Early-Transition-Metal Macrocycles as Metalloligands: Synthesis and Structure of Dinuclear Zirconocene Thioglycolates [Cp°<sub>2</sub>Zr{OOC(CH<sub>2</sub>SCH<sub>2</sub>)<i><sub>n</sub></i>COO}<sub>2</sub>ZrCp°<sub>2</sub>] (<i>n</i> = 1, 2) and Their Heterobimetallic Complexes with Mo<sup>0</sup> and Pd<sup>II</sup> <sup>‡</sup>
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The reactions of [Cp°2ZrMe2] (Cp° = C5EtMe4) with the thioglycolic acids HOOC(CH2SCH2)nCOOH (n = 1, 2) resulted in evolution of methane and formation of the macrocyclic, dimeric zirconocene complexes [Cp°2Zr(OOCCH2SCH2COO)2ZrCp°2] (1) and [Cp°2Zr(OOCCH2SCH2CH2SCH2COO)2ZrCp°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 [PdCl2(CH3CN)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.
