fig. 1. ORTEP drawing of 2. The thermal ellipsoids are plotted with 50% probability.
GeH is observed at
d
¼ 5.45 ppm. A resonance for WH appears
Hydrogen atoms except H1 and H2 are omitted for clarity. Selected bond distances (Å)
and angles (ꢂ) are as follows: W1eGe1
¼
2.5711(4), W1eC1
¼
1.947(4),
1.70(4),
1
at ꢀ5.44 ppm with JWH ¼ 48.6 Hz. This chemical shift is slightly
shifted downfield compared with that of a base-free complex 1
(ꢀ8.15 ppm, 1JWH ¼ 60.0 Hz) [6]. Two strong nCO absorption bands
appear at 1880 and 1784 cmꢀ1 in the IR spectrum, which are
considerably lower in wavenumber compared with those of base-
free complex 1 (1927 and 1853 cmꢀ1). This tendency is the same
as that for their silicon analogues Cp*(CO)2(H)WSi(H)(MeIMe)(Tsi)
(6) (1871 and 1780 cmꢀ1) [11] and Cp*(CO)2(H)W¼Si(H)(Tsi) (7)
(1928 and 1853 cmꢀ1) [8]. These results indicate that the electronic
structure of 2 is well described as a zwitterionic single-bonded
structure, Cp*(CO)2(H)WꢀeGe(H)(MeIMeþ)(Tsi) in Scheme 2. The
structure of 2 was further confirmed by X-ray crystallography
(Fig. 1). The WeGe bond length (2.5711(4) Å) is longer than that of a
base-free germylene complex Cp*(CO)2(D)W¼Ge(D)(Tsi) (1-D)
(2.4288(7) Å) [6] and is within the range of WeGe single bond
lengths (2.51e2.68 Å) [12]. The sum of the three bond angles
around Ge(1) except for those with the C(13)eGe(1) bond is
C1ꢀO1
¼
1.166(5), W1eC2
¼
1.947(4), C2ꢀO2
¼
1.162(5), W1ꢀH1 ¼
Ge1ꢀH2 ¼ 1.49(5), Ge1ꢀC13 ¼ 2.091(4), Ge1ꢀC20 ¼ 2.071(3), C1eW1eC2 ¼ 77.0(2),
C1eW1eGe1 89.34(11), Ge1eW1eH1 65.4(15), H1eW1eC2 66.4(14),
W1eGe1eH2 ¼ 110(2), H2eGe1eC20 ¼ 96(2), C20eGe1eW1 ¼ 129.29(10).
¼
¼
¼
335(2)ꢂ, indicating that the Ge atom is nearly sp3-hybridized. In
addition, the interatomic distance between the Ge1 and the
hydrido ligand H1 is ca. 2.4 Å, which is much longer than that of
germylene complex 1-D having a Ge$$$D interligand interaction
(2.07(6) Å) [6,13]. This Ge$$$H distance indicates that there is no
Ge$$$H interligand interaction in 2.
Interestingly, isolated base-coordinated complex 2 was ther-
mally unstable at room temperature, and was observed by 1H NMR
in a C6D6 solution to convert gradually to a germylyne complex
Cp*(CO)2W≡Ge(Tsi) (4) in 73% conversion yield with release of H2
MeIMe (5a) in 58% conversion yield at the conversion of 93% of 2 in 6
Scheme 2. Reaction of germylene complex 1 with MeIMe. aThe yields are conversion yields at the conversion of 93% of 2.

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T. Fukuda et al. / Journal of Organometallic Chemistry 848 (2017) 89e94
100
90
80
70
60
50
40
30
20
10
0
became zero after 6 days. On the other hand, the amount of 4
constantly increased and reached to 68% (¼ 73% conversion yield at
the 93% conversion of 2) after 6 days. Since the pattern of the
change of the ratio of these three complexes is typical of that of the
A/B/C consecutive first-order reaction [16], complex
considered to be an intermediate for formation of 4.
3 is
Though isolation of the intermediate [3][HMeIMe] was unsuc-
cessful because of its thermal instability, we succeeded in isolation
of [Cp*(CO)2W¼Ge(H)(Tsi)][HMeIiPr] ([3][HMeIiPr]), a salt of 3 hav-
ing a bulkier counter cation, which is the first example of an anionic
germylene complex. This complex was formed instantaneously by
the reaction of complex 1 and MeIiPr at room temperature, and was
isolated as very air-sensitive red crystals in 74% yield after recrys-
tallization (Scheme 3). Formation of base-stabilized germylene
complex analogous to 2 was not observed in this reaction, probably
0
20
40
60
80
100
120
140
160
Fig. 2. Time course of the thermal conversion of isolated 2 to 3 and 4 in C6D6 at 300 K.
days [14]. Complex 4 was isolated in 52% yield by a larger scale
reaction and was identified by comparison of its 1H and 13C{1H}
NMR spectroscopic data with the literature data [2h]. Furthermore,
formation of an intermediate that can be characterized as a salt of
anionic germylene complex [Cp*(CO)2W¼Ge(H)(Tsi)]- (3) and imi-
dazolium cation [HMeIMe]þ, [3][HMeIMe], was observed spectro-
scopically at the early stage of this reaction (vide infra) [15]. In the
1H NMR spectrum,
a characteristic signal was observed at
13.28 ppm, which can be assigned to the hydrogen on the germy-
lene ligand of 3. The other signals assigned to 3 were observed at
0.70 ppm for SiMe and 2.46 ppm for Cp*, which are shifted
downfield compared with those of neutral complex 1 (SiMe,
0.36 ppm; Cp*, 1.88 ppm). The chemical shifts for these signals of 3
agree well with those of isolated [3][HMeIiPr] that will be discussed
later. The signal assignable to the imidazoliumC(2) proton of the
counter cation was observed at 8.93 ppm. The time course of the
conversion of 2 to 3 and 4 at 300 K is shown in Fig. 2. In the early
stage of this reaction (0e4 h), along the decrease of complex 2, the
anionic germylene complex 3 rapidly increased, while the germy-
lyne complex 4 slowly increased. The amount of 3 reached a
maximum after 4 h, and then started to decrease and nearly
Fig. 3. ORTEP drawing of [3][HMeIiPr]. The thermal ellipsoids are plotted with 50%
probability. The position of a hydrogen atom attached to Ge1 was not determined. The
other hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles
(ꢂ): W1eGe1 ¼ 2.3886(8), W1eC1 ¼ 1.925(8), W1eC2 ¼ 1.921(8), GeeC13 ¼ 2.042(7),
C1eW1eC2
¼
83.0(3), C1eW1eGe1
¼
94.1(2), C2eW1eGe1
¼
95.4(2),
W1eGe1eC13 ¼ 145.7(2).
Scheme 3. Reaction of germylene complex 1 with MeIiPr. aThe yields are conversion yields at the conversion of 92% of [3][HMeIiPr].

T. Fukuda et al. / Journal of Organometallic Chemistry 848 (2017) 89e94
93
Scheme 4. A possible reaction mechanism.
because MeIiPr is too bulky to coordinate to the sterically congested
germanium center of 1. Complex [3][HMeIiPr] was stable at room
temperature, but was slowly converted into germylyne complex
4 at 60 ꢂC accompanied by formation of hydrogenated NHC, i.e. H2
MeIiPr (5b) [15]. The conversion yields of 4 and 5b reached to 71%
and 43%, respectively, at the conversion of 92% of [3][HMeIiPr], after
9 days.
CeH elimination of imidazolium (HMeIMeþ) from 2 then takes place
to afford the salt of complex anion 3 and imidazolium cation (H-
NHC), probably via 1,1-elimination from the Ge center followed by
hydrogen migration from W center. Another possible mechanism,
i.e. 1,2-elimination from the WeGe moiety, appears unfavorable
because the imidazolium group and the hydrido ligand are in the
anti-conformation through the WeGe bond in the crystal structure
of 2. This geometry makes the migration of the hydride to the C2
atom of the NHC difficult, which is considered to be a requirement
for the 1,2-elimination. Subsequent hydride abstraction from the
GeeH moiety of 3 by the imidazolium counter cation (H-NHC)
provides germylyne complex 4 and 5a. In the reaction of 1 with
MeIiPr, the salt of 3 and [HMeIiPr]þ was formed either through an
intermediate analogous to 2 or by direct deprotonation of 1 with
MeIiPr. The intermediate analogous to 2 having MeIiPr instead of
MeIMe on the germylene ligand, even if it exists, must be signifi-
cantly destabilized by the steric repulsion between bulky MeIiPr and
Tsi groups. Hydride abstraction in [3][HMeIiPr], on the other hand, is
retarded by the larger steric hindrance of the substituents on the
counter cation.
In the 1H NMR spectrum of [3][HMeIiPr] in C6D6, the signal of the
hydrogen on the germylene ligand appears at
d
¼ 13.18 ppm. The
chemical shift is comparable to that of base-free neutral germylene
complex 1 (13.33 ppm) [6]. The signals of the SiMe groups and Cp*
ligand are observed at 0.66 and 2.47 pm, respectively. A resonance
assigned to the ring proton of the imidazolium cation appears at
8.84 ppm with an intensity of one proton. The IR spectrum of [3]
[HMeIiPr] displays two strong nCO absorption bands at 1801 and
1720 cmꢀ1 that are much lower in wavenumber than those of base-
stabilized neutral complex 2 (1880 and 1784 cmꢀ1). The decrease of
wavenumber values in these bands indicates that the W center of
anionic complex 3 is more electron-rich than that of neutral com-
plex 2, which causes stronger p-back donation to the CO ligands in
[3][HMeIiPr]. X-ray crystal structure analysis confirmed that [3]
[HMeIiPr] was an anionic germylene complex accompanied by a
counter cation [HMeIiPr]þ, although the position of the H atom
attached to the Ge1 atom was not determined (Fig. 3). The WeGe
bond length of 3 (2.3886(8) Å) is significantly shorter than that of
neutral germylene complex Cp*(CO)2(D)W¼Ge(D)(Tsi) (1-D)
(2.4288(7) Å) [6], indicating that the W¼Ge double bond of 3 is
stronger than that of 1-D. The two bond angles of 3, :Ge(1)ꢀ
W(1)ꢀC(1) (94.1(2)ꢂ) and :Ge(1)ꢀW(1)ꢀC(2) (95.4 (2)ꢂ), are
nearly identical, which is different from those of 1-D where one of
GeꢀWꢀC(CO) angles is much larger than the other (86.25(15)ꢂ and
110.4(2)ꢂ). This is consistent with the change of geometry around
the W center, i.e. the four-legged piano-stool geometry of 1
changed to the three-legged piano-stool geometry of 3 by this
deprotonation process. The two WeCO bond lengths of 3 (1.925(8)
Å and 1.921(8) Å) are also shorter than those of 1-D (1.933(6) Å and
1.930(7) Å). The shortening of these WeGe and WeCO bonds is
4. Conclusions
We discovered a new route for conversion of a (H)W¼Ge(H)
system to the W≡Ge system through stepwise proton and hydride
transfer to NHC giving H2NHC. Full characterization of intermediate
complexes corresponding to (H)Wꢀ¼Ge(H)(NHCþ) (zwitterionic)
and Wꢀ¼Ge(H) (anionic) systems strongly supports this novel re-
action mechanism induced by the high and unique reactivity of the
carbene center of NHC. The unprecedented anionic germylene
complex is particularly interesting as a versatile precursor for
various germylene and germyl complexes. Its reactivity is now
under active research.
Acknowledgments
obviously caused by stronger p-back donation from the anionic W
center to the germylene ligand and the CO ligands compared with
that in neutral complex 1-D.
A possible reaction mechanism for formation of germylyne
complex 4 and 5a/5b is illustrated in Scheme 4. In the reaction of 1
with 1 equiv. of MeIMe, coordination of MeIMe to the germylene
ligand occurs to give MeIMe-coordinated germylene complex 2.
This work was supported by the Ministry of Education, Culture,
Sports, Science and Technology, Japan (Grants-in-aid for Scientific
Research Nos. JP15H03782, JPK05444, and JP25∙1537) and a Grant-
in-Aid for Scientific Research on Innovative Areas, “Stimuli-
responsive Chemical Species for the Creation of Functional Mole-
cules” [#2408] (JSPS KAKENHI Grant Number No. JP24109011), and
JSPS Research Fellowships for Young Scientists (T. F.).

94
T. Fukuda et al. / Journal of Organometallic Chemistry 848 (2017) 89e94
Angew. Chem. Int. Ed. 42 (2003) 445e447;
Supplementary material
(b) A.C. Filippou, A.I. Philippopoulos, G. Schnakenburg, Organometallics 22
(2003) 3339e3341;
CCDC 1557586 and 1557587 contain the supplementary crys-
tallographic data for 2 and [3][HMeIiPr]. These data can be obtained
free of charge from the Cambridge Crystallographic Data Center via
http://www.ccdc.cam.ac.uk/data_request/cif.
(c) P.G. Hayes, C.W. Gribble, R. Waterman, T.D. Tilley, J. Am. Chem. Soc. 131
(2009) 4606e4607;
(d) A.C. Filippou, P. Ghana, U. Chakraborty, G. Schnakenburg, J. Am. Chem. Soc.
135 (2013) 11525e11528.
[4] M≡Pb complexes: (a) A.C. Filippou, H. Rohde, G. Schnakenburg, Angew. Chem.
Int. Ed. 43 (2004) 2243e2247;
(b) A.C. Filippou, N. Weidemann, G. Schnakenburg, H. Rohde,
A.I. Philippopoulos, Angew. Chem. Int. Ed. 43 (2004) 6512e6516;
(c) A.C. Filippou, N. Weidemann, G. Schnakenburg, Angew. Chem. Int. Ed. 47
(2008) 5799e5802.
Appendix A. Supplementary data
Supplementary data related to this chapter can be found at
http://dx.doi.org/10.1016/j.jorganchem.2017.07.027.
[5] (a) T. Fukuda, H. Hashimoto, H. Tobita, Chem. Commun. 49 (2013)
4232e4234;
(b) T. Fukuda, H. Hashimoto, H. Tobita, J. Am. Chem. Soc. 136 (2014) 80e83.
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