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Electronic Fine‐tuning of Ruthenium(II) Transfer Hydrogenation Catalysts with Ethanol as the Hydrogen Source
Author(s) -
Weingart Pascal,
Sun Yu,
Thiel Werner R.
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.202001370
Subject(s) - ruthenium , chemistry , transfer hydrogenation , triphenylphosphine , catalysis , phosphine , pyridine , osmium , chelation , photochemistry , medicinal chemistry , inorganic chemistry , organic chemistry
A series of ruthenium(II) complexes bearing tridentate N,N’‐diallyl‐2,6‐di(5‐butylpyrazol‐3‐yl)pyridine ligands was synthesized and characterized. Introduction of substituents in the 4‐position of the pyrazole rings tune the electron density at the ruthenium center, which was proved by correlation of the 31 P NMR chemical shifts with the σ p parameters of the Hammett equation. The structural elucidation of a phosphine‐free ruthenium(II) complex proves that one of the allyl side‐chains undergoes chelating coordination to the ruthenium site to realize a 18 VE center. This compound is the starting point for complexes of the type (N,N,N)Ru(L)(Cl) 2 bearing ligands L other than triphenylphosphine. The ruthenium(II) complexes were investigated for their activity in the transfer hydrogenation with ethanol as the hydrogen source. Here the logarithms of the measured turn‐over frequencies (TOF) correlate with the σ p parameters of the Hammett equation in terms of a linear free‐energy relationship.