Carboxylate Ligand-Induced Intramolecular C−H Bond Activation of Iridium Complexes withN-Phenylperimidine-Based Carbene Ligands

Abstract

We report the synthesis and structure of iridium(I) complexes with N,N 0 -disubstituted perimidine carbene ligands and halides or carboxylate ligands. Iodo-, chloro-, and acetate-Ir(carbene)(cod) complexes were selectively prepared by changing the bases and silver salts. Intramolecular C-H bond activation to prepare a cyclometalated Ir(III) complex, (C ∧ C:) 2 Ir(OAc) (6), where C ∧ C: is a cyclometalated perimidine carbene ligand, was achieved using a carboxylate-ligated iridium complex; otherwise, C-H activation did not proceed. Acetate-Ir(carbene)(cod) (3c) reacted with benzoic anhydride at room temperature to afford benzoate-Ir(carbene)(cod) (3d). A perimidine-carbene-and phenylpyridine-ligated Ir(III) complex, (C ∧ C:)(C ∧ N)Ir(OCOR) (8), where C ∧ N is a cyclometalated phenylpyridine ligand, was isolated in good yield by mixing 3c or 3d and phenylpyridine under reflux in toluene. On the basis of the formation of 1,3-cyclooctadiene from the reaction mixture, we propose the following reaction mechanism for the intramolecular C-H activation: carboxylate-induced C-H bond activation and subsequent pyridine-or carbene-directed C-H bond oxidative addition, followed by the isomerization of 1,5-cyclooctadiene and reaction with carboxylic acid produces (C ∧ C:)(N ∧ C:)Ir(OCOPh). The cyclometalated complex 6 reacts with sodium acetylacetonate to form (C ∧ C:) 2 Ir(acac) (11), which exhibits phosphorescent emission at λ max = 555 nm (τ = 0.65 μs, Φ PL = 0.0018) in CH 2 Cl 2 solution at room temperature.

Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis

“…Such intramolecular C-H bond activations assisted by carboxylate ligands have been reported in other organometallic complexes. 10 Based on these previous reports, a plausible mechanism for the C-H bond activation in 3a contains 6-membered ( A ) or 4-membered ( B ) transition state shown in Figure 1. It should be noted that no other anionic ligands including sulfonate, 5b phosphonate, 5b and trifluoroacetate 11 promote such intramolecular C-H bond activation in 1a .…”

Decomposition Pathways of Z-Selective Ruthenium Metathesis Catalysts

“…5a Carboxylate-driven C-H bond activations of this type has been studied for a variety of late transition metal complexes. 6 With this mode of activation, a carbon-metal bond is formed with concurrent generation of the corresponding carboxylic acid. In contrast, previous generations of ruthenium metathesis catalysts have been proposed to decompose upon C-H activation by oxidative addition.…”

Microwave-Assisted Synthesis of Novel Perimidinium Salts as N-Heterocyclic Carbene Precursors: Involvement in Palladium-Catalyzed Cross-Coupling Reactions

“…Perimidine-based NHCs and its Rh complexes were investigated first time in 2003 by Richeson and coworkers 20 but only a few perimidine-based catalysts have been reported in literature so far by the other research groups. [21][22][23][24][25][26] In addition to catalytic applications of perimidine derivatives, their anti-inflammatory, 27 antioxidant, 28 antimicrobial, 29 antibacterial, 30 antitumor, 31 and dyestuff 32 properties were reported.…”

“…In the literature the synthesis of 1-alkylperimidines is reported in ethanol or methanol under reflux conditions at longer reaction times. 24,26 After the synthesis of compound 1, five perimidinium salts 2a-e were synthesized by reaction of compound 1 and five different alkyl chlorides in good yields (82-96%) at 110°C under microwave irradiation (Scheme 1). Thus, the use of microwave irradiation shortens the reaction time significantly at nearly the same temperature as compared with literature data.…”

“…Thus, the use of microwave irradiation shortens the reaction time significantly at nearly the same temperature as compared with literature data. 23,24,26 If we consider the difficulties in producing perimidine derivatives and the short reaction time, the achieved yields are quite satisfactory. Elemental analysis data are in unison with the structures of compounds 2a-e.…”