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Titration Calorimetry for the Determination of Basicities of Transition Metal Complexes

  • Robert J. Angelici
Part of the NATO Science Series book series (ASIC, volume 535)

Abstract

When one thinks of Brønsted bases, ions or molecules that come to mind are those that contain a non-metal atom with a lone pair of electrons that is capable of forming a donor-acceptor bond with a proton (H+). Examples of common Brønsted bases are OH NH3, CH3CO2 , CN, Et2S, and Ph3P, among many others. In molecules that contain a metal, the metal is normally not considered Brønsted basic. Yet, since the 1930’s, transition metal complexes that are protonated at the metal center have become quite common. Initially such basic complexes were those that were anionic with carbonyl or organometallic ligands, such as Fe(CO)4 2− Re(CO)5 , (η5-C5H5)W(CO)3 and Co(CO)4 . However, it has become increasingly obvious that neutral complexes, such as W(CO)3(PMe3)3, (η5-C5H5)2ReH, Fe(H)2(Me2PCH2CH2PMe2)2, and (η5-C5Me5)Ir(l,5-cyclooctadiene), can also be protonated at the metal center. And there are even a few examples of cationic metal complexes, such as Os(H)(CH3CN)(dppe)2 + and Ir(CO)(dppe)2 +, where dppe = Ph2PCH2CH2PPh2, that can be protonated at the metal. In all of these acid-base reactions (eq 1), an electron pair on the metal forms a donor-acceptor bond with H+ to give a metal hydride complex (H-MLn +) whose
$$:M{L_n} + HA \rightleftharpoons H - M{L_n}^ + {A^ - }$$
(1)
structure is necessarily different than that of the precursor Brønsted base (:MLn). In reactions of the type in eq (1), the metal in :MLn normally has an inert gas configuration, i.e., obeys the 18-electron rule, and therefore will generally not also react with the anion (A) of the acid (HA) by including A as a ligand in the coordination sphere. As many Brønsted basic metal complexes are insoluble in or react with water, most protonation reactions are performed in non-aqueous solvents.

Keywords

Transition Metal Complex Bond Dissociation Energy Bond Dissociation Energy Phosphine Ligand Protonation Reaction 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media Dordrecht 1999

Authors and Affiliations

  • Robert J. Angelici
    • 1
  1. 1.Department of Chemistry and Ames LaboratoryIowa State UniversityAmesUSA

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