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, II 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 II interactions varying between 3.5170(6) and 3.6389(14) A. 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)2tBuPSePh] 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 Cs, 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) A and 1.643(12) A, and are consistent with the previously reported short P-N bonds in phosphonium salts featuring tris-dialkylamino substituted phosphines.

Structural isomerism in tris-tolyl halo-phosphonium and halo-arsonium tri-halides, [(CH3C6H4)3EX][X3], (E = P, As; X = Br, I)

“…The 31 P{ 1 H} NMR spectra of 1-3 display peaks located between +4.6 and −12.1 ppm, which are consistent for [R 3 PI] + species. [19][20][21][22][23] This suggests that the R 3 PI 4 compounds 1-3 are iodo-phosphonium iodides, as expected. Similarly, the R 3 PBr 4 compounds 7-9 display peaks located between 45.3 and 52.6 ppm, which is consistent with previously reported data for cationic [R 3 PBr] + species.…”

Formation of M4Se4 cuboids (M = As, Sb, Bi) via secondary pnictogen–chalcogen interactions in the co-crystals MX3·SeP(p-FC6H4)3 (M = As, X = Br; M = Sb, X = Cl; M = Bi, X = Cl, Br)

“…However, these are all lengthened when compared with the PvSe bonds of 2.1100(13) Å and 2.1115(12) Å in the structure of SeP( p-FC 6 H 4 ) 3 (which contains two independent molecules). 25 The P-Se bonds in 2, 3, 5 and 6 still have considerable double bond character, (sum of the single bond covalent radii of P and Se is 2.27 Å, compared to the sum of the double bond covalent radii, which is 2.09 Å), 17 and are shorter than typical single P-Se bonds observed for phenyl-seleno phosphonium cations [2.2189(15) to 2.2686( 18) Å], [26][27][28][29] or in phosphine adducts of selenium substituted N-heterocycles [2.284(1) to 2.327(1) Å]. 30 However, it should be noted that the P-Se bonds in 2, 3, 5 and 6 are similar in magnitude to those of 2.1659(18) to 2.1673(18) Å observed for the two independent…”

Alternative Motifs for Halogen Bonding

“…In addition to the examples with [R 3 PX] + ‐type donors, investigations of compounds containing [(R 2 N) 3 PX] + ‐type cations also show a propensity to form halogen bonds 63. However, these are generally weaker than in the case of [R 3 PX] + ‐type donors, whereas in the case of [(Me 2 N) 3 PX] + salts, both weak C–H ··· I hydrogen bonds and P–I ··· N≡C–CH 3 halogen bond compete successfully with the expected P–X ··· I halogen bonds 64…”