NEUTRALIZATION-REIONIZATION MASS-SPECTROMETRY APPLIED TO ORGANOMETALLIC AND COORDINATION CHEMISTRY

Neutralization-reionization mass spectrometry (NRMS) was first described about twenty-five years ago, but it became a relatively widespread technique only in the 1980s, when several laboratories obtained or developed the accessories necessary for performing NR experiments in double-focusing, reversed geometry mass spectrometers. NRMS has been used to assist in gas-phase ion structure assignment, but its main use has been for the generation and characterization of elusive and/or hitherto unknown radicals and molecules. The impetus for such studies has often come from the predictions of high-level molecular orbital theory calculations concerning the stability of novel species. The results of these investigations have been thoroughly reviewed by several authors (1). The first article on the neutralization of organometallic ions appeared in 1987 (2). More than 35 articles describing NR experiments on organometallic and coordination compounds have been published since then (3-40). However, this total is substantially smaller than that for organic ions, and is probably insufficient for broad generalizations to be made. Nevertheless, some of the results were very exciting, permitting one to predict advantages, limitations, and future prospects for NRMS in coordination chemistry and related fields. Transition-metal containing species are the major subject of this review, which covers the data published up to 1994 and also includes a few later publications, as well as some original results of the authors. In addition, results of NR investigations of nonmetal atom-containing derivatives will be discussed, where the data were complementary to those from organometallic compounds. Major contributions to the NRMS study of coordination compounds and organometallic ions have come from the group of Prof. H. Schwarz at the Technische Universitat, Berlin. Their efforts have been mostly focused on the generation of elusive neutrals to prove their possible existence as stable intermediates. For example, NRMS investigations of silicon-containing species were related to postulated reaction mechanisms in interstellar chemistry. The authors of the present review began NR experiments with transition metal complexes in 1992, with particular attention given to species containing a metal atom, whose coordination and electron arrangements are close to being saturated.