In-situ IR spectroelectrochemistry study of one-electron oxidations of bis(cyclopentadienyl) molybdenum(II)-alkyne or -alkene compounds

摘要

Anodic oxidations of the bis-cyclopentadienyl. alkyne compound MoCp2 (eta(2) -C2Ph2), 1, and three metal-alkene analogues MCp2(eta(2)-C2H2 trans-R-2) (M = Mo, R = CO2Me, 2; M = Mo, R = H, 3; M = W, R = H, 4) have been studied by a combination of electrochemistry and in-situ IR spectroelectrochemistry. The primary redox process for all compounds is a reversible one-electron oxidation at very facile potentials (from -0.30 V vs FeCP20/+ for 2 to -0.80 V for 4). The v(CC) alkyne stretch in the IR spectrum of 17-electron Mo-alkyne ion 1(+) (1824 cm(-1)) was shifted 50 cm(-1) to higher energy than the same band in 1, consistent with a decrease in the metal-alkyne interaction in the Mo(III) cation. Compounds 2-4 all gave Mo(III) cations that were stable on the cyclic voltammetry (CV) time scale. In bulk electrolyses monitored by a combination of voltammetric and in-situ IR spectroelectrochemical analyses, the Mo(III) cation 2(+) was shown to undergo some loss of alkene. The fiber-optic in-situ IR technique is a powerful method for characterizing organometallic redox processes in which slow chemical reactions are coupled to the electron-transfer step.