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, [HP 7 ] 2– ( 1 ), with carbodiimides RN═C═NR (R = Dipp (2,6-diisopropylphenyl), i Pr, Cy) afforded the amidine-functionalized Zintl ions [P 7 C(NHR)(NR)] 2– (R = Dipp ( 2 ), i Pr ( 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 [NH 4 ][BPh 4 ] or [H(OEt 2 ) 2 ][BAr F 4 ] affords the protonated monoanionic species [HP 7 C(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 {[P 7 [C(NHDipp)(NDipp)][C(NHR)(NR)]} − (R = Dipp ( 6 ), i Pr ( 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.