Masatsugu Kajitani

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.

A new synthetic method for ruthenium complexes of β-diketones from ‘ruthenium blue solution’ and their properties

Abstract The ‘ruthenium blue solution’ obtained by reducing hydrated ruthenium(III) trichloride with ethanol was used a convenient starting material in the synthesis of thirteen tris(β-diketonato)ruthenium (III) and six tris(β-diketonato)ruthenate(II) complexes. The procedure of preparing the ‘ruthenium blue solution’ requires no catalyst and is much simpler than the previous methods. A variety of complexes were synthesized in good yields with small changes of the conditions. The Hammett constants of the substituents on the ligand serve as a helpful guide for choosing the operating conditions for the preparation of β-substituted complexes. The yields of the complexes with β-substituted ligands are relatively small, since the presence of a bulky substituent at the β-position decreases the fraction of the enol form of the free ligand. The melting points, magnetic moments, R f values in TLC, UV-Vis, IR, and 1 H NMR spectra were measured. The substituent effects on these properties are discussed.

Studies on extraction of copper(II) with 1-phenyl-3-methyl-4-acyl-5-pyrazolone

Abstract The extraction of Cu(II) with 1-phenyl-3-methyl-4-acyl-5-pyrazolone (HA), in different organic solvents has been studied. The extraction mechanism of Cu(II) and the composition of the extracted species has been determined. Cu(II) was extracted as CuA2, or in the presence of TOPO, as CuA2TOPO. The extraction constants do not change regularly with increasing the length of acyl chain in the 1-phenyl-3-methyl-4-acyl-5-pyrazolone derivatives. The effect of the temperature on the extraction of Cu(II) has also been investigated.

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.

Microwave-enhanced radical reactions at ambient temperature

The microwave-enhanced synthesis of 3-cyclohexyl-1-phenyl-1-butanone (CPB) from crotonophenone and iodocyclohexane in the presence of t-BuOOH and triethylborane was examined at ambient temperature and under reflux conditions in bulk solution using no less than four different synthetic protocols. Chemical yields of CPB (93 and 95%, respectively) obtained after 60 and 120 min under microwave dielectric heating coupled to a cooling system (MW/Cool protocol) for a reaction temperature of 20–24 °C exceeded the yields from the reaction occurring at room temperature (24 °C; no microwaves; 40% and 72%) for the same reaction times and temperature. The competitive radical reaction to produce CPB and a small amount of by-products generated from the thermally-induced synthesis by the non-selective radical reaction was restricted solely to the process occurring at ambient temperature (RT protocol), under microwave dielectric heating to reflux (MW protocol) and heating with an oil-bath also to reflux (Oil-bath protocol). By contrast, no by-products were generated or detected for the reaction taking place by the MW/Cool method. Comparison of product yields under conditions of identical temperature conditions must involve some specific microwave effect in the synthesis of the title compound.

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.