Preparation and Characterization of CoII, NiII, and ZnII Complexes of Sterically Demanding Hexaazamacrocyclic Dithiophenolates

Abstract

AbstractN‐Alkylated variants of a Robson‐type 24‐membered hexaazamacrocyclic dinucleating dithiophenolate ligand bearing ethyl and propyl groups have been prepared and their ligating properties towards the 3d elements Ni, Co and Zn have been examined. The new ligands support the formation of dinuclear complexes of the type [(LR)MII2(L')]+, i.e. [(LEt)Ni2(Cl)]+ (7), [(LPr)Ni2(Cl)]+ (8), [(LEt)Ni2(OAc)]+ (9), [(LPr)Ni2(OAc)]+ (10), [(LEt)Ni2(O2COMe)]+ (11), [(LEt)Ni2(O2COEt)]+ (12), [(LEt)Zn2(OAc)]+ (14), [(LEt)Co2(Cl)]+ (17), and [(LEt)Co2(OAc)]+ (18), the overall structures of which are very similar to the corresponding complexes of the parent permethylated ligand system. The use of the longer alkyl chains expands the binding pocket of the complexes to a more conical, “calixarene”‐like cavity and has allowed for the isolation of the trication [(HLEt)Ni2]3+ (13), which is an intermediate in the substitution reactions of 7. Complex 13 reveals a new coordination mode of the supporting ligand with adjacent four‐ and five‐coordinate nickel atoms. Its higher stability is presumably a consequence of the increased steric crowding imposed by the longer alkyl chains of (LEt)2–. These results have thus demonstrated that these highly functionalized ligand systems allow for the stabilization of reactive intermediates. This information can now be used as a guide to further modulate the chemical reactivity of these compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)