Low-valent chemistry: An alternative approach to phosphorus-containing oligomers

Article abstract of DOI:10.1021/ic502229w

A convenient preparative approach to low-valent phosphorus-rich oligomers is presented. Ligand substitution reactions involving anionic diphosphine ligands of the form [(PR₂)₂N]^- and [(PPh₂)₂C₅H₃]^- and a triphosphenium bromide P^I precursor result in the formation of phosphorus(I)-containing heterocycles, several of which are of types that have never been prepared before. The methodology described also allows for the preparation of the known heterocycle cyclo-[P(PPh₂)N(PPh₂)]₂ in better yields and purity than the synthetic approach reported previously. Preliminary reactivity studies demonstrate the viability of such zwitterionic oligomers as multidentate ligands for transition metals.

Full text of DOI:10.1021/ic502229w

Article
pubs.acs.org/IC
Low-Valent Chemistry: An Alternative Approach to Phosphorus-
Containing Oligomers
Stephanie C. Kosnik, Gregory J. Farrar, Erin L. Norton, Benjamin F. T. Cooper, Bobby D. Ellis,
and Charles L. B. Macdonald*
Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
S
* Supporting Information
ABSTRACT: A convenient preparative approach to low-valent phosphorus-rich oligomers is presented. Ligand substitution
reactions involving anionic diphosphine ligands of the form [(PR2)2N]− and [(PPh2)2C5H3]− and a triphosphenium bromide PI
precursor result in the formation of phosphorus(I)-containing heterocycles, several of which are of types that have never been
prepared before. The methodology described also allows for the preparation of the known heterocycle cyclo-[P(PPh2)N(PPh2)]2
in better yields and purity than the synthetic approach reported previously. Preliminary reactivity studies demonstrate the
viability of such zwitterionic oligomers as multidentate ligands for transition metals.
INTRODUCTION
■
Phosphorus-containing oligomers and macromolecules have
been and continue to be materials of tremendous investigation,
both from academic and industrial perspectives. The interest in
such molecules stems primarily from the different properties
that are engendered in these species by the presence of the
phosphorus atoms in comparison to their “carbon copy”
analogues. For example, the sometimes unique and often
improved performance of phosphorus-containing polymers
renders them useful for a very large number of applications,
including: biomedical applications, catalysis, light-harvesting,
sensing lubrication, flame-retardant materials, and much
more.1−5 In this context, the development of new or improved
Figure 1. Triphosphenium species: a general depiction (A) and
reported compounds (B, C), zwitterionic compounds (D, E, 1)
methods for the production of phosphorus-containing macro-
molecules is desirable.
featuring at least one PI fragment.
Triphosphenium salts are a remarkable class of compounds
first prepared by Schmidpeter and co-workers in the
1980s6,7that feature a dicoordinate and low-valent PI atom
but are unusually stable (Figure 1A,B). More recently, our
development of a facile approach to cyclic triphosphenium
iodide and bromide salts (cf. Figure 1C)8 provided materials
that are particularly amenable to anion-exchange metathesis
reactions.9 The availability of a convenient and high-purity
route to such compounds is important because it has already
been demonstrated that triphosphenium salts may be used as
reagents for the preparation of other polyphosphorus
compounds9,10 or as convenient PI sources.7 In particular,
access to other triphosphenium PI salts is possible via ligand-
exchange reactions10 in which a relatively poor phosphine
donor is replaced with a more strongly donating phosphine.
The use of monodentate phosphine ligands to form acyclic PI
complexes has also been reported7,11 (Figure 1A), although
only a handful of these have been characterized comprehen-
sively.
Received: September 12, 2014
© XXXX American Chemical Society
A
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Given the foregoing, anionic phosphinous ligands are
particularly good ligands for generating PI-containing com-
pounds as they can readily displace neutral phosphine ligands.
Importantly, the resultant zwitterionic products (e.g., Figure
1D)12,13 are soluble in most organic solvents, and they can act
as excellent ligands to various transition metals13−15 with the
capacity to bind one or two metal fragments simultaneously.14
In the context of larger molecules, we reasoned that the use
of anionic, nonchelating linkers with PI ions should lead to
phosphorus-containing oligomers that are neutral overall. In
fact, Schmidpeter and co-workers had previously reported
compounds of this type (Figure 1E), which they had isolated
from reactions of a phosphinous amide with P4.16 Notably, the
heterocycle E is a phosphorus-rich isovalent analogue of
phosphazenes, which are arguably the most useful class of
phosphorus−nitrogen compounds and are precursors for
polymers. Although phosphazenes are usually drawn with
alternating single and double bonds to satisfy the rules of
formal Lewis structures (Figure 2I), the more justifiable
However, the material was isolated in low yield (20%), and the
reaction is complicated by the use of the highly toxic and
pyrophoric P4 reagent and by the formation of several
polyphosphorus byproducts. Our experience with triphosphe-
nium salts led us to posit that ligand exchange using a readily
prepared, air-stable PI precursor might provide a more
convenient and generalizable route to such species.
Tο prove that hypothesis, we investigated the reaction of our
easily prepared PI source [dppeP][Br] (dppe = 1,2-bis-
(diphenylphosphino)ethane) with [Li][N(PPh2)2] in tetrahy-
drofuran (THF) in an effort to make 1. Note that metalated
phosphinous amide is notoriously difficult to isolate, so the
lithiated amide was prepared and used in situ by adding excess
butyl lithium to the amine precursor at −78 °C. The resultant
mixture was allowed to stir for an hour and was then added to a
solution of [dppeP][Br] in THF at −78 °C to produce
compound 1 in very good isolated yield (79%). We have found
that [dppeP][Br] is stable in the presence of many strong
basesat least for brief periodsso the reaction can also be
done in one pot.
Surprisingly, the 31P NMR spectrum of the compound we
obtained is not consistent with the values reported originally for
1 by Schmidpeter and co-workers: they had noted that the
spectrum of heterocycle E is indicative of an AA′A″A‴BB′ spin
system using a spectrometer with a 31P NMR frequency of
1
40.48 MHz (35.0 ppm, −141.5 ppm, JP‑P = 429 Hz). In
Figure 2. Lewis-type drawings structures of some phosphazene
analogues. The typical depiction (I), a more justifiable depiction (II),
and a related isolobal analogue in which one nitrogen fragment has
been replaced by a PI center.
contrast, we observe a spectrum consistent with an (A2X)2 spin
1
system with signals at 35.5 (d, JP-P = 423 Hz) and −140.2 (t,
1JP-P = 422 Hz) using a spectrometer with a 31P NMR
frequency of 121.5 MHz (Supporting Information, S-2). Thus,
to confirm that we had indeed produced the same compound
given the differences in the spectral data, we crystallized our
compound from a concentrated dichloromethane solution and
performed X-ray diffraction (XRD) experiments on the
resultant material. The single-crystal structure (Figure 3) is
indistinguishable from that reported previously and confirms
the identity of the product and validates our synthetic
approach. Powder XRD experiments on the bulk recrystallized
material indicate that the only crystalline material is consistent
with the single-crystal structure, and the reason for the
difference in appearance of the 31P NMR spectra remains
unanswered. We had postulated that Schmidpeter and co-
workers may have unintentionally collected the spectrum with
zwitterionic Lewis-type description of the electron distribution
(Figure 2II) highlights the electron-rich nature of the
dicoordinate atom. In this canonical form, the dicoordinate
nitrogen atom that bears two lone pairs of electrons is clearly
isovalent with the univalent phosphorus centers in triphosphe-
nium species. Given our experience in the development of
methods for the preparation of triphosphenium ions8 and our
interest in the exploitation of the unique reactivity of this
functional group, we reasoned that triphosphenium chemistry
could provide a convenient route to make phosphorus-
containing oligomers and perhaps polymers (Scheme 1).17
In this work, we demonstrate that the approach outlined in
Scheme 1 can indeed be used to generate oligomers containing
multiple PI centers, we report the structural characterization of
these heterocycles, and we demonstrate the utility of one of the
macrocycles as a zwitterionic bisphosphanide-type ligand for
noble metals.
1
1H coupling, but when we conducted our own H-coupled 31P
NMR experiments to test this hypothesis, we were unable to
obtain a spectrum similar to the reported one (Figures S-2 and
S-3, Supporting Information).
The convenient and clean preparation of 1 (and analogous P-
rich phosphazenes) allows for the investigation and develop-
ment of such species as polydentate ligands or supramolecular
building blocks. In fact, Schmidpeter had shown that 1 could
form bidentate P,P′-complexes to Pd and Pt, but further
RESULTS AND DISCUSSION
■
In the 1980s, Schmidpeter and co-workers were able to isolate
the neutral, eight-membered ring compound E through the
reaction of a phosphinous amide with elemental phosphorus.16
Scheme 1. Some Examples of Anion-Bridged Diphosphine Species That Could Undergo Ligand Exchange with a
Triphosphenium PI Salt (M = Li, Na, K, etc.)
B
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constraints of the ligand, the unique P−Cu distance of
2.2953(10) Å is at the long end of the range of distances
reported for phosphanido P−Cu bonds and is most comparable
to the 2.286(2) Å phosphanido P−Cu distance observed in
19
t
cyclo-(P5 Bu4)Cu(PPh3)2. The P−Cu−P angle of 120.17(5)°
is much wider than those observed in most other complexes of
chelating diphosphine donors; however, it is on the smaller side
of trans-spanning diphosphines and wide-bite angle diphos-
phines.20−22 This is almost certainly a consequence of the
geometrical constraints of the heterocyclic donor. It is perhaps
worth noting that the PI···PI distance of 3.979(3) Å in 1·CuBr
is shorter than the corresponding value of 4.1101(7) Å in 1.
Consequently, the N···N distance of 3.449(1) in 1·CuBr is
longer than the N···N distance of 3.3018(6) Å in 1. The
molecules of 1·CuBr pack in a manner reminiscent to the
packing of badminton shuttlecocks: the Cu−Br fragment of one
molecule is “cupped” by the aromatic substituents on an
adjacent molecule (featuring six Caryl−H···Br contacts under 3.3
Å with a closest pair being 3.1421(2) Å).
Figure 3. Thermal ellipsoid plot (30% probability surface) of the
molecular structure of 1. The hydrogen atoms and dichloromethane
solvent of crystallization were removed for clarity. Selected metrical
parameters are listed in Table 1.
The related compound 1·AgBr is generated upon the
treatment of 1 with a suspension of silver(I) bromide in
1
dichloromethane as evidenced by the signals at 30.5 (d, JP‑P
=
1
1
376), −157.3 (dt, JP−P = 383 Hz, JAg−P ≈ 113 Hz) in the 31P
NMR spectrum. Crystals of the complex 1·AgBr were obtained
from acetonitrile solution, and the material crystallizes in the
space group C2; there is no solvent of crystallization, but the
structure of the metal complex is roughly isomorphous with
that of 1·CuBr (Figure 4). Both the Ag−Br distance
(2.5000(12) Å) and P−Ag distance (2.4907(12) Å) are within,
but toward the short end of, the range of bond lengths for
reported compounds in the CSD containing a phosphine ligand
coordinated to a terminal Ag−Br fragment. The P−Ag−P bond
angle of 1·AgBr (114.26(6)°) is considerably narrower than
that of the lighter copper analogue (120.17(5)°); this is almost
certainly a consequence of the larger size of the AgI ion, and it
results in a much larger PI···PI separation (4.1837(2) Å) within
the ligand. The N···N separation in 1·AgBr (3.3699(1) Å) is
also more similar to the value in the free ligand 1 rather than
that seen in 1·CuBr, so it appears as if the binding to silver(I)
requires considerably less distortion of the ligand. However, it
is worth noting that both coordination compounds 1·AgBr and
1·CuBr feature longer P−PI bond lengths and wider P−PI−P
investigations do not appear to have been pursued.16 Thus, to
probe the utility of 1 for other catalytically relevant species, we
treated the zwitterion with some univalent group 11 halides.
NMR investigations indicate that the reaction of 1 with 1
equiv of CuBr results in the immediate formation of a complex
featuring a different AX2 spin system with chemical shifts at
1
1
28.6 (d, JP−P = 371.1 Hz) and −162.6 (t, JP−P = 369.0 Hz),
which are consistent with the formation of a bidentate P,P′-
complex. For the compound 1·CuBr, we were able to grow
crystals suitable for single-crystal X-ray diffraction from a
concentrated solution in dichloromethane. The complex
crystallizes in the space group C2 with half a molecule and
one disordered CH2Cl2 solvent molecule in the asymmetric
unit. The molecular structure of the compound is illustrated in
Figure 4 and confirms the formation of a κ2-P,P′ bidentate
complex of 1 with CuBr. The Cu−Br distance of 2.3427(8) Å is
consistent with those reported in the Cambridge Structural
Database (CSD)18 for compounds containing copper(I)
bromide coordinated by two phosphorus atoms. Perhaps
expectedly given the zwitterionic nature and geometrical
Figure 4. Thermal ellipsoid (30% probability) and ball-and-stick plots of 1·CuBr and 1·AgBr. Hydrogen atoms and the CH2Cl2 of crystallization for
1·CuBr were removed; the phenyl substituents are presented in wire frame for clarity. Selected metrical parameters are listed in Table 1.
C
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Table 1. Selected Bond Lengths (Å), Angles (deg), and 31P NMR Data for Structurally-Characterized Molecules in This Work
molecule
1
1·CuBr
1·AgBr
3
6
P−PI (Å)
2.1390(6)
2.1310(6)
95.44(2)
2.1654(12)
2.1672(12)
98.15(5)
1.595(3)
1.600(3)
2.2952(10)
2.2953(10)
28, d
2.1625(16)
2.1546(16)
98.50(6)
1.596(4)
1.596(4)
2.4906(12)
2.4907(12)
31, d
2.1635(7)
2.2097(7)
95.72(3)
2.1259(11)
2.1259(11)
100.82(4)
1.746(3)
P−PI−P (deg)
a
P−A (Å)
1.5957(14)
1.6019(14)
1.6009(16)
1.6629(16)
1.758(3)
P−M (Å)
δ
31P (ppm)
35, d
123*, d
19, d
−140, t
−162, t
−157, t
104**, d
−23, m
−148, t
−150, m
510*, 332**
1Jp−p (Hz)
423
373
376
459
a
Where A represents the bridging functionality: nitrogen for compounds 1, 1·CuBr, 1·AgBr, and 3; and carbon for compound 6.
angles than proligand 1 (Table 1) as one would anticipate in
light of the necessary decrease in negative hyperconjugation
(i.e., PI → PR2 backbonding) upon metal binding.
Although the ligand-exchange methodology outlined in
Scheme 2 clearly works for 1, we wish to emphasize that the
4, Supporting Information) experiments reveal the initial
formation of a product (2) that exhibits a spectrum consistent
with an AX2 spin system with shifts at 78.9 (d, 1JPP = 271.7 Hz)
and −162.6 (t, JPP = 271.7 Hz)this could be either a four-
1
membered triphosphenium zwitterion or the eight-membered
ring analogue of 1but the compound rapidly transforms into
a material that exhibits four chemically distinct phosphorus
environments and generates byproducts including both the
protonated proligand (iPr2P)2NH and the anticipated dppe.
The identity of the product (3) was elucidated using single-
crystal X-ray diffraction on a crystalline sample obtained at low
temperature. The compound crystallizes in the space group
P21/n with one molecule in the asymmetric unit. The molecular
structure of 3 (Figure 5) features two five-membered P4N rings
that are linked by a P−P bond to make an approximately
centrosymmetric [P2(PC2)2N]2 dimer core. Although there are
no examples of any P4N rings in the CSD, the overall structure
is clearly similar to that of the isolobal As2P2C dimer reported
by Karsch and co-workers23,24 and many other polyphosphorus
compounds.25 Each ring in 3 contains one dicoordinate PI
center featuring a short P−P bond distance (Table 1) to the
adjacent tetracoordinate phosphorus atom (2.1435(7) Å and
2.1417 (7) Å) and a marginally longer bond to the
tricoordinate phosphorus atom that links the two heterocycles
(2.1635(7) Å and 2.1651(7) Å). Such short P−P bonds are
Scheme 2. Reaction of a Triphosphenium Bromide Reagent
with a Salt Containing an Anionic, Nonchelating
Bis(diphenylphosphino)amide Proligand to Produce 1
stability of the resultant heterocycles is substituent-dependent,
and this can affect the nature of the product obtained. For
example, attempts to prepare the isopropyl-substituted
analogue of 1 consistently produced the linked two-ring
compound 3 (Scheme 3) rather than the analogous eight-
membered ring. Even at low temperatures, 31P NMR (Figure S-
Scheme 3. Reaction of the Triphosphenium Bromide Precursor and Bis(isopropyl)phosphinoamide Ligand, Generating the
a
Intermediate Molecule 2 and the Resulting Rearrangement Product 3
a
Which may be either a four-membered or eight-membered ring.
D
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The formation of 3 from 2 involves the formal extrusion of
one (iPr2P)2N fragment for each five-membered ring and the
oxidative coupling of two PI centers (Scheme 3). Although the
mechanistic details of the process remain unclear, examination
i
of putative models of the Pr-substituted eight-membered ring
(using the P6N2 core from 1) suggest that the steric
requirements of the isopropyl groups would engender
considerable repulsion. Density functional theory geometry
optimization (Supporting Information) suggests that the eight-
membered ring is stable but only with a much more planar
P6N2 core structure featuring a considerably longer PI···PI
distance (4.90 vs 4.10 Å in 1). Moreover, the nearly complete
absence of bis(isopropyl)-substituted phosphazenes from the
literature is noteworthy: in fact, there appears to be only one
structurally characterized compound containing the repeat unit
[iPr2PN]2 in the CSD, and it is not a simple phosphazene.29
Low-temperature 31P NMR experiments only exhibit peaks
attributable to 2 (Figure S-4, Supporting Information), and
there is no indication of an anion of the form [P((iPr2P)2N)2]−.
Taken together, the evidence suggests that 3 is likely formed via
the four-membered ring intermediate analogous to the
compound P(PPh2)2CSiMe3 reported by Karsch and co-
workers,24,30 rather than the eight-membered alternative.
We conducted a series of experiments in which the
stoichiometry of the reagents was altered in an effort to
optimize the yield of 3. Interestingly, intermediate 2 is always
observed regardless of the stoichiometric ratio of [Na]-
[(iPr2P)2N]/[dppeP][Br] used, but compound 3 is formed
only when the ratio is 1:1. We postulate that the extrusion of
HN(P(iPr)2)2 is essential in the formation of 3 and is not
particularly surprising as this type of extrusion has been
reported for compounds featuring similar ligands.31 Unfortu-
nately, efforts to characterize or identify intermediates other
than 2 using NMR and EPR spectroscopy have not yet been
successful.
Figure 5. Thermal ellipsoid plots (30% probability) of 3. Hydrogen
atoms were removed for clarity. (upper) Ellipsoids for all atoms.
(lower) Steplike dimeric arrangement. Selected metrical parameters
are listed in Table 1.
In light of the successful generation of 1, we wished to probe
the applicability of the method to other diphosphines bridged
by anionic linkers to produce larger neutral heterocycles
containing multiple PI centers. Toward this end we targeted the
heterocycles derived from nonchelating 1,3-bis-
(diorganophosphine)cyclopentadienide ligands.
Although there are two reported syntheses of lithium 1,3-
bis(diphenylphosphino)cyclopentadienide,32,33 we were unable
to isolate material of sufficient purity for further use with either
of those methods, so we undertook the development of an
improved approach to the preparation of such proligands. The
method described by Brasse et al. had produced the most
promising results in our hands, so we used this as a starting
point.32 Our modified synthesis (Scheme 4) is a stepwise
consistent with those observed for other cyclic triphosphenium
ions and related species.9,26 In contrast, the 2.2647(7) Å P−P
bond linking the two heterocycles lies at the long end of the
range of P−P bonds reported in the CSD for tetraorganodi-
phosphines18 and is considerably longer than the distances of
2.200 and 2.187 Å reported by Fritz and co-workers for two
tetraphosphinodiphosphines.27,28 The P−P−P angles for the
dicoordinate phosphorus atoms of 95.72(3)° and 94.96(3)° are,
as one would anticipate given the larger size of phosphorus,
somewhat larger than those observed for five-membered ring
triphosphenium cations of the type [dppeP]+ and are more
comparable to those observed in six-membered ring triphos-
phenium species.9,10,12,26
Scheme 4. Synthesis of Potassium 1,3-(Diphenylphosphino)cyclopentadienide, 5
E
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Scheme 5. Synthesis of the Heterocyclic Dimer 6 from 5 and the Triphosphenium Bromide PI Precursor
approach that produces potassium 1,3-bis(diphenylphosphino)-
cyclopentadienide (5) in excellent yield with no unanticipated
byproducts.
With a pure salt of the anionic diphosphine ligand 5 in hand,
the ligand-substitution reaction with [dppeP][Br] was inves-
tigated. 31P NMR spectroscopy reveals that when a THF
solution of 5 is mixed with a THF solution of [dppeP][Br], the
heterocycle subsequently characterized as 6 is produced in
quantitative yield (Scheme 5) with the concomitant generation
of the anticipated dppe byproduct.
We discovered that is possible to precipitate the oligomeric
product 6 selectively by exposing a diethyl ether solution of the
crude product mixture (containing 6 and dppe) to sonication;
the oligomer 6 may be collected as a pure product by filtration.
It is worth noting, however, that the sonication of the mixture
for a longer period (more than a few hours) results in the
precipitation of mixtures containing some dppe in addition to
6.
should be capable of generating endocyclic sandwich-type
complexes. The powder XRD pattern of the bulk material
isolated by this recrystallization method is in excellent
agreement with the pattern simulated on the basis of the
single-crystal structure and confirms that sample contains only
a single crystalline product (Figure S-9, Supporting Informa-
tion). However, note that on one occasion we obtained a
polymorph of this compound (also in the space group P1; see
̅
the Supporting Information) in which the asymmetric unit
contains an entire heterocycle and more than one diethyl ether
molecule; data are of low quality, but the nonparallel
arrangement of the cyclopentadienyl (Cp) fragments in the
molecule suggests that macrocycle 6 can exhibit considerable
conformational flexibility.
CONCLUSION
■
We have demonstrated that ligand exchange using stable PI
reagents is a viable synthetic approach for the preparation of
electron-rich phosphorus-rich oligomers. The use of this
protocol for the generation of such heterocycles appears only
to be constrained by the preparation of suitable diphosphine
ligands. We are currently evaluating a variety of methods for the
reliable production of larger oligomers and the related
polymeric species. Furthermore, the macrocycles presented
herein are also being studied to assess their abilities to serve as
multifunctional donors using both the dicoordinate P atoms
and the bridging functionality (i.e., N or Cp).
Crystals of 6 suitable for examination by single-crystal XRD
were obtained by the slow vapor diffusion of diethyl ether into a
concentrated CH2Cl2 solution of the heterocycle. The
compound crystallizes in the space group P1 with half of the
̅
molecule present in the asymmetric unit; the complete
molecular structure is depicted in Figure 6. The P−P bond
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out using
standard inert atmosphere techniques. Phosphorus(III) bromide,
sodium cyclopentadienide, and all other chemicals and reagents were
purchased from Aldrich. Phosphorus(III) bromide was distilled before
use, and all other reagents were used without further purification. All
solvents were dried using a series of Grubbs’-type columns and were
degassed prior to use. Deuterated THF (THF-d8) was dried over
sodium and benzophenone. The precursors HN[P(iPr2)]2 and
NaN[P(iPr2)]2 were synthesized based on modified literature
procedures,38 and Cu(I)Cl was purified by a literature procedure.39
NMR spectra were recorded at room temperature in THF-d8 or
CD2Cl2 solutions on a Bruker Advance 300-MHz spectrometer or
Bruker Advance III 500 MHz spectrometer. Chemical shifts are
reported in ppm, relative to external standards (SiMe4 for 1H and 13C,
85% H3PO4 for 31P). Coupling constant magnitudes, |J|, are given in
Hz. The high-resolution mass spectra (HRMS) were obtained using
electrospray ionization of acetonitrile solutions of species either by
The McMaster Regional Centre for Mass Spectrometry, Hamilton,
Canada or in house; calculated and reported mass/charge ratios are
reported for the most intense signal of the isotopic pattern. Melting
points were obtained on samples sealed in glass capillaries under dry
nitrogen using an Electrothermal Melting Point Apparatus. Elemental
analysis was performed by Atlantic Microlabs, Norcross, Georgia, USA.
Specific Procedures. [−N−PPh2−P−PPh2]2−, (1). To a flask
containing NH(PPh2)2 (1.000 g, 2.59 mmol) in THF (50 mL) was
added 1.3 equiv of n-BuLi (1.62 mL, 3.37 mmol) via syringe at −78
°C. The reaction mixture was stirred for 2 h and was then added to a
−78 °C solution of [dppeP][Br] (1.321 g, 2.59 mmol) in THF (20
mL). The reaction was allowed to stir overnight before the resulting
Figure 6. Thermal ellipsoid plot (30% probability plot) of the contents
of the unit cell for 6. Hydrogen atoms are removed and phenyl groups
are in wire frame for clarity. Selected metrical parameters are listed in
Table 1.
distances (Table 1) in macrocycle 6 fall within the ranges of
distances (2.113(2)−2.184(2) Å) for cyclic triphosphenium
complexes6,8,10,34−36 reported in the CSD, but the P−P−P
angle of 100.82(4)° is considerably larger and is more
consistent with those of acyclic triphosphenium cations35,37
The centroid-to-centroid distance between the two cyclo-
pentadiene rings is 3.590 Å, and the interplanar spacing of the
rings is 3.195 Å. Thus, it would appear as if the heterocycle
F
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Table 2. Summary of X-ray Diffraction Collection and Refinement Details for the Feature Compounds Reported in This Work
1
1·CuBr
1·AgBr
3
6
formula
C49H42Cl2N2P6
915.56
C49H42BrCl2CuN2P6
1059.01
C48H40N2P6AgBr
1018.42
C24H56N2P8
620.46
C58H46P6
928.77
FW (g/mol)
T (K)
173(2)
173(2)
173(2)
150(2)
173(2)
λ (Å)
0.710 73
monoclinic
P2/n
0.710 73
0.710 73
0.710 73
0.710 73
triclinic
crystal system
space group
a (Å)
monoclinic
C2
monoclinic
C2
monoclinic
P21/n
P1
̅
12.153(2)
9.3574(16)
20.114(3)
90
21.2636(18)
10.1246(7)
15.1840(12)
90
20.9310(9)
10.3138(4)
12.3702(5)
90
15.4287(13)
13.3702(12)
17.2421(15)
90
8.8331(7)
11.4721(10)
12.3802(10)
74.9880(10)
72.7380(10)
80.5270(10)
1151.90(16)
1
b (Å)
c (Å)
α (deg)
β (deg)
90.115(2)
90
133.915(5)
90
124.1150(10)
90
109.4820(10)
90
γ (deg)
V (Å3)
2287.3(7)
2
2354.8(3)
2
2210.91(16)
2
3353.1(5)
4
Z
ρ (Mg/m3)
absorption coeff.
F(000)
1.329
1.494
1.530
1.229
1.339
0.389 mm−1
1.667 mm−1
1.613 mm−1
0.433 mm−1
0.274 mm−1
948
1076
1028
1336
484
crystal size (mm3)
θ data collection (deg)
index ranges
0.9 × 0.7 × 0.7
2.401 to 27.498
−15 ≤ h ≤ 15,
−12 ≤ k ≤ 12,
−26 ≤ l ≤ 25
24 924
0.4 × 0.35 × 0.25
3.567 to 30.00
−27 ≤ h ≤ 29,
−21 ≤ l ≤ 21
14 ≤ k ≤ 14
31 572
0.19 × 0.10 × 0.02
3.296 to 26.383
−24 ≤ h ≤ 26,
−12 ≤ k ≤ 12,
−15 ≤ l ≤ 15
26 616
0.5 × 0.5 × 0.4
1.536 to 27.498
−20 ≤ h ≤ 20,
−17 ≤ k ≤ 17,
−22 ≤ l ≤ 21
37 787
0.1 × 0.1 × 0.1
1.767 to 27.492
−11 ≤ h ≤ 11,
−14 ≤ k ≤ 14,
−15 ≤ l ≤ 16
13 098
reflections collected
indep. reflect.
5192
6779
4464
7654
5142
R(int)
0.0265
0.0806
0.0722
0.0412
0.0395
max., min. trans.
refinement method
data/restraints/parameters
0.762, 0.618
0.659, 0.537
0.973, 0.836
full-matrix least-squares on F2
4464/1/264
1.031
0.841, 0.790
0.973, 0.916
5192/0/267
1.083
6779/14/282
1.032
7654/0/323
1.103
5142/0/289
1.210
a
GOF , F2
a
R1, wR2 [I > 2σ (I)]
0.0392,
0.0950
0.0472,
0.1270
0.0323,
0.0399,
0.0565,
0.0669
0.0903
0.1433
a
R1, wR2 (all data)
0.0434,
0.0978
0.0503,
0.1302
0.0392,
0.0499,
0.0749,
0.0697
0.0966
0.1764
diff. peak and hole (e·Å−3
)
0.518, −0.226
1.194, −1.243
4
0.387, −0.698
2
0.551, −0.249
0.484, −0.488
a
R1 = Σ(|Fo| − |Fc|)/ΣFo, wR2 = [ Σ(w(Fo − Fc2)2)/Σ(wFo ) ]. GOF = [Σ(w(Fo − Fc2)2)/(No. of reflns. − No. of params.)]1/2
.
2
solid was filtered and the solution was collected. Solvent was removed
under reduced pressure and washed with hexane, which yielded a
yellow solution containing dppe. The solvent was removed under
reduced pressure, and the subsequent paste was then sonicated for 1 h
in hexane and was filtered and washed with hot hexane (100 mL) to
give the pale yellow solid 1, 79% (0.850 g). Note: Although this is a
known compound, the NMR data are not consistent with those
previously reported, so these data are presented here: 31P{1H} NMR
(THF-d8): δ 35.5 (d, JPP = 423 Hz), −140.2 (t, JPP = 422 Hz); H
NMR (THF-d8): δ 7.66−7.59 (m, 2H, Ph-meta); 7.12−7.09 (m, 1H,
Ph-para); 7.10−6.98 (m, 2H, Ph-ortho); 13C{1H} NMR (CD2Cl2) δ
135.3 (d, JPC = 93.98 Hz, Ph-ipso); 131.3 (s, Ph-meta); 129.7 (s, Ph-
para); 129.7 (m, JPC = 5.9 Hz, Ph-ortho).
[−N−PPh2−P−Ph2−]2AgBr, (1·AgBr). As AgBr is light-sensitive,
the reaction was performed in a dark room to avoid any degradation of
the starting material. A suspension of AgBr (0.0137g, 0.734 mmol) in
dichloromethane was added to a stirring orange solution of 1 (0.061g,
0.734 mmol) in dichloromethane over 10 min. The mixture was stirred
for 30 min thereafter, yielding a light orange suspension. Solvent was
removed under reduced pressure, the resulting powder was washed
with THF, and the orange powder was collected using a frit. The
product does not appear to be light-sensitive. Yield: 81% (0.061g)
1
1
1
1
1
31P{1H} NMR (CD2Cl2): δ 30.5 (d, Jp‑p = 376), −157.3 (dt, JP−P
=
1
383 Hz, JAg−P ≈ 113 Hz; due to a broadening of the triplet peaks,
individual coupling to 107Ag and 109Ag could not be resolved). H
1
NMR (DMSO-d6): δ 6.97 (m, Ph-meta, 1H), 7.04 (m, Ph-meta, 1H),
7.15 (m, Ph-para, 1H), 7.36 (m, Ph-ortho, 1H), 7.56 (m, Ph-ortho, 1H)
Reaction of NaN(P(iPr)2)2 and [dppeP][Br] (2, 3). The white solids
[Na][N(P(iPr)2)2] (0.184 g, 0.677 mmol) and [dppeP][Br] (0.379 g,
0.745 mmol) were added to a Schlenk flask and cooled to −78 °C in a
dry ice−acetone bath. Approximately 40 mL of cold dichloromethane
was added to the flask. The solution turned yellow immediately and
was allowed to stir for 6 h at −78 °C. 31P{1H} NMR spectroscopy was
performed on an aliquot of this stirring solution, showing evidence of
[−N−PPh2−P−Ph2−]2CuBr, (1·CuBr). To an orange solution of 1
(0.085g, 0.102 mmol) in dichloromethane was slowly added a
suspension of white Cu(I)Br (0.0146g, 0.102 mmol) in dichloro-
methane, over the course of 5 min. The mixture was allowed to stir for
2 h, yielding a dark red mixture. The solution was centrifuged, and the
resulting yellow-orange precipitate was collected. The solid was
washed with cold dichloromethane twice to yield a golden-orange
powder. Gold-colored crystals were obtained from dichloromethane.
1
Yield: 60% (0.061g) 31P{1H} NMR (CD2Cl2): δ 28.6 (d, JPP = 373
1
the formation of 2 [31P{1H} NMR: δ 82.0 (d, JPP = 273 Hz), δ
1
1
Hz), −162.5 (t, JPP = 373 Hz) 1H NMR (deuterated dimethyl
−142.5 (t, JPP = 267 Hz)]; see Supporting Information, Figure S-4.
sulfoxide (DMSO-d6)): δ 7.43 (m, 2H, Ph-meta); δ 7.56−7.59 (m, 1H,
Ph-para); δ 7.71 (m, 2H, Ph-ortho). Anal. Calcd for C48H40BrCuP6N2·
(CH2Cl2): C, 55.57; H, 4.00; N, 2.65; found: C, 53.57; H, 4.23; N,
2.04%.
The dichloromethane was removed from the resulting yellow-orange
solution under reduced pressure, while maintaining a temperature of
approximately 0 °C. To the resulting precipitate was added cold
pentane, yielding a pale yellow solution. The solution was decanted
G
dx.doi.org/10.1021/ic502229w | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
and stored in a Schlenk flask under reduced pressure at −10 °C,
yielding pale yellow crystals. Because of similarities in solubility, the
isolated product, 3, and the byproduct, HN[P(iPr)2]2, were not able to
C5H3P2); (C1 in C5H3P2 not visible). Mp. 164−168 °C. Anal. Calcd
for C58H46P6·(C4H10O): C, 74.2; H, 5.63; found: 72.9; H, 5.02%.
X-ray Crystallography. Each crystal was covered in Nujol and
placed rapidly into a cold N2 stream of the Kryo-Flex low-temperature
device. The data were collected using the SMART40 software package
on a Bruker APEX CCD diffractometer employing a graphite
monochromated Mo Kα radiation (λ = 0.710 73 Å) source or using
the APEX2 software on a Bruker Photon 100 diffractometer with a
graphite monochromated Mo Kα radiation (λ = 0.710 73 Å) source.
Hemispheres of data were collected using counting times of 10−30 s
per frame at −100 °C. The details of crystal data, data collection, and
structure refinement are listed in Table 2. Data reductions were
performed using the SAINT41 implementations in the SMART or
APEX2 software packages, and the data were corrected for absorption
using SADABS.42 The structures were solved by direct methods using
SIR9743 and refined by full-matrix least-squares on F2 with anisotropic
displacement parameters for the non-H atoms using SHELXL-201244
and the WinGX45 software package; thermal ellipsoid plots were
produced using SHELXTL.46 Please note that for the metal complexes
1·CuBr and 1·AgBr, although only the predominant enantiomeric
form within each experimental chiral crystal is depicted, both
enantiomers should have an equal probability of formation. Powder
XRD experiments were performed with a Bruker D8 Discover
diffractometer equipped with a Hi-Star area detector using Cu Kα
radiation (λ = 1.541 86 Å).
be separated in our hands. 31P{1H} NMR of the product mixture
1
(CD2Cl2): 67.7 (s, HN[P(iPr)2]2), −11.2 (s, dppe), 123.8 (d, JPP
=
1
510 Hz, (iPr)2P−N−P(iPr)2−PI−P), 104.77 (d, JPP = 332.7 Hz),
(iPr)2P−N−P(iPr)2−I−P), −23.3 (m, (iPr)2P−N−P(iPr)2−P−P),
−150.6 (m, (iPr)2P−N−P(iPr)2−P1−P).
Potassium (Diphenylphosphino)cyclopentadienide, (4). NaCp in
diethyl ether (5.0 mL, 10.0 mmol) was added to a stirring solution of
ClPPh2 (2.251 g, 10.2 mmol) in diethyl ether (ca. 15 mL) at 30 °C.
Upon addition, the reaction mixture turned red and gradually became
orange after stirring for 2 h at which point the mixture was filtered
through Celite© to remove NaCl. The filtrate was washed with diethyl
ether, and volatiles were removed under reduced pressure. The
resulting oil was dissolved in toluene and cooled to −78 °C, and a
solution of KN(SiMe3)2 (2.074 g, 10.4 mmol) in toluene was added. A
white precipitate that appeared upon the addition was isolated after
stirring for 3 h and subsequently washed with diethyl ether yielding a
white solid powder characterized as 4. 97% (2.800 g, 0.97 mmol).
1
31P{1H} NMR (THF-d8): δ −17.6; H NMR (THF-d8): δ 7.33−7.29
(m, 4H, Ph-ortho); 7.14−7.07 (m, 8H, Ph- meta/para); 5.97−5.87 (m,
4H, C5H4); 13C{1H} NMR (THF-d8): δ 147.26 (d, JPC = 13.2 Hz, Ph-
ipso); 133.72 (d, JPC = 18.3 Hz, Ph-ortho); 127.98 (d, JPC = 6.2 Hz, Ph-
meta); 126.70 (s, Ph-para); 114.44 (d, JPC = 22.7 Hz, C5H4P); 109.1
(d, JPC = 10.1 Hz, C5H4P); 104.78 (d, JPC = 4.2 Hz, C5H4P). HRMS:
calcd for C17H14P− 249.0840, found 249.0833 (−2.8 ppm).
ASSOCIATED CONTENT
■
Potassium 1,3-Bis(diphenylphosphino)cyclopentadienide, (5). A
solution of chlorodiphenylphosphine (2.306 g, 10.05 mmol) in toluene
(ca. 80 mL) was added by cannula to a solution containing the
previously prepared 4 (2.955 g, 10.2 mmol) in toluene (ca. 20 mL) at
−78 °C. Upon addition, the solution underwent a color change to
orange and gradually became yellow over time. The resulting solution
was allowed to stir for 2 h and was then filtered through Celite© to
remove the potassium chloride precipitate, which was subsequently
washed with additional toluene (ca. 10 mL). The filtrate was cooled to
−78 °C, and then a solution of KN(SiMe3)2 (2.125 g, 10.7 mmol) in
toluene (ca. 30 mL) was slowly added. The resultant mixture
immediately produced a white precipitate and was refluxed for 3 h.
Diethyl ether (ca. 50 mL) was then added to the mixture, which was
stirred for an additional hour. The resulting solid was collected by
filtration and washed with diethyl ether (ca. 50 mL). Any remaining
volatile components were removed from the solid under reduced
pressure to afford a white powder characterized as 5. 99% (4.800 g,
S
* Supporting Information
31P{1H} NMR spectra of compounds 1−6. Crystal data and
structure refinement for the polymorph of compound 6.
Crystallographic structural data in CIF format of studied
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: cmacd@uwindsor.ca.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
1
10.2 mmol). 31P{1H} NMR (THF-d8): δ −18.2; H NMR (THF-d8):
■
We thank the Natural Science and Engineering Research
Council (NSERC) of Canada for funding and scholarships.
C.L.B.M. thanks the Province of Ontario’s Ministry of Research
and Innovation for an Early Researcher Award.
δ 7.36−7.30 (m, 4H, Ph-ortho); 7.17−7.10 (m, 8H, Ph-meta/para);
7.36−7.30 (m, 1H, C5H3); 7.17−7.10 (m, 2H, C5H3); 13C{1H} NMR
(THF-d8): δ 146.0 (d, JPC = 13.1 Hz, Ph-ipso); 133.8 (d, JPC = 19.2 Hz,
Ph-ortho); 128.2 (d, JPC = 5.7 Hz, Ph-meta); 127.1 (s, Ph-para); 124.0
(t, JPC = 20.1 Hz, C in C5H3P2); 117.1 (dd, JPC = 18.5 Hz, JPC = 8.5
Hz, C5H3−P2); 110.4 (d, JPC = 9.0 Hz, C in C5H3P2). HRMS: calcd for
C29H23P2 433.1283, found 433.1275 (−1.8 ppm). Anal. Calcd for
C29H23P2K: C, 73.7; H, 4.91; found: 71.2; H, 4.94%.
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