Linear Inverse Sandwich Complexes of Tetraanionic Benzene Stabilized by Covalent δ-Bonding with Late Lanthanides
K. Randall McClain, Alexandre H. Vincent, Ahmadreza Rajabi, Danh X. Ngo, Katie R. Meihaus, Filipp Furche, Benjamin G. Harvey, Jeffrey R. Long
Abstract
High Resolution Image Download MS PowerPoint Slide A series of dilanthanide benzene inverse sandwich complexes of the type (Cp iPr5 Ln) 2 (μ–η 6:η 6 -C 6 H 6 ) ( 1-Ln ) (Ln = Y, Gd, Tb, Dy, Tm) are reported. These compounds are synthesized by reduction of the respective trivalent dimers Cp iPr5 2 Ln 2 I 4 (Ln = Y, Gd, Tb, Dy, Tm) in diethyl ether with potassium graphite in the presence of benzene, and they feature an unusual linear coordination geometry with a highly planar benzene bridge as verified by single-crystal X-ray diffraction. The Ln–Bz centroid distances of 1-Ln are the shortest distances observed to date, ranging from 1.943(1) Å for 1-Tm to 2.039(6) Å for 1-Gd . Structural, spectroscopic, and magnetic analyses together with density functional theory calculations support the presence of a rare, unsubstituted tetraanionic benzene in each compound, which is stabilized by strong covalent δ bonding interactions involving the filled π* orbitals of (C 6 H 6 ) 4– and vacant d xy and d x 2 –y 2 orbitals of the Ln 3+ ions. Notably, 1-Ln are the first examples of compounds of the later lanthanides to feature an unsubstituted tetraanionic benzene.