Addition of Amine-Substituted Heteroaromatic Rings to Alkynyl Bridging Ligands to Generate Phosphorescent Emitters Incorporating Iridaimidazoles with Fused Heterocyclic Rings

Alkynyl ligands are versatile building blocks in the
design of
luminescent iridium(III) complexes due to their ability to support
postcoordination functionalization that gives rise to ligands non
available through conventional coordination chemistry. Here, we report
the synthesis and characterization of a new family of heteroleptic
iridium(III) green emitters based on cyclometalated 2-p-tolylpyridine as main ligands and new C,N-chelating units as the auxiliary ligand that yield iridaimidazole
structures. The alkynyl bridging dimer cis-[Ir(μ-CCtBu){κ2-C,N-(MeC6H3-py)}2]2 (1) reacts with amine-substituted five-membered
heterocycles bearing two heteroatoms, such as 1-methyl-1H-imidazol-2-amine, 1-methyl-1H-benzo[d]imidazol-2-amine, 4-methyloxazol-2-amine, benzo[d]oxazol-2-amine, 4-methylthiazol-2-amine, and benzo[d]thiazol-2-amine, giving the iridaimidazole derivatives Ir{κ2-C,N-(MeC6H3-py)}2{κ2-C,N-[C(CH2tBu)N-im]}
(im = imidazole, 2), Ir{κ2-C,N-(MeC6H3-py)}2{κ2-C,N-[C(CH2tBu)N-bzim]} (bzim = benzimidazole, 3), Ir{κ2-C,N-(MeC6H3-py)}2{κ2-C,N-[C(CH2tBu)N-oxazol]} (4), Ir{κ2-C,N-(MeC6H3-py)}2{κ2-C,N-[C(CH2tBu)N-bzoxazol]}
(5), Ir{κ2-C,N-(MeC6H3-py)}2{κ2-C,N-[C(CH2tBu)N-thiazol]} (6), and Ir{κ2-C,N-(MeC6H3-py)}2{κ2-C,N-[C(CH2tBu)N-bzthiazol]}
(7), respectively. The iridium center in these complexes
is in an octahedral environment with nitrogen and carbon atoms in
a facial disposition. Complexes 2, 4, and 6 feature one five-membered heteroaromatic ring fused to the
iridaimidazole cycle whereas 3, 5, and 7 additionally contain a benzo group fused to the organic
heterocycle. All complexes are green phosphorescent emitters (474–558 nm) upon photoexcitation, with high quantum yields
(0.55–0.92) in poly(methyl methacrylate) films
and 2-MeTHF at 298 K.

炔基配体(alkynyl ligands)是一类用途广泛的构建模块，可用于设计发光铱(III)配合物，因其能够支持配位后官能化(postcoordination functionalization)，从而获得传统配位化学无法合成的配体。本文报道了一类新型异配位型铱(III)绿色发光体的合成与表征：该类配合物以环金属化2-对甲苯基吡啶作为主配体，以新型C,N螯合单元作为辅助配体，进而形成铱杂咪唑(iridaimidazole)结构。
桥联炔基二聚体顺式-[Ir(μ-叔丁基炔基){κ2-C,N-(2-(对甲苯基)吡啶)}2]2（1）可与含双杂原子的氨基取代五元杂环发生反应，包括1-甲基-1H-咪唑-2-胺、1-甲基-1H-苯并[d]咪唑-2-胺、4-甲基恶唑-2-胺、苯并[d]恶唑-2-胺、4-甲基噻唑-2-胺以及苯并[d]噻唑-2-胺，分别得到如下铱杂咪唑衍生物：Ir{κ2-C,N-(2-(对甲苯基)吡啶)}2{κ2-C,N-[C(叔丁基甲基)N-咪唑]}（2，咪唑缩写为im）、Ir{κ2-C,N-(2-(对甲苯基)吡啶)}2{κ2-C,N-[C(叔丁基甲基)N-苯并咪唑]}（3，苯并咪唑缩写为bzim）、Ir{κ2-C,N-(2-(对甲苯基)吡啶)}2{κ2-C,N-[C(叔丁基甲基)N-恶唑]}（4）、Ir{κ2-C,N-(2-(对甲苯基)吡啶)}2{κ2-C,N-[C(叔丁基甲基)N-苯并恶唑]}（5）、Ir{κ2-C,N-(2-(对甲苯基)吡啶)}2{κ2-C,N-[C(叔丁基甲基)N-噻唑]}（6）以及Ir{κ2-C,N-(2-(对甲苯基)吡啶)}2{κ2-C,N-[C(叔丁基甲基)N-苯并噻唑]}（7）。
上述配合物中的铱中心处于八面体配位环境，氮原子与碳原子呈面式排布。配合物2、4和6带有一个与铱杂咪唑环稠合的五元杂芳环，而配合物3、5和7则额外带有一个与有机杂环稠合的苯环。
所有配合物在光激发下均表现出绿色磷光发射（波长范围474~558 nm），在298 K下的聚甲基丙烯酸甲酯（PMMA）薄膜及2-甲基四氢呋喃（2-MeTHF）中具有较高的量子产率（0.55~0.92）。