Heterotrinuclear complexes with palladium, rhodium, and iridium ions assembled by conformational switching of a tetraphosphine ligand around a palladium center

Article abstract of DOI:10.1021/om2006744

Reaction of [PdCl₂(cod)] with a tetraphosphine, meso-bis[((diphenylphosphino)methyl)phenylphosphino] methane (dpmppm), afforded the mononuclear Pd^II complexes [PdCl(dpmppm-κ³)]X (X = Cl (1a), PF₆ (1b)); the pincer-type dpmppm ligand coordinates to the Pd atom with two outer and one inner phosphorus atom to form fused six- and four-membered chelate rings. The remaining inner phosphine is uncoordinated and readily reacts with [Cp*MCl₂]₂ to give the heterodimetallic complexes [PdCl-(Cp*MCl₂)(μ-dpmppm- κ³,κ¹)]X (X = Cl, M = Rh (21a), Ir (21b); X = PF₆, M = Rh (23a), Ir (23b)). Attachment of the second metal fragment to the uncoordinated phosphine caused a crucial conformational change of the six-membered chelate ring from a stable chair conformation to a twist-boat structure, which concomitantly destabilizes the four-membered ring for its opening reactions. Complexes 21 (X = Cl) were converted to [PdCl ₂(Cp*MCl₂)(dpmppm=O)], in which the terminal P atom is dissociated and oxidized as Ph₂P(=O)CH₂P(Ph)CH ₂P(Ph)CH₂PPh₂ (dpmppm=O), and in the presence of another 1 equiv of [Cp*M′Cl₂]₂, complexes 21 were readily transformed into the heterotrinuclear complexes [PdCl ₂(Cp*M′Cl₂)(Cp*MCl₂)(μ- dpmppm-κ²,κ¹,κ¹)] (M = M′ = Rh (31a), Ir, (31b); M = Ir, M′ = Rh (31c)), where the third metal M′ is trapped by the terminal P atom with its four-membered-ring opening. Complexes 23 also reacted with another 1 equiv of [Cp*M′ Cl₂]₂ to afford the heterotrinuclear complexes [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl₂)(μ-dpmppm- κ²,κ¹,κ¹)]PF₆ (M = M′ = Rh (32a), Ir, (32b); M = Ir, M′ = Rh (32c), M = Rh, M′ = Ir (32d)); the additional metal M′ is ligated by the terminal phosphine and is further connected to the Pd atom via a chloride bridge, resulting in a rather electron-deficient M′ center on the basis of cyclic voltammetry. These results exhibited that the addition of a bulky metal fragment to the uncoordinated phosphine of 1 brings about a conformational switch around the Pd center to promote the ring-opening reaction of the four-membered chelate ring, which leads to an incorporation of the third metal fragment to construct heterotrinuclear structures.

Full text of DOI:10.1021/om2006744

Article
pubs.acs.org/Organometallics
Heterotrinuclear Complexes with Palladium, Rhodium, and Iridium
Ions Assembled by Conformational Switching of a Tetraphosphine
Ligand around a Palladium Center
Akiko Yoshii, Hiroe Takenaka, Hiroko Nagata, Sayo Noda, Kanako Nakamae, Bunsho Kure,
Takayuki Nakajima, and Tomoaki Tanase*
Department of Chemistry, Faculty of Science, Nara Women’s University, Kitauoya-nishi-machi, Nara 630-8506, Japan
S
* Supporting Information
ABSTRACT: Reaction of [PdCl2(cod)] with a tetraphos-
phine, meso-bis[((diphenylphosphino)methyl)phenyl-
phosphino]methane (dpmppm), afforded the mononuclear
PdII complexes [PdCl(dpmppm-κ3)]X (X = Cl (1a), PF6
(1b)); the pincer-type dpmppm ligand coordinates to the Pd
atom with two outer and one inner phosphorus atom to form
fused six- and four-membered chelate rings. The remaining
inner phosphine is uncoordinated and readily reacts with
[Cp*MCl2]2 to give the heterodimetallic complexes [PdCl-
(Cp*MCl2)(μ-dpmppm-κ3,κ1)]X (X = Cl, M = Rh (21a), Ir
(21b); X = PF6, M = Rh (23a), Ir (23b)). Attachment of the
second metal fragment to the uncoordinated phosphine caused
a crucial conformational change of the six-membered chelate
ring from a stable chair conformation to a twist-boat structure, which concomitantly destabilizes the four-membered ring for its
opening reactions. Complexes 21 (X = Cl) were converted to [PdCl2(Cp*MCl2)(dpmppmO)], in which the terminal P atom
is dissociated and oxidized as Ph2P(O)CH2P(Ph)CH2P(Ph)CH2PPh2 (dpmppmO), and in the presence of another 1 equiv
of [Cp*M′Cl2]2, complexes 21 were readily transformed into the heterotrinuclear complexes [PdCl2(Cp*M′Cl2)(Cp*MCl2)(μ-
dpmppm-κ2,κ1,κ1)] (M = M′ = Rh (31a), Ir, (31b); M = Ir, M′ = Rh (31c)), where the third metal M′ is trapped by the terminal
P atom with its four-membered-ring opening. Complexes 23 also reacted with another 1 equiv of [Cp*M′Cl2]2 to afford the
heterotrinuclear complexes [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = M′ = Rh (32a), Ir, (32b); M =
Ir, M′ = Rh (32c), M = Rh, M′ = Ir (32d)); the additional metal M′ is ligated by the terminal phosphine and is further connected
to the Pd atom via a chloride bridge, resulting in a rather electron-deficient M′ center on the basis of cyclic voltammetry. These
results exhibited that the addition of a bulky metal fragment to the uncoordinated phosphine of 1 brings about a conformational
switch around the Pd center to promote the ring-opening reaction of the four-membered chelate ring, which leads to an
incorporation of the third metal fragment to construct heterotrinuclear structures.
than three P atoms have still been limited, owing to their
synthetic difficulty and complicated stereoisomerism.6−11
Recently, we have prepared a methylene-bridged linear tetra-
phosphine ligand, meso-bis[((diphenylphosphino)methyl)phenyl-
phosphino]methane (dpmppm), and demonstrated that it
effectively stabilized versatile tetrametallic chains of group 11
metal ions.12 Two dpmppm ligands assembled four AuI ions in
a syn arrangement with respect to the bent AuI4 string, and the
flexible tetragold(I) chain {Au4(μ-dpmppm)2}4+ incorporated a
counteranion (X) in its bent pocket to afford {[Au4(μ-
dpmppm)2]X}3+ (X = PF6, Cl) adducts, the structures of
which varied depending on the trapped anions and modulated
their intriguing luminous properties.12a The flexible AuI4
chain was further converted to the cyclic hexagold(I)
INTRODUCTION
■
Synergistic effects of heterometallic centers are of extensive
interest in relation to developing multimetallic catalytic systems,
electronic, optical, and magnetic devices, and biomimetic func-
tional molecules.1 Exploring tunable assemblages of heterodinu-
clear and heteromultinuclear complexes would be thus an
important subject and has closely been indebted to designing
metal supporting ligands. Among a number of polydentate ligands
used to stabilize multimetallic systems, di- and tridentate phos-
phines, including bis(diphenylphosphino)methane (dppm) and
bis[(diphenylphosphino)methyl]phenylphosphine (dpmp), have
widely been used to create metal−metal-bonded homo- and hetero-
multinuclear structures.1f,2−5 In general, polyphosphine ligands
possess the potential ability to organize heteromultimetallic
centers because their variation of denticity may generate
uncoordinated dangling phosphorus atoms capable of trapping
additional metals; however, polyphosphines containing more
Received: July 23, 2011
Published: December 22, 2011
© 2011 American Chemical Society
133
dx.doi.org/10.1021/om2006744 | Organometallics 2012, 31, 133−143

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Article
a
Table 1. 31P{1H} NMR Spectral Data for the dpmppm Part of 1a,b, 20a,b, 23a,b, 31a−c, and 32a−d
compd
δ(PA), ppm
δ(PB), ppm
δ(PC), ppm
δ(PD), ppm
b
1a
−43.4 (dd, JPP′ = 479, 75)
−44.7 (dd, JPP′ = 475, 82)
−41.4 (dd, JPP′ = 420, 77)
−41.4 (dd, JPP′ = 440, 78)
−62.4 (dd, JPP′ = 466, 82)
−62.4 (dd, JPP′ = 468, 81)
−30.6 (t, JPP′ = 75, 73)
−33.2 (dd, JPP′ = 82, 79)
−25.9 (t, JPP′ = 77, 39)
−33.2 (m)
−43.5 (ddd, JPP′ = 82, 30, 4)
−44.2 (dd, JPP′ = 81, 23)
14.2 (br)
−38.8 (dd, JPP′ = 73, 45)
−40.3 (dd, JPP′ = 79, 52)
5.0 (dd, JPP′ = 479, 45)
5.7 (dd, JPP′ = 475, 52)
−8.7 (dd, JPP′ = 420, 33)
−8.7 (dd, JPP′ = 440, 32)
−6.9 (ddd, JPP′ = 466, 20, 4)
−7.8 (dd, JPP′ = 468, 13)
9.2 (d, JPP′ = 20)
c
1b
c
1
20a
−18.6 (br ddd, JPP′ = 39, 33, JAgP = 775)
d
1
20b
−19.2 (br d, JAgP = 780)
c
1
23a
30.8 (ddd, JPP′ = 30, 20, JRhP = 149)
c
23b
−1.2 (dd, JPP′ = 23, 13)
c
1
1
31a
28.4 (d, JRhP = 147)
31.3 (d, JRhP = 147)
c
e
e
31b
−1.3 (br)
13.2 (br)
−1.3 (br)
8.3 (br)
c
1
31c
−1.4 (br)
14.6 (br)
30.9 (dt, JPP′ = 23, JRhP = 148 )
8.9 (d, JPP′ = 23)
c
1
1
32a
28.5 (d, JRhP = 144)
16.8 (br)
28.2 (dt, JPP′ = 27, JPhP = 148)
11.5 (d, JPP′ = 26)
c
32b
4.0 (d, JPP′ = 4)
4.2 (d, JPP′ = 3)
16.2 (d, JPP′ = 16)
16.5 (br)
−5.4 (dd, JPP′ = 20, 16)
12.6 (d, JPP′ = 20)
c
1
32c
27.2 (dt, JPP′ = 27, JRhP = 145)
13.9 (d, JPP′ = 28)
c
1
32d
28.3 (d, JRhP = 145)
16.9 (br)
−4.6 (t, JPP′ = 21)
10.3 (d, JPP′ = 21)
a
Measured at 121 MHz. J values are given in Hz. The assignments of P atoms are shown in Figures 2 and 6 and Figures S2 and S5 (Supporting
b
c
d
e
Information). In CDCl3. In CD2Cl2. In DMF-d7. Overlapped and not resolved.
1
complex [Au6Cl4(μ-dpmppm)2]2+ and the linear octagold(I)
complex [Au8(μ-I)2(μ3-I)2(μ-dpmppm)4]4+. Silver(I) ions
are also assembled by two dpmppm ligands in both syn and
anti arrangements to form the bent and linear AgI4 chains,
respectively, with a variety of ancillary ligands.12b In case of
copper(I) ions, interconversion between ladder-type CuI8
complexes, [Cu8(μ-X)2(μ3-X)6(μ-dpmppm)2] (X = Cl, Br, I),
and CuI4 chains with a bent {Cu4(μ-X)3(μ-dpmppm)2}+ core
proceeded through a labile {Cu4(μ-X)3(μ-dpmppm)}+
intermediate.12c These suggested potential versatility for
coordination modes of the flexible dpmppm ligand which
might be utilized, therefore, to construct heteromultimetallic
complexes.
In the present study, we have found that the dpmppm ligand
surrounded a PdII mononuclear center in a pincer-type fashion
to form [PdCl(dpmppm-κ3)]+ (1), in which six- and four-
membered chelate rings are fused with a uncoordinated
phosphine unit involved in the six-membered ring. An
attachment of the Cp*MCl2 fragment (M = Rh, Ir) to the
uncoordinated phosphine, forming dinuclear species of [PdCl-
(Cp*MCl2)(μ-dpmppm-κ3,κ1)]+ (21, 23; M = Rh, Ir),
interestingly brought about a conformational change of the
six-membered ring from a stable chair to a twist-boat structure,
which further destabilized the strained four-membered chelate
ring and promoted a capture of the third metal ions via its
ring opening. The conformational switch around the Pd
center can be called an “allosteric effect”, was very effective
to control the reactivity of Pd, and enabled us to construct the
heterotrimetallic complexes [PdCl2(Cp*M′Cl2)(Cp*MCl2)-
(μ-dpmppm-κ2,κ1,κ1)] (31) and [PdCl(μ-Cl)(Cp*M′Cl)-
(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (32) (M, M′ = Rh, Ir),
in stepwise ways. We wish to report herein the synthesis,
characterization, and electrochemistry of di- and trinuclear
complexes with Pd, Rh, and Ir metal ions assembled by the
flexible tetraphosphine ligand.
121 MHz, respectively. H NMR spectra were referenced to TMS as
external standard, and 31P{1H} NMR spectra were referenced to 85%
H3PO4 as external standard. ESI-TOF MS spectra were recorded on
Applied Biosystems Mariner and JEOL JMS-T100LC high-resolution
mass spectrometers with positive ionization mode. A Hokuto-denko
Model HZ-3000 electrochemical analyzer was used in all electro-
chemical measurements. Tetra-n-butylammonium hexafluorophos-
phate (0.1 M) was used as supporting electrolyte. Cyclic voltammetry
was performed with a conventional electrochemical cell consisting of a
glassy-carbon working electrode, a Ag/AgPF6 (0.1 M in CH3CN)
reference electrode, and a platinum-wire counter electrode. The
potentials were calibrated to the ferrocene/ferrocenium (Fc/Fc+)
redox couple (1 mM in acetonitrile).
[PdCl(dpmppm-κ3)]Cl (1a). To a solution of dpmppm (146 mg,
0.232 mmol) in dichloromethane (10 mL) was added [PdCl2(cod)]
(55.5 mg, 0.194 mmol), and the reaction mixture was stirred at room
temperature for 12 h. The solvent was removed under reduced
pressure to dryness and the residue was washed with diethyl ether
(3 mL × 3) and crystallized from a dichloromethane/diethyl ether/
n-hexane mixed solvent, allowed to stand in a refrigerator, to give pale
yellow crystals of 1a·CH2Cl2, which were collected by filtration,
washed with diethyl ether, and dried under vacuum (108 mg, 62%).
Anal. Calcd for C40H38P4Cl4Pd: C, 53.94; H, 4.30. Found: C, 54.58; H,
4.33. IR (KBr): ν 1483 (m), 1435 (s), 1106 (m), 1095 (m), 745 (s),
712 (m), 693 (s), 509 (m), 487 (m) cm−1. UV−vis (CH2Cl2): λmax
(log ε) 338 nm (3.04). 1H NMR (CDCl3): δ 1.87 (br, CH2, 1H), 2.46
(br, 1H, CH2), 4.38 (br, 2H, CH2), 4.65 (br, 1H, CH2), 5.24 (br, 1H,
CH2), 6.9−8.4 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1.
ESI-MS (CH2Cl2): m/z 769.078 (z1, [PdCl(dpmppm)]+ (769.050)),
1575.155 (z1, {[PdCl(dpmppm)]2Cl}+ (1575.069)).
[PdCl(dpmppm-κ3)]PF6 (1b). The detailed synthetic procedures
are described in the Supporting Information. Yield: 73%. Anal. Calcd
for C39H36P5F6ClPd: C, 51.17; H, 3.96. Found: C, 50.89; H, 4.12. IR
(KBr): ν 1484 (m), 1436 (s), 1017 (m), 999 (m), 836 (s), 740 (s),
689 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε) 341 nm (4.0). H
1
NMR (CD2Cl2): δ 2.80 (br, 2H, CH2), 3.12 (br, 1H, CH2), 3.41 (br,
1H, CH2), 4.31 (br, 1H, CH2), 4.62 (br, 1H, CH2), 6.05−8.27 (m,
30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS (CH2Cl2):
m/z 769.062 (z1, [PdCl(dpmppm)]+ (769.050)). Recrystallization of
1b from an acetonitrile/diethyl ether mixed solvent yielded block-
shaped crystals of 1b·CH3CN, which were suitable for X-ray
crystallographic analysis.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out under a
nitrogen atmosphere using standard Schlenk techniques. meso-
Bis[((diphenylphosphino)methyl)phenylphosphino]methane
(dpmppm) was prepared by the method already reported.12a Reagent
grade solvents were dried by the standard procedures and were freshly
distilled prior to use. IR spectra were recorded on a Jasco FT/IR-410
[PdX(AgX)(μ-dpmppm-κ3,κ1)]X (X = OTf (20a), OTs (20b)).
Complex 20a was prepared from 1a in 49% yield (see the Supporting
Information). Anal. Calcd for C42H36O9P4F9S3PdAg: C, 39.10; H, 2.81.
Found: C, 38.84; H, 2.67. IR (KBr): ν 1485 (m), 1436 (s), 1252, 1102,
1027 (br, s), 819 (s), 740 (s), 688 (s), 629 (s), 573 (m), 517 (m)
cm−1. UV−vis (CH2Cl2): λmax (log ε) 337 nm (4.36). 1H NMR
(CD2Cl2): δ 3.15 (br, 2H, CH2), 4.36 (br, 3H, CH2), 5.32 (m br, 1H,
1
spectrophotometer. H and 31P{1H} NMR spectra were recorded on
Varian Gemini 2000 and Bruker AV-300N spectrometers at 300 and
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CH2), 7.11−8.21 (m, 30H, Ph). 31P{1H} NMR data are given in
Table 1. By a procedure similar to that of 20a with 1a and AgOTs,
20b·0.5CH2Cl2 was isolated as colorless crystals (53%). Anal. Calcd
for C60.5H58O9P4S3ClPdAg: C, 51.94; H, 4.18. Found: C, 51.61; H,
4.23. IR (KBr): ν 1485 (m), 1436 (s), 1252, 1102, 1027 (br, s), 819
(s), 740 (s), 688 (s), 629 (s), 573 (m), 517 (m) cm−1. UV−vis
6.4−8.0 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-
MS (CH2Cl2): m/z 1567.120 (z1, {(Cp*IrCl2)2PdCl(dpmppm)}+
(1567.082)), 1169.084 (z1, {(Cp*IrCl2)PdCl(dpmppm)}+
(1169.066)).
[PdCl2(Cp*IrCl2)(Cp*RhCl2)(μ-dpmppm-κ2,κ1,κ1)] (31c).
31c·CH2Cl2 was obtained from 1a in 80% yield (see the Supporting
Information). Anal. Calcd for C60H68P4Cl8PdRhIr: C, 45.09; H, 4.29.
Found: C, 44.89; H, 4.19. IR (KBr): ν 1485 (m), 1435 (s), 1159 (m),
1097 (s), 1026 (m), 791 (m), 766 (m), 742 (s), 725 (m), 692 (s)
cm−1. UV−vis (CH2Cl2): λmax (log ε) 346 sh (3.92), 386 sh nm (3.89).
1H NMR (CD2Cl2): δ 1.33 (br, 15H, Cp*), 1.44 (d, 4JHP = 4 Hz, 15H,
1
(DMF): λmax (log ε) 414 nm (3.81). H NMR (DMF-d7): δ 2.32 (s,
9H, p-CH3), 3.88 (br, 2H, CH2), 4.32−4.63 (m br, 3H, CH2), 5.34−
5.43 (m, 1H, CH2), 7.24−8.66 (m, 42H, Ph). 31P{1H} NMR data are
given in Table 1. Careful crystallization of 20b for a long time afforded
block-shaped crystals of 20b·H2O which were suitable for X-ray
crystallography.
Cp*), 2.5−6.5 (m, 6H, CH2), 6.4−8.0 (m, 30H, Ph). 31P{1H} NMR
data are given in Table 1. ESI-MS (CH2Cl2): m/z 1477.046 (z1,
{(Cp*RhCl2)(Cp*IrCl2)PdCl(dpmppm)}+ (1477.026)), 1567.096
(z1, {(Cp*IrCl2)2PdCl(dpmppm)}+ (1567.082)), 1386.964 (z1,
{(Cp*RhCl2)2PdCl(dpmppm)}+ (1386.970)).
[PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]Cl (M = Rh (21a), Ir (21b))
and [PdCl2(Cp*MCl2)(dpmppmO-κ2,κ1)] (M = Rh (22a)). A
dichloromethane solution (10 mL) of 1a (28.0 mg, 0.035 mmol) and
[Cp*RhCl2]2 (12.2 mg, 0.020 mmol) was stirred at room temperature
for 12 h. The solvent was removed under reduced pressure to dryness,
and the residue was extracted with 10 mL of CH2Cl2. The extract was
passed through a filter and concentrated to ca. 3 mL, to which ca.
5 mL of diethyl ether was carefully added. The solution was allowed to
stand in a refrigerator to deposit a mixture of 21a and 22a in a 1:2
ratio, which were analyzed by 31P{1H} NMR spectra and X-ray
crystallography (22a·4CH2Cl2). 31P{1H} NMR (CD2Cl2) of 21a: δ
−63.7 (dd, JPP = 464, 82 Hz, 1P, PA), −45.7 (dd, JPP = 82, 31 Hz, 1P,
[PdCl(μ-Cl)(Cp*MCl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M =
Rh (32a), Ir (32b)). Compound 32a was obtained from 1b in 60%
yield (see the Supporting Information). Anal. Calcd for
C59H66P5F6Cl5PdRh2: C, 46.21; H, 4.34. Found: C, 45.94; H, 4.32.
IR (KBr): ν 1485 (m), 1437 (s), 1160 (m), 1097 (m), 1022 (m), 999
(m), 845 (s), 791 (m), 768 (m), 742 (m), 694 (m) cm−1. UV−vis
(CH2Cl2): λmax (log ε) 397 nm (4.15). 1H NMR (CD2Cl2): δ 1.23 (d,
4JHP = 4 Hz, 15H, Cp*), 1.39 (d, 4JHP = 4 Hz, 15H, Cp*), 3.0−3.7 (m,
1
6H, CH2), 7.0−7.8 (m, 30H, Ph). 31P{1H} NMR data are listed in
Table 1. ESI-MS (CH2Cl2): m/z 1387.008 (z1, [(Cp*RhCl2)2PdCl-
(dpmppm)]+ (1386.970)). Recrystallization of 32a from a dichloro-
methane/acetone/diethyl ether mixed solvent gave orange needle
crystals of 32a·(CH3)2CO suitable for X-ray crystallography. By a
procedure similar to that for 32a, 32b was isolated in 76% yield. Anal.
Calcd for C59H66P5F6Cl5PdIr2: C, 41.39; H, 3.89. Found: C, 40.99; H,
3.61. IR (KBr): ν 1485 (m), 1437 (s), 1161 (m), 1097 (s), 1028 (m),
843 (s), 793 (m), 768 (m), 742 (m), 727 (m), 692 (s) cm−1. UV−vis
(CH2Cl2): λmax (log ε) 354 sh nm (4.15). 1H NMR (CD2Cl2): δ 1.45
(d, 4JHP = 2 Hz, 15H, Cp*), 1.57 (d, 4JHP = 2 Hz, 15H, Cp*), 3.0−4.0
(m br, 6H, CH2), 7.2−8.0 (m, 30H, Ph). 31P{1H} NMR data are given
in Table 1. ESI-MS (CH2Cl2): m/z 1567.073 (z1, [(Cp*IrCl2)2PdCl-
(dpmppm)]+ (1567.082)), 1169.063 (z1, {(Cp*IrCl2)PdCl-
(dpmppm)}+ (1169.066)).
PB), −6.2 (dd, JPP = 464, 18 Hz, 1P, PD), 31.7 (ddd, JRhP = 148 Hz,
JPP = 31, 18 Hz, 1P, PC). 31P{1H} NMR (CD2Cl2) of 22a: δ 9.8 (d,
JPP = 22 Hz, 1P, PD), 12.8 (t, JPP = 27 Hz, 1P, PB), 27.5 (d, JPP = 27 Hz,
1
1P, PA), 29.0 (dt, JRhP = 148 Hz, JPP = 22 Hz, 1P, PC). Treatment of
1a (29.0 mg, 0.036 mmol) and [Cp*IrCl2]2 (14.5 mg, 0.018 mmol)
similar to that described above gave 21b with uncharacterized
compounds. 31P{1H} NMR (CD2Cl2) of 21b: δ −63.7 (dd, JPP
=
468, 82 Hz, 1P, PA), −46.6 (dd, JPP = 82, 24 Hz, 1P, PB), −6.9 (dd,
JPP = 468, 11 Hz, 1P, PD), 0.5 (dd, JPP = 24, 11 Hz, 1P, PC).
[PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]PF6 (M = Rh (23a), Ir
(23b)). Complex 23a was prepared from 1b in 72% yield (see the
Supporting Information). Anal. Calcd for C49H51P5F6Cl3PdRh: C,
48.06; H, 4.20. Found: C, 47.55; H, 4.07. IR (KBr): ν 1483 (m), 1437
(s), 1099 (m), 1024 (m), 999 (m), 845 (s), 795, 740, 723 cm−1. UV−
1
vis (CH2Cl2): λmax (log ε) 400 sh (3.72), 346 nm (4.18). H NMR
(CD2Cl2): δ 1.40 (d, 4JHP = 4 Hz, 15H, Cp*), 2.8−5.3 (m, 6H, CH2),
6.8−8.3 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-
MS (CH2Cl2): m/z 1078.998 (z1, [(Cp*RhCl2)PdCl(dpmppm)]+
(1079.009)). By a procedure similar to that for 23a, using 1b and
[Cp*IrCl2]2, yellow crystals of 23b·0.5CH2Cl2 were isolated (77%).
Anal. Calcd for C49.5H52P5F6Cl4PdIr: C, 43.84; H, 3.86. Found: C,
44.16; H, 3.77. IR (KBr): ν 1485 (m), 1437 (s), 1163 (m), 1099 (m),
1028 (m), 849 (s), 795 (m), 690 (s) cm−1. UV−vis (CH2Cl2): λmax
[PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M =
Rh, M′ = Ir (32c); M = Ir, M′ = Rh (32d)). Complex 32c·0.5CH2Cl2
was prepared from 31c in 51% yield (see the Supporting Information).
Anal. Calcd for C59.5H67P5F6Cl6PdRhIr: C, 42.91; H, 4.06. Found: C,
42.95; H, 3.95. IR (KBr): ν 1485 (m), 1436 (s), 1097 (m), 842 (s),
783 (m), 743 (m), 691 (m) cm−1. UV−vis (CH2Cl2): λmax (log ε)
1
4
393 nm (4.04). H NMR (CD2Cl2): δ 1.25 (d, JHP = 4 Hz, 15H,
4
Cp*), 1.41 (d, JHP = 2 Hz, 15H, Cp*), 2.9−3.7 (m, 6H, CH2), 7.1−
1
4
7.7 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-MS
(CH2Cl2/MeOH): m/z 1476.270 (z1, [(Cp*IrCl2)PdCl(dpmppm)-
(Cp*RhCl2)]+ (1477.026)). Recrystallization of 32c from a dichloro-
methane/acetone/diethyl ether mixed solvent gave orange needle
crystals of 32c·(CH3)2CO suitable for X-ray crystallography. Complex
32d was prepared from 23b in 68% yield (see the Supporting
Information). Anal. Calcd for C59H66P5F6Cl5PdRhIr: C, 43.67; H,
4.10. Found: C, 43.40; H, 3.77. IR (KBr): ν 1485 (m), 1437 (s), 1095
(s), 844 (s), 795 (m), 743 (m), 694 (s) cm−1. UV−vis (CH2Cl2): λmax
(log ε) 346 nm (4.20). H NMR (CD2Cl2): δ 1.41 (d, JHP = 3 Hz,
15H, Cp*), 1.6 (br, 1H, CH2), 2.9 (br, 1H, CH2), 3.4 (br, 1H,
CH2), 3.9 (br, 1H, CH2), 4.5 (br, 1H, CH2), 4.7 (br, 1H, CH2),
6.8−8.3 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1. ESI-
MS (CH2Cl2): m/z 1169.0634 (z1, [(Cp*IrCl2)PdCl(dpmppm)]+
(1169.066)).
[PdCl2(Cp*MCl2)2(μ-dpmppm-κ2,κ1,κ1)] (M = Rh (31a), Ir
(31b)). Complex 31a·1.5CH2Cl2 was prepared from 1a in 91%
yield (see the Supporting Information). Anal. Calcd for
C60.5H69P4Cl9PdRh2: C, 46.84; H, 4.48. Found: C, 46.45; H, 4.19.
IR (KBr): ν 1483 (m), 1435 (s), 1159 (m), 1097 (s), 1022 (m), 793
(m), 766 (m), 742 (s), 725 (m), 692 (s) cm−1. UV−vis (CH2Cl2): λmax
1
4
(log ε) 386 nm (3.92). H NMR (CD2Cl2): δ 1.23 (d, JHP = 3 Hz,
4
15H, Cp*), 1.40 (d, JHP = 3 Hz, 15H, Cp*), 2.9−4.7 (m br, 6H,
CH2), 6.9−8.2 (m, 30H, Ph). 31P{1H} NMR data are given in Table 1.
ESI-MS (CH2Cl2/MeOH): m/z 1476.248 (z1, [(Cp*RhCl2)PdCl-
(dpmppm)(Cp*IrCl2)]+ (1477.026)).
1
(log ε) 397sh (3.93), 349sh nm (4.04). H NMR (CD2Cl2): δ 1.37 (d,
4JHP = 3 Hz, 15H, Cp*), 1.45 (d, 4JHP = 4 Hz, 15H, Cp*), 2.5−6.5 (m,
6H, CH2), 6.8−8.0 (m, 30H, Ph). 31P{1H} NMR data are given in
Table 1. ESI-MS (CH2Cl2): m/z 1386.986 (z1, {(Cp*RhCl2)2PdCl-
(dpmppm)}+ (1386.970)). By a method similar to that of 31a, using
1a and [Cp*IrCl2]2, 31b·CH2Cl2 was obtained (83%). Anal. Calcd for
C60H68P4Cl8PdIr2: C, 42.70; H, 4.06. Found: C, 42.94; H, 4.47. IR
(KBr): ν 1485 (m), 1435 (s), 1159 (m), 1097 (s), 1029 (m), 793 (m),
768 (m), 742 (s), 725 (m), 694 (s) cm−1. UV−vis (CH2Cl2): λmax (log
X-ray Crystallography. The crystals of 1a·2CH2Cl2, 1b·CH3CN,
20b·H2O, 22a·4CH2Cl2, 23a·CH2Cl2·Et2O, 23b·3CH2Cl2,
31a·2CH2Cl2, 31b·2CH2Cl2, 31c·2CH2Cl2, 32a·(CH3)2CO, and
32c·(CH3)2CO were quickly coated with Paratone N oil and mounted
on top of a loop fiber at room temperature. Crystal and experimental
data are summarized in Tables 2 and 3. All data were collected at −120 °C
(1a,b, 20b, 22a, 23a,b, 32a,c), −105 °C (31a,b), and −100 °C (31c)
on a Rigaku AFC8R/Mercury CCD diffractometer equipped with
graphite-monochromated Mo Kα radiation using a rotating-anode
1
ε) 340 (3.99), 461sh nm (2.88). H NMR (CD2Cl2): δ 1.33 (br, 15H,
4
Cp*), 1.46 (d, JHP = 2 Hz, 15H, Cp*), 2.5−6.3 (m br, 6H, CH2),
135
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Article
Table 2. Crystallographic Data of the Complexes 1a·2CH2Cl2, 1b·CH3CN, 20b·H2O, 22a·4CH2Cl2, 23a·CH2Cl2·Et2O, and
23b·3CH2Cl2
1a·2CH2Cl2
1b·CH3CN
20b·H2O
22a·4CH2Cl2
23a·CH2Cl2·Et2O
23b·3CH2Cl2
formula
C41H40Cl6P4Pd
C41H39NCl-
F6P5Pd
C60H59O10P4-
S3PdAg
C53H59OCl12P4-
RhPd
C54H63OF6P4-
Cl5RhPd
C52H57F6P5-
Cl9P5Pd
formula wt
cryst syst
space group
a, Å
975.78
2780.82
triclinic
1374.46
triclinic
1470.69
1383.52
triclinic
1568.58
triclinic
monoclinic
P21/c
monoclinic
P21/c
P1
̅
P1
̅
P1
̅
P1
̅
11.1295(15)
29.706(3)
13.217(2)
11.9315(11)
12.4707(11)
15.8027(11)
91.876(3)
105.7458(19)
112.566(3)
2064.9(3)
2
15.072(4)
15.753(4)
15.813(4)
117.773(3)
102.0868(4)
107.3202(8)
2889.5(13)
2
12.063(5)
24.465(9)
20.922(8)
12.242(4)
15.428(5)
17.398(6)
90.395(4)
108.107(4)
109.1568(15)
2928.3(16)
2
12.380(2)
14.534(3)
17.841(3)
80.825(4)
75.624(5)
79.221(4)
3033.4(9)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
96.1866(18)
92.1987(11)
V, Å3
4344.3(10)
4
6170(4)
4
Z
temp, °C
D
μ, mm−1 (Mo Kα)
2θ range, deg
Rint
−120
1.492
0.972
6−55
0.017
38 661
9565
−120
1.538
−120
1.580
−120
1.583
1.218
6−55
0.037
55 913
13 726
7908
−120
1.569
−120
1.717
calcd, g cm−3
0.767
0.927
1.009
3.075
6−55
0.015
6−55
0.019
6−55
0.048
6−55
0.017
no. of rflns coll
no. of unique rflns
18 231
27 218
27 350
26 470
9218
12 756
12 938
13 317
no. of obsd rflns (I >
2σ(I))
7065
7746
10 109
7736
12 490
no. of variables
471
497
737
650
671
668
a
R1
0.030
0.075
1.095
0.045
0.115
1.071
0.049
0.124
1.062
0.084
0.205
0.075
0.249
1.130
0.027
0.063
1.034
b
wR2
GOF
1.182
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo| (for observed reflections with I > 2σ(I)). wR2 = [∑w(Fo − Fc2)2/∑w(Fo )2]1/2 (for all reflections).
Table 3. Crystallographic Data of the Complexes 31a·2CH2Cl2, 31b·2CH2Cl2, 31c·2CH2Cl2, 32a·(CH3)2CO, and 32c·(CH3)2CO
31a·2CH2Cl2
31b·2CH2Cl2
31c·2CH2Cl2
32a·(CH3)2CO
32c·(CH3)2CO
formula
formula wt
cryst syst
space group
a, Å
C61H70Cl10P4Rh2Pd
1593.86
C61H70Cl10P4PdIr2
1772.49
C61H70Cl10P4RhPdIr
1683.17
C62H72OF6P5Cl5Rh2Pd
1591.59
monoclinic
P21/n
C62H72OF6P5Cl5RhPdIr
1680.90
monoclinic
P21/n
orthorhombic
Pca21
orthorhombic
Pca21
orthorhombic
Pca21
23.354(5)
15.269(3)
18.148(4)
23.3745(5)
15.3030(4)
18.1393(4)
23.3351(7)
15.3353(4)
18.1485(6)
10.848(2)
33.528(6)
19.391(4)
94.726(3)
7029(2)
4
10.964(5)
33.961(15)
19.270(9)
94.775(4)
7151(5)
4
b, Å
c, Å
β, deg
V, Å3
6471(2)
4
6488.4(3)
4
6494.5(3)
4
Z
temp, °C
D
μ, mm−1 (Mo Kα)
−105
1.636
1.328
6−55
0.033
59 170
14 561
13 412
714
−105
1.814
4.926
6−55
0.029
55 250
14 022
13 209
704
−100
1.721
3.122
6−55
0.025
55 897
13 818
13 247
713
−120
1.504
−120
1.561
calcd, g cm−3
1.073
2.689
2θ range, deg
6−55
0.034
6−55
0.061
Rint
no. of rflns coll
no. of unique rflns
no. of obsd rflns (I > 2σ(I))
no. of variables
63 232
58 665
15 935
15 965
13 966
13 154
741
804
a
R1
0.039
0.096
1.243
0.025
0.053
0.981
0.030
0.075
0.062
0.084
b
wR2
0.172
0.204
GOF
1.013
1.039
1.037
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo| (for observed reflections with I > 2σ(I)). wR2 = [∑w(Fo − Fc2)2/∑w(Fo )2]1/2 (for all reflections).
X-ray generator (50 kV, 180 mA) and a Rigaku VariMax Mo/Saturn
CCD diffractometer equipped with graphite-monochromated Mo Kα
radiation using an RA-Micro7 rotating-anode X-ray generator (50 kV,
24 mA). A total of 1440−2160 oscillation images, covering a whole
sphere of 6° < 2θ < 55°, were corrected by the ω-scan method
(−70° < ω < 110° (1a), −62° < ω < 118° (1b, 20b, 22a, 23a,b, 31a−c,
32a,c)) with Δω = 0.25°. The crystal-to-detector (70 × 70 mm) distance
was set at 45 or 60 mm. The data were processed using the Crystal Clear
1.3.5 program (Rigaku/MSC)13 and corrected for Lorentz−polarization
and absorption effects.14 The structures of complexes were solved by
136
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Organometallics
Article
direct methods with DIRDIF-9415 (1b, 20b, 31b), SIR-9216a (1a, 20b,
22a, 23a,b, 31a,c, 32a), and SIR-9716b (32c) and were refined on F2
with full-matrix least-squares techniques with SHELXL-9717 using the
Crystal Structure 3.7 package.18 All non-hydrogen atoms were refined
with anisotropic thermal parameters, and the C−H hydrogen atoms
were calculated at ideal positions and refined with riding models. All
calculations were carried out on a Pentium PC with Crystal Structure
3.7 package.18 In the refinement of 20b, the water molecule of
crystallization is disordered in two sites with 0.5 occupancy. In 23a,
one of the phenyl groups on P4 atom is disordered and refined with a
two-site rotating model with half-occupancy. In 31a,c, a Cl atom of
one solvated dichloromethane is disordered and refined with two site
2
1
models with
/ and / occupancies for 31a and 0.7 and 0.3
3 3
occupancies for 31c. In 32c, the PF6− anion is disordered in two sites,
each refined anisotropically with 0.5 occupancy.
RESULTS AND DISCUSSION
■
Figure 1. ORTEP diagram for the complex cation of [PdCl(μ-
dpmppm-k3)]PF6 (1b). The thermal ellipsoids are drawn at the 40%
probability level, and the hydrogen atoms are omitted for clarity.
Mononuclear Pd Complexes with dpmppm, [PdCl-
(dpmppm-κ3)]X (X = Cl (1a), PF6 (1b)). When [PdCl2-
(cod)] was treated with 1 equiv of dpmppm in dichloro-
methane, pale yellow crystals of [PdCl(dpmppm-κ3)]Cl (1a)
were obtained in 62% yield. Complex 1a was further converted
by treatment with excess of NH4PF6 in acetonitrile into
[PdCl(dpmppm-κ3)]PF6 (1b) in 73% yield (Scheme 1).
P3−Pd1−P4 = 71.59(2)° (1a), 71.16(2)° (1b), as in [PdCl2-
(dppm)] (P−Pd−P = 72.68(3)°),19 where the methylene carbon
atom appreciably deviates from the [PdP2] plane. The bicyclic
chelate ring system constrains three phenyl groups of P1, P3, and
P4 atoms in an axial direction with respect to the Pd square plane.
The other three phenyl groups are in an equatorial orientation on
the other side of the plane, onto which the counteranions Cl− and
PF6− are incorporated.
Scheme 1
The dpmppm-κ3 structure confirmed by the X-ray analyses is
very stable in the solution state. The 31P{1H} NMR spectrum
of 1b in CD2Cl2 showed four sets of resonances at δ −44.7,
−40.3, −33.2, and 5.7 ppm, which are assignable to PA, PC, PB,
and PD atoms in the light of PP′ coupling constants (JPP′) as
indicated in Figure 2a (the labels of phosphorus atoms are
1
Complexes 1a,b were characterized by elemental analysis, H
and 31P{1H} NMR and ESI-MS spectra, and X-ray crystallog-
raphy to have almost identical structures except for the
counteranions. A perspective view for the complex cation of
1b is shown in Figure 1 (that of 1a is given in Figure S1 as
Supporting Information), and the representative structural
parameters are given in Table S1 (see the Supporting
Information). The structures of complex cations 1a,b are
essentially identical, involving a square-planar Pd(II) center
coordinated by a dpmppm ligand and a chloride anion. The
dpmppm ligand attaches to the Pd atom with two outer (P1,
P4) and one inner (P3) phosphorus atoms to form a pincer-
type κ3 structure, in which six- and four-membered chelate
rings are fused, and the remaining inner P atom (P2) is
uncoordinated (Pd1···P2 = 4.0820(7) (1a), 4.1112(7) Å (1b)).
The six-membered ring takes a stable chair conformation, and the
phenyl group on the P2 atom occupies an equatorial position,
similar to the six-membered ring in [PdCl2(dpmp-κ2)].4b,d The
four-membered ring shows approximately planar structure with
Figure 2. The 31P{1H} NMR spectra of 1b (a), 23a (b), and 23b (c)
in CD2Cl2 at room temperature with the assignments for the P atoms
of dpmppm.
indicated with the spectrum); the large trans PP′ coupling
(2JP P ) of 475 Hz clearly demonstrated retainment of the κ3
A
D
pincer-type structure. The 31P{1H} spectrum of 1a in CDCl3
137
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Organometallics
also exhibited a similar trans coupling of JP P = 479 Hz. The
Article
2
Scheme 2
A
D
ESI-MS spectra of 1a,b in CH2Cl2 showed the parent peak for
[PdCl(dpmppm)]+ (m/z 769.050), which is consistent with the
X-ray and NMR results.
PdAg Dinuclear Complexes of [PdX(AgX)(μ-dpmppm-
κ3,κ1)]X (X = TfO (20a), TsO (20b)). Reaction of 1a with an
excess amount of AgI salt (silver triflate or tosylate) in
acetonitrile afforded PdIIAgI dinuclear complexes formulated as
[PdX(AgX)(μ-dpmppm-κ3,κ1)]X (X = TfO (20a), TsO (20b))
in 49 and 53% yields, respectively (Scheme 1). In the 31P{1H}
NMR spectra (Figure S2a in the Supporting Information for
20a), the peak for the PC atom, which is uncoordinated in 1a
to resonate at δ −38.8 ppm, shifted to δ −18.6 (20a) and
−19.2 (20b) ppm as a doublet of multiplets due to coupling
to 107Ag and 109Ag (1JAgP = 775 (20a), 780 Hz (20b)), and
the large trans PP′ coupling was observed with the peaks of
PA and PD atoms (2JP P = 420 (20a), 440 Hz (20b)). The
a long time. The 31P{1H} NMR spectrum (Figure S2b,
Supporting Information) indicated that complex 21a retained
the fused-ring structure of dpmppm (2JP P = 464 Hz) and
A
D
A
D
trapped a Cp*RhCl2 fragment on the uncoordinated phosphine
structure of 20b was determined by X-ray crystallography
(Table S1 and Figure 3) to confirm that a AgOTs fragment is
of 1a (δP 31.7 ppm, 1JRhP = 148 Hz). In contrast, the spectral
C
C
patterns for 22a were entirely different, with the absence of the
large trans PP′ coupling corresponding to the pincer chelate
system; the four resonances were all shifted to higher frequency
2
(δ 9.8−29.0 ppm) and coupled with small JPP′ values (27, 22
Hz), in addition to the 103Rh−31P coupling (1JRhP = 148 Hz)
C
observed for the PC peak (Figure S2c, Supporting Information).
The detailed structure of 22a (Figure S3, Supporting
Information) showed that the inner P2 atom is bound to the
Rh atom and the remaining terminal phosphine (P4) is
dissociated from the metal center and converted into a
phosphine oxide. The six-membered chelate ring is remarkably
deformed to take a skew or twist-boat conformation. The axial
phenyl group on the P2 atom is pushed to hang over the Pd
center, and on the other hand, the bulky Cp*RhCl2 fragment is
directed in the equatorial position.
These structural features of 22a suggested that an addition of
the Cp*RhCl2 fragment on the uncoordinated P2 atom of 1a
caused a crucial conformational change of the six-membered
chelate ring from a stable chair to a twist-boat structure, which
may further destabilize the four-membered chelate ring for its
ring opening to form [PdCl2(Cp*RhCl2)(μ-dpmppm-κ2,κ1)]
(21a*) with ligation of the counter chloride anion (Scheme 2),
although the plausible intermediate 21a* was not detected by
31P{1H} NMR spectra. The dangling phosphine groups of 21a*
are likely to be oxidized when exposed to air. From the reaction
of 1a with 0.5 equiv of [Cp*IrCl2]2, the analogous PdIIIrIII
complex of [PdCl(Cp*IrCl2)(μ-dpmppm-κ3,κ1)]Cl (21b) was
generated as a main product (Figure S2d, Supporting
Information) but was not isolated as a pure form probably
Figure 3. ORTEP diagram for the complex cation of [Pd(OTs)-
(AgOTs)(μ-dpmppm-κ3,κ1)](TsO) (20b). The thermal ellipsoids are
drawn at the 40% probability level and the hydrogen atoms are omitted
for clarity. One of the phenyl groups on P1 atom is disordered.
incorporated onto the uncoordinated P2 atom in 1a and the
chloride ligand of 1a is replaced by a tosylate anion. The
fused chelate ring structure with dpmppm-κ3,κ1 as observed
in 1a is not perturbed by the addition of an AgOTs unit, and
the six-membered ring adopts a chair conformation, with the
AgI ion occupying the axial site of the P2 atom. The linear
structure of the Ag1 atom could avoid the repulsive
interactions with the phenyl groups on P1 and P3 atoms.
The four-membered chelate ring of 20a,b is stable and would
not undergo a ring-opening reaction even when treated with
an excess amount of AgX salt.
PdM Dinuclear Complexes of [PdCl(Cp*MCl2)(μ-
dpmppm-κ3,κ1)]X (X = Cl, M = Rh (21a), Ir (21b); X =
PF6, M = Rh (23a), Ir (23b)). With an aim of introducing
more bulky metal species onto the free phosphine group,
complex 1a was treated with 0.5 equiv of [Cp*RhCl2]2 in
dichloromethane to yield a mixture of [PdCl(Cp*RhCl2)(μ-
dpmppm-κ3,κ1)]Cl (21a) and [PdCl2(Cp*RhCl2)(μ-
dpmppmO-κ2,κ1)] (22a, dpmppmO = Ph2PCH2P(Ph)-
CH2P(Ph)CH2PPh2(O)) (Schemes 1 and 2); the former
was initially formed as a major product and the latter as a minor
one, but the ratio of 22a increased with keeping the solution for
due to the ring-opening reaction leading to the PdIIIrIII
2
trinuclear complex 31b as described later.
To isolate the PdIIMIII dimetallic complexes, complex 1b with
−
a noncoordinating PF6 counteranion was reacted with 0.5
equiv of [Cp*MCl2]2 to afford [PdCl(Cp*MCl2)(μ-dpmppm-
κ3,κ1)]PF6 (M = Rh (23a), Ir (23b)) in 72 and 77% yields,
respectively (Scheme 1). Complexes 23a,b were quite stable in
the solution state, as confirmed by spectroscopic analyses. In
the 31P{1H} NMR spectra (Figure 2b,c), large trans PP′
couplings were observed for the peaks of PA and PD (2JP P
=
A
D
466 (23a), 468 (23b) Hz). The peaks for PA, PB, and PD shifted
to lower frequency compared with those of 1b, and the
resonances for PC were shifted to higher energy at δ 30.8 (23a)
and −1.2 ppm (23b); the former was observed as a doublet of
138
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Organometallics
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multiplets with 1JRhP = 149 Hz. The ESI-MS spectra of 23a,b in
dichloromethane showed the parent peaks at m/z 1078.998 and
1169.0634, which were assigned to [PdCl(Cp*MCl2)-
(dpmppm)]+ (M = Rh, m/z 1079.009; Ir, m/z 1169.066) by
simulating distributions of isotopomers. The structures of 23a,b
were determined by X-ray crystallography to be isomorphous with
each other; an ORTEP view for the complex cation of 23a is
given in Figure 4 (Figure S4 (Supporting Information) for 23b),
and the structural parameters are given in Table S1 (Supporting
[PdCl2(Cp*MCl2)2(μ-dpmppm-κ2,κ1,κ1)] (M = Rh (31a), Ir
(31b)) in 91 and 83% yields, respectively (Scheme 3).
Scheme 3
The ESI-MS spectra in dichloromethane showed monovalent
parent peaks at m/z 1386.986 (31a) and 1567.120 (31b)
corresponding to {PdCl(Cp*MCl2)2(dpmppm)}+ with m/z
1386.970 (M = Rh) and 1567.082 (M = Ir). The 31P{1H}
NMR spectra of 31a,b were somewhat broad with the absence
of the trans PP′ coupling as observed in 23 (Figure S5,
Supporting Information), indicating that ring opening of the
four-membered chelate ring occurred during the reaction. In
the spectrum of 31a, four peaks were observed at δ 9.2, 14.2,
28.4, and 31.3 ppm in a 1:1:1:1 integration ratio, of which the
Rh−P coupled (1JRhP = 147 Hz) peaks, the doublet of broad
doublets at δ 28.4 and the doublet of broad triplets at δ 31.3,
were assigned to PA and PC atoms bound to the Rh ions (the
labels of P atoms are shown with the spectrum in Figure S5).
Figure 4. ORTEP diagram for the complex cation of [PdCl-
(Cp*RhCl2)(μ-dpmppm-κ3,κ1)]PF6 (23a). The thermal ellipsoids
are drawn at the 40% probability level, and the hydrogen atoms are
omitted for clarity.
2
The doublet at δ 9.2 with JPP′ = 20 Hz was assignable to PD
Information). The complex cation of 23 contains a [P3Cl]
square-planar Pd(II) center with the fused bicyclic chelation rings
of the dpmppm ligand, which further traps a Cp*MCl2 fragment
through the uncoordinated inner phosphine unit. The
[PdPCPCP] six-membered ring adopts a twist-boat conforma-
tion, as observed in 22a. The Cp*RhCl2 and Ph groups bound to
the P2 atom occupy the equatorial and axial sites, respectively,
and the Pd1···P2 distance (3.8916(18) Å (23a), 3.8978(7) Å
(23b)) is appreciably shorter than that in 22a (3.985(2) Å)
and considerably reduced from those of 1a,b (4.0820(7)−
4.1112(7) Å). The conformational switch should increase the steric
repulsion between the phenyl groups on P1, P2, and P4 atoms and
the strain involved in the [PdPCP] four-membered ring.
Whereas the methylene carbon atom definitely deviates from
the [Pd1P3P4] plane in 1a,b and 20b, in which the six-
membered ring takes a chair conformation, the carbon atom
(C1) in 23a,b is constrained to be involved in the [Pd1P3P4]
plane. This difference can be monitored by the dihedral angle
between the Pd1P3P4 and P3P4C1 planes of 14.98 (23a) and
16.00° (23b), which are smaller than those of 30.98 (1a), 28.63
(1b), and 25.41° (20b), while the P3−Pd1−P4 bite angles
(72.64(6) (23a), 72.14° (23b)) do not show a significant change.
PdMM′ Trinuclear Complexes [PdCl2(Cp*M′Cl2)-
(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)] (M = M′ = Rh (31a), Ir
(31b); M = Rh, M′ = Ir (31c)). During the reaction of 1a to
give 22a, ligation of the chloride counteranion of 21 was
assumed to accelerate the ring-opening reaction of the four-
membered chelate ring, and this nature could be utilized for the
preparation of a PdIIRhIII2 trinuclear complex assembled by the
dynamically flexible dpmppm ligand. Treatment of complex 1a
with 1 equiv of [Cp*MCl2]2 in CH2Cl2 readily afforded
and the remaining broad peak centered at δ 14.2 to PB. In the
spectrum of 31b, while the resonances for PB and PD atoms
were almost identical in frequency and shape with those of 31a,
the peaks for PA and PC were considerably shifted to lower
frequency and accidentally overlapped at around δ −1.3 ppm.
When complex 1a was treated with 0.5 equiv of [Cp*RhCl2]2
at first and then with 0.5 equiv of [Cp*IrCl2]2, the PdIIRhIIIIrIII
trimetallic complex [PdCl2(Cp*IrCl2)(Cp*RhCl2)(μ-dpmppm-
κ2,κ1,κ1)] (31c) was isolated in 80% yield (Scheme 3). However,
a similar procedure with [Cp*IrCl2]2 followed by [Cp*RhCl2]2
resulted in providing a mixture of the PdIr2 and PdRh2
trinuclear complexes 31a,b together with a small amount of
the PdIrRh mixed-metal compound 31d, and eventually, failure
to obtain the trinuclear complex [PdCl2(Cp*RhCl2)(Cp*IrCl2)-
(μ-dpmppm-κ2,κ1,κ1)] (31d) as a main product (Scheme 3).
This might be attributed to the instability of complex 21b,
which was likely to be transformed into the PdIIIrIII trinuclear
2
complex 31b via a ring-opening reaction assisted by Cl−
coordination to the PdII center. In the ESI-MS spectrum of
31c in CH2Cl2, an intense monovalent peak for [PdCl-
(Cp*IrCl2)(Cp*RhCl2)(dpmppm)]+ was found at m/z
1477.046 together with very weak peaks for [PdCl-
(Cp*MCl2)2(dpmppm)]+ (M = Rh, Ir). The 31P{1H} NMR
spectrum of 31c consisted of four peaks at δ −1.4 (PA), 8.9
(PD), 14.6 (PB), and 30.9 (PC, 1JRhP = 148 Hz) and showed the
presence of 31b in only a small amount (Figure S5c).
The solid state structures of 31a−c, determined by X-ray
crystallographic analyses, are isomorphous, revealing that a
dpmppm ligand chelates to a square-planar cis-PdCl2 center via
the outer and inner P atoms (P1, P3) to form a six-membered
ring and is further bound to the first Cp*MCl2 fragment (M site)
through the inner P2 atom (M = Rh (31a,c), Ir (31b)) and to
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the second Cp*M′Cl2 unit (M′ site) via the outer P4 atom (M =
Rh (31a), Ir (31b,c)), resulting in the trinuclear structures. A
perspective view of complex 31b is shown in Figure 5 and the
structural parameters are given in Table S2 (perspective views of
Scheme 4
Cp*IrCl2 counterpart is assumed to proceed rapidly and the
resultant 23b would react with the Cp*IrCl2 unit to give
complex 32b (Scheme 4).
To isolate the trimetallic complex 32c in pure form, we used
another procedure, in which complex 31c was treated with an excess
of NH4PF6 in a dichloromethane/acetone mixed solvent to afford
32c in a 51% isolated yield. Notably, complexes 32a,b were also
prepared by treatment of 31a,b with NH4PF6 in quantitative yields.
The 31P{1H} NMR spectra of 32a−d together with the
assignment of the P atoms are shown in Figure 6. In the spectrum
Figure 5. ORTEP diagram of [PdCl2(Cp*IrCl2)2(μ-dpmppm-
κ2,κ1,κ1)] (31b). The thermal ellipsoids are drawn at the 40%
probability level, and the hydrogen atoms are omitted for clarity.
31a,c are given in Figures S6 and S7 in the Supporting
Information). The overall structure is similar to that of 22a, in
which the oxo unit of the dangling P atom is replaced by the
Cp*MCl2 fragment as expected, and in particular, the group 9
heterometal positions in 31c indicated the stepwise incorpo-
ration of the additional metals induced by the conformational
change around the Pd center. The [PdPCPCP] six-membered
ring takes a twist-boat conformation with P1−Pd1−P3 angles
of 89.82(4) (31a), 89.95(3) (31b), and 89.89(3)° (31c),
which are appreciably smaller than the corresponding values
of 23a,b due to release of strain by opening of the four-
membered ring. The structures around the Pd atom are almost
the same, and the M−P bond length clearly demonstrated
that the Ir−P bond distances are shorter than the Rh−P
distances at both M and M′ sites (Ir−P = 2.294(1)−2.298(2)
Å, Rh−P = 2.306(1)−2.312(1) Å), which is interestingly
reverse to the covalent radii of the metals and may suggest
a stronger affinity of the IrIII center over the RhIII to the
phosphine groups of dpmppm. The three metal ions PdMM′
form an equilateral triangle without any interaction between
them (Table S2).
PdMM′ Trinuclear Complexes [PdCl(μ-Cl)(Cp*M′Cl)-
(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (M = M′ = Rh (32a), Ir
(32b); M = Rh, M′ = Ir (32c); M = Ir, M′ = Rh (32d)). When
complex 1b was treated with 1 equiv of [Cp*MCl2]2 or the
isolated PdIIMIII dimetallic complexes 23a (M = Rh) and 23b
(M = Ir) were reacted with 0.5 equiv of the respective
homometallic [Cp*MCl2]2, the PdIIMIII trinuclear complexes
2
[PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6
(M = M′ = Rh (32a), Ir (32b)) were obtained as crystalline
forms in good yields (Scheme 4). Reaction of 23b with 0.5
equiv of [Cp*RhCl2]2 afforded a mixture of [PdCl(μ-
Cl)(Cp*Rh′Cl)(Cp*IrCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (32d)
and 32b in ca. 9:1 ratio as monitored by 31P{1H} NMR
spectroscopy, from which complex 32d was isolated in pure
form in a yield of 68%. In contrast, reaction of 23a with 0.5
equiv of [Cp*IrCl2]2 yielded a mixture of 32c, 32a, and 32b, in
a ca. 6:1:3 ratio; in this case, complex 32c was not isolated in
pure form from the mixture. In the presence of [Cp*IrCl2]2,
exchange reaction of the Cp*RhCl2 fragment of 23a with the
Figure 6. 31P{1H} NMR spectra of 32a (a), 32b (b), 32c (c), and 32d
(d) in CD2Cl2 at room temperature with assignments for the P atoms
of dpmppm.
of 32a (Figure 6a), three peaks for PB, PC, and PD were observed
at δ 16.8, 28.2, and 11.5 ppm with small PP′ couplings and a
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Article
characteristic coupling with 1JRhP = 148 Hz for the PC signal. The
resonance for the PA atom was observed at δ 28.5 ppm as a
doublet due to 1JRhP = 144 Hz without any PP′ coupling to the PB
nucleus, although the reason was not clear. In the spectrum of 32b
(Figure 6b), the PA and PC signals significantly shifted to lower
frequency and were observed at δ 4.0 and −5.4 ppm as a doublet
(JPP′ = 4 Hz) and a doublet of doublets (JPP′ = 20, 16 Hz), while
the peaks for the PB and PD atoms were found at δ 16.2 and 12.6
ppm as somewhat broad doublets, as in that of 32a. The 31P{1H}
NMR spectra of 32c,d were entirely different (Figure 6c,d), clearly
demonstrating that no scrambling of Cp*MCl2 fragments between
the M and M′ sites occurred in solution. In particular, the peaks for
the PA and PC atoms were quite informative, the former being
observed as a doublet (JPP′ = 3 Hz) at 4.2 ppm for 32c and a
Rh−P coupled doublet (1JRhP = 145 Hz) at 28.3 ppm for 32d and,
instead, the latter observed as a Rh−P coupled doublet of triplets
(1JRhP = 145 Hz) at 27.2 ppm for 32c and a triplet (JPP′ = 21 Hz)
at −4.6 ppm for 32d. The peaks for the PB and PD atoms of 32c,d
were relatively similar in shape, as broad signals for PB at δ 16.5
(32c) and 16.9 (32d) and doublets for PD at δ 13.9 (32c) and
10.3 (32d). The ESI-MS spectra of 32a−d showed the parent
peaks corresponding to [PdCl(Cp*M′Cl2)(Cp*MCl2)-
(dpmppm)]+, indicating that the solid-state structures were
retained in the dichloromethane solutions.
[Pd1P3C3P4Ir1Cl2] six-membered ring is constrained as a
half-chair conformation tentatively due to steric repulsion
between the phenyl groups of P3 and P4 atoms and the Cp*
unit. The large value of 97.38(8)° for the Cl2−Pd1−P3 angle
indicates some strains involved in the Pd(μ-Cl)Ir moiety. The
complex cation structure of 32a is almost identical with that of
32c, in which the PdII ion and two Cp*RhCl2 units are
organized in the bicyclic chelate ring system by a dpmppm-
κ2,κ1,κ1 ligation. The Pd1 and Rh1 atoms are bridged by the Cl2
anion (Pd1−Cl2 = 2.3822(13) Å, Rh2−Cl2 = 2.4229(14),
Pd1−Cl2−Rh2 = 124.41(5)°) without a bonding interaction
(Pd1···Rh2 = 4.2507(5) Å) as in 32c.
In the reactions of 1b, the bulky Cp*MCl2 fragment (M =
Rh, Ir) was trapped at first by the uncoordinated inner P atom
of 1b on its equatorial site, which should bring about a
conformational change of the [PdPCPCP] six-membered ring
from the stable chair structure in 1b to the twist-boat one in 23.
Induced by this structural change, the successive ring opening
of the [PdPCP] four-membered ring was promoted to trap the
second Cp*M′Cl2 fragment (M = Rh, Ir) by the dangling
terminal P atoms, resulting in the [PdPCPM′Cl] six-membered
ring completed by the chloride bridging to the Pd center, which
was ensured by the absence of a Cl− counteranion. The
structurally characterized complexes involving the PdII(μ-
Cl)MIII heterodimetallic moieties (M = Rh, Ir) have extremely
been limited to only a few examples,4e,20 despite the fact that
each metal has extensively been used in homogeneous catalytic
reactions.1,21 Hence, the PdII(μ-Cl)MIII group of 32 may
provide a useful platform for heterometallic reactive sites
exerting their cooperative effects.
The structures of 32a,c were determined by X-ray
crystallography. A perspective view for the complex cation of
32c is illustrated in Figure 7, and the structural parameters are
Electrochemical Properties of PdIIMIIIM′III Trinuclear
Complexes (32: M, M′ = Rh, Ir). Cyclic voltammograms of
complexes 32a−d were measured in acetonitrile containing 0.1 M
[nBu4N][PF6] with a glassy-carbon working electrode (Figure S9,
Supporting Information), and the peak potentials vs Fc/Fc+ redox
couple are given in Table 4 together with those for 1b and 23a,b as
Table 4. Redox Potentials for Reduction of PdII, MIII, and
M′III Sites of 32a−d and Reference Compounds 1b and
a
23a,b
b
Epc1, V
Epc2, V
Epc3, V
Figure 7. ORTEP diagram for the complex cation of [PdCl(μ-
Cl)(Cp*IrCl)(Cp*RhCl2)(μ-dpmppm-κ2,κ1,κ1)]PF6 (32c). The ther-
mal ellipsoids are drawn at the 40% probability level, and the hydrogen
atoms are omitted for clarity.
32a
32b
32c
32d
1b
−1.08 (Pd)
−1.09 (Pd)
−1.11 (Pd)
−1.06 (Pd)
−1.29 (Pd)
−1.31 (Pd)
−1.32 (Pd)
−1.40 (Rh′)
−1.51 (Ir′)
−1.47 (Ir′)
−1.47 (Rh′)
−1.53 (Rh)
−2.16 (Ir)
−1.57 (Rh)
−2.15 (Ir)
summarized in Table S2 (the plot of 32a is shown as Figure S8
in the Supporting Information). The complex cation of 32c
contains the PdII, RhIII, and IrIII metal ions assembled by a
dpmppm ligand in κ2,κ1,κ1 fashion, in such a way that the
[Pd1P1C1P2C2P3] and the [Pd1P3C3P4Ir1Cl2] six-mem-
bered rings are fused by sharing the Pd1−P3 bond. The Pd1
atom is coordinated by the inner (P3) and outer (P1)
phosphorus atoms of dpmppm and the terminal (Cl1) and the
bridging (Cl2) chloride anions in a square-planar geometry.
The Cp*RhCl2 fragment is bound to the inner P2 atom of
dpmppm, and the [Pd1P1C1P2C2P3] six-membered ring takes
a twist-boat conformation as observed in 23a,b and 31a−c. The
CpIrCl2 fragment is ligated by the outer P4 atom of dpmppm,
with one of the Cl atoms (Cl2) further bridging to Pd1 (Ir1−
Cl2 = 2.453(2) Å, Pd1−Cl2 = 2.418(2) Å, Ir1−Cl2−Pd1 =
123.0(1)°). The Pd1···Ir1 interatomic distance of 4.2801(8) Å
indicates the absence of a direct metal−metal interaction. The
23a
23b
−1.47 (Rh)
−2.04 (Ir)
a
Cyclic voltammograms were measured in acetonitrile (0.1 M
[nBu4N][PF6]) with a glassy-carbon working electrode at a scan rate
b
of 100 mV/s. See Scheme 4 for the labels of M and M′ atoms. The
potentials are referenced to the redox couple of Fc/Fc+ (1 mM in
acetonitrile).
reference compounds. At first, the mononuclear PdII complex 1b
showed an irreversible reduction peak at −1.29 V, which was
assumed to be a one-electron-reduction process by a coulometric
analysis, and those of the PdIIMIII bimetallic complexes 23a (M =
Rh) and 23b (M = Ir) exhibited two irreversible reduction peaks at
−1.31 and −1.47 V (23a) and −1.32 and −2.04 V (23b); the
more positive peak is assignable to the reduction process of the PdII
center and the negative peak to that of RhIII (23a) or IrIII (23b).
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coordinates to the square-planar PdII center with two outer and
one inner phosphorus atom to form pincer-type six- and four-
membered bicyclic rings (Figure 8). The remaining inner
phosphine, involved in the [PdPCPCP] six-membered chelate
ring with a stable chair conformation, is uncoordinated and
readily reacted with metal fragments such as AgX (X = TfO,
TsO) and Cp*MCl2 (M = Rh, Ir). Whereas the less bulky AgX
unit is just attached to the uncoordinated phosphine without
any structural changes (20 in Figure 8), the bulky Cp*MCl2
was trapped onto the free phosphine to bring about a crucial
conformational change of the [PdPCPCP] six-membered ring
from the stable chair structure in 1 to the twist-boat one in 21
and 23. This structural switch further promoted the ring
opening of the four-membered chelate ring to trap the second
Cp*M′Cl2 fragment to assemble the PdIIMIIIM′III trinuclear
systems [PdCl2(Cp*M′Cl2)(Cp*MCl2)(μ-dpmppm-κ2,κ1,κ1)]
(31) and [PdCl(μ-Cl)(Cp*M′Cl)(Cp*MCl2)(μ-dpmppm-
κ2,κ1,κ1)]PF6 (32) (M, M′ = Rh, Ir). The flexible coordination
behavior of dpmppm is able to organize a so-called “allosteric
switch” around the PdII center, that is, a trap of the Cp*MCl2
species on the free phosphine involved in the six-membered
ring destabilizing the fused four-membered ring, and establish
the stepwise construction of the trinuclear metal ions. These
results are interesting and useful to develop heterometallic
systems with synergistic effects.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, tables, figures, and CIF files giving synthetic procedures,
structural parameters, the structures of 1a, 22a, 23a, 31b,c, and
32a, 31P{1H} NMR spectra of 21a, 22a, and 31a−c, cyclic
voltammograms of 1b, 23a, 23b, and 32a−d, and crystal data
for 1a,b, 20b, 22a, 23a,b, 31a−c, and 32a,c. This material is
available free of charge via the Internet at http://pubs.acs.org.
Figure 8. Structural changes of dpmppm around the PdII center during
reactions of complexes 1 with AgX (X = TfO, TsO) and the Cp*MCl2
fragments (R = Rh, Ir), leading to complexes 20, 21, 23, 31, and 32.
[M] = Cp*MCl2.
It should be noted that the Cp*RhCl2 center is reduced more
easily than the Cp*IrCl2 center, which might be attributed to the
short Ir−P bond length of 23b. In the cyclic voltammograms of
32a−d, three irreversible reduction peaks corresponding to the
PdII, M′III, and MIII centers were observed. In all complexes, the
peak potentials for the reduction of PdII (Epc1 = −1.06 to −1.11 V)
were more positive by ca. 0.2 V than those of 1b and 23a,b (−1.29
to −1.32 V), suggesting that the electron deficiency of the PdII
center increased by the Cl− bridging instead of the terminal P
chelation. The irreversible reduction peaks for the M center of Rh
were observed at −1.53 (32a) and −1.57 V (32c) and those of Ir
at −2.16 (32b) and −2.15 V (32d), which were similar to the
potentials of 23a,b as mentioned above. In contrast, the reduction
potentials for the M′ site involved in the PdII(μ-Cl)M′III moiety
were found at −1.40 (32a) and −1.47 V (32d) for RhIII and at
−1.51 (32b) and −1.47 V (32c) for the IrIII center. Interestingly,
the IrIII site in the PdII(μ-Cl)M′III unit is significantly electron
deficient and is reduced at quite positive potentials in comparison
with the IrIII center of the M site, whereas the two RhIII centers of
the M and M′ sites showed similar redox responses. The detailed
electrochemical reactions of 32 will be investigated, in particular, on
the possibility of PdI−MII bond formation upon their reductions.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: tanase@cc.nara-wu.ac.jp. Fax: +81 742-20-3847. Tel:
+81 742-20-3399.
ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Scientific
Research and that on Priority Area 2107 (no. 22108521) from
the Ministry of Education, Culture, Sports, Science and
Technology of Japan. T.T. is grateful to Nara Women’s
University for a research project grant.
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