24476-72-0Relevant articles and documents
Formation of metal-metal bonds by ion-pair annihilation. Dimanganese carbonyls from manganate(-I) anions and manganese(I) cations
Lee,Kuchynka,Kochi
, p. 1886 - 1897 (2008/10/08)
The coupling of the anionic Mn(CO)5- and the cationic Mn(CO)6+ occurs upon mixing to afford the dimeric Mn2(CO)10 in essentially quantitative yields. Dimanganese decacarbonyl is formed with equal facility from the coupling of Mn(CO)5- with Mn(CO)5(py)+ and Mn(CO)5(NCMe)+. By way of contrast, the annihilation of Mn(CO)4PPh3- with Mn(CO)6+ yields a pair of homo dimers Mn2(CO)10 and Mn2(CO)8(PPh3)2 together with the cross dimer Mn2(CO)9PPh3. Extensive scrambling of the carbonylmanganese moieties also obtains with Mn(CO)4P(OPh)3- and Mn(CO)5PPh3+, as indicated by the production of Mn2(CO)8[P(OPh)3]2, Mn2(CO)8[P(OPh)3](PPh3), and Mn2(CO)8(PPh3)2 in more or less statistical amounts. These diverse Mn-Mn couplings can be accounted for by a generalized formulation (Scheme VI), in which the carbonylmanganese anions Mn(CO)4P- and the cations Mn(CO)5L+ undergo an initial electron transfer to produce Mn(CO)4P? and Mn(CO)5L?, respectively. The behaviors of these 17- and 19-electron radicals coincide with those independently generated in a previous study of the anodic oxidation of Mn(CO)4P- and the cathodic reduction of Mn(CO)5L+, respectively. The facile associative ligand substitution of 17-electron carbonylmanganese radicals by added phosphines provides compelling evidence for the interception of Mn(CO)4P? and its interconversion with 19-electron species in the course of ion-pair annihilation. The reactivity trend for the various ion pairs qualitatively parallels the driving force for electron transfer based on the oxidation and reduction potentials of Mn(CO)4P- and Mn(CO)5L+, respectively, in accord with the radical-pair mechanism in Scheme VI.
