Cyclometalated Iridium(III) Complexes Containing Hydroxide/Chloride Ligands: Isolation of Heterobridged Dinuclear Iridium(III) Compounds Containing μ-OH and μ-Pyrazole Ligands

Abstract

The reaction of the cyclometalated chloro-bridged iridium(III) dimers [(ppy)(2) Ir(μ-Cl)](2) (ppyH = 2-phenyl pyridine) and [(tpy)(2)Ir(μ-Cl)](2) (tpyH = 2-p-tolylpyridine) with 3,5-diphenylpyrazole (Ph(2)PzH) in the presence of sodium methoxide resulted in the formation of heterobridged dimers [(ppy)(2)Ir(μ-OH)(μ-Ph(2)Pz)Ir(ppy)(2)] (1) and [(tpy)(2)Ir(μ-OH)(μ-Ph(2)Pz)Ir(tpy)(2)] (2). Interestingly, the reaction of [(ppy)(2)Ir(μ-Cl)](2) with 3(5)-methyl-5(3)-phenylpyrazole (PhMePzH) afforded both a heterobridged dimer, [(ppy)(2)Ir(μ-OH)(μ-PhMePz)Ir(ppy)(2)] (3), and the monomer [(ppy)(2)Ir(PhMePz)Cl] (4). The compound [(ppy)(2)Ir(PhMePz)OH] (5) containing a terminal OH was obtained in a hydrolysis reaction involving 4, sodium methoxide, and PhMePzH. Complexes 1-5 were characterized by X-ray crystallography and electrospray ionization high-resolution mass spectrometry. All of the complexes are luminescent at room temperature in their dichloromethane solutions. The luminescence of the dinuclear complexes is characterized by a single structureless band centered at λ(max) = 550 nm (1 and 3) and 546 nm (2). The emission spectra of the mononuclear complexes 4 and 5 display vibronic structures with their λ(max) values at 497 nm (4) and 513 nm (5). In each case, the main emission bands are accompanied by shoulder bands at 526 (4) and 534 nm (5). The quantum yields, calculated with reference to [Ir(ppy)(2)(bpy)]PF(6) (Φ(CH(3)CN) = 0.0622), range from 0.11 to 0.17 for the dinuclear complexes and 0.045 to 0.048 for the mononuclear complexes. The lifetimes of the emission are in the microsecond region, suggesting the phosphorescent nature of the emission. Density functional theory (DFT) and time-dependent DFT calculations were performed on complexes 1 and 4 in the ground state to gain insight into the structural, electronic, and photophysical properties. Electrochemical studies on complexes 1-3 showed the presence of two consecutive one-electron-oxidation processes, assigned as the stepwise oxidation of the two Ir(III) centers, i.e., Ir(III)-Ir(III)/Ir(III)-Ir(IV) and Ir(III)-Ir(IV)/Ir(IV)-Ir(IV) couples, respectively. The monomers displayed single-oxidation peaks. No reduction process was observed within the solvent cathodic potential limit.

Synthesis, Diastereomer Separation, and Optoelectronic and Structural Properties of Dinuclear Cyclometalated Iridium(III) Complexes with Bridging Diarylhydrazide Ligands

“…1, 2 and 3 ( Figure 1). [18][19][20][21][22][23][24][25][26][27][28][29] Consequently, for luminescence applications research has primarily concentrated on monoiridium complexes. 30,31 Nevertheless, the study of phosphorescent diiridium complexes is a rapidly expanding topic and a range of complexes with various conjugated bridging ligands have been reported to possess efficient photo-(PL) and electroluminescence (EL).…”

Synthesis and Molecular Structure of the New Green Emitting Complex [Ir2(μ2‐oxamidato‐N,N′,O,O′)(2‐(p‐tolyl)pyridinato)4]

“…In the last years, we described the syntheses of several cyclometalated M III complexes of the elements rhodium and iridium,5 and particularly, we reported the synthesis and structural characterization of some complexes containing several biomolecules as the ancillary ligands 6. Most of the known cyclometalated Rh and Ir complexes are mononuclear, and except for the chloride‐bridged dimers formed from high‐temperature reactions of the corresponding metal(III) chlorides and the cyclometallating ligand, rather few di‐ or oligomeric complexes of this type have been reported 7–10. This can be mainly attributed to the opinion that such dinuclear compounds are not suitable for opto‐electronical devices, a view that might have to be revised according to some recent findings 8.…”

“…This can be mainly attributed to the opinion that such dinuclear compounds are not suitable for opto‐electronical devices, a view that might have to be revised according to some recent findings 8. With Ir III , so far neutral NN ligands of the 4, 4'‐bipyridyl‐ type as well as anionic ligands, such as pyrazole, cyanide, and cyanate have been used as the bridging units 7–10. With cyclometallated Pd II complexes a series of anionic imidato ligands have been shown to act as N, O‐bridging units, [11, 12] while there seem to be no reports of the closely related amidato ligands as bridging groups with cyclometallated complex fragments.…”

Bimetallic Cyclometalated Iridium(III) Diastereomers with Non‐Innocent Bridging Ligands for High‐Efficiency Phosphorescent OLEDs

“…[1b, 3-5] Cyclometalated iridium(III) complexes are widely exploited because of their excited-state lifetimes on the microsecond time scale, high quantum yields, good thermal and chemical stability, and tunability of the emission color. [6][7][8][9][10] In this context, the prototype complex is fac-[Ir(ppy) 3 ] (ppy = 2-phenylpyridine).The photoluminescence quantum yields of dinuclear metal complexes [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] are usually considerably lower than those of their mononuclear analogues [12,14,23,24] (although there are exceptions), [25] leading to the established view that dinuclear complexes give poor device performance. [26,27] For example, the quantum yield of the bis(m-Cl) bridged dimer [{Ir(ppy) 2 Cl} 2 ] (1) is only 0.5 %, [11] whereas that of fac-[Ir(ppy) 3 ] is 40(AE0.1) % (both in toluene).…”

“…We are not aware of a previous computational study on diiridium complexes where the bridge has been shown to be heavily involved in the HOMO: Typically, either the LUMO involves bridge character, [16,18,23,32] or the bridge is not involved in either frontier orbital. [19,24] The photophysical data for 2, 3, and 4 are shown in Figures S8 and S9 and Tables S3 and S4; data for [Ir(ppy) 3 ] and 1 obtained under directly comparable conditions are included for comparison. The PL emissions of 3 and 4 at 521 nm and 523 nm are featureless, which indicates a dominant 3 MLCT contribution and little signature of 3 LC contribution.…”