Unusual rearrangement of modified PNP ligand based Ru complexes relevant to alcohol dehydrogenation catalysis

2019 ◽  
Vol 55 (76) ◽  
pp. 11350-11353 ◽  
Author(s):  
Shubham Deolka ◽  
Naziha Tarannam ◽  
Robert R. Fayzullin ◽  
Sebastian Kozuch ◽  
Eugene Khaskin
Keyword(s):  
Transition State ◽  
Bond Cleavage ◽  
Unusual Rearrangement ◽  
Ru Complexes ◽  
Alcohol Dehydrogenation

Hangman PNP pincer Ru complexes undergo an unusual sp2–sp3 C–C bond cleavage and formation via a spyrocyclopropane transition state.

Unusual Rearrangement of Modified PNP Ligand based Ru Complexes Relevant to Alcohol Dehydrogenation Catalysis

2019 ◽  
Author(s):  
Shubham Deolka ◽  
Naziha Tarannam ◽  
robert fayzullin ◽  
sebastian kozuch ◽  
Eugene Khaskin
Keyword(s):  
Bond Cleavage ◽  
Pincer Ligands ◽  
Formation Processes ◽  
Mechanistic Studies ◽  
Unusual Rearrangement ◽  
Isomerization Process ◽  
Ru Complexes ◽  
Alcohol Dehydrogenation

We report the synthesis of ‘hangman-type’ PNP pincer ligands and their associated Ru complexes. Upon deprotonation, the complexes undergo sp<sup>2</sup>-sp<sup>3</sup> C-C bond cleavage and subsequent C-C formation processes to form a new, one carbon unit longer backbone motif. Unlike the starting geometry, the products are completely inactive in alcohol dehydrogenation catalysis. DFT and mechanistic studies suggest an intramolecular isomerization process via a spyrocycle cyclopropane intermediate, dependent upon arm pyridine coordination and ligand sterics.

Unusual Rearrangement of Modified PNP Ligand based Ru Complexes Relevant to Alcohol Dehydrogenation Catalysis

2019 ◽  
Author(s):  
Shubham Deolka ◽  
Naziha Tarannam ◽  
robert fayzullin ◽  
sebastian kozuch ◽  
Eugene Khaskin
Keyword(s):  
Bond Cleavage ◽  
Pincer Ligands ◽  
Formation Processes ◽  
Mechanistic Studies ◽  
Unusual Rearrangement ◽  
Isomerization Process ◽  
Ru Complexes ◽  
Alcohol Dehydrogenation

We report the synthesis of ‘hangman-type’ PNP pincer ligands and their associated Ru complexes. Upon deprotonation, the complexes undergo sp<sup>2</sup>-sp<sup>3</sup> C-C bond cleavage and subsequent C-C formation processes to form a new, one carbon unit longer backbone motif. Unlike the starting geometry, the products are completely inactive in alcohol dehydrogenation catalysis. DFT and mechanistic studies suggest an intramolecular isomerization process via a spyrocycle cyclopropane intermediate, dependent upon arm pyridine coordination and ligand sterics.

Nitro–Nitrite Isomerization and Transition State Switching in the Dissociation of Ionized Nitromethane: A Threshold Photoelectron–Photoion Coincidence Spectroscopy Study

2009 ◽  
Vol 15 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Brandon Ferrier ◽  
Anne-Marie Boulanger ◽  
David M.P. Holland ◽  
David A. Shaw ◽  
Paul M. Mayer
Keyword(s):  
Transition State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Bond Cleavage ◽  
Cleavage Reaction ◽  
Nitrite Ion ◽  
Methyl Nitrite ◽  
Bond Cleavage Reaction ◽  
Entropy Of Activation ◽  
Lower Entropy

Threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has been employed to investigate the competition between bond cleavage and rearrangement reactions in the dissociation of ionized nitromethane, 1. Modeling TPEPICO breakdown diagrams with a combination of RRKM theory and ab initio calculations at the G3 level of theory allowed the derivation of the activation energy for the isomerisation of 1 to ionized methyl nitrite, 2, 82 kJ mol−1. In addition, evidence was found for a transition state switch in the bond cleavage reaction in 1 leading to CH3• + NO2+. As internal energy increases, the effective transition state for this reaction becomes tighter (i.e. is characterized by a lower entropy of activation, Δ‡S). Fitted thresholds for NO+ and CH2OHO+ ions, originating from the isomeric methyl nitrite ion, are consistent with G3 level ab initio calculations.

C-S Bond Cleavage of Allyl Thioethers by Zerovalent Ru Complexes

1998 ◽  
Vol 27 (2) ◽  
pp. 123-124 ◽  
Author(s):  
Jose Giner Planas ◽  
Masafumi Hirano ◽  
Sanshiro Komiya
Keyword(s):  
Bond Cleavage ◽  
Ru Complexes

Aglycon mimicking: Glycoside bond cleavage transition state mimics based on hydroxypyrrolidine inhibitors

1995 ◽  
Vol 36 (36) ◽  
pp. 6541-6544 ◽  
Author(s):  
Gitte Mikkelsen ◽  
Troels V. Christensen ◽  
Mikael Bols ◽  
Inge Lundt ◽  
Michael R. Sierks
Keyword(s):  
Transition State ◽  
Bond Cleavage ◽  
Glycoside Bond

The Influence of the 2-Alkoxy Group and of C-5 Substituents on the Direction of Reductive Cleavage of 2-Alkoxytetrahydrofurans by AlH2Cl in Ether Solution

1972 ◽  
Vol 50 (10) ◽  
pp. 1502-1512 ◽  
Author(s):  
P. C. Loewen ◽  
Miss L. P. Makhubu ◽  
R. K. Brown
Keyword(s):  
Transition State ◽  
Alkyl Group ◽  
Steric Effect ◽  
Bond Cleavage ◽  
Alkoxy Group ◽  
Ring Cleavage ◽  
Relative Ease ◽  
Ether Solution ◽  
A Minor ◽  
Minor Extent

The AlH2Cl hydrogenolysis of ether solutions of 2-alkoxytetrahydrofurans in which the alkoxy group is either CH3O, C2H5O, i-C3H7O, or t-C4H9O, gives only those products resulting from ring C—O bond cleavage. However, substituents at C-5 of 2-methoxytetrahydrofuran exert a strong effect on the ratio of ring to exo C—O bond cleavage. Thus, alkyl (electron donor) groups at C-5 promote an increase in the amount of exo cleavage, the proportion increasing from 62.5 to 100% as the C-5 alkyl group is changed from CH3 to t-C4H9. In contrast, electron withdrawing substituents, CH3OCH2— and C6H5, at C-5 favor ring cleavage to the extent of 93 and 84% respectively.The results are interpreted in terms of the influence that these substituents exert through their electronic properties on the relative ease of attainment of the transition state leading to either ring C—O or exo C—O bond cleavage. However, evidence is provided to show that the bulk steric effect of these substituents also controls, though to a minor extent, the proportion of ring to exo cleavage.

Transition-state structure for the hydronium-ion-promoted hydrolysis of α-d-glucopyranosyl fluoride

2015 ◽  
Vol 93 (4) ◽  
pp. 463-467 ◽  
Author(s):  
Jefferson Chan ◽  
Ariel Tang ◽  
Andrew J. Bennet
Keyword(s):  
Transition State ◽  
Kinetic Isotope Effect ◽  
Bond Cleavage ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Theoretical Modelling ◽  
Kinetic Isotope ◽  
Hydronium Ion ◽  
Anomeric Carbon ◽  
Hydrolysis Of

The transition state for the hydronium-ion-promoted hydrolysis of α-d-glucopyranosyl fluoride in water has been characterized by combining multiple kinetic isotope effect measurements with theoretical modelling. The measured kinetic isotope effects for the C1-deuterium, C2-deuterium, C5-deuterium, anomeric carbon-13, and ring oxygen-18 are 1.219 ± 0.021, 1.099 ± 0.024, 0.976 ± 0.014, 1.014 ± 0.005, and 0.991 ± 0.013, respectively. The transition state for the hydronium ion reaction is late with respect to both C–F bond cleavage and proton transfer.

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