Effective Control of the Electron-donating Ability of Phosphines by using Phosphazenyl and Phosphoniumylidyl Substituents

Article abstract of DOI:10.1002/zaac.202000028

Phosphoniumylidyl and phosphazenyl groups are effective substituents to increase the electron-donating ability of tertiary phosphines. However, the influence of structural variations among those substituents on the electronic properties of the phosphines is little explored. Herein, we show that protonation of the ylidic carbon atom of phosphoniumylidyl phosphines increases the Tolman electronic parameter (TEP) by ΔTEP = 16.0–18.8 cm^–1. Furthermore, phosphazenyl phosphines were synthesized with isopropyl groups (NP{iPr}₃) and tetramethylguanidino groups (NP{tmg}₃) at the phosphonium center. Determination of their TEP values reveals a remarkable low substituent parameter of χ = –18.5 cm^–1 for the NP(tmg)₃ group. In addition, we prepared the corresponding gold(I) complexes and determined their solid-state structures using single-crystal X-ray diffraction studies to analyze the steric profile of the new phosphine ligands.

Full text of DOI:10.1002/zaac.202000028

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202000028
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Effective Control of the Electron-donating Ability of Phosphines by
using Phosphazenyl and Phosphoniumylidyl Substituents
Janina A. Werra,[a] Marius A. Wünsche,[a] Patrick Rathmann,[a] Paul Mehlmann,[a] Pawel Löwe,[a] and
Fabian Dielmann*[a]
Dedicated to Professor Manfred Scheer on the Occasion of his 65th Birthday with our Warmest Congratulations
Abstract. Phosphoniumylidyl and phosphazenyl groups are effective
phosphines were synthesized with isopropyl groups (NP{iPr}3) and
substituents to increase the electron-donating ability of tertiary phos-
tetramethylguanidino groups (NP{tmg}3) at the phosphonium center.
phines. However, the influence of structural variations among those Determination of their TEP values reveals a remarkable low substitu-
substituents on the electronic properties of the phosphines is little ex-
plored. Herein, we show that protonation of the ylidic carbon atom of
phosphoniumylidyl phosphines increases the Tolman electronic param-
eter (TEP) by ΔTEP = 16.0–18.8 cm–1. Furthermore, phosphazenyl
ent parameter of χ = –18.5 cm–1 for the NP(tmg)3 group. In addition,
we prepared the corresponding gold(I) complexes and determined their
solid-state structures using single-crystal X-ray diffraction studies to
analyze the steric profile of the new phosphine ligands.
ies on the synthesis of guanidine-functionalized phosphines by
Schmutzler and Kuhn,[12] we used different imidazolin-2-yl-
idenamino groups to generate phosphines (IAPs) with signifi-
cantly lower TEP values than those of N-heterocyclic carbenes
or abnormal carbenes[13] (Scheme 1a).[11,14]
Introduction
The success of tertiary phosphines as ancillary ligands in
coordination chemistry and catalysis is closely related to the
outstanding ease to rationally tune their steric and electronic
properties via the substituents at the phosphorus atom.[1] This
flexibility provides a convenient approach to fine-tuning the
performance of known catalysts.[2] In this context, various ste-
ric and electronic descriptors of phosphine ligand properties
have been proposed,[3] the Tolman electronic parameter being
the most commonly used among them.[4] With respect to the
accessible electron-donating character, alkylphosphines, par-
ticularly tri-tert-butylphosphine, have been regarded as the up-
per limit for more than half a century. Advances to increase
the electron-donating power of phosphines include the func-
tionalization with electropositive plumbyl,[5] carboranyl,[6]
N-heterocyclic boryl,[7] anionic boratabenzene,[8] or anionic
secondary phosphine oxide[9] substituents. Recently, Carrow
reported a synthesis for tris-adamantylphosphine[10] and
showed that the donor strength is in the range of classical N-
heterocyclic carbene ligands. We have contributed to this field
with the discovery that strong π-donating substituents bound
to the phosphorus atom can substantially increase the electron-
donating power of phosphines.[11] Following up on early stud-
* Dr. F. Dielmann
E-Mail: dielmann@uni-muenster.de
[a] Institut für Anorganische und Analytische Chemie
Westfälische Wilhelms-Universität Münster
Corrensstrasse 30
48149 Münster, Germany
Scheme 1. (a) Resonance structures of electron-rich phosphines with
selected π-donor substituents. (b) Early examples of phosphoniumyl-
idyl and phosphanzenyl phosphines.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.202000028 or from the au-
thor.
© 2020 The Authors. Published by Wiley-VCH Verlag GmbH &
Co. KGaA. · This is an open access article under the terms of the
Creative Commons Attribution License, which permits use, distri-
bution and reproduction in any medium, provided the original work
is properly cited.
We recently expanded this concept to pyridinylidenamino
phosphines (PyAPs) which are accessible in a much shorter
synthetic route than IAPs starting from commercially available
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aminopyridines and chlorophosphines (Scheme 1a).[15] The
potential of IAPs as strongly donating ligands in catalysis has
been demonstrated in Au-catalyzed hydroamination reactions
and Pd-catalyzed cross-coupling reactions.[11,16] Moreover,
owing to their highly basic character, IAPs became valuable
tools in stoichiometric and catalytic phosphine-mediated trans-
formations.[17,18] As a natural continuation of these studies,
we became interested to explore the effect of other π-donor
substituents such as phosphoniumylidyl and phosphazenyl
groups on the electronic properties of phosphines (Scheme 1a).
Phosphines with phosphoniumylidyl groups (YPhos) were first
prepared in 1966 by Issleib and Lindner (Scheme 1b).[19] Fur-
ther contributions to the chemistry of YPhos can be traced
back to the groups of Appel and Schmidbaur.[20] Recently,
Gessner and co-workers explored the ligand properties of
phosphoniumylidyl phosphines and used them in Au-catalyzed
hydroamination and Pd-catalyzed cross-coupling reac-
tions.[21,22] However, the donor properties of the first reported
YPhos P(CHPPh3)Ph2 and the effect of protonation at the yl-
idic carbon atom on the electronic properties of the phosphine
P atom remained unexplored.
First reports by Schmidbaur and Jonas on the synthesis of
phosphines with phosphazenyl groups (PAP) date back to 1968
(Scheme 1b).[23] The synthesis and reactivity of PAPs was
studied by different groups in the following years.[24] How-
ever, the electronic properties of PAPs as a ligand remained
unexplored until Sundermeyer recently showed that phos-
phines carrying three tris(dialkylamino)phosphazenyl groups
P(NP{NR2}3)3 are among the strongest neutral superbases and
display the lowest TEP values of all phosphine ligands.[25]
Herein we study the influence of structural variations among
phosphoniumylidyl and phosphazenyl groups on the electronic
properties of the resulting phosphines and compare their sub-
stituent effects to those of N-heterocyclic imine substituents.
Scheme 2. Synthesis of phosphanzenyl phosphines 2 and 3. (tmg =
N,N,NЈ,NЈ-tetramethylguanidino).
Single-crystal X-ray diffraction (XRD) studies of 1a·HCl
and 1b·HCl (Figure 1) confirm the proposed structure by
Issleib and Lindner[19] with the additional proton attached to
the ylidic carbon atom. For both compounds hydrogen bonding
interactions are observed between one of the acidic methylene
protons and the chloride counteranion with H···Cl distances of
2.694 Å (1a·HCl) and 2.746 Å (1b·HCl). The P1–C1–P2
angels of 1a·HCl (111.4°) and 1b·HCl (115.5°) are slightly
larger than expected for an ideal tetrahedral arrangement of
109.5°. The P2–C1 bonds (1a·HCl: 1.798 Å, 1b·HCl: 1.791 Å)
are in the typical range of phosphonium P–C bonds
([Ph3PCH3]+: 1.783 Å),[27] and the P1–C1 bond lengths
(1a·HCl: 1.877 Å, 1b·HCl: 1.867 Å) are of similar magnitude
to those in PCy3 (1.866 Å).[28]
Results and Discussion
The phosphoniumylidyl phosphines P(CHPPh3)iPr2 (1a),
P(CHPPh3)Ph2 (1b), and their corresponding protonated phos-
phines 1a·HCl and 1b·HCl were synthesized according to the
reported procedure from Issleib and Lindner.[19] Phosphazenyl
phosphine P(NPiPr3)iPr2 (2) was synthesized following
Schmidbaur’s approach[23] by deprotonation of aminotri-
isopropylphosphonium chloride with n-butyllithium and subse-
quent treatment with chlorodiisopropyl phosphine, which gave
2 as a colorless oil in 66% yield (Scheme 2). To avoid the
formation of coordination compounds with lithium salts,[14]
phosphine 3 was synthesized by reacting two equivalents of
tris(tetramethylguanidino)phosphazene imine[26] with chloro-
diisopropylphosphine (Scheme 2), the second equivalent of
imine being used as a base. After extraction with n-hexane, the
phosphazenyl phosphine 3 was obtained as a white solid in
72% yield. The air and moisture sensitive compounds 2 and 3
both show two characteristic doublets at δ = 68.4 ppm,
Figure 1. Molecular structures of 1a·HCl (left) and 1b·HCl (right).
Only the hydrogen atoms of the PCH2P unit are depicted; thermal
ellipsoids are set at 50% probability. Solvent molecules are not dis-
played. Selected bond lengths /Å and angles /°: 1a·HCl: P1–C1
1.877(2), P2–C1 1.798(2), P1–C1–P2 111.42(12). 1b·HCl: P1–C1
1.867(2), P2–C1 1.791(2), P1–C1–P2 115.52(9).
To analyze the influence of the individual π-donor substitu-
ents on the donor strength of the phosphines, we prepared the
corresponding nickel(0) complexes [Ni(CO)3(L)] (L = phos-
phine ligand) from the reaction of the phosphines with
nickel(0) tetracarbonyl. The frequency of the A1 CO stretching
mode of these complexes, referred to as Tolman electronic pa-
rameter (TEP),[4] is a method to gauge the overall electron-
donating ability of ligands (Table 1). Tolman also defined a
3
single substituent parameter χi [∑χi = TEP – 2056.1 cm–1],[4]
33.0 ppm (2) and δ = 67.9 ppm, –10.7 ppm (3) in the 31P{1H}
i=1
2
NMR spectra with JPP coupling constants of 54 Hz (2) and which reflects the individual contributions of a substituent Ri
83 Hz (3), respectively.
to the overall donor strength of a phosphine PR1R2R3. Since
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these contributions are largely additive, it in turn enables the Table 2. Substituent parameters
χ of phosphoniumylidyl, phos-
phazenyl and selected other substituents for comparison. Values were
prediction of TEP values of unknown phosphines. However,
the substituents parameters can differ significantly depending
calculated from PiPr2R.
on the nature of the remaining substituents.[29] Hence, for a Substituent (R)
χ /cm–1
+
better comparison of the π-donor substituents, we calculated
the χ values using the TEP values of phosphines with two
additional isopropyl groups [χ(iPr) = 1.0] at the phosphorus
atom (Table 2).
CH2PPh3
OMe
Ph
12.6
a)
7.7
4.3
1.5
a)
b)
C(CN)PPh3
iPr
C(SO2Tol)PPh3
a)
–1.0
–1.2
–4.5
–6.2
–6.2
–10.6
b)
Table 1. TEP values of phosphines 1a, 1b, 1a·HCl, 1b·HCl, 2, 3 and
selected phosphines for comparison. Values were obtained in CH2Cl2.
R2
c)
CHPPh3
C(CH3)PPh3
R1
b)
c)
NPiPr3
NP(NMe2)3
NP(tmg)3
–11.0
–11.2
–18.5 (–21.0)
a)
d)
a) Calculated from PR3.[4,25] b) Calculated from PCy2R. The corre-
sponding TEP value was calculated from the relationship between νCO
for [Ni(CO)3(L)] and [Rh(acac)(CO)(L)].[22] c) Calculated from litera-
ture TEP values.[11,18] d) Calculated from the TEP value of the solid
compound.
in the range of the C6F5 group[4] (χ = 11.2 cm–1) but less posi-
tive than Alcarazo’s cationic cyclopropenium substituents (χ =
18.2 cm–1).[31]
Upon protonation, the TEP values of phosphines 1a and 1b
shift by ΔTEP = 16.0 cm–1 and ΔTEP = 18.8 cm–1 to higher
wave numbers, respectively (see the Supporting Information
for the XRD study of [Ni(CO)3(1b·HCl)]). Similar proton re-
sponsive properties have been observed for imidazolin-2-ylide-
namino phosphines, which allow for switching the phosphine’s
Phosphine (L)
TEP /cm–1
a)
P(OMe)3
2079.5
[P(CH2PPh3)Ph2]Cl (1b·HCl)
[P(R1H)iPr2]OTf
[P(CH2PPh3)iPr2]Cl (1a·HCl)
PPh3
2075.0
2070.4
a)
donor strength within
43.4 cm–1).[32]
a larger range (ΔTEP up to
2070.7
2068.9
a)
P(CHPPh3)Ph2 (1b)
2059.0
2059.2
2053.6
Sundermeyer and co-workers recently showed that phos-
phazenyl groups are most effective in increasing the electron-
donating ability and the basicity of phosphines.[25] From the
TEP value of P(NP{NMe2}3)3 (2022.4 cm–1) a substituent pa-
rameter of χ = –11.2 cm–1 can be derived. Surprisingly, the
TEP value of 2 (2047.1 cm–1) suggests a similar substituent
parameter for the NP(iPr)3 group (χ = –11.0 cm–1). This simi-
larity agrees with the similar basicities of proton sponges
equipped with those substituents [with NP(iPr)3: pKα(THF) =
21.9, with NP(NMe2)3: pKα(THF) = 22.6].[33]
a)
PiPr3
P(R2)iPr2
a)
P(CHPPh3)iPr2 (1a)
2051.9
2047.5
P(R1)iPr2
a)
P(NPiPr3)iPr2 (2)
P(R2)3
2047.1
2044.3
a)
b)
P(NP{tmg}3)iPr2 (3)
2039.6 (2037.1)
P(R1)3
2029.7
a)
a) Values taken from Tolman et al.[4] and Dielmann et al.[11,14,18,32]
b) Value obtained using the solid compound.
.
The TEP values of phosphoniumylidyl phosphines 1a
In phosphine 3, strongly π-donating tetramethylguanidino
(2051.9 cm–1) and 1b (2059.0 cm–1) are in the range of alkyl- (tmg) groups are attached to the phosphonium center resulting
phosphines[4] and N-heterocyclic carbenes (NHCs),[30] respec- in a χ value of –18.5 cm–1 for the NP(tmg)3 substituent. This
tively. With an χ of –6.2 cm–1 the contribution of the CHPPh3 homologization concept leads to a further delocalization of the
substituent to the donor strength of the phosphine is in the positive charge into the guanidine groups and has been intro-
range of that of benzimidazonlin-2-ylidenamino groups duced by Schwesinger to increase the basicity of phosphazene
(R2).[14,18] The comparison with phosphoniumylidyl phos- nitrogen superbases.[26,34] Although phosphine 3 carries only
phines developed by Gessner and co-workers reveals similar one π-donor group at the P atom, the TEP value of 3
substituent parameters if the ylidic H atom is replaced by a (2039.5 cm–1) is significantly lower than those of the IAP
methyl group, while the introduction of cyanide or tosyl groups P(R2)3 (see Table 1) and has comparable donor abilities to ab-
at this position results in significantly less negative χ values normal NHCs[35] and cyclic alkyl amino carbenes.[36] Given
(Table 2).[22] The most significant effect on the χ value is ob- the additivity of the substituent effects, TEP values of
served upon protonation of the ylidic carbon atom, which 2020.1 cm–1 and 2000.6 cm–1 can be estimated for the hypo-
transforms the neutral phosphoniumylidyl group into a cationic thetical phosphines P{NP(tmg)3}2iPr and P{NP(tmg)3}3,
substituent comprising a substituent parameter (χ = 12.6 cm–1) respectively. Note that the determination of the donor strength
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of 3 using a solid sample of [Ni(CO)3(3)] gives an even lower parable to PMes3 (45.0%).[39] The investigated phosphazenyl
TEP value of 2037.1 cm–1. It has been observed that the inter- phosphines 2 (37.3%) and 3 (42.9%) show a lower steric de-
action of the basic nitrogen atoms adjacent to the phosphorus mand than the carbon analogues. This presumably derives
atom with acidic CH protons such as those in dichloromethane from the larger P–N–P angles of 2 and 3 in relation to P–C–P
can increase the TEP value.[15,32]
angles of 1a and 1b. The obtained %Vbur of 2 and 3 are similar
In order to compare the stability of the phosphines towards to values of alkylphosphines as PtBu3 or P(o-tol)3 (Table 4).[39]
oxidation with molecular oxygen, phosphines 1a and 3 were
exposed to an oxygen atmosphere at room temperature. 31P
NMR analysis of the reaction mixture showed partial decom-
position (30%) of 1a and complete decomposition of 3 after
nine hours (see the Supporting Information). These prelimi-
nary results indicate a higher stability of the YPhos 1a towards
oxygen compared to PAP 3, which agrees with the higher ba-
sicity of the latter.
To explore the coordination behavior of the electron-rich
phosphines 1a, 1b, 2 and 3, we prepared the corresponding
Aul complexes [AuCl(L)] (4a, 4b, 5, 6) from the reaction of
[AuCl(tht)] with the respective phosphines. After removing the
volatiles under reduced pressure the complexes were obtained
as colorless solids in quantitative yields.
The 31P NMR signals of phosphines 1–3 and their corre-
sponding complexes 4–6 are listed in Table 3. Regarding the
YPhos compounds, the PIII signals are significantly shifted to
higher frequencies upon coordination, while the chemical shift
of the PV are largely unaffected. For the PAPs, only minor
changes were observed among the 31P NMR chemical shifts
upon coordination. However, the 2JPP coupling constants of all
investigated phosphines decrease significantly upon coordina-
tion to the gold(I) chloride fragment. These results are consis-
tent with previous observations.[20,21,37,38]
Figure 2. Molecular structures of 4a (top, left), 4b (top, right), 5 (bot-
tom, left) and 6 (bottom, right). Only the hydrogen atoms of the PCHP
unit are depicted; thermal ellipsoids are set at 50% probability. Disor-
ders and solvent molecules are not displayed. Selected bond lengths
/Å and angles/°: 4a: Au–Cl 2.2939(6), Au–P1 2.2407(6), P1–C1
1.737(2), P2–C1 1.696(2), P1–Au–Cl 178.01 (2), P2–C1–P1
126.43(14). 4b: Au–Cl 2.3067(8), Au–P1 2.2438(8), P1–C1 1.719(3),
P2–C1 1.700(3), P1–Au–Cl 179.25(3), P2–C14–P1 124.3(2). 5: Au–
Cl 2.3112(4), Au–P1 2.2446(4), P1–N 1.6089(14), P2–N 1.5682(14),
P1–Au–Cl 176.64(2), P2–N–P1 144.97(10). 6: Au–Cl 2.3302(6), Au–
P1 2.2489(6), P1–N1 1.609(2), P2–N1 1.585(2), P1–Au–Cl 178.00(2),
P2–N1–P1 131.33(13).
2
Table 3. 31P NMR shifts and JPP coupling constants of phosphines
1a, 1b, 2 and 3, and the corresponding gold complexes 4a, 4b, 5 and
6.
Compound
δ(PIII) /ppm
δ(PV) /ppm
2JPP /Hz
1a
1b
4a
4b
2
3
5
–2.7
–18.4
37.6
15.2
68.4
67.9
71.3
65.4
22.4
23.5
21.8
23.7
33.0
–10.7
38.4
–14.1
132
149
45
64
54
83
5
Table 4. Percent buried volume (%Vbur) for P–M length at 2.28 Å of
1a, 1b, 2 and 3 and selected phosphines for comparison. The values
were calculated from the complexes 4a, 4b, 5, 6 using the SambVca
[39]
2.1 web application
(r = 3.5 Å, bond radii are scaled to 1.17 Å).
6
5
Phosphine (L)
%Vbur
The solid-state structures of 4a, 4b, 5 and 6 were established
using XRD studies (Figure 2). The Au–Cl bonds in trans posi-
tion to the phosphines (4a: Au–Cl 2.2939 Å, 4b: Au–Cl
2.3067 Å, 5: Au–Cl 2.3112 Å, 6: Au–Cl 2.3302 Å) are signifi-
cantly elongated with increasing donor character of the phos-
phines. The P–C–P angles of the phosphines in 4a (126.4°)
a)
PCy3
P(NPiPr3)iPr2 (2)
PtBu3
P(o-tol)3
P(NP(tmg)3)iPr2 (3)
P(CHPPh3)Ph2 (1b)
PMes3
33.4
37.3
38.1
41.4
42.9
44.1
45.0
a)
a)
a)
and 4b (124.3°) are larger than those of the free protonated P(CHPPh3)iPr2 (1a)
45.1
a) Values taken from Nolan et al.[40]
phosphines 1a·HCl (111.4°) and 1b·HCl (115.5°). The proton-
ation of the ylidic carbon in 1a,b also effects the P–C1 bond
lengths. For example, the P1–C1 bond (1.877 Å) and P2–C1
bond (1.798 Å) in 1a·HCl are elongated compared to those in
4a (P1–C1: 1.737 Å, P2–C1: 1.696 Å). From the solid-state
structures of complexes 4a, 4b, 5 and 6 the percent buried
Conclusions
In summary, the influence of structural variations among
volume (%Vbur) of the phosphines was calculated (Table 4). phosphoniumylidyl and phosphazenyl groups on the stereo-
The values calculated for 1a (45.1%) and 1b (44.1%) are com- electronic properties of the resulting phosphines was studied
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2
3JHH = 6.9, JPH = 1.6 Hz, 2 H, CH(CH3)2], 1.49 [dd, 3JPH = 9.3, 3JHH
upon synthesis and characterization of two phosphoniumylidyl
3
3
= 6.9 Hz, 6 H, CH(CH3)2], 1.44 [dd, JPH = 13.9, JHH = 6.9 Hz, 6 H,
phosphines (1a, 1b), two phosphazenyl phosphines (2, 3) and
their corresponding gold(I) complexes. Structural analyses of
the new phosphines indicate that the phosphoniumylidyl
groups generate more bulky phosphines than the phosphazenyl
groups due to the larger P–N–P angle of the latter. The deter-
mination of the TEP values reveals that the electron-donating
ability of phosphines is generally increased more efficiently by
phosphazenyl than by phosphoniumylidyl substituents
1
CH(CH3)2]. H{31P} NMR (400 MHz, C6D6): δ (ppm) = 2.76 [s, 36
H, N(CH3)2], 1.84 [hept, 3JHH = 6.9 Hz, 2 H, CH(CH3)2], 1.49 [d, 3JHH
3
= 6.9 Hz, 6 H, CH(CH3)2], 1.44 [d, JHH = 6.9 Hz, 6 H, CH(CH3)2].
13C{1H} NMR (101 MHz, C6D6): δ (ppm) = 157.2 [s, NC(N(CH3)2)2],
40.3 [d, JCP = 2 Hz, NC(N(CH3)2)2], 29.7 [dd, JCP = 18, JCP
12 Hz, CH(CH3)2], 20.3 [d, JCP = 22 Hz, CH(CH3)2], 18.9 [d, JCP
10 Hz, CH(CH3)2]. 31P{1H} NMR (162 MHz, C6D6): δ (ppm) = 67.9
4
1
3
=
=
2
2
2
2
[d, JPP
= 83 Hz, iPr2PNP(tmg)3], –10.7 [d, JPP = 83 Hz,
[χ(NPiPr3) = –11.0 cm–1, χ(CHPPh3) = –6.2 cm–1]. This con- iPr2PNP(tmg)3]. 31P NMR (162 MHz, C6D6): δ (ppm) = 67.9 [m,
2
iPr2PNP(tmg)3], –10.7 [d, JPP = 83 Hz, iPr2PNP(tmg)3]. HR-MS
(ESI): m/z calculated for [C21H51N10P2]+ [M + H]+: 505.37383, found:
505.36992. The matching isotope pattern was found.
tribution can be significantly amplified by attaching π-donat-
ing tetramethylguanidino substituents at the phosphonium cen-
ter [χ(NP(tmg)3) = –18.5 cm–1], as demonstrated by the re-
markably low TEP value of 3 (2039.5 cm–1) with only one
phosphazenyl substituent. Additionally, we have shown that
protonation of the ylidic carbon atom of phosphoniumylidyl
phosphines increases their TEP values by ΔTEP = 18.8 cm–1
(1a) and ΔTEP = 16.0 cm–1 (1b). Given this considerable in-
fluence on the phosphine’s donor properties, this finding may
inspire the design of the next generation proton-switchable cat-
alysts.
Supporting Information (see footnote on the first page of this article):
The supporting information contains the experimental procedures and
the characterization data of all new compounds, including their NMR
spectra and crystallographic data.
Acknowledgements
Financial support was generously provided by the DFG (Emmy
Noether program) (DI 2054/1–1, IRTG 2027, SFB 858). We thank
Prof. F. E. Hahn for his generous support.
Experimental Section
The synthesis of the phosphazenyl phosphines is described below. For
further information on the synthesis of the phosphoniumylidyl phos-
phines, nickel(0) and gold(l) complexes please see the Supporting In-
formation.
Keywords: Ligand design; Phosphines; Gold; Single substitu-
ent parameter; Phosphazenyl; Phosphoniumylidyl
Phosphine 2: At –78 °C a solution of n-butyllithium in n-hexane
(4.50 mmol, 2.8 mL, 1.6 m) was added dropwise to a suspension of
triisopropylphosphoniumamine chloride (2.25 mmol, 476 mg) in THF.
After allowing the reaction mixture to warm up to room temperature
and stirring for 3 h it was cooled to –78 °C again. A chlorodiisopropyl-
phosphine solution (2.25 mmol, 9.0 mL, 0.25 m) in toluene was added
dropwise and the mixture was allowed to warm up to room temperature
slowly overnight. All volatiles were removed in vacuo and the residue
was extracted with n-hexane (2ϫ40 mL). The solvent was removed
in vacuo to give the product as a colorless oil (66% yield, 1.51 mmol,
439 mg). 1H NMR (400 MHz, C6D6): δ (ppm) = 1.85 [m, 3 H,
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P(CH(CH3)2)3], 1.66 [sept, JHH = 7.1 Hz, 2 H, P(CH(CH3)2)2],
3
3
1.24 [dd, JPH = 10.0, JHH = 7.1 Hz, 6 H, P(CH(CH3)2)2],1.18 [dd,
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0.68 m) in toluene was added dropwise to a solution of (tmg)3PNH
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removed in vacuo. After extraction with n-hexane (2ϫ10 mL) the sol-
vent was removed under reduced pressure and the product was ob-
tained as a colorless solid (72% yield, 0.49 mmol, 247 mg). 1H NMR
(500 MHz, C6D6): δ (ppm) = 2.76 [s, 36 H, N(CH3)2], 1.84 [heptd,
Z. Anorg. Allg. Chem. 2020, 1–7
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Received: January 24, 2020
Published Online: ᭿
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
J. A. Werra, M. A. Wünsche, P. Rathmann, P. Mehlmann,
P. Löwe, F. Dielmann* ...................................................... 1–7
Effective Control of the Electron-donating Ability of Phos-
phines by using Phosphazenyl and Phosphoniumylidyl Substit-
uents
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