Azidophosphenium cations: Versatile reagents in inorganic synthesis

Article abstract of DOI:10.1021/ic500332s

This work describes the synthesis and characterization of a series of iminophosphorane-substituted phosphenium cations of the type [R ₂NPNP(Cl)₂NPNR′₂][GaCl₄] [R = iPr; R′ = iPr (7[GaCl₄]), SiMe₃ (8)], which are directly derived from azidophosphenium salt [iPrNPN₃][GaCl ₄] (2iPr[GaCl₄]) and the corresponding chlorophosphane R₂NPCl₂. The reactivity of 7[GaCl₄] toward 2,3-dimethylbutadiene (dmb) and 2,2′-bipyridine (bipy) was investigated, resulting in the formation of 7-dmb[GaCl₄] and 7-Cl. In addition, self-condensation of [(Me₃Si)₂NPN₃][GaCl ₄] (2SiMe₃[GaCl₄]) was studied in detail, and [(Me₃Si)₂NPNP(XY)N(SiMe₃)₂] [GaCl₄] [X = Cl; Y = Cl (13), N₃ (14)] were determined as products on the basis of ³¹P NMR spectroscopy. The reaction of 2SiMe₃[GaCl₄] with [(Me₃Si)₂NPCl] [GaCl₄] (1SiMe₃[GaCl₄]) yielded an unprecedented bicyclic 1,3,2λ³,4λ⁵- diazadiphosphetidine (15), which was formed via a GaCl₃-assisted Me₃SiCl elimination starting from 13. Furthermore, cations of the type [R₂NPNPR′₃][GaCl₄] [R = iPr; R′ = cHex (19)] were obtained by the effective combination of 2R[GaCl ₄] (R = iPr, SiMe₃) with PR′₃ (R′ = Ph, cHex). Azidochlorophosphanes R₂NP(N₃)Cl [R = iPr, SiMe₃ (20R)] are shown to be accessible when 2R[GaCl₄] was combined with bipy. All new compounds were fully characterized by means of X-ray, vibrational spectroscopy, CHN analysis, and NMR experiments. All compounds were further investigated by means of density functional theory, and the bonding situation was accessed by natural bond orbital analysis.

Full text of DOI:10.1021/ic500332s

Article
pubs.acs.org/IC
Azidophosphenium Cations: Versatile Reagents in Inorganic
Synthesis
Christian Hering,† Maximilian Hertrich,† Axel Schulz,*,†,‡ and Alexander Villinger†
†Institut fur Chemie, Abteilung Anorganische Chemie, Universitat Rostock, Albert-Einstein-Strasse 3a, 18059 Rostock, Germany
̈
̈
‡Leibniz-Institut fur Katalyse eV, Universitat Rostock, Albert-Einstein-Strasse 29a, 18059 Rostock, Germany
̈
̈
S
* Supporting Information
ABSTRACT: This work describes the synthesis and characterization of a series of
iminophosphorane-substituted phosphenium cations of the type [R2NPNP-
(Cl)2NPNR′2][GaCl4] [R = iPr; R′ = iPr (7[GaCl4]), SiMe3 (8)], which are
directly derived from azidophosphenium salt [iPrNPN3][GaCl4] (2iPr[GaCl4]) and
the corresponding chlorophosphane R2NPCl2. The reactivity of 7[GaCl4] toward
2,3-dimethylbutadiene (dmb) and 2,2′-bipyridine (bipy) was investigated, resulting in
the formation of 7-dmb[GaCl4] and 7-Cl. In addition, self-condensation of
[(Me3Si)2NPN3][GaCl4] (2SiMe3[GaCl4]) was studied in detail, and
[(Me3Si)2NPNP(XY)N(SiMe3)2][GaCl4] [X = Cl; Y = Cl (13), N3 (14)] were
determined as products on the basis of 31P NMR spectroscopy. The reaction of
2SiMe3[GaCl4] with [(Me3Si)2NPCl][GaCl4] (1SiMe3[GaCl4]) yielded an
unprecedented bicyclic 1,3,2λ3,4λ5-diazadiphosphetidine (15), which was formed
via a GaCl3-assisted Me3SiCl elimination starting from 13. Furthermore, cations of the type [R2NPNPR′3][GaCl4] [R = iPr; R′ =
cHex (19)] were obtained by the effective combination of 2R[GaCl4] (R = iPr, SiMe3) with PR′3 (R′ = Ph, cHex).
Azidochlorophosphanes R2NP(N3)Cl [R = iPr, SiMe3 (20R)] are shown to be accessible when 2R[GaCl4] was combined with
bipy. All new compounds were fully characterized by means of X-ray, vibrational spectroscopy, CHN analysis, and NMR
experiments. All compounds were further investigated by means of density functional theory, and the bonding situation was
accessed by natural bond orbital analysis.
structure of chlorophosphenium cations of the type [R2NPCl]+
INTRODUCTION
■
6
+
remained unknown until recently [R = SiMe3 (1SiMe3 ),
Dimroth and Hoffmann reported on the synthesis of the first
low-valent dicoordinated phosphorus compounds in phospha-
methine cyanines in 1964.1 The term “phosphenium cation”
indicates a positively charged divalent phosphorus atom, which
formally possesses an empty p orbital and a lone pair (LP) of
electrons and thus can be considered as a main-group
carbenoid, in which the central carbon atom is replaced by
an isovalent P+. These highly reactive species [R1−P−R2]+ are
stabilized best when R1 and R2 are π-electron-donating groups,
such as amino functions NR2 (R = Me, iPr). The first examples
of acyclic aminophosphenium salts of the type [(R2N)2P]-
[AlCl4] and [R2NPCl][AlCl4] [R = Me, Et, iPr (1R[AlCl4])]
were prepared by Parry et al. by the effective combination of
chlorophosphane and halogen-abstracting reagent ECl3 (E = Al,
Ga, Fe) in CH2Cl2 (Scheme 1).2 Since then, the reactivity and
coordination properties of these species have been studied in
detail and reviewed regularly.3−5 Nevertheless, the molecular
cHex7].
In 1984, Wolf et al. reported for the first time that
[R2NPCl]+ [R = Me, iPr (1iPr+)] can be further functionalized
on the phosphenium center by treatment with pseudohalo-
gensilanes such as Me3SiN3, whereupon Me3SiCl is liberated
(Scheme 2).8
In the absence of X-ray crystal structures, the intermediate
formation of azidophosphenium cation [R2NPN3]+ [R = Me,
iPr (2iPr+)] was established by 31P NMR spectroscopy.9
Scheme 2. Synthesis of Azidophosphenium Salts Starting
from Chlorophosphenium Salts in the Reaction with
Me3SiN3 at −50 °C, Whereupon Me3SiCl Is Released [E = Al
(R = Me, iPr), Ga (R = SiMe3)]
Scheme 1. Synthesis of Bis(aminophosphenium) Salts by the
Combination of Chlorophosphane (R = Me, Et, iPr) and
ECl3 (E = Al, Ga, Fe) as a Halogen-Abstracting Reagent
Received: February 11, 2014
Published: March 21, 2014
© 2014 American Chemical Society
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Figure 1. Depiction of selected Kohn−Sham orbitals calculated for the azidophosphenium cation 2SiMe3+ (left, middle). Ball-and-stick drawing of
the anion···cation interactions in the azidophosphenium salt 2SiMe3[GaCl4] (right). Four close contacts are observed (distances in angstroms): P1−
Cl1 3.1582(6), P1−Cl3 3.7630(7), P1−Cl3′ 3.273(7), P1−Cl4′ 4.0212(9).
Scheme 3. (i) Formation of the Phosphenium−Phosphonium Dication 32+ as a AlCl4− Salt According to Early Studies by Wolf
et al.6,7,16 and (ii) Preparation of the First Isolable Iminophosphorane Cation [4Me][CF3SO3]14,15
Scheme 4. Formation of Iminophosphorane−Iminophosphanes 5 and Rearrangement in a 1−3-Trimethylsilyl Shift toward
Diazadiphosphetidines 6 According to Studies by Boeske et al.17,18
Azidophosphenium ions are considered highly labile and only
of transient nature because they can decompose in a Staudinger
reaction.10 In the classical Staudinger reaction, organic azides
react with PIII compounds in an oxidative coupling between
phosphorus and nitrogen, in which phosphorus is oxidized to
PV and dinitrogen is liberated, affording a great variety of
iminophosphoranes, which are an important class of substances
in organic synthesis and can be further hydrolyzed to give
amines.11
NCO, NCS, OSiMe3), which were shown to react with Lewis
bases such as 4-(N,N-dimethylamino)pyridine and as dien-
ophiles with dienes such as 2,3-dimethyl-1,3-butadiene (dmb)
or 1,3-cyclo-hexadiene.12
However, in solution, only traces of 2SiMe3[GaCl4] [δ(31P)
= 368.6 ppm, at −65 °C] were detected by means of low-
temperature 31P NMR techniques because the salt readily
precipitates from cold CH2Cl2 solutions. At room temperature,
only the resonances of unidentified decomposition products
could be detected. A thorough search of the literature revealed
that Wolf and co-workers investigated the reactivity of
2iPr[AlCl4], which they assumed to self-condense, affording
polymers and phosphenium−phosphonium salts of the type
[iPr2NPNP(Cl)NiPr2][AlCl4]2 (3; Scheme 3, reaction i). In
accordance with the proposed molecular structure of 32+, an AX
spin system was observed in the 31P{1H} NMR spectrum with
distinct resonances for the phosphenium phosphorus and
phosphonium center (cf. [iPr2 NPNP(Cl)NiPr2 ]+
δphosphenium(31P) = 311 ppm, δphosphonium(31P) = 26 ppm,
Nevertheless, our group succeeded in the isolation of an
azidophosphenium cation in the salt [(Me3Si)2NPN3][GaCl4]
(2SiMe3[GaCl4]) at −50 °C, which, as an isolated crystalline
solid, is stable below −30 °C for at least 1 year.6 This
astonishing stability stems from delocalization of the positive
charge and formal π-electron density along the NPN3 skeleton
(Figure 1, left) as well as from four close van der Waals contacts
−
to chlorine atoms of the GaCl4 anion (Figure 1, right).
Furthermore, we succeeded in isolation of the analogous
pseudohalogen-substituted salts [(Me3Si)2NPX][GaCl4] (X =
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J(31P−31P) = 111.5 Hz; Scheme 3). However, the formation of
a tricoordinated iminophosphonium species is unlikely. Because
of the high electrophilicity of the phosphorus center in such
iminophosphorane cations, the counterion usually binds
covalently to the phosphorus center.13 Just recently, the first
isolable cationic iminophosphorane cation ([4Me][CF3SO3])
was prepared by methylation of an isolable σ3λ5-nitridophos-
phorane [4; also σ3λ5-nitridophosphane(V)], which is stabilized
by bulky imidazolin-2-iminato substituents, therefore effectively
denying interaction with the anion (Scheme 3, reaction ii).14,15
Systems that are related to the phosphenium−phosphonium
species 3 are iminophosphane−iminophosphoranes of the type
(Me3Si)2NP(Cl)(NSiMe3)NPN(SiMe3)2 (5a), which possesses
similar 31P NMR shifts for the dicoordinated PIII and
tetracoordinated PV atoms, respectively (cf. 5a δ(31P) = 341.1
(PIII) and −10.6 (PV) ppm, J(P−P) = 79.9 Hz; Scheme 4).17
Moreover, they display an N−P−N−P−N backbone similar to
that found in 32+. Furthermore, 5a was shown to be in
equilibrium with its cyclic form 5b, which undergoes a 1,3-
trimethylsilyl migration to yield a cyclic 1,3,2λ3,4λ5-diazadi-
phosphetidine (6; Scheme 4).18
Herein, by utilizing 2iPr[GaCl4] as a model compound, we
describe the decomposition products of azidophosphenium
species 2SiMe3[GaCl4]. The work of Wolf and co-workers has
been reevaluated, the missing solid-state structures of 1iPr+ and
2iPr+ have been determined, and self-condensation products of
2iPr[AlCl4] need to be revised on the basis of our findings.
Furthermore, 2iPr[GaCl4] is shown to be a versatile starting
material for the formation of complex cations with an N−P−
N−P−N backbone. Starting from 2SiMe3[GaCl4], we
succeeded in isolating a unique bicyclic system bearing a
P2N2 ring, which is connected to a NGa2Cl four-membered ring
representing the first structurally characterized 1,3-diaza-
2λ3,4λ5-diphosphetidine.
Figure 2. Crystallographically determined structures of molecules
formally incorporating 1iPr+.
1.590 Å; ∑rcov(PN) = 1.60 Å], in accordance with natural
bond orbital (NBO) analysis.19,24 The P−Cl bond is shortened
with respect to the sum of the covalent radii [2.003(1) Å;
∑rcov(P−Cl) = 2.04 Å; cf. [(Me3Si)2NPCl][GaCl4] 2.019(4)
Å].19,24 The GaCl4 counteranion significantly interacts with
−
the electron-deficient phosphenium center because two P1−
Clanion contacts are detected within the sum of the respective
van der Waals radii of phosphorus and chlorine [3.014(1) Å;
∑rvdW(P−Cl) = 3.55 Å].25 Hence, a significant charge transfer
of 0.15e from the anion to the cation further enhances its
stability by ion pairing. Salt formation is also visualized in the
Raman spectrum, which reveals a sharp band at 347 cm−1 for
the A1 asymmetric Ga−Cl stretching mode, whereas free GaCl3
is not observed.26
For the first time, Wolf and co-workers discussed the
existence of an azidophosphenium salt of the type [iPr2NPN3]-
[AlCl4] (3) in 1984. They reported that 1iPr[AlCl4] reacts
with Me3SiN3 to intermediately yield 2iPr[AlCl4], which self-
condenses to yield phosphorus bis(cations) (Scheme 3,
reaction i).8,9 However, the solid-state structure of such
phosphenium azides remained unknown until our group
uncovered the molecular structure of [(Me3Si)2NPN3][GaCl4]
(2SiMe3[GaCl4]).19 2SiMe3[GaCl4] can be prepared at −50
°C by treating a CH2Cl2 solution of 1SiMe3[GaCl4] with
Me3SiN3. Nevertheless, 2SiMe3[GaCl4] is only stable in the
solid state below −30 °C and decomposes rapidly in a CH2Cl2
solution as vigorous gas evolution is observed upon thawing.6
Following the synthetic protocol that yielded 2Si-
Me3[GaCl4], 2iPr[GaCl4] was prepared in good yield (81%)
and its structure was determined by X-ray crystallographic
measurements. 2iPr[GaCl4] possesses two major advantages
compared to 2SiMe3[GaCl4]: (i) 2iPr[GaCl4] cannot be
engaged in chlorine/methyl exchange reactions in the presence
of GaCl3, which is common for silylated aminopnictanes;27−30
(ii) 2iPr[GaCl4] is not sensitive toward the thermal release of
Me3SiCl, which is well documented for silylated amino-
pnictanes in the presence of GaCl3.19,31,32 Moreover, 2iPr-
[GaCl4] is thermally stable up to 78 °C. Therefore, we
envisaged 2iPr[GaCl4] as a model system for thermal
decomposition reactions of azidophosphenium salts. 2iPr-
[GaCl4] crystallizes solvent-free in the monoclinic space
group C2/c with eight formula units in the unit cell (Figure
3, right). The geometry of the NPN3 skeleton resembles that of
the azidophosphenium ion in 2SiMe3[GaCl4] with a Namino−P1
RESULTS AND DISCUSSION
■
Phosphenium salts of the type [R2NPCl][GaCl4] [R = iPr,
SiMe3 (1R[GaCl4])] are most efficiently generated by the
combination of dichlorophosphane R2NPCl2 and GaCl3 in
CH2Cl2 at −80 °C. Concentration of the respective reaction
mixtures at −50 °C yielded colorless crystalline materials,
which in the case of 1iPr[GaCl4] are stable at ambient
temperatures for at least 1 h (vide infra). In contrast to
1iPr[GaCl4], 1SiMe3[GaCl4] decomposes in isolated form
even at temperatures below −30 °C by thermal elimination of
Me3SiCl. The dynamic solution chemistry of 1iPr[GaCl4] and
1SiMe3[GaCl4] was extensively studied by means of variable-
temperature 31P NMR spectroscopy, and a dynamic equilibrium
between R2NPCl2 and GaCl3 and the respective phosphenium
salt [R2NPCl][GaCl4] is characteristic for these species.7,19
Although 1iPr[AlCl4] was first reported in 1976 by Parry and
co-workers, its solid-state structure has not been reported so
far.2,20 Crystal structures have just been reported for products
in which 1iPr+ was incorporated by means of the oxidative
addition of substrates to the phosphenium center (A,21 B,22 and
C;23 Figure 2).
double bond [2iPr+ 1.6003(9) Å; cf. 2SiMe3 1.597(3) Å]19
+
and a short P1−Nazide distance [1.665(1) Å; cf. ∑rcov(PN) =
Treating iPr2NPCl2 with GaCl3 in a CH2Cl2 solution at −80
°C and letting the mixture stand overnight at −80 °C afforded
crystals of 1iPr[GaCl4] suitable for X-ray analysis. 1iPr[GaCl4]
crystallizes solvent free in the monoclinic space group P21/c
with four formula units in the unit cell (Figure 3, left). The
short P−Namino distance [1.591(3) Å] is best described as a P−
N pπpπ double bond [cf. P−Namino of 1SiMe3[GaCl4] (avg)
1.60, ∑rcov(P−N) 1.82 Å].24 The N−P−N angle [100.57(5)°;
cf. 2SiMe3 101.03(9)°]6 is rather acute, and the azide group
+
shows the typical trans-bent configuration (regarding the
phosphorus atom, P1−N1−N2−N3 180°) with an N1−N2−
N3 angle of 171.4(2)°, with a formally sp2-hybridized Nα atom
[P1−N1−N2 121.19(9)°]. The closest P1−Clanion contact
[3.0448(4) Å] is shorter than the sum of the respective van der
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Figure 3. ORTEP drawings of the molecular structures of 1iPr[GaCl4] (left) and 2iPr[GaCl4] (right). Ellipsoids are drawn at 50% probability.
Selected bond lengths (Å) and angles (deg): 1iPr[GaCl4], P1−N1 1.591(3), P1−Cl1 2.003(1), P1−Cl2 3.014(1), N1−C1 1.502(4), N1−C4
1.520(4); N1−P1−Cl1 106.9(1); Σ(<N1) 360.0; C1−N1−P1−Cl1 −0.6(3), C1−N1−P1−Cl2 94.9(3); 2iPr[GaCl4], P1−N4 1.6003(9), P1−N1
1.665(1), N1−N2 1.248(1), N2−N3 1.114(2), N4−C1 1.509(1), N4−C4 1.504(1); N1−P1−N4 100.57(5), N1−N2−N3 171.4(1); Σ(<N4)
359.97; C4−N4−P1−N1 2.8(1), P1−N1−N2−N3 171.6(9).
Scheme 5. Different Pathways for the Preparation of 7[GaCl4] (Reactions i and ii) and Examples of Transformations Starting
from 7[GaCl4] (Reactions iii and iv)
Figure 4. ORTEP drawings of the molecular structures of 7[GaCl4] (left) and 7-Cl (right). Ellipsoids are drawn at 50% probability at −100 °C.
Selected bond lengths (Å) and angles (deg): 7[GaCl4], P1−N1 1.1611(2), P1−N2 1.597(2), P2−N2 1.557(2), P2−N3 1.597(2), P2−Cl1
1.9987(8), P2−Cl2 2.0055(8), P1−Cl5 3.532(1); N1−P1−N2 104.97(9), P2−N2−P1 129.4(1), N2−P2−N3 112.4(1), ∑(<P2) 334.58; ∑(<N1)
359.95; ∑(<N3) 359.88; N2−P1−N1−C4 178.0(2), N1−P1−N2−P2 176.6(2), N3−P2−N2−P1 −165.0(2), N2−P2−N3−C10 178.6(2); 7-Cl,
P1−N1 1.640(4), P1−N2 1.660(4), P2−N2 1.504(2), P2−N3 1.603(4), P1−Cl1 2.207(2), P2−Cl2 2.020(2), P2−Cl3 2.038(2); N1−P1−N2
101.8(2), P2−N2−P1 138.1(3), N2−P2−N3 114.7(2), ∑(<P1) 301.1, ∑(<P2) 333.3, ∑(<N1) 358.6, ∑(<N3) 359.1; N2−P1−N1−C4 28.4(4),
N3−P2−N2−P1 149.7(4).
Waals radii [∑rvdw(P−Cl) = 3.55 Å].25 Additionally, three
more contacts between chlorine atoms from the anion and the
phosphenium center are found, a geometrical arrangement that
is in accordance with other pseudohalogen-substituted
phosphenium salts (e.g., Figure 1).12 This implicates a small
charge transfer from the anion to the phosphenium ion, which
was calculated by means of NBO analysis and amounts to only
0.08 e; therefore, the cation can be considered almost
“naked”.33
In a first series of experiments, we followed the procedure
described by Wolf et al., in which they carried out the reaction
of 2iPr[GaCl4] with 1 equiv of the chlorophosphenium salt
1iPr[GaCl4], which resulted according to their interpretation in
the formation of a bis(cation) (32+) on the basis of 31P NMR
spectroscopy (Scheme 3, reaction i).8 Treating 2iPr[GaCl4]
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Figure 5. Structures of phospholenium salt 9, Staudinger product 10, triaminoiminophosphorane 11, terphenyl-substituted aminochlorophosphane
12, cyclodiphospha(V)diazene 16, and cyclo-diphospha(III)diazenium salt 23.
with equimolar amounts of 1iPr[GaCl4] in CH2Cl2 at −50 °C
and subsequent warming to room temperature led to vigorous
gas evolution, and after workup and recrystallization from
CH2Cl2, phosphenium species [iPr2NPNP(Cl)2NiPr2][GaCl4]
(7[GaCl4]) could be isolated (Scheme 5, reaction ii; Figure 4,
left). The formation of 7[GaCl4] was unequivocally proven by
X-ray crystallographic analysis and is best described as a
Staudinger reaction between the azide 2iPr[GaCl4] and the
parent phosphine iPr2NPCl2, which is present in solutions of
1iPr[GaCl4] according to 31P NMR experiments (vide infra).
Hence, in this reaction, 1 equiv of GaCl3 must remain in the
mixture.
observed;8 even if such a species was formed transiently, it can
be assumed that it forms the iminophosphorane moiety by
abstracting a chloride from the GaCl4 anion.13
−
Adding (Me3Si)2NPCl2 instead of iPr2NPCl2 to a solution of
2iPr[GaCl4] at −50 °C and warming to room temperature
yielded after workup a colorless solid, which was recrystallized
from fluorobenzene (C6H5F) at 5 °C and found to be the
addition product of (Me3Si)2NPCl2 to 2iPr[GaCl4], the
iminophosphorane−phosphenium salt [iPr2NPNP(Cl2)N-
(SiMe3)2][GaCl4] (8). 8 displays the expected AX spin system
in the 31P NMR spectrum, with the phosphenium center
resonating at 311.3 ppm (cf. 7[GaCl4] 311.2 ppm), whereas
the PV atom is detected at 30.4 ppm, which is downfield-shifted
compared to that of 7[GaCl4] (27.4 ppm). The compound was
characterized by X-ray analysis, and a representation of the
molecular structure of 8 is shown in Figure 6 (right). Owing to
their similarity, the molecular structures of 7[GaCl4] and 8 are
discussed in one context.
7[GaCl4] crystallizes in the monoclinic space group P21/c
with eight formula units in the cell and thus two independent
formula units in the asymmetric unit, whereas 8 crystallizes in
the monoclinic space group P21/n with four formula units in
the unit cell. The discussion of the structure is led for one
independent formula unit, respectively. The cations in
7[GaCl4] and 8 possess both a dicoordinated phosphenium
phosphorus atom P1 with a P1−Namino double bond [7[GaCl4]
1.611(2) Å; 8 1.612(4) Å] and a phosphonium phosphorus
atom P2, which is also bound to another amino group with a
short P2−N3 distance [7[GaCl4] 1.597(3) Å, 8 1.588(5) Å; cf.
9 P−N 1.6089(8) Å,12 10 PV−Namino 1.634(5) Å; Figure 5],35
which can be considered a PV−N single bond. The imino−
nitrogen phosphorus distances N2−P1 [7[GaCl4] 1.557(2) Å;
8 1.597(4) Å] and N2−P2 [7[GaCl4] 1.597(2) Å; 8 1.550(4)
Å] are rather short (cf. 10 PV−Nimino 1.558(4) Å],35 with both
distances being shorter than the sum of the respective covalent
radii for a P−N double bond [∑rcov(PN) = 1.60 Å],24
indicating a certain degree of π delocalization along the N2P2
moiety, which is further underlined by the two canonical Lewis
formulas for 7[GaCl4] shown in Scheme 6. Overall, N3P2 is W-
shaped, with a rather acute N1−P1−N2 angle [7[GaCl4]
104.97(9)°; 8 105.0(2)°], a slightly larger N2−P2−N3 angle
[7[GaCl4] 112.4(1)°; 8 113.6(2)°], and a typical P1−N2−P2
angle (7[GaCl4] 129.4(1)°; 8 133.2(3)°] for the sp2-hybridized
imino nitrogen, with a LP of electrons on the nitrogen site
according to NBO analysis. The closest contacts between
7[GaCl4] is a thermally robust (Tdec = 125 °C) colorless
crystalline solid that dissolves in polar solvents such as CH2Cl2
and C6H5F and is insoluble in n-hexane and benzene. 7[GaCl4]
features an AX spin system in the 31P NMR spectrum with two
distinct doublets for the phosphenium phosphorus and the
iminophosphorane moiety [7[GaCl4]; δphosphenium(31P) = 311.2,
δiminophosphorane(31P) = 27.4; 2J(31P−31P) = 111.5 Hz], which lies
in the typical range of four-coordinate PV compounds [cf.
δ(31P) = 33.4 ppm for (iPr)2NP(Cl)(N3)N(Ph)·AlCl3].34 In
1
the H spectrum, four sets of signals are detected for the iPr
groups, with one of the septets of the methine protons being
split into a septet of doublets, indicating interaction of that
proton with the phosphenium phosphorus atom, which results
in deshielding and therefore a rather strong downfield-shifted
signal.
To render the formation of 7[GaCl4] stoichiometrically,
2iPr[GaCl4] and an equimolar amount of iPr2NPCl2 were
combined at −50 °C and allowed to slowly warm to room
temperature, which was accompanied by the evolution of
dinitrogen (Scheme 5, reaction i). 7[GaCl4] is the sole product
and can be crystallized by gradually cooling the saturated
reaction mixture to −24 °C overnight (isolated yield 63%). The
formation of 7[GaCl4] underlines the Staudinger-type
reactivity of azidophosphenium species with phosphanes. In
the Staudinger reaction, organic azides typically react with PPh3
in an oxidative addition to yield iminophosphoranes as an
intermediate, which can be further hydrolyzed to give amines
and phosphane oxides.10 In the case of 2iPr[GaCl4] in the first
reaction step, either the phosphenium cation 1iPr+ or
iPr2NPCl2 adds with its phosphorus atom to the Nazide atom
while eliminating dinitrogen and forming the corresponding
iminophosphorane-substituted phosphenium cation. The dica-
tionic structure proposed by Wolf and co-workers was not
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obtained by extracting the crude reaction mixture with n-hexane
Scheme 6. Two Canonical Lewis Formulas of the Cation in
7[GaCl4] Displaying π Delocalization along the N−P−N−
P−N Backbone in 7+
1
and identified by 31P and H NMR spectroscopy. As expected,
the tricoordinated PIII resonates in the 31P NMR spectrum at
156.2 ppm (cf. 12 129.9 ppm; Figure 5),17,18,39 whereas PV is
high-field-shifted compared to the starting material 7[GaCl4]
31
V
[δP ( P) = −6.4; cf. 7[GaCl4] 27.4 ppm], indicating the loss of
positive charge. 7-Cl crystallizes in the monoclinic space group
P21 with two molecules in the unit cell (Figure 6, right). Upon
chlorine back-substitution, the N1−P1 [1.640(4) Å] and N2−
P1 [1.660(4) Å] distances elongate significantly toward values
typical for N−P single bonds in chlorophosphanes [cf. 12 (avg)
1.644 Å; Figure 5].39 The N2−P2 [1.504(4) Å] bond is found
to be shorter than that in the parent cation 7+, indicating a
localized PV−N double bond, whereas the P2−N3 [1.603(4)
Å] distance can still be considered a PV−N single bond. The
PIII atom P1 is trigonal-pyramidally coordinated, whereas P2
exhibits the expected distorted tetrahedral environment. The
striking structural feature of 7-Cl is the P−Cl bond [2.207(2)
Å], which is significantly elongated with respect to the
respective sum of the covalent radii of phosphorus and chlorine
[cf. ∑rcov(P−Cl) = 2.10 Å]. Therefore, it is plausible to discuss
a certain degree of phosphenium character due to strong
hyperconjugative effects, which is underlined by a calculated
positive charge of 0.43e for the isolated 7+ cation, which is only
slightly more positive than the formal cation in
[(Me3Si)2NPCl][Cl] with a cationic charge of 0.34e.19
Having fully characterized 7[GaCl4], we turned back to our
initial starting point to uncover the decomposition products of
azidophosphenium salt 2SiMe3[GaCl4] (Scheme 7). In a first
series of experiments, a CH2Cl2 solution of 2SiMe3[GaCl4] was
allowed to slowly warm to room temperature and the reaction
was followed by 31P NMR spectroscopy. At −40 °C, only
minimal amounts of the parent azidophosphenium cation
2SiMe3+ were present in solution (green, Figure 7). In addition,
two broad doublets could be detected in the downfield region
of the spectrum at 357.6 and 354.4 ppm, respectively, with a
splitting of 90.8 and 79.9 Hz and a corresponding second set of
doublets at 29.3 and 22.1 ppm, respectively, supportive of a
species that contains both a phosphenium phosphorus atom
and a four-coordinated PV. Alongside these three species,
impurities are detected in the high-field region, which could not
be identified. Hence, these data are supportive of the formation
−
phosphorus and GaCl4 [7[GaCl4] 3.532(1) Å; 8 3.289(2) Å]
are in the range of the respective van der Waals radii of
phosphorus and chlorine [∑rvdw(P−Cl) = 3.55 Å].25 There-
fore, the anion and cation are well separated, which is
supported by the calculated charge transfer.33 Overall, P2 is
distorted tetrahedrally coordinated, which is in accordance with
a four-coordinate phosphonium phosphorus.
To test the reactivity of 7[GaCl4] as a dienophile, we added
2,3-dimethyl-1,3-diene (dmb) because phosphenium cations,
which might be regarded as nucleophilic carbenes with respect
to the reactivity, are known to react with suitable dienes in
chelotropic [4 + 1] cycloaddition reactions. This reaction
resulted in the formation of the expected phospholenium
species 7-dmb[GaCl4] (Scheme 5, reaction iii), which was
crystallographically characterized (Figure 5, left). 7-dmb-
[GaCl4] crystallizes in the monoclinic space group P21/n
with four formula units in the unit cell. Upon the addition of
dmb, the P−Namino [1.624(2) Å] and Nimino−P1 [1.618(2) Å]
bonds elongate, whereas the P2−Nimino [1.533(2) Å] bond
shortens significantly compared to 7[GaCl4] (cf. 11 1.511 Å;
Figure 5).36 The anion and cation are well separated, and no
contacts are observed between them. The phosphole moiety is
almost planar and slightly bent toward the PVCl2 fragment.
Furthermore, we wanted to set free the parent chlorophos-
phane iPr2NPClNP(Cl)2NiPr2 (7-Cl). Therefore, GaCl3 needs
to be removed from the reaction mixture, which can easily be
achieved by adding 2,2′-bipyridine (bipy) to a CH2Cl2 solution
of 7[GaCl4] because GaCl3 is known to form a chelating
complex with bipy in [GaCl2(bipy)2][GaCl4], which is hardly
soluble in CH2Cl2 and can be removed by filtration (Scheme 5,
reaction iv).37,38 In the course of this reaction, chlorine is back-
substituted to the phosphenium phosphorus and 7-Cl is
Figure 6. ORTEP drawings of the molecular structures of 7-dmb[GaCl4] (left) and 8 (right). Ellipsoids are drawn at 50% probability at −100 °C,
and only the major part is displayed. Selected bond lengths (Å) and angles (deg): 7-dmb[GaCl4], P1−N1 1.624(2), P1−N2 1.618(2), P2−N2
1.533(2), P2−N3 1.607(2), P2−Cl1 2.0207(9), P2−Cl2 2.0073(9), P1−C7 1.799(2), P1−C10 1.796(2); P2−N2−P1 137.7(1), N2−P2−N3
114.1(1); Σ(<P1) 335.26, Σ(<P2) 335.62, Σ(<N1) 358.76, Σ(<N3) 360; N2−P1−N1−C1 79.8(2), P1−C7−C8−C11 −164.9(2); 8, P1−N1
1.612(4), P1−N2 1.597(4), P2−N2 1.550(4), P2−N3 1.588(5), P2−Cl1 1.996(2), P2−Cl2 2.010(2), P1−Cl3 3.289(2); N1−P1−N2 105.0(2),
P2−N2−P1 133.2(3), N2−P2−N3 113.6(2); Σ(<P1) 337.64, Σ(<N1) 359.9, Σ(<N3) 359.4; N2−P1−N1−C4 178.0(2), N1−P1−N2−P2 9.4(4),
N3−P2−N2−P1 −130.5(4), Cl2−P2−N3−Si1 120.8(3).
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Scheme 7. Self-Condensation via a Staudinger Reaction in Azidophosphenium Species 2SiMe3[GaCl4]
Figure 7. 31P NMR spectrum of a CH2Cl2 solution of 2SiMe3[GaCl4] recorded at −40 °C. The signal at 368.6 ppm ( ) corresponds to the cation
▲
+
+
+
■
▼
2SiMe3 , and the doublets correspond to 13 ( ) and 14 ( ), respectively, and unidentified impurities.
of [(Me3Si)2NPNP(Cl)2N(SiMe3)2][GaCl4] (13) as the major
Scheme 8. Comprehensive Solution Chemistry of
(Me3Si)2NPCl2 in the Presence of GaCl3 and Me3SiN3
31
31
V
product [δphosphenium( P) = 357.6 ppm, δP ( P) = 29.3 ppm;
Figure 7]. However, the second set of doublets indicates the
formation of mixed species [(Me3Si)2NPNP(Cl)(N33)1N-
31
V
(SiMe3)2][GaCl4] (14; δphosphenium( P) = 354.3 ppm, δP ( P)
= 22.1 ppm; Figure 7 and Scheme 7). In analogy to the
formation of 7[GaCl4], 2SiMe3[GaCl4] was treated with an
equimolar amount of (Me3Si)2NPCl2, which afforded 13 in a
higher purity according to 31P NMR experiments. However,
traces of 14 are still present in the reaction mixture, indicating a
dynamic solution chemistry of 2SiMe3[GaCl4], GaCl3, and
(Me3Si)2NP(N3)Cl with respect to chlorine/azide scrambling,
which is regularly observed in CH2Cl2 solutions.40 Neither
crystals of 13 nor 14 could be grown because in all cases oily
residues remained and showed no propensity to become solid.
Interestingly, treating 1SiMe3[GaCl4] with 0.5 equiv of
Me3SiN3 at −50 °C in CH2Cl2 and warming the mixture to
room temperature over a period of 2 h yielded after
concentration and storage at −24 °C under exclusion of light
for 48 h a colorless crystalline solid. The compound was
characterized by X-ray crystallography as the unprecedented
bicyclic compound [(Me3Si)2N2P2Cl2N(Ga2Cl5)] (15; Scheme
8 and Figure 8, left). The formation of 15 is best understood as
GaCl3-assisted elimination of two molecules of Me3SiCl from
13 and rearrangement of the naked [(Me3Si)2N3P2Cl2]−
fragment to a cyclic intermediate, which is subsequently
+
stabilized by adduct formation with a Ga2Cl5 fragment.
Intermediates of this transformation could not be observed.
To test this hypothesis, we added GaCl3 to a solution
containing 13 and followed the reaction with 31P NMR
spectroscopy, which clearly indicated the formation of 15. The
stabilization of anionic intermediates by a Ga2Cl5+ fragment has
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Figure 8. ORTEP drawings of 15 (left) and 19+ (right). The anion is omitted for clarity. Ellipsoids are drawn at 50% probability. Selected bond
lengths (Å) and angles (deg): 15, P1−N1 1.634(2), C1−P1 1.773(3), N1−C4 1.504(3), N1−Si1 1.769(2), C1−C2 1.518(3), C2−C3 1.331(3),
P1−C7 1.801(3), P1−C10 1.797(3), C7−C8 1.498(4), C8−C9 1.322(4); Σ(<N1) 359.26, Σ(<P1) 324.63; Si1−N1−P1−C7 59.5(2), C4−N1−
P1−C10 115.27(19), C2−C1−P1−N1 51.2, C4−N1−P1−C1 −7.0(2); 5, P2−N2 1.643(2), P2−C23 1.812(3), P2−C26 1.824(3), P2−C29
1.833(3), N2−C20 1.539(3), N2−Si2 1.790(2), C20−C21 1.499(4), C21−C22 1.328(4), C26−C27 1.538(5), C27−C28 1.298(5); Σ(<N2)
356.74, Σ(<P2) 340.59. Selected bond lengths and angles of 19+ are listed in Table 1
Scheme 9. Different Reactivities Observed in the Reaction of 2R[GaCl4] with Phosphanes PPh3 and PcHex3
been previously described in the reaction of HypN(SiMe3)PCl2
(Hyp = Si(SiMe3)3) with GaCl3.41 In the 31P NMR spectrum of
isolated 15, two resonances were detected for the NP(Cl)N
group at 142.6 ppm, in good agreement with other strained
NPIII heterocyclic compounds [cf. 6 δ(31P) = 102.5 ppm;
Scheme 4],18 and for the tetracoordinated PV at 23.9 ppm, with
both signals being split into doublets with a 2J(31P−31P)
coupling of 64.5 Hz, which is in good agreement with the few
examples of 1,3,2λ3,4λ5-diazaphosphetidines, which were shown
to form by a 1,3-SiMe3 shift from iminophosphane−
iminophosphoranes (Scheme 4).17,18 15 crystallizes in the
orthorhombic space group Pbca with eight molecules in the cell
(Figure 8, left). The characteristic structural feature of 15 is the
(Me3Si)2N2P2Cl2 four-membered ring with two long P2−Namino
bonds [1.733(2) and 1.736(2) Å] and two significantly shorter
P1−Namino distances [1.640(2) and 1.636(2) Å], in accordance
with related systems that also incorporate a four-coordinated
phosphorus atom [cf. 16 P−N 1.665(2) Å; Figure 5].42 The
N1−P2−N2 angle [83.5(1)°] is rather acute, whereas the N1−
P1−N2 angle is close to 90°. The exocyclic SiMe3 groups are
attached to the amino nitrogen by single bonds [1.789(2) and
1.786(2) Å; ∑rcov(Si−N) = 1.87 Å]24 and lie below a plane
that is formed by the central P2N2 ring. The exocyclic NGa2Cl
ring is attached to the central P2N2 moiety via the nitrogen
atom N3 with a comparably short P1−N3 [1.565(2) Å]
distance, which can be regarded as a PV−N single bond, with a
partial charge on N3 of −1.87e according to NBO analysis and
an overall negative charge of the [(Me3Si)2N3P2Cl2] fragment
of −0.95e. The charge is compensated for via the unusual
Ga2Cl5 fragment, which is covalently bound to N3 with Ga−N
single bonds [1.903(2) and 1.906(2) Å; ∑rcov(Ga−N) = 1.92
Å, cf. 10 Ga−Nimino 1.946 Å; Figure 5].35 Within the Ga2Cl5
moiety, two long Ga−Cl bonds are detected between Ga and
the bridging chlorine atom Cl7 [2.3273(8) and 2.3450(7) Å,
∑rcov(Ga−Cl) = 2.23 Å],24 whereas the exocyclic Ga−Cl
distances can be considered as typical polar covalent single
bonds (avg 2.121 Å). In agreement with this observation is the
calculated partial charge of −0.40e for Cl7, which is less
negative than the other chlorine atoms at −0.47e.
Having prepared 7[GaCl4], we wanted to investigate the
possibility of utilizing azidophosphenium cations as building
blocks for the generation of cations with multiple phosphorus
atoms. Reacting 2iPr[GaCl4] or 2SiMe3[GaCl4] with
phosphanes of the type PR3 (R = cHex, Ph) should yield
iminophosphorane-substituted phosphenium cations of the
type [R2NPNPR′3][GaCl4] (Scheme 9). In the earlier studies
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Table 1. Selected Structural Data (Distances in Å and Angles in deg) and 31P NMR Data (Chemical Shifts in ppm) of
+
Aminophosphenium Species 1iPr+, 2iPr+, 2SiMe3 , 7[GaCl4], 8, 15, 7-dmb[GaCl4], and 7-Cl
a
a
P−N1
P−X
N2−P2
P2−N3
Namino−P−X
P1−Nimino−P2
Σ(<P2)
31P P1
31P P2
1iPr+
1.591(3)
2.003(1)
1.665(2)
106.8(1)
294.7
310.9
367.5
311.2
48.1
2iPr+
1.6003(9)
100.57(5)
+
2SiMe3
7[GaCl4]
1.611(2)
1.624(2)
1.640(4)
1.612(4)
1.597(2)
1.618(2)
1.660(4)
1.597(4)
1.573(3)
1.557(2)
1.533(2)
1.597(2)
1.607(2)
104.97(9)
112.4(1)
129.4(1)
137.7(1)
334.58
335.26
333.26
335.62
327.48
27.4
−4.4
−6.4
30.4
49.1
7-dmb[GaCl4]
7-Cl
8
156.2
311.3
303.8
1.550(4)
1.588(5)
105.0(2)
107.6(4)
133.2(3)
128.3(2)
b
15
1.62
1.628(3)
a
b
+
X = Cl (1), Nazide (2iPr+, 2SiMe3 ), Nimino (8−15). NiPr moiety disordered; therefore, averaged P−N distance.
by Wolf and co-workers, such cations were prepared in the
reaction of 2iPr[AlCl4] with PBu3 and PPh3, whereas at low
temperatures, PBu3 formed a Lewis acid base adduct with a
phosphenium cation, as indicated by the characteristic 31P
NMR shifts for these adducts and a large P−P coupling
constant [cf. [4···PBu3][AlCl4] δphosphenium(31P) = 102.3 ppm,
were observed. The main reason for the different reactivities
observed supposedly lies in the steric congestion that stems
+
from the N(SiMe3)2 moiety in 2SiMe3 , which effectively
denies the formation of an iminophosphorane-substituted
phosphenium salt.
The formation of 20SiMe3 prompted us to investigate the
possibility of using 2iPr[GaCl4] and 2SiMe3[GaCl4] as
precursors for azido(chloro)phosphanes because these species
cannot be prepared using standard routes such as the addition
of 1 equiv of AgN3, Me3SiN3, or NaN3 because in all cases a
mixture of mono- and disubstituted azidophosphanes was
obtained. In contrast, in the presence of an excess of Me3SiN3,
complete conversion to iPr2NP(N3)2 (22iPr) and (Me3Si)2NP-
(N3)2 (22SiMe3) was accomplished. It is worth noting that the
synthesis of 22R can also be achieved by addition of 2 equiv of
AgN3 or NaN3 in CH2Cl2 and workup from n-hexane (Scheme
10).
δPBu (31P) = 20 ppm, J(31P−31P) = 327 Hz].43 We therefore
3
treated 2iPr[GaCl4] and 2SiMe3[GaCl4] with PR3 (R = Ph,
cHex) at −50 °C, and the mixtures were rapidly warmed to
room temperature, resulting in vigorous gas evolution. The 31P
NMR spectra showed a species with an AX spin system
supportive of a iminophosphorane-substituted phosphenium
salt of the type [iPr2NPNPPh3][GaCl4] [17[GaCl4];
δphosphenium(31P) = 310.9 ppm, δPBu (31P) = 28.8 ppm,
3
J(31P−31P) = 68 Hz] because Wolf et al. reported identical
values for [iPr2NPNPPh3][AlCl4] (17[AlCl4]), indicating that
there is no electronic effect upon a change in the anion from
−
GaCl4− to AlCl4 . 2SiMe3[GaCl4] as a starting material yielded
Scheme 10. Attempted Synthesis of Azidochlorophosphanes
Resulting in the Formation of Diazides 22R (R = iPr, SiMe3)
and Synthetic Access to 20R via bipy-Induced Chlorine
Back-substitution to Azidophosphenium Species 2R[GaCl4]
[(Me3Si)2NPNPPh3][GaCl4] (18[GaCl4]) with a more
deshielded phosphenium phosphorus atom because the
resonance for this atom at 361.5 ppm is 50 ppm downfield-
shifted compared to 17[GaCl4], which clearly shows that the
(Me3Si)2N substituent is more electron-withdrawing than
iPr2N (vide infra). However, the molecular structure of
17[GaCl4] and 18[GaCl4] could not be determined. The
introduction of P(cHex)3 as a base in the reaction with
2iPr[GaCl4] in CH2Cl2 resulted after concentration of the
reaction mixture in the deposition of colorless crystals, which
were identified by a single-crystal structure determination as
[iPr2NPNP(cHex)3][GaCl4] (19). 19 crystallizes in the
monoclinic space group P21/c with two formula units and
one molecule of CH2Cl2 in the asymmetric unit. In one cation,
the iPr2NP group is disordered and split into two parts. In the
other independent cation, one NiPr moiety is found to be
disordered. Because the molecular geometry is similar in both
formula units, just one of the two cations is discussed. The
metrical parameters are in the expected range and compare well
with the values in 7+ and 8+ (Table 1). The bond distances
N1−P1 (avg 1.62 Å), P1−N2 [1.573(3) Å], and N2−P2
[1.628(3) Å] are supportive of a phosphonium formulation
similar to that discussed for 9+.
To circumvent these drawbacks, to a CH2Cl2 solution of
2R[GaCl4] (R = iPr, SiMe3) was added a stoichiometric
amount of bipy to remove GaCl3 and obtain the chloride-back-
substituted chlorophosphane. Removal of the solvents in vacuo
and extraction of the residues with n-hexane afforded in the
case of 2iPr[GaCl4] a mixture of chlorophosphanes iPr2NP-
(N3)Cl (20iPr) [20iPr δ(31P) 155.1 ppm] and iPr2NPCl2 (in
an analogous procedure, 20SiMe3 is obtained; 20SiMe3 δ(31P)
173.4 ppm). This mixture solidifies at ca. −25 °C, crystals
suitable for X-ray analysis were selected at −50 °C, and the
molecular structure was successfully determined (Figure 9).
In contrast, the addition of P(cHex)3 to a CH2Cl2 of
2SiMe3[GaCl4] was not accompanied by gas evolution, and in
the 31P NMR spectrum of the reaction mixture, two species
were detected. On the one hand, the azidochlorophosphane
(Me3Si)2NP(N3)Cl (20SiMe3) and, on the other hand, the
GaCl3 adduct of P(cHex)3 (cHex)3P···GaCl3 (21),44 which
crystallize from concentrated reaction mixtures (Scheme 9),
The crystal structure revealed, in good accordance with the 31
P
NMR data, a mixture of both 20iPr and iPr2NPCl2 in an
occupational disorder of 0.79/0.21 (Figure 9). 20iPr crystallizes
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= 8.25 Hz, CH(CH3)2). 31P{1H} NMR (25 °C, CD2Cl2, 202.46
MHz): δ 294.7 (br s, NPCl). Raman (100 mW, 25 °C, 3 scans, cm−1):
3305(1), 3237(1), 3181(1), 2976(1), 2944(1), 1459(2), 1399(2),
1360(2), 1320(2), 1263(2), 1201(2), 1163(2), 1131(2), 1121(2),
1032(5), 927(2), 884(2), 634(3), 567(5), 506(3), 479(3), 397(3),
374(4), 360(3), 345(10), 265(3), 201(4).
Synthesis of [iPr2NPN3][GaCl4] (2iPr[GaCl4]). A CH2Cl2 (5 mL)
solution of GaCl3 (0.283 g, 1.61 mmol) was added dropwise to a
stirred solution of iPr2NPCl2 (0.325 g, 1.61 mmol) in CH2Cl2 (2 mL)
at −75 °C. The clear colorless mixture was allowed to stir for 30 min
at this temperature and treated with a CH2Cl2 solution (5 mL) of
Me3SiN3 (0.186 g, 1.61 mmol) afterward. The yellowish solution was
concentrated to incipient crystallization, whereas the temperature was
maintained below −30 °C. Standing overnight in a freezer (−80 °C)
afforded, after removal of the supernatant liquid, 0.460 g (1.20 mmol,
75%) of 2iPr[GaCl4] as colorless crystals.
Mp: 78 °C (dec). Anal. Calcd (found): C, 18.73 (19.32); H, 4.21
(3.90); N, 14.56 (14.30). 1H NMR (−20 °C, CD2Cl2, 500.13 MHz): δ
1.44−1.57 (m, 12H, CH(CH3)2), 4.31−4.44 (m, 2H, CH(CH3)2).
13C{1H} NMR (0 °C, CD2Cl2, 125.76 MHz): δ 20.20 (s, CH(CH3)2),
21.70−22.24 (m, CH(CH3)2), 50.29−50.44 (m, CH(CH3)2), 51.01 (s,
CH(CH3)2). 31P{1H} NMR (−20 °C, CD2Cl2, 202.46 MHz): δ
310.93 (s, NPN3). IR (ATR, 25 °C, 32 scans, cm−1): 3174 (w), 3101
(w), 2981 (w), 2939 (w), 2899 (w), 2879 (w), 2505 (w), 2159 (s),
1574 (w), 1468 (m), 1460 (w), 1411 (m), 1391 (w), 1373 (m), 1558
(s), 1207 (s), 1181 (m), 1165 (s), 1154 (s), 1139 (s), 1111 (s), 1020
(s), 965 (s), 909 (m), 885 (m), 848 (s), 754 (m), 638 (m), 569 (s),
552 (s), 542 (s). Raman (100 mW, 25 °C, 3 scans, cm−1): 2988(1),
2969(1), 2947(1), 2896(1), 2873(1), 2733(1), 2174(10), 2166(4),
1464(3), 1441(3), 1413(3), 1372(3), 1307(3), 1207(3), 1167(3),
1023(6), 967(3), 886(3), 759(3), 639(3), 554(3), 543(3), 469(3),
398(3), 362(3), 347(7), 275(4), 241(3), 203(4).
Figure 9. ORTEP drawing of the molecular structure of 20iPr.
Ellipsoids are drawn at 50% probability, and just the main part of the
mixed phosphane is shown because 20iPr crystallizes as a mixture of
the general formula iPr2NPCl(N3)0.79(Cl)0.21. Selected bond lengths
(Å) and angles (deg): P1−N1 1.658(1), N2−P1 1.76(3), N2−N3
1.24(1), N3−N4 1.125(4), P1−Cl1 2.1075(9); Σ(<N1) 359.26,
Σ(<P1) 324.63; N2−N3−N4 177.3; N2−P1−N1−C4 −44.9.
in the monoclinic space group P21/m with two molecules in the
unit cell. 20iPr lies on a crystallographically imposed mirror
plane, which results in disorder of the whole molecule. The P−
Namino bond [1.658(1) Å] is in the expected range for a P−N
single bond in chlorophosphanes [cf. (Me3Si)2NPCl2
1.6468(8) Å],19 with the azido group bound to the phosphorus
via a P−Nazide [1.76(3) Å] single bond [cf. 1035 P−Nazide
1.698(5) Å, 2332 P−Nazide1.706(3) Å; Figure 5]. Conclusively,
chlorine back-substitution with the aid of bipy is a viable route
toward chlorophosphanes starting from phosphenium precur-
sors, but in the presence of an azide substituent, scrambling of
the substituents might result in mixed phosphanes.40
Synthesis of [iPr2NPNP(Cl)2NiPr2][GaCl4] (7[GaCl4]). Procedure
1. A CH2Cl2 (5 mL) solution of GaCl3 (0.283 g, 1.6 mmol) was added
dropwise to a stirred solution of iPr2NPCl2 (0.325 g, 1.6 mmol) in
CH2Cl2 (2 mL) at −80 °C. The colorless mixture was allowed to stir
for 30 min at this temperature. Afterward, a CH2Cl2 solution (2.5 mL)
of Me3SiN3 (0.093 g, 0.8 mmol) was added at −60 °C, and the mixture
was allowed to slowly warm to ambient temperature and stirred for 2
h. The mixture attained a yellow color, and gas evolution could be
observed. After removal of the solvent in vacuo, a yellow oil is obtained
as the crude product, from which colorless crystals grew. The crude
mixture was taken up in fresh CH2Cl2 (0.5 mL) and placed in a freezer
(−24 °C) for 12 h. After removal of the supernatant liquid, 0.394 g
(0.71 mmol, 44%) of 7[GaCl4] was isolated as colorless crystals.
Procedure 2. A CH2Cl2 (3 mL) solution of GaCl3 (0.186 g, 1.06
mmol) was added dropwise to a stirred solution of iPr2NPCl2 (0.213 g,
1.05 mmol) in CH2Cl2 (3 mL) at −80 °C. The colorless mixture was
allowed to stir for 30 min at this temperature. Afterward, a CH2Cl2
solution (2.5 mL) of Me3SiN3 (0.123 mg, 1.05 mmol) was added at
−60 °C, and the mixture was stirred for another 30 min, followed by
the addition of another 1 equiv of iPr2NPCl2 (0.213 g, 1.05 mmol).
Subsequently, the mixture was rapidly warmed to room temperature,
which was accompanied by vigorous gas evolution. After stirring for 1
h and removal of the solvent in vacuo, a yellow oil was obtained as the
crude product, which was washed with n-hexane (1 mL). The crude
mixture is redissolved in CH2Cl2 (0.5 mL) and placed in a freezer
(−24 °C) for 12 h. After removal of the supernatant liquid, 0.370 g
(0.66 mmol, 63%) of 7[GaCl4] was isolated as colorless crystals.
Mp: 122−123 °C. Anal. Calcd (found): C, 25.79 (25.69); H, 5.05
CONCLUSION
■
Azidophosphenium cations 2R[GaCl4] (R = iPr, SiMe3) were
shown to be susceptible to the loss of dinitrogen in the
presence of phosphanes. Starting from 2iPr[GaCl4] or
2SiMe3[GaCl4], different iminophosphorane-substituted poly-
phosphorus salts 7[GaCl4], 8, 13, and 14 could be obtained
from Staudinger reactions with different chlorophosphanes, and
the comprehensive chemistry of 7[GaCl4] was studied in detail.
This study clearly demonstrates a misinterpretation of data
published by Wolf and co-workers. In an effort to develop a
route toward chlorophosphanes, phosphenium cations were
shown to be transformed to chlorophosphanes by the addition
of bipyridine as the chelating ligand, which effectively removes
−
GaCl3 from GaCl4 salts. The new topology of the NPNPN
cations formulated in this work might result in the formation
and design of new polyphosphorus ligands for transition-metal
fragments.
EXPERIMENTAL SECTION
■
Synthesis of [iPr2NPCl][GaCl4] (1iPr[GaCl4]). A CH2Cl2 (2 mL)
solution of GaCl3 (0.189 g, 1.07 mmol) was added dropwise to a
stirred solution of iPr2NPCl2 (0.213 g, 1.05 mmol) in CH2Cl2 (3 mL)
at −75 °C. The clear colorless mixture was allowed to stir for 15 min
and concentrated to incipient crystallization at −50 °C. Standing
overnight at −80 °C yielded, after removal of the supernatant solution,
0.203 g (0.53 mmol, 51%) of 1iPr[GaCl4] as colorless crystals.
Mp: 51 °C. Anal. Calcd (found): C, 19.06 (19.10); H, 3.73 (3.70);
N, 3.70 (3.72). 1H NMR (25 °C, CD2Cl2, 500.13 MHz): δ 1.49−1.59
(m, 12H, CH(CH3)2), 4.41−4.63 (m, 2H, CH(CH3)2). 13C{1H}
NMR (25 °C, CD2Cl2, 125.76 MHz): δ 23.48 (d, J(31P−13C) = 8.25
Hz, CH(CH3)2), 56.24−57.74 (m, CH(CH3)2), 58.19 (d, J(31P−13C)
1
(5.13); N, 7.52 (7.59). H NMR (25 °C, CD2Cl2, 300.13 MHz): δ
1.41 (d, J(1H−1H) = 6.80 Hz, 12H, CH(CH3)2), 1.44 (d, J(1H−1H) =
6.99 Hz, 6H, CH(CH3)2), 1.61 (d, J(1H−1H) = 6.80 Hz, 6H,
CH(CH3)2), 3.91 (sept, J(1H−1H) = 6.80 Hz, CH(CH3)2), 4.03 (sept,
J(1H−1H) = 6.80 Hz, CH(CH3)2), 4.08−4.25 (sept, CH(CH3)2),
4.88−4.98 (sept, CH(CH3)2). 13C{1H} NMR (25 °C, CD2Cl2, 75.48
MHz): δ 22.16 (d, J(31P−13C) = 2.20 Hz, CH(CH3)2), 22.31 (d,
J(31P−13C) = 2.75 Hz, CH(CH3)2), 27.09 (d, J(31P−13C) = 11.55 Hz,
CH(CH3)2), 51.67 (d, J(31P−13C) = 5.50 Hz, CH(CH3)2), 52.63 (d,
J(31P−13C) = 27.51 Hz, CH(CH3)2), 54.23 (d, J(31P−13C) = 11.00 Hz,
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CH(CH3)2). 31P{1H} NMR (25 °C, C6D6, 121.51 MHz): δ 27.40 (d,
J(31P−31P) = 111.5 Hz, NPCl2N), 311.16 (d, J(31P−31P) = 111.5 Hz,
NPN). IR (ATR, 25 °C, 16 scans, cm−1): 3167 (w), 2976 (w), 2935
(w), 2874 (w), 2164 (w), 1454 (w), 1413 (m), 1400 (w), 1390 (w),
1375 (m), 1282 (m), 1251 (m), 1237 (s), 1203 (m), 1170 (m), 1146
(s), 1122 (m), 1109 (s), 1027 (s), 989 (s), 968 (s), 887 (w), 859 (m),
797 (m), 738 (w), 659 (m), 754 (m), 636 (w), 607 (w), 564 (s), 551
(s). Raman (12 mW, 25 °C, 3 scans, cm−1): 3238(1), 2984(1),
2940(1), 2456(1), 1456(1), 1444(1), 1415(1), 1318(1), 1205(1),
1168(1), 1144(1), 1123(1), 1031(1), 969(1), 945(1), 893(2), 861(1),
799(1), 756(1), 706(1), 660(1), 637(1), 570(1), 554(1), 504(2),
485(1), 469(1), 406(1), 378(1), 346(10), 326(1), 300(1), 289(1),
252(1), 220(1), 202(1).
Synthesis of [iPr2NPNP(Cl)2N(SiMe3)2][GaCl4] (8). To a cooled
sample of 2iPr[GaCl4] (0.326 g, 0.85 mmol) at −50 °C was added a
CH2Cl2 (3 mL) solution of (Me3Si)2NPCl2 (0.223 g, 0.85 mmol) at
that temperature, and the mixture was slowly warmed to room
temperature over a period of 2 h. At ca. −30 °C, vigorous gas
evolution was observed. Removal of the solvents in vacuo resulted in
an oily colorless residue, which was washed with n-hexane (1 mL).
The residual oil was redissolved in minimal amounts of C6H5F, and
standing at 5 °C for 12 h afforded colorless crystals of 8 (0.280 g, 0.45
mmol, 53%).
Synthesis of [iPr2NP(Cl)NP(Cl)2NiPr2][GaCl4] (7-Cl). A CH2Cl2
(5 mL) solution of 2,2′-bipyridine (0.157 g, 1.01 mmol) was dropwise
added to a CH2Cl2 solution of 7[GaCl4] (0.559 g, 1.00 mmol) at 0 °C.
The obtained suspension was allowed to stir at room temperature over
a period of 2 h, the solvent was removed in vacuo afterward, and the
residues were extracted with n-hexane and filtered. Removal of n-
hexane in vacuo yielded 0.283 g (0.74 mmol, 74%) of 7-Cl as a
colorless crystalline solid.
Mp: 60 °C (dec). Anal. Calcd (found): C, 37.66 (38.091); H, 7.37
1
(7.31); N, 10.98 (11.30). H NMR (25 °C, CD2Cl2, 300.14 MHz): δ
1.09−1.43 (m, 24H, CH(CH3)3), 3.76 (sept, J(1H−1H) = 6.80 Hz,
2CH(CH3)3), 3.86 (sept, J(1H−1H) = 6.80 Hz, 2CH(CH3)3). 31P{1H}
NMR (25 °C, CD2Cl2, 121.51 MHz): δ 156.2 (d, J(31P−31P) = 140.85
Hz, NPClN), −6.4 (d, J(31P−31P) = 140.85 Hz, NPCl2N). IR (ATR,
25 °C, 32 scans, cm−1): 2971 (m), 2932 (w), 2871 (w), 2835 (w),
2760 (w), 2722 (w), 1463 (w), 1407 (m), 1395 (w), 1367 (m), 1315
(s), 1273 (m), 1199 (m), 1173 (s), 1150 (s), 1116 (s), 1021 (m), 991
(s), 972 (s), 880 (m), 857 (m), 725 (m), 653 (m), 634 (m), 551 (s),
528 (s). Raman (632 nm, 100 mW, 25 °C, 5 scans, cm−1): 2973(5),
2957(5), 2946(7), 2934(7), 2896(4), 2874(4), 2725(2), 2715(2),
1463(4), 1455(4), 1408(2), 1391(2), 1380(3), 1372(3), 1323(3),
1315(3), 1200(2), 1174(2), 1142(2), 1120(2), 1031(2), 1023(2),
992(2), 974(3), 944(2), 936(2), 924(1), 892(4), 880(3), 858(1),
655(2), 634(5), 552(2), 504(4), 494(2), 453(7), 407(5), 398(3),
386(3), 366(2), 337(2), 318(1), 287(10), 235(2).
Anal. Calcd (found): C, 23.29 (23.59); H, 5.21 (4.92); N, 6.79
(7.32). 1H NMR (25 °C, CD2Cl2, 300.13 MHz): δ 1.38 (d, 3J(1H−1H)
= 6.8 Hz, 6H, C(CH3)2), 1.61 (d, 3J(1H−1H) = 6.8 Hz, 6H, C(CH3)2),
4.1 (sept, 3J(1H−1H) = 6.8 Hz = 1H, CH(CH3)2), 5.03 (sept, d,
3J(1H−1H) = 6.8 Hz, J(31H−1H) = 2.8 Hz, CH(CH3)2). 31P{1H}
Decomposition of [(Me3Si)2NPN3][GaCl4]. A CH2Cl2 solution of
freshly prepared 2SiMe3[GaCl4] in CH2Cl2 (5 mL) at −75 °C was
allowed to slowly warm to room temperature over a period of 4 h,
resulting in a yellowish reaction mixture, while gas evolution was
observed. The solvents were removed in vacuo, and the oily residues
were washed with n-hexane (1 mL). The residual yellowish oil was
redissolved in CH2Cl2 (2 mL) and concentrated to a volume of 0.3
mL. Crystallization attempts from CH2Cl2 and C6H5F and vapor
diffusion of n-hexane into a saturated CH2Cl2 solution failed in all
cases, and the products were identified by 31P NMR spectroscopy.
31P{1H} NMR (−40 °C, CD2Cl2, 121.49 MHz): for 2Si-
Me3[GaCl4], 368.6 (s); 13+), 357.6 (d, J(31P−31P) = 90.8 Hz), 29.3
(d, J(31P−31P) = 90.8 Hz); for 14+, 354.4 (d, J(31P−31P) = 79.9 Hz),
22.1 (d, J(31P−31P) = 79.9 Hz).
Synthesis of [(Me3Si)2N2P2Cl2N(Ga2Cl5)] (15). A CH2Cl2
solution (4 mL) of GaCl3 (0.177 g, 1.00 mmol) was dropwise
added to a stirred solution of (Me3Si)2NPCl2 (0.263 g, 1.00 mmol) in
CH2Cl2 (2 mL) at −75 °C. The resulting colorless solution was
maintained at that temperature for 30 min and treated with a CH2Cl2
(2 mL) solution of Me3SiN3 (0.060 g, 0.52 mmol) afterward. The
colorless clear mixture was slowly warmed to room temperature, with
bubbling setting in at −20 °C. Stirring at room temperature for 1 h
resulted in a yellowish solution, from which the solvents were removed
in vacuo and the oily residues were washed with n-hexane (1 mL). The
residual yellowish oil was redissolved in CH2Cl2 and concentrated to
incipient crystallization. After standing at −24 °C for 72 h, colorless
crystalline plates of 15 were obtained but could not be effectively
separated from the supernatant oil.
Anal. Calcd (found): C, 11.30 (12.63); H, 2.84 (3.13); N, 6.59
(5.61). 1H NMR (25 °C, CD2Cl2, 300.13 MHz): δ 0.50 (s, 18H,
Si(CH3)3). 13C{1H} NMR (25 °C, CD2Cl2, 75.48 MHz): δ 0.37 (dd,
J(31P−13C) = 2.7 Hz, J(31P−13C) = 3.7 Hz, Si(CH3)3). INEPT 29Si
NMR (25 °C, CD2Cl2, 59.62 MHz): δ 16.09 (s, Si(CH3)3). 31P{1H}
NMR (25 °C, CD2Cl2, 121.49 MHz): δ 23.86 (d, J(31P−31P) = 64.5
Hz), 142.64 (d, J(31P−31P) = 64.5 Hz).
Synthesis of [R2NPNPPh3][GaCl4] [R = iPr2 (17), SiMe3 (18)]. A
CH2Cl2 solution of GaCl3 (0.174 g, 0.99 mmol) was dropwise added
to a stirred solution of R2NPCl2 (R = iPr, SiMe3) (0.202 or 0.263 g, 1
mmol) in CH2Cl2 (2 mL) −75 °C. The resulting colorless solution
was maintained at that temperature for 30 min and treated with a
CH2Cl2 (2 mL) solution of Me3SiN3 (113 mg, 0.98 mmol) afterward,
resulting in the formation of a colorless crystalline solid that
precipitates from the reaction mixture. Subsequently, a CH2Cl2 (5
mL) solution of PPh3 (263 mg, 1.0 mmol) was dropwise added at −50
°C and the mixture rapidly warmed to ambient temperature, which
NMR (25 °C, CD2Cl2/CH2Cl2, 121.51 MHz): δ 311.3 (d, 2J(31P−31P)
= 111.5 Hz, NPNiPr2), 30.4 (d, NP(Cl)2N). Raman (100 mW, 25 °C,
4 scans, cm−1): 2986(3), 2970(2), 2944(2), 2906(4), 2732(1),
1459(3), 1361(2), 1331(2), 1168(2), 1142(2), 1136(2), 1033(3),
1011(2), 972(2), 969(2), 892(3), 862(2), 773(2), 659(6), 641(5),
576(2), 554(2), 500(3), 471(2), 451(3), 419(2), 402(2), 370(3),
345(10), 290(2), 213(2).
Synthesis of [iPr2NP(dmb)NP(Cl)2NiPr2][GaCl4] (7-dmb-
[GaCl4]). A CH2Cl2 (5 mL) solution of dmb (0.071 g, 0.86 mmol)
was added dropwise to a CH2Cl2 solution of 7[GaCl4] (0.200 g, 0.36
mmol) at −20 °C. The colorless mixture was allowed to slowly warm
to room temperature over a period of 2 h. Afterward, the solvent was
removed in vacuo, and the white solids were washed with n-hexane,
taken up in CH2Cl2 (0.5 mL), and placed in a freezer (−40 °C) for 12
h. After removal of the supernatant liquid, 0.100 g (0.16 mmol, 44%)
of 7-dmb[GaCl4] was isolated as colorless crystals.
Mp: 156 °C. Anal. Calcd (found): C, 33.73 (33.53); H, 5.98 (5.36);
1
N, 6.56 (6.46). H NMR (25 °C, CD2Cl2, 300.14 MHz): δ 1.34 (d,
J(1H−1H) = 6.80 Hz, 24H, CH(CH3)3), 1.84 (s, 6H, CCH3), 2.87−
3.18 (m, 4H, PCCH2), 3.64 (sept, J(1H−1H) = 6.80 Hz, CH(CH3)3),
3.69 (sept, J(1H−1H) = 6.80 Hz, CH(CH3)3), 3.79 (sept, J(1H−1H) =
6.80 Hz, CH(CH3)3), 3.89 (sept, J(1H−1H) = 6.80 Hz, CH(CH3)3).
13C{1H} NMR (25 °C, CD2Cl2, 75.48 MHz): δ 16.88 (d, J(31P−13C)
= 15.41 Hz, CCH3), 21.89 (d, J(31P−13C) = 2.20 Hz, CH(CH3)2),
23.32 (d, J(31P−13C) = 3.30 Hz, CH(CH3)2), 38.64 (d, J(31P−13C) =
3.30 Hz, PCCH2), 39.79 (d, J(31P−13C) = 3.30 Hz, PCCH2), 49.87 (d,
J(31P−13C) = 2.20 Hz, CH(CH3)2), 50.73 (d, J(31P−13C) = 6.05 Hz,
CH(CH3)2), 128.22 (d, J(31P−13C) = 12.11 Hz, C2CCC2). 31P{1H}
NMR (25 °C, CD2Cl2, 121.51 MHz): δ −4.35 (d, J(31P−31P) = 5.87
Hz, NPCl2N), 48.08 (d, J(31P−31P) = 5.87 Hz, NPC2N). IR (ATR, 25
°C, 32 scans, cm−1): 2981 (w), 2937 (w), 2913 (w), 2877 (w), 2856
(w), 2168 (w), 1468 (w), 1441 (w), 1412 (m), 1391 (m), 1375 (m),
1288 (s), 1215 (m), 1206 (m), 1192 (w), 1175 (m), 1153 (m), 1136
(m), 1112 (m), 1082 (w), 1018 (s), 990 (s), 949 (w), 926 (w), 894
(w), 866 (w), 852 (m), 841 (m),796 (m), 742 (w), 709 (m), 658 (m),
646 (w), 547 (s), 527 (m). Raman (100 mW, 25 °C, 4 scans, cm−1):
2990(1), 2971(1), 2945(1), 2930(1), 2907(1), 2737(1), 2722(1),
1667(1), 1468(1), 1445(1), 1416(1), 1405(1), 1385(1), 1326(1),
1311(1), 1292(1), 1210(1), 1180(1), 1154(1), 1137(1), 1127(1),
1117(1), 1033(1), 1000(1), 946(1), 928(1), 895(3), 854(1), 842(1),
797(1), 720(1), 711(1), 660(1), 647(1), 551(1), 527(1), 493(1),
456(3), 429(1), 408(3), 377(1), 347(10), 296(1), 254(1), 201(2).
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was accompanied by vigorous gas evolution. Stirring for 1 h resulted in
a yellowish solution, from which the solvent was removed in vacuo,
and the oily residues were washed with n-hexane (1 mL).
Crystallization attempts from CH2Cl2 and C6H5F and vapor diffusion
of n-hexane into a saturated CH2Cl2 solution failed in all cases, and the
products were identified by 31P NMR spectroscopy.
°C for 4 days, resulting in the deposition of colorless crystals of 20iPr.
At room temperature, crystals of 20iPr rapidly melt, whereas only
NMR data could be collected for this compound. 20SiMe3 can be
obtained in an analogous procedure.
1H NMR (25 °C, CD2Cl2, 500.13 MHz): δ 1.19 (d, J(1H−1H) =
6.94 Hz, 6H, CH(CH3)2), 1.28 (d, J(1H−1H) = 6.62 Hz, 6H,
CH(CH3)2), 3.76 (sept, J(1H−1H) = 6.94 Hz, CH(CH3)2), 3.92 (sept,
J(1H−1H) = 6.62 Hz, 6H, CH(CH3)2). 13C{1H} NMR: δ 23.56 (d,
J(31P−13C) = 11.00 Hz, CH(CH3)2), 24.25 (d, J(31P−13C) = 3.67 Hz,
CH(CH3)2), 48.12 (d, J(31P−13C) = 11.91 Hz, CH(CH3)2), 48.94 (d,
J(31P−13C) = 13.75 Hz, CH(CH3)2). 31P{1H} NMR (25 °C, CD2Cl2,
202.46 MHz): δ 155.12 (s, NPClN3), 173.4 (s, NPClN3) (20SiMe3).
1
[iPr2NPNPPh3][GaCl4] (17). H NMR (25 °C, CD2Cl2/CH2Cl2,
300.13 MHz): δ 1.47 (d, J(1H−1H) = 6.80 Hz, 6H, CH(CH3)2), 1.52
(d, J(1H−1H) = 6.80 Hz, 6H, CH(CH3)2), 4.08 (sept, J(1H−1H) =
6.80 Hz, CH(CH3)2), 4.77−4.88 (m, CH(CH3)2), 7.57−7.70 (m,
12H, m-CH, o-CH), 7.76−7.82 (m, 3H, p-CH). 31P{1H} NMR (25
°C, CD2Cl2/CH2Cl2, 121.51 MHz): δ 28.82 (d, J(31P−31P) = 67.5 Hz,
NPPh3), 310.85 (d, J(31P−31P) = 67.5 Hz, NPN).
[(Me3Si)2NPNPPh3][GaCl4] (18). 1H NMR (25 °C, CD2Cl2,
300.13 MHz): δ 0.47 (d, J(31P−1H) = 1.51 Hz, 18H, Si(CH3)3), 7.52−
7.70 (m, 12H, o-CH, m-CH), 7.75−7.84 (m, 3H, p-CH). 31P{1H}
NMR (25 °C, CD2Cl2, 121.51 MHz): δ 30.09 (d, J(31P−31P) = 59 Hz,
NPPh3), 361.50 (d, J(31P−31P) = 59 Hz, NPN).
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic data in CIF format, general information,
structure elucidation, synthesis, and computational details. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Synthesis of [iPr2NPNPcHex3][GaCl4] (19). A CH2Cl2 solution
of GaCl3 (0.174 g, 0.99 mmol) was dropwise added to a stirred
solution of iPr2NPCl2 (0.263 g, 1.0 mmol) in CH2Cl2 (2 mL) at −75
°C. The resulting colorless solution was maintained at that
temperature for 30 min and was treated with a CH2Cl2 (2 mL)
solution of Me3SiN3 (113 mg, 0.98 mmol) afterward, resulting in the
formation of a colorless crystalline solid that precipitates from the
reaction mixture. Subsequently, a CH2Cl2 (4 mL) solution of PcHex3
(278 mg, 0.99 mmol) was added dropwise at −60 °C and the mixture
rapidly warmed to ambient temperature, which was accompanied by
vigorous gas evolution. Stirring for 1 h resulted in a yellowish solution
from which the solvents were removed in vacuo, and the oily residues
were washed with n-hexane (1 mL). The residual yellowish oil was
redissolved in CH2Cl2 and concentrated to incipient crystallization.
After standing for 48 h at −24 °C, colorless crystals of 19 were
obtained (0.275 g, 0.41 mmol, 41%).
Mp: 159−164 °C (dec). Anal. Calcd (found): C, 43.80 (43.58); H,
7.06 (6.98); N, 4.09 (3.78). 1H NMR (25 °C, CD2Cl2, 300.13 MHz):
δ 1.23−1.52 (m, 14H, P(C6H11)3), 1.37 (d, J(1H−1H) = 6.80 Hz, 6H,
CH(CH3)2), 1.48 (d, J(1H−1H) = 6.80 Hz, 6H, CH(CH3)2), 1.76−
1.83 (m, 3H, P(C6H11)3), 1.87−1.98 (m, 12H, P(C6H11)3), 2.11−2.27
(m, 4H, P(C6H11)3), 4.00 (sept, J(1H−1H) = 6.80 Hz, CH(CH3)2),
4.60−4.74 (m, CH(CH3)2). 13C{1H} NMR (25 °C, CD2Cl2, 75.46
MHz): δ 19.90 (s, P(C6H11)3), 22.24 (d, J(31P−13C) = 2.20 Hz,
P(C6H11)3), 25.49 (s, P(C6H11)3), 26.11 (d, J(31P−13C) = 1.10 Hz,
CH(CH3)2), 26.25 (s, P(C6H11)3), 26.61 (s, P(C6H11)3), 26.78 (s,
P(C6H11)3), 26.83−27.06 (m, P(C6H11)3), 28.48 (s, P(C6H11)3), 28.61
(d, J(31P−13C) = 3.85 Hz, P(C6H11)3), 34.75 (d, J(31P−13C) = 55 Hz,
P(C6H11)3), 49.62 (s, CH(CH3)2), 49.85−50.17 (m, CH(CH3)2),
50.54 (s, CH(CH3)2). 31P{1H} NMR (25 °C, CD2Cl2/CH2Cl2, 121.51
MHz): δ 49.1 (d, J(31P−31P) = 23.5 Hz, NP(C6H11)3), 303.81 (s,
NPN). IR (ATR, 25 °C, 32 scans, cm−1): 3183 (w), 2973 (w), 2933
(s), 2856 (s), 2725 (w), 2674 (w), 2092 (w), 1591 (w), 1447 (s), 1408
(w), 1397 (w), 1386 (w), 1371 (m), 1296 (m), 1260 (s), 1228 (m),
1202 (s), 1174 (s), 1157 (m), 1116 (s), 1041 (m), 1004 (s), 981 (s),
919 (m), 889 (s), 850 (s), 824 (m), 773 (m), 760 (m), 739 (m), 693
(w), 636 (w), 578 (w), 540 (s), 530 (s). Raman (12 mW, 25 °C, 3
scans, cm−1): 3237(1), 2977(1), 2941(1), 2904(1), 2877(1), 2858(1),
2398(1), 1445(1), 1389(1), 1381(1), 1354(1), 1331(1), 1294(1),
1284(1), 1217(1), 1206(1), 1174(1), 1119(1), 1087(1), 1051(1),
1023(2), 1005(1), 982(1), 942(1), 887(1), 848(1), 818(2), 792(1),
774(1), 761(1), 740(1), 694(1), 687(1), 637(2), 556(2), 541(1),
518(1), 506(1), 469(1), 444(1), 421(1), 375(2), 343(10), 321(1),
309(1), 298(1), 220(3).
AUTHOR INFORMATION
Corresponding Author
*E-mail: axel.schulz@uni-rostock.de.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Dr. Dirk Michalik is gratefully acknowledged for his help with
variable-temperature 31P NMR experiments. Financial support
by the Fonds der chemischen Industrie (fellowship to C.H.)
and the DFG (Grant SCHU 1170/8-1) is gratefully acknowl-
edged.
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