Preparations and structures of nickel(II) compounds of 2,9-rac-2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane

Abstract

The imine functions of 3,10-rac-[(3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradec-4,11-diene)nickel(II)]2+ are reduced by NaBH4 in water forming the 2RS,7SR, 9RS,14SR-, [Ni(rac-rac-1-L)]2+, and 2RS,7SR,9RS,14RS-[Ni(rac-meso-L)]2+, isomeric [(2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane)nickel(II)] cyclic tetraamine cations. The structures of [Ni(rac-rac-1-L)](ClO4)2, [Ni(rac-rac-1-L)]ZnCl4, [Ni(rac-rac-1-L)(acac)]ClO4 and [Ni(rac-meso-L)](ClO4)2·H2O were determined by X-ray diffractometry. The perchlorate and tetrachlorozincate salts of the cation [Ni(rac-rac-1-I-L)]2+ have near twofold symmetry about the nickel(II) ion, normal to the NiN4 plane, with “basket” cyclam nitrogen configuration I (1RS,4RS,8RS,11RS). The C2 and C9 methyl substituents are axially oriented to the same side of the plane as the four NH groups, with the axially oriented components of the C5 and C12 gem-dimethyl groups oriented to the other side. The salt [Ni(rac-rac-1-L)](NCS)2 has uncoordinated thiocyanate ions. The compound [Ni(rac-rac-1-V-L)(acac)]ClO4, with pentane-2,4-dionate chelate, has the macrocycle in configuration 1RS,2SR,4RS,7RS,8RS,9SR,11RS,14RS, folded along N4–Ni–N11, with methyl substituents on C2 and C9 equatorially oriented. The [Ni(rac-meso-L)]2+ cation was isolated as the trans-dithiocyanato compound, [Ni(rac-meso-III-L)(NCS)2], which was converted into the square-planar perchlorate salt [Ni(rac-meso-III-L)](ClO4)2H2O, with configuration 1RS,2SR,4SR,7SR,8SR,9SR,11RS,14RS. This cation has the C2 methyl substituent axially and the C9 substituent equatorially oriented.