Akira Sugimori

An “adduct” between CpRh(S2C2Z2) and ZCCZ (Z= COOCH3) as an intermediate in CpRhI-catalyzed synthesis of tetramethyl-2,3,4,5-thiophenetetracarboxylate from elemental sulfur and ZCCZ

A novel rhodiadithiolene complex, η5-cyclopentadienyl(1,2-dicarbomethoxy-1,2-ethylenedithiolato-S,S)rhodium, CpRh(S2C2Z2), which is formed by the reaction of CpRh(COD) with elemental sulfur (S8) and ZCCZ (Z = COOCH3; DMAD = dimethyl acetylenedicarboxylate) reacts further with DMAD to form a 11 adduct between CpRh(S2C2Z2) and DMAD. This adduct which upon pyrolysis gives 2,3,4,5-tetramethylthiophenetetracarboxylate (TTME) is a key intermediate for the synthesis of TTME in the reaction of S8 and DMAD catalyzed by CpRh(COD).

Reactions of dithiolenes with diazo compounds : cycloaddition and dissociation of alkylidene groups

Abstract 1,2-Ethylenedithiolatometal complexes CpM(S 2 C 2 R 1 R 2 ) (Cp  η 5 -C 5 H 5 ; M  Co, Rh; R 1 , R 2  CO 2 Me, Ph, H, CN) ( 1a–h ) react with diazo compounds N 2 CR 3 R 4 (R 3 , R 4  H, Ph, CO 2 Et, CO 2 Me) to yield 1 : 1 alkylidene-adducts CpM(S 2 C 2 R 1 R 2 (CR 3 R 4 ( 2–18 ) containing a CMS three-membered ring, with the evolution of N 2 . Highly regioselective cycloaddition is observed in the reactions of unsymmetrical complexes 1f (M  Co, R 1  H, R 2  CO 2 ME) and 1g (M  Rh, R 1  H, R 2  CO 2 Me). The reaction of 1h (M  Co, R 1  H, R 2  Ph) with N 2 CH 2 gives two stereoisomers in the ratio of 35:22. The reaction of the alkyne-adduct CpRh{S 2 C 2 (CO 2 Me) 2 }{C 2 (CO 2 Me) 2 } with N 2 CH 2 gives methylene-adduct 6 (M  Rh, R 1  R 2  CO 2 Me, R 3  R 4  H). The crystal and molecular structure of adduct 15 (M  Co, R 1  R 3  H, R 2  CO 2 Me, R 4  CO 2 Et) has been determined; the five-membered dithiolene ring is planar, and the plane of the CCOS three-membered ring is almost perpendicular to the dithiolene ring. 1,2-Benzenedithiolatometal complexes CpM(S 2 C 6 R 5 2 R 6 2 )(M  Co, Rh; R 5 , R 6  H, Cl) ( 1i–l )also react with diazo compounds N 2 CR 3 R 4 (R 3 , R 4  H, CO 2 Et, CO 2 Me) to yield alkylidene-adducts CpM(S 2 C 6 R 5 2 R 6 2 )(CR 3 R 4 ) ( 19–23 ). Thermal dissociations of adducts 2 (M  Co, R 1  R 2  CO 2 Me, R 3  R 4  H) and 3 (M  Co, R 1  R 2  Ph, R 3  R 4  H) in cyclohexene give the corresponding parent complexes ( 1a : M  Co, R 1  R 2  CO 2 Me; and 1b ; M Co, R 1  R 2  Ph) and cyclohexene derivatives. Adduct 3 undergoes photodissociation to give the parent complex 1b . A possible reaction mechanism for the cycloaddition is suggested and 1 H and 13 C NMR data of the alkylidene-adducts are also reported.

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.

Adduct between quadricyclane and (η5-cyclopentadienyl)(1,2-benzenedithiolato)cobalt(III): formation and structure

The reaction of (η5-cyclopentadienyl)(1,2-benzenedithiolato)cobalt(III) (1) in quadricyclane (Q) at 90°C gives 1:1 adducts of 1 and Q. The main adduct (40% yield) has a unique structure, in which the 5-and 7-positions of norbornene are bonded to Co and S of 1. A mechanism of the formation of the adduct (by the use of deuterium-labeled Q), including a skeletal rearrangement of Q, is proposed.

Formation, Structure, spectra, and reactivity of the adduct between (η5-Cyclopentadienyl)(1,2-dimethoxycarbonyl-1,2-ethylenedithiolato) rhodium(III) and Dimethyl acetylenedicarboxylate

A dithiolatorhodium complex [Rh(Cp)(S2C2Z2)] (2, ZCOOMe) reacts with dimethyl acetylenedicarboxylate (DMAD) to give a 1:1 adduct (3) in 85% yield. The same adduct is obtained in a prolonged reaction of [Rh(Cp)(cod)] (1) with Sg and DMAD in 39% yield. In the adduct, DMAD adds between Rh and S. The adduct has been characterized by spectroscopic and by X-ray diffraction techniques. Red-brown crystals of the adduct are triclinic P1, with a = 11.789(4), b = 10.789(3), c = 7.960(1) A, α = 92.33(2), β = 94.07(2), γ = 101.51(2)°, and Dc = 1.736(calcd) g cm−1 for Z = 2. Least-squares refinement gives a final conventional R value of 0.028 for 4091 independent observed reflections. The adduct has a piano-stool structure consisting of a four-memebered ring of and a five-membered ring of rhodiadithiolene. The adduct is pyrolyzed to afford the decomposition product, tetramethyl 2,3,4,5-thiophenetetracarboxylate (TTME), together with a dissociation product, [Rh(Cp)(S2C2Z2)] (2). Adduct 3 is also photochemically dissociated to regenerate [Rh(Cp)(S2C2Z2)] 2.

Formation constants of some phosphine and phosphite adducts of (η5-cyclopentadienyl) (substituted 1,2-ethylenedichalcogenolato) cobalt(III) complexes and their 1H, 13C and 31P NMR spectra

The formation constants of the phosphine and phosphite adducts of several (η5-cyclopentadienyl) (substituted 1,2-ethylenedithiolato) cobalt(III) complexes in acetonitrile were determined spectrophotometrically. The complexes with more electron-withdrawing substituents on the ditholate ligand form more stable adducts. The NMR chemical shifts (1H, 13C and 31P) of the complexes, phosphines, phosphites and adducts were measured in CDCl3. The shifts were changed on adduct formation. These changes indicate that the phosphines act as σ-donors and the phosphites as π-acceptors and that the cobaltadithiolene ring, which is aromatic in the unbound complex, becomes olefinic in the adduct.

Electro-oxidative and electro-reductive dissociation of adducts between (η5-cyclopentadienyl) (1,2-disubstituted 1,2-ethylenedithiolato) cobalt (III) complexes and tributylphosphane or tributyl phosphite

Abstract The voltammetric characteristics of the title adducts [Co(Cp) (S 2 C 2 X 2 L] (X CN, CF 3 , COOCH 3 , 4-pyridyl, phenyl; L = tributylphosphane or tributyl phosphite) in acetonitrile solutions are reported. Both the phosphane and the phosphite adducts were oxidized and reduced through one-electron transfer processes followed by homogeneous chemical reactions for all X except phenyl; the oxidized adduct dissociated into the free complexes [Co III (Cp) (S 2 C 2 X 2 ] and the cation radical L +· , and the reduced adduct rapidly dissociated into the reduced form of the free complexes [Co II (Cp) (S 2 C 2 X 2 )] − and L. When X = phenyl, the oxidation was similar but the reduction was preceded by the dissociation of L. The oxidation and reduction half-wave potentials of the adducts were more negative than those of the corresponding free complexes, and they were linearly dependent on the adduct formation constant.

Effects of substituents and chalcogen atoms on the reduction half-wave potentials of (substituted η-cyclopentadienyl)-1,2-substituted 1,2-ethylenedichalcogenolato)cobalt(III) complexes in acetonitrile solutions

Abstract Twenty-six (substituted η-cyclopentadienyl)(substituted 1,2-ethylenedithiolato)cobalt(III) complexes underwent Nernstian one-electron reduction at a platinum electrode in 0.1 mol dm−3 tetraethylammonium perchlorate + acetonitrile solutions at 25 °C. Their reversible half-wave potentials were linearly dependent on the sum of the field parameters of the substituents. A substituent at the cyclopentadienyl ligand affects the half-wave potential to a larger extent than one at the dithiolato ligand does. The chemical shifts of cyclopentadienyl carbon and hydrogen atoms varied linearly with the half-wave potential when the substituents at the dithiolato ligand were changed. A linear relationship was found also between the half-wave potential and the chemical shift of dithiolene carbon atoms of the complexes having substituted cyclopentadienyl ligands. A substituent at one ligand affects the electron density at the other ligand through the central atom. The effects of substituents were almost additive. Six complexes in which the sulphur atoms were replaced by selenium were also reduced through a Nernstian one-electron reduction step, and the half-wave potential changed linearly with the number of selenium atoms. The effect of replacement of the chalcogen atoms was independent of the substituents at the two ligands.

Addition of CHSiMe3 to the CoS Bond of 1,2,5,3-cobaltadithiazole. Formation and reactions of stereoisomeric cobaltathiirane complexes

In the reaction between (ν5-cyclopentadienyl) (1-phenylmethanimine-N,1-dithiolato)cobalt(III), ([CpCoSNC(Ph)S], 1) and trimethylsilyldiazomethane, trimethylsilylmethylene adds between Co and S adjacent to N. Two geometrical isomers of cobaltathiirane complexes are formed: in the major addition product 2a, the trimethylsilyl group is located at the anti-position with respect to the cobaltadithiazole ring and in the minor product 2b, at the syn-position. These two stereoisomers are in equilibrium. Equilibrium is attained in 10 h at 80°C, when the reaction is started either from 2a or from 2b. From the temperature dependence of the equilibrium, δC value of the isomerization of the stereoisomers is estimated to be 34 kJ mol−1. These isomeric trimethylsilylmethylene adducts react with HCl to give a common product, chloro(7ν5-cyclopentadienyl)[N-(trimethylsilylmethylthio)-κS-1-phenylmethanimine-1-thiolato-κS]cobalt(III) (4). By treatment with tetrabutylammonium fluoride, 4 undergoes a ring reforming reaction to give a methylene adduct, (ν5-cyclopentadienyl)-[N-(methylene-κC)-thio-κS]-1-phenylmethanimine-1-thiolato-κS]cobalt(III).