Tris(pyrazolyl)methanide Complexes of Trivalent Rare-Earth Metals

Abstract

Three types of trivalent rare-earth-metal complexes supported by a monoanionic tris­(pyrazolyl)­methanide ligand were synthesized and structurally characterized, and the catalytic activity of the dialkyl derivatives for isoprene polymerization was investigated. Reactions of the lithium salt of tris­(3,5-dimethylpyrazolyl)­methanide LLi­(THF) with 1 equiv of ScCl3(THF)3, YCl3, or LuCl3 in THF provided the ion-pair complexes [LLnCl3]­[Li­(THF)4] (Ln = Sc (1), Y (2), Lu (3)). Dialkyl complexes LLn­(CH2SiMe3)2(THF) (Ln = Y (4), Lu (5)) were prepared by salt metathesis of LLi­(THF) with 1 equiv of [Y­(CH2SiMe3)2(THF)3]­[BPh4] or [Lu­(CH2SiMe3)2(THF)3]­[BPh4] in toluene. Reaction of 5 with PhSiH3 provided the unexpected alkylidene-bridged dinuclear complex L 2Lu2(μ-η1:η1-3,5-(CH3)­C3HN2)2(μ-CHSiMe3) (6). Complexes 1–6 were structurally characterized by single-crystal X-ray diffraction, showing that the tris­(pyrazolyl)­methanide ligand acts as a κ3-coordinating six-electron donor in all complexes. The dialkyl complexes catalyzed 1,4-cis polymerization of isoprene with high selectivity upon activation with borate and alkylaluminum.

Open-Shell Early Lanthanide Terminal Imides

“…The last two decades have witnessed ever-increasing interest in rare-earth-metal (Ln) complexes featuring multiply bonded (organo)­imido ligands. − Contrary to d-transition metal and 5f-element chemistry, − the feasibility of terminal “unsupported” (organo)­imides [LnNR] has posed a major challenge. − Predominantly ionic bonding situations in rare-earth-metal complexes direct multiply charged, hard monodentate ligands such as [CR 2 ] 2– , and [NR] 2– in bridging positions. , On the other hand, kinetic stabilization (via sterically demanding imido ligands) necessitates advanced synthesis protocols . The linking element of most applied syntheses is the use of highly reactive rare-earth-metal alkyl precursors in order to ensure the complete deprotonation of comparatively Brønsted acid aromatic amines and silylamines .…”

The Tripodal Ligand’s 4f Complexes: Use in Molecular Magnetism

“…The electronic analog of tris(3,5-dimethylpyrazolyl)borate anion is a deprotonated TPM: tris(3,5-dimethylpyrazolyl)-methanide (TPM*). Only a few Ln complexes of TPM* are known to date [105]. Among them, the three complexes with diamagnetic central Ln 3) Å [24]), but are closer to those of 2.425(6) Å for DyCl 3 (Tp Me 2 )] − [90].…”

Rare‐Earth‐Metal Alkyl and Aryl Compounds in Organic Synthesis

“…[156] Furthermore, there are also a few examples of structurally characterized silylalkylidene complexes derived from the CH 2 SiMe 3 (neosilyl) group. [157][158][159] Figure 2/left shows the structurally characterized complexes 79 which undergo olefination reactions with ketones. [157] Moreover, complexes with donorfunctionalized alkylidene ligands such 80 and 81, originally discovered by the group of Cavell, [160] were shown to undergo olefination reactions (Figure 2/middle).…”

“…Furthermore, there are also a few examples of structurally characterized silylalkylidene complexes derived from the CH 2 SiMe 3 (neosilyl) group [157–159] . Figure 2/left shows the structurally characterized complexes 79 which undergo olefination reactions with ketones [157] .…”