Heteroleptic Rare-Earth Tris(metallocenes) Containing a Dibenzocyclooctatetraene Dianion.

Isolable heteroleptic tris(metallocenes) containing five-membered and larger rings remain extremely scarce. The utilization of tripositive rare-earth-metal ions with ionic radii >1 Å allowed access to unprecedented and sterically congested dibenzocyclooctatetraenyl (dbCOT) metallocenes, [K(crypt-222)][CpRE(η-dbCOT)] (RE = Y (), Dy (); Cp = tetramethylcyclopentadienyl), through a salt metathesis reaction involving CpRE(BPh) and the potassium salt of the dbCOT dianion. The solid-state structures were investigated by single-crystal X-ray diffraction, magnetometry, and IR spectroscopy and provided evidence for the first crystallographically characterized (dbCOT) anion in a complex containing d- or f-block metals. Remarkably, the (Cp) ligands force a distortion from planarity within the (dbCOT) moiety, engendering a rare η-bonding motif, as opposed to the classical η conformation observed in complexes bearing a (COT) ion. The η coordination mode was proven crystallographically between 100 and 298 K and computationally (DFT and NBO). Furthermore, nucleus independent chemical shift (NICS) calculations uncovered significant ring current within the dbCOT ligand. The solution-state properties of and were analyzed via cyclic voltammetry, NMR, and UV-vis spectroscopy. Cyclic voltammograms of and exhibit a quasi-reversible feature indicating the accessibility of complexes with dbCOT in two oxidation states (dbCOT). Importantly, the dysprosium congener, , is a zero-field single-molecule magnet (SMM).