Investigations on the Steric Accessibility of the Carbanionic Moiety in Zwitterionic Magnesium Tris(pyrazolyl)methanide Complexes. Synthesis and Characterisation of Bi‐ and Tri­metallic Complexes

Abstract

Reactions of HC(pz)3 and HC(4‐Mepz)3 with MgBu2 and Mg{N(SiMe3)2}2 gave the zwitterionic complexes [Mg{C(pz)3}2] (2) and [Mg{C(4‐Mepz)3}2] (4), respectively, containing “free” pyramidal carbanions (pz = pyrazolyl). The solid‐state structure of 2 has been determined. Reactions of 2 and 4 as well as the recently reported homo‐ and heteroleptic complexes [Mg{C(3, 5‐Me2pz)3}2] (1) and [Mg{C(3, 5‐Me2pz)3}{C(pz)3}] (3) with the Lewis acid AlEt3 furnished the bi‐ and trimetallic complexes [Mg{C(pz)3}2(AlEt3)2] (5), [Mg{C(pz)3}(AlEt3){C(3, 5‐Me2pz)3}] (6), and [Mg{C(4‐Mepz)3}2(AlEt3)2] (7). Based on NMR spectroscopic investigations, including an X‐ray structural analysis on single crystals of 5, only the parent tris(pyrazolyl)methanide {C(pz)3}– and the 4‐methyl‐substituted ligand scaffolds form C‐bound adducts with the Lewis acid. By quantifying the steric bulk of κ3N‐coordinated {C(pz)3}– it could be shown that its steric features are similar to those of bulky phosphine ligands.

s‐Block Metal Complexes with Bis‐ and Tris(pyrazolyl)methane and ‐methanide Ligands

“…Thus, triethylalane has been introduced to bis[tris(pyrazolyl)methyl]magnesium species containing differently substituted pyrazolyl rings. Whereas substituents in the 4‐position allow the formation of a heterobimetallic adduct, substituents in the 3‐position hinder this adduct formation . Consequently, heteroleptic [(Pz 3 C)(Pz Me₂ 3 C)Mg] consumes only one equivalent of AlEt 3 , which binds exclusively to the unsubstituted tris(pyrazolyl)methanide moiety; see Equation .…”

“…Whereas substituents in the 4‐position allow the formation of a heterobimetallic adduct, substituents in the 3‐position hinder this adduct formation . Consequently, heteroleptic [(Pz 3 C)(Pz Me₂ 3 C)Mg] consumes only one equivalent of AlEt 3 , which binds exclusively to the unsubstituted tris(pyrazolyl)methanide moiety; see Equation . In analogy to these preparative procedures, the bis(trimethylsilyl)amides of the heavier alkaline earth metals represent suitable reagents for the deprotonation of diversely substituted tris(pyrazolyl)‐ and bis(pyrazolyl)methanes; see Equation …”

Heterobimetallic Cuprates Consisting of a Redox‐Switchable, Silicon‐Based Metalloligand: Synthesis, Structures, and Electronic Properties

“…[12] Compared to common and well-established silyl ligands like {SiMe 3 } À , {SitBu 3 } À (tBu = tert-butyl), or {SiA C H T U N G T R E N N U N G (SiMe 3 ) 3 } À , the methyl groups in the 5-positions of the pyrazolyl framework in IV imply an increased Abstract: A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon-based metalloA C H T U N G T R E N N U N G liA C H T U N G T R E N N U N G gand [k 3 N-Si(3,5-Me 2 pz) 3 Mo(CO) 3 ] À is presented (pz = pyrazolyl). [13] Consequently, we anticipated to isolate unusual monomeric copper compounds (in contrast to the literature-known complexes, which usually consist of oligomeric structures). The compound features a fac-coordinated tripodal chelating ligand and an outward pointing, "free" pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers.…”

“…Chemical shifts are given relative to TMS for 1 H,13 C, and Si, 1 m LiBr in D 2 O for 7 Li, and NH 3 for 15 N. Coupling constants (J) are given in Hertz as positive values regardless of their real individual signs. Solution NMR spectra were recorded by using Bruker Avance instruments operating at 1 H Larmor frequencies of 300 and 400 MHz.…”

Cyclopropylmagnesium Scorpionates: A Missing Member of the Series with Both Staggered and Eclipsed Rotamers in the Crystal

“…Accordingly HTpm Me2 reacts with Mg( n Bu) 2 to yield the zwitterionic complex [(κ 3 ‐Tpm Me2 ) 2 Mg], which has no Mg–C bond . The anionic carbon is available for bonding to AlEt 3 as in the less‐crowded mixed [(κ 3 ‐Tpm)Mg(µ‐κ 4 ‐Tpm)AlEt 3 ] . [(Tpm Me2 )MgPh(THF)], most probably an intermediate for the formation of [(κ 3 ‐Tpm Me2 ) 2 Mg], is obtained in low yield from MgPh 2 .…”