Alen Hadzovic

The title compound, C ₁₁ H ₁₃ NO ₂ , crystallizes in the monoclinic space group P 2 ₁ / c with four molecular units per unit cell and Z ′ = 1. A strong intramolecular N—H...O interaction results in a six-membered hydrogen-bridged ring. An intermolecular O—H...O hydrogen bond leads to a helix formation. The Hirshfeld surface analysis of intermolecular interactions is presented.

NMR spectroscopy is a powerful tool for monitoring molecular interactions and is widely used to characterize supramolecular systems at the atomic level. NMR is limited for sensing purposes, however, due to low sensitivity. Dynamic processes such as conformational changes or binding events can induce drastic effects on NMR spectra in response to variations in chemical exchange (CE) rate, which can lead to new strategies in the design of supramolecular sensors through the control and monitoring of CE rate. Here, we present an indirect NMR anion sensing technique in which increased CE rate, due to anion‐induced conformational flexibility of a relatively rigid structure of a novel sensor, allows ultrasensitive anion detection as low as 120 nM.

Six complexes of the type trans-[Fe(NCMe)₂(P−N−N−P)]X₂ (X = BF₄⁻, B{Ar^f}₄⁻) (Ar^f = 3,5-(CF₃)₂C₆H₃) containing diiminodiphosphine ligands and the complexes trans-[Fe(NCMe)₂(P−NH−NH−P)][BF₄]₂ with a diaminodiphosphine ligand were obtained by the reaction of Fe(II) salts with achiral and chiral P−N−N−P or P−NH−NH−P ligands, respectively, in acetonitrile at ambient temperature. The P−N−N−P ligands are derived from reaction of ortho-diphenylphosphinobenzaldehyde with the diamines 1,2-ethylenediamine, 1,3-propylenediamine, (S,S)-1,2-disopropyl-1,2-diaminoethane, and (R,R)-1,2-diphenyl-1,2-diaminoethane. Some complexes could also be obtained for the first time in a one-pot template synthesis under mild reaction conditions. Single crystal X-ray diffraction studies of the complexes revealed a trans distorted octahedral structure around the iron. The iPr or Ph substituents on the diamine were found to be axial in the five-membered Fe−N−CHR−CHR−N− ring of the chiral P−N−N−P ligands. A steric clash between the imine hydrogen and the substituent probably determines this stereochemistry. The diaminodiphosphine complex has longer Fe−N and Fe−P bonds than the analogous diiminodiphosphine complex. The new iron compounds were used as precatalysts for the hydrogenation of acetophenone. The complexes without axial substituents on the diamine had moderate catalytic activity while that with axial Ph substituents had low activity but fair (61%) enantioselectivity for the asymmetric hydrogenation of acetophenone. The fact that the diaminodiphosphine complex has a slightly higher activity than the corresponding diiminodiphosphine complex suggests that hydrogenation of the imine groups in the P−N−N−P ligand may be important for catalyst activation. Evidence is provided, including the first density-functional theory calculations on iron-catalyzed outer-sphere ketone hydrogenation, that the mechanism is similar to that of ruthenium analogues.

The reaction between (Ar(2)nacnac)H (Ar = C6H5, ligand a; 2,6-(Pr-i)(2)C6H3, ligand b) and [Pd(OAc)(2)] produces red complexes [Pd(Ar(2)nacnac)(OAc)] (1a: Ar = C6H5; 1b: Ar = 2,6-(Pr-i)(2)C6H3). Complex la has a dimeric structure in the solid state with two bridging acetates, while a monomer-dimer equilibrium establishes in solution. Complex I b is monomeric in both the solid state and solution. Both are air- and moisture-stable compounds, unlike [Pd(Ph(2)nacnac)(2)] (2), which easily hydrolyzes in the presence of moisture to give [Pd(Phnacac)(2)] (3) (Phnacac = {CH3C(NPh)CHC(O)CH3}(-)). Compound 1a reacts with metal acetates to produce heterotrimetallic complexes of a general formula [Pd(Ph(2)nacnac)](2)-mu-[M(OAc)(4)] (4, M = Cu; 5, M = Zn). Treating 1a with KOH in THF, or alternatively [Pd(Ph(2)nacnac)Cl](2) with (KOBu)-Bu-i in wet THF, produces [Pd(Ph(2)nacnac)(OH)](2) (6).

We report the formation of an unexpected trinuclear palladium β-diiminate complex from the decomposition of [Pd(Ph₂nacnac)(Cl)(4-H₂NC₆H₄-^tBu)] (nacnac = β-diiminate derived from acetylacetone), the proposed reaction pathway, and the synthesis of the first dinuclear palladium complex with an amido–chloro double-bridge.