Stabilization of bis(chlorogermyliumylidene)s within bifunctional PNNP ligand frameworks and their reactivity studies

Article abstract of DOI:10.1039/c9dt00109c

The diiminodiphosphine (L_im) and diaminodiphosphines (l-NH and l-NMe) with a bifunctional PNNP ligand framework have been employed to host two [GeCl]⁺ units leading to the formation of bis(chlorogermyliumylidene) 1-3, respectively. T

Full text of DOI:10.1039/c9dt00109c

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Sahoo, R. K. Raut, D. Maurya, V. Kumar, P. Rani and R. G. Gonnade, Dalton Trans., 2019, DOI:
10.1039/C9DT00109C.
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DOI: 10.1039/C9DT00109C
Journal Name
ARTICLE
Stabilization of bis(chlorogermyliumylidene)s within bifunctional
PNNP ligand frameworks and their reactivity studies
a
a
a
a
a
Padmini Sahoo , Ravindra K. Raut , Devesh Maurya , Vikas Kumar , Pooja Rani , Rajesh G.
Gonnadeb and Moumita Majumdar*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
The diiminodiphosphine (Lim) and diaminodiphosphine (L-NH and L-NMe) with bifunctional PNNP ligand framework have
been employed to host two [GeCl]+ units leading to the formation of bis(chlorogermyliumylidene) 1-3 respectively. The
synthetic route involves 1:2 stoichiometric reaction between PNNP ligand and GeCl2.dioxane and subsequent addition of
two equivalents of chloride abstracting agent. Compound 1 is unstable towards coordinating solvents and Lewis bases,
resulting in the displacement of GeCl unit and formation of rearranged products 4 and 5. However, the diaminodiphosphine
coordinated Ge(II) bis(monocation)s 2 and 3 proved to be stable and revealed their electrophilic behaviour towards Lewis
bases studied.
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Introduction
In the last couple of decades the chemistry of Ge(II)
(poly)cations underwent a proliferative phase due to their
potential applications in small-molecule activation and
catalysis.1 The seminal report of [(C5Me5)Si:]+ by Jutzi et al. kick-
started the growth of this field.2 Since then a large number of
germyliumylidenes and Ge(II) dications, featuring both the lone
pair and positive charge on the Ge(II) center have been
synthesized and isolated using classical kinetic or electronic
stabilization approaches.3 Nonetheless, there are only sporadic
reports on bis(germyliumylidene)s. A borata-bis(N-Heterocyclic
Carbene) stabilized bis(germyliumylidene) possessing a Ge-Ge
Scheme 1. Synthesis of Bis(chlorogermyliumylidene)s.
preference for a single Ge(II) monocation stabilization. The two
[:GeCl]+ units in the resultant Ge(II) bis(monocation) are canted
bond has been reported by Driess et al.4 and
a
dimetallodigermene-1,2-diylium ion has been reported by
Tobita et al.5 The other relevant example is the N-Heterocyclic
imine stabilized germylene-germyliumylidene that has been
by an angle of 99
orientation (Cl-GeGe-Cl dihedral angle
disposition of the two [:GeCl]+ units proved conducive for the
elusive reductive cyclization of bis(
-iminopyridine).7

instead of the sterically favoured anti-
=
180 ). Such

computationally predicted to
possess considerable

bis(germyliumylidene) character.6 The build-up of net positive
charges and associated Coulombic repulsions that may arise
within the molecule stand as electrostatic impairment to their
frequent isolations.
In this study, we have consciously positioned ((2-
diphenylphosphino)phenyl) on the imino-carbons in place of 2-
pyridyl substituents (ligand Lim; Scheme 1), targeting
straightforward synthetic route to Ge(II) bis(monocation) from
the 1:2 stoichiometric reaction between ligand and
GeCl2.dioxane in the presence of chloride abstracting agent. The
PNNP coordinating framework may potentially forge
bifunctionality grounded on both sterics and electronics at the
a
Very recently, we have reported the stabilization of the first
bis(chlorogermyliumylidene) within
a redox-active bis(-
iminopyridine) ligand framework.7 The synthetic manipulation
involves redistribution of chloride between the bis(-
iminopyridine) stabilized Ge(II) dication8 and GeCl2.dioxane as
the two reactant molecules in order to elude electrostatic
P
center. There are reported examples of bifunctional
behaviour of the diiminodiphosphine (Lim) resulting in dinuclear
transition metal complexes from reactions with 1:2
stoichiometry.9 However, chiral diiminodiphosphine and
diaminodiphosphine has been also used as a tetradentate
ligand stabilizing Fe, Ru etc. complexes as efficient catalysts for
asymmetric transfer hydrogenation of ketones,10 asymmetric
epoxidation of olefins with H2O2,11 dehydrogenation of
a.Department of Chemistry, Indian Institute of Science Education and Research,
Pune-411008, Maharashtra, India.
b.Centre for Material Characterization, CSIR-National Chemical Laboratory, Pune-
411008, Maharashtra, India
†
Electronic Supplementary Information (ESI) available: All relevant spectra,
crystallographic detail, and DFT calculations. CCDC 1889378-1889380 and 1889433-
1889434. For the ESI and crystallographic data in the CIF or other electronic format
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Figure 2. Molecular structure of the di-cationic part of 2 in the solid
state (thermal ellipsoids at 30%, H atoms and triflate counter anions
omitted for clarity). Selected bond lengths [Å] and angles []: Ge1-N1
2.125 (7), Ge1-P1 2.500 (3), Ge1-Cl1 2.258 (3); N1-Ge1-P1 89.6 (2),
N1-Ge1-Cl1 88.1 (2), P1-Ge1-Cl1 97.18 (9).
Figure 1. Molecular structure of the di-cationic part of
solid state (thermal ellipsoids at 30%, H atoms, solvent
molecules and triflate counter anions omitted for clarity).
Selected bond lengths [Å] and angles []: Ge1-N1 2.258(3), Ge1-
P1 2.440(9), Ge1-Cl1 2.271(9); N1-Ge1-P1 78.81(7), N1-Ge1-Cl1
94.75 (7), P1-Ge1-Cl1 88.59 (3).
1 in the
indicating probable decomposition of 1 (Figures S10-S13, ESI†).
Therefore, efforts were made to identify the formation of compound
1 through carrying out reaction at lower temperatures and
monitoring the variable temperature NMR of the reaction mixture.
The addition of two equivalents of TMSOTf to a 1:2 mixture of Lim and
GeCl2.dioxane taken in CDCl3 solvent was done at -50 C and the NMR
of the reaction mixture were measured at this temperature. The
reaction temperature was increased up to room temperature with
the NMR being measured at regular intervals of 10 C elevations.
While no discernable peaks appeared in the 31P NMR spectra at lower
temperatures (Figure S14, ESI†), the 1H NMR spectra clearly discloses
the formation of compound 1 (Figure S15, ESI†). Evidently, there
appears a downfield chemical shift in the 1H NMR spectra compared
ammonia-borane12 etc. The more flexible diaminodiphosphine
(L-NH and L-NMe) ligand varieties (Scheme 1) have also been
used
in
this
study
for
the
synthesis
of
bis(chlorogermyliumylidene) involving similar methodology.
Additionally, the torsional amplitude of the –CH2-CH2- linker
determines the proximity between the two [:GeCl]+ units within
the ligand framework. Preliminary reactivity of these
bis(chlorogermyliumylidene)s with Lewis bases have been
studied and reported herein.
Results and Discussion
Syntheses
to the free Lim due to the coordination of two cationic Ge(II) units. 31
P
NMR spectrum of the reaction mixture procured immediately after
elevating to room temperature shows majorly peak at -1.48 ppm
assigned to the formation of 1 (Figure S14, ESI†). Nonetheless,
additional weaker intensity peaks appear in the range of 3-4 ppm in
the 31P NMR spectrum (Figure S14, ESI†). On standing at room
temperature for 24 hours lead to the complete disappearance of
compound 1 and four peaks at 4.53, 3.80, -2.13, -3.81 ppm become
obvious in the 31P NMR spectrum (vide supra) (Figure S12, ESI†).
Thus, compound 1 (Figures S16-S19, ESI†) disintegrates over a short
period of time under room temperature conditions.
Three PNNP type ligands Lim, L-NH and L-NMe have been chosen for
the purpose of bis(chlorogermyliumylidene) stabilization and
isolation.
The
N,N’-bis[o-
(diphenylphosphino)benzylidene]ethylenediamine (Lim) (Figures S1-
S3, ESI†) has been synthesized according to the literature
procedure.13 The diaminodiphosphine ligands L-NH and L-NMe have
been synthesized following modified literature methods (Figures S4-
S9, ESI†).14 All the three ligand systems exhibited bifunctionality
towards coordination of cationic Ge(II). The Lim stabilized
bis(chlorogermyliumylidene)
1 has been prepared at room
The L-NH and L-NMe stabilized bis(chlorogermyliumylidene)s 2 and 3
were synthesized following the similar synthetic routes in moderate
yields (Scheme 1). Colourless single crystals for both the compounds
were grown by layering the respective reaction mixtures in
dichloromethane with pentane and the structures were determined
using X-ray diffraction techniques. Compounds 2 and 3 were
reluctant to solubilize in any polar or non-polar solvents, analogous
to compound 1. The in situ generated NMR studies in CDCl3 reveal
the sole formation and solution-state stability of both compounds 2
temperature in a simple manner by the addition of two equivalents
of trimethylsilyl trifluoromethanesulfonate (TMSOTf) to a mixture of
Lim and GeCl2.dioxane taken in 1:2 ratio in dichloromethane as the
solvent (Scheme 1). The reaction mixture was concentrated within
half an hour and layered with pentane. Colourless crystals suitable
for single crystal X-ray diffraction studies were obtained
(crystallization yield = 55%) upon overnight standing. However,
neither the crude solid product nor the crystals were found soluble
in any polar or non-polar solvent sufficient for NMR spectroscopy.
Therefore, compound 1 was characterized from single crystal X-ray
crystallography and elemental analysis. Compound 1 was in situ
generated at room temperature in CDCl3 and the NMR spectra
recorded after two hours showed a complicated spectra,
1
and 3 (Figures S20-S27, ESI†), unlike the case of 1. H NMR spectra
of both 2 and 3 undergo downfield shift in comparison to the free
ligand (L-NH and L-NMe respectively), indicating the coordination of
[:GeCl]+ with the binding sites of the ligand. The 31P NMR chemical
2 | J. Name., 2012, 00, 1-3
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Figure 4. Relevant contour plots of 1’ at an isovalue of 0.03 au.
Figure 3. Molecular structure of the di-cationic part of 3 in the solid
state (thermal ellipsoids at 30%, H atoms, solvent molecules,
disordered solvent and triflate counter anions omitted for clarity).
Selected bond lengths [Å] and angles []: Ge1-N1 2.173 (5), Ge1-P1
2.4993 (18), Ge1-Cl1 2.2646 (18); N1-Ge1-P1 88.95 (15), N1-Ge1-Cl1
91.70 (15), P1-Ge1-Cl1 90.06 (6).
Compound 2 crystallized in the P-1 space group with two molecular
units within the unit cell, differing marginally in their metric
parameters (Table S2†). On each side of the diaminodiphosphine
ligand L-NH, the N and P coordinating atoms with the saturated
carbon now forms a highly puckered six-membered ring stabilizing
the [:GeCl]+ unit (Figure 2). The Ge1-P1 and Ge2-P2 have similar bond
distances 2.500 (3) Å and 2.479 (3) Å respectively. The Ge1-N1 and
Ge2-N2 bond distances are 2.125 (7) Å and 2.073 (8) Å respectively.
The difference in Ge-N bond distances can be rationalized based on
the close proximity of the triflate anions to the respective Ge centers
(Ge1O1 = 2.906 (6) Å, Ge2O6 = 3.231 (6) Å). The two [:GeCl]+ units
are arranged in anti-configuration with dihedral angle of 180
between them and an average GeGe separation of 6.57 Å.
shifts of compounds 2 and 3 appear at -12.83 and -11.48 ppm
respectively. The upfield chemical shift values of 2 and 3 compared
to 1 may be attributed to the stronger P → Ge electron donation in
case of 1 due to its relative structural rigidity (vide infra). Compounds
1-3 are highly air- and moisture sensitive. Notably, the tetradentate
coordination
of
PNNP
ligand
to
stabilize
mono(chlorogermyliumylidene) or a Ge(II) dication has not been
observed, despite maintaining 1:1 stoichiometry of the ligand and
GeCl2.dioxane with adequate equivalents of TMSOTf.
Compound 3 crystallized in the P21/c space group (Table S3†), with
the unit cell having one disordered solvent molecule. The
geometrical parameters are very similar to that observed in the case
of 2 (Figure 3). The closest approaching triflate anion to the Ge(II)
center has a Ge1O1 separation of 2.646 (5) Å. The two GeCl units
are widely separated by 7.25 (11) Å, compared to the earlier cases.
Crystal Structure
Compound 1 crystallized in P-1 space group (Table S1†). The
dicationic part in the molecular structure consists of the ligand Lim
stabilizing the two [:GeCl]+ units that are each coordinated by Nim and
-PPh2 groups. Worth mentioning, phosphine coordination for
stabilizing low-valent electrophilic tetrels is rare. There is only one
precedence, where a bis(phosphine)borate ligand stabilizes [:E-Cl]+
(E = Ge, Sn) fragments.15 Each of the coordinating sites in the
bifunctional ligand Lim forms six-membered ring with Ge(II) cationic
center (Figure 1). The environment around the Ge(II) center is
distorted pyramidal16 with the [:GeCl]+ unit located 1.22 Å above the
average P-C-C-C-N basal plane (Figure 1). The metrical parameters
show that Ge1-P1 bond distance is 2.440 (9) Å, which is slightly longer
than the Ge-P single bonds (2.33-2.37 Å)17, and akin to the lower end
of the Ge-P dative bond distances (2.44-2.52 Å)18. This signifies a high
dative bond strength between the Ge and P. However, the Ge1-N1
bond distance (2.258 (3) Å) is slightly longer than the usual range,
suggesting weaker N → Ge donations. The triflate anion is in close
contact with Ge (Ge1O1 = 2.523 (3) Å), resulting in elongated S1-
O1 (1.459(2) Å) bond distance compared to the remaining S-O bond
distances. The Ge-Cl covalent bond distance is 2.271 (9) Å,
reproducing the reported parameters.16 The sum of bond angles at
the Ge site Ge = 262, indicating sufficient pyramidalization due to
the obvious presence of lone pair electrons. The Cl1-Ge1Ge1-Cl1
dihedral angle is 180 with the Ge1Ge1 separation of 6.680 (9) Å.19
DFT Calculations
DFT calculations were carried out at the B3LYP level, using 6-31G(d,p)
as the basis set in order to discern the electronics of the
bis(chlorogermyliumylidene)s.20 The optimized geometries 1’, 2’ and
3’ (the two triflate anions were omitted) of the corresponding crystal
structures 1-3 satisfactorily reproduces the key metrical parameters.
The only anomaly is the decreased Ge-N bond distance (2.123 Å) in
1’ compared to 1, which clearly arises from the exclusion of the
triflate anions in the optimization process. The HOMO and HOMO-1
in 1’ reveal the maximum contributions from the lone pairs on the
two Ge(II) centers (Figure 4). The energetically deep-seated HOMO-
18 to HOMO-21 reveal the interaction between the vacant p-orbital
on Ge and the lone pairs on N and P. The LUMO and LUMO+1 in 1’
are majorly the ligand centered π*C=N orbitals. Therefore the ligand
center stands as the most susceptible reactive site of 1 (vide infra).
The optimized geometries 2’ and 3’ exhibit similar electronic features
except that the LUMO and LUMO+1 in both the cases are the bonding
interaction between the Ge vacant p-orbitals and the *P-C orbitals
(see ESI†). The presence of vacant p-orbital on Ge in 2’ and 3’
rationalizes the coordination of Lewis bases at the Ge site leading to
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equivalents of TMSOTf in CDCl3. A rapid growth of crystals of 1 and
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DOI: 10.1039/C9DT00109C
its isolation was possible only by the addition of excess pentane as
the non-polar non-coordinating solvent to the reaction mixture.
Single crystals of the rearranged product 4 from 1 could be isolated
by
fractional
crystallization
from
long-standing
dichloromethane/pentane mixture (Figure 5, Table S4†). Alternately,
4 has been crystallized quantitatively from the reaction of 1 with
strong Lewis base such as 4-dimethylaminopyridine (DMAP) in
dichloromethane and subsequently layered with pentane (Scheme
2). Dissolution of the crystals of 1 in tetrahydrofuran also led to the
formation of 4. One of the two diastereomers of 4 crystallized out
1
which was confirmed from its H NMR spectrum in THF-d8 (Figure
S28, ESI†). The corresponding 31P NMR spectrum shows peak at
+3.95 ppm attributed to the single diastereomer (Figure S29, ESI†).
Notably, the other peak that appear within 3-4 ppm range in the
long-standing 31P NMR spectrum of 1 taken in CDCl3 (Figure S12, ESIϮ)
may be assigned arising from another diastereomer of 4. The weaker
intensity peaks in the upfield region of Figure S12† are probably the
undetermined tri-coordinated phosphorous centers. Thus, from the
solution-state NMR studies, it is clear that compound 1 rearranges to
give compound 4 in the presence of base/coordinating solvents
under room temperature conditions. Apparently, the coordination of
Lewis acidic [:GeCl]+ units to Lim facilitates the nucleophilic attack on
the imino carbons in 1 by the Lewis bases, resulting in the
displacement of the GeCl units and formation of the bicyclic ring 4.
The polar protic solvents are the proton sources in the formation of
4. The ligand Lim is however stable towards Lewis bases. A GaCl3
coordinated to the pendant –NH2 group of the rearranged product 5
(Scheme 2, Figure 6 and Table S5†) was crystallized from the reaction
between in situ generated 1 and GaCl3, thereby reconfirming the role
of coordinating solvent or Lewis base on 1. Notably, such
rearrangements of coordinated diiminodiphosphines in the presence
of electron donor groups is unprecedented. The reaction of a chiral
diiminodiphosphine ligand with PdCl2(PhCN)2 in THF has been
reported to involve only a C-H bond activation of the phenyl ring,
keeping the imine bonds intact.23
Scheme 2. Reactivity of 1 with coordinating solvents and Lewis base.
the formation of donor-acceptor complexes (vide infra). All the three
optimized geometries have average Ge-N Wiberg bond indices (WBI)
of 0.35. Whereas, the WBI for Ge-P has a high average value of 0.69,
reflecting the much stronger nature of the bond. The Wiberg Bond
Indices provide a reasonable estimate of bond order.21 The P → Ge
dative bonds in compounds 1-3 have a high average WBI value, when
compared to Ge-P single bond with 0.89 WBI value.22 Natural bond
orbital analysis indicate that the Ge-P coordinate bond is
approximately 75% P-based with high p-character of P lone pair.22
The average WBI for Ge-Cl covalent bond is 0.80. The Mulliken
charges on Ge is approximately 0.25 in all the three Ge(II)
bis(monocation)s.
Reactivity Study
The diiminodiphosphine Lim stabilized bis(chlorogermyliumylidene) 1
was found to be unstable in the presence of coordinating solvents
such as dioxane (vide supra) as is evident from the 1H NMR of the in
situ reaction between Lim and GeCl2.dioxane in 1:2 ratio and two
Figure 5. Molecular structure of the tri-cationic part of 4 in the solid
state (thermal ellipsoids at 30%, H atoms and triflate counter anions
omitted for clarity). Selected bond lengths [Å]: P1-C4 1.844 (5), P2-
C3 1.873 (5), N2-C3 1.457 (7), N2-C4 1.446 (7), N2-C2 1.475 (7), N1-
C1 1.486 (8).
Figure 6. Molecular structure of the di-cationic part of 5 in the solid
state (thermal ellipsoids at 30%, H atoms, solvent molecules and
counter anions omitted for clarity). Selected bond lengths [Å]: P1-
C10 1.866 (8), P2-C3 1.836 (8), N2-C10 1.451 (9), N2-C3 1.461 (9), N2-
C2 1.477 (9), N1-C1 1.488 (10), N1-Ga1 1.977 (7).
4 | J. Name., 2012, 00, 1-3
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3.54 (s, 4H, -CH2-CH2-) ppm. 13C{1H} NMR (101 MHz, VCieDwCAl3rt,icTleMOSnl)inδe
On the other hand, the diaminodiphosphine L-NMe stabilized
bis(chlorogermyliumylidene) undergoes coordination of strong Lewis
bases such as DMAP24 and PMe3 to the electrophilic Ge(II) center as
is evident from the NMR studies. In the case of DMAP coordination,
the 1H NMR spectra of the reaction mixture show the upfield shift of
the alkyl protons (Figures S30-31, ESI†). While in the case of PMe3
coordination, 31P NMR spectra of the reaction mixture reveals a
downfield shift of the coordinated PMe38 and an upfield shift for the
–PPh2 (Figures S32-33, ESI†). Thus, the diaminodiphosphine
stabilized bis(chlorogermyliumylidene)s 2 and 3 turns out to be the
stable bifunctional units for further synthetic manipulations.
2
160.27 (d, Cim, 3JP-C =20.80 Hz); 138.66 (d, C-6, JP-C =17.37 Hz), 136.52
DOI: 10.1039/C9DT00109C
1
2
(d, C-1, JP-C =19.69 Hz); 135.77 (d, C-2, JP-C = 9.69 Hz); 133.17 (d,
1
ArCipso, JP-C =19.99 Hz); 132.43 (s, Ar-CH); 129.25 (s, Ar-CH); 127.95
(s, Ar-CH); 127.86 (s, Ar-CH); 127.70 (d, ArCo, 2JP-C = 7.171 Hz); 126.87
(d, ArCm, 3JP-C = 4.141 Hz); 60.49 (s, -CH2-CH2-) ppm. 31P{1H} NMR (162
MHz, CDCl3, H3PO4) δ = -13.00 ppm.
Synthesis of Ligand L-NH: Ligand Lim (1 g, 1.65 mmol) and LiAlH4
(0.282 g, 7.44 mmol) were taken in 50 mL of diethyl ether and stirred
at room temperature for 24 hours. The mixture was quenched with
15 mL water and extracted in (10 mL X 3) dichloromethane. The
organic layer was separated and dried over anhydrous Na2SO4. The
solvent was evaporated under vacuum to obtain a pale yellow sticky
solid yielding 0.58 g (58%) of L-NH. 1H NMR (400 MHz, CDCl3, TMS ) δ
7.45 (ddd, 3JH-H =7 Hz, 4JH-H =4.8 Hz, 5JH-H = 0.8 Hz, 2H, HC-2); 7.34-7.24
(m, 22 H, Ar-H); 7.17 (dt, 3JH-H = 7.6 Hz, 4JH-H = 0.8 Hz, 2H, HC-4); 6.90
(ddd, 3JH-H = 7.6 Hz, 4JH-H = 4.4 Hz, 5JH-H = 1.2 Hz, 2H, HC-5); 3.92 (s, 4H,
Ar-CH2-NH); 2.50 (s, 4H, -CH2-CH2-); 1.55 (br s, 2H, NH) ppm. 13C{1H}
NMR (101 MHz, CDCl3, TMS) δ 144.47 (d, C-1, 1JC-P =23.81 Hz); 136.79
(d, C-6, 2JP-C =10.15 Hz), 135.67 (d, ArCipso, 1JP-C =13.75Hz); 134.05 (d,
Conclusions
In this study, we have brought forward a simplified route based
on ligand choice to synthesize bis(chlorogermyliumylidene)s
and their preliminary reactivity have been discussed. In each
case, the strong
center in addition to the N
preferential stabilization of the two [:GeCl]+ units within the
ligand framework. The diaminodiphosphine ligand framework
gave more stable bis(chlorogermyliumylidene)s than the
diiminodiphosphine ligand system.
moieties are potential synthetic handles for ionene polymers25
through Ge-Ge
-bond formation26 upon reduction, possible
post-reduction modifications etc. Research along these lines are
underway in our laboratory.

-donation from the P center to the cationic Ge
→
Ge lone pair donation, fosters the
2
3
ArCo, JP-C =19.81Hz); 133.66 (C-5); 129.15 (d, ArCm, JP-C =5.48 Hz);
129.03 (ArCp); 128.80 (C-3); 128.60 (d, C-2, 2JP-C =6.96 Hz); 127.27 (C-
These bifunctionalized
4); 52.16 (d, N-CH2, JP-C =21.16Hz); 48.59 (-CH2-CH2-) ppm. 31P{1H}
3
NMR ( 162 MHz, CDCl3, H3PO4) δ = -15.42 ppm. Elemental Analysis:
Calcd. for C40H38N2P2: C, 78.93; H, 6.29; N, 4.60. Found: C, 78.91; H,
6.43; N, 4.55.

Synthesis of Ligand L-NMe: Ligand L-NH (0.58 g, 0.95 mmol) was
dissolved in 30 mL THF and the solution was cooled to -78oC. To this
solution n-BuLi (1.6 M in hexane) (1.31 mL, 2.09 mmol) was added
and the mixture was thawed to room temperature; stirred for
additional 30 minutes. To the resultant mixture methyl iodide (2 M
in methyl tert-butyl ether) (1.05 mL, 2.09 mmol) was added at room
temperature. The reaction mixture was stirred for 24 hrs. The
mixture was then quenched with 15 mL water and extracted in n-
hexane (10 mL X 3). The organic layer was separated and dried over
anhydrous Na2SO4. The solution was evaporated to obtain a white
solid yielding 0.48 g (79%) of L-NMe. 1H NMR (400 MHz, CDCl3, TMS)
δ 7.45 (m, 2H, HC-2); 7.29-7.26 (m, 16H, Ar-H); 7.23-7.19 (m, 8H, Ar-
Experimental
General Remarks. All manipulations were carried out under a
protective atmosphere of argon applying standard Schlenk
techniques or in a dry box. Tetrahydrofuran and pentane were
refluxed over sodium/benzophenone. Dichloromethane (DCM)
and chloroform-d were stirred and refluxed over calcium
hydride and kept over molecular sieves. All solvents were
distilled and stored under argon and degassed prior to use. All
chemicals were used as purchased. Chloroform-d was provided
with the tetramethylsilane as internal standard appearing at
0.00 ppm chemical shift value in the 1H NMR spectra. Ligand Lim
was synthesized following the reported literature
procedures.13. 19F and 31P{1H} NMR were referenced to external
C6H5CF3 (TFT) and 85% H3PO4 respectively. NMR spectra were
recorded on Bruker AVANCE III HD ASCEND 9.4 Tesla/400
MHz and Jeol 9.4 Tesla/400 MHz spectrometer. Melting points
were determined under argon in closed NMR tubes and are
uncorrected. Elemental analyses were performed on Elementar
vario EL analyzer. Single crystal data were collected on Bruker
SMART APEX four-circle diffractometer equipped with a CMOS
3
3
H); 7.13 (t, JH-H = 7.2 Hz, 2H, HC-4); 6.87 (ddd, JH-H = 7.6 Hz, 4JH-H
=
4.4 Hz, 5JH-H = 0.8 Hz, 2H, HC-5); 3.62 (s, 4H, Ar-CH2-NH); 2.23 (s, 4H, -
CH2-CH2-); 1.93 (s, 6H, NCH3) ppm. 13C{1H} NMR (101 MHz, CDCl3,
TMS) δ 144.48 (d, C-1, 1JP-C =22.82 Hz); 137.74 (d, C-6, 2JP-C =10.40 Hz),
1
2
136.45 (d, ArCipso, JP-C =15.04 Hz); 133.86 (d, ArCo, JP-C =19.79 Hz);
3
133.81 (C-5); 129.06 (d, ArCm, JP-C =5.25 Hz); 128.54 (ArCp); 128.35
(d, C-2, 2JP-C =6.17 Hz); 128.29 (C-3); 126.90 (C-4); 60.91 (d, N-CH2, JP-
3
C =18.98 Hz); 54.54 (-CH2-CH2-); 41.74 (N-CH3) ppm. 31P{1H} NMR (162
MHz, CDCl3, H3PO4) δ = -15.17 ppm. Elemental Analysis: Calcd. For
C42H42N2P2: C, 79.22; H, 6.65; N, 4.40. Found: C, 79.31; H, 6.45; N,
4.31.
photon 100 detector (Bruker Systems Inc.) with a Cu K
radiation (1.5418 Å).
Characterization of Ligand Lim: 1H NMR (400 MHz, CDCl3, TMS) δ 8.78

Synthesis of 1: Ligand Lim (0.3 g, 0.50 mmol) and GeCl2.dioxane (0.23
g, 1.00 mmol) were dissolved in 30 mL DCM and stirred at room
temperature. Subsequently trimethylsilyl triflate (0.18 mL, 1.00
(d, 4JP-H = 4.8 Hz, 2H, HCim); 7.91 (ddd, 3JH-H = 7.6 Hz, 4JH-H = 3.6 Hz, 5JH- mmol) was added to the reaction mixture. The solution was stirred
for 30 minutes; concentrated to 10 mL and layered with 5 mL
pentane. Colourless crystals of 1 were obtained. Crystallization yield
H = 1.2 Hz, 2H, HC-2); 7.36-7.30 (m, 15H, Ar-H); 7.28-7.22 (m, 10H, Ar-
3
H); 6.86 (ddd, JH-H = 7.6 Hz, 4JH-H = 4.8 Hz, 5JH-H = 1.2 Hz, 2H, HC-5);
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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ARTICLE
Journal Name
= 0.31 g (55%). (Decomposition Temp.: 142-144C). 1H NMR (400 Reaction of 1 with Gallium trichloride (GaCl3): Ligand LIm (0.050 g,
View Article Online
MHz, CDCl3, TMS) δ = 9.14 (s, 2H, N-CH), 8.16 (t, 3JH-H =8 Hz, 2H, HC- 0.082 mmol), GeCl2.dioxane (0.038 g, 0.165 DmOmI:o1l0).1a0n3d9/tCri9mDeTt0h0y1l0si9lyCl
2), 7.83 (t, 3JH-H =8 Hz, 3H, Ar-H ); 7.73-7.64 (m, 9H, Ar-H); 7.56 (t, 3JH- triflate (29 μL, 0.165 mmol) were added in 15 mL DCM and kept for
H =4 Hz, 12H, Ar-H); 7.22 (t, 3JH-H =12 Hz, 2H, HC-6); 3.89 (s, 4H, -CH2- 10 minutes. GaCl3 (0.029 g, 0.165 mmol) was added to the mixture in
CH2-) ppm. 13C{1H} NMR (101 MHz, CDCl3, TMS) δ 173.86 (s, Cim); DCM and stirred for 30 minutes. The solution was then concentrated
138.73; 135.39; 134.09; 133.82; 133.71; 133.40; 130.25; 123.29; and layered with 5 mL pentane. After 24 hours colourless block
120.14; 116.98 (CF3SO3); 113.82; 59.63 (s, -CH2-CH2-) ppm. 31P{1H} crystals of the rearranged product 5 were obtained.
NMR (162 MHz, H3PO4) δ = -1.48 ppm. 19F{1H} NMR (377 MHz, TFT) δ
= -77.32 ppm. Elemental Analysis: Calcd. For C42H36Cl2F6Ge2N2O6P2S2:
C, 45.08; H, 3.06; N, 2.50. Found: C, 44.98; H, 3.20; N, 2.56.
NMR scale reaction of 3 with 4-Dimethylaminopyridine(DMAP): In
a NMR tube L-NMe (0.02 g, 0.031 mmol), GeCl2.dioxane (0.014 g,
0.062 mmol) and trimethylsilyl triflate (10.5 μL, 0.062 mmol) were
added 0.6 mL CDCl3. After dissolution of all the contents DMAP
(0.0076 g, 0.062 mmol) was added to the tube in CDCl3 and was left
for 24 hrs. After 24 hrs the NMR data was obtained.
Synthesis of 2: Ligand L-NH (0.3 g, 0.5 mmol) and GeCl2.dioxane (0.23
g, 1.00 mmol) were dissolved in 50 mL DCM and stirred at room
temperature. Subsequently trimethylsilyl triflate (0.18 mL, 1.00
mmol) was added to the reaction mixture. The solution was stirred
for 30 minutes. The solvent was then removed completely under
vacuum yielding 0.40 g (72%) of 2 (Decomposition Temp.: 122-
124C). Colourless single crystals were obtained by layering in situ
NMR scale reaction of 3 with Trimethyl phosphine (PMe3): In a NMR
tube L-NMe (0.02 g, 0.031 mmol), GeCl2.dioxane (0.014 g, 0.062
mmol) and trimethylsilyl triflate(10.5 μL, 0.062 mmol) were added in
CDCl3. After dissolution of all the contents PMe3 (6 μL, 0.062 mmol)
was added to the tube in CDCl3 and was left for 24 hrs. After 24 hrs
1
generated 2 taken in DCM with pentane. H NMR (400 MHz, CDCl3,
TMS) δ = δ 7.70 (s, 2H, HC-2); 7.54-7.34 (m, 26H, Ar-H); 7.06 (t, 3JH-H the NMR data was obtained.
= 7.2 Hz, 2H, HC-4); 5.93 (br, s, 2H, NH); 4.34 (s, 4H, Ar-CH2-NH); 3.34
(s, 4H, -CH2-CH2-) ppm. 13C{1H} NMR (101 MHz, CDCl3, TMS) δ 137.77;
134.77; 134.02; 132.92; 131.61 (br); 130.76 (br); 129.49; 120.87,
Conflicts of interest
117.70 (CF3SO3); 52.34 (N-CH2); 48.76 (-CH2-CH2-) ppm. 31P{1H} NMR
(162 MHz, CDCl3, H3PO4) δ = -12.83 ppm. 19F{1H} NMR (377 MHz,
CDCl3, TFT) δ = -77.65 ppm. Elemental Analysis: Calcd. For
C42H38Cl2F6Ge2N2O6P2S2: C, 44.92; H, 3.41; N, 2.49. Found: C, 44.98;
H, 3.50; N, 2.38.
“There are no conflicts to declare”.
Acknowledgements
The authors thank the Department of Science and Technology
(DST), India (EMR/2015/001135) and DST Nano-mission
Thematic Unit, India (SR/NM/TP-13/2016) for their financial
support. The authors thank the reviewers for their critical
insights to improve the quality of this work.
Synthesis of 3: Ligand L-NMe (0.05 g, 0.08 mmol) and GeCl2.dioxane
(0.036 g, 0.16 mmol) were dissolved in 15 mL DCM and stirred at
room temperature. Subsequently trimethylsilyl triflate (28.5 μL, 0.16
mmol) was added to the reaction mixture. The solution was stirred
for 30 minutes. The solvent was then removed completely under
vacuum yielding 0.06 g (65%) of 3 (Decomposition Temp.: 128-
130C). Colourless single crystals were obtained by layering in situ
Notes and references
1
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generated 3 taken in DCM with pentane. H NMR (400 MHz, CDCl3,
TMS) δ 7.73 (m, 2H, HC-2); 7.58-7.40 (m, 20H, Ar-H); 7.32-7.28 (m,
3
2
3
4
5
6
7
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4H, Ar-H); 7.07 (t, JH-H =7.6 Hz, 2H, HC-5); 4.27 (s, 4H, Ar-CH2-NH);
3.44 (s, 4H, -CH2-CH2-); 2.54 (s, 6H, N-CH3) ppm. 13C{1H} NMR (101
MHz, CDCl3, TMS) δ 136.95; 134.83; 133.93; 133.84; 132.26; 131.79;
131.52; 130.56; 129.80; 129.59; 121.02, 117.86 (CF3SO3); 61.45 (N-
CH2); 55.08 (-CH2-CH2-); 43.14 (N-CH3) ppm. 31P{1H} NMR (162 MHz,
CDCl3, H3PO4) δ = -11.48 ppm. 19F{1H} NMR (377 MHz, CDCl3, TFT) δ =
-77.71 ppm. Elemental Analysis: Calcd. For C44H44Cl2F6Ge2N2O6P2S2:
C, 45.91; H, 3.68; N, 2.43. Found: C, 45.92; H, 3.72; N, 2.49.
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8
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+
10H, Ar-H); 7.64-7.52 (m, 7H, Ar-H); 7.37-7.18 (m, 5H, Ar-H, NH3 );
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7.06 (br., 2H, Ar-H); 6.90 (br., 2H, Ar-H); 6.76-6.57 (m, 2H, Ar-H); 3.58
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(t, 3JH-H = 6 Hz, 2H, N-CH2-CH2-NH3 ); 2.91 (s, 2H, P-CH); 1.74 (p, 3JH-H
+
= 6 Hz, 2H, N-CH2-CH2-NH3 ) ppm. 31P{1H} NMR (162 MHz, THF-d8,
H3PO4) δ = +3.94 ppm. Elemental Analysis: Calcd. For C42H42N2P2: C,
79.06; H, 6.14; N, 4.61. Found: C, 79.00; H, 6.10; N, 4.65.
6 | J. Name., 2012, 00, 1-3
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C. –B. Yang, Y. –Y. Li, Z. –R. Donga, J. –X. Gao, H. Nakamura, K.
ARTICLE
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DOI: 10.1039/C9DT00109C
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DOI: 10.1039/C9DT00109C
TOC for submitted Manuscript Titled: “Stabilization of bis(chlorogermyliumylidene)s
within bifunctional PNNP ligand frameworks and their reactivity studies”
TOC text: Bis(chlorogermyliumylidene)s stabilized within PNNP frameworks show diverge
reactivity with Lewis base depending on the coordinated ligand backbone.