Synthesis, Structure and Physical Properties of "wire-like" Metal Complexes

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Synthesis, Structure and Physical Properties of “Wire-like” Metal

Complexes

†

̈

Masnun Naher, Soren Bock, Zakary M. Langtry, Kieran M. O ’Malley, Alexandre N. Sobolev,

Brian W. Skelton, Marcus Korb, and Paul J. Low *

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ABSTRACT: The syntheses and crystallographically determined structures of

metal complexes trans-[M(CCR)₂L_n] (ML_n= Ru(dppe)₂, Ru{P(OEt)₃}₄,

Pt(PEt₃)₂) featuring acetylide ligands further functionalized by aryl thioether

groups are reported, together with those of analogous organic buta-1,3-diyne

(RCCCCR) and 1,4-diethynylbenzene (RCCC₆H₄CCR) compounds

for comparative purposes. The terminal thioether functional groups have an

aﬃnity for binding to the surface of gold electrodes and are considered as “anchor”

groups in the design of molecules for study within metal|molecule|metal molecular

junctions. The inﬂuence of the Lewis acidic and π-basic thioether moiety on a

number of physical properties important to the electrical behavior of molecules

within molecular junctions has been explored using spectroscopic, electrochemical, and quantum chemical methods. The thioether

functional group serves as a moderately strong π-electron-donating substituent, similar in electronic character to the OMe group,

resulting in relatively high lying HOMOs that are delocalized over the length of the molecule and well-suited to promote coherent

tunneling within the junction. In addition, the facile oxidation processes and the relatively small reorganization energies associated

with the one-electron oxidation of these compounds indicate the potential for eﬀective hopping mechanisms of charge transport

through longer structures based on these organometallic motifs.

molecular junctions, a more detailed design strategy requires

consideration of the underlying mechanism of charge trans-

port. For compounds in which the primary mechanism of

conductance can be satisfactorily described in terms of

coherent tunneling through a single rectangular barrier,

important parameters include the length and height of the

tunnel barrier. In turn, these concepts might be related to the

distance between the designated atoms that provide electrode

contacts in the anchor groups through the molecule,¹⁴and the

energy oﬀset between the electrode Fermi level and the

molecular level (orbital) responsible for conductance,¹⁵

respectively. As the molecular length increases, nonresonant

hopping mechanisms in which the transporting charge

progresses along the molecular backbone through one or

more “steps” become increasingly important to the charge

transport process.¹⁶The stepwise transfer of charge along the

molecular backbone in the hopping mechanism implies that

the transporting charge resides on the molecular backbone for

a ﬁnite period of time. A description of the hopping

INTRODUCTION

■

The development of experiential platforms through which to

construct electrode|molecule|electrode molecular junctions and

measure molecular conductance (or resistance if one prefers)

(Figure 1) has seen a renaissance in the ﬁeld of molecular

Figure 1. Cartoon depiction of an electrode|molecule|electrode

molecular junction.

electronics.¹⁻⁵This interest has in turn led to a demand for

molecular structures in which some central moiety designed to

oﬀer some speciﬁed electronic function (e.g., wire-like

conductance, bistable switching properties, rectiﬁcation,

transistor-like response, etc.) is connected, often via some

intermediary “leads”, to “anchor groups”⁶suitable for

contacting physically, electronically, and/or magnetically to

the macroscopic electrodes of the junction (Figure 1).^7,8

However, despite the appeal of such idealized “modular

design” principles,⁹⁻¹³the electrical properties of the complete

junction cannot be so simply partitioned. Beyond the

elementary features of anchor groups, linkers, and the

functional core required of molecules to be assembled within

Received: October 20, 2020

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Scheme 1. Preparation of Terminal Alkynes 1a,b and Butadiynes 2a,b

mechanism through a molecular junction therefore features

concepts contained within Marcus theory and descriptions of

RESULTS AND DISCUSSION

■

Synthetic Chemistry. The molecular design strategies for

the compounds investigated here include functional groups

intended to serve as contacts or anchors to secure the molecule

within a molecular junction.^8,34The acyclic thioether 4-

thioanisole is a well-established anchor group capable of

supporting both hole- and electron-mediated transport in

molecular junctions.³⁵Although not yet widely employed in

studies of molecular junctions, the cyclic thioether

benzodihydro[b]thiophene (BT) oﬀers many desirable fea-

tures for use as an anchor group, including high junction

formation probability in STM-break junction experiments.³⁶

The BT anchor group has been used as an anchor group for

the formation of molecular junctions from both organic

compounds³⁶⁻³⁹and inorganic complexes⁴⁰and supramolec-

ular assemblies,⁴¹as have related six-membered cyclic

thioethers.⁴²Here we have chosen to use 3,3-dimethyl-2,3-

dihydrobenzo[b]thiophene (DMBT) as a complementary

anchor group,⁴³with the 3,3-dimethyl groups being introduced

to enhance the solubility of the resulting products as well as

providing an element of synthetic expedience relative to the

rather protracted synthesis of ethynyl BT derivatives.³⁶

The parent alkyne 4-ethynylthioanisole (1a) is a well-known

compound that is readily available from Sonogashira cross-

coupling of commercially available 4-iodothioanisole with

trimethylsilylacetylene ([Pd(PPh₃)₄]/CuI/NEt₃) and subse-

quent removal of the protecting group (K₂CO₃/MeOH)

(Scheme 1).

charge transport in the junction can be made in terms of, for

example, the Kusnetsev−Ulstrup two-step model, where the

molecular reorganization energy accompanying a redox state

change plays an important role in the overall process.¹⁷⁻¹⁹

Destructive quantum interference can also play a profound role

in the transmission of charge through a molecular backbone

and is particularly important in cross-conjugated, branched,

and pendant-decorated structures.²⁰

As a result of these considerations, metal complexes have

been identiﬁed as particularly interesting systems with which to

construct molecular junctions.²¹⁻²⁵Metal complexes and

organometallic compounds are well suited to the modular

design of molecules represented in Figure 1, with a well-

deﬁned geometry at the metal center and ready introduction of

“linker” ligands further functionalized with anchor groups.²⁶

The nature of the metal and the ancillary ligands can be used

to readily tune the frontier orbital energies,²⁷while the

additional magnetic, (opto)electronic, and redox properties of

metal complexes provide ample scope for the introduction of

useful properties within the junction.²⁸⁻³⁰

Here we report the syntheses and crystallographically

determined structures of the metal complexes trans-[M(C

CR)₂L_n] (ML_n= Ru(dppe)₂, Ru{P(OEt)₃}₄, Pt(PEt₃)₂),

together with further investigations of the redox characteristics

and electronic structures of the one-electron oxidation

products, trans-[M(CCR)₂L_n]⁺, that would be important

in future studies assessing coherent tunneling vs hopping-based

mechanisms of charge transport^19,31,32and redox-switching

events within a molecular junction.^18,33Data from closely

related organic compounds are provided for comparison and

completeness.

The related ethynyl-functionalized cyclic thioether 5-

ethynyl-3,3-dimethyl-2,3-dihydrobenzo[b]thiophene (2b) was

obtained from 5-bromo-3,3-dimethyl-2,3-dihydrobenzo[b]-

thiophene, in turn prepared by a minor modiﬁcation of the

literature route.⁴²The bromo moiety in 5-bromo-3,3-dimethyl-

2,3-dihydrobenzo[b]thiophene is somewhat deactivated by the

electron-donating cyclic thioether, prompting Bryce and

colleagues to introduce a bromide/iodide exchange step in

B

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a

Scheme 2. Preparation of Compounds and Complexes 3a,b−6a,b

a

Legend: (a) 0.5 equiv of 1,4-diethynylbenzene, [Pd(PPh₃)₄], CuI, NEt₃; (b) 0.5 equiv of 1b, 1,4-dibromobenzene, [Pd₂(dba)₃], JohnPhos, CuI,

NHⁱPr₂; (c) [RuCl(dppe)₂]OTf, NaPF₆, NEt₃; (d) trans-[RuCl₂{P(OEt)₃}₄], KPF₆, NHⁱPr₂; (e) [PtCl₂(PEt₃)₂], CuI, NEt₃.

their synthesis of ethynyl derivatives of 2,3-dihydrobenzo[b]-

thiophene.³⁶After exploration of a range of palladium

precursors and ligand systems, the [Pd₂(dba)₃]/JohnPhos/

CuI catalyst system was found to be optimal to promote the

smooth cross-coupling of 5-bromo-3,3-dimethyl-2,3-

dihydrobenzo[b]thiophene with either trimethylsilylacetylene

or 2-methyl-3-butyn-ol, thereby avoiding the halogen exchange

step. Deprotection (NBu₄F or NaOH/toluene respectively)

gave 1b as a crystalline solid after workup (Scheme 1).

The terminal alkynes 1a and 1b smoothly homocoupled

using the Navale catalyst system^44,45to give the buta-1,3-

diynes 2a (55%)⁴⁶and 2b (56%), which oﬀer a π-conjugated

backbone of well-deﬁned molecular length between the

thioether anchor groups, making such compounds ideal for

use in molecular electronics (Scheme 1).^36,47However,

derivatives of 1,4-bis(phenylethynyl)benzene are perhaps the

archetypal molecular wires and have formed the basis for many

studies of the fundamental transport properties of molecular

junctions,^14,48−58meriting the preparation and characterization

of such compounds for reference purposes. It proved

convenient to prepare 3a (54%)^59,60by the reaction of 1,4-

diethynylbenzene with bromothioanisole under standard

Sonogashira conditions while 3b (37%) was better obtained

from 1,4-dibromobenzene and 1a (Scheme 2).

The metal complexes trans-[Ru(CCR)₂(dppe)₂] have

proven to be eﬀective test beds for the construction of

molecular junctions based on organometallic com-

plexes.^{27,28,61−68}Here, reactions of [RuCl(dppe)₂]OTf with

1a and 1b in the presence of NaPF₆and triethylamine⁶⁹⁻⁷¹

gave 4a (98%) and 4b (65%), respectively (Scheme 2). With a

view to decreasing potential adventitious contacts (short

circuits) to the π-electron-rich aryl moieties of the dppe

ligands within the junctions,⁷²the closely related complexes

trans-[Ru(CCR)₂{P(OEt)₃}₄] bearing “insulating” trialkyl

phosphite ancillary ligands were also prepared from reactions

between trans-[RuCl₂{P(OEt)₃}₄] and 1a or 1b in the

presence of KPF₆and diisopropylamine,⁷³giving 5a (58%)

and 5b (35%), respectively (Scheme 2). The behavior of

square-planar platinum complexes trans-[Pt(CCR)₂(PR′₃)₂]

within molecular junctions has also attracted interest. Initially

proposed as molecular insulators,⁷⁴the wire-like properties of

these systems have been gradually exposed.^{11,62,63,72,75,76}The

platinum complexes 6a (38%)⁷⁷and 6b (46%) were prepared

by conventional CuI-catalyzed reactions of [PtCl₂(PEt₃)₂] with

1a and 1b, respectively (Scheme 2).

Molecular Structures. The interpretation of conductance

data from molecular junctions operating under a bias, often as

a further function of electrode separation, is assisted by

information concerning the molecular geometry within the

junction and hence the molecular length. The crystallo-

graphically determined structures of the compounds 1a,⁷⁸2a,⁷⁹

and 3a⁸⁰have been reported earlier by others, the structures of

1b−3b and 4a,b−6a,b being determined in the course of this

work (Table 1). Plots of molecules of additional solvates (4a),

disolvates (4b), and polymorphs (6b) and associated data are

included in the Supporting Information.

The molecular structure of 1b (Figure 2) presents no

unusual features, with an approximately linear acetylene moiety

and expected parameters associated with the aromatic ring.

The dihydrothiophene moiety adopts an envelope conforma-

tion, with C23 lying ca. 0.55 Å from the mean plane through

S1−C1−C21−C22.

Compound 2b (Figure 3) adopts a linear structure in the

solid state, with the two arene rings adopting a mutual angle of

−19.134(2)° and a clear pattern of long−short bond

alternation along the buta-1,3-diyne backbone (Table 1). In

the solid state, adjacent molecules are linked by a zigzag-like

array following the b axis through intermolecular T-shaped C−

H···π interactions involving H21B and the π system of the

C13−C18 labeled aryl ring (Figure S1). There are no close S···

S interactions.

In contrast to the solid-state structure of 3a, in which the

aromatic rings adopt a largely coplanar orientation in the solid

state,⁸⁰the central phenylene ring of 3b, which sits on an

inversion center, is canted by 50.10(6)° (root-mean-square

deviation (rmsd) = 0.0009 Å) with respect to the outermost

aryl rings, which are ideally coplanar (0.00(9)°, rmsd = 0.0098

Å) (Figure 4). Weak T-shaped C−H···π interactions between

C3 and C14 (3.3940(19) Å) dominate the crystal packing.

The complexes 4a (Figure S2) and 4b (Figure 5) both sit on

centers of inversion, with the aryl rings of the anchor group

lying approximately in the same plane and roughly intersecting

the P1−Ru−P2A angles (α = 97.78(2)° (4a), 97.95(2)° (4b))

between both dppe fragments by θ = 77, 71° (4a) and θ = 65,

C

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E

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and 5, ruthenium; 6, platinum), or the acyclic (a) or cyclic (b)

nature of the thioether anchor. The constrained ring system in

the cyclic thioether systems b results in only a very slight

contraction of d_S···Srelative to the analogous acyclic thiomethyl

derivatives a (Table 1). Together, the compounds and

complexes 2a,b−6a,b give a series of linear compounds with

wire-like structures with S···S distances (“length”, d_S···S) ranging

from 15.66 to 20.07 Å.

The exponential decay of conductance (G) with distance in

a simple single-barrier tunnel model of a molecular junction

gives rise to the well-known expression

G ∝ e^−βl

Figure 2. ORTEP drawing (50% probability level) of the molecular

structure of 1b with the atom-numbering scheme. All C-bonded

hydrogen atoms except H42 have been omitted for clarity.

where l is the tunnel barrier length, usually approximated by

the electrode separation in the junction and hence related to

the molecular length, and β is a decay constant that reﬂects the

wire-like eﬃcacy of the molecule within the junction.¹⁴The

similar d_S···Svalues from the cyclic and thiomethyl function-

alized pairs would permit a closer investigation of the nature of

the anchor group largely free of complications arising from

signiﬁcant variations in molecular lengths. Similarly, the nearly

identical values of d_S···Sfor the ruthenium and platinum

complexes 4−6 would also allow a comparison of the eﬀects of

the metal centers on the electrical characteristics of a junction

largely free of the inﬂuence of variation in molecular lengths.

Electrochemistry. Estimates of the relative tunnel barrier

heights or energy of a key transport channel (molecular

orbital) relative to the electrode Fermi level have been made in

studies conducted elsewhere from electrochemically deter-

mined oxidation potentials as a proxy for HOMO energy

levels¹⁵and DFT calculations.⁹In addition, redox processes

associated with a molecule within a junction can lead to in situ

doping of the molecular species²⁷or switching events as a

function of the junction bias.²⁸Further consideration of

molecular conductance mediated by hole (electron) hopping

mechanisms also raises interest in the electronic structures of

the one-electron-oxidation (-reduction) products and associ-

ated reorganization energies. However, a note of caution is

made, in that these approaches neglect the eﬀect of the

molecule−electrode interface and concepts such as charge

pinning within the junction, the inﬂuence of solvation and ion-

pairing on electrochemical potentials, and basis set and

functional dependence of DFT estimates of orbital energies.

Nevertheless, these concepts raise interest in the electro-

75° (4b), and therefore allowing a degree of d−π overlap with

the molecular backbone.⁶⁹There are no signiﬁcant diﬀerence

in bond lengths along the trans-bis(acetylide) backbone (Table

1), and the structures are entirely consistent with those of

related complexes discussed elsewhere.⁶⁹

The tetrakis(triethyl phosphite) complexes 5a (Figure S5)

and 5b (Figure 6) oﬀer the anticipated octahedral environment

at ruthenium and trans-disposed acetylide ligands.⁷³The

aromatic rings associated with the anchor groups are cantered

with respect to each other by 55.67(2)° (5a) or 71.97(2)°

(5b). The bond distances along the trans-bis(acetylide)

backbone in 5a and 5b are strikingly consistent with each

other and also with those of 4a and 4b, with no evidence for

any signiﬁcant inﬂuence of the ancillary ligands on the metal−

alkynyl bonding (Table 1).

Complex 6a (Figure S6) displays an almost ideal square-

planar geometry at the platinum atom (P1−Pt1−C1,

89.90(3)°), which sits on an inversion center. The geometry

at platinum in 6b is somewhat more distorted in each of the

two independent molecules in the asymmetric unit (Figure 7).

The aromatic rings of the anchor groups are essentially

coplanar and oriented orthogonally to the metal square plane.

In the case of 6b, strong S···S interactions link molecules into

chain-like arrays in the solid state (Figure S8).

The data compiled in Table 1 indicate little systematic

change in the structure of the arylacetylide moieties as a

function of the central moiety (2, bond; 3, phenylene ring; 4

Figure 3. ORTEP drawing (50% probability level) of the molecular structure of 2b with the atom-numbering scheme. All hydrogen atoms have

been omitted for clarity.

F

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Figure 4. ORTEP drawing (50% probability level) of the molecular structure of 3b with the atom-numbering scheme. All hydrogen atoms have

been omitted for clarity. Symmetry operation for generating equivalent atoms: (A) −2 − x, 3 − y, 2 − z.

Figure 5. ORTEP drawing (50% probability level) of the molecular structure of 4b·CH₂Cl₂with the atom-numbering scheme. Hydrogen atoms,

one disordered molecule of CH₂Cl₂, disordered parts of the DMBT moiety (0.696:0.304 occupancy ratio), and the phenyl rings, except for their

ipso atoms, have been omitted for clarity. Symmetry operation for generating equivalent atoms: (A) 1 − x, −y, −z.

Figure 6. ORTEP drawing (50% probability level) of the molecular structure of 5b with the atom-numbering scheme. All hydrogen atoms have

been omitted for clarity.

chemical properties of the compounds and complexes 2a,b−

6a,b and the electronic structures of the resulting oxidation

products.

At a platinum electrode, the organic buta-1,3-diynes 2a and

2b and 1,4-bis(aryleneethynyl)benzenes 3a and 3b each

higher-lying HOMO. The platinum complexes 6 also display

an irreversible electrochemical response, with E_p/2values lower

again than those of 3. In contrast, the ruthenium complexes 4

and 5 displayed the near-reversible electrochemical response

expected of species of this type^69,73,82,83and, as would be

expected, the oxidation potentials of complexes 4 and 5 are the

lowest of the series explored here. The signiﬁcant contribution

from the alkynyl ligands to the oxidation processes of

ruthenium acetylide complexes leads to a strong dependence

of the oxidation potentials on the ligand substituents; here the

exhibited an irreversible oxidation process in their cyclic

81

voltammograms (Table 2). The half-peak potentials (E_p/2

)

indicate the more facile oxidation of compounds 3 vs

compounds 2, consistent with the extended π system of the

1,4-bis(aryleneethynyl)benzene core of 3 and indicative of a

G

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Figure 7. ORTEP drawing (50% probability level) of the molecular structure of one molecule of 6b in the asymmetric unit with the atom-

numbering schemes. All hydrogen atoms have been omitted for clarity.

a

Table 2. Summary of Electrochemical Data from Compounds 2−6, HOMO Energies Estimated from the Electrochemical

Data (E_HOMO), and Calculated HOMO Energies (E_HOMO′), and Ionization Potentials (IP)

b

c

compound

E

_1/2/V

|E_pa− E_pc|/mV

i_pc/i_pa

E

_HOMO/eV

E_HOMO′/eV

IP /eV

d

2a

2b

3a

3b

4a

4b

5a

5b

6a

6b

0.67

0.87

0.49

0.50

0

1.0

0.9

1.0

0.9

0

−5.5

−5.7

−5.3

−4.7

−5.2

−6.14

−6.07

−6.04

−5.99

−4.97

−4.95

−5.12

−5.09

−5.52

−5.45

5.86

5.79

5.77

5.72

4.47

4.45

4.76

4.74

5.25

5.18

d

−0.10

−0.12

−0.06

−0.13

0.41

60

80

60

d

0.37

0

a

b

Conditions: CH₂Cl₂(0.1 M NBu₄PF₆), Pt working electrode, ν = 100 mV/s. Vs ferrocene/ferrocenium (i.e., E(Fc/Fc⁺) = 0.00 V) relative to an

c

internal decamethylferrocene/decamethylferrocenium redox couple (E(Fc*/Fc*⁺) = − 0.53 V vs Fc)). Calculated vertical ionization potential

d

(vide infra). E_p/2of the anodic wave of an irreversible process.

thioether group has an eﬀect similar to that of OMe on the

redox potentials measured under the same conditions (trans-

[Ru(CCC₆H₄OMe)₂(dppe)₂], E_1/2= −0.15 V;⁶⁹trans-

[Ru(CCC₆H₄OMe)₂{P(OEt)₃}₄], E_1/2= −0.11 V⁷³). We

note that the irreversible electrochemical response of the

organic and platinum complexes is due to decomposition of

the redox products at the electrode surface on the time scale of

the electrochemical experiment. However, the residence time

of charges on a long molecular wire (ca. 40 fs to 0.1 μs)⁸⁴

during a hopping-based charge transport is very much less than

the time taken for the potential sweep in the voltammetry

experiments carried out here, and long molecular wires based

on structures similar to 3 that conduct via hopping

mechanisms are known.^14,49

The HOMO levels of the compounds and complexes 2−6

can be broadly estimated from these electrochemical data

relative to ferrocene (E_HOMO= 4.8 eV) (Table 2).⁸⁵However,

these estimates of orbital energies drawn from electrochemical

data are convoluted by the eﬀects of solvation, ion pairing, and

reorganization energy on the electrochemical data and should

be treated with appropriate caution and regarded as a relative

measure rather than absolute values.

junctions. These calculations not only allow an estimate of the

HOMO energy levels across the series but also provide some

insight concerning the relative reorganization energies

associated with the oxidation processes. We note that previous

investigations have shown that the electronic structures of

complexes trans-[Ru(CCC₆H₄R)₂(dppe)₂] are dependent

on both the conformation and electronic character of the

arylacetylide fragments.⁶⁹Thus, while the major features of the

electronic spectra of 4 and 5 can be attributed to transitions

arising from the lowest energy conformer in which the

arylacetylide ligands lie in the same plane and bisect a P−Ru−

P angle, the ﬁne details of the spectrum are more fully

explained in terms of the population of a number of diﬀerent

conformers in solution that diﬀer in the relative orientation of

the arylacetylide fragments.⁶⁹Given the fairly extensive

exploration of these features in previous works, here attention

will be directed to the most signiﬁcant experimental features

and the characteristics of the most stable (lowest energy)

geometry.

Important bond lengths and angles from the geometry

optimizations are given in Table 1 alongside the analogous

parameters from the crystallographically determined structures.

Plots, compositions, and energies of selected molecular orbitals

of the neutral compounds and complexes 1a,b−6a,b are given

in Figures S9 −S13, with the illustrative example of 5a shown in

Figure 8. These data provide a point for initial comparison of

the electronic structures across the series. In each case, the

HOMO is well described in terms of a π-electron system

Electronic Structure Calculations. Electronic structure

calculations (BLYP35/LANL2DZ for Ru, Pt/6-31G** for all

other atoms/CPCM CH₂Cl₂solvent model) were carried out

for the complete suite of compounds 1a,b−6a,b and the one-

electron-oxidized products [2a,b]⁺−[6a,b]⁺most relevant to

the hopping model of charge transport within a molecular

H

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largely to the HOMO−LUMO transition with π−π* character,

with weak LMCT bands also found at lower energies (Table 1

and Figure S22).

The particular nature of the metal−ligand bonding in the

square-planar complexes ensures that the LUMO of platinum

complexes 6a and 6b is an unoccupied 6p_zorbital, while the π*

complement of the HOMO is found as the [LUMO+1]

(Figures S12 and S13). In the case of 6a and 6b the HOMO−

LUMO transition, which has signiﬁcant LMCT character, is

calculated to have low oscillator strength. The [HOMO-1]−

LUMO and HOMO−[LUMO+1] transitions have similar

character and mix to give more intense absorption features of

similar energy (Table 4) and together account for the

appearance of the optical spectra of these complexes (Figure

S23). However, the variation in the character of the lowest

energy electronic transitions of any appreciable intensity points

to a signiﬁcant challenge in using the “optical gap” as a

measure of the HOMO−LUMO gap across the series (Table

4).

The optimized structures of the radical cations reveal

informative trends, similarities, and diﬀerences between the

organic compounds and the various organometallic complexes

concerning the underlying electronic structures. An inspection

of the structures reveals that the organic compounds [2a,b]⁺

and [3a,b]⁺oﬀer more cumulated character than their neutral

precursors, with slightly longer CC (Δ_CC+0.01 Å) and

shorter C−C (Δ_C−C−0.03 Å) bonds (Table 1). This suggests

that the unpaired electron (or hole) is distributed more or less

evenly over the molecular backbone, which is consistent with

the distribution of the β-LUMO in each case (Figure S14).

The conformers of the metal complexes [4a,b]⁺examined here

also oﬀer a symmetrical structure with slightly increased

cumulenic character on oxidation being evident from the small

changes in bond lengths relative to those of [4a,b] (Δ_Ru−C

−0.05; Δ_CC+0.005; Δ_C−C−0.008 Å). These relatively small

changes across the molecular backbone are again consistent

with the distribution and composition of the β-LUMO (Figure

S15).

The molecular structures calculated for the tetrakis(trialkyl

phosphite)-supported ruthenium complexes [5a,b]⁺and

platinum complexes [6a,b]⁺are more consistent with the

eﬀects of oxidation being localized on one of the alkynyl

ligands. Further inspection of the distribution and composition

of the β-HOMO and β-LUMO in each case conﬁrms that one

of the alkynyl ligands plays an important role in the redox

activity of these complexes (Figures S16 and S17), which

might be described as ligand-based mixed-valence systems. The

ligand redox activity of trans-[Ru(CCR){P(OEt)₃}₄] has

been proposed on the basis of model computational results

reported earlier,⁷³and localized conformers of ligand-based

redox character have been reported for trans-[Pt{C

CC₆H₄NAr₂}(PR₃)₂]⁺complexes bearing redox-active triar-

ylamin-functionalized alkynyl ligands.^86,87

Figure 8. (a) HOMO and (b) LUMO of 5a (surfaces plotted at

0.02 (e/bohr³)^1/2).

distributed along the length of the molecular backbone. The

sulfur atoms of the anchor groups make a signiﬁcant

contribution to the HOMOs, as summarized in Table 3.

The HOMO energies (E_HOMO, Table 4) vary in the expected

manner, increasing in energy with (idealized) conjugation

length for 1−3 and higher again for the readily oxidized

ruthenium complexes 4 (E_1/2= − 0.13 V vs ferrocene/

ferrocenium) and 5 (E_1/2= − 0.05 V vs ferrocene/

ferrocenium). The contributions from low-lying 6s, 6p, and

5d orbitals to the bonding in square-planar Pt complexes 6

decrease the HOMO energy, which is calculated to be lower

lying than those of 4 and 5 but higher than those of the organic

compounds (Table 4).

For the organic compounds 1−3 the LUMO is well

described as the π* orbital counterpart of the HOMO (Figure

S9), decreasing in energy with increasing conjugation length

and causing the expected decrease in the HOMO−LUMO gap

from 1 to 2 to 3 (Table 4). This trend in orbital energies is

consistent with the decreasing wavenumbers of the lowest

energy optical transition in these compounds (Table 4 and

Figures S18 −S20), which in turn is reproduced by TD-DFT

calculations (Table 4).

In the case of the dppe-coordinated complexes 4a and 4b,

the low-lying aryl phosphine π* orbitals comprise the LUMO,

while the π* complement of the HOMO, which is delocalized

along the molecular backbone, is found as the [LUMO+3]

(Figure S10). The lowest energy optical absorption band is

found at 28570 cm⁻¹(4a; Figure S21) or 28730 cm⁻¹(4b;

Figure S21) and assigned by TD-DFT calculations (Table 4)

to oﬀer predominantly MLCT character associated with charge

transfer to the dppe ligands. The most intense low-energy

transitions in the phosphite complexes 5a and 5b correspond

Reorganization Energies. While the tunnel barrier height

and length are important parameters describing tunneling

through a single rectangular barrier, the Marcus-type

Table 3. Summary of S Atom Contributions (%) to the HOMO and LUMO of Compounds and Complexes 1a,b−6a,b

1a

1b

2a

2b

3a

3b

4a

4b

5a

5b

6a

6b

S (LUMO)

S (HOMO)

3

42

3

42

4

26

4

26

2

18

2

20

0

8

0

8

4

10

4

12

0

18

0

18

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Table 4. Summary of the Onset and Apparent Maximum of the Lowest Energy Transition in the UV−Vis Spectra of 1a,b−6a,b,

a

DFT Calculated HOMO and LUMO Energies, TD DFT Calculated Transitions, and Assignment

oscillator strength

v

̅

_onset/cm⁻¹

v

̅

_max/cm⁻¹

E_HOMO/eV

E

_HOMO/eV

E

_LUMO/eV ΔE_HOMO−LUMO/eV TD DFT/cm⁻¹

(f)

assignment

1a

1b

2a

2b

3a

3b

4a

4b

−6.54

−0.48

−0.46

−1.34

−1.31

−1.47

−1.45

−0.30

6.06

5.99

4.80

4.76

4.57

4.54

4.67

4.65

39202

38314

29534

29284

28526

28294

32228

32045

0.6790

HOMO−LUMO (96%)

−6.45

−6.14

−6.07

−6.04

−5.99

−4.97

−4.95

0.5173

1.8006

1.7120

2.6685

2.5804

1.13179

1.2266

HOMO−LUMO (92%)

HOMO−LUMO (94%)

HOMO−[LUMO+3] (68%)

26310

26110

25910

25125

25310

25440

27470

27030

27100

26660

28570

28730

−5.5

−5.7

−5.3

−4.7

HOMO-[LUMO+3] (56%)

HOMO−[LUMO+2] (16%)

5a

26180

29410

−4.7

−5.12

+0.30

5.42

30203

31155

0.0026

0.0022

HOMO-[LUMO+4] (71%)

[HOMO-2]−[LUMO+4]

(46%)

[HOMO-1]−[LUMO+4]

(36%)

34083

30156

1.9374

0.0025

HOMO−LUMO (80%)

5b

26110

28670

−4.7

−5.09

+0.30

5.39

HOMO−[LUMO+4] (70%)

[HOMO-3]−[LUMO+4]

(12%)

31110

33852

0.0023

1.8305

[HOMO-2]−[LUMO+4]

(49%)

[HOMO-1]−[LUMO+4]

(34%)

HOMO−LUMO (78%)

[HOMO-1]−[LUMO+1]

(17%)

6a

6b

26600

26040

28570

28490

−5.2

−5.52

−5.45

−0.07

−0.05

5.45

5.40

33200

35358

0.0492

1.0573

HOMO−LUMO (88%)

[HOMO-1]−LUMO (66%)

HOMO-[LUMO+1] (19%)

HOMO-[LUMO+1] (48%)

[HOMO-2]-LUMO (67%)

35916

36605

0.7266

0.6591

33027

35478

0.1205

0.9948

HOMO−LUMO (88%)

HOMO−[LUMO+1] (34%)

[HOMO-1]−LUMO (45%)

[HOMO-1]−[LUMO+2]

(11%)

35595

0.8148

[HOMO]−[LUMO+1]

(36%)

[HOMO-1]−LUMO (41%)

[HOMO-1]−[LUMO+2]

(13%)

a

Estimates of the HOMO energy (E_HOMO) from electrochemical data are given for comparison.

reorganization energy is a primary factor inﬂuencing the

description of charge hopping through a molecular junction.

Reorganization energies associated with the oxidation of each

species (λ_(0,+1)) were calculated from the optimized geometries

of the wire-like species 2a′,b′−6a′,b′ in both the neutral and

radical cation electronic conﬁgurations and the relationship

where E_(x,y)is the energy of the molecule in the optimized

geometry x with electronic conﬁguration y (i.e., E_(0,0)is the

energy of the neutral molecule in the neutral geometry, which

is taken as the energy reference point in each case, E_(0,+1)is the

energy of the neutral molecule in the cation geometry, etc.)

(Table 5 and Figure 9).⁸⁸

Perhaps unsurprisingly, the larger values of the reorganiza-

tion energy are associated with 5a,b and 6a,b, which also give

λ_(0,+1)= [E_(0,+1)− E_(0,0)] + [E_(+1,0)− E_(+1,+1)

]

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and 5a (2073 cm⁻¹) fall at slightly larger wavenumbers in

comparison to the comparable phosphite examples 4b (2053

cm⁻¹) and 5b (2067 cm⁻¹), consistent with a small additional

back-bonding contribution from the more electron rich

Ru{P(OEt)₃}₄fragments to the alkynyl ligand moieties.

Upon one-electron oxidation to the monocations in the

spectroelectrochemical cell, the ν(CC) bands shift to one

major, lower frequency band envelope by between 170 and

165 cm⁻¹(4a, 4b) and between 185 and 180 cm⁻¹(5a, 5b).

The large shift to lower wavenumbers is indicative of a

substantial role of the alkynyl ligands in the oxidation process,

while the single principal feature in the ν(CC) spectra of the

oxidized complexes indicates a predominant description of

these species in terms of a delocalized electronic structure

along the −CC−Ru−CC− chain. The breadth and

asymmetry of the ν(CC) vibrational band envelopes in

the oxidation products [4a,b]⁺and [5a,b]⁺is consistent with

the presence of a number of conformers that diﬀer in the

relative orientation of the aromatic rings of the ethynyl ligands

with respect to the RuP₄core in each case;^69,73similar but less

pronounced features are apparent in the neutral precursors.

These diﬀerent conformations will moderate the degree of

d−π overlap along the molecular backbone. In the case of

[5a]⁺and [5b]⁺, the presence of an additional weak feature at

2022 or 2025 cm⁻¹, respectively, is consistent with a

population of conformers with more localized electronic

structures Ar−CC−[Ru−CC−Ar]⁺, consistent with the

computational studies described above.

Table 5. Summary of Molecular Energies and

Reorganization Energies Associated with the One-Electron

Oxidation of 2a,b−6a,b

E

_(0,0)/eV

E

_(0,+1)/eV

E

_(+1,+1)/eV

E_(+1,0)/eV

λ_(0,+1)/eV

2a

2b

3a

3b

4a

4b

5a

5b

6a

6b

0.00

0.13

0.14

0.12

0.13

0.18

0.14

0.23

5.73

5.66

5.61

4.34

4.32

4.58

4.56

5.03

5.08

5.86

5.79

5.77

5.72

4.47

4.46

4.76

5.25

5.18

0.26

0.27

0.23

0.26

0.36

0.37

0.34

Figure 9. Sketch of the relative energies an geometries for the neutral

and cation states of molecules [2a,b]ⁿ⁺−[6a,b]ⁿ⁺. The energy of the

neutral compound in the neutral geometry is taken as the reference

point (E_(0,0)= 0 eV).

The similar electronic character of complexes trans-[Ru(C

CR)₂(dppe)₂] and trans-[Ru(CCR)₂{P(OEt)₃}₄] is further

evinced by the UV−vis−NIR spectra of 4a, 4b, 5a, and 5b,

which are characterized in each case by a relatively high lying

electronic transition near 29000 cm⁻¹(Figure 11). The

monocations generated within the spectroelectrochemical cell

exhibit a more complex series of electronic transitions with

prominent features near 35000, 23000, and 7500 cm⁻¹,

together with a series of weaker transitions through the NIR

region.

rise to the more localized one-electron-redox products.

Nevertheless, the reorganization energies are generally quite

low and are comparable to reorganization energies calculated

from a number of triarylamine-based hole transport materi-

als.^89,90This suggests that compounds such as these might be

suitable for the construction of longer wire-like molecules in

which charge-hopping mechanisms would be expected to play

a more signiﬁcant role than coherent tunneling.

Spectroelectrochemistry. Spectroelectrochemical studies

of metal acetylide and bis(acetylide) complexes have proven to

be useful tools in the experimental investigation of the nature

of redox processes and redox products⁹¹and were adopted

here to gain supporting evidence for the computational results

presented above. While the poor electrochemical reversibility

of the electrochemical events associated with the organic buta-

1,3-diynes 2a and 2b and 1,4-bis(aryleneethynyl)benzene

compounds 3a and 3b, as well as the platinum complexes 6a

and 6b, prohibited meaningful spectroelectrochemical inves-

tigations of these species and collection of data associated with

[2]⁺, [3]⁺, and [6]⁺, the ruthenium species [4]⁺and [5]⁺were

more readily studied. Although complexes of the general form

trans-[Ru(CCR)₂(dppe)₂] have been thoroughly investi-

gated using spectroelectrochemical methods,^69,83,92analogous

studies of trans-[Ru(CCR)₂{P(OEt)₃}₄] are far less

common.

As noted above, the [β-LUMO] levels of [4a]⁺and [4b]⁺

each have nodal properties and composition similar to those of

the HOMO levels of the neutral precursors, consistent with the

unpaired electron extensively delocalized over the molecular

backbone. The low energy (NIR) absorption bands of the

radical cations [4a]⁺and [4b]⁺are attributed by TD DFT

calculations to the [β-HOMO]−[β-LUMO] transition with

pronounced LMCT character with appreciable charge transfer

from the S atoms as well as the ethynyl ligands to the metal

center in each case.

The one-electron-oxidation products [5a]⁺and [5b]⁺give a

more “localized” electronic structure, with the [β-LUMO]

asymmetrically distributed over the ethynyl ligands, beﬁtting a

description of these compounds as ligand-based mixed-valence

systems (Figure S16). The major NIR bands in these cases

arising from the [β-HOMO]−[β-LUMO] transitions oﬀer a

degree of interligand charge-transfer character. Similar

scenarios have been described for conformers of trans-

[Ru(CCC₆H₄NH₂)₂(dppe)₂]⁺.⁶⁹

CONCLUSIONS

The IR spectroelectrochemical response of complexes 4a,b

and 5a,b are illustrated in Figure 10. Each complex is

characterized by a single ν(CC) band envelope in the

narrow range 2053−2073 cm⁻¹. In pairwise comparisons, the

ν(CC) bands of the phosphine derivatives 4a (2061 cm⁻¹)

■

A series of organic and organometallic complexes with “wire-

like” π-conjugated backbone structures and acyclic or cyclic

thioether “anchor groups” have been synthesized and

characterized through crystallographic, electrochemical, spec-

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Figure 10. IR spectra of complexes [4a]ⁿ⁺, [4b]ⁿ⁺, [5a]ⁿ⁺, and [5b]ⁿ⁺(n = 0, 1) recorded in a spectroelectrochemical cell (CH₂Cl₂/0.1 M

NBu₄PF₆).

MHz and Bruker Avance 500 and 600 MHz spectrometers and

referenced against solvent resonances (CHCl₃, ¹H 7.26 ppm, ¹³C{¹H}

troelectrochemical, and computational methods. The molec-

ular lengths, deﬁned by the S···S distance (d_S···S), are consistent

across the ruthenium (4a,b; 5a,b) and platinum (6a,b) metal

complexes and are only slightly shorter than those in the 1,4-

diethynylbenzene derivatives 3a,b. The nature of the thioether

has little bearing on the HOMO energy levels or redox

potentials, which in turn are more sensitive to the nature of the

central moiety (2, bond; 3, 1,4-phenylene; 4, trans-Ru(dppe)₂;

5, trans-Ru{P(OEt)₃}₄; 6, trans-Pt(PEt₃)₂). The delocalized

nature of the electronic structures leads to only small changes

in molecular structure and hence relatively low values of the

Marcus-type reorganization energy on one-electron oxidation

across the series. The localized electronic structures of [5a,b]⁺

and [6a,b]⁺coupled with their low reorganization energy

suggest that such motifs may be useful in the design of longer

wire-like components that promote conductance via facile

thermally activated charge-hopping mechanisms.

1

77.16 ppm; CH₂Cl₂, H 5.32 ppm, ¹³C{¹H} 53.84 ppm; (CH₃)₂CO,

¹H 2.05 ppm, ¹³C{¹H} 29.84, 206.26 ppm). Infrared spectra were

recorded on a Thermo 6700 spectrometer from CH₂Cl₂solution in a

cell ﬁtted with CaF₂windows or an Agilent Technologies Cary 630

spectrometer using ATR sampling methods. High-resolution mass

spectra were recorded using a Waters LCT Premier XE mass

spectrometer using electrospray ionization or atmospheric pressure

chemical ionization with leucine enkephalin as reference.

Synthesis of 4-(Trimethylsilylethynyl)thioanisole.⁹⁸

To a solution of 4-iodothioanisole (1.00 g, 4.00 mmol) in dry,

degassed triethylamine (25 mL), were added [Pd(PPh₃)₄] (46 mg,

0.04 mmol) and CuI (8 mg, 0.04 mmol). After addition of

trimethylsilylacetylene (0.49 g, 5.00 mmol), the mixture was stirred

for 4 h at room temperature. After this time, the solvent was removed

in vacuo, the residue was extracted with hexanes, and the extracts were

ﬁ ltered through a silica plug. Removal of the solvent from the ﬁ ltrate

gave the product as a white, crystalline solid (0.88 g, 100%). IR (solid

EXPERIMENTAL SECTION

■

General Conditions: Synthetic Chemistry. All reactions were

performed under an N₂atmosphere using standard Schlenk

techniques unless noted otherwise. Reaction solvents were puriﬁed

and dried by appropriate means prior to distillation and storage under

nitrogen. No special precautions were taken to exclude air or moisture

during workup. The compounds 4-ethynylthioanisole (1a),^78,93cis-/

trans-[PtCl₂(PEt₃)₂],⁷²trans-[RuCl₂{P(OEt)₃}₄],⁹⁴[RuCl(dppe)₂]-

OTf,⁹⁵[Pd₂(dba)₃],⁹⁶and [Pd(PPh₃)₄]⁹⁷were prepared by literature

methods or minor variations as described below. All other materials

were obtained from commercial suppliers and used as received. NMR

spectra were recorded in deuterated solvent solutions on Varian 300

1

state, ATR)/cm⁻¹: ν (C C) 2153. H NMR (CDCl₃, 500 MHz, δ /

ppm): 0.24 (s, 9H, H⁸), 2.48 (s, 3H, H⁷), 7.15 (d, J = 8.1 Hz, 2H,

H⁵), 7.36 (d, J = 8.1 Hz, 2H, H⁴). ¹³C{¹H} NMR (CDCl₃, 126 MHz,

δ /ppm): 11.15 (C⁸), 15.45 (C⁷), 94.28 (C¹), 105.01 (C²), 119.51

(C³), 125.78 (C⁵, C⁶), 132.36 (C³, C⁴), 139.73 (C⁶). MS (APCI-

TOF) m /z : calcd for C₁₂H₁₆OSSi [M]⁺220.0742; found 220.0734.

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Figure 11. UV−vis−NIR spectra of complexes [4a]ⁿ⁺, [4b]ⁿ⁺, [5a]ⁿ⁺, and [5b]ⁿ⁺(n = 0, 1) recorded in a spectroelectrochemical cell (CH₂Cl₂/0.1

M NBu₄PF₆).

Synthesis of 4-Ethynylthioanisole (1a).⁹⁸

δ /ppm): 28.81 (s, C¹¹), 53.55 (s, C¹⁰), 70.85 (s, C⁹), 120.04 (s, C³),

130.98 (s, C⁵,C⁷), 132.06 (s, C⁴,C⁸), 136.48 (s, C⁶). MS (APCI-TOF)

m /z : calcd for C₁₀H₁₃BrOS [M]⁺261.9850; found 261.9870.

Synthesis of 5-bromo-3,3-Dimethyl-2,3-dihydrobenzo[b]-

thiophene.⁴²

Potassium carbonate (0.83 g, 6 mmol) and 4-(trimethylsilylethynyl)-

thioanisole (0.88 g, 4.00 mmol) were dissolved in methanol (50 mL)

and stirred at room temperature for 2 h. After the solvent was

removed under reduced pressure, the residue was puri ﬁ ed by column

chromatography (silica, hexane). After the solvent of the appropriate

fraction was removed, the product was obtained as a dark yellow oil

(0.54 g, 91%). IR (CH₂Cl₂/cm⁻¹): ν (C C −H ) 3298, ν (C C)

2108. ¹H NMR (CDCl₃, 300 MHz, δ /ppm): 2.48 (s, 3H, H⁷), 3.07 (s,

1H, H¹), 7.17 (d, J = 8.4 Hz, 2H, H⁵), 7.40 (d, J = 8.4 Hz, 2H, H⁴).

¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /ppm): 15.36 (C⁷), 77.37 (C¹),

83.55 (C²), 118.37 (C³), 125.81 (C⁵), 132.47 (C³), 140.16 (C⁶). MS

(APCI-TOF) m /z : calcd for C₉H₈S [M]⁺148.0347; found 148.0351.

Synthesis of 4-Bromophenylthio-2-methylpropan-2-ol.⁴²

To a solution of 4-bromophenylthio-2-methyl-propan-2-ol (3.00 g,

11.5 mmol) in CH₂Cl₂(140 mL) was added aluminum trichloride

(9.00 g, 67.5 mmol), causing the solution to quickly develop from

colorless to dark red. The mixture was stirred for 7 days at room

temperature. After this time, the mixture was ﬁ ltered through a large

silica plug (Caution ! The evolution of HCl from unreacted Al₂Cl₆

demands that this process be carried out in a well-ventilated hood.)

and the plug washed with dichloromethane until the eluent was

colorless (ca. 400 mL). Removing the solvent under reduced pressure

yielded the crude product as a yellow oil (1.20 g, 44%). As this

cyclization reaction was found to be capricious at larger scales, four

separate preparations were typically carried out in parallel to give ca. 5

g of crude material, which was puri ﬁ ed by Kugelrohr distillation (ca.

100 °C, ca. 1.5 mbar) to give ca. 4.2 g of the title compound as a

A Schlenk ﬂ ask was charged with acetone (150 mL), 4-

bromothiophenol (3.00 g, 15.9 mmol, and 1,2-dimethyloxirane

(2.28 g, 31.8 mmol) and the solution degassed by sparging with N₂

for 20 min. To the degassed solution was added degassed

triethylamine (10 mL), and the reaction mixture was stirred overnight

at room temperature. The solvent was removed under reduced

pressure to give the product as a colorless oil that solidi ﬁ ed upon

1

yellow oil. H NMR (CDCl₃, 500 MHz, δ /ppm): 1.36 (s, 6H, H¹¹),

3.09 (s, 2H, H¹⁰), 7.04 (d, J = 8 Hz, 1H, H⁵), 7.14 (d, J = 2 Hz, 1H,

H⁸), 7.22 (dd, J = 8 Hz, 2 Hz, 1H, H⁴). ¹³C{¹H} NMR (CDCl₃, 126

MHz, δ /ppm): 27.26 (s, C¹⁰), 47.50 (s, C¹¹), 47.54 (s, C⁹), 117.81 (s,

C³), 123.79 (s, C⁵), 126.06 (s, C⁷), 130.20 (s, C⁴), 139.77 (s, C⁶),

150.35 (s, C⁸). MS (APCI-TOF) m /z : calcd for C₁₀H₁₁BrS [M]⁺

243.9744; found 243.9745.

1

standing (4.00 g, 96%). H NMR (CDCl₃, 300 MHz, δ /ppm): 1.30

(s, 6H, H¹¹), 2.09 (br s, 1H, H¹²), 3.09 (s, 2H, H¹⁰), 7.27 (d, J = 8.5

Hz, H⁵), 7.39 (d, J = 8.5 Hz, H⁴). ¹³C{¹H} NMR (CDCl₃, 500 MHz,

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Synthesis of 5-(Trimethylsilylethynyl)-3,3-dimethyl-2,3-

dihydrobenzo[b]thiophene.

phase was dried (MgSO₄) and the volume reduced under reduced

pressure before being ﬁ ltered through a silica plug, with further

elution with hexanes. After the solvent was removed from the

combined fractions, the product was obtained as a yellow oil, which

crystallized on standing (1.3 g, 84%). IR (CH₂Cl₂/cm⁻¹): ν (C C −

H) 3296, ν (C C) 2105. ¹H NMR (CDCl₃, 500 MHz, δ /ppm): 1.37

(s, 6H, H¹¹), 3.23 (s, 1H, H¹), 3.59 (s, 2H, H¹⁰), 7.18 (dd, J = 7.9, 0.6

Hz, 1H, H⁵), 7.21 − 7.22 (m, 1H, H⁸), 7.25 (dd, J = 7.9, 1.5 Hz, 1H,

H⁴). ¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /ppm): 27.3 (s, C¹¹), 47.5

(s, C⁹), 47.9 (s, C¹⁰), 78.4 (s, C¹), 84.5 (s, C²), 119.1 (s, C³), 123.0 (s,

C⁵), 127.1 (s, C⁸), 132.0 (s, C⁴), 142.0 (s, C⁶), 148.4 (s, C⁷). MS

(APCI) m /z : calcd for C₁₂H₁₂S [M + H]⁺189.0693; found 189.0737.

Method 2. A 100 mL Schlenk ﬂask ﬁtted with a distillation head

was charged with 4-(3,3-dimethyl-2,3-dihydrobenzo[b]thienyl)-2-

methyl-3-butyn-2-ol (2.46 g, 10.02 mmol) and dry toluene (50

mL). The distillation head was ﬁtted to a short-path distillation

apparatus and two-necked receiver ﬂask. The receiver ﬂask was vented

to an oil bubbler through the second neck. The apparatus was purged

with a steady ﬂow of N₂that swept through the assembly from the

Schlenk ﬂask to the oil bubbler. The reaction mixture was treated with

freshly powdered NaOH (0.23 g, 5.7 mmol) and then heated to a

gentle reﬂux point. The progress of the reaction could be followed by

analytical TLC (hexane). After the reaction was judged to be

complete (ca. 2 h) the reaction solution was ﬁltered, and the solvent

was removed under reduced pressure. The solid residue was puriﬁed

by column chromatography (silica, hexanes) to give the title

compound (0.94 g, 59%). Analytical data were as above.

A Schlenk ﬂ ask was charged with diisopropylamine (150 mL) and

thoroughly degassed and ﬁ tted with an e ﬃ cient condenser. To the

solvent were added 5-bromo-3,3-dimethyl-2,3-dihydrobenzo[b ]-

thiophene (3.40 g, 14.0 mmol), [Pd₂(dba)₃] (180 mg, 0.2 mmol),

JohnPhos (120 mg, 0.4 mmol), CuI (76 mg, 0.4 mmol), and

trimethylsilylacetylene (2.45 g, 25.0 mmol), and the mixture was

stirred for 48 h at 50 °C. After the solvent was removed, the residue

was puri ﬁ ed by column chromatography on silica, from which the

product was eluted with hexane. Removal of the solvent from the

product-containing fractions gave the compound as a viscous oil (2.13

g, 59%). IR (solid state, ATR)/cm⁻¹: ν (C C) 2151. ¹H NMR

(CDCl₃, 500 MHz, δ /ppm): 0.19 (s, 9H, H¹²), 1.36 (s, 6H, H¹¹), 3.09

(s, 2H, H¹⁰), 7.10 (d, J = 7.9 Hz, 1, H⁵), 7.13 (d, J = 1.5 Hz, 1H, H⁸),

7.23 (dd, J = 7.9 Hz, 1.5 Hz, 1H, H⁴). ¹³C{¹H} NMR (CDCl₃, 126

MHz, δ /ppm): 0.19 (s, C¹²), 27.44 (s, C¹⁰), 47.34 (s, C¹¹), 47.40 (s,

C⁹), 93.39 (s, C¹), 105.64 (s, C²), 119.05 (s, C³), 122.26 (s, C⁵),

126.30 (s, C⁷), 131.37 (s, C⁴), 141.94 (s, C⁶), 148.18 (s, C⁸). MS

(APCI-TOF) m /z : calcd for C₁₅H₂₀SSi [M]⁺260.1055; found

260.1048.

Synthesis of 2a.⁴⁶

Synthesis of 4-(3,3-Dimethyl-2,3-dihydrobenzo[b]thiophen-5-

yl)-2-methyl-3-butyn-2-ol.

A solution of 4-dimethylaminopyridine (16 mg, 0.130 mmol), 4-

ethynylthioanisole (1a ; 200 mg, 1.349 mmol), and CuI (13 mg, 0.068

mmol) in acetonitrile (15 mL) was stirred at room temperature in a

vessel open to the atmosphere for 18 h. After the solvent was

removed, the residue was washed with hexane three times to remove

unreacted alkyne. The remaining product was further puri ﬁ ed by

passing through a silica plug to give a greenish yellow solid. Yield: 219

A solution of 5-bromo-3,3-dimethyl-2,3-dihydrobenzo[b ]thiophene

(3.14 g, 12.98 mmol) in dry NHⁱPr₂(50 mL) was thoroughly

degassed and treated with 2-methylbut-3-yn-2-ol (2.69 g, 27.5 mmol),

(2-biphenylyl)-di-tert -butylphosphine (JohnPhos, 116 mg, 0.893

mmol), CuI (24 mg, 0.89 mmol), and [Pd₂dba₃] (0.057 g, 0.46

mmol). The reaction mixture was heated to 100 °C and allowed to

react at this temperature overnight. After this time a second charge of

catalyst and 2-methylbut-3-yn-2-ol (1.0 mL) were added to the dark

mixture and the reaction was allowed to proceed for a further day.

After this time the reaction mixture was allowed to cool, the solvent

removed under reduced pressure and the residue puri ﬁ ed by column

chromatography (silica, 1/1 CH₂Cl₂/hexane). The product was

obtained as a yellow oil (2.46 g, 77%). IR (solid state, ATR)/cm⁻¹:

1

mg (55%). IR (solid state, ATR)/cm⁻¹: ν (C C) 2214, 2055. H

NMR (CDCl₃, 300 MHz, δ /ppm): 2.49 (s, 6H, H⁷), 7.18 (d, J_HH= 8

Hz, 4H, H⁴), 7.42 (d, J_HH= 8 Hz, 4H, H⁵). ¹³C{¹H} NMR (CDCl₃,

76 MHz, δ /ppm): 15.31 (C⁷), 74.23, 81.75 (C¹and C²), 117.98 (C³),

125.79 (C⁵), 132.82 (C⁴), 140.98 (C⁶). MS (APCI-TOF) m /z : calcd

for C₁₈H₁₄S₂[M + H]⁺295.0614; found 295.0615.

Synthesis of 2b.

1

ν (O −H ) 3611 −3100, ν (C C) 2232. H NMR (CDCl₃, 500 MHz,

δ /ppm): 1.36 (s, 6H, H¹⁰), 1.61 (s, 6H, H¹³), 1.98 (s, 1H, H¹⁴), 3.18

(s, 2H, H¹¹), 7.10−7.08 (m, 2H, H⁴and H⁷), 7.17 (dd, J = 8.0 Hz, 2

Hz, 1H, H⁵). ¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /ppm): 27.46 (s,

C¹⁰), 31.69 (s, C¹³), 47.36 (s, C¹¹), 47.41 (s, C⁹), 65.83 (s, C¹²),

82.53 (s, C¹), 93.19 (s, C²), 118.67 (s, C³), 122.32 (s, C⁵), 126.07 (s,

C⁷), 130.98 (s, C⁴), 141.58 (s, C⁶), 148.28 (s, C⁸). MS (APCI-TOF)

m /z : calcd for C₁₅H₁₈OS [M]⁺246.1078; found 246.1054.

Synthesis of 5-Ethynyl-3,3-dimethyl-2,3-dihydrobenzo[b]-

thiophene (1b).

A ﬂ ask was charged with acetonitrile (15 mL), 4-dimethylaminopyr-

idine (24 mg, 0.20 mmol), and CuI (19 mg, 0.10 mmol), and the

mixture turned green after stirring for ca. 1 min. To this green

solution was added 5-ethynyl-3,3-dimethyl-2,3-dihydrobenzo[b ]-

thiophene (1b ; 376 mg, 2.00 mmol), and the mixture was stirred in

air for 18 h. After the solvent was removed, the residue was puri ﬁ ed by

column chromatography (hexane, silica). The crude product was then

further puri ﬁ ed by recrystallization from hot n -heptane (210 mg,

56%). Crystals suitable for X-ray single-crystal crystallography were

obtained by recrystallization from hot n -heptane. IR (CH₂Cl₂/cm⁻¹):

ν (C C) 2211, 2136. ¹H NMR (CDCl₃, 500 MHz, δ /ppm): 1.37 (s,

12H, H¹¹), 3.19 (s, 4H, H¹⁰), 7.13 (d, J = 8.0 Hz, 2H, H⁵), 7.18 (d, J =

1.5 Hz, 2H, H⁸), 7.28 (dd, J = 8.0, 1.5 Hz, H⁴). ¹³C{¹H} NMR

(CDCl₃, 126 MHz, δ /ppm): 27.5 (s, C¹¹), 47.38 (s, C⁹or C¹⁰), 47.44

(s, C⁹or C¹⁰), 73.7 (s, C¹), 82.2 (s, C²), 117.8 (s, C³), 122.5 (s, C⁵),

126.8 (s, C⁸), 131.8 (s, C⁴), 143.1 (s, C⁶), 148.5 (s, C⁷). HRMS

Method 1. A solution of 5-(trimethylsilylethynyl)-3,3-dimethyl-2,3-

dihydrobenzo[b ]thiophene (2.13 g, 8.21 mmol) in THF (50 mL) was

treated with NBu₄F (commercial 1 M solution in THF (5% water),

8.3 mL) and the mixture stirred for 2 h. After the solvent was

removed, the residue was extracted with hexanes (3 × 30 mL) and the

combined extracts were washed with water (20 mL). The organic

N

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(APCI-TOF) m /z : calcd for C₂₄H₂₃S₂[M + H]⁺375.1241; found

slow di ﬀ usion. IR (solid state, ATR)/cm⁻¹: ν (C C) 2057. ¹H NMR

(CDCl₃, 600 MHz, δ /ppm): 2.49 (s, 6H, H⁷), 2.57−2.63 (m, 8H,

H⁸), 6.67 (d, J = 8.1 Hz, 4H, H⁵), 6.93−6.97 (m, 18H, H¹¹), 7.06 (d, J

= 8.1 Hz, 4H, H⁴), 7.14−7.19 (m, 8H, H¹²), 7.48−7.53 (m, 16H,

H¹⁰). ¹³C{¹H} NMR (CDCl₃, 151 MHz, δ /ppm): 16.8 (s, C⁷), 31.60

(s, C⁸), 116.3 (m, C²), 126.8 (s, C⁵), 127.2 (s, C¹¹), 128.1 (s, C³),

128.7 (s, C¹²), 130.6 (s, C⁴), 131.4 (s, C⁶), 134.4 (s, C¹⁰), 137.2 (m,

C⁹) (C¹not observed). ³¹P{¹H} NMR (CDCl₃, 243 MHz, δ /ppm):

53.8 (s). ESI(+)-MS m /z : calcd for C₇₀H₆₂P₄RuS₂1193.2320 [M +

H]⁺; found 1193.2509 [M + H]⁺. Anal. Calcd for C₇₀H₆₂P₄RuS₂·

CH₂Cl₂: C, 66.75; H, 5.05. Found: C, 67.57; H, 5.80.

375.1231.

Synthesis of 3a.⁵⁹

A solution of 1,4-diethynylbenzene (200 mg, 1.59 mmol) in dry,

degassed triethylamine (20 mL) was treated with 4-bromothioanisole

(676 mg, 3.33 mmol), [Pd(PPh₃)₄] (90 mg, 0.08 mmol), and CuI (15

mg, 0.08 mmol) and heated to the re ﬂ ux point for 24 h. After this

time, the solution was cooled, the solvent removed under reduced

pressure, and the residue extracted into CH₂Cl₂before being washed

with brine and subsequently aqueous 0.1 M KOH. The organic layer

was dried (MgSO₄) and the solvent removed to give the title

compound as a yellow solid (318 mg, 54%). IR (solid state, ATR)/

cm⁻¹: ν (C C) 2116. ¹H NMR (CDCl₃, 600 MHz, δ /ppm): 2.51 (s,

6H, H⁷), 7.21 (d, J_HH= 8 Hz, 4H, H⁴or H⁵), 7.44 (d, J_HH= 8 Hz, 4H,

H⁴or H⁵), 7.49 (s, 4H, H⁹). ¹³C{¹H} (CDCl₃, 151 MHz, δ /ppm):

15.50 (C⁷), 89.39, 91.24 (C¹and C²), 119.43 (C³), 123.19 (C⁸),

126.00 (C⁵), 131.59, 132.03 (C⁴and C⁹), 139.79 (C⁶). MS (APCI-

TOF) m /z : calcd for C₂₄H₁₈S₂[M]⁺370.0851; found 370.0850.

Synthesis of 3b.

Synthesis of 4b.

A solution of [RuCl(dppe)₂]OTf (100 mg, 0.092 mmol), NaPF₆(31

mg, 0.19 mmol), and 5-ethynyl-3,3-dimethyl-2,3-dihydrobenzo[b ]-

thiophene (1b ; 37 mg, 0.20 mmol) in CH₂Cl₂(5 mL) and

triethylamine (1 mL) was stirred at room temperature for 1.5 h.

During this time the initially red solution changed to ﬁ rst orange and

then yellow and large amounts of a pale precipitate formed. The

precipitate was collected by ﬁ ltration and washed with methanol to

give the title compound as a pale yellow solid (76 mg, 65%). Crystals

suitable for X-ray di ﬀ raction were obtained from CH₂Cl₂/EtOH. IR

(solid state, ATR)/cm⁻¹: ν (C C) 2051. ¹H NMR (CDCl₃, 500

MHz, δ /ppm): 1.38 (s, 12H, H¹¹), 2.55−2.65 (m, 8H, H¹²), 3.17 (s,

4H, H¹⁰), 6.40 (d, J = 1.3 Hz, 2H, H⁸), 6.63 (dd, J = 8.0, 1.3 Hz, 2H,

H⁴), 6.93−6.99 (m, 18H, H⁵and H¹⁵), 7.14−7.19 (m, 8H, H¹⁶),

7.51 −7.56 (m, 16H, H¹⁴). ¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /

ppm): 27.6 (s, C¹¹), 31.6 (m, C¹²), 47.3 (s, C⁹), 47.6 (s, C¹⁰), 116.7

(s, C²), 121.5 (s, C⁵), 124.7 (s, C⁸), 127.1 (br s, C³and C¹⁵), 128.7 (s,

C¹⁶), 129.2 (s, C⁴), 133.9 (s, C⁶), 134.5 (s, C¹⁴), 137.3 (m, C¹³),

To a solution of 1,4-dibromobenzene (200 mg, 1.59 mmol) and 5-

ethynyl-3,3-dimethyl-2,3-dihydrobenzo[b ]thiophene (1b ; 676 mg,

3.33 mmol) in diisopropylamine (15 mL) were added [Pd₂(dba)₃]

(12 mg, 0.013 mmol), (2-biphenylyl)-di-tert -butylphosphine-

(JohnPhos, 4 mg, 0.013 mmol), and CuI (2.4 mg, 0.013 mmol).

The reaction mixture was heated at re ﬂ ux for 24 h, after which time

the solvent was removed under reduced pressure and the residue

puri ﬁ ed by preparative TLC (1/9 CH₂Cl₂/hexane) to give the

product as an orange solid (133 mg, 37%). The product could be

further puri ﬁ ed by recrystallization from hot n-heptane. Crystals

suitable for X-ray di ﬀ raction were obtained by slow evaporation of a

toluene solution. IR (CH₂Cl₂)/cm⁻¹): ν (C C) 2202. ¹H NMR

(CDCl₃, 600 MHz, δ /ppm): 1.40 (s, 12H, H¹¹), 3.21 (s, 4H, H¹⁰),

7.17 (d, J = 8.0 Hz, 2H, H⁵), 7.20 (d, J = 1.4 Hz, 2H, H⁸), 7.30 (dd, J

= 8.0, 1.4 Hz, 2H, H⁴), 7.48 (s, 4H, H¹⁴). ¹³C{¹H} NMR (CDCl₃, 126

MHz, δ /ppm): 27.5 (s, C¹¹), 47.4 (s, C⁹), 47.5 (s, C¹⁰), 88.8 (s, C²),

91.8 (s, C¹), 119.0 (s, C³), 122.5 (s, C⁵), 123.2 (s, C¹³), 126.0 (s, C⁸),

131.0 (s, C⁴), 131.5 (s, C¹⁴), 142.0 (s, C⁶), 148.4 (s, C⁷). MS (APCI-

TOF) m /z : 451 [M + H]⁺. HRMS (APCI-TOF) m /z : calcd for

C₃₀H₂₇S₂[M + H]⁺451.1554; found 451.1562. found: 451.1562.

Anal. Calcd for C₃₀H₂₆S₂: C, 79.95; H, 5.82. Found: C, 79.87; H,

5.78.

1

147.1 (s, C⁷) (a signal for C²could only be observed in the H-¹³C-

HMBC NMR spectrum, and no signal for C¹could be observed at

all). ³¹P{¹H} NMR (CDCl₃, 202 MHz, δ /ppm): 53.8 (s). ESI(+)-MS

m /z : calcd for C₇₆H₇₀P₄RuS₂1272.2913 [M]⁺; found 1272.3032.

Anal. Calcd for C₇₆H₇₀P₄RuS₂: C, 71.74; H, 5.54. Found: C, 71.58; H,

5.68.

Synthesis of 5a.

Synthesis of 4a.⁶⁸

A solution of [RuCl₂{P(OEt)₃}₄] (0.108 g, 0.129 mmol), 4-

ethynylanisole (1a ; 0.100 g, 0.679 mmol) and KPF₆(0.082 g, 0.446

mmol) in a mixture of ethanol (5 mL) and diisopropylamine (2.5

mL) was stirred at room temperature for 4 days under an inert

atmosphere. The progress of the reaction was conveniently monitored

by unlocked ³¹P NMR spectroscopy, with the formation of the

intermediate mono(alkynyl) complex trans -[RuCl(C CC₆H₄SMe)-

{P(OEt)₃}₄] evinced by a singlet near 132.7 ppm, which was

consumed over the course of the reaction and the bis(alkynyl)

complex was formed (δ_Pca. 137.7 ppm). Upon completion of the

reaction, the solvent was removed from the reddish brown solution

and the residue extracted with hexanes. The extracts were combined,

ﬁ ltered, and taken to dryness to give a reddish brown solid that was

crystallized (CHCl₃/MeOH) to give the title complex as yellow-

brown crystals suitable for X-ray di ﬀ raction (80 mg, 58%). IR (solid

A solution of [RuCl(dppe)₂]OTf (0.100 g, 0.097 mmol), NaPF₆

(0.061 g, 0.36 mmol), and 4-ethynylthioanisole (1a ; 0.039 g, 0.263

mmol) in CH₂Cl₂(5 mL) and triethylamine (1 mL) was stirred at

room temperature for 1.5 h. During this time the initially red solution

became yellow and large amounts of a pale precipitate formed, which

was collected by ﬁ ltration, washed with methanol, and air-dried to

a ﬀ ord 4a as a yellow solid (0.110 g, 0.095 mmol, 98%). Crystals

suitable for X-ray di ﬀ raction were obtained from CH₂Cl₂/MeOH by

1

state, ATR)/cm⁻¹: ν (C C) 2104. H NMR (CDCl₃, 500 MHz, δ /

ppm): 1.19 (t, J = 7 Hz, 36H, H⁹), 2.43 (s, 6H, H⁷), 4.29 (q, J = 7 Hz,

O

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24H, H⁸), 6.94 (d, J = 8 Hz, 4H, H⁵), 7.04 (d, J = 8 Hz, 4H, H⁴).

¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /ppm): 16.52 (s, C⁷), 16.92 (s,

C⁹), 60.95 (s, C⁸), 113.31 (s, C²), 127.28 (s, C³), 128.82 (s, C⁵),

130.44 (s, C⁴), 130.79 (s, C⁶) (C¹not observed). ³¹P{¹H} NMR

(CDCl₃, 202 MHz, δ /ppm): 136.84 (s). ESI(+)-MS m /z : Calcd for

C₄₂H₇₅O₁₂P₄RuS₂1061.2694 [M + H]⁺; found 1061.2766 [M]⁺,

1061.2694. Anal. Calcd for C₄₂H₇₄O₁₂P₄RuS₂: C, 47.58; H, 7.04.

Found: C, 47.46; H, 6.97.

2372 Hz). MS (APCI-TOF) m /z : calcd for C₃₀H₄₅P₂PtS₂[M + H]⁺

726.2086; found 726.2087.

Synthesis of 6b.

Synthesis of 5b.

A solution of [PtCl₂(PEt₃)₂] (250 mg, 0.50 mmol), CuI (10 mg, 0.05

mmol), and 5-ethynyl-3,3- dimethyl-2,3-dihydrobenzo[b ]thiophene

(1b ; 210 mg, 1.12 mmol) in triethylamine (25 mL) was heated under

re ﬂ ux overnight. After the solvent was removed, the residue was

extracted with hexane and the extract ﬁ ltered through a silica plug.

While the ﬁ ltrate was concentrated under reduced pressure, the

product precipitated as a yellow solid (187 mg, 46%). Crystals

suitable for X-ray single-crystal crystallography were obtained by

recrystallization from hot n -heptane or CH₂Cl₂/hexane. IR (solid

state, ATR)/cm⁻¹: 2098, 2085. ¹H NMR (CDCl₃, 500 MHz, δ /ppm):

1.17 −1.26 (m, 18H, H¹³), 1.35 (s, 12H, H¹¹), 2.11−2.23 (m, 12H,

H¹²), 3.15 (s, 4H, H¹⁰), 6.95 (d, J = 1.0 Hz, 2H, H⁸), 7.17 (d, J = 8.0

Hz, 2H, H⁵), 7.05 (dd, J = 8.0, 1.0 Hz, 2H, H⁴). ¹³C{¹H} NMR

(CDCl₃, 126 MHz, δ /ppm): 8.5 (s, C¹³), 16.5 (m, C¹²), 27.4 (m,

C¹¹), 47.3 (s, C⁹), 47.5 (s, C¹⁰), 106.7 (m, C¹), 109.5 (s, C²), 122.0

(s, C⁵), 125.2 (br s, C³and C⁸), 130.2 (s, C⁴), 137.0 (s, C⁷), 147.7 (s,

C⁶). ³¹P{¹H} NMR (CDCl₃, 202 MHz, δ /ppm): 11.0 (s, J_PtP= 2373

Hz). ESI(+)-MS m /z : calcd for C₃₆H₅₂P₂PtS₂806.2612 [M + H]⁺,

found 806.2578. Anal. Calcd for C₃₆H₅₂P₂PtS₂: C, 53.59; H, 6.50.

Found: C, 53.54; H, 6.62.

Single-Crystal X-ray Diﬀraction Studies. General Conditions:

Single-Crystal X-ray Diﬀraction. Crystallographic data for the

structures were collected at 100(2) K on an Oxford Diﬀraction

Gemini diﬀractometer or an Oxford Diﬀraction Xcalibur X-Ray

diﬀractometer. The data were corrected for Lorentz and polarization

eﬀects and absorption. The structures were solved by direct methods

and reﬁned against F²with full-matrix least squares using the program

suite SHELXL-97 or SHELXL-2014.⁹⁹Anisotropic displacement

parameters were employed for the non-hydrogen atoms. All hydrogen

atoms were added at calculated positions and reﬁned by use of a

riding model with isotropic displacement parameters based on those

of the parent atom. Crystallographic data for the structures reported

in this paper can be found in the Supporting Information of this paper

and have been deposited at the Cambridge Crystallographic Data

Centre. Copies of the data with CCDC numbers 1938546−1938557

can be obtained free of charge via https://www.ccdc.cam.ac.uk/

structures/, or from the Cambridge Crystallographic Data Centre, 12

Union Road, Cambridge CB2 1EZ, U.K (fax + 441223336033; email

deposit@ccdc.cam.ac.uk).

A solution of [RuCl₂{P(OEt)₃}₄] (105 mg, 0.126 mmol) was

dissolved in a dry, degassed solvent mixture of EtOH (5 mL) and

diisopropylamine (2.5 mL). To the solution were added KPF₆(95

mg, 0.51 mmol) and 5-ethynyl-3,3-dimethyl-2,3-dihydrobenzo[b ]-

thiophene (1b ; 135 mg, 0.720 mmol). The solution was stirred for 7

days at room temperature. The progress of the reaction could be

followed by unlocked ³¹P NMR, showing the initial increase in the

intensity of a peak near 132.7 ppm for the intermediate mono-

(alkynyl) complex, which was consumed over time with the formation

of the bis(alkynyl) product (δ_Pca. 137.8 ppm). When the reaction

was judged to be complete, the solvent was removed from the reddish

brown solution under reduced pressure and the residue extracted into

hexanes. The combined extracts were ﬁ ltered, and the solvent was

removed to give a reddish brown solid that was crystallized (CH₂Cl₂/

MeOH) to give yellow-brown crystals of the title complex suitable for

X-ray di ﬀ raction (47 mg, 35%). On occasion, the presence of an

unidenti ﬁ ed yellow impurity necessitated repeated crystallization to

obtain analytically pure samples. IR (solid state, ATR)/cm⁻¹: ν (C 

1

C) 2070. H NMR (CDCl₃, 500 MHz, δ /ppm): 1.21 (t, J = 7 Hz,

36H, H¹³), 1.31 (s, 12H, H¹¹), 3.13 (s, 4H, H¹⁰), 4.31 (q, J = 7 Hz, 24

H, H¹²), 6.77−6.80 (m, 4H, H⁴and H⁸), 6.93 (d, J = 8 Hz, 2H, H⁵).

¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /ppm): 16.6 (s, C¹³), 27.5 (s,

C¹¹), 47.1 (s, C⁹), 47.4 (s, C¹⁰), 61.0 (s, C¹²), 113.5 (s, C²), 115.0 (m,

C¹), 121.7 (s, C⁵), 124.9 (s, C⁸), 127.9 (s, C³), 128.8 (s, C⁴), 133.3 (s,

C⁶), 147.3 (s, C⁷). ³¹P{¹H} NMR (CDCl₃, 202 MHz, δ /ppm): 136.9

(s). HRMS (APCI-TOF) m /z : calcd for C₄₈H₈₃O₁₂P₄RuS₂[M + H]⁺

1141.3333; found 1141.3013. Anal. Calcd for C₄₈H₈₂O₁₂P₄RuS₂: C,

50.56; H, 7.25. Found: C, 50.45; H, 7.07.

Synthesis of 6a.⁷⁷

Crystal Data. 1b: C₁₂H₁₂S, M = 188.28 g/mol, yellow needle, 0.35

× 0.19 × 0.13 mm³, orthorhombic, space group P2₁2₁2₁(No. 19), a =

6.79890(10) Å, b = 9.2508(2) Å, c = 15.8759(2) Å, V = 998.52(3) Å³,

Z = 4, D_c= 1.252 g cm⁻³, μ = 0.271 mm⁻¹. F₀₀₀= 400, Mo Kα

radiation, λ = 0.71073 Å, 2θ_max= 75.3°, 34907 reﬂections collected,

5177 unique (R_int= 0.0400), ﬁnal GOF = 1.001, R1 = 0.0285, wR2 =

A Schlenk ﬂ ask was charged with [PtCl₂(PEt₃)₂] (250 mg, 0.50

mmol), 4-ethynylthioanisole (1a , 220 mg, 1.49 mmol), CuI (2 mg,

0.01 mmol) and dry triethylamine (30 mL). The mixture was heated

under re ﬂ ux overnight. After the solvent was removed, the residue was

puri ﬁ ed by chromatography on silica using a hexane/CH₂Cl₂gradient.

After removal of the solvent from the product-containing fractions,

the compound was recrystallized from EtOH by slow evaporation,

yielding large crystals suitable for X-ray crystallography (137 mg,

38%). IR (solid state, ATR)/cm⁻¹: ν (C C) 2101. ¹H NMR (CDCl₃,

500 MHz, δ /ppm): 1.15 −1.27 (m, 18H, H⁹), 2.10−2.23 (m, 12H,

H⁸), 2.45 (s, 6H, H⁷), 7.12 (d, J = 8.3 Hz, H⁵), 7.19 (d, J = 8.3 Hz,

H⁴). ¹³C{¹H} NMR (CDCl₃, 126 MHz, δ /ppm): 8.5 (m, C⁹), 16.47

(s, C⁷), 16.48 (pseudo-t (dd), apparent J = 17.6 Hz, C⁸), 108.1 (m,

C¹), 109.1 (br s, C²), 126.1 (s, C³), 126.9 (s, C⁵), 131.4 (s, C⁴), 134.6

0.0703, R indices based on 4835 reﬂections with I > 2σ(I), |Δρ|_max

=

0.38(5) e Å⁻³, 166 parameters, 0 restraints, absolute structure

parameter −0.002(17).¹⁰⁰CCDC number: 1938546.

2b: C₂₄H₂₂S₂, M = 374.53 g/mol, pale yellow needle, 0.242 × 0.053

× 0.051 mm³, monoclinic, space group P2₁/n (No. 14), a = 7.0705(1)

Å, b = 17.0655(2) Å, c = 16.2546(3) Å, β = 97.428(1)°, V =

1944.85(5) Å³, Z = 4, D_c= 1.279 g cm⁻³, μ = 2.491 mm⁻¹. F₀₀₀= 792,

Cu Kα radiation, λ = 1.54178 Å, 2θ_max= 134.8°, 16578 reﬂections

collected, 3478 unique (R_int= 0.0376), ﬁnal GOF = 1.001, R1 =

0.0386, wR2 = 0.0945, R indices based on 2863 reﬂections with I >

2σ(I), |Δρ|_max= 0.27(5) e Å⁻³, 239 parameters, 0 restraints. CCDC

number: 1938547.

3b: symmetry operation for generating equivalent atoms (A) −x −

2, 3 − y, 2 − z; C₃₀H₂₆S₂, M = 450.63 g/mol, colorless block, 0.40 ×

(s, C⁶). ³¹P{¹H} NMR (CDCl₃, 200 MHz, δ /ppm): 10.9 (s, J_Pt‑P

=

P

https://dx.doi.org/10.1021/acs.organomet.0c00685

Organometallics XXXX, XXX, XXX−XXX

Organometallics

pubs.acs.org/Organometallics

Article

0.30 × 0.20 mm³, monoclinic, space group P2₁/n (No. 14), a =

7.1172(3) Å, b = 10.4490(4) Å, c = 16.2683(7) Å, β = 94.466(3)°, V

6a: symmetry operation for generating equivalent atoms (A) 1 − x,

1 − y, 1 − z; C₃₀H₄₄P₂PtS₂, M = 725.80 g/mol, yellow prism, 0.659 ×

0.405 × 0.331 mm³, triclinic, space group P1

̅

(No. 2), a = 8.7144(3)

= 1206.16(9) Å³, Z = 2, D_c= 1.241 g cm⁻³, μ = 0.236 mm⁻¹. F₀₀₀

=

Å, b = 9.4046(4) Å, c = 11.1777(4) Å, α = 97.754(3)°, β =

102.336(3)°, γ = 116.694(4)°, V = 771.05(6) Å³, Z = 1, D_c= 1.563 g

cm⁻³, μ = 4.806 mm⁻¹, F₀₀₀= 364, Mo Kα radiation, λ = 0.71073 Å,

476, Mo Kα radiation, λ = 0.71073 Å, 2θ_max= 52.00°, 4736 reﬂections

collected, 2362 unique (R_int= 0.0178), ﬁnal GOF = 1.037, R1 =

0.0330, wR2 = 0.0844, R indices based on 2173 reﬂections with I >

2σ(I), |Δρ|_max= 0.34(4) e Å⁻³, 147 parameters, 0 restraints. CCDC

number: 1938548.

2θ_max= 75.3°, 14871 reﬂections collected, 7739 unique (R_int

=

0.0171), ﬁnal GOF = 1.044, R1 = 0.0153, wR2 = 0.0366, R indices

based on 7739 reﬂections with I > 2σ(I), |Δρ|_max= 1.2(1) e Å⁻³, 164

parameters, 0 restraints. CCDC number: 1938553.

4a: symmetry operation for generating equivalent atoms (A) 1 − x,

1 − y, 1 − z; C₇₀H₆₂P₄RuS₂, M = 1192.26 g/mol, yellow needle, 0.196

× 0.042 × 0.020 mm³, triclinic, space group P1

̅

(No. 2), a =

6b: symmetry operation for generating equivalent atoms (A) −x, 1

− y, 1 − z; C₃₆H₅₂P₂PtS₂, M = 805.92, yellow block, 0.267 × 0.196 ×

9.2372(3) Å, b = 13.0132(4) Å, c = 13.1830(4) Å, α = 66.006(3)°, β

= 88.900(2)°, γ = 77.291(2)°, V = 1407.87(8) Å³, Z = 1, D_c= 1.406 g

cm⁻³, μ = 4.354 mm⁻¹. F₀₀₀= 618, Cu Kα radiation, λ = 1.54178 Å,

0.094 mm³, triclinic, space group P1

̅

(No. 2), a = 13.4351(3) Å, b =

13.8251(3) Å, c = 15.8416(3) Å, α = 83.638(2)°, β = 66.108(2)°, γ =

80.253(2)°, V = 2648.56(11) Å³, Z = 3, D_c= 1.516 g cm⁻³, μ = 4.206

mm⁻¹, F₀₀₀= 1224, Mo Kα radiation, λ = 0.71073 Å, 2θ_max= 64.7°,

54728 reﬂections collected, 17368 unique (R_int= 0.0378), ﬁnal GOF

= 1.001, R1 = 0.0336, wR2 = 0.0734, R indices based on 14058

reﬂections with I > 2σ(I), |Δρ|_max= 4.5(1) e Å⁻³, 637 parameters, 31

restraints. CCDC number: 1938554.

2θ_max= 134.5°, 26946 reﬂections collected, 4988 unique (R_int

=

0.0526), ﬁnal GOF = 1.000, R1 = 0.0315, wR2 = 0.0782, R indices

based on 4293 reﬂections with I > 2σ(I), |Δρ|_max= 0.56(7) e Å⁻³, 350

parameters, 0 restraints. CCDC number: 1938549.

4a·CH₂Cl₂: selected bond properties summarized in Table 1;

symmetry operation for generating equivalent atoms (A) 1 − x, 1 − y,

1 − z; C₇₁H₆₄Cl₂P₄RuS₂, M = 1277.19 g/mol, pale yellow plate, 0.310

× 0.210 × 0.130 mm³, monoclinic, space group P2₁/c (No. 14), a =

13.1788(2) Å, b 22.8241(3) Å, c = 10.1272(1) Å, β = 102.857(1)°, V

6b (polymorph): symmetry operation for generating equivalent

atoms (A) −x, −y, 1 − z; C₃₆H₅₂P₂PtS₂, M = 805.92 g/mol, pale

orange plate, 0.354 × 0.121 × 0.032 mm³, triclinic, space group P1

̅

(No. 2), a = 8.2254(13) Å, b = 8.3524(8) Å, c = 13.8460(16) Å, α =

83.493(9)°, β = 80.404(12)°, γ = 71.421(12)°, V = 887.2(2) Å³, Z =

1, D_c= 1.508 g cm⁻³, μ = 9.510 mm⁻¹, F₀₀₀= 408, Cu Kα radiation, λ

= 1.54184 Å, 2θ_max= 134.8°, 5438 reﬂections collected, 3047 unique

(R_int= 0.0631), ﬁnal GOF = 1.090, R1 = 0.1047, wR2 = 0.2811, R

indices based on 2651 reﬂections with I > 2σ(I), |Δρ|_max= 3.4(3) e

Å⁻³, 250 parameters, 100 restraints. CCDC number: 1938557.

= 2969.83(7) Å³, Z = 2, D_c= 1.428 g cm⁻³, μ = 0.576 mm⁻¹. F₀₀₀

=

1320, Mo α radiation, λ = 0.71073 Å, 2θ_max= 64.6°, 63032 reﬂections

collected, 10055 unique (R_int= 0.0461), ﬁnal GOF = 1.001, R1 =

0.0400, wR2 = 0.0970, R indices based on 8602 reﬂections with I >

2σ(I), |Δρ|_max= 2.5(1) e Å⁻³, 368 parameters, 0 restraints. CCDC

number: 1938555.

4b·CH₂Cl₂: selected bond properties summarized in Table 1;

symmetry operation for generating equivalent atoms (A) 1 − x, −y,

−z; C₇₇H₇₂Cl₂P₄RuS₂, M = 1357.31 g/mol, orange needle, 0.313 ×

ASSOCIATED CONTENT

■

0.066 × 0.020 mm³, triclinic, space group P1

̅

(No. 2), a = 9.2078(3)

sı

* Supporting Information

Å, b = 13.1380(5) Å, c = 13.4746(6) Å, α = 85.802(3)°, β =

87.326(3)°, γ = 83.114(3)°, V = 1612.77(11) Å³, Z = 1, D_c= 1.398 g

cm⁻³, μ = 4.614 mm⁻¹. F₀₀₀= 704, Cu Kα radiation, λ = 1.54184 Å,

TThe Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.organomet.0c00685.

2θ_max= 134.6°, 13061 reﬂections collected, 5693 unique (R_int

=

Additional plots of crystallographically determined

molecular structures and reﬁnement information, plots

and composition of selected molecular orbitals, and plots

of UV−vis spectra of 1a,b−6a,b (PDF)

0.0390), ﬁnal GOF = 1.036, R1 = 0.0385, wR2 = 0.1008, R indices

based on 5114 reﬂections with I > 2σ(I), |Δρ|_max= 0.81(7) e Å⁻³, 435

parameters, 3 restraints. CCDC number: 1938550.

4b·2CH₂Cl₂: symmetry operation for generating equivalent atoms

(A) 2 − x, 1 − y, 1 − z; C₇₈H₇₄Cl₄P₄RuS₂, M = 1442.24 g/mol,

colorless needle, 0.500 × 0.070 × 0.050 mm³, monoclinic, space

group P2₁/c (No. 14), a = 9.2236(2) Å, b = 13.0589(3) Å, c =

27.6792(7) Å, β = 94.976(2)°, V = 3321.40(13) Å³, Z = 2, D_c= 1.442

g cm⁻³, μ = 0.602 mm⁻¹. F₀₀₀= 1492, Mo Kα radiation, λ = 0.71073

Accession Codes

CCDC 1938546−1938557 contain the supplementary crys-

tallographic 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.

Å, 2θ_max= 64.0°, 69822 reﬂections collected, 11033 unique (R_int

=

0.0769), ﬁnal GOF = 1.002, R1 = 0.0452, wR2 = 0.0970, R indices

based on 8108 reﬂections with I > 2σ(I), |Δρ|_max= 0.8(1) e Å⁻³, 405

parameters, 0 restraints. CCDC number: 1938556.

5a: C₄₂H₇₄O₁₂P₄RuS₂, M = 1060.08 g/mol, colorless plate, 0.386 ×

0.218 × 0.137 mm³, monoclinic, space group P2₁/n (No. 14), a =

11.7457(1) Å, b = 12.4496(2) Å, c = 35.9949(5) Å, β = 94.175(1)°, V

AUTHOR INFORMATION

■

Corresponding Author

= 5249.54(12) Å³, Z = 4, D_c= 1.341 g cm⁻³, μ = 0.553 mm⁻¹. F₀₀₀

=

Paul J. Low − School of Molecular Sciences, University of

Western Australia, Crawley, Western Australia 6009,

Australia; orcid.org/0000-0003-1136-2296;

Email: paul.low@uwa.edu.au

2232, Mo Kα radiation, λ = 0.71073 Å, 2θ_max= 63.9°, 107960

reﬂections collected, 17459 unique (R_int= 0.0342), ﬁnal GOF =

1.003, R1 = 0.0325, wR2 = 0.0797, R indices based on 14902

reﬂections with I > 2σ(I), |Δρ|_max= 0.91(7) e Å⁻³, 574 parameters, 0

restraints. CCDC number: 1938551.

Authors

5b: C₄₈H₈₂O₁₂P₄RuS₂, M = 1140.20 g/mol, pale yellow needle,

0.467 × 0.317 × 0.301 mm³, orthorhombic, space group Pca2₁(No.

29), a = 24.8920(5) Å, b = 20.7702(4) Å, c = 11.2651(2) Å, V =

Masnun Naher − School of Molecular Sciences, University of

Western Australia, Crawley, Western Australia 6009,

Australia

5824.19(19) Å³, Z = 4, D_c= 1.300 g cm⁻³, μ = 0.504 mm⁻¹. F₀₀₀

=

̈

Soren Bock − School of Molecular Sciences, University of

2408, Mo Kα radiation, μ = 0.71073 Å, 2θ_max= 65.4°, 35710

reﬂections collected, 18467 unique (R_int= 0.0320), ﬁnal GOF =

1.006, R1 = 0.0577, wR2 = 0.1342, R indices based on 13869

reﬂections with I > 2σ(I), |Δρ|_max= 2.3(1) e Å⁻³, 624 parameters, 18

restraints, absolute structure parameter −0.053(13).¹⁰⁰CCDC

number: 1938552.

Western Australia, Crawley, Western Australia 6009,

Australia

Zakary M. Langtry − School of Molecular Sciences, University

of Western Australia, Crawley, Western Australia 6009,

Australia

Q

https://dx.doi.org/10.1021/acs.organomet.0c00685

Organometallics XXXX, XXX, XXX−XXX

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Article

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Berke, H.; Stadler, R.; Lortscher, E. High-Conductive Organometallic

Molecular Wires with Delocalized Electron Systems Strongly Coupled

to Metal Electrodes. Nano Lett. 2014, 14, 5932−5940.

(10) Lissel, F.; Schwarz, F.; Blacque, O.; Riel, H.; Lortscher, E.;

Venkatesan, K.; Berke, H. Organometallic Single-Molecule Elec-

tronics: Tuning Electron Transport through X(diphosphine)₂FeC₄Fe-

(diphosphine)₂X Building Blocks by Varying the Fe-X-Au Anchoring

Scheme from Coordinative to Covalent. J. Am. Chem. Soc. 2014, 136,

14560−14569.

(11) Duan, P.; Liu, J. Y.; Wang, J. Y.; Chen, L. C.; Wang, F.; Zhang,

Q. C.; Hong, W.; Chen, Z. N. Modulation of the conductance in

platinum(II) bis(acetylide) molecules through “gating ” metal ions. J.

Mater. Chem. C 2019, 7, 7259−7266.

(12) Davidson, R.; Al-Owaedi, O. A.; Milan, D. C.; Zeng, Q.; Tory,

J.; Hartl, F.; Higgins, S. J.; Nichols, R. J.; Lambert, C. J.; Low, P. J.

Effects of Electrode-Molecule Binding and Junction Geometry on the

Single-Molecule Conductance of bis-2,2 ‘:6 ‘,2 “-Terpyridine-based

Complexes. Inorg. Chem. 2016, 55, 2691−2700.

(13) Davidson, R.; Liang, J. H.; Milan, D. C.; Mao, B. W.; Nichols,

R. J.; Higgins, S. J.; Yufit, D. S.; Beeby, A.; Low, P. J. Synthesis,

Electrochemistry, and Single-Molecule Conductance of Bimetallic

2,3,5,6-Tetra(pyridine-2-yl)pyrazine-Based Complexes. Inorg. Chem.

2015, 54, 5487−5494.

(14) Zhao, X. T.; Huang, C. C.; Gulcur, M.; Batsanov, A. S.;

Baghernejad, M.; Hong, W. J.; Bryce, M. R.; Wandlowski, T.

Oligo(aryleneethynylene)s with Terminal Pyridyl Groups: Synthesis

and Length Dependence of the Tunneling-to-Hopping Transition of

Single-Molecule Conductances. Chem. Mater. 2013, 25, 4340−4347.

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Oxidation potentials correlate with conductivities of aromatic

molecular wires. J. Am. Chem. Soc. 2007, 129, 12376−12377.

(16) Kastlunger, G.; Stadler, R. Density functional theory based

direct comparison of coherent tunneling and electron hopping in

redox-active single-molecule junctions. Phys. Rev. B: Condens. Matter

Mater. Phys. 2015, 91, 125410.

(17) Zhang, J. D.; Kuznetsov, A. M.; Medvedev, I. G.; Chi, Q. J.;

Albrecht, T.; Jensen, P. S.; Ulstrup, J. Single-molecule electron

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(18) Osorio, H. M.; Catarelli, S.; Cea, P.; Gluyas, J. B. G.; Hartl, F.;

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Ulstrup, J.; Vezzoli, A.; Milan, D. C.; Zeng, Q. Electrochemical Single-

Molecule Transistors with Optimized Gate Coupling. J. Am. Chem.

Soc. 2015, 137, 14319−14328.

Kieran M. O’Malley − School of Molecular Sciences,

University of Western Australia, Crawley, Western Australia

6009, Australia

Alexandre N. Sobolev − School of Molecular Sciences,

University of Western Australia, Crawley, Western Australia

6009, Australia

Brian W. Skelton − School of Molecular Sciences, University of

Western Australia, Crawley, Western Australia 6009,

Australia

Marcus Korb − School of Molecular Sciences, University of

Western Australia, Crawley, Western Australia 6009,

Australia

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.organomet.0c00685

Author Contributions

^†M.N. and S.B. contributed equally.

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

́

This paper is dedicated to Professor Jean-Rene Hamon on the

occasion of his 65th birthday, in celebration of his many

achievements in chemistry and with thanks for his friendship.

The Australian Research Council (ARC) is thanked for

ﬁnancial support under the Discovery Program

(DP190100073; DP190100074). M.N. holds a Forrest

Scholarship from the Forrest Research Foundation. M.K.

holds a Forrest Fellowship from the Forrest Research

Foundation. S.B. held an International Postgraduate Research

Scholarship and Scholarship for International Research Fees

from the University of Western Australia and Faculty of

Science. The authors gratefully acknowledge the facilities and

the scientiﬁc and technical assistance of Microscopy Australian

at the Centre for Microscopy, Characterisation & Analysis,

The University of Western Australia, a facility funded by the

University and State and Commonwealth Governments.

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