Gas-phase reactions of cobalt(III) beta-ketoenolates with Bronsted acid reagents

The gas-phase reactions of a variety of 3-substituted pentane-2,4-dionate cobalt(III) complexes of formula [Co{MeC(O)CR(1)C(O)Me}(2){MeC(O)CR(2)C(O)Me}](R(1) = R(2) = H a; R(1) = H, R(2) = Cl b, Br c, NO2 d, SCN e, Me f or Et g; R(2) = H, R(1) = Cl h, Br i, NO2 j, SCN k, Me l or Et m) with various Bronsted acid systems, e.g. [CH5](+), [t-C4H9](+), [H-3](+), [D-3](+), [NH4](+) and [ND4](+), were studied by chemical ionization (CIMS) and ion-trap mass spectrometry (ITMS). In all cases the following main reactions were observed: (i) ion-to-molecule charge transfer with formation of the corresponding molecular ions, [Co{MeC(O)CR(1)C(O)Me}(2){MeC(O)CR(2)-C(O)Me}](.+); (ii) unprecedented [H-2](+) (or [D-2](+)) transfer from the gaseous Bronsted acids to the neutral cobalt complexes with the formation of the ions [M+2H](+) or [M+2D](+), respectively, which give rise by fragmentation to the ions [MeC(O)CRC(O)Me + 2H](+) or [MeC(O)CRC(O)Me + 2D](+), which in many cases, are the most abundant species; (iii) H+ (or D+) transfer from the Bronsted acids to the neutral cobalt complexes with the formation of the ions [M + H](+) or [M + D](+), respectively. The ITMS study of the gas-phase reaction between the ion [Co(acac)(2)](+) (acac = pentane-2,4-dionate) and complexes a-g revealed two processes, the ion-to-molecule charge transfer which results in the formation of the radical cations [Co(acac)(2){MeC(O)CRC(O)Me}](.+), and a largely predominant process which leads to two bimetallic ions, [Co-2(acac)(4)](+) and [Co-2(acac)(3)](+), which, according to kinetic studies, arise from two parallel reactions. The results are discussed in terms of analogies and differences between the gas- and the solution-phase reactions of tris(beta-ketoenolato)cobalt(III) complexes with Bronsted acids. The preparation of the complexes e, g and k-m, not previously reported, is described; furthermore, f has been obtained in higher yields through an alternative one-step synthesis. All new compounds have been characterized by elemental analysis, mass and H-1 NMR spectrometry.