Catalytic synthesis of an unsymmetrical PNP-pincer-type phosphaalkene ligand

Article abstract of DOI:10.1021/acs.organomet.5b00195

An unsymmetrical PNP-pincer-type phosphaalkene ligand, 2-(phospholanylmethyl)-6-(2-phosphaethenyl)pyridine (PPEP), has been prepared from 2,6-bis(2-phosphaethenyl)pyridine (BPEP) by intramolecular C-H addition/cyclization of the 2-phosphaethenyl group with a 2,4,6-tri-tert-butylphenyl substituent (CH=PMes). The reaction proceeds in hexane in the presence of a catalytic amount of [Pt(PCy₃)₂] (20 mol %) at 80 C in a sealed tube, giving PPEP in 32% isolated yield, along with byproduction of 2,6-bis(phospholanylmethyl)pyridine (BPMP) and a Pt(II) phosphanido complex (5). The PPEP ligand reacts with [Rh(μ-Cl)(C₂H₄)₂]₂ and [RuCl₂(PPh₃)₃] to afford [RhCl(PPEP)] (6) and [RuCl₂(PPh₃)(PPEP)] (8), respectively. Complex 6 easily undergoes C-H addition/cyclization at the other CH=PMes group to afford the 2,6-bis(phospholanylmethyl)pyridine complex [RhCl(BPMP)] (7), whereas 8 is stable against C-H addition/cyclization. Treatment of 8 with ^tBuOK forms [RuCl(PPh₃)(PPEP)] (9), coordinated with an unsymmetrical PNP-pincer-type phosphaalkene ligand containing a dearomatized pyridine unit (PPEP). The X-ray structures of 5 and 9 are reported. The reaction processes from BPEP to PPEP and to 5 are discussed based on NMR observations.

Full text of DOI:10.1021/acs.organomet.5b00195

Article
pubs.acs.org/Organometallics
Catalytic Synthesis of an Unsymmetrical PNP-Pincer-Type
Phosphaalkene Ligand
Hiro-omi Taguchi, Yung-Hung Chang, Katsuhiko Takeuchi, and Fumiyuki Ozawa*
International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji,
Kyoto 611-0011, Japan
*
S Supporting Information
ABSTRACT: An unsymmetrical PNP-pincer-type phosphaal-
kene ligand, 2-(phospholanylmethyl)-6-(2-phosphaethenyl)-
pyridine (PPEP), has been prepared from 2,6-bis(2-phos-
phaethenyl)pyridine (BPEP) by intramolecular C−H addition/
cyclization of the 2-phosphaethenyl group with a 2,4,6-tri-
tert-butylphenyl substituent (CHPMes*). The reaction
proceeds in hexane in the presence of a catalytic amount of
[
Pt(PCy ) ] (20 mol %) at 80 °C in a sealed tube, giving
3 2
PPEP in 32% isolated yield, along with byproduction of 2,6-
bis(phospholanylmethyl)pyridine (BPMP) and a Pt(II) phosphanido complex (5). The PPEP ligand reacts with [Rh(μ-Cl)(C H ) ]
2
4 2 2
and [RuCl (PPh ) ] to afford [RhCl(PPEP)] (6) and [RuCl (PPh )(PPEP)] (8), respectively. Complex 6 easily undergoes C−H
2
3 3
2
3
addition/cyclization at the other CHPMes* group to afford the 2,6-bis(phospholanylmethyl)pyridine complex [RhCl(BPMP)]
t
(
7), whereas 8 is stable against C−H addition/cyclization. Treatment of 8 with BuOK forms [RuCl(PPh )(PPEP*)] (9),
3
coordinated with an unsymmetrical PNP-pincer-type phosphaalkene ligand containing a dearomatized pyridine unit (PPEP*).
The X-ray structures of 5 and 9 are reported. The reaction processes from BPEP to PPEP and to 5 are discussed based on
NMR observations.
INTRODUCTION
Scheme 1. PNP-Pincer-Type Phosphaalkene Complexes of
Ir(I) (ref 5a)
■
Metal−ligand cooperative activation of chemical bonds has
attracted much attention as a powerful approach to highly
1
,2
active catalysis. A key to this elementary process is the
rational design of functional ligands. In this context, Milstein
et al. have demonstrated a particular function of pyridine-based
PNP-pincer ligands causing heterolytic cleavage of various
chemical bonds via metal−ligand cooperation involving
3
,4
aromatization/dearomatization of the pyridine ring. This
novel ligand system has been applied to catalytic organic
transformations that meet the criteria of green and sustainable
chemistry.
Recently, we found that the reactivity of a PNP-pincer
complex of iridium toward N−H bond cleavage of ammonia is
dramatically enhanced by introducing a phosphaalkene unit to
5
the pyridine-based ligand. As shown in Scheme 1, dearomatized
PNP-pincer-type phosphaalkene complex 3, derived from
2
,6-bis(2-phosphaethenyl)pyridine complex 1 by a two-step
procedure, instantly reacts with ammonia (1 atm) at room
temperature to afford parent amido complex 4 quantitatively.
Phosphaalkene is a low-coordinate phosphorus compound
with a PC bond, which possesses an extremely low-lying
π*-orbital and thus serves as an extremely strong π-acceptor
prepare 2-(phospholanylmethyl)-6-(2-phosphaethenyl)pyridine
(
PPEP) in a free state, with expectations of expanding the
utility of this particular ligand system in organometallic
chemistry.
As seen from Scheme 1, the PPEP ligand is formed from 2,6-
bis(2-phosphaethenyl)pyridine (BPEP) by C−H addition/
cyclization at one of the 2-phosphaethenyl groups with a
6
toward transition metals. DFT calculations revealed a
remarkable situation where the phosphaalkene ligands
(
PPEP/PPEP*) stabilize reaction intermediates and transition
states via effective dπ−pπ interactions, leading to extremely
high reactivity toward ammonia. In this study, we attempted to
Received: March 9, 2015
Published: April 8, 2015
©
2015 American Chemical Society
1589
DOI: 10.1021/acs.organomet.5b00195
Organometallics 2015, 34, 1589−1596

Organometallics
Article
2
,4,6-tri-tert-butylphenyl substituent (CHPMes*). Since the
Table 1. Catalytic Conversion of BPEP under Various
a
conversion of BPEP to PPEP on iridium (1 → 2) did not pro-
ceed catalytically, we examined a platinum-catalyzed reaction,
referring to a closely related study on catalytic conversion
of 1,5-bis(2-phosphaethenyl)benzene (I) to 1,5-bis(2-
Conditions
b
ratio
time
(h)
7
entry
catalyst
additive
BPEP PPEP BPMP
phospholanylmethyl)benzene (II) (Scheme 2). Although the
1
2
3
[Pt(PCy ) ]
12
40
12
39
100
42
55
0
6
0
5
3
2
[Pt(cod)2]
[Pt(cod)2]
Scheme 2. Platinum-Catalyzed C−H Addition/Cyclization of
2
PCy (2 equiv/
53
3
Pt)
,6-Bis(2-phosphaethenyl)benzene (ref 7)
4
5
6
7
8
[Pt(PCy ) ]
PCy (1 equiv/
12
24
27
9
65
71
0
8
20
100
0
3
2
3
Pt)
[Pt(PCy ) ]
PCy (1 equiv/
3
2
3
Pt)
[Pt(PCy ) ]
PCy (1 equiv/
264
12
0
3
2
3
Pt)
[PtMe (μ-
PCy (2 equiv/
100
100
0
2
3
SMe )]2
Pt)
2
[PtCl (PCy ) ]
PCy (2 equiv/
12
0
0
C−H addition/cyclization of the benzene analogue proceeds
successively at both phosphaalkene units, the reaction of BPEP
proceeds in a stepwise manner, allowing us to isolate the free
PPEP.
2
3
2
3
Pt)
a
All reactions were run in hexane (0.5 mL) at 80 °C, using BPEP
0.015 mmol), catalyst (20 mol %), and additive. Product ratio in
solution as confirmed by P{ H} NMR analysis.
b
(
31
1
RESULTS AND DISCUSSION
Catalytic Conversion of BPEP to PPEP. The BPEP ligand
9.8 mg) was treated with a catalytic amount of [Pt(PCy ) ]
20 mol %) in hexane at 80 °C in a sealed NMR sample tube
■
column chromatography, giving free PPEP as a white solid in
3
2% yield. This product contained small amounts of BPEP and
(
(
3
2
the Z-isomer of PPEP, but was successfully applied to the synthesis
of PPEP complexes of ruthenium and rhodium (vide infra).
Identification of 5. Figure 1 shows the X-ray structure of 5,
demonstrating a distorted square planar configuration around
for 12 h (Scheme 3), and the reaction system was examined by
NMR spectroscopy. The result is given in entry 1 in Table 1.
This reaction also formed a solid product of 5 (vide infra), but
its amount was too small to confirm (<1 mg). Therefore, the
product ratio observed in the solution is reported.
3
1
1
The P{ H} NMR spectrum exhibited signals arising
from BPEP (δ 283.5), PPEP (δ 283.4 and −6.5), and 2,6-
bis(phospholanylmethyl)pyridine (BPMP; δ −6.2 and −6.4, a
1
:1 mixture of diastereomers) in a 39:55:6 ratio (entry 1). The
reaction did not proceed with [Pt(cod) ] (entry 2), but
2
addition of free PCy resulted in the formation of PPEP in
3
comparable selectivity to entry 1 (entry 3). The conversion of
BPEP was improved, keeping the selectivity for PPEP, when
1
equiv/Pt of PCy was added to [Pt(PCy ) ] (entry 4). The
3 3 2
conversion was further enhanced in a prolonged reaction
time; however, the product ratio of PPEP gradually decreased
(
(
entry 5), and eventually the doubly cyclized compound
BPMP) became the sole product (entry 6). Unlike the Pt(0)
catalysts, Pt(II) complexes did not show catalytic activity
Figure 1. Molecular structure of 5 with 50% probability ellipsoids.
Hydrogen atoms and disordered carbon atoms ( Bu) are omitted for
(
entries 7 and 8).
Next, we attempted to isolate free PPEP under the catalytic
t
clarity. Selected bond distances (Å) and angles (deg): Pt−N 2.073(3),
conditions of entry 4 in Table 1. BPEP (131 mg) was heated
with [Pt(PCy ) ] and PCy (both 20 mol %) in hexane
Pt−P1 2.3259(11), Pt−P2 2.3892(11), Pt−P3 2.2839(11), P1−C1
3
2
3
1
.747(4), P2−C2 1.879(2), C1−C3 1.382(6), C2−C7 1.486(6), N−
(
3.5 mL) at 80 °C in a sealed Schlenk tube for 12 h, where a
Pt−P3 167.49(10), P1−Pt−P2 162.89(4), C2−P2−Pt 89.30(13),
C2−P2−C44 92.33(18), C44−P2−Pt 117.18(13).
small quantity of orange solid (11 mg) was precipitated from
the solution. As described in the next section, this solid was
identified as phosphanido complex 5 depicted in Scheme 3.
The solution part was concentrated to dryness and subjected to
platinum. The PNP-pincer ligand adopts a meridional co-
ordination with the P1−Pt−P2 angle of 162.89(4)°, whereas
Scheme 3. Platinum-Catalyzed C−H Addition/Cyclization of 2,6-Bis(2-phosphaethenyl)pyridine (BPEP)
1
590
DOI: 10.1021/acs.organomet.5b00195
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Scheme 4. Plausible Catalytic Process for the Formation of PPEP from BPEP
PCy is located trans to the pyridine unit. The P1−C1 bond
BPEP (δ 113.7) was too upfield for a phosphaalkene ligand
3
6
(
1.747(4) Å) is clearly shorter than typical P−C single bonds,
(ca. δ 240−260), it was investigated by DFT calculations.
and the C1−C3 bond (1.382(6) Å) is between those expected
for a single and double bond. These bond variations are char-
acteristic of PNP-pincer ligands with a dearomatized pyridine
Figure 2a shows the optimized structure for model com-
t
pound A1, in which the 2,4,6- Bu C H (Mes*) groups and
3
6
2
4
,5
unit.
The most remarkable feature of 5 is a significantly pyramidalized
geometry around P2. Because the P2−C2 bond is saturated
(
1.879(2) Å), the P2 unit can be identified as a phosphanido
ligand, formed by protonation at the C2 atom of the parent
phosphaethenyl group. The sum of the bond angles around
P2 is 298.81°; this value is among the smallest of terminal
8
phosphanido complexes of platinum (306−333°). Moreover,
since the C2−P2−Pt bond bends to nearly 90° (89.30(13)°),
the least contribution of the s-orbital of phosphorus to the
3
1
1
Pt−P2 bond is suggested. Indeed, the P{ H} NMR signal of
P2 (δ 35.3) exhibited an extremely small coupling to platinum
1
1
(
(
JPtP = 599 Hz). On the other hand, the J couplings for P1
PtP
1
1
δ 26.6, J = 1986 Hz) and P3 (δ 14.7, J = 3515 Hz) were
PtP
PtP
consistent with the phosphorus ligands trans to the anionic
1
phosphanido and neutral pyridine ligand, respectively. The H
NMR spectrum displayed characteristic signals of a dearomat-
Figure 2. (a) Optimized structure of [Pt(PMe )(BPEP′)] (A1). (b)
3
ized pyridine unit at δ 6.24, 6.00, and 4.98 (pyridine ring
t
4,5
Resonance structures of A1 (Ar = 2,6- Bu C H ). Selected bond
2 6 3
protons) and at δ 3.73 (vinylic proton).
distances (Å) and angles (deg): Pt−N 2.11, Pt−P1 2.35, Pt−P2 2.29,
P1−C1 1.73, C1−C2 1.41, N−Pt−P1 80.5, N−Pt−P2 174.6.
Study on the Formation Process of PPEP from BPEP.
Complex 5 gradually decomposed in toluene in the presence of
1
equiv of PCy at 80 °C, but did not generate free PPEP. Thus,
t
3
PCy ligand in A are replaced with 2,6- Bu C H (Ar) and
3
2
6
3
we concluded that this complex is a dead-end side-product,
responsible for the relatively large catalyst loading (20 mol %).
Scheme 4 shows a plausible catalytic process for the formation
of PPEP from BPEP, including the side reaction to afford 5.
Although Le Floch et al. previously reported DFT calculations
showing a C−H addition/cyclization process via a π-coordinated
phosphaalkene intermediate, we could obtain evidence for
the catalytic process involving meridional coordination of PNP-
pincer ligands.
PMe , respectively. Although this complex is formally a Pt(0)
3
species, the platinum center adopts a square planar configura-
tion typical of Pt(II) species; the sum of the four bond angles
around Pt is 361.3°. Moreover, the P1−C1 bond (1.73 Å) is
clearly elongated compared with ordinary phosphaalkene
ligands (1.68 Å). These structural variations should be caused
by strong π-back-donation from platinum to phosphaalkene
units. Thus, it is reasonable that the complex possesses a great
contribution of canonical structures A1′ and A1″ in Figure 2b,
in which one of the phosphaalkene ligands changes to an
anionic phosphanido ligand along with dearomatization of the
pyridine unit. The 31P NMR chemical shift estimated by the
GIAO method (δ 102.7) was in good agreement with the
observed value for the real complex A (δ 113.7).
7
The first step is the coordination of BPEP to platinum along
with liberation of PCy (step a). To gain structural information
about [Pt(PCy )(BPEP)] (A), a 1:1 mixture of [Pt(PCy ) ]
3
3
3 2
and BPEP was dissolved in toluene-d at −78 °C and examined
8
31
1
by P{ H} NMR spectroscopy at −10 °C, showing the signals
2
assignable to coordinated BPEP and PCy at δ 113.7 (d, J
=
=
When the solution of A was allowed to stand at room tem-
perature, the P{ H} NMR signals of A decreased, and three
signals with nearly the same intensities increased at δ 247.4,
3
PP
1
2
1
31
1
3
4
1 Hz, J = 1543 Hz) and 17.9 (t, J = 31 Hz, J
154 Hz) in a 2:1 ratio. In this case, since the chemical shift of
PtP
PP
PtP
1
591
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Scheme 5. Synthesis of PPEP Complexes of Rh(I) and Ru(II)
2
8.2 (1JPtP = 3480 Hz), and 25.3 (1JPtP = 1985 Hz). These
temperature led to [RuCl (PPh )(PPEP)] (8) quantitatively.
2
3
signals were assigned to hydrido complex B, formed by C−H
Unlike rhodium complex 6, this ruthenium complex was stable
t
oxidative addition of a Bu group, followed by P−C reductive
enough to be isolated as a purple solid in 69% yield (path c in
Scheme 5). The 31P{ H} NMR spectrum showed three sets of
1
elimination from intermediate E, based on the following NMR
observations (step b in Scheme 4). The presence of a hydrido
ligand was evidenced by the appearance of a double doublet
2
signals arising from PPEP (δ 292.0 (dd) and 50.5 (dd); J
=
PP
2
411 and 29 Hz) and PPh (δ 34.8 (t), J = 29 Hz).
3
PP
1
t
signal at δ −6.82 in the H NMR spectrum. This signal
Complex 8 reacted with BuOK in THF at room temperature
2
195
involved two sets of J couplings (182 and 16 Hz) and Pt
to give [RuCl(PPh )(PPEP*)] (9) as a dearomatized complex,
PH
3
2
satellites (996 Hz); the large and small J values are con-
which was isolated as dark green crystals in 69% yield (path d).
PH
1
sistent with trans and cis arrangements of the hydrido ligand to
The H NMR signals of the dearomatized pyridine unit were
3
1
phosphorus ligands in a square planar configuration. The
P
observed at δ 6.06, 5.78, and 5.25 (pyridine ring protons) and
1
95
31
1
NMR signal at δ 247.4 did not involve Pt satellites, showing
at δ 3.76 (vinylic proton). The P{ H} NMR signals appeared
2
2
dissociation of the phosphaalkene unit. On the other hand, the
at δ 217.9 (dd, J = 298 and 24 Hz), 58.4 (dd, J = 40 and
PP
PP
3
1
195
2
P NMR signals at δ 28.2 and 25.3 involved Pt satellites. In
this case, the relatively large coupling for the former signal
3480 Hz) was consistent with the PCy ligand trans to the
2
4 Hz), and 46.7 (dd, J = 298 and 40 Hz). The signals at δ
217.9 and 46.7 ppm with a large J coupling (298 Hz) are due
to PPEP, whereas the signal at δ 58.4 with small J couplings
PP
2
PP
2
(
3
PP
pyridine unit, whereas the small coupling for the latter signal
1985 Hz) was in accord with the phospholanyl group trans to
the hydrido ligand with strong trans influence.
(40 and 24 Hz) is due to PPh located cis to the PPEP ligand.
3
(
Figure 3 shows the X-ray structure of 9, which adopts a
10
square pyramidal configuration around Ru (τ = 0.12). The
The next step is the 1,3-shift of the hydrido ligand to the exo-
methylene carbon or phosphaalkene carbon of the dearomat-
ized PNP-pincer ligand (step c → step d or f in Scheme 4). In
this step, the hydrido ligand very probably changes the co-
ordination site from the equatorial to apical position (B → C in
step c), to ensure the orbital interaction between the Pt−H
bond and π*-orbitals on the carbon atoms. Migration of the
hydrido ligand to the α-position on C forms PPEP complex D,
which subsequently undergoes ligand substitution with free
PCy to give free PPEP and [Pt(PCy ) ] (step d → step e). On
3
3 2
the other hand, migration to the β-position affords 5 (step f).
Synthesis of PPEP Complex of Rh(I). Next, we
introduced free PPEP to rhodium and ruthenium complexes
(
(
Scheme 5). The reaction of [Rh(μ-Cl)(C H ) ] with PPEP
2 4 2 2
1 equiv/Rh) in THF-d readily proceeded at −70 °C to form
8
3
1
1
Figure 3. Molecular structure of 9 with 50% probability ellipsoids.
[
RhCl(PPEP)] (6) exclusively (path a). The P{ H} NMR
2
1
Hydrogen atoms, a crystal solvent (pentane), and disordered carbon
signals appeared at δ 243.4 (dd, J = 463 Hz, J = 186 Hz)
and 26.0 (dd, J = 463 Hz, J
shifts and coupling patterns were consistent with complex 6
coordinated with PPEP as an unsymmetrical PNP-pincer-type
phosphaalkene ligand. However, this complex could not be
isolated due to the high reactivity of the phosphaethenyl unit
PP
RhP
t
2
1
atoms ( Bu) are omitted for clarity. Selected bond distances (Å) and
= 167 Hz); the chemical
PP
RhP
angles (deg): Ru−N 2.0990(18), Ru−P1 2.2974(6), Ru−P2
2
.5208(6), Ru−P3 2.2534(6), Ru−Cl 2.4120(6), P1−C1 1.753(2),
P2−C2 1.672(2), C1−C3 1.379(3), C2−C7 1.438(3), N−Ru−Cl
67.51(6), P1−Ru−P2 160.39(2), N−Ru−P3 96.99(5).
1
(
CHPMes*) to C−H addition/cyclization. Instead, the
PPh ligand is accommodated at the apical position, whereas
3
doubly cyclized complex [RhCl(BPMP)] (7) was obtained in
7
the Cl ligand is located trans to the pyridine unit on the basal
plane. The bond lengths of Ru−N (2.0990(18) Å), Ru−P1
(2.2974(6) A), and Ru−P3 (2.2534(6) A) are ordinary for a
five-coordinated Ru(II) complex, whereas the Ru−P2 bond
9
1% yield as a 5:1 mixture of diastereomers (path b).
Synthesis of PPEP Complex of Ru(II). Treatment of
[
RuCl (PPh ) ] with PPEP (1 equiv/Ru) in THF at room
2 3 3
1
592
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(
2.5208(6) Å) is clearly elongated as compared with the anal-
(9.8 mg, 15 μmol) and PCy
3
(0.8 mg, 3.0 μmol) was added dropwise
11
to a suspension of [Pt(PCy ) ] (2.3 mg, 3.0 μmol) in hexane (0.3 mL)
ogous complex [RuCl(CO) (PPEP*-Ph)] (2.3571(14) Å).
3 2
2
at room temperature. The mixture was heated at 80 °C for 12 h, and
the ratio of BPEP, PPEP, and BPMP was determined by P{ H}
NMR analysis at room temperature.
The elongation of the Ru−P2 bond may be caused by steric
3
1
1
repulsion between PPh and bulky substituents of PPEP*.
3
In any event, the elongation of the Ru−P2 bond results in
weakening of π-back-donation from ruthenium to the PC
bond. Actually, the P2−C2 bond length (1.672(2) Å) was in
agreement with that of a nonactivated PC double bond
Preparation of PPEP and 5. A mixture of BPEP (131 mg,
0
0
.20 mmol), [Pt(PCy ) ] (30 mg, 0.040 mmol), and PCy (11 mg,
3
2
3
.040 mmol) in hexane (3.5 mL) was heated at 80 °C for 12 h. The
color of the solution gradually changed from green to brown, and
orange crystals of 5 were precipitated. The solution was separated by
decantation, and the crystals of 5 were washed with hexane (1 mL × 3)
and dried under vacuum (11 mg, 25% yield/Pt). The solution part was
concentrated to dryness and subjected to column chromatography on
(
1.66−1.68 Å). Moreover, the P1−C1 (1.753(2) Å) and
C1−C3 (1.379(3) Å) bond lengths were typical of PNP-pincer
ligands with a dearomatized pyridine unit.
4
3
-aminopropyl-functionalized silica gel using hexane as the eluent, to
CONCLUSION
■
afford PPEP as a white solid (41 mg, 0.063 mmol, 32%). This product
contained small amounts of impurities including BPEP and the Z-isomer
of PPEP, as confirmed by NMR analysis (see Figures S1−S3).
We succeeded in platinum-catalyzed synthesis of an unsym-
metrical PNP-pincer-type phosphaalkene ligand (PPEP) from
bis(phosphaethenyl)pyridine (BPEP) via intramolecular C−H
addition/cyclization of the CHPMes* group. Unlike the
reaction of benzene analogue I in Scheme 2, the reaction of
BPEP proceeded in a stepwise manner, and the desired product
free PPEP) could be isolated in moderate yield (32%). The
PPEP ligand reacted with Rh(I) and Ru(II) precursors to afford
RhCl(PPEP)] (6) and [RuCl (PPh )(PPEP)] (8), respec-
tively. The CHPMes* group in 6 was still reactive to C−H
addition/cyclization, giving [RhCl(BPMP)] (7) with a doubly
cyclized PNP-pincer ligand (BPMP). On the other hand,
ruthenium complex 8 was sufficiently stable for isolation and
1
2
PPEP: H NMR (C D , 25 °C): δ 8.27 (d, J = 25.6 Hz, 1H, P
6
6
PH
4
4
CH), 7.63 (s, 2H, Ar), 7.55 (dd, JPH = 4.0, JHH = 1.7 Hz, 1H, Ar),
4
3
7
6
1
.24 (d, J = 1.7 Hz, 1H, Ar), 6.98 (t, J = 7.7 Hz, 1H, 4-H of Py),
.75 (d, J = 7.7 Hz, 2H, 3,5-H of Py), 3.38 (dd, J = 3.6, J =
HH
2.8 Hz, 1H, PyCH P), 3.32 (dd, J = 4.8, J = 12.8 Hz, 1H,
HH HH
3
2
2
HH
PH
2
2
2
PH
HH
(
2
2
PyCH P), 2.59 (dd, J = 2.0, J = 14.7 Hz, 1H, PCH ), 1.95 (dd,
2
PH
HH
2
2
2
JPH = 22.5, J = 14.7 Hz, 1H, PCH ), 1.73 (s, 3H, CH ), 1.66 (s,
HH
2
t
3
[
2
3
t
t
9
1
2
1
H, CH of Bu), 1.62 (s, 18H, CH of Bu), 1.36 (s, 9H, CH of Bu),
.34 (s, 9H, CH of Bu), 1.30 (s, 3H, CH ). C{ H} NMR (C D ,
5 °C): δ 176.1 (d, JPC = 35 Hz), 160.5 (d, JPC = 6 Hz), 160.1 (s),
58.1 (d, JPC = 12 Hz), 155.1 (s), 153.1 (d, JPC = 15 Hz), 152.9 (s),
3
3
3
t
13
1
3
3
6
6
150.4 (s), 141.3 (d, JPC = 54 Hz), 137.1 (s), 136.7 (d, JPC = 23 Hz),
122.6 (s), 122.4 (t, JPC = 5 Hz), 119.7 (s), 118.7 (d, JPC = 16 Hz), 47.6
(d, JPC = 7 Hz), 40.8 (d, JPC = 27 Hz), 39.0 (s), 38.1 (d, JPC = 2 Hz),
t
underwent the abstraction of a benzylic proton with BuOK to
form [RuCl(PPh )(PPEP*)] (9) with a dearomatized PNP-
3
3
6.9 (d, JPC = 10 Hz), 35.6 (d, JPC = 2 Hz), 35.0 (d, JPC = 4 Hz), 34.6
pincer-type phosphaalkene ligand (PPEP*).
(
d, J = 7 Hz), 34.2 (s), 33.2 (d, JPC = 9 Hz), 32.1 (s), 32.0 (s).
Plausible intermediates A and B in the catalytic conversion of
BPEP to PPEP could be detected by NMR spectroscopy. The
PC
3
1
1
P{ H} NMR (C D , 25 °C): δ 282.5 (s), −7.4 (s). HRMS (ESI):
6
6
+
3
1
1
calcd for C H NP 656.4509 ([M + H] ); found 656.4509.
43 64 2
P{ H} NMR signal of A appeared at an extremely high
1
4
4
5
: H NMR (THF-d , 25 °C): δ 7.49 (dd, J = 4.2 Hz, J
=
HH
8
PH
magnetic field. This is due to the occurrence of strong π-back-
donation from platinum to phosphaalkene units. DFT calcula-
tions for the model compound (A1) revealed a square planar
configuration around platinum despite the formal Pt(0) species.
Complex B was assignable to a four-coordinated platinum hydride
with an uncoordinated phosphaalkene unit and a dearomatized
pyridine unit. It was rationalized that B undergoes coordination of
the phosphaalkene unit, followed by 1,3-shift of the hydrido ligand
to the exo-methylene carbon of the dearomatized pyridine unit,
4
4
1
.7 Hz, 1H, Ar), 7.33 (br t, J = 2.9 Hz, J = 2.2 Hz, 1H, Ar), 7.22
PH HH
4
4
(
d, J = 1.7 Hz, 1H, Ar), 7.16 (d, J = 2.2 Hz, 1H, Ar), 6.24 (ddd,
HH HH
3
5
3
JHH = 8.6 and 6.6 Hz, J = 1.8 Hz, 1H, Py), 6.00 (br d, J = 8.6,
PH
HH
3
1
H, Py), 4.98 (br, J = 6.6 Hz, 1H, Py), 3.73 (vt, J = 2.4 Hz, 1H,
HH app
2
2
CCHP), 2.90 (dd, J = 26.2 Hz, J = 14.9 Hz, 1H, PyCH P),
PH
HH
2
2
2
2
2.84 (d, J = 14.9 Hz, 1H, PCH ), 2.17 (dd, J = 14.9 Hz, J
=
HH
2
HH
PH
2
2
5.3 Hz, 1H, PyCH
PCH ), 1.92−1.98 (br, 3H, PCy ), 1.75 (s, 9H, CH of Bu), 1.54 (s,
P), 1.94 (dd, JHH = 14.9 Hz, JPH = 7.8 Hz, 1H,
2
t
2
3
3
t
t
3
9
1
H, CH ), 1.57 (s, 9H, CH of Bu), 1.47 (s, 9H, CH of Bu), 1.32 (s,
H, CH of Bu), 1.33 (s, 3H, CH ), 1.29 (s, 9H, CH of Bu), 1.25−
.34 (br, 18H, PCy ), 1.10−1.24 (br, 12H, PCy ). P{ H} NMR
3
3
3
t
t
3
3
3
giving [Pt(PCy )(PPEP)] (D), which subsequently releases PPEP
3
31
1
3
3
by ligand substitution with PCy . On the other hand, 1,3-shift to
the phosphaalkene carbon forms a novel phosphanido complex
5), whose structure was confirmed by X-ray diffraction analysis.
3
2
1
(THF-d , 25 °C): δ 35.3 (br d, J = 65 Hz, J = 599 Hz), 26.6 (dd,
8 PP PtP
1 2 1
2
JPP = 65 and 19 Hz, J = 1986 Hz), 14.7 (d, J = 19 Hz, J =
PtP
PP
PtP
(
13
1
3
515 Hz). The C{ H} NMR spectrum was not recorded because of
the low solubility of 5. Anal. Calcd for C H NP Pt: C, 64.75; H,
61
96
3
EXPERIMENTAL SECTION
General Considerations. All manipulations were carried out
under a nitrogen atmosphere using standard Schlenk techniques or a
glovebox. Nitrogen gas was dried by passing through a P O column.
8
.55; N, 1.24. Found: C, 64.34; H, 8.77; N, 1.39.
Preparation of BPMP. A toluene solution (2 mL) of BPEP
131 mg, 0.20 mmol) and PCy (11 mg, 0.040 mmol) was added to a
■
(
3
suspension of [Pt(PCy ) ] (30 mg, 0.040 mmol) in toluene (1.5 mL)
3
2
2
5
at room temperature. The solution was heated at 100 °C for 50 h and
concentrated to dryness under reduced pressure. The crude product
was purified by column chromatography on 3-aminopropyl-function-
alized silica gel using hexane as the eluent, to give a white solid of
BPMP as a 6:4 mixture of diastereomers (48 mg, 0.073 mmol, 36%).
With consideration of the steric conditions, the major isomer was
THF, Et O, hexane, and pentane (dehydrated) were used as received.
2
C D and THF-d were dried over sodium/benzophenone, distilled,
6
6
8
and stored over activated MS4A. 2,6-Bis(phosphaethenylpyridine)
1
2
13
13
14
(
BPEP), [Pt(PCy ) ], [PtCl (PCy ) ], [Rh(μ-Cl)(C H ) ] ,
3 2 2 3 2 2 4 2 2
15
and [RuCl (PPh ) ] were prepared according to the literature. The
2
3 3
other chemicals were obtained from commercial sources and used
without purification. NMR spectra were recorded on a 400 MHz
spectrometer. Chemical shifts are reported in δ (ppm), referenced to
assigned to the dl-isomer. Anal. Calcd for C43
H63NP : C, 78.74; H,
2
9.68; N, 2.14. Found: C, 78.45; H, 9.94; N, 2.20.
1
13
1
4
H (residual) and C signals of deuterated solvents as internal
dl-BPMP: H NMR (C D , 25 °C): δ 7.57 (d, JHH = 2.9 Hz, 2H,
6 6
3
standards or to the 31P signal of 85% H PO as an external standard.
4
Ar), 7.25 (d, JHH = 1.7 Hz, 2H, Ar), 7.07 (t, JHH = 6.7 Hz, 1H, 4-H of
3
4
3
Elemental analysis was performed by ICR Analytical Laboratory,
Kyoto University.
Catalytic Conversion of BPEP to PPEP (Table 1). A typical
Py), 6.81 (d, JHH = 7.6 Hz, 2H, 3,5-H of Py), 3.29−3.42 (m, 4H,
2
2
PyCH P), 2.46 (dd, JPH = 1.8, JHH = 14.6 Hz, 2H, PCH ), 2.02 (dd,
2
2
2
2
t
JPH = 22.4, JHH = 14.7 Hz, 2H, PCH ), 1.69 (s, 18H, CH of Bu),
2 3
1.66 (s, 6H, CH ), 1.35 (s, 18H, CH of Bu), 1.29 (s, 6H, CH ).
t
procedure (entry 2) is as follows. A hexane solution (0.2 mL) of BPEP
3
3
3
1
593
DOI: 10.1021/acs.organomet.5b00195
Organometallics 2015, 34, 1589−1596

Organometallics
Article
1
3
1
3.52 (dvt, 2JHH = 18.5, Japp = 3.8 Hz, 2H, PyCH P), 2.95 (d, J
2
C{ H} NMR (C D , 25 °C): δ 160.3 (d, J = 8 Hz), 159.8 (s),
=
HH
6
6
PC
2
2
1
5
(
53.1 (s), 152.9 (s), 136.9 (d, JPC = 19 Hz), 136.8 (s), 122.5 (d, JPC
=
14.7 Hz, 2H, PCH
2
), 2.18 (d, JHH = 14.7 Hz, 2H, PCH
of Bu), 1.50 (s, 6H, CH ), 1.41 (s, 6H, CH ), 1.34 (s, 18H,
of Bu). C{ H} NMR (THF-d , 25 °C): δ 164.6 (br), 159.5
2
), 1.63 (s,
t
Hz), 121.0 (d, JPC = 4 Hz), 119.6 (s), 47.6 (d, JPC = 7 Hz), 41.3
18H, CH
3
3
3
t
13
1
d, JPC = 25 Hz), 38.2 (s), 37.9 (d, J = 10 Hz), 35.6 (s), 34.9 (s),
4.4 (s), 33.3 (s), 32.1 (s). P{ H} NMR (C D , 25 °C): δ −7.0 (s).
CH
3
8
PC
31
1
3
(br), 154.7 (s), 154.1 (s), 131.3 (s), 130.5 (br), 123.0 (s), 121.2 (s),
119.3 (s), 49.6 (br), 45.0 (s), 43.5 (br), 38.1 (s), 33.6 (s, two signals
6
6
1
4
meso-BPMP: H NMR (C D , 25 °C): δ 7.58 (d, J = 2.8 Hz,
6
6
HH
4
3
31
1
2
4
4
H, Ar), 7.27 (d, J = 1.6 Hz, 2H, Ar), 7.08 (t, J = 6.7 Hz, 1H,
-H of Py), 6.81 (d, J = 7.6 Hz, 2H, 3,5-H of Py), 3.29−3.42 (m,
H, PyCH P), 2.42 (dd, J = 1.7, J = 14.8 Hz, 2H, PCH ), 1.96
are overlapped), 33.4 (s), 31.8 (s). P{ H} NMR (C
25.8 (d, JRhP = 152 Hz).
D
6
6
, 25 °C): δ
HH
HH
3
1
HH
2
2
Preparation of [RuCl (PPh )(PPEP)] (8). A THF solution
0.3 mL) of PPEP (13 mg, 0.020 mmol) was added to a suspension
of [RuCl (PPh ) ] (19 mg, 0.020 mmol) in THF (0.2 mL) at room
temperature. The color of the mixture instantly changed to bluish-
purple. After stirring for 30 min, solvent was removed under reduced
pressure. The residue was washed with pentane (5 mL) to remove free
2
3
2
PH
HH
2
2
2
(
(
dd, J = 24.1, J = 14.7 Hz, 2H, PCH ), 1.71 (s, 18H, CH of
PH HH 2 3
t
t
Bu), 1.66 (s, 6H, CH ), 1.35 (s, 18H, CH of Bu), 1.29 (s, 6H, CH ).
2
3 3
3
3
3
1
3
1
C{ H} NMR (C D , 25 °C): δ 160.1 (d, J = 8 Hz), 159.9 (s),
6
6
PC
1
5
(
53.2 (s), 152.9 (s), 136.9 (d, JPC = 19 Hz), 136.8 (s), 122.4 (d, JPC
=
Hz), 121.0 (d, JPC = 4 Hz), 119.7 (s), 47.6 (d, JPC = 7 Hz), 41.1
PPh and dissolved in THF (5 mL). The solution was concentrated,
3
d, JPC = 25 Hz), 38.2 (s), 37.2 (d, J = 10 Hz), 35.6 (s), 34.9 (s),
PC
4.4 (s), 33.2 (s), 32.1 (s). 31P{ H} NMR (C D , 25 °C): δ −7.1 (s).
1
layered with pentane, and allowed to stand at room temperature
overnight to give purple crystals of 8 (15 mg, 0.013 mmol, 69%). The
same reaction was performed in a large scale using 262 mg of PPEP,
3
6
6
Stoichiometric Reaction of BPEP with [Pt(PCy ) ]. A solution
3
2
of BPEP (10 mg, 0.015 mmol) and [Pt(PCy ) ] (11 mg, 0.015 mmol)
in toluene-d (0.5 mL) was prepared in an NMR sample tube at
3
2
and 248 mg of 8 (63%) was isolated.
8
1
31
1
H NMR (THF-d
8
, 25 °C): δ 7.72−7.65 (m, 3H, PyCHP + Ar),
−
78 °C. After 5 min at −10 °C, the P{ H} NMR spectrum exhibited
2 1
PP
7.54−7.50 (m, 7H, PPh
3
+ 4-H of Py), 7.47 (br, 1H, Ar), 7.29 (br d,
two sets of signals assignable to A at δ 113.7 (br d, J = 31 Hz, J
=
PtP
3
3
2
1
JHH = 8.4 Hz, 2H, 3,5-H of Py), 7.07 (t, JHH = 7.2 Hz, 3H, p-H of
1
543 Hz) and 17.9 (br t, J = 31 Hz, J = 4154 Hz), along with the
PP PtP
3
4
PPh ), 6.81 (t, J = 7.2 Hz, 3H, m-H of PPh ), 6.78 (d, J = 1.7
3
HH
3
HH
signal of free PCy at δ 9.8 (s) (Figure S4). After 3 h at room
3
2
2
temperature, the 3 P{ H} NMR signals of A vanished, and three new
1
1
Hz, 1H, Ar), 4.74 (dd, JHH = 16.2, JPH = 10.4 Hz, 1H, PyCH
(dd, JHH = 16.2, JPH = 9.8 Hz, 1H, PyCH
PH = 5.5 Hz, 1H, PCH
2
P), 4.21
P), 3.35 (dd, JHH = 15.2,
), 2.57 (br d, JHH = 15.2 Hz, 1H, PCH ),
1.46 (s, 9H, CH of Bu), 1.43 (s, 9H, CH of Bu), 1.39 (s, 9H, CH
3
of Bu), 1.34 (s, 9H, CH of Bu), 1.17 (s, 9H, CH of Bu), 1.11 (s,
3H, CH ), 0.80 (s, 3H, CH ). C{ H} NMR (THF-d , 25 °C): δ
3 3 8
67.9 (d, JPC = 4 Hz), 165.1 (s), 162.5 (d, JPC = 39 Hz), 160.0 (dd,
JPC = 14 and 3 Hz), 157.2 (s), 157.1 (d, JPC = 9 Hz), 157.0 (d, JPC
Hz), 156.52 (s), 156.49 (s), 153.3 (d, JPC = 2 Hz), 151.9 (s), 138.4
2
2
2
1
2
signals appeared at δ 247.4 (br), 28.2 (br, J = 3480 Hz), and 25.3
(
Moreover, the H NMR spectrum exhibited the signals assignable to
PtP
2
2
br, 1JPtP = 1985 Hz) in almost the same intensity (Figure S5).
J
2
2
t
t
1
3
3
t
t
t
2
1
3
3
Pt−H at δ −6.82 (dd, J = 182 and 16 Hz, J = 996 Hz) and to
PH
PtH
13
1
2
PCH at δ 9.15 (d, J = 24.4 Hz) in almost the same intensity
PH
1
(
Figure S6).
=
Reaction of PPEP with [Rh(μ-Cl)(C H ) ] . A solution of PPEP
2
4 2 2
1
(
21 mg, 0.032 mmol) and [Rh(μ-Cl)(C H ) ] (6.2 mg, 0.016 mmol)
2
4 2 2
(
d, JPC = 39 Hz, PCH), 135.9 (s), 135.8 (s), 134.7 (d, J = 20 Hz),
PC
in THF-d (0.6 mL) was prepared in an NMR sample tube at −78 °C.
8
1
129.5 (s), 127.8 (d, JPC = 9 Hz), 127.5 (d, JPC = 8 Hz), 126.3 (d, JPC
4 Hz), 122.7 (d, JPC = 6 Hz), 121.6 (d, JPC = 26 Hz), 119.2 (d, JPC
=
=
=
The color of the solution instantly changed to reddish-brown. The H
and 3 P{ H} NMR spectra indicated selective formation of [RhCl-
1
1
8
Hz), 118.8 (t, JPC = 10 Hz), 51.1 (d, JPC = 20 Hz), 43.9 (d, JPC
5 Hz), 43.5 (d, JPC = 33 Hz), 39.5 (s), 38.9 (s), 38.8 (s), 36.3 (s), 35.9
(s), 35.6 (s), 35.4 (s), 35.3 (s), 34.5 (s), 31.8 (s), 31.7 (s), 29.9 (d,
, 25 °C): δ 292.0 (dd, JPP = 411
and 29 Hz), 50.5 (dd, JPP = 411 and 29 Hz), 34.8 (t, JPP = 29 Hz).
(
PPEP)] (6).
1
2
6
: H NMR (THF-d , −70 °C): δ 7.68 (d, J = 17.6 Hz, 1H, P
8
PH
3
CH), 7.64 (t, J = 7.6 Hz, 1H, Py), 7.56 (s, 1H, Ar), 7.55 (s, 1H,
Ar), 7.45 (s, 1H, Ar), 7.35 (s, 1H, Ar), 7.17 (d, J = 7.6 Hz, 1H, Py),
7
1
2
HH
31
1
2
3
J
PC = 10 Hz). P{ H} NMR (THF-d
8
HH
2
2
3
2
2
.03 (d, J = 7.6 Hz, 1H, Py), 4.41 (dd, J = 18.4, J = 9.4 Hz,
H, PyCH P), 4.14 (dd, J = 18.4, J = 9.4 Hz, 1H, PyCH P),
.67 (br d, J = 14.8, 1H, PCH ), 2.47 (br d, J = 14.8 Hz, 1H,
HH HH PH
2
2
Anal. Calcd for C61
67.42; H, 7.14; N, 1.26.
Preparation of [RuCl(PPh
3
H
78Cl
2
NP
3
Ru: C, 67.21; H, 7.21; N, 1.28. Found: C,
2
HH
PH
2
2
2
HH
2
HH
t
t
)(PPEP*)] (9). A THF solution (2 mL)
PCH ), 1.78 (s, 9H, CH of Bu), 1.55 (br, 9H, CH of Bu), 1.45 (s,
3
2
3
3
t
t
of BuOK (18 mg, 0.16 mmol) was added dropwise to a THF
solution (1.5 mL) of 8 (134 mg, 0.12 mmol) at room temperature.
The color of the solution changed from purple to dark green. The
reaction mixture was allowed to stand for 30 min and filtered through
a Celite pad to remove the precipitate of KCl. The solvent was
removed under reduced pressure, and the residue was dissolved in
H, CH ), 1.41 (s, 3H, CH ), 1.39 (s, 9H, CH of Bu), 1.36 (s, 18H,
3 3 3
t
31
1
CH of Bu × 2). P{ H} NMR (THF-d , −70 °C): δ 243.4 (dd,
3
8
2
1
2
1
JPP = 463 Hz, J
67 Hz).
= 186 Hz), 26.0 (dd, J = 463 Hz, J
=
RhP
PP
RhP
1
Upon standing the sample at room temperature for 1 h, the 31P{ H}
1
NMR signals of 6 disappeared, and two doublet signals at δ 29.5
(
of diastereomers of [RhCl(BPMP)] (7), appeared. Drying the reaction
mixture under vacuum gave an orange solid of 7 as a 5:1 mixture of
diastereomers (18 mg, 0.023 mmol, 71%). With consideration of the
steric conditions, the major isomer was assigned to the dl-isomer.
Et O (0.6 mL) and allowed to stand at room temperature to afford
1
1
2
JRhP = 151 Hz) and 26.8 ( J = 154 Hz), assignable to a 5:1 mixture
RhP
dark green crystals of 9 (87 mg, 0.083 mmol, 69%). Single crystals for
X-ray diffraction analysis were grown from a THF/pentane (1:1)
solution.
H NMR (THF-d , −20 °C): δ 8.49−7.48 (br, 6H, PPh ), 7.53 (br,
H, Ar), 7.41 (dd, 1H, J = 4.3 Hz, J = 1.3 Hz, 1H, Ar), 7.39 (br,
1
8
3
4
4
1
1
6
6
1
2
1
+
PH HH
HRMS (ESI): calcd for C H NP Rh 792.3096 ([M − H] ); found
7
4
43
63
2
H, Ar), 7.36−7.05 (br, 9H, PPh ), 7.13 (d, J = 1.3 Hz, 1H, Ar),
3
HH
92.3092.
2
3
.99 (d, J = 20.4 Hz, 1H, PCH), 6.06 (ddd, J = 8.6 and
1
3
PH
HH
dl-7: H NMR (THF-d , 25 °C): δ 7.46 (s, 2H, Ar), 7.42 (t, J
=
HH
5
3
4
8
.5 Hz, J = 1.2 Hz, 1H, Py), 5.78 (dd, J = 8.6 Hz, J = 4.9 Hz,
3
PH
HH
PH
7
3
.6 Hz, 1H, 4-H of Py), 7.21 (s, 2H, Ar), 6.93 (d, J = 7.6 Hz, 2H,
,5-H of Py), 3.62 (s, 4H, PyCH P), 2.79 (d, J = 14.4 Hz, 2H,
3
4
HH
H, Py), 5.25 (t, J = 6.5 Hz, J = 5.9 Hz, 1H, Py), 3.76 (vt, J
=
=
2
HH
PH
app
t
2
2
HH
.7 Hz, 1H, PyCHP), 1.90 (s, 9H, CH of Bu), 1.67 (br dd, J
2
3
HH
PCH ), 2.18 (d, J = 14.4 Hz, 2H, PCH ), 1.83 (s, 18H, CH of
2
t
2
HH
2
3
4.5 Hz, J = 12.7 Hz, 1H, PCH ), 1.34 (s, 9H, CH of Bu), 1.32 (s,
t
t
PH
2
3
Bu), 1.46 (s, 6H, CH ), 1.39 (s, 6H, CH ), 1.35 (s, 18H, CH of Bu).
t
3
3
3
9H, CH of Bu), 1.25 (s, 3H, CH ), 1.09 (s, 3H, CH ), 1.03 (s, 9H,
CH of Bu), 0.91 (s, 9H, CH of Bu), 0.72 (dd, J = 14.5 Hz,
3 3 HH
3
3
3
1
3
1
C{ H} NMR (THF-d , 25 °C): δ 164.0 (br), 159.9 (br d, J
=
t
t
2
8
PC
2
13
1
7
1
Hz), 154.7 (s), 154.2 (s), 131.5 (s), 130.5 (br), 123.7 (s), 121.4 (br),
19.3 (s), 49.3 (br), 44.8 (s), 43.0 (br), 39.1 (s), 35.9 (s), 34.2 (br),
4.0 (s), 32.6 (s), 31.9 (s). 31P{ H} NMR (C D , 25 °C): δ 28.9 (br d,
JPH = 2.6 Hz, 1H, PCH2). C{ H} NMR (THF-d , −20 °C): δ 179.1
8
(d, JPC = 31 Hz, PCH), 174.1 (d, J = 16 Hz), 160.4 (s), 158.2 (br
PC
1
3
d, JPC = 2 Hz), 157.7 (dd, J = 15 and 3 Hz), 157.0 (s), 152.8 (d,
6
6
PC
1
JRhP = 150 Hz).
JPC = 2 Hz), 151.4 (s), 151.3 (s), 151.0 (s), 137.3 (br, PPh ), 135.4
(dd, JPC = 38 and 18 Hz), 134.2 (br, PPh ), 130.5 (br), 130.2 (br,
PPh ), 129.5 (dd, J = 39 and 5 Hz), 128.2 (br, PPh ), 126.6 (s),
125.6 (d, JPC = 8 Hz), 121.3 (d, JPC = 4 Hz), 119.1 (d, JPC = 8 Hz),
3
1
3
meso-7: H NMR (THF-d , 25 °C): 7.24 (t, J = 7.6 Hz, 1H,
8
HH
3
3
4
2
-H of Py), 7.40 (s, 2H, Ar), 7.21 (s, 2H, Ar), 6.91 (d, J = 7.6 Hz,
H, 3,5-H of Py), 3.89 (dvt, J = 18.5, Japp = 3.8 Hz, 2H, PyCH P),
HH
3
PC
3
2
HH
2
1
594
DOI: 10.1021/acs.organomet.5b00195
Organometallics 2015, 34, 1589−1596

Organometallics
Article
1
5
3
17.2 (dd, JPC = 18 and 14 Hz), 111.0 (d, JPC = 32 Hz), 78.9 (d, JPC
5 Hz), 43.5 (dd, JPC = 5 and 3 Hz), 40.6 (d, JPC = 39 Hz), 39.4 (s),
=
Type Complexes: Applications in Organic Synthesis and Catalysis; Szabo,
K. J.; Wendt, O. F., Eds.; Wiley-VCH: Weinheim, Germany, 2014;
Chapter I. (c) Gunanathan, C.; Milstein, D. Chem. Rev. 2014, 114,
12024−12087.
(4) For representative examples, see: (a) Zhang, J.; Gandelman, M.;
Shimon, L. J. W.; Rozenberg, H.; Milstein, D. Organometallics 2004,
23, 4026−4033. (b) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J.
Am. Chem. Soc. 2005, 127, 10840−10841. (c) Zhang, J.; Leitus, G.;
Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed. 2006, 45, 1113−
́
8.8 (s), 36.2 (s), 35.6 (s), 35.5 (s), 35.1 (s), 33.8 (s), 33.5 (s), 32.0
d, JPC = 10 Hz), 31.8 (s), 31.6 (s), 30.1 (d, J = 4 Hz). 31P{ H}
1
(
PC
2
NMR (THF-d , −20 °C): δ 216.9 (dd, J = 299 and 23 Hz), 57.7
(
8
PP
2
2
dd, J = 40 and 23 Hz), 46.2 (dd, J = 299 and 40 Hz). Anal.
PP PP
Calcd for C H ClNP Ru: C, 69.53; H, 7.37; N, 1.33. Found: C,
6
61
77
3
9.71; H, 7.63; N, 1.30.
X-ray Structural Analysis. The intensity data were collected
at 103 K on a Rugaku VariMax diffractometer using graphite-
monochromated Mo Kα radiation (λ = 0.710 75 Å). The intensity data
were corrected for Lorentz and polarization effects and for absorption
1
3
2
115. (d) Gunanathan, C.; Ben-David, Y.; Milstein, D. Science 2007,
17, 790−792. (e) Gunanathan, C.; Milstein, D. Angew. Chem., Int. Ed.
008, 47, 8661−8664. (f) Gunanathan, C.; Shimon, L. J. W.; Milstein,
16
(
numerical). The structures were solved by direct methods (SHELXS-97)
D. J. Am. Chem. Soc. 2009, 131, 3146−3147. (g) Gnanaprakasam, B.;
Zhang, J.; Milstein, D. Angew. Chem., Int. Ed. 2010, 49, 1468−1471.
2
and refined by least-squares calculations on F for all reflections
16
(
SHELXL-97). Non-hydrogen atoms, except for disordered groups
(h) Khaskin, E.; Iron, M. A.; Shimon, L. J. W.; Zhang, J.; Milstein, D. J.
t
in 5 ( Bu), were refined anisotropically. Hydrogen atoms were placed
at calculated positions using AFIX instructions and included in least-
squares calculations without refinement of their parameters. The
crystallographic data and the summary of solution and refinement are
listed in Table S1.
Am. Chem. Soc. 2010, 132, 8542−8543. (i) Balaraman, E.;
Gunanathan, C.; Zhang, J.; Shimon, L. J. W.; Milstein, D. Nat.
Chem. 2011, 3, 609−614. (j) Balaraman, E.; Fogler, E.; Milstein, D.
Chem. Commun. 2012, 48, 1111−1113. (k) Feller, M.; Diskin-Posner,
Y.; Shimon, L. J. W.; Ben-Ari, E.; Milstein, D. Organometallics 2012,
DFT Calculations. All calculations were carried out with the
3
1, 4083−4101. (l) Anaby, A.; Butschke, B.; Ben-David, Y.; Shimon, L.
17
Gaussian 09 program package. The geometric optimization of A1
was performed with the DFT method using the B3LYP functional.
The Pt was described with the LANL2TZ(f) basis set. The 6-31G(d)
basis sets were applied to other atoms. The NMR chemical shifts were
evaluated by the GIAO method using the B3LYP functional with the
J. W.; Leitus, G.; Feller, M.; Milstein, D. Organometallics 2014, 33,
3716−3726.
(
18
5) (a) Chang, Y.-H.; Nakajima, Y.; Tanaka, H.; Yoshizawa, K.;
Ozawa, F. J. Am. Chem. Soc. 2013, 135, 11791−11794. (b) Chang, Y.-
H.; Nakajima, Y.; Tanaka, H.; Yoshizawa, K.; Ozawa, F. Organo-
metallics 2014, 33, 715−721.
18
LANL2TZ(f) basis set for Pt and 6-311+G(2d,p) basis sets for other
atoms. As a result, the 31P NMR chemical shifts of A1 were estimated
(6) (a) Dugal-Tessier, J.; Conrad, E. D.; Dake, G. R.; Gates, D. P. In
to be δ 102.7 (BPEP) and 10.7 (PMe3).
Phosphorus(III) Ligands in Homogeneous Catalysis: Design and Synthesis;
Kamer, P. C. J., van Leeuwen, P. W. N. M., Eds.; Wiley: Chichester,
U.K., 2012; Chapter 10. (b) Le Floch, P. Coord. Chem. Rev. 2006, 250,
ASSOCIATED CONTENT
■
*
S
Supporting Information
6
27−681. (c) Ozawa, F.; Yoshifuji, M. Dalton Trans. 2006, 4987−
NMR spectra; crystallographic details and data (CIF) for 5 and
4995. (d) Weber, L. Coord. Chem. Rev. 2005, 249, 741−763.
(e) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578−1604.
9
; Cartesian coordinates for the optimized structure of A1. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(7) Houdard, R.; Mez
Organometallics 2009, 28, 5952−5959.
8) For review, see: Mastrorilli, P. Eur. J. Inorg. Chem. 2008, 2008,
́
ailles, N.; Le Goff, X.-F.; Le Floch, P.
(
4
835−4850. See also for a phosphanido platinum complex with a
AUTHOR INFORMATION
Corresponding Author
E-mail: ozawa@scl.kyoto-u.ac.jp.
■
Mes* substituent: Waterman, R.; Mindiola, D. J.; Clough, C. R.;
Hillhouse, G. L. Inorg. Chim. Acta 2014, 422, 57−64.
(
*
9) With consideration of the steric conditions, we presume the
Notes
major product to be the dl-isomer.
The authors declare no competing financial interest.
(10) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.
(11) Nakajima, Y.; Okamoto, Y.; Chang, Y.-H.; Ozawa, F.
Organometallics 2013, 32, 2918−2925. PPEP*-Ph stands for a
PPEP* ligand substituted with Ph groups at the exo-methylene and
phosphaalkene carbons.
ACKNOWLEDGMENTS
■
This work was supported by KAKENHI (26288050) from JSPS
and by a MEXT Grant-in-Aid for Scientific Research on
Innovative Areas “Stimuli-Responsive Chemical Species”
(
1
(
12) Jouaiti, A.; Geoffroy, M.; Bernardinelli, G. Tetrahedron Lett.
992, 33, 5071−5074.
13) Yoshida, T.; Otsuka, S.; Jones, D. G.; Spencer, J. L.; Binger, P.;
(
24109010).
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