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

Abstract

The cerium(IV) pyrazolate complexes [Ce(Me2pz)4]2 and [Ce(Me2pz)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(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.

New Interventions by silicone grease in synthesis

“…[Ce(Me 2 pz) 4 (Me 2 pzH)] 2 c , a Ce IV species, crystallised as deep red blocks, similar to [Ce(Me 2 pz) 4 L] (L=thf, Me 2 pzH or 0) and toluene solvates of the L=0 species, [12] and contrasts 2 a (pale pink) or 2 b (white). It is a different crystal form from that previously isolated [12c] . Polymorphism has been observed with other [Ce(Me 2 pz) 4 L] species [12] .…”

Trivalent Rare‐Earth Metal Amide Complexes as Catalysts for the Hydrosilylation of Benzophenone Derivatives with HN(SiHMe2)2 by Amine‐Exchange Reaction

“…First, 4 a reacts with 1 equivalent of 2 a , giving monohydrosilylated complex 6 aa via interaction of the carbonyl moiety with the cationic silicon center of A : [4p, 19] interaction of Lewis bases with the silicon atom of the M−Si−H β‐agostic species due to the increased Lewis acidity of the silicon atom was reported for a cationic zirconium bis(dimethylsilyl)amide complex with 4‐(dimethylamino)pyridine by Sadow et al. (Figure 3, left) [15a] and a cerium complex bearing a dimethylpyrazolyl‐substituted silylamido ligand (Figure 3, right) [20a] . Further, another equivalent of 2 a spontaneously reacts with an Si−H bond in 6 aa through intermediate B to form double‐hydrosilylated complex 5 aa .…”

Cerium Pyrazolates Grafted onto Mesoporous Silica SBA-15: Reversible CO2 Uptake and Catalytic Cycloaddition of Epoxides and Carbon Dioxide

“…Likewise, any signals for Me 2 pzH have been absent in the supernatants examined from the grafting experiments of cerous pyrazolates 3 – 5 , clearly suggesting the formation of donor-stabilized surface species. Such donor stabilization through “free” pyrazoles is well-known for pyrazolate complexes, e.g., Hf­(Me 2 pz) 4 (Me 2 pzH) or Ce­(Me 2 pz) 4 (Me 2 pzH) . ICP-OES measurements and elemental analyses of the hybrid materials revealed high metal contents as well as high CHN values.…”