Multivalent, Sulfur‐Rich PyBox Asterisk Ligands in Asymmetric Metal Catalysis

Abstract

Multivalent PyBox asterisk ligand 1 and monovalent ligand 2 are reported. The innovative feature in 1 is a sulfur‐rich persulfurated benzene core as a template joining six PyBox units in close proximity. An efficient persulfuration of C6Cl6 with p‐methoxybenzenethiol (95 %, >99 % per C–S bond) and deprotection led to hexaphenol 4. Six O‐arylations of 4 with Cl‐PyBox 3 (94 %, >99 % per C–O bond) provided 1. The electronic delocalization of 1 and 2 was analyzed by UV/Vis spectroscopy and cyclic voltammetry. PyBox ligands 1 and 2 were successfully used for Rh‐catalyzed hydrosilylation of acetophenone, in spite of competitive bindings from six proximal sulfur atoms. The concept of multivalency and the presence of donating and oxidizable sulfur atoms in asymmetric metal catalysis were tested. The reactivities and the enantiocatalytic behavior of 1 and 2 with varying rhodium content were determined. Lability of the Rh complexes under certain conditions, was demonstrated by some crossover experiments with other PyBox ligands. Conformational and competitive metal binding studies of 1 with the aid of molecular modeling (GenMol™) helped to explain the results. This work suggests new directions for simple multivalent ligands in metal‐mediated catalysis.

Turn-on Phosphorescence by Metal Coordination to a Multivalent Terpyridine Ligand: A New Paradigm for Luminescent Sensors

“…Although the structure is represented on a plane, it is not realistic. It is expected that a low-energy conformer would position the tpy arms in a 3D radial extension, in an alternating up and down pattern from the plane of the central benzene core …”

An overview on synthetic strategies for the construction of star-shaped molecules

“…Complex 195 showed a much weaker lowlying emission. In general, the Pt(II) complexes 195 displayed lower aggregation with a controllable excimer emission.Aubert et al100 described the synthesis of star shaped compound with (phenylthio)benzene core 198 in 94% overall yield, via coupling of (4S,4 0 S)-2,2 0 -(4-chloropyridine-2,6diyl)bis(4-isopropyl-4,5-dihydrooxazole) 197 with hexakis(4-hydroxyphenylthio)benzene 196 in the presence of Cs 2 CO 3 as a base (Scheme 49). Star compound 198 acted as a catalyst for Rh-catalyzed hydrosilylation of acetophenone.…”

Multiwavelength Anti-Kasha’s Rule Emission on Self-Assembly of Azulene-Functionalized Persulfurated Arene

“…Compounds 2 and 3 were synthesized according to the reported procedures. 26,36 Preparation of the Solid Films. Compounds 1 and 2 (20 mg) and PMMA (200 mg) were dissolved in 1 mL of CHCl 3 .…”