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

• Published in: CrystEngComm 2016-01, Vol.18 (11), p.1892-193
• Main Authors: Gumbau-Brisa, R, Hayward, J. J, Wallis, J. D, Rawson, J. M, Pilkington, M
• Format: Article
• Language: English
• Subjects: Crystal structure; Crystals; Hydrolysis; Ligands; Mathematical models; Nucleophiles; Rendering; Tuning
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/c5ce02349a

The coordination chemistry of the bis-salicyl-appended Schiff-base ligand L8 with Lewis acidic metal ions affords the mononuclear complex [Sn( L9 )Cl 4 ] ( 1 ) and two paramagnetic dimers [Cu( L9 )(sal)] 2 (ClO 4 ) 2 , ( 2 ) and [Mn( L9 )Cl 2 (EtOH)] 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 Sn( iv ) 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 [Fe( L10 ) 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)[Fe( L8 )] 2 ·2CH 3 CN ( 5 ) in which intact L8 coordinates to the Fe( iii ) 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. The coordination chemistry of the title ligand L8 is explored by X-ray crystallography, revealing its propensity to undergo metal catalysis and hydrolysis.