The synthesis and characterization of a series of new cationic gold(I) complexes with hydroxyl-functionalized N-heterocyclic carbene (NHC) ligands is described. They are valuable building blocks for further derivatization: as a first example, coupling with amino acids and a dipeptide, respectively, successfully results in amino acid and peptide conjugates that are hard to obtain by other synthetic routes.

We report the synthesis and characterization of 12 new dinuclear gold(I) N-heterocyclic carbene (NHC) complexes and the corresponding imidazolium precursors. The focus lies in a systematic study of conformational changes and intra- and intermolecular gold–gold and π–π interactions of dinuclear gold(I) carbene complexes. Common to all members of the series of gold macrocycles are NHC ligands on the basis of imidazole with ethyl side chains and bromide as well as hexafluorophosphate counterions, respectively. The compounds vary in the length of a flexible alkyl linker between the NHC units. For the methylene and ethylene bridged macrocycles, a ring inversion movement can be observed by VT-NMR. In total, 11 molecular structures have been characterized by X-ray diffraction. Open ring conformations with intermolecular π–π and Au–Au interactions prevail, but a backfolded conformation with a short intramolecular Au–Au distance has been found for the ethylene-bridged species. The presence of Au–Au interactions could be proven by quantum chemical calculations.

A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2,2′-dihydroxy-1,1′-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly preferred compared to the next stable diastereomers. Due to this strong preference, the self-assembly of the helicates from racemic 1 proceeds in a completely narcissistic self-sorting manner with an extraordinary high degree of self-sorting that proves the power and reliability of this approach to achieve high-fidelity diastereoselective self-assembly via chiral self-sorting to get access to stereochemically well-defined nanoscaled objects. Furthermore, mass spectrometric methods including electron capture dissociation MSn experiments could be used to elucidate the redox behavior of the copper helicates.

A self-assembled tetranuclear metallosupramolecular complex was brought into the gas phase by electrospray ionization (ESI), mass-selected, and fragmented via infrared multi-photon dissociation (IRMPD) and electron capture dissociation (ECD) in a Fourier-transform ion-cyclotron resonance mass spectrometer (FT-ICR). The resulting spectra were compared. The ECD spectra show some identical fragments to IRMPD which suggest similar fragmentation pathways, but also different fragments which can be assigned to radical cations. Further experiments were performed to investigate the location of the captured electron and results hint at the formation of complexes containing a bipyridyl anion.

A series of heterometallic metallamacrocycles have been constructed from self-assembly reactions between the fluorinated Au(I) organometallic compounds [(AuC6F4py)2(μ2-diphosphane)] [diphosphane = bis(diphenylphosphanyl)methane (dppm) (1), 1,2-bis(diphenylphosphanyl)ethane (dppe) (2), trans-1,2-bis(diphenylphosphanyl)ethylene (dppet) (3), 1,3-bis(diphenylphosphanyl)propane (dppp) (4), 1,4-bis(diphenylphosphanyl)butane (dppb) (5), and 4,4′-bis(diphenylphosphanyl)-1,1′-biphenyl (dppdph) (6)] and the cis-blocked complexes [M(P–P)(H2O)2](OTf)2 (M = Pd) (P–P = dppp, dppf) (a,c), (M = Pt) (P–P = dppp, dppf) (b,d). Changes of the backbone of the diphosphanes were seen to have an influence on the resulting species. While the self-assembly reactions involving [(AuC6F4py)2(μ2-dppm)] (1), [(AuC6F4py)2(μ2-dppb)] (5), and [(AuC6F4py)2(μ2-dppdph)] (6) donors gave exclusively [2 + 2] heterometallomacrocycles, the assemblies arising from [(AuC6F4py)2(μ2-dppe)] (2) as well as the combinations between [(AuC6F4py)2(μ2-dppp)] (4) and [M(dppp)(H2O)2](OTf)2 (a, b) and [(AuC6F4py)2(μ2-dppet)] (3) and [M(dppf)(H2O)2](OTf)2 (c, d) consisted of an equilibrium between two macrocyclic species ([2 + 2] and a higher-order aggregate [3 + 3], [4 + 4],...). Multinuclear (1H, 19F, 31P) and diffusion NMR spectroscopy in combination with a complete set of ESI-FT-ICR mass spectrometry experiments were used to elucidate the nature of the different assemblies. DFT calculations were performed in order to calculate the molecular geometry and estimate the relative stability of different conformations of [2 + 2], [3 + 3], and [4 + 4] supramolecular species for two of the used diphosphanes.

SOMO catalysis has lately obtained large interest as a new and powerful version of enantioselective organocatalysis which includes radical steps initiated by a one-electron oxidation. The intermediate enamine radical cation has been postulated, but has not been observed directly so far. This communication now reports the direct detection of this key intermediate.

The synthesis and characterization of a series of new cationic gold(I) complexes with hydroxyl-functionalized N-heterocyclic carbene (NHC) ligands is described. They are valuable building blocks for further derivatization: as a first example, coupling with amino acids and a dipeptide, respectively, successfully results in amino acid and peptide conjugates that are hard to obtain by other synthetic routes.

SOMO catalysis has lately obtained large interest as a new and powerful version of enantioselective organocatalysis which includes radical steps initiated by a one-electron oxidation. The intermediate enamine radical cation has been postulated, but has not been observed directly so far. This communication now reports the direct detection of this key intermediate.