Phenyl argentate aggregates [AgnPhn+1]- (n = 2-8): Models for the self-assembly of atom-precise polynuclear organometallics.

Electrospray ionization of phenyl argentates formed by transmetalation reactions between phenyl lithium and silver cyanide provides access to the argentate aggregates, [AgnPhn+1]-, which were individually mass-selected for n = 2-8 in order to generate their gas-phase Ultraviolet Photodissociation (UVPD) "action" spectra over the range 304-399 nm. A strong bathochromic shift in optical spectra was observed with increasing size/n. Theoretical calculations allowed the assignment of the experimental UVPD spectra to specific isomer(s) and provided crucial insights into the transition from the 2D to 3D structure of the metallic component with the increasing size of the complex. The [AgnPhn+1]- aggregates contain neither pronounced metallic cluster properties nor ligated metallic cluster features and are thus not superatom complexes. They therefore represent novel organometallic characteristics built from Ag2Ph subunits.

Argentate(i) and (iii) complexes as intermediates in silver-mediated cross-coupling reactions.

Despite the potential of silver to mediate synthetically valuable cross-coupling reactions, the operating mechanisms have remained unknown. Here, we use a combination of rapid-injection NMR spectroscopy, electrospray-ionization mass spectrometry, and quantum chemical calculations to demonstrate that these transformations involve argentate(i) and (iii) complexes as key intermediates.

The Role of Ate Complexes in the Copper-Mediated Trifluoromethylation of Alkynes.

Trifluoromethylation reactions have recently received increased attention because of the beneficial effect of the trifluoromethyl group on the pharmacological properties of numerous substances. A common method to introduce the trifluoromethyl group employs the Ruppert-Prakash reagent, that is, Si(CH3 )3 CF3 , together with a copper(I) halide. We have applied this method to the trifluoromethylation of aromatic alkynes and used electrospray-ionization mass spectrometry to investigate the mechanism of these reactions in tetrahydrofuran, dichloromethane, and acetonitrile as well as with and without added 1,10-phenanthroline. In the absence of the alkyne component, the homoleptic ate complexes [Cu(CF3 )2 ](-) and [Cu(CF3 )4 ](-) were observed. In the presence of the alkynes RH, the heteroleptic complexes [Cu(CF3 )3 R](-) were detected as well. Upon gas-phase fragmentation, these key intermediates released the cross-coupling products R-CF3 with perfect selectivity. Apparently, the [Cu(CF3 )3 R](-) complexes did not originate from homoleptic cuprate anions, but from unobservable neutral precursors. The present results moreover point to the involvement of oxygen as the oxidizing agent.

H(C)Ag: a triple resonance NMR experiment for (109) Ag detection in labile silver-carbene complexes.

In silver complexes, indirect detection of (109) Ag resonances via (1) H,(109) Ag-HMQC frequently suffers from small or absent JHAg couplings or rapid ligand dissociation. In these cases, it would be favourable to employ H(X)Ag triple resonance spectroscopy that uses the large one-bond JXAg coupling (where the donor atom of the ligand X is the relay nucleus). We have applied an HMQC-based version of the H(C)Ag experiment to a labile silver-NHC complex (NHC=N-heterocyclic carbene) at natural (13) C isotopic abundance and variable temperature. In agreement with simulations, H(C)Ag detection became superior to (1) H,(109) Ag-HMQC detection above -20 °C.