Microsolvated and Chelated Butylzinc Cations: Formation, Relative Stability, and Unimolecular Gas-Phase Chemistry

Chem. Eur. J., 2009, 15(46), 12745-12753, doi 10.1002/chem.200901963 published on 23.10.2009
Chem. Eur. J., online article
Solutions of butylzinc iodide in tetrahydrofuran, acetonitrile, and N,N-dimethylformamide were analyzed by electrospray ionization mass spectrometry. In all cases, microsolvated butylzinc cations [ZnBu(solvent)n]+, n=1-3, were detected. The parallel observation of the butylzincate anion [ZnBuI2]- suggests that these ions result from disproportionation of neutral butylzinc iodide in solution. In the presence of simple bidentate ligands (1,2-dimethoxyethane, N,N-dimethyl-2-methoxyethylamine, and N,N,N',N'-tetramethylethylenediamine), chelate complexes of the type [ZnBu(ligand)]+ form quite readily. The relative stabilities of these complexes were probed by competition experiments and analysis of their unimolecular gas-phase reactivity. Fragmentation of mass-selected [ZnBu(ligand)]+ leads to the elimination of butene and formation of [ZnH(ligand)]+. In marked contrast, the microsolvated cations [ZnBu(solvent)n]+ lose the attached solvent molecules upon gas-phase fragmentation to produce bare [ZnBu]+, which subsequently dissociates into [C4H9]+ and Zn. This difference in reactivity resembles the situation in organozinc solution chemistry, in which chelating ligands are needed to activate dialkylzinc compounds for the nucleophilic addition to aldehydes.

TU München
Helmholtz München
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MPI of Biochemistry