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Issue 29, 2011
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Gas-phase study of new organozinc reagents by IRMPD-spectroscopy, computational modelling and tandem-MS

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Abstract

An extensive set of organozinc iodides, useful for Negishi-type cross-coupling reactions, are investigated as respective cations after formal loss of iodide in the gas phase. Firstly, two new alkylzinc compounds derived from Tyrosine (Tyr) and Tryptophan (Trp) are closely examined. Secondly, the influence of specific protecting groups on the subtle balance between intra- and intermolecular coordination of zinc in these reagents is probed through trifluoroacetyl (TFA)-derivatized alkylzinc compounds. Finally, the influence of the strongly coordinating bidentate ligand N,N,N,N′-tetramethylethylenediamine (TMEDA) on the structure of alkylzinc cations is further explored in order to better understand the stability of the respective complexes towards water. A combination of electrospray (ESI)-MS/MS, accurate ion mass measurements, infrared multiple-photon dissociation (IRMPD) spectroscopy and computational modelling allowed the full characterisation of all dimethylformamide (DMF)-solvated and TMEDA-coordinated alkylzinc cations in the gas phase. The calculations indicate that the zinc cation in gas-phase alkylzinc–DMF or TMEDA–complex ions preferentially adopts a tetrahedral coordination sphere with four ligands. Additionally, conformers with only three binding partners bound to zinc but with effectively combined hydrogen-bond interactions are also found. Collision induced dissociation (CID) patterns demonstrate that the zinc–DMF interaction in tetrahedral four-coordinate mono-DMF–zinc complex ions as well as the interaction between TMEDA and zinc in the corresponding complex ions is even stronger than typical covalent bonds. In most cases, all major features of the IRMPD spectra are consistent with only a single major isomer, allowing secured identification and assignment.

Graphical abstract: Gas-phase study of new organozinc reagents by IRMPD-spectroscopy, computational modelling and tandem-MS

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Publication details

The article was received on 14 Mar 2011, accepted on 27 May 2011 and first published on 22 Jun 2011


Article type: Paper
DOI: 10.1039/C1CP20747D
Citation: Phys. Chem. Chem. Phys., 2011,13, 13255-13267
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    Gas-phase study of new organozinc reagents by IRMPD-spectroscopy, computational modelling and tandem-MS

    A. R. Massah, F. Dreiocker, R. F. W. Jackson, B. T. Pickup, J. Oomens, A. J. H. M. Meijer and M. Schäfer, Phys. Chem. Chem. Phys., 2011, 13, 13255
    DOI: 10.1039/C1CP20747D

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