The Effect of Selenium-Based Ligands on Tungsten Acetylene Complexes

Bioinspired tungsten acetylene complexes containing pyridine-2-selenolato (PySe) or 6-methyl-pyridine-2-selenolato (6-MePySe) ligands were synthesized. 77Se NMR spectroscopy allowed for an assessment of the resonance structures in the pyridine-2-selenolato ligands and the rationalization of chemoselectivity observed in regard to 1,2 migratory insertion of HC≡CH. [W(CO)(C2H2)(CHCH-PySe)(PySe)] is formed exclusively via insertion of HC≡CH into the W-N bond, while the use of bulkier 6-MePySe allows for the isolation of [W(CO)(C2H2)(6-MePySe)2], which only partially reacts with excess HC≡CH to give [W(CO)(C2H2)(CHCH-6-MePySe)(6-MePySe)]. Oxidation of [W(CO)(C2H2)(6-MePySe)2] with pyridine-N-oxide gave the tungsten(IV) complex [WO(C2H2)(6-MePySe)2]. Complexes [W(CO)(C2H2)(6-MePySe)2] and [WO(C2H2)(6-MePySe)2] react with trimethyl phosphine to carbyne complex [W(CO)(CCH2PMe3)(PMe3)2(6-MePySe)]Cl and alkylidene complex [WO(CHCHPMe3)(PMe3)2(6-MePySe)]Cl, respectively. The addition of substituted alkynes to [W(CO)3(PySe)2] via thermal decarbonylation gave complexes [W(CO)(MeC≡CMe)(PySe)2] and [W(CO)(HC≡Ct-Bu)(PySe)2], respectively. The here presented complexes are relevant for the modeling of the active site of acetylene hydratase from Pelobacter acetylenicus, in which a tungsten atom is enclosed in a sulfur-rich coordination sphere. A recently published theoretical study concluded that the exchange of sulfur for selenium would increase the activity of the enzyme. Our findings contrast this claim as comparative analysis concludes negligible structural and electronic differences between the selenium-based and previously published sulfur-based complexes.

Diorganyl diselenides: a powerful tool for the construction of selenium containing scaffolds

Organoselenium compounds find versatile applications in organic synthesis, materials synthesis, and ligand chemistry. Organoselenium heterocycles are widely studied agents with diverse applications in various biological processes. This review highlights the recent progress in the synthesis of selenium heterocycles using diorganyl diselenides with keen attention on green synthetic approaches, scopes, C-H selanylation, the mechanisms of different reactions and insights into the formation of metal complexes. The C-H selanylation using diorganyl diselenides with different catalysts, bases, transition metals, iodine salts, NIS, hypervalent iodine, and other reagents is summarised. Finally, the diverse binding modes of bis(2/4-pyridyl)diselenide with different metal complexes are also summarised.

Anion-Recognition Studies of a Rhenium(I) 4-Mercaptopyridine Compound and Its Ligand-Coupling Products

The reaction of Re(CO)₅Cl with 4-mercaptopyridine (4-PySH) led to the formation of [Re(CO)₃(4-HPyS)₃]Cl (1), showing three hydrogen-bonding donors of 4-PySH ligands as well as a characteristic ligand-to-metal charge-transfer absorption at ca. 380 nm. In this regard, a variety of anions, i.e., CN^-, OAc^-, F^-, Cl^-, Br^-, I^-, PF₆^-, NO₃^-, ClO₄^-, and H₂PO₄^-, were examined to study anion-recognition studies through hydrogen-bonding functionalities. Upon the addition of CN^- to a methanolic solution of complex 1, a remarkable spectral change with an isosbestic point at ca. 314 nm in the absorption spectra was observed, with a binding constant (K_b) calculated to be 24770 M^-1. Moreover, the OAc^- anion also shows a similar trend, but a mild spectral change, with K_b calculated to be 2170 M^-1. Unlike those of CN^- and OAc^-, the addition of F^-, Cl^-, Br^-, and I^- anions causes a less pronounced spectral change with an isosbestic point at ca. 350 nm and K_b calculated to be 2863-750 M^-1. However, almost no spectral change can be observed for other anions (i.e., PF₆^-, NO₃^-, H₂PO₄^-, and ClO₄^-). Interestingly, the molecular loops of [Re(CO)₃Cl(Py₂S₂)]₂ (2; Py₂S₂ = 4,4'-dipyridyl disulfide) and [Re(CO)₃Cl(Py₂S)_0.35(Py₂S₂)_0.65]₂ (3; Py₂S = 4,4'-dipyridyl sulfide) can be isolated and structurally characterized by X-ray diffraction, where those crystals were grown from diethyl ether diffusion into a methanolic solution of complex 1 with [Bu₄N]CN and [Bu₄N]NO₃, respectively. It is noted that such unusual ligand-coupling reactions toward the homoligand and hybrid-ligand loops of complexes 2 and 3 can be achieved at room temperature in this study.

Synthesis of mono/dinuclear rhenium(i) tricarbonyl substituted with 4-mercaptopyridine related ligands: spectral and theoretical evidence of thiolate/thione interconversion

κ¹-S complexes show solvent-mediated tautomerism. The S–S bridge cleavage in κ¹-N derivatives is attributed to the presence of a proton source.