Cobaloxime Complexes Research Articles

特殊条件下の構造研究の新展開 迅速Ｘ線データ収集および解析による固相反応の追跡

The rapid X-ray diffraction data collection method has advantages for the time-resolved observation of solid-state reactions in crystal and structure analysis of unstable crystals. The new diffractometers for rapid data collection using two-dimensional detector have been developed to achieve both high speed measurement and high data accuracy. Step-by-step molecular structure changes of cobaloxime complex, distibene molecule are observed by using the new diffractometer first time.

Solid State Photoisomerization of But-3-en-1-yl Group in Cobalt Complexes

Abstract The but-3-en-1-yl group bonded to the cobalt atom in some cobaloxime complexes is isomerized to the but-2-en-1-yl group in the solid state on exposure to a xenon lamp. In order to make clear the relationship between the reaction rate and the crystal structure, six complexes with different axial base ligands were prepared; piperidine, 1, 1-vinylimidazole, 2, pyrrolidine, 3, 1-methylimidazole, 4, 4-t-butylpyridine, 5, and triphenylphosphine, 6. The crystal structures were determined by X-ray analyses and the reaction rates were estimated from the change of the 1H NMR spectra observed in several intermediate stages. One of the photo products, which has 1-vinylimidazole as an axial base ligand, 7, was prepared separately and its crystal structure was also analyzed. A pair of the but-3-en-1-yl groups are in contact with each other around an inversion center in the crystal structures of 2, 5, and 6, whereas the but- 3-en-1-yl groups in 1, 3, and 4 are isolated from the other but-3-en-1-yl groups of the neighboring molecules in their crystal structures. The reaction rates of the former complexes are significantly greater than those of the latter complexes, except 2. This suggests that the cooperative motion of the but-3-en-1-yl groups plays an important role in the process of the isomerization. A pair of the but-3-en-1-yl groups around an inversion center in 2 are too closely packed for the isomerization to occur even if the cooperative motion is taken into account.

Reactions in Solid and Constrained State. IV. Preparation and Solid-State Photoracemization of Optically Active Alkyl Cobaloxime Complexes

Abstract Various optically active 1-substituted and 1,2-disubstituted ethyl cobaloxime [bis(dimethylglyoximato)cobalt(III)] complexes including deuterium-labeled complexes were prepared. Their photoracemization was found to occur upon irradiation of visible light in the solid-state. The reaction rate was much greater than that of solid-state racemization by irradiation of X-rays. The rates were not controlled by the electronic character of axial base and alkyl group but by the crystal lattice: the volume and shape of the reaction cavity, flexibility of the cavity, and intermolecular interaction such as hydrogen bonding. The experiments using deuterium-labeled complexes revealed the main reaction path in which the racemization proceeds mainly through out-of-plane rotation of the alkyl radical.

X-ray Analysis of Successive Reaction in Crystalline State Photoisomerization of Cobaloxime Complexes

The γ-cyanopropyl group bonded to the cobalt atom in some cobaloxime complexes was isomerized to the α-cyanopropyl group through β-cyanopropyl group on exposure to visible light in the solid state. For the complex with 1-phenylethylamine as an axial base ligand almost chiral α-cyanopropyl group was produced with retention of the single crystal form. The mechanism is discussed on the basis of the structural change.

Photoisomerization of Cobaloxime Complexes in Isostructural Host-Guest Complexes

The cobaloxime complex with the β-cyanoethyl group and isonicotinic acid as axial ligands forms host-guest complexes with several kinds of host molecules. Whe the crystals of the host-guest complexes were irradiated with visible light, the β-cyanoethyl group of the guest molecule was changed to the α-cyanoethyl group. The rate of the photoisomerization was controlled by the shape of the host molecule. Designing the host structures, the isotructural host-guest crystals were prepared and the controlled reaction rates were obtained.

Direct Observation of Correlation between Crystalline-State Deuterium Transfer and Racemization of 1-Cyanoethylcobaloxime Complex by Neutron Diffraction

Abstract The [(R)-1-cyanoethyl-dα] group, which has a deuterium atom attached to the chiral carbon and is bonded to the cobalt atom, in a cobaloxime complex with pyridine as an axial base ligand is inverted to the opposite configuration on exposure to visible light with retention of the single crystal form. The C-D bond is not cleaved in the process of the inversion.

Variation of the reaction rate in the solid-state photoisomerization of cobaloxime complexes by forming host–guest complexes

The 2-cyanoethyl–isonicotinic acid–cobaloxime complex forms host–guest complexes with secondary amines such as dicyclopentylamine and diphenylamine. The 2-cyanoethyl group in the two host–guest complexes as well as the pure guest complex was isomerized to the 1-cyanoethyl group on exposure to a xenon lamp in the solid state. The analyzed structures of the three crystals indicate that the different reaction rates of the three crystals have a quantitative correlation with the volumes of the reaction cavities for the 2-cyanoethyl groups in the crystals. The reaction rate can be altered by forming the host–guest complexes.

Kinetics and mechanism of the cobaloxime(II)-catalysed oxidative dehydrogenation of 3,5-di-tert-butylcatechol by O2. A functional oxidase model

Triphenylphosphinecobaloxime(II) has been found to be a selective catalyst for the oxidative dehydrogenation of 3,5-di-tert-butylcatechol to the corresponding 1,2-benzoquinone at room temperature and atmospheric dioxygen pressure. In a rapid initial phase the catalyst is reversibly transformed to a previously characterised catecholatocobaloxime(III) species, which persists throughout the reaction, keeping CoII at a low level. The semiquinone anion radical (dbsq˙–) and its cobaloxime(III) complex CoIII(dbsq˙–) have been detected as intermediates by ESR spectroscopy. The kinetics was followed by volumetry. According to the proposed mechanism, in the rate-determining step superoxocobaloxime (CoIIIO2) abstracts an H atom from the cathechol via an hydrogen-bonded intermediate. The system investigated is a functional model of catecholase (oxidase) activity, based on free-radical intermediates, a possibility recently demonstrated for certain oxidoreductases.

β–α Photoisomerization of Cobaloxime Complexes in the Solid State. 6. Asymmetric Induction Due to Chiral Crystal Environment

Abstract The crystal structure of (S)-s-butylamine(2-cyanoethyl)cobaloxime was determined by X-ray analysis; the crystal is monoclinic, and the space group is C2, Z = 4 with a = 15.656(2), b = 11.699(2), c = 11.553(1) Å, β = 96.979(9)° and V = 2100.5(5) Å3. The structure was refined by a full-matrix least-squares method to the final R value of 0.052 for 1678 observed reflections. The 2-cyanoethyl group takes a perpendicular conformation to the cobaloxime plane and has disordered conformations (A, B, and C) around the Co–C bond. The occupancy factors of A, B, and C are 0.48, 0.34, and 0.18, respectively. The crystalline sample was irradiated with a xenon lamp. The (R)-1-cyanoethyl group is preferentially produced from the (S)-s-butylamine complex. The conversion rates, which were determined by HPLC analysis using the chiral stationary phase, were obtained to be 1.17 × 10−5 and 0.59 × 10−5 s−1 for the (R)- and (S)-1-cyanoethyl groups, respectively. The diastereomeric excess is 27%. Such asymmetric induction is well explained by the shape of the reaction cavity for the 2-cyanoethyl group, and is also in good agreement with a packing-energy calculation by molecular mechanics.

Synthesis and characterization of long-chain ω-functionalized alkyl cobaloxime complexes

Two new series of cobaloxime complexes of formulae [Co(Hdmg) 2{(CH 2) n I}(py)] (Hdmg = the monoanion of dimethylglyoxime, py = pyridine and n = 5, 6, 8, 9 or 10) and [Co(Hdmg) 2{(CH 2) 3OC(O)C 6H 4R}(py)] (R = H, o-, m- or o-OCH 3, p-OC 7 H 15 or p-OC 9H 19) have been synthesized and fully characterized. The former series provides versatile precursor species for a wide range of polymethylene homo- and heteronuclear complexes, while the latter series confirms that, under mild conditions, elaboration from an ω-hydroxyl group can be achieved to generate stable metal complexes.

β–α Photoisomerization of Cobaloxime Complexes in the Solid State. 5. Reaction Rate Reduced by a Hydrogen Bond

Abstract The crystal structures of three cobaloxime complexes with different axial base ligands have been analyzed by X-ray analysis at room temperature. I: (2-Cyanoethyl)bis(dimethylglyoximato)((S)-phenylalaninol)cobalt(III); the crystal is orthorhombic, the space group being P212121, Z = 4 with a = 9.416(3), b = 27.184(3), c = 9.184(3) Å. II: (2-Cyanoethyl)bis(dimethylglyoximato)((S)-phenyl-alanine methyl ester)cobalt(III); the crystal is monoclinic, the space group being P21, Z = 4 with a = 14.376(2), b = 11.988(2), c = 14.874(1) Å, and β = 101.05(1)°. III: (2-Cyanoethyl)bis(dimethylglyoximato)(methyldiphenylphosphine)cobalt(III); the crystal is monoclinic, the space group being P21/n, Z = 4 with a = 11.558(4), b = 15.542(3), c = 14.393(5) Å, and β = 91.02(4)°. The structures were refined by the full-matrix least-squares method to final R values of 0.041, 0.052, and 0.044 for 2340, 3287, and 4400 observed reflections, respectively. The photoisomerization rates of I, II, and III in the solid state were obtained from the changes in the IR spectra. The rate of I was insignificantly small, but the rates of II and III were calculated to be 0.1 × 10−4 and 1.9 × 10−4 s−1, respectively, assuming first-order kinetics. The 2-cyanoethyl groups in the three complex crystals take perpendicular conformations to their cobaloxime planes. The 2-cyanoethyl group of I makes a hydrogen bond with the N–H group of the neighboring molecule. The non-reactivity of I may be brought about by the hydrogen bond.

Solid-state photoisomerization of cobaloxime complex in different clathrate crystals

Solid-state photoisomerization of cobaloxime complex in different clathrate crystals

Four polymorphs of a cobaloxime complex with different solid-state photoisomerization rates

The complex (2-cyanoethyl)bis(dimethylglyoximato)(triphenylphosphine)cobalt(III), [Co(C4H7N2O2)2(C3H4N){P(C6H5)3}], when it was crystallized rapidly from an aqueous methanol solution, has four crystal forms, three of which were obtained separately from different solvents in large amounts. The crystal structures of the four forms were determined by X-rays. The molecular structures in the four forms have different conformations around the Co—C and Co—P bonds. The packing energy calculation indicated that the four forms have approximately the same energy. The 2-cyanoethyl group of this complex was isomerized to the 1-cyanoethyl group when the powdered sample of the complex was irradiated with a xenon lamp. For three crystal forms prepared separately, the solid-state photoisomerization rates were measured from the change in the IR spectra, assuming first-order kinetics. A quantitative relationship between the rate constant and the size of the reaction cavity for the 2-cyanoethyl group has been obtained for the three crystal forms.

Mechanism of Solid-State Racemization for Optically Active Alkyl Cobaloxime Complexes — Synthesis and Solid-State Reaction of Deuterium-Labeled Complexes

Abstract The deutelium-labeled chiral 1,2-disubstituted ethyl cobaloxime complexes were synthesized, and the rate constants of the solid-state photo-racemization and photoisomerization of these complexes were determined. The reaction mechanism for the solid-state photoracemization was elucidated by rationalization of these results.

Crystalline-State Trans-Cis Photoisomerization of Cobaloxime Complexes

Abstract It was observed by X-ray single crystal analysis that trans-2-buten-1-y1 cobaloxime complex with pyridine or 4-bromopyridine as a axial ligand isomerizes to the cis isomer with retaining the single crystal form on exposure to a Xe lamp. The complex with 3-chloropyridine or methylsulfide as a axial ligand did not show the isomerization. The reaction cavities for the trans-2-butenyl groups calculated from four crystal structures showed that those of reactive crystals are significantly larger than those of non-reactive ones.

Chiral Lattice-Controlled Asymmetric (β-α)PHOTOISOMERIZATION OF 2-SUBSTITUTED ETHYL COBALOXIME COMPLEXES

Abstract Chiral lattice-controlled asymmetric photoisomerization of 2-methoxycarbonyl-ethyl, 2-carbamoylethyl, 2-(N-methylcarbamoyl)ethyl and 2-(N-phenylcarbamoyl)ethyl cobaloxime complexes was found to occur which afforded corresponding, optically active 1-substituted ethyl cobaloxime complexes in enantioselectivities ranging from 4 to 69%ee.

Quantitative comparison of photoisomerization of three cobaloxime complexes in the solid and crystalline states

The β-cyanoethyl group bonded to the cobalt atom in cobaloxime complexes with 3-methyl-, 3-chloro- and 3-bromopyridines as axial base ligands was found, on exposure to a xenon lamp, to be isomerized to the α-cyanoethyl group with retention of the single-crystal form. The reaction rate of each compound was estimated from the change of unit-cell dimensions on a diffractometer (crystalline state) and from the change of the IR spectra of the powdered sample (the solid state). The reaction rates thus obtained were compared with the volumes of the reaction cavities for the cyanoethyl groups in the crystal structures of the three cobaloxime complexes. A quantitative relationship was observed between structure and reactivity.

Quantitative comparison of photoisomerization of three cobaloxime complexes in the solid and crystalline states

The β-cyanoethyl group bonded to the cobalt atom in cobaloxime complexes with 3-methyl-, 3-chloro- and 3-bromopyridines as axial base ligands was found, on exposure to a xenon lamp, to be isomerized to the α-cyanoethyl group with retention of the single-crystal form. The reaction rate of each compound was estimated from the change of unit-cell dimensions on a diffractometer (crystalline state) and from the change of the IR spectra of the powdered sample (the solid state). The reaction rates thus obtained were compared with the volumes of the reaction cavities for the cyanoethyl groups in the crystal structures of the three cobaloxime complexes. A quantitative relationship was observed between structure and reactivity.

Effect of Cobalt-59 Self-Decoupling on the Solid-State31P CP/MAS NMR Spectra of Cobaloximes

Phosphorus-31 NMR spectra of three solid cobaloxime complexes containing phosphorus donor ligands have been examined. At room temperature, the 31P CP/MAS NMR spectra of PBu3Co(DH)2Cl (I) are broad and rather featureless, while PPh3Co(DH)2CH3 (II) and P(OEt)3Co(DH)2N3 (III) exhibit well-resolved eight-peak patterns which result from 59Co (spin 7/2), 31P spin−spin coupling. Variable temperature measurements on compound I indicate that the peak broadening observed at room temperature results from the onset of 59Co self-decoupling. At 155 K, the 59Co spin−lattice relaxation time is sufficiently long that well-resolved octets are observed. The experimental 31P CP/MAS NMR spectra were simulated using the first-order perturbation approach of Olivieri and the information available from these simulations is discussed in detail. The 31P NMR spectra of compound I provide the first reported example of recoupling of the direct and indirect spin−spin interactions between a quadrupolar nucleus and a spin 1/2 nucleus in the solid state by means of low temperature CP/MAS NMR experiments.

Crystalline-State Photoisomerization and Photoinduced Phase Transition of a Cobaloxime Complex

Abstract The crystal of (β-cyanoethyl)bis(dimethylglyoximato)(4-methylpyridine)cobalt(III) exhibits a reversible single crystal-to-single crystal thermal phase transition at 343 K. The β-cyanoethyl group of the crystal was isomerized to α-cyanoethyl group retaining the single crystal form when the crystal was irradiated with a strong Xe lamp above 343 K, although the crystal was decomposed below the temperature. On the other hand, when the crystal was exposed to a weak Xe lamp at 340 K, the crystal showed the phase transition after 20 hours exposure keeping the single crystal form. The crystal after the phase transition also exhibited the β-α photoisomerization on exposure to the strong Xe lamp. The mechanism has clearly been elucidated on the basis of the analyzed structures before and after the photoisomerization or phase transition.