Triangular gold(i) N-arylimidazolate clusters have been prepared by a pNHC metalation protocol and their photoluminescence has been switched on by the addition of Ag+.

The isocyanide ligands in complexes fac-[Mn(CNR)(bipy)(CO)3]+ are selectively transformed into formamidines, carbodiimides and formimidates upon nucleophilic addition of NH2Me or alkoxides and subsequent treatment with Ag2O, which promotes tautomerization or oxidation processes of the former carbene ligands.

A series of mononuclear gold­(I) protic N-heterocyclic carbene (pNHC) complexes was prepared by a reaction of trinuclear gold­(I) imidazolate clusters with acids of variable strength (pK a ranging from −14 to 6.7), which induce the opening of the Au3 ring cluster by protonation. Thus, the reaction of [Au3(μ-Im)3] (Im = N-alkyl or N-arylimidazolate) with weak acids such as phosphonium salts or 4-methoxythiophenol yields mononuclear derivatives of the general formula [Au­(pNHC)­PR3]+ or [Au­(pNHC)­SR], respectively, whereas with HCl complexes [Au­(pNHC)­Cl] are obtained. The noncoordinating strong acid CF3SO3H reacts with [Au3(μ-Im)3] in the presence of isocyanide (CNR) to afford the cationic species [Au­(pNHC)­CNR]+, from which the rare example of bis-carbene derivative [Au­(pNHC)­(pADC)]+ (pADC = protic acyclic diamino carbene) is formed by a reaction with NHMe2. Additionally, a number of neutral complexes were obtained by substitution reactions of the chloride ligand in [Au­(pNHC)­Cl] with anions such as cyanide, thiocyanate, and diethyldithiocarbamate.

A subtle change in the substituents at the nitrogen atoms in the N,N′-diarylformamidine complexes of formula fac-[Mn­(RNC­(H)­NHR)­(bipy)­(CO)3]+ (1a, R = phenyl; 1b, R = 4-dimethylaminophenyl) produces, upon deprotonation, either the monodentate formamidinate complex fac-[Mn­(PhNC­(H)­NPh)­(bipy)­(CO)3] (2a) or metallacylic complex 3b, which features a carbamoyl residue arising from nucleophilic attack to a vicinal carbonyl ligand. Complexes type 3 are also formed when using N-aryl-N′-alkyl-formamidines as well as N,N′-dialkylformamidines. Quantum Theory of Atoms in Molecules computations show the existence of a weak bond critical point of mainly noncovalent electrostatic type between the uncoordinated nitrogen atom of the formamidinate and a carbonyl ligand in 2a, which appears to be an isolable intermediate species that precedes the formation of metallacyclic complexes 3.