Synthesis, Structure, and Bonding of d0/f n Metallacarboranes Incorporating the η7-Carboranyl Ligand

Treatment of 1,2-(C6H5CH2)2-1,2-C2B10H10 with excess Na or Li metal in THF followed by reaction with MCl3 in the presence of excess alkali metal gave novel 13-vertex closo-metallacarboranes {[(C6H5CH2)2C2B10H10]M(THF)}2{Na(THF)3}2·2THF (M = Dy (1), Y (2), Er (3)) or [{(C6H5CH2)2C2B10H10}M(THF)]2[Li(THF)4]2 (M = Y (5), Er (6)) in moderate to good yield, respectively. Recrystallization of 3 from a DME solution afforded DME-coordinated metallacarborane {[(C6H5CH2)2C2B10H10]Er(DME)}2{Na(DME)2}2 (4). 2 and 5 are the first examples of d0 metallacarboranes incorporating a η7-carboranyl ligand. All of these complexes have been fully characterized by various spectroscopic date, elemental analyses, and X-ray diffraction studies. Molecular orbital calculations indicate that the metal−carborane bonding is well delocalized and can be described as the orbital interactions between the metal's five d orbitals and the cage's five symmetry-adapted frontier orbitals. It is anticipated that only the d0/f n transition metal ion with the proper size is capable of being η7-bound to an arachno-carboranyl ligand.