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

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.