Abstract
The rhenadicarbaborane carbonyl nitrosyls (C2Bn−3Hn−1)Re(CO)2(NO), (n = 8 to 12), of interest in drug delivery agents based on the experimentally known C2B9H11Re(CO)2(NO) and related species, have been investigated by density functional theory. The lowest energy structures of these rhenadicarbaboranes are all found to have central ReC2Bn−3 most spherical closo deltahedra in accord with their 2n + 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 C2B6H8Re(CO)2(NO) system are alternative isocloso deltahedral isomers found within ~8 kcal/mol of the lowest energy closo isomer. Such 9-vertex isocloso structures provide a degree 6 vertex for the rhenium atom flanked by degree 4 vertices for each carbon atom.
Highlights
Carboranes in general are accepted as synthons not unlike organic ones insofar as biological and medical applications are concerned [1]
The very common icosahedral C2 B10 synthon is regarded as similar to rotating phenyl groups. This similarity is seen in terms of steric requirements, polarity/hydrophobicity, and availability of regioselective functionalization with substituents at the carbon atoms [1]
Such regioselective functionalization has been shown to work with all classes of bioactive substances, including aminoacids, lipids, and nucleosides, as well as incorporation into dendrimers, liposomes, and other biocompatible methods of nanoencapsulation [1]. In this connection carboranes provide two specific advantages: the presence of boron, which allows for radiotherapeutical techniques such as boron neutron capture therapy (BNCT), and the availability of viable syntheses leading to endo-substitution with transition metal synthons to yield metallacarboranes [1,2,3,4,5,6,7,8,9]
Summary
Carboranes in general are accepted as synthons not unlike organic ones insofar as biological and medical applications are concerned [1]. Such regioselective functionalization has been shown to work with all classes of bioactive substances, including aminoacids, lipids, and nucleosides, as well as incorporation into dendrimers, liposomes, and other biocompatible methods of nanoencapsulation [1] In this connection carboranes provide two specific advantages: the presence of boron, which allows for radiotherapeutical techniques such as boron neutron capture therapy (BNCT), and the availability of viable syntheses leading to endo-substitution with transition metal synthons to yield metallacarboranes [1,2,3,4,5,6,7,8,9].
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