Preparation, Properties, and Structures of Pentanuclear [{Ni2L}2(μ‐csalen)M]2+ Complexes (L = Macrocyclic N6S2 ­Donor Ligand)

Abstract

AbstractThe dinuclear nickel complex [Ni2L(μ‐Cl)]+ (1), where L2– is a 24‐membered macrocyclic N6S2 ligand, reacts readily with 3‐formyl‐4‐hydroxy‐benzoic acid (Hfhba) to form the carboxylato‐bridged complex [Ni2L(μ‐fhba)]+ (2). Complex 2 undergoes a condensation reaction with ethylene diamine to produce a tetranuclear complex [{Ni2L}2(μ‐H2csalen)]2+ (3), in which two dinuclear {Ni2L} units are bridged via the deprotonated carboxylate functions of the csalen ligand N,N′‐bis(4‐carboxysalicylidene)‐1, 2‐diaminoethane. The same compound can also be prepared directly from 1 and H2csalen. The complexation of 3 with NiCl2·6H2O, Cu(OAc)2·H2O or Pd(OAc)2 provides pentanuclear complexes of the type [{Ni2L}2(μ‐csalen)M]2+ [M = Ni (4a), Cu (4b), Pd (4c)]. All complexes were isolated as perchlorate salts and studied by ESI‐MS, infrared, and UV/Vis spectroscopy. The tetraphenylborate salt of 4c was also characterized by X‐ray crystallography. The [(csalen)M] complex units act in all cases as quadridentate bridging ligands linking two bioctahedral {Ni2L} units via μ‐1, 3‐bridging carboxylate functions. The palladium complex 4c was found to catalyze Heck‐coupling reactions of various iodobenzenes with methyl acrylate and styrene.