N-Substituted Iminopyridine Arene-Ruthenium Complexes for the Regioselective Catalytic Hydration of Terminal Alkynes

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF3: the case of alkyne hydration. Chemistry vs electrochemistry

In order to replace the expensive metal/ligand catalysts and classic toxic and volatile solvents, commonly used for the hydration of alkynes, the hydration reaction of alkynes was studied in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) adding boron trifluoride diethyl etherate (BF3·Et2O) as catalyst. Different ionic liquids were used, varying the cation or the anion, in order to identify the best one, in terms of both efficiency and reduced costs. The developed method was efficaciously applied to different alkynes, achieving the desired hydration products with good yields. The results obtained using a conventional approach (i.e., adding BF3·Et2O) were compared with those achieved using BF3 electrogenerated in BMIm-BF4, demonstrating the possibility of obtaining the products of alkyne hydration with analogous or improved yields, using less hazardous precursors to generate the reactive species in situ. In particular, for terminal arylalkynes, the electrochemical route proved to be advantageous, yielding preferentially the hydration products vs the aldol condensation products. Importantly, the ability to recycle the ionic liquid in subsequent reactions was successfully demonstrated.

Synthesis, Characterization and Catalytic Property Studies for Isoprene Polymerization of Iron Complexes Bearing Unionized Pyridine-Oxime Ligands

Iron complexes of the types [Fe(HL)2Cl2] (Fe1: HL1 = pyridine-2-aldoxime; Fe2: HL2 = 6-methylpyridine-2-aldoxime; Fe3: HL3 = phenyl-2-pyridylketoxime; Fe4: HL4 = picolinaldehyde O-methyl oxime) were prepared and characterized by elemental analysis and IR spectroscopy. The crystal structure of Fe2, determined by single-crystal X-ray diffraction, featured a distorted octahedral coordination of the iron center binding with two ligands of HL2. The X-ray structure and infrared spectral data indicated that pyridine-oxime ligands act as unionized bidentate ligand by coordinating with Npyridine and Noxime. The catalytic performance for isoprene polymerization, catalyzed by these pyridine-oxime-ligated iron complexes, was examined. For a binary catalytic system combined with MAO, complexes Fe1, Fe3 and Fe4 were found to be highly active (up to 6.5 × 106 g/mol·h) in cis-1,4-alt-3,4 enchained polymerization, with average molecular weights in the range of 60–653 kg/mol and narrow PDI values of 1.7–3.5, even with very low amounts of MAO (Al/Fe = 5). Upon activation with [Ph3C][B(C6F5)4]/AlR3 for the ternary catalytic system, theses complexes showed extremely high activities, as well about 98% yield after 2 min, to afford cis-1,4-alt-3,4-polyisoprene with a molecular weight of 140–420 kg/mol.

Half-Sandwich Iridium Complexes Bearing a Diprotic Glyoxime Ligand: Structural Diversity Induced by Reversible Deprotonation

Synthesis and deprotonation reactions of half-sandwich iridium complexes bearing a vicinal dioxime ligand were studied. Treatment of [{Cp*IrCl(μ-Cl)}₂ ] (Cp*=η⁵ -C₅ Me₅ ) with dimethylglyoxime (LH₂ ) at an Ir:LH₂ ratio of 1:1 afforded the cationic dioxime iridium complex [Cp*IrCl(LH₂ )]Cl (1). The chlorido complex 1 undergoes stepwise and reversible deprotonation with potassium carbonate to give the oxime-oximato complex [Cp*IrCl(LH)] (2) and the anionic dioximato(2-) complex K[Cp*IrCl(L)] (3) sequentially. Meanwhile, twofold deprotonation of the sulfato complex [Cp*Ir(SO₄ )(LH₂ )] (4) resulted in the formation of the oximato-bridged dinuclear complex [{Cp*Ir(μ-L)}₂ ] (5). X-ray analyses disclosed their supramolecular structures with one-dimensional infinite chain (1 and 2), hexagonal open channels (3), and a tetrameric rhomboid (4) featuring multiple intermolecular hydrogen bonds and electrostatic interactions.