Synthesis, Structure, and Stability of Lithium Arylphosphanidyl-diarylphosphane Oxide

Article abstract of DOI:10.1002/zaac.201900327

The reaction of LiP(H)Tipp (2a) and KP(H)Tipp (2b, Tipp = C₆H₂-2,4,6-iPr₃), which are accessible via metalation of Tipp-PH₂ (1), with bis(4-tert-butylphenyl)phosphinic chloride yields Tipp-P=P(OM)Ar₂ [M = Li (3a) and K (3b)]. These complexes show characteristic chemical ³¹P shifts and large ¹J_PP coupling constants. These compounds degrade with elimination of the phosphinidene Tipp-P: and the alkali metal diarylphosphinites M–O–PAr₂ [M = Li (4a) and K (4b)]. The phosphinidene forms secondary degradation products (like the meso and R,R/S,S-isomers of diphosphane Tipp-P(H)–P(H)Tipp (5) via insertion into a P–H bond of newly formed Tipp-PH₂), whereas the crystallization of [Tipp-P=P(OLi)Ar₂·LiOPAr₂·LiCl·2Et₂O]₂ (i.e. [3a·4a·LiCl·2Et₂O]₂) succeeds from diethyl ether. The metathesis reactions of LiP(SiiPr₃)Tipp and LiP(SiiPr₃)Mes (Mes = C₆H₂-2,4,6-Me₃) with Ar₂P(O)Cl yield Ar*-P=P(OSiiPr₃)Ar₂ (Ar* = Mes, Tipp) which degrade to Ar₂POSiiPr₃ and other secondary products.

Full text of DOI:10.1002/zaac.201900327

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201900327
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Synthesis, Structure, and Stability of Lithium Arylphosphanidyl-
diarylphosphane Oxide
Damian Bevern,[a] Helmar Görls,[a] Sven Krieck,[a] and Matthias Westerhausen*[a]
Dedicated to Professor Dr. Manfred Scheer on the Occasion of his 65th Birthday
Abstract. The reaction of LiP(H)Tipp (2a) and KP(H)Tipp (2b, Tipp the meso and R,R/S,S-isomers of diphosphane Tipp-P(H)–P(H)Tipp (5)
=
C
6
H
2
-2,4,6-iPr
3
), which are accessible via metalation of Tipp-PH
2
via insertion into a P–H bond of newly formed Tipp-PH
the crystallization of [Tipp-P=P(OLi)Ar ·LiOPAr ·LiCl·2Et
[3a·4a·LiCl·2Et O] ) succeeds from diethyl ether. The metathesis reac-
tions of LiP(SiiPr )Tipp and LiP(SiiPr )Mes (Mes = C -2,4,6-Me
with Ar P(O)Cl yield Ar*-P=P(OSiiPr )Ar (Ar* = Mes, Tipp) which
POSiiPr and other secondary products.
2
), whereas
(1), with bis(4-tert-butylphenyl)phosphinic chloride yields Tipp-
2
2
2
2
O] (i.e.
P=P(OM)Ar
2
[M = Li (3a) and K (3b)]. These complexes show char-
2
2
acteristic chemical 31P shifts and large JPP coupling constants. These
1
H
2
3
3
6
3
)
compounds degrade with elimination of the phosphinidene Tipp-P: and
the alkali metal diarylphosphinites M–O–PAr
2
3
2
2
[M = Li (4a) and K degrade to Ar
2
3
(4b)]. The phosphinidene forms secondary degradation products (like
Introduction
oxygen have not been observed in ArP(H)–P(O)(H)Ar with
bulky aryl groups (Ar = C H -2,6-Mes ) and the crystal struc-
6
3
2
Phosphorus and carbon are often considered being copies of
each other, based on very similar reactivity due to the diagonal
relationship in the periodic Table and based on comparable
electronegativity values [Allred-Rochow electronegativity:
EN(C) = 2.50, EN(P) = 2.06] leading to similar bond po-
larity.[ This analogy is significantly more expressed than the
similitudes within the homologous N/P pair due to a larger
electronegativity difference [EN(N) = 3.07]. In Scheme 1, the
ture determination gave a P–P single bond length of 219.46(8)
[7]
pm for this diphosphane monoxide. Organyl diarylphosphi-
nates C and S-organyl diphenylphosphinothioates CЈ are com-
mon compounds in organophosphorus chemistry and therefore
[8]
often commercially available.
1]
isoelectronic compounds of the type Ar P(O)–ER [E = CH2
2
(A), NH (B), O (C)] are depicted; homologous congeners are
marked with an apostrophe. Phosphane oxides A are stable
compounds, whereas it has been known for many years[ that
silyl congeners rearrange yielding siloxy-diarylphosphanes AЈ,
which often are now commercially available. The amino-di-
arylphosphane oxides B represent a widely used substance
class.[ Substituted diphosphane monoxides B’ are also easily
2]
3]
[4]
prepared and gained academic interest due to unexpected re-
activity.[ The equilibrium between diphosphane monoxides
R P–P(O)R and anhydrides of phosphorus acids R P–O–PR
5]
2
2
2
2
has already been studied in dependency of the substituents at
phosphorus.[ Tautomeric proton shifts from phosphorus to
6]
2
Scheme 1. Isoelectronic compounds of the type Ar P(O)-ER with E =
CH (A), NH (B), O (C) (left column). The homologous derivatives
2
*
Prof. Dr. M. Westerhausen
E-Mail: m.we@uni-jena.de
are marked with an apostrophe (right column). Note that Ar P(O)H
2
has a P–H bond, whereas the silyl-substituted congener immediately
rearranges to a siloxy phosphane.
[
a] Friedrich Schiller University Jena
Chair for Inorganic Chemistry 1
Humboldtstraße 8
0
7743 Jena, Germany
Lithiation (deprotonation) of benzyl-diarylphosphane oxides
under http://dx.doi.org/10.1002/zaac.201900327 or from the au- A, amino-diarylphosphane oxides B and phosphanyl-diaryl-
phosphane oxides BЈ yields compounds with two tautomeric
Co. KGaA. · This is an open access article under the terms of the forms as depicted in Scheme 2. More than 40 years ago, lithi-
Supporting information for this article is available on the WWW
thor.
©
2020 The Authors. Published by Wiley-VCH Verlag GmbH &
Creative Commons Attribution-NonCommercial License, which
ated benzyl-diarylphosphane oxides have been prepared and
permits use, distribution and reproduction in any medium, provided
[9]
isolated as yellow substances, but in other cases these com-
pounds have been proposed as intermediates.[
the original work is properly cited and is not used for commercial
purposes.
10]
Z. Anorg. Allg. Chem. 2020, 646, 1–12
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Journal of Inorganic and General Chemistry
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Therefore, we have chosen the 2,4,6-triisopropylphenyl (Tipp)
substituent for our investigations to decelerate degradation re-
actions.
Results and Discussion
Syntheses and Reactivity Studies
Metalation of 2,4,6-triisopropylphenylphosphane (Tipp-PH2,
1
) with n-butyllithium and subsequent recrystallization from a
solvent mixture of THF, n-hexane and TMEDA yielded quanti-
tatively mononuclear [(thf)(tmeda)Li-P(H)-Tipp] (2a,
2 2
P(O)-ER with E = CH
(A), NH (B), P Scheme 3) with a characteristic P–H stretching vibration at
Scheme 2. Lithiation of Ar
BЈ) and depiction of the tautomeric forms with O-Li or E–Li bonds.
–1
(
2297 cm . Deprotonation of 1 with KH in diethyl ether/THF
at 0 °C gave amorphous [(thf) K-P(H)-Tipp] recrystallization
;
from a mixture of diethyl ether and TMEDA led to substitution
Lithiation of B with n-butyllithium yields lithium amido- of the ligated Lewis base and to crystallization of
diarylphosphane oxides which crystallize from tetrahydrofuran [(tmeda)0.5K-P(H)-Tipp] (2b) with a P–H stretching mode at
ϱ
–1
as a dimeric thf adduct with a central eight-membered (Li–N– 2259 cm .
[11]
P–O) ring.
Homologous derivatives of sodium and potas-
2
sium have also been prepared using the metals or their amides,
[12]
alkoxides, and bis(trimethylsilyl)amides.
Lithiated diphosphane monoxides are unknown as of yet.
However, early investigations on comparable derivatives show
fast degradation. Thus the sodium salt Ph P(O)–P(Na)–CN has
2
been prepared via the reaction of sodium diphenylphosphinite
with [(18-C-6)KP(CN) ] with elimination of a cyanide. The
2
2
Scheme 3. Metalation of Tipp-PH (1) and synthesis of lithium (2a)
formation of Ph P(O)–P(Na)-CN [or Ph P(ONa)=P–CN after and potassium 2,4,6-triisopropylphenylphosphanide (2b).
2
2
migration of the sodium atom] has been verified immediately
3
1
1
The lithium derivative 2a, dissolved in diethyl ether, was
quickly added to a precooled solution (–50 °C) of bis(4-tert-
butylphenyl)phosphinic chloride in diethyl ether (Scheme 4).
After stirring for one hour at –40 °C the yellow solution was
filtered through a frit that was covered with diatomaceous
earth. From an aliquot of the filtrate all volatiles were removed
under reduced pressure and the residue dried in vacuo. There-
after the reaction by the characteristic P{ H} NMR spectrum
1
with two doublets at δ = +55.7 and –161.4 ppm and a J
PP
coupling constant of 362.5 Hz.[
13]
However, this compound
degrades very fast and shortly after the initial spectrum only
NaO–PPh =P–PPh =O has been detected. This complex has
2
2
also been prepared via the reaction of lithium or sodium di-
phenylphosphinite with white phosphorus. The structure of the
acetonitrile adduct of the lithium derivative with a chelating
O–PPh =P–PPh =O ligand shows two quite equal P–P bond
after this material was redissolved in [D ]THF and investigated
8
31
by P NMR spectroscopy.
2
2
lengths of 212.3(5) and 215.9(5) pm.[
14]
The compounds of the types RЈ P=ER and Ar P(OM)=ER
3
2
can be looked at as phosphane- or phosphinite-stabilized phos-
phinidenes (E = P), respectively.[
15]
Phosphinidenes RP:
generated in the presence of trialkylphosphane PR’ can easily
3
be
trapped
yielding
phosphanylidenephosphoranes,
Scheme 4. Metathetical reaction of LiP(H)-C
bis(4-tert-butylphenyl)phosphinic chloride.
6 2 3
H –2,4,6-iPr with
[
16,17]
RЈ P=P–R.
Furthermore, phosphaalkenes can also act as
3
[18]
phosphinidene sources under certain reaction conditions.
Another large compound class containing singlet phosphinid-
This solution showed several phosphorus-containing com-
ene ligands are metal complexes of the type [L M=PR], which pounds that could be identified unambiguously. The metathesis
n
have been studied extensively; often these complexes are suit- product 3a with a P–P bond could be recognized by the large
1
able synthons to investigate the chemistry and reactivity of
JPP coupling constant of approx. 511 Hz and two resonances
ligated singlet phosphinidenes.[ In all these compounds sing- at δ = +55.1 and –126.2 ppm. However, other compounds also
19]
let phosphinidene moieties have been observed. formed during this reaction. Lithium diarylphosphinite (4a, δ
The objective of this study was the unequivocal characteri- = +88.1 ppm), excess LiP(H)-Tipp (δ = –161.6 ppm) and Tipp-
zation of compounds of the type Ar P(O)–P(M)–ArЈ to eluci- PH as well as the meso and R,R/S,S isomers of the diphos-
2
2
date the nature of the P–P bonding situation. Preliminary ex- phane Tipp-P(H)-P(H)-Tipp (5, δ = –113.5 and –118.0 ppm)
periments showed that the mesityl (Mes = 2,4,6-trimeth- could be assigned without any doubt. In the proton-coupled
31
ylphenyl) was not bulky enough to stabilize such complexes.
P NMR spectrum, the characteristic XX’ part of an AAЈXXЈ
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spectrum could be assigned (see Supporting Information). In is a typical single bond value without interaction of the aryl π-
addition, a resonance at δ = +25.7 ppm with rather low inten- system and the P-centered electron pair. The pyramidal envi-
sity was observed which could hint toward the formation of ronment of the phosphorus atom [P1-bound H1P1 atom was
Ar P(O)–O–P(O)Ar . This compound could arise from a well- found and isotropically refined, angle sum of P1: 297(2)°] is
2
2
known disproportionation of the lithium phosphinite Li–O– in agreement with this interpretation. Intramolecular steric re-
PAr2 into the lithium phosphanide LiPAr2 and the lithium pulsion leads to significantly different P1–C1–C2/6 bond
[20]
phosphinate LiO–P(O)Ar as described earlier,
followed by angles.
2
the reaction of the latter phosphinate complex with still present
phosphinic chloride.
We also reacted KP(H)-Tipp with a stoichiometric amount
of bis(4-tert-butylphenyl)phosphinic chloride and monitored
3
1
the reaction again by P NMR spectroscopy. As before we
observed the targeted potassium complex Ar P(O)-P(K)Tipp
2
(
3b) that could be unambiguously assigned by characteristic
1
chemical shifts (δ = +53.4 and –126.4 ppm) and the large J
PP
coupling constant of 481 Hz. However, this complex degraded
fast to the potassium diarylphosphinite 4b and to the meso and
R,R/S,S isomers of the diphosphane Tipp-P(H)-P(H)-Tipp (5)
as observed for the lithium derivative, too.
Based on these observations, we propose a mechanism for
the degradation of Ar P(O)-P(M)-Tipp [M = Li (3a), K (3b)] Figure 1. Molecular structure and atom labeling scheme of
2
[
(thf)(tmeda)Li-P(H)-Tipp] (2a). The ellipsoids represent a probability
that is depicted in Scheme 5. The P–P bond breaks rather eas-
ily, producing well-known metal diarylphosphinites M–O–
of 30%. C-bound hydrogen atoms are omitted for clarity reasons. Se-
lected bond lengths /pm: Li1–O1 195.5(9), Li1–N1 215.2(9), Li1–N2
211.8(10), Li1–P1 264.4(9), P1–H1P1 132(4), P1–C1 184.1(4); angles /
PAr and 2,4,6-triisopropylphenylphosphinidene. Due to the
2
fact that phosphinidenes have an electron sextet they are ex- °: Li1–P1–C1 95.4(2), Li1–P1–H1P1 101(2), C1–P1–H1P1 100.7(19),
tremely reactive. Thus these short-lived species attack Tipp- P1–C1–C2 125.6(4), P1–C1–C6 118.2(4), C2–C1–C6 116.2(4).
PH and insert immediately into a P–H bond yielding 1,2-
bis(2,4,6-triisopropylphenyl)diphosphane (5).
2
The molecular structure and atom labeling scheme of
[
(tmeda)0.5K-P(H)-Tipp] (2b) is shown in Figure 2. The po-
ϱ
Scheme 5. Proposed mechanism for the degradation of 3a and 3b via
cleavage of the P–P bond, formation of the intermediate phosphinidene
which inserts into a P–H bond of Tipp-PH .
2
Molecular Structures
Lithium phosphanides represent
substance class with many representatives.
structure and atom labeling scheme of mononuclear
(thf)(tmeda)Li-P(H)-Tipp] (2a) are depicted in Figure 1. The
a
well-recognized
The molecular
[21]
[
Figure 2. Molecular structure and atom numbering scheme of
lithium atom has a distorted tetrahedral coordination sphere [(tmeda)0.5K-P(H)-Tipp]ϱ (2b, top). The ellipsoids represent a prob-
with a Li–P bond length of 264.4(9) pm. The structure ability of 30%, C-bound hydrogen atoms are neglected for the sake of
clarity. Selected bond lengths /pm: K1–N1 297.3(2), K1–P1 377.13(9),
K1–P1A 330.49(9), K1–P1B 330.82(8), K1–C1 300.9(2), K1–C2
is comparable to those of other lithiated primary phosphanes
[22]
such
as,
for
example,
[(thf) Li-P(H)-Mes],
3
3
22.3(2), K1–C3 347.4(2), K1–C5 340.6(2), P1–C1 182.7(2); angles /
°: P1–C1–C2 125.95(19), P1–C1–C6 117.43(18), C2–C1–C6 116.6(2).
The P–C bond length of 184.1(4) pm At the bottom, a cut-out of the strand structure is depicted.
[23]
[24]
[
[
(thf)(tmeda)Li-P(H)-Mes],
[(py) Li-P(H)-Mes*],
and
3
[25]
(thf) Li-P(H)-Mes*].
3
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tassium atom K1 is side-on bound to one arylphosphanide li- in Figure 4. The central four-membered (LiCl) ring contains
2
gand [K1–P1 377.13(9) pm] and two shorter contacts to neigh- a crystallographic center of symmetry and Li-Cl distances of
boring phosphanides are observed [K1–P1A 330.49(9) and 241.2(5) and 245.2(5) pm. Such dimeric [(L)
K1–P1B 330.82(8) pm]. This coordination behavior leads to have been observed earlier in e.g. [(thf)
LiCl]
structures
with
2
2
Li(μ-Cl)]
2
2
[
32]
formation of an undulated strand structure of alternating potas- slightly shorter Li–Cl bonds of 230.8(3) and 234.2(3) pm.
33]
sium and phosphorus atoms. The potassium atoms of every Lithium[ and potassium diarylphosphinites form tetranuclear
34]
heterocubane cores.[ In these
second four-membered K P ring are bridged by a tmeda li- complexes with inner M O
2
2
4 4
gand with K1–N1 bond lengths of 297.3(2) pm. The P1–C1 cage compounds the phosphinite oxygen atoms bridge three
alkali metal atoms. In [3a·4a·LiCl·2Et O] the diarylphosphin-
bond length of 182.7(2) pm is slightly shorter than observed
for the lithium congener 2a supporting a weak interaction be-
tween the lone pair at P and the π-system of the aryl group.
The thf adduct [(thf) K-P(H)-Tipp] forms a strand structure
2
2
ite substructures show comparable binding properties and O5
is positioned above the plane of Li1, Li2 and Li3 with Li-O5
bond lengths of 196.7(5), 200.6(5) and 189.7(5) pm, respec-
2
ϱ
in the crystalline state, too, but here two one-dimensional K-
P(H)-Tipp chains are interconnected by bridging thf bases.[
26]
However, the rubidium congener [(thf)Rb-P(H)-Tipp] shows
ϱ
a comparable wavy ladder structure.[ In contrast to this ag-
gregation behavior, the smaller mesityl substituents lead to a
three-dimensional polymeric structure[ whereas three-den-
tate pmdeta bases are able to stabilize dinuclear structures of
26]
27]
[
28]
the type [(pmdeta]K-P(H)-Mes]2.
Larger terphenyl groups
lead to lower aggregation degrees[ and the crown ether is
even able to form mononuclear [(18-C-6) K-P(H)-Mes*].[
The molecular structure and atom labeling scheme of 1,2-
bis(2,4,6-triisopropylphenyl)diphosphane (5) is depicted in
Figure 3. The P-bound hydrogen atoms are disordered due to
co-crystallization of meso and R,R/S,S-isomeric molecules.
The P1–P1A [221.8(1) pm] and P1–C1 bond lengths [184.6(2)
pm] lie in the expected ranges as also observed for 1,2–dimesi-
tyldiphosphane (P–P 222.84[11], P–C 183.7(2) pm) and 1,2-
29]
30]
bis(2,6-diisopropylphenyl)diphosphane [P–P 220.60(8), P–C
84.14(13) pm].[
31]
1
Figure 4. Molecular structure and atom labeling Scheme of
Figure 3. Molecular structure and atom labeling scheme of 1,2-
bis(2,4,6-triisopropylphenyl)diphosphane (5). The ellipsoids represent
a probability of 30%, C-bound hydrogen atoms are omitted for the
sake of clarity. Selected bond lengths /pm: P1–P1A 221.80(10), P1–
C1 184.62(18); angles /°: P1–C1–C2 119.44(14), P1–C1–C6
[
3a·4a·LiCl·2Et
2 2
O] (top) The ellipsoids represent a probability of
30%, hydrogen atoms are omitted for clarity reasons. Selected bond
lengths /pm: P1–P2 210.50(10), P1–C1 181.6(3), P1–C11 182.4(3),
P1–O4 153.69(19), P2–C21 186.4(3), P2–Li3A 256.4(5), Li1–Cl1
246.6(5), Li1–O4 190.0(5), Li1–O5 196.7(5), Li1–O6 197.1(5), Li2–
121.07(13), C2–C1–C6 119.45(16).
Cl1A 247.9(5), Li2–O4 193.2(5), Li2–O5 200.6(5), Li2–O7 196.3(5),
Li3–Cl1 241.2(5), Li3–Cl1A 245.2(5), Li3–O5 189.7(5); angles /°: P1–
P2–C21 105.51(9), P1–P2–Li3A 102.86(12), C21–P2–Li3A
Due to ongoing degradation processes during crystallization 144.58(14), P2–P1–O4 106.17(8), P2–P1–C1 114.80(9), P2–P1–C11
1
15.57(9), O4–P1–C1 108.63(12), O4–P1–C11 106.32(11), C1–P1–
efforts, an isolation of analytically pure Ar P(O)-P(Li)Tipp
2
C11 104.93(12), P2–C21–C22 118.3(2), P2–C21–C26 123.1(2), C22–
C21–C26 118.4(3). At the bottom, the inner cage is depicted to clarify
the bonding situation. Hydrogen and carbon atoms are omitted with
(3a) failed. Nevertheless, we could crystallize a complex of
the type [3a·4a·LiCl·2Et O] from diethyl ether. The molecular
2
2
structure and atom labeling Scheme of this complex is depicted the exception of the ipso-carbon atoms.
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tively. The P3–O5 bond length of 160.12(19) pm is slightly depend on the coordination number of P with the shortest P–
elongated compared to the distances in tetranuclear lithium di- P bonds of approx. 203–205 pm in diphosphenes (entry 1)
phenylphosphinite [P–O between 158.4(2) and 158.8(2) symptomatic for P=P double bonds. Diphosphanes have a typi-
pm].[ All lithium atoms have distorted tetrahedral coordina- cal single bond of approx. 222 pm (entry 2). Mono-oxidation
tion spheres, Li1 and Li2 complete their coordination number leads to a slight shortening (entries 5 and 6), whereas the dou-
by ligated diethyl ether ligands [Li1–O6 197.1(5), Li2–O7 bly oxidized diphosphane dioxide has a longer P–P bond due
33]
196.3(5) pm]. The Li1–O4 and Li2–O4 bonds are the shortest to electrostatic repulsion between the positively charged P
Li–O distances due to the smaller coordination number of 3 atoms. (entry 7). Charge delocalization shortens the P–P bonds
for O4. In addition, the enhanced electrostatic attraction be-
tween the negatively charged oxygen atom and the lithium cat-
ion also shortens these Li-O4 contacts.
(
entries 8 and 9). Deprotonation of a diphosphane monoxide
leads to rather short P–P bonds with partly double bond char-
acter, supported by electrostatic attraction between a nega-
tively charged phosphanide unit and a phosphoryl moiety with
a positively polarized P atom (entries 14 and 15). The P1–O4
bond length (entry 15) is significantly larger than observed
for phosphane oxides with mainly P–O double bond character
The phosphanidylphosphane oxide Tipp-P–P(O)Ar2 sub-
structure has a P1–P2 bond length of 210.50(10) pm. The O4
atom is bound at P1 [153.69(19) pm] and bridges the lithium
atoms Li1 and Li2. The P2 atom coordinates to Li3A with
a distance of 256.4(5) pm which is smaller than observed in
mononuclear 2a and supports significant electrostatic attrac-
tion between the lithium cation and the P2 atom. The P2–C21
bond length is slightly larger than observed in the alkali metal
phosphanides 2a and 2b. We interpret these findings in the
sense of a phosphanidyl-phosphonium oxide as depicted in
Scheme 6.
(
entries 3–7) but this bond is also elongated compared to the
P–O bond in lithium diarylphosphinate (formal bond order of
.5, entry 12) supporting a dominating single bond character
1
of the P1–O4 bond. The bridging coordination mode of the
P1–O4 unit and accompanying enhancement of the coordina-
tion number of O4 also make a contribution to the elongation
of the P1–O4 bond.
The diverse products of the reaction of Tipp-P(H)Li or Tipp-
P(H)K with bis(4-tert-butylphenyl)phosphinic chloride in di-
ethyl ether at –50 °C can be explained by the following reac-
tion
sequence.
Initially
the
metathesis
product,
Tipp-P(H)-P(O)Ar , is formed which is immediately lithiated
by still present Tipp-P(H)Li yielding observable phosphanidyl-
2
Scheme 6. Schematic representation of the mesomeric forms of the
substructure of the anion of 3a with ionic and covalent P–P bonding
modes (see text, Ar = C H -4-tBu).
6 4
phosphane oxide, Tipp-P(Li)-P(O)Ar [or Tipp-P=P(OLi)Ar2
2
via 1,3-Li shift], besides Tipp-PH2. The product
Tipp-P(Li)-P(O)Ar slowly degrades with formation of lithium
In order to correlate P–P bond order, oxidation state and
coordination number of the phosphorus atoms and P–P bond diarylphosphinite, Li–O–PAr
lengths, diverse P-containing compounds are compared in phosphinidene Tipp-P:. The phosphinidene inserts immediately
Table 1. The P–O bond lengths lie in a very narrow range (en- into a P–H bond of Tipp-PH leading to the formation of the
2
, and liberation of (unobserved)
2
2
tries 3–7 and 12–14) with the exception of the lithium diaryl- observed diphosphane Tipp-P(H)-P(H)-Tipp. Lithium diaryl-
phosphinites (entries 10 and 11) with large values due to the phosphinite slowly dismutates into lithium diarylphosphanide
coordination number of four for the oxygen atoms (μ -coordi- LiPAr and lithium diarylphosphinate LiO PAr . The latter
3
2
2
2
nation mode of the phosphinite ligands). The P–P bond lengths compound can react with still present diarylphosphinic chlor-
Table 1. Comparison of selected P-containing compounds to elucidate the dependency between bond order and bond length for P–P and P–O
bonds (average values are given without estimated standard deviations).
Compound
P–P
P–O
Ref.
1
2
3
4
5
6
7
8
9
1
Ar-P=P-Ar
Tipp-P(H)-P(H)-Tipp (5)
203–205
221.8(1)
–
–
219.46(8)
218.54(7)
227.4(1)
213.3(6)
216.1
–
–
–
–
–
–
[35]
This work
[36]
[37]
[7]
[38]
[39]
[13]
[13]
This work
[33]
[20]
[11]
[7]
Ph
Mes
2
P(O)H
P(O)H
148.81(11)
148.54(13)
147.8(2)
147.16(13)
149.2
2
Ar*P(H)-P(O)(H)Ar*
Mes*P(H)-P(O)(OEt)
Ph(tBu)P(O)-P(O)(tBu)Ph
2
+
–
[Ph
3
P-P-PPh
3
] [AlCl
4
]
–
–
[ArP(Ph)-P[Li(thf)
3
]-P(Ph)Ar]
a)
0
Ar
[Ph
[Mes
[Ph P(O)-N(Mes)Li(thf)
[Ar*P-P(O)(H)Ar*] [Im]
2
POLi (4a)
POLi(thf)]
P(O)-OLi(thf)
160.12(19)
158.6
149.9
149.7
149.2(2)
153.69(19)
1
1
2
4
12
13
14
15
2
2
]
2
2
2
]+ b)
–
210.99(11)
210.50(10)
a)
Tipp-P(Li)-P(O)Ar
2
(3a)
This work
a) Substructures of [3a·4a·LiCl·2Et
2
O]
2
. b) Im = 1,3,4,5-tetramethylimidazolium, bound via a C–H···O hydrogen bridge.
Z. Anorg. Allg. Chem. 2020, 1–12
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
ide, yielding the observed diarylphosphinic anhydride O bonds are quite labile, often enabling the formation of sol-
3
1
[40]
Ar P(O)–O–P(O)Ar [δ( P) = 25.7 ppm].
This proposed vent-separated ion pairs in ethereal solutions. After the 1,3-
2
2
mechanism requires the assumption that the metathetical reac- triisopropylsilyl shift the P=P bond was cleaved yielding the
tion step is significantly slower than the metalation and phos- established trialkylsilylphosphinite (9a), which was identified
31
phinidene insertion steps.
by P NMR spectroscopy (δ = 98.3 ppm), as the major end
P
Zurmühlen and Regitz performed the reaction of product as depicted in Scheme 7. The intermediately formed
LiP(SiMe )Mes with bis(tert-butyl)phosphinic chloride and phosphinidene was very reactive and immediately trapped
3
observed the formation of Mes-P=P(OSiMe )tBu (δ = +96 forming secondary yet unknown degradation products.
3
2
P
1
and –213 ppm, J = 429 Hz) after immediate 1,3-shift of the
PP
trimethylsilyl group from the phosphorus to the oxygen
atom.[ In a preliminary study we tried to stabilize the phos-
phanidylphosphane oxide by a metathesis reaction of bulky
41]
LiP(SiiPr )Mes (6a) with bis(4-tert-butylphenyl)phosphinic
3
chloride in THF. For this experiment we have chosen the triiso-
propylsilyl group to shield the reactive P–P bond and to decel-
3
1
erate degradation. Again the P NMR spectra unambiguously
verified a fast 1,3-silyl shift from P to O and the quantitative
formation of the targeted product Mes-P=P(OSiiPr )Ar (8a)
3
2
1
(
δ = 76.4 and –118.2 ppm, J = 623 Hz). However, within
P PP
very few hours a complete degradation occurred and could
quantitatively be monitored by addition of triphenylphosphane
as an internal standard. The time-dependent first-order decom-
position is depicted in Figure 5.
6 2
Scheme 7. Metathetical reaction of LiP(SiiPr3)-C H -2,4,6-R [R = Me
(
6a), iPr (6b)] with bis(aryl)phosphinic chloride yielding complexes 8a
and 8b, respectively, which degrade to the triisopropylsiloxy-bis(aryl)
phosphanes (9a: Ar = 4-tert-butylphenyl and 9b: Ar = Ph) as the major
secondary degradation product.
Enhancement of steric shielding by substitution of the mes-
ityl group by a Tipp substituent decelerated the degradation,
but again the trialkylsilyl-diarylphosphinite (trialkylsiloxy-di-
arylphosphane) was identified and the enormous reactivity of
the liberated triisopropylphenyl-phosphinidene led to second-
ary products.
NMR Spectroscopy
The phosphanidylphosphane oxides show characteristic 31P
Figure 5. Degradation of Mes-P=P(OSiiPr
THF at room temperature, monitored for the resonances at δ = –118.2
3 6 4 2
)(C H -4-tBu) (8a) in
NMR spectra which are summarized in Table 2. The proton-
31
(
black circles) and 76.4 ppm (black squares) via P NMR spec-
troscopy with the internal PPh standard. The exponentially fitted
curves are drawn with broken lines.
1
ated derivatives have J coupling constants that are indica-
PP
3
tive of a P-P single bond and the hydrogen atom is bound at
the phosphanyl unit giving R-P(H)-P(O)RЈ (entries 1 and 2).
2
To study the influence of the bulkiness of the aryl group we In the imidazolium salt a hydrogen bridge is formed between
prepared Tipp-P=P(OSiiPr )Ph (8b) analogously and moni- the imidazolium cation and the phosphoryl moiety (entry 3).
3
2
3
1
tored its decay by P NMR spectroscopy. The substitution of Furthermore, the alkali metal congeners (entries 9–16) form
1
the Mes group by the bulkier Tipp substituent decelerated the contact ion pairs with rather large J coupling constants.
PP
degradation process significantly by the factor of 3, yielding These values are in the same order of magnitude as observed
Ph P-OSiiPr (9b) as the major degradation end product. Thus, for the silylated congeners (entries 4–8), which contain strong
2
3
after approx. 1.5 hours at room temperature only half of the Si–O bonds, supporting a P–P multiple bond in all these deriv-
1
amount of Tipp-P=P(OSiiPr )Ph (8b) was still present in THF atives. In contrast, the J values of the hydrogen-substituted
3
2
PP
solution.
congeners with P-bound hydrogen atoms (entries 1 and 2) are
Presumably, the degradation proceeded analogously to the roughly only half as large.
above discussed pathway. The half-life time was significantly
A comparison of the Mes and Tipp substituted phosphanid-
larger because the bulky triisopropylsilyl substituent shielded ylphosphane oxides with M = SiiPr (entries 6 and 8), Li (en-
3
the reactive P=P bond much more effectively than the alkali tries 11 and 12), and potassium (entries 15 and 16) shows a
1
metal ions. Generally, Si–O bonds are very strong whereas M– decreasing J coupling constant supporting decreasing P–P
PP
Z. Anorg. Allg. Chem. 2020, 1–12
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Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
2
Table 2. Selected NMR parameters for compounds of the general type RP=P(OM)RЈ regardless of the essentially contributing mesomeric form
(see Scheme 6).
R a)
RЈ a)
M
δ
P
(RP)
δ
P
(PO)
1JPP
Ref.
1
2
3
4
5
6
7
8
9
1
Mes*
Ter
Ter
OEt
H/Ter
H/Ter
tBu
Alkyl
Ph
Ph
Ar
OEt
H
H
Im
SiMe
SiMe
SiiPr
SiMe
SiiPr
Li
Li
Li
Li
Na
Na
K
–88.8
–77.4
–46.8
–213
+35.0
+9.6
+28.5
+96
222
[38]
[7]
[7]
[41]
[41]
[42]
[42]
This work
[38]
[13]
[42]
This work
[13]
[13]
248.7
464.2
429
433
634
628
623
615
347.9
501
b)
Mes
Mes
Tipp
Tipp
Mes
Mes*
CN
Mes
Tipp
CN
3
3
c)
–209
+78
3
–143.2
–132.5
–118.2
+81.2
+77.8
+76.4
3
3
d)
d)
n.a.
n.a.
0
NMe
Ar
2
–205.0
–103.7
–126.2
–161.4
–202.8
–103.9
–126.4
+73.6
+53.2
+55.1
+55.7
+68.5
+53.5
+53.4
1
1
12
13
14
15
16
Ar
Ph
OEt
Ar
Ar
511.5
362.5
392.5
484
CN
Mes
Tipp
[42]
This work
K
481
a) Ar = 4-tert-butylphenyl, Mes = 2,4,6-trimethylphenyl, Mes* = 2,4,6-tri(tert-butyl)phenyl, Ter = 2,6-dimesitylphenyl, Tipp = 2,4,6-triisoprop-
ylphenyl. b) Im = 1,3,4,5-tetramethylimidazolium. c) Alkyl = 2,3,4-trimethylpentane-2,4-diyl. d) n.a. = not assigned.
double bond character caused by an increasing electrostatic
attraction between M and the phosphanidylphosphane oxide
anion (see Scheme 6). This interpretation is in agreement with
the observation that phosphanylphosphane oxides (entries 1
and 2) exhibit the smallest coupling constants between the P
atoms, indicative for a P–P single bond. It is noteworthy that
1
for RP=P(OSiR" )RЈ with RЈ = alkyl (entries 4 and 5) the J
3
2
PP
coupling constants are apparently significantly smaller than for
derivatives with RЈ = aryl (entries 6–8).
Conclusions
The reaction of lithium (2a) and potassium 2,4,6-triisoprop-
ylphenylphosphanide (2b), MP(H)-Tipp, with bis(4-tert-but-
ylphenyl)phosphinic chloride, Ar P(O)Cl, yields the unob-
2
served metathesis product, Tipp-P(H)-P(O)Ar . This interme-
2
diate immediately reacts with another equivalent of MP(H)-
Tipp, leading to the formation of Tipp-P=P(OM)Ar [M = Li
2
(
3a) and K (3b)] and Tipp-PH (1). The phosphanidylphos-
2
phane oxides 3a and 3b slowly degrade under release of the
extremely reactive phosphinidene Tipp-P: with an electron sex-
tet. This unobserved species inserts immediately into a P–H
bond of Tipp-PH yielding the diphosphane Tipp-P(H)-P(H)-
2
Tipp (5). The compounds have unambiguously been identified
3
1
by their characteristic P NMR spectra with typical chemical
shifts and coupling constants. Furthermore, the major products
have been verified by crystal structure determinations of 2a, Scheme 8. Sequence of the reaction of MP(H)-Tipp with diarylphos-
phinic chloride with a 2:1 stoichiometry. Compounds in square brack-
2
b, 5, and the unique co-crystallization product
ets are unobserved whereas all other compounds have been identified
[3a·4a·LiCl·2Et O] . The latter molecular structure allows for
2
2
31
unambiguously by P NMR spectroscopy and/or X-ray structure
the first time to elucidate the P–P bond length in a mixed-
analysis.
valent phosphorus derivative of the type Ar-P=P(OM)Ar . The
2
proposed reaction sequence is depicted in Scheme 8. Unob-
served intermediates are included in square brackets.
In addition to these experiments we tried to stabilize the P–P
multiple bond by trialkylsilyl substituents. Thus the metathesis
Z. Anorg. Allg. Chem. 2020, 1–12
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Journal of Inorganic and General Chemistry
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reaction of LiP(SiR )Ar* (Ar* = Mes, Tipp; R = Me, iPr) with 2,4,6-triisopropylbenzene (17 g, 60 mmol) was added dropwise until
3
the Grignard reaction started. The remaining bromo-2,4,6-triisoprop-
diarylphosphinic chloride, Ar P(O)Cl, yields quantitatively
2
ylbenzene was added slowly to keep the solution under reflux condi-
tions. After complete addition of the bromoarene the mixture was
heated to reflux for additional 1.5 h. After cooling to room tempera-
ture, the Grignard reagent was added dropwise under vigorous stirring
at –78 °C to 15 mL of PCl (171 mmol) in a two neck round-bottomed
3
flask. During addition the solution turned yellow and a white solid
precipitated. The mixture was heated to room temperature and was
Ar*-P=P(OSiR )Ar . This metathesis product releases the un-
3
2
observable phosphinidene Ar*–P:, which immediately forms
secondary degradation products, and the already known trialk-
ylsiloxy-diarylphosphanes (trialkylsilyl-diarylphosphinites) are
formed.
The compounds with the P–P multiple bonds, the alkali
metal phosphanidyl-diarylphosphane oxides 3a and 3b as well stirred for additional 0.5 h. All volatiles were removed under reduced
as the silylated congeners Ar*-P=P(OSiR )Ar 8a and 8b, ex- pressure. The remaining solid was suspended in 100 mL of Et O and
2
3
2
3
1
hibit characteristic chemical δ( P) shifts for the two- and four- filtered. The filtration residue was washed two times with 20 mL of
1
2
Et O. The volume of the combined ethereal filtrates was reduced to
coordinate P atoms and large J coupling constants. These
PP
40 mL. DIBAL-H/n-hexane (150 mL of a 1 m solution, 150 mmol) was
coupling constants increase in the series 3b, 3a and
Ar*-P=P(OSiR )Ar in agreement with the expectation that a
strengthening of the O–M bond from the ionic O–K interaction
to O–Li and finally to very strong O–Si bonds and hence
decreasing ionic character lead to increasing P–P double bond
character and to larger coupling constants. These silyl deriva-
added dropwise at –50 °C. The orange solution was heated to room
temperature and stirred for 1 h. Conversion to the phosphane was mon-
3
2
3
1
itored by P NMR spectroscopy. Excess of DIBAL-H was carefully
quenched with 40 mL of degassed water at 4 °C. After separation of
the organic layer the aqueous phase was extracted twice with 20 mL
of n-pentane. The solvent of the organic extracts was evaporated. Sub-
tives Ar*-P=P(OSiR )Ar also release the phosphinidene sequently, 2,4,6-triisopropylphenylphosphane (1) was isolated as a col-
3
2
–
2
Ar*-P: yielding trialkylsilyl-diarylphosphinites and secondary orless liquid by vacuum distillation (6ϫ10 mbar, 85–95 °C). Yield:
1
by-products. Bulky groups Ar* and SiR decelerate degrada- 9.54 g (40.4 mmol), 68%. H NMR (400.13 MHz, C
6
D
6
, 297 K): δ =
3
4
1
7
.08 (d, JP,H = 2.4 Hz, 2 H, meta-H), 3.84 (d, JP,H = 203.2 Hz, 2 H,
PH ), 3.45 [heptd, JP,H = 3.2, J(H,H) = 6.7 Hz, 2 H, ortho-CH(iPr)],
2
.77 [hept, JH,H = 6.9 Hz, 1 H, para-CH(iPr)], 1.22 [d, JH,H = 7.0 Hz,
(iPr)], 1.21 [d, JH,H = 6.9 Hz, 12 H, ortho-CH
C{ H} NMR (100.62 MHz, C , 297 K): δ = 152.3 (d, J = 9.7 Hz,
ortho-C), 149.2 (s, para-C), 122.9 (d, J = 12.9 Hz, ipso-C), 121.3 (d,
J = 2.8 Hz, meta-C), 34.8 [s, para-CH(iPr)], 33.3 [d, J = 11.6 Hz,
ortho-CH(iPr)], 24.3 [s, para-CH (iPr)], 23.9 [s, ortho-CH (iPr)].
tion processes.
4
3
-
2
6
1
In conclusion, derivatives of the type Ar*-P=P(OM)Ar (M
2
3
3
=
Li, K) and Ar*-P=P(OSiR )Ar (Ar = aryl, Ar* = bulky aryl,
3 2
3
H, para-CH
3
3
(iPr)].
R = alkyl) are intrinsically unstable and release highly reactive
phosphinidene species Ar*-P: (which form secondary degrada-
tion products), leaving the well-known phosphinites of the type
3
1
6 6
D
Ar P–OM and Ar P–O–SiR , respectively.
31
2
2
3
P
3
3
1
NMR (161.98 MHz, C
IR (nujol): ν˜ = 2959 (s), 2924 (s), 2864 (s), 2297 (m), 1600 (w), 1559
w), 1527 (w), 1459 (s), 1417 (s), 1380 (m), 1359 (m), 1313 (m), 1300
(m), 1256 (m), 1237 (w), 1189 (m), 1166 (w), 1127 (m), 1105 (m),
060 (s), 1041 (m), 941 (w), 922 (w), 884 (s), 871 (s), 829 (w), 807
6 6
D , 297 K): δ = –159.0 (tm, JP,H = 203.2 Hz).
(
Experimental Section
1
(
General Remarks: All manipulations were carried out under an inert
nitrogen atmosphere using standard Schlenk techniques. The solvents
were dried with KOH and subsequently distilled over sodium/benzo-
phenone in a nitrogen atmosphere prior to use. Deuterated solvents
were dried with sodium, distilled, degassed, and stored in nitrogen over
–
1
w), 754 (s), 732 (m), 714 (m), 640 (m), 623 (m), 510 (m) cm .
Synthesis of (tmeda)(thf)lithium 2,4,6-Triisopropylphenylphos-
phanide (2a): TippPH (1, 1 g, 4,23 mmol) was dissolved in 20 mL
of n-hexane. Then 2,6 mL of 1.6 m BuLi/n-hexane (4.23 mmol) were
added dropwise at –78 °C. The solution was slowly heated to room
temperature and stirred for 2 h. Evaporation to dryness under reduced
pressure yielded an amorphous yellow powder. Crystallization could
be achieved from a solvent mixture of THF/n-hexane/TMEDA at
20 °C. Yield: 1 g (4.13 mmol), 98%. H NMR (400.13 MHz,
8
[D ]THF, 297 K): δ = 6.60 (s, 2 H, meta-H), 3.74 [s, 2 H, ortho-
CH(iPr)], 2.69 [s, 1 H, para-CH(iPr)], 2.06 (d, JP,H = 164.5 Hz, 2 H,,
2
sodium. 1H, C{ H} and P{ H} NMR spectra were recorded on
13
1
31
1
Bruker Avance III 400. Chemical shifts are reported in parts per mil-
1
13
lion relative to SiMe
4
( H, C) as an external standard referenced to
[
43]
the solvents residual signals.
IR spectra were recorded on a Bruker
Alpha spectrometer. Due to the extreme sensitivity of the phosphanides
of lithium (2a) and potassium (2b) toward air, these compounds were
covered with nujol prior to the IR measurement. All substrates were
purchased from Alfa Aesar, abcr, Sigma Aldrich or TCI and used with-
1
–
1
-
PH
2
), 1.21 [d, J = 6.8 Hz, 12 H, ortho-CH
3
(iPr)], 1.18 [d, J = 6.9 Hz,
[
44]
out further purification. 2,4,6-Triisopropylphenylphosphane (1)
and
1
3
1
6
H, para-CH
3
(iPr)]. C{ H} NMR (100.62 MHz, [D ]THF, 297 K):
8
its lithium[ and potassium salts have been prepared via modified
45]
δ = 152.7 (ipso-C), 146.6 (ortho-C), 137.2 (para-C), 118.8 (meta-C),
5.3 [para-CH(iPr)], 33.3 [d, J = 14.8 Hz, ortho-CH(iPr)], 25.2 [para-
CH (iPr)], 24.2 [ortho-CH (iPr)]. P NMR (161.98 MHz, [D ]THF,
3 3 8
97 K): δ = –166.4 (d, JP,H = 165.4 Hz).
[
26]
procedures described earlier.
The yields given are not optimized.
3
Purity of the compounds was verified by NMR spectroscopy. The ob-
jective of this study was the elucidation of structural parameters for
an alkali metal phosphanidylphosphane oxide and mechanistic studies
of its decay in ethereal solvents, based on NMR experiments.
3
1
1
2
Synthesis of Semi(tmeda)potassium 2,4,6-Triisopropylphenylphos-
phanide (2b): To a suspension of 200 mg of KH (4.99 mmol) in a
mixture of 7 mL of Et O and 2 mL of THF, 876 mg of (2,4,6-triiso-
2
propylphenyl)phosphane were added at 0 °C. After removal of the
cooling bath, evolution of hydrogen gas was observed. After stirring
Caution: Isolated and dried lithium and potassium phosphanides 2a
and 2b inflame spontaneously if exposed to air. Therefore, we did not
accomplish combustion analyses of these compounds.
Synthesis of 2,4,6-Triisopropylphenylphosphane (1): A three neck for 12 h the excess of KH was removed by filtration. The yellow fil-
round-bottomed flask with reflux condenser and dropping funnel was trate was evaporated to dryness under reduced pressure yielding an
loaded with 3.4 g of Mg (132 mmol) and 100 mL of THF. Bromo- amorphous yellow solid. Crystallization could be achieved from a sol-
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Journal of Inorganic and General Chemistry
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vent mixture of Et
solid): 982 mg. 31P-NMR titration (internal standard: Ph
quantitative conversion. IR (nujol): ν˜ = 3502 (w), 2953 (s), 2926 (s), and 14 mg of triphenylphosphane and used for immediate NMR analy-
2
O/TMEDA with a ratio of 20:1. Yield (amorphous phosphinic chloride (324 mg, 1.37 mmol) in 5 mL of THF at –78 °C.
3
P) verified a A 0.4 mL aliquot was taken from solution, mixed with 0.1 mL of C D
6 6
3
1
2
1
1
888 (s), 2864 (s), 2259 (m), 1987 (w), 1766 (w), 1665 (w), 1593 (m),
535 (w), 1460 (s), 1411 (s), 1377 (m), 1360 (m), 1306 (m), 1252 (m),
sis of the degradation process. P NMR (162 MHz, C
= 97.7 (quin, JPH = 7.9 Hz, 9b), 77.5 (dt, JPP = 636.6, JPH = 12.7 Hz,
),
–100.23 (d, JPP = 179.2 Hz), –133.5 (t, JPP = 179.2 Hz), –147.0 (d,
JPP = 637.0 Hz, 8b), –184.3 [d, JPH = 212.2 Hz, TippP(H)TIPS].
6 6
D , 297K): δ
237 (m), 1252 (m), 1237 (m), 1224 (m), 1165 (m), 1127 (m), 1100 8b), 33.4 (s), 29.8 (s), 20.1 (s), –5.5 (sept, JPH = 8.2 Hz, PPh
3
(m), 1057 (s), 1038 (s), 939 (m), 920 (m), 878 (s), 808 (w), 755 (m),
7
4
31 (w), 714 (w), 636 (m), 622 (m), 562 (w), 514 (w), 479 (w),
1
8
25(w). H NMR (400.13 MHz, [D ]THF, 297 K): δ = 6.57 (s, 2 H,
4
meta-H), 3.67 [m,
J
P,H = 6.4 Hz, 2 H, ortho-CH(iPr)], 2.65 [hept, X-ray Structure Determinations: The intensity data for the com-
3
3
J
H,H = 6.9 Hz, 1 H, para-CH(iPr)], 1.18 [d,
J
H,H = 6.8 Hz, 12 H,
(iPr)].
]THF, 297 K): δ = 154.7 (ipso-C),
45.77 (ortho-C), 135.7 (para-C), 118.9 (meta-C), 35.3 [para- a semi-empirical basis using multiple-scans.
pounds were collected on a Nonius KappaCCD diffractometer using
graphite-monochromated Mo-K radiation. Data were corrected for
Lorentz and polarization effects; absorption was taken into account on
3
ortho-CH
3
(iPr)], 1.14 [d,
C{ H} NMR (150.93 MHz, [D
J
H,H = 7.0 Hz, 6 H, para-CH
3
α
13
1
8
[
46–48]
1
The structures were
and refined by full-matrix
least-squares techniques against F
o
(SHELXL-97[44] and SHELXL-
[
49]
CH(iPr)], 33.1 [d, J = 15.0 Hz, ortho-CH(iPr)], 25.1 [para-CH
3
(iPr)], solved by Direct Methods (SHELXS)
(iPr)]. 31P NMR (161.98 MHz, [D
]THF, 297 K): δ =
2
2
–
4.0 [ortho-CH
153.8 (d, JP,H = 153.1 Hz).
3
8
1
[50]
2014 ). All hydrogen atoms of 5 and those bonded to the phosphorus
atoms P1 of compounds 2a and 2b were located by difference Fourier
synthesis and refined isotropically. All other hydrogen atoms were in-
cluded at calculated positions with fixed thermal parameters. All non-
hydrogen atoms were refined anisotropically.
Synthesis of Lithium Phosphanidylphosphane Oxide (3a): Bis(4-
tert-butylphenyl)phosphinic chloride (323 mg, 0,93 mmol) was sus-
pended in 8 mL of Et
O and cooled to –50 °C. TippPHLi (2a, 444 mg,
O and added quickly. After
[49,50]
2
Crystallographic
1
,83 mmol) was dissolved in 12 mL of Et
2
data as well as structure solution and refinement details are summa-
stirring for 1h at –40 °C the cloudy yellow solution was filtered
through a frit covered with diatomaceous earth. An aliquot of the solu-
tion was evaporated to dryness and redissolved for NMR analysis in
[51]
rized in Table S1. XP
was used for structure representations.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository numbers CCDC-1970034 for 2a, CCDC-1970035 for 2b,
CCDC-1970036 for 3a·4a·LiCl·2Et
Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://
www.ccdc.cam.ac.uk)
8 2
[D ]THF. After 1 week at –20 °C crystals precipitated from an Et O
solution. Crystallization of TippP(H)-P(H)Tipp was achieved after a
month from DME solution. The NMR spectroscopic monitoring of
this reaction gave the following NMR spectra: 31P NMR (162 MHz,
1
[D
8
]THF, 297 K): δ = 87.9 (s, Ar
2
POLi, 4a), 55.1 (d, JP,P = 511.5 Hz,
2
O, and CCDC-1970037 for 5
1
1
2
P-P, 3a), –113.47 [AA’XX’, JP,H = 206.5, JP,P = 202, JP,H = 12.5,
(
3
H,H = 6 Hz, D,l-(tippPH)
2
, 5], –118.02 [AA’XX’, JP,H = 206.5, 1JP,P
1
J
202, 2JP,H = 12.5, JH,H = 6 Hz, meso-(tippPH)
3
, 5], –126.20 (d, J =
=
5
2
11.5 Hz, 3a), –161.57 (tm, JP,H = 203.4 Hz, tippPHLi, 2a). 31P{ H}
1
1
Supporting Information (see footnote on the first page of this article):
POLi), 55.1 (d, NMR spectra, NMR spectroscopic monitoring of the decay, and details
P(O)-O-P(O)Ar ], –113.5 [s, to the crystal data and structure refinement procedures
], –126.2 (d, 1JP,P = 511.5 Hz), –161.6
s, tippPHLi). Due to the fact that pure 3a was not accessible and
O]
NMR (162 MHz, [D
8
]THF, 297 K): δ = 88.1 (s, Ar
P,P = 511.5 Hz; P-P), 25.7 [s, Ar
tippPH) ], –118.02 [s, (tippPH)
2
1
J
2
2
(
(
2
2
that degradation of the cocrystallization product [3a·4a·LiCl·2Et
2
2
continued after dissolution in ethereal solvents, isolation of analytically Acknowledgements
pure 3a and its further characterization did not succeed.
We acknowledge the valuable support of the NMR
Synthesis of Mes-P=P(OSiiPr
3
)(C
6
H
4
-4-tBu)
2
(8a): Potassium
(
(
www.nmr.uni-jena.de/) and mass spectrometry service platforms
www.ms.uni-jena.de/) of the Faculty of Chemistry and Earth Sciences
(2,4,6-triimethylphenyl)phosphanide (2b, 755 mg, 3.97 mmol) was
dissolved in 16 mL of THF and dropwise added to a solution of triiso-
propylsilyl chloride (TIPS-Cl) in 10 mL of THF at –50 °C. Sub-
sequently, 2.5 mL of 1.6 M/nBuLi in n-hexane were added at –78 °C.
The resulting yellow solution was added to bis(4-tert-butylphenyl)
of the Friedrich Schiller University Jena, Germany.
phosphinic chloride (1.34 g, 3.84 mmol) in 40 mL of THF at –78 °C. Keywords: Phosphanides; Lithium; Potassium; Phosphanid-
A 0.4 mL aliquot was taken from solution, mixed with 0.1 mL of C
ylphosphane oxides; Mechanistic study
6 6
D
and 15 mg of triphenylphosphane as internal standard and this solution
was used for immediate NMR analysis of the quantitative degradation
studies. 31P NMR (162 MHz, C
D
6
, 297K): δ = 98.3 (quin, JPH
=
6
7
.6 Hz, 9a), 76.4 (d, JPP = 622.3 Hz, 8a), 31.3 (s), 20.2 (s), –5.5 (sept, References
JPH = 7.7 Hz, PPh
3
), –110.2 (d, JPP = 184.5 Hz;), –118.17 (d, J =
[
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Z. Anorg. Allg. Chem. 2020, 1–12
www.zaac.wiley-vch.de
9
© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
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Published Online: ᭿
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D. Bevern, H. Görls, S. Krieck, M. Westerhausen* ....... 1–12
Synthesis, Structure, and Stability of Lithium Arylphosphan-
idyl-diarylphosphane Oxide
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