Acetamide Coordination in a Nickel(I) Macrocyclic Complex:  Synthesis, Properties, and X-ray Crystal Structure of a Five-Coordinate Nickel(I) Iminol Complex of 1,3,6,8,12,15-Hexaazatricyclo[13.3.1.1<sup>8,12</sup>]icosane

Suh, Myunghyun Paik; Oh, Kye Young; Lee, Jae Woo; Bae, Yeon

doi:10.1021/ja953106g

Cited by 56 publications

(22 citation statements)

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“…5 Bond distances within the iminol moiety of 5 (Table 2) lie closer to that expected for alcohol/imine structure, even when compared with one of few previously reported transition-metal iminol complexes, ( R , S , R , S )-[Ni( L )(NHC(OH)CH 3 )] + (C–O= 1.242(7) Å; C–N= 1.314(7) Å; L= 1,3,6,8,12,15-hexaazatricyclo[13.3.1.18,12]icosane). 40 An O-bound linkage isomer for iminol 5 is ruled out by an increase in R-value during refinement of the X-ray structure. Although transition-metal iminol compounds are rare, 38–41 the N-bound linkage isomer (observed in 5 ) tends to be the thermodynamically favored form.…”

Section: Resultsmentioning

confidence: 99%

Nitrile Hydration by Thiolate- and Alkoxide-Ligated Co-NHase Analogues. Isolation of Co(III)-Amidate and Co(III)-Iminol Intermediates

et al. 2011

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Nitrile hydratases (NHases) are thiolate–ligated Fe(III)- or Co(III)-containing enzymes, which convert nitriles to the corresponding amide under mild conditions. Proposed NHase mechanisms involve M(III)–NCR, M(III)–OH, M(III)–iminol and M(III)–amide intermediates. Spectroscopic and kinetic data support the involvement of a M(III)–NCR intermediate. A H–bonding network facilitates this enzymatic reaction. There have been no reported crystallographically characterized examples of these key intermediates. Herein we describe two biomimetic Co(III)–NHase analogues that hydrate MeCN. Four key crystallographically characterized NHase intermediate anaologues, [CoIII(SMe2N4(tren))(MeCN)]2+ (1), [CoIII(SMe2N4(tren))(OH)]+ (3), [CoIII(SMe2N4(tren))(NHC(O)CH3)]+ (2), and [CoIII(OMe2N4(tren))(NHC(OH)CH3)]2+ (5) are described. Iminol–bound 5 represents the first example of a Co(III)-iminol compound in any ligand environment. Kinetic parameters (k1(298 K)= 2.98(5) M−1s−1, ΔH‡ = 12.65(3) kcal/mol, ΔS‡ = −14(7) e.u.) for nitrile hydration by 1 are reported, and the activation energy Ea= 13.2 kcal/mol is compared with that (Ea= 5.5 kcal/mol) of the NHase enzyme. A mechanism involving initial exchange of the bound MeCN for OH− is ruled out by the fact that nitrile exchange from 1 (kex(300 K)= 7.3(1) x10−3 s−1) is two orders of magnitude slower than nitrile hydration, and that hydroxide bound 3 does not promote nitrile hydration. Reactivity of an analogue that incorporates an alkoxide as a mimic of the highly conserved NHase serine residue shows that this moiety facilitates nitrile hydration under milder conditions. Hydrogen-bonding to the alkoxide stabilizes a Co(III)-iminol intermediate. Comparison of the thiolate versus alkoxide intermediate structures shows that C≡N bond activation and C=O bond formation proceed further along the reaction coordinate when a thiolate is incorporated into the coordination sphere.

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Section: Resultsmentioning

confidence: 99%

Nitrile Hydration by Thiolate- and Alkoxide-Ligated Co-NHase Analogues. Isolation of Co(III)-Amidate and Co(III)-Iminol Intermediates

et al. 2011

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“…The axial signal builds up within 10 min. Upon further gassing with 100% H 2 , a second methyl-coenzyme M reductase derived signal appears, designated MCR red2 , which is rhombic rather than axial [Albracht et al, 1988; for a Ni(I) macrocyclic complex exhibiting a rhombic EPR spectrum seeSuh et al, 1996]. Cell extracts of such reduced cells also show a high specific activity and also exhibit the MCR red2 signal.…”

Section: Epr-signal-exhibiting Forms Of Methylcoenzyme M Reductase: Mmentioning

confidence: 99%

Biochemistry of methanogenesis: a tribute to Marjory Stephenson:1998 Marjory Stephenson Prize Lecture

1998

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Historical overview In 1933, Stephenson & Stickland (1933a) published that they had isolated from river mud, by the single cell technique, a methanogenic organism capable of growth in an inorganic medium with formate as the sole carbon source. 4 H C 0 0-+ 4H' + CH, + 3 C 0 , + 2H,O AGO' =-144-5 kJ mol-' Methane formation from formate was shown to occur in a stepwise manner, by the preliminary decomposition of formic acid into CO, and H, followed by a reduction of CO, by H,, suggesting that formate was not an intermediate in the reduction of CO, to methane. HCOO-+ H+-+ H, + CO, 4H,+CO,-+ C H , + 2 H 2 0 AGO' =-3-5 kJ mol-' AGO' =-131 kJ mol-' Cell suspensions of the microorganism catalysed the reduction of methylene blue with H,, indicating that the methanogen contained an enzyme which activates molecular hydrogen. H,-+ 2e-+ 2H+ E; =-414mV This enzyme had been discovered by Stephenson & Stickland (1931a) 2 years before in a number of bacterial species and was named by them 'hydrogenase'. The paper by Stephenson & Stickland (1933a) is considered to mark the beginning of the modern era for study of methanogenesis (Wolfe, 1993). It is the first Except when otherwise noted, the free energy changes given for methanogenic reactions were calculated from the free energies of formation from the elements of the substrates and products with non-gaseous compounds at 1 M aqueous solution and gaseous compounds in the gaseous state at 1 atmosphere pressure (101 kPa). The free energy changes of formation were taken from Thauer eta/. (1977). 0002-2667 0 1998 SGM Glucose-+ 3C0, + 3CH, AGO' =-418.1 kJ mol-' This reaction is not catalysed by single microorganisms but by syntrophic associations of microorganisms. First the glucose is fermented to acetate, CO, and H, or to acetate, formate and H, : Glucose + 2H,O + 2CH3COO-+ 2H' + 2C0, + 4H2 AGO' =-215.7 kJ mol-' Glucose + 2H20-+ 2CH3COO-+ 2HC00-+ 4H' + 2H, AGO' =-208.7 kJ mol-1 These fermentations are brought about by strictly anaerobic bacteria and/or protozoa. In a second step, the products of glucose fermentation are then converted to methane, the rate of conversion being such that the concentrations of acetate (< 1 mM), formate (< 0.1 mM) and H, (< 1 pM) in the anaerobic sediments remain very low (Zinder, 1993). CH3COO-+Hf-+ C02+CH, AGO' =-36 kJ mol-' 4H, + CO,-+ CH, + 2H20 AGO' =-131 kJ mol-' 4HC00-+4H+ + CH,+3C02+2H,0 AGO' =-144.5 kJ mol-' H-S-CoM, coenzyme M ; H-S-COB, coenzyme B ; H,SPT, tetrahydrosarcinapterin, which is the modified tetrahydromethanopterin (for structures see Fig. 3) present in the Methanosarcinales (Gorris & van der Drift, 1994). Reaction" Enzyme (gene) Most recent literature Acetate + CoA + acetyl-CoA + H,O AGO' = + 35.7 k J rnol-lt

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“…[3] With a d 9 -electron configuration, mononuclear Ni I is a rather uncommon oxidation state. Previously isolated Ni I -compounds were typically stabilized by electron rich ligands such as phosphanes [4] , amines [5] , carbenes [6] , β -diketiminates [4g,7] , Cp − (Cyclopentadienyl) [6c,8] , or were incorporated in alumo-phosphates [9] . All mononuclear compounds include strongly σ-donating C-, N-, P-, S-, O-, or halogen atoms in their ligands.…”

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confidence: 99%

“…All mononuclear compounds include strongly σ-donating C-, N-, P-, S-, O-, or halogen atoms in their ligands. [4,5,6,7,8,10] An open question is, if Ni I leads to better performance in catalysis than Ni 0 or Ni II . Towards this goal, Stephan's dinuclear Ni I β -diketiminates were used by Driess and Limberg for small molecule activation.…”

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confidence: 99%

[Ni(cod)₂][Al(OR^F)₄], a Source for Naked Nickel(I) Chemistry

et al. 2015

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The straightforward synthesis of the cationic, purely organometallic NiI-salt [Ni(cod)2]+[Al(ORF)4]– was realized through a reaction between Ni(cod)2 and Ag[Al(ORF)4]. Crystal structure, EPR, XANES and cyclic voltammetry confirmed the presence of a homoleptic NiI-olefin complex. Weak interactions between the metal centre, the ligands and the anion provide a good starting material for further cationic NiI-chemistry.

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Acetamide Coordination in a Nickel(I) Macrocyclic Complex: Synthesis, Properties, and X-ray Crystal Structure of a Five-Coordinate Nickel(I) Iminol Complex of 1,3,6,8,12,15-Hexaazatricyclo[13.3.1.1^8,12]icosane

Cited by 56 publications

References 64 publications

Nitrile Hydration by Thiolate- and Alkoxide-Ligated Co-NHase Analogues. Isolation of Co(III)-Amidate and Co(III)-Iminol Intermediates

Nitrile Hydration by Thiolate- and Alkoxide-Ligated Co-NHase Analogues. Isolation of Co(III)-Amidate and Co(III)-Iminol Intermediates

Biochemistry of methanogenesis: a tribute to Marjory Stephenson:1998 Marjory Stephenson Prize Lecture

[Ni(cod)₂][Al(OR^F)₄], a Source for Naked Nickel(I) Chemistry

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Acetamide Coordination in a Nickel(I) Macrocyclic Complex: Synthesis, Properties, and X-ray Crystal Structure of a Five-Coordinate Nickel(I) Iminol Complex of 1,3,6,8,12,15-Hexaazatricyclo[13.3.1.18,12]icosane

Cited by 56 publications

References 64 publications

Nitrile Hydration by Thiolate- and Alkoxide-Ligated Co-NHase Analogues. Isolation of Co(III)-Amidate and Co(III)-Iminol Intermediates

Nitrile Hydration by Thiolate- and Alkoxide-Ligated Co-NHase Analogues. Isolation of Co(III)-Amidate and Co(III)-Iminol Intermediates

Biochemistry of methanogenesis: a tribute to Marjory Stephenson:1998 Marjory Stephenson Prize Lecture

[Ni(cod)2][Al(ORF)4], a Source for Naked Nickel(I) Chemistry

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Product

Resources

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Acetamide Coordination in a Nickel(I) Macrocyclic Complex: Synthesis, Properties, and X-ray Crystal Structure of a Five-Coordinate Nickel(I) Iminol Complex of 1,3,6,8,12,15-Hexaazatricyclo[13.3.1.1^8,12]icosane

[Ni(cod)₂][Al(OR^F)₄], a Source for Naked Nickel(I) Chemistry