Synthetic access and luminescence tuning in a series of β-H and β-silyl substituted phospholes

Abstract

Starting from substituted 1,3-diynes a straightforward strategy to prepare phospholes has been explored for a series of substituents with electron poor and electron rich character (C6H5, C6H4CF3, C6F4OCH3, C5H4N, C4H3S, C4H3O, C6H4OCH3). The reaction involves formal addition of PhPTMSLi to the diyne resulting in the respective β-silyl phosphole bearing the substituents of the diyne in the α-positions. Subsequent desilylation afforded the corresponding β-H substituted phospholes which otherwise are difficult to obtain or inaccessible. The β-H phospholes showed attractive luminescence features including high quantum yields. Their β-silyl analogs revealed hypsochromic shifts in their absorption bands as a consequence of reduced coplanarity of the adjacent rings in vicinity of the silyl unit owing to steric repulsion. The structure property relationship was established on structural data from the solid state, quantum chemical DFT calculations and experimental UV vis and luminescence spectra. The identity of all new compounds was established using multinuclear NMR, mass spectrometry, elemental analysis and XRD where available.