Molecular modelling of carboranes using distance restraints: The molecular dynamics simulation of appended thioether macrocycles

A molecular mechanics model for o-carborane cages has been developed, using distance restraints to hold the polyhedron in position. The combination of o-carborane cage interatomic distance restraints (a modified central force field) and CHARMm parameters gives a good representation of the carborane cage geometry. Molecular dynamic simulations of macrocyclic thioethers ligated to the carbons of the carborane have been carried out. The rigid cage section seems to provide an accessible interconversion route between conformers of the macrocycle, effectively an entatic state. The new carborane 1,2-(6′-oxa-3′,9′-dithiaundecane-1′,11′-diyl)-1,2- dicarba-closo-dodecborane, the four-step synthesis and crystal structure of which are presented, provided a contrasting macrocyclic appendage with thioethers indirectly linked to the o-carborane cage through ethane bridges. Molecular dynamics simulation of this molecule was also carried out.