Synthesis and Catalytic Benefits of Tetranuclear Gold(I) Complexes with a C₄-Symmetric Tetratriazol-5-ylidene

Abstract

The facile preparation of a C 4 -symmteric tetratriazolium salt and its subsequent metalation to generate a series of tetranuclear mesoionic carbene gold(I) complexes is presented. The complete structural characterization of the metallic carbenes and the benefits of cooperative catalysis in the processes of hydroamination and hydrohydrazination of terminal alkynes are discussed.

Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights

“…On the other hand, we also observed a significantly higher catalytic activity for the complex bearing a propylene bridge between the NHC units; we know from previous investigations that this bridge allows the gold centers to come in close proximity [96], hence we speculate that in this case a cooperative reaction mechanism can be present to some extent, in which one gold center in a dinuclear complex coordinates the alkyne and the other one coordinates the amine, subsequently directing its attack to the coordinated alkyne. Analogous observations have been made by other groups in studies on polynuclear gold(I) complexes [97]. Apparently, a similar mechanism is instead not operative in the case of alkyne hydroalkoxylation, where we record similar activity irrespective of the length of the bridge [51]; this obviously correlates with the much lower tendency of an alcohol substrate to coordinate to gold.…”

Triple the fun: tris(ferrocenyl)arene-based gold(i) complexes for redox-switchable catalysis

“…Notably, [1c(Au) 3 ] does not show aurophilic interactions [83][84][85] or close ferrocene/metal contacts 86 in the solid state (for M/M distances see Table 2), setting it apart from related structures regularly displaying aurophilic interactions (Table S7 †). In the context of cooperative effects operating in multimetallic catalysis, 49,52,[87][88][89][90] [1c(Au) 3 ] thus falls short of the proximity criterion formulated by Feringa as the gold/gold separation exceeds 6Å. 49 Yet, owing to the exibility of the ligand backbone, gold/gold distances in solution might well become much closer.…”

“…This mirrors results from Mendoza-Espinosa and co-workers who have observed a similar effect in comparing tetranuclear mesoionic carbene gold(I) halide complexes and their mononuclear analogues in the hydroamination and hydrohydrazination of terminal alkynes. 90 Peris and co-workers found a less prominent cooperative effect for the gold(I)-catalysed hydroamination of phenylacetylene using a trinuclear gold(I) chloride complex with a triphenylene-based tris(N-heterocyclic carbene) ligand. 53 Contrastingly, an anti-cooperative effect was found when [1a(Au) 3 ] and 7 were activated by halide abstraction (Fig.…”

Efficient One-Pot, Two-Component Modular Synthesis of 3,5-Disubstituted Pyrazoles

“…All reagents, ketones, aldehydes, and solvents were purchased from commercial suppliers and used without purification unless stated otherwise. Hydrazones 2 , 15 13 , 16 14 , 17 15 , 18 and 27 (19) were prepared using literature procedures.…”

“…Crystals for X-ray diffraction studies were obtained by crystallization in 20% EtOAc–hexane, 304 mg, 92%, mp 201–203 °C (lit. : 19 202–204 °C). 1 H NMR (DMSO- d 6 , 500 MHz): δ 13.41 (s, 1H), 7.89 (bs, 2H), 7.84 (bs, 2H), 7.45 (bs, 4H), 7.33 (bs, 2H), 7.19 (s, 1H).…”