Shunji Utsuno

Proton and carbon-13 NMR studies of cis-eq- and trans-eq-ethylenediamine-N,N,N′-triacetatocobalt(III) and cis-eq-N-methylethylenediamine-N,N,′N′-triacetatocobaltate(III). Crystal structure of NH4cis-eq-[Co(ed3a)CN]

Abstract The complexes K cis - eq -[Co(ed3a)CN], K cis - eq -[Co(med3a)CN)], and K trans - eq -[Co(ed3a)CN] were synthesized and characterized. The 1 H and 13 C NMR spectra obtained with a 300 MHz spectrometer are reported and compared to corresponding aqua and nitro complexes. The PMR spectra show good resolution for all protons, including those of the ethylenediamine backbone. The NMR spectra of the cyano complexes are most similar to those of the corresponding nitro complexes. The major changes in the 13 C NMR spectra can be explained based on β-substituent effects involving the N-methyl group or conversion from the cis - eq to the trans - eq isomers. Racemic NH 4 [Co(ed3a)CN]·2H 2 O·0.5CH 3 OH was found to be triclinic, P -1 with the cell dimensions: a = 6.597(2), b = 7.783(4), c = 15.72(1) A, α = 88.63(5), β = 85.55(5), and γ = 69.89(4)°. There are two molecules in the unit cell.

OXIDATIVE DEHYDROGENATION OF THE LIGAND COORDINATED TO THE FAC-TRIS(2-AMINOMETHYLPYRIDINE)COBALT(III) COMPLEX

Abstract Kinetics of the oxidative dehydrogenation of the tris (2-aminomethylpyridine) cobalt (III) complex, [Co (pic) 3] 3, have been studied following spectrophotometrically the appearance of blue species under nitrogen atmosphere. The mechanism involves a deprotonation step, in a pre-equilibrium, generating an intermediate which is susceptible to an oxidation by either the complex itself or the perchlorate ion. The equilibrium constant (KOH=27.2±0.2 M−1) and the rate constant (kel=0.41±0.001 M−1 s−1) were obtained by two distinct and independent treatments as well as different sets of experiments.

Solid-state circular dichroism spectra of trans-diamminetetranitrocobaltate (III) salts and mer-triamminetrinitrocobalt (III)

Abstract Circular dichroism spectra of solid complexes of trans -diamminetetranitrocobaltate (III) salts and mer -triamminetrinitrocobalt (III) have been observed and attributed to the propeller arrangements of the nitro groups. Their absolute conformations are discussed in terms of the hexadecadal regional rule.

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.

Reaction of bis(diethylenetriamine)cobalt(III) with formaldehyde and ammonia

Abstract Condensation reactions of three isomers of bis(diethylenetriamine)cobalt(III) with formaldehyde and ammonia were studied. The s-fac isomer gave a main product containing two molecules of the cyclic amine, 1,3,5,8-tetraazacyclodecane. It was unstable in acidic solution to give several decomposition products. The encapsulated complex in which all the nitrogens were attacked by formaldehyde could not be obtained. The main product of the u-fac isomer was a half encapsulated complex, i.e. , three of the four primary amino groups reacted with formaldehyde and ammonia to produce a cobalt(III) complex of 3-(7-amino-2,5-diazaheptyl)-1,3,5,8-tetraazacyclodecane. The mer isomer gave a complex of 1,4,7,9,11,14,17-heptaazaheptadecane, together with the same reaction product as the one from the u-fac isomer.

CHIROPTICAL PROPERTIES OF FIVE-COORDINATE COMPLEXES OF NICKEL(II) AND COBALT(II) CONTAINING AN OPTICALLY ACTIVE LIGAND WITH NITROGEN AND PHOSPHORUS DONOR ATOMS

Abstract A new tripodal ligand with an asymmetric carbon atom, Ph2PCH2CH(Me)N(CH2CH2PPh2)2 (S-mnp3) was prepared using L-alanine as an optically active starting material; a series of its complexes, [M(X)(S-mnp3)]BPh4(M = Ni(II) and Co(II); X = NCS−, Cl−, Br− and I−) was prepared. Electronic spectra of these complexes indicated that their coordination geometries are essentially the same as those of corresponding complexes containing the tripodal ligand tris (diphenylphosphinoethyl) amine. Thus, all the present nickel complexes in solution exhibit electronic spectra typical of trigonal-bipyramidal complexes of diamagnetic configuration. CD spectra of these nickel complexes have been discussed on the basis of the selection rules for magnetic dipole transitions under C 3v symmetry. Cobalt(II) complexes are either high-spin or low-spin, depending on the nature of the unidentate ligand. The high-spin cobalt(II) complexes did not show CD spectra typical of trigonal-bipyramidal geometry.

PRELIMINARY COMMUNICATIONS: SUBSTITUTION OF tris(2,2′-BIPYRIDINE)COBALT(III) BY CARBONATE ION

Abstract This communication reports the instability of tris(2,2′-bipyridine)cobalt(III) toward ligand substitution. 2,2′-Bipyridine(“bpy”) has been recognized as one of the most potent ligands and used to prepare many kinds of metal complexes. Nevertheless, one of the authors1 reported the preparation of [Co(CN)2(bpy)2]Cl, which was obtained by the reaction of [Co(bpy)3]3+ with cyanide ion in water. The reaction was reported to occur within five minutes at room temperature. The strong nucleophilicity of the cyanide ion might be responsible for this kind of substitution.