Tuning PtII-Based Donor–Acceptor Systems through Ligand Design: Effects on Frontier Orbitals, Redox Potentials, UV/Vis/NIR Absorptions, Electrochromism, and Photocatalysis

Chemistry - A European Journal

10.1002/chem.201903700

Tuning Pt(II)-Based Donor-Acceptor Systems Through Ligand Design: Effects on Frontier Orbitals,

Redox Potentials, Vis-NIR Absorptions, Electrochromism and Photocatalysis

[

a]

[a]

[a,b]

[c]

[a]

Sebastian Sobottka , Maite Nößler , Andrew L. Ostericher , G. Hermann , Noah Z. Subat , Julia Beerhues ,

[a]

[a,d]

[a]

[a,e]

[f]

Margarethe Behr-van der Meer , Lisa Suntrup , Uta Albold , Stephan Hohloch , J.-C. Tremblay , Biprajit

[a,g],*

Sarkar

th

Dedicated to Prof. G. K. Lahiri on the ocassion of his 60 birthday

Abstract

2-

Asymmetric platinum donor acceptor complexes [(pimp)Pt(Q )] are presented in this work with pimp =

[

(2,4,6-trimethylphenylimino)methyl]pyridine and Q²^-= various catecholate-type donor ligands. The

properties of the complexes are evaluated as a function of the donor ligands, and correlations are drawn

among electrochemical, optical and theoretical data. Special focus has been put on the spectroelectrochemical

investigation of the complexes featuring sulfonyl-substituted phenylendiamide ligands, which show redox-

induced linkage isomerism upon oxidation. (TD)DFT as well as electron flux density analysis has been

employed to rationalize the optical spectra of the complexes and their reactivity. Compound 1 ([(pimp)Pt(Q²^-

2

-

)

] with Q = 3,5-di-tertbutylcatecholate) was shown to be an efficient photosensitizer for molecular oxygen,

which was subsequently employed in photochemical cross dehydrogenative coupling reactions. Our results

thus display new avenues for donor-acceptor systems, including their role as photocatalysts for organic

transformations, and the possibility to introduce redox-induced linkage isomerism in these compounds

through the use of sulfonamide substituents on the donor ligands.

[

a]

Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstrasse

4-36, 14195, Berlin, Germany.

3

[

b]

Current Address: Department of Chemistry and Biochemistry, University of California San Diego,

500 Gilman Drive, La Jolla, United States.

9

[c]

Quantum on Demand, c/o Freie Universität Berlin, Altensteinstraße 40, 14195, Berlin, Germany

[d]

Current Address: Department of Chemistry, University of Massachusetts Boston, 100 Morrissey

Boulevard, Boston, Massachusetts 02125, United States

[

e]

Current Address: University of Paderborn, Warburger Straße 100, 33098, Paderborn, Germany.

Laboratoire de physique et chimie théoriques, CNRS/Université de Lorraine - UMR 7019, 1 bd

[

f]

Arago, 57070 Metz, France

[

g]

Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart,

Germany. Email: biprajit.sarkar@iac.uni-stuttgart.de

Key-words: Redox-active ligands, platinum, donor-acceptor complexes, electrochemistry,

spectroelectrochemistry

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Introduction

8

Group 10 metals in their d electronic configuration have served to synthesize a range of donor-acceptor metal

complexes.^[¹^,²^–⁵^]These compounds are usually characterized by an intense ligand-to-ligand charge transfers, which

impart unique photochemical and photophysical properties on the resulting metal complexes.^[²^,⁶^]Applications

range from dye-sensitized solar cells to small molecule activation and catalysis.^[⁴^,⁷^,⁸^]

Chart 1. Typical acceptor (left) and donor (right) ligands.

In order to obtain a compound with a strong LL’CT transition it is desirable to use a strong π-acceptor and a strong

σ- and/or π-donor ligand, with favorable orbital energies. Chart 1 shows prototypical ligands that have been

successfully employed in this regard. Well established acceptor ligands are 2,2’-bipyridine (bpy),

phenylazopyridine (pap) and also phenyliminomethylpyridines (pimp), with the latter only sparingly used in the

construction of such systems.^[⁹^–¹¹^]Another interesting application for compounds with optoelectronically

switchable properties are electrochromic devices.^[¹²^]

As donor ligands catecholate/semiquinone/quinone ligands have been well established due to their strong donor

properties and well-defined redox-behavior.^[⁷^,¹³^]A change in oxidation state for this ligand system results in

drastically altered donor and acceptor properties with the catecholate ligand being a strong π- and σ donor and

poor acceptor ligand, whereas the fully oxidized quinone is a strong π-acceptor and a very weak π-donor ligand.

If the oxygen donor atom is replaced by an isolobal [NR] residue, the quinones can be sterically and electronically

tuned rather easily.^[¹⁴^]All of the depicted ligands are redox-active and thus can act in a potentially noninnocent

manner, when coordinated to a metal center. The stabilization of additional charges or charge separation becomes

important, if one wishes to harvest solar energy. Our previous work revealed, that such compounds show

interesting and diverse reactivity, if different donor ligands were employed.^[³^,⁴^]

Special emphasis is put on the redox-induced reactivity of the systems featuring o-bis-sulfonamide ligands in this

work. Although this ligand class was described for the first time more than half a century ago^[¹⁵^]the application of

these highly tuneable ligand class is still rather limited^[¹⁶^,¹⁷^]and only one platinum complex was reported.^[¹⁸^]For

the most part, these reports discuss fundamental structural aspects of the complexes. Recently, we have reported

on mono- and dinuclear cobalt(II) complexes with chelating and bridging bissulfonamidobenzene ligands resulting

in air-stable single molecular magnets with high switching barriers, highlighting the potential of this ligand

class.^[¹⁹^]

Perutz and co-workers studied rhodium(III) complexes with symmetrically and asymmetrically sulfonylated

bisamidobenzenes for transfer hydrogenation, showing the catalytic applications of these ligands.^[²⁰^–²²^]

Interestingly, they have also observed the dimerization of the aforementioned rhodium compounds, in which the

oxygen atoms of the sulfonyl group bridge two rhodium centers.^[²⁰^]Kavallieratos and co-workers observed the

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formation of coordination polymers using lead(II) salts emphasizing the versatile and dynamic coordination

chemistry these ligands may engage in.^[¹⁷^]

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Results and Discussion

Synthesis and Structural Characterization

The complexes

ligands have been prepared by literature-known reactions.^[²³^,²⁴^]The reaction of phenyliminomethylpyridin

with (dmso) PtCl yielded the platinum dichloride complex in good yield. In the presence of

triethylamine, the respective quinoid ligands H were deprotonated under inert conditions in acetonitrile

1-5 (

Scheme 1) have been prepared by following a previously established routes.^[³^,⁵^]The

6

2

7

2

Q

x

to give the title complexes in low to acceptable yields, as shown in Scheme 1. The compounds have been

initially characterized by means of H NMR, ¹³C NMR, mass spectrometry and elemental analysis. All

complexes are stable towards air and moisture in the solid-state and in solution and can be stored for

several months without detectable decomposition.

1

2

Scheme 1. Syntheses of the precursor (pimp)PtCl and the complexes 1-5.

For complex

1

and

5

two regioisomers can be formed, however only one isomer is isolated in contrast to

even four possible isomers are conceivable, if the position of the

previous studies.^[³^]For complex

5

methylsulfonyl group relative to the plane spanned by the two binding pockets and the platinum center is

taken into account. However, the barrier for the rotation is probably so low, that the isomers interconvert

too quickly at room temperature. A systematic screening of various reaction conditions (time, temperature,

solvent, type of base) did not result in formation of the other regioisomer or a mixture of both isomers.

This is not observed for the strongly related pap (Phenylazopyridine) complexes of platinum and

palladium, which we have reported on earlier.^[³^]This result is quite surprising, however it may be partly

explained, if the trans-influence of the pyridine and imino fragment are compared. From the crystal

2

structure of (pimp)PtCl 7, we see that the platinum-chloride bond in trans-position to the imino-function

is slightly elongated compared to the platinum-chloride bond in trans-position to the pyridine. Assuming

that the imino function is an overall stronger donor than the pyridyl fragment, the first substitution is

favoured here. The aminosulfonyl function is more acidic and thus will likely coordinate first, which

would explain the stereochemistry, with the amidosulfonyl function trans to the imino group, resulting in

complex

hydroxy groups is less pronounced.

This finding is reproduced by DFT calculations, which predicts the experimentally isolated isomer to be

.2 eV lower in energy for pimp and thus to be thermodynamically more stable. This is in contrast to an

5. The same argument can be used for complex 1, just that the difference in acidity for the

0

energy difference of 0.02 eV for the pap derivatives.^[³^]This already suggests that a small change from the

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azo group to the imino group can have a significant influence on the stereochemistry of the resulting

compound.

Figure 1. Crystal structures for the compounds 1-5 and 7.

Additionally, all complexes and precursors could be characterized by means of single crystal X-ray

diffraction (see Figure 1). This has been especially useful for the determination of the stereochemistry of

and . The single crystals have been obtained by either vapour diffusion or evaporation of the solvent (see

experimental part for details). All complexes display a distorted square planar geometry as expected for

diamagnetic platinum(II) metal centers. Compounds and crystallize in the monoclinic P2 /c space

group, whereas 2 crystallizes in the monoclinic P2 /n space group and 4 and 5 both crystallize in the triclinic space

group P^ꢀ1

1

5

1

,

3

6

1

.

Figure 2. Tilt (designated by the angle θ) of the donor ligand compared to the pimp acceptor ligand for complexes

, 4 and 5. The complexes are arranged in such a way, that the mesyl group of pimp is in the foreground.

3

Almost perfectly coplanar aromatic π-systems for the donor and acceptor ligands are observed for 1 and 2,

featuring two oxygen donor atoms (measured between the planes spanned by the two chelates). For the compounds

3

2

and 4 featuring a NSO R donor group, we observe a deviation from coplanarity of up to 22° (designated by angle

θ) and for compound 5 featuring an oxygen and nitrogen donor an intermediate deviation (see Figure 2). Table 1

shows selected bond lengths and angles for the discussed complexes 1-5, the precursor and the free pimp ligand.

A close inspection of the bond lengths shows that the aromaticity of the catecholato ligands is retained with bond

lengths around 1.40 Å. The C1-O1 and C2-O2 bond lengths of around 1.35 Å and C1-N1 and C2-N2 of around

2

-

1

.44 Å are normally observed for C-O/C-N single bonds, thus pointing to a fully reduced catecholate Q form in

all cases.^[³^]The bond lengths for the complexes 3 and 4 with diamidosulfonyl ligands also show bond lengths, that

are in good agreement with the bond lengths of the free ligand.^[²³^]

An inspection of the bond lengths for the free pimp acceptor ligand^[²⁵^]suggests an unreduced ligand, as

the N1-C7, C7-C8 and C8-N2 bond lengths do not drastically change (around 0.03

Å) upon coordination

with the [PtCl ] fragment or subsequent catecholate coordination. This also applies for the N1-Pt and the

2

N2-Pt bonds, which get slightly shorter when a OO-donor ligand is employed as compared to the NN-

donors. The torsion angle ϕ in the pimp ligand ranges from 70 to almost 100°. The observed values agree

with previous literature reports for related donor-acceptor systems^[⁵^,²⁶^]and also for related platinum

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chloride complexes.^[⁹^,¹⁰^,²⁷^]

The nitrogen donors of the diamidosulfonyl ligands in complexes

3 and 4 show a different coordination

2

geometry. A trigonal-planar coordination is expected for sp -hybrized nitrogen atoms, which is

characterized by a sum of 360° for all surrounding angles. The nitrogen atom in trans-position to the

pyridine shows a trigonal-planar coordination with angles of 355.0° (DFT: 357.1°) for

50.1°) for . The nitrogen in trans-position to the imino function however, shows a tetrahedral distortion

as evidenced by an angle of 341.9° (DFT: 338.8°) for , 339.7° (DFT: 341.5°) for and 338.6° (DFT:

43.0°) for complex . This has been attributed to an absence of π-bonding of the diamidosulfonyl ligands

3 and 352.7° (DFT:

3

4

3

4

3

5

to the metal center, when compared to unsubstituted diamidobenzenes, as similar deviations are observed

for platinum(II) and rhodium(III) complexes with symmetric co-ligands.^[¹⁸^]A steric effect can most likely

be ruled out, since the less bulky mesyl group in

in

4 shows almost the same deviations as the tosyl groups

3

.

2

Table 1 Selected bond lengths (Å) for complexes 1-5, (pimp)PtCl (7) and the free ligand (6).

1

2

3

4

5

6

7

2.297(1)

2.292(1)

2.016(3)

2.001(3)

---

a

Pt-E

Pt-N

1

2

1.991(3)

1.965(3)

1.997(4)

1.969(3)

1.996(5)

1.982(5)

1.968(6)

1.982(6)

2.029(2) 2.042(5)

2.042(2) 2.033(5)

2.023(2) 2.011(5)

2.048(2) 2.046(5)

1.450(3) 1.449(8)

1.430(3) 1.431(8)

2.036(3)

1.971(3)

2.003(3)

1.997(3)

1.443(5)

1.352(4)

1.401(5)

---

1

2

E

1

-C

1

2

1.369(5)E 1.328(8)

2

1.354(5)

1.397(6)

1.404(6)

1.394(6)

1.397(6)

1.403(6)

1.386(6)

1.368(4)

1.448(4)

1.290(5)

176°

1.337(8)

1.409(10) 1.390(4) 1.396(9)

1.383(10) 1.400(4) 1.380(9)

1.397(10) 1.391(4) 1.377(10) 1.406(6)

1.387(11) 1.393(4) 1.386(10) 1.402(6)

1.396(10) 1.393(4) 1.384(10) 1.386(6)

1.403(10) 1.393(4) 1.382(9)

1.366(9) 1.368(4) 1.366(8)

1.436(10) 1.448(4) 1.453(8)

C

1

-C

2

-C

3

-C

4

-C

5

-C

6

-C

2

3

4

5

6

1

---

1.389(5)

1.378(5)

1.449(6)

1.289(5)

167°

N

1

-C

-N

7

1.342(2) 1.369(4)

1.478(2) 1.448(5)

1.259(2) 1.289(5)

C

7

8

2

1.283(9)

176°

180°

1.290(4) 1.278(8)

158°

161°

-75.79°



ϕ

exp

161°

168°

-99.18°

---

-76.87°

180°

169°

DFT

torsion

-99.21°

are O or N.

-70.48°

72.11°

-77.81°

[

a]

E

1

and E

2

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Cyclic Voltammetry

Cyclic voltammetry reveals that the complexes 1-5 show at least one reversible oxidation and one reversible

reduction in a 0.1 M NBu PF dichloromethane solution. The precursor 7 shows only a single, reversible

4

6

reduction at -1.35 V and no oxidation processes. This observation already indicates that the reduction is

centered on the pimp ligand. Depending on the substitution pattern of the donor ligand and the respective

donor atoms different additional redox events are observable within the solvent window. For cathodic

processes, an electron-deficient donor ligand renders the observation of a second reduction more likely as

observed for complexes 2 and 4. The redox potentials for all complexes are shown in Table 2.

Compound 1 shows two reversible oxidation processes most likely due to the strongly electron donating 3,5-

di-tert-butylcatecholato ligand, which renders the complex easy to oxidize with potentials at -0.21 V and

+

0.79 V vs ferrocene/ferrocenium, with both oxidations centered on the catecholato ligand. The reduction is

as already stated centered on the pimp ligand, which may be formally reduced twice, with the formal second

reduction shifted outside of the solvent window owing to the strong donation of the catecholato ligand.

Interestingly, complex 1 is the only one in the series that exhibits a significant shift for the reduction potential

in this series. The redox processes are exemplified for 1 in Scheme 2 and are also valid analogously for the

complexes 2-5, the second reduction was not always observed under the measurement conditions.

Figure 3. Cyclic voltammetry for complexes 1-5 in CH

2 2 4 6

Cl / NBu PF measured with a glassy carbon working

electrode at 100 mV/s.

Complex 2 shows two additional redox processes (oxidation and reduction), which are completely

irreversible and likely result in a decomposition of the compound. The second reduction for 2 is probably

irreversible due to the imine proton, since the second reduction on the isolobal azo-functions is oftentimes

reversible. The oxidation for all compounds likely takes place on the donor ligand, which is reflected in the

fact that the oxidation potentials are dependent on the nature of the donor ligand. For complexes 3-5 a second

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oxidation is observed, which exhibits a certain degree of reversibility. The processes do not become more

reversible at faster scan rates (see page S21). This subset of the investigation also nicely demonstrate the

tunability of the oxidation potential by variation of either donor atoms (3 and 4 versus 5) or the substitution

pattern on the nitrogen atom (3 versus 4) for the investigated series.

Scheme 2. Redox processes for complex 1.

The “electrochemical” HOMO-LUMO gaps of the complexes correlate almost perfectly with the calculated

HOMO-LUMO gaps (B3LYP/def2-TZVP), owing to the strong localization of the HOMO on the donor

ligand and the LUMO on the acceptor ligand, respectively (see Figure 4). However, it should be mentioned

that there is a slight offset in values if they are directly compared. The magnitude of the HOMO-LUMO gap

is determined by the donor-ligand, since the acceptor ligand is not changed. The more strongly electron-

withdrawing the substituents of the donor ligand are, the lower is the HOMO energy and thus the bigger the

HOMO-LUMO gap. With this information in hand a series can be established on how electron-withdrawing

the ligands are, with the least withdrawing (or strongest donor) to the most electron-withdrawing (or weakest

donor): [QtBu < QNO < QCl < QTos < QMs²^-].

2

-

2-

Figure 4. Correlation of the electrochemical HOMO-LUMO gap with the calculated HOMO-LUMO gap.

+

-1

Table 2: Redox potentials (E1/2 in V) vs FcH/FcH measured in CH

2

Cl

2

at 100 mVs with 0.1 M Bu

4

NPF

6

at

room temperature.

st

nd

st

nd

E

1/2 (1 Ox)

E

1/2 (2 Ox)

E

1/2 (1 Red)

E1/2(2 Red)

1

2

3

4

5

6

-0.21

---

0.54

0.67

0.17

---

0.79

0.47

1.11

1.06

0.99

---

-1.65

-1.38

-1.43

-1.40

-1.49

-1.35

---

-2.36^[

b]

[

b]

[b]

-2.40

---

[

b]

[b]

---

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[a]

[b]

All measured with a glassy carbon electrode. Potential of the peak current.

UV/Vis-NIR spectroelectrochemistry

2 2 4 6

Figure 5. UV/Vis/NIR spectra for complexes 1-5 in CH Cl / NBu PF .

In order to probe the interplay of the optical and electrochemical properties, UV/Vis-NIR

spectroelectrochemistry -using an Optically Transparent Thin Layer Electrochemical (OTTLE) cell- was

employed. Since the CV measurements already showed, that the higher oxidation states of the compounds

likely show follow-up reactions complicating the electrochemical response we have concentrated on the first

oxidation and first reduction. Early in the investigation we observed a decay in the absorption bands when

measuring the spectrum in the OTTLE cell without applying a current. We witnessed rather quick

reaction/decomposition with electromagnetic radiation in the mid-UV range. Upon removing this part of the

spectrum (200 – 300 nm) by using an appropriate filter, we did not observe any change of the spectrum during

a simple absorption measurement in the OTTLE cell. The quantitative UV/Vis/NIR measurements in a

standard cuvette did not parallel these observations. If the mid-UV range is used during the

spectroelectrochemical measurement we observe only irreversible processes, indicating a decomposition for

the simultaneous application of mid-UV radiation and a certain redox potential.

The UV/Vis/NIR spectra for complexes 1-5 are shown in Figure 5. It is evident that the variation of the donor

ligand has two distinct effects on the absorption spectrum. Firstly, the strong decrease of the extinction

coefficient for the long-wavelength bands, starting from 1 with a strong donor ligand to 2 with the electron-

deficient tetrachlorocatecholato ligand. This decrease is matched by complexes 3 and 4 for which the donor

functions change from “oxido” to amidosulfonyl. The “mixture” of both ligands, the complex employing the

amidosulfonylphenolato ligand 5 neatly lies in the middle between the two extremes. Secondly, we see a shift

to higher energies (or shorter wavelengths) for complexes with electron-withdrawing ligands. This nicely

agrees with the intuitive assumption that we have to excite electrons from a ligand with an energetically

lower-lying HOMO and hence require more energy to do so. Again, complex 5 is in between the two extremes

of 1 and 4. These broad and intense bands from roughly 540- 700 nm can be ascribed to an LL’CT process,

which is also nicely reproduced by TD-DFT calculations.

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Figure 6 shows the results of UV/Vis/NIR-spectroelectrochemistry for complex 1 upon oxidation, reduction

-

+

2+

and comparison of the spectra for 1, 1 , 1 and 1 . For the difference densities of the respective transitions

see pages S32-S37. Upon oxidation the LL’CT band at 717 nm loses intensity and shifts to higher energies,

since less electron density is available on the donor ligand. Simultaneously we observe the increase of a weak

band around 1000 nm, which can be attributed to the ILCT process of the semiquinonato ligand. The new

+

bands in the visible region for 1 can be attributed to metal-to-ligand charge transfers (MLCT) and π-π*

2+

transitions from the mesityl to the donor-ligand. Further oxidation to 1 results in the loss of the NIR band

around 1000 nm and the band in the visible region shift slightly, but maintain their shape. These bands of 1²⁺

can be assigned to MLCT processes for the now fully oxidized donor ligand.

The reduction takes place on the acceptor ligand the LL’CT band again loses intensity and a couple of new

and relatively sharp bands arise in the visible/near UV region of the spectrum. These can be assigned to intra-

ligand charge transfer (ILCT) processes taking place on the pimp ligand. There are also minor d-orbital

contributions. This is observed for all the complexes, showing again that the reduction is taking place on the

ligand, which is also reproduced by our TD-DFT calculations (see pages S32-S45).

Figure 6. UV/Vis/NIR spectroelectrochemistry for complex 1.

In contrast to the absorption spectra of the native compounds, which look qualitatively similar, the spectra

for the oxidized and reduced complexes differ substantially in some regards (see page S31). If the spectra of

all the singly oxidized compounds are compared, we observe rather intense NIR bands for the complexes 3⁺,

4⁺

and 5 , which all feature a nitrogen donor on the semiquinonato ligand, whereas the complexes 1 and 2

+

with oxygen-only donors show no absorption in this region (Figure S78). In contrast, complexes 1 and 2

show strong absorption in the visible region of the spectrum.

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-

The spectra for the reduced species 1 , 2 , 3 , 4 and 5 look relatively similar (Figure S77), which again

indicates that the reduction steps are primarily pimp-centered. We observe a relatively sharp double peak

between 400 and 500 nm for all compounds, including the precursor 6. All compounds exhibit NIR bands as

-

well that look similar, except for 1 , for which the band is shifted significantly to higher energy. For 2 the

band is extremely week. This indicates a varying degree of influence of the donor ligand on the reduced

-

acceptor ligand, with the influence for 1 and 2 with the oxygen-bearing donor ligands being the most

pronounced.

As discussed above, in these complexes, the LUMO is located on the pimp ligand and the HOMO is located

on the donor ligand and we have additionally confirmed that the low-energy band can be assigned to a

HOMO-LUMO transition. Thus, we can use UV/Vis/NIR spectroscopy to directly measure the HOMO-

LUMO gap. The UV/Vis/NIR data can now be correlated analogously to the CV data with the DFT

calculations (B3LYP/def2-TZVP). As shown in Figure 7 the maximum of the LL’CT correlates almost

perfectly with the theoretical calculations and the electrochemical data. These correlations independently

validate the trend for the donor strength that we have already concluded from the CV measurements in order

of decreasing donor strength: [QtBu < QNO < QCl < QTos < QMs²^-].

2

-

2-

Figure 7. Correlation of the optical HOMO-LUMO gap (=LL’CT) with the electrochemical HOMO-LUMO gap

(

left) and the correlation of the calculated HOMO-LUMO gap with the optical HOMO-LUMO gap (right).

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Rearrangements in complexes 3 and 4

Complex 3 showed a particular behavior during the UV/Vis-NIR spectroelectrochemical investigation. Upon

oxidation of 3 a broad and very intense band at 950 nm emerged with a shoulder at around 750 nm (see Figure

8

(a)). This process can be ascribed to an MLCT and ILCT processes, which have been observed for

diiminiosemiquinonato ligands coordinated to a metal center.^[²⁸^]Reversal of the scan direction resulted in

loss of intensity of the newly emerged bands as expected. However, new bands at even lower energies around

1

550 nm emerged, which have not been observed at the start of the electrolysis (see Figure 8 (b)). These

intermediate bands vanish once the initial potential has been reached and the complex is fully re-reduced (see

Figure 8 (c)). The starting spectrum is regained with roughly 80% of its initial intensity for the LL’CT

transition(see Figure 8 (d)), indicating a chemical reaction or substantial rearrangement of the investigated

complex. A rearrangement is already evident from Figure 8 (a), in which an band is observed around 1300

nm, which vanishes again in the course of the constant potential electrolysis (olive trace).

2 2 4 6

Figure 8. UV/Vis/NIR-spectroelectrochemistry for complex 3 in CH Cl / NBu PF measured with a gold

working electrode.

Such time- and potential-dependent NIR absorptions are not observed for the oxidative

spectroelectrochemistry of 1, 2 and 5. It is reasonable to assume, that these low-energy band are caused by

an intra-ligand charge transfer (ILCT)^[²⁸^]of the QTos ligand and metal-to-ligand charge transfer (MLCT),

which is also corroborated by TD-DFT calculations. These rearrangements possibly involve a change in the

position of the tosyl groups and the coordination geometry of the nitrogen donor atoms (see discussion

above). However, it is quite unlikely that simple rotational movements exert such a heavy influence on the

absorption spectrum. The two independent isosbestic points at around 1200 and 530 nm also point to two

•–

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different species that are during the measurement. An alternative explanation would be the cleavage of one

of the platinum-nitrogen bonds and coordination of the oxygen atoms of the sulfonyl groups. Such

rearrangements have been proposed for rhodium complexes employing the same ligands by Perutz and co-

workers.^[²⁰^,²¹^]Also a possible dimerization cannot be ruled out, as discussed by Chang and co-workers

recently.^[²⁹^]Upon oxidation of compound 3 to 3 the electron density on the already electron-poor

bisamidosulfonyl ligand is further reduced, resulting in a weaker platinum–nitrogen bond. This possibly

results in a linkage isomerization at the platinum center with one of the oxygen atoms of the sulfonyl group

coordinating to it instead of the nitrogen atom (Scheme 3). A seven-membered or a four-membered chelate

ring are possible with the oxygen atom coordinating in trans-position to either the pyrdine or imino donor

function of the pimp ligand (Scheme 3). Since the initial UV/Vis spectrum cannot be fully recovered after

re-reduction it is reasonable to assume that the resulting compound formed after oxidation is not very stable.

+

The DFT geometry optimization for 3 starting from the XRD geometry of 3 did not indicate significant

rearrangements either. However, if the intermediates shown in Scheme 3 are used as starting point for the

geometry optimization, the calculation quickly converges for all intermediates. The calculations have been

performed exemplarily for complex 4 only. The relative energies of all investigated rearranged complexes

+

predict 3 with its original five-membered chelate ring to be most stable and the most unstable tetracyclic

+

trans-pyridin 3 to be energetically disfavored by around 1 eV (Scheme 3). Bearing in mind that an energy

of 1 eV corresponds to a wavelength of around 1240 nm, the light source could easily trigger this

isomerization. Given the fact that the compounds decompose if a wavelength < 300 nm is used, this

photoisomerization likely occurs. For all five isomers the optical spectra have been computed (see page S23).

Although some changes become apparent from the calculations, they are not sufficient to make a definitive

assignment.

The structurally similar complex 4 also showed some similarities to 3 during oxidative

+

spectroelectrochemistry. For the oxidation of 4 to 4 we observe two bands around 900 and 1500 nm of

+

medium intensity. The spectrum for 4 (see Figure 9 (a)) looks very similar to the spectrum, which is obtained

+

during the re-reduction of 3 to 3 (see Figure 8 (c)) and can be interpreted analogously (see above). Upon

+

2+

further oxidation, from 4 to 4 , the long-wave-length band at 1500 nm vanishes (see Figure 9 (b)), whereas

+

the band around 900 nm strongly increases, this time resembling the spectrum of 3 (Figure 8 (a)).

Interestingly the starting spectrum is almost perfectly recovered upon re-reduction, however the LL’CT band

+

at around 550 nm does not increase simultaneously with the decrease of the NIR bands of 4 at 900 and 1500

nm (see Figure 9 (d)).

Due to the different steric demands of the tosyl and mesyl substituents, it makes sense to assume that the

rearrangements for complex 4 will be less sterically hindered and thus faster compared to the ones for 3. The

above results thus strongly point to the operation of redox-induced linkage isomerism in the sulfonamide

substituted ligands, which is linked with intriguing changes in the NIR region of their absorption spectrum.

To the best of our knowledge, such electron-transfer driven linkage isomerism was never observed before

for metal complexes of diamidobenzenes. Unfortunately it was not possible to probe this rearrangements by

other means (e.g. infrared spectroscopy) on isolated complexes in the absence of light, since the complexes

were not stable towards chemical oxidizing agents ([NO]BF

4

or AgPF ) under an inert atmosphere (see Figure

6

13

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10.1002/chem.201903700

S81).

After these observations, the question arises why complex 5 does not display this type of linkage isomerism.

A tentative explanation may be the θ angle between the π-systems of donor and acceptor ligand. This is

slightly closer to 180° for 5 (see Table 1) and thus results in a better orbital interaction, which results in a

+

stronger stabilization of 5 through backbonding of the Pt(II) d-orbitals, in comparison to 3 and 4 .

Additionally, one can argue that the transition state (which likely involves a tilting with respect to the acceptor

ligand) is already preformed in complexes 3 and 4, and thus facilitates the rearrangement.

+

Scheme 3. Possible isomerization for compounds 3 and 4 .

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Figure 9. UV/Vis/NIR-spectroelectrochemistry for complex 4 in CH

electrode.

2 2 4 6

Cl / NBu PF measured with a gold

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EPR spectroelectrochemistry

In order to gain further insights into the electronic structure of the redox intermediates EPR

spectroelectrochemistry was applied. Electrolysis inside the EPR cavity led to the observation of signals for

the one-electron reduced and one-electron oxidized forms of all complexes 1-5. All spectra could be

simulated (see pages S24-S25) and show a coupling to ¹⁹⁵Pt (abundance of 33.3% and nuclear spin, I = ½)

with no other resolved hyperfine splitting.

The nature of the donor atoms on the donor ligand has a certain influence on the g-value of the radical cationic

compounds, with the g value being slightly higher for the phenylendiamide ligands as compared to the

catecholates or the amidophenolate ligands. The hyperfine coupling constants (hfcc) vary rather broadly from

2

.73 mT for 1 to 11.90 mT for 3, indicating varying degrees of contribution from the platinum center (see

page S23)

The g-values of the radical anionic forms are almost the same with the only exception being complex 2, most

likely owing to the tetrachloro-substitution. The same goes for the hfcc, which is on an average around 9 mT,

except for 2. These values further substantiate that the first reduction is based on the acceptor ligand. The

experimental observations are well reproduced by a spin population analysis, which correctly predicts the

spin to be localized mostly on the pimp acceptor ligand for the reduced species and mostly centered on the

quinoid donor ligand for the oxidized species (see page S25).

DFT calculations and electron flux

To further rationalize the electronic structure of the complexes DFT calculations on the B3LYP/def2-TZVP

level were employed. The optimized structures (BP86/def2-TZVP) are in good agreement with the

crystallographic data. Figure 0 shows the molecular orbital energies from these calculations along with the

HOMO-LUMO gaps of complexes 1 – 5, which we have already employed for various correlations (see

above). The frontier orbital for all complexes show a certain metal character, but are nevertheless mostly

ligand-based and display mostly π-character. The discussed deviation of the two nitrogen-donor atoms for 3,

4

and 5 is also apparent in the orbital picture. The HOMOs for 1 and 2 exhibit a mirror plane (perpendicular

to the π-system and dissecting the OCCO chelate), whereas we observed a “distorted symmetry” for 3, 4 and

5.

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Figure 10. Frontier orbitals of complexes 1-5 along with the calculated energies.

To characterize the ligand-to-ligand charge transfer mechanism for complexes 1-5, it is insightful to analyze

the electronic flux densities for the optically active transitions from the ground state to the first absorption

band. The electronic flux density yields space-resolved information about the flow of electrons during the

excitation process. Since the first absorption band at the TDDFT/B3-LYP level is dominated by a HOMO-

LUMO transition, the electronic flux densities are calculated in the single-active electron approximation. All

quantities are computed using ORBKIT^[³⁰^]and depicted using ZIBAmira^[³¹^], as shown in Figure 101.

As discussed above, the complexes all reveal an intense ligand-to-ligand charge transfer for the lowest energy

transition, from the various ligand donors to the iminopyridine acceptor. On the acceptor ligand of all five

complexes, the electronic flux exhibits a large degree of delocalization, with a pincer-type electron flow

incoming via the platinum center, over both nitrogen atoms and to the neighboring carbons through the

conjugated π-system. The delocalized flow is particularly laminar for complexes 1, 2, and 5, which correlates

with a laminar, pincer-type electron flow on the donor ligand as well. The planarity between the donor and

acceptor ligand leads to a simple x-shaped flow of the electrons from the coordination atoms of the donor

ligand over the platinum atom to the nitrogen atoms of the acceptor ligand. Despite their similarities, a

stronger, more localized electron flow is observed on complex 2. This is possibly due to the symmetry of the

substituents on the phenyl ring of the donor. In contrast, the electron flow pattern at the donor ligands of the

complexes 3 and 4 is more intricate due to their non-planar structure. This indicates that more electrons are

available in the space between the donor ligand and the metal center, which in turns favors a through-space

mechanism for the electron transfer. The electron flow on the acceptor ligand is perturbed and reduced in

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intensity in both complexes but, surprisingly, not the spatial extent reached by the transferred electron. For a

more quantitative measure, the charge transfer number can be computed as the product of the donor

population and the acceptor population

(1)

CT = ⟨LUMO|Pacceptor|LUMO⟩⟨HOMO|Pdonor|HOMO⟩

where P

i

are Mulliken projectors on the donor and acceptor, respectively. Despite the marked differences in

the electron flow mechanisms observed above, the charge transfer numbers are found to be similar in

complexes 2-4, ranging from 0.757 for complex 2 to 0.784 for complex 4. Of the three planar structures, only

complex 1 is found to have a slightly smaller CT number (0.711). This correlates well with the smaller

electron flow observed on the donor ligand. By looking at the three largest CT numbers, complexes 3-5, it

appears that choosing a ligand which increases through-space electron flow can increase the degree of charge

transfer. This can come at the expense of a less laminar flow, as in complexes 3-4, which we rather attribute

to a structural effect.

Figure 101. Electronic flux densities for the transition between the ground state and the first absorption band of

complexes 1-5. The arrows are colored according to their magnitude. The charge transfer numbers are (0.711,

0

.757, 0.784, 0.774, 0.781) for complexes 1-5, respectively. (carbon in black, hydrogen in white, nitrogen in

blue, oxygen in red, sulfur in yellow, platinum in purple, chlorine in green).

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Application in Cross-Dehydrogenative Coupling (CDC) reactions

The CDC has gained considerable popularity among organic chemists as an atom-efficient method for C-C

bond formation.^[³²^]Inspired by previous works, which have utilized platinum for this reaction we wanted to

test the synthesized complexes and investigate their photocatalytic potential.^[³³^,³⁴^]They were employed in the

cross-dehydrogenative coupling of N-phenyltetrahydroisoquinolin (ISQ) with acetone and nitromethane.

Special focus was put on the role of the donor atoms, which is why complexes 1, 4 and 5 were used for a

preliminary study with an [OO], [NN] and [ON] donor ligand respectively. We have optimized the reaction

conditions in terms of oxygen saturation and overall irradiation time (excitation@360 nm). Pure oxygen was

bubbled through the solution for 2 minutes, 30 minutes or not all (equal to atmospheric conditions).

Interestingly, we observe a high yield for complex 1 after only 2 minutes of bubbling and a long irradiation

time of 15 hours in nitromethane and a considerably lower yield for the same conditions in acetone (see Table

3

). If atmospheric conditions or shorter reaction times are used the yield diminishes drastically, such that

only traces of the product are isolated. Complex 4 also showed only traces under similar reaction conditions.

Complex 5 interestingly showed considerably lower conversions, however a still acceptable isolated yield of

4

0% in nitromethane and only 18% in acetone was observed. As control experiment, the precursor 7 was also

tested in the CDC and displayed considerable activity for the coupling of ISQ and acetone, whereas complex

was still superior for the coupling of ISQ with nitromethane. This may have to with possible side reactions

caused by the substionally labile chloride ligands. This further highlights the high potential of the

underdeveloped (pimp)PtX system for photocatalysis and other applications.

1

2

In order to further substantiate the involvement of dioxygen as oxidizing agent, we have irradiated a solution

of complex 1 in DMF (bubbled for 30 min) for 3 minutes with an excess of of N-tert-Butyl-α-phenylnitrone

(PBN). The EPR spectrum shows a triplet (Figure 12), indicating the generation of a reactive oxygen species

(ROS). Since PBN is a non-specific ROS scavenger, complex 1 could serve as a sensitizer for either singlet

oxygen or the superoxide radical as depicted in Figure 123. In oder to selectively probe the involvement of

1

singlet oxygen ( O

2

) in the catalytic cycle, complex 1 was tested in the oxidation of 1,5-dihydroxynaphthalene

to 5-hydroxy-1,4-naphthoquinone (or juglone). The observation of new bands in the visible region (see

Figures S14 and S15), which correspond to juglone are indicative of singlet oxygen being involved in the

reaction.^[³⁵^]Given the fact that complex 1 will most likely have a relatively low excited state oxidation

potential, that will not suffice to oxidize ISQ.^[³⁶^]Thus, we repeated the catalysis at a lower excitation

wavelength (around 700 nm) and observed no conversion for the reaction of ISQ with nitromethane or

acetone. This supports the fact that singlet oxygen is the active species generated with this sensitizer.

However, by using an irradiation wave length of 360 nm, higher energy excited states may be generated,

which have a sufficiently high potential to oxidize ISQ. More detailed studies on the photophysics of the

complexes will be necessary to answer these questions.

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Figure 112. Spin trapping with Phenyl-N-t-butylnitrone (PBN) in an oxygen-saturated DMF solution of 1.

This leads us to the conclusion, that a similiar catalytic cycle as already described in various literature reports

is operating here (see Figure 11.).^[³⁴^,³⁷^]The platinum complex is photochemically excited and quenched by

the isoquinonline, resulting in the monoanionic platinum complex and a cationic tertiary amine. The

molecular oxygen oxidizes the reduced platinum complex, recovering the sensitizer and redox-mediator and

generating superoxide radical, which abstracts a hydrogen atom from the oxidized isoquinoline. The

hydroperoxyl radical serves as base for the nucleophile (acetone or nitromethane), generating a monoanionic

nucleophile, which combines with the cationic isoquinoline resulting in the product. While we have only

1

shown an electron transfer pathway involving O

cannot be completely ruled out.

2

in Figure 13, the operation of an energy transfer pathway

Further studies will be targeted towards a deeper understanding of the mechanism and the fine-tuning of the

catalyst.

SET

N

Ph

Nu

H O

Ph

[Pt]

[Pt]*

HO₂

2

O₂

hv

[Pt]

Nu

O₂

N

Ph

Nu

Figure 123. Tentative reaction mechanism for the CDC. Adapted from Chen, Fu and co-workers.^[³⁴^]

Table 3 Overview of catalytic reactions.

Entry

Catalyst

Substrate

MeNO

Acetone

MeNO

Acetone

Yield in %

Conditions

1

2

3

4

1

2

88

24

O2: 2 min, t: 15 h

O2: –, t: 16.5 h

2

Traces (< 5)

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5

6

7

8

1

2

3

4

5

6

1

2

3

4

5

6

1

2

1

2

1

3

MeNO

Acetone

MeNO

Acetone

MeNO

Aceton

2

Traces (< 5)

Stability test

Traces (< 5)

No conversion

Traces (< 5)

40

O2: 2 min, t: 2 h

O2: –, t: 2 h

2

O2: –, t: 2 h

2

O2: 2 min, t: 16.5 h

O2: 2 min, t: 2 h

w/o catalyst

MeNO

Aceton

2

3

5

7

1

MeNO

Aceton

2

MeNO

Aceton

2

O2: 2 min, t: 2 h

MeNO

Aceton

2

O2: 2 min, t: 16.5 h

O2: 30 min, t: 16.5 h

O2: 30 min, t: 16.5 h, 700 nm

MeNO

Aceton

2

18

50

65

MeNO

Aceton

2

MeNO

Aceton

2

No conversion

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Conclusions

In conclusion, we have presented a series of novel platinum(II) donor-acceptor systems with the lesser used

phenyliminomethylpyridin (pimp) ligand and a focus on the influence of the donor ligand. The title

compounds were extensively characterized by cyclic voltammetry, UV/Vis-NIR- and EPR-

spectroelectrochemistry. All complexes displayed from two up to four redox events of varying reversibility.

Density functional theory reproduced the experimental absorption spectra nicely and for the first time the

dynamic electron fluxes in such systems were investigated. UV/Vis/NIR-SEC revealed interesting redox-

driven linkage isomerism during the oxidation of complexes 3 and 4, an observation which to the best of our

knowledge has been made for the first time in metal complexes of phenylenediamines. The isomerism leads

to intriguing changes in the NIR region of the spectrum of the isomers. The stabilization of these isomers

remains a challenge with potential applications in photocatalysts or the development of new materials. It was

found that the frontier orbitals are strongly localized on the respective ligand, which resulted in an excellent

correlation of the “different” HOMO-LUMO gaps. The calculation of dynamic electron flux densities

provided an insight into the electron dynamics of these systems for the first time and will help in the design

of better photocatalysts and optical materials. Lastly, we could show that these systems are also interesting

for catalysis. Complex 1 showed high yield in the cross-dehydrogenative coupling of nucleophiles to N-

phenyltetrahydroisoquinoline. Future investigations will be dedicated to the exploitation of the different

redox states of the complexes 1-5, exploiting their switching (redox-induced isomerism) and catalytic

potential to the full, and synthesizing the nickel and palladium analogs for their potential use in catalysis and

switching.

Acknowledgments

The High‐Performance Computing resources of the Zentraleinrichtung für Datenverarbeitung (ZEDAT) of

Freie Universität Berlin. The authors are grateful to the DFG Priority Program SPP 2102, “Light‐controlled

reactivity of metal complexes” (SA 1840/7‐1) for financial support.

References

[

1] a) E. Baggaley, J. A. Weinstein, J. G. Williams, Coord. Chem. Rev. 2012, 256, 1762; b) L. K. McKenzie, H.

E. Bryant, J. A. Weinstein, Coord. Chem. Rev. 2019, 379, 2; c) J. Best, I. V. Sazanovich, H. Adams, R. D.

Bennett, E. S. Davies, Meijer, Anthony J. H. M., M. Towrie, S. A. Tikhomirov, O. V. Bouganov, M. D.

Ward et al., Inorg. Chem. 2010, 49, 10041; d) J. Best, I. V. Sazanovich, H. Adams, R. D. Bennett, E. S.

Davies, Meijer, Anthony J. H. M., M. Towrie, S. A. Tikhomirov, O. V. Bouganov, M. D. Ward et al.,

Inorg. Chem. 2010, 49, 10041; e) J. A. Weinstein, N. N. Zheligovskaya, M. Y. Mel’nikov, F. Hartl, J.

Chem. Soc., Dalton Trans. 1998, 2459; f) K. Tahara, Y. Ashihara, T. Higashino, Y. Ozawa, T. Kadoya, K.

Sugimoto, A. Ueda, H. Mori, M. Abe, Dalton Trans. 2019, 48, 7367; g) L. A. Cameron, J. W. Ziller, A. F.

Heyduk, Chem. Sci. 2016, 7, 1807; h) W. W. Kramer, L. A. Cameron, R. A. Zarkesh, J. W. Ziller, A. F.

Heyduk, Inorg. Chem. 2014, 53, 8825; i) G. K. Rauth, S. Pal, D. Das, C. Sinha, A. M.Z. Slawin, J.D.

Woollins, Polyhedron 2001, 20, 363; j) J. Yang, D. K. Kersi, L. J. Giles, B. W. Stein, C. Feng, C. R.

Tichnell, D. A. Shultz, M. L. Kirk, Inorg. Chem. 2014, 53, 4791; k) S. Roy, I. Hartenbach, B. Sarkar, Eur. J.

Inorg. Chem. 2009, 2009, 2553.

[2] P. A. Scattergood, P. Jesus, H. Adams, M. Delor, I. V. Sazanovich, H. D. Burrows, C. Serpa, J. A.

Weinstein, Dalton Trans. 2015, 44, 11705.

[

3] N. Deibel, D. Schweinfurth, J. Fiedler, S. Záliš, B. Sarkar, Dalton Trans. 2011, 40, 9925.

4] N. Deibel, D. Schweinfurth, S. Hohloch, J. Fiedler, B. Sarkar, Chem. Commun. 2012, 48, 2388.

[

22

Chemistry - A European Journal

10.1002/chem.201903700

[5] B. Sarkar, R. Hübner, R. Pattacini, I. Hartenbach, Dalton Trans. 2009, 4653.

[

6] a) W. B. Connick, D. Geiger, R. Eisenberg, Inorg. Chem. 1999, 38, 3264; b) S. D. Cummings, R.

Eisenberg, J. Am. Chem. Soc. 1996, 118, 1949; c) N. M. Shavaleev, E. S. Davies, H. Adams, J. Best, J. A.

Weinstein, Inorg. Chem. 2008, 47, 1532; d) J. A. Weinstein, M. T. Tierney, E. S. Davies, K. Base, A. A.

Robeiro, M. W. Grinstaff, Inorg. Chem. 2006, 45, 4544.

[7] S. Archer, J. A. Weinstein, Coord. Chem. Rev. 2012, 256, 2530.

[

8] a) J. Jacquet, P. Chaumont, G. Gontard, M. Orio, H. Vezin, S. Blanchard, M. Desage-El Murr, L.

Fensterbank, Angew. Chem. Int. Ed. 2016, 55, 10712; b) J. L. Boyer, J. Rochford, M.-K. Tsai, J. T.

Muckerman, E. Fujita, Coord. Chem. Rev. 2010, 254, 309.

[

9] S. Reinhardt, K. Heinze, Z. anorg. allg. Chem. 2006, 632, 1465.

10] K. Heinze, S. Reinhardt, Chem. Eur. J. 2008, 14, 9482.

11] R. Roy, P. Chattopadhyay, C. Sinha, S. Chattopadhyay, Polyhedron 1996, 15, 3361.

12] a) P. M. S. Monk, D. R. Rosseinsky, R. J. Mortimer, Electrochromism and electrochromic devices,

Cambridge University Press, Cambridge, 2007; b) J. García-Cañadas, A. P. Meacham, L. M. Peter, M.

D. Ward, Angew. Chem. Int. Ed. 2003, 42, 3011; c) M. D. Ward, J. Solid State Electrochem. 2005, 9,

778; d) N. M. Shavaleev, E. S. Davies, H. Adams, J. Best, J. A. Weinstein, Inorg. Chem. 2008, 47, 1532.

[

13] a) C. G. Pierpont, R. M. Buchanan, Coord. Chem. Rev. 1981, 38, 45; b) D. L. J. Broere, R. Plessius, van

der Vlugt, Jarl Ivar, Chem. Soc. Rev. 2015, 44, 6886; c) M.-K. Tsai, J. Rochford, D. E. Polyansky, T.

Wada, K. Tanaka, E. Fujita, J. T. Muckerman, Inorg. Chem. 2009, 48, 4372; d) G. C. Paul, K. Das, S.

Maity, S. Begum, H. K. Srivastava, C. Mukherjee, Inorg. Chem. 2019, 58, 1782.

[14] a) S. Pascal, O. Siri, Coord. Chem. Rev. 2017, 350, 178; b) A. I. Poddel'sky, V. K. Cherkasov, G. A.

Abakumov, Coord. Chem. Rev. 2009, 253, 291.

[15] H. Stetter, Chem. Ber. 1953, 86, 161.

[

16] a) C. Pai-Hsiu, C. Hei-Ying, L. Cheng-Chen, P. Shie-Ming, Inorg. Chim. Acta 1990, 169, 19; b) H.-Y.

Cheng, P.-H. Cheng, C.-F. Lee, S.-M. Peng, Inorg. Chim. Acta 1991, 181, 145; c) H.-Y. Cheng, G.-H. Lee,

S.-M. Peng, Inorg. Chim. Acta 1992, 191, 25; d) W.-H. Leung, E. K.-F. Chow, S.-M. Peng, Polyhedron

1993, 12, 1635; e) K. Kavallieratos, J. M. Rosenberg, J. C. Bryan, Inorg. Chem. 2005, 44, 2573; f) K. J.

Kilpin, W. Henderson, B. K. Nicholson, Polyhedron 2007, 26, 434; g) M. Li, K. Takada, J. I. Goldsmith, S.

Bernhard, Inorg. Chem. 2016, 55, 518; h) D. Kalinina, C. Dares, H. Kaluarachchi, P. G. Potvin, A. B. P.

Lever, Inorg. Chem. 2008, 47, 10110; i) M. Li, S. Bernhard, Catal. Today 2017, 290, 19.

[17] R. J. Alvarado, J. M. Rosenberg, A. Andreu, J. C. Bryan, W.-Z. Chen, T. Ren, K. Kavallieratos, Inorg.

Chem. 2005, 44, 7951.

[18] C. Evans, W. Henderson, B. K. Nicholson, Inorg. Chim. Acta 2001, 314, 42.

[

19] a) Y. Rechkemmer, F. D. Breitgoff, M. van der Meer, M. Atanasov, M. Hakl, M. Orlita, P. Neugebauer,

F. Neese, B. Sarkar, J. van Slageren, Nat. Commun. 2016, 7, 10467; b) U. Albold, H. Bamberger, P. P.

Hallmen, J. van Slageren, B. Sarkar, Angew. Chem. Int. Ed. 2019, 58, 9802.

[20] A. J. Blacker, S. B. Duckett, J. Grace, R. N. Perutz, A. C. Whitwood, Organometallics 2009, 28, 1435.

[21] A. J. Blacker, E. Clot, S. B. Duckett, O. Eisenstein, J. Grace, A. Nova, R. N. Perutz, D. J. Taylor, A. C.

Whitwood, Chem. Commun. 2009, 6801.

[22] A. Nova, D. J. Taylor, A. J. Blacker, S. B. Duckett, R. N. Perutz, O. Eisenstein, Organometallics 2014, 33,

3

433.

23] T. Kato, H. Masu, H. Takayanagi, E. Kaji, K. Katagiri, M. Tominaga, I. Azumaya, Tetrahedron 2006, 62,

458.

[

8

23

Chemistry - A European Journal

10.1002/chem.201903700

[

24] a) S. Zai, H. Gao, Z. Huang, H. Hu, H. Wu, Q. Wu, ACS Catal. 2012, 2, 433; b) O. I. Shadyro, V. L.

Sorokin, G. A. Ksendzova, O. V. Savinova, N. I. Pavlova, E. I. Boreko, Pharm. Chem. J. 2012, 46, 414.

25] Y.-W. Dong, R.-Q. Fan, P. Wang, Y.-L. Yang, Acta Crystallogr., Sect. E Struct. Rep. Online 2012, 68,

o1427.

26] a) X. Sun, H. Chun, K. Hildenbrand, E. Bothe, T. Weyhermüller, F. Neese, K. Wieghardt, Inorg. Chem.

2002, 41, 4295; b) P. Ghosh, A. Begum, D. Herebian, E. Bothe, K. Hildenbrand, T. Weyhermüller, K.

Wieghardt, Angew. Chem. Int. Ed. 2003, 42, 563.

[

27] a) M. L. Conrad, J. E. Enman, S. J. Scales, H. Zhang, C. M. Vogels, M. T. Saleh, A. Decken, S. A.

Westcott, Inorg. Chim. Acta 2005, 358, 63; b) J. Roberto Pioquinto-Mendoza, D. Martínez-Otero, N.

Andrade-López, J. G. Alvarado-Rodríguez, V. Salazar-Pereda, G. Sánchez-Cabrera, F. J. Zuno-Cruz,

Polyhedron 2013, 50, 289.

[28] M. M. Khusniyarov, K. Harms, O. Burghaus, J. Sundermeyer, B. Sarkar, W. Kaim, J. van Slageren, C.

Duboc, J. Fiedler, Dalton Trans. 2008, 1355.

[29] S. Yamada, T. Matsumoto, H.-C. Chang, Chem. Eur. J. 2019, 25, 8268.

[30] a) G. Hermann, V. Pohl, J. C. Tremblay, B. Paulus, H.-C. Hege, A. Schild, J. Comput. Chem. 2016, 37,

1511; b) V. Pohl, G. Hermann, J. C. Tremblay, J. Comput. Chem. 2017, 38, 1515; c) G. Hermann, V.

Pohl, J. C. Tremblay, J. Comput. Chem. 2017, 38, 2378.

[31] D. Stalling, M. Westerhoff, H.-C. Hege in The visualization handbook (Eds.: C. D. Hansen, C. R.

Johnson), Elsevier Butterworth-Heinemann, Burlington, MA, 2005, pp. 749–767.

[

32] a) T. Gensch, M. N. Hopkinson, F. Glorius, J. Wencel-Delord, Chem. Soc. Rev. 2016, 45, 2900; b) S. A.

Girard, T. Knauber, C.-J. Li, Angew. Chem. Int. Ed. 2014, 53, 74; c) H. Yi, G. Zhang, H. Wang, Z. Huang,

J. Wang, A. K. Singh, A. Lei, Chem. Rev. 2017, 117, 9016.

[

33] X.-Z. Shu, Y.-F. Yang, X.-F. Xia, K.-G. Ji, X.-Y. Liu, Y.-M. Liang, Org. Biomol. Chem. 2010, 8, 4077.

34] D. P. Shelar, T.-T. Li, Y. Chen, W.-F. Fu, ChemPlusChem 2015, 80, 1541.

35] a) Y. Yang, M. Ishida, Y. Yasutake, S. Fukatsu, C. Fukakusa, M.-A. Morikawa, T. Yamada, N. Kimizuka,

H. Furuta, Inorg. Chem. 2019, 58, 4647; b) F. Geist, A. Jackel, P. Irmler, M. Linseis, S. Malzkuhn, M.

Kuss-Petermann, O. S. Wenger, R. F. Winter, Inorg. Chem. 2017, 56, 914.

[36] S. Otto, A. M. Nauth, E. Ermilov, N. Scholz, A. Friedrich, U. Resch-Genger, S. Lochbrunner, T. Opatz, K.

Heinze, ChemPhotoChem 2017, 1, 344.

[

37] a) L. Huang, J. Zhao, RSC Adv. 2013, 3, 23377; b) B. Wang, D. P. Shelar, X.-Z. Han, T.-T. Li, X. Guan, W.

Lu, K. Liu, Y. Chen, W.-F. Fu, C.-M. Che, Chem. Eur. J. 2015, 21, 1184; c) M. Rueping, C. Vila, R. M.

Koenigs, K. Poscharny, D. C. Fabry, Chem. Commun. 2011, 47, 2360; d) Q. Liu, Y.-N. Li, H.-H. Zhang, B.

Chen, C.-H. Tung, L.-Z. Wu, Chem. Eur. J. 2012, 18, 620.

24

Chemistry - A European Journal

10.1002/chem.201903700

TOC

A series of platinum-based donor-acceptor complexes are presented. The effect of the donor ligands on

the frontier orbitals, the redox potentials, on redox-induced isomerism, and on photocatalysis is

probed.

25

Article Doi

Tuning PtII-Based Donor–Acceptor Systems through Ligand Design: Effects on Frontier Orbitals, Redox Potentials, UV/Vis/NIR Absorptions, Electrochromism, and Photocatalysis

DOI: 10.1002/chem.201903700

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Article abstract of DOI:10.1002/chem.201903700

Full text of DOI:10.1002/chem.201903700

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