Enhanced Fe-Centered Redox Flexibility in Fe–Ti Heterobimetallic Complexes

Previously, we reported the synthesis
of Ti­[N­(o-(NCH2P­(iPr)2)­C6H4)3] and
the Fe–Ti complex, FeTi­[N­(o-(NCH2P­(iPr)2)­C6H4)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]− (2ox and 2red, respectively)
were synthesized and characterized, along with BrFeTiL (2-Br) and the monometallic [TiL]+ complex (1ox). 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 57Fe 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%).