Angewandte
Communications
Chemie
compound 3 results from 2 through unprecedented photolytic
reductive elimination of the entire PCO group and subse-
I
I
quent Ge –Ge bond formation. The fate of the PCO fragment
is currently unknown but led to unidentified phosphorus-
3
1
containing compounds in the reaction mixture ( P-NMR).
1
13
Compound 3 has been fully characterized by H- and C-
NMR spectroscopy, elemental analysis, and IR spectroscopy.
The molecular structure of 3 determined by an X-ray
diffraction analysis exhibits a [Ge -Ge ] moiety supported
by two bis-NHC borate ligands in the trans conformation
I
I
2+
Figure 3. Molecular structure of 4. Ad=1-adamantyl. Thermal ellip-
soids are set at 50% probability. For clarity, all H atoms and benzene
molecules as co-crystalized solvent are omitted for clarity. Symmetry
transformations used to generate equivalent atoms with (’): ꢀx+2,
(
Figure 2). The average Ge–C distance of 2.058(3) ꢁ in 3 is
ꢀ
y+2, ꢀz+1. Selected interatomic distances [ꢄ] and angles [8]: Ge1–
C1 2.045(2), Ge1–C4 2.049(2), Ge1–P1 2.291(1), Ge1–P1’ 2.272(1),
Ge1–Ge1’ 2.867(1); C1-Ge1-C4 88.29(7), C1-Ge1-P1’ 120.70(6), C4-
Ge1-P1’ 124.63(6), C1-Ge1-P1 110.98(5), C4-Ge1-P1 109.82(5), P1’-
Ge1-P1 102.16(2), Ge1’-P1-Ge1 77.84(2).
Ge–C distance of 2.047(2) ꢁ is close to those in 2 (2.045(2) ꢁ)
and in 3 (2.058(3) ꢁ), indicating a similar bonding situation
between the bis-NHC and the Ge atoms in these complexes.
In contrast, the Ge–P distances of 2.272(1) ꢁ and 2.291(1) ꢁ
in 4 are significantly shorter than the Ge–P bond in 2
(
2.483(1) ꢁ). Consistently, the calculations show slight alter-
Figure 2. Molecular structure of 3. Ad=1-adamantyl. Thermal ellip-
soids are set at 50% probability. H atoms are omitted for clarity.
Symmetry transformations used to generate equivalent atoms with (’):
ation in the bond length of Ge–P bonds (2.320 and 2.297 ꢁ)
and the MBO exhibits two distinct Ge–P bonds (1.01 and 1.12,
respectively). This is obviously owing to the extensive s- and
p-electron resonance stabilization within the Ge P ring and
reminiscent of the bonding situation of D (Ge–P distances
ranging from 2.255(1) to 2.272(1) ꢁ).
ꢀ
x+1, ꢀy+1, ꢀz+1. Selected interatomic distances [ꢄ] and
angles [8]: Ge1–C1 2.062(3), Ge1–C4 2.053(3), Ge1–Ge1’ 2.673(1); C1-
Ge1-C4 89.65(11), C4-Ge1-Ge1’ 93.26(8), C1-Ge1-Ge1’ 96.74(8).
2
2
[
5]
quite close to that in 2 (2.045(2) ꢁ). Both Ge atoms in 3 are
three-coordinated and each adopts a trigonal-pyramidal
geometry, implying their germyliumylidene character. The
Ge–Ge distance of 2.673(1) ꢁ in 3 is longer than the Ge–Ge
distance (2.569(5) ꢁ) in the neutral digermylene {[PhC-
Compound 5 is insoluble in common organic solvents and
no solution NMR data could be obtained. The solid state
3
1
P NMR spectrum of the dark-red crystals of 5 exhibits
3
1
a singlet at d = 903.5 ppm (vs. GIAO P NMR: d = 916 ppm),
which is strongly shifted downfield compared with those of
[
8a]
(
NtBu) ]GeD} by about 0.1 ꢁ, presumably, a result of the
other reported diphosphene species such as tBu Si-P=P-
2
2
3
[
9]
[4b]
steric congestion caused by the adamantyl groups and the
electronic interaction between the two Ge atoms. In agree-
ment with that, DFT calculations revealed a Ge–Ge distance
of 2.701 ꢁ (vs. 2.673(1) ꢁ by X-ray) with Mayer Bond Order
SitBu3 (d = 818.6 ppm),
B
(Scheme 1, d = 682 ppm),
[
10]
a
boryl-substituted diphosphene (d = 605 ppm),
and
[
11]
organo-substituted diphosphenes (d = 440–599 ppm). The
unusual downfield shift of 5 indicates a very strong electron-
II
(
MBO) of 0.58, indicating a weak Ge–Ge single bond. It
withdrawing property of the L Ge moiety.
2
should be mentioned here that two mono NHCs supported
The molecular structure of 5 has been determined by an
single-crystal X-ray diffraction analysis. As shown in Figure 4,
the centrosymmetric structure features a GePP’Ge’ moiety in
a “Z” form with the Ge1-P1-P1’ angle of 95.43(4)8. Similar to
that observed in 2, each Ge atom in 5 is three coordinated and
adopts a trigonal-pyramidal geometry. The average Ge–C
distance of 2.059(2) ꢁ and the Ge–P distance of 2.439(1) ꢁ in
5 are comparable to the corresponding values in 2 (Ge–C
2.045(2) ꢁ, Ge–P 2.483(1) ꢁ). The P–P distance of 2.045(1) ꢁ
in 5 is close to those in a boryl-substituted diphosphene
diatomic DGe=GeD species were described recently by Jones
[6b]
and co-workers.
Recently,
a
cryptand-encapsulated
germanium(II) dication was reported by Baines as the first
2
+
structurally characterized Ge dication supported by Lewis
[
8b]
donors. The zwitterionic compound 3 represents the first
example of a bis(germyliumylidene) complex bearing the
2
+
Ge2 ion with Ge in the oxidation state + 1.
Compound 4 is sparingly soluble in organic solvents. Its
3
1
P NMR spectrum recorded in C D exhibits a signal at d =
6
6
3
1
[10]
[4b]
2
8.4 ppm (vs. GIAO P NMR: d = 15 ppm). This signal is
(2.066(2) ꢁ) and in B (2.021(1) ꢁ), indicating P=P bond
significantly shifted upfield compared to that of D (Scheme 1,
character and confirmed by DFT calculations which revealed
[5]
d = 87.0 ppm for R = H; d = 131.9 ppm for R = Me). The
molecular structure of 4 established by an X-ray single crystal
diffraction analysis reveals a planar four-membered Ge P
a PꢀP bond of 2.048 ꢁ with MBO of 1.87. Remarkably,
although there have been many examples of diphosphenes
reported in the literature since the first isolation of a stable
2
2
[12]
ring supported by two anionic bis-NHC borate ligands
Figure 3). The two Ge atoms are thus each coordinated by
derivative by Yoshifuji and co-workers in 1981, most of the
[
9–12]
(
P=P species are supported by organic substituents
coordinated by transition metals.
or
Compound 5 represents
the first example of a Ge-substituted diphosphene.
[4b,13]
two bis-NHC-carbene carbon and two P atoms and adopt
a distorted tetrahedral coordination geometry. The average
Angew. Chem. Int. Ed. 2017, 56, 1 – 5
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3
These are not the final page numbers!
Xiong, Yun
