.
Angewandte
Communications
Phosphorus Ring Systems
Low-Temperature Isolation of the Bicyclic Phosphinophosphonium
Salt [Mes* P Cl][GaCl ]**
2
4
4
Jonas Bresien, Kirill Faust, Axel Schulz,* and Alexander Villinger
Dedicated to Professor Manfred Scheer on the occasion of his 60th birthday
Abstract: The reaction of [ClP(m-PMes*)] (1) with the Lewis
[XP(m-PR)] ) to evaluate possible reaction routes to similar,
2
2
acid GaCl yielded a hitherto unknown tetraphosphabicyclo-
unprecedented phosphorus species. For example, reports of
3
[
[
1.1.0]butan-2-ium salt, [Mes*P (Cl)Mes*][GaCl ] (3-
cationic phosphorus ring systems include phosphinophospho-
4
4
[
16–20]
GaCl ]), which incorporates a positively charged phosphoni-
nium frameworks (I–III, Scheme 2),
related cyclic and
4
um center within its bicyclic P scaffold. The formation of the
4
title compound was studied by means of low-temperature
NMR experiments. This led to the identification of an
intermediate cyclotetraphosphenium cation, which was trap-
ped by reaction with dimethylbutadiene (dmb). All of the
compounds were fully characterized by experimental and
computational methods.
R
ing systems composed of Group 15 elements (pnictogens,
[
1–3]
Pn) are a fascinating aspect of main-group chemistry.
In
particular, (pseudo)halogen-substituted cyclic dipnictadia-
zanes (B, Scheme 1) proved to be versatile starting materials
for the synthesis of (transient) compounds with NPn multiple
bonds (for example, A) generated by cycloreversion reac-
Scheme 2. Structural motifs found in cationic phosphorus ring sys-
tems.
[4–8]
[21]
tions,
reactions or ring expansion,
which are formed by abstraction of halogen atoms (C).
larger ring systems by subsequent cycloaddition
bicyclic polyphosphorus frameworks (V, VI) and, in a wider
[4,9,10]
[22–25]
as well as cationic species
sense, several cluster cations (IV),
systems with cationic substituents.
as well as bicyclic
[11–15]
[25,26]
However, cyclic tetra-
In this regard, we are currently interested in the reactivity
of analogous ring systems solely based on phosphorus (that is,
phosphenium cations similar to C have not yet been reported.
Only recently we developed a synthesis for dichloro-
cyclotetraphosphane [ClP(m-PMes*)] (1, Mes* = 2,4,6-tri-
2
[
27]
tert-butylphenyl),
enabling us to study the reactivity of
this little-known class of compounds.
[28,29]
Our approach
focuses on the selective functionalization of the P scaffold
4
by substitution or abstraction of the Cl atoms, which is in
contrast to the widely used method of direct functionalization
Scheme 1. A formal equilibrium between monomeric iminopnictanes
of white phosphorus (P ), for example, by use of Lewis acids
4
(A; Pn=P, As; X=(pseudo)halogen) and cyclodipnictadiazanes
and bases, transition metals, or singlet carbenes such as N-
(B; Pn=P, As, Sb, Bi) depending on the steric strain of the substituent
heterocyclic carbenes (NHCs) and cyclic alkylaminocarbenes
R gives rise to different reaction pathways, including formation of
cyclodipnictadiazenium salts (C; Pn=P, As, Sb, Bi).
[
30–33]
(CAACs).
Whereas the chemistry of cyclophosphanes with carbon-
[34]
or nitrogen-based substituents has been well investigated,
no information about the reactivity of halogen substituted
cyclotetraphosphanes has been reported. Herein, we wish to
present results concerning the reaction of 1 with the Lewis
acid GaCl3.
[
*] J. Bresien, K. Faust, Prof. Dr. A. Schulz, Dr. A. Villinger
Institut für Chemie, Universität Rostock
Albert-Einstein-Strasse 3a, 18059 Rostock (Germany)
E-mail: axel.schulz@uni-rostock.de
Prof. Dr. A. Schulz
Leibniz-Institut für Katalyse e.V. an der Universität Rostock
Albert-Einstein-Strasse 29a, 18059 Rostock (Germany)
In analogy to the synthesis of cyclodipnictadiazenium salts
(
C), a colorless dichloromethane solution of 1·C H F was
6 5
treated with GaCl at low temperatures. Instantly, a deep-red
3
[
**] We thank Dr. Dirk Michalik for measuring low-temperature NMR
spectra, Malte Willert for his aid with SLURM resource manager
31
coloration was observed. In situ P NMR spectroscopy
revealed formation of a transient cyclotetraphosphenium
(
compute cluster), and the Fonds der Chemischen Industrie as well
+
intermediate (2 , Scheme 3), as indicated by a broadened,
as the Deutsche Forschungsgemeinschaft (SCHU 1170/11-1) for
financial support.
significantly downfield-shifted AM X spin system (358.9,
2
1
45.9, 88.6 ppm). The highest partial concentration of the
intermediate was detected directly at the beginning of the
6926
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 6926 –6930