Aggregation and Reactivity of Organocuprates

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Organocuprates are exceedingly valuable organometallic reagents, the classical variants of which are formed by the transmetallation of copper(I) precursors with organolithium or magnesium compounds. In the first funding period, the speciation of these reagents in solution and their reactivity were examined in considerable detail. In the requested second funding period, the preparation of organocuprates, -argentates, and -aurates by the transmetallation with organozinc, -boron, and -silicon compounds shall be explored. These reagents have the great advantage of a higher functional-group tolerance, but at the same time can be expected to transfer their organyl groups less readily to the coinage-metal center. The present proposal aims at identifying the factors that control the transmetallation of the coinage metals in order to find new and improved ways to access organocuprates and their heavier homologues. To this end, a twofold strategy will be pursued. First, a rigorously reductionist approach will be applied by probing the unimolecular reactivity of well-defined bimetallic ions in the gas phase. Tandem-mass spectrometry will determine the tendency of these ions to undergo transmetallation and show how the reaction efficiency depends on the nature of the metals, the electronic and steric properties of the organyl group, and the presence of metal-bound halides and other anions. Second, the composition of the reaction systems in solution will be elucidated by a combination of electrospray-ionization mass spectrometry, multinuclear NMR spectroscopy, and nanocalorimetry. Both the gas- and the solution-phase experiments will be complemented by quantum chemical calculations to obtain information on the energetics and structures of the involved intermediates and transition states. The proposed studies, thus, shall not only afford fundamental insight into the mechanism of prototypical transmetallation reactions, but also enable the rational development of new coinage metallates, whose synthetic potential will be tested for selected examples.