Stereospecific Syntheses and Structures of Planar Chiral Bidentate η5:κS-Indenyl-Sulfanyl and -Sulfinyl Complexes of Rhodium(III)

Axially chiral rac-1-(2-methyl-1H-inden-3-yl)-2-(methylsulfanyl)­naphthalene (rac-3) was synthesized from methyl 2-(methylsulfanyl)-1-naphthoate through reaction with the di-Grignard reagent derived from 1-bromo-2-(2-bromopropyl)­benzene, followed by acid-catalyzed dehydration of the intermediate indanol. Oxidation of rac-3 with m-CPBA gave the diastereomeric sulfoxides (aR*,RS*)-5 and (aR*,SS*)-6, with the relative configuration of 5 established using single-crystal X-ray diffraction. The dichloro­[η5:κS-indenyl-sulfanyl and -sulfinyl]rhodium complexes rac-4, (pR*,SS*)-7, and (pR*,RS*)-8 were synthesized through reaction of the ligands rac-3, (aR*,RS*)-5, and (aR*,SS*)-6, respectively, with rhodium trichloride in 9:1 methanol/water solution heated under reflux. The use of water as a cosolvent was found to be critical for obtaining good yields in the complexation reactions. Solid-state structures for the racemic rhodium complexes were determined through single-crystal X-ray diffraction. The enantiomers of the ligands 3, 5, and 6 were obtained in high enantiopurity through subjecting rac-3 to a series of Kagan asymmetric sulfoxidation, deoxygenation, and resulfoxidation reactions. The enantiomeric relationship of the rhodium complexes derived from the enantio-enriched ligands was confirmed by CD spectroscopy, and the high enantiopurity of the complexes established by 1H NMR analysis using the chiral shift reagent Eu­(hfc)3. The absolute configurations of the nonracemic ligands and rhodium complexes were established by a single-crystal X-ray diffraction determination of the solid-state structure of (pS,SS)-8, with the Flack parameter refining to 0.00(2).