117872-92-1Relevant articles and documents
Equilibrium of 17-electron and 19-electron organometallic radicals derived from carbonylmanganese anions and cations
Kuchynka,Kochi
, p. 855 - 863 (2008/10/08)
The transient 17-electron carbonylmanganese(0) radical Mn(CO)5? produced from the oxidation of Mn(CO)5- is detected with the reversible potential E° = 0.085 V vs SCE by fast-scan cyclic voltammetry using platinum microelectrodes. The persistence of the substituted carbonylmanganese(0) radicals is prolonged by increasing numbers of phosphine ligands (P) in Mn(CO)4P? and Mn(CO)3P2? radicals. In contrast, the 19-electron counterpart Mn(CO)6? cannot be detected by the corresponding electroreduction of the carbonylmanganese(I) cation Mn(CO)6+ even at very high scan rates. Furthermore, extensive substitution of the carbonylmanganese cation with different types of ligands did not increase the lifetimes of Mn(CO)5L? (where L = nitriles, isonitriles, phosphites, and phosphines), with τ estimated to be less than 100 ns. Finally, the evidence for the existence of the fugitive 19-electron carbonylmanganese(0) radical is obtained indirectly by the use of the diphosphine PPh2CH2CH2PPh2 (DPPE) as a chelating ligand. Thus, the quantitative analysis of the cathodic reduction of cis-Mn(CO)2(DPPE)2+ by digital simulation of the cyclic voltammograms, especially those generated upon repetitive cycling, reveals the presence of the reversible interchange between the 19e radical Mn(CO)2(η2-DPPE)2? and the 17e radical Mn(CO)2(η1-DPPE)(η1-DPPE) ?. The tethered diphosphine ligand allows such an unprecedented equilibrium to be observed despite a formation constant of K ? 106 that overwhelmingly favors the 17-electron radical.
