Cyclometallated imine complexes with oxygen-functionalised side-chains: Effect of the nature of the functional group, chain length and charge on coordination of the oxygen

Imines 1a-e derived from benzaldehyde or 3,4-dimethoxy benzaldehyde and ether- or alcohol-functionalised amines H₂NR (R = C₂H₄OMe, C₃H₆OMe, C₂H₄OH, C₃H₆OH,) all undergo cyclometallation with [Pd(OAc)₂]₃ (in some cases the dimeric products 2 were isolated) and subsequently react with lithium chloride to give chloride complexes, which are dimeric 3a-c, or monomeric for the C₃H₆OH-functionalised complexes 4d,e which have a C,N,O tridentate imine. The chloride complexes subsequently react with triphenylphosphine, and in some cases pyridine, to give mononuclear complexes 5 and 6, respectively with bidentate C,N imines. Treatment of 5 with silver salts leads to cations, the length of the tether (C2 or C3) and nature of the donor (ether or alcohol) and the counterion all effect whether or not the oxygen is coordinated.     

Structural and Morphological Transformations of Covalent Organic Nanotubes

Covalent organic nanotubes (CONTs) are porous one-dimensional frameworks connected through imine bonds via Schiff base condensation between aldehydes and amines. The presence of two amine groups at the ortho position in the structurally demanding tetraaminotriptycene (TAT) building block leads to multiple reaction pathways between the ditopic aldehyde and the tetratopic amine. We have synthesized five different monomers of CONT-1 by the Schiff base condensation reaction between TAT and o-anisaldehyde. The conversion of imine to imidazole bonding in a monomer is probed using NMR, mass spectrometry, and X-ray diffraction techniques. Solid-state NMR provide insights into the CONTs’ structural connectivity. A theoretical investigation suggests that the π-π stacking could be the driving force for rapid imine to imidazole conversion within the CONT-1. Microscopic imaging sheds further light on the self-assembly process of the CONTs, indicating both head-to-head and side-by-side assembly.     

Facile synthesis of β,β′-diketophosphine sulfides from imines and Lawesson’s reagent

In a convenient one-pot sequence, treatment of imines with Lawesson’s reagent (LR) followed by hydrolytic work-up leads to β,β′-diketophosphine sulfides in good to excellent yields. These compounds were isolated exclusively in their tautomeric β-keto-β′-enol form as was evident from IR and NMR spectroscopic data.