Masakazu Kita

Synthesis and crystal structures of cobalt(III) complexes containing pyridine-2-selenolato and its oxidation products

Abstract A series of mixed cobalt(III) complexes [Co(pySe)3−n(NN)n]n+ [pySe=pyridine-2-selenolato (1−); NN=1,2-ethanediamine (en) and 2,2′-bipyridine (bpy); n=0, 1 and 2] was prepared. The geometrical preference and trans influence of pySe are fairly different from those of pyridine-2-thiolate. These selenolato complexes were oxidized by peracetic acid to give the corresponding pyridine-2-seleninato (pySeO2) and pyridine-2-selenonato (pySeO3) complexes. The crystal structures of the pySeO2 and pySeO3 complexes revealed that the coordination mode change from an original N,Se-four-membered to the N,O-five-membered chelate ring occurred during oxidation and intramolecular hydrogen bonds between the non-coordinated oxygen of pySeO2 or pySeO3 and the amine protons of en stabilize the N,O-coordination mode.

Cyclopalladation of N,N,N′,N′-tetramethylisophthalthioamide

SummaryN,N,N′,N′-Tetramethylisophthalthioamide (Hmpt) was cyclopalladated with PdCl2 in hot dimethylsulphoxide to give [PdCl(mpt)]. The structure was determined by X-ray analysis. The thioamide is metallated at C(2) to act as an S528-01C528-02S tridentate anionic ligand. There is appreciable steric repulsion between the benzene ring H(4, 6) and the dimethylamino groups. The hydrogens and the methyl groups mutually deviate from the coordination plane in opposite directions. The stability of the fused 5,5-membered chelate ring formed by the S528-03C528-04S ligand seems to overcome the steric hindrance. Derivatives were prepared by replacement of the chloride ion with iodide, diethyldithiocarbamate, 4-tert-butylpyridine, or tri-n-butylphosphine, and characterized spectroscopically. The S528-05C528-06S-fused chelate ring was maintained in these derivatives.

Cobalt(III) promoted ligand fusion reactions of thiobarbituric acid and 4,6-diamino-2-thiouracil (or 4-amino-2-thiouracil)

Abstract Novel cobalt(III) complexes containing three kinds of assembled ligands, L1L2=dapymt–tbba(2-), tbba–dapymt(1-) and apymt–tbba(1-) (H3tbba=thiobarbituric acid; Hdapymt=4,6-diamino-2-thiouracil; Hapymt=4-amino-2-thiouracil), were prepared from the mixed ligand systems, where L2 indicates the coordinated ligand to the Co(III) ion and L1 is a pendant ligand bonded to L2. These complexes were characterized by UV–Vis absorption spectra and NMR spectroscopy. The crystal structures of [Co(Htbba)(en)2]ClO4·2H2O (2) (en=ethane-1,2-diamine), [Co{dapymt–tbba(2-)}(en)2]ClO4·3H2O (3) and [Co{apymt–tbba(1-)}(en)2](ClO4)Cl·3H2O (5′) revealed that coordination occurs through the S(1) and N(1) donors of tbba and the latter complexes 3 and 5′ have an assembled ligand; a new bond is formed between the C(5) atom of tbba and the S(2) atom of dapymt or apymt. An intramolecular hydrogen bond between O(1) of tbba and NH of en was found in all crystals. An interesting intermolecular π–π stacking interaction was found in 5′.

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.

Redox potentials of a series of bis(2,4-pentanedionato)cobalt(III) complexes containing amine, phosphine, arsine, or their hybrid donor didentate ligands. σ and π contributions in the CoIIIN, P and As bonding

Reduction (E12(red)) and oxidation potentials (E12(ox)) of [Co(acac)2(L)]+ (acac = 2,4-pentanedionate) complexes containing an NN, NN′, N′N′, NP, PP, NAs, or AsAs′ didentate ligand as L(N = −CH2NH2; N′ = −CH2NMe2; P = −CH2PMe2; As = −CH2AsMe2; As′ = −CH2CH2AsMe2) were determined by electrochemical measurements. The E12(red) values which reflect the dσ∗(Co) orbital (homo) energy shift negatively in the following order: (i) L = N′N′>N′N>NN; (ii) L = N′N > AsN > PN; and (iii) L = N′N′ > AsAs′ > PP. The E12(ox) values shift positively in the following order: L = PP, AsAs′ < PN, AsN < NN, N N′, N′N′. This order suggests that the dπ(Co) orbital is more destabilized by the phosphine or arsine ligands than the amine ones.

CYCLOMETALLATION OF N,N-DIMETHYL-2-BROMOTHIOBENZAMIDE AND SOME RELATED THIOAMIDES WITH PALLADIUM(0) AND PALLADIUM(II)

N,N-Dimethyl-2-X-thiobenzamide [XCl (abbreviated as Hcbt) and Br (Hbbt)] and N,N-dimethyl-2-(2-bromophenyl) thioacetamide (Hbpt) were cyclopalladated at one of the N-methyl groups upon reaction with lithium tetrachloroparalladate(II), while oxidative addition took place at the aryl-halogen bond of Hbbt, Hbpt and N,N-dimethyl-2-iodothiobenzamide (Hibt) upon reaction with bis(dibenzylideneacetone)palladium(0). The reaction products, and their tri-n-butylphosphine (PBu3) and 4-tert-butylpyridine (tbp) derivatives, were characterized by IR and NMR spectroscopies. All the complexes were composed of a palladathiaheterocycle with sulphur coordination of a thioamide group. The structure of (N,N-dimethylthiobenzamido) (N,N-diethyldithiocarbamato)palladium(II) was determined by X-ray analysis. There is steric hindrance between one of the NCH3 groups and one benzene ring hydrogen atom. This should result in disfavoured benzene ringccyclopalladation of N,N-dimethylthiobenzamide (Hbt) with lithium tetrachloropalladate(II) and induce NCH3 cyclopalladation.

Synthesis and crystal structures of palladium(II) complexes containing benzyl 8-quinolyl sulfide and phenethyl 8-quinolyl sulfide

Abstract Four palladium(II) complexes [PdX2(L-N,S)] (X=Cl, Br; L: BzSq=benzyl 8-quinolyl sulfide, PheneSq=phenethyl 8-quinolyl sulfide) were prepared. The crystal structure of [PdCl2(BzSq-N,S)] revealed the presence of an intraligand stacking between the phenyl and quinolyl groups of BzSq. This stacking interaction was confirmed even in Me2SO, MeCN and MeNO2. On the other hand, [PdCl2(PheneSq-N,S)] did not show such an intraligand stacking both in the solid and in solutions.

Supporting Teachers to Educate Marginalized Children: Teachers and Teacher Education in Afghanistan

The Taliban effectively marginalized the school population of Afghanistan, particularly girls, who were legally forbidden to attend school. Since the fall of the Taliban Government, education has become one of the key priorities in the process of reconciliation, reconstruction and development agreed to in Bonn (Government of the Federal Republic of Germany 2001). The Ministry of Education has had to respond to a number of crucial issues in the drastic and rapid reconstruction and transformation process. Not least of these are issues related to quality—classroom teaching, the curriculum, teacher preparation. The Ministry’s Compilation and Translation Department was charged with developing a new Curriculum Framework for basic education in Afghanistan, and, with the assistance of international organizations, revising textbooks in light of that new framework. This paper considers the gap between intended curriculum as represented by an ambitious and progressive new Curriculum Framework and the implemented curriculum, as observed in primary school classrooms. These observations were carried out during the course of a JICA project, STEP or Strengthening Teacher Education Program, which set out to prepare teachers’ guides and train teachers in their use. The paper reports on the processes by which teachers’ guides were developed and teachers trained and on largely positive effects of the introduction of these teachers’ guides. The paper concludes with several recommendations as to improvements in the quality of teaching and teacher education in Afghanistan.

Synthesis, stereochemistry and crystal structures of cobalt(III) complexes containing 5,8-diphenyl-2,11-dithia-5,8-diphosphadodecane or 5,9-diphenyl-2,12-dithia-5,9-diphosphatridecane

Twelve new cobalt(III) complexes containing a tetradentate phosphine ligand of the type MeS(CH 2 ) 2 PPh(CH 2 ) n PPh(CH 2 ) 2 SMe (n = 2 L 1 or 3 L 2 ) were prepared. Their structures were assigned on the basis of electronic absorption and 1 H NMR spectra and the molecular structures of cis-α-[CoCl 2 {rac(P)-L 1 }]BF 4 and trans-[CoCl 2 {meso(P)-L 2 }]BF 4 were determined by single-crystal X-ray diffraction. The last two complexes comprise a slightly distorted octahedron with bond distances Co–P 2.210(1), Co–S 2.254(1) and Co–Cl 2.281(1) and Co–P 2.227(3), Co–S 2.327(3) and Co–Cl 2.241(3) ∠ (all averages) respectively. The differences in Co–S and Co–Cl bond distances are attributable to the strong trans influence of the phosphino group. Acetylacetonate complexes of rac(P)-SPPS in organic solvents form equilibrium mixtures of the cis-α and cis-β isomers, the molar ratio in MeNO 2 solution at 60 °C being 2∶1 for the L 1 complex and 3∶2 for the L 2 complex.