Synthesis, crystal structures, and quantum chemical calculations of Novel Phosphonium Salt-1,5-diphospha-3-phosphonia-tricyclo pentane cations

Article abstract of DOI:10.1016/j.jorganchem.2017.05.052

This work deals with reactions between the kinetically stable 2-tert-butyl-1λ³-phospha-alkyne, ^tBu-C[tbnd]P, and various halodiorganylphosphines (X = Cl, Br). The isolated ionic salts with the 2,4-di-tert-butyl-3,3-diorganyl-1λ³,5λ³-diphospha-3-phosphonia-tricyclo[2.1.0.0^2,5]pentane cations, [R₂C₂^tBu₂P₃]^⊕ (R = ethyl, isopropyl, methyl, phenyl), were characterized by spectroscopic methods; additionally, the results of X-ray structure analyses were confirmed by quantum chemical calculations with Gaussian 03 program which were performed on the hydrogen substituted phosphonium and phosphenium cations in order to ascertain optimized structural data and relative energies for different isomers. As for the phosphonium cation ([H₂P(CH)₂P₂]^⊕) generated from our work the conventional trigonal bipyramidal framework of point group C_2v represents the absolute minimum on the potential energy surface. To our surprise this situation is followed by a second one which has to be attributed to the so-called housene structure of point group C₁ showing a somewhat higher energy value + 77.9 kJ/mol. Quite a reverse situation is encountered for the phosphenium cation [P(CH)₂P₂]^⊕. Here the pseudo square-based pyramidal nido structure of point group C_2v known from Russell's tetrachloroaluminate(III) compound is found to be the only minimum on the potential energy surface. A phosphenium cation with a trigonal bipyramidal framework of point group C_2v is higher in energy by only 35.7 kJ/mol, but due to one imaginary frequency it has to be considered the structure of a transition state. The opened housene structure corresponds neither to a minimum nor to a saddle point on the potential energy surface. In the pseudo square-based pyramidal nido structure (point group C_2v) of the phosphenium cation [P(CH)₂P₂]^⊕ the s-orbital and all p-orbitals of the apical four-coordinate phosphorus atom are used to form two P–C and two P–P bonds. Further addition of two hydrogen atoms to entail the phosphonium cation [H₂P(CH)₂P₂]^⊕ of point group symmetry C₂ not only increases the coordination number of the apical phosphorus atom to six but also requires two electrons and two orbitals for P–H bonding. These are no longer available to the bonding system within the nido structure; as a consequence, its energy increases to +246.6 kJ/mol and the cation rearranges to give the conventional structure of ours.

Full text of DOI:10.1016/j.jorganchem.2017.05.052

Accepted Manuscript
Synthesis, crystal structures, and quantum chemical calculations of Novel
Phosphonium Salt-1,5-diphospha-3-phosphonia-tricyclo pentane cations
Mutasem Z. Bani-Fwaz, Ahmed E. Fazary, Gerd Becker
PII:
S0022-328X(17)30367-4
10.1016/j.jorganchem.2017.05.052
JOM 19978
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 16 March 2017
Revised Date: 19 May 2017
Accepted Date: 25 May 2017
Please cite this article as: M.Z. Bani-Fwaz, A.E. Fazary, G. Becker, Synthesis, crystal structures,
and quantum chemical calculations of Novel Phosphonium Salt-1,5-diphospha-3-phosphonia-tricyclo
pentane cations, Journal of Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.05.052.
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ACCEPTED MANUSCRIPT
Graphical Abstract
tBu
tBu
tBu
C
P
tBu
X
2
C
+
P
R`
C
C
R`
R`
P
P
P
P
P
P
R``
R"
R'
P
P
C
R``
C
P
X
R``
C
tBu
X
tBu
tBu
X
tBu = tert-butyl
3
3
1λ , 3λ -diphosphete
postulated intermediate
1
1
1
1
1
1
1
a: R' = R" = methyl, X = Cl;
b: R' = R" = ethyl, X = Cl;
c: R' = Phenyl, R" = isopropyl, X = Cl;
d.1: R' = R" = phenyl, X = Cl;
d.2: R' = R" = phenyl, X = Br;
e: R' = R" = isopropyl.

1
ACCEPTED MANUSCRIPT
Synthesis, Crystal Structures, and Quantum
Chemical Calculations of Novel Phosphonium
Salt-1,5-Diphospha-3-Phosphonia-Tricyclo
Pentane Cations
a,b (*)*
a,c (
*
)
Mutasem Z. Bani-Fwaz
, Ahmed E. Fazary ,
b**
Gerd Becker
a
Department of Chemistry, Faculty of Science, King Khalid University, P. O. Box
004, Abha 61413, Saudi Arabia.
Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-
0569 Stuttgart, Germany.
9
b
7
c
Egyptian Organization for Biological Products and Vaccines [VACSERA
Holding Company], 51 Wezaret El-Zeraa St., Agouza, Giza, Egypt.
Authors informations
Corresponding author e-mail address:banifawaz@yahoo.com ; mbanifawaz@kku.edu.sa (Dr.
Mutasem Z. Bani-Fwaz). Work Tel.: +966-7-241-7041. +962-7-96882368. Fax: +966-7-
417637.
*
2
Second author e-mail address: E-mail: aefazary@gmail.com ; afazary@kku.edu.sa (Dr. Ahmed
E. Fazary)
**This paper is dedicated to the memory of Professor Gerd Becker, who passed away on 10
Januaury 2017. E-mail: becker@iac.uni-stuttgart.de
Keywords: Phosphonium salts ; Phospha-alkyne ; Crystal structures; Trigonal bipyramidal
framework

2
ACCEPTED MANUSCRIPT
Abstract
3
This work deals with reactions between the kinetically stable 2-tert-butyl-1λ -phospha-alkyne,
t
Bu-C≡P, and various halodiorganylphosphines (X = Cl, Br). The isolated ionic salts with the
3
3
2,5
2
,4-di-tert-butyl-3,3-diorganyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane
t
2
⊕
cations, [R C Bu P ] (R = ethyl, isopropyl, methyl, phenyl), were characterized by
2
2 3
spectroscopic methods; additionally, the results of X-ray structure analyses were confirmed by
quantum chemical calculations with Gaussian 03 program which were performed on the
hydrogen substituted phosphonium and phosphenium cations in order to ascertain optimized
structural data and relative energies for different isomers. As for the phosphonium cation
⊕
(
[H P(CH) P ] ) generated from our work the conventional trigonal bipyramidal framework of
2
2 2
point group C2v represents the absolute minimum on the potential energy surface. To our
surprise this situation is followed by a second one which has to be attributed to the so-called
housene structure of point group C showing a somewhat higher energy value + 77.9 kJ/mol.
1
⊕
Quite a reverse situation is encountered for the phosphenium cation [P(CH) P ] . Here the
2
2
pseudo square-based pyramidal nido structure of point group C2v known from Russell’s
tetrachloroaluminate(III) compound is found to be the only minimum on the potential energy
surface. A phosphenium cation with a trigonal bipyramidal framework of point group C is
2
v
higher in energy by only 35.7 kJ/mol, but due to one imaginary frequency it has to be
considered the structure of a transition state. The opened housene structure corresponds neither
to a minimum nor to a saddle point on the potential energy surface. In the pseudo square-based
⊕
pyramidal nido structure (point group C ) of the phosphenium cation [P(CH) P ] the s-orbital
2
v
2 2
and all p-orbitals of the apical four-coordinate phosphorus atom are used to form two P–C and
two P–P bonds. Further addition of two hydrogen atoms to entail the phosphonium cation
⊕
[
H P(CH) P ] of point group symmetry C not only increases the coordination number of the
2
2
2
2
apical phosphorus atom to six but also requires two electrons and two orbitals for P–H bonding.
These are no longer available to the bonding system within the nido structure; as a
consequence, its energy increases to + 246.6 kJ/mol and the cation rearranges to give the
conventional structure of ours.

3
ACCEPTED MANUSCRIPT
1
. Introduction
3
It was known that the synthesis of 2-organyl-1λ -phosphaalkynes [1-2] starts from
tris(trimethylsilyl)phosphine which is isolated in high yield from the reaction of
sodium/potassium alloy with white [2] or red [3] phosphorus in 1,2-dimethoxyethane followed
by addition of a slight excess of chlorotrimethylsilane. Treatment of such compounds with acyl
halides results in the formation of acylbis(trimethylsilyl)phosphines [1-2]. These phosphines
are thermally unstable and rearrange at room temperature via 1,3-migration of one
3
trimethylsilyl group from phosphorus to oxygen to give the corresponding E/Z-1λ -
phosphaalkenes [1-2]. The final elimination of hexamethyldisiloxane is catalyzed by small
3
pieces of solid sodium hydroxide and furnishes the corresponding 1λ -phosphaalkynes in very
high yields [1,2]. Solutions of phosphorus(III) chloride, bromide and iodide in benzene react
3
with two equivalents of 2-tert-butyl-1λ -phosphaalkyne to form the corresponding 2,4,5-
3
3
3
trihalo-2λ ,4λ ,5λ -triphosphabicyclo[1.1.1]pentane heterocycles as final products [4-9].
Scheme 1 showed the formation steps of phosphorus oligocyclic cage compounds in which the
3
3
P≡C unit of the 1λ -phosphaalkyne inserts into the element–halogen bond to furnish the λ -
3
phosphaalkene (I) in a first step, followed by a subsequent [2+2]cycloaddition of a second 1λ -
phosphaalkyne molecule affording the 1,2-dihydro-1λ ,3λ -diphosphete (II) [5,7]. Further
3
3
stabilization is achieved either by a 1,3-migration of a halide anion from element E to
3
phosphorus or by the addition of a third 1λ -phosphaalkyne molecule to furnish the 2-elementa-
3
3
3
3
5
4
λ ,5λ -diphosphabicyclo[1.1.1]pentane (III) [4-8] or the 7-elementa-2λ ,3λ ,5λ -
2
,6
triphosphatricyclo[3.2.0.0 ]hept-3-ene-5-ium-7-uide (IV) [6,7], respectively. The resulting
highly reactive zwitterion comprises a dihalogen-substituted negatively charged as well as a
halogen-free positively charged phosphorus atom and stabilizes by 1,3-migration of a halide
anion.
3
3
3
The synthesis of 2,4,5-tribromo-1,3-di-tert-butyl-2λ ,4λ ,5λ -triphosphabicyclo-
3
[
1.1.1]pentane starts with phosphorus(III) bromide and 2-tert-butyl-1λ -phosphaalkyne, and its
X-ray structure determination reveals molecular C symmetry; bond lengths and angles do not
3
deviate substantially from expected values [4,5,7] (Scheme 1). In the presence of electron-rich
5
transition metal fragments such as [M(η -C R )] (M = Co, Rh, Ir; R = H or Me) and Fe(CO)
5
5
3
3
[
10-12], 1λ -phosphaalkynes are known to undergo cyclization reactions which preferentially
afford 1λ ,3λ -diphosphacyclobutadienes. The 14 valence electron species Cp Zr which is
3
3
2
generated in situ from corresponding dichloride and two equivalents of n-butyllithium,
5
3
3
however, furnishes the tricyclic 5,5-bis(η -cyclopentadienyl)-2,4-diorganyl-1λ ,3λ -diphospha-5-
1,3
zirconia-tricyclo[2.1.0.0 ]pentane compounds (V) [13-17]. With phosphorus(III) chloride at 110
ºC in n-hexane, the P–Cl bridged compound 2,4-di-tert-butyl-3-chloro-1λ ,3λ ,5λ -triphospha-
tricyclo[2.1.0.0 ]pentane (VI) can be obtained as shown in Scheme 1[18]. Treating these
complexes with phosphorus(V) pentachloride in n-hexane at 90 ºC give compounds (III). The
reaction of compound (VI) with stoichiometric amounts of aluminium(III) chloride in solution
3
3
3
2
,5
t
⊕
y
leads to nido-[3,5- Bu -1,2,4-C P ] cations and separated [AlCl ] anions [19]. Remarkably,
the analogous but neutral compound nido-2- Bu-1,2-PCB H has been obtained from the
2
2
3
4
t
3
5
3
reaction of 2-tert-butyl-1λ -phosphaalkyne and B H in⊕ a gas phase reaction [20]. In the
4
10
valence shell both species are isoelectronic to the [Me C ] cation [19,20].
5
5
5
Furthermore, so-called housene structure is favoured when 5,5-bis(η -cyclopentadienyl)-
,4-diorganyl-1λ ,3λ -diphospha-5-zirconia-tricyclo-[2.1.0.0 ]pentane
3
3
1,3
2
is
treated
with
antimony(III) chloride due to a transannular electronic interactions between the σ* (Sb–Cl) orbital
and the π-system of the P=C unit and additionally between the empty π*-system of the P=C
3
3
3
unit and the σ (Sb–P) orbital [21]. As well, reduction of 2,4-di-tert-butyl-3-chloro-1λ ,3λ ,5λ -
2
,5
triphospha-tricyclo[2.1.0.0 ]pentane with magnesium or potassium in tetrahydrofuran
t
3
3
3
furnished almost quantitatively the compounds [Mg (µ-Cl) (thf) ], [2,5- Bu -1λ ,3λ ,4λ -P C ]
2
3
6
2
3 2

4
ACCEPTED MANUSCRIPT
t
3
3
3
and K[2,5- Bu -1λ ,3λ ,4λ -P C ] [22]. The mechanistic insight gained from these studies
2
3
2
t
3
3
3
opened a new and “economic” synthesis of the already known anion [2,5- Bu -1λ ,3λ ,4λ -
P C ] [4,23]. Surprisingly, reactions of organophosphorus dihalides turned out to be rather
2
y
3
2
complex and, in particular, the formation of by-products is scarcely understood such as
3
3
heterocycle 2,4,5-tri-tert-butyl-1-phenyl-1λ ,3λ -diphosphole (VII) along with the expected
3
3
3
1
,3-di-tert-butyl-2,4-dichloro-5-phenyl-2λ ,4λ ,5λ -triphosphabicyclo[1.1.1]pentane (VIII) [8].
In the present work, we also studied the addition of bromo- and
3
chlorodiphenylphosphine to 2-tert-butyl-1λ -phosphaalkyne and determined the crystal
structure of the oligocycle prepared from halodiphenylphosphines [8]. In extension of our
3
investigations on the reactivity of 2-tert-butyl-1λ -phosphaalkyne, we have confirmed these
results, additionally employed several chlorodiorganylphosphines with different alkyl and aryl
substituents as starting materials in order to improve the crystallographic parameters.
Additionally, quantum chemical calculations were performed on the hydrogen substituted
phosphonium and phosphenium cations to ascertain optimized structural data and relative
energies for different isomers confirming the most experimental details as expected.
<Scheme 1>
2
. Results and Discussions
2
.1. Reaction Mechanism. Solutions of the halodiorganylphosphine and of slightly more than
3
two equivalents of 2-tert-butyl-1λ -phosphaalkyne in cyclopentane are combined dropwise at –
0 °C and the mixture is allowed to warm up slowly to room temperature. Within about four
7
days it changes its colour to brown-yellow and a white solid precipitates. Without further
separation the solvent is removed to leave a brown-yellow solid. This crude product is
extracted with hot toluene until the suspension changes its colour to yellow-orange. Whereas
the solution removed at + 4 °C with a pipet is rejected, the remaining solid is dissolved in
3
3
5
dichloromethane. On cooling the ionic compound containing the 1λ ,5λ -diphospha-3λ -
2
,5
phosphonia-tricyclo[2.1.0.0 ]pentane cation precipitates as a colourless solid; relatively high
yields of 73 to 79% were obtained. Renewed recrystallization of the compounds 1a, 1b, 1c,
1
d.1, 1d.2 (Figure 1) and 1e from dichloromethane gave colourless crystals suitable for X-ray
structure analyses.
<Figure 1>
Since all attempts to crystallise the oily compound 1e which had been prepared from
chlorodiisopropylphosphine, failed, its structure had to be deduced from NMR data only.
Unfortunately chloro-di-tert-butylphosphine did not react. One has to realise, however, that
with halodiorganylphosphines only one phosphorus–halogen bond is available for an initial
3
insertion of the 1λ -phosphaalkyne. Therefore a slight variation of the original mechanism
outlined in the general scheme has to be taken into consideration. Again, a transannular attack
`
``
2
of the R R P group at the sp -hybridized carbon atom of the still undetectable 1,2-dihydro-
1
3
3
λ ,3λ -diphosphete is expected to occur, but in contrast to general Scheme 1 this attack has to
be nucleophilic and an umpolung has to be assumed. The postulated intermediate specified in
Scheme 2, stabilises by formation of a P–P bond and an accompanying elimination of a halide
3
3
5
2,5
anion to give the corresponding 1λ ,5λ -diphospha-3λ -phosphoniatricyclo[2.1.0.0 ]pentane
cation.
<
Scheme 2>
3
1
1
2
1
.2. IR, Raman, and NMR characterization. The P{ H} NMR spectra of the compounds 1a,
b, 1d.1, 1d.2, and 1e dissolved in chloroform-d reveal the signals of an A X spin system.
1
2
With an intensity ratio of 2:1 the doublets of the two chemically equivalent phosphorus atoms
P1 and P5 and the triplets of the positively charged phosphorus atoms P3 appear at rather high
2
and at relatively low field, respectively (Supplementary Figure 1a). The appertaining J(
P3,P1/P5)

5
ACCEPTED MANUSCRIPT
coupling constants (Table 1) are very small and vary between 10.8 Hz and 1.3 Hz. The
spectrum of compound 1c, prepared from chloro(isopropyl)phenylphosphine, however, is found
to be more complicated. Since the cation no longer exhibits a mirror plane through the atoms
C2, C4 and P3, the two phosphorus atoms P1 and P5 become chemically inequivalent. With an
3
1
1
intensity ratio of 1:1:1 the P{ H} NMR spectrum reveals the signals of an AMX spin system;
2
it is characterised by a singlet of the positively charged phosphorus atom ( J(
< 0.5 Hz)
of 172.2
P3,P1/P5)
1
and two doublets of the atoms P1 and P5, coupled with a rather large constant J(
Hz (Supplementary Figure 1b).
P1,P5)
<Table 1>
1
3
1
In the C{ H} NMR spectra of compound 1c, however, several C,P couplings to the a
priori chemically non-equivalent phosphorus atoms P1 and P5 become so similar that the P–P
group can be treated as a pseudo-A2 system. As a consequence, for all compounds the bridging
quaternary carbon atoms of the central oligocycles reveal doublets of triplets (Table 1 and
Supplementary Figure 2e). Whereas in all cations the methyl carbon atoms of the tert-butyl
substituents give rise to pseudo-quintets with an intensity ratio of approximately 1:2:2:2:1
(
Supplementary Figure 2b) – or in an alternative description to doublets of triplets –, due to an
2
unobservable. J
coupling the adjacent quaternary carbon atoms show only triplets in the
(C,P3)
spectra of the compounds 1a, 1b, 1c (Supplementary Figure 2d), 1d.1, and 1e. The spectrum of
2
compound 1d.2, however, exhibits a doublet of triplets with a very small J
value of 0.96
(C,P3)
1
13
1
Hz (Table 2). Singlets at about 5.2 ppm in the H NMR and at about 53.3 ppm in the C{ H}
NMR spectra, respectively, spring from the co-crystallizing solvent dichloromethane. Due to a
different treatment of the compounds in vacuo the contents may vary from 0.0 to 0.8 mole per
1
formula unit. Furthermore, a strong H NMR singlet in a range of 0.74 to 1.03 ppm is assigned
to the tert-butyl groups.
<
Table 2>
1
In the H NMR spectrum of compound 1a the signal of the two methyl groups
connected directly to the positively charged phosphorus atom appears at 3.1 ppm and is split
2
13
1
into a doublet with a coupling constant J(
= 12.9 Hz. The pertinent C{ H} NMR
H,P3)
spectrum reveals a doublet of triplets at 18.7 ppm arising from a coupling with two different
1
3
types of the phosphorus atoms and exhibits J
and J
constants of 32.9 Hz and 4.9
(
C,P3)
(C,P1 and P5)
1
Hz, respectively. The methyl and methylene H NMR-signals of the ethyl groups of compound
b are observed at 1.63 and 3.43 ppm, respectively. They are split into a doublet of triplets with
two different coupling constants of 7.4 Hz for J
1
3
3
and of 17.6 Hz for J(H,P3), and into a
(
H,H)
2
13
1
doublet of quartets with a J
value of 11.8 Hz. In the C{ H} NMR spectrum the methyl
(H,P3)
and methylene carbon atoms give rise to two doublets of triplets at 8.8 ppm and 26.6 ppm,
2
4
1
exhibiting J
and J
constants of 5.7 Hz and 2.9 Hz in the high field and J
(
C,P3)
(C,P1 and P5) (C,P3)
3
1
and J
constants of 26.9 Hz and 3.8 Hz in the low field region, respectively. In the H
(
C,P1 and P5)
NMR-spectrum of compound 1c the two methyl groups of the isopropyl substituent are
3
3
observed at 1.6 ppm as a doublet of doublets with J(
and J
coupling constants of 6.9
H,H)
(H,P3)
Hz and 17.9 Hz, respectively. Furthermore, the neighboring CH-group appears as a multiplet in
a range of 4.9 to 5.05 ppm. Two multiplets between 7.54 and 7.72 ppm and between 8.56 and
1
3
1
8
.65 ppm come from the hydrogen atoms of the phenyl group. In the pertinent C{ H} NMR
2
spectrum the two methyl carbon atoms reveal a doublet of doublets at 17.8 ppm with J
J(C,P1 or P5) coupling constants of 4.6 Hz and of 2.03 Hz, respectively. The neighboring
methylidyne carbon atom gives rise to a doublet of doublets of doublets at 31.0 ppm with a
and
(C,P3)
4
1
3
J(C,P3) coupling constant of 23.9 Hz and of two different J
values of 5.1 Hz and of 1.5
(C,P1 or P5)
Hz.
1
3
1
Furthermore, four different low field C{ H} NMR signals (Table 3) can be ascribed to
the phenyl group at phosphorus atom P3. Here, the assignment is based on data reported for the
carbon atoms in the phenyl substituents of the two different (8-dimethylamino-naphth-1-
yl)(dialkyl)phenylphosphonium iodides A1 and A2 (Scheme 3) [24]. The doublet of doublets of

6
ACCEPTED MANUSCRIPT
1
doublets at 124.8 ppm springs from the ipso-carbon atom and is characterized by a J
(C,P3)
3
coupling constant of 53.3 Hz and by two different J
values of 6.2 Hz and 2.1 Hz. A
(C,P1 or P5)
4
doublet at 135.3 ppm with a J
coupling constant of 3.1 Hz is attributed to the para-carbon
(C,P3)
2
4
atom, whereas a doublet of doublets at 132.6 ppm with J(
and J
coupling constants
(C,P1 or P5)
C,P3)
of 8.9 Hz and of 4.3 Hz, respectively, springs from the carbon atoms in ortho-position. Finally,
3
the doublet at 130.2 ppm with a J
coupling constant of 10.7 Hz has to be assigned to the
(C,P3)
3
the meta-carbon atoms. As in the two reference compounds the J
carbon atoms are found to be slightly larger than the J(
atoms [24].
couplings to the meta-
C,P)
(
2
values involving the ortho-carbon
C,P)
<Scheme 3>
1
The H NMR spectra of the two nearly identical compounds 1d.1 and 1d.2 show very
similar data for the phenyl region; two multiplets between 7.7 and 7.80 ppm and between 7.8
and 8.2 ppm are observed for compound 1d.1, whereas the corresponding signals of compound
1
d.2 appear in ranges of 7.7 to 7.9 ppm and 8.2 to 8.3 ppm. As in compound 1c, the pertinent
C{ H} NMR spectra reveal four different signals for the phenyl carbon atoms (Table 3).
1
3
1
<Table 3>
The ipso-position gives rise to a doublet of triplets at 124.2 ppm in compound 1d.1 and
1
at 124.6 ppm in compound 1d.2; for the appertaining coupling constants J
values of 58.6
(C,P3)
3
and 58.2 Hz and J
values of 4.7 and 4.5 Hz, respectively, have been ascertained. The
(C,P1 and P5)
doublet of the para-carbon atom is similarly observed at 136.2 (1d.1) and 136.3 ppm (1d.2)
4
with J
coupling constants of 3.2 and 3.1 Hz, respectively. Doublets at 133.0 and 133.4
(C,P3)
2
ppm come from the ortho-carbon atoms of 1d.1 and 1d.2; they are characterized by J(
C,P3)
coupling constants of 10.0 and 10.1 Hz, respectively. Finally, the doublets at 130.4 (1d.1) and
3
1
30.6 ppm (1d.2) with J
coupling constants of 11.1 and 11.3 Hz, respectively, have been
(C,P3)
1
ascribed to the meta-position. In the H NMR spectrum of compound 1e the methyl groups of
the isopropyl substituents at phosphorus atom P3 appear at 1.4 ppm and are found to be split
3
3
into a doublet of doublets with J
and J
coupling constants of 7.1 Hz and 16.3 Hz,
(H,H)
(H,P3)
respectively. A multiplet between 2.9 and 3.2 ppm is assigned to the neighboring CH-groups.
1
3
1
The pertinent C{ H} NMR spectrum reveals a doublet of triplets at 17.6 ppm for the methyl
carbon atoms and a second doublet of triplets at 31.65 ppm for the methylidyne carbon atoms.
2
4
The high field doublet of triplets is characterized by J(
and J
coupling constants
C,P3)
(C,P1 and P5)
1
3
of 5.2 and 2.5 Hz, whereas the low field doublet of triplets shows J(
and J
values
(C,P1 and P5)
C,P3)
of 20.2 and 3.7 Hz, respectively. Since Infrared and Raman spectra of different crystalline
3
3
solids
containing
the
2,4-di-tert-butyl-3,3-diorganyl-1λ ,5λ -diphospha-3-phosphonia-
2
,5
tricyclo[2.1.0.0 ]pentane cation could be measured as nujol mull between CsBr disks and in
glass capillaries, respectively, by comparison a tentative assignment is possible for the majority
of vibrations in the low wave number region (Table 4). Bands near 1000 cm in both the
Infrared and Raman spectra may be attributed to the C–C pulsation of the phenyl substituents.
In accordance with a publication of Randle and Whiffen on halo-benzenes [25] it refers to the
-1
-1
phenyl breathing mode p (Supplementary Figure 3). Bands in the 940 – 825 cm region spring
from the C–C vibrations of the ethyl and isopropyl groups at phosphorus as well as the tert-
butyl substituents in 2,4-position and from the methyl rocking vibration ρCH of the methyl
3
-1
-1
entities. Bands near 815 cm and at 674 cm have to be assigned to the symmetric CC -
vibration of the tert-butyl substituents and the P–C stretching vibration of the P– Pr unit,
respectively. In the 726 – 694 cm region bands can be ascribed to the stretching vibrations of
3
i
-1
P–C units which most probably are antisymmetricly combined with the ring deformation γ of
-1
the skeleton. Moreover, vibrations between 637 and 612 cm can be assigned to the in-plane
ring deformation δCCC of the phenyl substituents (s) and the deformation γ of the trigonal
-1
bipyramidal skeleton. Bands between 588 and 565 cm may be attributed to the pulsation of
the skeleton and comprise the P–C and P–P stretching vibrations. Since bands in the 560 – 587
-1
cm region are observed in phenyl derivatives only, they are assigned to “X”-sensitive

7
ACCEPTED MANUSCRIPT
-1
puckering mode y of the P–Ph unit. Bands near 530 cm may ascribed to a combination of
stretching vibration and deformation (ν δ) of the skeleton, whereas bands between 513 and 481
,
-1
cm can be assigned to the “X”-sensitive vibration mode t of the phenyl ring. Finally, two
partially overlapping bands between 422 and 384 cm probably spring from a combination of
P–C and P–P stretching vibrations within the skeleton.
-1
<Table 4>
2
.3. Crystal Data and its Packing. By recrystallization from dichloromethane the co-
crystallisates 1a•CH Cl (1/1) and 1b•CH Cl (2/4) could be obtained as colourless thick
2
2
2
2
needles (columns) within a period of three to four weeks at –60 °C. From the same solvent
similarly shaped crystals of 1c•CH Cl (1/2), 1d.1•CH Cl (1/1), and 1d.2•CH Cl (1/1)
2
2
2
2
2
2
precipitated already within one week at –13 °C. Repeatedly too large crystals had to be cut into
small block-shaped fragments suitable for X-ray structural analyses. For a better understanding
of the following discussion one has to realize that all structures were found to be ionic with
separated cations and halide anions and to contain one or two solvent molecules per formula
unit depending on the substituents methyl, ethyl, isopropyl, and phenyl at the positively
charged phosphorus atoms. Moreover, from the notations of the co-crystallisates the ratio of
cations and anions to solvent molecules may easily be deduced. For example, the asymmetric
unit of the adduct 1b•CH Cl (2/4) comprises two crystallographically independent cations, two
2
2
anions and four solvent molecules. Compound 1d.1•CH Cl (1/1) and 1d.2•CH Cl (1/1) differ
2
2
2
2
only in the halide anions chloride and bromide. Data essential for structure determinations of
the adducts 1b•CH Cl (2/4), 1c•CH Cl (1/2), and 1d.1•CH Cl (1/1) were collected on a four-
2
2
2
2
2
2
circle diffractometer P2 (Syntex, Cupertino, USA), whereas for 1a•CH Cl (1/1) and
1
2
2
1
d.2•CH Cl (1/1) a P4 diffractometer (Siemens Analytical X-ray Instruments Inc.,
2 2
Madison/Wisconsin, USA) was applied and, as before, graphite monochromatized Mo-Kα-
radiation (λ = 71.073 pm) was used. Lattice parameters were calculated from the exact
positions of a selected number of reflections (Supplementary Table 1) and refined thereafter.
The determination of the monoclinic space group P2 /c for 1c•CH Cl (1/2) or P2 /n for
1
2
2
1
1
d.1•CH Cl (1/1) and 1d.2•CH Cl (1/1) is based on unit cell dimensions and systematic
2 2 2 2
absences (Supplementary Table 1), whereas for 1a•CH Cl (1/1) and 1b•CH Cl (2/4) space
2
2
2
2
group P1 was chosen over P1 mainly on grounds of E-value statistics and successful structure
refinements.
The crystal structures were solved by statistical methods employing the software
package SHELXTL Version 5.10 which also includes the program XP used for the analyses of
molecular geometry and the preparation of drawings. Due to relatively low calculated
absorption coefficients for nearly all structures (Supplementary Table 1) and despite column
shaped crystals absorption corrections were considered to be not necessary. Only the data set of
co-crystallisate 1d.2•CH Cl (1/1) prepared from bromodiphenylphosphine was corrected by
2
2
application of the computer program DIFABS (Tmin = 0.416, Tmax = 1.000) [26]. After the
halogen, phosphorus and carbon atoms had been located step by step and their positions as well
as their isotropic replacement parameters had been refined by full-matrix least-squares
calculations, the structure determinations were continued applying individual anisotropic Uij-
values. At the end the atomic coordinates of hydrogen atoms could either be taken from a
different Fourier map and refined with their isotropic replacement parameters or were
calculated on the basis of an idealized geometry which means a C–H distances of 96 pm and 97
pm of methyl and methylene groups, repectively, tetrahedral angles and a staggered
arrangement of bonds at carbon. Furthermore the riding model applied ensures that a change in
the carbon position is automatically transferred to the adjacent hydrogen atoms. The individual
isotropic U-values of these hydrogen atoms were adopted from the pertinent carbon atoms and
increased by a factor of 1.5 for the methyl groups and of 1.2 for the phenyl substituents, the
methylene units of the cations and all of dichloromethane molecules. Finally the parameters of

8
ACCEPTED MANUSCRIPT
all heavier atoms were subjected to a last least squares refinement to take into account the
incorporation of hydrogen atoms. As for the structures discussed here the solution of the
hydrogen problem developed as follows: in the co-crystallisates 1c•CH Cl (1/2) and
2
2
1
d.1•CH Cl (1/1) all hydrogen atoms of the cations could be located and their individual
2 2
parameters were refined, but in the dichloromethane molecules the positions had to be
calculated as described above. For the co-crystallisates 1a•CH Cl (1/1), 1b•CH Cl (2/4) and
2
2
2
2
1
d.2•CH Cl (1/1), all hydrogen atoms in the cations as well in the dichloromethane molecules
2 2
were calculated as described above. Only in the phenyl substituents for the co-crystallisate
d.2•CH Cl (1/1) the position of hydrogen atoms were treated as idealized contributions with a
1
2
2
C–H distance of 93 pm. Furthermore, the X-ray structure analysis of the adduct
a•CH Cl (1/1) shows disorder with respect to the positions of the two chlorine atoms in the
1
2
2
dichloromethane molecule. Crystallographic parameters [26-30], and details of data collection
have been summarized in Supplementary Table 1. Bond lengths and angles as well as
characteristic torsion angles [31,32] can be found in Supplementary Table 2. Final atomic
coordinates and equivalent isotropic as well as anisotropic displacement parameters are given
in Supplementary Table 3.
Supplementary Figures 4 – 8 show plots of the five analogous 2,4-di-tert-butyl-3,3-
3
3
2,5
diorganyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane cations as determined by
X-ray structure analyses of the co-crystallizates 1a – 1d • x CH Cl together with the pertinent
2
2
halides in stereoscopic view. The central tricyclic framework consists of the unit P1–P5 on one
side and the phosphonium cation with the atom P3 on the other. They are bridged by two
quarternary carbon atoms C2 and C4 each of which is connected further to a tert-butyl group.
The remaining substituents at phosphorus atom P3 might be either alkyl or aryl groups or both.
For a detailed discussion of bond lengths and angles one has to realize the high structural
conformity of all cationic frameworks and the existence of a pseudo-mirror plane comprising
the atoms P1, P5 and P3; they allow the use of mean values as classified in Supplementary
Table 4. Consequently, each framework consists of two nearly identical face-sharing tetrahedra
and may therefore be considered a trigonal bipyramide. Since, however, the number of bonds
along the equatorial edges has been reduced from three to only one (P1–P5), the polyhedron is
surrounded by two triangles (P1, P5, C2 and P1, P5, C4) and two quadrangles (C2, P3, C4, P1
and C2, P3, C4, P5).
Already a first inspection of Supplementary Table 2a, reveals a completely unexpected
shortening of the bond P1–P5 with respect to the standard value of 221 pm [33]. At an average
of 213.0 pm the distances in all these cations vary only slightly between 211.9 pm (1a:
Me/Me/Cl) and 214.9 pm (1d.1: Ph/Ph/Cl). Surprisingly, similar P–P bond lengths have been
⊕
5
observed with analogous compounds (Table 5) in which the R P unit is replaced by a (η -
2
C H ) Zr (V; 214.7 pm [17]), O=C (IX; 211.8 pm [34]), I Ge (Xa; 214.4 pm [35]), and I–P
5
5 2
2
3
3
3
group (Xb; 215.4 pm [35]. Even the 1λ ,2λ ,3λ -triphospha-bicyclo[1.1.0]butane derivates
Mes P C(SiMe ) (XI [36]) and [(Me Si) N–(Me Si)N]P C(SiMe ) (XII [37]) with an
*
3
3 2
3
2
3
3
3 2
unbridged butterfly structure exhibit short P–P bonds of 213.6 and 215.8 pm, respectively, and
fit therefore very well in this type of diphosphanes (Table 5). Remarkably, the shortening of the
central P–P distance is accompanied by elongations of the neighbouring P–C bonds. In the
cations discussed here average values for P1–C2, P1–C4, P5–C2, and P5–C4 (Supplementary
Table 2 and Supplementary Figure 9) are found in a narrow range of 189.2 pm to 190.3 pm; the
individual distances vary only slightly between 187.0 pm and 191.7 pm and exceed
significantly the standard value of 185 pm [38] for an ordinary P–Calkyl bond. Similar mean
bond lengths of 188.2 pm to 189.7 pm have been published for the compounds V and IX to XII
with bridged and unbridged butterfly structures. Unfortunately, no interpretation of the bonding
situation is available up to know; therefore, theoretical calculations are required very urgently.
In contrast to the elongated mean distance of 189.7 pm to the phosphorus atoms P1 and
P5 of the P–P group (Supplementary Table 4), the average bond length between the quarternary

9
ACCEPTED MANUSCRIPT
carbon atoms C2 and C4 in apical position of the trigonal bipyramidal framework and
phosphorus atom P3 of the phosphonium group is found in all cations to be rather short. At an
average of 179.1 pm it tallies the mean value of 179.0 pm as determined by X-ray structure
analyses for the P–C bond in tetramethylphosphonium cations [39]. An explanation of the P–C
bond shortening in phosphonium salts and compounds with pentavalent phosphorus atoms is
given in Gilheany’s review articles [38, 40, 41].
<Table 5>
The angles in the peripheric faces of the tricyclic framework are found almost as
expected. In both the largely isosceles triangles P1, C2, P5 and P1, C4, P5 values near 60° are
encountered, but they differ slightly in that the wider angles at carbon exhibit a mean of 68.4°,
whereas at the two phosphorus atoms an average of 55.8° has been determined (Supplementary
Table 4). Due to the presence of three- (P1 and P5) and four-coordinate phosphorus atoms (P3)
the angles in both the peripheric P,C,P,C-quadrangles differ somewhat stronger. Moreover, a
total sum of 339.4° only indicates these two planes to be folded; mean values of 129.1° and
1
28.6° have been determined for the dihedral angles between the two triangles P1, C2, P3// P1,
C4, P3 and P5, C2, P3// P5, C4, P3, respectively (Supplementary Table 5).
Whereas an average of 92.7° for P1–C2/ C4–P3 and P5–C2/ C4–P3 (Supplementary
Table 4) exceeds the mean C–P–C angle of 74.4° at the trivalent phosphorus atoms
considerably, an intermediate value of 79.6° is found at the phosphonium center. This strong
deviation from a tetrahedral geometry as e.g. reported for undistorted tetramethylphosphonium
cations [39] is compensated solely by an increase of the C–P3–Corganyl angles to an average of
1
1
17.5°, whereas the angle between the two carbon atoms of the organyl groups is found to be
06.1° (Supplementary Table 2b). Most probably, the expansion of the C–C–P angles at the two
apical carbon atoms to an average of 127.7° is caused by steric requirements of the bulky tert-
butyl substituents. Furthermore, the quadrangle P5, C2, P1, C4 is folded along the bond P5–P1 by a
mean value of 92.5° (Supplementary Table 5). Since the sides of both the appertaining largely
isosceles triangles P5, C2, P1/ P5, P1, C4 differ somewhat in length, two slightly longer (P1–
C4 190.2, P5–C2 190.2) and two slightly shorter distances (P1–C2 189.1, P5–C4 189.5 pm) are
observed on apposite sides of the quadrangle. Intramolecular distances involving phosphorus
atoms are given in Supplementary Table 5. The atoms P1 and P5 of the P–P unit approach the
central atom (P3) of the phosphonium cation at an average distance of 267.0 pm. This value
differs from the standard P–P bond length of (221 pm [33]) by only 46 pm. At 402.5 to 519.7
y
y
pm the shortest interionic distance between the phosphorus atom P3 and the halide (Cl , Br ),
however, is about twice as long as the uncorrected sum of the corresponding covalent radii of
the two elements involved: P…Cl 209, P…Br 224 pm [30]. Supplementary Figures 10 to 14
depict stereoscopic views of the crystal packing; no intermolecular contacts significantly
shorter than the van der Waals distances were found.
2
.4. Quantum Chemical Calculations. In the introduction of this paper the preparation of the
⊕
y
ionic compound [3,5-(Me C) -1,2,4-C P ] [AlCl ]
1
from 2,4-di-tert-butyl-3-chloro-
3
2
2
3
4
3
3
3
2,5
λ ,3λ ,5λ -triphospha-tricyclo[2.1.0.0 ]-pentane
and
aluminium(III) chloride in
dichloromethane by M. Green, Ch. A. Russell and others [19] has been discussed. Very
surprisingly, the cation of this species exhibits a pseudo square-based pyramidal framework
consisting of a diamond-shaped P C base with alternating phosphorus and carbon atoms and a
2
2
capping four-coordinate phosphorus. Due to this unusual geometry it has to be considered a 14-
electron Wadian nido-cluster. Since the phosphonium cations of compounds 1a to 1d prepared
3
in this thesis directly from 2-tert-butyl-1λ -phosphalkyne and halodiorganylphosphines in a
molar ratio of 2:1 differ from Russell’s phosphenium cation (Figure 2) not only in two
additional organyl substituents but also in the structure of the oligocyclic framework which
here can best be described quite conventually as a trigonal bipyramide, quantum chemical
calculations were performed on the hydrogen substituted cations first and on compound 1c

1
0
ACCEPTED MANUSCRIPT
subsequently in order to ascertain optimized structural data and relative energies for different
isomers.
<Figure 2>
The results of quantum chemical calculations at B3LYP/6–311+G** (Gaussian 03)
⊕
⊕
level [42] are depicted in Figures 3 and 4 for the [H P(CH) P ] and the [P(CH) P ] cation. As
2
2
2
2 2
for the phosphonium-cation (Figure 3) the conventional trigonal bipyramidal framework of
point-group C represents the absolute minimum on the potential energy surface. Remarkably,
2
v
the P–P bond is found to be shortened to 216.8 pm, whereas the adjacent P–C distances are
elongated to 191.5 pm. Both values are only slightly larger than the average bond lengths of
2
13.0 and 189.7 pm, respectively, determined from the data of compounds 1a to 1d
(Supplementary Table 6). The P–C distances 178.5 and 179.1 pm of the phosphonium group do
not differ in the calculated structure and the experimentally determined one. To our surprise the
absolute minimum in energy of the trigonal bipyramidal framework is followed by a second
one which has to be attributed to the so-called housene structure [21] of point group C showing
1
-1
a difference of + 77.9 kJ mol only.
<Figure 3>
In view of such a small value the realisation of this opened structure should be possible
with appropriate substituents at phosphorus. In order to obtain a better insight on the influence
of substituents at the bipyramidal skeleton analogous quantum chemical calculations have been
performed for the cation of compound 1c characterized by a tert-butyl group on each apical
carbon atom and an isopropyl as well as phenyl substituent at the phosphonium center P3. As a
-1
result the energy of the housene structure is found to be increased only slightly to 81.5 kJ mol .
⊕
Finally, the [H P(CH) P ] cation with a pseudo square-based pyramidal framework of point-
2
2 2
-1
group C is found to be very high in energy; it exceeds the first minimum by 246.6 kJ mol and
2
due to one imaginary frequency is considered to be a transition state only.
⊕
Quite a reverse situation is encountered for the [P(CH) P ] -cation (Figure 4). Here the
2
2
pseudo square-based pyramidal nido structure of point-group C well known from Russell’s
2
v
tetrachloroaluminate(III) [19] is found to be the only minimum on the potential energy surface.
Calculated P–P and P–C bond lengths compare very well with the average of experimentally
determined data. A phosphenium cation with a trigonal-bipyramidal framework of point-group
-1
C is higher in energy by 35.7 kJ mol only but due to one imaginary frequency it is the
2
v
structure of a transition state. The opened housene structure corresponds neither to a minimum
nor a saddle point on the potential energy surface.
<Figure 4>
As illustrated by the representations of molecular orbitals (Figure 5), in the pseudo
⊕
square-based pyramidal nido structure of the [P(CH) P ] cation featuring point group C all
2
2
2v
p-orbitals of the apical four-coordinate phosphorus atom are used to form two P–C and two P–
P bonds. When, however, two hydrogen atoms are added to the apical phosphorus atom of this
⊕
nido structure, the symmetry of the resulting [H P(CH) P ] cation is lowered to point group C
2
2
2
2
(Figure 2) and less p-orbitals are available to form two P–C and two P–P bonds. Quite evidently, a
substantial part of these p-orbitals at the apical but now six-coordinate phosphorus atom are
⊕
applied for the P–H bonds of PH unit; as a consequence, the energy of such a [H P(CH) P ]
2
2
2 2
cation increases and the nido structure becomes less stable.
Since a straightforward interpretation of the bonding situation can be achieved on the
theoretical basis of the Wadian rules [43] the difference in the ground state structures of the
⊕
⊕
phosphenium cation [P(CH) P ] and the phosphonium cation [H P(CH) P ] is only at first
2
2
2
2 2
sight surprising. In clusters which obey these rules the skeleton atoms are supposed to be sp-
hybridized with one of the two sp-hybrid orbitals pointing inwards to the center and the second
one being aligned outwards in the opposite direction. The two remaining p-orbitals overlap
with analogous orbitals of adjacent skeleton atoms and form the so-called surface orbitals. With
⊕
a pseudo square-based pyramidal structure and one vertex removed the [P(CH) P ] cation
2
2

1
1
ACCEPTED MANUSCRIPT
belongs to the group of 14-electron nido-clusters. This arrangement of atoms enables the apical
phosphorus atom of the phosphenium cation to increase its coordination number from two to
four and to form two P–C and two P–P bonds which, however, are supposed to be somewhat
weaker than conventional bonds. On the left side of Figure 5, the five highest occupied
molecular orbitals (HOMOs) and the lowest unoccupied molecular orbital (LUMO) are shown;
the contributions of different surface orbitals as well as of the sp-hybrid orbital which is aligned
outwards, are clearly discernible.
For comparison the five highest occupied molecular orbitals and the lowest unoccupied
⊕
molecular orbital of the phosphonium cation [H P(CH) P ] which shows an analogous pseudo
2
2 2
square-based pyramidal nido-structure, are also presented on the left side of Figure 5. Since this
isomer refers to a transition state only, any further discussion may be renounced. As for the
conventional trigonal bipyramidal ground state structure one the right side of Figure 5 the
phosphorus atom of the phosphonium cation is now located in the center of a strongly distorted
tetrahedron. Consequently, the sp-hybridisation of all skeleton atoms characterizing the
phosphenium cation showing the pseudo square-based pyramidal nido structure, has to be
3
abandoned and changes towards sp for all four-coordinate atoms. Since now the two remaining
p-orbitals of an sp-hybridisation are no longer available, the construction of surface-orbitals
becomes impossible and conventional two-electron two-center bonds are formed. Remarkably,
3
3
an analogous structural change is observed, when the 1λ ,3λ -diphosphacyclobutadienyl
4
t
2
germanium compound Ge(η -P C Bu ) with a divalent germanium atom is oxidized with
2
2
iodine to give an oligocycle which contains a GeI -group [19, 44]. As before, the five highest
2
occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbital (LUMO)
⊕
of the phosphenium cation [P(CH) P ] featuring an analogous trigonal bipyramidal structure
2
2
are presented on the right side of Figure 5. Again this isomer refers to a transition state;
therefore, a further discussion is considered to be unnecessary. The optimized Cartesian
Coordinates and Total Energies [Hartree] for all species reported of this paper could be also
found in Supplementary Table 7.
<Figure 5>
3
. Experimental Section
3
.1. General Considerations. All detailes about chemicals, materials, solvents, instruments,
techniques [45-48], and software programs used to solve crystal structures [49-51] used in this
work could be found in Supplememntary Information attached in a separate file with this
research article.
3
.2.Preparation and analytical characterization of Tris(trimethylsilyl)phosphine, [2,2-
Dimethyl-1-(trimethylsiloxy)propylidene]trimethylsilylphosphine, 2,2-
3
Dimethylpropylidynephosphine (2-tert-butyl-1λ -phosphaalkyne), Bromodiphenylphosphine,
and Chlorophenylisopropylphosphine. A detailed synthetic methods used to prepare these
starting chemical compounds and their analytical characterization were reported in
Supplementary Informations attached with this article.
3
3
3
.3. Preparation and analytical characterization of 2,4-Di-tert-butyl-3,3-diorganyl-1λ ,5λ -
2
,5
diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane halides.
3
3
2,5
3
.3.1. 2,4-Di-tert-butyl-3,3-dimethyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane chloride (1a).
3
1
A solution of chlorodimethylphosphine (0.24g, 2.50 mmol, δ P{H} = + 96.0 ppm in C D ) in
6
6
cyclopentane (10 mL) was added dropwise to a stirred solution (0.51 g, 5.1 mmol) in
3
cyclopentane (10 mL) of 2-tert-butyl-1λ -phosphaalkyne at –70 °C over a period of 30 minutes.
When the reaction mixture had been allowed to warm up to room temperature, stirring was
continued for four days. The solution slowly turned yellow-brown, and a colourless solid

1
2
ACCEPTED MANUSCRIPT
precipitated. Without filtration solvent was removed under reduced pressure at room
temperature to give the crude product as a yellow-brown solid. The residue was dried under
vacuum for several hours, and then 10 mL of toluene was added to the residue and the mixture
refluxed with stirring for 4 hours, after which the mixture changed colour from yellow-brown
to yellow-orange. The mixture was then allowed to settle overnight in a refrigerator at 4°C and
then the yellow-orange solution was removed by a pipette, and the residue was dried under
vacuum for several hours. Colourless crystals were obtained by recrystallisation (25 °C/–60 °C,
3
-4 weeks) from dichloromethane (10 mL). The crystals were dried several times under
–
3
vacuum at 10 mbar and then the compound was isolated in 77% yield (0.6 g, 1.91 mmol).
Melting point: 157°C (dec.). Elemental analysis (Supplementary Table 8):
C H ClP •0.2CH Cl ; calc.: C 46.71%; H 7.84%; Cl 15.82%; P 29.62%, found: C 45.96%; H
1
2
24
3
2
2
3
1
1
8
.37%; Cl 15.59%; P 28.81%, NMR (solution in CDCl ): P{ H} (101.256 MHz): δ = –264.07
3
2
2
1
ppm (d, J
=10.81 Hz; P1/P5), δ = 104.02 ppm (t, J
= 10.81 Hz; P3), H
(
P1/P5,P3)
(P1/P5,P3)
2
(250.133 MHz): δ = 1.02 ppm (s, H C–C–C–P3/P1,P5; 18H), δ = 3.08 ppm (d, J
=112.85
3
(H,P3)
1
3
1
Hz; H C–P3; 6H), δ = 5.27 ppm (s; CH Cl ). C{ H} (62.896 MHz): δ = 18.7 ppm (dt, J
(C,P3)
3
2
2
3
=
32.89 Hz, J
= 4.89 Hz; H C–P3), δ = 30.12 ppm (pseudo-quintet–equal to dt,
(
C,P1 and P5)
3
3
3
2
J(
C,P3)
= 5.1 Hz, J
(C,P1 and P5)
= 2.42 Hz; H C–C–C–P3/P1 and P5), δ = 31.69 ppm (t, J
3
(C,P1 and
1
1
=
4.83 Hz; H C–C–C–P3/P1 and P5), δ = 48.11 ppm (dt, J
= 59.51 Hz, J
(C,P1 and P5)
=
P5)
3
(C,P3)
4
2.09 Hz; H C–C–C–P3//P1 and P5), δ = 53.38 ppm (s; CH Cl ). IR (Nujol mull between CsBr
3 2 2
~
-1
disks;
ν [cm ]): 870(m), 814(w,b), 722(vs), 698(m), 637(mw), 565(w), 534(w), 457(w, b),
~
-1
4
8
3
12(m(w)). Raman (crystalline solid in glass capillary; ν [cm ]): 940(vw), 932(w(m)),
71(mw), 815m(w), 699(mw), 697(mw), 637(mw), 611(w), 568(vs), 534(m(w), 412m(s),
96m(w).
3
3
2,5
3
.3.2. 2,4-Di-tert-butyl-3,3-diethyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane chloride (1b).
A similar procedure to that described for 1a was used here, except that chlorodiethylphosphine
3
1
(0.31 g, 2.5 mmol,
δ
P{H} = + 118.5 ppm in C D ) was employed instead of
6 6
chlorodimethylphosphine. Colourless crystals were obtained by recrystallisation (25 °C/–60 °C;
–
3
3
-4 weeks) from dichloromethane. The crystals were dried several times under vacuum at 10
mbar and then the compound was isolated in 74% yield (0.6 g, 1.85 mmol). Melting point: 168
C (dec.). Elemental analysis (Supplementary Table 9): C H ClP , calc.: C 51.78%; H 8.69%;
°
1
4
28
3
Cl 10.92%; P 28.61%, found: C 51.51%; H 8.42%; Cl 10.50%; P 28.00%. NMR (solution in
3
1
1
2
CDCl3): P{ H} (101.256 MHz):
δ
H
= –286.52 ppm (d, J
= 1.5 Hz; P1
/
P5),
= 1.03 ppm (s, H3C–C–C–P3/P1, P5;
=17.60 Hz; H3C–CH –P3; 6H), = 3.43 ppm
= 5.08 ppm (s; CH2Cl ) .
δ = 119.50
(P1/P5,P3)
2
1
ppm (t, J
= 1.5 Hz; P3).
P1/P5,P3)
(250.133 MHz): δ
(
3
3
1
8H),
δ
= 1.63 ppm (dt, J
= 7.43 Hz, J
δ
(H,H)
(H,P3)
2
3
2
(
dq, J
= 7.43 Hz, J
=11.82 Hz; H C–CH2–P3; 4H),
δ
(
H,H)
(H, P3)
3
2
1
3
1
2
4
C{ H} (100.614MHz):
P3//P1 and P5), = 26.59 ppm (dt, J
and P5),
H3 –C–C–P3//P1 and P5),
δ
= 8.84 ppm (dt, J
= 5.72 Hz, J
= 2.86 Hz; H3
C–CH2–
(
C,P3)
(C,P1 and P5)
1
3
δ
= 26.91 Hz, J
= 3.82 Hz; H C–
CH –P3//P1
2
(C,P3)
(C,P1 and P5)
3
3
3
δ
= 30.30 ppm (pseudo-quintet–equal to dt, J
= 5.09 Hz, J
= 2.65 Hz;
(C,P1 and P5)
(C,P3)
2
C
δ
= 31.47 ppm (t, J
= 4.93 Hz; H C–
C–C–P1 and P5),
δ
=
=
(C,P1 and P5)
3
1
1
4
5
8
0.82 ppm (dt, J
3.29 ppm (s;
= 52.45 Hz, J
= 41.80 Hz; H C–C–
H Cl ), IR (Nujol mull between CsBr disks;
C
–P3//P1 and P5), δ
(C,P3)
(C,P1 and P5)
3
~
-1
C
ν
[cm ]): 933(w), 871(s),
2
2
14(vw), 721(m(w)), 714(ms), 706(ms), 633(mw), 568(vw),m 528(w, b), 409(mw). Raman
crystalline solid in glass capillary;
~
-1
(
ν
[cm ]): 934(mw,b), 929(mw,b), 872(mw), 831(mw),
8
14(m(w)), 726(vs), 709(s), 694(s(vs)), 633(mw), 569(vs), 534(m(w)), 384(s).
3
3
2,5
3
.3.3. 2,4-Di-tert-butyl-3-isopropyl-3-phenyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane
chloride (1c). A similar procedure to that described for 1a was used here, except that
3
1
chloroisopropylphenylphosphine (0.47 g, 2.5 mmol,
δ
P{H} = + 102.55 ppm in C D ) was
6 6
employed instead of chlorodimethylphosphine. Colourless crystals were obtained by

1
3
ACCEPTED MANUSCRIPT
recrystallisation (25 °C/–13 °C; one week) from dichloromethane. The crystals were dried
–
3
several times under vacuum at 10 mbar and then the compound was isolated in 79% yield
0.76 g, 1.96 mmol). Melting point: 184 °C (dec.). Elemental analysis (Supplementary Table
0): C H ClP , calc.: C 59.00%; H 7.82%; Cl 9.17%; P 24.02%, found: C 58.91%; H 8.09%;
(
1
1
9
30
3
3
1
1
Cl 8.92%; P 23.96%. NMR (solution in CDCl3), P{ H} (101.256 MHz):
δ
= –289.57 ppm (d)
= 172.2 Hz, P1 or P5), = 110.63
= 1.60 ppm
= 4.90–5.05 ppm (m, H C–CH–
1
1
J(P1,P5) = 172.2 Hz, P1 or P5),
δ
= –278.28 ppm (d) J
= 0.84 ppm (s, H3C–C–C–P1 and P5; 18H),
= 17.90 Hz; H3C–CH–P3; 6H),
δ
(P1,P5)
1
Hz (s; P3).
H
(250.1329 MHz):
δ
δ
3
3
(dd, J
= 6.88 Hz, J
δ
(H,H)
(H,P3)
3
P3; 1H),
m, (phenyl); 2H), C{ H} (50.323 MHz):
.03 Hz; H3 –CH–P3//P1 or P5), = 30.52 ppm (pseudo-quintet–equal to dt, J
δ
= 5.17 ppm (s, CH2Cl2),
δ
= 7.54–7.72 ppm (m,
H(phenyl); 3H), δ = 8.56–8.65 ppm
1
3
1
2
4
(
H
δ
= 17.80 ppm (dd, J(
= 4.6 Hz, J
=
C,P3)
(C,P1 or P5)
3
2
C
δ
= 5.60 Hz,
(C,P3)
3
1
J(C,P1 and P5) = 3.05 Hz; H3
C
–C–C–P3//P1 and P5),
δ
= 31.00 ppm (ddd, J
= 23.90 Hz,
(C,P3)
3
3
2
J(
C,P1 or P5)
= 5.09 Hz, J
(C,P1 or P5)
= 1.53 Hz; H C–
3
C
H–P3//P1, P5),
δ
= 31.48 ppm (t, J
(C,P1 and
1
1
=
4.58 Hz; H C–
C
–C–P1 and P5),
–P3//P1 and P5),3 = 53.31 ppm (s;
= 6.23 Hz, J
δ
= 42.93 ppm (dt, J
= 51.54 Hz, J = 41.71
(C,P1 and P5)
P5)
3
(C,P3)
1
Hz; H C–C–
3.28 Hz, J
C
δ
C
H Cl ),
δ
δ
= 124.82 ppm (ddd, J
= 130.21 (d, J
=
(C,P3)
3
2
2
3
3
5
= 2.05 Hz; ipso
-C
),
= 8.91 Hz, J = 4.33 Hz; ortho
(C, P1 or P5)
= 10.68 Hz;
(C,P3)
-
(C,P1 or P5)
(C,P1 or P5)
2
4
meta
ppm (d, J
8
5
9
5
-
C
),
δ
(
= 132.64 ppm (dd, J
C
),
δ
= 135.27
[cm ]): 994(m),
80(ms), 857(s-vs), 814(mw), 713(mw), 708(w), 703(w), 674(s), 630(ms), 575(m), 560(m),
(C,P3)
4
~
-1
= 3.06 Hz; para-C). IR (Nujol mull between CsBr disks; ν
C,P3)
~
-1
32(mw), 512(m), 505(mw), 422(mw). Raman (crystalline solid in glass capillary;
ν [cm ]):
93(s), 931(mw), 883(vw), 859(mw), 825((m)w), 813(mw), 674(ms,b), 629(mw), 612(m),
76(vs), 561(ms), 532(mw), 510(s), 487(m), 422(ms).
3
3
2,5
3
.3.4. 2,4-Di-tert-butyl-3,3-diphenyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane chloride
(
1d.1). A similar procedure to that described for 1a was used here, except that
3
1
chlorodiphenylphosphine (0.45 g, 2.5 mmol,
δ P{H} = + 82.80 ppm in C D ) was employed
6 6
instead of chlorodimethylphosphine. Colourless crystals were obtained by recrystallisation (25
C/–13 °C; one week) from dichloromethane. The crystals were dried several times under
°
–
3
vacuum at 10 mbar and then the compound was isolated in 80% yield (0.80 g, 1.90 mmol).
Melting point: 196 °C. Elemental analysis (Supplementary Tables 11): C H ClP , calc.: C
22
28
3
6
2.80%; H 6.71%; Cl 8.42%; P 22.08%, found: C 63.16%; H 6.80%; Cl 8.21%; P 21.62 %.
3
1
1
2
NMR (solution in CDCl ); P{ H} (101.256 MHz):
δ
= –281.93 ppm (d, J
= 4.14 Hz;
(P1/P5,P3)
3
2
1
P1
P3/P1, P5; 18H).
.17 ppm (m, (phenyl); 4H). C{ H} (62.896 MHz): δ
/
P5),
δ
= 85.14 (t, J
= 4.14 Hz; P3).
H
(250.133 MHz):
= 7.69–7.80 ppm (m,
= 30.38 ppm (pseudo-quintet–equal to
δ
= 0.74 ppm (s, H3C–C–C–
(
P1/P5,P3)
δ
= 5.16 ppm (s; CH2Cl2),
δ
H
(phenyl); 6H), = 7.81–
δ
1
3
1
8
H
3
3
2
dt, J
= 5.26 Hz, J
= 2.63 Hz; H3C–C–C–P3//P1 and P5), δ = 32.05 ppm (t, J
(C,P1 and P5) (C,P1
(C,P3)
1
1
=
4.74 Hz; H C–
C–C–P3//P1 and P5),
δ
= 47.59 ppm (dt, J
= 53.26 ppm (s;
= 58.23 Hz, J
(C,P3)
and P5)
3
(C,P1 and P5)
1
=
=
1
43.28Hz; H C–C–
58.58 Hz, J
32.98 ppm (d, J
C
–P3//P1 and P5),
δ
C
H Cl ),
δ
= 124.24 ppm (dt, J
(C,P3)
3
2
3
2
3
= 4.74 Hz; ipso
-C),
δ
= 130.39 (d, J
= 136.20 ppm (d, J
= 11.05 Hz; meta-C δ =
),
= 3.15 Hz; para-C). IR
(C,P3)
(
C,P1 and P5)
(C,P3)
4
2
= 9.99 Hz; ortho
-C
),
δ
(
C,P3)
~
-1
(Nujol mull between CsBr disks;
ν
[cm ]): 997(sh), 992(m), 938(w,b), 893(vvw), 895(s),
8
4
9
5
15((m)w), 726(w,b), 698(mw), 631(ms), 615(w), 588(s), 570(m), 529(w), 513(ms), 507(s-vs),
~
-1
81(ms), 407(m,b). Raman (crystalline solid in glass capillary;
ν [cm ]): 999(ms), 993(m),
39(w), 857(w-vw), 815(w), 727(vs), 709(s), 693(s), 631(w,b), 614(mw), 587(vvs), 587(vvs)?,
30(mw), 512(m), 408(mw), 405(sh).
3
3
2,5
3
.3.5. 2,4-Di-tert-butyl-3,3-diphenyl-1λ ,5λ -diphospha-3-phosphonia tricyclo[2.1.0.0 ]pentane bromide
(
1d.2). A similar procedure to that described for 1a was used here, except that
31
bromodiphenylphosphine (0.663 g, 2.50 mmol,
δ
P{H} = + 73.32 ppm in C D ) was
6 6
employed instead of chlorodimethylphosphine. Colourless crystals were obtained by

1
4
ACCEPTED MANUSCRIPT
recrystallisation (25 °C/–13 °C; one week) from dichloromethane. The crystals were dried
–
3
several times under vacuum at 10 mbar and then the compound was isolated in 73 % yield
0.85 g, 1.82 mmol). Melting point: 243 °C. Elemental analysis (Supplementary Table 12):
C H BrP •0.8 CH Cl ; calc.: C 51.36%; H 5.60%; Br 14.98%; Cl 10.6%; P 17.42%, found: C
(
2
2
28
3
2
2
3
1
1
5
1.94%; H 5.92%; Br 15.07%; Cl 9.92%; P 17.16%. NMR (solution in C D ); P{ H} (101.256
MHz):
6 6
2
2
δ
= –280.82 ppm (d, J
= 4.45 Hz; P1/P5),
δ
= 85.02 (t, J = 4.45 Hz; P3).
(P3/P1,P5)
(
P1/P5,P3)
1
H NMR (200.1323 MHz):
H2Cl2), = 7.74–7.89 ppm (m,
C{ H} (50.323 MHz): = 30.68 ppm (pseudo-quintet–equal to dt, J
2.73 Hz; H3 –C–C–P3//P1 and P5),
Hz; H C–C–C–P3//P1 and P5), = 47.95 ppm (dt, J
δ
= 0.85 ppm (s, H3C–C–C–P3/P1, P5; 18H),
δ
= 5.25 ppm (s;
C
δ
H
(phenyl); 6H), = 8.23–8.32 ppm (m, H(phenyl); 4H).
δ
1
3
1
3
3
δ
= 5.47 Hz, J
(C,P1 and
= 0.96, J = 5.06
(C,P1 and P5)
(
C,P3)
2
2
=
C
δ
= 32.38 ppm (dt, J
P5)
(C, P3)
1
1
δ
= 57.81 Hz, J
= 43.41 Hz;
= 124.60 ppm (dt, J = 58.21 Hz,
(C,P3)
3
(C,P3)
(C,P1 and P5)
1
H C–C–
C
–P3//P1 and P5),
δ
C
= 53.41 ppm (s;
C
H Cl ),
δ
3
2
2
3
3
J(C,P1 and P5) = 4.54 Hz; ipso
J(C,P3) = 10.10 Hz; ortho
between CsBr disks;
-
),
δ
= 130.62 (d, J
= 11.34 Hz; meta
-
C
), = 133.38 ppm (d,
= 3.09 Hz; para-C). IR (Nujol mull
[cm ]): 996(sh), 994(m), 942(w,b), 891(vw), 858(s,b), 814(m(w)),
δ
(C,P3)
4
2
-
C), δ = 136.31 ppm (d, J
(C,P3)
~
-1
ν
7
4
8
4
26(w,b), 698(mw), 629(ms), 615(w), 587(s), 569(m), 569(m), 527(w), 512(m), 505(mw),
~
-1
06(mb). Raman (crystalline solid in glass capillary;
ν [cm ]): 999(ms), 993(m), 935(w),
58(w), 815(w), 631(w,b), 614(mw), 587(vvs), 587(vvs), 529(mw), 513(ms), 506(vs), 480(ms),
08(mw), 406(sh).
3
3
2,5
3
.3.6. 2,4-Di-tert-butyl-3,3-diisopropyl-1λ ,5λ -diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane chloride
(
1e). A similar procedure to that described for 1a was used here, except that
3
1
chlorodiisopropylphosphine (0.381 g, 2.5 mmol,
δ
P{H} = + 134.5 ppm in C D ) was
6 6
employed instead of chlorodimethylphosphine and refrigeratoion at different temperatures did
not crystallize the oily crude product even after a long period. NMR (solution in CDCl3);
3
1
1
2
P{ H} (101.256 MHz):
δ
H
= –285.81 ppm (d, J(
= 1.3 Hz; P1
/
P5),
= 0.69 ppm (s; H3C–C–C–P3/P1,P5; 18H),
= 7.07 Hz, J = 16.3 Hz; H3C–CH–P3; 12H), = 2.9–3.2 ppm (m;
(H,P3)
δ = 130.45 ppm (t,
P1/P5,P3)
2
1
J(P3/P1,P5) = 1.3 Hz; P3).
(250.133 MHz):
δ
δ =
3
3
1
.40 ppm (dd, J
δ
(
H,H)
1
3
1
2
4
H C–C
2
Hz, J
H
–P3; 2H). C{ H} (50.323 MHz):
δ
= 17.60 ppm (dt, J
= 29.97 ppm (pseudo-quintet–equal to dt, J
–C–C–P3//P1 and P5),
= 5.2 Hz, J
(C, P1 and P5)
=
3
(C, P3)
3
.48 Hz; H3
C–CH–P3//P1 and P5),
δ
= 4.55
(C,P3)
3
2
= 3.10 Hz; H3
C
δ
= 30.36 ppm (t, J
= 5.36 Hz,
(C,P1 and P5)
(C,P1 and P5)
1
3
H C–
C
–C–P1 and P5),
P3//P1 and P5), = 37.99 ppm (dt, J(
P3//P1 and P5). IR (Nujol mull between CsBr disks;
15(mw), 710(w), 635(s), 633(mw), 576(m), 535(w), 460(w), 412(mw).
δ
= 31.65 ppm (dt, J
= 20.21 Hz, J
= 3.71 Hz; H C–
CH–
3
(C,P3)
(C,P1 and P5)
3
1
1
δ
= 45.78 Hz, J
= 41.45 Hz; H C–C–C–
C,P3)
(C,P1 and P5)
3
~
-1
ν
[cm ]): 885(m), 871(s), 815(mw),
7
4
. General Crystallographic Information
Four-circle diffractometer P2 (Syntex, Cupertino, USA) and P4 (Siemens Analytical X-ray
1
Instruments Inc., Madison, Wisconson, USA); Mo-K radiation with graphite monochromator
α
(λ = 71.073 nm); control of intensity and orientation by two measurements after a period of 98
reflections; registration of the background at the beginning and at the end of the measurement
with an overall duration equal to the time of measurement; application of the software package
program SHELXTL, version 5.10 from the company Bruker AXS Inc., Madison, Wisconsin
[
49-51] for the treatment of data, determination of structures with statistical methods and
subsequent refinements: calculation of the quality factors R1 and wR2 using measured values
with F > 4 (F ); scattering factors for the neutral atoms C, P, Cl and Br from D. T. Cromer and
σ
o
J. B. Man [52] and for the hydrogen atoms from R. F. Stewart, E. R. Davidson and W. T.
2
Simpson [53]; full-matrix least squares refinement on F ; several cycles of refinement with
complete matrix and following difference Fourier synthesis; minimizing of the function
Σw

1
5
ACCEPTED MANUSCRIPT
2
2 2
(
F – F ) . The quality factors are defined by the following formulas with m (number of
o c
reflections) and n (number of parameters):
2
∑ Fo
− F
c
∑w(
F
o
− F
c
)
R = R
1
=
wR =
2
F
o
o
2
wF
o
∑
∑
2
2
2
2
2
∑w
(
∑
F
− F
c
)
∑w
(
F
o
− F
c
)
wR
2
=
GOF =
2
2
(m − n
)
w
(F
o
)
-
23
2
2
*2
2
The anisotropic displacement parameters U (10 m ) refer to the expression: e[–2
π (a h
ij
*2
2
*2
2
*
*
*
*
*
*
U + b k U + c l U + 2b c k l U + 2a c h l U + 2 a b h k U )]; the equivalent
1
1
22
33
23
13
12
-23
2
isotropic parameters Ueq (10 m ) are calculated from the anisotropic values applying the
*
*
∗
formula Ueq = 1/3 ∑ ∑jUij a a ai.aj
(
a
is real-cell and
a
reciprocal-cell length [54].
i
i
j
Therefore the equivalent isotropic Ueq value is defined as one-third of the trace of the
orthogonalized U tensor [54]. The structures solved from the crystallographic data of the
ij
compounds 1a, 1b, 1c, 1d.1, and 1d.2 (Figure 1) were deposited to the Cambridge
Crystallographic Data Centre (CCDC) under numbers 1532759, 1532752, 1532757, 1532765,
and 1532766, respectively.
5
. Conclusions
3
We reported the reaction between 2-tert-butyl-1λ -phosphaalkyne, and various
halodiorganylphosphines to study the influence of alkyl and aryl groups on reaction routes and
molecular structures. The structures of all compounds were found to be ionic with separated
cations and halide anions and to contain one or two molecules of CH Cl per formula unit.
2
2
Most of the mean bond lengths and angles are as expected; the P–P distance of 213.0 pm,
however, is found to be shortened and the P–C distance of 189.7 pm elongated with respect to
2
standard values. A transannular nucleophilic attack of the R`R``P group at the sp -hybridised
3
3
carbon atom of the 1,2-dihydro-1λ ,3λ -diphosphete is expected to occur. Its stabilization is
achieved by elimination of a halide anion to form the phosphonium cations. These salts differ
from Russell’s phosphenium cation not only in two additional organyl substituents, but also in
the structure of the oligocyclic framework which here can best be described quite conventually
as a trigonal bipyramide. Quantum chemical calculations were performed on the hydrogen
substituted cations to ascertain optimized structural data and relative energies for different
isomers. Surprising, the absolute minimum in energy of the trigonal bipyramidal framework
with point-group C2v is followed by a second one which must be attributed to the so-called
-1
housene structure of point group C1 showing a difference of only +77.9 kJ mol of phosphonium
⊕
cation ([H P(CH) P ] ). The pseudo square-based pyramidal nido structure with point-group
2
2 2
C2v is found to be the only minimum on the potential energy surface of phosphenium cation
⊕
[
P(CH) P ] .
2 2
6
. Supplementary Information
Supplementary Experimental Subsections, Suppelemntary Tables (1 to 12) and Supplementary
Figures (1 to 14) could be found in a separate file attached with this research article.
7
. Acknowledgement
Authors wishe to thanks for Prof. Dr . Mark. Niemeyer, Anorganische und Analytische Chemie,
Universität Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany for help us in running
quantum chemical calculations
. This paper is based on a one chapter of the Ph.D dissertation
(
ISBN 978-3-86186-549-0) of the first author and a part of his postdoctoral research work done

1
6
ACCEPTED MANUSCRIPT
in the laboratory of Professor Gerd Becker at Institut für Anorganische Chemie, Universität
Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
8
. References
[
[
[
1] G. Becker, G. Gresser, W. Uhl, Z. Naturforsch., 36b (1981) 16.
2] G. Becker, H. Schmidt, G. Uhl, W. Uhl, Inorg. Synth., 27 (1990) 243.
3] H. H. Karsch, F. Bienlein, T. Rupprich, F. Uhlig, E. Herrmann and M. Scheer in:
Synthetic Methods of Organometallic and Inorganic Chemistry (Hrsg.: W.A. Herrmann),
Vol. 3: Phosphorus, Arsenic, Antimony, and Bismuth, edited by H. H. Karsch, Georg
Thieme Verlag, Stuttgart. (1996) 58.
[
[
[
4] G. Becker, W. Becker, R. Knebl, H. Schmidt, U. Weeber, M. Westerhausen, Nova Acta
Leopoldina Neue Folge Nr. 264., 59 (1985) 55.
5] G. Becker, W. Becker, R. Knebl, H. Schmidt, A. Hildenbrand and M. Westerhausen.
Phosphorus Sulfur., 30 (1987) 349.
6] G. Becker, J. Dautel, R. Knebl, R. Löw, R. Ruf, J. Schüler, in W. Siebert (ed.), Advances
in Boron Chemistry (Proceedings of the Ninth International Meeting on Boron Chemistry),
Special Publication No. 201, The Royal Society of Chemistry, Cambridge. (1997) 248.
[
[
7] R. Knebl, Ph.D. Disseration, 2,2-Dimethylpropylidinphosphan und Halogenide der
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2
0
ACCEPTED MANUSCRIPT
Scheme 1. Formation of phosphorus oligocyclic cage compounds.

2
1
ACCEPTED MANUSCRIPT
tBu
tBu
tBu
C
P
tBu
X
2
C
+
P
R`
C
C
R`
R`
P
P
P
P
P
P
R``
R"
R'
P
P
C
R``
C
P
X
R``
C
tBu
X
tBu
tBu
X
tBu = tert-butyl
3
3
1λ , 3λ -diphosphete
postulated intermediate
1
1
1
1
1
1
1
a: R' = R" = methyl, X = Cl;
b: R' = R" = ethyl, X = Cl;
c: R' = Phenyl, R" = isopropyl, X = Cl;
d.1: R' = R" = phenyl, X = Cl;
d.2: R' = R" = phenyl, X = Br;
e: R' = R" = isopropyl.
3
3
Scheme 2. Preparation and Postulated Mechanism of 2,4-Di-tert-butyl-3,3-diorganyl-1λ ,5λ -
2
,5
diphospha-3-phosphonia-tricyclo[2.1.0.0 ]pentane halides.

2
2
ACCEPTED MANUSCRIPT
Scheme 3. Two different (8-dimethylamino-naphth-1-yl)(dialkyl)phenylphosphonium iodides
A1 and A2 [24].

2
3
ACCEPTED MANUSCRIPT
1
a•CH Cl (1/1)
1b•CH Cl (2/4)
2 2
2
2
H321
1
c•CH Cl (1/2)
1d.1•CH Cl (1/1)
2 2
2
2
1d.2•CH Cl (1/1)
2 2
Figure 1. Structures of the cation and anion in the co-crystallisates 1a – 1d• x CH Cl . Thermal ellipsoids are at
2
2
3
0% probability. Hydrogen atoms and the co-crystallizing dichloromethane molecules have been omitted for
clarity; only the CH– hydrogen atom of the isopropyl group is shown.

2
4
ACCEPTED MANUSCRIPT
Figure 2. Structures of the cationic 14-electron Wadian nido-cluster and the trigonal
bipyramidal skeleton in the cations of compounds 1a to 1d.

2
5
ACCEPTED MANUSCRIPT
a)
C2v
178.5
191.5
–
1
0
kJ mol
2
16.8
(
N
=0)
imag
b)
C1
181.9
2
26.7
189.9
190.0
–
1
181.4
+
77.9 kJ mol
169.9
(
N
=0)
imag
c)
C2
2
05.4
2
26.9
179.0
–
1
+
246.6 kJ mol
(
N
=1)
183.8
imag
Figure 3. Optimized geometries and relative energies (B3LYP/6-311+G**, Gaussian 03) of the
⊕
[
H P(CH) P ] cation a) conventional trigonal bipyramidal structure; b) opened housene
2 2 2
structure; c) pseudo square-based-pyramidal structure.

2
6
ACCEPTED MANUSCRIPT
a)
C2v
2
28.1
2
00.3
0
kJ mol–1
(
Nimag =0)
181.3
b)
C2v
177.6
2
13.1
192.5
–
1
+
35.7 kJ mol
(
N
=1)
imag
Figure 4. Optimized geometries and relative energies (B3LYP/6-311+G**, Gaussian 03) of the
⊕
[
P(CH) P ] cation. a) pseudo square-based-pyramidal nido-structure (average bond lengths of
2 2
⊕
⊕
Russell’s tetrachloroaluminate(III) [19]: P–C 180.4, P –C 199.9, P –P 224.5 pm); b) trigonal
bipyramidal structure.

ACCEPTED MANUSCRIPT
27
Square-based pyramidal
Square-based pyramidal
Trigonal bipyramidal
Trigonal bipyramidal
⊕
⊕
⊕
⊕
MO nido-[P(CH) P ] (C )
nido-[H P(CH) P ] (C )
[P(CH) P ] (C )
[H P(CH) P ] (C )
2
2
2v
2
2
2
2
2
2
2v
2
2
2
2v
LUMO
HOMO
HOMO-1

ACCEPTED MANUSCRIPT
28
Square-based pyramidal
Square-based pyramidal
Trigonal bipyramidal
Trigonal bipyramidal
⊕
⊕
⊕
⊕
MO nido-[P(CH) P ] (C )
nido-[H P(CH) P ] (C )
[P(CH) P ] (C )
[H P(CH) P ] (C )
2
2
2v
2
2
2
2
2
2
2v
2
2
2
2v
HOMO-2
HOMO-3
HOMO-4
⊕
⊕
Figure 5. Molecular orbitals of the square-based pyramidal nido structures of the [P(CH) P ] and [H P(CH) P ] cations (left) and the trigonal
2
2
2
2 2
⊕
⊕
bipyramidal structures of the [P(CH) P ] and [H P(CH) P ] cations (right)
2
2
2
2 2