Catalytic ring-closing reactions of gold compounds containing bis(phosphino)ferrocene ligands.

The efficiency of various gold compounds containing bis(phosphino)ferrocene ligands for catalyzing ring-closing reactions was examined. Six commercially available bis(phosphino)ferrocene ligands: 1,1′-bis(di tert -butylphosphino)ferrocene (dtbpf), 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,1′-bis(dicylohexylphosphino)ferrocene (dcpf), 1,1′-bis(di iso -propylphosphino)ferrocene (dippf), 1-diphenylphosphino-1′-di- tert -butylphosphinoferrocene (dppdtbpf) and 1,1′-bis(5-methyl-2-furanylphosphino)ferrocene (dfurpf) were employed in this study. In addition to the previously reported [Au 2 Cl 2 (μ-PP)] (PP = dtbpf, dppf, dcpf, dippf or dppdtbpf) compounds, [Au 2 Cl 2 (μ-dfurpf)] was synthesized and characterized by NMR spectroscopy, cyclic voltammetry and X-ray crystallography. All of these gold compounds react with Na[BArF 24 ] (BArF 24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) to remove a chloride and yield the cationic monochlorides, [Au 2 (μ-Cl)(μ-PP)]+. The effectiveness of the [Au 2 Cl 2 (μ-PP)] and [Au 2 (μ-Cl)(μ-PP)][BArF 24 ], either pre-formed or generated in situ , compounds for the catalytic intramolecular alkyne hydroalkoxylation of (Z)-3-methylpent-2-en-4-yn-1-ol was examined in CDCl 3 and toluene-d 8. The ring-closing of N -(prop-2-yn-1-yl)benzamide was also examined and was efficiently carried out in toluene-d 8 using [Au 2 (μ-Cl)(μ-PP)][BArF 24 ] (PP = dtbpf, dppf, dcpf, dippf, dppdtbpf or dfurpf). In addition, [Au 2 Cl 2 (μ-dppe)] and [Au 2 (μ-Cl)(μ-dppe)][BArF 24 ] were examined as catalysts for these ring-closing reactions in order to determine if the ferrocene backbone of the bis(phosphino)ferrocene ligands was important for catalysis. For several ring-closing reactions, catalytically inactive [Au 2 Cl 2 (bis(phosphino)ferrocene)] compounds were activated by the addition of Na[BArF 24 ] (BArF 24 = [B(3,5-C 6 H 3 (CF 3) 2) 4 ]-) to give [Au 2 (μ-Cl)(bis(phosphino)ferrocene)][BArF 24 ]. The activated compound were generally good catalysts, and the substituents on the phosphorus atoms influence the effectiveness of the catalysts. Image 1 • Activation of [Au 2 Cl 2 (PP)] (PP = bis(phosphino)ferrocene) by Na[B(3,5-C 6 H 3 (CF 3) 2) 4 ]-. • [Au 2 (μ-Cl)(PP)][B(3,5-C 6 H 3 (CF 3) 2) 4 ] catalysis of several ring-closing reactions. • [Au 2 Cl 2 (dfurpf)] (dfurpf = 1,1′-bis(5-methyl-2-furanylphosphino)ferrocene) structure. • Electrochemistry of [Au 2 Cl 2 (PP)] compounds. [ABSTRACT FROM AUTHOR]