# Bimetallic electroactive titanocene dithiolene complexes

Yann Le Gal, Antoine Vacher, Oscar Charpentier, Thierry Roisnel, Marc Fourmigué, Dominique Lorcy

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Yann Le Gal, Antoine Vacher, Oscar Charpentier, Thierry Roisnel, Marc Fourmigué, et al. Bimetallic electroactive titanocene dithiolene complexes. Polyhedron, 2025, 281, pp.117731. 10.1016/j.poly.2025.117731. hal-05303893

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# Bimetallic electroactive titanocene dithiolene complexes

Yann Le Gal, Antoine Vacher, Oscar Charpentier, Thierry Roisnel, Marc Fourmigué, Dominique Lorcý*

Université de Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) – UMR 6226, F-35000 Rennes, France

<figure><img src="image_2.png" /></figure>

## ARTICLE INFO

**Keywords:**

Dithiolene

Titanocene

Bimetallic complex

Molecular structure

Electroactivity

## ABSTRACT

Three tetrathiolate derivatives have been investigated as bridging ligands to prepare redox active (titanocene dithiolene)-based bimetallic complexes, namely 1,2,4,5-benzenetetrathiolate, 1,2,3,4-butadiene tetrathiolate and benzene-1,4-di(ethylenedithiolate). The corresponding bimetallic bis(cyclopentadienyl) Ti(IV) dithiolene complexes were synthesized and structurally characterized. Comparison of the electrochemical properties of these bimetallic complexes with those of the corresponding monometallic complex, highlights the instability of the reduced species Ti(III) which was so far unknown in the monometallic one. UV-vis-NIR spectroelectrochemical studies confirm a more rapid decomposition of the reduced species for the bimetallic complexes compared to the monometallic one, as already observed for the oxidized species.

## 1. Introduction

Ditopic dithiolene derivatives are interesting precursors of binuclear complexes exhibiting attractive optical properties upon oxidation due to intramolecular interactions between the two metallacycles. Among the different ditopic ligands allowing sizeable interactions, four of them have retain our attention. The most studied ligands are certainly the one where the two dithiolene moieties are constrained to coplanarity (Chart 1), particularly the 1,2,4,5-benzenetetrathiolate (btt) [1] as a large variety of metallic centers have been investigated (M = Fe [2], Ni and Pd [3], Au [4], Cr [5], Ti, Zr and Hf [1], Co [6], Mo [7], Rh and Ir [8]) and the tetrathiooxalate (tto) [9] which was also used to form various bimetallic complexes (M = Ti [10], Ni [11], Cu [12], Co, Pd and Pt [13], Ir [14]). Two other ditopic ligands exhibit a possible flexibility as the two dithiolene moieties are not constrained to coplanarity (Chart 1), namely the 1,2,3,4-butadiene tetrathiolate (bdtt) [15,16], and the benzene-1,4-di(ethylenedithiolate) (bdedt) [17,18]. These two later ligands were less investigated as precursors of bimetallic complexes and only a few metallic centers have been studied such as Co [15], Ni and Pt [16] for the bdtt ligand, and Pt [18] and Mo [17] for the bdedt one. Herein we investigated, with three ligands, namely btt, bdtt and bdedt (Chart 1), the possibility to form the corresponding bis(titanocene) complexes. Monometallic Cp₂Ti(dithiolene) complexes, first described by Köpf and Schmidt 60 years ago [19] are usually obtained in good yields, are air stable and can be considered as inorganic protected forms

of the air-sensitive 1,2-dithiolate. These diamagnetic Cp₂Ti(dithiolene) complexes belong to an interesting family of redox active, 16e⁻, d⁰ complexes, and they generally present a reversible metal-centered reduction process (Ti(IV)/Ti(III)) and two irreversible oxidation processes associated to the oxidation of the TiS₂C₂ metallacycle [20]. In the literature, only the bimetallic complex involving the tetrathiaoxalate as ditopic ligand, (Cp₂Ti)₂(tto), named here for an easier reading, Ti₂T was fully characterized and its electrochemical analysis revealed two monoelectronic reversible processes indicating electronic interactions between the two redox active metallacycles as the two metal-centered (Ti(IV)/Ti(III)) processes occur sequentially [10]. Even if the bimetallic complex Ti₂B was previously prepared [1], its electrochemical behavior was not described. Therefore, we decided to prepare the target complexes; Ti₂B, Ti₂D and Ti₂P and to study the influence of the different organic spacers between the two Cp₂Ti(dithiolene) moieties on their electrochemical behavior. Herein, we report the synthesis of these complexes together with their structural, electrochemical and spectroelectrochemical properties.

## 2. Results and discussion

### 2.1. Syntheses

The general synthetic route used to generate a Cp₂Ti(dithiolene) moiety involves the reaction of a dithiolene ligand with Cp₂TiCl₂ [20].

<footnote>* Corresponding author.
E-mail address: dominique.lorcý@univ-rennes1.fr (D. Lorcý).</footnote>
<figure><img src="image_3.png" /><figcaption>Chart 1. Tetrathiolate ligands and corresponding titanocene bimetallic complexes.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Scheme 1.** Synthesis of the bis titanocene complex Ti₂B.</figcaption></figure>

As a dithiolene ligand is not stable, we focused our attention on two proligands where the dithiolene is protected, either within a dithiole-2-one ring or with a dibutyltin group. Both proligands are known to give metal dithiolene complexes in different ways. Indeed, when a dithiole-2-one ring is used as starting material, the use of NaOMe or BuLi is needed to deprotect the dithiolene proligand. Concerning the dibutyltin protecting group, it presents several advantages because it reacts in a clean way and usually with high yields with dihalogenated metallic fragments through a transmetalation to form the desired metal complex [21–23].

For the preparation of the bimetallic benzo-fused bis(dithiolene) complex, **Ti₂B**, we first attempted with the proligand **1**, **1,3,5,7-tetra-thia-s-indacene-2,6-dione** [24] (**Scheme 1**). For the deprotection step, we used four equivalents of MeLi followed by the addition of two equivalents of Cp₂TiCl₂. Following this approach, we isolated **Ti₂B** in 17 % yield as a dark green powder insoluble in most solvents. No trace of either the monotitanocene complex or the starting compound **1** was detected but rather unidentified degradation products. We also inves-tigated the reactivity of the dibutyltin protected bis(dithiolene) ligand fused to the benzene ring, **Sn₂B** [6] towards Cp₂TiCl₂. In the presence of two equivalents of Cp₂TiCl₂ in refluxing acetone with **Sn₂B**, trans-metalation allows for the formation of the desired complex with the same yield (17 % yield). Their again, we did not identify any side products, either the monosubstituted complex or the starting material **Sn₂B**. The complex **Ti₂B** was purified via Soxhlet extraction and crystals were obtained after cooling down the solution of 1,1,2-trichloroethane.

Then we explored the reactivity of 4,4'-bis(1,3-dithiole-2-one) precursor **2** with the aim of forming the bis(cyclopentadienyl) titanocene complexes **Ti₂D** (Chart 1). The 4,4'-bis(1,3-dithiole-2-one) precursor **2** was prepared according to literature procedure by reacting 1,4-dibromo-2,3-butanedione with potassium isopropylxanthate in dichloromethane [16,25]. Cyclization and dehydration were performed through the addition of concentrated H₂SO₄. Bereman et al. demonstrated that through the addition of two equivalents of NaOEt it is possible to selectively deprotect only one dithiolene ligand while after the addition of four equivalents of NaOEt, deprotection of the two dithiolene ligands occurred, probably sequentially, leading to the formation of a bimetallic complex after the addition of (COD)PtCl₂ [16].

<figure><img src="image_5.png" /><figcaption>**Scheme 2.** Synthesis of the mono titanocene complex, TiOD.</figcaption></figure>

Accordingly, we first investigated the formation of the monosubstituted titanocene(dithiolene) complex, **TiOD** (Scheme 2). After the addition of two equivalents of MeONa to **2** followed by the addition of Cp₂TiCl₂, the mono metallic complex was isolated in 24 % yield (Scheme 2). Attempts to form the bimetallic complex by treating **2** with four equivalents of MeONa or with BuLi were unsuccessful in our hands. We assume that the tetranion is not formed or not stable in solution. Instead, in these conditions, only the monometallic complex, **TiOD**, could be isolated in 35 % yield demonstrating that the bimetallic complex **Ti₂D** cannot be obtained from **TiOD**. Crystals of the mononuclear complex **TiOD** were obtained by slow concentration of a dichloromethane solution. We also attempted to convert the bis(1,3-dithiol-2-one) **2** into the corresponding bis(2,2-dibutyl-1,3,2-dithiastannole) **Sn₂D**. There again, after the addition of 4 equivalents of MeONa followed by the addition of dibutyltin dichloride, Bu₂SnCl₂, we did not succeed into the formation of neither the corresponding bimetallic **Sn₂D** nor the monometallic complex **SnOD** even by modifying the nature of the base, the time and temperature of the reaction. It is surprising as oxophilicity of tin derivatives is known to be smaller than their thiophilicity [26].

Then we investigated the reactivity of the bis(dithiolene) proligand where the two dithiolene moieties are connected to the 1,4 positions of a benzene ring, **Sn₂P** [17], towards Cp₂TiCl₂ (Scheme 3). By simply mixing **Sn₂P** with 2.5 equivalents of Cp₂TiCl₂ in an acetonitrile solution at room temperature, the desired complex **Ti₂P** was successfully formed in 22 % yield together with the mono titanocene complex, **TiSnP** in 57 % yield. Attempts to promote the formation of the bimetallic complex **Ti₂P** at the expense of the monometallic one failed. Both complexes were easily separated by column chromatography. Crystals of **Ti₂P** were obtained by slow concentration of a dichloromethane solution.

## 2.2. Molecular structures

Single crystals were obtained for two bimetallic complexes **Ti₂P** and **Ti₂B** and one monometallic complex, **TiOD**. The monometallic complex,
<figure><img src="image_6.png" /><figcaption>Scheme 3. Synthesis of the Ti₂P and TiSnP complexes.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 1. Molecular structures of (a) the monometallic complex TiOD, (b) the bimetallic complex Ti₂P and (c) the bimetallic complex Ti₂B.</figcaption></figure>

<table><caption>**Table 1**
Selected bond lengths (Å) and angles for titanocene(dithiolene) complexes.</caption><thead><tr><th>Complex</th><th>TiOD</th><th>Ti₂P</th><th>Ti₂B</th></tr></thead><tbody><tr><td>Ti-S1</td><td>2.4357(7)</td><td>2.4215(8)</td><td>2.4082(9)</td></tr><tr><td>Ti-S2</td><td>2.4210(8)</td><td>2.4174(8)</td><td>2.4216(9)</td></tr><tr><td>S1-C12</td><td>1.751(2)</td><td>1.758(3)</td><td>1.755(3)</td></tr><tr><td>C11-S2</td><td>1.727(2)</td><td>1.728(3)</td><td>1.750(3)</td></tr><tr><td>C12-C11</td><td>1.368(7)</td><td>1.367(4)</td><td>1.431(4)</td></tr><tr><td>C12-C13</td><td>1.468(3)</td><td>1.483(3)</td><td>1.391(4)</td></tr><tr><td>S-Ti-S (°)</td><td>82.79(2)</td><td>83.03(3)</td><td>82.74(3)</td></tr><tr><td>θ (°)</td><td>39.9(3)</td><td>45.7(5)</td><td>46.7(2)</td></tr></tbody></table>

TiOD, crystallizes in the orthorhombic system, space group *Pbca* and the bimetallic complexes in monoclinic system, space group *C2/c* and *P2₁/n* for Ti₂P and Ti₂B respectively. The molecular structures of these complexes are presented in Fig. 1 and selected bond lengths and angles are collected in Table 1. As presented in Fig. 1, TiOD exhibits a planar dithiol-2-one ring while the metallacycle shows a strong distortion from planarity with a pronounced folding along the S•••S hinge of 39.8°. Concerning the bimetallic complexes, Ti₂P and Ti₂B, both molecules are located on an inversion center and adopt a chair conformation (Fig. 1). The metallacycles are folded along the S•••S hinge with a more pronounced distortion angle of 45.7(5)° and 46.7(2)° for Ti₂P and Ti₂B respectively. This strong folding along the S•••S axis finds its origin in the stabilizing overlap interaction between the empty/occupied frontier orbitals of respectively the Cp₂Ti and dithiolene fragments [27,28].

As the two metallacycles are connected to a phenyl ring in Ti₂P through only one C—C bond the phenyl ring and the C₂S₂ moiety of the metallacycle are not constrained to lie in the same plane. Actually, a dihedral angle of 34.5(6)° is observed between the C₂S₂ plane of the metallacycle and the phenyl ring. For all these complexes, the Ti—S and S—C bond lengths, as well as the bond angles, the S-Ti-S angle and the

<figure><img src="image_8.png" /><figcaption>Fig. 2. Variable-temperature ¹H NMR spectra of (a) TiOD in (CD₃)₂C=O and (b) Ti₂P in CD₂Cl₂ showing the inversion process between the two conformations.</figcaption></figure>

torsion angle θ in the metallacycles are in the same range as those observed for other titanocene(dithiolene) complexes (Table 1) [20].

Due to the non-planarity of the metallacycles, the two cyclopentadienyl groups are in different surroundings. Nevertheless, upon
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 3. CV of Ti₂P (A), TiSnP (B) and Ti₂B (C) in CH₂Cl₂ with Bu₄NPF₆ 0.1 M.</figcaption></figure>

raising the temperature a rapid inversion process can occur and the two cyclopentadienyl ligands become equivalent. This conformational inversion mechanism was first suggested by Köpf in 1971 [29]. As a consequence, on the ¹H NMR spectra at room temperature, the two cyclopentadienyl groups led to one broad singlet (6.15 ppm for TiOD). In order to determine the activation energies for the ring inversion process, we performed variable temperature ¹H NMR experiments. These experiments were carried out on the soluble complexes which is to say TiOD in (CD₃)₂C=O and Ti₂P in CD₂Cl₂. Upon decreasing the

<caption>Table 2</caption>

Redox potentialsª of the various investigated complexes, E in V vs SCE using [Bu₄N][PF₆] as electrolyte.

<figure><img src="image_12.png" /></figure>

<table><thead><tr><th></th><th>E<sub>red</sub></th><th>E<sup>1</sup><sub>ox</sub></th><th>E<sup>2</sup><sub>ox</sub></th><th>λ<sub>max</sub></th></tr></thead><tbody><tr><td>TiOD</td><td>-0.99</td><td>+0.87*</td><td></td><td></td></tr><tr><td>TiSnP</td><td>-1.13</td><td>+0.74*</td><td>0.89*</td><td></td></tr><tr><td>Ti₂P</td><td>-1.18</td><td>+0.67*</td><td></td><td>662</td></tr><tr><td>Ti₂B</td><td>-0.91</td><td>+0.74*</td><td></td><td>720</td></tr><tr><td>TiP<sup>b</sup></td><td>-1.32 (-1.16)</td><td>**</td><td></td><td>646</td></tr><tr><td>TiB<sup>b</sup></td><td>-1.18</td><td>**</td><td></td><td>610</td></tr></tbody></table>

ªreduction process, taken as the average of the anodic and the cathodic peak potentials, *Irreversible process. b investigated in CH₂Cl₂ using [Bu₄N][BF₄].** not investigated in this publication.

temperature, the broad signal observed at room temperature, due to the rapid inversion process, transforms into two signals at T_c (coalescence temperature, two signals at 6.35 and 5.95 ppm for TiOD and 5.82 ppm and 6.22 ppm for Ti₂P), as shown in Fig. 2. This process is reversible as upon raising the temperature the two signals for the Cp coalesce into the broad signal. A T_c of 293 and 300 K was determined for the TiOD and Ti₂P complexes respectively. The use of Eyring equation [30] allowed us to determine the activation energy ΔG‡ which amounts to 58.1 kJ.mol⁻¹ for TiOD and 58.8 kJ.mol⁻¹ for Ti₂P. It can be noticed here again that there is no significant differences between these activation energy values for the inversion process with those observed for other monometallic titanocene dithiolene complexes [31–34].

## 2.3. Electrochemical investigations

The redox properties of the four titanocene complexes, TiOD, Ti₂B, TiSnP and Ti₂P were investigated by cyclic voltammetry using the same conditions, dichloromethane solutions and NBu₄PF₆ (0,1 M) as supporting electrolyte. For comparison purposes, we also studied the redox behavior of the mono titanocene complexes, i.e. Cp₂Ti(bdt) and Cp₂Ti (sdt), (bdt: benzenedithiolate, sdt: styrenedithiolate), named TiB and TiP for easy reading, in the same conditions. It should be noted that under these conditions, the Ti₂B complex is very weakly soluble, but a redox signature could nevertheless be observed (Fig. 3). The redox potentials are collected in Table 2 and are given in V vs SCE. The bimetallic complexes, Ti₂P and Ti₂B, exhibit very similar cyclic voltammograms compared to the monometallic complexes TiOD, TiP and TiB. On the anodic scan, an irreversible oxidation peak attributed to the oxidation of the dithiolene is observed. The irreversibility of this process is a consequence of the decoordination of the oxidized ligand from the complex as the removal of electron from the HOMO severely weakens the metal ligand interaction of these 16 e⁻ complexes [35]. Contrariwise, on the cathodic scan, a reversible reduction process corresponding to the Ti(IV)/Ti(III) reduction of the metal is observed. Due to the presence of the dithiole-2-one ring in the monometallic complex TiOD, the oxidation potential is shifted to higher values, while it can be noticed that for the bimetallic complexes, the nature of the organic spacer has an influence on the value of the oxidation or reduction potentials. Indeed, the fused benzene ring exerts an electron withdrawing effect and displaces the oxidation potentials towards higher values while the reduction process is shifted to lower redox potentials. This influence of the substituent on the dithiolene moieties was also observed on the corresponding mononuclear complexes, namely TiP and TiB [36]. Another interesting aspect is the occurrence of a second irreversible oxidation process for the TiSnP which is attributed to the oxidation of the 2,2-dibutyl-1,3,3,2-dithiastannole ring (Fig. 3B).

During the study of the CVs at different scan rates, a noticeable
<figure><img src="image_13.png" /><figcaption>**Fig. 4.** UV-vis-NIR spectral changes upon reduction of the monometallic complex and then oxidation of the reduced species (A) TiB and (B) TiP complexes.</figcaption></figure>

difference occurs between the bimetallic, Ti₂P and Ti₂B, and the monometallic complexes. Indeed, when increasing the scan rate, the monometallic complexes exhibit a clear reversible monoelectronic reduction process while progressively the signal disappears for the bimetallic complexes. This is presumably due either to the deposit onto the electrode of a non-conducting deposit or simply to the decomposition of the reduced species which is faster in the case of the bimetallic complexes. This phenomenon, absence of reversibility during reduction after reduction, has already been observed on Cp₂TiCl₂ and has been attributed to the loss of one Cl⁻ after reduction [37]. This tends to indicate that the reduction of the bimetallic complexes leads to unstable species inducing a decoordination of the dithiolene ligand. We also realized a comparative experiment for Ti₂B using THF and NBu₄PF₆ as supporting electrolyte but this time with either a platinum working electrode or a glassy carbon one. In THF, the first cathodic scan with the Pt working electrode is reversible but after several scans, the same phenomenon was observed which is to say the progressive loss of the redox system. Contrariwise, with the glassy carbon electrode, the redox system remains after several cycles.

In order to get more insight into the formation of the various reduced species, UV-vis-NIR spectroelectrochemical investigations were carried out on a dichloromethane solution of the complexes using a platinum grid. All the neutral complexes exhibit absorption bands in the visible range, between 610 and 720 nm. These lowest energy absorption bands are assigned to ligand metal transitions (LMCT). It can be observed that this band is red shifted in the bimetallic complexes, Ti₂P and Ti₂B, compared to the monometallic complexes, TiP and TiB. This phenomenon has already been noticed on other bimetallic complexes involving

<figure><img src="image_14.png" /><figcaption>**Fig. 5.** Differential UV-vis-NIR spectra of Ti₂P monitored upon gradual reduction of the neutral complex to the reduced one (A) and then oxidation of the reduced complex (B) in CH₂Cl₂ with Bu₄NPF₆ 0.2 M. (C) Differential UV-vis-NIR spectra of Ti₂P monitored upon gradual oxidation of the neutral complex and then reduction of the oxidized species (for comparison the red curve corresponding to the reduced species has been added). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

the btt ditopic ligand compared to the bdt ligand and is due to an increased conjugation across the ditopic ligand [6]. Note that this red shift is more pronounced, by about 94 nm, in the case of the btt ligand than for the bdt one [18].

First, we carried out our spectroelectrochemical investigations on the monometallic complexes, TiP and TiB. The spectral changes upon electrochemical reduction of the monoanionic complexes are shown in Fig. 4. In both cases, upon reduction a progressive decrease of the lowest energy absorption band (LMCT) occurs. No novel absorption band at longer wavelengths can be noticed upon reduction to –1.2 V for TiB or –1.5 V for TiP. Then after oxidation of the generated reduced species it can be observed that the process is not, as expected, totally reversible in the case of TiB and even less so in the case of TiP.

After studying the monometallic complexes, we performed similar
spectro-electrochemical investigations on the bimetallic complexes Ti₂B and Ti₂P. As shown in Fig. 5, upon gradual reduction of Ti₂P or Ti₂B similar evolutions of the spectra are noticed which is to say progressive disappearance of the LMCT absorption bands resulting from the reduction of the metal Ti(IV)/Ti(III) center. No other absorption band appears at higher wavelength during this reduction (Fig. 5A). We then progressively oxidized the solution and, in both cases, no spectral signature of the neutral species could be detected, indicating that for bimetallic complexes, this process is irreversible on the spectroelectrochemical timescale (Fig. 5B). We also performed the spectroelectrochemical investigation upon oxidation. Interestingly, in the case of oxidation, the evolution of the absorption spectra is similar to that observed in the case of reduction. Since oxidation leads to decoordination of the dithiolene ligand, it appears that reduction also generates this decoordination which is faster in the case of the bimetallic complexes compared to the monometallic one. This kinetic effect might be a consequence of the increased reactivity of such complexes upon two-electron reduction of the bimetallic complexes.

### 3. Conclusions

Bimetallic Cp₂Ti(dithiolene) complexes formed with tetrathiolate ligands were prepared and characterized. The synthesized bimetallic complexes exhibit a good stability in the neutral state and structural flexibility of the TiS₂C₂ metallacycles was evidenced through variable temperature ¹H NMR experiments. The investigation of their structural properties show that the nature of the conjugated organic linker does not influence significantly the spectral and structural properties, especially the folding angles (θ) and the activation energy for the inversion process. A peculiarity of these bimetallic complexes was demonstrated through electrochemical investigations as, upon reduction, the stability of the reduced species is decreased in the bimetallic complexes compared to the monometallic one. This instability of the reduced titanocene was unknown so far. UV-vis-NIR spectroelectrochemical analyses have provided evidence that both during the reduction and the oxidation processes decoordination of the ligand occurs leading to a non-electroactive molecule with similar spectral signature.

### 4. Experimental

#### 4.1. General

Chemicals and materials from commercial sources were used without further purification. All the reactions were performed under an argon atmosphere. NMR spectra were obtained in CDCl₃ unless indicated otherwise. Chemical shifts are reported in ppm, ¹H NMR spectra were referenced to residual CHCl₃ (7.26 ppm) and ¹³C NMR spectra were referenced to CHCl₃ (77.2 ppm). Melting points were measured on a Kofler hot-stage apparatus and are uncorrected. Mass spectra were recorded by the Centre Régional de Mesures Physiques de l'Ouest, Rennes. Methanol, acetonitrile and dichloromethane were dried using Inert pure solvent column device. CVs were carried out on a 10⁻³ M solution of complex in CH₂Cl₂-[NBu₄][PF₆] 0.1 M. CVs were recorded on a Biologic SP-50 instruments at 0.1 Vs⁻¹ on a platinum disk electrode. Potentials were measured versus KCl Saturated Calomel Electrode (SCE).

#### 4.2. Synthesis and characterization

**TiOD:** To a solution of 4,4'-bis(1,3-dithiole-2-one) 1 (200 mg, 0.85 mmol) in dry THF (20 mL) under inert atmosphere was added a solution of NaOMe (freshly prepared from 39 mg (1.7 mmol) of sodium in 10 mL of dry methanol). The solution was stirred 30 min then Cp₂TiCl₂ (212 mg, 0.85 mmol) was added. The solvent was evaporated in vacuo. Dichloromethane (200 mL) was added and the solution was washed with water (3 × 50 mL) and dried over MgSO₄. The resulting dark green oil was purified by flash chromatography on silica gel using

dichloromethane:petroleum ether (1:9 to 3:2) to afford 80 mg (24 %) of the complex TiOD as a green powder. Mp = 132 °C; NMR ¹H (300 MHz): δ = 6.02 (s, 10H, Cp); 6.86 (s, 1H, C₁H); 7.58 (s, 1H, C₄H); NMR ¹³C (CD₃)₂S=O, 75 MHz): δ = 111.3, 113.7, 135.3, 147.0, 148.4, 191.8 (C=O); IR ν̄ = 1633 cm⁻¹ (C=O); UV-vis (CH₂Cl₂) λ (nm) (ε [L.mol⁻¹ cm⁻¹]): 650 (2060); 444 (2160); 326 (8240); 292 (11000); HRMS (ESI) calcd for C₁₅H₁₂ONaS₄⁴⁸Ti [M + Na]⁺: 406.91427. Found: 406.9146; Anal. calcd for C₁₅H₁₂OS₄Ti + 0.5CH₂Cl₂: C, 43.62; H 3.07. Found: C, 43.54; H 3.12.

**TiSnP and Ti₂P:** To a solution of Sn₂P complex (200 mg, 0.27 mmol) in dry acetonitrile (25 mL) was added Cp₂TiCl₂ (173 mg, 069 mmol) under inert atmosphere. The solution was stirred 15 h and the solvent was evaporated in vacuo. Dichloromethane (200 mL) was added and the solution was washed with water (3 × 50 mL) and dried over MgSO₄. After evaporation of the solvent, the oil was purified by chromatography on silica gel using dichloromethane:petroleum ether (10:1) to afford 131 mg (57 %) of the complex TiSnP as a green oil and 39 mg (22 %) of the complex Ti₂P as a green powder. Crystals of sufficient quality of complex Ti₂P for X-ray diffraction were obtained by slow evaporation of a dichloromethane solution.

**TiSnP:** ¹H NMR (300 MHz) δ = 0.94 (t, 6H, CH₃), 1.41 (m, 4H, CH₃-CH₂), 1.70 (m, 8H, CH₃-CH₂-CH₃), 5.96 (broad, 10H, Cp), 6.82 (s, 1H, =CH), 7.55 (m, 4H, Ar), 7.83 (s, 1H, =CH); ¹³C NMR (75 MHz) δ = 13.7 (CH₃); 22.6 (CH₃-CH₂); 26.7 (CH₃-CH₂-CH₃); 27.9 (CH₂-Sn); 117.6 (Cp); 126.8 (Ar); 127.0 (Ar); 136.6 (SC=CC); 139.3 (SC=CC). UV-Vis (CH₂Cl₂)λ (nm) (ε [L.mol⁻¹ cm⁻¹]): 662 (3640); 446 (5080); 344 (21660); HRMS (ESI) calcd for C₂₈H₃₄NaS₄⁴⁸Ti¹²⁰Sn [M + Na]⁺: 688.9937. Found: 688.9931; Anal. calcd for C₂₈H₃₄SnTi: C, 50,69; H, 4,86; S, 19,33. Found: C, 50,57; H, 4,92; S, 19,38.

**Ti₂P**, Mp = 144 °C; ¹H NMR room temperature (300 MHz, CDCl₃) δ = 5.97 (broad, 20H, Cp); 7.61 (s, 4H, Ar); 7.85 (s, 2H,=CH); HRMS (ESI) calcd for C₃₀H₂₆NaS₄⁴⁸Ti₂ [M + Na]⁺: 632.97685. Found: 632.9777; UV-Vis (CH₂Cl₂) λ (nm) (ε [L.mol⁻¹ cm⁻¹]): 662 (9200); 446 (12830); 344 (54,670). RMN = F(T⁻): Tc = 300 K; Δν = 160 Hz; ΔG⁰ = 58.8 (kJ.mol⁻¹); HRMS (ESI) calcd for C₃₀H₂₆NaS₄⁴⁸Ti₂ [M + Na]⁺: 632.97685. Found: 632.9769.

**Ti₂B:** To a solution of Tin complex Sn₂B (134 mg, 0.2 mmol) in dry acetone (50 mL) under inert atmosphere bis(cyclopentadienyl)titanium dichloride (100 mg, 0.4 mmol) was added. The solution was stirred under reflux for 15 h. After cooling the solution to room temperature a dark green precipitate was obtained. The desired complex was purified via Soxhlet extraction using 1,1,2-trichloroethane. Crystals of sufficient quality were obtained upon cooling the trichloroethane solution. The obtained crystals are poorly soluble even in DMSO and ¹H NMR and ¹³C NMR could not be obtained. Ti₂B was obtained in 17 % yield, Mp >250 °C. UV-vis (CH₂Cl₂) λ (nm) (ε [L.mol⁻¹ cm⁻¹]): 268 (16120); 290 (16090); 308 (3980); 484 (3400); 718 (5350); HRMS (ESI) calcd for C₂₆H₂₃S₄⁴⁸Ti₂ [M + H]⁺: 558.96361. Found: 558.9639. Anal. calcd for C₂₆H₂₂S₄Ti₂: C, 55.92; H, 3.97; Found: C, 55.70; H, 3.76.

#### 4.3. Crystallography

Data collections were performed on an APEXII Bruker-AXS diffractometer equipped with a CCD camera for Ti₂P and on a D8 VENTURE Bruker AXS diffractometer equipped with a (CMOS) PHOTON 100 detector, Mo-Kα radiation (λ = 0.71073 Å, multilayer monochromator) for TiOD and Ti₂B. The structures were solved by dual-space algorithm using the SHELXT program [38] and then refined with full-matrix least-square methods based on F² (SHELXL) [39] For TiOD, the contribution of the disordered solvents to the calculated structure factors was estimated following the BYPASS algorithm [40] implemented as the SQUEEZE option in PLATON [41]. A new data set, free of solvent contribution, was then used in the final refinement. For the three structures, all non-hydrogen atoms were refined with anisotropic atomic displacement parameters. H atoms were finally included in their
<table><caption>**Table 3**
Crystallographic data.<sup>a,b</sup></caption><thead><tr><th></th><th>Ti<sub>2</sub>B</th><th>TiOD</th><th>Ti<sub>2</sub>P</th></tr></thead><tbody><tr><td>Formulae</td><td>C<sub>26</sub>H<sub>22</sub>S<sub>4</sub>Ti<sub>2</sub></td><td>C<sub>15</sub>H<sub>12</sub>OS<sub>4</sub>Ti</td><td>C<sub>30</sub>H<sub>26</sub>S<sub>4</sub>Ti<sub>2</sub></td></tr><tr><td>FW (g.mol<sup>-1</sup>)</td><td>558.47</td><td>384.39</td><td>610.55</td></tr><tr><td>System</td><td>monoclinic</td><td>orthorombic</td><td>monoclinic</td></tr><tr><td>Space group</td><td>P2<sub>1</sub>/n</td><td>Pbca</td><td>C2/c</td></tr><tr><td>a (Å)</td><td>6.5736(5)</td><td>11.1690(10)</td><td>17.9046(19)</td></tr><tr><td>b (Å)</td><td>13.4174(12)</td><td>12.4105(13)</td><td>14.3103(17)</td></tr><tr><td>c (Å)</td><td>13.4669(9)</td><td>22.321(2)</td><td>13.3336(13)</td></tr><tr><td>α (deg)</td><td>90</td><td>90</td><td>90</td></tr><tr><td>β (deg)</td><td>98.404(3)</td><td>90</td><td>118.264(4)</td></tr><tr><td>γ (deg)</td><td>90</td><td>90</td><td>90</td></tr><tr><td>V (Å<sup>3</sup>)</td><td>1175.03(16)</td><td>3094.0(5)</td><td>3009.0(6)</td></tr><tr><td>T (K)</td><td>293(2)</td><td>150(2)</td><td>150(2)</td></tr><tr><td>Z</td><td>2</td><td>8</td><td>4</td></tr><tr><td>D<sub>calc</sub> (g.cm<sup>-3</sup>)</td><td>1.578</td><td>1.650</td><td>1.348</td></tr><tr><td>μ (mm<sup>-1</sup>)</td><td>1.049</td><td>1.086</td><td>0.825</td></tr><tr><td>Total refls</td><td>8363</td><td>17,448</td><td>12,937</td></tr><tr><td>Abs corr</td><td>Multi-scan</td><td>Multi-scan</td><td>Multi-scan</td></tr><tr><td>Uniq refls (R<sub>int</sub>)</td><td>2674(0.0401)</td><td>3509(0.0469)</td><td>3434(0.0404)</td></tr><tr><td>Uniq refls (I > 2σ(I))</td><td>1973</td><td>2902</td><td>2909</td></tr><tr><td>R<sub>1</sub>, wR<sub>2</sub></td><td>0.0369, 0.0979</td><td>0.0341, 0.0739</td><td>0.0391, 0.0952</td></tr><tr><td>R<sub>1</sub>, wR<sub>2</sub> (all data)</td><td>0.0604, 0.1278</td><td>0.0468, 0.0800</td><td>0.0494, 0.1013</td></tr><tr><td>GOF</td><td>1.037</td><td>1.033</td><td>1.056</td></tr></tbody></table>

$$ ^{a}R_{1} = \frac{|F_{o}| - |F_{c}|}{|F_{o}|} \cdot ^{b}wR_{2} = \frac{[w(F_{o}^{2} - F_{c}^{2})]}{[w(F_{o}^{2})]^{1/2}}. $$

calculated positions and treated as riding on their parent atom with constrained thermal parameters. Crystallographic data on X-ray data collection and structure refinements are given in Table 3.

### CRediT authorship contribution statement

**Yann Le Gal:** Investigation. **Antoine Vacher:** Investigation, Formal analysis. **Oscar Charpentier:** Investigation. **Thiery Roisnel:** Investigation, Formal analysis. **Marc Fourmigué:** Writing – review & editing, Resources. **Dominique Loryc:** Writing – review & editing, Supervision, Methodology, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.poly.2025.117731.

### Data availability

Data will be made available on request.

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