Reduction–oxidation properties of organotransition-metal complexes. Part 5. The one-electron oxidation of tricarbonyl(η-cyclopentadienyl)-manganese derivatives and the reactivity of the resulting radical cations

Abstract

Cyclic-voltammetric studies in CH₂Cl₂ have shown that [Mn(η-C₅H_5–nMe_n)(CO)_3–xL_x][n= 0, 1, or 5, x= 1, L = phosphine or phosphite (1); n= 0 or 1, x= 2, L =½dppe (dppe = Ph₂PCH₂CH₂PPh₂), PPh₃, or PMePh₂] each undergo a reversible one-electron oxidation to [Mn(η-C₅H_5–nMe_n)(CO)_3–xL_x]⁺[x= 1 (3) or 2 (4)]. The paramagnetic cations (3) may be generated chemically by silver(I) ion oxidation of (1), and (4) may be isolated from either silver(I) ion or diazonium ion oxidation of (2). On reaction with [N(C₆H₄Br-p)₃][SbCl₄], SbCl₅, Br₂, or I₂, (1) and (2) afford the diamagnetic complexes [MnX(η-C₅H_5–nMe_n)(CO)_3–xL_x]⁺[X = Cl, Br, or I, x= 1 (5) or 2 (6)], via the attack of halogen radicals on (3) or (4). The relation between the oxidation potential, E_p, and k(CO), the force constant for the carbonyl-stretching vibrations, for (1), (2), and [Mn(η-C₅H_5–nMe_n)(CO)₃] is discussed with reference to that previously reported for the isoelectronic chromium complexes [Cr(η-C₆Me₆)(CO)₂L].