Novel 4-(diphenylphosphoryl)-1-phenylbutane-1,3-dione was synthesized by the reaction of diketone enamine with diphenylchloro phosphine followed by oxidation and hydrolysis of the enamine phosphine formed. Tautomeric transformation of the diketone moiety of phosphine oxide was investigated by ¹H NMR. Three out of five possible tautomers were observed in the 4-(diphenylphosphoryl)-1-phenylbutane-1,3-dione solution. The major tautomer was the form with a diketone fragment.

Valence tautomerism (VT) may occur if a molecule contains two chemically different redox-active units, which differ only slightly in their intrinsic redox potential. Herein, we present three new half-sandwich complexes [(η6arene)Cr(CO)2L]+ with a triarylmethylium substituent appended to the -coordinated arene and different coligands L (L = CO, P(OPh)3, PPh3, 1+  3+) at the chromium atom. Ligand substitution purposefully lowers the half-wave potential for chromium oxidation and thereby the redox potential difference towards tritylium reduction. For the PPh3-substituted complex 3+, cyclic voltammetry measurements indicate that chromium oxidation and tritylium reduction occur at (almost) the same potential. This renders the diamagnetic Cr(0)C6H4CAr2+ form 3+ and its paramagnetic diradical Cr(I)+•C6H4CAr2• valence tautomer 3+•• energetically nearly degenerate. Temperature-dependent IR spectroscopy shows indeed two pairs of carbonyl bands assignable to a Cr(0) and a Cr(I) species, coexisting in a T-dependent equilibrium with almost equal quantities for both at 70 °C. The diradical form with one unpaired spin at the trityl unit engages in a monomer ⇌ dimer equilibrium, which was investigated by means of quantitative EPR spectroscopy. The diradical species 1+••  3+•• were found to be highly reactive, leading to several identified reaction products, which presumably result from hydrogen atom abstraction by the trityl C atom, e.g. from the solvent.

With the aim to produce new heterocycle molecules, the previously reported 2-(aminomethyl)-2-(4-chlorophenyl)-2,3-dihydroquinazolin-4(1H)-one was converted efficiently by reacting with N,N’-dithiocarbonyldiimidazole (DTCI), to produce the substituted imidazolidine-2-thione moiety inserted in a three fused ring scaffold of the title compound. The molecular composition was confirmed by a high-resolution MS experiment, and its structure was elucidated by 1H, 13CNMR, and IR analyses. The thioacetamide form of the product was supported by density functional theory (DFT)-NMR analysis where 13C chemical shifts of thioacetamide form and of its iminothiol tautomer were calculated in chloroform at the BP86 /Jgauss-TZP2 level of theory. The very good linear correlation between 13C chemical shifts by experiment and by calculation for the NHC=S form confirmed the structure.