Carbon(0)-Bridged Pt/Ag Dinuclear and Tetranuclear Complexes Based on a Cyclometalated Pincer Carbodiphosphorane Platform

Article abstract of DOI:10.1021/acs.organomet.6b00700

A carbon(0)-bridged Pt₂Ag₂ cluster was synthesized from the reaction of a cyclometalated pincer carbodiphosphorane platinum complex with AgOTf, by forming Pt(II)←C(0)→Ag(I) dative bonds along with Pt(II)-Ag(I) and Ag(I)-Ag(I) metal-metal interactions. X-ray diffraction analysis reveals that the cluster adopts an antiparallel sandwich structure with a ladder-shaped PtC/AgAg/CPt core. The coordination plane of the platinum unit is highly distorted due to the in-plane steric repulsion between the PEt₃ ligand on the platinum and the nearest proton on each of the two cyclometalated phenyl rings in the pincer carbodiphosphorane framework. The cluster is very labile and displays different reactivity patterns toward trivalent phosphorus ligands. In the reaction with bulky PPh₃, a dinuclear complex was formed because of coordination of PPh₃ to the silver atom upon cleavage of the tetranuclear core. In contrast, replacement of the PEt₃ on the platinum center by P(OPh)₃, which is sterically less demanding, led to a dinuclear complex where the eliminated PEt₃ ligand recoordinated to the silver atom.

Full text of DOI:10.1021/acs.organomet.6b00700

Article
pubs.acs.org/Organometallics
Carbon(0)-Bridged Pt/Ag Dinuclear and Tetranuclear Complexes
Based on a Cyclometalated Pincer Carbodiphosphorane Platform
Kazuyuki Kubo,*,† Hiroyuki Okitsu,† Hiroto Miwa,† Shoko Kume,† Ronald G. Cavell,‡
and Tsutomu Mizuta*,†
†Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima
739-8526, Japan
‡Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
S
* Supporting Information
ABSTRACT: A carbon(0)-bridged Pt2Ag2 cluster was synthe-
sized from the reaction of a cyclometalated pincer carbodi-
phosphorane platinum complex with AgOTf, by forming
Pt(II)←C(0)→Ag(I) dative bonds along with Pt(II)−Ag(I)
and Ag(I)−Ag(I) metal−metal interactions. X-ray diffraction
analysis reveals that the cluster adopts an antiparallel sandwich
structure with a ladder-shaped PtC/AgAg/CPt core. The
coordination plane of the platinum unit is highly distorted
due to the in-plane steric repulsion between the PEt3 ligand on
the platinum and the nearest proton on each of the two
cyclometalated phenyl rings in the pincer carbodiphosphorane
framework. The cluster is very labile and displays different reactivity patterns toward trivalent phosphorus ligands. In the reaction
with bulky PPh3, a dinuclear complex was formed because of coordination of PPh3 to the silver atom upon cleavage of the
tetranuclear core. In contrast, replacement of the PEt3 on the platinum center by P(OPh)3, which is sterically less demanding, led
to a dinuclear complex where the eliminated PEt3 ligand recoordinated to the silver atom.
utility of this unusual entry of carbon compounds with respect
to developing novel catalysts4−6 and small-molecule trans-
formations.7,8
INTRODUCTION
■
Recently, the investigation of carbodiphosphorane (CDP)
chemistry has seen a resurgence as the concept of “coordination
compounds of carbon(0)” has become widely accepted.1
Although the first synthesis of CDP, specifically hexaphenyl-
carbodiphosphorane (1; Scheme 1), dates back to 19612 and its
Typically, CDPs coordinate to transition metals as terminal
ligands5,9−33 to afford mononuclear complexes (Scheme 1i);
however, the availability of the second lone pair allows them to
serve as bridging ligands to form a variety of geminal dinuclear
complexes (Scheme 1ii).10,21,24,34−39 This binucleate property
of the CDPs constitutes a noticeable difference from carbenes,
in which the central carbon(II) atom possesses only one lone
pair. Even so, CDPs are strongly reminiscent of bis-
(iminophosphorano)methandiide and related dianionic carbon
ligands, which produce a number of terminal and bridging
alkylidene complexes of various metals.40 The second metal-
ation of the carbon(0) atom modifies the steric and electronic
properties of the ligand framework and may result in enhanced
reactivity of the first metal center. Recently, Meek and co-
workers have reported the hydroarylation of dienes using a
rhodium catalyst containing a carbodicarbene ligand: i.e., a bis-
carbene complex of carbon(0).41 The catalytic activity was
significantly enhanced by Lewis acidic additives such as CuCl,
AgCl, AuCl, and lithium salts. This performance enhancement
was rationalized regarding the reversible coordination of the
Lewis acid to the second lone pair on the carbon(0) atom so
Scheme 1. Metalation of Hexaphenylcarbodiphosphorane
distinctly bent structure was established by X-ray diffraction
analyses some years later,3 until recently, the general formula
L→C(0)←L, where L is a two-electron donor, has infrequently
been used to represent the bonding situation in these
molecules. Current experimental and theoretical studies have
substantiated the donor−acceptor character of the P−C bond
and have shown that the central carbon atom preserves its
valence electrons as two carbon-centered lone pairs, thereby
acting as an excellent donor toward a variety of Lewis acids.1
Recently, there has been growing interest in extending the
Received: September 3, 2016
© XXXX American Chemical Society
A
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that the electron density on the rhodium center is modulated,
enabling facile molecular transformations. Furthermore, multi-
nuclear systems can potentially exhibit fascinating physical and
chemical properties or reactivities fundamentally different from
those of the corresponding mononuclear units. To explain this
distinctive multinuclear behavior, direct interaction between the
metals in proximity is often the key.42 To date, only a limited
number of well-defined CDP dinuclear complexes that involve
apparent direct metal−metal interactions have been reported,
where examples include triangular Au(I)−C(0)−Cu(I),10
Au(I)−C(0)−Au(I),10,21 Pd(II)−C(0)−Au(I),35 and Pd(II)−
C(0)−Pd(II)34 cores.43
future development of new multinuclear compounds that might
exhibit interesting physical properties and catalytic and
stoichiometric reactivities.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Tetranuclear
Cluster 3. The pincer-CDP framework can be readily
constructed from the successive double-cyclometalation re-
action of 1 with 0.5 equiv of [Me2Pt(μ-SMe2)]2 with the
concomitant release of 2 equiv of methane (Scheme 2).19
Scheme 2. Synthesis of Tetranuclear Cluster 3
As illustrated in Chart 1, we16,19,40h (L = SMe2, PMe3) and
others13 (L = CO) have reported the syntheses and
Chart 1. CCC Pincer CDP-Platinum Complexes
characterization of platinum(II) complexes bearing a dianionic
CCC pincer CDP ligand in which one of three phenyl groups
attached to each of the two CDP phosphorus atoms is
cyclometalated. Given the broad practical and fundamental
interest in this molecular architecture, we envisioned that the
cyclometalated pincer CDP-platinum platforms might be
efficient precursors for promising carbon(0)-containing cluster
systems. To date, cyclometalated platinum complexes have
received widespread attention because they exhibit remarkable
photophysical, photochemical, and biological properties, which
may have applications in light-emitting materials,44 photo-
catalysts,45 bioimaging probes,46 and anticancer drugs.45,47 In
particular, the pincer scaffold is now well recognized as an
extremely versatile ligand motif for developing catalysts and
materials.48−51 Furthermore, electron-rich cyclometalated
platinum(II) units are frequently employed as valuable building
blocks for multinuclear complexes. The d8 metals in a square-
planar geometry can be regarded as pseudo-closed-shell
systems, and weak metallophilic interactions52 have been invoked
in many multinuclear complexes containing various d8, d10, or
d10s2 (pseudo-) closed-shell systems.53,54 In addition, the
platinum complexes can behave as donors toward a second
metal center, forming a Pt→M dative bond55−57 through the
Pt{C[PPh2(o-C6H4)]2-κ3C,C,C}(SMe2) was then reacted with
PEt3 to yield 2 almost quantitatively. The 13C{1H} NMR
spectrum of 2 gives rise to six characteristic resonances for the
cyclometalated aromatic carbons over a 50 ppm range of
chemical shifts. The 31P{1H} NMR spectrum shows a triplet at
14.6 ppm and a doublet at 28.5 ppm, assignable to mutually
coupled PEt3 and CDP phosphorus, respectively. The signal for
PEt3 is flanked by a large 195Pt−31P coupling satellite with JPtP
=
3174 Hz, confirming the formation of a direct Pt−P bond,
whereas that for CDP displays a much smaller 195Pt satellite
1
with JPtP = 147 Hz. The H NMR spectrum is also consistent
with the structure for 2, which we confirmed by X-ray
crystallography (vide infra).
The reaction of 2 with an equimolar amount of AgOTf in
CH2Cl2 at ambient temperature resulted in a rapid color change
from yellow to red. After recrystallization, product 3 was
isolated as a yellow powder in high yield. In solution, 3
decomposed slowly in the light, forming a black precipitate,
suggesting that 3 is light sensitive. The NMR spectra of 3 show
somewhat broadened peaks, probably due to the instability of
the compound and/or dynamic processes that occur on the
NMR time scale; this broadening precluded the satisfactory
characterization of the product in solution. VT NMR
experiments of 3 in CD2Cl2 over the temperature range −70
to +30 °C did not show any remarkable change in the shape of
the broad signals, and we could not obtain any meaningful
information on the dynamic behavior of 3. The 31P{1H} NMR
resonance due to the CDP ligand shifted downfield (Δδ = 4.9
ppm), whereas that assignable to PEt3 slightly shifted upfield
(Δδ = 1.3 ppm), in comparison to the corresponding signals of
2. Each signal is flanked by a 195Pt satellite with JPtP = 71 Hz for
CDP and 3027 Hz for PEt3, which are both smaller than those
observed for 2. More importantly, the 13C{1H} NMR spectrum
58,59
2
occupied dz orbital on the platinum atom.
The electron-
donating ability of the platinum increases with increasing ligand
field strength afforded by the ancillary ligands around the
platinum center due to the enhancement of antibonding
2
character of the dz orbital. Consequently, the cyclometalated
system, which contains a strong M−C covalent bond, has
proved to be one of the most effective ligand motifs to
encourage the formation of Pt→M dative bonds.56
Here we report the synthesis and characterization of a novel
heterotetranuclear cluster complex having a sandwich structure
based on the pincer CDP−platinum platform. The resulting
PtII AgI2 tetranuclear core is highly labile and is readily
2
converted to two dinuclear components bearing a Pt(II)−
C(0)−Ag(I) triangular core after reaction with phosphines.
The present work provides further indications of the structural
diversity underlying the complexation behavior of the pincer
CDP complex with Lewis acids, serving as a foundation for
B
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contains several aromatic carbon signals, the observed pattern
of which is consistent with the presence of two inequivalent
phenyl groups on the CDP phosphorus in addition to the
cyclometalated phenyl groups. Since the two cyclometalated
P(Ph)2C6H4 fragments are equivalent, as indicated by the single
CDP signal in the 31P{1H} NMR spectrum, the observation of
two different environments of the phenyl groups strongly
suggests that the silver ion interacts with the platinum complex
from one side of the coordination plane, making the phenyl
groups above and below the plane inequivalent. However,
couplings from 107Ag and 109Ag nuclei were not visible in the
NMR spectra because of the line broadening.
The structure of the product was confirmed by single-crystal
X-ray diffraction. Precursor 2 was also structurally characterized
to allow for comparison with 3. Molecular diagrams of 2 and 3
are shown in Figures 1 and 2, respectively. Selected bond
distances and angles are summarized in Table 1, and full details
are provided in the Supporting Information.
Figure 2. Molecular diagram (50% probability ellipsoids) of 3 showing
the crystallographic labeling scheme. Atoms labeled with an asterisk
are generated by a crystallographic inversion center. All hydrogen
atoms, triflate anions, solvent, and minor disordered components of
PEt3 have been omitted for clarity.
model compounds suggest that this large distortion from
square-planar geometry is caused by the strong in-plane steric
repulsion between the PEt3 ligand and the protons on C18 and
C36 in the cyclometalated phenyl rings cis to the phosphine
(Supporting Information). The optimized geometry of Pt{C-
[PMe2(o-C6H4)]2-κ3C,C,C}(PEt3) is in good agreement with
the observed solid-state structure of 2, whereas that of
Pt{C[PMe2(C2H2)]2-κ3C,C,C}(PEt3), having a sterically less
demanding pincer framework, is planar at both the platinum
and carbon(0) atoms. Since the natural charges on the platinum
and carbon(0) atoms are similar in the two models, electronic
effects60 are unlikely to be responsible for the distortion. It is
reasonable to assume that the pyramidalization should lead to a
partial change in the hybridization of the carbon(0) atom from
sp2 to sp3, providing the second lone pair of carbon(0) with
enhanced donor abilities. The other structural parameters are
comparable to those in previously reported analogues.13,16,19
The complex 3 crystallizes as a dicationic Ag2Pt2 cluster with
−OTf anions and highly disordered ether molecules from the
solvent of crystallization. There are no close contacts between
the metal centers and the −OTf anions or the solvent
molecules. The cluster unit has an antiparallel sandwich
structure with a ladder-shaped PtC/AgAg/CPt core, resulting
from dimerization of 2 through two silver ions. The two halves
of 3 are related by a crystallographic inversion center bisecting
the Ag1−Ag1* bond, and the corresponding structural
parameters for the dinuclear subunits are thus crystallo-
graphically identical. The Pt1−Ag1*−C1* angle of
154.54(8)° deviates substantially from the idealized linear
Figure 1. Molecular diagram (50% probability ellipsoids) of 2 showing
the crystallographic labeling scheme. All hydrogen atoms and minor
disordered components of PEt3 have been omitted for clarity.
In complex 2, a highly distorted square planar coordination
geometry around the platinum(II) is observed, the doubly
cyclometalated CDP ligand adopts a pincer structure, and a
PEt3 ligand is trans to the carbon(0) atom in the CDP. Atom
P3 in PEt3 is located significantly out of the plane defined by
the platinum and three carbon atoms of the pincer CDP ligand
(C1, C19, and C37), although the location of the PEt3 ligand is
somewhat ambiguous because of disorder associated with the
different Et group orientations; the C1−Pt1−P3(P3A) bond is
significantly bent with an angle of 159−169°. In addition, the
cyclometalated phenyl rings are tilted away from the
coordination plane around the metal with torsion angles of
160−162° (C1−Pt1−C37−C36 and C1−Pt1−C19−C18).
The pincer framework is significantly warped, with the
otherwise planar carbon(0) center being pyramidalized, as
demonstrated by the sum of the angles around C1 of 351.16°.
Such a distortion cannot be observed for the analogous pincer
CDP−platinum complex having CO instead of PEt3; both the
platinum and CDP carbon atoms are almost planar.13
Preliminary DFT calculations (mPW1PW91, SDD for Pt, 6-
31+G(d) for C(0), and 6-31G(d) for all other atoms) on
C
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a
Table 1. Selected Bond Distances (Å) and Angles (deg) for 2−5
2
3
4
5a
5b
C1−P1, C1−P2
av C1−P
1.702(2), 1.692(2)
1.697
1.745(3), 1.752(3)
1.749
1.734(4), 1.739(4)
1.737
1.741(4), 1.745(4)
1.743
1.746(4), 1.742(4)
1.744
C1−Pt1
2.067(2)
2.128(3)
2.130(4)
2.105(3)
2.104(4)
C1−Ag1
Ag1−Pt1
2.195(3)
2.185(4)
2.224(4)
2.191(4)
b
2.7832(4), 3.1946(4)
2.8602(4)
111.02(18)
126.0(2)
2.8848(4)
112.14(17)
122.9(2)
2.8829(4)
109.88(18)
124.9(2)
P1−C1−Pt1
P2−C1−P1
P2−C1−Pt1
sum (around C1)
C1−Pt1−P3
Pt1−C1−Ag1
C1−Pt1−Ag1
C1−Ag1−P4
113.88(12)
106.10(15)
125.29(18)
108.60(15)
339.99
124.88(14)
112.40(13)
106.02(18)
343.0
110.73(18)
345.8
111.37(18)
346.2
351.16
c
159.03(9), 168.87(14)
165.86(8)
95.27(12)
167.98(10)
83.03(13)
49.31(10)
177.02(10)
174.19(10)
83.53(13)
49.99(10)
167.50(10)
173.25(11)
84.30(13)
49.13(10)
172.02(10)
d
92.70(8), 43.17(8)
a
b
c
d
Data for two inequivalent molecules 5a and 5b. Ag1*−Pt1. C1−Pt1−P3A for the minor disordered component in 2. C1−Pt1−Ag1*.
angle expected for two-coordinate Ag(I) complexes, and this
bending might result from weak intramolecular interactions
between Ag1* and Ag1 (vide infra) and from the coordination
of one of the cyclometalated phenyl rings to the silver atom, as
indicated by the short C19−Ag1* (2.533(3) Å) and C18−
Ag1* (2.675(3) Å) distances, which are significantly less than
the sum of the van der Waals radii (3.42 Å).61 Similar Ag−
C(aromatic) contacts have often been observed in related
adducts of silver and cyclometalated complexes.62 The
distances for Pt1−Ag1* (2.7832(4) Å) and Pt1−Ag1
(3.1946(4) Å) both fall within the range of Ag−Pt distances
found previously for related Ag2Pt2 clusters.63−73 The C1 atom
is located 3.582 Å away from Ag1*, and thus, there is no
discernible interaction between the two atoms. In contrast, the
C1−Ag1 distance of 2.195(3) Å is only slightly longer than
those found in [Ag{C(PPh3)2}2]Cl (2.115(8) and 2.134(7) Å),
where CDPs bind to the silver atom in a terminal mode.15 The
second metalation results in a higher degree of pyramidalization
at C1 with the sum of the angles at C1 being 339.99°,
associated with slight elongation of the Pt1−C1 (2.128(3) Å),
C1−P1 (1.745(3) Å), and C1−P2 (1.752(3) Å) bonds.
Frenking et al. have performed detailed theoretical and
experimental studies on Lewis acid adducts of CDPs. The P−
C bonds are significantly elongated as the number of
coordinated Lewis acids A increases (A = halogen cations,
H+, BH3, CO2, AuCl; R3P→C←PR3 < R3P→C(A1)←PR3 <
R3P→C(A1)(A2)←PR3).74 This elongation has been rational-
ized based on a reduced π-back-bonding interaction between
the central carbon lone-pair orbitals and the P−Cphenyl
antibonding orbitals, although π-orbital delocalization is
intrinsically small in CDPs. These structural changes around
the carbon(0) atom are likely to be responsible for the smaller
NMR coupling constants of JPPt and JPP in 3 in comparison to
those found in 2. The PEt3 ligand remains displaced out of the
platinum coordination plane (C1−Pt1−P3 = 165.86(8) Å)
because of the still severe in-plane steric congestion as in 2.
It is plausible that the reaction of 2 with AgOTf involves the
initial formation of a Pt−Ag dinuclear species that dimerizes to
give the tetranuclear cluster 3. Considering the fact that there is
previously reported for closely related Ag2Pt2 clusters,63−73
suggesting substantial Ag(I)−Ag(I) interactions. This counter-
intuitive attraction derives partially from argentophilic inter-
actions, which often result in the formation of polycationic
arrays of silver complexes.75 The dimerization ultimately
resulted in the parallel binding of pincer platinum units to
the Ag−Ag component through C(0)−Ag(I) and Pt(II)−Ag(I)
bonds, leading to a ladder core. To date, only a few examples of
heterodinuclear CDP complexes have been reported10,35 and,
to our knowledge, dimer 3 represents a unique example of a
heterotetranuclear cluster supported by bridging CDP ligands.
Reactions of 3 with Trivalent Phosphorus Ligands.
From a fundamental view, one of the most salient properties of
multinuclear systems that is advantageous for catalysis is the
facile generation of coordinatively unsaturated, highly active
species, which arise due to the lability of the metal−metal bond.
Accordingly, we investigated the reaction of 3 with trivalent
phosphorus donors to examine the lability of the tetranuclear
core that might lead to incorporation of extraneous substrates
(Scheme 3).
Scheme 3. Reactions of 3 with Trivalent Phosphorus Ligands
Complex 3 was treated with 2 equiv of PPh3 in CH2Cl2 at
ambient temperature, and the yellow color of the solution
immediately became paler. The 31P{1H} NMR spectrum of the
mixture has two phosphine signals at 12.9 and 17.6 ppm,
together with the CDP signal (32.5 ppm), showing character-
istic coupling patterns owing to JPP, JPPt, and JPAg. The signals
centered at 12.9 ppm appear as two doublets of triplets, one set
with J = 510 and 3 Hz and the other with J = 588 and 3 Hz.
−
no direct interaction between the cluster unit and OTf in 3,
the formation of 3 can be viewed because of attractive
interactions between the two cationic dinuclear units against
the charge repulsion. Notably, the Ag1−Ag1* separation of
2.7346(7) Å, which is less than the sum of the van der Waals
radii (3.44 Å),61 is relatively short in comparison to those
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The large couplings of 510 and 588 Hz are evidently due to
107Ag and 109Ag nuclei, respectively, indicating the formation of
a pair of isotopologues having a direct Ag−P bond. The small 3
Hz coupling is likely due to the to two CDP phosphorus atoms.
On the other hand, the signal at 17.6 ppm appears as a triplet of
doublets due to two CDP phosphorus atoms (8 Hz) and
107/109Ag (3 Hz). This signal also exhibits a prominent
195Pt−31P coupling satellite of 3462 Hz, indicative of a Pt−P
bond. The same product was obtained on starting from a
mixture of complex 2 and Ag(PPh3)OTf, thus allowing
confident assignment of the signal at 12.9 ppm for PPh3
attached to Ag and the other at 17.6 ppm for PEt3 attached
to Pt. The CDP signal at 32.5 ppm appears as an apparent
triplet of doublets arising from couplings to the phosphines and
107/109Ag. These observations strongly suggest the formation of
dinuclear complex 4, the structure of which was unambiguously
1
determined by X-ray diffraction analysis (vide infra). The H
and 13C{1H} NMR spectra are also compatible with the
formulation of 4.
Complex 3 also rapidly reacted with 2 equiv of P(OPh)3
under conditions similar to those employed for the reaction
with PPh3. Interestingly, however, the main product shows the
signal for the added P(OPh)3 at 97.8 ppm as a triplet (JPP = 12
Hz) flanked by a large 195Pt−31P coupling satellite with JPtP
=
5752 Hz in the 31P{1H} NMR spectrum. This large satellite
coupling confirms that the P(OPh)3 is directly bonded to the
platinum center. Instead, the signal for PEt3 at 11.1 ppm
appears as two doublets with large 107Ag−31P (JPAg = 517 Hz)
and 109Ag−31P (JPAg = 597 Hz) couplings, indicating that the
PEt3 is attached to the silver center. The observed coupling
pattern is consistent with the formulation of 5, where the PEt3
initially bound to the platinum center is replaced by added
P(OPh)3 and then recoordinated to the silver. The reaction
mixture contained small amounts of unidentified compounds,
but no signal assignable to a byproduct containing a Ag−
P(OPh)3 bond was observed.
Figure 3. Molecular diagram (50% probability ellipsoids) of 4 showing
the crystallographic labeling scheme. All hydrogen atoms, the triflate
anion, the solvent molecule, and minor disordered components of
PEt3 have been omitted for clarity.
The structures of 4 and 5 were confirmed by single-crystal X-
ray diffraction analyses, and the molecular diagrams are shown
in Figures 3 and 4, respectively. In the crystal of 4, the
asymmetric unit contains a cationic dinuclear unit of 4 and
−OTf together with a dichloromethane solvent molecule. The
dinuclear unit can be viewed as being composed of a half-
molecule of the tetranuclear cluster 3 and a PPh3 ligand
coordinated to the silver center. The platinum center exhibits a
heavily distorted square planar environment, the structural
parameters of which are comparable to those of 3. The C1−
Ag1 distance of 2.185(4) Å is also similar to that in 3, but the
geometry around the silver atom is essentially linear, with a
C1−Ag1−P4 angle of 177.02(10)°, and it appears that there is
no interaction between the silver atom and the cyclometalated
phenyl ring such as that as found in 3. The Pt1−Ag1 distance of
2.8602(4) Å in 4 is within the range of those observed in
related PtAg dinuclear complexes,64,70,72,76−85 suggesting the
presence of an intramolecular metal−metal interaction.
Correspondingly, the linear silver moiety is slightly tilted
toward the platinum atom, as indicated by the smaller angle of
Pt1−C1−Ag1 (83.03(13)°) in comparison to that in 3
(95.27(12)°), and this value is the smallest in the similar M−
C(0)−M′ frameworks (86.80(11)−98.44(11)°) reported pre-
viously for the related dinuclear CDP complexes.10,21,34,35
The crystal of 5 contains two crystallographically independ-
ent molecules together with a dichloromethane solvent
Figure 4. Molecular diagram (50% probability ellipsoids) of 5 showing
the crystallographic labeling scheme. One of the two crystallo-
graphically independent molecules in the asymmetric unit is shown.
All hydrogen atoms, the triflate anions, solvent molecules, and minor
disordered components of PEt3 have been omitted for clarity.
molecule in the asymmetric unit; one of the cationic dinuclear
units is shown in Figure 4. Complex 5 has structural features
similar to those seen for 4, except that the PEt3 ligand, which is
initially coordinated to platinum, is located on the silver atom
and the added P(OPh)3 ligand is bonded to the platinum atom
instead. The C1−Pt1−P3 angle of 173.7° (av) approaches
linearity, implying the alleviation of steric crowding around the
platinum center. The C1−Ag1−P4 angle of 169.8° (av)
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indicates that the PEt3 ligand is bent away from the P(OPh)3
ligand, probably because of steric repulsion between them.
Since the identity of 3 in solution is not yet known, a detailed
discussion of the mechanism must await additional inves-
tigation. To gain further insight into the origin of the different
reactivities of 3 against PPh3 and P(OPh)3, we investigated the
The intriguing molecular architecture of the present double-
cyclometalated CDP−platinum system might offer great
potential applications in metal cluster chemistry. Future studies
will focus on exploring catalytic applications as well as
examining photophysical characteristics of mixed-metal com-
plexes based on the cyclometalated pincer CDP platform.
EXPERIMENTAL SECTION
■
Scheme 4. Reactions of 2 with Trivalent Phosphorus Ligands
General Considerations. All manipulations were conducted
under an N2 atmosphere using standard Schlenk techniques. Unless
otherwise stated, all reagents were purchased from commercial
suppliers and used without further purification. Tetrahydrofuran,
diethyl ether, hexane, and toluene were distilled under an N2
atmosphere from sodium or sodium benzophenone ketyl. Dichloro-
methane was dried over P2O5 and distilled under N2. Pt{C[PPh2(o-
C6H4)]2-κ3C,C,C}(SMe2) was synthesized as previously reported.19
NMR spectra were recorded on a JEOL Lambda 300 spectrometer,
and chemical shifts are reported in ppm. 1H and 13C{1H} NMR
1
chemical shifts were referenced to tetramethylsilane using residual H
and 13C signals of the deuterated solvents as internal standards.
31P{1H} NMR chemical shifts were referenced to an external 85%
H3PO4 standard sample. Elemental analyses were performed on a
PerkinElmer 2400 Series II CHNS/O Elemental Analyzer.
reactions of 2 with the phosphorus ligands (Scheme 4). The
31P{1H} NMR studies revealed that complex 2 failed to react
with PPh3 but rapidly reacted with P(OPh)3, eliminating PEt3
from platinum to produce 6.86 This result strongly suggests that
the difference in reactivity of 3 with each phosphorus ligand
reflects the inherent reactivity of the pincer CDP−platinum
subunit. Generally, the electron-donating ability of trivalent
phosphorus ligands increases in the order P(OPh)3 < PPh3 <
PEt3, whereas the ligand size increases in the order P(OPh)3 <
PEt3 < PPh3.87 Therefore, one might reasonably anticipate that
the substitution reaction of PEt3 by less electron donating and
more sterically demanding PPh3 is unlikely to occur,
considering the crowded environment around platinum in 3
(vide supra). In contrast, this steric congestion would facilitate
PEt3 substitution by the less bulky phosphite P(OPh)3, despite
the weaker electron donating ability of P(OPh)3.
X-ray Crystal Structure Determinations. Single crystals of 2
were grown by slow evaporation from tetrahydrofuran, while those of
3−5 were obtained by slow diffusion of ether into dichloromethane
solutions. For X-ray measurement, each crystal was coated with an
inert oil, mounted on a MiTeGen polyimide MicroMount, and
transferred to a low-temperature nitrogen stream. Intensity data were
collected on a Bruker APEX-II Ultra CCD diffractometer using the
Apex2 software.88 The structures were solved using direct methods
and refined against F2 by full-matrix least-squares techniques using the
SHELX89 and Olex290 program packages. Non-hydrogen atoms other
than those in heavily disordered components were refined anisotropi-
cally. The disordered atoms were restrained and refined isotropically
with a set of restraints. Hydrogen atoms were placed in ideal positions
and refined isotropically as riding atoms. Molecular diagrams were
generated with the Mercury CSD 3.8 program.91,92 Further details of
the crystallographic works are available in the Supporting Information.
Synthesis of 2. To a toluene solution (40 mL) of Pt{C[PPh2(o-
C6H4)]2-κ3C,C,C}(SMe2) (3.52 g, 4.44 mmol) was added PEt3 (0.65
mL, 4.84 mmol) at ambient temperature, and the resulting mixture
was stirred for 1 h. The volatile compounds were then removed under
vacuum. The residue was washed twice with hexane (20 mL × 2) and
dried under vacuum to give 2 as a yellow powder. Yield: 3.72 g (99%).
1H NMR (δ, in C6D6): 0.98 (dt, JHP = 15.2 Hz, JHH = 7.6 Hz, 9H,
PCH2CH3), 1.90 (quint, JHH = JHP = 7.8 Hz, 6H, PCH2CH3), 6.82−
8.35 (m, 28H, PC6H5 and PC6H4). 13C{1H} NMR (δ, in C6D6): 9.4
(s, JCPt = 29 Hz, PCH2CH3), 18.7 (d, JCP = 29 Hz, JCPt = 29 Hz,
PCH2CH3), 121.4 (t, JCP = 7 Hz, PC6H4), 127.9 (d, JCP = 6 Hz,
PC6H5), 129.4 (s, PC6H4), 129.5 (t, JCP = 11 Hz, PC6H4), 130.1 (s,
PC6H5), 132.9 (t, JCP = 5 Hz, PC6H5), 135.4 (m, PC6H5), 142.4 (m,
PC6H4), 155.8 (m, PC6H4), 172.6 (m, PC6H4). 31P{1H} NMR (δ, in
C6D6): 14.6 (t, JPP = 8 Hz, JPPt = 3174 Hz, PEt3), 28.5 (d, JPP = 7 Hz,
JPPt = 147 Hz, PCP). Anal. Calcd for C43H43P3Pt: C, 60.92; H, 5.11.
Found: C, 60.97; H, 5.20.
CONCLUSIONS
■
In summary, we have demonstrated that the platinum complex
2 bearing a cyclometalated pincer CDP ligand serves as a
valuable building block for mixed-metal multinuclear com-
plexes. The platinum coordination plane in 2 is severely
distorted from planarity because of the in-plane steric
congestion. This distortion eventually leads to appreciable
pyramidalization at the carbon(0) atom in the pincer
framework and thus may enhance the donor ability of the
second lone pair on carbon. The reaction of 2 with AgOTf
affords the Pt2Ag2 tetranuclear cluster 3. The cluster exhibits an
antiparallel sandwich structure with two planar platinum units
connected by two silver ions, where the core array contains
Pt(II)←C(0)→Ag(I) dative bonds and Pt(II)−Ag(I) and
Ag(I)−Ag(I) metal−metal interactions, thereby forming a
three-rung ladder core.
Synthesis of 3. A solution of 2 (155 mg, 0.18 mmol) in
dichloromethane (7 mL) was added by cannula to a stirred solution of
AgOTf (48 mg, 0.19 mmol) in dichloromethane (3 mL) at ambient
temperature. The solution immediately changed from yellow to red.
After it was stirred for 1 h, the resulting mixture was filtered to remove
a black powder that had formed; then, all volatiles were removed
under vacuum. The remaining solid was recrystallized twice using
dichloromethane (2 mL) and diethyl ether (15 mL) and dried under
vacuum to give 3 as a yellow powder. Yield: 181 mg (90%). 1H NMR
(δ, in CD2Cl2): 0.64 (dt, JHH = 7.7 Hz, JHP = 16.0 Hz, 18H,
PCH2CH3), 1.67 (br, 12H, PCH2CH3), 6.91−7.84 (m, 56H, PC6H5
Cluster 3 proved to be highly reactive with donor ligands.
The reactions of 3 with PPh3 and with P(OPh)3 provide
dinuclear complexes 4 and 5, respectively, which have different
coordination patterns. The sterically demanding and less
electron donating PPh3 coordinates to the silver atom upon
the cleavage of the tetranuclear core, whereas the sterically less
demanding P(OPh)3 displaces the PEt3 ligand from the
platinum coordination plane to alleviate the steric congestion
around platinum.
and PC6H4). 13C{1H} NMR (δ, in CD2Cl2): 9.2 (d, JCP = 3 Hz, JCPt
=
19 Hz, PCH2CH3), 19.3 (d, JCP = 32 Hz, JCPt = 30 Hz, PCH2CH3),
F
DOI: 10.1021/acs.organomet.6b00700
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
121.3 (q, JCF = 322 Hz, CF3), 125.4 (br, PC6H5), 126.4 (br, PC6H4),
127.8 (br, PC6H5), 128.7 (br, PC6H5), 130.0 (br, PC6H5), 132.2 (br,
PC6H5), 132.8 (br, PC6H5), 133.9 (br, PC6H5), 140.8 (br, PC6H4),
153.0 (br, PC6H4), 156.2 (br, JCPt = 604 Hz, PC6H4). 31P{1H} NMR
(δ, in CD2Cl2): 13.3 (br, JPPt = 3027 Hz, PEt3), 33.4 (br, JPPt = 71 Hz,
PCP). Anal. Calcd for C88H86Ag2F6O6P6Pt2S2: C, 47.84; H, 3.92.
Found: C, 47.95; H, 3.93.
Synthesis of 4. To a stirred solution of 3 (131 mg, 0.059 mmol) in
dichloromethane (5 mL) was added a solution of PPh3 (31 mg, 0.12
mmol) in dichloromethane (5 mL) at ambient temperature. The
solution immediately faded to pale yellow. After 30 min of stirring, all
volatiles were removed under vacuum. The resulting solid was
recrystallized twice using dichloromethane (1 mL) and diethyl ether
(10 mL) and dried under vacuum to give 4 as a yellow powder. Yield:
115 mg (71%). Compound 4 was also obtained from the reaction of 2
(148 mg, 0.18 mmol) with Ag(PPh3)OTf (93 mg, 0.18 mmol) in 10
mL of dichloromethane and recrystallization using dichloromethane/
diethyl ether. Yield: 220 mg (92%). 1H NMR (δ, in CDCl3): 1.07 (dt,
Cartesian coordinates for calculated structures (XYZ)
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail for K.K.: kkubo@sci.hiroshima-u.ac.jp.
*E-mail for T.M.: mizuta@sci.hiroshima-u.ac.jp.
ORCID
Kazuyuki Kubo: 0000-0002-3889-5802
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by JSPS KAKENHI Grant Number
23550079. Elemental analyses were performed on a Perki-
nElmer 2400 Series II CHNS/O analyzer at the Natural
Science Center for Basic Research and Development (N-
BARD), Hiroshima University.
JHP = 16.3 Hz, JHH = 7.8 Hz, 9H, PCH2CH3), 2.13 (quint, JHP = JHH
=
7.8 Hz, 6H, PCH2CH3), 6.95−7.94 (m, 43H, AgPC6H5, C0PC6H5 and
PC6H4). 13C{1H} NMR (δ, in CDCl3): 9.3 (s, JCPt = 27 Hz,
PCH2CH3), 18.3 (d, JCP = 31 Hz, JCPt = 32 Hz, PCH2CH3), 121.1 (q,
JCF = 321 Hz, SCF3), 122.8 (t, JCP = 7 Hz, CPC6H4), 126.3 (dd, J = 8
Hz, J = 2 Hz, C0PC6H5), 127.3 (dd, J = 8 Hz, J = 2 Hz, C0PC6H5),
128.3 (t, JCP = 6 Hz, C0PC6H5), 129.1 (t, JCP = 6 Hz, C0PC6H5), 129.3
(d, J = 11 Hz, AgPC6H5), 130.8 (br, PC6H4), 131.3 (d, J = 2 Hz,
AgPC6H5), 131.4 (s, C0PC6H5), 132.3 (t, JCP = 5 Hz, C0PC6H5), 132.5
(t, JCP = 4 Hz, C0PC6H5), 132.7 (s, C0PC6H5), 133.4 (dd, J = 17 Hz, J
= 2 Hz, AgPC6H5), 141.8 (m, PC6H4), 152.1 (m, JCPt = 43 Hz,
PC6H4), 166.8 (m, JCPt = 648 Hz, PC6H4). 31P{1H} NMR (δ, in
REFERENCES
■
(1) For recent overviews on carbodiphosphoranes and related
carbon(0) chemistry, see: (a) Frenking, G.; Hermann, M.; Andrada, D.
M.; Holzmann, N. Chem. Soc. Rev. 2016, 45, 1129−1144. (b) Petz, W.
́
Coord. Chem. Rev. 2015, 291, 1−27. (c) Fliedel, C.; Schnee, G.; Aviles,
T.; Dagorne, S. Coord. Chem. Rev. 2014, 275, 63−86. (d) Frenking, G.;
Tonner, R.; Klein, S.; Takagi, N.; Shimizu, T.; Krapp, A.; Pandey, K.
K.; Parameswaran, P. Chem. Soc. Rev. 2014, 43, 5106−5139.
(e) Schmidbaur, H.; Schier, A. Angew. Chem., Int. Ed. 2013, 52,
176−186. (f) Alcarazo, M. Dalton Trans. 2011, 40, 1839−1845.
(g) Melaimi, M.; Soleilhavoup, M.; Bertrand, G. Angew. Chem., Int. Ed.
2010, 49, 8810−8849. (h) Patel, D. S.; Bharatam, P. V. Curr. Sci. 2010,
425−426. (i) Petz, W.; Frenking, G. Carbodiphosphoranes and
Related Ligands. In Transition Metal Complexes of Neutral η1-Carbon
Ligands; Chauvin, R., Canac, Y., Eds.; Springer: Berlin, Germany,
2010; Vol. 30, pp 49−92. (j) Dyker, C. A.; Bertrand, G. Nat. Chem.
2009, 1, 265−266. (k) Kaufhold, O.; Hahn, F. E. Angew. Chem., Int. Ed.
2008, 47, 4057−4061.
109
Ag
107
CDCl3): 12.9 (2 × dt, JP
= 588 Hz, JP
= 510 Hz, JPP = 3 Hz,
Ag
JPPt = 70 Hz, PPh3), 17.6 (td, JPP = 8 Hz, JPAg = 3 Hz, JPPt = 3462 Hz,
PEt3), 32.5 (td, JPP = JPAg = 8 Hz, JPP = 3 Hz, JPPt = 107 Hz, PCP).
Anal. Calcd for C62H58AgF3O3P4PtS: C, 54.47; H, 4.28. Found: C,
54.05; H, 4.28.
Synthesis of 5·CH2Cl2. To a stirred solution of 3 (128 mg, 0.058
mmol) in dichloromethane (5 mL) was added a solution of P(OPh)3
(0.045 mL, 0.17 mmol) in dichloromethane (5 mL) at ambient
temperature. The solution immediately faded to pale yellow. After 1 h
of stirring, all volatiles were removed under vacuum. The resulting
solid was recrystallized three times using dichloromethane (1 mL) and
diethyl ether (2 mL) and dried under vacuum to give 5 as a yellow
(2) Ramirez, F.; Desai, N. B.; Hansen, B.; McKelvie, N. J. Am. Chem.
Soc. 1961, 83, 3539−3540.
powder. Yield: 89 mg (51%). 1H NMR (δ, in CDCl3): 0.68 (dt, JHP
=
19.3 Hz, JHH = 7.7 Hz, 9H, PCH2CH3), 1.38 (quintd, JHP = JHH = 7.9
Hz, JHAg = 4.8 Hz, 6H, PCH2CH3), 6.99−8.48 (m, 43H, POC6H5,
PC6H5 and PC6H4). 13C{1H} NMR (δ, in CDCl3): 9.1 (dd, J = 4 Hz, J
= 2 Hz, PCH2CH3), 16.5 (dd, JCP = 22 Hz, JCAg = 5 Hz, PCH2CH3),
120.6 (d, JCP = 6 Hz, POC6H5), 121.0 (q, JCF = 321 Hz, SCF3), 123.6
(t, JCP = 7 Hz, PC6H4), 124.6 (s, POC6H5), 126.1 (d, J = 4 Hz,
PC6H5), 127.1 (d, J = 4 Hz, PC6H5), 128.4 (t, JCP = 6 Hz, PC6H5),
129.2 (t, JCP = 6 Hz, PC6H5), 129.5 (s, POC6H5), 131.2 (s, PC6H4),
131.4 (s, PC6H5), 132.1 (t, JCP = 5 Hz, PC6H5), 132.5 (t, JCP = 4 Hz,
PC6H5), 133.0 (s, PC6H5), 143.1 (m, PC6H4), 150.1 (m, JCPt = 50 Hz,
PC6H4), 151.1 (d, JCP = 7 Hz POC6H5), 163.9 (m, JCPt = 629 Hz,
(3) (a) Vincent, A. T.; Wheatley, P. J. J. Chem. Soc., Dalton Trans.
1972, 617−622. (b) Vincent, A. T.; Wheatley, P. J. J. Chem. Soc. D
1971, 582a−582a.
(4) El-Hellani, A.; Bour, C.; Gandon, V. Adv. Synth. Catal. 2011, 353,
1865−1870.
́
(5) Corberan, R.; Marrot, S.; Dellus, N.; Merceron-Saffon, N.; Kato,
T.; Peris, E.; Baceiredo, A. Organometallics 2009, 28, 326−330.
(6) Tonner, R.; Frenking, G. Chem. Commun. 2008, 1584−1586.
(7) Dobrovetsky, R.; Stephan, D. W. Angew. Chem., Int. Ed. 2013, 52,
2516−2519.
(8) Alcarazo, M.; Gomez, C.; Holle, S.; Goddard, R. Angew. Chem.,
Int. Ed. 2010, 49, 5788−5791.
109
PC6H4). 31P{1H} NMR (δ, in CDCl3): 11.1 (2 × d, JP Ag = 597 Hz,
107
JP Ag = 517 Hz, JPPt = 60 Hz, PEt3), 36.0 (t, JPP = JPAg = 9 Hz, JPPt
=
(9) Pranckevicius, C.; Iovan, D. A.; Stephan, D. W. Dalton Trans.
2016, 45, 16820−16825.
118 Hz, PCP), 97.8 (t, JPP = 12 Hz, JPPt = 5752 Hz, P(OPh)3). Anal.
Calcd for C62H58AgF3O6P4PtS•CH2Cl2: C, 50.44; H, 4.03. Found: C,
50.65; H, 3.62.
(10) Alcarazo, M.; Radkowski, K.; Mehler, G.; Goddard, R.; Furstner,
̈
A. Chem. Commun. 2013, 49, 3140−3142.
(11) Reitsamer, C.; Stallinger, S.; Schuh, W.; Kopacka, H.; Wurst, K.;
Obendorf, D.; Peringer, P. Dalton Trans. 2012, 41, 3503−3514.
(12) Petz, W.; Neumuller, B.; Klein, S.; Frenking, G. Organometallics
ASSOCIATED CONTENT
■
̈
S
* Supporting Information
2011, 30, 3330−3339.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00700.
(13) Petz, W.; Neumuller, B. Polyhedron 2011, 30, 1779−1784.
(14) Petz, W.; Neumuller, B. Eur. J. Inorg. Chem. 2011, 2011, 4889−
̈
̈
4895.
̈
(15) Petz, W.; Oxler, F.; Neumuller, B. J. Organomet. Chem. 2009,
̈
Summary of X-ray crystallographic data, NMR spectra for
2−5, and computational data (PDF)
Crystallographic data for 2−5 (CIF)
694, 4094−4099.
(16) Cavell, R. G. Pincer and chelate carbodiphosphorane complexes
of noble metals. In The Chemistry of Pincer Compounds; Morales-
G
DOI: 10.1021/acs.organomet.6b00700
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Morales, D., Jensen, C. M., Eds.; Elsevier: Amsterdam, The
Netherlands, 2007; Chapter 15, pp 347−355.
(43) For some related examples, see: (a) Morosaki, T.; Suzuki, T.;
Fujii, T. Organometallics 2016, 35, 2715−2721. (b) Morosaki, T.; Fujii,
T. Phosphorus, Sulfur Silicon Relat. Elem. 2016, 191, 159−162.
(c) Morosaki, T.; Wang, W.-W.; Nagase, S.; Fujii, T. Chem. - Eur. J.
2015, 21, 15405−15411. (d) Alcarazo, M.; Lehmann, C. W.; Anoop,
(17) Stallinger, S.; Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.;
Peringer, P. Chem. Commun. 2007, 510−512.
(18) Marrot, S.; Kato, T.; Gornitzka, H.; Baceiredo, A. Angew. Chem.,
Int. Ed. 2006, 45, 2598−2601.
A.; Thiel, W.; Furstner, A. Nat. Chem. 2009, 1, 295−301.
̈
(19) Kubo, K.; Jones, N. D.; Ferguson, M. J.; McDonald, R.; Cavell,
R. G. J. Am. Chem. Soc. 2005, 127, 5314−5315.
(44) For recent reviews, see: (a) Yam, V. W.-W.; Au, V. K.-M.;
Leung, S. Y.-L. Chem. Rev. 2015, 115, 7589−7728. (b) Huo, S.;
Carroll, J.; Vezzu, D. A. K. Asian J. Org. Chem. 2015, 4, 1210−1245.
(c) Yang, X.; Yao, C.; Zhou, G. Platinum Met. Rev. 2013, 57, 2−16.
(d) Kalinowski, J.; Fattori, V.; Cocchi, M.; Williams, J. A. G. Coord.
Chem. Rev. 2011, 255, 2401−2425. (e) Díez, l.; Lalinde, E.; Moreno,
M. T. Coord. Chem. Rev. 2011, 255, 2426−2447. (f) Chi, Y.; Chou, P.-
T. Chem. Soc. Rev. 2010, 39, 638−655.
(20) Petz, W.; Kutschera, C.; Neumuller, B. Organometallics 2005, 24,
̈
5038−5043.
(21) Vicente, J.; Singhal, A. R.; Jones, P. G. Organometallics 2002, 21,
5887−5900.
(22) Petz, W.; Weller, F.; Uddin, J.; Frenking, G. Organometallics
1999, 18, 619−626.
(23) Sundermeyer, J.; Weber, K.; Peters, K.; von Schnering, H. G.
Organometallics 1994, 13, 2560−2562.
(45) To, W.-P.; Zou, T.; Sun, R. W.-Y.; Che, C.-M. Philos. Trans. R.
Soc., A 2013, 371, 20120126.
(24) Schmidbaur, H.; Scherbaum, F.; Huber, B.; Muller, G. Angew.
̈
(46) For recent reviews, see: (a) Mauro, M.; Aliprandi, A.; Septiadi,
D.; Kehr, N. S.; Cola, L. D. Chem. Soc. Rev. 2014, 43, 4144−4166.
(b) Baggaley, E.; Weinstein, J. A.; Williams, J. A. G. Coord. Chem. Rev.
2012, 256, 1762−1785. (c) Lo, K. K.-W.; Choi, A. W.-T.; Law, W. H.-
T. Dalton Trans. 2012, 41, 6021−6047. (d) Thorp-Greenwood, F. L.
Organometallics 2012, 31, 5686−5692. (e) Zhao, Q.; Huang, C.; Li, F.
Chem. Soc. Rev. 2011, 40, 2508−2524.
(47) For recent reviews, see: (a) Omae, I. Coord. Chem. Rev. 2014,
280, 84−95. (b) Cutillas, N.; Yellol, G. S.; de Haro, C.; Vicente, C.;
Rodríguez, V.; Ruiz, J. Coord. Chem. Rev. 2013, 257, 2784−2797.
(48) The Privileged Pincer-Metal Platform: Coordination Chemistry &
Applications; van Koten, G., Gossage, R. A., Eds.; Springer: Cham,
Switzerland, 2016; Vol. 54.
Chem., Int. Ed. Engl. 1988, 27, 419−421.
(25) Endrich, K.; Alburquerque, P.; Korswagen, R. P.; Ziegler, M. L.
Z. Naturforsch., B: J. Chem. Sci. 1988, 43, 1293−1306.
(26) Bruce, A. E.; Gamble, A. S.; Tonker, T. L.; Templeton, J. L.
Organometallics 1987, 6, 1350−1352.
(27) Zybill, C.; Muller, G. Organometallics 1987, 6, 2489−2494.
̈
(28) Muller, G.; Kruger, C.; Zybill, C.; Schmidbauer, H. Acta
̈
̈
Crystallogr., Sect. C: Cryst. Struct. Commun. 1986, 42, 1141−1144.
(29) Schmidbaur, H.; Zybill, C. E.; Muller, G.; Kruger, C. Angew.
Chem., Int. Ed. Engl. 1983, 22, 729−730.
̈
̈
(30) Baldwin, J. C.; Kaska, W. C. Inorg. Chem. 1979, 18, 686−691.
(31) Kaska, W. C.; Mitchell, D. K.; Reichelderfer, R. F.; Korte, W. D.
J. Am. Chem. Soc. 1974, 96, 2847−2854.
(49) Pincer and Pincer-Type Complexes: Applications in Organic
(32) Kaska, W. C.; Reichelderfer, R. F. J. Organomet. Chem. 1974, 78,
C47−C50.
Synthesis and Catalysis; Szabo,
Weinheim, Germany, 2014.
́
K. J., Wendt, O. F., Eds.; Wiley-VCH:
(33) Kaska, W. C.; Mitchell, D. K.; Reichelderfer, R. F. J. Organomet.
Chem. 1973, 47, 391−402.
(50) Organometallic pincer chemistry; van Koten, G., Milstein, D. M.,
Eds.; Springer: Berlin, Germany, 2013; Vol. 40.
(51) The chemistry of pincer compounds; Morales-Morales, D., Jensen,
(34) Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.; Ellmerer, E.
P.; Peringer, P. Organometallics 2011, 30, 4220−4223.
(35) Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.; Peringer, P.
Organometallics 2009, 28, 6617−6620.
C. M., Eds.; Elsevier: Amsterdam, The Netherlands, 2007.
(52) Pyykko, P. Chem. Rev. 1997, 97, 597−636.
̈
(53) Doerrer, L. H. Dalton Trans. 2010, 39, 3543−3553.
(54) For some theoretical calculations on d8−d10 metallophilic
interactions see: (a) Pan, Q.-J.; Guo, Y.-R.; Zhang, H.-X. Organo-
metallics 2010, 29, 3261−3270. (b) Mendizabal, F. Int. J. Quantum
Chem. 2008, 108, 1164−1172. (c) Xia, B.-H.; Zhang, H.-X.; Jiao, Y.-Q.;
Pan, Q.-J.; Li, Z.-S.; Sun, C.-C. J. Chem. Phys. 2004, 120, 11487−
11492. (c) Xia, B.-H.; Zhang, H.-X.; Che, C.-M.; Leung, K.-H.;
Phillips, D. L.; Zhu, N.; Zhou, Z.-Y. J. Am. Chem. Soc. 2003, 125,
10362−10374.
(36) Kaska, W. C. Coord. Chem. Rev. 1983, 48, 1−58.
(37) Schmidbaur, H.; Costa, T.; Milewski-Mahrla, B. Chem. Ber.
1981, 114, 1428−1441.
(38) Schmidbaur, H.; Costa, T. Chem. Ber. 1981, 114, 3063−3069.
(39) Schmidbaur, H.; Gasser, O. Angew. Chem., Int. Ed. Engl. 1976,
15, 502−503.
(40) For selected reviews, see: (a) Gessner, V. H.; Becker, J.;
Feichtner, K.-S. Eur. J. Inorg. Chem. 2015, 2015, 1841−1859.
(b) Ephritikhine, M. C. R. Chim. 2013, 16, 391−405. (c) Liddle, S.
T.; Mills, D. P.; Wooles, A. J. Chem. Soc. Rev. 2011, 40, 2164−2176.
(d) Harder, S. Coord. Chem. Rev. 2011, 255, 1252−1267. (e) Panda, T.
K.; Roesky, P. W. Chem. Soc. Rev. 2009, 38, 2782−2804. (f) Cantat, T.;
(55) Bauer, J.; Braunschweig, H.; Dewhurst, R. D. Chem. Rev. 2012,
112, 4329−4346.
(56) Moret, M.-E. Organometallic Platinum(II) and Palladium(II)
Complexes as Donor Ligands for Lewis-Acidic d10 and s2 Centers. In
Higher Oxidation State Organopalladium and Platinum Chemistry;
Canty, A. J., Ed.; Springer: Berlin, Germany, 2011; Vol. 35, pp 157−
184.
́
Mezailles, N.; Auffrant, A.; Le Floch, P. Dalton Trans. 2008, 1957−
1972. (g) Cavell, R. G. Pincer, chelate and spirocyclic metal carbene
complexes from bis(iminophosphorano)methane ligands. In The
Chemistry of Pincer Compounds; Morales-Morales, D., Jensen, C. M.,
Eds.; Elsevier: Amsterdam, The Netherlands, 2007; Chapter 14, pp
311−346. (h) Jones, N. D.; Cavell, R. G. J. Organomet. Chem. 2005,
690, 5485−5496. (i) Cavell, R. G.; Kamalesh Babu, R. P.; Aparna, K. J.
Organomet. Chem. 2001, 617−618, 158−169. (j) Cavell, R. G. Curr.
Sci. 2000, 78, 440−451.
(57) Uson
(58) Aullon
́
, R.; Fornies
́
, J. Inorg. Chim. Acta 1992, 198-200, 165−177.
́
, G.; Alvarez, S. Inorg. Chem. 1996, 35, 3137−3144.
(59) Mealli, C.; Pichierri, F.; Randaccio, L.; Zangrando, E.; Krumm,
M.; Holtenrich, D.; Lippert, B. Inorg. Chem. 1995, 34, 3418−3424.
(60) Some electronic effects were noted on pyramidalization of a
methanediide carbon. See: (a) Gessner, V. H.; Meier, F.; Uhrich, D.;
Kaupp, M. Chem. - Eur. J. 2013, 19, 16729−16739. (b) Cantat, T.;
(41) Roberts, C. C.; Matías, D. M.; Goldfogel, M. J.; Meek, S. J. J.
Am. Chem. Soc. 2015, 137, 6488−6491.
(42) For recent reviews, see: (a) Buchwalter, P.; Rose,
́
J.; Braunstein,
́
Mezailles, N.; Ricard, L.; Jean, Y.; Le Floch, P. Angew. Chem., Int. Ed.
2004, 43, 6382−6385.
P. Chem. Rev. 2015, 115, 28−126. (b) Mata, J. A.; Hahn, F. E.; Peris, E.
Chem. Sci. 2014, 5, 1723−1732. (c) Bratko, I.; Gomez, M. Dalton
́
(61) Bondi, A. J. Phys. Chem. 1964, 68, 441−451.
(62) See the examples in ref 64 and references therein.
(63) Moussa, J.; Chamoreau, L. M.; Gullo, M. P.; Esposti, A. D.;
Barbieri, A.; Amouri, H. Dalton Trans. 2016, 45, 2906−2913.
Trans. 2013, 42, 10664−10681. (d) Park, J.; Hong, S. Chem. Soc. Rev.
2012, 41, 6931−6943. (e) Cooper, B. G.; Napoline, J. W.; Thomas, C.
M. Catal. Rev.: Sci. Eng. 2012, 54, 1−40. (f) Thomas, C. M. Comments
Inorg. Chem. 2011, 32, 14−38. (g) Ritleng, V.; Chetcuti, M. J. Chem.
Rev. 2007, 107, 797−858.
(64) Baya, M.; Belío, r.; Fornies
V. Inorg. Chim. Acta 2015, 424, 136−149.
́ ́
, J.; Martín, A.; Peralvarez, M.; Sicilia,
H
DOI: 10.1021/acs.organomet.6b00700
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
́ ́
(65) Fornies, J.; Sicilia, V.; Casas, J. M.; Martín, A.; Lopez, J. A.;
Larraz, C.; Borja, P.; Ovejero, C. Dalton Trans. 2011, 40, 2898−2912.
(66) Jamali, S.; Mazloomi, Z.; Nabavizadeh, S. M.; Dalibor, M.; Kia,
R.; Rashidi, M. Inorg. Chem. 2010, 49, 2721−2726.
(67) Moret, M.-E.; Chen, P. J. Am. Chem. Soc. 2009, 131, 5675−
5690.
(68) Chen, Y.-D.; Zhang, L.-Y.; Shi, L.-X.; Chen, Z.-N. Inorg. Chem.
2004, 43, 7493−7501.
(69) Vicente, J.; Chicote, M. T.; Huertas, S.; Bautista, D.; Jones, P.
G.; Fischer, A. K. Inorg. Chem. 2001, 40, 2051−2057.
́
(70) Fornies, J.; Martín, A.; Navarro, R.; Sicilia, V.; Villarroya, P.;
Orpen, A. G. J. Chem. Soc., Dalton Trans. 1998, 3721−3726.
(71) Fornies, J.; Martínez, F.; Navarro, R.; Urriolabeitia, E. P.
́
Organometallics 1996, 15, 1813−1819.
(72) Uson, R.; Fornies, J.; Menjon, B.; Cotton, F. A.; Falvello, L. R.;
Tomas, M. Inorg. Chem. 1985, 24, 4651−4656.
(73) Uson, R.; Fornies, J.; Tomas, M.; Cotton, F. A.; Falvello, L. R. J.
Am. Chem. Soc. 1984, 106, 2482−2483.
(74) Examples include: (a) Petz, W.; Kuzu, I.; Frenking, G.; Andrada,
D. M.; Neumuller, B.; Fritz, M.; Munzer, J. E. Chem. - Eur. J. 2016, 22,
̈
̈
8536−8546. (b) Takagi, N.; Tonner, R.; Frenking, G. Chem. - Eur. J.
2012, 18, 1772−1780. (c) Esterhuysen, C.; Frenking, G. Chem. - Eur. J.
̈
2011, 17, 9944−9956. (d) Petz, W.; Oxler, F.; Neumuller, B.; Tonner,
̈
R.; Frenking, G. Eur. J. Inorg. Chem. 2009, 2009, 4507−4517.
(e) Frenking, G.; Tonner, R. Pure Appl. Chem. 2009, 81, 597−614.
(f) Tonner, R.; Frenking, G. Chem. - Eur. J. 2008, 14, 3273−3289.
̈
(g) Tonner, R.; Oxler, F.; Neumuller, B.; Petz, W.; Frenking, G.
̈
Angew. Chem., Int. Ed. 2006, 45, 8038−8042.
(75) Schmidbaur, H.; Schier, A. Angew. Chem., Int. Ed. 2015, 54,
746−784.
(76) Martín, A.; Belío, r.; Fuertes, S.; Sicilia, V. Eur. J. Inorg. Chem.
2013, 2013, 2231−2247.
́ ́
(77) Fornies, J.; Ibanez, S.; Lalinde, E.; Martín, A.; Moreno, M. T.;
̃
Tsipis, A. C. Dalton Trans. 2012, 41, 3439−3451.
(78) Fornies, J.; Ibanez, S.; Martín, A.; Sanz, M.; Berenguer, J. R.;
Lalinde, E.; Torroba, J. Organometallics 2006, 25, 4331−4340.
(79) Uson, R.; Fornies, J.; Tomas, M.; Ara, I. Inorg. Chem. 1994, 33,
4023−4028.
́
́
̃
́
́
́
(80) Albinati, A.; Chaloupka, S.; Demartin, F.; Koetzle, T. F.;
Ruegger, H.; Venanzi, L. M.; Wolfer, M. K. J. Am. Chem. Soc. 1993,
115, 169−175.
(81) Uson
186, 67−71.
(82) Uson, R.; Fornies
́
, R.; Fornies
́
, J.; Tomas
́
, M.; Ara, I. Inorg. Chim. Acta 1991,
́
́
, J.; Tomas
́
, M.; Ara, I.; Casas, J. M.; Martín, A.
J. Chem. Soc., Dalton Trans. 1991, 2253−2264.
(83) Uson, R.; Fornies, J.; Tomas, M.; Ara, I.; Casas, J. M. Inorg.
Chem. 1989, 28, 2388−2392.
(84) (a) Cotton, F. A.; Falvello, L. R.; Uson
M.; Casas, J. M.; Ara, I. Inorg. Chem. 1987, 26, 1366−1370. (b) Uson
R.; Fornies, J.; Tomas
Am. Chem. Soc. 1985, 107, 2556−2557.
(85) Uson, R.; Fornies, J.; Tomas, M.; Casas, J. M.; Cotton, F. A.;
́
́
́
́
, R.; Fornies
́
, J.; Tomas
́
,
́
,
́
́
, M.; Casas, J. M.; Cotton, F. A.; Falvello, L. R. J.
́
́
́
Falvello, L. R. Inorg. Chem. 1986, 25, 4519−4525.
(86) 31P{1H} NMR spectrum (δ, in CH2Cl2) of 6: 33.8 (d, JPP = 9
Hz, JPPt = 176 Hz, PCP), 107.9 (t, JPP = 9 Hz, JPPt = 5143 Hz,
P(OPh)3).
(87) Tolman, C. A. Chem. Rev. 1977, 77, 313−348.
(88) Apex2, Version 2009.9-0; Bruker AXS Inc., Madison, WI, 2009.
(89) Sheldrick, G. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71,
3−8.
(90) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341.
(91) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.;
McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de
Streek, J.; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466−470.
(92) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Shields, G. P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl.
Crystallogr. 2006, 39, 453−457.
I
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