ABSTRACT
A new one-pot solvent-less reaction to convert benzylic, allylic, ferrocenyl or tertiary alcohols into S-thioesters, bench-stable and less odorous precursors of the corresponding thiols, which is based on reactions in neat thioacetic acid in the presence of tetrafluoroboric acid, is presented. Reaction monitoring by NMR and GC of the benzyl alcohol conversion indicated the intermediate formation of benzyl acetate and benzyl thionoacetate (PhCH2 OC(S)CH3 ) prior to the slower conversion to the final S-benzyl thioacetate product. Increasing the HBF4 concentration enhanced the reaction rate, giving good to excellent yield (up to 99 %) for a large scope of alcohols. Control experiments, with support of DFT calculations, have revealed a thermodynamically favorable, though requiring HBF4 -activation, disproportionation of CH3 C(O)SH to CH3 C(O)OH and CH3 C(S)SH, the latter immediately decomposing to H2 S and (MeC)4 S6 but also generating the hitherto unreported [MeC(O)C(Me)S]2 (µ-S)2 . Kinetic investigations demonstrated that the rate of benzyl alcohol conversion is second-order in [PhCH2 OH] and second order in [HBF4 ], while the rate of conversion of the benzyl acetate intermediate to S-benzyl thioacetate is second order in [PhCOOMe] and fourth order in [HBF4 ]. The DFT calculations rationalize the need to two alcohol molecules and two protons to generate the reactive benzyl cation.
ABSTRACT
As part of our interest in the synthesis and catalytic applications of chiral (diphenylphosphanyl)ferrocene ligands, we designed a number of P,N-containing ligands for use in asymmetric transfer hydrogenation (ATH). During the synthetic procedure to obtain rac-1-[(N,4-dimethylbenzenesulfonamido)methyl]-2-(diphenylphosphanyl)ferrocene, the title compound, [Fe(C5H5)(C26H25NO2PS)]0.55 · [Fe(C5H5)(C26H25NO3PS)]0.45, was obtained as a by-product. It is composed of a ferrocene group disubstituted by a partially oxidized diphenylphosphanyl group, as confirmed by (31)P NMR analysis, and an (N,4-dimethylbenzenesulfonamido)methyl substituent. Owing to the partially oxidized diphenylphosphanyl group, it is best to view the crystal as being composed of a mixture of non-oxidized and oxidized phosphane, so it can be regarded as a cocrystal. It is also a racemate. To the best of our knowledge, the P=O distance [1.344 (4) Å] is the shortest observed for related (diphenylphosphoryl)ferrocene compounds. The packing is stabilized by weak C-H...O interactions, forming R2(2)(10) hydrogen-bonding motifs, which build up a chain along the c axis.
Subject(s)
Coordination Complexes/chemistry , Ferrous Compounds/chemistry , Crystallography, X-Ray , Hydrogen Bonding , Ligands , Metallocenes , Molecular StructureABSTRACT
Following our continuing inter-est in developing new chiral phosphine-containing ferrocenyl ligands, we synthesized the title compound, [Fe(C(5)H(5))(C(26)H(24)OPS)], in which there are two nearly identical mol-ecules in the asymmetric unit. The conformation of the cyclo-penta-dienyl (Cp) rings in each ferrocenyl group are inter-mediate between eclipsed and staggered, with twist angles of 16.6â (2) and 8.9â (2)°. The protecting S atom is located endo with respect to the substituted Cp ring. In the crystal, mol-ecules are connected through inter-molecular C-Hâ¯π inter-actions.
