Kinetic determination of transition metal-alkyl bond dissociation energies: application to organocobalt compounds related to B12 coenzymes

Tsou, Tsung Ting; Loots, Melanie J.; Halpern, Jack

doi:10.1021/ja00366a046

Cited by 148 publications

(77 citation statements)

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“…[1][2][3][4][5][6][7][8] Reactions of organic radicals (CCA C H T U N G T R E N N U N G (CH 3 )(X)R) with metalcentered radicals either produce an organometallic complex ([M À CA C H T U N G T R E N N U N G (CH 3 )(X)R]) or a metal hydride ([M À H]) and an olefin (CH 2 =C(X)R) by the metallo-radical abstracting a bhydrogen from the organic radical CCA C H T U N G T R E N N U N G (CH 3 )(X)R (Scheme 1a). [9] Abstract: The mechanisms for hydrogen-atom transfer from the cyanoisopropyl radical CCA C H T U N G T R E N N U N G (CH 3 ) 2 CN to [Co …”

Section: Reactions Of Metal-centered Radicals ([M]c) and Organometal supporting

confidence: 44%

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Bruin

Dzik

et al. 2009

Chemistry A European J

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The mechanisms for hydrogen-atom transfer from the cyanoisopropyl radical (*)C(CH(3))(2)CN to [Co(II)(por)](*) (yielding [Co(III)(H)(por)] and CH(2)=C(CH(3))(CN); por = porphyrinato) and the insertion of vinyl acetate (CH(2)=CHOAc) into the Co-H bond of [Co(H)(por)] (giving [Co(III){CH(OAc)CH(3)}(por)]) were investigated by DFT calculations. The results are compared with experimental data. These reactions are relevant to catalytic chain transfer (CCT) in radical polymerization of olefins mediated by [Co(II)(por)](*), the formation and homolysis of organo-cobalt complexes that mediate living radical polymerization of vinyl acetate, and cobalt-mediated hydrogenation of olefins. Hydrogen transfer from (*)C(CH(3))(2)CN to [Co(II)(por)](*) proceeds via a single transition state that has structural features resembling the products [Co(H)(por)] and CH(2)=C(CH(3))CN. The separated radicals approach to form a close-contact radical pair and then pass through the transition state for hydrogen-atom transfer to form [Co(III)(H)(por)] and CH(2)=C(CH(3))CN. This process provides a very low overall barrier for the hydrogen-atom transfer reaction (DeltaG(double dagger) = +3.8 kcal mol(-1)). The reverse reaction corresponding to the addition of [Co(H)(por)] to CH(2)=C(CH(3))CN has a low barrier (DeltaG(double dagger) = +8.9 kcal mol(-1)) as well. Insertion of vinyl acetate into the Co-H bond of [Co(III)(H)(por)] also proceeds over a low barrier (DeltaG(double dagger) = +11.4 kcal mol(-1)) hydrogen-transfer step from [Co(III)(H)(por)] to a carbon atom of the alkene to produce a close-contact radical pair. Dissociation of the radical pair, reorientation, and radical-radical coupling to form an organo-cobalt complex are the culminating steps in the net insertion of an olefin into the Co-H bond. The computed energies obtained for the hydrogen-atom transfer reactions from (*)C(CH(3))(2)CN to [Co(II)(por)](*) and from [Co(H)(por)] to olefins, as well as the organo-cobalt bond homolysis energies correspond well with the experimental observations. The mechanism of alkene insertion into the Co-H bond of [Co(III)(H)(por)] is of general interest, because the species does not contain any cis-vacant sites to the hydride and the usual migratory insertion pathway is not available. The low barrier predicted here for the multistep insertion process suggests that (depending on the bond strengths) even for systems that do have a cis-vacant site, the radical-type insertion might compete with classical migratory insertion.

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Section: Reactions Of Metal-centered Radicals ([M]c) and Organometal supporting

confidence: 44%

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Bruin

Dzik

et al. 2009

Chemistry A European J

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“…[3,4]. Inaddition, they are also used asmodels of reaction centers of metalloenzymes [5,6], and nonlinearopticalmaterials [7]. Moreover,inbiologicaland artificialsystems allosteric regulation is effective in controlling molecularf unctions, such asm olecularr ecognition and biological activity [8].…”

Section: Discussionsupporting

confidence: 45%

Crystal structure of 2,2'-[(1,4-butylene)dioxybis(nitrilomethylidyne)]- dinaphthol, C26H24N2O4

Dong¹,

Duan²,

Wu³

et al. 2006

Zeitschrift Für Kristallographie - New Crystal Structures

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Source of materialToane thanol solution (10 ml) of 2-hydroxy-1-naphthaldehyde (349.5 mg, 2.01 mmol) wasadded anethanol solution (3 ml) of 1,4-bis(aminooxy)butane (120.12 mg, 1.0 mmol). After the solution hadbeen stirred at55°Cfor 4h,the mixture wasfiltered, washed successively with ethanoland ethanol/hexane (1:4), respectively. DiscussionRecently, agreatdealofattention hasfocused on aseriesof N , N ¢ -bis(salicylidene)ethylenediamine (salen) and its derivatives [1,2], because these compounds easily form metallosalenc omplexes and some of them have excellent catalyticactivities for epoxidation, aziridination, etc. [3,4]. Inaddition, they are also used asmodels of reaction centers of metalloenzymes [5,6], and nonlinearopticalmaterials [7]. Moreover,inbiologicaland artificialsystems allosteric regulation is effective in controlling molecularf unctions, such asm olecularr ecognition and biological activity [8]. Totune or improve such functions, chemicalmodifications of abasic salen skeleton is very interesting and important [9][10][11][12]. Sothe introduction of some functionalgroups or substitution of some partswith appropriate ones are effective and inevitable. Some of such compounds have two salicylidene units, but the linkage waslimited to analkylene (-CH = N-C-X-C-N = CH-) group due to the ease of preparation. Ifan O -alkyloxime moiety which is observed for 2-hydroxy-1-naphthaldehyde. The title compound is sufficiently stable to resist scrambling of the C = N bonds. This maybeascribed to lower reactivity of the oxime C = N bonds toward nucleophiles.

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“…These compounds can easily form metallosalen complexes, and some of them show excellent catalytic activities for epoxidation and aziridination [3,4]. In addition, they are also used as models of reaction centers of metalloenzymes [5,6], and nonlinear optical materials [7]. Moreover, in biological and artificial systems allosteric regulation is effective in controlling molecular functions, such as molecular recognition and biological activity [8].…”

Section: Discussionsupporting

confidence: 41%

Crystal structure of 4,4',6,6'-tetra(tert-butyl)-2,2'-[(1,4-butylene)dioxybis( nitrilomethylidyne)]diphenol, C34H52N2O4

Dong¹,

Jun²,

Yang³

2007

Zeitschrift Für Kristallographie - New Crystal Structures

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C34H52N2O4, monoclinic, P121/c1 (no. 14), a = 15.166(3) Å, b = 9.981(2) Å, c = 11.899(3) Å, b = 110.898(3)°, V = 1682.7 Å 3 , Z = 2, Rgt(F) = 0.068, wRref(F 2 ) = 0.227, T = 298 K. Source of materialTo an ethanol solution (10 ml) of 3,5-di(tert-butyl)-2-hydroxybenzaldehyde (236.7 mg, 1.00 mmol) was added an ethanol solution (3 ml) of 1,4-bis(aminooxy)butane (60.1 mg, 0.50 mmol). After the solution had been stirred at 55°C for 6 h, the mixture was filtered, washed successively with ethanol and ethanol/hexane (1:4), respectively. The isolated product was dried under reduced pressure and purified with recrystallization from ethanol to yield 133.8 mg of colorless crystalline solid (yield 48.4 %, m.p. 136-137°C). Block-like colorless single crystals of the title compound suitable for X-ray diffraction studies were obtained by slow evaporation of an acetone solution at room temperature. Elemental analysis found: C, 73.76 %; H, 9.67 %; N, 5.16 %; calc. for C34H52N2O4: C, 73.87 %; H, 9.48 %; N, 5.07 %. IR data are available in the CIF. DiscussionRecently, great attention was focused on N,N¢-bis(salicylidene)-ethylenediamine (salen) and its derivatives [1,2]. These compounds can easily form metallosalen complexes, and some of them show excellent catalytic activities for epoxidation and aziridination [3,4]. In addition, they are also used as models of reaction centers of metalloenzymes [5,6], and nonlinear optical materials [7]. Moreover, in biological and artificial systems allosteric regulation is effective in controlling molecular functions, such as molecular recognition and biological activity [8]. To improve such functions, chemical modifications of a basic salen skeleton are very interesting and important [9][10][11][12][13][14]. So, the introduction of some functional groups or substitution of some parts with appropriate ones are effective and inevitable. If an O-alkyl oxime moiety (-CH=N-O-(CH2)n-O-N=CH-) is used instead of (-CH=N-C-X-C-N=CH-) group, the large electronegativity of oxygen atoms is expected to affect strongly the electronic properties of N2O2 coordination sphere, which can lead to different and novel properties and structures of the resulted complexes. Thus, we have recently studied some novel salen-type bisoxime chelating compounds on the basis of O-alkyloxime instead of the imine moiety [13,14]. Here, we report another novel salen-type bisoxime chelating compound, which is sufficiently stable to resist scrambling of the C=N bonds.In the crystal structure of the title compound, the molecule adopts an conformation where the two salicylaldoxime moieties are apart from each other. The oxime groups and phenolic alcohols

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Kinetic determination of transition metal-alkyl bond dissociation energies: application to organocobalt compounds related to B12 coenzymes

Cited by 148 publications

References 0 publications

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Crystal structure of 2,2'-[(1,4-butylene)dioxybis(nitrilomethylidyne)]- dinaphthol, C26H24N2O4

Crystal structure of 4,4',6,6'-tetra(tert-butyl)-2,2'-[(1,4-butylene)dioxybis( nitrilomethylidyne)]diphenol, C34H52N2O4

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Kinetic determination of transition metal-alkyl bond dissociation energies: application to organocobalt compounds related to B12 coenzymes

Cited by 148 publications

References 0 publications

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [CoII(por)]. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [CoII(por)]. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Crystal structure of 2,2'-[(1,4-butylene)dioxybis(nitrilomethylidyne)]- dinaphthol, C26H24N2O4

Crystal structure of 4,4',6,6'-tetra(tert-butyl)-2,2'-[(1,4-butylene)dioxybis( nitrilomethylidyne)]diphenol, C34H52N2O4

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Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins

Hydrogen‐Atom Transfer in Reactions of Organic Radicals with [Co^II(por)]^. (por=Porphyrinato) and in Subsequent Addition of [Co(H)(por)] to Olefins