Encapsulation of tetramethylphosphonium cations

Abstract

The weak interactions and capsule formation of tetramethylphosphonium (TMP) cation with resorcinarenes 1 and 2 and the corresponding pyrogallarenes 3 and 4 were studied in the solid state by single-crystal X-ray diffraction, in solution by NMR and in the gas phase by mass spectrometry. In methanol-d 4, the NMR titration studies reveal that the association constants for the 1:1 complexes of TMP@3 and TMP@4 are much higher (TMP@4:390 ± 37 M− 1) than for the corresponding TMP@1 and TMP@2 (TMP@2:130 ± 10 M− 1) complexes. In the gas phase both monomeric 1:1 TMP@1-TMP@4 complexes as well as the dimeric 1:2 capsule complexes, TMP@1 2–TMP@4 2 were observed. The 1:1:2 molar mixtures of 1:2:TMP or 3:4:TMP resulted in homo- and heterocapsules TMP@1 2, TMP@1+2 and TMP@2 2, with the expected statistical 1:2:1 ratio. Using the 1:1:2 ratio of 1:3:TMP, 1:4:TMP, 2:3:TMP or 2:4:TMP showed a marked prefence to the homopyrogallarene capsules TMP@3 2 and TMP@4 2, thus supporting the stronger complexation of TMP with 3 and 4 as observed in solution. The X-ray structures1 confirmed the dimeric capsular structures with only minor structural differences to the corresponding tetramethylammonium (TMA) capsules reported earlier. 1. Crystallographic data for structures 5 +@1 2 · Br− · 16H2O and 5 +@2 2 · Br− · 4MeOH have been deposited with the Cambridge Crystallographic Data Centre as CCDC 687169 and 687170. Copies of the data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.