A reversible formation of hemiacetals represents a useful tool in covalent dynamic chemistry. Heterocyclic hemiacetals can be stabilized effectively via either protonation or metal cation coordination. The resulting hemiacetal systems are highly dynamic, show fast response, and display component selection.

The reaction of 1'-(diphenylphosphanoyl)ferrocenecarbonyl chloride, generated in situ by the reaction of 1'-(diphenylphosphanoyl)ferrocenecarboxylic acid and oxalyl chloride, with chiral aminoalcohols gave amidoalcohols [Fe(η5-C5H4P(O)Ph2)(η5-C5H4C(O)NHCHRCH2OH)] 13, (R = i-Pr, (S); R = i-Pr, (R); R = t-Bu, (S) and R = Ph, (R). The amidoalcohols 13 were converted to 2-[1'-(diphenylphosphanoyl)ferrocen-1-yl]-4,5-dihydrooxazoles 14 by ring-closing reaction with a tosyl chloride-triethylamine mixture. Subsequent reduction of 14 with trichlorosilane in the presence of triethylamine afforded the corresponding 2-[1'-(diphenylphosphanyl)ferrocenyl]-4,5-dihydrooxazoles 10. Compounds 13d, 14d and 10d were subjected to a detailed 1H, 13C and 31P NMR analyses. CD spectra of all 10 were measured. trans-Dichlorobis{(S)-2-[1'-(diphenylphosphanyl)ferrocenyl]-4-isopropyl-4-5-dihydrooxazole-κP}palladium(II) (15) was synthesised and its solid-state structure was determined by single-crystal X-ray diffraction.

Hemiacetals of pyridine-2-carbaldehyde derivatives and volatile alcohols can be stabilized in organic solution in the presence of protons or different metal cations. Despite the inherent instability of hemiacetals in H(2) O, stabilizing them with zinc(II) triflate and adding them to a cationic surfactant formulation resulted in the slow release of the alcohol from cotton surfaces being treated with the hemiacetal complex. Stabilized hemiacetals might thus be suitable delivery systems of bioactive volatiles by rapid hydrolysis in H(2) O-based media.

A C2-symmetric enantiopure 4,5-bis(pinene)-2,2'-bipyridine ligand (-)-L was used to investigate the diastereoselectivity in the formation of [ML3]2+ coordination species (M = Fe(II), Ru(II), Os(II), Zn(II), Cd(II), Cu(II), Ni(II)), and [ML2Cl2] (M = Ru(II), Os(II)). The X-ray structures of the [ML3]2+ complexes were determined for Delta-[FeL3](PF6)2, Delta-[RuL3](PF6)2, Lambda-[RuL3](PF6)2, Delta-[OsL3](PF6)2, and Lambda-[OsL3](TfO)2. All of these compounds were also characterized by NMR, CD and UV/VIS absorption spectroscopy. The [FeL3]2+ diastereoisomers were studied in equilibrated solutions at various temperatures and in several solvents. The [RuL3]2+ complexes, which are thermally stable up to 200 degrees C, were photochemically equilibrated.

Preparation of starting amidesGeneral. Melting points were determined on a Kofler block and are uncorrected. NMR spectra were measured on either a Varian Gemini 300 or Bruker DRX 500 Avance spectrometer at 25 °C. Unambiguous assignment of NMR signals is based on 13 C{ 1 H}, 13 C APT, COSY and 13 C HMBC spectra. Infrared spectra were recorded on a Nicolet 740 instrument. Elemental analyses were carried out with a Perkin-Elmer 2400 instrument. 2 M i-PrMgCl in THF was purchased from commercial suppliers and was used without purification.