Jean-Yves Thépot

Rhodium complexes of 3,4-di(β-naphthyl)-2,5-diarylcyclopentadienone: indirect detection of slowed naphthyl rotation

Abstract In the solid state, [(acetylacetonate)-3,4-di(β-naphthyl)-2,5-diarylcyclopentadienone]rhodium(I) ( 4a , aryl=phenyl, 4b , aryl= m -xylyl) exist as head-to-tail dimers in which each rhodium is bonded to the γ-carbon of the acetylacetonate ligand in the other half of the molecule. These dimers are also favoured in solution at low temperature, and restricted naphthyl rotation results in the formation of numerous conformers whereby the naphthyls can adopt either proximal or distal orientations. These rotamers can be detected by observation of the 1 H- and 13 C-NMR methyl resonances in the acetylacetonate moiety. Triphenylphosphine cleaves the dimers ( 4a and 4b ) to give the corresponding monomers, (C 4 Ar 2 (naphthyl) 2 CO)Rh(acac)PPh 3 ( 5a and 5b ), and the crystal structure of 5a exhibits a proximal/distal disorder of one naphthyl substituent. The rotamers of 5a and 5b are also present in solution, and the variable-temperature 31 P-NMR spectra yield activation enthalpies of 8.2±0.5 kcal mol −1 for naphthyl rotation in each compound.

Resonant Cavity Gas-Phase Polarimeter

A high-sensitivity polarimeter is demonstrated for application to gas-phase chirality measurement. This device is based on the physics of the eigenstates of a Fabry-Perot cavity, permitting improvement in the sensitivity with respect to the usual polarimeters. Typical measurements of rotations of 50 (±1) × 10(-)(5)° induced by the optical activity of (R)-(+)-limonene and (S)-(-)-limonene in the vapor phase are shown. A noise level corresponding to a rotation of 10(-)(6)° is experimentally demonstrated. Application to the polarimetric monitoring of an enantiomer mixing racemization of limonene in the gas phase is also presented.

A convenient synthesis of bromopentaarylcyclopentadienes containing methyl or fluorine substituents

Abstract The ketones C 5 (3,5-C 6 H 3 Me 2 ) 4 (O) ( 5b ) and C 5 -2,5(3,5-C 6 H 3 Me 2 ) 2 (C 6 H 5 ) 2 (O) ( 5c ) were prepared and characterized. The pentaarylcyclopentadienols C 5 (C 6 H 5 ) 4 (Ar′)(OH) (Ar′=3,5-C 6 H 3 Me 2 , 6a3 ; Ar′=2,4,6-C 6 H 2 Me 3 , 6a5 ; Ar′=3-C 6 H 4 F, 6a6 ; Ar′=3,5-C 6 H 3 F 2 , 6a7 ), C 5 (3,5-C 6 H 3 Me 2 ) 4 (Ar′)(OH) (Ar′=3-C 5 H 4 Me, 6b2 ; 3,5-C 5 H 3 Me 2 , 6b3 ; 3,6-C 5 H 3 Me 2 , 6b4 ; 2,4,6-C 5 H 2 Me 3 , 6b5 ; Ar′=3-C 6 H 4 F, 6a6 ; Ar′=3,5-C 6 H 3 F 2 , 6a7 ; Ar′=2,6-C 6 H 3 F 2 , 6a8 ) were obtained by reaction of the corresponding Ar′Li with the ketones C 5 (C 6 H 5 ) 4 (O) ( 5a ), or C 5 (3,5-C 6 H 3 Me 2 ) 4 (O) ( 5b ). The synthesis and characterization of the bromopentaarylcyclopentadienes C 5 (C 6 H 5 ) 4 (Ar′)(Br) (Ar′=3,5-C 6 H 3 Me 2 , 7a3 ; Ar′=2,4,6-C 6 H 2 Me 3 , 7a5 ) and C 5 (3,5-C 6 H 3 Me 2 ) 4 (Ar′)(Br) (Ar′=3-C 5 H 4 Me, 7b2 ; 3,5-C 5 H 3 Me 2 , 7b3 ; 3,6-C 5 H 3 Me 2 , 7b4 ; 2,4,6-C 5 H 2 Me 3 , 7b5 ; Ar′=3-C 6 H 4 F, 7a6 ; Ar′=3,5-C 6 H 3 F 2 , 7a7 ; Ar′=2,6-C 6 H 3 F 2 , 7a8 ) containing methyl groups or fluorine atoms on the Ar′ rings are reported. The bromopentaarylcyclopentadienes are isolated as a 1:2:2 mixture of three isomers when Ar and Ar′ are different, except when the latter substituent bears two fluorine or two methyl groups in the ortho positions. In these cases the reaction is regiospecific and provides a unique isomer with the di- ortho -substituted arene located in the β-position with respect to the carbon bearing the bromine atom.

S-alkylation of α-thioether iron compounds by [Ph3C]+ and [Fe(η-C5Me5)(CO)2(CH2)]+

Treatment of the thiomethyl complexes [Fe(η-C5Me5)(CO)2(CH2SR)](R = Me or Ph) with [Ph3C]+ or [Fe(η-C5Me5)(CO)2(CH2)]+ results in S-alkylation, affording the sulphonium salts [Fe(η-C5Me5)(CO)2{CH2S(R)CPh3}]+ and [{Fe(η-C5Me5)(CO)2CH2}2SR}]+ respectively; the former show promise as agents for methylene transfer to alkenes.