Early-Transition-Metal Macrocycles as Metalloligands: Synthesis and Structure of Dinuclear Zirconocene Thioglycolates [Cp°2Zr{OOC(CH2SCH2)nCOO}2ZrCp°2] (n = 1, 2) and Their Heterobimetallic Complexes with Mo0 and PdII

Abstract

The reactions of [Cp° 2 ZrMe 2 ] (Cp° = C 5 EtMe 4 ) with the thioglycolic acids HOOC(CH 2 -SCH 2 ) n COOH (n = 1, 2) resulted in evolution of methane and formation of the macrocyclic, dimeric zirconocene complexes [Cp° 2 Zr(OOCCH 2 SCH 2 COO) 2 ZrCp° 2 ] (1) and [Cp° 2 Zr(OOCCH 2 -SCH 2 CH 2 SCH 2 COO) 2 ZrCp° 2 ] (2), which can act as metalloligands toward complex fragments of a second metal. Both complexes were characterized by NMR and IR spectroscopy, ESI mass spectrometry, and X-ray diffraction analysis. In solution at room temperature both complexes are dynamic, and the carboxylato groups alternate between mono- and bidentate bonding modes. For complex 1 the free energy of activation for this process was determined to be ΔG = 37 ′1 kJ/mol by variable-temperature NMR experiments. Compound 1 reacts with [Mo(CO) 4 (NBD)] (NBD = norbornadiene) to give the tetranuclear Zr/Mo complex 3, the crystal structure of which showed that an Mo(CO) 4 fragment is coordinated to one S and one O donor center of each bridging ligand of 1. This heterobimetallic complex 3 was also characterized by NMR and IR spectroscopy, and in contrast to 1, it is not dynamic in solution at room temperature, owing to the coordination of the Mo(CO) 4 fragments. Compounds 1 and 2 also react with [PdCl 2 (CH 3 CN) 2 ] to give the trinuclear Zr/Pd complex 4 and the tetranuclear Zr/Pd complex 5. Both complexes were characterized by NMR and IR spectroscopy and by elemental analysis.