Organometallate ions

In a completely different kind of process, alkyl halides can be converted to certain organometallic compounds by treatment with organometallate ions, for example,... 

Armentrout, R B., Kickel, B. L., 1996, Gas-Phase Thermochemistry of Transition Metal Ligand Systems Reassessment of Values and Periodic Trends in Organometallic Ion Chemistry, Freiser, B. S. (ed.), Kluwer, Amsterdam. 

Perhaps of high interest to the hydrogenation chemist are the pertinent details of how gas-phase ions of organometallic catalysts are prepared. Of specific interest are the types of fragmentation events that can occur during the preparation of the gas phase ions, and what forms coordinatively unsaturated organometallic ions adopt in the gas phase. 

A point of interest at this stop in our tour is that fragmentation of organometallic ions in ESI-MS often proceeds via ligand dissociation (e.g., phosphane loss) to generate coordinatively unsaturated organometallic ions [1-9]. One of the strengths of this technique is that such unsaturated ions are typically proposed as reactive intermediates in catalytic reactions carried out in solution (vide infra), allowing ESI-tandem-MS systems to study directly the gas-phase reactivity of such species. 

Based upon their data and upon results in the literature, the authors concluded that hydrogenations using 24 or related species as catalyst precursor proceed in solution by mechanisms involving iridium(I)/(III) formal oxidation states. During the course of their discussions, the authors made the interesting observation that the rate of gas-phase collisions between the thermalized iridium organometallic ions and D2 under their experimental conditions in the oc-topole were similar to the rate of diffusion-controlled encounters between iridium species and D2 in solution. 

ESI represents a powerful method by which to transfer organometallic ions from catalytically active solutions into the gas phase. ESI-MS systems allow the characterization of the gas-phase ions using CID, reactivity, and isotope-labeling studies. The application of ESI-tandem-MS systems allows gas-phase preparations and isolation of desired organometallic ions in the first ESI-octopole-quad-rupole, followed by characterization or reactivity studies in the second octopole-quadrupole. 

B. S. Freiser, Ed., Organometallic Ion Chemistry, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1996. 

Berkowitz J, Ellison GB, Gutman D (1994) J Phys Chem 98 2744 Preiser BS (ed) (1996) Organometallic ion chemistry. Kluwer, Dordrecht Schroder D, Shaik S, Schwarz H (2000) Struct Bond 97 91... 

DFT calculations on the Mg(L—H)+ complex also reveal how HNCO might be lost (Scheme 10). Thus the bidentate interaction of the acetamide ligand with Mg in 51 must be disrupted to yield either of the monodentate structures 52 or 54. These intermediates can insert into the CH3—C bond via four-centered transition states to yield the organometallic ions 53 or 55, which can then lose HNCO to form MgCH3+. The DFT calculations reveal that path (A) of Scheme 10 is kinetically favored. 

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