Emergence of a New [NNN] Pincer Ligand via Si−H Bond Activation and β‐Hydride Abstraction at Tetravalent Cerium

• Published in: Chemistry : a European journal Vol. 26; no. 53; pp. 12194 - 12205
• Main Authors: Werner, Daniel, Bayer, Uwe, Schädle, Dorothea, Anwander, Reiner
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 21.09.2020; John Wiley and Sons Inc
• Subjects: Cerium; Chemistry; hydride abstraction; Hydrides; Ligands; lithium; Oxidation; pincer ligands; Silicon; Species; Valence
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202000625

The cerium(IV) pyrazolate complexes [Ce(Me2pz)4]2 and [Ce(Me2pz)4(thf)] initiate β‐hydride ion of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl‐substituted silylamido ligand, namely [Ce(Me2pz)3(bpsa)] (bpsa=bis((3,5‐dimethylpyrazol‐1‐yl)dimethylsilyl)amido; Me2pz =3,5‐dimethylpyrazolato), along with some cerium(III) species. Remarkably, the nucleophilic attack of the pyrazolyl at the silicon atom and concomitant Si−H‐bond cleavage is restricted to the tetravalent cerium oxidation state and appears to proceed via the formation of a transient cerium(IV) hydride, which engages in immediate redox chemistry. When [Ce(Me2pz)4]2 is treated with [Li{N(SiMe3)2}], that is, in the absence of the SiH functionality, any redox chemistry did not occur. Instead, the ceric ate complex [LiCe2(Me2pz)9] and the stable mixed‐ligand ceric species [Ce(Me2pz)2{N(SiMe3)2}2] were obtained. Putative heteroleptic ceric species [Ce(Me2pz)x{N(SiHMe2)2}4−x] promote the formation of a new monoanionic dipyrazolylamido pincer ligand, while both tetravalent [Ce(Me2pz)2{N(SiMe3)2}2] and trivalent [Li2(thf)2Ce(Me2pz)2{N(SiHMe2)2}3] are isolable and stable.