Complexes of copper with 1,4-diphenyl, 1,4-dimesityl, and 1-(2,6-diisopropylphenyl)-4-(3,5-xylyl)-1,2,3-triazol-5-ylidene (abnormal NHC = N-heterocyclic carbene) were prepared by consecutive treatment of the corresponding azolium salts with silver oxide and copper chloride. The new CuCl(aNHC) complexes efficiently catalyzed click reactions of azides with alkynes to give 1,4-substituted 1,2,3-triazoles in excellent yields at room temperature with short reaction times. CuCl(TPh) was particularly effective for the reaction between sterically hindered azides and alkynes.

As chiral ligands for transition metal complex-catalyzed asymmetric reactions, a variety of novel chiral ferrocenyl chalcogen compounds, which possess planar chirality due to the 1,2-unsymmetrically disubstituted ferrocene structure, have been prepared from chiral ferrocenes. There are seven diferrocenyl dichalcogenides (4-10), nine alkyl or aryl ferrocenyl chalcogenides (11)(12)(13)(14)(15)(16)(17)(18)(19), two bis(ferrocenylseleno)alkanes (20 and 21), two 1-(phenylchalcogeno)-1-[2-(diphenylphosphino)ferrocenyl]ethanes (22 and 24), and two 1-(phenylchalcogeno)-1-[1′,2-bis(diphenylphosphino)ferrocenyl]ethanes (23 and 25). 2,3-O,O′-Isopropylidene-2,3-dihydroxy-1,4-bis(phenylchalcogeno)butanes (26-28) are also synthesized. The Rh(I) complex-catalyzed hydrosilylation of ketones with diphenylsilane in the presence of these chiral ligands including the reported [R,S;R,S]-bis[2-[1-(dimethylamino)ethyl]ferrocenyl] dichalcogenides (1-3), followed by hydrolysis with dilute HCl, affords the corresponding chiral alcohols (R-configuration) in moderate to quantitative yield with up to 88% enantiomeric excess (ee). Similar treatment of acetophenone in the presence of diferrocenyl dichalcogenides (1, 2, 3, and 10) and a catalytic amount of Ir(I) complex gives chiral 1-phenylethanol of the opposite configuration (S) compared with the Rh case in high yield with up to 23% ee. The new complex prepared from a cationic rhodium compound and the diferrocenyl diselenide (2) shows an activity for asymmetric hydrosilylation of acetophenone to afford 1-phenylethanol in 60% chemical yield with 60% ee. Asymmetric hydrosilylation of imines and asymmetric hydrogenation of an enamide also proceed smoothly using the Rh(I)-diselenide (2) catalytic system to give the corresponding sec-amines and amide with up to 53% and 69% ee, respectively. A catalytic cycle involving the formation of tetracoordinated rhodium(I)-dichalcogenide complex (two Se and two N atoms to one Rh) followed by oxidative addition of the Si-H bond to Rh(I) and carbonyl addition to the produced rhodium(III) hydride complex is proposed for hydrosilylation of ketones.

A series of allyl 1,2,3-triazol-5-ylidene (tzNHC) palladium complexes was prepared, and the structures of the complexes were fully characterized by NMR and X-ray diffraction analyses. The donor properties of these ligands were evaluated by studying the vibrational spectra of their carbonyliridium complexes and their X-ray photoelectron spectra. These evaluations showed that the structures of the tzNHC palladium complexes are almost identical to those of the corresponding imidazole carbene palladium complexes, and that the tzNHC ligands have stronger donor properties than the [a] 1387 imidazole carbene ligands. The relationship between catalytic activity and structure was examined by carrying out a room-temperature Suzuki-Miyaura coupling reaction, and the cinnamylpalladium complex bearing 1,4-bis(2,6-diisopropylphenyl)-3-methyl-1,2,3-triazol-5-ylidene (TPr) was found to be the most active catalyst. (cinnamyl)(TPr)PdCl showed high activity in the room-temperature reaction performed with aryl chlorides regardless of the electronic and steric properties of the substituents, and was effective in reactions with sterically crowded arylboronic acids.www.eurjic.org 1388 Scheme 1. Synthesis of (R-allyl)(tzNHC)PdCl complexes.

The samarium(II) iodide mediated asymmetric Reformatsky-type reaction of chiral 3-bromoacetyl-2-oxazolidinones with various aldehydes was studied. A series of chiral 4-substituted 2-oxazolidinones 1-3 and 5,5-disubstituted "SuperQuat" oxazolidinones 4-5 were employed as chiral auxiliaries of the alpha-bromoacetic acid. The reaction of 1 with various aldehydes gave the alpha-unbranched beta-hydroxy carboximides in good yields with high diastereomeric excess values (up to >99% de). The majority of the reaction product derived from 5,5-diphenyl SuperQuat 5 were highly crystallinity; a single recrystallization yielding a diastereomerically pure product with the other diastereomer not detectable by spectroscopic methods. The absolute configurations of the beta-hydroxy carboximides were determined by signs of optical rotations of the corresponding known ethyl esters referring to the literature values. Hydrolytic cleavage of the appended of beta-hydroxy moieties from the auxiliary SuperQuats was readily achieved under mild conditions using lithium hydroxide; the corresponding carboxylic acids and the returned SuperQuats were obtained in good yields without any evidence of racemization. The first step of the reaction is the reduction of the alpha-bromo group to produce the samarium enolate, which adds to an aldehyde. The absolute configuration of the adduct (7i) derive from benzaldehyde was found to be R, with the samarium enolate favoring the transition state predicted from chelation control of the reagent; this is in analogy to the discussion that has been used for the corresponding titanium enolate. The stereochemistry of the reaction may be explained by incorporating the Nerz-Stormes-Thornton chair transition structure model.