Reactions of pyridyl-functionalized, chelating λ3- phosphinines in the coordination environment of RhIII and Ir III

Article abstract of DOI:10.1002/chem.201300321

Rh^III and Ir^III complexes based on the λ³-P,N hybrid ligand 2-(2′-pyridyl)-4,6- diphenylphosphinine (1) react selectively at the PC double bond to chiral coordination compounds of the type [(1H×OH)Cp*MCl]Cl (2,3), which can be deprotonated with triethylamine to eliminate HCl. By using different bases, the pK_a value of the P-OH group could be estimated. Whereas [(1H×O)Cp*IrCl] (4) is formed quantitatively upon treatment with NEt₃, the corresponding rhodium compound [(1H×O)Cp*RhCl] (5) undergoes tautomerization upon formation of the λ⁵σ ⁴-phosphinine rhodium(III) complex [(1×OH)Cp*RhCl] (6) as confirmed by single-crystal X-ray diffraction. Blocking the acidic P-OH functionality in 3 by introducing a P-OCH₃ substituent leads directly to the λ⁵σ⁴-phosphinine iridium(III) complex (8) upon elimination of HCl. These new transformations in the coordination environment of Rh^III and Ir^III provide an easy and general access to new transition-metal complexes containing λ⁵σ ⁴-phosphinine ligands. Rh^III and Ir^III complexes based on the λ³-P,N hybrid ligand 2-(2′-pyridyl)-4,6-diphenylphosphinine (1) react selectively at the PC double bond to give chiral coordination compounds of the type [(1H×OH)Cp*MCl]Cl, which can be deprotonated to form [(1H×O)Cp*IrCl] and [(1×OH)Cp*RhCl] (see figure). These new transformations in the coordination environment of Rh^III and Ir^III provide an easy and general access to new transition-metal complexes containing λ⁵σ⁴-phosphinine ligands. Copyright

Full text of DOI:10.1002/chem.201300321

FULL PAPER
DOI: 10.1002/chem.201300321
Reactions of Pyridyl-Functionalized, Chelating l3-Phosphinines in the
Coordination Environment of RhIII and IrIII
Iris de Krom,[a] Evgeny A. Pidko,[a] Martin Lutz,[b] and Christian Mꢀller*[a, c]
Dedicated to Professor Werner Uhl on the occasion of his 60th birthday
Abstract: RhIII and IrIII complexes
based on the l3-P,N hybrid ligand 2-(2’-
titatively upon treatment with NEt3,
the corresponding rhodium compound
[(1H·O)Cp*RhCl] (5) undergoes tauto-
merization upon formation of the l5s4-
single-crystal X-ray diffraction. Block-
À
ing the acidic P OH functionality in 3
À
pyridyl)-4,6-diphenylphosphinine
(1)
by introducing a P OCH3 substituent
react selectively at the P=C double
bond to chiral coordination compounds
of the type [(1H·OH)Cp*MCl]Cl (2,3),
which can be deprotonated with trie-
thylamine to eliminate HCl. By using
leads directly to the l5s4-phosphinine
phosphinine rhodium
N
iridiumACTHUGNETRNNU(G III) complex (8) upon elimina-
[(1·OH)Cp*RhCl] (6) as confirmed by
tion of HCl. These new transforma-
tions in the coordination environment
of RhIII and IrIII provide an easy and
general access to new transition-metal
complexes containing l5s4-phosphinine
ligands.
Keywords: chelates · coordination
chemistry · heterocycles · N,P li-
gands · phosphorus
À
different bases, the pKa value of the P
OH group could be estimated. Where-
as [(1H·O)Cp*IrCl] (4) is formed quan-
Introduction
2,2’-Bipyridine derivatives are well-studied bidentate nitro-
gen ligands and their corresponding transition-metal com-
plexes find widespread application in various areas of chem-
istry, such as molecular electronics, homogeneous catalysis,
or material science.[1] The replacement of a pyridine unit by
a p-accepting l3-phosphinine entity[2,3] leads to 2-(2’-pyri-
dyl)phosphinine, a semi-equivalent of 2,2’-bipyridine. Such
chelates are intriguing ligands that contain a low-coordinate
“soft” phosphorus and a “hard” nitrogen heteroatom. The
first example of this type of P,N hybrid ligand has been de-
scribed by Mathey et al. in 1982 with the synthesis of 2-(2’-
pyridyl)-4,5-dimethylphosphinine (NIPHOS, Figure 1).[4] We
have recently developed a facile synthetic route to 2-(2’-pyr-
idyl)-4,6-diphenylphosphinine (1, Figure 1), which is readily
Figure 1. Pyridyl-functionalized phosphinines NIPHOS and 2-(2’-pyridyl)-
4,6-diphenylphosphinine 1.
available from the corresponding pyridyl-functionalized
pyrylium salt.[5–7]
It is by now well established that the coordination chemis-
try of phosphorus-analogues of 2,2’-bipyridines is markedly
different from that of classical tertiary diphosphines or their
all-nitrogen-counterparts.[8–12] In contrast to (bi)pyridines,
phosphinine-based ligands are especially suitable for the sta-
bilization of electron-rich metal centers due to the pro-
nounced p-acceptor properties of the aromatic phosphorus
heterocycle.[8–13]
On the other hand, the aromaticity of the phosphinine
heterocycle is significantly disrupted upon coordination to
metal centers in especially higher oxidation states and with
reduced p-back-donation capability. Accordingly, the phos-
phinine core behaves like a cyclophosphahexatriene contain-
ing a highly reactive P=C double bond.[14] Venanzi et al.
have shown that cationic PdII and PtII complexes of
NIPHOS react with traces of water and alcohols to the cor-
[a] I. de Krom, Dr. E. A. Pidko, Prof. Dr. C. Mꢀller
Chemical Engineering and Chemistry
Eindhoven University of Technology
Den Dolech 2, 5600 MB Eindhoven (The Netherlands)
[b] Dr. M. Lutz
Bijvoet Center for Biomolecular Research
Utrecht University
Padualaan 8, 3584 CH Utrecht (The Netherlands)
responding dihydrophosphinine species of type
A
[c] Prof. Dr. C. Mꢀller
(Figure 2).[15] The regioselective addition of methanol exclu-
sively to the external P=Ca double bond can be attributed to
the somewhat higher nucleophilicity of the external Ca-atom
due to the electron-withdrawing character of the pyridine
ring connected to the internal Ca atom, leading to a prefer-
Institut fꢀr Chemie und Biochemie
Anorganische Chemie
Freie Universitꢁt Berlin
Fabeckstrasse 34–36, 14195 Berlin (Germany)
Fax : (+49)30-83852440
E-mail: c.mueller@fu-berlin.de
Chem. Eur. J. 2013, 19, 7523 – 7531
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7523

though the product was never structurally characterized.[15]
We have now started to investigate the reaction of racemic
mixtures of chiral phosphinine-metal complexes with water
and alcohols in more detail and report here on reactions of
the P,N hybrid ligand 1 in the coordination environment of
RhIII and IrIII.
Results and Discussion
1
Figure 3 shows the H NMR spectrum of 3 in CD2Cl2 (spec-
trum 2), which was prepared according to the literature.[16]
The starting material for 3, [(1)Cp*IrCl]Cl, is illustrated as
well (spectrum 1) for comparison reasons (see also
Scheme 1).[16]
Figure 2. Coordination compounds A–C containing dihydrophosphinine
ligands.
red addition of the proton exclusively to the external Ca-
atom.[7] Nevertheless, as the external Ca-atom in NIPHOS is
not prochiral, the structural characterization of A does not
allow one to draw any conclusion as to whether the addition
of ROH to the P=C double bond proceeds in a syn- or anti-
fashion, or even randomly.
Figure 3. 1H NMR spectra (CD2Cl2) of [(1)Cp*IrCl]Cl (bottom), 3 (spec-
trum 2), and 4 (spectrum 3). The aliphatic region is omitted for clarity.
Interestingly, the pyridyl-functionalized phosphinine
1
does contain a prochiral center at the external Ca-atom, pro-
viding the possibility to gain more insight into the mecha-
nism of the addition process once the ligand is coordinated
to a metal center. As a matter of fact, we could recently
demonstrate for the first time that the reaction of the neu-
tral phosphinine-MII complexes [(1)PdCl2] and [(1)PtCl2]
with MeOH does not proceed randomly but quantitatively
and selectively to the syn-addition product of type B
(Figure 2) as confirmed by the X-ray crystal structure.[7] This
indicates that the reaction proceeds in a concerted way,
rather than in a two-step process. In contrast, we found that
treatment of the cationic phosphinine-MIII complexes
[(1)Cp*RhCl]Cl and [(1)Cp*IrCl]Cl with water leads quanti-
tatively and selectively to the anti-addition products 2 (Rh)
and 3 (Ir), respectively (type C, Figure 2), as confirmed by
crystal structure determina-
Compound 3 shows the characteristic resonances for the
2
protons Ha and Hb at d=4.61 (dd, 3JHÀH =2.8 Hz; JHÀP
=
3
12.4 Hz) and 6.66 ppm (d, br, JHÀP =9.6 Hz) (see Figure 2,
C). Upon treating 3 with NEt3 (ꢀ10 equiv) in CD2Cl2 the
NMR spectroscopic data revealed the clean and quantitative
formation of a new species. In the 1H NMR spectrum
(Figure 3, spectrum 3) the signals for the hydrogen atoms Ha
3
and Hb shift from d=4.61 to 4.38 ppm (dd, JHÀH =3.2 Hz;
3
2JHÀP =14.0 Hz) and from d=6.66 to 6.73 ppm (dd, JHÀH
=
3.2 Hz, JHÀP =8.4 Hz). In the 31P{1H} NMR spectrum of the
new compound, a shift from d=58.0 to 38.9 ppm is ob-
served. On the basis of the NMR spectroscopic data we pro-
3
tions.[16] Additionally, hydrogen
À
bonding between the OH hy-
drogen atom and the ClÀ coun-
teranion was observed.
Venanzi et al. have already
À
demonstrated that the OH
group
in
[(NIPHOSH·-
OH)(L)PtCl]+ (A, Figure 1)
can be deprotonated with dii-
sopropylamine
A
to
form
al-
Scheme 1. Reaction of 3 with NEt3.
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Chem. Eur. J. 2013, 19, 7523 – 7531

Reactions of Pyridyl-Functionalized, Chelating l3-Phosphinines
FULL PAPER
Table 1. Selected bond lengths and angles in compounds 4, 6, and 8.
pose elimination of HCl from [(1H·OH)Cp*IrCl]Cl (3) by
NEt3 upon formation of the zwitterionic species 4 according
to Scheme 1.
Compound
4 (Ir)
6(Rh)
(mol. 1)
6(Rh)
ACHTUNGTRNE(NUNG mol. 2)
8 (Ir)
G
Crystals of 4 suitable for X-ray diffraction were isolated
in 54% yield by slow diffusion of Et2O into a diluted solu-
tion of 4 in CD2Cl2. The compound crystallizes as a race-
mate in the orthorhombic space group Pna21 with one metal
complex molecule in the asymmetric unit. The molecular
structure is depicted in Figure 4 and selected bonding geo-
metries are compared in Table 1.
bond lengths [ꢃ]
M(1) centroid
1.8477(12)
2.4002(7)
2.2806(7)
2.115(2)
1.507(2)
1.863(3)
1.830(3)
1.510(4)
1.341(4)
1.470(4)
1.336(4)
1.353(3)
1.459(3)
1.8352(12)
2.4075(7)
2.2791(9)
2.118(2)
1.638(2)
1.759(3)
1.761(3)
1.390(4)
1.411(4)
1.411(4)
1.382(4)
1.366(4)
1.448(4)
1.8324(13)
2.4084(7)
2.2899(9)
2.111(2)
1.635(2)
1.766(3)
1.758(3)
1.394(4)
1.407(4)
1.394(4)
1.388(4)
1.369(4)
1.446(4)
1.8403(7)
2.4019(4)
2.2646(4)
2.1119(13)
1.6357(11)
1.7782(15)
1.7507(16)
1.371(2)
1.425(2)
1.387(2)
1.404(2)
1.3724(19)
1.434(2)
À
M(1) Cl(1)
À
P(1) M(1)
À
N(1) M(1)
À
P(1) O(1)
À
P(1) C(1)
À
P(1) C(5)
À
C(1) C(2)
À
C(2) C(3)
À
C(3) C(4)
À
C(4) C(5)
À
N(1) C(6)
À
C(5) C(6)
bond angles [8]
C(1)-P(1)-C(5)
P(1)-M(1)-N(1)
95.20(11)
82.70(6)
102.88(13)
76.76(7)
103.16(13)
77.41(7)
102.52(7)
80.42(4)
8.75), on the other hand, gave a mixture of 3 and 4 in the
À
ratio of 1:2. These results show that the pKa value of the P
OH group is similar to the one of the pyridinium ion, which
is pKa =5.25.
Likewise, treatment of 2 (Rh) with NEt3 (ꢀ10 equiv) in
CD2Cl2 reveals again the predominant formation of a new
1
species. In the H NMR spectrum, the characteristic signals
for the hydrogen atoms Ha and Hb shift from d=4.78 to
Figure 4. Molecular structure of 4 in the crystal. Displacement ellipsoids
are shown at the 50% level.
3
2
4.65 ppm (dd, JHÀH =3.2 Hz; JHÀP =12.0 Hz) and from d=
3
3
6.53 to 6.63 ppm (dd, JHÀH =8.0 Hz, JHÀP =4.0 Hz). In the
31P{1H} NMR spectrum of this compound, a shift from d=
The molecular structure of 4 in the crystal indeed con-
firms that elimination of HCl from 3 took place, and the
complex can thus best be described as a formally zwitterion-
ic species (Scheme 1). The P(1)–O(1) distance of 1.507(2) ꢃ
is somewhat shorter than in 3 (1.5755(18) ꢃ), indicating par-
tial P=O double-bond character. Consequently, the P(1)–
C(1) and the P(1)–C(5) distances of 1.863(3) ꢃ and
1.830(3) ꢃ are slightly longer than in 3 (1.827(2) ꢃ and
1.803(2) ꢃ), whereas the C(1)-P(1)-C(5) angle of 95.20(11)8
1
1
86.0 (d, JPÀRh =133 Hz) to 80.0 ppm (d, JPÀRh =133.0 Hz) is
observed. However, after 1 day at room temperature, a
minor amount of a second species (ꢀ5%) is present in the
solution, which shows a single pseudo-triplet at d=6.80 ppm
(3JHÀP, HÀH =6.0 Hz) in the H NMR spectrum and a doublet
1
(1JPÀRh =128.8 Hz) at d=91.0 ppm in the 31P{1H} NMR spec-
trum. Nevertheless, on the basis of the NMR spectroscopic
data we propose again elimination of HCl from
[(1H·OH)Cp*RhCl]Cl (2) upon formation of the zwitterion-
ic species [(1H·O)Cp*RhCl] (5) according to Scheme 2.
Crystals suitable for X-ray diffraction were obtained by slow
diffusion of diethyl ether into the reaction mixture. The
product crystallizes as a racemate in the monoclinic space
À
is slightly smaller than in 3 (98.74(11)8). The remaining C
C bond lengths in the phosphorus heterocycle are similar to
the ones in 3.
We were further interested in estimating the pKa value of
À
the P OH functionality in 3. Whereas addition of NEt3
(pKb =3.3) to 3 gives quantita-
tive conversion to compound 4
as described above, we added
an excess (ꢀ10 equiv) of 2,2’-
bipyridine (pKb =9.56) to
a
solution of 3 in CD2Cl2. No de-
protonation was observed by
using 1H NMR spectroscopy,
indicating that the pKa value of
À
the P OH group is somewhere
between pKa =10.7 and 4.35.
Addition of pyridine (pKb =
Scheme 2. Reaction of 2 with NEt3.
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C. Mꢀller et al.
1
group Cc (No. 9) with two metal-complex molecules in the
asymmetric unit. The molecular structure of one enantiomer
is depicted in Figure 5 and the selected structure parameters
are compared in Table 1. The crystallographic characteriza-
of the second species observed in the H NMR spectrum as
mentioned above might thus be attributed to the tautomeric
form 6, which should show a single pseudo-triplet for the
proton Hb, due to coupling with the phosphorus nucleus as
well as Hc. As a matter of fact, heating a sample of 2 and
NEt3 in CD2Cl2 for several hours to T=608C reveals that
the amount of 6 increases substantially.
The phosphorus heterocycle is essentially planar as ob-
served in the complex [(1)Cp*RhCl]Cl containing a l3-phos-
phinine (Figure 5, bottom).
The phosphorus atom escapes from the plane defined by
the C1-C2-C3-C4-C5 atoms by only 0.1933(8) ꢃ (Figure 5,
À
À
bottom view). The P(1) C(1) and P(1) C(5) bond lengths
in 6 at 1.758(3)–1.766(3) ꢃ are slightly longer than in
À
[(1)Cp*RhCl]Cl (1.720(2)/1.720(2) ꢃ), whereas the C C
bond lengths in the phosphinine moiety of 6 are essentially
identical compared to the ones in [(1)Cp*RhCl]Cl.[16] The
À
OH group at the phosphorus atom forms an intramolecu-
lar hydrogen-bond to the metal-coordinated chloride. It
should be noted here that an inversion of configuration had
apparently occurred during the proton-transfer step, either
at the phosphorus atom or the Rh center. Both the oxygen
atom and the chloride ligand in 6 are now located on the
same side of the molecule, which is in contrast to the situa-
tion observed in compound 4.
The deprotonation reactions of 2 and 3 suggest that the
À
pKa value of the OH group is somewhat lower than the
À
one of the Ca H unit, but essentially very similar, as the
tautomeric form can apparently be easily formed. We
assume that the gain in energy by the more extended deloc-
alization within the phosphorus heterocycle is the driving
force for this rearrangement. Taking these results into ac-
count, it should be possible to generate the l5s4-species di-
rectly by deprotonation of a coordination compound, in
À
which no OH acidic proton is present. We therefore treat-
ed [(1)Cp*IrCl]Cl with an excess of MeOH to form the di-
hydrophosphinine species 7 (Scheme 3).
Compound 7 shows again the characteristic signals for the
3
hydrogen atoms Ha and Hb at d=4.79 (dd, JHÀH =3.2 Hz;
3
2JHÀP =11.2 Hz) and 6.95 ppm (ddd, 5JHÀH =0.8 Hz, JHÀH
=
3.2 Hz, 2JHÀP =11.0 Hz). Moreover,
a doublet at d=
3.76 ppm (3JHÀP =11.2 Hz) is observed for the MeO group
attached to the phosphorus atom (Figure 6, spectrum 2). In
the 31P{1H} NMR spectrum of 7 a signal at d=77.0 ppm is
observed. Any attempts to grow crystals of compound 7
failed because 7 reacts with traces of water to form coordi-
Figure 5. Molecular structure of
6 in the crystal. A noncoordinated
CH2Cl2 solvent molecule is omitted for clarity. Only one independent
molecule is shown. Displacement ellipsoids are shown at the 50% level.
Bottom representation: side view.
tion reveals indeed elimination
of HCl from 2. Most strikingly,
however, is the fact that the
zwitterionic species 5 has not
been formed and isolated, but
instead its tautomeric form 6,
containing a hydroxyl-group at
the phosphorus atom, is pres-
ent
in
the
solid
state
(Scheme 2). The minor amount
Scheme 3. Reaction of [(1)Cp*IrCl]Cl with MeOH and NEt3.
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Reactions of Pyridyl-Functionalized, Chelating l3-Phosphinines
FULL PAPER
Figure 6. 1H NMR spectra (CD2Cl2) of [(1)Cp*IrCl]Cl (bottom), 7 (spec-
trum 2) and 8 (spectrum 3).
À
nation compound 3, containing an OH functionality rather
À
than an
OCH3 group at the phosphorus atom
(Scheme 4).[15] We anticipate that the formation of hydrogen
bonding between the OH functionality and the Cl counter-
anion, as previously observed for 3, might be the driving
force for this process.[16]
Scheme 4. Reaction of 7 with water under formation of 3.
Figure 7. Molecular structure of 8 in the crystal. Displacement ellipsoids
are shown at the 50% level. Bottom representation: side view along the
Upon treatment of 7 with excess NEt3, however, a new
species is formed instantaneously, which was apparent from
the disappearance of the signal at d=4.79 ppm in the
1H NMR spectrum. Only one pseudo-triplet remains at d=
6.48 ppm in the 1H NMR spectrum and one signal at d=
56.0 ppm observed in the 31P{1H} NMR spectrum. This
result suggests that indeed a deprotonation with the loss of
Ha and the formation of a l5s4-species (Figure 6, spectrum
3).
Crystals of the new compound were obtained by a slow
diffusion of diethyl ether into the reaction mixture. The
complex crystallizes as a racemate in the monoclinic space
group P21/n (No. 14) with one independent molecule in the
asymmetric unit. The molecular structure of one enantiomer
is depicted in Figure 7 and selected bonding geometries are
compared in Table 1. The crystallographic characterization
indeed reveals formation of compound 8 according to
À
C(5) C(6) bond. Phenyl groups are omitted for clarity and only the ipso-
C-atoms are shown.
phosphinine core in 6 is basically planar as mentioned
above, the phosphorus atom in 8 escapes from the plane de-
fined by the C1-C2-C3-C4-C5 atoms by as much as
0.4717(4) ꢃ (Figure 7, bottom).
It should be mentioned here that Le Floch et al. has re-
ported already on the synthesis of Pd-complexes containing
ACTHNUTRGNEUNG
l5-SPS(OH) or l5-SPS(OMe) phosphinines (Scheme 5).[17]
This route, however, is only operative because the l3-SPS
phosphinine already reacts with water or alcohols to form
the corresponding l5-phosphinines. Consequently, such reac-
tions are generally not applicable to other phosphinines that
do not react with water or alcohols, such as 2,4,6-triarylphos-
phinines.
À
À
Scheme 3. The P(1) C(1) and P(1) C(5) bond lengths in 8,
being 1.7782(15) and 1.7507(16) ꢃ, respectively, are longer
In the upper reaction depicted in Scheme 5 the 1,2-dihy-
drophosphinine oxide reacts with [Pd
ACHTUNGTERN(NNUG cod)Cl2] upon elimi-
À
than in [(1)Cp*IrCl]Cl (1.717(7)/1.710(6) ꢃ). The C C bond
nation of HCl to [Pd(SPS·OH)], most likely through a [1,3]-
ACHTUNGTRENNUNG
lengths in the phosphinine moiety of 8 are essentially identi-
cal compared to the ones in [(1)Cp*IrCl]Cl.[15] However, the
transformation of [(1)Cp*IrCl]Cl into 8 through 7 induces a
distortion of the phosphinine heterocycle. Whereas the
H-shift from the C2 carbon atom to the P=O double bond.
In the reaction using alcohols, the corresponding l5-phosphi-
nines are formed directly by a formal insertion of the phos-
À
phorus lone pair into the RO H bond (Scheme 5, bottom).
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C. Mꢀller et al.
difference in the distortion of
the phosphinine heterocycle in
6 and 8 suggest a different
electronic situation in the
phosphorus moiety of both
compounds. In fact, the phos-
phorus-containing 6-membered
ring can be described either as
a l5s4 phosphinine consisting
of an anionic l4s3 ligand, or, al-
ternatively, as a l4s4-phosphi-
nine consisting of a classical
tertiary l3s3-phosphinite ligand
(Figure 8).
To clarify this question we
started to analyze the electron-
ACTHNUTRGNEUNG
Scheme 5. Conversion of an SPS pincer ligand into l5-SPS(OH) or l5-SPS(OMe) phosphinine-based PdII com-
plexes.
ic properties of 6 and 8 by
These reactions are most likely the result of a significant
dearomatization of the phosphorus heterocycles due to
strong acceptor groups at the a position of the phosphorus
atom. Nevertheless, uncoordinated 2,4,6-triphenylphosphi-
nine derivatives, as in the case of the P,N hybrid ligand 1, do
not react with water or alcohols, making this type of conver-
sion consequently impossible. The direct conversion of the
transition-metal complexes into the new l5-phosphini-
ne(OH) and l5-phosphinine(OR)-containing compounds by
the reaction with water or alcohols and subsequent deproto-
nation, as reported here by us, is therefore an elegant and
new route to such coordination compounds. We could fur-
ther show, that these transformations are even possible in
“one pot”, starting directly from the l3-phosphinine-based
[(1)Cp*MCl]Cl complexes.
means of DFT calculations starting from the corresponding
X-ray crystal structures of these coordination com-
pounds.[18–20] All calculations were performed at the B3LYP/
def2-TZVP level and the optimized structures are shown in
Figure 9.
DFT calculations: As evident from the X-ray crystal struc-
À
À
ture determination of compound 6 (P OH) and 8 (P
OCH3), the P atom deviates from the plane of the ring, al-
though this effect is much less pronounced and hardly no-
ticeable in 6 (Rh) in comparison to 8 (Ir). The significant
Figure 9. Optimized structures (DFT) of 6 (Rh) and 8 (Ir).
In analogy to the X-ray crystal structure determination of
À
À
compound 6 (P OH) and 8 (P OCH3), the P atom deviates
in the optimized structures from the plane of the ring by q=
8.8 (6, Rh) and 25.38 (8, Ir), respectively. (Figure 9, left; q
corresponds to the angle between the planes of the triades
of atoms of the ring).
We further analyzed the natural bond orbital (NBO)
charges for both the Rh- and Ir-complex and the results are
listed in Table 2.
From the results it is clear that the negative charge in
both compounds is delocalized over the phosphinine ring.
The total charge in the heterocycle of 6 and 8 is estimated
Figure 8. Resonance structures of 6 and 8 and of the corresponding li-
gands.
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Chem. Eur. J. 2013, 19, 7523 – 7531

Reactions of Pyridyl-Functionalized, Chelating l3-Phosphinines
Table 2. NBO charges calculated for 6 (Rh) and 8 (Ir).
FULL PAPER
Atom/moiety
6 (Rh)
8 (Ir)
Rh/Ir
À0.236
À0.419
+1.65
0.085
À
Cl
À
P
À0.391
+1.545
+0.546
À0.498
À0.395
À
P benzene (approx.)
+0.67
À
À
OH/ OMe
À0.473
À
N
À0.360
to be almost exactly 1e lower than the atomic charge on P.
This implies that despite the strong difference in the distor-
tion of the phosphorus heterocycle, both compounds can
best be described as a species that consists of a l4s4-phos-
phorus heterocycle with an ylide structure. The difference in
the distortion of the phosphorus heterocycle might be attrib-
uted to the presence of efficient hydrogen bonding between
Figure 11. Frontier orbitals of the l5-phosphinine C5H5PH2.
À
the P OH group of 6 and the Cl ligand at the metal center.
We also analyzed the frontier orbitals of compound 6 and
8 and the results are depicted in Figure 10.
(Figure 11).[21] This comparison again suggests that com-
pounds 6 and 8 are best described by the presence of a l4s4-
phosphorus heterocycle consisting of an ylide structure.
Nevertheless, from Figure 10 it is furthermore apparent
that the LUMOs are significantly different for both com-
pounds 6 and 8. In both cases, there is an important contri-
bution from the metal-centered d orbitals. Whereas in the
case of compound 6 (Rh), the states due to the Cp* ligand
dominate the LUMO, the LUMO of the Ir complex 8 con-
tains substantial contribution from the bidentate ligand.
From Figure 10 it is obvious that the HOMO in both com-
pounds shows a substantial delocalization over the C P C
À À
moiety. The metal fragment and the -OR residue at the
phosphorus atom form antibonding domains within the
HOMO. As a matter of fact, the shape of the HOMO
strongly resembles that of the parent l5-phosphinine, which
is best described by an ylidic resonance structure as well
Conclusion
We have demonstrated that the cationic RhIII und IrIII com-
plexes [(1H·OH)Cp*MCl]Cl can be deprotonated with NEt3
under the elimination of HCl to form zwitterionic species of
the type [(1H·O)Cp*MCl]. By using different bases, the pKa
À
value of the P OH group could be estimated (pKa =5.25).
In the case of RhIII, subsequent tautomerization through a
[1,3]-H shift occurs and the l5s4-complex [(1·OH)Cp*RhCl]
is formed exclusively. Starting from the corresponding
À
[(1H·OCH3)Cp*IrCl]Cl species, in which no acid P OH
group is present, direct deprotonation of the phosphorus
heterocycle was observed to form [(1·OCH3)Cp*IrCl]. This
transformation of l3-phosphinine-based complexes into l5-
phosphinine(OH) and l5-phosphinine(OR) complexes in the
coordination environment of transition metals is a new and
elegant route to such coordination compounds. It should be
mentioned here, however, that the role of the pyridine
moiety has not yet been clearly understood. We are current-
ly investigating comparable reactions with IrIII and RhIII
complexes containing cyclometalated 2-phenylphopshinines
to see whether this reaction is also transposable to other
phosphinine complexes. Whereas bipyridine complexes of
the type [(bpy)Cp*RhCl]Cl find application in the oxidation
of H2O, it appears also attractive to further investigate the
application of the here presented cationic and neutral transi-
tion-metal complexes in catalytic reactions. Research in this
direction is currently being performed in our laboratories.
Figure 10. Frontier orbitals of 6 (Rh) and 8 (Ir).
Chem. Eur. J. 2013, 19, 7523 – 7531
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7529

C. Mꢀller et al.
CH), 129.3 (CH), 129.5 (CH), 129.7 (d, 3J(C,P) =2.7 Hz, CH), 130.2 (CH),
130.3 (CH), 133.9 (Cq), 134.4 (Cq), 134.5 (d, 2J(C,P) =5.3 Hz, Cq), 136.8
(CH), 136.9 (CH), 138.4 (Cq), 138.9 (d, 1J(C,P) =10.1 Hz, Cq), 104.4 (CH),
141.6 (d 3J(C,P) =1.6 Hz, CH), 155.9 (CH), 158.4 ppm (d, 1J(C,P) =18.4 Hz,
Cq). The compound was not isolated and used without further purifica-
tion (see below).
Experimental Section
General: All reactions were performed under argon using Schlenk tech-
niques or in an MBraun dry box unless stated otherwise. All glassware
was dried prior to use. All common solvents and chemicals were commer-
cially available. Coordination compounds 2 and 3 were prepared accord-
ing to literature procedures.[15] The dry solvents were prepared by using
custom-made solvent purification columns filled with Al2O3. Elemental
analyses were performed by H. Kolbe, Mikroanalytisches Laboratorium,
Mꢀlheim a. d. Ruhr (Germany). 1H, 13C{1H}, and 31P{1H} NMR spectra
were recorded on a Varian Mercury 400 MHz spectrometer and all chem-
ical shifts are reported relative to residual proton resonance of the deu-
terated solvents.
ACHUTNGREN[NUG Cp*IrHCATUNGTRENN(UGN 1·OMe)Cl] (8): An excess of triethylamine (30 mg, 0.30 mmol,
10.0 equiv) was added to the reaction mixture of 7 in CD2Cl2, in a Young
NMR-Tube under argon. Compound 8 was formed instantaneously. Crys-
tals were obtained through slow diffusion of diethyl ether into the reac-
tion mixture. The yield after crystallization was 80%. 1H NMR (CD2Cl2,
400 MHz): d=1.55 (15H, d, 4J(H,P) =2.4 Hz, Cp* CH3), 3.08 (3H, d,
3J(H,P) =11.6 Hz, CH3), 6.48 (1H, m, Hb), 7.10 (1H, m, Hc), 7.23 (1H, m,
2
Harom), 7.31 (5H, m, Harom), 7.40 (1H, t, Harom), 7.47 (1H, d, J(H,H)
=
ACHTUNGTRENNUNG[Cp*IrACHTUNGTRENNUNG(1H·O)Cl] (4): Compound 3 (22 mg, 0.03 mmol, 1.0 equiv) was sus-
7.8 Hz, Harom), 7.53 (1H, dd, 4J(H,P) =14.4 Hz, 4J(H,H) =1.2 Hz, Carom), 7.58
pended in CD2Cl2 (0.5 mL) and transferred to a Young NMR-Tube under
argon. An excess of triethylamine (30 mg, 0.30 mmol, 10.0 equiv) was
added to the mixture, which resulted in the instantaneous formation of
compound 4. The reaction mixture was filtered over celite and crystals
were obtained through slow diffusion of diethylether into the reaction
mixture. The yield after crystallization was 54%. 1H NMR (CD2Cl2,
400 MHz): d=1.44 (15H, d, 4J(H,P) =2.3 Hz, Cp*-CH3), 4.38 (1H, dd,
2J(H,P) =14.0 Hz, 3J(H,H) =3.2 Hz, Ha’), 6.73 (1H, ddd, 3J(H,P) =8.4 Hz,
3J(H,H) =3.2 Hz, 5J(H,H) =0.8 Hz, Hb’), 7.11 (1H, m, Harom), 7.21 (1H, s,
Harom), 7.25 (1H, s, Harom), 7.29 (1H, m, Harom), 7.36 (4H, m, Harom), 7.47
2
(1H, dd, 4J(H,P) =7.2 Hz, 4J(H,H) =1.6 Hz, Carom), 7.74 (2H, d, J(H,H)
=
8.0 Hz, Carom), 7.99 ppm (1H, d, J(H,H) =6.0 Hz, Carom); 31P NMR (CD2Cl2,
162 MHz): d=56.0 ppm; 13C NMR (CD2Cl2, 100.6 MHz): d=8.9 (CH3
from Cp*), 93.8 (d, 3J(C,P) =3.0, Cq from Cp*), 100.4 (d, 1J(C,P) =69.2 Hz,
Cq), 115.0 (d, 1J(C,P) =72.3 Hz, Cq), 116.5 (CH), 116.6 (CH), 117.1 (CH),
118.9 (d, 3J(C,P) =9.8 Hz, Cq), 124.5 (CH), 125.6 (CH), 126.1 (CH), 126.2
3
3
(CH), 128.5 (CH), 128.5 (CH), 128.7 (CH), 129.3 (d, J(C,P) =4.9 Hz, CH),
2
130.0 (CH), 130.1 (CH), 136.9 (CH), 139.8 (CH), 144.3 (d, J(C,P)
=
12.6 Hz, Cq), 144.5 (d, 4J(C,P) =1.2 Hz, Cq), 154.3 (CH), 169.1 ppm (d,
2J(C,P) =21.4 Hz,
Cq); elemental analysis calcd (%) for
3
(1H, s, Harom), 7.49 (1H, d, J(H,H) =1.2 Hz, Harom), 7.53 (1H, s, Harom), 7.55
C33H34NPOClIr·CH2Cl2·NEt3 (905.40): C 53.06, H 5.68, N 3.06; found: C
54.76, H 5.63, N 3.22.
(1H, d, 3J(H,H) =2.0 Hz, Harom), 7.81 (1H, t, Harom), 7.92 (1H, d, J(H,H)
=
3
8.0 Hz, Harom), 8.66 ppm (1H, d, 3J(H,H) =5.6 Hz, Harom); 31P NMR
(CD2Cl2, 162 MHz): d=38.0 ppm; 13C NMR (CD2Cl2, 100.6 MHz): d=8.8
X-ray crystal-structure determinations: X-ray intensities were measured
on a Bruker Kappa ApexII diffractometer with sealed tube and Triumph
monochromator (l=0.71073 ꢃ). The intensities were integrated by using
Eval15.[22] Absorption correction and scaling was performed with
SADABS or TWINABS.[23] The structures were solved using automated
Patterson methods in the program DIRDIF-08[24] (compound 4) and
SHELXT[25] (compounds 6 and 8). Least-squares refinement was per-
formed refined with SHELXL-97[26] against F2 of all reflections. Non-hy-
drogen atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were located in difference Fourier maps (compounds 4
2
(-CH3 from Cp*), 51.4 (CH), 51.0 (CH), 94.4 (d, J(C,P) =10.0 Hz, Cq from
Cp*), 110.4 (Cq), 120.9 (CH), 121.0 (CH), 124.8 (CH), 126.8 (CH), 127.8
2
(CH), 128.4 (d, J(C,P) =8.8 Hz, CH), 128.9 (CH), 130.6 (CH), 130.6 (CH),
134.2 (d, 2J(C,P) =9.6 Hz, CH), 135.9 (Cq), 136.0 (Cq), 137.7 (CH), 139.8
(CH), 140.0 (CH), 140.35 (Cq), 140.39 (Cq), 140.7 (Cq), 155.6 ppm (CH).
ACHTUNGTRENNUNG[Cp*RhACHTUNGTRENNUNG(1·OH)Cl] (6): Compound 2 (19 mg, 0.03 mmol, 1.0 equiv) was
suspended in CD2Cl2 (0.5 mL) and transferred to a Young NMR-Tube
under argon. An excess of triethylamine (30 mg, 0.30 mmol, 10.0 equiv)
was added to the mixture. Compound 5 was formed instantaneously.
À
and 8) or included in calculated positions (compound 6). The O H hy-
4
1H NMR (CD2Cl2, 400 MHz): d=1.41 (15H, d, J(H,P) =2.8 Hz, Cp* CH3),
drogen atoms were refined freely with isotropic displacement parameters,
2
3
3
4.65 (1H, dd, J(H,P) =12.0 Hz, J(H,H) =3.2 Hz, Ha’), 6.63 (1H, ddd, J(H,P)
=
À
whereas C H hydrogen atoms were refined with a riding model. Geome-
8.0 Hz, 3J(H,H) =4.0 Hz, 5J(H,H) =1.0 Hz, Hb’), 7.22 (2H, t, 3J(H,H) =6.4 Hz,
try calculations and checking for higher symmetry was performed with
3
Harom), 7.33 (5H, m, Harom), 7.53 (5H, m, Harom), 7.81 (1H, t, J(H,H)
=
the PLATON program.[27]
7.8 Hz, Harom), 7.91 (1H, d, 3J(H,P) =8.0 Hz, Harom), 8.71 ppm (1H, d,
3J(H,H) =5.2 Hz, Harom); 31P NMR (CD2Cl2, 162 MHz): d=80.0 ppm (d,
1J(Rh,P) =133 Hz); 13C NMR (CD2Cl2, 100.6 MHz): d=9.2 (CH3 from
Compound 4: C32H32ClIrNOP, Fw =705.21, orange block, 0.27ꢄ0.13ꢄ
0.09 mm3, orthorhombic, Pna21 (No. 33), a=12.9795(3), b=14.0625(3),
c=14.6631(3) ꢃ, V=2676.35(10) ꢃ3, Z=4, Dx =1.750 gcmÀ3
,
m=
Cp*), 100.8 (Cq from Cp*), 121.1 (CH), 121.2 (CH), 124.2 (CH), 126.8 (d,
5.18 mmÀ1. 43545 Reflections were measured up to a resolution of (sin q/
l)max =0.65 ꢃÀ1 at a temperature of 150(2) K. 6140 Reflections were
unique (Rint =0.030), of which 5594 were observed [I>2s(I)]. 340 Param-
eters were refined with 1 restraint. R1/wR2 [I>2s(I)]: 0.0150/0.0315. R1/
wR2 [all reflns]: 0.0189/0.0322. S=1.028. Flack parameter x=
4J(C,P) =1.4 Hz, CH), 127.0 (CH), 127.1(CH), 127.9 (CH), 128.5 (d, J(C,P)
=
4
2.2 Hz, CH), 128.9 (CH), 130.9 (CH), 131.0 (CH), 133.7 (CH), 133.8
(CH), 135.9 (Cq), 136.0 (Cq), 140.0 (CH), 140.1 (d, 3J(C,P) =3.9 Hz, Cq),
140.2 (CH), 140.8 (d, 4J(C,P) =2.9 Hz, Cq), 145.8 (Cq), 154.3 (CH),
160.3 ppm (Cq). The reaction mixture was filtered over celite and crystals
of 6 were obtained through slow diffusion of diethyl ether into the reac-
tion mixture. The yield of the isolated product after crystallization was
53%. Elemental analysis calcd (%) for C32H32NPOClRh·CH2Cl2·NEt3
(802.06): C 58.40, H 6.1; N 3.49; found: C 58.40, H 6.10, N 3.22%.
À0.012(3).[24] Residual electron density between À0.49 and 0.64 eꢃÀ3
.
Compound 6: C32H32ClNOPRh·0.5ACHTUNGRTNEUNG(CH2Cl2), Fw =658.38, red needle,
0.48ꢄ0.19ꢄ0.07 mm3, monoclinic, Cc (No. 9), a=25.4883(8), b=
19.5808(6), c=11.9853(5) ꢃ, b=105.322(2)8, V=5769.1(3) ꢃ3, Z=8,
Dx =1.516 gcmÀ3, m=0.86 mmÀ1. The crystal appeared to be twinned with
a twofold rotation about hkl=(1,0,0) as twin operation. The intensity in-
tegration was consequently based on two orientation matrices. 34917 Re-
flections were measured up to a resolution of (sin q/l)max =0.65 ꢃÀ1 at a
temperature of 150(2) K. 12989 Reflections were unique (Rint =0.031), of
which 11725 were observed [I>2s(I)]. 713 Parameters were refined with
2 restraints. R1/wR2 [I>2s(I)]: 0.0244/0.0534. R1/wR2 [all refl.]: 0.0303/
0.0550. S=1.050. Flack parameter x=À0.013(15).[27] Twin fraction=
[Cp*Ir
(1H·OMe)Cl]Cl
(7):
Compound
[(1)Cp*IrCl]Cl
(22 mg,
0.03 mmol, 1.0 equiv) was suspended in CD2Cl2 (0,5 mL) and transferred
to a Young NMR-Tube under argon. An excess of methanol (38 mg,
1.20 mmol, 40.0 equiv) was added to the mixture and compound 7 was
formed instantaneously. 1H NMR (CD2Cl2, 400 MHz): d=1.51 (15H, d,
4J(H,P) =2.8 Hz, Cp* -CH3), 3.76 (3H, d, 3J(H,P) =11.2 Hz, CH3), 4.79 (1H,
dd, 2J(H,P) =11.2 Hz, 3J(H,H) =3.2 Hz, Ha), 6.95 (1H, ddd, 2J(H,P) =7.6 Hz,
3J(H,H) =3.2 Hz, 5J(H,H) =0.6 Hz, Hb), 7.38–7.54 (10H, m, Harom), 7.83 (1H,
0.4331(6). Residual electron density between À0.47 and 0.39 eꢃÀ3
.
2
s, Harom), 7.88 (1H, s, Harom), 8.10 (1H, t, Harom), 8.22 (1H, d, J(H,H)
=
8.0 Hz, Harom), 8.63 ppm (1H, d, 2J(H,H) =5.6 Hz, Harom); 31P NMR
Compound 8: C33H34ClIrNOP, Fw =719.23, red needle, 0.56ꢄ0.17ꢄ
(CD2Cl2, 162 MHz): d=77.0 ppm; 13C NMR (CD2Cl2, 100.6 MHz), 9.0 (d,
0.12 mm3, monoclinic, P21/n (No. 14), a=8.6491(2), b=14.3269(4), c=
3J(C,P) =0.8 Hz, CH3 from Cp*), 46.6 (CH), 50.2 (CH3), 58.7 (d, J(C,P)
=
23.3997(8) ꢃ, b=95.788(1)8, V=2884.80(15) ꢃ3, Z=4, Dx =1.656 gcmÀ3
,
2
13.3 Hz, CH), 97.3 (d, 2J(C,P) =2.8 Hz, Cq from Cp*), 122.1 (CH), 122.2
m=4.80 mmÀ1. 42821 Reflections were measured up to a resolution of
(sin q/l)max =0.65 ꢃÀ1 at a temperature of 150(2) K. 6627 Reflections
(CH), 126.8 (d, 3J(C,P) =1.4 Hz, CH), 127.5 (CH), 129.1 (d, 2J(C,P) =3.3 Hz,
7530
www.chemeurj.org
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 7523 – 7531

Reactions of Pyridyl-Functionalized, Chelating l3-Phosphinines
FULL PAPER
were unique (Rint =0.016), of which 6106 were observed [I>2s(I)]. 349
Parameters were refined with no restraints. R1/wR2 [I>2s(I)]: 0.0129/
0.0292. R1/wR2 [all refl.]: 0.0150/0.0298. S=1.048. Residual electron den-
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Acknowledgements
This research has been funded by The Netherlands Organization for Sci-
entific Research (NWO-Vidi and NWO-ECHO grant for C.M.). The
COST-Action PhoSciNet (CM0802) is gratefully acknowledged.
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Received: January 28, 2013
Published online: April 4, 2013
Chem. Eur. J. 2013, 19, 7523 – 7531
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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