Peptide Coupling between Amino Acids and the Carboxylic Acid of a Functionalized Chlorido-gold(I)-phosphane

We have developed a protocol for the direct coupling between methyl ester protected amino acids and the chlorido-gold­(I)-phosphane (<i>p</i>-HOOC­(C₆H₄)­PPh₂)­AuCl. By applying the EDC·HCl/NHS strategy (EDC·HCl = <i>N</i>-ethyl-<i>N</i>′-(3-(dimethylamino)­propyl)­carbodiimide hydrochloride, NHS = <i>N</i>-hydroxysuccinimide), the methyl esters of l-phenylalanine, glycine, l-leucine, l-alanine, and l-methionine are coupled with the carboxylic acid of the gold complex in moderate to good yields (62–88%). All amino acid tagged gold complexes were characterized by ¹H and ¹³C NMR spectroscopy and high-resolution mass spectrometry. As corroborated by measurement of the angle of optical rotation, no racemization occurred during the reaction. The molecular structure of the leucine derivative was determined by single-crystal X-ray diffraction. In the course of developing an efficient coupling protocol, the acyl chlorides (<i>p</i>-Cl­(O)­C­(C₆H₄)­PPh₂)­AuX (X = Cl, Br) were also prepared and characterized

Unprecedented Large Temperature Dependence of Silver(I)–Silver(I) Distances in Some N‑Heterocyclic Carbene Silver(I) Complex Salts

Six examples from a series of complex salts containing bis­(1,3-dialkylimidazol-2-ylidene)­silver­(I) cations (with dialkyl = dimethyl, diethyl, methyl, ethyl, diisopropyl) with [PF₆]⁻, [SbF₆]⁻, [ClO₄]⁻, or [AgBr₂]⁻ anions, respectively, were prepared in high yields and characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction experiments reveal unprecedentedly large contractions of the metallophilic Ag­(I)–Ag­(I) distances in the solid-state structures upon cooling. In the salt containing diisopropyl-substituted ligands and [PF₆]⁻ anions, a contraction from 3.498(8) to 3.180(2) Å was observed on cooling from 293(1) to 100(1) K. Photochemical measurements show strong hypsochromic shifts of the emission maxima upon cooling, underlining the metallophilic-based nature of the emission bands. Ab initio calculations show that the strong temperature dependence of the observed Ag–Ag distances can be attributed to some extent to both the shallowness and the anharmonicity of the intermetallic interaction potential. The Ag–Ag interaction potentials are found to be attractive only when relativity is accounted for in the calculations