Structural Characterization of Novel ortho‐Lithiated Imines

Abstract

Keywords: Lithiation / Ligand design / Schiff bases / Imines / Coordination polymer ortho-Metallated imines are commonly used as ligands for late transition metals. Unfortunately, not all metals, such as titanium, zirconium, and niobium, can undergo the necessary oxidative addition reactions to form the desired ortho-metallated complexes directly. Therefore, a synthetic methodology allowing easy access to this binding mode from simple early transition metal halides via an ortho-lithiated imine precursor is desirable. ortho-Lithiation of benzylamines and other systems has been well studied; in contrast, that of imines is poorly developed. However, inclusion of a 3,4-methylenedioxy group on phenyl imines allows for straightforward lithiation and simple isolation of the ortho-lithiated imines. NMR spectroscopy and single-crystal X-ray diffraction allowed for the structural elucidation of the clustering in these lithium complexes. It has been determined that the nature of the im-

Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

“…In the case of aryl imines,t he carbon-nitrogen functionality is weakly directing, hence ortho-directed lithiation is typically not observed, thoughi th as been observed in some specific cases. [5] More commonly, aryl imines undergo 1,2-nucleophilic addition, providing access to optically pure amines in the presenceo fa chiral,n on-racemic ligand.T he facile and thermodynamically favouredn ature of this 1,2-addition reaction has been reinforced by recent studies from the groups of Hevia and Capriati showings uch reactivity even in deep eutectic solvents and water. [6] Given the challengeo fr ing metalation, specifically ortho-lithiation,a na lternative methodology of lithium-bromide exchange at the ortho-site has been successfully employed.…”

Main Group Metal‐Mediated Transformations of Imines

“…In contrast, structural and solution state elucidation of the reactive ortho ‐lithiated imine intermediates, generally used in situ , have been rarely studied. It was not until 2010 that Schmidt isolated and structurally characterised eight ortho ‐lithiated alkyl and/or aryl imines bearing the 3,4‐methylenedioxy directing group [41] . A variety of structural motifs were obtained, ranging from simple dimers to more complex tetrameric and polymeric compositions, all of which are highly dependent on solvent choice (polar or non‐polar) and imine substituent bulk (Scheme 5).…”

(μ-1,2-Dimethoxyethane-κ2O:O′)bis[(1,2-dimethoxyethane-κ2O,O′)tris(1,1,1,5,5,5-hexafluoro-4-oxopent-2-en-2-olato-κ2O,O′)cerium(III)]

“…The crystal structures of complexes in which dme acts as a bridging ligand are not uncommon for cations of alkali metals (Li, Na, K and Rb) [Cambridge Structural Database (CSD; Allen, 2002) refcodes IMADAC (Beck et al, 2010), OJEKIY (Hsu & Liang, 2010), XAHZOX (Wong et al, 2010), CIMTAU and CIMTEY (Maudez et al, 2007), VEPJAC (Wang et al, 2006) and QEXWAR (Neander et al, 2000)]. The molecular structure of (II).…”