Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

Abstract

Triazolylidenes are a prominent class of mesoionic carbenes (MICs) that are currently widely used in organometallic chemistry. Usually the metal complexes of such ligands are used as homogeneous catalysts even though they have vast potential in other branches of chemistry. We present here three related gold(I) complexes with MIC ligands: a neutral mononuclear chlorido complex [AuCl(MIC)], a cationic mononuclear complex containing two MIC ligands [Au(MIC)2]BF4, and a dicationic digold(I) complex containing two di‐MIC ligands [Au2(κ1,κ1,µ‐di‐MIC)2](BF4)2. The complexes were characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The gold(I) centers are linearly coordinated through either one MIC‐C and chlorido donors or through two MIC‐C donors. The triazolylidenes display a delocalized bonding situation within the ring. Additionally, a short Au–Au distance of about 3 Å is observed for the digold(I) complex. All complexes display reduction steps in their cyclic voltammograms, and these are assigned to the reduction of the MIC ligands, as opposed to the generation of gold(0). The complexes emit at ca. 500 nm, with lifetimes of several microseconds in deoxygenated solutions; the emission intensity and lifetime are strongly decreased by the presence of oxygen, supporting the triplet origin of the emissive state. The present results display the utility of MIC ligands for generating electro‐ and photoactive molecules.

Synthesis and Photophysical Properties of T‐Shaped Coinage‐Metal Complexes

“…A T‐shape geometry is unambiguously shown in the molecular structure obtained for a single crystal of 2 (Figure ); only the third known example of a T‐shaped silver complex . Both the chemical resonance observed for the carbene carbon atom, as well as the carbene carbon‐silver bond lengths fall within range with that reported for known silver(I) triazolylidene complexes, whereas the rigid carbazole backbone deviates from planarity as seen also for rhodium(I) complexes of carbazolide‐pincer ligands …”

“Abnormal” Addition of NHC to a Conjugate Acid of CAAC: Formation of N‐Alkyl‐Substituted CAAC

“…This behavior appeared to be quite general for all kinds of azolium salts. For instance, similar irreversible reduction waves were recently observed for 1,2,3‐triazolium salts, which are precursors to mesoionic carbenes . Thus, substitution at the acidic C−H bonds of the azolium salts is likely to be a good strategy to gain access to stable radicals that are based on such carbene precursors.…”

“…For instance,s imilar irreversible reduction waves were recently ob- served for1 ,2,3-triazolium salts, which are precursors to mesoionic carbenes. [21] Thus, substitution at the acidic CÀHb onds of the azolium salts is likelyt ob eag ood strategy to gain access to stable radicals that are based on such carbene precursors. Even though several redox processes were observed for the free carbene 8,n ow ell-defined electrochemical responsew as detected for this compound in THF (see the Supporting Information, Figure S23).…”

Synthesis of heterobimetallic gold(i) ferrocenyl-substituted 1,2,3-triazol-5-ylidene complexes as potential anticancer agents

“…29 No redox event associated with the gold metal center was observed, consistent also with prior electrochemistry reports on gold(I) ferrocenyl triazolylidene complexes. 42,43 Both complexes only have one redox event on both the CV timescale and in the solvent window, namely the oxidation and reduction of the ferrocenyl substituent (See Fig. S15, ESI).…”