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On the Catalytic Activity of [RuH 2 (PPh 3 ) 3 (CO)] (PPh 3 =triphenylphosphine) in Ruthenium‐Catalysed Generation of Hydrogen from Alcohols: a Combined Experimental and DFT study
Author(s) -
Lorusso Patrizia,
Ahmad Shahbaz,
Brill née Schmid Karin,
ColeHamilton David J.,
Sieffert Nicolas,
Bühl Michael
Publication year - 2020
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202000159
Subject(s) - dehydrogenation , chemistry , formaldehyde , kinetic isotope effect , triphenylphosphine , methanol , catalysis , decarbonylation , ruthenium , medicinal chemistry , density functional theory , reaction mechanism , rate determining step , photochemistry , hydrogen , computational chemistry , organic chemistry , deuterium , physics , quantum mechanics
Using density functional theory calculations (at the B97‐D2//BP86 level) and measurements of kinetic isotope effects, we explored the mechanism of [RuH 2 (PPh 3 ) 3 (CO)] ( 22 ) in catalytic acceptor‐less dehydrogenation of methanol to formaldehyde. 22 is found to exhibit a similar activity as the previously studied [RuH 2 (H 2 )(PPh 3 ) 3 ] ( 1 b ) complex. On the computed pathway, η 2 →η 1 slippage of Ru‐bound formaldehyde prior to decoordination is indicated to be rate‐limiting, consistent with the low k H / k D KIE of 1.3 measured for this reaction. We also explored computationally the possibility of achieving complete dehydrogenation of methanol (into CO 2 and H 2 ), through subsequent decarbonylation of formaldehyde and water‐gas shift reaction of the resulting carbonyl complex. Complete pathways of this kind are traced for 22 and for [RuH 2 (PPh 3 ) 2 (CO) 2 ]. An alternative mechanism, involving a gem‐diol intermediate (obtained upon attack of OH − to coordinated formaldehyde), has also been investigated. All these pathways turned out to be unfavourable kinetically, in keeping with the lack of CO 2 evolution experimentally observed in this system. Our calculations show that the reactions are hampered by the low electrophilicities of the CO and HCHO ligands, making OH − uptake unfavourable. Consequently, the subsequent intermediates are too high‐lying on the reaction profiles, thus leading to high kinetic barriers and preventing full dehydrogenation of methanol to occur by this kind of mechanism.