Soichi Sato

Transannular and intermolecular interactions between chalcogen atoms: syntheses and properties of dichalcogena dications and trichalcogena hypervalent dications

Intramolecular (transannular) and intermolecular through-space interactions between chalcogen atoms have been described. This account includes the following three topics. (1) Various types of bis-chalcogenides and their mono-oxides, which have the two chalcogen atoms in close proximity in a molecule, give the dichalcogena dications upon the oxidation with two equivalents of NOBF4 or treatment with one equivalent of triflic anhydride (Tf2O). The stability of the dichalcogena dications increases in the order S<Se<Te. The dichalcogena dications with flexible scaffolds cause dealkylation via an SN1 type reaction to form chalcogenachalcogenonium salts and alkyl cations. (2) The reaction of 2,6-bis[(phenylthio- or phenylseleno)methyl]phenyl phenyl telluride or the corresponding Teoxide with NOBF4 or Tf2O affords the positively-charged hypervalent species, dicationic telluranes. Dicationic telluranes can be prepared by the remote oxidation through π-conjugation. The stable sulfenium cation can be isolated by taking advantage of 2,6-bis[(dimethylamino)methyl]phenyl ligand. (3) The remote oxygen migration and Pummerer reactions of p-bis(methylthio)-aromatic mono-oxides are discussed in light of an intermolecular through-space interaction between sulfur atoms, and a cyclic bis(dithia dication) dimer is proposed as an intermediate.

Reactions of triaryl selenonium salts and diaryl selenoxides with phenyllithium: First detection of tetraaryl, selenuranes [10-SE-4(C4)] by 77SE, 1H, and 13C NMR

First evidence for the formation of tetraaryl selenuranes was presented in the reaction of triphenyl selenonium salt or 2,2′-biphenylylene phenyl selenonium salt with phenyllithium by 77Se, 1H, 13C and CH-COSY NMR studies at low temperature, These selenuranes were also formed in the reactions of the corresponding selenoxides with two equivalents of phenyllithium.

Tetraphenyl sulfurane: first detection as intermediate in the reactions of triphenylsulfonium salt and diphenyl sulfoxide with phenyllithium by low temperature 1H and 13C nmr

Abstract Direct evidence for the formation of tetraphenyl sulfurane was presented in the reactions of triphenylsulfonium hexafluorophosphate and diphenyl sulfoxide with phenyllithium by 1 H, 13 C, and CH-COSY NMR studies at low temperature.

First detection of 2,2′-biphenylylenediphenylsulfurane and -selenurane [10-M-4(C4), M = S, Se] by low temperature NMR experiments and isolation of the tellurane

Formation of 2,2′-biphenylylenediphenylsulfurane and -selenurane was detected in the reactions of 2,2′-biphenylylenephenylchalcogenium compounds with phenyllithium by 1H, 13C, 77Se, and CH-COSY NMR studies at low temperature. Isolation of the tellurane (C) was reported as an example of the tellurane bearing four carbon ligands.

Dynamic NMR studies on the solution-state structure and the pseudorotation of bis(2,2′-biphenylylene)selenurane and tellurane

Abstract Solution-state structures of bis(2,2′-biphenylylene)selenurane ( 1 ) and tellurane ( 2 ) were studied by 1 H and 13 C NMR at low temperature. The first examples of the activation parameters for intramolecular ligand exchange (pseudorotation) of these pentacoordinated group 16 elements bound to four carbon ligands were presented by DNMR experiments. Solution-state structures and activation parameters for pseuodorotation of bis(2,2′-biphenylylene)selenurane ( 1 ) and tellurane ( 2 ) have been studied by variable-temperature NMR experiments.

Kinetic studies on the ligand coupling reactions of tetraphenyl sulfurane, selenurane, and tellurane. Thermal stability for hypervalent chalcogen compounds with four carbon-chalcogen bonds

Abstract Ligand coupling kinetics of tetraphenyl sulfurane, selenurane, and tellurane have been studied by the variable temperature NMR experiments. The first examples of the activation parameters for the ligand coupling (self decomposition and CC bond formation) have been obtained for the reactions at three pentacoordinated chalcogenium centers; S, Se, Te.

New Aspects of Hypervalent Organosulfur Compounds

The chemistry of sulfuranes has developed greatly and has attracted attention of many organic chemists over the past two decades. This work describes the historical background, the development, and the synthesis of sulfuranes and persulfuranes. The concept of hypervalent bonding was introduced by Rundle and Musher; before the pioneering work of Martin and Kapovits on the preparation of sulfuranes, these compounds were considered only to be unstable intermediates or simple transition states in nucleophilic substitution reactions at sulfur atoms. There are many reports of unstable sulfuranes being formed during the substitution reactions of dicoordinated, tricoordinated and even tetracoordinated sulfur atoms with various nucleophiles. However, neither direct nor spectroscopic evidence for the formation of sulfuranes had been reported until in the 1970s, when Martin found methods for syntheses of the stable sulfuranes. Ligand exchange and coupling reactions are typical reactions of tricoordinated sulfur compounds with nucleophiles, and are considered to be diagnostic for the formation of sulfuranes. According to Martin’s definition, stable sulfuranes should contain electronegative substituents to provide the hypervalent bonds. However, quite recently, sulfuranes bearing only carbon substituents have been synthesized. This work describes both the intermediary formation of sulfuranes and stable isolable sulfuranes, together with their chemical behaviors.

Recent progress in hypervalent organochalcogenuranes bearing four carbon ligands

Abstract Tetraphenyl- and 2,2′-biphenylylenediphenylsulfuranes and -selenuranes were detected directly by low-temperature NMR experiments. Bis(2,2′-biphenylylene)sulfurane was first isolated as a stable sulfurane having four carbon ligands. Kinetic studies for the ligand coupling reaction of tetraphenylchalcogen compounds Ph4X (X=S, Se, Te) were monitored by VT - 1 H NMR studies to estimate the activation parameters for these reactions. We also found that the pseudorotations of bis(2,2′-biphenylylene)selenurane and -tellurane take place slowly with respect to the NMR timescale at low temperature. The energy barriers for their pseudorotations were estimated from VT − 13 C NMR studies. Furthermore, theoretical MO studies of chalcogenuranes(IV) bearing four carbon ligands were carried out concerning their structures, Berry pseudorotations, ligand coupling reactions and non-Berry pseudorotations using the tetramethylchalcogenuranes Me4X (X=S, Se, Te).

Generation and Reactions of Hypervalent Organic Selenium and Tellurium Compounds Having Aryl Ligands

Abstract The evidence for the formation of tetraaryl selenuranes as intermediates was presented in the ligand coupling reaction of triaryl-selenonium or diaryl selenoxide with phenyllithium (PhLi) by NMR studies. Triaryl telluranes were also formed as intermediates in the ligand exchange and disproportionation reactions of diaryl tellurides with PhLi.

First preparation of a sulfurane with four carbon–sulfur bonds: synthesis and molecular structure of bis(2,2′-biphenylylene)sulfurane

The first stable pentacoordinated sulfur compound with four carbon–sulfur bonds, bis(2,2′-biphenylylene)sulfurane 1, is prepared and its molecular structure is determined by X-ray crystallographic analysis.