Formation of Iridium(III) Complexes via Selective Activation of the C–H and N–H Bonds of a Dipyridylpyrrole Ligand

Abstract

Treatment of [Ir(PPh 3 ) 3 Cl] with 2-[5-(pyridin-2-yl)-1H-pyrrol-2-yl]pyridine (Hdpp) in refluxing toluene affords an unexpected pyrrole-metalated iridium(III) hydride complex, [Ir(K 2 C,N -dpp)(H)(Cl)(PPh 3 ) 2 ] (1), via C pyrrole −H activation, while the presence of the base KO t Bu as the deprotonation reagent produces a pyridine-metalated iridium(III) hydride complex, [Treatment of [Ir(PPh 3 ) 3 Cl] prepared by a convenient method with Hdpp in the presence of KO t Bu under the refluxing mixture solvent toluene/methanol (2:1, v/v) generates the N,N-chelating complex [Ir(K 2 N,N -dpp)(H)(Cl)(PPh 3 ) 2 ] (3) together with 1 and the N,N-chelating dihydride complex [Ir(K 2 N,N -dpp)(H) 2 (PPh 3 ) 2 ] (4). Complex 4 is also readily produced by the reaction of [Ir(PPh 3 ) 3 Cl] and Hdpp in the presence of KO t Bu under refluxing methanol or by the reaction of IrCl 3 and PPh 3 in refluxing 2-ethoxyethanol. Complexes 1−4 are fully characterized by NMR, IR, and UV−vis spectroscopy and X-ray diffraction analysis. The dpp − /dpp 2− ligand shows rich coordination capability, of which pyridine-and pyrrole-cyclometalated coordination modes are first reported. The formation of structural isomers 1 and 3 involved the selective activation of the C−H and N−H bonds of Hdpp is rationalized by theoretical calculations.

Osmium- and Iridium-Promoted C–H Bond Activation of 2,2′-Bipyridines and Related Heterocycles: Kinetic and Thermodynamic Preferences

“…Treatment of toluene solutions of 8 with 2,2′-bipyridine and 6-phenyl-2,2′-bipyridine, under reflux, for 12 h leads to the iridium(III)-dihydride counterparts of 2 and 3, complexes IrH 2 {κ 2 -C,N-[C 5 (R)H 2 N-py]}(P i Pr 3 ) 2 (R = H, (9), Ph ( 10 The 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectra, in benzene-d 6 , at room temperature of 9−11 are consistent with the structures proposed in Scheme 14. In agreement with the presence of two inequivalent hydride ligands in 9 and 10, their 1 H NMR spectra contains two doublets of triplets ( 2 J H−H ≈ 4.9 Hz, 2 J H−P ≈ 19 Hz) about −12.5 and between −21 and −25 ppm, whereas the spectrum of 11 displays a triplet ( 2 J H−P = 20 Hz) at −16.01 ppm.…”

“…1 H NMR (300.13 MHz, C 6 D 6 , 298 K) δ 1.72 (m, 6H, PCH(CH 3 ) 2 ), 1.13 (dvt, 3 J H−H = 6.8, N = 13.7, 36H, PCH(CH 3 ) 2 ), −10.85 (t, 2 J H−P = 12.4, 0.27H, corresponding to a 5% of nondeuterated product, Ir−H). 31 (9). A mixture of 8 (200 mg, 0.386 mmol) and 2,2′-bipyridine (603 mg, 3.863 mmol) in toluene (8 mL) was refluxed for 14 h. After cooling the resulting dark yellow solution to room temperature, it was filtered through Celite and the solvent removed in vacuo, affording a yellowish residue with was extracted into pentane (4 × 10 mL).…”

“…For instance, 2,2′-bipyridine is the unique molecular scaffold of the bioactive natural products represented by caerulomycins and collismycins . Although 2,2′-bipyridines are well-known N , N -chelate ligands, which form extremely stable compounds with all transition metals, some unsaturated d 8 -complexes of iridium­(I), palladium­(II), platinum­(II), and gold­(III), and IrCl 3 ·3H 2 O have proved to promote their C–H bond activation in solution. This unusual reaction, so-called “rollover cyclometalation”, is viewed as originated from a chelated κ 2 - N , N -adduct.…”

“…All hydrogen atoms (except the hydrides) are omitted for clarity. Selected bond distances (Å) and angles (deg) for the two independent molecules in the asymmetric unit: Os(1)−P(1) = 2.3469(9), 2.3450(9), Os(1)−P(2) = 2.3416(9), 2.3338(9), Os(1)− C(1) = 2.071(3), 2.060(3), Os(1)−C(10) = 2.132(4), 2.135(4); P(1)−Os(1)−P(2) = 162.24(3), 162.67(3), C(1)−Os(1)−C(10) = 75.76(13), 76.04(13).…”

Selectivity and competition between N–H and C–H bond activation using an organoplatinum (II) complex

“…Although cyclometalation reactions via C-H bond activation have been widely studied, and different classes of cycloplatinated and rollover cycloplatinated complexes have been synthesized, [31][32][33][34][35][36][37][38][39][40][41][42] a detailed investigation when both N-H and C-H bonds are available for activation has not been reported for platinum complexes and is limited to a few studies for Ir and Co complexes. [43][44][45] In the present study, 2-(2 0 -pyridyl)benzimidazole (Hpbz) is selected as the ligand with both C-H and N-H to investigate its reaction with a dimethylplatinum (II) complex, (PtMe 2 (DMSO) 2 ), 1, (DMSO = dimethyl sulfoxide). [46] This ligand provides an ideal system to consider the competition between C-H and N-H activation.…”