Synthesis, Reactivity, and Catalytic Behavior of Iron/Zinc-Containing Species Involved in Oxidation of Hydrocarbons under Gif-Type Conditions

Abstract

The present study explores the nature and reactivity of iron-and zinc-containing species generated in hydrocarbon-oxidizing Gif IV -type solutions (Fe catalyst/Zn/O 2 in pyridine/acetic acid (10:1 v/v). The ultimate goal of this investigation is to unravel the role of metal sites in mediating dioxygen-dependent C-H activation, which in the case of Gif chemistry demonstrates an enhanced selectivity for the ketonization of secondary carbons. Reaction of [Fe 3 O(O 2 CCH 3 ) 6 (py) 3 ]‚py (1) with zinc powder in CH 3 CN/CH 3 COOH or CH 2 Cl 2 /CH 3 COOH affords the trinuclear compound [Zn 2 Fe II (O 2 CCH 3 ) 6 (py) 2 ] (2). Single-crystal X-ray analysis confirms that one monodentate and two bidentate acetate groups bridge adjacent pairs of metals with the iron atom occupying a centrosymmetric position. The analogous reduction of 1 in py/CH 3 COOH (10:1, 5:1, 2:1 v/v) yields [Fe II (O 2 CCH 3 ) 2 (py) 4 ] (3), [Fe II 2 (O 2 CCH 3 ) 4 (py) 3 ] n (4), and [Zn(O 2 CCH 3 ) 2 (py) 2 ] (5) depending on the isolation procedure employed. Compound 3 possesses a distorted octahedral geometry, featuring a C 2 axis bisecting the equatorial, pyridine-occupied plane, whereas the two acetate groups reside along the perpendicular axis. Compound 4 is a one-dimensional solid constructed by asymmetric diferrous units. Two bidentate and one monodentate acetate groups bridge the two iron sites, with the monodentate bridge also acting as a chelator to one ferrous center. The two iron centers exhibit weak antiferromagnetic coupling. Compounds 3 and 4 are also accessible from the reduction of 1 with iron powder or treatment with H 2 /Pd. Solutions of 3 and 4 in pyridine or py/CH 3 COOH react with pure dioxygen or air to eventually regenerate 1 in a concentrationdependent manner. Oxidation of 2 in py/CH 3 COOH with pure dioxygen or air yields [Fe 2.22(2) Zn 0.78(2) O(O 2 CCH 3 ) 6 -(py) 3 ]‚py (1′) and [Zn 2 (O 2 CCH 3 ) 4 (py) 2 ] (6). Compound 1′ is isostructural to 1, exhibiting rhombohedral symmetry at 223 K. The filtrate of the reduction of 1 with zinc in neat pyridine, when exposed to dioxygen, affords dichroic red-green crystals of monoclinic [Fe 2 ZnO(O 2 CCH 3 ) 6 (py) 3 ]‚py (1′′). Species 1′′ yields products identical with those provided by 1 under reducing conditions. Compounds 2-6 are related by pyridine-dependent equilibria, as demonstrated by mutual interconversions and electronic absorption data in pyridine and py/CH 3 COOH solutions. In nonpyridine solutions, Zn-containing species 5 and 6 rearrange to the crystallographically characterized species [Zn-(O 2 CCH 3 ) 2 (py)] n (7) and [Zn 3 (O 2 CCH 3 ) 6 (py) 2 ] (8). Compound 7 is a one-dimensional solid featuring a chain of Zn sites linked by a bidentate acetate group while additionally coordinated by a chelating acetate. Compound 8 is isostructural to 2. Further perturbations of the described structures are apparent in ionic iron-containing species, such as the pseudo-seven-coordinate iron in [Ph 3 PdNdPPh 3 ][Fe II (O 2 CCH 3 ) 3 (py)] (9), which is obtained from the react...

Crystal and Molecular Structure of Bis(1-Vinylimidazole)diacetatozinc

“…Three monodentate acetate groups (Ac 1 , Ac 3 , Ac 4 ) coordinate with the Zn atom via O 1 , O 5 , and O 7 atoms, with virtually equal bond lengths and bond angles (Table 2). The Zn3O bonds in these groups (mean length 1.957 + 0.001 A) are typical of tetrahedral zinc complexes and close to those in the structures of bis(imidazole)diacetatozinc (II) (1.96531.991 A)[13] and bis(pyridine)diacetatozinc (III) (1.94131.945 A)[14]. The Zn 1 3O 3 bond with ace-…”

3,5-Lutidine coordinated zinc(II) aryl carboxylate complexes: Precursors for zinc(II) oxide

“…Complex 1 crystallized as a monohydrate and in this complex the zinc atom surrounded by two oxygen atoms of the monodentate acetate and nitrogen atoms of two 3,5-lutidine and thus attains a tetrahedral geometry. Zn(OAc) 2 (pyridine) 2 was shown to crystallize in triclinic and tetragonal space groups [47]. ascribed to higher basicity of 3,5-lutidine (pK a : 6.15) in the former compared with pyridine (pK a : 5.23) [46] in Zn(OAc) 2 (pyridine) 2 and the involvement of C@O oxygen in 1 in intermolecular O-HÁÁÁO/C-HÁÁÁO hydrogen bonding in the crystal lattice.…”

Syntheses and photoluminescent properties of four zinc coordination polymers based on 1,4-bis[2-(4-pyridyl)ethenyl]-2,3,5,6-tetramethylbenzene and aliphatic dicarboxylates

“…1a, each Zn atom exhibits a tetrahedral coordination environment (T-4) formed by three carboxylate oxygen atoms from three different l 3 -g 1 :g 0 :g 1 :g 1 -AZA ligands and one nitrogen atom from the l 2 -1,4-bpetmb ligand. The Zn-N and mean Zn-O bond lengths (2.0411(16) Å vs. 1.9608(16) Å) are in-between those of the corresponding ones in [Zn 3 (CH 3 COO) 6 (py) 2 ] (2.017(3) Å vs. 1.949(3) Å) and [Zn(CH 3 COO) 2 (py)] n (2.055(3) Å vs. 2.000(3) Å)[15]. It is noted that the conformations of flexible ligands are critical for determining the structures of coordination polymers[16].…”