Unique and contrasting structures of homoleptic lanthanum(iii) and cerium(iii) 3,5-dimethylpyrazolates

Abstract

Homoleptic [La(Me2pz)3]n (Me2pz = 3,5-dimethylpyrazolato) is a μ-η2:η5-Me2pz coordination polymer with 12-coordinate La atoms in an unusual η5:η5 Me2pz sandwich, whilst the cerium congener forms a molecular tetrametallic cage [Ce4(Me2pz)12] featuring six different Me2pz coordination modes.

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

“…The overall structure of 2 c is similar to polymeric [La(Me 2 pz) 3 ] ∞ , but the putative polymeric chain is capped by two terminating Me 2 pzH ligands to form the tetrametallic species 2 c . Such an oligomer formation is interesting considering that the homoleptic species forms a tetrametallic [Ce 4 (Me 2 pz) 12 ] cluster . Nevertheless, it is evident that at ambient temperature release of free amine is presumably not the direct cause of the initial rapid degradation observed during the synthesis of 1 , and it is more likely that the amido ligand engages into Si−H bond activation in the form of transient heteroleptic complexes [Ce(Me 2 pz) x {N(SiHMe 2 ) 2 } 4− x ] ( x= 2 ( 4 a ) or x= 3 ( 4 b ), cf., Scheme ).…”

Effective and Reversible Carbon Dioxide Insertion into Cerium Pyrazolates

“…Carbon Dioxide Insertion into a Cerous Pyrazolate: To examine the role of the oxidation state of cerium (Ce IV versus Ce III ) and, therefore, the impact of its Lewis acidity, cerous donor-free [Ce 4 (Me 2 pz) 12 ] [28] (4) was used as a precursor for CO 2 insertion (Scheme 5). Remarkably, while retaining the Ce 4 nuclearity, all of the CeÀN(Me 2 pz) moieties engaged in CO 2 insertion, leading to the complex [Ce 4 (Me 2 pz·CO 2 ) 12 ] (5; Figure 4).…”

“…However, a simultaneous increase of the temperature to 90 8C and the CO 2 pressure to 10 bar led to a marked improvement in the catalytic activity, resulting in TONs of up to 300 for the sterically demanding 3,3-dimethyl-1,2-butylene oxide (entries 24 and 26). The latter conditions were also applicable for the cycloaddition of CO 2 and cyclohexene oxide, an internal epoxide (entries [27][28][29]. Having optimized the reaction conditions, we determined the initial turnover frequencies for the different epoxides (entries 5, 12, 20, and 25).…”

Can Bismuth Replace Mercury in Redox Transmetallation/Protolysis Syntheses from Free Lanthanoid Metals?

“…We now report the successful syntheses of a range of pyrazolatolanthanoid(III) complexes from a wide range of lanthanoid metals, tris(pentafluorophenyl)bismuth(III), and pyrazoles of varying size, shape and acidity, providing proof of concept for the method. The initial choice of pyrazoles was based on the well‐established chemistry of lanthanoid pyrazolates, and the wide variety of binding modes possible to which new examples are still being added . Importantly, a number of the products have previously been prepared by RTP reactions utilizing Hg(C 6 F 5 ) 2 (reaction (2) Ar=C 6 F 5 ),, enabling a direct comparison of effectiveness between Bi(C 6 F 5 ) 3 and Hg(C 6 F 5 ) 2 as oxidants.…”

“…The initial choice of pyrazolesw as based on the well-established chemistry of lanthanoid pyrazolates [22a,b, 23, 35] and the wide variety of binding modesp ossible [36] to which new examples are still being added. [37] Importantly,a number of the products have previously been preparedb y RTP reactions utilizing Hg(C 6 F 5 ) 2 (reaction( 2) Ar = C 6 F 5 ), [35c,d, 38] enablingadirect comparison of effectiveness between Bi(C 6 F 5 ) 3 and Hg(C 6 F 5 ) 2 as oxidants. Pyrazoles (1,2-diazacyclopentadienes)h ave pK a valuesf rom ca.…”