Reductive Elimination at an Ortho-Metalated Iridium(III) Hydride Bearing a Tripodal Tetraphosphorus Ligand

Abstract

The synthesis of the novel C 3 -symmetric tripodal, tetradentate ligand 1, bearing only phosphorus atoms as donor groups, is described, starting from commercially available o-tolyldiphenylphosphine, and its molecular structure has been determined by X-ray crystallographic analysis. Coordination to the cationic Ir I precursor [Ir(COE) 2 (acetone) 2 ]PF 6 led to a highly unsymmetrical species (90% yield) with four inequivalent phosphorus atoms, as evidenced by 31 P NMR spectroscopy. The corresponding 1 H NMR spectrum exhibited a pseudo doublet of quartets at δ −5.9 ppm with one large trans P−H coupling ( 2 J P−H = 115.4 Hz) and a much smaller cis coupling ( 2 J P−H = 10.8 Hz). X-ray crystallography confirmed the formation of complex 2, [Ir(H)(κ 5 P,P,P,P,C-1)]PF 6 , which is a rare example of a structurally characterized mononuclear Ir hydride species bearing an ortho-metalated phosphine ligand. This species does not react with hydride sources, but addition of 1 equiv of CF 3 COOH resulted in facile overall formal protonation of the Ir−C bond. DFT calculations support a pathway involving initial reductive elimination, forming the highly distorted four-coordinate Ir I species 2′, followed by protonation at iridium to give the dicationic monohydride species 3, with an activation barrier ΔG † of 28.2 kcal mol −1 . Deuteration experiments support this mechanism. Reductive elimination can also be induced by reaction of 2 with carbon monoxide, yielding the monocationic carbonyl complex [Ir I (CO)(1)]PF 6 as the sole product.

Formation and Site-Selective Reactivity of a Nonsymmetric Dinuclear Iridium BisMETAMORPhos Complex

“…Correspondingly, a single bond between S 1 –O 21 of 1.493(3) Å exists, while the S 1 –O 11 bond is significantly shorter at 1.447(4) Å, indicating SO character. The iridium–carbon bond length (Ir 2 –C 241 ) of 2.059(5) Å is in the range for previously reported Ir–C aryl bonds . In agreement with the retention of an Ir–C bond in solution, C 241 appears as a doublet-of-doublets at 153.2 ppm in the 13 C­{ 1 H} NMR spectrum, with coupling to both phosphorus nuclei ( 2 J C–P 14.2 and 13.6 Hz) .…”

Iridium(III) Complexes Bearing a Formal Tetradentate Coordination Chelate: Structural Properties and Phosphorescence Fine-Tuned by Ancillaries

“…Hence, the surge in employing multidentate chelate has led to the design of tetradentate chelate and the preparation of emissive Ir­(III) or Pt­(II) metal phosphors. − Furthermore, tetradentate chelates, in comparison to the tridentate chelate of octahedral complexes, are anticipated to have an even better capability in encapsulating the central metal ion and forming well-defined environments. Hence, they have been thoroughly examined for fundamental studies to serve as the durable template in the construction of redox mediators or catalysts for the activation of small molecules. − However, as for the application in making emissive metal complexes, it is essential to introduce some conjugated segment into the chelate backbone to allow systematic fine-tuning of the ππ* energy gap and emission hue. To account for this requirement, porphyrin-based chelates were known to afford red to NIR-emitting Ir­(III) complexes, such as Ir-OEP-Py 2 , due to the extended conjugation (Chart ).…”

The Hydrogenation of Aromatic Compounds under Mild Conditions by Using a Solid Lewis Acid and Supported Palladium Catalyst

“…However, remarkable exceptions were reported for cyclometalated phosphane complexes where intramolecular C–H activations (oxidative addition) facilitate reductive elimination processes from Ir III complexes 9. Previously, a similar reductive elimination at an ortho ‐metalated hydridoiridium(III) complex containing a tripodal tetraphosphorus ligand was reported 10. However, in this case, a cyclometalated, coordinatively saturated Ir III species bearing a hydrido ligand underwent inversion of the cyclometalation during reaction with carbon monoxide.…”