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

Title: 

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

Year of Publication:

2022

Authors:

Pugliese, ER, Benner, F, Castellanos, E, Delano, F, Demir, S

Journal:

Inorganic Chemistry

Abstract:

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)][Cptet2RE(η2-dbCOT)] (RE = Y (1), Dy (2); Cptet = tetramethylcyclopentadienyl), through a salt metathesis reaction involving Cptet2RE(BPh4) 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)2– anion in a complex containing d- or f-block metals. Remarkably, the (Cptet)− ligands force a distortion from planarity within the (dbCOT)2– moiety, engendering a rare η2-bonding motif, as opposed to the classical η8 conformation observed in complexes bearing a (COT)2– ion. The η2 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 1 and 2 were analyzed via cyclic voltammetry, NMR, and UV–vis spectroscopy. Cyclic voltammograms of 1 and 2 exhibit a quasi-reversible feature indicating the accessibility of complexes with dbCOT in two oxidation states (dbCOT2–/3–•). Importantly, the dysprosium congener, 2, is a zero-field single-molecule magnet (SMM).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)][Cptet2RE(η2-dbCOT)] (RE = Y (1), Dy (2); Cptet = tetramethylcyclopentadienyl), through a salt metathesis reaction involving Cptet2RE(BPh4) 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)2– anion in a complex containing d- or f-block metals. Remarkably, the (Cptet)− ligands force a distortion from planarity within the (dbCOT)2– moiety, engendering a rare η2-bonding motif, as opposed to the classical η8 conformation observed in complexes bearing a (COT)2– ion. The η2 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 1 and 2 were analyzed via cyclic voltammetry, NMR, and UV–vis spectroscopy. Cyclic voltammograms of 1 and 2 exhibit a quasi-reversible feature indicating the accessibility of complexes with dbCOT in two oxidation states (dbCOT2–/3–•). Importantly, the dysprosium congener, 2, is a zero-field single-molecule magnet (SMM).

URL:

https://doi.org/10.1021/acs.inorgchem.1c03230