Lithium Salts of 2,4,6-Triaryl-λ4-phosphinine anions - A comparison study

Article abstract of DOI:10.1002/ejic.201301259

The λ³-phosphinine derivatives 2,6-diphenyl-4-(p-tolyl) phosphinine and 2-(2′-pyridyl)-4,6-diphenylphosphinine were quantitatively converted into the corresponding λ⁴-phosphinine anions by reaction with phenyllithium. Systematic hydr

Full text of DOI:10.1002/ejic.201301259

FULL PAPER
DOI:10.1002/ejic.201301259
Lithium Salts of 2,4,6-Triaryl-λ4-phosphinine Anions –
A Comparison Study
CLUSTER
ISSUE
Marlene Bruce,[a] Gisa Meissner,[a] Manuela Weber,[a]
Jelena Wiecko,[a] and Christian Müller*[a]
Dedicated to Professor Dr. Lothar Weber on the occasion of his 70th birthday
Keywords: Phosphorus heterocycles / Phosphinines / Rhodium / Coordination Chemistry / Chelates
The λ3-phosphinine derivatives 2,6-diphenyl-4-(p-tolyl)phos-
phinine and 2-(2Ј-pyridyl)-4,6-diphenylphosphinine were
quantitatively converted into the corresponding λ4-phosphin-
ine anions by reaction with phenyllithium. Systematic hy-
drolysis experiments with H2O and MeOH show that a subtle
interplay between the pKa values of the generated 1,2-di-
hydrophosphinine derivatives and the pKb value of the
formed bases, LiOH and LiOCH3, respectively, leads either
to the kinetic or thermodynamic product. The coordination
chemistry of the λ4-phosphinine anions towards RhI was fur-
ther investigated, and the anions based on 2,6-diphenyl-4-
(p-tolyl)-phosphinine and 2-(2Ј-pyridyl)-4,6-diphenylphos-
phinine demonstrate different coordination modes. Whereas
the former coordinates in an η5 fashion towards the RhI atom,
the latter acts as a bidentate chelating ligand with an η1 coor-
dination to the metal center through the phosphorus lone
pair.
Introduction
It is well established that the reactivities of pyridine (A)
and λ3-phosphinine (B) are completely opposed as a result
of the significant difference in charge distribution in these
heterocycles (Figure 1).[1] This effect is due to the lower
electronegativity of phosphorus in comparison to those of
carbon and nitrogen (Pauling electronegativities: 2.2 for P,
2.5 for C, and 3.0 for N).[2] As a consequence, phosphinines
react with organolithium reagents at the electrophilic phos-
phorus atom to form the corresponding 1-R phosphacy-
clohexadienyl anions, as demonstrated by Märkl and Ashe
III (Figure 1).[3,4] For simplicity, these salts are usually de-
fined as species that contain a λ4σ3-phosphinine anion (C),
although they are better described as classical tertiary λ3σ3-
phosphanes with a pseudo-ylidic structure (D) on the basis
of crystallographic data (vide infra).
Figure 1. Comparison between pyridine and phosphinine and the
coordination modes of anionic λ4-phosphinine anions.
anions coordinate preferentially in an η5-fashion (E),
whereas donor-functionalized 1-R phosphacyclohexadienyl
anions coordinate through the phosphorus lone pair (F).
We have recently studied in detail the synthesis and coor-
dination chemistry of chiral as well as functionalized 2,4,6-
triarylphosphinine derivatives, including phosphorus ana-
logues of 2,2Ј-bipyridine and terpyridine.[6] Although the
reaction of 2,4,6-triphenylphosphinine with organolithium
reagents is well documented, the coordination chemistry of
2,4,6-triphenyl-λ4-phosphinine anions has hardly been
studied, and the few investigated complexes have only been
characterized spectroscopically.[3c,5a] We report here on the
reaction of 2,6-diphenyl-4-(p-tolyl)-phosphinine (1) and the
structurally related 2-(2Ј-pyridyl)-4,6-diphenylphosphinine
The coordination chemistry of these interesting λ4-phos-
phinine anions has been studied mainly by Le Floch et al.[5]
The ambidentate nature of such anionic ligands allows co-
ordination to a metal center either through the anionic π
system (η5) or through the lone pair (η1) of the phosphorus
atom. Depending on the substitution pattern at the hetero-
cycle, different coordination modes can thus be adopted. In
the absence of additional donor groups, the λ4-phosphinine
[a] Institut für Chemie und Biochemie, Freie Universität Berlin,
Fabeckstr. 34/36, 14195 Berlin
E-mail: c.mueller@fu-berlin.de
www.bcp.fu-berlin.de/ak-mueller
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(2), which are derivatives of 2,4,6-triphenyl-λ3-phosphinine,
with phenyllithium. Moreover, we describe the reactivity of
the corresponding lithium salts and the coordination chem-
istry of the generated 2,4,6-triaryl-λ4-phosphinine anions
towards RhI (Figure 2).
Figure 2. 2,4,6-Triphenylphosphinine derivatives 1 and 2.
Figure 3. Molecular crystal structure of 1. Thermal ellipsoids are
shown at the 50% probability level. Selected bond lengths [Å] and
angles [°]: P(1)–C(1) 1.757(3), P(1)–C(5) 1.743(3), C(1)–C(2)
1.391(4), C(2)–C(3) 1.407(4), C(3)–C(4) 1.393(4), C(4)–C(5)
1.384(4), C(1)–C(12) 1.491(4), C(5)–C(18) 1.483(4), C(1)–P(1)–C(5)
101.09(14).
Results and Discussion
During the course of our investigations on functionalized
2,4,6-triaryl-λ3-phosphinines, we noticed that the unsubsti-
tuted 2,4,6-triphenylphosphinine and its coordination com-
pounds are generally difficult to crystallize and conse-
quently difficult to characterize crystallographically. To cir-
cumvent this problem, we decided to introduce a –CH3
group in the para position of the 4-phenyl group at the
phosphorus heterocycle. Compound 1 was obtained in a
straightforward manner from p-methylbenzaldehyde ac-
cording to Scheme 1. The new phosphinine was charac-
Figure 3 shows one of the very few crystallographically
characterized 2,4,6-triarylphosphinine derivatives reported
to date. The P heterocycle is essentially planar owing to the
aromatic character of the phosphinine ring. The P–C bond
lengths are 1.757(3) and 1.743(3) Å, respectively, and the
C–P–C angle is 101.09(14)°. The P–C bond lengths thus lie
between those of a P–C single bond (PPh3 1.83 Å[7]) and a
P–C double bond [(diphenylmethylene)(mesityl)phosphine,
MesP=CPh2 1.704 Å[8]]. As expected for an aromatic sys-
tem, there is no bond alternation in the carbocyclic part,
and the C–C bond lengths are between 1.384(4) and
1.407(4) Å. The tolyl substituent at the para position as well
as the phenyl groups at the 2- and 6-positions are slightly
rotated out of the plane with respect to the phosphorus
heterocycle.
1
terized by H, 31P{1H}, and 13C NMR spectroscopy. The
31P{1H} NMR spectrum of 1 shows a single resonance at δ
1
= 182.6 ppm. In the H NMR spectrum, a doublet at δ =
8.24 ppm (3JH,P = 5.6 Hz) is observed and is characteristic
of the two heteroaromatic protons coupling to the phos-
phorus atom.
The pyridyl-functionalized phosphinine 2 was prepared
as recently reported by us.[6a] As anticipated, the λ3σ2-phos-
phinines 1 and 2 can easily be converted into the corre-
sponding λ4σ3-phosphinine species 3 and 4 by reaction with
stoichiometric amounts of PhLi in tetrahydrofuran (THF)
at –78 °C (Scheme 2). Upon addition of the organolithium
compound, the solutions change from yellow to dark green
and blue, respectively.
Moreover, a large variation in the chemical shifts is ob-
served by 31P{1H} NMR spectroscopy between the neutral
phosphinines [δ = 182.6 ppm (1); δ = 187.4 ppm (2)] and
the anionic forms [δ = –54.9 ppm (3); δ = –58.6 ppm (4)];
Scheme 1. Synthesis of the 2,4,6-triphenylphosphinine derivative 1.
Colorless crystals of 1 suitable for X-ray diffraction this indicates that the aromaticity of the ring has been sub-
could be obtained by slow crystallization from acetonitrile. stantially disrupted owing to the presence of a rather basic
Compound 1 crystallizes in the monoclinic space group phosphorus center with a formal sp3 hybridization (PMe3:
P21/c with four independent molecules in the asymmetric 31P{1H} NMR, δ = –60 ppm). Le Floch et al. have isolated
unit. The molecular structure is depicted in Figure 3 along and crystallographically characterized lithium salts of λ4-
with selected bond lengths and angles.
phosphinine anions and shown that the lithium cation is
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Scheme 3. Reaction of the λ4-phosphinine anion 3 with H2O.
Enantiomers are not shown.
Scheme 2. Reactions of 1 and 2 to form the corresponding λ4-phos-
phinine anions.
ation of 3 and 4 with H2O by NMR spectroscopy. Interest-
ingly, the reaction of 3 with H2O in [D8]THF leads indeed
to the formation of a main product (94% based on integra-
tion) with a signal at δ = –50.8 ppm (31P{1H} NMR),
whereas a minor species (6%) is detected at δ = –38.0 ppm
(Figure 5, a).
coordinated in an η5 fashion and that the phosphorus atom
is strongly pyramidalized and points out of the plane de-
fined by the five carbon atoms of the heterocycle.[5c] Taking
these findings into consideration, the nucleophilic attack of
the organolithium reagent should in principal lead to two
different stereoisomers, as depicted in Figure 4.
Figure 4. Possible configurations of λ4-phosphinine anions.
Figure 5. 31P{1H} NMR spectra of 5-E/Z in [D8]THF, generated
However, it is interesting to note that we found only one
sharp signal in the 31P{1H} NMR spectra of the 1-R phos- from the hydrolysis of 3 with (a) H2O and (b) MeOH.
phahexadienyl salts 3 and 4, even when the spectra were
recorded at –70 °C. Apparently, only one isomer is present
In the 1H NMR spectrum of the hydrolysis products (see
in solution, as the barrier for inversion is expected to be
Figure 5, a), traces of the minor compound can also be next
to the characteristic signal of the proton Hb at δ = 5.97 ppm
and the proton Ha at δ = 4.23 ppm (Figure 6). An assign-
ment of the exact configuration (E or Z) of 5 on basis of
the size of the coupling constants appeared, however, to be
problematic.
high for such trivalent σ3-coordinated phosphorus species,
although the interconversion might be facilitated by an aro-
matically stabilized λ4σ3-intermediate.
As demonstrated before by Märkl and Ashe III, the reac-
tion of λ4-phosphinine anions with H2O quantitatively and
selectively leads to the corresponding 1,2-dihydrophosphin-
ine derivatives.[3d] For 2,4,6-triphenyl-substituted phosphin-
ines such as 3, the formation of four stereoisomers is conse-
quently expected upon protonation, as a stereogenic center
forms at both the phosphorus atom and the carbon atom
at the 2-position of the heterocycle. This leads to the pres-
ence of the two diastereomeric pairs of enantiomers 5-E
and 5-Z, depending on the relative location of the phenyl
groups at the 1- and 2-positions with respect to one another
(Scheme 3).
On the basis of the sharp melting points of the reaction
1
Figure 6. H NMR spectrum of 5-E/Z in [D8]THF.
products formed by protonation of the 2,4,6-triphenyl-λ4-
phosphinine anion with H2O, it was assumed that only one
pair of enantiomers formed predominantly, although the
exact nature of the hydrolysis product(s) remained elus- tion of the main product. Single crystals of the neutral hy-
ive.[3d]
drolysis product, suitable for X-ray diffraction, could in-
Therefore, we attempted a crystallographic characteriza-
As the hydrogen atoms Ha and Hb (Scheme 3) usually deed be obtained from the main product (as verified by
1
give very characteristic signals in the H NMR spectrum, 31P{1H} NMR spectroscopy) by slow crystallization from
whereas diastereomers should also be distinguishable by acetonitrile, and the molecular structure is depicted in Fig-
31P{1H} NMR spectroscopy, we also analyzed the proton- ure 7 along with selected bond length and angles.
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by integration), –43.4 (28.9%), –49.6 (32.7%), and
–52.6 ppm (37.2%; Figure 9, a). By comparing the chemical
shift and intensity of the signals of these data with those
obtained for 5-E/Z (Figure 5, a), we propose that the reso-
nances at δ = –40.9 and –49.6 ppm correspond to 6-E1/Z1,
generated by protonation of the carbon atom at the 2-posi-
tion (Figure 8). By comparison of the 31P{1H} NMR spec-
troscopic data and the crystallographic results for 5-Z de-
scribed above, the signal at δ = –49.6 ppm most likely corre-
sponds to the isomer 6-Z1, whereas the signal at δ =
–40.9 ppm can be assigned to the 6-E1 isomer, although no
exact proof can be provided here. The signals at δ = –43.4
and –52.6 ppm consequently belong to 6-E2/Z2, generated
from the protonation of the carbon atom at the 6-position,
which is next to the pyridine ring (Figure 9, a). If these as-
sumptions are correct, the protonation at the carbon atom
next to the pyridine ring is much less selective than the pro-
tonation of the carbon atom at the 2-position of the hetero-
cycle, as 6-E2/Z2 are formed in a ratio of approximately
40:60, in contrast to 6-E1/Z1, which are formed in a ratio
of 4:96 (Figure 9, a), similar to the situation observed for
5-E/Z in the 31P{1H} NMR spectrum shown in Figure 5.
Figure 7. Molecular crystal structure of 5-Z. Thermal ellipsoids are
shown at the 50% probability level. Selected bond lengths [Å] and
angles [°]: P(1)–C(1) 1.873(2), P(1)–C(5) 1.827(2), C(1)–C(2)
1.497(2), C(2)–C(3) 1.339(2), C(3)–C(4) 1.469(2), C(4)–C(5)
1.343(2), P(1)–C(25) 1.825(2), C(1)–P(1)–C(5) 97.46(8).
The crystallographic characterization reveals that the
main product, which is formed by hydrolysis of 3 with H2O,
has the Z configuration. The molecular structure of the 1,2-
dihydrophosphinine derivative 5-Z can be compared with
that of the λ3-phosphinine 1. The P–C distances of 1.873(2),
1.827(2), and 1.825(2) Å are much longer than those in 1,
and the phosphorus atom is strongly pyramidalized (Σangles
= 304.5°), as expected for a formally sp3-hybridized phos-
phorus atom. Consequently, the C–C bond lengths are con-
sistent with the presence of a C–C single bond [C(1)–C(2)]
and a conjugated diene with double bonds between C(2)
and C(3) and C(4) and C(5). Therefore, we could identify
for the first time the exact nature of the hydrolysis products
of the anions derived from λ4-2,4,6-triphenylphosphinine,
and this allows the assignment of the signals observed in
the 31P{1H} NMR spectra (Figures 5 and 6).
Figure 9. 31P{1H} NMR spectra of the species formed by proton-
ation of the λ4-phosphinine anion 4 with (a) H2O or (b) MeOH.
As LiOH is formed upon protonation of the λ4-phos-
phinine anion with H2O, this difference in reactivity and
selectivity might be attributed to a small, but significant,
difference in the pKa values of 5-E/Z and 6-E1/Z1/E2/Z2, as
the protonation at the 2- or 6-position is reversible.
As LiOCH3 is a slightly stronger base than LiOH, we
decided to quench solutions of 3 and 4 with MeOH to form
the corresponding 1,2-dihydrophosphinines and LiOCH3.
Interestingly, the protonation of the λ4-phosphinine anions
3 and 4 with methanol leads indeed to a dramatic change in
selectivity. The relative amounts of 5-E/Z, after quenching 3
with MeOH, change from 6:94 to approximately 50:50
(based on the integrals in the 31P{1H} NMR spectra shown
in Figure 5, b). On the other hand, the product composition
observed when 4 is quenched with methanol changes signif-
icantly only for the species that were formally assigned as
6-E1/Z1 and generated from the protonation of the carbon
atom at the 2-position (Figure 8). Despite the presence of
On the other hand, the reaction of the pyridyl-function-
alized λ4-phosphinine anion 4 with H2O to form the hydrol-
ysis product 6 is more complicated. In addition to proton-
ation of the carbon atom at the 2-position of the heterocy-
cle, the protonation at the carbon atom at the 6-position
should also be expected (Figure 8).
Figure 8. Possible hydrolysis products of 4. Enantiomers are not
shown.
Indeed, the reaction of 4 with H2O in THF is much less the pyridyl group at the 6-position, 6-E1/Z1 is very similar
selective than the reaction of 3 with H2O. Four signals are to 5-E/Z and should consequently result in similar NMR
detected in the 31P{1H} NMR spectrum at δ = –40.9 (1.2% spectroscopic data (Scheme 3, Figure 5). Indeed, the ratio
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again changes from 6:94 to approximately 50:50, whereas
the ratio of the formally assigned 6-E2/Z2 species remains
unchanged at 40:60 (Figure 9, b). These results nicely indi-
cate that the assignment according to Figure 8 is most likely
correct. Moreover, they show that the quenching of solu-
tions of λ4-phosphinine anions is more complex than pre-
viously assumed and that there is a subtle interplay between
the pKa values of the generated 1,2-dihydrophosphinine
species and the pKb values of the formed bases. Although
quenching of the Li salts with H2O leads preferentially to
the kinetic product (5-Z in the case of 3), the presence of
the stronger base LiOCH3 clearly leads ultimately to the
thermodynamic product 5-E. It can also be concluded that
the 1,2-dihydrophosphinine 6-E2/Z2 is apparently slightly
more acidic than the 1,2-dihydrophosphinine 6-E1/Z1, as
the thermodynamic equilibrium is already reached with
LiOH as a base.
After the investigation of the reactivity of 3 and 4
towards H2O and MeOH, we became interested in the coor-
dination chemistry of the λ4-phosphinine anions towards
RhI. The reaction of 3 with 0.5 equiv. of the rhodium(I)
dimer [Rh(cod)Cl]2 (cod = 1,5-cyclooctadiene) leads quan-
titatively to the new species 7, which shows a doublet in the
31P{1H} NMR spectrum at δ = –58.6 ppm. The small JP,Rh
coupling constant of 11.1 Hz is indicative of η5 coordina-
tion of the phosphorus heterocycle to the metal center, as
an η1 coordination through the phosphorus lone pair
should result in
a much larger coupling constant
(Scheme 4).[1e,5d] It is interesting to note, again from the
31P{1H} NMR spectroscopic data, that only one isomer of
the RhI complex has been formed, as the lone pair could in
principle be oriented either in an axial or equatorial posi-
tion of the heterocycle.
Figure 10. Molecular crystal structure of 7. Thermal ellipsoids are
shown at the 50% probability level. Selected bond lengths [Å], dis-
tances [Å], and angles [°]: P(1)–C(1) 1.842(3), P(1)–C(5) 1.822(3),
C(1)–C(2) 1.434(3), C(2)–C(3) 1.409(3), C(3)–C(4) 1.440(4), C(4)–
C(5) 1.392(4), P(1)–C(25) 1.848(3), C(1)–C(12) 1.499(3), C(5)–
C(18) 1.493(4), Rh(1)–C(31) 2.164(3), Rh(1)–C(32) 2.159(3),
Rh(1)–C(35) 2.115(3), Rh(1)–C(36) 2.114(3), C(1)–P(1)–C(5)
94.70(11).
Scheme 4. Reaction of 3 with the RhI complex [Rh(cod)Cl]2.
made between the bond lengths in the complexed anionic
λ4-phosphinine 3 in compound 7, and the structurally re-
After removal of LiCl, crystals of 7 suitable for X-ray lated neutral λ3-phosphinine 1 (see Figure 3). The C–C
diffraction could be obtained after recrystallization from di- bond lengths in the carbocyclic part of 1 as well as in the
ethyl ether. Figure 10 shows the molecular crystal structure coordination compound 7 are very similar with 1.384(4)–
of 7, along with selected bond lengths, distances, and 1.407(4) Å in (1) and 1.392(4)–1.440(4) Å in (7). On the
angles. The graphical representation of 7 indeed confirms other hand, significant lengthening of the P(1)–C(1) and the
that the phosphorus heterocycle coordinates in an η5 fash- P(1)–C(5) bonds is observed in 7. The corresponding values
ion to the RhI atom with the phenyl group in axial position. increase from the neutral λ3-phosphinine [P(1)–C(1)
The phosphorus atom is clearly located above the plane of 1.757(3), P(1)–C(5) 1.743(3) Å] to the complexed anionic
the five carbon atoms (Figure 10, b) and is strongly pyrami- λ4-phosphinine [P(1)–C(1) 1.842(3), P(1)–C(5) 1.822(3) Å]
dalized, as expected for a formally sp3-hybridized phos- and reflect the transition of a C(sp2)–P(sp2) to a C(sp2)–
phorus atom (Σangles = 301.4°). A comparison can also be P(sp3) system upon reaction with PhLi and subsequent co-
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ordination. It should be mentioned here that a few related
Conclusions
RhI complexes containing substituted η5-coordinated λ4-
phosphinines anions have been structurally characterized
by Le Floch et al.[5d]
We have presented a detailed comparison study between
2,6-diphenyl-4-(p-tolyl)phosphinine and the structurally re-
lated 2-(2Ј-pyridyl)-4,6-diphenylphosphinine and could
demonstrate that the neutral 2,4,6-triphenyl-λ3-phosphinine
derivatives can quantitatively be converted into the corre-
sponding λ4-phosphinine anions by reaction with phen-
yllithium. The lithium salts are very sensitive towards hy-
drolysis, which leads to the corresponding 1,2-dihydrophos-
phinine derivatives. The systematic protonation of the λ4-
phosphinine anions with either H2O and MeOH showed
that there is a subtle interplay between the pKa values of
the generated 1,2-dihydrophosphinines and the pKb value
of the base formed LiOH or LiOMe; this leads either to the
kinetic or thermodynamic hydrolysis product as confirmed
We were further interested in the coordination chemistry
of the pyridyl-functionalized λ4-phosphinine anion
4
towards the RhI precursor [Rh(cod)Cl]2, as we recently re-
ported on the reaction of the neutral pyridyl-functionalized
phosphinine 2 (Figure 1) with [Rh(cod)2]BF4 to form the
cationic RhI complex [(2)Rh(cod)]BF4. In this case, the
P,N-hybrid ligand coordinates in a bidentate chelating fash-
ion to the metal center (Scheme 5, a).[1e]
1
by H and 31P{1H} NMR spectroscopy. For hydrolysis of
the λ4-2,6-diphenyl-4-(p-tolyl)phosphinine anion, the main
product could be characterized crystallographically, and the
Z isomer was revealed as the major species and kinetic
product. We could further show that the phosphinine deriv-
atives differ in their coordination chemistry towards RhI, as
different coordination modes were observed for the anions
based on 2,6-diphenyl-4-(p-tolyl)phosphinine and the do-
nor-functionalized 2-(2Ј-pyridyl)-4,6-diphenylphosphinine.
Whereas the former one coordinates in an η5 fashion
towards the RhI atom, the latter one acts as a bidentate,
chelating ligand with an η1 coordination through the phos-
phorus lone pair to the metal center.
Scheme 5. Comparison between the neutral P,N-hybrid ligand 2
and the corresponding λ4-phosphinine anion 4 with respect to its
coordination chemistry towards RhI.
Experimental Section
General: All reactions were performed under argon by using
Schlenk techniques. All glassware was dried prior to use. Dry sol-
vents were prepared by using custom-made solvent purification col-
umns filled with Al2O3 from Braun Solvent systems. THF was dis-
tilled under argon from potassium/benzophenone prior to use. All
common solvents and chemicals were commercially available.
NMR spectra were recorded with a JEOL LAMBADA 400 NMR
Spectrometer (1H NMR 399.74 MHz, 13C{1H} NMR 100.51 MHz,
Inspired by these results, we wondered whether a related
neutral RhI complex could be formed by reaction of 4 with
the abovementioned RhI dimer [Rh(cod)Cl]2. The addition
of a solution of 4 in THF to 0.5 equiv. of [Rh(cod)Cl]2 in-
deed leads instantaneously to the new species 8, which
shows a single doublet at δ = 13.0 ppm in the 31P{1H}
NMR spectrum with a JP,Rh coupling constant of 152.2 Hz.
This value is typical for phosphinine–RhI complexes, in
which the ligand is bound in an η1 fashion through the
phosphorus lone pair to the metal center. It should be
1
31P{1H} NMR 161.82 MHz); the 13C and 31P spectra were H de-
1
coupled. The H and 13C chemical shifts are given relative to tet-
ramethylsilane (TMS), and the residual solvent peaks were used as
the reference signal; the 31P chemical shifts are referenced to an
85% aqueous solution of H3PO4. Compound 2 was prepared ac-
cording to literature procedures.[6a]
1
2,6-Diphenyl-4-(p-tolyl)-λ3-phosphinine (1): Compound 1 was syn-
noted here that the JP,Rh coupling constant in [(2)Rh-
(cod)]BF4 has a value of 188.6 Hz. Moreover, the typical
thesized according to the pyrylium salt route from acetophenone
signals for cod-containing metal complexes could be de- and p-methylbenzaldehyde.[6a] The obtained pyrylium salt (3.00 g,
1
7.31 mmol) was dissolved in acetonitrile (20 mL), and tris(trime-
thylsilyl)phosphine (4.26 mL, 14.6 mmol) was added dropwise. The
resulting dark red reaction mixture was heated under reflux for six
hours and then cooled to room temperature. After removal of the
solvent under high vacuum, the residue was purified by flash col-
umn chromatography under inert conditions (SiO2, petroleum
ether/ethyl acetate 1:0, 19:1). After removal of the solvent under
high vacuum, a pale yellow solid was obtained (1.70 g, 5.02 mmol,
tected in the H NMR spectrum of 8. These results are in
agreement with previous findings that donor-functionalized
λ4-phosphinine anions preferentially coordinate through
the phosphorus lone pair in an η1 fashion towards a metal
center (Figure 1).[5d] However, we were so far unable to con-
firm the exact nature of 8 by single-crystal X-ray diffrac-
tion. Nevertheless, the NMR spectroscopic data are quite
evident that the proposed schematic structure of 8, in which
the phosphinine derivatives acts as a bidentate ligand, is
correct.
1
69%). H NMR (399.74 MHz, [D8]THF, 25 °C): δ = 2.39 (s, 3 H,
CH3), 7.31 (d, JH,H = 8.4 Hz, 2 H, Har), 7.38 (t, JH,H = 6.8 Hz, 2
H, Har), 7.46 (t, JH,H = 7.7 Hz, 4 H, Har), 7.69 (d, JH,H = 8.1 Hz,
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2 H, Har), 7.76 (d, JH,H = 7.1 Hz, 4 H, Har), 8.24 (d, JP,H = 5.6 Hz,
2 H, Har) ppm. 13C{1H} NMR (100.51 MHz, [D8]THF, 25 °C): δ
rated under vacuum. Dichloromethane was added, and the solution
was filtered through Celite. The solvent was removed under vac-
= 21.3 (s), 128.6 (d, JC,P = 1.7 Hz), 128.6 (d, JC,P = 12.7 Hz), 128.9 uum, and a dark red powder was obtained. The product was quan-
(d, JC,P = 1.9 Hz), 129.8 (s), 130.6 (s), 132.4 (d, JC,P = 12.2 Hz),
138.9 (d, JC,P = 0.9 Hz), 140.3 (d, JC,P = 3.3 Hz), 144.7 (d, JC,P
titatively formed according to 31P NMR spectroscopy. Crystals
suitable for X-ray diffraction were obtained after several days by
recrystallization from ether. 1H NMR (399.74 MHz, [D8]THF,
=
24.3 Hz), 145.3 (d, JC,P = 13.7 Hz), 173.1 (d, JC,P = 51.8 Hz) ppm.
31P{1H} NMR (161.82 MHz, [D8]THF, 25 °C): δ = 182.6 (s) ppm. 25 °C): δ = 1.77–1.87 (m, 4 H, Hcod), 1.90–2.01 (m, 4 H, Hcod),
2.31 (s, 3 H, CH3), 3.21–3.29 (m, 4 H, Hcod), 6.57 (d, JH,H = 3.0 Hz,
1,2,6-Triphenyl-4-(p-tolyl)cyclophosphahexadienyllithium (3): Phos-
2 H, Har), 6.93–7.00 (m, 5 H, Har), 7.11 (t, JH,H = 7.3 Hz, 2 H,
phinine 1 (30.4 mg, 0.09 mmol) was dissolved in THF (2 mL), and
Har), 7.19 (d, JH,H = 8.0 Hz, 2 H, Har), 7.28 (t, JH,H = 7.7 Hz, 4
the solution was cooled to –78 °C. Phenyllithium (1.8 m in OBu2,
0.05 mL, 0.09 mmol) was added and the obtained dark green mix-
ture was warmed to room temperature. The solvent was removed
under vacuum, and a red viscous oil was obtained. This oil led
H, Har), 7.62 (d, JP,H = 8.1 Hz, 2 H, Har), 7.93–7.99 (m, 4 H, Har)
ppm. 13C{1H} NMR (100.51 MHz, [D8]THF, 25 °C): δ = 26.5 (s),
32.2 (s), 79.1 (d, JC,P = 12.5 Hz), 100.5 (dd, JC,P = 6.6, 2.8 Hz),
107.5 (dd, JC,Rh = 7.7, JC,P = 4.6 Hz), 126.4 (d, JC,P = 1.9 Hz),
again to a dark green solution when it was dissolved. The product
127.7 (d, JC,P = 16.9 Hz), 128.0 (s), 128.2 (s), 128.5 (d, JC,P
3.8 Hz), 129.4 (s), 129.4 (s), 129.6 (s), 130.3 (s), 137.6 (d, JC,P
=
=
was quantitatively formed according to 31P NMR spectroscopy. 1H
NMR (399.74 MHz, [D8]THF, 25 °C): δ = 2.18 (s, 3 H, CH3), 6.64
(tt, JH,H = 7.2, 1.1 Hz, 2 H, Har), 6.74–6.79 (m, 1 H, Har), 6.80–
6.88 (m, 4 H, Har), 7.02 (t, JH,H = 7.7 Hz, 4 H, Har), 7.19–7.26 (m,
3 H, Har), 7.28–7.33 (m, 1 H, Har), 7.59 (d, JH,H = 7.0 Hz, 2 H,
Har), 7.74–7.81 (m, 4 H, Har) ppm. 13C{1H} NMR (100.51 MHz,
[D8]THF, 25 °C): δ = 21.1 (s), 98.5 (d, JC,P = 6.5 Hz), 113.7 (s),
120.1 (s), 122.7 (s), 124.7 (d, JC,P = 18.8 Hz), 125.2 (s), 127.1 (d,
JC,P = 2.9 Hz), 128.3 (s), 128.4 (d, JC,P = 8.6 Hz), 129.2 (s), 131.0
(d, JC,P = 2.9 Hz), 131.1 (d, JC,P = 6.8 Hz), 144.7 (s), 149.5 (d,
JC,P = 30.6 Hz), 152.5 (d, JC,P = 37.4 Hz) ppm. 31P{1H} NMR
(161.82 MHz, [D8]THF, 25 °C): δ = –54.9 (s) ppm.
0.8 Hz), 138.2 (s, JC,P = 63.1 Hz), 143.9 (d, JC,P = 25.5 Hz), 148.0
(d, JC,P = 44.0 Hz) ppm. 31P{1H} NMR (161.82 MHz, [D8]THF,
25 °C): δ = –49.9 (d, JP,Rh = 11.3 Hz) ppm.
[(cod)Rh(η1-4)] (8): Compound 4 (58.5 mg, 0.18 mmol) was dis-
solved in THF, and the solution was cooled to –78 °C. A THF
solution of [Rh(cod)Cl]2 (44.38 mg, 0.09 mmol) was added drop-
wise. The mixture was warmed to room temperature, and the sol-
vent was evaporated. Dichloromethane was added, and the solution
was filtered through Celite. The solvent was evaporated, and a
black shiny powder was obtained. The product formed quantita-
tively according to 31P NMR spectroscopy. 1H NMR (400 MHz,
[D8]THF, 25 °C): δ = 1.73 (br. s, 4 H, Hcod), 2.33 (br. s, 4 H, Hcod),
4.03 (br. s, 4 H, Hcod), 6.88 (tt, d, JH,H = 7.3, JH,H = 1.2 Hz, 1 H,
Har), 7.01–7.15 (m, 10 H, Har), 7.26–7.33 (m, 8 H, Har), 8.08–8.13
(m, 2 H, Har) ppm. 13C{1H} NMR (100.51 MHz, [D8]THF, 25 °C):
δ = 26.2 (s), 31.6 (s), 76.9 (br. s), 114.0 (s), 118.8 (d, JC,P = 11.5 Hz),
123.5 (s), 124.2 (s), 126.2 (d, JC,P = 0.9 Hz), 127.5 (s), 127.8 (d, JC,P
1,4,6-Triphenyl-2-(2-pyridyl)-cyclophosphahexadienyllithium
(4):
Phosphinine 2 (29.5 mg, 0.09 mmol) was dissolved in THF (2 mL),
and the solution was cooled to –78 °C. Phenyllithium (1.8 m in
OBu2, 0.05 mL, 0.09 mmol) was added, and the obtained deep blue
mixture was warmed to room temperature. The solvent was re-
moved, and a red sticky solid was obtained. This oil led again to a
dark blue solution when it was dissolved. The product was quanti-
tatively formed according to 31P NMR spectroscopy. 1H NMR
(399.74 MHz, [D8]THF, 25 °C): δ = 6.82–6.75 (m, 2 H, Har), 6.96–
6.88 (m, 4 H, Har), 7.05 (t, JH,H = 8 Hz, 2 H, Har), 7.24–7.14 (m,
4 H, Har), 7.33–7.31 (m, 2 H, Har), 7.51 (d, JH,H = 8 Hz, 1 H, Har),
7.72–7.63 (m, 4 H, Har), 7.85–7.83 (m, 2 H, Har) ppm. 13C{1H}
NMR (100.51 MHz, [D8]THF, 25 °C): δ = 90.6 (d, JC,P = 23.4 Hz),
= 5.9 Hz), 128.4 (s), 128.5 (d, JC,P = 22.7 Hz), 128.9 (d, JC,P
=
2.4 Hz), 129.0 (s), 129.2 (d, JC,P = 2.6 Hz), 129.31 (s), 130.1 (d, JC,P
= 2.3 Hz), 132.4 (d, JC,P = 13.66 Hz), 136.8 (s), 140.6 (s), 144.5 (s),
144.7 (d, JC,P = 3.0 Hz), 144.5 (s) ppm. 31P{1H} NMR (162 MHz,
[D8]THF, 25 °C): δ = –13.0 (d, JRh,P = 152.2 Hz) ppm.
X-ray Crystal Structure Determination of 1: Crystals suitable for X-
ray diffraction were obtained by cooling a saturated solution of 1
in acetonitrile.
103.7 (d, JC,P = 23.4 Hz), 112.3 (d, JC,P = 1.0 Hz), 116.7 (d, JC,P
=
8.1 Hz), 117.3 (d, JC,P = 3.0 Hz), 121.4 (s), 122.3 (d, JC,P = 1.2 Hz),
123.2 (s), 123.8 (s), 124.8 (d, JC,P = 15.2 Hz), 125.6 (s), 126.7 (d,
JC,P = 5.1 Hz), 127.5 (s), 127.5 (d, JC,P = 1.0 Hz), 128.0 (s), 129.3
Crystallographic
data:
C24H19P;
Fw
=
338.4;
0.40ϫ0.20ϫ0.05 mm; colorless platelet, monoclinic; P21/c; a =
11.6267(13), b = 20.773(3), c = 7.3953(9) Å; α = 90, β = 91.777(10),
γ = 90°; V = 1785.2(4) Å3; Z = 4; Dcalcd. = 1.259 gcm–3; μ =
1.56 mm–1. 12005 reflections were measured by using a Stoe IPDS
2T diffractometer with a rotating anode (Mo-Kα radiation; λ =
0.71073 Å) to a resolution of (sinθ/λ)max = 0.69 Å–1 at a tempera-
ture of 200 K. 4791 reflections were unique (Rint = 0.079). The
structures were solved with SHELXS-97[9] by using direct methods
and refined on F2 for all reflections with SHELXL-97.[9] Non-hy-
drogen atoms were refined with anisotropic displacement param-
eters. The positions of the hydrogen atoms were calculated for ide-
alized positions. 227 parameters were refined without restraints. R1
= 0.063 for 2022 reflections with IϾ2σ(I), and wR2 = 0.160 for
4791 reflections, S = 0.815, the residual electron density was be-
tween –0.37 and 0.96 eÅ–3. Geometry calculations and checks for
higher symmetry were performed with the PLATON program.[10]
(d, JC,P = 15.2 Hz), 130.9 (d, JC,P = 15.2 Hz), 133.4 (d, JC,P
=
2.0 Hz), 133.8 (s), 135.5 (d, JC,P = 2.0 Hz), 143.0 (s), 145.2 (s), 145.9
(s), 146.1 (s), 146.1 (s), 146.2 (s), 146.8 (d, JC,P = 2.0 Hz), 166.0 (d,
JC,P = 25.4 Hz) ppm. 31P{1H} NMR (161.82 MHz, [D8]THF,
25 °C): δ = –58.6 (s) ppm.
1,2,6-Triphenyl-4-(p-tolyl)-1,2-dihydrophosphinine (5): Compound 3
(14.6 mg, 0.045 mmol) was redissolved in THF, and water or meth-
anol (0.045 mmol) was added. The solvent was removed, and a pale
red powder was obtained. 31P{1H} NMR (161.82 MHz, [D8]THF,
25 °C): δ = –38.0 (s, E isomer), –50.8 (s, Z isomer) ppm.
1,4,6-Triphenyl-2-(2-pyridyl)-1,2-dihydrophosphinine (6): Com-
pound 4 (14.6 mg, 0.045 mmol) was redissolved in THF, and water
or methanol (0.045 mmol) was added. The solvent was removed,
and a dark red powder was obtained. 31P{1H} NMR (161.82 MHz,
[D8]THF, 25 °C): δ = –40.9, –43.4, –49.6, –52.6 ppm.
[(cod)Rh(η5-3)] (7): A THF solution of 1 (60.9 mg, 0.18 mmol) and X-ray Crystal Structure Determination of 5-Z: Crystals suitable for
[Rh(cod)Cl]2 (44.4 mg, 0.09 mmol) was cooled to –78 °C, and
phenyllithium was added dropwise (0.05 mL, 0.09 mmol). The mix-
ture was warmed to room temperature, and the solvent was evapo-
X-ray diffraction could be obtained after the mixture was stirred
with water for only 10 min, the solvent was evaporated, and aceto-
nitrile was added for removal of the LiOH by filtration over Celite.
Eur. J. Inorg. Chem. 2014, 1719–1726
1725
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
The Solvent was again removed, and the yellow powder obtained
was recrystallized from acetonitrile.
Acknowledgments
Crystallographic data: C30H25P;
Fw
=
416.51;
The authors thank the Freie Universität Berlin for financial sup-
port.
¯
0.43ϫ0.3ϫ0.21 mm; colorless block, triclinic; P1; a = 10.347(2),
b = 11.003(2), c = 11.191(2) Å; α = 97.92(3), β = 94.78(3), γ =
112.51(3)°; V = 1152.7(5) Å3; Z = 2; Dcalcd. = 1.1999 gcm–3; μ =
0.134 mm–1. 12916 reflections were measured by using a Stoe IPDS
2T diffractometer with a rotating anode (Mo-Kα radiation; λ =
0.71073 Å) to a resolution of (sinθ/λ)max = 0.69 Å–1 at a tempera-
ture of 210 K. 6163 reflections were unique (Rint = 0.055). The
structures were solved with SHELXS-97[9] by using direct methods
and refined on F2 for all reflections with SHELXL-97.[9] Non-hy-
drogen atoms were refined with anisotropic displacement param-
eters. The positions of the hydrogen atoms were calculated for ide-
alized positions. 284 parameters were refined without restraints. R1
= 0.046 for 6163 reflections with IϾ2σ(I), and wR2 = 0.100 for
6163 reflections, S = 0.837, the residual electron density was be-
tween –0.58 and 0.42 eÅ–3. Geometry calculations and checks for
higher symmetry were performed with the PLATON program.[10]
[1] a) N. Mézailles, F. Mathey, P. Le Floch, Prog. Inorg. Chem.
2001, 49, 455; b) J. J. M. Weemers, J. Wiecko, E. A. Pidko, M.
Weber, M. Lutz, C. Müller, Chem. Eur. J. 2013, 19, 14458–
14469; c) I. de Krom, L. E. E. Broeckx, M. Lutz, C. Müller,
Chem. Eur. J. 2013, 19, 3676–3684; d) L. E. E. Broeckx, M.
Lutz, D. Vogt, C. Müller, Chem. Commun. 2011, 47, 2003–
2005; e) A. Campos Carrasco, E. A. Pidko, A. M. Masdeu-
Bultó, M. Lutz, A. L. Spek, D. Vogt, C. Müller, New J. Chem.
2010, 34, 1547–1550.
[2] IUPAC Compendium of Chemical Terminology (the “Gold
Book”), DOI: 10.1351/goldbook.E01990.
[3] a) G. Märkl, F. Lieb, A. Merz, Angew. Chem. 1967, 79, 59; b)
G. Märkl, A. Merz, Tetrahedron Lett. 1968, 9, 3611; c) G.
Märkl, C. Martin, Angew. Chem. 1974, 86, 445; Angew. Chem.
Int. Ed. Engl. 1974, 13, 408; d) G. Märkl, C. Martin, W. Weber,
Tetrahedron Lett. 1981, 22, 1207–1210.
X-Ray Crystal Structure Determination of 7: Crystals suitable for
X-ray diffraction were obtained after several days by cooling a sat-
urated solution of 7 in dry diethyl ether.
[4] A. J. Ashe III, T. W. Smith, Tetrahedron Lett. 1977, 18, 407–
410.
[5] a) T. Dave, S. Berger, E. Bilger, H. Kaletsch, J. Pebler, J.
Knecht, K. Dimroth, Organometallics 1985, 4, 1565–1572; b)
G. Baum, W. Massa, Organometallics 1985, 4, 1572–1574; c) A.
Moores, L. Ricard, P. Le Floch, N. Mézailles, Organometallics
2003, 22, 1960–1966; d) A. Moores, N. Mézailles, L. Ricard, P.
Le Floch, Organometallics 2005, 24, 508–513; e) M. Dochnahl,
M. Doux, E. Faillard, L. Ricard, P. Le Floch, Eur. J. Inorg.
Chem. 2005, 125–134; f) T. Arliguie, M. Blug, P. Le Floch, N.
Mézailles, P. Thuéry, M. Ephritikhine, Organometallics 2008,
27, 4158–4165.
[6] a) C. Müller, D. Wasserberg, J. J. M. Weemers, E. A. Pidko, S.
Hoffmann, M. Lutz, A. L. Spek, S. C. J. Meskers, R. A.
Janssen, R. A. van Santen, D. Vogt, Chem. Eur. J. 2007, 13,
4548–4559; b) C. Müller, E. A. Pidko, M. Lutz, A. L. Spek, D.
Vogt, Chem. Eur. J. 2008, 14, 8803–8807; c) C. Müller, E. A.
Pidko, A. J. P. M. Staring, M. Lutz, A. L. Spek, R. A.
van Santen, D. Vogt, Chem. Eur. J. 2008, 14, 4899–4905; C.
Müller, D. Vogt, C. R. Chim. 2010, 13, 1127–1143.
[7] J. J. Daly, J. Chem. Soc. 1964, 3799–3810.
Crystallographic
data:
C38H36PRh;
Fw
=
626.6;
3
¯
0.20ϫ0.19ϫ0.18 mm ; orange block, triclinic; P1; a = 11.4403(8),
b = 11.7642(9), c = 12.3651(10) Å; α = 72.295(6), β = 69.699(6),
γ = 70.685(6)°; V = 1438.8(2) Å3; Z = 2; Dcalcd. = 1.446 gcm–3; μ
= 6.75 mm–1. 14088 reflections were measured by using a Stoe
IPDS 2T diffractometer with a rotating anode (Mo-Kα radiation;
λ = 0.71073 Å) to a resolution of (sinθ/λ)max = 0.69 Å–1 at a tem-
perature of 200 K. The reflections were corrected for absorption
and scaled on the basis of multiple measured reflections by using
the X-Red program (0.85–0.93 correction range).[11] 7725 reflec-
tions were unique (Rint = 0.062). The structures were solved with
SHELXS-97[9] by using direct methods and refined on F2 for all
reflections with SHELXL-97.[9] Non-hydrogen atoms were refined
by using anisotropic displacement parameters. The positions of the
hydrogen atoms were calculated for idealized positions. 363 param-
eters were refined without restraints. R1 = 0.038 for 5844 reflections
with IϾ2σ(I), and wR2 = 0.096 for 7725 reflections, S = 0.915, the
residual electron density was between –1.06 and 0.77 eÅ–3. Geome-
try calculations and checks for higher symmetry were performed
with the PLATON program.[10]
[8] M. Yam, J. H. Chong, C.-W. Tsang, B. O. Patrick, A. E. Lam,
D. P. Gates, Inorg. Chem. 2006, 45, 5225–5234.
[9] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[10] A. L. Spek, Acta Crystallogr., Sect. D 2009, 65, 148–155.
[11] P. Coppens, in: Crystallographic Computing (Eds.: F. R.
Ahmed, S. R. Hall, C. P. Huber), Munksgaard, Copenhagen,
1979, p. 255–270.
CCDC-962497 (for 1), -962499 (for 5-Z), and -962498 (for 7) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Received: September 26, 2013
Published Online: December 3, 2013
Eur. J. Inorg. Chem. 2014, 1719–1726
1726
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim