Lithium Complexes with Bridging and Terminal NHC Ligands: The Decisive Influence of an Anionic Tether

Abstract

Deprotonation of the fluorenyl‐tethered imidazolinium salt [9‐(C13H9)C2H4N(CH)C2H4N(2,4,6‐Me3C6H2)][BF4] gave a spirocyclic compound that reacted with a synergic mixture of LiPh/LiN(SiMe3)2 or LinBu/LiN(SiMe3)2 to give a dilithium complex incorporating a bridging N(SiMe3)2 ligand. In contrast, deprotonation of the imidazolium salt [9‐(C13H9)C2H4N(CH)C2H2N(Me)][Br] instead yielded the free NHC, which reacted with nBuLi to form a dimeric, NHC‐bridged dilithium complex. Addition of LiN(SiMe3)2 led to coordination and the formation of a dilithium complex with a bridging N(SiMe3)2 ligand, which was characterised in the solid state as a 1D coordination polymer. The reaction of 1,3‐bis(2,6‐diisopropylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene (SIPr) with lithium indenide and lithium fluorenide gave soluble species with terminal binding of the NHC to the lithium cation and η5 coordination of indenyl or fluorenyl. A symmetrical bridging mode for an NHC donor was therefore observed only if a tethered fluorenyl anion was present with no additional amide ligand.

Coordination-Induced Trigger for Activity: N-Heterocyclic Carbene-Decorated Ceria Catalysts Incorporating Cr and Rh with Activity Induction by Surface Adsorption Site Control

“…The modeled structure of ICy- r -Cr 0.19 Rh 0.06 CeO z (ICy-Rh 4 /CeO 2 ) was structurally optimized, and the ICy ligand was favorably coordinated at a bridge site between Rh atoms (Figures S13­(B), S14). , Bader charge analysis of Rh 4 /CeO 2 and ICy-Rh 4 /CeO 2 showed similar charge distributions of Rh (Figure S15), supporting the experimental results of Rh K-edge XANES and Rh 3d XPS analyses.…”

Rhodium Indenyl NHC and Fluorenyl‐Tethered NHC Half‐Sandwich Complexes: Synthesis, Structures and Applications in the Catalytic C−H Borylation of Arenes and Alkanes

“…Fluorenyl‐tethered NHC Rh complexes were synthesised from the LiN(SiMe 3 ) 2 adducts recently reported (Scheme 4). [63] The dimeric LiN(SiMe 3 ) 2 ‐free lithium salt [63a] [Li{ μ ‐( μ ‐ η 1 : η 1 ‐( η 5 ‐C 13 H 8 )C 2 H 4 N(C)C 2 H 2 NMe}] 2 was not a successful ligand transfer reagent and our progress towards indenyl‐tethered ligands is currently limited by their challenging synthesis [64] . Despite many attempts, and the use of different conditions, yields for the tethered complexes (5–31 %) are much lower than the monodentate analogues, reminiscent of the low yields seen for the “fly‐trap” method of synthesising strained metallocenophanes [65] .…”

The Fascinating Flexibility and Coordination Modes of a Pentamethylene Connected Macrocyclic CNC Pincer Ligand

“…The other coordinating bonds are pronouncedly shorter (Li-C7′ = 2.141(8) Å, Li-N = 1.965(5) Å). The formation of bridging Li(NHC) complexes with constrained geometry Cp-ligands has been recognized before [ 16 ].…”