Aluminum complexes of the redox-active [ONO] pincer ligand

Abstract

A series of aluminum complexes containing the tridentate, redox-active ligand bis(3,5-di-tert-butyl-2-phenol)amine ([ONO]H(3)) in three different oxidation states were synthesized. The aluminum halide salts AlCl(3) and AlBr(3) were reacted with the doubly deprotonated form of the ligand to afford five-coordinate [ONHO(cat)]AlX(solv) complexes (1a, X = Cl, solv = OEt(2); 1b, X = Br, solv = THF), each having a trigonal bipyramidal coordination geometry at the aluminum and containing the [ONHO(cat)](2-) ligand with a protonated, sp(3)-hybridized nitrogen donor. The [ONO] ligand platform may also be added to aluminum through the use of the oxidized ligand salt [ONO(q)]K, which was reacted with AlCl(3) in the presence of either diphenylacetylacetonate (acacPh(2)(-)) or 8-oxyquinoline (quinO(-)) to afford [ONO(q)]Al(acacPh(2))Cl (2) or [ONO(q)]Al(quinO)Cl (3), respectively, with well-defined [ONO(q)](-) ligands. Quinonate complexes 2 and 3 were reduced by one electron to afford the corresponding complexes K{[ONO(sq)]Al(acacPh(2))(py)} (4) and K{[ONO(sq)]Al(quinO)(py)} (5), respectively, containing well-defined [ONO(sq)](2-) ligands. The addition of tetrachloro-1,2-quinone to 1a in the presence of pyridine resulted in the expulsion of HCl and the formation of an aluminum complex with two different redox active ligands, [ONO]Al(o-O(2)C(6)Cl(4))(py) (6). Similar results were obtained when 1a was reacted with 9,10-phenanthrenequinone to afford [ONO]Al(o-O(2)C(14)H(8))(py) (7) or with pyrene-4,5-dione to afford [ONO]Al(o-O(2)C(16)H(8))(py) (8). Structural, spectroscopic and preliminary magnetic measurements on 6-8 suggest ligand non-innocent redox behavior in these complexes.

Structural and spectroscopic investigations of nine-coordinate redox active lanthanide complexes with a pincer O,N,O ligand

“…These modifications are accompanied by the appearance of a sharp band at 410 nm, which is reminiscent of phenoxyl radical species. 53 It is worth noting that similar spectra were obtained for EuL 3 and the other anions. Furthermore a similar spectral evolution was reported for the one-electron reduction of the related bis(aminophenolate)zinc complex.…”

“…They are assigned to the successive oxidations of the aminophenolate moieties to iminosemiquinone radicals. [45][46][47][48][49][51][52][53][54] At 298 K the first oxidation process is reversible for all four complexes, attesting that the stability of the monocation is noteworthy.…”

Near-IR absorbing donor–acceptor ligand-to-ligand charge-transfer complexes of nickel(ii)

“… 9 In addition to the low-energy LL'CT transition, complex 3 with the phenanthrenediolate donor ligand shows intense absorption bands in the 300–600 nm region that are characteristic of phenanthrene π–π* transitions. 59 …”

Carbonylative Suzuki coupling reactions catalyzed by ONO pincer–type Pd(II) complexes using chloroform as a carbon monoxide surrogate

“…Therefore, it was thought worthwhile to synthesize pincer complexes and use them as catalysts. Complexes having different pincer skeleton such as CCC, NNN, CNC, NCN, PNP, SNS, ONO, and SCS have been used in catalysis and materials science . In particular, the ONO pincer–type palladium complexes have proved to be very effective catalysts for Suzuki–Miyaura coupling, C‐2 arylation of quinoline scaffolds, Domino reaction of benzoyl chloride with arylboronic acids, and synthesis of tetrazoles, etc.…”

“…Complexes having different pincer skeleton such as CCC, NNN, CNC, NCN, PNP, SNS, ONO, and SCS have been used in catalysis and materials science. [41][42][43][44][45][46][47][48] In particular, the ONO pincertype palladium complexes have proved to be very effective catalysts for Suzuki-Miyaura coupling, [49] C-2 arylation of quinoline scaffolds, [50] Domino reaction of benzoyl chloride with arylboronic acids, [51] and synthesis of tetrazoles, [52] etc. In recent years, hydrazonebased ONO pincer complexes have also been reported to exhibit interesting biological and catalytic properties.…”