Synthesis of a Rhenium(VII) Trioxo Complex Supported by a Triphyrin Ligand: Oxygenation Chemistry and Deposition on Au(111)

Abstract

A new [14]triphyrin(2.1.1) ligand (TriPEt, 1) is synthesized, and its rhenium(I) and rhenium(VII) complexes [Re(TriPEt)(CO)₃] (2) and [ReO₃(TriPEt)] (3) are characterized in the bulk and on Au(111) surfaces. Self-assembled monolayers on Au(111) are prepared via wet-chemical deposition. IRRAS, supported by DFT, reveals a shift of the carbonyl stretching modes to higher wavenumbers, indicating an electron-withdrawing effect of the gold surface. On the other hand, XPS measurements of a monolayer of 3 show a reduction to Re(VI). A tilted adsorption geometry is observed, with reduced tilt compared to previous systems due to a shortening of the alkyl chains. Catalytic studies show that 3 promotes oxygen-transfer reactions, efficiently oxidizing triphenylphosphine with N-oxides and, more slowly, with molecular oxygen. While 3 is inactive for TBHP-mediated epoxidation of cyclooctene, irradiation in the presence of cyclooctene and oxygen leads to cyclooct-2-ene-hydroperoxide, indicating photooxygenation activity attributable to the complex, as the free ligand 1 decomposes under irradiation.