Chikako Takayama

Structure and electrochemical behavior of alkylidene-bridged metalladithiolene complexes (metals: cobalt and rhodium): bond cleavage of alkylidene moieties by electrochemical redox reactions

Abstract We prepared thirteen alkylidene-bridged metalladithiolene complexes [(Cp)M(S 2 C 2 Y 2 )(CR 1 R 2 )] (M=Co and Rh) including two novel ones. We succeeded in X-ray structure analyses of six alkylidene-bridged dithiolene complexes together with three original dithiolene complexes. The Co–S bond distance of the dithiolene ring becomes long due to the formation of alkylidene-bridged complexes. Investigation of the redox process in a series of those alkylidene-bridged metalladithiolene complexes by cyclic voltammetry reveals a large dependence for the redox potentials on the nature of M, Y and R. In the reduction, the radical anion formed in the initial process eliminates the alkylidene moiety slowly to give the radical anion of the original dithiolene complexes. One-electron oxidation gives detectable cation radicals due to some structural change, but when these cation radicals are re-reduced, they rapidly eliminate the bridging moieties to give original dithiolene complexes. We could succeed in detecting the intermediary species in the elimination process. This is one of the very rare and important successes in the trapping of the intermediate in the elimination mechanism. We conclude that both reduction and oxidation weaken the M–C and S–C bonds in the M–S–C triangle ring to regenerate the original metalladithiolene complexes.

Formation and reaction of three-membered cobaltathiaziridine ring in (η5-cyclopentadienyl)(substituted imido-κN-thio-κS-ethene-2-thiolato-κS)cobalt(III). Ring opening and closure and transfer of imido group

Abstract Three-membered cobaltathiaziridine rings are formed in the reactions of [CpCo{S 2 C 2 (COOMe) 2 }] either with some azides (RN 3 : p -toluenesulfonyl azide (TsN 3 ), methanesulfonyl azide (MsN 3 ), and ethyl azidoformate (EtOOCN 3 )) or with N -(phenyliodonio)- p -toluenesulfonamidate (PhI=NTs) to afford imido-bridged complexes, [CpCo{S 2 C 2 (COOMe) 2 }(NR)]. The ring undergoes unique ring opening and reforming reactions. Hydrogen chloride brings about the cleavage of the CoN bond to give S -iminodithiolatocobalt(III) complexes [Cp(Cl)Co{S(NR)C(COOMe)C(COOMe)S)}], which very easily regenerates the cobaltathiaziridine ring on treatment with bases, such as pyridine and even with the very weak base, water. The reaction with triphenylphosphine at room temperature results in the ring opening to give an ylide. The heating of a benzene solution of the ylide at 80°C (under reflux) gives a product in which a sulfonylimido moiety migrates to a carbon atom of the cyclopentadienyl ring. The reduction halfwave potential values of the imido-bridged complexes depend on the substituent of bridging moiety. The CV of sulfonylimido-bridged complex shows one-electron two-step reduction processes. We found that the reductant of the original complex is regenerated not by the first reduction, but by the second reduction according to CV and OTTLE measurements.

Imido-transfer reactions to carbonyl moiety induced by the reactions of imido-bridged cobaltadithiolene complexes with trivalent phosphorus halides

Abstract The reactions of the imido-bridged cobaltadithiolene complexes [CpCo{S2C2(COOMe)2}(NR)] (R=Ts, Ms) with PCl3 led to the imido-transfer reactions to the carbonyl moiety, and these reactions gave the novel imine complexes [CpCo{S2C2(COOMe)(CNROMe)}]. In the case of PI3, another imido-transfer reaction to carbonyl moiety occurred and the novel amide complexes [CpCo{S2C2(COOMe)(CONHR)}] were formed. PBr3 showed an intermediate reactivity value in between that of PCl3 and that of PI3. Both novel imido-transfer reactions were caused by intermolecular reactions, these reaction processes were determined by crossover experiments.

Reactions of cobaltadithiolene complexes with aryl azides: Formations of metal chelate rings containing nitrogen atoms by substitution reactions via nitrene

Abstract In the reactions of cobaltadithiolene complexes [CpCo(S 2 C 2 Z 2 )] (Z=CN, COOMe, Ph, Me) with aryl azides, two types of substitution reactions occurred. One is the replacements of the sulfur of cobaltadithiolene by arylimido groups and the other is the replacements of the SCZCZ moiety of cobaltadithiolene. The product of latter reaction was also formed by the reactions of the metal cluster complex [Cp 4 Co 4 S 6 ] with aryl azides. The azides with electron-donating substituents gave these products in higher yields than those with electron-withdrawing substituents. In these reactions, arylnitrenes as intermediates were predictable. The reactions of [CpCo(dmit)] (dmit=C 3 S 5 ) with phenyl azide and tosyl azide led to the replacements of the terminal sulfur (CS) of the dmit ligand by imido groups to give novel imine complexes [CpCo(S 2 C 2 S 2 CNR)] (R=Ph, Ts).

Electrochemistry of [(Cp)M(S2C2R2)]-Type Metalladithiolene Complexes and their Derivatives

Abstract Our studies on the electrochemical properties and electrochemical reactions of the [(Cp)M(S2C2R1R2)]-type metalladithiolene complexes (M = Co and Rh) and their derivatives are reviewed. We discuss on (1) the dependences of redox potentials of the metalladichalcogenolene complexes on the components (metal, chalcogen, and substituents) of the complexes, (1′) the electrochemical properties of dinuclear metalladithiolene complexes, (2) the relationship between redox potentials and the reactions of the metalladithiolenes (addition of phosphorus compounds and catalysis for isomerization of quadricyclane to norbornadiene), and (3) the reactions of some addition products of the metalladithiolenes (phosphine or phosphite adducts, alkylidene adducts, and “three-component-adducts” among [(Cp)M(S2C2R2)]-type metalladithiolene, alkylidene, and hydrogen halide, elemental halogen, phosphine, or phosphite) induced by electrochemical reduction or oxidation. These studies have been done by means of ESR and UV-visible spectral measurement by the use of optically transparent thin layer electrodes (OTTLE) as well as by means of the electrochemical measurements.