Mechanical vs Electronic Strain: Oval-Shaped Alkynyl-Pt(II)-Phosphine Macrocycles

Article abstract of DOI:10.1021/acs.organomet.9b00633

Pyridine-terminated molecular rods and either (i) the cis-(dppp)(I)Pt(CC-triptycene-CC)Pt(I)(dppp) rod or (ii) the trans-(PEt₃)₂(I)Pt(CC-biphenyl-CC)Pt(I)(PEt₃)₂ rod assemble into macrocycles, characterized by NMR, ESI-IMS, and in two cases also single-crystal X-ray diffraction. The former form rectangles with bidentate phosphine-containing cis-coordinated Pt(II)-alkyne corners. In the latter, the preference of the Pt centers for a trans configuration overrules the preference of the triple bonds for linearity and NMR shows that they have oval structures with alternating bent rod and bent trans (CC)Pt(PEt₃)₂(CC) components, in agreement with density functional theory calculations.

Full text of DOI:10.1021/acs.organomet.9b00633

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Mechanical vs Electronic Strain: Oval-Shaped Alkynyl-Pt(II)-
Phosphine Macrocycles
†,¶
§
Jan Plutnar,† Cecile Givelet,†,‡ Cyprien Lemouchi,†,‡ Jana Jaklova Dytrtova, Ivana Císarova,
́
́
̌
́
Simon J. Teat,∥ and Josef Michl*,†,‡
†
́
Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nam. 2, 16610 Prague 6, Czech
Republic
‡Department of Chemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
¶
́
́
Department of Physiology and Biochemistry, Faculty of Physical Education and Sport, Charles University, Jose Martıho 269/31,
162 52 Prague 6, Czech Republic
§Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 12843 Prague 2, Czech Republic
∥Advanced Light Source, Berkeley Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
S
* Supporting Information
ABSTRACT: Pyridine-terminated molecular rods and either (i) the cis-
(dppp)(I)Pt(CC-triptycene-CC)Pt(I)(dppp) rod or (ii) the trans-
(PEt3)2(I)Pt(CC-biphenyl-CC)Pt(I)(PEt3)2 rod assemble into macro-
cycles, characterized by NMR, ESI-IMS, and in two cases also single-crystal X-
ray diffraction. The former form rectangles with bidentate phosphine-
containing cis-coordinated Pt(II)-alkyne corners. In the latter, the preference
of the Pt centers for a trans configuration overrules the preference of the triple
bonds for linearity and NMR shows that they have oval structures with
alternating bent rod and bent trans (CC)Pt(PEt3)2(CC) components, in
agreement with density functional theory calculations.
Although the synthesis of the cis isomers of bis(phosphine)-
bis(alkynyl)Pt(II) complexes is more demanding than that of
the trans isomers, they too have been used for the formation of
macrocycles. The procedure requires a stepwise construction
and careful control of reaction conditions17,18 in order to
prevent the formation of multinuclear zigzag oligomers.19 In
addition to Sonogashira’s original procedure for the prepara-
tion of the cis complexes, an alternative consisting of a ligand-
INTRODUCTION
■
Organometallic platinum(II)-acetylide complexes have at-
tracted the attention of researchers for over 40 years. The
development of this area was accelerated by Sonogashira’s
discovery of a simple synthesis of bis(phosphine)bis(alkynyl)-
Pt(II) and bis(phosphine)(alkynyl)(halo)Pt(II) complexes
using a Cu(I) halide and secondary amine-based catalyst.1,2
Although the formation of both cis and trans isomers is
possible, depending on the temperature and solvent,1 in most
cases the trans isomer of the Pt(II) complex is formed
exclusively. The availability of these trans isomers makes them
the preferred building blocks in the construction of platinum-
(II)-based supramolecular structures. The almost linear
arrangement of the C−Pt−C environment requires the
introduction of a shape-forming structural unit to assemble a
cyclic compound. Most often, a clip-type acceptor is combined
with a linear donor, and the shape of the resulting macrocycle
is determined by the shape of the bridging ligand with
acetylide functionalities. This combination usually yields
rectangular3,4 and sometimes triangular5 complexes. The
bridging donors often are pyridines3−9 or carboxylates,10−13
but other ligands have also been used.14 The reverse approach,
a self-assembly of a linear acceptor with a clip-type donor, is
possible as well (Scheme 1).15,16
exchange reaction of
a preformed trans-bis-
(triphenylphosphine) complex with a bidentate phosphine
was developed, and several examples of its application were
reported.20,21
In order to make the use of the cis isomers in the self-
assembling reactions possible, the cis-bis(phosphine)(alkynyl)-
(halo)Pt(II) complex has to be prepared first. While this is
difficult to achieve for monodentate phosphines, complexes
containing 1,2-bis(dimethylphosphino)ethane (dmpe) and
1,3-bis(diphenylphosphino)propane (dppp) were synthesized
by oxidative addition of an alkynyliodonium salt to Me2Pt-
(dmpe) followed by reductive elimination of ethane22 or by
Sonogashira’s original procedure.1 Trigonal cage-shaped
trimetallic macrocycles were formed with 1,3,5-tris(4-
Received: September 19, 2019
© XXXX American Chemical Society
A
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Scheme 1. Building Blocks Used for the Preparation of Rectangular Macrocycles, with the Shape Dictated by an Organic (A)15
or an Organometallic Clip with (B) Trans3 or (C) Cis (This Work) Ligands on Pt
pyridylethynyl)benzene.23,24 The use of three-dimensional
macrocycles for the construction of longitudinal surface-
mounted molecular rotors25 is our long-term interest, and it
generally requires the participation of a more than bidentate
donor.
macrocycles actually have a rather unusual oval structure
containing trans (CC)2Pt(PEt3)2 centers, with the P atoms
above and below the ring.
RESULTS
■
In an effort to improve the control of the synthesis of sturdy
structures via self-assembly, we briefly communicated an
extension of the reverse formation of covalent macrocycles to
a two-step process.16 First, pyridine-terminated rods were
reversibly self-assembled with binuclear Pt-terminated rods to
charged supramolecular macrocycles via dative N→Pt+ bonds.
Second, covalent stabilization under preservation of topology
was achieved by replacement of the pyridine-terminated rods
with 4,4′-diethynylbiphenyl rods, in which the labile dative
N→Pt+ bonds are converted to sturdy uncharged covalent C−
Pt bonds. The two-step procedure combines the facility and
high yield of a self-correcting reversible assembly with the
robustness of covalent synthesis. At the time, we took it for
granted that the resulting covalent macrocycles had to contain
cis (CC)2Pt(PEt3)2 centers and had a rectangular shape with
the P atoms in the plane of the ring, since the trans
arrangement of the alkynes at the Pt atoms would be too
strained. Prompted by results of density functional theory
(DFT) calculations, we realized more recently that in this case
the preference of the Pt centers for a trans configuration
overrules the resistance of triple bonds to bending and that the
Cis Dialkynyl-Pt(II)-Diphosphine Macrocycles and
Their Datively Bonded Precursors. The diphosphine ligand
forces a cis arrangement at the Pt atom and dictates the nature
of the self-assembled structures.
Rods. We prepared two Pt-terminated rods for the self-
assembly and characterized both by single-crystal X-ray
diffraction. The first rod is the already known24 triptycene-
9,10-diethynylbis{cis-[bis(diphenylphosphino)propane]-
iodoplatinum(II)} (1, Chart 1), obtained in a mediocre yield
by treatment of a 4-fold stoichiometric excess of cis-
[bis(diphenylphosphino)propane]platinum(II) diiodide (cis-
(dppp)PtI2, 3) with 9,10-diethynyltriptycene (2) under
Sonogashira1 coupling conditions. Before self-assembly, the
Pt centers were activated by replacement of the iodide with the
nitrate anion or with pyridine.
A similar reaction of 2,5-bis(trimethylsilyl)-1,4-diethynyl-
benzene (4) with 3 produced a low yield of the other rod, 2,5-
bis(trimethylsilyl)phenyl-1,4-diethynylbis{cis-[bis-
(diphenylphosphino)propane]platinum(II)} (5).
The rod 1 crystallizes in monoclinic space groups P21/n (1a,
from CH2Cl2) and P21/c (1b, from CH2Cl2/THF). Two rod
B
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Chart 1. Structures of Reagents and Products
molecules together with two highly disordered molecules of
methylene chloride per structural unit are present in 1a, and
one rod molecule is present in 1b (Figures S71−S73 in the
Supporting Information). The Pt atom is in a nearly perfect
square-planar environment. The main difference in rod
structure between 1a and 1b is the I−Pt−Pt−I torsion
angle: −78.28 and 133.81° in the former and 109.15° in the
latter.
The rod 5 crystallizes in triclinic space group P1 with one
rod molecule and two distorted DMF molecules per structural
unit (Figure S74 in the Supporting Information). As in 1, the
Pt atom is in a nearly ideal square-planar environment. The
C
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a
Scheme 2. Reaction Pathways from 1 to 13
a
Nitrate anions are not shown.
a
Scheme 3. Formation of Oligomers from 5
a
Nitrate anions are not shown.
center of the rod resides at an inversion center, and the I−Pt−
Pt−I torsional angle is 180°. The van der Waals radii packing
image reveals close contacts between the TMS groups and the
phenyl groups of the dppp ligands.
D
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Figure 1. 31P NMR spectrum of 9. 195Pt satellites are marked with arrows.
Datively Bonded Rectangles. A replacement of the iodide
anion in the rod 1 with nitrate followed by reaction with
bis(4′-pyridyl)acetylene (6) or bis(4′-pyridyl)butadiyne (7)
resulted in the formation of charged rectangles 8 and 9
(Scheme 2). Analogous reactions of the rod 5 with 6 or 7
always yielded a linear polymer, and no rectangles were
detected or isolated (Scheme 3).
m/z 1781.2. No fragments with charge higher than 4+ were
observed. In all cases the isotopic pattern envelopes
corresponded to the shapes expected for the postulated
elemental composition and the peak separation fitted the
calculated charge of the fragment (Figures S64−S67 in the
Supporting Information).
The smaller rectangle 8 exhibits spectroscopic patterns very
The structure of the rectangular complexes 8 and 9 was
deduced from an examination of their NMR and mass spectra.
The rectangle 9 exhibits a set of two P−P doublets (2JP−P = 28
Hz) in the solution 31P NMR spectrum, accompanied by two
sets of 195Pt satellites. The Pt−P coupling constants were used
as a diagnostic tool for evaluation of the coordination
environment of the platinum(II) center.26 The signal at
similar to those of 9. Two P−P doublets are present in the 31
P
2
NMR spectrum at −10.65 (1JPt−P = 3152 Hz, JP−P = 28 Hz)
2
and −0.63 ppm (1JPt−P = 2218 Hz, JP−P = 28 Hz). The
patterns of the dppp signals in the 1H and 13C NMR spectra of
the complex are affected by the lowered symmetry of their
close environment similarly as in 9. HR ESI-IMS results show
four major peak envelopes corresponding to the tetracation 8
and to the dication of half of the molecule (m/z 847.7), a
dinuclear fragment with two ligands 6 (dication, m/z 937.7),
1
−10.64 ppm has two satellites with JPt−P = 3142 Hz,
indicating the presence of a P atom trans to the pyridyl
1
−
ligand. The JPt−P = 2210 Hz value of the signal located at
an ion pair of NO3 with a tetranuclear fragment with one
−
−0.54 ppm corresponds to a P atom trans to the alkyne
ligand 6 missing (trication, m/z 1090.9), and an 8−NO3 ion
1
(Figure 1). The H and 13C NMR signals of the dppp ligand
pair (trication, m/z 1150.9). As with 9, no higher charge
signals were detected, nor were there any signals above m/z
1200 (Figures S58−S62 in the Supporting Information).
Encouraged by the success with rod 1, and in analogy to the
conversion of 1,3,5-tris(4-pyridylethynyl)benzene to a hex-
anuclear prismatic complex,24 we attempted to prepare a three-
dimensional block-shaped octanuclear complex by treating
5,10,15,20-tetrakis(4-pyridyl)-21H,23H-porphyrin with 1 in a
1:2 ratio. However, instead of the expected octanuclear
complex, the remarkable tetranuclear planar complex 11 was
isolated.
are split into two sets due to the decreased symmetry in the
complex. A combination of H−31P and H−13C correlation
experiments allowed us to assign all the signals in the proton
and carbon spectra to the structure (Figures S29−S32 in the
Supporting Information). The assigned cyclic structure follows
from the absence of any 1H NMR signal that could be assigned
1
1
to a noncoordinated terminus of 7 and the absence of any 31
P
NMR signal attributable to an environment found in the
starting nitrato version of 1.24
However, any larger macrocycle formed from the same
components would exhibit the same NMR spectra. To
determine the actual size of the molecule, we used electrospray
ionization/ion mobility spectrometry (ESI-IMS). The mass
spectrum contains six major peak envelopes. The most intense
signal at m/z 1166.8 corresponds to an ion pair of the
1
The H NMR spectrum of this product did not have the
expected symmetry. The signals of the pyrrole protons were
split into two peaks of equal intensity, and one of them was
shifted far upfield, from 8.45 to 5.84 ppm. The resonances of
the triptycene protons were split into four multiplets with
relative intensities 2:2:1:1 instead of the expected two sets of
multiplets of equal intensity. A comparison of the solid-state
structure of the starting rod 1 with that of tetrapyridylporphyr-
in27 revealed a similarity between its Pt−Pt separation (11.97
−
tetracation 9 and NO3 . The free tetracation 9 is located at
m/z 859.5, together with a dication of a fragment that
corresponds to half of the molecule. An additional peak
corresponding to the nitrato dication ion pair was found at
E
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Å) and the lateral N−N distance between two pyridyl groups
in the porphine (10.93 Å). This suggested that the unusual
NMR shifts and splittings observed in 11 could be explained
by a tetranuclear complex structure in which two units of 1 are
coordinated laterally to the porphyrin. The shielding of the
pyrrole protons by two benzene rings of a nearby triptycene
8 and 9. A pair of P−P doublets (2JP−P = 28 Hz) with
resonances at −12.79 (1JPt−P = 3132 Hz) and −0.25 ppm
(1JPt−P = 2207 Hz) is assigned to P atoms trans to the pyridine
1
and trans to the alkynyl, respectively. The H and 13C NMR
spectra exhibit signal patterns due to the unsymmetrical dppp
ligand similar to those of 8 and 9.
1
would then cause the observed upfield shift of their H NMR
There are two major peak envelopes in the ESI mass
spectrum of 14. They correspond to the molecular dication at
m/z 836.7 and to the ion pair of nitrate with a molecular
fragment without one pyridine ligand at m/z 1656.4. The
isotopic pattern and the peak separations correspond to the
calculated composition and charge of the fragments.
resonance. The proximity of the triptycene to the porphyrin
would also block the free rotation of the former about its 3-fold
1
saxis and lead to the observed splitting of its signals in the H
NMR spectrum.
Ultimately, a single-crystal X-ray diffraction study of 11 on a
synchrotron confirmed the correctness of these arguments (see
Figure 2 for an ORTEP image of the structure). The very small
The poor solubility of 13 slightly hinders its characterization
by NMR. Nevertheless, the results of the NMR analysis
confirm the expected structure. An absolute assignment of the
signals is not possible, because some are overlapped by solvent
signals (especially some signals of phenyl rings and CH2
groups of the dppp ligand). There are two resonances in the
31P NMR spectrum of the complex (−5.77 and −5.75 ppm,
1JPt−P ≈ 2200 Hz), but no P−P splitting is observed due to the
close position and overlap of the signals in the spectrum. Also,
the 1H and 13C NMR spectra reveal the overall symmetrization
of the platinum coordination centers relative to the charged
macrocycles 8 and 9 or the rod 14 (Supporting Information).
Crystals of 13 belong to the triclinic space group P1. The
center of the rectangle is located at the inversion center,
leaving almost 38% of the cell unit void. The cavity is filled
with several very disordered molecules of the DMF solvent.
The Pt corners of the rectangle are in a nearly ideal square-
planar arrangement and are slightly twisted, with the Pt−C
C− bonds to triptycenes bent out of the rectangle and the Pt−
CC− bonds to the biphenyls bent into the rectangle (Figure
3).
Figure 2. ORTEP drawing of 11 with 30% thermal probability
ellipsoids (yellow, Pt; red, P; blue, N; black, C). Hydrogen atoms,
solvent molecules (DMF), and atom labels are omitted for clarity.
single crystals available belonged to the monoclinic space
group P21/n. The structural unit contains two molecules of 11,
eight molecules of DMF, and four molecules of water, all of
them distorted. The coordination environment of platinum is
slightly distorted in order to fit the demands of the porphine
ligand. The C−Pt−N angle of ∼83° contrasts with the ∼89°
C−Pt−I angle in the structure of 1. The position of the Pt
corner deviates significantly from the triptycene 3-fold axis, and
the CC−Pt angle is only ∼165°. The pyridyl groups of the
porphine ligand are slightly tilted from their positions in the
free molecule, with a C−C−N angle of ∼173° (see the
Supporting Information).
Covalent Rectangles. Covalent stabilization of complexes 8
and 9 by treatment with 4,4′-diethynylbiphenyl (12) in a 1:2
stoichiometric ratio under Sonogashira coupling conditions
proceeded smoothly, and the covalent rectangle 13 was
obtained in excellent yields. However, the intermediacy of
the charged rectangle 8 or 9 is not necessary for the efficient
conversion of 1 to 13. Starting with the double nitrate of 1 and
1 equiv of 12, we also obtained very good yields of 13 (Scheme
2).
It is equally possible to activate 1 for the synthesis of 13 by
converting it to the double pyridine rod 14, prepared similarly
to 8 and 9 using pyridine instead of 6 or 7. This rod has a
diagnostic pattern in its 31P NMR spectrum similar to those of
Figure 3. ORTEP drawing of 13 with 30% thermal probability
ellipsoids (yellow, Pt; red, P; black, C). Hydrogen atoms, solvent
molecules (DMF), and atom labels are omitted for clarity.
Trans Dialkynyl-Pt(II)-Bismonophosphine Macro-
cycles and Their Datively Bonded Precursors. An earlier
brief communication16 on the “covalent stabilization” process
focused on the use of several pyridine-terminated rods as
macrocycle-forming linkers (Scheme 4) and did not deal with
the configuration at the Pt atoms. Only the Supporting
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new signals in the product. In 16b, the signal at 7.92 ppm
belongs to the β protons (Hβ′′) of the doubly coordinated 6,
that at 7.84 ppm (Hβ′) belongs to the coordinated pyridyl and
that at 7.46 ppm (Hβ) to the uncoordinated pyridyl of singly
coordinated 6 (Figure 4). The intensity ratio of the Hβ′′ to Hβ′
(or similarly of the Hβ′′ to Hβ) signals establishes the ratio of
these two kinds of 6, and thus the degree of oligomerization.
For 16b, the ratio was close to 3:1. Thus, on average, the
oligomer contains four Pt−Pt units joined through three
ligands 6 and is terminated with two additional molecules of 6.
DOSY was used to check that no free 6 was present. For 16a,
the ratio was 1:1 (two Pt−Pt units and three ligands 6 on
average), and for 16c, it was 4:1 (five Pt−Pt units and six
ligands 6 on average).
Scheme 4. Formation of Complex 17
These oligomers were subsequently used in the “covalent
stabilization” step, and the previously reported products16 were
obtained. Like that of 15, the 31P NMR spectrum of 17 is
compatible with the presence of Pt atoms carrying two
phosphines in trans positions (1JPt−P = 2360 Hz) and 1H NMR
spectra contain only one set of signals of 12. Terminal
acetylene signals are absent, showing that the product is cyclic.
Previous size exclusion chromatography results16 and obser-
vations of the solubility of model compounds, together with
the HRMS results,16 suggest that the ring contains four Pt
atoms.
Information reflected our automatic belief that the cis isomers
are formed initially and isolated at the end, since the trans
isomers would be too strained. This suggested that oddities in
the number of 31P NMR signals and values of the 195Pt−31P
coupling constants could be due to ligand exchange processes.
We have now taken a closer look, reproduced the syntheses,
prepared a set of model compounds, performed a series of
density functional theory (DFT) calculations,28 and realized
that the automatic belief was incorrect. Isomers containing
some cis Pt centers may be formed initially, but the isolated
macrocycles have a trans configuration at the Pt atoms and an
unusual oval shape.
DISCUSSION
■
Four issues require comment.
(i) The acceptor building blocks 1 and 5 both appear to be
perfectly capable of producing covalent rectangular macro-
cycles in analogy to the prior synthesis of prismatic
macrocycles built from a triptycene-containing rod.24 Yet,
while 1 produces macrocycles readily (Scheme 2), all attempts
to form cycles with 5 yielded only linear oligomers or a
polymer and no rectangles were isolated or detected (Scheme
2). In both cases, a syn attachment of new ligands on the Pt
atoms appears necessary and sterically possible. We propose
that the difference has to do with a difference in the ease with
which the Pt termini rotate about the Pt−Pt axis to the syn
conformation.
The large range of I−Pt−Pt−I dihedral angle values in X-ray
diffraction crystal structures of 1 (Supporting Information)
suggests that the triptycene bridge has no unfavorable steric
interactions with the ligands on platinum. The nearly free
rotation of the PtII(dppp) moiety about the Pt−Pt axis then
allows the desirable syn conformation to be reached easily and
facilitates the macrocyclic ring closure.
The reinterpretation of the NMR data for compounds 15
and 16a−c in Scheme 4 as due to the trans isomers is
straightforward and involves no irregularities. The single 31P
1
NMR signal of 15 with JPt−P ≈ 2300 Hz is perfectly
compatible with the trans structure,26 and the data are also
nicely compatible with originally unavailable results for a
structure secured by single-crystal X-ray diffraction.15
With this result in mind, the formation of the rectangular
complexes 16 is improbable. A detailed examination of the
products of the reaction of the nitrato complex 15 with the
pyridine-terminated linkers by 1H NMR (COSY, NOESY,
DOSY) showed that macrocycles are not formed (Scheme 4).
The results for 16a−c were similar. Upon coordination to
platinum, the signals of the α and β pyridyl protons in 6 move
downfield from their initial values (8.65 and 7.43 ppm,
respectively). Instead of the single signal for each expected in
the macrocycle, the α and β pyridyl protons of 6 appear as six
The situation is different in 5, where the trimethylsilyl
groups carried by the rod would interfere with the
diphenylphosphinyl moiety of the dppp ligand during an
attempted rotation of the PtII(dppp) moiety about the Pt−Pt
axis. The anti geometry observed in the crystal structure is
apparently favored but is not conducive to macrocycle
Figure 4. Proton assignment in 16.
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Scheme 5. Mechanism Suggested for Formation of 17 via Several Intermediates Containing Trigonal-Bipyramidal Pt
a
Coordination Centers
a
The bond angles in C and D are exaggerated, and in reality the Pt−C−C bond angle may deviate by up to 10° from linearity (cf. the structures of
complexes 1, 5, 11, and 13).
formation, and the syn geometry is not being reached fast
enough during the coupling process.
activation with AgNO3, however, the yield is lower. It is
possible that, under the reaction conditions used, the self-
assembly is reversible and the reaction actually is under
thermodynamic control.
(ii) The unexpected isolation of the unusual tetranuclear
planar complex 11 is presumably enabled by the compatible
structural parameters of the porphine and the dinuclear rod
and reveals how easily the alkyne moiety bends to
accommodate structural requirements elsewhere. In 11, the
normally facile rotation of triptycene about its 3-fold axis
appears to be suppressed entirely.
(iii) Given the essentially free rotation of the cis Pt centers
about the rod axis in 1, it is intuitively understandable that the
self-assembly of 1 with 6 or 7 is able to produce charged
rectangles 8 and 9, while the combination of 1 or 14 with 12
produces the neutral rectangle 13 (Scheme 2). We have
suggested above that a barrier to such rotation in 5 provides an
explanation for the exclusive formation of linear oligomers
from 5 and 6 or 7 (Scheme 2).
The self-assembly of 15 with 6 or 7 yields exclusively the
linear oligomers 16 (Scheme 4), and this is perhaps not
surprising considering that the trans form on Pt is more stable
than the cis form and the concentration of 6 or 7 is fairly high.
In contrast, the self-assembly of 12 with 14 or activated 1
furnishes the macrocycle 13 (Scheme 2), but in this case the
necessary cis geometry at Pt is enforced by the diphosphine
ligand and high dilution is used. The charged macrocycles are
formed more reluctantly than the electroneutral species. It is
also possible that the electrostatic repulsion of positive charges,
only partially compensated by counterions, destabilizes the
cyclic form.
(iv) The covalent tetranuclear rectangle 13, in which a cis
geometry is secured by the use of a diphosphine, is accessible
in the same good to excellent yields from the reaction of 12
with 1, as long as the latter is activated with AgNO3. The
reaction can be performed either directly or via 8, 9, or 14
(Scheme 2). We conclude that a preformation of a rectangle
with a pyridine-terminated ligand16 is not necessary for the
successful formation of the covalent rectangle. Without
The configuration of the macrocyclic product is different
when two monophosphines are present on each Pt atom
instead and the cis geometry is thus not enforced (Scheme 4).
The initial activation by placement of pyridine residues on the
Pt atoms produces a linear and not a macrocyclic product
when doubly pyridine-terminated rods are used, and yet, after
covalent stabilization, the macrocyclic covalent product 17 is
formed in the end. However, as judged by NMR spectra,
instead of a rectangle with four cis ligated Pt atoms, an
intriguing oval with four trans-ligated Pt atoms is formed, and
DFT calculations28 agree that the all-trans configuration is
much more stable than the originally expected all-cis form. It is
unfortunate that all our attempts to grow a suitable single
crystal for diffraction analysis have failed.
The mechanism of the macrocyclization that yields 17 is
presently not known, and we hesitate to speculate about it
excessively. It seems unlikely that the reactive ends of a linear
oligomer with all-trans-ligated Pt atoms would find each other
to form a cycle, and it is more probable that the coupling
process proceeds by an associative mechanism that enables
cyclization in a temporary structure that contains trigonal-
bipyramidal Pt atoms and places the reactive ends of the
oligomer much closer to each other. Scheme 5 depicts a
possible cyclization pathway involving several trigonal-bipyr-
amidal intermediates. A lifetime of the intermediate A has to
be sufficiently long either to react with another molecule of
complex 16 to form the intermediate B, with both metal
centers remaining trigonal bipyramidal, or to react with
another molecule of A to form the intermediate C. The
presence of a Cu(I) salt in the reaction mixture could be
beneficial in that an interaction of Cu(I) with the π electrons
of both alkynes could extend the lifetime of intermediates such
as B and C.29 We presume that the presence of two alkynes in
H
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NMR spectra were recorded with Bruker AVANCE III
spectrometers operating at 300, 400, 500, and 600 MHz at room
temperature (25 °C) unless stated otherwise. 1H and 13C spectra were
referenced to residual solvent peaks.
Crystals for structure determination by X-ray diffraction were
prepared as follows. Single crystals of 1 were grown from a methylene
chloride solution either by vapor diffusion of THF into it (1b) or by
slow solvent evaporation (1a), those of 5 were grown upon slow
cooling of a warm solution in DMF-d7, those of 11 were grown from
its saturated DMF solution by hexane vapor diffusion, and those of 13
grew from a DMF solution upon standing.
these intermediates is crucial for the stabilization. A
subsequent cyclization reaction between two ends of complex
C then leads to D, and reversion of the Pt atoms to a square-
planar geometry yields 17, which precipitates from the
solution. The all-trans configuration is not formed until after
the macrocycle has been closed. Regardless of the mechanism
of formation, the structure of the all-trans macrocycle is
intriguing.
The competition between suffering mechanical strain by
bending structural elements such as triple bonds that would
prefer to remain linear and suffering electronic strain by
placing phosphine ligands into a cis configuration is clearly
won by the latter, and both the calculated and observed
preferences are for the all-trans and not the all-cis macrocycle.
The situation is discussed further in a separate article on the
basis of DFT calculations.28
Crystallographic data for all of the complexes except 11 were
collected on a Nonius KappaCCD diffractometer equipped with a
Bruker APEX-II CCD detector by monochromated Mo Kα radiation
(λ = 0.71073 Å) at a temperature of 150(2) K. The structures were
solved by direct methods (SHELXT)35 and refined by full-matrix least
squares based on F2 (SHELXL98).36 The hydrogen atoms were
calculated into idealized positions and were refined as fixed (riding
model) with assigned temperature factors Uiso(H) = 1.2Ueq (pivot
atom) or 1.5Ueq (methyl groups). It was necessary to remove the
contribution of the disordered solvent molecules to the diffraction
pattern during the refinement of structures 1a, b and 13 using the
PLATON/SQUEEZE37 procedure. For the structures 1a and 13, also
constraints on displacement parameters of all the carbon atoms were
applied. However, the poor quality of the crystal of 1a still affects the
precision of the final structure and the structure thus does not pass the
evaluation procedure without serious alerts. The respective .cif file can
be found in the Accession Codes paragraph at the end of the paper.
Crystallographic data for 11 were collected on a Bruker D8
diffractometer equipped with a PHOTON100 CMOS detector and
Oxford Cryosystems Cryostream 700 plus, on Beamline 11.3.1 of the
Advanced Light Source at Lawrence Berkeley National Laboratory. A
sphere of data was collected at 100 K using Bruker APEX38 software
in shutterless mode with ω rotations at fixed Φ values at λ = 0.7749 Å,
from a channel cut silicon [111] monochromator. The intensity data
were integrated and correction was applied with SAINT v8.38a;39
absorption and other corrections were made using SADABS 2016/
2.40 Dispersion corrections appropriate for this wavelength were
calculated using the Brennan method in XDISP41 with WinGX.42 The
structures were solved with a dual-space method with SHELXLT
2014/435 and refined using SHELXL 2014/7.35 Hydrogen atoms
were placed geometrically where possible and added using HFIX 137
on the DMF solvent molecules constrained and refined using a riding
model. The hydrogen atoms were placed on the nitrogen with the
most symmetrical bonding in the porphyrin. The hydrogen atoms on
the water molecules could not be found in the difference map and
were therefore omitted from the refinement but not the chemical
formula.
ESI-IMS experiments were performed with a Synapt G2 Q-ToF
mass spectrometer (Waters, U.K.) fitted with an electrospray
ionization source. Dilute solutions (2 mg L−1) in chloroform were
introduced into the ESI source via a fused-silica capillary at a flow rate
of 0.6 mL h−1. Nitrogen was used as the nebulizer gas. The operating
conditions for the ion-trap mass spectrometer were as follows:
capillary voltage 3.5 kV, sampling and extraction cone 38 and 4 V,
source and desolvation temperature 100 and 350 °C, and cone and
desolvation gas 50 and 450 L h−1. Mass spectra were recorded from
m/z 50 to 1200 (2000). The collision cross section Ω (collision
momentum transfer integral) was determined using spectral
calibration on the basis of polyalanine IMS separation.
Combustion elemental analysis (CHNS-O) was performed using a
PE 2400 Series II CHNS/O Analyzer (PerkinElmer, USA) in the
CHN operating mode (the most robust and interference-free mode)
to convert the sample elements to simple gases (CO2, H2O, and N2).
The PE 2400 analyzer automatically performed combustion,
reduction, homogenization of product gases, separation, and
detection. An MX5 microbalance (Mettler Toledo) was used to
weigh the samples (1.5−2.5 mg per single sample analysis). Using this
procedure, the accuracy of CHN determination is better than 0.30%
absolute. Internal calibration was performed using N-phenylurea. The
CONCLUSIONS
■
This work has produced three significant results. The first is a
finding that the structure of the charged complexes formed
upon reaction of 1 or 5 with 6 or 7 is determined by the type
of the connecting dialkyne ligand. Excessively bulky functional
groups, such as the trimethylsilyl groups in 5, hinder free
rotation of the platinum termini decorated with the dppp
ligands and prevent a rearrangement of the molecule to a shape
favorable to formation of a rectangular product; open-chain
oligomers are formed instead. In contrast, the triptycene linker
in 1 introduces no such constraints on the rearrangement of
the complex and tetranuclear rectangular platinum macrocycles
are formed under the same reaction conditions. These charged
rectangular complexes can be converted to neutral compounds
upon reaction with 12. Surprisingly, the same products are
obtained upon reaction of the rod 1 or the noncyclic charged
complex 14 with 12.
Second, an attempted preparation of a “three-dimensional”
octanuclear platinum complex resulted in an unexpected
formation of the flat polycyclic complex 11 due to a
coincidental match of the dimensions of 1 and 10. Although
the match is only approximate, the flexibility of the system
makes formation of the complex 11 possible and even
preferable over the formation of complexes with more
porphine molecules linked together.
The third intriguing and most surprising result is the
formation of the tetranuclear all-trans ring complex 17 from
linear charged oligomers. Although the originally expected
geometry of this compound was all-cis,16 the additional
experimental and computational work convinced us that the
arrangement of the ligands on the platinum coordination
centers is all-trans.
EXPERIMENTAL SECTION
■
Preparation of the starting materials, 4,4′-diethynylbiphenyl (12),30
1,2-bis(pyridin-4-yl)ethyne (6),31 1,4-bis(pyridin-4-yl)buta-1,3-diyne
(7),32 [PtMe2(1,5-COD)],33 and 1,4-bis(trimethylsilyl)-2,5-diethy-
nylbenzene34 followed published procedures. cis-(dppp)(I)Pt(CC-
triptycene-CC)Pt(I)(dppp) (1) was prepared and converted to cis-
(dppp)(NO3)Pt(CC-triptycene-CC)Pt(NO3)(dppp) as previ-
ously described.24 The solvents, diethylamine and triethylamine and
the inorganic salts were purchased and distilled over CaH2
(dichloromethane), P4O10/Na-K alloy (THF), sodium (toluene), or
KOH (HNEt2, HNi-Pr2, Et3N). K2PtCl4, dppm, dppe, and dppp were
purchased from Strem Chemicals Inc. Other reagents were purchased
from Sigma-Aldrich and used as received. Deuterated solvents were
purchased from Eurisotop, Saclay, France.
I
DOI: 10.1021/acs.organomet.9b00633
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
platinum content was determined using a Spectro iQII X-ray
fluorescence analyzer (Spectro Analytical Instruments Inc., USA).
1,4-Bis({[1′,3′-bis(diphenylphosphino)propane](iodo)-
platinum(II)}ethynyl)-3,5-bis(trimethylsilyl)benzene (5). cis-
(dppp)PtI2 (3.9 g, 4.5 mmol, 4 equiv) was suspended in 450 mL of
freshly distilled methylene chloride in a dry round-bottom flask (1 L).
1,4-Bis(trimethylsilyl)-2,5-diethynylbenzene (300 mg, 1.11 mmol, 1
equiv) dissolved in 10 mL of freshly distilled methylene chloride was
added, followed by freshly distilled diethylamine (126 mL), and the
suspension was stirred at room temperature for 20 min. CuI (66 mg,
10 mol %) was added at once, and the mixture was stirred for 48 h at
room temperature. The reaction mixture was concentrated to half of
its original volume, and 300 mL of hexane were added with vigorous
stirring to precipitate the product together with the remaining starting
material and the diethylammonium iodide side product. The
precipitate was filtered off, washed with hexane, and air-dried. The
dry powder was suspended in 150 mL of distilled water and stirred for
30 min to ensure dissolution of the diethylammonium salt. The
remaining solid material was filtered off, washed with acetone, and air-
dried. The dry powder was suspended in 100 mL of methylene
chloride and sonicated for 5 min. As the product is only sparingly
soluble in this solvent, it remained undissolved and was filtered,
washed with methylene chloride (3 × 10 mL) and then 20 mL of
diethyl ether, and air-dried to give a yellowish powder (1 g, 52%
yield). 1H NMR (500 MHz, DMF-d7, 120 °C): δ 7.97 (m, 8H), 7.84
(m, 8H), 7.46 (m, 18H), 7.39 (m, 8H), 2.74 (m, 8H), 2.06 (m, 4H),
0.22 (s, 18H) ppm. 13C{1H} NMR (126 MHz, DMF-d7, 120 °C): δ
139.8, 137.7, 135.4 (d, J = 9.9 Hz), 134.6 (d, J = 10.6 Hz), 133.7 (d, J
= 55.4 Hz), 132.2 (d, J = 63.1 Hz), 131.8, 131.5, 130.7, 129.2 (d, J =
11.2 Hz), 129.0 (d, J = 10.5 Hz), 117.1 (d, J = 30.0 Hz), 107.8 (dd, J
= 153.0, 13.9 Hz), 26.7 (dd, J = 36.7, 6.9 Hz), 26.3 (dd, J = 33.0, 5.0
Hz), 20.5, 0.7 ppm. 31P{1H} NMR (202 MHz, DMF-d7, 120 °C): δ
−13.01 (d, JP−P = 25 Hz, JPt−P = 2174 Hz). −14.45 (d, JP−P = 25 Hz,
(m, 8H). 13C{1H} NMR(126 MHz, DMF-d7): δ 152.9, 145.9, 134.8
(d, 2JC−P = 10.7 Hz), 134.6 (d, 2JC−P = 10.7 Hz), 133.0, 132.6, 131.7,
3
130.7, 130.2 (d, 3JC−P = 11.0 Hz), 130.0 (d, JC−P = 11.2 Hz), 129.5,
129.1, 111.1 (dd, H, cis-2JC−P = 135.2, trans-2JC−P = 14.1 Hz), 98.1 (d,
3JC−P = 30.0 Hz), 81.2, 79.6, 54.1, 25.8 (d, 1JC−P = 40.7 Hz), 23.8 (d,
1JC−P = 34.7 Hz), 19.9. 31P{1H} NMR (202 MHz, DMF-d7): δ
−10.63 (d, 2JP−P = 28 Hz, 1JP−Pt = 3142 Hz), −0.54 (d, 2JP−P = 28 Hz,
1JP−Pt = 2210 Hz). 195Pt NMR (107 MHz, DMF-d7): δ −4593 (dd,
1JP−Pt = 2215, 3162 Hz). HRMS: calcd for C184H144N4P8Pt4 859.1965,
found (ESI+) 859.3018. Anal. Calcd for C184H144N8O12P8Pt4: C,
59.94; H, 3.94; N, 3.04; Pt, 21.16. Found: C, 59.76; H, 3.90; N, 2.99;
Pt, 20.87.
Triptycene-Tetrapyridylporphine Rectangle (11). Complex 1
(40 mg, 22.6 μmol) was dissolved in dry methylene chloride (100
mL) in an aluminum-foil-wrapped flask. 5,10,15,20-Tetrakis(4-
pyridyl)-21H,23H-porphyrin (7 mg, 11.3 μmol) and silver(I) nitrate
(8 mg, 43 μmol) were added, and the mixture was stirred under an
argon atmosphere in the dark for 48 h. The silver(I) iodide precipitate
was filtered off using a Whatman 0.2 μm filter, and the filtrate was
concentrated under reduced pressure to give a violet powder (40 mg,
97% yield). Mp: 243−247 °C dec. 1H NMR (500 MHz, DMF-d7): δ
8.96 (dt, 8H, J = 4.4, 2.7 Hz), 8.45 (s, 4H), 7.99−7.88 (m, 16H), 7.79
(d, 8H, J = 5.5 Hz), 7.73−7.62 (m, 16H), 7.45 (dt, 8H, J = 7.0, 3.5
Hz), 7.43−7.38 (m, 8H), 7.35−7.27 (m, 40H), 6.21 (dd, 8H, J = 5.5,
3.2 Hz), 6.17 (dd, 4H, J = 5.4, 3.2 Hz), 5.84 (s, 4H), 5.71 (dd, 4H, J =
5.4, 3.2 Hz), 3.06−3.15 (m, 8H), 2.77−2.88 (m, 8H), 2.06−1.87 (m,
8H). 13C{1H} NMR (126 MHz, DMF-d7): δ 153.2, 150.8, 146.4,
2
145.3, 134.9 (d, 2JC−P = 10.6 Hz), 134.6 (d, JC−P = 10.6 Hz), 133.0,
132.8, 131.5, 130.8, 130.2 (d, 3JC−P = 10.4 Hz), 130.1, 130.0 (d, 3JC−P
= 11.4 Hz), 129.7, 125.8, 125.7, 123.6, 123.0, 112.9 (dd, cis-2JC−P
=
136.8, trans-2JC−P = 13.8 Hz), 99.2 (d, 3JC−P = 30.4 Hz), 54.6, 25.7 (d,
JC−P = 39.3 Hz), 23.4 (d, JC−P = 36.0 Hz), 20.2. 31P{1H} NMR(162
MHz, DMF-d7): δ 2.7 (d, JP−P = 27.4 Hz, 1JPt−P = 2204 Hz), −7.9 (d,
JPt−P = 3364 Hz). Anal. Calcd for C70H72I2P4Pt2Si2: C, 48.39; H, 4.18;
J
P−P = 27.4 Hz, 1JPt−P = 3156 Hz). HRMS: calcd for C196H154N8P8Pt4
Pt, 22.46. Found: C, 48.15; H, 4.14; Pt, 21.35.
911.7192, found (ESI+) 911.8331. Anal. Calcd for C196H154N8P8Pt4:
C, 64.51; H, 4.25; N, 3.07; Pt, 21.38. Found: C, 64.27; H, 4.31; N,
3.23; Pt, 21.17.
Triptycene-Dipyridylacetylene Rectangle (8). Complex 1 (50
mg, 28 μmol) and 6 (5.1 mg, 28 μmol) were dissolved in dry
methylene chloride (150 mL) in an aluminum-foil-wrapped flask. To
the stirred solution was added silver(I) nitrate (9.6 mg, 57 μmol), and
the slurry was stirred in the dark at room temperature overnight.
Precipitated silver(I) iodide was removed by filtration through a
Whatman 0.2 μm filter, and the filtrate was concentrated under
reduced pressure to provide a quantitative yield (50 mg) of a light
yellow solid. Mp: 245−250 °C dec. 1H NMR (400 MHz, DMF-d7): δ
8.99−8.82 (m, 8H), 8.23 (dd, 12.3 Hz, 6.7 Hz, 16H), 7.73 (dd, 11.4
Hz, 7.5 Hz, 16H), 7.73 (dd, 11.4 Hz, 7.5 Hz, 16H), 7.66−7.54 (m,
32H), 7.51 (d, 6.1 Hz, 8H), 7.48−7.33 (m, 16H), 6.78−6.72 (m,
12H), 6.66−6.60 (m, 12H), 3.32−3.17 (m, 8H), 3.13−2.98 (m, 8H),
2.22−1.99 (m, 8H). 13C{1H} NMR (100 MHz, DMF-d7): δ 152.0,
145.0, 134.1, 134.0, 133.9, 133.8, 132.2, 131.8, 130.0, 129.4, 129.3,
129.2, 128.8, 128.5, 128.2, 124.8, 122.1, 97.6, 97.3, 91.8, 24.9 (d, 2JC−P
Triptycene-Diethynylbiphenyl Rectangle (13). Dry methylene
chloride (30 mL) was cannulated to a dry mixture of 1, 9 (0.01
mmol) or 14 (0.005 mmol), 12 (0.01 mmol), and cuprous iodide (10
mg). After the mixture was cooled to −25 °C, triethylamine (1 mL)
was added and this mixture was warmed to room temperature and
stirred overnight. The solution was extracted twice with water (10
mL) and washed twice with brine (10 mL). The organic phase was
dried over sodium sulfate and evaporated under reduced pressure to
give a beige-white solid: yields from 1, 9, and 14 64%, 100%, and 96%,
1
respectively. Mp: >350 °C. H NMR (400 MHz, DMF-d7): δ 8.12
3
(m, 32H), 7.52 (m, 60H), 2.03 (m, 8H6), 7.38 (d, 8H22, JH−H = 8
3
Hz), 6.89 (d, 8H21, JH−H = 8 Hz), 6.75 (m, 12H17), 2.89 (m, 8H,
overlap with DMF-d7), 2.83 (m, 8H, overlap with DMF-d7), 2.05 (m,
8H). 13C NMR (101 MHz): δ 146.4, 137.0, 134.4 (d, 2JC−P = 9 Hz),
2
= 36 Hz), 23.0 (d, JC−P = 36 Hz), 19.1. 31P{1H} NMR (162 MHz,
2
3
1
134.1 (d, JC−P = 9 Hz), 132.8, 132.2, 131.6, 131.0, 130.8, 129.8,
DMF-d7): δ −0.63 (d, JP−P = 28 Hz, JP−Pt = 2218 Hz), −10.65 (d,
3
3
3JP−P = 28 Hz, 1JP−Pt = 3152 Hz). 195Pt NMR (64.5 MHz, DMF-d7): δ
128.7 (d, JC−P = 10 Hz), 128.6 (d, JC−P = 10 Hz), 125.7, 124.5,
1
123.0, 108.6 (HMBC), 53.9 (HMBC), 26.0 (HSQC), 25.3 (HSQC),
−4595 (dd, JP−Pt = 2218, 3152 Hz). HRMS: calcd for
20.3 31P NMR (162 MHz): δ −5.75 (s, 1JP−Pt = 2212 Hz), δ −5.77 (s,
C180H144N4P8Pt4 847.1965, found (ESI+) 847.1912 ([M4+]). Anal.
Calcd for C180H144N8O12P8Pt4: C, 59.41; H, 3.99; N, 3.08; Pt, 21.44.
Found: C, 59.17; H, 3.95; N, 3.01; Pt, 20.95.
1
1JP−Pt = 2212 Hz). 195Pt NMR (64.5 MHz): δ −4884 (dd, JP−Pt
=
2257 Hz). Anal. Calcd for C194H158N2O2P8Pt4: C, 65.13; H, 4.45; N,
0.78; Pt, 21.81. Found: C, 64.97; H, 4.39; N, 0.82; Pt, 21.69.
Triptycene-9,10-diethynylbis(cis-{[bis(diphenylphosphino)-
propane](pyridine)platinum(II)} nitrate) (14). Dry methylene
chloride (80 mL) was cannulated to a dry mixture of 1 (106 mg, 0.06
mmol) and silver(I) nitrate (21 mg, 0.12 mmol). After the mixture
was stirred overnight under inert conditions in a flask wrapped in
aluminum foil, 35 μL of anhydrous pyridine were added. After 15 h,
the mixture was filtered through a Whatman 0.2 μm filter and
concentrated under reduced pressure to give a white solid (107 mg,
97%). Mp: >258−264 °C dec. 1H NMR (300 MHz, CD2Cl2): δ
8.51−8.33 (m, 4H), 8.08−7.95 (m, 8H), 7.59 (m, 2H), 7.54−7.42
(m, 20H), 7.42−7.34 (m, 4H), 7.31−7.20 (m, 8H), 7.13−7.04 (m,
Triptycene-Dipyridylbutadiyne Rectangle (9). Dry methylene
chloride (160 mL) was cannulated to a dry mixture of 1 (106 mg,
0.06 mmol) and silver(I) nitrate (21 mg, 0.12 mmol). After the
mixture was stirred overnight under inert conditions in a flask
wrapped with aluminum foil, 7 (12 mg, 0.06 mmol) was added. After
15 h, the mixture was filtered through a Whatman 0.2 μm filter and
concentrated under reduced pressure to give a beige solid (110 mg,
99%). Mp: 235−240 °C dec. 1H NMR (400 MHz, DMF-d7): δ 8.98−
8.86 (m, 8H), 8.30−8.15 (m, 16H), 7.81−7.71 (m, 16H), 7.66 (d,
8H, J = 6.2 Hz), 7.65−7.55 (m, 24H), 7.55−7.49 (m, 8H), 7.45−7.38
(m, 16H), 6.74−6.69 (m, 12H, J = 5.4, 3.3 Hz), 6.67−6.61 (m, 12H, J
= 5.4, 3.4 Hz), 3.29−3.18 (m, 8H), 3.10−2.99 (m, 8H), 2.20−2.01
J
DOI: 10.1021/acs.organomet.9b00633
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4H), 6.68−6.60 (m, 6H), 6.60−6.52 (m, 6H), 3.04−2.91 (m, 4H),
2.85−2.73 (m, 4H), 2.25−1.98 (m, 4H). 13C{1H} NMR (75 MHz,
(4) Kaim, W.; Schwederski, B.; Dogan, A.; Fiedler, J.; Kuehl, C. J.;
Stang, P. J. Metalla-supramolecular rectangles as electron reservoirs
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2
CD2Cl2): δ 151.7, 145.12, 139.1, 133.9 (d, JC−P = 18 Hz), 133.7 (d,
4
3
2JC−P = 18 Hz), 132.4 (d, JC−P = 4 Hz), 130.0, 129.7 (d, JC−P = 12
3
Hz), 129.51 (d, JC−P = 13 Hz), 129.1, 128.7, 128.0, 126.8, 125.1,
2
2
122.3, 53.1, 25.5 (d, JC−P = 36 Hz), 24.2 (d, JC−P = 36 Hz), 19.6.
31P{1H} NMR (122 MHz, CD2Cl2): δ −0.43 = (d, JP−P = 28 Hz,
3
1JP−Pt = 2207 Hz), −12.05 (d, 3JP−P = 28 Hz, 1JP−Pt = 3132 Hz). 195Pt
1
NMR (64.5 MHz, CD2Cl2): δ −4578 (dd, JP−Pt = 2213, 3150 Hz).
MS (ESI+): m/z 1656.4 [(M − py + NO3)+, 13], 836.7 (M2+, 100).
Anal. Calcd for C88H74N4O6P4Pt2: C, 58.80; H, 4.15; N, 3.12; Pt,
21.70. Found: C, 58.53; H, 4.07; N, 3.09; Pt, 20.93.
́
́
́
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.9b00633.
■
S
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NMR spectra of compounds 5, 8, 9, 11, 13, and 14, ESI-
IMS spectra of compounds 8, 9, and 11, and
crystallographic data of compounds 1, 5, 11, and 13
(PDF)
Accession Codes
CCDC 1950566, 1953719−1953720, and 1953984 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail for J.M.: michlj@colorado.edu.
■
ORCID
Cyprien Lemouchi: 0000-0002-2236-496X
Josef Michl: 0000-0002-4707-8230
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Work in Boulder was supported by the U.S. National Science
Foundation (DMR 1608424). Work in Prague was supported
by the European Research Council under the European
Community’s Framework Programme (FP7/2007-2013) ERC
grant agreement no. 227756, and by the Institute of Organic
Chemistry and Biochemistry, Academy of Sciences of the
Czech Republic (RVO: 61388963). This research used
resources of the Advanced Light Source, which is a DOE
Office of Science User Facility under contract no. DE-AC02-
05CH11231.
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