Neutral Rhenadicarbaboranes with Re(CO)(NO) Vertices: A Theoretical Study of Building Blocks for Rhenacarborane-Based Drug Delivery Agents.

The rhenadicarbaborane carbonyl nitrosyls (CBH)Re(CO)(NO), ( = 8 to 12), of interest in drug delivery agents based on the experimentally known CBHRe(CO)(NO) and related species, have been investigated by density functional theory. The lowest energy structures of these rhenadicarbaboranes are all found to have central ReCB most spherical deltahedra in accord with their 2 + 2 Wadean skeletal electrons. Carbon atoms are found to be located preferentially at degree 4 vertices in such structures. Furthermore, rhenium atoms are preferentially located at a highest degree vertex, typically a vertex of degree 5. Only for the 9-vertex CBHRe(CO)(NO) system are alternative deltahedral isomers found within ~8 kcal/mol of the lowest energy isomer. Such 9-vertex structures provide a degree 6 vertex for the rhenium atom flanked by degree 4 vertices for each carbon atom.