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 (ArMes2), 2,6-di(2,6-diisopropylphenyl)phenyl (ArDipp2), 2,6-di(2,4,6-triisopropylphenyl)phenyl (ArTripp2), and 4-fluorophenyl (PhF) to 2,6-di{3,5-di(trifluoromethyl)phenyl}4-fluorophenyl (p-FArDarF2). 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 Se¹³CNArDipp2 prepared from a sample of ¹³CNArDipp2 (isotopic enrichment: 99%). A small amount of a selenourea-type product, (i-Prop)₂NC(Se)NHp-FArDarF2, was isolated from a reaction mixture of CNp-FArDarF2 with selenium and diisopropylamine as the supporting base, which indicates an influence of the supporting base used for the course of the reaction.