N-Heterocyclic Carbene-Stabilized Germanium and Tin Analogues of Heavier Nitriles: Synthesis, Reactivity, and Catalytic Application

Article abstract of DOI:10.1021/jacs.9b08741

The synthesis of stable heavier analogues of nitriles as monomeric tetrylene-phosphinidenes ^MesTerEP(IDipp) (E = Ge, Sn; ^MesTer = 2,6-Mes₂C₆H₃, IDipp = C([N-(2,6-iPr₂C₆H₄)CH]₂) was achieved by taking advantage of NHC (N-heterocyclic carbene, here IDipp) coordination to the low-valent phosphorus center. Multiple bonding character of the E-P bonds was examined experimentally and computationally. Both germanium and tin compounds undergo [2+2] cycloaddition with diphenylketene, whereas reaction of the tin derivative with tris(pentafluorophenyl)borane provided unique "push-pull" phosphastannene (^MesTer)(Ar)Sn = P(IDipp) (Ar = C₆F₄[B(F)(C₆F₅)₂]). Going further, we demonstrated the potential of tetrylene-phosphinidene complexes in catalytic hydroboration of carbonyl compounds.

Full text of DOI:10.1021/jacs.9b08741

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Communication
NHC-Stabilized Germanium and Tin Analogues of Heavier
Nitriles: Synthesis, Reactivity, and Catalytic Application
Vitaly Nesterov, Ramona Baierl, Franziska Hanusch, Arturo Espinosa Ferao, and Shigeyoshi Inoue
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 02 Sep 2019
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NHC-Stabilized Germanium and Tin Analogues of Heavier Nitriles: Synthesis, Reactivity, and
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Catalytic Application
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Vitaly Nesterov,† Ramona Baierl,† Franziska Hanusch,† Arturo Espinosa Ferao,§ and Shigeyoshi Inoue*,†
†Department of Chemistry, WACKER-Institute of Silicon Chemistry and Catalysis Research Center, Technische Universität
München, Lichtenbergstraße 4, 85748 Garching bei München, Germany
§Departamento de Química Orgánica, Facultad de Química, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain
Supporting Information
cyclobutadiene analogue IV (Chart 1B)6 considered as a phosphasilyne
ABSTRACT: The synthesis of stable heavier analogues of nitriles as
dimer. Related heterocyclic system [LGeP]2 V (Chart 1B),7 as well as
monomeric tetrylenephosphinidenes MesTerEP(IDipp) (E = Ge, Sn;
cationic derivatives VI and VII (Chart 1B)8 were obtained after UV
irradiation of the corresponding L[Ge]PCO phosphaketenes. Cyclic
germylene VIII was synthesized using similar synthetic approach.9
MesTer = 2,6-Mes2C6H3, IDipp = C([N-(2,6-iPr2C6H4)CH]2) was
achieved by taking advantage of NHC (N-heterocyclic carbene, here
IDipp) coordination to the low-valent phosphorus center. Multiple
bonding character of the EP bonds was examined experimentally and
computationally. Both germanium and tin compounds undergo [2+2]
cycloaddition with diphenylketene, reaction of the tin derivative with
Chart 1. (A) Heavier Nitrile Analogues I; (B) Dimers IV-VII, and
Germylene VIII
R
E
R
tris(pentafluorophenyl)borane
provided
unique
“push-pull”
(Ar
(A)
(B)
R
E P
(E = Si, Ge, Sn, Pb)
E
P
P
phosphastannene
(
MesTer)(Ar)Sn=P(IDipp)
=
II
IA
IB
C6F4[B(F)(C6F5)2]). Going further, we demonstrated the potential of
tetrylene–phosphinidene complexes in catalytic hydroboration of
carbonyl compounds.
R''
Dipp
N
Ph
tBu
N
E
R
P
R
P
E
Dipp
N
Ge
P
P
Si
P
P
Si
N
R''
N
tBu
tBu
N
R'
Ge
Dipp
E = Ge, Sn; R = N(R'')Si(OtBu)3,
N(R'')Si(iPr)3; R' = 2,4-[CH(3,5-
tBu2C6H4)2]2-4-MeC6H2
N
N
tBu
Dipp
Ph
R'
III
V
, R'' = H, Me
Stable heavier main group alkene, alkyne, nitrile analogues and their
derivatives continuously attract increased research attention due to
unique synthetic potential and growing application in catalysis.1,2
Among these compounds, heavier nitrile analogues RE≡P IA (E = Si,
Ge, Sn, Pb; Chart 1A) still remain very challenging synthetic targets
due to low thermodynamic stability and tendency to oligomerize.
Theoretical calculations3 on model compounds with small substituents
suggest higher stability of the linear form RE≡P (IA) over the isomeric
bent structure RP=E: (II) only for silicon derivatives (E = Si) with
electronegative groups.3a For the silicon compounds with
electropositive substituents3a and tin analogues independent from the
substitution pattern,3b the isomer II is energetically more favored.4 Low
thermodynamic stability of heavier nitriles is attributed to drastically
decreased ability of heavier elements to form multiple covalent bonds.
This can be viewed as increased contribution of the valence isomer
tetrylene–phosphinidene resonance structure IB into the ground state
of the molecule descending the Group 14. Although sufficiently bulky
aryl substituents were predicted to stabilize the heavier nitrile form IA
(E = Si, Sn),3b,c reported experimental attempts to access these
compounds using this strategy alone were not successful so far.5 Most
recently, an approach using very sterically demanding amido ligands
resulted in tetrylene–phosphinidenes dimers, diphosphenes III (Chart
1B).5d
IV
Ad
Ge
Ad
Ad
Ad
Ge
N
N
N
N
Ge
Tipp
N
B
N
N
P
P
P
N
B
N
N
B Tol2
N
tBu
N
SiMe2
N
P
Tol2
Ge Ge
P
Tol2
P
B Tol2
N
tBu
N
N
N
N
Ad
N
Ad Ad
Ad
VI
VIII
VII
NHCs are widely recognized as excellent ligands for stabilization of
low-valent main group elements.10 Herein, we describe the synthesis
and isolation of NHC-stabilized tetrylene–phosphinidenes, as well as
first insights into the structure, bonding, and reactivity of these heavier
nitrile analogues, including application in catalysis.
Recently, we developed a number of synthetic methods to stabilize
low-coordinate Group 14 element compounds using N-heterocylic
imines (NHIs) as supporting ligands.11 To expand this chemistry, we
approached the problem exploring synthetic potential of their heavier
analogues, NHC–phosphinidene (NHCP) adducts.10,12 Aiming at
target compounds with aryl substituents, which would provide some
“pull” effect and steric protection, we reacted germylene and
stannylene chloride dimers
13
[
MesTerECl]2
with trimethylsilyl
14
phosphinidene complex (IDipp)PSiMe3 (Scheme 1). At elevated
temperature, the reaction led to elimination of trimethylsilyl chloride
and selective formation of stable tetrylene-phosphinidenes 1 and 2
isolated in good yields as red and orange crystals, respectively. Their
signals in the 31P NMR spectra (C6D6) appeared at 216.8 ppm (1) and
Alternative approach, implying coordination of a Lewis base to a
heavier low-coordinate Group 14 element, have also been explored.
Several groups independently reported isolation of [LSiP]2
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176.4 ppm (1J(119Sn,P) = 1648 Hz) (2) lying downfield related to the
starting material (δ(31P) = –129.5 ppm)14 and within the range
reported for phosphagermenes (175 416 ppm) and
σ(SnP) bonds, unlike to cyclic germylene VIII, where the HOMO is
the π(GeP) orbital. The HOMO1 of the germanium derivative 1a
displays π(EP) symmetry and mainly located at more
1
2
3
4
5
6
7
8

a
phosphastannenes (170  204 ppm).1 The 119Sn NMR spectrum of 2
showed a doublet at 1689.8 ppm (1J(119Sn,P) = 1648 Hz), which falls
into the region reported for bis(aryl)stannylenes (980 – 2323 ppm)15
and significantly downfield shifted related to phosphastannenes signals
(499  658 ppm)2 indicating pronounced tetrylene character of this
electronegative phosphorus, while in the heavier analogue 2a it is
mostly a phosphorus’ p orbital (Figure 2A). Relatively low singlet-
triplet gaps of 34.9 and 34.2 kcal/mol were found for 1a and 2a,
respectively at B3LYP-D3/def2-TZVPP(ecp) level of theory. The
HOMOLUMO separation of the germanium derivative is slightly
higher than that of its tin congener (3.49 vs. 3.34 eV). Wiberg bond
indices (WBIs) of the EP (1a: 1.300 2a: 1.063) and CNHCP bonds
(1a: 1.122; 2a: 1.194) indicate a presence of partial double bond
character.
Natural bond orbital (NBO) analysis of 1a revealed the absence of a
formal (natural) (GeP) orbital, while second-order perturbation
theory (SOPT) unveiled strong electron donation from s-type lone
pair at P (1.915e), as well as from the  and * (CNHCP) MOs
(occupancies 1.672e and 0.398e, respectively) to a scarcely filled p-
type orbital at Ge (0.398e), amounting altogether to 82.0 kcal/mol.
Natural population (NPA) analysis indicates substantial net electron
transfer from the NHC moiety to the phosphorus atoms (0.27e and
0.21e in 1a and 2a, respectively) suggesting significant dative bond
character of the CNHCP bonds. Thus, the calculations suggest
essential contribution of the resonance structure B into the ground
state of these molecules, whereas the contribution of the structure C is
not negligible and higher for the lighter germanium analogue (Figure
2B).
1
compound. The J(119Sn,P) coupling constant lies between the typical
values for Sn–P single (ca. 1000 Hz) and double (2208 – 2295 Hz)
bonds.2
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Scheme 1. Synthesis of Germylene– and Stannylene–
Phosphinidene NHC Complexes 1 and 2
Toluene, 75 °C
2 h (E = Ge)
24 h (E = Sn)
Dipp
Mes
ECl
Mes
Mes
N
Dipp
E
P
P
1/2
+
N
Me3Si
N
- Me3SiCl
2
N
Dipp
Mes
Dipp
1
2
(E = Ge, 82 %)
(E = Sn, 72 %)
Single crystal X-ray diffraction analysis revealed similar structural
features of 1 and 2 (Figure 1). The bond angles around the Group 14
metals are very acute (89.56(5)° at Ge, and 86.69(6)° at Sn) and close
to those reported for (amido)germylenes
(
MesTer)(NHDipp)Ge:
(88.6(2)°)16a and (MesTerNH)2E: (88.6(2)° at Ge, and 87.07(8)° at
Sn).16b
(A)
HOMO1
HOMO1
HOMO
HOMO
2a
1a
(B)
Figure 1. Molecular Structures of 1 (left) and 2 (right). Thermal
ellipsoids are shown with 50% probability; hydrogen atoms are omitted
for clarity.
R
R
R
R
R
R
R
R
R'
N
R'
N
R'
N
E
P
E
P
E
P
E
P
R'
N
N
N
N
The EP bond distances in 1 (2.2364(6) Å) and 2 (2.4562(7) Å)
R'
N
R'
R'
R'
are
(
shorter
than
those
in
(aryl)(phosphido)tetrylenes
A
B
C
TippTer)[(Me3Si)2P]E: (Ge–P: 2.291(4) Å, Sn–P: 2.527(1) Å;
TippTer = 2,4-(2,4,6-iPr3C6H2)2C6H3),5c but very close the bond
lengths between a planar phosphorus of one of the phosphido ligands
and a tetrylene atom in bis(phosphido)tetrylenes [(Dipp)2P]2E: (Ge–
P(planar): 2.2337(11) Å, Sn–P(planar): 2.4458(8) Å).17 The Ge–P bond
distance in 1 is also shorter than that in cyclic germylene VIII
(2.247(2) Å),9 but longer than those in phosphagermenes R2Ge=PR’
(2.138(3)–2.1748(14) Å).2 Altogether, this strongly suggests multiple
bond character of the E–P bonds in 1 and 2 due to the lone pair
delocalization from the monovalent phosphorus into the vacant p-
orbitals of the divalent germanium or tin atoms. It should be noted,
that so far reported related tetrylenes supported by P-donor ligands
with two-coordinate phosphorus (except III and VIII) are limited to
the examples with three-coordinate Group 14 elements and intrinsic
single E–P bonds (E = Si–Pb).18
Figure 2. (A) The HOMO and HOMO–1 in 1a and 2a; (B) Resonance
Lewis Structures of 1 and 2.
Evidence for dative nature of the CNHCP bonds in 1 and 2 was also
obtained from the analysis of the bond dissociation energies and using
Bader’s quantum theory of atoms in molecules (QTAIM).19
Further experimental study revealed inertness of complexes 1 and 2
toward small molecules (H2, CO, CO2) and equimolecular amounts of
1,3-dimethyl-1,3-butadiene, benzaldehyde, and pinacolborane.
Surprisingly, reactions with diphenylketene Ph2C=C=O afforded
selectively the formal [2+2] cycloaddition products, heterocycles 3 and
4 (Scheme 2).
Scheme 2. Synthesis of Heterocycles 3 and 4
To understand the bonding nature in 1 and 2 better, quantum
chemical calculations were carried out using simplified model
compounds 1a and 2a (2,6-Me2C6H4 groups at N atoms). The
optimized geometries at B3LYP-D3/def2-TZVP(ecp) level of theory
showed good agreement with the experimental structural data. The
highest occupied molecular orbitals (HOMOs) in both germanium
and tin model compounds correspond to the respective σ(GeP) and
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Ph
Ph
Ph
Ph
H
H
1
4
5
3
3
67c
47c
O
C
1
2
3
4
5
6
7
8
9
(IDipp)PH
Ph
P
toluene, rt,
12 h
Ph
Dipp
O
aReaction conditions: RC(O)R’ (0.5 mmol), HBpin (0.55 mmol),
C6D6 (0.4 mL), ambient temperature. Catalyst loading relative to a
carbonyl substrate. bNo further conversion was observed. cFull reaction
time was not estimated.
Mes
Mes
Mes
Mes
Mes
Dipp
Dipp
E
E
P
E
P
N
N
N
N
N
N
C6D6,
Mes
Dipp
Dipp
Dipp
3
80 °C (
)
4
100 °C (
)
3
4
1
2
(E = Ge, 93 %)
(E = Sn, 77 %)
(E = Ge)
(E = Sn)
Ph
Benzaldehyde reduction in the presence of 0.1 mol % of 2 was
completed in 15 min and in a few minutes using 2 mol % of the catalyst.
Reduction of acetophenone in the presence of only 0.05 mol % of 2 led
to full conversion within 30 min. All reductions in the presence of 2 are
selective and clean. Catalytic activity of the germanium analogue 1
appeared to be significantly lower than that of
Interestingly, comparable acceleration of the benzaldehyde reduction
was also observed in the presence of 5 mol % of (IDipp)PH.
Finally, we attempted to remove the NHC from 1 and 2 using
tris(pentafluorophenyl)borane (BCF) as a strong Lewis acid, but no
formation of (IDipp)B(C6F5)3 adduct was observed for both reactions
after heating at 65 °C. Instead, reaction of 1 gave an unstable product
((31P) = 111.5 ppm, (11B) = 15.2 ppm, C6D6), while providing a
stable adduct 5 in the case of 2 (Scheme 3).25,26
-
O
C
Ph
Spectroscopic evidence for reversible retro-cycloaddition was
obtained after consecutive heating and cooling of the C6D6 solutions of
3 and 4. Similar reactivity is known for compounds with genuine GeP
and SnP double bonds.20 The mechanism for the formation of 2 and 4
was confirmed as concerted [2+2] cycloaddition by our quantum
chemical calculations using model compounds.
Heterocycles 3 and 4 were isolated as pale yellow solids in good
yields. They displayed very similar chemical shifts in the 31P NMR
spectra (3: 18.2 ppm; 4: 20.2 ppm). The signal of 4 in the 119Sn NMR
spectrum was observed as a doublet at 344.2 ppm (1J(119Sn,P) = 253
Hz).
Molecular structures of 3 and 4 were confirmed using single crystal
X-ray diffraction analysis (Figure 3). The four-membered rings in 3
and 4 are non-planar, the bulky aryl and NHC ligands are trans-
oriented. Both compounds contain elongated single E–P (GeP:
2.5319(14) Å; SnP: 2.7299(10) Å) and E–O (GeO: 1.946(4) Å;
SnO: 2.126(2) Å) bonds exceeding the sum of covalent radii of the
corresponding atoms. 21,22
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2 (Table 1).
Scheme 3. Synthesis of Phosphastannene 5
Mes
B(C6F5)3,
benzene
Mes
Dipp
N
Mes
Mes
Sn
P
F
Dipp
N
Sn
P
65 °C, 16 h
N
F
F
N
Dipp
Dipp
F
(C6F5)2B
F
5
2
(60 %)
Structural analysis of the single crystals revealed phosphastannene 5
(Figure 4) showing a planar geometry at the tin atom (sum of the bond
angles is 359.9°). Compared to 2, the CNHCP bond in 5 (1.816 (3) Å)
is elongated, while the SnP bond distance (2.3450(10) Å) is
substantially shorter (4.5 %) indicating a double bonding character. To
the best of knowledge, this is the shortest SnP bond distance reported
to date.
Figure 3. Molecular Structures of 3 (left) and 4 (right). Thermal
ellipsoids are shown with 50% probability; hydrogen atoms are omitted
for clarity).
Catalytic application of low-valent Group 14 element compounds is
an emerging field of main group chemistry.1 Only few examples of
catalytic hydroboration of carbonyl compounds using tetrylenes
(neutral species) are reported to date.23,24 Our preliminary study on
catalytic application of complexes 1 and 2 revealed high activity of the
latter in hydroboration of aromatic aldehydes and ketones with
pinacolborane (Table 1).
Figure 4. Molecular Structure of 5 (thermal ellipsoids are shown with
50% probability; hydrogen atoms are omitted for clarity).
Table 1. Hydroboration of Aldehydes or Ketones RC(O)R’ with
pinacolborane, catalyzed by 2 or 1a
Due to unique “push-pull” zwitterionic structure, phosphorus and
tin nuclei in 5 are significantly shielded compared to those in the
starting material and known aryl phosphastannenes. Unusual high-field
resonances at (31P) = 93.05 ppm (1JSat
(
119Sn,P) = 3046 Hz,
R
R’
Cat.
Loading, Time, Conv.,
mol %
%
h
< 0.3
< 0.25
5
1JSat 117Sn,P) = 2919 Hz) and (119Sn) = 152.2 ppm (1J(119Sn,P) =
(
3069 Hz) were observed in the 31P and 119Sn NMR spectra (THF-d8).
The 1J(119/117Sn,P) coupling constants are significantly greater than
those reported for two known phosphastannenes (2295/2191 and
2208/2110 Hz).2
Ph
Ph
H
H
2
2
2
2
2
0.05
0.1
50b
>99
75c
4-MeOPh
Ph
H
0.1
The DFT calculations at B3LYP-D3/def2-TZVPP(ecp) level
support a presence of a weak double bond in 5a with WBI = 1.170. The
HOMO is located at fluorinated aromatic rings, while the HOMO–1
Me
Ph
0.05d
0.3
>99
>99
Ph
0.5
2.5
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Frenking, G., Are They Linear, Bent, or Cyclic? Quantum Chemical
Investigation of the Heavier Group 14 and Group 15 Homologues of HCN and
HNC. Chem. Asian J. 2012, 7, 1296-1311.
(4) Parent phosphasilenylidene HP=Si:, as well as Mes*P=Si(IDipp), an aryl
derivative stabilized at silicon, are reported, see: (a) Lattanzi, V.; Thorwirth, S.;
Halfen, D. T.; Mück, L. A.; Ziurys, L. M.; Thaddeus, P.; Gauss, J.; McCarthy, M.
C., Bonding in the Heavy Analogue of Hydrogen Cyanide: The Curious Case of
Bridged HPSi. Angew. Chem. Int. Ed. 2010, 49, 5661-5664; (b) Geiß, D.; Arz,
M. I.; Straßmann, M.; Schnakenburg, G.; Filippou, A. C., Si=P Double Bonds:
and LUMO are essentially pz atomic orbitals at phosphorus and tin
atoms, respectively.
1
2
3
4
5
6
7
8
In conclusion, we described the synthesis and electronic structure of
germylene– and stannylene–phosphinidenes stabilized by NHC at the
phosphorus atom. These compounds contain reactive P–E bonds (E =
Ge, Sn), and open an access to zwitterionic heavier imine analogues, as
was demonstrated for the tin derivative. Notably, the latter showed
high catalytic activity in the hydroboration of aromatic aldehydes and
ketones, drastically different to that of the germanium congener.
Further coordination chemistry and catalytic applications are currently
under investigation.
Experimental
and
Theoretical
Study
of
an
NHC-Stabilized
Phosphasilenylidene. Angew. Chem. 2015, 127, 2777-2782; c) Nesterov, V.;
Breit, N. C.; Inoue, S., Advances in Phosphasilene Chemistry. Chem. Eur. J.
2017, 23 , 12014-12039
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K.; Henn, J.; Stalke, D.; Demers, J.-P.; Lange, A., Zwitterionic Si-C-Si-P and Si-
P-Si-P Four-Membered Rings with Two-Coordinate Phosphorus Atoms.
Angew. Chem. Int. Ed. 2011, 50 , 2322-2325; c) Seitz, A. E.; Eckhardt, M.;
Erlebach, A.; Peresypkina, E. V.; Sierka, M.; Scheer, M., Pnictogen–Silicon
Analogues of Benzene. J. Am. Chem. Soc. 2016, 138 , 10433-10436.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI:.
Full synthetic and characterizing data for new compounds,
representative NMR spectra, details of computational studies (PDF)
Crystallographic data (CCDC Compound 1: 1946724, Compound 2:
1946725, Compound 3: 1946726, Compound 4: 1946727, Compound
5: 1946728)(CIF)
AUTHOR INFORMATION
Corresponding Author
(7) (a) Yao, S.; Xiong, Y.; Szilvási, T.; Grützmacher, H.; Driess, M., From a
s.inoue@tum.de
Phosphaketenyl-Functionalized
Germylene
to
1,3-Digerma-2,4-
diphosphacyclobutadiene. Angew. Chem. Int. Ed. 2016, 55, 4781-4785; (b)
Wu, Y.; Liu, L.; Su, J.; Zhu, J.; Ji, Z.; Zhao, Y., Isolation of a Heavier
ORCID
Cyclobutadiene
Analogue:
2,4-Digerma-1,3-diphosphacyclobutadiene.
Vitaly Nesterov: 0000-0003-4744-5843
Franziska Hanusch: 0000-0002-9509-194X
Arturo Espinosa Ferao: 0000-0003-4452-0430
Shigeyoshi Inoue: 0000-0001-6685-6352
Organometallics 2016, 35, 1593-1596.
(8) Xiong, Y.; Yao, S.; Szilvási, T.; Ballestero-Martínez, E.; Grützmacher, H.;
Driess, M., Unexpected Photodegradation of a Phosphaketenyl-Substituted
Germyliumylidene Borate Complex. Angew. Chem. Int. Ed. 2017, 56, 4333-
4336.
(9) (a) Del Rio, N.; Baceiredo, A.; Saffon-Merceron, N.; Hashizume, D.;
Notes
The authors declare no competing financial interests.
Lutters, D.; Müller, T.; Kato, T.,
A
Stable Heterocyclic
Amino(phosphanylidene-σ4-phosphorane) Germylene. Angew. Chem. Int. Ed.
2016, 55 , 4753-4758.
(10) Nesterov, V.; Reiter, D.; Bag, P.; Frisch, P.; Holzner, R.; Porzelt, A.; Inoue,
S., NHCs in Main Group Chemistry. Chem. Rev. 2018, 118 , 9678-9842.
(11) Wendel, D.; Reiter, D.; Porzelt, A.; Altmann, P. J.; Inoue, S.; Rieger, B.,
Silicon and Oxygen’s Bond of Affection: An Acyclic Three-Coordinate Silanone
and Its Transformation to an Iminosiloxysilylene. J. Am. Chem. Soc. 2017, 139,
17193-17198; (b) Wendel, D.; Szilvási, T.; Henschel, D.; Altmann, P. J.; Jandl,
C.; Inoue, S.; Rieger, B., Precise Activation of Ammonia and Carbon Dioxide by
an Iminodisilene. Angew. Chem. Int. Ed. 2018, 57, 14575-14579 and references
therein; (c) Ochiai, T.; Franz, D.; Inoue, S., Applications of N-heterocyclic
imines in main group chemistry. Chem. Soc. Rev. 2016, 45, 6327-6344.
(12) (a) Krachko, T.; Slootweg, J. C., N-Heterocyclic Carbene–Phosphinidene
Adducts: Synthesis, Properties, and Applications. Eur. J. Inorg. Chem. 2018,
2734-2754; (b) Doddi, A.; Peters, M.; Tamm, M., N-Heterocyclic Carbene
Adducts of Main Group Elements and Their Use as Ligands in Transition Metal
Chemistry. Chem. Rev. 2019, 119 , 6994-7112
ACKNOWLEDGMENT
We gratefully acknowledge financial support from the European
Research Council (SILION 637394) and WACKER Chemie AG. We
thank Dr. Philipp Altmann for SC-XRD analysis of 2, and Debotra
Sarkar M. Sc. for providing [MesTerGeCl]2.
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