Synthetic and NMR studies on hexaphenylcarbodiphosphorane (Ph3P[dbnd]C[dbnd]PPh3)

Article abstract of DOI:10.1016/j.ica.2017.04.018

Bisylides of the type R₃P[dbnd]C[dbnd]PR₃, also known as carbodiphosphoranes, are very reactive compounds having numerous unusual and promising properties. The first representatives of this class of divalent carbon(0) compounds have already been synthesized over 50 years ago, but aspects of their chemistry and properties remain ambiguous. Herein, we report on specific characteristics of a simple carbodiphosphorane, hexaphenylcarbodiphosphorane Ph₃P[dbnd]C[dbnd]PPh₃, based on ¹H, ¹³C, and ³¹P NMR studies. The chemical shift and ¹J_CP coupling characteristics of the central sp-hybridized carbon atom are compared to those of other sp-hybridized carbons. Our spectroscopic findings are supported by simulations, which are in very good agreement with the experimentally determined values.

Full text of DOI:10.1016/j.ica.2017.04.018

Inorganica Chimica Acta xxx (2017) xxx–xxx
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Synthetic and NMR studies on hexaphenylcarbodiphosphorane
(Ph3P@C@PPh3)
⇑
Marco Gruber, Walter Bauer, Harald Maid, Kilian Schöll, Rik R. Tykwinski
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Department of Chemistry and Pharmacy, Organic Chemistry I, Henkestraße 42, 91054 Erlangen, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Bisylides of the type R3P@C@PR3, also known as carbodiphosphoranes, are very reactive compounds hav-
ing numerous unusual and promising properties. The first representatives of this class of divalent
carbon(0) compounds have already been synthesized over 50 years ago, but aspects of their chemistry
and properties remain ambiguous. Herein, we report on specific characteristics of a simple carbodiphos-
phorane, hexaphenylcarbodiphosphorane Ph3P@C@PPh3, based on 1H, 13C, and 31P NMR studies. The
Received 16 February 2017
Received in revised form 5 April 2017
Accepted 10 April 2017
Available online xxxx
1
chemical shift and JCP coupling characteristics of the central sp-hybridized carbon atom are compared
Dedicated to Professor Luis Echegoyen, with
thanks for years of advice, collaboration, and
fun – thanks Luis!
to those of other sp-hybridized carbons. Our spectroscopic findings are supported by simulations, which
are in very good agreement with the experimentally determined values.
Ó 2017 Published by Elsevier B.V.
Keywords:
Carbodiphosphorane
WITTIG reaction
WITTIG reagent
Cumulene
NMR spectroscopy
1. Introduction
compounds is, at present, more limited [8,9]. One such example
includes divalent carbon(0) in molecules in which four valence
The chemical element carbon provides the basic building block
for every known organic compound. The molecular diversity
achieved by both Nature and synthetic efforts derives from the
ability of carbon to use its four valence electrons to form single,
double, or triple bonds with other elements throughout the peri-
odic table. Prior to the 1980s, the majority of known, stable (i.e.,
persistent) organic compounds consists of molecules, which were
constructed from tetravalent carbon(IV) (Fig. 1). By the end of
the 1980s, however, the situation changed rather dramatically
with the groundbreaking works of Bertrand [1] and Arduengo [2],
who reported on persistent organic molecules containing divalent
carbon [3] with one non-bonded pair of electrons. These molecules
were, of course, carbenes :CR2 [4], and, in case of Arduengo carbe-
nes, more precisely N-heterocyclic carbenes (NHCs). NHCs now
occupy an indispensable role, not only in inorganic chemistry as
ligands in transition metal complexes and catalysis [5], but also
in, for example, organic synthesis [6] and materials chemistry [7].
Beyond divalent and tetravalent carbon compounds, carbon can
also assume other bonding motifs, although the breadth of such
electrons are retained as lone pairs at carbon. Such species have
been referred to as carbones [10–13], and, at first glance they are
clearly related to the more common carbodiimides and allenes.
The first representative from this class of compounds was reported
in 1961 by Ramirez et al., who successfully isolated hexaphenyl-
carbodiphosphorane (Ph3P@C@PPh3, 1). Carbodiphosphorane
(CDP) 1 is a yellow crystalline compound that is extremely suscep-
tible to reaction with water, but is indefinitely stable when kept
under dry argon [14]. In subsequent years, studies on the chem-
istry of 1 and other analogs has revealed strong Lewis basicity,
which accounts for its rapid reactivity with, for example, H2O
[15,16], HCl [17,18], BH3 [18,19], S8 [20], CS2 [21], InMe3 and AlBr3
[22], (CO)AuCl [23,24], as well as transition metal complexes such
as Fe(CO)5 [25]. The reaction with the bulkier Lewis acids such as B
(C6F5)3, however, was unsuccessful due to steric shielding of the
central carbon by the six phenyl groups [26].
Our interest in CDP 1 arose from its potential to function as a
bisylide toward WITTIG or WITTIG-like reactions. Examples for
successful WITTIG reactions of 1 have been reported by several
groups such as Bestmann, who could convert heterocumulenes to
the corresponding betain-compounds [18,27], while Soliman and
coworkers investigated the interactions of 1 with a series of
carbonyls, hydrazine, and MANNICH bases [28]. Furthermore,
⇑
Corresponding author at: Department of Chemistry, University of Alberta,
Edmonton, AB T6G 2G2, Canada.
E-mail address: rik.tykwinski@ualberta.ca (R.R. Tykwinski).
http://dx.doi.org/10.1016/j.ica.2017.04.018
0020-1693/Ó 2017 Published by Elsevier B.V.
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2
M. Gruber et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
synthesized from triphenylphosphine and dibromomethane in
molten triphenylphosphate in accordance with a procedure pub-
lished by Driscoll and coworkers [17]. Dehydrobromination to 1
was effected with sodium amide in boiling, dry THF as described
by Zybill and Müller [46]. Recrystallization from rigorously dry,
hot MeCN yielded 1 as a yellow crystalline solid that is very sus-
ceptible to hydrolysis. In solution, 1 decomposes to diphenyl
((triphenyl-k5-phosphaneylidene)methyl)phosphine oxide (5) over
a period of several minutes to a few hours in the presence of trace
amounts of water, while in the solid state it reacts with ambient
moisture over a period of several days [14–16]. In order to prevent
decomposition, the pure solid was stored in a glove box, and solu-
tions for NMR analyses were also prepared in the glove box.
Fig. 1. Some examples illustrating the breadth of bonding of carbon.
2.2. NMR spectroscopy of 1
The 13C{1H} NMR spectrum of 1 is shown in Fig. 2. In addition to
the expected signals from the aromatic carbons in the range of
125–140 ppm and the associated carbon-phosphorus coupling, a
triplet is observed at d 13.4 that is consistent with the chemical
shift expected for the sp-hybridized ylide carbon (vide infra). The
1
Scheme 1. Test reactions of 1 with carbonyls to afford allenes 3.
observed one-bond coupling constant, at JCP = 130 Hz, is some-
what higher than that reported for other bisylides, such as Me3-
P@C@PMe3 (1JCP = 78 Hz) and MePh2P@C@PPh2Me (1JCP = 93 Hz)
[44].
Matthews and Birum successfully isolated a stable four-mem-
bered-ring ylide-ketone adduct from 1 [29]. A report by Verma
et al., in particular, caught our attention since it reported the suc-
cessful synthesis of tetraphenylallene using the reaction of 1 with
benzophenone via intermediate 2 [30].
In order to unequivocally assign the identity of the ylide carbon,
a 2D-correlation of 13C with 31P has been conducted based on the
classical X,H shift correlation sequence (HETCOR) [47–49], with
13C-detection and the 1H replaced by 31P (under conditions of con-
stant broadband 1H decoupling). An intense cross peak is observed
(Fig. 3a), confirming the strong correlation between the ylide car-
bon and phosphorus. It is worth noting that scalar coupling
between 13C and 31P is eliminated by additional 31P–decoupling
during acquisition, and thus, a single cross peak is observed.
In Fig. 3b, the X-part (13C) of the A2X spin system that results
from the coupling of the ylide carbon to the two magnetically
equivalent 31P nuclei is clearly observed in both spectral simula-
tion (Fig. 3b, top) and experimental acquisition (Fig. 3b, middle).
When additional 31P-decoupling is applied, the triplet collapses
to a singlet, as expected (Fig. 3b, bottom), providing confirmation
that the observed triplet in the 13C spectrum originates from
13C,31P-coupling.
As part of our ongoing interest in cumulenic systems [31–33],
we saw potential of this simple reaction for the synthesis of unsym-
metrical molecules, such as push-pull allenes 3 (Scheme 1), whose
syntheses are usually quite complex [34,35]. Using a variety of
ketones, conditions, and dry solvents, however, we have been
unable to develop WITTIG-type reactions using 1, and, to date, all
reactions between 1 and a range of carbonyl compounds have been
unsuccessful (see supporting information for details). At this point,
we abandoned our efforts in this direction, but we became enam-
ored with the idea that CDP 1 might formally be considered as
the limiting structure for [n]cumulenes (i.e., n = 1), namely a single
sp-hybridized carbon. While this analogy is clearly not rigorously
accurate, it does offer the framework for an interesting analysis of
CDP 1. We were curious if NMR spectroscopy could be used to
explore, for example, the bonding in 1, especially considering the
carbon-phosphorus coupling constants [36]. NMR spectroscopic
investigations of mono-functional phosphorus ylides (e.g., R3-
P@C@X or R3P@CX2) have been conducted by several groups during
the past 50 years [37–42]. Bisylides of the type R3P@C@PR3, on the
other hand, have attracted less attention, and NMR studies carried
out in the late 1970s by Schmidbaur and coworkers dominate these
efforts. These studies report on the NMR spectroscopic characteri-
zation of, for example, Me3P@C@PMe3 [43,44], MePh2P@C@PPh2Me
[44], and MePh2P@C@PPh3 [45]. Rather surprisingly, NMR data
describing the ‘‘parent” molecule 1 have not been reported to the
best of our knowledge. In the following report, we describe the
NMR spectroscopy of 1 using a number of techniques, including
2D NMR correlation experiments that unequivocally assign the sig-
nal of the ylide carbon atom. We then examine the carbon-phos-
Fig. 3c depicts the 31P{1H} spectrum of 1, highlighting the 13C-
satellite signals, and two sets of 13C-satellite signals are observed.
The first is an A2X spin system derived from 31P-coupling to 13C at
the central sp-hybridized carbon (Fig. 3c, the ylide-isotopomer,
open circles ‘‘s”). The second is an AA’X spin system derived from
31P-coupling to a 13C atom at the ipso-position of one of the phenyl
rings (Fig. 3c, the ipso-isotopomer, filled circles ‘‘d”, see supporting
information for more detail). Statistically, the AA’X spin system of
the ipso-isotopomer is statistically sixfold more likely to occur (i.e.,
six ipso carbons vs one ylide carbon) than the A2X spin system of
the ylide-isotopomer, and the satellites of the former are thus more
intense. The second order AA’X pattern of the ipso-isotopomer is
nicely reproduced using spin simulation (Fig. 3c, bottom).
2.3. Chemical shift comparisons and coupling constants
phorus spin-spin coupling constants (1JCP
) in comparison to
structurally related compounds with sp-hybridized carbon.
It is well established that the chemical shifts for 13C do not fol-
low the well-known empirical trends expected for protons based
on electronegativity and ‘‘shielding”, since 13C shifts are dominated
by paramagnetic rather than diamagnetic shielding [50]. As one
considers the range of chemical shifts for sp-hybridized carbon
that is directly bonded to phosphorus (Fig. 4, Table 1), it is clear
that the range of chemical shifts is quite amazing, from ca. 185
to –10 ppm. The chemical shift of the central sp-hybridized carbon
2. Results and discussion
2.1. Synthesis
Compound 1 is readily accessible from commercially available
reagents within two steps (Scheme 2). Phosphonium salt 4 was
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M. Gruber et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
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Scheme 2. Synthetic pathway to 1 starting from triphenylphosphine and dibromomethane, and hydrolysis to 5.
Fig. 2. 13C{1H} spectrum of 1, measured in C6D6 at 70 °C and 100 MHz.
of carbodiphosphoranes dominates the upfield region of the scale,
from ca. 15 to –7 ppm, with the exact chemical shift depending on
the substituent (Table 1, entries 1–9). For example, with more elec-
tronegative heteroatom substituents N or F, the carbon resonance
generally shifts upfield (e.g., entries 7–9). The sp-hybridized car-
bons of phosphaalkynes [51], on the other hand, occupy the down-
field region 185–160 ppm, with slight upfield shifts as the organic
residue becomes more electron rich (entries 14–20). Finally, sp-
hybridized carbons Cb of phosphacumulenes show downfield
into the chemical bonding of 1 through examination of chemical
shifts and coupling constants of the ylide carbon of 1. The ylide car-
bon of 1 gives rise to a triplet at 13.4 ppm with strong coupling to
phosphorus (1JCP = 130 Hz in benzene). This signal has been
unequivocally assigned to the ylide carbon by C,P-HETCOR experi-
ments. With the chemical shift of 13.4 ppm, 1 has the most down-
field shift of all ylide carbons of the class of carbodiphosphoranes
reported to date. The carbon-phosphorus spin-spin coupling of 1
suggests strong CAP bonding, in comparison to other structurally
related compounds having an sp-hybridized carbon bonded to
phosphorus.
chemical shifts (entries 10–13), while that of C is shifted substan-
a
tially upfield, as far as –10.5 ppm for a phosphaketene (entry 11).
Coupling constants between phosphorus and a neighboring sp-
hybridized carbon range from only 73 Hz for Me2PhP@C@PPhMe2
(entry 5) to 130 Hz for CDP 1 (entry 1) to upwards of 300 Hz for
derivatives with increasingly electron deficient substituents
(entries 7–9), which is empirically consistent with bond strength
based on electronegativity of the substituents. On the other hand,
there is, perhaps surprisingly, no clear correlation between cou-
pling constant and electronegativity of the substituents for either
4. Experimental section
4.1. Methods and Materials
All reagents were purchased in reagent grade from commercial
suppliers and used without further purification. Unless otherwise
stated, all reactions were performed in standard, dry glassware
under an inert atmosphere of argon. All solvents were dried and/
or distilled. Dry THF was distilled from sodium/benzophenone.
Deoxygenated solutions were prepared by bubbling argon through
the solution for at least 30 min. Unless otherwise noted, 1H, 13C{1H},
and 31P{1H} NMR spectra for compound characterization (Figs. S2–
S10) were recorded on a Bruker Avance 300 spectrometer operating
phosphaalkynes or C of the phosphaheterocumulenes. While very
a
few examples appear in the literature that provide coupling data
for phosphacumulenes, coupling constants for these derivatives
are apparently even smaller (entry 13). Finally, it is interesting to
note that the coupling constants for phosphaalkynes are substan-
tially smaller than found in, for example, carbon–carbon triple
bonds which can reach values near 200 Hz [52,53].
at 300 MHz (1H NMR), 75 MHz (13C NMR), and 121.5 MHz (31
P
NMR) or on a Bruker Avance 400 spectrometer operating at
100 MHz (13C NMR). NMR spectra were recorded at ambient probe
temperature (rt) unless otherwise noted and referenced to the sol-
vent signal (1H: CD3OD, 3.31 ppm; 13C: CD3OD, 49.0 ppm; 1H: C6D6,
7.16 ppm; 13C: C6D6, 128.1 ppm; 1H: toluene-d8, 2.08 ppm; 13C:
toluene-d8, 20.4 ppm; d in parts per million (ppm); coupling con-
stants are reported as observed. CD3OD (99.8%, Deutero GmbH),
C6D6 (99.5%, Deutero GmbH), and toluene-d8 (99.5%, Deutero
3. Conclusions
We have synthesized hexaphenylcarbodiphosphorane (1) via
adaptation of reported procedures. Preliminary attempts to use
CDP 1 as a synthon to functionalized allenes via reactions with
ketones have been, unfortunately, unsuccessful. NMR spectro-
scopic analysis of 1, on the other hand, reveals interesting insight
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M. Gruber et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
Fig. 3. a) 2D 13C,31P shift correlation spectrum (HETCOR) of 1, b) 13C NMR analysis of 1 based on the X-component of the A2X spin system (i.e., the ylide carbon), showing the
calculated simulation (top), the spectrum acquired with 1H-broadband decoupling (middle), and the spectrum acquired with simultaneous 1H- and 31P-decoupling (bottom).
c) Experimental (top) and simulated (bottom) 31P NMR spectra of 1 with 1H-broadband decoupling. The spectrum highlights the observed 13C satellites and represents the A-
part of overlayed A2X and AA’X spin systems in a 1:6 ratio (only one of the six expected ipso-isotopomers is shown). In the experimental spectrum, filled circles ‘‘d” refer to
signals of the AA’ part, open circles ‘‘s” are due to the A2 part. A slight shim artifact (Z4) causes some ‘‘tailing” of the main signal. The * denotes an unknown decomposition
product due to heating to 70 °C during measurements.
Fig. 4. Overview of the 13C shifts of phosphaalkynes (green), phosphaheterocumulenes (red), and carbodiphosphoranes (blue). (For interpretation of the references to colour
in this figure legend, the reader is referred to the web version of this article.)
GmbH) were used as solvents. High-resolution mass spectra were
obtained from a Bruker maxis 4G (APPI, ESI) instruments. IR spectra
were recorded as solids on a Varian 660-IR spectrometer in ATR-
mode. Melting points were measured with an Electrothermal
9100 instrument under an inert atmosphere of argon.
To a stirred solution of triphenylphosphine (7.89 g, 30.0 mmol)
in molten triphenylphosphate (13 g, 40 mmol) at 90 °C under an
atmosphere of nitrogen was added methylene bromide (2.61 g,
1.05 mL, 15.0 mmol). The ensuing mixture was heated at 110 °C
for 24 h and then at 150 °C for an additional 6 h. After allowing
to cool to 100 °C, benzene (100 mL) was added, and the resulting
slurry was stirred for further 60 min at 100 °C. The mixture was fil-
tered, the filter residue was washed with benzene (20 mL) and
dried in vacuo. Purification was achieved by precipitating the pro-
duct twice from hot methanol (50 mL) by the addition of EtOAc
4.2. Synthesis
The synthesis of hexaphenylcarbodiphosphorane (1) was based
on adaptation of known procedures [17,46].
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M. Gruber et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
5
Table 1
1JCP (Hz) values for selected compounds with sp-hybridized carbon.
entry
1
compound
13C shift (ppm)
1JCP (Hz)
solvent
Ref
13.4
12.9
12.6
t, 130
t, 125
t, 93
benzene
toluene
benzene
this work
this work
[44,54]
MePh2P=C=PPh2Me
2
3
4
MePh2P=C=PPh2Me
MePh2P=C=PPh2iPr)
C
1.04
–3.4
dd, 122/128
t, 76
benzene
benzene
[55]
[54,56]
Ph2P
PPh2
5
5.8
t, 73
t, 78a
t, 305b
dd, 226/249
t, 230
benzene
benzene
benzene
benzene
benzene
[54,57]
[44,54,57]
[54,58]
[54]
Me2PhP=C=PPhMe2
Me3P=C=PMe3
(Me2N)3P=C=P(NMe2)3
(Me2N)3P=C=PMe(NMe2)2
(Me2N)2(F)P=C=P(F)(NMe2)2
6
10.8
–6.8
0.4
7
8
9
0.5
24.9c
150.3
[54]
10
d, 147
d, 27
pyridine
pyridine
[59]
Ph3P=Cα=C=N
–
Ph
–
Ph3P=C=Cβ=N Ph
Ph3P=Cα=C=O
11
12
13
–10.5
145.7
d, 185
d, 42
pyridine
pyridine
[60]
[59]
[61]
Ph3P=C=Cβ=O
Ph3P=Cα=C=S
36.3
152.4
d, 217
d, 41
pyridine
pyridine
Ph3P=C=Cβ=S
Ph3P=Cα=C(H)(OC2H5)
122.5
158.3
d, 23
d, 21
benzene
benzene
Ph3P=C=Cβ(H)(OC2H5)
14
15
16
17
18
19
20
164.9
163.4
170.8
177.0
176.4
180.4
183.4
d, 48
d, 46
d, 49
d, 44
d, 43
d, 36
d, 41
CD2Cl2
benzene
CD2Cl2
CDCl3
[62]
[63]
[64]
[65]
[65]
[65]
[66]
–
P≡C Ph
P≡C-Mes
P≡C-Me
P≡C-Et
P≡C-nBu
P≡C-C6H11
P≡C-iPr
CDCl3
CDCl3
benzene
aGasser and Schmidbaur (reference 43) have also reported a 1JCP value of 32 Hz in benzene, but this value is possibly in error, vis-a-vis other reported values. b The 1JCP value of
305 Hz, reported in reference 58 is seemingly quite large in comparison to other comparable CDP coupling constants. c In reference 59, two conflicting 13C shifts are reported,
d 27.9 in the text and d 24.9 in the experimental section.
(450 mL). Drying of the precipitate at 100 °C in vacuo afforded bis-
phosphonium salt 4 (3.89 g, 37%) as a hydrophilic tan powder. Mp
307–309 °C (lit. mp 311–314 °C) [17]. IR (ATR): 2985 (w), 2614 (w),
12H), 7.06–7.00 (m, 18H). 1H NMR (300 MHz, toluene-d8):
d 7.83–7.75 (m, 12H), 7.01–6.94 (m, 18H). 13C NMR (100 MHz,
C6D6, 70 °C): d 139.5–137.5 (m), 132.8–132.7 (m), 129.43–129.40
(m), 128.0–127.8 (m), 13.4 (t, J = 130 Hz). 13C NMR (75 MHz,
toluene-d8): d 139.4–136.7 (m), 132.6–132.5 (m), 129.3, 127.8–
127.7 (m), 12.9 (t, J = 125 Hz). 31P NMR (121.5 MHz, C6D6): d –
2.79 (s, P) [46]. 31P NMR (121.5 MHz, toluene-d8): d –3.01 (s, P).
APPI HRMS (toluene) m/z calcd for C37H31P2 ([M+H]+), 537.1896,
found 537.1895.
1435 (m), 1106 (s) cm–1 1H NMR (400 MHz, CD3OD): d 7.95–7.90
.
(m, 12H), 7.80–7.76 (m, 6H), 7.58–7.54 (m, 12H), 6.73 (broad t,
J=16.4 Hz, 2H, CH2). 13C NMR (75 MHz, CD3OD): d 137.0 (s),
135.4–134.9 (m), 131.9–131.4 (m), 118.3–117.0 (m) (methylene
carbon not observed). 31P NMR (121.5 MHz, CD3OD): d 19.9 (s, P).
APPI HRMS (THF) m/z calcd for C37H31P2 ([M – 2Br – H]+),
537.1903, found 537.1895.
Bisphosphonium salt 4 (6.18 g, 8.85 mmol) was suspended in
dry THF (75 mL), purged with argon for 15 min, and heated to
50 °C. Sodium amide (1.73 g, 44.3 mmol) was added in one portion
and the mixture was heated to reflux for 60 min. Subsequently,
additional sodium amide (1.73 g, 44.3 mmol) was added and the
mixture was then heated to reflux for further 16 h. While the reac-
tion proceeded, gas evolution was observed (NH3), and the mixture
was slowly decoloring to yellow. After cooling to rt, the yellow sus-
pension was filtered under argon by the use of a return frit, and the
filtrate was concentrated in vacuo. The bright yellow residue was
purified by recrystallization from boiling dry, deoxygenated MeCN
(10 mL) by allowing the mixture to slowly cool to rt. The formed
crystals were filtered under argon and dried in vacuo to obtain
CDP 1 (4.27 g, 90%) as a bright yellow crystalline solid. Note: The
product is extremely sensitive toward moisture and thus, should be
kept under argon to prevent hydrolysis. Mp 208–211 °C (lit. mp
208–210 °C) [14]. IR (ATR): 3047 (w), 1476 (w), 1431 (m), 1304
4.3. NMR spectroscopy
The NMR spectrum of 1 in Fig. 2 was recorded in C6D6 on a Bru-
ker Avance 400 spectrometer operating at 100 MHz (13C NMR) at
70 °C, due to the poor solubility at rt. The spectrum was referenced
to the residual solvent signal and coupling constants are reported
as observed.
NMR spectra of 1 in Fig. 3 were recorded on a JEOL Alpha500,
11.7T spectrometer operating at 500 MHz (1H NMR), 125 MHz
(
13C NMR), and 202.5 MHz (31P NMR) at 70 °C, due to the poor sol-
ubility at rt. A saturated solution of 1 in a mixture of C6H6/C6D6
(2:1 v/v) was employed (use of C6H6 allowed for NOE under
conditions of 1H-decoupling, C6D6 used for the lock). A special tri-
ple-resonance probe-head was employed (XH5CH): inner coil for
X-nucleus measurement (31P in this case), outer coil triply tuned
to fixed 1H, 2H, and 13C. Selective band pass filters were inserted
into the 13C- and 31P-channels. Specific data of these filters are:
13C-band pass, center 125.7 MHz, attenuation at center
(s), 1094 (s) cm–1 1H NMR (400 MHz, C6D6): d 7.88–7.82 (m,
.
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M. Gruber et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
frequency = –1.99 dB, attenuation at 31P-frequency = –90 dB. 31P-
band pass, center 202.5 MHz, attenuation at center frequency = –
2.42 dB, attenuation at 13C-frequency = –90 dB.
Excellence ‘‘Engineering of Advanced Materials”, and the project
‘‘Solar Technologies go Hybrid (SolTech)” from Bavarian Ministry
of Science. MG thanks the German Fonds der Chemischen Industrie
(FCI) for financial support.
4.3.1. Specific parameters
Fig. 3a (2D 13C, 31P HETCOR experiment). Pulse sequence
adapted from ‘‘normal detected” C,H-shift correlation (HETCOR)
[47–49], modified for 1H broad band decoupling and triple
nucleus = 31P, 256 data points in t2 (13C), zero filled to 512, spectral
width in f2 = 482 Hz, acquisition time in t2 = 0.53 s, 32 increments
in t1, zero filled to 64, 1408 scans per t1-increment, spectral width
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2017.04.018.
in f1 = 482 Hz, pulse width = 50 l l
s (13C), 15 s (31P), exponential
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