An examination of the effects of borate group proximity on phosphine donor power in anionic (phosphino)tetraphenylborate ligands

• A series of anionic (phosphino)tetraphenylborate ligands, [Ph4P][Ph2P-R-C6H4BPh3], is described.
• The borate group enhances the σ-donor power of the phosphine.
• The effect decreases with increasing separation between the borate and phosphorus centre.

The ligand electron-donating abilities are compared among a series of monodentate, anionic (phosphino)tetraphenylborate phosphines [Ph4P][Ph2P-R-C6H4BPh3] (R = –C6H4–, –CH2–, –CH2CH2– or none), and their neutral counterparts Ph2PR (R = biphenyl, -CH2Ph, -CH2CH2Ph or Ph). Among the anionic ligands, the position of the tetraphenylborate group relative to the diphenylphosphino donor moiety was systematically varied in an effort to examine how its proximity impacts donor power. The donor power was determined by measuring the 31P–77Se coupling constant for the corresponding selenide of each phosphine ligand via 31P NMR spectroscopy. The anionic ligands yield lower 31P–77Se coupling constants than those measured for their respective neutral counterparts. Moreover, the 31P–77Se coupling constants among the anionic ligands increase when the tetraphenylborate group is positioned further from the phosphorus centre.

The importance of the tetraphenylborate group's position relative to the diphenylphosphino donor moiety in the anionic (phosphino)tetraphenylborate phosphines [Ph4P][Ph2P-R-C6H4BPh3] (R = –C6H4–, –CH2–, –CH2CH2– or none) was examined. The effects of borate group proximity on phosphine donor power were examined by comparing the 31P–77Se coupling constants of the corresponding selenides.Figure optionsDownload as PowerPoint slide