Structural analysis of (5-methyl-[1,3,5]-dithiazinan-2-yl)phosphines and their oxides. N-Borane adducts as conformational probes

Add time:07/18/2019    Source:sciencedirect.com

(5-Methyl-[1,3,5]-dithiazinan-2-yl)diphenylphosphine (1) and its oxide (4), sulphide (5) and selenide (6), bis(5-methyl-[1,3,5]-dithiazinan-2-yl)phenylphosphine (2) and its sulphide (7) and selenide (8) and tris(5-methyl-[1,3,5]-dithiazinan-2-yl)phosphine (3) and its sulphide (9) and selenide (10), were synthesised and their structures studied. The new molecules are analogous to cyclohexanylphosphines, they are bulky with many lone pairs. Conformational analyses of 1, 4–6 were performed by variable temperature NMR spectroscopic experiments. 13C, 1H and 31P chemical shifts were used to assign the preferred conformation of phosphines studied. The chair conformers of 1 were observed at low temperature. Borane coordination to the nitrogen was used to anchor the heterocyclic rings in 1, 4–6 giving the syn and anti isomers. Slow transformation of N-BH3 adducts afforded [1,3,5,6]-dithiazaboracyclohexanes. X-Ray diffraction analysis of compounds 4–6, 8 and 10 are reported. Calculations were performed to evaluate the molecular structures, their electronic distribution and the free enthalpy of formation. Intramolecular interactions as hydrogen bonds, and short contacts between chalcogen and phosphorus and between chalcogen atoms were analysed by measuring their distances in the solid state and by observing their gradient of the reduced electronic density in the calculated structures.

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