Isoselenocyanates with Sterically Encumbered Substituents─Synthesis, Structures, and Spectroscopic Properties

A series of isoselenocyanates, SeCNR, spanning over a variety of organic residues in terms of steric encumbrance and electronic effects, was synthesized by reactions of corresponding isocyanides with elemental selenium. The residues range from tertiary butyl (^tBu), phenyl (Ph), 2,4,6-trimethylphenyl (Mesityl), 2,6-diisopropylphenyl (^i-Prop2Ph), 2,6-di(2,4,6-trimethylphenyl)phenyl (Ar^Mes2), 2,6-di(2,6-diisopropylphenyl)phenyl (Ar^Dipp2), 2,6-di(2,4,6-triisopropylphenyl)phenyl (Ar^Tripp2), and 4-fluorophenyl (PhF) to 2,6-di{3,5-di(trifluoromethyl)phenyl}4-fluorophenyl (p-FAr^DarF2). They were formed as crystalline solids or viscous oils in medium to good yields, which recommends this synthetic approach as generally suitable. The products were studied by X-ray diffraction and spectroscopic methods, including ⁷⁷Se NMR spectroscopy. The influence of the organic substituents on the ⁷⁷Se NMR chemical shifts of the isoselenocyanates is in good accordance with DFT-modeled values. Experimental ⁷⁷Se-¹³C couplings of 280 Hz could be derived for Se¹³CNAr^Dipp2 prepared from a sample of ¹³CNAr^Dipp2 (isotopic enrichment: 99%). A small amount of a selenourea-type product, (i-Prop)₂NC(Se)NHp-FAr^DarF2, was isolated from a reaction mixture of CNp-FAr^DarF2 with selenium and diisopropylamine as the supporting base, which indicates an influence of the supporting base used for the course of the reaction.