Synthesis and Characterization of a Novel Heteroditopic Macrocyclic System – Monometallic Nickel(II) and Uranyl Complexes and Their Corresponding Heterobimetallic Carbonylrhodium(I) Complexes

Abstract

AbstractA novel heteroditopic macrocyclic ligand system for selective coordination of two different transition metal ions has been obtained in the form of monometallic salen complexes of NiII (LNi, 1) and uranyl (LUO2, 2). The system is characterized by the presence of a dianionic, tetradentate salen donor system (N2O2) derived from cis‐1,2‐diaminocyclohexane and of a neutral, tridentate 2,6‐bis(alkylthiomethyl)pyridine group (NS2). The two binding sites are connected by two oxyethyl chains. The synthetic procedure involves the coupling of the disodium salt of 2,6‐bis(mercaptomethyl)pyridine with two equivalents of 3‐(2‐bromoethoxy)‐2‐(2‐propenyloxy)benzaldehyde. Removal of the protecting allyl groups from the reaction product (I) by palladium catalysis yields the ligand synthon 2,6‐bis[2‐(3‐formyl‐2‐hydroxyphenyl)oxyethyl]thiomethylpyridine (II). The monometallic macrocyclic complexes 1 and 2, obtained by metal‐templated synthesis from cis‐1,2‐diaminocyclohexane, ligson II, and the corresponding NiII or uranyl acetate salts, respectively, in the presence of barium bis(trifluoroacetate), have been fully characterized by spectroscopic techniques in solution and by X‐ray diffraction analyses in the solid state. Both complexes react readily at room temperature with [Rh(CO)2Cl]2 in methanol to form the bimetallic cationic carbonyl complexes [LNiIIRh(CO)]PF6 (3) and [LUO2Rh(CO)]PF6 (4) upon addition of NH4PF6. Two conformers of complex 3 are observed in solution by IR and NMR spectroscopy, in a 5:1 ratio in [D2]dichloromethane, which exhibit a fluxional behavior and are shown to interconvert above room temperature in [D3]acetonitrile. The carbonylrhodium group in the bimetallic systems reacts further with methyl iodide in dichloromethane solution to form oxidative‐addition products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)