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

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