Formation of metallacarboxylic acids through Hieber base reaction. A density functional theory study

Abstract

Using density functional theory (B97-D/ECP2/PCM//RI-BP86/ECP1 level), we have studied the effects of ligand variation on OH− uptake by transition-metal carbonyls (Hieber base reaction), i.e., LnM(CO) + OH− → [LnM(CO2H)]−, M = Fe, Ru, Os, L = CO, PMe3, PF3, py, bipy, Cl, H. The viability of this step depends notably on the nature of the co-ligands, and a large span of driving forces is predicted, ranging from ΔG = −144 kJ/mol to +122 kJ/mol. Based on evaluation of atomic charges from natural population analysis, it is the ability of the co-ligands to delocalize the additional negative charge (through their π-acidity) that is the key factor affecting the driving force for OH− uptake. Implications for the design of new catalysts for water gas shift reaction are discussed. Graphical abstractᅟ Electronic supplementary materialThe online version of this article (10.1007/s00894-018-3915-1) contains supplementary material, which is available to authorized users.

On the Catalytic Activity of [RuH2(PPh3)3(CO)] (PPh3=triphenylphosphine) in Ruthenium‐Catalysed Generation of Hydrogen from Alcohols: a Combined Experimental and DFT study

“…As a result, the WGSR reaction could not be achieved in this system, even though it is well known in parent Rh or Ru complexes. Some of us recently showed that the formation of metallacarboxylic acids through OH − attack on [ L n M (CO)] complexes ( M =Fe, Ru, Os, and L =CO, PMe 3 , PF 3 , py, bipy, Cl, H) can exhibit a large span of driving forces (ΔG=−144 kJ/mol to +122 kJ/mol) . The π‐acidity of the co‐ligands has been recognized as a key factor in the process, and the more electron‐withdrawing ligands were predicted to favour OH − uptake .…”

“…Some of us recently showed that the formation of metallacarboxylic acids through OH − attack on [ L n M (CO)] complexes ( M =Fe, Ru, Os, and L =CO, PMe 3 , PF 3 , py, bipy, Cl, H) can exhibit a large span of driving forces (ΔG=−144 kJ/mol to +122 kJ/mol) . The π‐acidity of the co‐ligands has been recognized as a key factor in the process, and the more electron‐withdrawing ligands were predicted to favour OH − uptake . Because the WGSR pathways are unfavourable, the resulting cycles for full dehydrogenation of methanol and water, Cycle‐1 or Cycle‐3 (Scheme ), have prohibitively high overall activation barriers (between 197.2 and 208.1 kJ/mol, see values for Cycle‐1 , Cycle‐3 and Cycle‐3′ in Table ).…”