The reaction of tertiary phosphines with (Ph₂Se₂I₂)₂—the influence of steric and electronic effects

Abstract

The reaction of (Ph(2)Se(2)I(2))(2) with a wide variety of tertiary phosphines possessing different steric and electronic properties has been studied, leading in most cases to R(3)PSe(Ph)I adducts; [R(3)P = (p-CH(3)C(6)H(4))(3)P (1), (m-CH(3)C(6)H(4))(3)P (2), (o-OCH(3)C(6)H(4))(3)P (4), Ph(2)MeP (6), Me(2)PhP (7), Me(3)P (8), Cy(3)P (9)]. All of the products formed were characterised by elemental analysis, Raman and multinuclear NMR spectroscopy. Both steric and electronic factors are important in determining the structural motif (CT vs. ionic) observed in the solid-state. In general, highly basic phosphines result in a lengthening of the Se-I interaction, and a preference for an ionic structure. The reaction with (o-CH(3)C(6)H(4))(3)P does not yield a stable R(3)PSe(Ph)I adduct, and instead (o-CH(3)C(6)H(4))(3)PI(2) (3) is formed. The unusually long P-I bond, [2.5523(12) A], and short I-I bond, [3.0724(4) A], exhibited by is a result of the high steric requirements of this phosphine. The similarly bulky (o-SCH(3)C(6)H(4))(3)P yields a mixture of (o-SCH(3)C(6)H(4))(3)PSe(Ph)I (5a) and [(o-SCH(3)C(6)H(4))(3)PSePh]I(3) (5b). The crystal structures of (m-CH(3)C(6)H(4))(3)PSe(Ph)I, 2, (o-CH(3)C(6)H(4))(3)PI(2), 3, [(o-OCH(3)C(6)H(4))(3)PSePh]I.CH(2)Cl(2), 4, [(o-SCH(3)C(6)H(4))(3)PSePh]I(3), 5b, two pseudo-polymorphs of Ph(2)MePSe(Ph)I, 6a/6b, and [Me(3)PSe(Ph)I](2).CH(2)Cl(2), 8, are reported. The R(3)PSe(Ph)I adducts formed exhibit one of four types of behaviour. Type I products, (such as 2) are CT in the solid-state and display fluxionality in solution. Type II products (such as 6a/6b) lie close to the CT/ionic structural borderline, displaying long Se-I bonds, and are more appropriately classified as [R(3)PSePh] (acceptor)/I(-) (donor) CT complexes. Type II complexes ionise in solution to [R(3)PSePh]I. Type III products, such as 8, are ionic in solution, but frequently show cation-anion, or cation-solvent interactions in the solid-state, although these interactions are weak and the linear P-Se-I motif is lost. Type IV products (such as 4) are ionic and feature bulky phosphines. They display no short cation-anion interactions in the solid-state.

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…”

Evidence for a SN2-type pathway in the exchange of phosphines at a [PhSe]+centre

“…These structures are . 17 An excess of triphenylphosphine was added to the reaction mixtures resulting in the observation of additional peaks in the 31 P NMR spectrum. 12 Upon further investigation it was found that free PPh 3 was exchanging with the coordinated PPh 3 and that the rate of this exchange varied with the specific organochalcogen moiety being studied.…”

Phosphine complexes of lone pair bearing Lewis acceptors

“…5c and d). [32][33][34][35][36][37] In the sole element of group 17 that is relevant to this perspective, the presence of three lone pairs and two bonding pairs at the acceptor iodine necessitates a linear geometry. The acceptor chemistry of molecular I 2 is not widely recognized and may appear unusual.…”