Heterobimetallic bis-NHC complexes have been obtained by the site-selective metallation of 8-iodotheophylline/imidazolium bis-NHC precursors using a combination of deprotonation-metallation and oxidative addition reactions.

N-Heterocyclic carbenes (NHCs) are commonly prepared by deprotonation of azolium salts using strong anionic bases. This reaction is often unselective, yielding alkali metal NHC complexes or dimerized NHCs. Alternatively, free NHCs are obtained by the dechlorination of 2-chloroazolium salts using electronrich phosphines. PPh 3 , PCy 3 , and PtBu 3 are unsuitable for Cl + abstraction, while the sterically encumbered tris(1,3-tert-butylimidazolidin-2-ylidenamino)phosphine 1 selectively removes Cl + from 2-chloroazolium salts. Since bulky 1 does not bind to metal complexes, it was used for the preparation of NHC complexes via in situ Cl + abstraction from 2-chloroazolium salts. The dechlorination was employed for the site-selective monometallation with Ir I , Ir III , Rh I , Rh III , and Ru II of a bis-NHC precursor composed of a 2-chlorobenzimidazolium and a 2-chlorobenzimidazole group, followed by the preparation of the heterobimetallic Ir III /Pd II complex [18] (BF 4 ) 2 by a dechlorination/oxidative addition reaction sequence.

The compound 4-bromo-3-methylthiazolium tetrafluoroborate (H-1(BF 4 )) has been chemoselectively metalated at C2 and C4 to give the heterobimetallic Ir/Pd complex [4] and Ir/Pt complexes [5] and trans- [6]. The complexes were prepared by the initial reaction of H-1(BF 4 ) with Ag 2 O followed by reaction with [Ir(Cp*)Br 2 ] 2 to give the mononuclear iridium complex [3] bearing a C2-metalated thiazolylidene with a remaining C4−Br bond. This bond was subsequently activated and oxidatively added to [M(PPh 3 ) 4 ] (M = Pd, Pt) to give the heterodinuclear complexes.

We report herein a series of organometallic Borromean rings (BRs) and [2]catenanes prepared from benzobiscarbene ligands. The reaction of dinickel complexes of the benzobiscarbenes 1 a–1 c with a thiazolothiazole bridged bipyridyl ligand L2 led by self‐assembly to a series of organometallic BRs. Solvophobic effects played a crucial role in the formation and stability of the interlocked species. The stability of BRs is related to the N‐alkyl substituents at the precursors 1 a–1 c, where longer alkyl substitutes improve stability and inter‐ring interactions. Solvophobic effects are also important for the stability of [2]catenanes prepared from 1 a–1 c and a flexible bipyridyl ligand L3. In solution, an equilibrium between the [2]catenanes and their macrocyclic building blocks was observed. High proportions of [2]catenanes were obtained in concentrated solutions or polar solvents. The proportion of [2]catenanes in solution could be further enhanced by lengthening of the N‐alkyl substitutes.

The electronic properties of two indole‐derived CAAC ligands, featuring N−Et (II) or N−H (IV) substituents, have been investigated by DFT calculations. The calculations revealed frontier orbitals (HOMO and LUMO) with energies closely related to those of the conventional N‐DIPP substituted CAAC I. The selenium adduct of the N−H substituted CAAC 1 has been prepared and characterized by X‐ray diffraction methods and 77Se NMR spectroscopy revealing π‐acceptor properties of the CAAC similar to classical CAACs of type I. While the electronic properties of the indole‐derived CAACs II and IV are similar to those of classical CAACs, their % Vbur is significantly smaller due to the smaller N‐substituents falling in the range of % Vbur for sterically less demanding N‐heterocyclic carbenes.