Synthesis and X-ray structure of a monoprotonated salt and of three transition-metal complexes of N,N '-ditertiobutyl-2,11-diaza[3.3](2,6)pyridinophane

Compound (t-Bu-N-4)H+BAr4- [t-Bu-N-4=N,N'-ditertiobutyl-2,11-diaza[3.3](2,6 )pyridinophane, Ar = 3,5-(CF3)(2)-C6H3] has been synthesized and characteri zed by X-ray diffraction. The 12-membered macrocyclic ring adopts a syn boa t-boat conformation at the center of which the protonating hydrogen is allo wed to interact with the four nitrogen atoms. Complexes [Fe(t-Bu-N-4)Cl-2]( 3). 4H(2)O, [Co(t-Bu-N-4)Cl-2](3). 4H(2)O and Ni(t-Bu-N-4)Br-2 were obtaine d from t-Bu-N-4 and FeCl2, CoCl2 or NiBr2(DME), respectively. Their molecul ar structure, determined by X-ray crystallography, is analogous. The macroc ycle acts as a tetradentate ligand, and the coordination geometry around th e metal center is a distorted cis-octahedral. Variation of the structural p arameters with the nature of the transition metal or on the replacement of the previously studied Me-N-4 ligand by t-Bu-N-4 is analyzed. The bulky t-b utyl groups weaken the axial metal-amine interactions and force the macrocy cle to twist more severely on complexation. (C) 2001 Elsevier Science Ltd. All rights reserved.