Junnosuke Fujita

Double cyclopalladation ofN,N,N′,N′-tetramethylferrocene-1,1′-dicarbothioamide

Abstract A method was developed for one-pot synthesis of N,N N′,N′ -tetramethylferrocene-1,1′-dicarbothioamide (H 2 fdt); ferrocene was lithiated wit

Cyclopalladated N,N-dimethylthiophene-2- and -3-carboselenoamide derivatives

Abstract N,N-Dimethylthiophene-2- and -3-carboselenoamides, abbreviated as Hats and Hbts, respectively, were easily obtained by the reaction of the corresponding carboxamide with phenyldichlorophosphine selenide. Hats and Hbts reacted with lithium tetrachloropalladate in methanol to give [PdCl(ats)]2 and [PdCl(bts)]2, respectively. Several derivatives of the two were prepared with ligands (L) such as pyridine (py) or tri-n-butylphosphine (PBu3). The new compounds were characterized spectroscopically and the structures of [PdCl(bts)(PBu3)] and [PdCl(ats)(tbp)] (tbp=4-tert-butylpyridine) were determined by X-ray analysis. The former was shown to be a trans-(C, Cl) isomer, while the latter a cis-(C, Cl) one, where C represents the palladated carbon atom. Hats was palladated at position 3 of the thiophene ring and Hbts exclusively at position 2 of the ring. The selenoamide group was coordinated through the selenium atom to form a five-membered palladaselenaheterocycle. The trans influence of a trans donor was reflected in the PdSe bonds: 2.4147(8) A (trans to PBu3) in [PdCl(bts)(PBu3)] and 2.359(1) A (trans to Cl) in [PdCl(ats)(tbp)].

Syntheses and crystal structures of geometrical isomeric pairs: Trans- and cis-(PPh4) [Co (acac)2 (CN)2] and trans- and cis-[Co(acac)2(PMe3 or PEt3)2]PF6 (acac = pentane-2,4-dionate)

Abstract Reactions of trans -[Co(acac) 2 (PPh 4 ) 2 ]PF 6 (aca = pentane-2,4-dionate) with PR 3 (R = Me or Et) in methanol afforded new complexes, trans -(PPh 4 ) [Co(acac) 2 (CN) 2 ] and trans -[Co(acac) 2 (PR 3 ) 2 ]PF 6 , respectively. The structures of the new trans -isomers, together with those of the corresponding known cis -isomers, were determined by single-crystal X-ray diffraction. Complexes trans -[Co(acac) 2 (PR 3 ) 2 ] =− were stable in dry organic solvents, but in wet methanol easily hydrolysed to give trans -[Co(acac) 2 (PR 3 )(H 2 O)] − and isomerized to cis -[Co(acac) 2 (PR 3 ) 2 ] − were stable in both dry and wet solvents. The X-ray structure analyses showed that the CoC and CoP bonds in the trans -isomers were longer by about 0.07 and 0.08 A, respectively, than those of the corresponding cis -isomers. The CoO bonds trans to cyanide and phosphine ligands were also longer than those of the mutually trans CoO bonds, owing to the strong trans influences of cyanide and phosphine ligands.

Preparation and characterization of rhodium(III) complexes containing 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme). Structures of [RhX3(tdmme)](X = Cl, Br or I), [Rh(NH3)3(tdmme)]3+ and [{Rh(tdmme)}2(µ-X)3]3+(X = Cl or OH) in the solid state and in solution

Several new rhodium(III) complexes containing a tripodal tridentate phosphine, MeC(CH2PMe2)3(tdmme), have been synthesized and their structures investigated both in the solid state and in solution. Single-crystal X-ray analyses revealed the smaller steric requirement and stronger trans influence of tdmme than those of the phenyl-substituted analogue, MeC(CH2PPh2)3(tdpme). The long Rh–Cl bond in the mononuclear trichloro complex, [RhCl3(tdmme)]1, due to the strong trans influence of tdmme, made the complex reactive in water; the structure of 1 in solution and its reaction products with some acids or bases were characterized. The triply chloro-bridged dinuclear complex, [{Rh(tdmme)}2(µ-Cl)3][BF4]3, also showed structural change in water, while the mononuclear triammine complex, [Rh(NH3)3(tdmme)][BF4]3, and the triply hydroxo-bridged dinuclear complex, [{Rh(tdmme)}2(µ-OH)3][BF4]3, were stable. The absorption spectra of the tdmme complexes suggested a stronger ligand field of tdmme to the rhodium(III) centre than those of corresponding didentate diphosphine ligands, in accordance with the short Rh–P bond lengths in 1 found by single-crystal X-ray analysis.

Chromatographic separation of the diastereomers of the bis(2,4-pentanedionato)[2-(methylseleno)ethylamine]-cobalt(III) ion on a column of sulphoethyl-toyopearl and determination of the rate of inversion at the selenium atom

Abstract A high-performance liquid chromatographic (HPLC) method was successfully applied to kinetic studies of the inversion at the selenium atom of [Co(acac) 2 -(CH 3 SeCH 2 CH 2 NH 2 )] + (acac — 2,4-pentanedionate ion). The complex was separated into two racemic pairs, Δ ( R ), Λ ( S ) and Δ ( S ), Λ ( R ), by column chromatography on sulphoethyl (SE)-Toyopearl. The racemate, Δ ( R ), Λ ( S ) or Δ ( S ), Λ ( R ), was epimerized in 0.05 mol dm -3 Na 2 SO 4 , and then the products, Δ ( R ), Λ ( S ) and Δ ( S ), Λ ( R ), were separated on SE-Toyopearl packed in an HPLC column. The activation enthalpy obtained, ΔH * — 113 kJ mol -1 , is the highest reported so far for inversion of coordinated selenide.

Inversion and proton exchange at chiral nitrogen centers of [Co(acac)2(Ph-en)]+ (acac=2,4-pentanedionate ion; Ph-en=N-phenylethylenediamine) and [Co(acac)2(Me-en)]+ Me-en=N-methylethylenediamine)

Abstract The rates of the base-catalyzed proton exchange and inversion (epimerization) at chiral nitrogen centers of [Co(acac) 2 (Ph-en)] + (acac=2,4-pentanedionate ion; Ph-en= N -phenylethylenediamine) and [Co(acac) 2 (Me-en)] + (Me-en= N -methylethylenediamine) in aqueous solutions have been measured at 34.0 °C. The Ph-en complex, which has an electron-withdrawing phenyl group on the nitrogen atom undergoes proton exchange about 10 4 times faster than the Me-en complex which has an electron-repelling methyl group. The proton-exchange rates are ca . 10 2 and 10 5 times greater than the inversion rates for the Ph-en and Me-en complexes, respectively. The faster rate of inversion for the Ph-en complex was explained by the lower barrier of inversion; an increased stabilization of the intermediate was due to (p-p) π conjugation between the amide nitrogen atom and the phenyl group.

Preparation and Stereochemistry of Cobalt(III) Complexes with Tetramines Derived from 1-(2-Pyridyl)ethylamine

The optically active ligands, (2S,7S)-2,7-di(2-pyridyl)-3,6-diazaoctane (S,S-peaen) and (2R,8R)-2,8-di(2-pyridyl)-3,7-diazanonane (R,R-peatn) have been prepared. The dichlorocobalt(III) complexes of these ligands have been prepared and several isomers isolated. The ligand, S,S-peaen yielded one cis-α and two types of cis-β isomers, while the R,R-peatn gave only one cis-β isomer. Oxalato and dinitro derivatives of the R,R-peatn complexes have been isolated and characterized and the stereochemistry of the isolated complexes discussed.

Kinetics and Steric Course of the Substitution of Various Olefins for the Asymmetric Olefin in trans(N,olefin)-Chloro-L-prolinato-trans-2-buteneplatinum(II)

Replacement of the coordinated trans-2-butene in trans(N,olefin)[PtCl(L-pro)(S,S-trans-2-butene)] (L-pro=L-prolinate anion) by various olefins in acetone has been studied at −20 to +23 °C. The rate is proportional to concentrations of the complex and the olefin nucleophile. No solvent path is observed. The second order rate constant k2 (10−4 to 10−1 M−1 s−1 at 8.0 °C) can be the measure of each substitution. The ΔH\eweq is around 10 kcal/mol, and ΔS\eweq ranges from −25 to −46 cal/mol K. Substitution of cis-2-butene for the asymmetrically coordinated trans-2-butene-3H gives equal k2’s on the measurement of CD strength and on that of isotopic exchange. Similar substitution of trans-2-butene gives significantly larger k2 on isotopic exchange than that on CD measurement, indicating sterically selective substitution with retention of configuration. Substitution of ethylene derivatives with various groups on the carbon atoms gives different k2’s depending on the kind of substituents. The steric interaction bet...

Isomerization and racemization of (acetylacetonato)bis(4,4′-dimethyl-2,2′-bipyridine 1,1′-dioxide)chromium(III), (acetylacetonato)bis(4,4′-dimethoxy-2,2′-bipyridine 1,1′-dioxide)chromium(III) and (acetylacetonato)bis(4,4′-diethoxy-2,2′-bipyridine 1,1′-dioxide)chromium(III) complexes

Abstract A series of chromium(III) complexes, [Cr(acetylacetonato)(4,4′-X 2 bpdo) 2 ] 2− (X = Me, MeO, EtO), where 4,4′-X 2 bpdo denotes 4,4′-substituted 2,2′-bipyridine 1,1′-dioxide, were prepared and resolved into pairs of enantiomers. The perchlorates of these complexes were found to crystallize in a lel 2 ( Δ ( λλ ), Λ ( δδ )) form; they isomerize to a lelob ( Δ ( λδ ), Λ ( δλ )) form in water, accompanied by rapid changes in the absorption spectra, and then racemize slowly. The rates of both isomerization and racemization are reduced with an increase in the electron-releasing ability of the 4,4′-X 2 substituent.

Preparation and characterization of the stereoisomers of [Co(acac)2(N-phenylethylenediamine or N,N′-diphenylethylenediamine)]+ (acac = 2,4-pentanedionateIon) and isomer distribution at equilibrium

Abstract The [Co(acac) 2 ( N -phenylethylenediamine)] + (acac= 2,4-pentanedionate ion)and[Co(acac) 2 ( N,N′ -diphenylethylenediamine)] + complexes were separated into two and three racemic pairs of the diastereomers, respectively, by means of column chromatography and the diastereomers were resolved by the chemical method. The diastereomers are stable in acidic water pH (2.5), but easily epimerize in neutral or basic water. The isomer distributions at equilibrium were determined and the results compared with those of the corresponding N -methyl-substituted ethylenediamine complexes.