Structural insights into the coordination chemistry and reactivity of a 3,3′-bis-imine-2,2′-bipyridine ligand

Abstract

The coordination chemistry of the bis-salicyl-appended Schiff-base ligand L8 with Lewis acidic metal ions affords the mononuclear complex [SnIJL9)Cl 4 ] (1) and two paramagnetic dimers [CuIJL9)IJsal)] 2 IJClO 4 ) 2 , (2) and [MnIJL9)Cl 2 IJEtOH)] 2 ] (3). The X-ray crystal structures of 1-3 reveal a propensity for L8 to undergo metal catalyzed hydrolysis and cyclization to the diazepine ligand L9. Theoretical calculations on L8 and a model SnIJIV) complex reveal that coordination to a metal ion weakens the imine bonds, rendering them more susceptible to hydrolysis reactions and/or attack by nucleophiles. In contrast, reaction of L8 with FeCl 3 in the presence of base affords the partial hydrolysis product [FeIJL10) 2 ]Cl•CH 3 CN (4). Tuning the reaction conditions via the addition of a second base slows down the hydrolysis of the ligand sufficiently to afford a few crystals of the μ 2 -oxo diferric complex (μ-O)ijFeIJL8)] 2 •2CH 3 CN (5) in which intact L8 coordinates to the FeIJIII) in a bis-bidentate manner through a deprotonated salicyl oxygen and a bis-imine nitrogen lone pair, with the nitrogen atoms of its 2,2′-bipyridine remaining uncoordinated.

Crystal Structure Determination of 4-[(Di-p-tolyl-amino)-benzylidene]-(5-pyridin-4-yl-[1,3,4]thiadiazol-2-yl)-imine along with Selected Properties of Imine in Neutral and Protonated Form with Camforosulphonic Acid: Theoretical and Experimental Studies

“…Some research was also dedicated to investigation of the influence of Lewis acids on selected properties of Schiff bases, also for molecules containing pyridine moieties [ 44 , 45 , 46 ]. Additionally, ligands based on the Schiff bases with pyridine are also investigated in coordination chemistry [ 47 ].…”

Synthesis of Tetracyclic 2,3-Dihydro-1,3-diazepines from a Dinitrodibenzothiophene Derivative

“…Since the last comprehensive survey of their synthesis 31 only a handful of new synthetic approaches have been reported for monocyclic, [32][33][34][35] singly- [36][37][38][39] or doubly-ringfused 1,3-diazepines. [40][41][42][43][44][45][46][47][48][49] In this work the introduction of sterically hindered nitro groups at the 1-and 9-positions of a dibenzothiophene-5,5-dioxide derivative provides access to a new two-electron accepting molecule, which is a precursor to luminescent four-ring-fused 2,3-dihydro-1,3-diazepines 6-8 using facile protocols in synthetically viable yields. To our knowledge these molecules represent the first examples of tetracyclic 1,3-diazepine derivatives.…”

“…Diazepines are of major pharmaceutical importance. − 1,2-Benzodiazepines and 1,4-benzodiazepines in particular comprise entire classes of drugs, including the antianxiety medications tofisopam (strictly a 2,3-diazepine) and diazepam. − 1,3-Diazepines, and the saturated analogues 1,3-diazepanes, are less prevalent; however they have been studied as HIV protease inhibitors, − as anticancer − and antiviral agents, ,− and also as N -heterocyclic carbene ligands. , In comparison with 1,2- and 1,4-diazepines, routes to 1,3-diazepines are less clearly established. Since the last comprehensive survey of their synthesis only a handful of new synthetic approaches have been reported for monocyclic, − singly − or doubly ring-fused 1,3-diazepines. − …”