C,C- and C,N-Chelated Organocopper Compounds

Copper-catalyzed and organocopper-involved reactions are of great significance in organic synthesis. To have a deep understanding of the reaction mechanisms, the structural characterizations of organocopper intermediates become indispensable. Meanwhile, the structure-function relationship of organocopper compounds could advance the rational design and development of new Cu-based reactions and organocopper reagents. Compared to the mono-carbonic ligand, the C,N- and C,C-bidentate ligands better stabilize unstable organocopper compounds. Bidentate ligands can chelate to the same copper atom via η²-mode, forming a mono-cupra-cyclic compounds with at least one acute C-Cu-C angle. When the bidentate ligands bind to two copper atoms via η¹-mode at each coordinating site, the bimetallic macrocyclic compounds will form nearly linear C-Cu-C angles. The anionic coordinating sites of the bidentate ligand can also bridge two metals via μ₂-mode, forming organocopper aggregates with Cu-Cu interactions and organocuprates with contact ion pair structures. The reaction chemistry of some selected organocopper compounds is highlighted, showing their unique structure-reactivity relationships.

Main Group Metal-Mediated Transformations of Imines

Main-group-metal-mediated transformations of imines have earned a valued place in the synthetic chemist's toolbox. Their versatility allows the simple preparation of various nitrogen containing compounds. This review will outline the early discoveries including metallation, addition/cyclisation and metathesis pathways, followed by the modern-day use of imines in synthetic methodology. Recent advances in imine C-F activation protocols are discussed, alongside revisiting "classic" imine reactivity from a sustainable perspective. Developments in catalytic methods for hydroelementation of imines have been reviewed, highlighting the importance of s-block metals in the catalytic arena. Whilst stoichiometric transformations in alternative reaction media such as deep eutectic solvents or water have been summarised. The incorporation of imines into flow chemistry has received recent attention and is summarised within.

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

By exploring lithium-bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium-bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium-bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et₂ O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et₂ O yielded almost double the conversion of cyclic products than in THF.

Di(imino)aryltin(IV) dichlorides as tectons for heterometallic coordination compounds

Hydrolysis of [2-{(CH2O)2CH}C6H4]2SnCl2 (1) [prepared from 2-[(CH2O)2CH]C6H4MgBr and SnCl4, in 2 : 1 molar ratio] gave [2-(O=CH)C6H4]2SnCl2 (2). Treatment of with the appropriate amine, in the absence of a solvent or catalyst, resulted in the isolation in high yields of [2-(RN[double bond, length as m-dash]CH)C6H4]2SnCl2 [R = 2'-C10H7 (3), 2',4',6'-Me3C6H2 (4), PhCH2 (5), Me2NCH2CH2 (6), 2'-PyCH2 (7)]. The reaction of with [Pd(COD)Cl2] provided the heterometallic species [Cl2Pd{2-(2'-PyCH2N[double bond, length as m-dash]CH)C6H4}2SnCl2] (8). The compounds were characterised by multinuclear NMR spectroscopy in solution, and mass spectrometry and IR spectroscopy in the solid state. The molecular structures of 1, 2, 4-7 and 8·CH3CN were established by single-crystal X-ray diffraction. For all diorganotin(IV) dichlorides intramolecular O→Sn or Nimine→Sn coordination results in hypercoordinated species with a distorted octahedral (C,E)2SnCl2 core (E = O, N). The presence of intramolecular N→Sn interactions in solution, responsible for the restriction of free rotation of mesityl groups around the C-N(=C) single bonds, is suggested by (1)H and (13)C NMR data. In the heterometallic dinuclear complex 8 the octahedral coordination around tin is preserved as in 7 and the nitrogen atoms from the pyridyl groups in the pendant arms are coordinated to palladium, leading to a trans-square planar PdCl2N2 core.