Reactions of Pentaphenylphosphorus with 2,6-Dihydroxy-benzoic and Succinic Acid

Abstract

Tetraphenylphosphonium carboxylates as solvates of [Ph₄P]⁺[OC(O)C₆H₃(OH)₂‑2,6]⁻×PhH (1) and [Ph₄P]₂⁺[O₂CCH₂CH₂CO₂]²⁻×TolH (2) types were synthesized by the reactions of pentaphenylphosphorus with 2,6-dihydroxybenzoic and succinic acids at the mole ratio of 2:1 and 1:1, respectively. The reactions were accomplished by heating the benzene or toluene solutions of the mixture of compounds inside an evacuated glass ampoule at 60 °С for 0.5 hour. The structure of compounds was characterized by IR spectroscopy and single-crystal X‑ray diffraction study. According to X-ray diffraction data, the crystals of tetraphenylphosphonium carboxylates 1 and 2 consist of the [Ph₄P]⁺ tetrahedral cations (the СРС angles are 106.4(3)–113.5(3)° (1), 107.8(2)–111.5(2)° (2), and the P-C bond lengths are 1.771(6)–1.809(6) Å (1), 1.791(4)–1.804(4) Å (2)), single charged (1) or double charged (2) carboxylate anions and solvate arene molecules. Two types of crystallographically independent cations and anions (a, b) exist in crystals 1. Anions of the compound 2 are centrosymmetric. In the carboxylate anions the C−O bonds are aligned (1.263(9), 1.273(9) Å 1а, 1.24(1), 1.257(9) Å 1b, 1.254(6), 1.272(5) Å 2), and the OCO angles at the carboxyl carbon atom are close to the theoretical value of 120°. The anions 1 are characterized by the presence of intermolecular short contacts О−Н∙∙∙О−С between oxygen atoms of the carboxyl group and o-hydroxyl groups; the Н∙∙∙О and О∙∙∙О distances are 1.73−2.03 Å and 2.450(8)−2.484(8) Å, respectively. Structural organization in the crystals is caused by weak hydrogen bonds of the С−Н···О type between the carboxylate groups and oxygen atoms of the hydroxyl groups (in crystal 1). Short contacts between the carboxylate oxygen atoms and a hydrogen atom of the methyl group of the solvated toluene molecule are observed in complex 2