An Unprecedented Family of Luminescent Iridium(III) Complexes Bearing a Six-Membered Chelated Tridentate C^N^C Ligand

A new family consisting of three luminescent neutral Ir(III) complexes with the unprecedented [Ir(C^N^C)(N^N)Cl] architecture, where C^N^C is a bis(six-membered) chelating tridentate tripod ligand derived from 2-benzhydrylpyridine (bnpy) and N^N is 4,4′-di-tert-butyl-2,2′-bipyridine (dtBubpy), is reported. X-ray crystallography reveals an unexpected and unusual double C–H bond activation of the two distal nonconjugated phenyl rings of the bnpy coupled with a very short Ir–Cl bond trans to the pyridine of the bnpy ligand. Depending on the substitution on the bnpy ligand, phosphorescence, ranging from yellow to red, is observed in dichloromethane solution. A combined study using density functional theory (DFT) and time-dependent DFT (TD-DFT) corroborates the mixed charge-transfer nature of the related excited states.


X-ray crystal structures
Single crystals of sufficient quality of 1-3 were grown from CH 2 Cl 2 /Et 2 O at -18°C. X-ray diffraction data for compound 1 were collected at 150 K by using a Bruker D8 VENTURE with an Incoatec microfocus source equipped with a multilayer monochromator (Mo Kα radiation, λ = 0.71073 Å) and a PHOTON 100 detection system. Intensity data were collected using rotation frames accumulating area detector images. Data for compounds 2 and 3 were collected at 173 K by using a Rigaku FR-X Ultrahigh brilliance Microfocus RA generator/confocal optics and Rigaku XtaLAB P200 system, with Mo Kα radiation (λ = 0.71075 Å). Intensity data were collected using ω steps accumulating area detector images spanning at least a hemisphere of reciprocal space. All data were corrected for Lorentz polarization effects. A multiscan absorption correction was applied by using SADABS 1 (1) or CrystalClear 2 (2 and 3). Structures were solved by either dual-space (SHELXT 3 ) or Patterson methods (PATTY 4 ) and refined by full-matrix least-squares against F 2 (SHELXL-2014). 3 In 1 the contribution of the disordered solvent to the calculated structure factors was calculated by the PLATON/SQUEEZE procedure. 5 Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using a riding model. CCDC 1519101-1519103 contain the supplementary crystallographic data for this paper. These data are provided free of charge by The Cambridge Crystallographic Data Centre. Table S1 contains a summary of crystallographic data.  Table S2. Selected photophysical data for complexes 1-3 [a] recorded in aerated CH 2 Cl 2 at 298 K Figure S31: Excited-state lifetime (λ exc = 378 nm) decay profile of 1 in deaerated dichloromethane at room temperature.

DFT and TD-DFT calculations
To perform DFT and TD-DFT calculations, we have used the Gaussian09 program. 9 Our calculations consisted in geometry optimization vibrational spectra determinations and TD-DFT calculations of the different structures. We have applied default procedures, integration grids, algorithms and parameters, except for improved energy (typically 10 −10 a.u.) and internal forces (10 −5 a.u.) convergence thresholds and the use of the ultrafine integration DFT grid. The ground-state geometrical parameters have been determined with the M06 functional. 10 The vibrational spectrum has been subsequently determined analytically at the same level of theory and it has been checked that all structures correspond to true minima of the potential energy surface. At least, the first forty low-lying excited-states have been determined within the vertical TD-DFT approximation using the same functional that is suited for optical spectra. [11][12] Phosphorescence wavelengths were obtained by first optimizing the lowest triplet excited-state with unrestricted DFT (M06 functional) and next computing the The simulated TD-DFT spectra obtained by convoluting the vertical stick contributions with a Gaussian of HWHH of 0.2 eV are displayed in Figure S35. Globally, the match with the experimental data ( Figure 4) is very satisfying, giving confidence in the theoretical analysis.
A list of the key singlet transitions is given in Table S3. For 1, PCM-TD-DFT calculations yield the lowest singlet excited-states at 489 nm (f=0.004) and 483 nm (f=0.057), which match well the weak experimental absorption band at ca. 500 nm (see Figure 4 in the main text). According to TD-DFT, the two lowest triplet excited-states are located in a very close region, 508 and 503 nm, respectively, though they present zero oscillator strengths due to the neglect of spin-orbit couplings in the non-relativistic approach used here. The S 1 (T 2 ) and S 2 (T 1 ) states mainly correspond to HOMO-1 to LUMO and HOMO to LUMO transitions, respectively. The occupied orbitals are shown in Figure S34 and a clear mixed charge-transfer (CT) character can be seen, the electron going from the metal, chlorine, and phenyl to the bipyridine (bpy) group. For the same compound, the next dipole-allowed transition found by TD-DFT are in the 420-370 nm region and correspond to the second maxima at ca. 400 nm S24 experimentally. The two transitions presenting the strongest f in this spectra region are located by TD-DFT at 419 nm (f=0.056) and 382 nm (f=0.093). The first can be mainly ascribed to a HOMO-2 to LUMO transition and therefore corresponds to a metal+chlorine to dtBubpy charge transfer, whereas the second is a HOMO-1 to LUMO+1 transition, of MLCT/ILCT nature not involving the dtBubpy. In 2, the addition of the tBu groups induces a small bathochromic displacement, the two lowest weakly allowed transitions appearing at 495 nm (f=0.005) and 493 nm (f=0.053), whereas the two next are at 423 nm (f=0.055) and 386 nm (f=0.092). The changes are indeed small as can be seen in both the calculated spectra and orbital energy levels (Figures S34 and S35). As expected, and consistently with the measurements, the CF 3 groups (3) Table S3. Key singlet excited-states determined by TD-DFT. We provide the corresponding wavelength (in nm), oscillator strength (in parenthesis) and the dominating orbital character.
Only states of interest for the analysis are given  We have also optimized the structure of the lowest triplet excited-state of the three complexes.
The corresponding spin density for the three compounds can be found in Figure S36. As can be seen, the triplet presents contributions on the metal centre, bipyridine and chlorine atom,