The reactions of alkylamino substituted phosphines with I2 and (Ph2Se2I2)2: structural features of alkylamino phosphonium cations

Abstract

The reactions of the tris-dialkylamino phosphines (Et₂N)₃P and (ⁿPr₂N)₃P, and the pyrrolidinyl substituted phosphines (C₄H₈N)₃P and ^tBuP(NC₄H₈)₂, with I₂ and (Ph₂Se₂I₂)₂, have been reported. The reactions with diiodine lead to the formation of [R₃PI]I adducts, which are essentially ionic, but show a tendency to display long, soft–soft, I⋯I interactions in the solid state. The crystal structures of [(Et₂N)₃PI]I, (1), [(ⁿPr₂N)₃PI]I, (2), and [(C₄H₈N)₃PI]I, (3), have all been determined, and display I⋯I interactions varying between 3.5170(6) and 3.6389(14) Å. The analogous reactions with (Ph₂Se₂I₂)₂ lead to the formation of phenylseleno-phosphonium salts, [R₃PSePh]I. The structures of [(C₄H₈N)₃PSePh]I, (6) and [(C₄H₈N)₂^tBuPSePh] I, (7), have been determined and do not display any soft–soft interactions between the selenium and iodine atoms. All of the phosphonium salts represent examples of structures containing tris-dialkylamino phosphine fragments which show no “special” nitrogen atom, i.e. all three nitrogen atoms are planar. This type of arrangement is usually observed when a C₃ symmetric conformation is observed, (which is the case for 1 and 2), but not for the (C₄H₈N)₃P adducts 3 and 6, where the conformation is closer to C_s, although the nitrogen atoms are still essentially planar. The P–N bonds in all the compounds reported herein are short, ranging between 1.599(12) Å and 1.643(12) Å, and are consistent with the previously reported short P–N bonds in phosphonium salts featuring tris-dialkylamino substituted phosphines.