Synthesis and Isolation of an Anionic Bis(dipyrido-annulated) N-Heterocyclic Carbene CCC-Pincer Iridium(III) Complex by Facile C–H Bond Activation

Abstract

Meridional tridentate N-heterocyclic carbene (NHC)-based pincer ligands contribute to a substantial growth in modern organometallic chemistry in both homogeneous catalysis and luminescence materials. Among all NHC-based pincer ligands, the dianionic LX 2 -type CCC-pincer ones constitute the smallest subcategory owing to their limited ligand frameworks suitable for complexation. This work reports a one-pot, high-yield synthesis of a homoleptic anionic all-carbon bis-pincer iridium(III) complex (4) directly from a bis(aryl)-substituted dipyrido-annulated (dpa Ar2 ) imidazolium salt and [Ir(COD)Cl] 2 via a cascade of deprotonation/C−H activation processes. Both experimental complexation chemistry and computational mechanistic investigation suggest that the large bite angle and π-rich character of the dpa Ar2 NHC are responsible for its facile complexation as a dianionic LX 2type CCC-pincer ligand precursor. The all-carbon ligated iridium(III) complex (4) bearing a π-conjugated ligand scaffold showed remarkably low oxidation potentials, which allows future investigations in its redox chemistry and photophysical properties.

Redox Activity of IrIII Complexes with Multidentate Ligands Based on Dipyrido‐Annulated N‐Heterocyclic Carbenes: Access to High Valent and High Spin State with Carbon Donors

“…The results revealed the lower and higher spin energy gap decreased as complex 4 [Ir] + (ΔE S-T = À 34.3 kcal/mol) is oxidized to 6 [Ir] 2 + (ΔE D-Q = À 13.1 kcal/mol) and 7 [Ir] 3 + (ΔE S-T = + 1.3 kcal/mol), showing a trend towards a more favourable high spin state as the positive charge of the complex increases. Variable Temperature (VT) 19 F NMR of complex 7 in THF-d 8 supported this prediction by showing a Curie behaviour (Figure S20), which is a general exp ) obtained from variable temperature EPR experiment is also included (see Figure 8). phenomenon for paramagnetic species.…”

“…phenomenon for paramagnetic species. [23] In addition, the line width of both 1 H and 19 F NMR signals broadened at lower temperature (Figures SA22 and SA24), suggesting the paramagnetic species are more prominent at lower temperatures. [24] NBO charges for each fragment of the cationic complexes 4, 6, and 7-T (triplet) showed that the atomic charges on the iridium atom and the acetonitrile ligands remain almost constant, whereas a drastic change occurs on the CCCC-ligand (Table 2).…”

“…A synthetic challenge for synthesizing carbon‐ligated metallacycles comes from selective C−H bond activation in the metalation step as opposed to an E−H activation, which can be readily achieved by deprotonation (E=O, N) or oxidative addition (E=B, Si, Al). Recently, we successfully developed a high yield synthesis of homoleptic anionic bis(dipyrido‐annulated) N‐heterocyclic carbene (NHC) CCC ‐pincer iridium(III) complex ( 1 ) [19] . We hypothesized the LX 2 type π‐rich planar structure of the CCC ‐ligand can tap into the AFOE for facile oxidation.…”

“…Recently, we successfully developed a high yield synthesis of homoleptic anionic bis(dipyrido-annulated) N-heterocyclic carbene (NHC) CCC-pincer iridium(III) complex (1). [19] We hypothesized the LX 2 type π-rich planar structure of the CCC-ligand can tap into the AFOE for facile oxidation. Herein, we report a four-electron oxidation sequence redox behavior of this all carbon ligated Ir III complex 1, which provided a formal Ir V tricationic complex with a triplet ground state (Figure 1).…”

Characterization of an unanticipated indium-sulfur metallocycle complex

“…Indium(III) fluoride and indium(III) triflate promote the cyanation of aldehydes and Diels-Alder reaction of imines [14,15]. Catalysis by indium(II) compounds is relatively uncommon [16].…”