Silver tetrakis(hexafluoroisopropoxy)aluminate as hexafluoroisopropyl transfer reagent for the chlorine/hexafluoroisopropyl exchange in imino phosphanes

Article abstract of DOI:10.1016/j.jorganchem.2009.11.014

Treating 1,3-dichloro-2,4-bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazane, [HypNPCl]₂ ((Me₃Si)₃Si = Hyp), or N-(2,4,6-tri-tert-butylphenyl)imino(chloro)phosphane, Mes^*-N{double bond, long}P-Cl (Mes^* = 2,4,6-tri-tert-butylphenyl), with Ag[Al(OCH(CF₃)₂)₄] leads to the abstraction of [OCH(CF₃)₂]^- from the counter ion [Al(OCH(CF₃)₂)₄]^- in a formal Lewis acid/Lewis base reaction. The final products Hyp₂N₂P₂(Cl)(OCH(CF₃)₂), Mes^*-N{double bond, long}P-OCH(CF₃)₂ and the dimeric Lewis acid [Al(OCH(CF₃)₂)₃]₂ have been characterized by means of X-ray analysis.

Full text of DOI:10.1016/j.jorganchem.2009.11.014

Journal of Organometallic Chemistry 695 (2010) 1006–1011
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Silver tetrakis(hexafluoroisopropoxy)aluminate as hexafluoroisopropyl transfer
reagent for the chlorine/hexafluoroisopropyl exchange in imino phosphanes
a
Marcus Kuprat a, René Kuzora a, Mathias Lehmann a, Axel Schulz a,b, , Alexander Villinger ,
*
Ronald Wustrack a
a Institut für Chemie Abt. Anorganische Chemie, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
b Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Treating 1,3-dichloro-2,4-bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazane, [HypNPCl]2 ((Me3Si)3Si =
Hyp), or N-(2,4,6-tri-tert-butylphenyl)imino(chloro)phosphane, Mes*–N@P–Cl (Mes* = 2,4,6-tri-tert-buty-
lphenyl), with Ag[Al(OCH(CF3)2)4] leads to the abstraction of [OCH(CF3)2]À from the counter ion
Received 30 September 2009
Received in revised form 12 November 2009
Accepted 13 November 2009
Available online 18 November 2009
[Al(OCH(CF3)2)4]À in
a formal Lewis acid/Lewis base reaction. The final products Hyp2N2P2(Cl)-
(OCH(CF3)2), Mes*–N@P–OCH(CF3)2 and the dimeric Lewis acid [Al(OCH(CF3)2)3]2 have been character-
ized by means of X-ray analysis.
On the occasion of the 75th birthday of Dr.
C.N.R. Rao.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Hypersilyl
Lewis acid
PN chemistry
Structure
Weakly coordinating anions
1. Introduction
cation as tetrachloridoaluminate salt [Mes*–N„P][AlCl4] was first
prepared by Niecke et al. by means of chloride abstraction from
In the last two decades 1,3-dichloro-cyclo-diphosphadiazanes
[RNPCl]2 with several groups R have been intensively studied, as
they are used as potential starting materials for e.g., ring-opening
and transformation reactions, oligomerization and polymerization
[1–4] or the preparation of macrocycles, polymers, main-group
complexes and the generation of cyclic binary PN cations [5,6].
Only little is known of 1-chloro-cyclo-diphosphadiazenium salts
of the type [R2N2P2Cl]+ [6a]. These cyclic phosphorus–nitrogen
cations have been synthesized by chloride abstraction from kinet-
ically stabilized 1,3-dichloro-cyclo-diphosphadiazanes. The mon-
ochlorodiphosphadiazenium cation ([R2N2P2Cl]+, R = tBu) was first
observed by Cowley et al. [7] in the reaction of the corresponding
cyclo-diphosphadiazane with AlCl3. Burford et al. [8] assumed 1-
halo-2,4-di(aryl)-cyclo-1,3-dipnicta-2,4-diazenium cations as reac-
tive intermediate species in the reaction of [RNPX]2 (R = 2,6-
dimethylphenyl, 2,6-diisopropylphenyl; X = Cl, Br) with GaX3,
which led to trimeric species [RNPX]3 via GaX3 induced heterocycle
expansion [9]. The supermesityl substituted iminophosphenium
Mes*–N@P–Cl with AlCl3 as Lewis acid [15].
Recent work in our group [10] has focused on a new strategy for
the generation and stabilization of cyclic and acyclic P(III)–N cat-
ions utilizing bulky groups such as the hypersilyl ((Me3Si)3Si = hyp)
[11,12] and the supermesityl group (Mes* = 2,4,6-tri-tert-butyl-
phenyl). For this reason we have studied a number of differently
substituted 1,3-dichloro-cyclo-diphosphadiazanes [RNPCl]2. More-
over, since Michaelis and Schroeter [13] discovered the first exam-
ple of a cyclo-diphosphadiazane, it is known, that there is a formal
monomer–dimer equilibrium depending on the organic group R:
2 RNPCl ¡ [RNPCl]2. Burford et al. assumed that dependent upon
steric strain in derivatives of [RPNR]2 the dimer can be destabilized
with respect to the monomer [8,9,14]. The intriguing equilibrium is
best illustrated by the fact, that Mes*–N@P–Cl is observed as an
iminophosphane monomer in the solid state [15], while slightly
smaller substituents such as 2,6-diisopropylphenyl or the m-ter-
phenyl allow dimerization [6,14].
To be able to isolate reactive PN+ ions two things need to be
considered: (i) A bulky group should be used to kinetically protect
the cation as well as (ii) a weakly coordinating anion, which should
be chemically robust [16]. Here we report on attempts to isolate
[Mes*–N„P]+ and [Hyp2N2P2Cl]+ ions as tetrakis(hexafluoro-
isopropoxy)aluminate salts, which led unintentionally to the
* Corresponding author. Address: Institut für Chemie Abt. Anorganische Chemie,
Albert-Einstein-Straße 3a, 18059 Rostock, Germany. Fax: +49 381 4986382.
E-mail address: axel.schulz@uni-rostock.de (A. Schulz).
URL: http://www.chemie.uni-rostock.de/ac/schulz (A. Schulz).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.11.014

M. Kuprat et al. / Journal of Organometallic Chemistry 695 (2010) 1006–1011
1007
Ag[Al(OCH(CF3)2)4]
Mes*NPOCH(CF3)2
[Al(OCH(CF3)2)3]2 + AgCl
Mes*NPCl
+ 1/2
CH2Cl2
-30 °C
1
2
3
Scheme 1. Synthesis of N-(2,4,6-tri-tert-butylphenyl)imino-(1,1,1,3,3,3-hexafluoro-2-propoxy)phosphane (2).
1) n-BuLi
discovery of a new hexafluoroisopropyl transfer reaction. The
decomposition of the aluminate anion [Al(OCH(CF3)2)4]À which is
accompanied by the formation of the free acid [Al(OCH(CF3)2)3]2
clearly demonstrates the reactivity of weakly coordinating anions
and illustrates the limitations of the use of such weakly coordinat-
ing anions in the presence of highly electrophilic cations.
2) Mes*NPCl
HOCH(CF3)2
Mes*NPOCH(CF3)2
+ LiCl + n-BuH
Et2O
0 °C
2
Scheme 2. Direct synthesis of N-(2,4,6-tri-tert-butylphenyl)imino-(1,1,1,3,3,3-
hexafluoro-2-propoxy)-phosphane (2).
2. Results and discussion
2.1. Reaction of Mes*–N@P–Cl with Ag[Al(OCH(CF3)2)4]
and addition of Mes*–N@P–Cl in diethyl ether at 0 °C as illustrated
in Scheme 2.
The stabilization of highly electrophilic cations such as [R–NP]+
is commonly achieved by replacing the small and strongly coordi-
nating counter ion by a large and weakly coordinating anion (wca)
such as tetrakis(hexafluoroisopropoxy)aluminate [16]. The easiest
way to introduce wca’s is to treat R–N@P–Cl with a wca containing
silver salt (see Scheme 1).
2.2. Reaction of [HypNPCl]2 with Ag[Al(OCH(CF3)2)4]
The dimer [HypNPCl]2 is stable in CH2Cl2 at ambient tempera-
ture for several days as shown by 31P NMR studies [d(31P) =
257.0 ppm] and does not dissociate into monomeric Hyp–N@P–Cl
[6b]. However, after adding Ag[Al(OCH(CF3)2)4] the NMR spectra
showed rapid, quantitative formation of a new phosphorus species
within 10 min at ambient temperatures. Furthermore, the colour-
less solution of the beginning turned dark red. NMR spectroscopic
investigations revealed the formation of the 1-chloro-2,4-
bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazenium ion [Hyp2-
N2P2Cl]+, which is stable in solution for more than 12 h as shown
by NMR spectroscopy. Removal of solvent in vacuo yields a red
oil, in which the slow formation of white crystals was observed.
X-ray studies revealed the formation of 1-chloro-3-(1,1,1,3,3,3-
hexafluoro-2-propoxy)-2,4-bis[tris(trimethylsilyl)silyl]-cyclo-dip-
hosphadiazane, [HypNPX]2 (X = Cl and OCH(CF3)2) (4), and again
the dimer of the free Lewis acid 3 (Scheme 3). It can be assumed,
that upon removal of CH2Cl2, the reactive PN+ cation approaches
Supermesityl iminochlorophosphane, Mes*–N@P–Cl (1), which
does not dimerize to give a 1,3-dichloro-cyclo-diphosphadiazane,
is easily prepared in the reaction of supermesityl amine Mes*–
NH2 with PCl3 followed by a basic work-up [15,17]. Addition of
silver tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)aluminate, Ag[A-
l(OCH(CF3)2)4], to a solution of Mes*–N@P–Cl in CH2Cl2 should
result in the formation of a solvated [Mes*–N„P]+ ion with
[Al(OCH(CF3)2)4]À as counter ion as well as in the precipitation
of AgCl. However, instead we observed the formation of N-(2,4,6-
tri-tert-butylphenyl)imino-(1,1,1,3,3,3-hexafluoro-2-propoxy)phos
-phane, Mes*–N@P–OCH(CF3)2 (2) and bis[tris(1,1,1,3,3,3-hexa-
fluoro-2-propoxy)aluminium], [Al(OCH(CF3)2)3]2 (3), respectively.
Obviously, the driving force of the formation of 2 is the instability
of the anion [Al(OCH(CF3)2)4]À towards strong electrophilic ions
such as [Mes*–N„P]+. Thus [Mes*–N„P]+ seems to be the stronger
Lewis acid compared to [Al(OCH(CF3)2)3]2 resulting in the abstrac-
tion of [OCH(CF3)2]À from the [Al(OCH(CF3)2)4]À ion finally yielding
2 and 3. The whole process can formally be regarded as a Lewis
acid/Lewis base reaction, which is triggered by the precipitation
of AgCl and the formation of the free electronically unstabilized
[Mes*–N„P]+ ion representing the stronger Lewis acid. Krossing
et al. have already shown in a series of papers [18] that wca’s such
as [Al(ORF)4]À decompose in the presence of very electrophile cat-
ions such as P2X5+ (X = Br, I) or Ag+/PCl3 or SiCl4 mixtures leading to
fluoride bridged [(RFO)3Al–F–Al(ORF)3]À anions [18b,c]. They al-
ready mentioned the [ORF]À abstraction, triggered by the action
of oxophilic cations such as P2Cl5+, results in the intermediate for-
mation of RFO–PCl2 [18d], while the generated free Lewis acid
Al(ORF)3 then abstracts a FÀ ion from RFO–PCl2 finally forming
the bridged anion [(RFO)3Al–F–Al(ORF)3]À. In case of the reaction
of Mes*–N@P–Cl with Ag[Al(OCH(CF3)2)4], it was possible to isolate
the free acid and to stop the whole decomposition process prior to
FÀ abstraction and formation of the bridged ion.
[Al(OCH(CF3)2)4]
P
Ag[Al(OCH(CF3)2)4]
[HypNPCl]2
Hyp
N
N
Hyp
+ AgCl
CH2Cl2
-30 °C
P
Cl
OCH(CF3)2
P
Hyp
N
N
Hyp
[Al(OCH(CF3)2)3]2
+ 1/2
In a next series of experiments it was interesting to see if 2 can
be generated in a direct synthesis. The attempted synthesis of acid
3 from AlMe3 and HOCH(CF3)2 has already been reported by Kros-
sing et al. but was not successful [19]. Mes*–N@P–OCH(CF3)2 (2) is
readily generated in good yields (95%) upon treatment of
HOCH(CF3)2 with n-BuLi (intermediate formation of Li[OCH(CF3)2])
P
4
3
Cl
Scheme 3. Synthesis of 1-chloro-3-(1,1,1,3,3,3-hexafluoro-2-propoxy)phosphane-
2,4-bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazane (4).

1008
M. Kuprat et al. / Journal of Organometallic Chemistry 695 (2010) 1006–1011
OCH(CF3)2
1) n-BuLi
P
2) [HypNPCl]2
HOCH(CF3)2
+
Hyp
LiCl + n-BuH
Hyp
N
N
Et2O
0 °C
P
4
Cl
Scheme 4. Attempted direct synthesis of 1-chloro-3-(1,1,1,3,3,3-hexafluoro-2-propoxy)phosphane-2,4-bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazane (4).
the [Al(OCH(CF3)2)4]À ion finally undergoing a similar Lewis acid/
Lewis base reaction as discussed before.
Again, several attempts were made to generate 4 in a direct syn-
thetic route. Firstly, a solution of Li[OCH(CF3)2] was treated with a
solution of [HypNPCl]2 in diethyl ether (Scheme 4). No reaction oc-
curred, which nicely demonstrates the kinetic protection of the
two hypersilyl groups in the dimer in contrast to the insufficient
protection of the Mes* group in monomeric Mes*–N@P–Cl.
Secondly, the reactivity of Li[OCH(CF3)2] was increased by addi-
tion of ethylenediamine, which however resulted in an ethylenedi-
amine bridged cyclo-diphosphadiazane (see supporting infor-
mation).
Separation of 3 and 4 obtained from the decomposition of the
red oil (see above) is possible when Li[OCH(CF3)2] was directly
added to a mixture of 3 and 4 in n-hexane. A rapid reaction was ob-
served leading to the precipitation of Li[Al(OCH(CF3)2)4] and unre-
acted 3 which remains dissolved in n-hexane.
Fig. 2. ORTEP drawing of the molecular structure of
2 in the crystal. Thermal
ellipsoids with 50% probability at 173 K. Hydrogen atoms of the tert-Bu groups are
omitted for clarity. Selected bond lengths in Å, angles in °: P–N 1.540(2), P–O
1.642(2), N–C3 1.429(2), O–C1 1.405(3); N–P–O 105.17(9), C3–N–P 127.0(1), C1–O–
P 125.1(1).
Compounds 2, 3 and 4 are thermally stable, moisture sensitive
but stable under argon atmosphere over a long period as solid
and in polar solvents at ambient temperature. Compound 2 is eas-
ily prepared in bulk and stable for a long time when stored in a
sealed tube.
2.3. X-ray crystallography
The solid-state structures of compounds 1, 2, 3 and 4 are shown
in Figs. 1–4. Crystallographic details are given in Table 1. More de-
tails are found in the supporting information file. X-ray quality
crystals of Mes*–N@P–Cl (1), Mes*–N@P–OCH(CF3)2 (2), [Al(OCH-
(CF3)2)3]2 (3), and Hyp2N2P2(Cl)OCH(CF3)2 (4) were selected in
Fomblin YR-1800 perfluoroether (Alfa Aesar) at ambient tempera-
tures. All samples were cooled to 173(2) K during measurement. It
should be mentioned, that a solid-state structure of compound 1
Fig. 3. ORTEP drawing of the molecular structure of
3 in the crystal. Thermal
ellipsoids with 50% probability at 173 K. Selected bond lengths in Å, angles in °: Al–
O2 1.666(2), Al–O1 1.685(2), Al–O3i 1.843(2), Al–O3 1.854(2), Al–Ali 2.818(2), O1–
C1 1.371(3); O2–Al–O1 124.9(1), O2–Al–O3i 114.5(1), O1–Al–O3i 108.11(9), O2–Al–
O3 109.14(9), O1–Al–O3 110.77(8), O3i–Al–O3 80.68(8), O2–Al–Ali 119.12(9), O1–
Al–Ali 115.89(7), C1–O1–Al 142.1(2).
has been reported [15], but in the present structure redetermina-
tion, a different modification was found with significantly different
structural data (see below).
Mes*–N@P–Cl (1) crystallizes in the monoclinic space group P21/
n with four formula units per cell. One of the t-Bu groups is found
to be disordered and was split in two parts. The structure consists
of Mes*–N@P–Cl (Fig. 1) molecules arranged in parallel layers
Fig. 1. ORTEP drawing of the molecular structure of
1 in the crystal. Thermal
allowing
p
stacking. Mes*–N@P–Cl adopts a cis configuration with
ellipsoids with 50% probability at 173 K. Hydrogen atoms are omitted for clarity.
Selected bond lengths in Å, angles in °: N–C1 1.413(3), N–P 1.506(2), P–Cl 2.118(1);
C1–N–P 146.7(2), N–P–Cl 111.30(9), C1–N–P–Cl 0.3(3).
respect to the position of the C1-atom and chlorine (<(C1–N–P–
Cl) = 0.3(3)°). A fairly short P–N bond lengths of N–P 1.506(2) Å is

M. Kuprat et al. / Journal of Organometallic Chemistry 695 (2010) 1006–1011
1009
111.30(9)°. Interestingly, Niecke et al. published a modification of
1 which crystallized in the space group Pnma and shows signifi-
cantly different structural data (cf. d(P–N) 1.495(4) Å, <(P–N–C1)
154.8(4)°, and N–P–Cl 112.4(2)°, nicely displaying the influence
and magnitude of lattice effects in the solid state [15].
Mes*–N@P–OCH(CF3)2 (2) crystallizes in the monoclinic space
group P21/m with two formula units per cell. One of the t-Bu
groups is found to be disordered and was split in two parts. As de-
picted in Fig. 2, the structure consists of Mes*–N@P–OCH(CF3)2
molecules also arranged in parallel layers in the unit cell. Mes*–
N@P–OCH(CF3)2 adopts a cis configuration with respect to the po-
sition of the C3-atom and the oxygen atom (<(O–P–N–C3) =
180.0°), while a trans arrangement is found along the C1–O–P–N
moiety (0.0 °C). Compared to 1 the P–N distance is slightly in-
creased with 1.540(2) Å (cf. 1: 1.506(2) Å) and the P–O bond length
of 1.642(2) Å is slightly shorter than a typical P–O single bond
P
(
rcov(O–P) = 1.76 Å) [21]. A short non-classical intramolecular
C–HÁÁÁN hydrogen bond is found with a donor–acceptor distance
of 2.872(3) Å.
[Al(OCH(CF3)2)3]2 (3) crystallizes in the monoclinic space group
P21/n with two formula units per cell. One of the OCH(CF3)2 groups
in 3 is found to be disordered and was split in two parts. The occu-
pancy of each part was refined freely (0.672(3)/0.328(3)) and the
group with larger occupancy is displayed in Fig. 3. As depicted in
Fig. 3, the Al2O2 ring is planar, but slightly distorted with two long-
Fig. 4. ORTEP drawing of the molecular structure of
4 in the crystal. Thermal
ellipsoids with 50% probability at 173 K. Hydrogen atoms of the Me3Si groups are
omitted for clarity. Selected bond lengths in Å, angles in °: P1–N1 1.697(2), P1–N2
1.711(1), P1–Cl1 2.139(1), P1–P2 2.521(1), P2–O1 1.658(1), P2–N1 1.721(1), P2–N2
1.725(2), N1–Si1 1.801(2), N2–Si5 1.806(1); O1–C1 1.409(2), N1–P1–N2 85.50(7),
N1–P1–Cl1 104.58(5), N2–P1–Cl1 102.46(5), N1–P1–P2 42.83(4), N2–P1–P2
43.01(5), Cl1–P1–P2 112.80(4), O1–P2–N1 106.05(7), O1–P2–N2 104.91(6), N1–
P2–N2 84.36(6), O1–P2–P1 115.26(5), N1–P2–P1 42.11(5), N2–P2–P1 42.58(4), P1–
N1–P2 95.07(7), P1–N1–Si1 127.88(8), P2–N1–Si1 127.14(7), P1–N2–P2 94.41(7),
P1–N2–Si5 125.44(7), P2–N2–Si5 132.49(7), C1–O1–P2 125.82(9).
er Al–O bond lengths (d(Al–O3) = 1.854(2) Å) and two slightly
P
shorter Al–O bond lengths (d(Al–O3i) = 1.843(2) Å; cf.
rcov(O–
Al) = 1.81 Å, Fig. 3). These Al–O bond lengths are again substan-
tially longer than those of the exocyclic Al–O bonds (d(Al–
O2) = 1.666(2), d(Al–O1) = 1.685(2) Å). The AlÁÁÁAl distance is rather
short with 2.818(2) Å and compares to the AlÁÁÁAl distance in alu-
minium metal (dmetal(Al–Al) = 2.864 Å) [21].
Hyp2N2P2(Cl)OCH(CF3)2 (4) crystallizes in the triclinic space
ꢀ
group P1 with four formula units per cell. The crystallographic
observed, which indicates a bond order larger than two due to
asymmetric unit contains two crystallographically independent
molecules, which are arranged in the unit cell in such a manner
that stacked chains of alternating polar ‘‘NPCl-units” and non-polar
‘‘hyp-units” are formed as already observed for Hyp–N(H)–PCl2
P
P
hyperconjugation [20] (cf.
rcov(N–P) = 1.8,
rcov(N@P) = 1.6 Å)
[21]. As expected, a large C1–N–P angle of 146.7(2)° is found for
the imino nitrogen atom, while the N–P–Cl angle amounts to
Table 1
Crystallographic details of 1–4.
1
2
3
4
Chemcal formula
Formula weight (g molÀ1
Colour
Crystal system
Space group
a (Å)
C18H29ClNP
325.84
Red
Monoclinic
P21/n
5.8515(12)
33.661(7)
9.6883(19)
90.00
98.72(3)
90.00
C21H30F6NOP
457.43
Orange
Monoclinic
P21/m
5.930(2)
14.828(6)
13.051(5)
90.00
91.064(11)
90.00
1147.4(7)
2
C18H6Al2F36O6
1056.19
Colourless
Monoclinic
P21/n
10.394(8)
10.206(9)
16.211(15)
90.00
91.439(18)
90.00
1719(3)
2
C21H55ClF6N2OP2Si8
787.78
Colourless
Triclinic
)
ꢀ
P1
14.748(7)
16.885(9)
18.920(9)
86.82(2)
69.247(16)
71.949(10)
4181(4)
4
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
1886.2(7)
4
1.147
Z
qcalc. (g cmÀ3
)
1.324
0.180
2.040
0.316
1.251
0.443
l
(mmÀ1
)
0.283
kMoK (Å)
T (K)
Measured reflections
Independent reflections
Reflections with I > 2
Rint.
0.71073
173(2)
16 368
4322
3157
0.0412
704
0.0590
0.1346
1.071
0.71073
173(2)
11 716
3128
2329
0.0355
480
0.0470
0.1310
1.045
0.71073
173(2)
14 477
3922
2490
0.0353
1024
0.0504
0.1406
1.020
0.71073
173(2)
98 586
24 279
18 042
0.0411
1664
0.0397
0.1033
1.047
a
r(I)
F(0 0 0)
R1 (R[F2 > 2
r
(F2)])
wR2 (F2)
Goodness-of-fit (GOF)
Parameters
212
160
344
775
CCDC #
753943
753944
753946
753945

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M. Kuprat et al. / Journal of Organometallic Chemistry 695 (2010) 1006–1011
[6b]. Only very weak intermolecular contacts are observed. As de-
picted in Fig. 4, the P2N2 ring is almost planar (deviation from pla-
narity: <(N–P1–N–P2) = 7.7°), but slightly distorted with two
longer P–N bond lengths (d(P2–N1) = 1.721(1), d(P2–N2)
1.725(2) Å) and two slightly shorter P–N bond lengths (d(P1–
N1) = 1.697(2), d(P1–N2) = 1.711(1). These P–N bond lengths are
again substantially shorter than the sum of the covalent radii
(see above). The P–O bond length is rather short with 1.658(1) Å,
and the P–Cl bond length amounts to 2.139(1) Å. A difference of
ca. 10° is found between the N–P–N and P–N–P angles (85.5/
84.4° vs. 95.1/94.4°), in accord with that found e.g. in [(C6H5)NPCl]2
(80.1° vs. 99.7°) [3]. A short non-classical intramolecular C–HÁÁÁCl
hydrogen bond is found for both molecules in the asymmetric unit
with donor–acceptor distances of 3.482(2) and 3.555(3) Å.
of 10 min. The resulting orange suspension is warmed to ambient
temperatures over a period of 30 min, and filtered (F4). The result-
ing clear orange solution is concentrated to an approximate vol-
ume of 3 mL in vacuo and is stored at À25 °C for 10 h, which
results in the deposition of colourless crystals. The crystals were
identified as bis[tris(1,1,1,3,3,3-hexafluoro-2-propoxy)aluminium]
(3), the only phosphorous containing product was identified as
N-2,4,6-tri-tert-butylphenyl)imino-(1,1,1,3,3,3-hexafluoro-2-pro-
poxy)phosphane (2) by 31P NMR.
4.3. Reaction of 1,3-dichloro-2,4-bis[tris(trimethylsilyl)silyl]-cyclo-
diphosphadiazane with silver tetrakis(1,1,1,3,3,3-hexafluoro-2-
propoxy)aluminate
To a stirred solution of 1,3-dichloro-2,4-bis-[tris(trimethyl-
silyl)silyl]-cyclo-diphosphadiazane [HypNPCl]2 (0.656 g, 1.0 mmol)
in dichloromethane (10 mL), silver tetrakis(1,1,1,3,3,3-hexafluoro-
2-propoxy)aluminate Ag[Al(OCH(CF3)2)4] (0.883 g, 1.1 mmol) in
dichloromethane (5 mL) is added dropwise at À30 °C over a period
of 10 min. The resulting dark red suspension is warmed to ambient
temperatures over a period of 30 min, and filtered (F4). Removal of
solvent in vacuo at ambient temperature yields a red oil, which is
characterized as 2-chloro-3,4-bis[tris(trimethylsilyl)silyl]-cyclo-
diphosphadiazenium tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)-
aluminate [Hyp2N2P2Cl][Al(OCH(CF3)2)4] by NMR. Storage at ambi-
ent temperatures for 10 h, results in the deposition of colourless
crystals. The crystals were identified as 1-chloro-3-(1,1,1,3,3,3-
hexafluoro-2-propoxy)-2,4-bis-[tris(trimethylsilyl)silyl]-cyclo-dip-
hosphadiazane Hyp2N2P2(Cl)OCH(CF3)2 (4).
3. Conclusion
In conclusion, we present here highly reactive hypersilylated
cyclo-diphosphadiazenium [Hyp2N2P2Cl]+ and supermesityl substi-
tuted iminophosphenium [Mes*–N„P]+ cations, which are capable
of abstracting [OCH(CF3)2]À from the [Al(OCH(CF3)2)4]À counter ion
in formal Lewis acid/Lewis base reactions. By this approach the
hitherto unknown Mes*–N@P–OCH(CF3)2 and Hyp2N2P2(Cl)OCH-
(CF3)2 as well as the dimer of the free Lewis acid [Al(OCH(CF3)2)3]2
have been obtained and fully characterized.
4. Experimental details
[Hyp2N2P2Cl][Al(OCH(CF3)2)4]: 1H NMR (25 °C, CD2Cl2,
300.13 MHz): d = 0.36 (s, 54 H, Si(Si(CH3)3)3), 4.50 (sept, 4H,
CH(CF3)2, 3J(19F–1H) = 6.0 Hz). 13C{1H} NMR (25 °C, CD2Cl2, 75.5
MHz): d = 0.95 (s, Si(Si(CH3)3)3). 71.5 (sept, CH(CF3)2,
2J(19F–13C) = 32.9 Hz), 123.7 (q, CF3, 1J(19F–13C) = 283.3 Hz). 29Si
NMR (25 °C, CD2Cl2, 59.6 MHz): d = À26.0 (m, Si(Si(CH3)3)3),
À12.8 (m, Si(Si(CH3)3)3).19F{1H} NMR (25 °C, CD2Cl2, 282.4 MHz):
d = À77.3 (s, CF3).
4.1. General Information
All manipulations were carried out under oxygen- and mois-
ture-free conditions in an argon atmosphere using standard
Schlenk or dry box techniques.
Dichloromethane was dried over P4O10 and freshly distilled
prior to use. Diethyl ether was dried over Na/benzophenone, n-
hexane was dried over Na/benzophenone/tetraglyme and freshly
distilled prior to use. 1,1,1,3,3,3-hexafluoro-2-propanole (99%, Du-
Pont) was distilled prior to use. N-BuLi (2.5 M, Acros) was used as
received. Silver tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)alumi-
4.4. Synthesis of N-(2,4,6-tri-tert-butylphenyl)imino-(1,1,1,3,3,3-
hexafluoro-2-propoxy)phosphane (2)
nate
Ag[Al(OCH(CF3)2)4],
N-(2,4,6-tri-tert-butylphenyl)imino-
(chloro)phosphane Mes*NPCl (1), and 1,2-dichloro-2,4-bis [tris(tri-
methylsilyl)silyl]-cyclo-diphosphadiazane [HypNPCl]2, were pre-
pared as previously reported [6b,15,17,19].
To
a stirred solution of 1,1,1,3,3,3-hexafluoro-2-propanole
HOCH(CF3)2 (0.252 g, 1.5 mmol) in diethyl ether (10 mL), n-BuLi
(2.5 M, 0.6 mL, 1.5 mmol) is added dropwise at 0 °C over a period
of 5 min. The resulting colourless, clear solution is stirred for
10 min at this temperature, and is then added dropwise to a stirred
solution of N-(2,4,6-tri-tert-butylphenyl)imino(chloro)phosphane
Mes*NPCl (1) (0.489 g, 1.5 mmol) in diethyl ether (8 mL) over a
period of 5 min at 0 °C. The resulting orange suspension is stirred
at this temperature for 30 min and is then slowly warmed to ambi-
ent temperatures. The solvent is removed in vacuo, resulting in an
orange residue which is extracted with n-hexane (15 mL), and fil-
tered (F4). The resulting clear orange solution is concentrated to
an approximate volume of 3 mL in vacuo and is stored at À25 °C
for 10 h, which results in the deposition of orange needlelike crys-
tals. The supernatant is removed by syringe and the crystalline res-
idue is dried in vacuo, which yields 0.652 g (1.43 mmol, 95%) of 2 as
an orange crystalline solid. M.p. 102 °C (dec.). Anal. Calc.: C, 55.14;
H, 6.61; N, 3.06. Found: C, 54.91; H, 6.59; N, 3.30%. 1H NMR (25 °C,
CD2Cl2, 300.13 MHz): d = 1.33 (s, 9H, p-C(CH3)3), 1.47 (s, 18H, o-
C(CH3)3), 5.18 (m, 1H, CH(CF3)2, 4J(31P–19F) = 5.9 Hz), 7.35 (d, 2H,
m-CH, 5J(31P–1H) = 1.4 Hz). 13C{1H} NMR (25 °C, CD2Cl2,
75.5 MHz): d = 30.8 (d, o-C(CH3)3, 5J(13C–31P) = 2.4 Hz), 31.8 (s, p-
C(CH3)3), 35.4 (s, p-C(CH3)3), 36.2 (d, o-C(CH3)3, 4J(13C–31P) =
0.9 Hz), 68.4 (m, CH(CF3)2, 2J(19F–13C) = 34.7 Hz, 2J(31P–13C) =
10.4 Hz), 121.5 (m, CF3, 1J(19F–13C) = 283.2 Hz, 3J(31P–13C) = 3 Hz),
NMR: 29Si INEPT, 19F{1H}, 13C{1H}, 13C DEPT, and 1H NMR spectra
were obtained on a Bruker AVANCE 250, or 300 spectrometer and
were referenced internally to the deuterated solvent (13C, CD2Cl2:
dreference = 54 ppm) or to protic impurities in the deuterated solvent
(1H, CDHCl2: dreference = 5.31 ppm). CD2Cl2 was dried over P4O10 and
freshly distilled prior to use.
IR: Nicolet 6700 FT-IR spectrometer with a Smart Endurance
ATR device was used. Raman: Bruker VERTEX 70 FT-IR with RAM
II FT-Raman module, equipped with a Nd:YAG laser (1064 nm)
was used. CHNanalyses: C/H/N/S-Mikronalysator TruSpec-932 from
Leco was used. Melting points are uncorrected (EZ-Melt, Stanford
Research Systems). Heating-rate 20 °C/min (clearing-points are
reported).
4.2. Reaction of N-(2,4,6-tri-tert-butylphenyl)imino(chloro)phosphane
(1) with silver tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)aluminate
To a stirred solution of N-(2,4,6-tri-tert-butylphenyl)imino-
(chloro)phosphane Mes*NPCl (1) (0.326 g, 1.0 mmol) in dichloro-
methane
(10 mL),
silver
tetrakis(1,1,1,3,3,3-hexafluoro-2-
propoxy)aluminate Ag[Al(OCH(CF3)2)4] (0.883 g, 1.1 mmol) in
dichloromethane (5 mL) is added dropwise at À30 °C over a period

M. Kuprat et al. / Journal of Organometallic Chemistry 695 (2010) 1006–1011
1011
122.5 (d, m-CH, 4J(31P–13C) = 2.3 Hz), 137.7 (d, p-C, 5J(31P–13C) =
31.4 Hz), 140.9 (d, o-C, 3J(31P–13C) = 9.1 Hz), 146.6 (d, ipso-C,
2J(31P–13C) = 4.2 Hz). 19F{1H} NMR (25 °C, CD2Cl2, 282.4 MHz):
d = À74.4 (m, CF3, 3J(19F–1H) = 5.9 Hz). 31P{1H} NMR (25 °C, CD2Cl2,
121.5 MHz): d = 138.4. IR (ATR, 16 scans): 3100 (w), 2962 (m),
2935 (m), 2911 (m), 2872 (m), 2744 (w), 1506 (w), 1477 (w),
1471 (w), 1464 (w), 1456 (w), 1451 (w), 1421 (m), 1390 (w),
1382 (m), 1362 (m), 1337 (m), 1310 (w), 1278 (m), 1260 (m),
1229 (s), 1219 (s), 1188 (s), 1145 (w), 1134 (w), 1106 (s), 1083
(s), 1020 (w), 979 (w), 925 (w), 901 (m), 878 (m), 868 (s), 811
(s), 786 (m), 764 (m), 730 (w), 710 (w), 686 (s), 669 (w), 644
(m), 567 (m), 552 (w), 535(m). Raman (200 mW, 25 °C, 219 scans,
cmÀ1): = 3101 (1), 2965 (10), 2933 (9), 2910 (9), 2880 (5), 2776 (1),
2710 (2), 1598 (4), 1470 (2), 1449 (3), 1423 (4), 1390 (2), 1364 (2),
1336 (3), 1310 (8), 1199 (3), 1153 (1), 1081 (1), 1055 (1), 1026 (1),
927 (2), 868 (1), 823 (3), 784 (1), 731 (2), 687 (1), 568 (2), 537 (1),
509 (1), 475 (1),,421 (1), 389 (1), 338 (1), 299 (1), 256 (1), 126 (5).
MS (CI+, isobutane): 458 [M+H]+, 402 [MÀtBu+2H]+.
CD2Cl2, 75.5 MHz): d = 1.6 (s, Si(Si(CH3)3)3). 71.4 (sept, CH(CF3)2,
2J(19F–13C) = 33.4 Hz). 29Si NMR (25 °C, CD2Cl2, 59.6 MHz):
d = À33.3 (m, Si(Si(CH3)3)3), À13.5 (m, Si(Si(CH3)3)3). 19F{1H} NMR
(25 °C, CD2Cl2, 282.4 MHz): d = À72.0 (d, CF3, 4J(19F–31P) = 4.3 Hz).
31P{1H} NMR (25 °C, CD2Cl2, 121.5 MHz): d = 199.8 (d,
2J(31P–31P) = 100 Hz), 233.1 (d, 2J(31P–31P) = 100 Hz). IR (ATR, 16
scans): 2949 (w), 2894 (w), 1371 (w), 1290 (m), 1258 (m), 1244
(m), 1220 (m), 1192 (s), 1162 (m), 1105 (m), 1075 (m), 1012 (w),
1000 (w), 953 (w), 898 (w), 890 (m), 875 (m), 820 (vs), 787 (s),
748 (m), 740 (m), 685 (s), 623 (s), 561 (m). MS (CI+, isobutane):
787 [M +H]+, 771 [MÀMe]+, 751 [MÀCl]+, 713 [MÀSiMe3]+, 678
[MÀSiMe3ÀCl]+, 619 [MÀOCH(CF3)2]+.
Acknowledgements
We thank Dr. Dirk Michalik (Universität Rostock) for helpful
advice.
Crystals suitable for X-ray crystallographic analysis were ob-
tained directly from the above reaction solution.
Appendix A. Supplementary material
CCDC 753943, 753944, 753946 and 753945 contains the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.jorganchem.2009.11.014.
4.5. Attempted synthesis of 1-chloro-3-(1,1,1,3,3,3-hexafluoro-2-
propoxy)-2,4-bis-[tris(tri-methylsilyl)silyl]-cyclo-diphosphadiazane
(4)
To
a stirred solution of 1,1,1,3,3,3-hexafluoro-2-propanole
HOCH(CF3)2 (0.168 g, 1.0 mmol) in diethylether (10 mL), n-BuLi
(2.5 M, 0.4 mL, 1.0 mmol) is added dropwise at 0 °C over a period
of 5 min. The resulting colourless, clear solution is stirred for
10 min at this temperature, and is then added dropwise to a stirred
solution of 1,3-dichloro-2,4-bis-[tris(trimethylsilyl)silyl]-cyclo-
diphosphadiazane [HypNPCl]2 (0.656 g, 1.0 mmol) in diethyl ether
(8 mL) over a period of 5 min at 0 °C. The resulting colourless solu-
tion is then slowly warmed to ambient temperatures. Even after
several hours at ambient temperatures, no reaction is observed
as shown by 31P NMR. The solvent is removed in vacuo, resulting
in a colourless residue which is extracted with n-hexane (15 mL),
and filtered (F4). The resulting clear colourless solution is concen-
trated to an approximate volume of 3 mL in vacuo and is stored at
À25 °C for 10 h, which results in the deposition of colourless crys-
tals of the starting material 1,3-dichloro-2,4-bis[tris(trimethyl-
References
[1] R. Keat, Top. Curr. Chem. 102 (1982) 89–116. and references therein.
[2] L. Stahl, Coord. Chem. Rev. 210 (2000) 203–250. and references therein.
[3] H.-J. Chen, R.C. Haltiwanger, T.G. Hill, M.L. Thompson, D.E. Coons, A.D. Norman,
Inorg. Chem. 24 (1985) 4725–4730.
[4] N. Burford, T.S. Cameron, K.-C. Lam, D.J. LeBlanc, C.L.B. Macdonald, A.D. Phillips,
A.L. Rheingold, L. Stark, D. Walsh, Can. J. Chem. 79 (2001) 342–348.
[5] (a) R. Keat, Top. Curr. Chem. 102 (1982) 89–116;
(b) M.S. Balakrishna, V.S. Reddy, S.S. Krishnamurthy, J.F. Nixon, J.C. Laurent,
Coord. Chem. Rev. 129 (1994) 1–90.
[6] (a) D. Michalik, A. Schulz, A. Villinger, N. Weding, Angew. Chem. 120 (2008)
6565–6568. Angew. Chem., Int. Ed. 47 (2008) 6465–6468;
(b) R. Kuzora, A. Schulz, A. Villinger, R. Wustrack, Dalton Trans. (2009) 9304–
9311.
[7] A.H. Cowley, M. Lattman, J.C. Wilburn, Inorg. Chem. 20 (1981) 2916–2919.
[8] N. Burford, J.C. Landry, M.J. Ferguson, R. McDonald, Inorg. Chem. 44 (2005)
5897–5902.
[9] N. Burford, K.D. Conroy, J.C. Landry, P.J. Ragogna, M.J. Ferguson, R. McDonald,
Inorg. Chem. 43 (2004) 8245–8251.
silyl)silyl]-cyclo-diphosphadiazane
[HypNPCl]2
almost
quantitatively.
[10] A. Villinger, A. Westenkirchner, R. Wustrack, A. Schulz, Inorg. Chem. 47 (2008)
9140–9142.
4.6. Synthesis of 1-chloro-3-(1,1,1,3,3,3-hexafluoro-2-propoxy)-2,4-
[tris(tri-methylsilyl)silyl]-cyclo-diphosphadiazane (4)
[11] H. Gilman, R.L. Harrell, J. Organomet. Chem. 5 (1966) 199–200.
[12] M. Westerhausen, W. Schwarz, Z. Anorg. Allg. Chem. 619 (1993) 1053–1063.
[13] A. Michaelis, G. Schroeter, Ber. Dtsch. Chem. Ges. 27 (1894) 490–497.
[14] (a) N. Burford, T.S. Cameron, K.D. Conroy, B. Ellis, M.D. Lumsden, C.L.B.
McDonald, R. McDonald, A.D. Phillips, P.J. Ragogna, R.W. Schurko, D. Walsh,
R.E. Wasylishen, J. Am. Chem. Soc. 124 (2002) 14012–14013;
(b) N. Burford, J.A.C. Clyburne, M.S.W. Chan, Inorg. Chem. 36 (1997) 3204–
3206.
[15] E. Niecke, M. Nieger, F. Reichert, Angew. Chem. 12 (1988) 1781–1782;
Angew. Chem., Int. Ed. 27 (1988) 1715–1716.
[16] (a) Reviews: I. Krossing, I. Raabe, Angew. Chem. 116 (2004) 2016–2142.
Angew. Chem. Int. Ed. 43 (2004) 2066–2090;
The mixture of 3 and 4 (from the decomposition reaction of 2-
chloro-3,4-bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazenium
tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)aluminate [Hyp2N2P2-
Cl]+[Al(OCH(CF3)2)4]À) is dissolved in n-hexane (10 mL) resulting
in a yellowish suspension, which is added dropwise to a colourless
suspension of Li[OCH(CF3)2] (prepared from 1,1,1,3,3,3-hexafluoro-
2-propanole HOCH(CF3)2 (0.168 g, 1.0 mmol) and n-BuLi (2.5 M,
0.4 mL, 1.0 mmol) in n-hexane (5 mL) at ambient temperatures
over a period of 10 min. The resulting colourless suspension is stir-
red for 1 h at ambient temperatures and filtered (F4). The resulting
colourless solution is concentrated to an approximate volume of
5 mL in vacuo and is stored at –25 °C for 10 h which leads to the
deposition of colourless crystals. Removal of supernatant by syr-
inge and drying in vacuo yields 0.190 g (0.24 mmol, 24%) of 4 as
colourless crystalline solid. Mp 127 °C; Tdec 186 °C. Anal. Calc.: C,
32.02; H, 7.04; N, 3.56. Found: C, 31.72; H, 7.03; N, 3.46%. 1H
NMR (25 °C, CD2Cl2, 300.13 MHz): d = 0.27 (s, 54 H, Si(Si(CH3)3)3),
5.38 (m, 1H, CH(CF3)2, 3J(19F–1H) = 3.9 Hz). 13C{1H} NMR (25 °C,
(b) C. Reed, Acc. Chem. Res. 31 (1998) 133–139;
(c) S.H. Strauss, Chem. Rev. 93 (1993) 927–942. and references therein.
[17] N. Burford, J.A.C. Clyburne, P. Losier, T.M. Parks, in: H.H. Karsch (Ed.),
Handbuch der Präparativen Anorganischen Chemie (Engl.), fourth ed.,
Thieme-Verlag, Stuttgart, 1996.
[18] (a) I. Krossing, A. Reisinger, Coord. Chem. Rev. 250 (2006) 2721–2744;
(b) M. Gonsior, I. Krossing, L. Müller, I. Raabe, M. Jansen, L. Van Wullen, Chem.
Eur. J. 8 (2002) 4475–4492;
(c) I. Krossing, Dalton Trans. 4 (2002) 500–512;
(d) I. Krossing, I. Raabe, Chem. Eur. J. 10 (2004) 5017–5030.
[19] I. Krossing, Chem. Eur. J. 7 (2001) 490–502.
[20] F. Weinhold, C. Landis, Valency and Bonding. A Natural Bond Orbital Donor–
Acceptor Perspective, Cambridge University Press, 2005.
[21] Holleman Wiberg, Lehrbuch der Anorganischen Chemie, Aufl., Walter de
Gruyter, Berlin, 2007, p. 102 (Anhang IV).