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Linear Pyrazole‐bridged Tetra(N‐heterocyclic carbene) Ligands and Their Hexanuclear Silver(I) Complexes
Author(s) -
Resch Stefan G.,
Dechert Sebastian,
Meyer Franc
Publication year - 2019
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201900028
Subject(s) - pyrazole , carbene , chemistry , ligand (biochemistry) , tetra , crystallography , stereochemistry , nuclear magnetic resonance spectroscopy , solvent , metal , medicinal chemistry , receptor , catalysis , organic chemistry , biochemistry
New hybrid ligands are reported that combine two types of popular donor groups within a single linear scaffold, viz., a central pyrazolate bridge and two appended bis( N ‐heterocyclic carbene) units; the ligand strands thus provide two potentially tridentate {NCC} compartments. The pyrazole/tetraimidazolium proligands, [H 5 L 1 ](PF 6 ) 4 and [H 5 L 2 ](PF 6 ) 4 , were synthesized via multi‐step protocols, and the NH prototropy of [H 5 L 1 ](PF 6 ) 4 was examined by variable temperature (VT) NMR spectroscopy, giving solvent dependent activation parameters (Δ H ‡ = 27.6 kJ · mol –1 , Δ S ‡ = –125 J · mol –1 · K –1 in [D 3 ]MeCN; Δ H ‡ = 40.4 kJ · mol –1 , Δ S ‡ = –86.9 J · mol –1 · K –1 in [D 6 ]DMSO) that are in the range typical for pyrazoles. Reaction of the proligands with Ag 2 O gave hexametallic complexes [Ag 6 (L 1 ) 2 ](PF 6 ) 4 and [Ag 6 (L 2 ) 2 ](PF 6 ) 4 that involve all six potential donor atoms of the ligands, viz. the four C NHC and two N pz donors, in metal coordination. X‐ray crystallography revealed a chair‐like central {Ag 6 } deck in both complexes but different arrangements of the ligand strands, which goes along with significantly different Ag I ··· Ag I distances that indicate more pronounced argentophilic interactions in case of [Ag 6 (L 1 ) 2 ] 4 + .