Previously, we reported the synthesis of Ti[N(o-(NCH 2 P( i Pr) 2 )C 6 H 4 ) 3 ] and the Fe-Ti complex, FeTi[N(o-(NCH 2 P( i Pr) 2 )C 6 H 4 ) 3 ], abbreviated as TiL (1), and FeTiL (2), respectively. Herein, we describe the synthesis and characterization of the complete redox families of the monometallic Ti and Fe-Ti compounds. Cyclic voltammetry studies on FeTiL reveal both reduction and oxidation processes at -2.16 and -1.36 V (versus Fc/Fc + ), respectively. Two isostructural redox members, [FeTiL] + and [FeTiL] - (2 ox and 2 red , respectively) were synthesized and characterized, along with BrFeTiL (2-Br) and the monometallic [TiL] + complex (1 ox ). The solid-state structures of the [FeTiL] +/0/- series feature short metal-metal bonds, ranging from 1.94-2.38 Å, which are all shorter than the sum of the Ti and Fe single-bond metallic radii (cf. 2.49 Å). To elucidate the bonding and electronic structures, the complexes were characterized with a host of spectroscopic methods, including NMR, EPR, and 57 Fe Mössbauer, as well as Ti and Fe K-edge X-ray absorption spectroscopy (XAS). These studies, along with hybrid density functional theory (DFT) and time-dependent DFT calculations, suggest that the redox processes in the isostructural [FeTiL] +,0,- series are primarily Fe-based and that the polarized Fe-Ti π-bonds play a role in delocalizing some of the additional electron density from Fe to Ti (net 13%).
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We thank Prof. John Lipscomb for access to the EPR spectrometer, Dr. Ryan Cammarota for collecting EPR data, Bernd Mienert for collecting the Mössbauer spectra, and Dr. Victor G. Young, Jr. for assistance with X-ray crystallography. C.C.L. acknowledges the NSF (CHE-1800110) for support of the synthetic work. K.M.L acknowledges NSF (CHE-1454455) and the Alfred P. Sloan Foundation for support. M.T., E.B., and S.Y. also gratefully acknowledge the financial support from the Max-Planck Society, in particular the joint work space between MPI-CEC and MPI-KOFO. X-ray diffraction experiments were performed using a crystal diffractometer purchased through a grant from NSF/MRI (1229400) and the University of Minnesota. The work at MPI has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 675020 (675020-MSCA-ITN-2015-ETN). Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393) . The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of NIGMS or NIH.
© 2019 American Chemical Society.