Bis(pyridylimino)isoindolato−Iridium Complexes as Epoxidation Catalysts for Alkenes

Abstract

The reaction of the sodium salts of ligands 1a,b (1a = 1,3-bis(2-(5-(3,5-xylyl)pyridyl)imino)-5,6-dimethylisoindole, 1b = 1,3-bis(2-(4-tert-butylpyridyl)imino)-5,6-dimethylisoindole) with [Ir(μ-Cl)(COD)]2 (COD = cyclooctadiene) and [Ir(μ-Cl)(C2H4)2]2 afforded the corresponding isoindolato complexes [{BPI(1a,b)}IrI(COD)] (2a,b) and [{BPI(1a,b)}IrI(C2H4)2] (3a,b), respectively. The catalytic activity of the complexes 2a,b was tested in the epoxidation of a wide range of non-electron-rich olefins, using PPO (PPO = 3-phenyl-2-(phenylsulfonyl)-1,2-oxaziridine) as oxidizing agent, giving the corresponding epoxides in moderate to high yields.

New Chemistry with Anionic NNN Pincer Ligands

“…On the other hand, if the smaller ethylene molecules are used instead of COD, the BPI ligand coordinates in the usual manner (Fig. 3) [53]. Similar results were observed with the asymmetrical pincer ligand o-(NMe 2 )Ph-QAH with (COD)PtCl 2 .…”

“…Square planar platinum(II) complexes such as (BPI)Pt(L) using BPI and additional strong field ligands have also been prepared [52]. However, while BPI ligands typically act as chelating tridentate ligands, sometimes one of the pyridine rings may rotate out of the plane when other [53]. This was observed in the isolation of [Ir(BPI) (COD)] in which, as a result of the strong coordination of the cyclooctadiene (COD) ligand, one of the pyridine rings does not coordinate to the metal center and is thus twisted away [53].…”

“…However, while BPI ligands typically act as chelating tridentate ligands, sometimes one of the pyridine rings may rotate out of the plane when other [53]. This was observed in the isolation of [Ir(BPI) (COD)] in which, as a result of the strong coordination of the cyclooctadiene (COD) ligand, one of the pyridine rings does not coordinate to the metal center and is thus twisted away [53]. On the other hand, if the smaller ethylene molecules are used instead of COD, the BPI ligand coordinates in the usual manner (Fig.…”

“…While iridium complexes are less well known in oxidation catalysis, iridium-BPI complexes were employed in the epoxidation of olefins using various oxidizing agents, the best being PPO (PPO¼3-phenyl-2-(phenylsulfonyl)-1,2-oxaziridine) (Scheme 29) [53].…”

Efficient and convenient epoxidation of alkenes to epoxides with H2O2 catalyzed by Co(OAc)2 in ionic liquid [C12py][PF6]

“…[3][4][5], and suffer from considerable drawbacks such as low yield, harsh or delicate reaction condition, and a large amount of waste byproducts. Oxidation with NaClO [6,7], PAA [8], TBHP [9,10], PhIO [11,12], NaIO 4 [13,14], CHP [15], oxone [16][17][18], peracetic acid [19,20], TADOOH [21], PPO [22], and other reagents [23][24][25][26][27][28] have also been developed for this conversion. However, these protocols are generally associated with one or more disadvantages, such as complex handling procedures, problematic side reactions, the use of expensive, toxic and moisture-sensitive reagents, long reaction times, low yields, and environmental concerns associated with the use of poorly manageable catalysts.…”