Synthesis of Bicyclic P,S-Heterocycles via the Addition of Thioketones to a Phosphorus-Centered Open-Shell Singlet Biradical

Abstract

Formal addition reactions between the open-shell singlet biradical [P­(μ-NTer)]2 (1Ter) and xanthione, thioxanthione, as well as ferrocenyl naphthyl thioketone were studied in detail. Reactions were performed at room temperature and led to the formation of strained [2.1.1]-cage P,S-heterocycles (3). All addition products were isolated and fully characterized by spectroscopic methods. Furthermore, reversible cleavage of the xanthenthione-biradical addition product into the parent compounds (biradical and thioketone) could be demonstrated by 31P­{1H} NMR spectroscopy. The thermodynamic stability of all cyclization products with respect to the elimination of thioketone was studied by quantum-chemical computations including solvent effects. Regarding the dissociation of addition products 3 into the fragment molecules 1Ter and ketone/thioketone, calculations prove that a significantly larger distortion energy in ketones compared with thioketones causes lower thermodynamic stability of the ketone adducts.

Metal–ligand bonding in tricarbonyliron(0) complexes bearing thiochalcone ligands

“…The thiochalcone ligands in these complexes are functionalized with hetaryl and ferrocenyl groups, which originates from our ongoing interest in aromatic and cycloaliphatic thioketones. [15][16][17][18][19][20][21][22] For comparison, the present study additionally includes model complex 7 (Chart 1) in order to assess the effect of aromatic groups Ar 1 and Ar 2 for 1-6. In the series of complexes 1-7, the metal-ligand bonds cover both the iron-thiadiene interaction and three iron-carbonyl bonds.…”

Concerted addition of aldehydes to the singlet biradical [P(μ-NTer)]2

“…∑ r cov (P–C) = 1.86 Å, d (P–C) = 1.83 Å), an effect that was also observed, for example, in adducts of 1 with acetone (1.92(1) Å) 34 or (thio)xanthione (1.975(2), 1.968(3) Å). 46 This is likely due to Pauli repulsion between the substituents at the aldehyde moiety and the bulky Ter groups, as well as the general strained nature of the bicyclic compounds. The C–O distances of the former carbonyl groups (1.450(2)–1.455(5) Å) are, as expected, in the range of typical C–O single bonds ( cf.…”

“…This is in line with the fact that we did not observe a reverse reaction even at elevated temperatures, contrary to the addition of, e.g., thioketones or dimethylbutadiene. 40,46 The symmetry of the frontier orbitals (see Fig. 2 for a model system) indicated a concerted mechanism for the addition of aldehydes to 1.…”

“…47) or d(N-P) = 1.74 Å when consider-Scheme 1 Reactivity of the singlet biradical [P(μ-NTer)] 2 (1, R = Ter; R' = alkyl/aryl). 17,[33][34][35]40,[42][43][44][45][46] For further examples of addition reactions, also including different hetero-cyclobutanediyls, see ref.…”

“…Consequently, biradical 1 was used in a large variety of activation reactions, including a number of unsaturated (e.g. alkynes, alkenes, ketones) 17,34,40,[42][43][44][45][46] and saturated compounds (e.g. H 2 , chalcogens, haloalkanes) 17,[33][34][35] as substrates (Scheme 1).…”