Encapsulation Studies on closo-Dicarbadodecaborane Isomers in Neutral Tetrahedral Palladium(II) Cages

The encapsulation of icosahedral closo-dicarbadodecaborane (o-, m-, and pcarboranes, Cb) as guest molecules at the intrinsic cavities of the three isostructural tetrahedral cages [{Pd3(NiPr)3PO}4(Cl-AN)6] (1), [{Pd3(NiPr)3PO}4(Br-AN)6] (2), and [{Pd3(NiPr)3PO}4(H-AN)6] (3) was studied. The formation of definite host-guest assemblies was probed with mass spectrometry, IR, and NMR spectral analysis. 2D DOSY 1H NMR of the Cb subset of Cage systems showed similar diffusion coefficient (D) values for the host and guest species, signifying the encapsulation of these guests inside the cage assemblies. The hydrodynamic radius (RH) derived from the D values of the host and guest species further confirmed the encapsulation of the Cb isomers at the cage pockets. The single-molecule energy optimization of the host-guest assemblies indicated the preferential binding of o-Cb as a guest inside the cages (1-3). The stabilization of these Cb guests inside these cages was further attributed to various possible nonclassical C-HmiddotmiddotmiddotX-type interactions.

Automated summary

The encapsulation of icosahedral closo-dicarbadodecaborane (o-, m-, and p-carboranes) as guest molecules in the three isostructural tetrahedral cages [{Pd3(NiPr3)PO}4(Cl-AN)6] (1), [{Pd3(NiPr)3PO}4(Br-AN)6] (2), and [{Pd3(NiPr)3PO}4(H-AN)6] (3) was investigated. The formation of definite host-guest assemblies was confirmed by mass spectrometry, IR, and NMR spectroscopy. Diffusion coefficient measurements and hydrodynamic radius calculations suggested that the carborane isomers were encapsulated inside the cage assemblies. Energy optimization studies indicated that o-Cb was preferentially bound as a guest inside the cages. The stabilization of the carborane guests was attributed to various nonclassical C-HmiddotmiddotmiddotX-type interactions.