abstract
The new redox-noninnocent azoaromatic pincers 2-(arylazo)-1,10-phenanthroline (L-1) and 2,9-bis(phenyldiazo)-1,10-phenanthroline (L-2) are reported. The ligand L-1 is a tridentate pincer having NNN donor atoms, whereas L-2 is tetradentate having two azo-N donors and two N-donor atoms from the 1,10-phenanthroline moiety. Reaction of FeCl2 with L-1 or L-2 produced the pentacoordinated mixed-ligand Fe(II) complexes (FeLCl2)-Cl-1 (1) and (FeLCl2)-Cl-2 (2), respectively. Homoleptic octahedral Fe(II) complexes, mer-[Fe(L-1)(2)] (ClO4)(2) [3] (ClO4)(2) and mer-[Fe(L-2)(2)] (ClO4)(2) [4] (ClO4)(2), have been synthesized from the reaction of hydrated Fe(ClO4)(2) and L-1 or L-2. The ligand L-2, although having four donor sites available for coordination, binds the iron center in a tridentate fashion with one uncoordinated pendant azo function. Molecular and electronic structures of the isolated complexes have been scrutinized thoroughly by various spectroscopic techniques, single-crystal X-ray crystallography, and density functional theory. Beyond mere characterization, complexes 1 and 2 were successfully used as catalysts for the aerobic oxidation of primary and secondary benzylic alcohols. A wide variety of substituted benzyl alcohols were found to be converted to the corresponding carbonyl compounds in high yields, catalyzed by complex 1. Several control reactions were carried out to understand the mechanism of this alcohol oxidation reactions.
keywords
TRANSITION-METAL-COMPLEXES; ANION-RADICAL COMPLEXES; ACTIVE TRIS(AMIDO) LIGAND; ELECTRON-TRANSFER SERIES; AEROBIC OXIDATION; NICKEL(II) COMPLEXES; GALACTOSE-OXIDASE; SULFUR CLUSTERS; ALKENES SCOPE; NON-INNOCENCE
subject category
Chemistry
authors
Sinha, S; Das, S; Sikari, R; Parua, S; Brandao, P; Demeshko, S; Meyer, F; Paul, ND
our authors
Paula Cristina Ferreira da Silva Brandão
Assistant Researcheracknowledgements
The research was supported by DST (Project: YSS/2015/001552). S.S. thanks the IIESTS, R.S. thanks the UGC-RGNF, and S.P. thanks the CSIR for fellowship support. Financial assistance from the IIESTS is acknowledged. P.B. thanks the CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. We thank Prof. T. K. Paine (IACS, Kolkata), Prof. K. Pramanick (JU, Kolkata), and Dr. A. Saha (JU, Kolkata) for EPR experiments and Dr. S. Chatterjee (Srerampore College, Howrah) for helpful discussions. We also thank all the reviewers for their constructive suggestions during the revision period.