Hydrophosphination of Carbodiimides Using Protic Heptaphosphide Cages: A Unique Effect of the Bimodal Activity of Protonated Group 15 Zintl Ions

Abstract

Direct reaction of the hydrogen heptaphosphide dianion, [HP7]2– (1), with carbodiimides RN═C═NR (R = Dipp (2,6-diisopropylphenyl), iPr, Cy) afforded the amidine-functionalized Zintl ions [P7C(NHR)(NR)]2– (R = Dipp (2), iPr (3), and Cy (4)). The bimodal activity of 1, which contains both negatively charged phosphide vertices alongside “electron-precise” phosphine-like nuclei allows for the direct hydrophosphination of the carbodiimides without need for an external proton source. Further reaction of the bis(2,6-diisopropylphenyl)amidine-functionalized cluster 2 with a proton source such as [NH4][BPh4] or [H(OEt2)2][BArF4] affords the protonated monoanionic species [HP7C(NHDipp)(NDipp)]− (5). As with 1, species 5 also has bimodal character, and additional hydrophosphination reactions are possible by reacting 5 with RN═C═NR to yield the bis-functionalized monoanions {[P7[C(NHDipp)(NDipp)][C(NHR)(NR)]}− (R = Dipp (6), iPr (7), and Cy (8)). All species were characterized by multielement NMR spectroscopy and electrospray mass spectrometry. In addition clusters 3, 5, and 6–8 were characterized by single-crystal X-ray diffraction in [K(18-crown-6)]2[3], [K(2,2,2-crypt)][5], [K(2,2,2-crypt)][6]·THF, [K(2,2,2-crypt)][7]·hex, and [K(2,2,2-crypt)][8]·0.65THF·0.35hex, respectively. Density functional theory level calculations were conducted on all anionic species to probe their electronic structure.