Tris(3‐phenylpyrazolyl)methanide Complex of Calcium – Unprecedented Coordination Chemistry and Degradation Reaction

Abstract

Keywords: Calcium / Scorpionates / Nitrogen heterocycles / Coordination modes / X-ray diffractionCalciation of tris(3-phenylpyrazolyl)methane in tetrahydrofuran and recrystallization from a mixture of toluene and 1,2-dimethoxyethane yielded [(dme)Ca{C(Pz Ph ) 3 } 2 ] (1). The molecular structure of this complex resembles a typical dialkylcalcium complex stabilized by long Ca-N contacts to two pyrazolyl fragments. The addition of 1,2-bis(dimethyl-[a] Institute

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

“…Consequently, hindrance of the isomerization from a κ 3 N to a κ 2 N ,κ C binding fashion should result in stabilization of the alkaline earth metal complexes. Preliminary results of additional calculations show that this stabilization can easily be achieved by incorporation of substituents in the 5‐positions of the pyrazolyl rings, which is consistent with the extreme stability of [(Pz Me₃ 3 C) 2 M] in contrast with the observed lability of [(Pz Ph 3 C) 2 M(dme)] and [(Pz Th 3 C) 2 M(dme)] (M = Ca, Sr, Ba) , …”

“…The findings discussed above also verify that the substitution patterns of the tris(pyrazolyl)methanide ions have a great influence on the final coordination modes of these methanides: a methyl group in the 5‐position stabilizes a κ 3 N coordination mode, leading to a stable complex . However, if there are only substituents in the 3‐positions, other coordination modes with different stabilities are preferred , . Very recently we isolated [(Pz Ph 3 C) 2 Ca(dme)] and [(Pz Th 3 C) 2 Ca(dme)], which degrade while warming to room temperature, verifying the lability of complexes with these methanides with κ 2 N ,κ C coordination modes.…”

“…In every derivative with a κ 2 N ,κ C binding mode the pyrazolyl groups contain a substituent in the 3‐position but no alkyl or aryl group in the 5‐position. Thus, [(Pz Me₂ 3 C) 2 Ca] contains exclusively Ca–N bonds,, whereas in [(Pz Ph 3 C) 2 Ca(dme)], with κ 2 N ,κ C ‐bound ligands, one pyrazolyl moiety of each ligand shows no short contacts to the calcium ion , . Such derivatives of strontium and barium are unknown as yet, due to quick degradation during the preparative efforts.…”

“…Depending on the substitution pattern, as well as on the central metal ion, tris(pyrazolyl)methanides show degradation processes that hinder isolation of analytically pure s‐block metal tris(pyrazolyl)methanides. Nevertheless, degradation end products and intermediates have been observed in the organocalcium and ‐strontium cases , . Inspection of Table illustrates that no tris(pyrazolyl)methanides of the heavier s‐block metal ions have been isolated and structurally characterized as of yet with the exception of [(Pz Me₃ 3 C) 2 Sr]; the barium homologue is also known and has been characterized by NMR spectroscopy (see Table ) .…”

Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis, Characterization, and Efficient Catalytic Intramolecular Hydroamination

“…CÀN bond cleavage in a tris(3-phenylpyrazolyl)methanide complex of calcium has also been reported. [38] The strontium analogue of 1 has also been similarly synthesized. [ 8 ]toluene.…”