Structure of the racemate produced by X-ray exposure of bis(2,3-butanedione dioximato) [(R)-methoxycarbonylethyl](pyridine)cobalt(III)

Kurihara, T.; Ohashi, Yuji; Sasada, Yoshio

doi:10.1107/s0567740882009133

Cited by 11 publications

(3 citation statements)

References 2 publications

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“…The question was answered in the structural change in the complex of 2, which has two py complexes and solvate methanol molecules in its asymmetric unit of the P2 1 cell [67,68]. The crystal structure viewed along the c-axis before photoirradiation at 223 K is shown in Figure 41.…”

Section: Cooperative Motion Of the Chiral 1-methoxycarbonylethyl Groupsmentioning

confidence: 99%

Dynamic motion and various reaction paths of cobaloxime complexes in crystalline-state photoreaction

Ohashi¹

2013

Crystallography Reviews

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The various alkyl groups bonded to the cobalt atom in (alkyl)(base)cobaloxime complex crystals are isomerized on exposure to visible light without degradation of the single crystal form. The solid-state reactions keeping the single crystal form were called crystalline-state reactions and the reaction mechanisms were explained with the concept of reaction cavity for the alkyl group. Changing the axial base ligands, a variety of crystalline-state reactions were examined not only by X-rays but also by neutron diffraction. The various reaction paths were made clear from the structures of initial, intermediate and final stages of the reactions. Moreover, the reaction rate was proved to have a positive relation with the volume of reaction cavity in each reaction. Not only various isomerizations but also unusual racemic-to-chiral transformations and a chirality inversion were also observed and the mechanisms were clearly explained and the shape of the reaction cavity made clear the mechanism. Two promising methods to observe the photoreaction with retention of the single crystal form, mixed crystal formation and bulky group insertion, are proposed and several successful results are shown.

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Section: Cooperative Motion Of the Chiral 1-methoxycarbonylethyl Groupsmentioning

confidence: 99%

Dynamic motion and various reaction paths of cobaloxime complexes in crystalline-state photoreaction

Ohashi¹

2013

Crystallography Reviews

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“…Cobaloxime complexes, model compounds of vitamin B 12 , have been of interest because the alkyl groups bonded to the cobalt atom in the complexes are isomerized on exposure to visible light with retention of the single crystal form. In serial studies of such crystalline-state reactions of cobaloxime complexes, a variety of racemizations of the chiral alkyl groups such as 1-cyanoethyl group, , 1-methoxycarbonylethyl group, − and 1,2-bis(methoxycarbonyl)ethyl group − have been reported. Recently, bulkier 1,2-bis(ethoxycarbonyl)ethyl and 1,2-bis(allyloxycarbonyl)ethyl groups were also found to be racemized with retention of the single crystal form by photoirradiation (Scheme ) .…”

Section: Introductionmentioning

confidence: 99%

“…9 These findings brought us a question how such bulky alkyl groups are racemized in the restricted crystalline lattice. We proposed from X-ray and ESR measurements that the photoracemization of smaller groups such as the 1-cyanoethyl group proceed in the three steps; the produced radical to face the opposite side to the cobalt atom, and then (3) the recombination between the radical and the Co atom. 10 However, the 1,2-bis(alkoxycarbonyl)ethyl group seems too bulky to be racemized with the same mechanism.…”

Section: Introductionmentioning

confidence: 99%

Direct Observation of Deuterium Migration in Crystalline-State Reaction by Single Crystal Neutron Diffraction IV. “Hula-Twist” Rotation of a Long Alkyl Radical Produced by Photoirradiation

et al. 2002

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When the crystal of [(R)-1,2-bis(ethoxycarbonyl)ethyl](pyridine)bis(dimethylglyoximato)cobalt(III) was exposed to a xenon lamp, the chiral 1,2-bis(ethoxycarbonyl)ethyl group was partly inverted to the opposite configuration and finally the racemic group was produced with retention of the single crystal form. To make clear the mechanism, the hydrogen atom bonded to the chiral carbon of the chiral group was exchanged with the deuterium atom and the crystal was exposed to the xenon lamp for 3 days. The crystal after irradiation was analyzed by neutron diffraction. About 33% of the (R)-isomers were inverted to the (S) isomers in a crystal. The deuterium atom in the (S)-isomer was bonded to the same chiral carbon atom. This result clearly indicates that the inversion proceeds in the three steps; (i) the Co-C bond was homolytically cleaved by photoirradiation and the 1,2-bis(ethoxycarbonyl)ethyl radical and Co(II) were produced, (ii) the radical rotated by 180 degrees directing the C-D bond to the cobalt atom and the opposite plane of the radical faced to the cobalt atom, and (iii) the radical made a bond with Co(II). Because the peripheral atoms of the long radical occupy approximately the same positions in the process of the radical rotation, the crystal was not decomposed. The above rotation is a good example of hula-twist rotation in the process of photoisomerization of polyenes such as rhodopsin.

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Crystalline‐State Reaction

Ohashi¹

1994

Reactivity in Molecular Crystals

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One special feature of solid-state reactions is that the spacial arrangement of the atoms at the beginning and sometimes also at the end of the reaction can be mapped quite precisely. This distinguishes them from reactions in solution or in the gas phase and provides the possibility for new insight into the geometric aspects of chemical reactivity in general. The molecules in a given crystal react in a single conformation (occasionally in more than one) and in well-defined surroundings. Thus, differences in chemical behavior among crystals that differ mainly in the packing of otherwise similar molecules can be interpreted by studying the packingdifferences. Many excellent works are collected in Orxanic SolidState Chrmistr-y ' ) and Structure and Properties of' Molrcular Crjsstals. 2, Among the above solid-state reactions, a single crystal-to-single crystal transformation is very attractive, because both structures of the reactant and product are obtained by X-ray analysis using only one crystal. And the topochemical process can be easily speculated.The first example reported is the [2 + 21 photocycloaddition of 2,5-distyrylpyradine."' Further details will be discussed in section 5.1 in this volume. Other typical examples are the photopolymerization of diacetylene d e r i~a t i v e s ,~) the [2 + 21 photodimerization of 5-benzylidenecy~lopentanones~) and thermal dimerization of o-benzenedithiol cobalt complex.') In all the case the reaction proceeds almost keeping the single crystal form and the movement of each atom can be presumed from the structures before and after the reaction. The composite diagram of the reactant and product structures is very informative. However, the reaction does not alway proceed smoothly, that is, obeying first-order kinetics, from the intial stage to the final stage. The structures at several intermediate stages are essential for elucidating the reaction process. Moreover, a systematic analysis of related crystals is necessary to obtain a quantitative mechanism.In this section we describe a systematic analysis of reactions occurring in crystals keeping their single crystal forms. From several intermediate structures obtained by X-ray analyses, we have observed various reaction pathways and obtained a quantitative relationship between the macroscopic reaction rate and the microscopic atomic arrangement in a series of related crystals. Since such a stepwise X-ray structure analysis is a very effective method for elucidating the reaction mechanism, we call the analysis "dynamic structure analysis", and the reaction that enables the dynamic structure analysis is termed "crystalline-state reaction".')

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Structure of the racemate produced by X-ray exposure of bis(2,3-butanedione dioximato) [(R)-methoxycarbonylethyl](pyridine)cobalt(III)

Cited by 11 publications

References 2 publications

Dynamic motion and various reaction paths of cobaloxime complexes in crystalline-state photoreaction

Dynamic motion and various reaction paths of cobaloxime complexes in crystalline-state photoreaction

Direct Observation of Deuterium Migration in Crystalline-State Reaction by Single Crystal Neutron Diffraction IV. “Hula-Twist” Rotation of a Long Alkyl Radical Produced by Photoirradiation

Crystalline‐State Reaction

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