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

Bis­(cyclometalated) diiridium complexes
[Ir­(ppy)2(μ–κCα:η2-CCR)]2 (R =
Tol 1, C6H4OMe-4 2, 1-Np 3, SiMe3 4, tBu 5), 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 1–3 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CtBu evolves with the formation of mixtures from which the unexpected
dinuclear complex [Ir­(ppy)2(μ-CH2CN)]2 6 was crystallized, as confirmed by X-ray diffraction
studies. Complexes 1–5 have been
characterized by NMR, IR, absorption and emission spectroscopies,
cyclic voltammetry, and mass spectrometric methods. Characterization
indicates that 1–3 and 5 are obtained as a unique diastereoisomer (ΛΛ/ΔΔ),
whereas 4 gives the two diastereoisomers (ΔΛ
and ΛΛ/ΔΔ). Single crystals of [Ir­(ppy)2(μ-CCTol)]2 1 contains
the inversion related ΛΛ/ΔΔ isomers, and crystals
of 4 (chosen from a mixture of two different types of
crystals) consist of the meso-ΔΛ isomer.
Electrochemical studies showed the presence in 1–3 and 5 of two consecutive one-electron-oxidation
IrIII/IrIV processes, whereas 4 displayed only one irreversible oxidation peak. In degassed fluid
solutions, complexes 1–5 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 3, 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 1 and 3 in the
ground and triplet states to gain insight into the structural, electronic,
and photophysical properties.

双环金属化二铱配合物[Ir(ppy)₂(μ–κCα:η²-C≡CR)]₂（其中ppy为2-苯基吡啶，R依次为甲苯基(Tol)1、4-甲氧基苯基(C₆H₄OMe-4)2、1-萘基(1-Np)3、三甲基硅基(SiMe₃)4、叔丁基(tBu)5），经双炔基桥联体系稳定，可通过[Ir(ppy)₂(μ-Cl)]₂与过量相应炔基锂LiC≡CR（摩尔比1:6或1:10）的炔基化反应合成。配合物1~3亦可通过[Ir(ppy)₂(MeCN)₂](OTf)与2.5当量的LiC≡CR反应制备，其中MeCN为乙腈，OTf为三氟甲磺酸盐。然而，与LiC≡CtBu的同类反应会生成复杂混合物，从中意外结晶得到双核配合物[Ir(ppy)₂(μ-CH₂CN)]₂ 6，该产物经X射线衍射研究确认。配合物1~5均通过核磁共振波谱(NMR)、红外光谱(IR)、吸收与发射光谱、循环伏安法及质谱法完成表征。表征结果显示，1~3与5均以单一非对映异构体(ΛΛ/ΔΔ)形式得到，而4则生成两种非对映异构体(ΔΛ与ΛΛ/ΔΔ)。[Ir(ppy)₂(μ-C≡CTol)]₂（即配合物1）的单晶包含互为反演对称的ΛΛ/ΔΔ异构体，而从两种不同晶体混合物中选取的配合物4的单晶则为内消旋ΔΛ异构体。电化学研究表明，1~3与5存在两个连续的单电子氧化Ir³+/Ir⁴+过程，而4仅表现出一个不可逆氧化峰。在脱气流体溶液中，配合物1~5在505~515 nm区间具有发射特性，其量子产率(ϕ=0.007~0.024)高于二氯桥联前驱体(0.0037)。本研究考察了炔基取代基对室温和低温下发射态的影响。对于萘乙炔基衍生物3，可观察到显著的激发态转变：在298 K时为混合电荷转移态³MLCT/³L′LCT（发射波长515 nm），而在低温(77 K)下则转变为特征的长寿命低能级萘发射。通过对配合物1与3的基态和三重态进行密度泛函理论(DFT)及含时密度泛函理论(TD-DFT)计算，以深入解析其结构、电子与光物理性质。