Synthesis, Characterization, and Reactivity Studies of Highly Reduced Early-Metal Complexes Supported by Imidazolin-2-Iminato Ligands
Abstract
Our group has shown that reduction of titanium complexes supported by the sterically encumbering N-donor ligands 1,3‐bis(Dipp)imidazolin‐2‐iminato (ImDippN−) and ketimine guanidinate (ketGuan = [(tBuC=N)C(NDipp)2]-) gives access to electron rich platforms featuring a metal coordinated, reduced, dearomatized arene substituent, which act as an electronic reservoir capable of facilitating multi-electron transfer chemistry driven by the rearomatization driving force. For instance, the arene-masked Ti(II) synthon (DippketGuan)(η6-ImDippN)Ti (Dipp = 2,6-iPr2C6H3) (TiDipp) is a versatile and potent one- and two-electron reductant capable of distinctive late-metal type reactivity such as transfer hydrogenation and catalytic olefin hydrogenation. Interestingly, TiDipp can mediate the reversible cleavage of thiophene and, as demonstrated here, thiophene hydrodesulfurization (HDS). Motivated by the rich redox chemistry displayed by complex TiDipp, we synthesized the related derivative (Xylketguan)(η6-ImDippN)Ti (Xyketguan = [(tBuC=N)C(NXylyl)2]-, Xylyl = 2,5-Me2C6H3) (TiXyl). Complex TiXyl exhibits an improved steric profile that allows for the intermolecular capture and activation of monocyclic and polycyclic arenes catalyzing their hydrogenation under mild conditions. Since the 2-electron chemistry of compounds TiDipp and TiXyl is enabled by the redox non-innocent character of the imidazolin-2-iminato ligand, we set to explore the lone ability of this ligand to support multinuclear systems with multiple metal-arene interactions. In this context, reduction of the monomeric species (ImDippN)TiCl3 with KC8 gives us access to the “masked” Ti(III)/Ti(III) and Ti(II)/Ti(II) dimers [(η6-ImDippN)Ti]2 (SynTi-I) and {[(Et2O)2K](μ-η6:η6-ImDippN)Ti}2 (SynTi-0). Preliminary reactivity studies show these bimetallic molecular platforms can effectively reduce several equivalents of substrates such as cyclooctatetraene and organoazides via 4, 6, and 8-electron transfers, stablishing these complexes as the first examples of discrete Ti(I)/Ti(I) and Ti(0)/Ti(0) synthons, respectively. Moreover, our efforts to extrapolate these studies to the earliest 3d metal, scandium have given us access to Sc(III) compound (DippKetguan)Sc(DippNIm)(Cl)(ScCl), which reduction with potassium naphthalenide affords [{(2,6-iPr2C6H3N)[2-iPrC6H3-6-(η1-CMe2)N]C(NCHtBu2)}Sc(DippNIm)(THF)][K(18-c-6)(Et2O)] (ScC-H) and [(DippKetguan)Sc(η4-C10H8)(DippNIm)][K(18-c-6)] (ScNaph). Cyclometalated complex ScC-H is the product of intramolecular C-H activation and shows interesting phase-dependent tautomerism. This example is notable as it shows the first example of a reductively induced C-H activation and cleavage by a Group 3 metal. On the other hand, ScNaph is a rare example of a scandium complex of reduced naphthalene. The studies presented here show the ability of inexpensive, abundant early transition metal-based complexes to perform challenging redox and multielectron transfer processes relevant to fields such as biological systems modeling, small molecule activation, and advanced electronic devices.
Subject Area
Inorganic chemistry
Recommended Citation
Gómez Torres, María Alejandra, "Synthesis, Characterization, and Reactivity Studies of Highly Reduced Early-Metal Complexes Supported by Imidazolin-2-Iminato Ligands" (2022). ETD Collection for University of Texas, El Paso. AAI29322476.
https://scholarworks.utep.edu/dissertations/AAI29322476