Crystal Structure and Chemical Properties of Tris(2,6-dimethoxyphenyl)phosphine Selenide

Abstract

Abstract The X-ray crystal structure of the title compound, Φ3PSe [Φ = 2,6-(MeO)2C6H3], showed that the P=Se bond distance [2.136(2) Å] was the longest among those of the reported triarylphosphine selenides, that the P–C bond distances [av. 1.839 Å] were longer than those of triphenylphosphine selenide, and that all the P···O interatomic distances [2.794—3.189 Å] were shorter than the sum of the van der Waals radii, implying a direct electron-donative interaction from the methoxy oxygen atom to the phosphorus atom. Some chemical evidence also showed that the P=Se bond was weaker than that of triphenylphosphine selenide. Alkyl halides, RX, reacted with Φ3PSe to give a mixture of alkylselenophosphonium salts, [Φ3P–SeR]X, and alkylphosphonium salts, [Φ3P–R]X, while they reacted with PhΦ2PSe to give [PhΦ2P-SeR]X almost selectively. Measurements of the reaction rates of Ph3−nΦnPY (n = 0—3; Y = none, O, S, Se) with butyl bromide in acetonitrile showed that the rate decreased in the order of Y = none > Se > S > O and n = 3 > 2 > 1 > 0. Benzylselenophosphonium salts, [Φ3P–SeCH2C6H4Z-4]Cl (Z = H, Me, Cl) and [PhΦ2P–SeCH2Ph]Cl, reacted easily with aqueous sodium hydroxide or with aqueous tin(II) chloride to give the diselenides, (4-ZC6H4CH2Se)2, and most of ArΦ2P [Ar = Φ or Ph] was recovered after these reactions. These properties of [ArΦ2P–SeR]X, as well as of ArΦ2PSe, were discussed in terms of the electronic effect and/or steric effect of methoxy groups at 2,6-positions.