2-Azetidinones as Precursors of Pincer Ligands: Preparation, Structure, and Spectroscopic Properties of CC′N-Osmium Complexes

Abstract

A metal-promoted degradation of 2-azetidinones to afford CC'N-pincer ligands is reported. The hexahydride complex OsH6(P(i)Pr3)2 (1) reacts with (±)-cis-1-(4-methoxyphenyl)-3-phenoxy-4-(pyridin-2-yl)azetidin-2-one (I), (±)-cis-1-(4-methoxyphenyl)-3-phenoxy-4-(isoquinolin-2-yl)azetidin-2-one (II), and (±)-cis-1-(4-methoxyphenyl)-3-phenoxy-4-(quinolin-2-yl)azetidin-2-one (III) to give the respective OsH2(P(i)Pr3)2(CC'N) (2-4) complexes, which add HBF4·OEt2 to yield [OsH2(P(i)Pr3)2(CC″N)]BF4 (5-7). These salts are the result of the addition of the proton of the acid to the dianionic CC'N-pincer ligand. The hydride ligands of these compounds undergo quantum mechanical exchange coupling, which has been experimentally quantified according to a two-dimensional harmonic oscillator model, where Jex is determined by the separation between the hydrides, their hard sphere radius, and a ν parameter describing the H-M-H vibrational wag mode allowing the movement along the H-H vector. The comparison of the results reveals that the phenomenon is particularly intense for 5-7. Furthermore, in these compounds, the separation between the hydrides is ∼0.1 Å shorter than in the respective neutral species 2-4, whereas the hydride hard sphere radius increases by ∼10%, and the ν value decreases by ∼20%.

Elongated Dihydrogen versus Compressed Dihydride in Osmium Complexes

“…[21] Chem. [15] The r bp value of 0.72 (3) ,w hich agrees well with those calculated for other d agostici nteractions, [16] is consistent with the fact of that the interaction persists in [D 2 ]dichloromethane at temperatures lower than 203 K. Thus, the INEPT 13 Cs pectrum at this temperature shows aC ÀH coupling constant of 108 Hz for ap henyl resonance at 100.6 ppm, which is about 40 Hz lower than the other 1 J C-H coupling constants, whereas the 1 HNMR spectrum contains an unusualu pfield phenyl resonance at 2.92 ppm. 2017, 23,1 526 -1530 www.chemeurj.org HÀCa gostic interactions.…”

“…The inclusion of a heteroatom between the pyridinic ring and one of its substituents could at first glance increase the steric requirement of the generated pincer in the plane containing the hydride ligands. As a consequence, the hydride ligands should approach, reducing the separation between them, according to that observed in previous cases . Thus, in the search for a shorter compressed dihydride we performed the reaction of 1 with 2‐phenoxy‐6‐phenylpyridine, which contains an oxygen atom between the pyridinic ring and one of the phenyl groups.…”

“…The structure (Figure 1) confirms the double CÀHb ond activation of the organic substrate with the corresponding formationo faC,N,C-pincer ligand.T he coordination geometry aroundt he osmium atom can be described as ad istorted pentagonal bipyramid with axial phosphines and the hydrides, separated by 1.46(4) ,l ying in the equatorialp lane alongw ith the pincer.T he compressed dihydride nature of the complex was confirmed by its DFT-optimized structure (B3LYP(GD3)// SDD/6-31G**), and the hydride resonance (dÀ8.05) in the 1 HNMR spectrum in [D 8 ]toluene. [13] Thus,i n the search for as horter compressed dihydride we performed the reaction of 1 with 2-phenoxy-6-phenylpyridine, which contains an oxygen atom between the pyridinic ring and one of the phenyl groups. As ac onsequence, the hydridel igands should approach, reducing the separation between them, according to that observedi np reviousc ases.…”

Recent Advances in Synthesis of Molecular Heteroleptic Osmium and Iridium Phosphorescent Emitters

“…Complex 27 is yellow emissive (540-571 nm) on photoexcitation in solid state at 298 K and in toluene solution at 298 and 77 K. The lifetimes are between 1.1 and 6.6 μs, whereas the emission quantum yield is 0.06 in the solid state. [35] Scheme 4. Preparation of complexes 16-20.…”

Assembly of a Dihydrideborate and Two Aryl Nitriles to Form a C,N,N′-Pincer Ligand Coordinated to Osmium

“…The pincer ligands coordinated to this element mainly involve neutral 10 or monoanionic 10f,11 moieties, which result from the simple coordination of tridentate molecules 10 or the coordination of bidentate groups along with the σ-bond activation of one of their substituents, 11 whereas osmium complexes bearing dianionic pincer ligands are very rare. Examples include C,C',N-donors, which are generated by coordination of a 2e-donor N atom and two σ-bond activations at the molecule skeleton, 12 or O,N,O-, 13 C,C',C-, 14 and C,N,C-donors, 15 which are formed as a consequence of the coordination of a 2e-donor atom and a σ-bond activation at two substituents of the molecular core. [13][14][15] This paper describes the discovery of a new class of formally dianionic pincer ligands coordinated to osmium, aryl-diimineborate (C,N,N´), which are furthermore generated on the metal coordination sphere by a novel procedure involving the coupling of a coordinated dihydrideborate anion with two aryl nitrile molecules and the activation of an ortho-CH bond of the aryl group of one of them.…”