Catalytic oxygenation of sp³ “C–H” bonds with Ir(iii) complexes of chelating triazoles and mesoionic carbenes

Abstract

Cp*-Ir(III) complexes with additional chelating ligands are known active pre-catalysts for the oxygenation of C-H bonds. We present here eight examples of such complexes where the denticity of the chelating ligands has been varied from the well-known 2,2'-bpy through pyridyl-triazole, bi-triazole to ligands containing pyridyl-triazolylidene, triazolyl-triazolylidene and bi-triazolylidenes. Additionally, we also compare the catalytic results to complexes containing chelating cyclometallated ligands with additional triazole or triazolylidene donors. Single crystal X-ray structural data are presented for all the new complexes that contain one or more triazolylidene donors of the mesoionic carbene type. We present the first example of a metal complex containing a chelating triazole-triazolylidene ligand. The results of the catalytic screening show that complexes containing unsymmetrical donors of the pyridyl-triazole or pyridyl-triazolylidene types are the most potent pre-catalysts for the C-H oxygenation of cyclooctane in the presence of either m-CPBA or NaIO4 as a sacrificial oxidant. These pre-catalysts can also be used to oxygenate C-H bonds in other substrates such as fluorene and ethyl benzene. The most potent pre-catalysts presented here work with a lower catalyst loading and under milder conditions while delivering better product yields in comparison with related literature known Ir(III) pre-catalysts. These results thus point to the potential of ligands with unsymmetrical donors obtained through the click reaction in oxidation catalysis.

RuII, OsII, and IrIII Complexes with Chelating Pyridyl–Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis

“…The N4Ir1 bond length is rather unaffected by such effects. For all complexes the triazolylidene rings have a delocalized structure as it was also observed before 6f. Angles are presented in Table 2, and dihedral angles in Table 3.…”

“…The C1Ir1 bond length is in agreement with previous reports of iridium–triazolylidene complexes being 2.009(5) Å, 2.027(9) Å and 2.06(1) Å for Ir‐ 1 , Ir‐ 3 , and Ir‐ 5 , respectively (Table 1). 6f As can be seen, the C1Ir1 bond also minimally elongates with the steric demands of the substituent on the 4‐position. This could probably also be lead back to the steric repulsion of these substituents with the Cp* ligand.…”

Versatile bonding and coordination modes of ditriazolylidene ligands in rhodium(iii) and iridium(iii) complexes

“…13 ,5.49;N,25.44%. Found: C,68.58;H,5.49;N,25.19%. Synthesis of 3c. According to method A, 1,6-heptadiyne (0.13 mL, 1.13 mmol), mesityl azide (0.40 g, 2.48 mmol), CuSO 4 (0.004 g, 23 µmol), sodium ascorbate (0.045 g, 0.23 mmol), THF (9 mL) and H 2 O (9 mL) were reacted in a microwave reactor for 2 h. After purification, the product was obtained as an off-white solid (0.37 g, 80%).…”

“…1 H NMR (CDCl 3 , 400 MHz): δ 7.67 (s, 2H, H trz ), 6.98 (s, 4H, H Mes ), 4.87 (s, 4H, OCH 2 ), 2.34 (s, 6H, CH 3-para ), 1.96 (s, 12H, CH 3-ortho ). 13 C{ 1 H} NMR (CDCl 3 , 100 MHz): δ 144.6 (C trz ), 140.1 (C para ) 135.2 (C ortho ), 133.5 (C ipso ), 129.2 (C meta ), 124.9 (C trz -H), 63.8 (OCH 2 ), 21.2 (CH 3-para ), 21;H,6.78;N,20.18%. Found: C,69.44;H,6.90;N,19.93%.…”

“…1 H NMR (CD 3 CN, 400 MHz): δ 9.04 (s, 2H, H trz ), 7.15 (s, 4H, H Mes ), 4.32 (s, 6H, NCH 3 ), 3.17 (t, 4H, 3 J HH = 7.8 Hz, C trz CH 2 ), 2.48 (quintet, 2H, 3 J HH = 7.8 Hz, CCH 2 CH 2 ), 2.37 (s, 6H, CH 3-para ), 2.10 (s, 12H, CH 3-ortho ). 13 C{ 1 H} NMR (CD 3 CN, 100 MHz): δ 145.4 (C trz ), 143.5 (C para ), 135.7 (C ortho ), 132.4 (C ipso ), 132.1 (C trz -H), 130.6 (C meta ), 39.7 (NCH 3 ), 24.6 (CCH 2 CH 2 ), 23.9 (C trz CH 2 ), 21.2 (CH 3-para ), ,46.43;H,5.20;N,12.03%. Found: C,46.11;H,5.06;N,11.94%. Synthesis of 6a(I).…”