The reaction between diferrocenylmercury and dimethylacetylenedicarboxylate results in the formation of orange dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate and diferrocene as the major products. Unexpectedly, the mercury-containing reaction intermediate was also obtained in the mixture as a minor byproduct. Dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate, differocene, and the mercury-containing intermediate were characterized using 1D and 2D NMR, IR, and UV-vis spectroscopy as well as X-ray crystallography. Single crystal X-ray diffraction studies of dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate revealed a locked anticonformation of the ferrocene substituents, which was explained on the basis of the steric properties of these groups. In addition, X-ray study of the mercury-containing intermediate reveals new insight on the palladium catalyzed reaction mechanism. Low temperature x-ray diffraction experiment of differocene were performed and accurate values for geometric parameters were reported. Electronic structures of dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate were investigated by UV-vis spectroscopy and polarized continuum model (PCM) density functional theory (DFT-PCM) as well as time-dependent DFT (TDDFT-PCM) approaches. The calculated vertical excitation energies are consistent with the experimental data and clearly suggest the dominance of  metal-to-ligand charge-transfer bands in the visible region of the UV-vis spectra for dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate. Redox properties of dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate were investigated using cyclic voltammetry, differential pulse voltammetry, and spectroelectrochemical and chemical oxidation approaches. In a DCM/(NBu4)[B(C6F5)4] system, ferrocene-centered oxidation processes in dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate are separated by 300 mV, respectively. Stepwise chemical and spectroelectrochemical oxidation of dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate allowed us to obtain spectroscopic signatures of the mixed-valence [dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate]+ cation. Hush analysis of the intervalence charge-transfer bands in [dimethyl (Z)-2,3-bis(ferrocenyl)-2-butenedioate]+ is suggestive of class II (in Robin and Day classification) behavior.Reference: Pavlo V. Solntsev, Semen V. Dudkin, Jared R. Sabin, and Victor N. Nemykin. Organometallics 2011, 30, 3037-3046.

Unexpected formation of mercury-containing organometallic intermediate in a palladium catalyzed reaction

243rd National Meeting (2012)

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