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Emergence of a New [NNN] Pincer Ligand via Si-H Bond Activation and ?-Hydride Abstraction at Tetravalent Cerium.

ABSTRACT: The cerium(IV) pyrazolate complexes [Ce(Me2 pz)4 ]2 and [Ce(Me2 pz)4 (thf)] initiate ?-hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl-substituted silylamido ligand, namely [Ce(Me2 pz)3 (bpsa)] (bpsa=bis((3,5-dimethylpyrazol-1-yl)dimethylsilyl)amido; Me2 pz =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(Me2 pz)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 (Me2 pz)9 ] and the stable mixed-ligand ceric species [Ce(Me2 pz)2 {N(SiMe3 )2 }2 ] were obtained.

SUBMITTER: Werner D

PROVIDER: S-EPMC7540680 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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

Werner Daniel D Bayer Uwe U Schädle Dorothea D Anwander Reiner R

Chemistry (Weinheim an der Bergstrasse, Germany) 20200907 53

The cerium(IV) pyrazolate complexes [Ce(Me2 pz)4 ]2 and [Ce(Me2 pz)4 (thf)] initiate β-hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl-substituted silylamido ligand, namely [Ce(Me2 pz)3 (bpsa)] (bpsa=bis((3,5-dimethylpyrazol-1-yl)dimethylsilyl)amido; Me2 pz =3,5-dimethylpyrazolato), along with some cerium(III) species. Remar ...[more]

PMID: 32239686

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Project description:This report describes a synthetic protocols and the crystal structures involving a novel pincer-type H3[NNN] ligand, namely di-μ-bromido-μ-{2-(2,2-di-methylpropanimido-yl)-N-[2-(2,2-di-methyl-propanimido-yl)-4-methyl-phen-yl]-4-methylaniline}-bis-[(diethyl ether)lithium], [Li2Br2(C24H33N3)(C4H10O)2] (1) and a dinuclear metal complex, namely di-μ-bromido-2:3κ4Br:Br-bis-{2-(2,2-di-methylpropanimido-yl)-N-[2-(2,2-di-methyl-propanimido-yl)-4-methyl-phen-yl]-4-methylaniline}-1κ3N,N',N'';4κ3N,N',N''-tetra-μ-iso-propano-lato-1:2κ4O:O;3:4κ4O:O-diiso-propano-lato-1κO,4κO-2,3-dilithium-1,4-dititanium, [Li2Ti2Br2(C24H32N3)2(C3H7O)6] or {[NHNNH]Ti(O i Pr)3(LiBr)2}2 (2). Complex 1, which sits on a twofold rotation axis, is a rare example of a pincer-type ligand which bears ketimine side arms. A unique feature of complex 1 is that the ketimine N atoms have an LiBr(Et2O) fragment bonded to them, with the Li atom adopting a distorted tetra-hedral geometry. This particular fragment creates an LiBr bridge between the two ketimine sidearms, which leads to a cage-type appearance of the ligand. Complex 2 consists of the previously described ligand and a TiIV metal atom in an octa-hedral environment, and is located on an inversion center. Complex 2 crystallizes as a dinuclear species with the metal atoms being bridged by an LiBr entity [the Br atoms are disordered and refined in two positions with their site occupation factors refining to 0.674 (12)/0.372 (12)], and the Li cation being bonded to the isopropoxide O atoms (Li having a tetra-hedral coordination as in 1). The organic ligand of compound 2 exhibits disorder in its periphery groups; isopropyl and tert-butyl groups (occupation factors fixed at 0.6/0.4). The novel [NNN]H3 pincer-type ligand was characterized by multinuclear and multidimensional NMR, HRMS and X-ray crystallography. The dinuclear metal complex 2 was characterized by X-ray crystallography. Although each structure exhibits donor N-H groups, no hydrogen bonding is found in either one, perhaps due to the bulky groups around them. One of the ethyl groups of the ether ligand of 1 is disordered and refined in two parts with site-occupation factors of 0.812 (8) and 0.188 (8). One and a half toluene solvent mol-ecules are also present in the asymmetric unit of 2. The toluene mol-ecules were significantly disordered and could not be modeled properly, thus SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] was used to remove their contributions to the overall intensity data.

Dataset Information

Emergence of a New [NNN] Pincer Ligand via Si-H Bond Activation and ?-Hydride Abstraction at Tetravalent Cerium.

Publications

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

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