Intramolecular carbon-hydrogen bond activation in aqueous solution:  preparation of a unique cobalt(III)-alkyl complex by deprotonation of an agostic intermediate.  Crystal structure of [Co(III)(dacoda-C(2))(H2O)].cntdot.2H2O

Kanamori, Kan; Broderick, William E.; Jordan, Richard F.; Willett, Roger D.; Legg, J. Ivan

doi:10.1021/ja00282a058

Cited by 54 publications

(19 citation statements)

References 3 publications

(6 reference statements)

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“…One of the hydrogen atoms is situated 3.066Å from the cobalt and this close proximity poises the hydrogen for an agostic interaction with the metal center, which may help facilitate C-H bond activation. 26,27 The X-ray structural data obtained for Co II (BQN) 2 supports our computational ndings that show the corresponding Co-H bond distance of 3.076Å. The p-p stacking interactions between the aryl rings and quinoline moieties predicted in the computation are also present in the experimentally determined structure.…”

Section: Initial Complex Formationsupporting

confidence: 80%

Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides

Liu

Bacsa

et al. 2020

Chem. Sci.

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Section: Initial Complex Formationsupporting

confidence: 80%

Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides

Liu

Bacsa

et al. 2020

Chem. Sci.

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“…This result might indicate that the bridging methylene group has a smaller trans influence than a normal alkyl group or that the distorted equatorial ligand has a smaller steric cis influence. In addition, the Co−C bond length of 1.927(5) Å is not only shorter than in normal imine/oxime-type structures, but shorter than almost all examples of organocobalt(III) compounds in which the coordinated alkyl is part of a polydentate ligand. ,− …”

Section: Resultsmentioning

confidence: 91%

Novel Chemistry of Carbon Bound to Cobalt in Organocobalt Complexes Related to B12

1996

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A rare Co−N−C three-membered ring has been formed by a novel pathway involving a facile interligand nucleophilic addition of an equatorial nitrogen donor to a ligated axial carbon in some organocobalt complexes. The highly distorted structure of a typical resulting complex provides clear experimental evidence useful in assessing hypotheses and computations concerning Co−C bond activation in B12 chemistry. Treatment of R = −CH2X (X = halogen) derivatives of imine/oxime B12 models of the type [LCo((DO)(DOH)pn)R]+ with base afforded major products with striking NMR spectral features in common, e.g., two one-proton olefinic doublets (J ≈ 3 Hz) and two one-proton singlets. The X-ray structure for the pyridine (py) derivative [pyCo(N-CH2-CHEL)]+ (1) reveals two unexpected features: a three-membered metallocycle containing an η2-aminomethylene group, and an enamine (N−CCH2) in place of one imine moiety (NC−CH3). The C−Co−N ring angle is acute (43.7°) with the distortion of the coordination sphere concentrated in the Co−C and the Co−N ring linkages, which move away from the normal pseudooctahedral positions. Studies of the formation of the aqua analog of 1, [H2OCo(N-CH2-CHEL)]+ (3), in aqueous solution suggest that the initial intermediate formed is deprotonated at one imine methyl. Ring closure in the short-lived deprotonated intermediate is facile. Published calculations predict that such ring closure could occur and that, of two processes which could facilitate Co−C bond cleavage (θ-bending of the N−Co−C angle and φ-bending of the Co−C−C angle), the latter factor should be more significant in weakening the Co−C bond. There is large θ-bending in 1; thus, the new metallocyclic B12 analogs afford the first experimental test of these calculations. Our findings that the Co−C bond in 1 is short and that the bond did not readily cleave support the predictions of the calculations.

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“…The reaction is reversed upon addition of HOTf (eq 2). While deprotonation of aliphatic agostically bound protons is a known process, it has not yet been demonstrated with aromatic hydrocarbons. In the latter, the HX elimination during metalation is solely attributed to the electrophilic pathway . ,, If 2a is however viewed as an arenium species, then its thermodynamic stability is somewhat unexpected, as most of the protonated Wheland intermediates can be observed only at low temperatures and/or in the presence of excess of superacids …”

Section: Resultsmentioning

confidence: 99%

Formation of η² C−H Agostic Rhodium Arene Complexes and Their Relevance to Electrophilic Bond Activation

et al. 1998

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Reaction of the ligand 1,3-bis((di-tert-butylphosphino)methyl)benzene (1a) with the [RhCO] + fragment in THF resulted in clean formation of the crystallographically characterized bis-chelated complex 2a which contains an η 2 agostic Rh C-H bond. Both the NMR data and the X-ray crystal structure show strong interaction between the metal center and the agostic C-H bond, which results in high acidity of the agostic proton. Reaction of 2a with a weak organic base (NEt 3 or collidine) affords the known cyclometalated complex 3. Reaction of the new ligand 1,3-bis((di-tert-butylphosphino)methyl)-4,5,6-trimethoxybenzene (1b) with the [RhCO] + fragment in THF gives the analogous to 2a agostic complex 2b. Analysis of the NMR data and the reactivity of both 2a and 2b showed that there is very little, if any, contribution of a metal arenium structure. This interpretation is supported by B3LYP/LANL2DZ density functional calculations on model compounds. Thus, deprotonation of η 2 aromatic C-H agostic complexes can be proposed as an alternative route to electrophilic metalation of aromatic compounds.

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Intramolecular carbon-hydrogen bond activation in aqueous solution: preparation of a unique cobalt(III)-alkyl complex by deprotonation of an agostic intermediate. Crystal structure of [Co(III)(dacoda-C(2))(H2O)].cntdot.2H2O

Cited by 54 publications

References 3 publications

Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides

Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides

Novel Chemistry of Carbon Bound to Cobalt in Organocobalt Complexes Related to B12

Formation of η² C−H Agostic Rhodium Arene Complexes and Their Relevance to Electrophilic Bond Activation

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Intramolecular carbon-hydrogen bond activation in aqueous solution: preparation of a unique cobalt(III)-alkyl complex by deprotonation of an agostic intermediate. Crystal structure of [Co(III)(dacoda-C(2))(H2O)].cntdot.2H2O

Cited by 54 publications

References 3 publications

Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides

Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides

Novel Chemistry of Carbon Bound to Cobalt in Organocobalt Complexes Related to B12

Formation of η2 C−H Agostic Rhodium Arene Complexes and Their Relevance to Electrophilic Bond Activation

Contact Info

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Formation of η² C−H Agostic Rhodium Arene Complexes and Their Relevance to Electrophilic Bond Activation