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

The reactions of the tris-dialkylamino phosphines (Et2N)(3)P and ((Pr2N)-Pr-n)(3)P, and the pyrrolidinyl substituted phosphines (C4H8N)(3)P and tBuP(NC4H8)(2), with I-2 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 center dot center dot center dot I interactions in the solid state. The crystal structures of [(Et2N)(3)PI]I, (1), [((Pr2N)-Pr-n)(3)PI]I, (2), and [(C4H8N)(3)PI]I, (3), have all been determined, and display I center dot center dot center dot I interactions varying between 3.5170(6) and 3.6389(14) angstrom. The analogous reactions with (Ph2Se2I2)(2) lead to the formation of phenylseleno-phosphonium salts, [R3PSePh]I. The structures of [(C4H8N)(3)PSePh]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 C-3 symmetric conformation is observed, (which is the case for 1 and 2), but not for the (C4H8N)(3)P 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) angstrom and 1.643(12) angstrom, and are consistent with the previously reported short P-N bonds in phosphonium salts featuring tris-dialkylamino substituted phosphines.