115162-69-1Relevant academic research and scientific papers
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.
Facile rearrangement and electron transfer of 19-electron radicals from the reduction of the bischelated manganese carbonyl cation Mn(CO)2[PPh2(CH2)2PPh 2]2+
Kuchynka,Kochi
, p. 2574 - 2581 (2008/10/08)
The cathodic reduction of the bischelated manganese carbonyl cation trans-Mn(CO)2(η2-DPPE)2+ (I+, where DPPE = PPh2-(CH2)2PPh2) produces the metastable anion Mn(CO)2(η2-DPPE)(η1-DPPE)- (II-) via an overall 2e process at a Pt electrode in either tetrahydrofuran or acetonitrile solution. The unusual observation of a cathodic curve crossing and two isopotential points in the cyclic voltammogram of I+ can be traced to an electron transfer with II- to afford a pair of neutral radicals, i.e., the 19e I? and the 17e II?. The former (which is also generated during the initial step in the reduction of I+) is a metastable species and spontaneously extrudes an end of one DPPE ligand to afford the second radical II? with the rate constant kr ≈ 4 × 106 s-1. The structures of the anionic and radical intermediates II-, II?, and I? are discussed in the context of their transient electrochemical behavior as well as their 31P NMR and ESR spectra. The rather slow rate of electron transfer between I+ and II- is ascribed to steric effects in carbonylmanganese ions encumbered with a pair of DPPE ligands.
