Rhodium phosphine-π-arene intermediates in the hydroamination of alkenes.

A detailed mechanistic study of the intramolecular hydroamination of alkenes with amines catalyzed by rhodium complexes of a biaryldialkylphosphine is reported. The active catalyst is shown to contain the phosphine ligand bound in a κ(1), η(6) form in which the arene is π-bound to rhodium. Addition of deuterated amine to an internal olefin showed that the reaction occurs by trans addition of the N-H bond across the C═C bond, and this stereochemistry implies that the reaction occurs by nucleophilic attack of the amine on a coordinated alkene. Indeed, the cationic rhodium fragment binds the alkene over the secondary amine, and the olefin complex was shown to be the catalyst resting state. The reaction was zero-order in substrate, when the concentration of olefin was high, and a primary isotope effect was observed. The primary isotope effect, in combination with the observation of the alkene complex as the resting state, implies that nucleophilic attack of the amine on the alkene is reversible and is followed by turnover-limiting protonation. This mechanism constitutes an unusual pathway for rhodium-catalyzed additions to alkenes and is more closely related to the mechanism for palladium-catalyzed addition of amide N-H bonds to alkenes.

Pentacoordinate organoantimony compounds that isomerize by turnstile rotation.

Two stereoisomers of pentacoordinate antimony compounds (stiboranes) with a new rigid tridentate ligand were synthesized, and the isomerization was found to proceed by the turnstile rotation (TR) mechanism with the tridentate ligand as a trio and the two monodentate ligands as a pair.

First isolation and kinetic study of hypervalent 10-As-5 organoarsenic compounds with a C-apical, O-equatorial configuration.

Hypervalent organoarsenic compounds violating the apicophilicity concept were isolated for the first time, and the energy of isomerization of these arsoranes to the more stable stereoisomers appeared to be lower than that of the phosphorus analogues based on the kinetic studies.

Synthesis and application of a bidentate ligand based on decafluoro-3-phenyl-3-pentanol: steric effect of pentafluoroethyl groups on the stereomutation of O-equatorial C-apical spirophosphoranes.

1,1,1,2,2,4,4,5,5,5-Decafluoro-3-phenyl-3-pentanol was prepared by a Cannizzaro-type disproportionation reaction, and the dimetallated compound was used as a bidentate ligand, which is bulkier than the Martin ligand (1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol). A P-H spirophosphorane was synthesized by utilizing the new bidentate ligand, and the structure of the product was essentially the same as that of the P-H phosphorane with Martin ligands. Phosphoranes that exhibit reversed apicophilicity (O-equatorial) were also synthesized and could be converted into the corresponding stable stereoisomers (O-apical). The crystal structures of O-equatorial phosphoranes and the O-apical isomers were slightly affected by the steric repulsion of pentafluoroethyl groups. Kinetic measurements revealed that the stereomutation of O-equatorial methylphosphorane to the O-apical isomer was slowed. The activation enthalpy for the stereomutation of the former to the latter was higher than that of the phosphorane with Martin ligands by 5.1 kcal mol(-1).