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-dion ate cobalt(III) complexes of formula [Co{MeC(O)CR(1)C(O)Me}(2){MeC(O)C R(2)C(O)Me}](R(1) = R(2) = H a; R(1) = H, R(2) = Cl b, Br c, NO2 d, SC N 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 io nization (CIMS) and ion-trap mass spectrometry (ITMS). In all cases th e following main reactions were observed: (i) ion-to-molecule charge t ransfer with formation of the corresponding molecular ions, Co{MeC(O)C R(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 c obalt 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 t he 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(ac ac)(2){MeC(O)CRC(O)Me}](.+), and a largely predominant process which l eads to two bimetallic ions, [Co-2(acac)(4)](+) and [Co-2(acac)(3)](+) , which, according to kinetic studies, arise from two parallel reactio ns. The results are discussed in terms of analogies and differences be tween the gas- and the solution-phase reactions of tris(beta-ketoenola to)cobalt(III) complexes with Bronsted acids. The preparation of the c omplexes e, g and k-m, not previously reported, is described; furtherm ore, f has been obtained in higher yields through an alternative one-s tep synthesis. All new compounds have been characterized by elemental analysis, mass and H-1 NMR spectrometry.