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Synthesis, Structure and Spectral, and Electrochemical Properties of New Mononuclear Ruthenium(III) Complexes of Tris[(benzimidazol‐2‐yl)methyl]amine: Role of Steric Hindrance in Tuning the Catalytic Oxidation Activity
Author(s) -
Murali Mariappan,
Mayilmurugan Ramasamy,
Palaniandavar Mallayan
Publication year - 2009
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200900119
Subject(s) - chemistry , ruthenium , steric effects , medicinal chemistry , ligand (biochemistry) , amine gas treating , catalysis , cyclohexene , allylic rearrangement , photochemistry , stereochemistry , inorganic chemistry , organic chemistry , biochemistry , receptor
The new mononuclear Ru III complexes [Ru(ntb)Cl 2 ]Cl ( 1 ), [Ru(ntb)Cl 2 ]ClO 4 ( 1a ), and [Ru(mntb)Cl 2 ]Cl ( 2 ) (ntb = tris(benzimidazol‐2‐ylmethyl)amine, mntb = tris( N ‐methylbenzimidazol‐2‐ylmethyl)amine) have been synthesized and characterized. The X‐ray crystal structure of 1 reveals that the coordination geometry around the Ru III center is distorted octahedral in which four sites are occupied by the tetradentate ligand ntb and the remaining cis positions by two chloride ions. The stronger Ru–N bzim bonds elongate the Ru–Cl bonds thereby labilizing the coordinated chloride ions. In the electronic absorption spectra the Ru III complexes show two bands corresponding to π(bzim) → t 2g (Ru) and pπ(Cl – ) → t 2g (Ru) ligand‐to‐metal charge transfer (LMCT) transitions along with intraligand transitions in the UV region. Complex 1 shows rhombic EPR spectral features ( g 1 , 2.238; g 2 , 2.071; g 3 , 1.790). The Ru III complexes display both Ru III → Ru II reduction and Ru III → Ru IV oxidation processes. Complexes 1 and 2 catalyze the allylic oxidation of cyclohexene, selective and higher epoxidation of cyclooctene, and hydroxylation of alkanes in the presence of the peroxide TBHP and the peracid m ‐CPBA as cooxidants illustrating that the electronic and steric effects of tripodal 4 N ligands can be tuned to catalyze the effective oxidative transformation of organic compounds. ESI‐MS studies reveal the formation of ruthenium peroxido species in these catalytic reactions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)