Synthesis, Characterization, and Properties of Doubly Alkynyl Bridging Dinuclear Cyclometalated Iridium(III) Complexes

Bis­(cyclometalated) diiridium complexes [Ir­(ppy)₂(μ–κ<i>C</i>^α:η²-CCR)]₂ (R = Tol <b>1</b>, C₆H₄OMe-4 <b>2</b>, 1-Np <b>3</b>, SiMe₃ <b>4</b>, ^<i>t</i>Bu <b>5</b>), stabilized by a double alkynyl bridging system, have been synthesized by alkynylation of [Ir­(ppy)₂(μ-Cl)]₂ with excess of the appropriate LiCCR (1:6 or 1:10 molar ratio). Complexes <b>1</b>–<b>3</b> were alternatively generated by treatment of [Ir­(ppy)₂(MeCN)₂]­(OTf) with 2.5 equiv of LiCCR. However, the related reaction with LiCC^<i>t</i>Bu evolves with the formation of mixtures from which the unexpected dinuclear complex [Ir­(ppy)₂(μ-CH₂CN)]₂ <b>6</b> was crystallized, as confirmed by X-ray diffraction studies. Complexes <b>1</b>–<b>5</b> have been characterized by NMR, IR, absorption and emission spectroscopies, cyclic voltammetry, and mass spectrometric methods. Characterization indicates that <b>1</b>–<b>3</b> and <b>5</b> are obtained as a unique diastereoisomer (ΛΛ/ΔΔ), whereas <b>4</b> gives the two diastereoisomers (ΔΛ and ΛΛ/ΔΔ). Single crystals of [Ir­(ppy)₂(μ-CCTol)]₂ <b>1</b> contains the inversion related ΛΛ/ΔΔ isomers, and crystals of <b>4</b> (chosen from a mixture of two different types of crystals) consist of the <i>meso</i>-ΔΛ isomer. Electrochemical studies showed the presence in <b>1</b>–<b>3</b> and <b>5</b> of two consecutive one-electron-oxidation Ir^III/Ir^IV processes, whereas <b>4</b> displayed only one irreversible oxidation peak. In degassed fluid solutions, complexes <b>1</b>–<b>5</b> are emissive in the 505–515 nm region with quantum yields higher (ϕ = 0.007–0.024) than that of the dichloro bridged precursor (0.0037). The influence of the alkynyl substituent in the emissive state at room and at low temperatures has been investigated. For the naphthylacetylide derivative <b>3</b>, a clear switch from a mixed charge transfer ³MLCT/³L′LCT excited state at 298 K (515 nm) to a characteristic long-lived low lying naphthalene emission at low temperature (77 K) is observed. DFT and TD-DFT calculations were performed on complexes <b>1</b> and <b>3</b> in the ground and triplet states to gain insight into the structural, electronic, and photophysical properties

Unexpected Formation of Ferrocenyl(vinyl)benzoquinoline Ligands by Oxidation of an Alkyne Benzoquinolate Platinum(II) Complex

Oxidation of [Pt­(bzq-κ<i>N</i>,κ<i>C</i>¹⁰)­(C₆F₅)­(η²-HCCFc)] (<b>1</b>) with PhICl₂ and I₂ affords the unusual halideferrocenyl­(vinyl)­benzoquinoline Pt^II derivatives [Pt­{bzq-κ<i>N</i>-η²-CHC­(X)­Fc}­(C₆F₅)­X] (X = Cl (<b>4a</b>), I (<b>4b</b>)), arising from C–X and C–C coupling processes, together with small amounts of the corresponding Pt^IV products [{Pt­(bzq-κ<i>N</i>,κ<i>C</i>¹⁰)­(C₆F₅)­X­(μ-X)}₂] (X = Cl (<b>5a</b>), I (<b>5b</b>)), respectively. Complexes <b>4</b> are very stable but they undergo easy displacement reactions with PPh₃, yielding <i>trans</i>-[Pt­(C₆F₅)­X­(PPh₃)₂] and the corresponding new functionalized (vinyl)­benzoquinoline ligands [(<i>Z</i>)-bzq-CHC­(X)­Fc] (X = Cl (<b>6a</b>), I (<b>6b</b>)). The dinuclear Pt^IV derivatives <b>5</b> are alternatively obtained in high yield by oxidation of the solvate [Pt­(bzq-κ<i>N</i>,κ<i>C</i>¹⁰)­(C₆F₅)­(CH₃COCH₃)] (<b>2</b>). Treatment of <b>5</b> with dmso or direct oxidation of [Pt­(bzq-κ<i>N</i>,κ<i>C</i>¹⁰)­(C₆F₅)­(tht)] (<b>3</b>) provides mononuclear [Pt­(bzq-κ<i>N</i>,κ<i>C</i>¹⁰)­(C₆F₅)­X₂(L)] (L = dmso (<b>7a</b>–<b>c</b>), tht (<b>8a</b>–<b>c</b>)) as a mixture of <i>cis</i> and <i>trans</i> isomers

An Extended Chain and Trinuclear Complexes Based on Pt(II)–M (M = Tl(I), Pb(II)) Bonds: Contrasting Photophysical Behavior

The syntheses and structural characterizations of a Pt–Tl chain [{Pt­(bzq)­(C₆F₅)₂}­Tl­(Me₂CO)]_<i>n</i> <b>1</b> and two trinuclear Pt₂M clusters (NBu₄)­[{Pt­(bzq)­(C₆F₅)₂}₂Tl] <b>2</b> and [{Pt­(bzq)­(C₆F₅)₂}₂Pb] <b>3</b> (bzq = 7,8-benzoquinolinyl), stabilized by donor–acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain <b>1</b> is formed by alternate “Pt­(bzq)­(C₆F₅)₂” and “Tl­(Me₂CO)” fragments, with Pt–Tl bond separations in the range of 2.961(1)–3.067(1) Å. The isoelectronic trinuclear complexes <b>2</b> (which crystallizes in three forms, namely, <b>2a</b>, <b>2b</b>, and <b>2c</b>) and <b>3</b> present a sandwich structure in which the Tl­(I) or Pb­(II) is located between two “Pt­(bzq)­(C₆F₅)₂” subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt–M bonds. The lowest-lying absorption band in the UV–vis spectra in CH₂Cl₂ and tetrahydrofuran (THF) of <b>1</b>, associated with ¹MLCT/¹L′LCT ¹[5d_π(Pt) → π*­(bzq)]/¹[(C₆F₅) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt–Tl fragments in solution, also supported by NMR spectroscopy. In <b>2</b> and <b>3</b>, it shows a blue shift in THF and a red shift in CH₂Cl₂, supporting a more extensive cleavage of the Pt–M bonds in THF solutions than in CH₂Cl₂, where the trinuclear entities are predominant. The Pt–Tl chain <b>1</b> displays in solid state a bright orange-red emission ascribed to ³MM′CT (M′ = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et₂O), related to the coordination/decoordination of the guest molecule to the Tl­(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt–Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH₂Cl₂) <b>1</b> shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt₂Tl complex <b>2</b> shows an emission close to <b>1</b>, ascribed to charge transfer from the platinum fragment to the thallium [³(L+L′)­MM′CT]. <b>2</b> also shows vapoluminescent behavior in the presence of vapors of Me₂CO, THF, and Et₂O, although smaller and slower than those of <b>1</b>. The trinuclear neutral complex Pt₂Pb <b>3</b> displays a blue-shift emission band, tentatively assigned to admixture of ³MM′CT ³[Pt­(d) → Pb­(sp)] with some metal-mediated intraligand (³ππ/³ILCT) contribution. In contrast to <b>1</b> and <b>2</b>, <b>3</b> does not show vapoluminescent behavior

Synthesis, Characterization, and Properties of Doubly Alkynyl Bridging Dinuclear Cyclometalated Iridium(III) Complexes

Bis­(cyclometalated) diiridium complexes [Ir­(ppy)₂(μ–κ<i>C</i>^α:η²-CCR)]₂ (R = Tol <b>1</b>, C₆H₄OMe-4 <b>2</b>, 1-Np <b>3</b>, SiMe₃ <b>4</b>, ^<i>t</i>Bu <b>5</b>), stabilized by a double alkynyl bridging system, have been synthesized by alkynylation of [Ir­(ppy)₂(μ-Cl)]₂ with excess of the appropriate LiCCR (1:6 or 1:10 molar ratio). Complexes <b>1</b>–<b>3</b> were alternatively generated by treatment of [Ir­(ppy)₂(MeCN)₂]­(OTf) with 2.5 equiv of LiCCR. However, the related reaction with LiCC^<i>t</i>Bu evolves with the formation of mixtures from which the unexpected dinuclear complex [Ir­(ppy)₂(μ-CH₂CN)]₂ <b>6</b> was crystallized, as confirmed by X-ray diffraction studies. Complexes <b>1</b>–<b>5</b> have been characterized by NMR, IR, absorption and emission spectroscopies, cyclic voltammetry, and mass spectrometric methods. Characterization indicates that <b>1</b>–<b>3</b> and <b>5</b> are obtained as a unique diastereoisomer (ΛΛ/ΔΔ), whereas <b>4</b> gives the two diastereoisomers (ΔΛ and ΛΛ/ΔΔ). Single crystals of [Ir­(ppy)₂(μ-CCTol)]₂ <b>1</b> contains the inversion related ΛΛ/ΔΔ isomers, and crystals of <b>4</b> (chosen from a mixture of two different types of crystals) consist of the <i>meso</i>-ΔΛ isomer. Electrochemical studies showed the presence in <b>1</b>–<b>3</b> and <b>5</b> of two consecutive one-electron-oxidation Ir^III/Ir^IV processes, whereas <b>4</b> displayed only one irreversible oxidation peak. In degassed fluid solutions, complexes <b>1</b>–<b>5</b> are emissive in the 505–515 nm region with quantum yields higher (ϕ = 0.007–0.024) than that of the dichloro bridged precursor (0.0037). The influence of the alkynyl substituent in the emissive state at room and at low temperatures has been investigated. For the naphthylacetylide derivative <b>3</b>, a clear switch from a mixed charge transfer ³MLCT/³L′LCT excited state at 298 K (515 nm) to a characteristic long-lived low lying naphthalene emission at low temperature (77 K) is observed. DFT and TD-DFT calculations were performed on complexes <b>1</b> and <b>3</b> in the ground and triplet states to gain insight into the structural, electronic, and photophysical properties