New Pyridazine‐Bridged NHC/Pyrazole Ligands and Their Sequential Silver(I) Coordination

Abstract

A family of new pyridazine‐bridged NHC/pyrazole ligand precursors HL1–5 were prepared and fully characterized including analysis by XRD {HL1 = 3‐[3‐(2,6‐diisopropylphenyl)‐3H‐imidazolium‐1‐yl]‐6‐(3‐pyridin‐2‐yl‐pyrazol‐1‐yl)‐pyridazine, HL2 = 3‐[3‐(2,4,6‐trimethylphenyl)‐3H‐imidazolium‐1‐yl]‐6‐(3‐pyridin‐2‐yl‐pyrazol‐1‐yl)‐pyridazine, HL3 = 3‐[3‐(2,4,6‐trimethylphenyl)‐3H‐imidazolium‐1‐yl]‐6‐(3,5‐dimethylpyrazol‐1‐yl)‐pyridazine, HL4 = 3‐(3‐tert‐butyl‐3H‐imidazolium‐1‐yl)‐6‐(3,5‐dimethylpyrazol‐1‐yl)‐pyridazine, HL5 = 3‐[3‐(2,4,6‐trimethylphenyl)‐3H‐imidazolium‐1‐yl]‐6‐(3‐methyl‐5‐phenylpyrazol‐1‐yl)‐pyridazine, X = PF6– or BF4–}. Reaction of the ligand precursors with Ag2O yielded various silver(I) complexes whose structures have been elucidated crystallographically. In complexes [(L3)2Ag](PF6) (4) and[(L4)2Ag](PF6) (4′) the single silver(I) ion is coordinated in a linear fashion by the NHC moieties of the two ligand strands. An NMR titration with AgBF4 reveals that 4 can bind two more silver(I) ions. The complex [(L5)2Ag2](PF6)2 (5′) features an additional silver(I) centre bound to the two pyrazole rings, whereas in [(L3)2Ag2](BF4)2 (6) ligand reshuffling has occurred to give antiparallel ligand strands with {CNHCNpyrazole} coordination of each metal ion. Secondary interactions with the pyridazine N‐atom are observed in some cases. An additional third silver(I) ion can be accommodated between the central pyridazine bridges, as shown in [(L3)2Ag3](PF6)2(BF4) (7). The sequence of binding events and the identity of the species in solution have been investigated by NMR spectroscopy and ESI mass spectrometry.

Bimetallic d10‐Metal Complexes of a Bipyridine Substituted N‐Heterocyclic Carbene

“…This results in a trigonal planar environment with a sum of angles of exactly 360°. The M−C distances in 16 are 1.890(3)/1.882(2) Å which matches the values of similar copper compounds (Figure S45), whereas in the silver complex 17 the Ag−C bond lengths (2.042(7)/2.045(7) Å) are about 3–4 pm shorter than in similar complexes reported in literature . Despite the larger van der Waals radius, the silver complex shows a smaller intermetallic distance (3.1034(11) Å) than the copper homologue (3.2168(9) Å).…”

A Planar π-Conjugated Naphthyridine-Based N-Heterocyclic Carbene Ligand and Its Derived Transition-Metal Complexes

“…An unsupported Ag–Ag interaction was also observed in an Ag–NHC complex due to electrostatic interactions between [Ag(NHC) 2 ] + and [AgBr 2 ] − . The Ag–C distances are 2.107(2) Å, showing no difference from those of the known silver–NHC complexes. , For comparison, 8-(2,6-diisopropylphenyl)-8 H -imidazo[1,5- a ][1,8]naphthyridin-9-ylidene ( C ) with Ag + forms [Ag(NHC) 2 ] + , showing very weak Ag–N interactions between the naphthyridinyl nitrogen and silver ion …”

Synthesis, Structure, Biological Evaluation, and Catalysis of Two Pyrazole‐Functionalized NHC–RuII Complexes

“…In previous reports, dinuclear complexes of pyridazine‐functionalized NHCs such as [Ru 2 Cl(L)(CH 3 CN) 4 ](PF 6 ) 3 , [Pd 2 (allyl) 2 L] {L = 3,6‐bis[ N ‐(pyridylmethyl)imidazolylidenyl]pyridazine}, [Ag 2 {3,6‐bis(1‐ n ‐butylimidazol‐2‐ylidyl)pyridine} 2 ][AgCl 2 ] 2 , and [Hg 2 {3,6‐bis(1‐methylimidazol‐2‐ylidyl)pyridine} 2 ](PF 6 ) 4 , are usually symmetrical. However, complex 3b represents a rare example of an unsymmetrical dinuclear complex coordinated by a pyridazine bridged NHC ligand …”