Formation, reactivity and redox properties of carbon- and sulfur-bridged diiron complexes derived from dibenzothienyl Schiff bases: effect of N,N- and N,P-chelating moieties

Abstract

Dibenzothienyl Schiff bases, DBT-NN and DBT-NP, were derived from condensation of 4-formyldibenzothiophene with N,N-dimethylethylenediamine and 2-(diphenylphosphino)ethylamine, respectively. A photochemical reaction of [Fe(CO)5] with DBT-NN produced diiron complexes, [Fe2(μ-DBT-NN)(CO)6] (1) and [{Fe(μ-BPT-NN-κ(3)S,C,N)(CO)2}Fe(CO)3] (2). Complex 1 has π coordination of a Schiff base C=N bond and an N,N-chelate, while 2 has an S,C,N-tridentate ligand having an uncoordinated dimethylamino group. The corresponding reaction with DBT-NP produced a diiron complex of an S,C,N,P-tetradentate ligand, [{Fe(μ-BPT-NP-κ(4)S,C,N,P)(CO)}Fe(CO)3] (3), which has an N,P-chelate, via the DBT-NP complex [Fe(DBT-NP-κP)(CO)4] (4). Reactions of 2 and 3 with one equivalent of PMe2Ph gave the monosubstituted complexes [{Fe(μ-BPT-NN-κ(3)S,C,N)(CO)2}Fe(CO)2(PMe2Ph)] (5) and [{Fe(μ-BPT-NP-κ(4)S,C,N,P)(CO)}Fe(CO)2(PMe2Ph)] (6), respectively. The corresponding reactions with an excess of PMe2Ph produced mononuclear complexes, trans-[Fe(BPT-NN-κ(3)S,C,N)(CO)(PMe2Ph)2] (7) and [Fe(BPT-NP-κ(4)S,C,N,P)(CO)(PMe2Ph)] (8), respectively. Complexes 1-3 and 5-8 were structurally characterized by X-ray crystallography. Complexes 2, 3, 5 and 6 have similar dinuclear structures with different carbonyl/phosphine substitution patterns. Cyclic voltammograms of 2, 3 and 5 showed two one-electron reduction processes, and more negative potentials were observed for 6. The shift of the redox potentials are rationalized by the electron-donating character of the phosphine ligands, which suggests that the reduction occurs at the asymmetrically bridged diiron core.

CO Release from N,C,S-Pincer Iron(III) Carbonyl Complexes Induced by Visible-to-NIR Light Irradiation: Mechanistic Insight into Effects of Axial Phosphorus Ligands

“…Complexes 2 and 3 were synthesized according to a literature procedure. The dinuclear iron complex 6 ([{Fe­(μ-PyBPT-κ 3 N,C,S )­(CO) 2 }­Fe­(CO) 3 ]) was used as a precursor for 2 and 3 . − A 1.0 M toluene solution of trimethylphosphine and triethylphosphite were purchased from Aldrich and Tokyo Chemical Industry Co., Ltd., respectively, and were used without further purification. Solvents were purchased from Kanto Chemical Co., Inc. Tris­( p -tolyl)­aminium hexafluorophosphate was prepared according to a literature procedure .…”

“…[18][19][20] We recently reported the synthesis and properties of a novel iron complex with an N,C,Stridentate ligand, trans- [Fe(PyBPT) ), where PyBPT is a doubly deprotonated form of 3'-(2''-pyridyl)-1,1'-biphenyl-2-thiol formed via the C-S bond cleavage of the dibenzothiophene derivative. [48][49][50][51] The N,C,S-pincer iron(III) carbonyl complex exhibited unusual stability in solution under ambient conditions in the dark, while the CO ligand readily underwent substitution reaction with the coordinative solvent in response to the short wavelength region of visible light. 52 A theoretical study indicated that SOMO of the iron(III) carbonyl complex mainly consisted of the dπ orbital of the central iron and pπ orbital of the sulfur atom.…”

Di- and Mononuclear Iron Complexes of N,C,S-Tridentate Ligands Containing an Aminopyridyl Group: Effect of the Pendant Amine Site on Catalytic Properties for Proton Reduction

“…This is consistent with the fact that the substitution of phosphines for CO in the thiolate-bridged diiron carbonyl complexes leads to the large shift of the redox potentials. 16,31,32 Thus, the introduction of the amino group into the pyridine ring is not effective in tuning the redox potentials for the diiron complexes [{Fe(μ-Lκ 3 N,C,S)(CO) 2 }Fe(CO) 3 ]. In contrast, the redox potentials for the Fe III /Fe II couple of the mononuclear iron(II) complexes trans-[Fe(L-κ 3 N,C,S)(CO)(PMe 2 Ph) 2 ] are dependent on the position of the amino group in the pyridine ring, which is described by electronic and steric effects of the amino group.…”

Synthesis, characterization and magnetic study of two new octahedral iron(III) complexes with pendant zwitterionic Schiff bases

“…Several iron(III) complexes of various geometry have been prepared using different chelating ligands [11][12][13], of which Schiff bases are special choices for the easy routes of their synthesis, the wide range of their stability and their very good complexing ability [14][15][16][17][18][19].…”