Electrochemistry and electron transfer induced substitution reactions of methylcyclopentadienylmolybdenum tricarbonyl complexes and electrospray ionization mass spectrometry and X-ray crystallographic characterization of related molybdenum complexes.

摘要

The complexes Cp'Mo(CO)3X (X = Cl, Br, I; Cp' = C5H4 CH3) and [Cp'Mo(CO)3(L)]+ (L = CH3CN, CH3COCH3) were synthesized and their electrochemistry and electron transfer induced substitution reactions were studied. Electrochemical studies of Cp'Mo(CO)3X showed that it is reduced via a DISP-type mechanism. The mechanism was confirmed both chemically and electrochemically. Attempts to perform electron transfer induced substitution reactions in the presence of 2e- ligands formed [Cp'Mo(CO) 3]- as the major product, in addition to Cp'Mo(CO) 2(L)X, which was formed in greater amounts when the reducing agent was added in aliquots. [Cp'Mo(CO)3]- is proposed to form via the disproportionation pathway while Cp'Mo(CO)2(L)X is formed via a self-exchange substitution pathway. The disproportionation reaction occurs because of the large formation constants of the 19e-[Cp'Mo(CO) 3X]- intermediates. The large formation constants of the 19e- [Cp'Mo(CO)3X]- complexes also prevent the electron transfer chain reaction pathway which has been observed for the isoelectronic CpFe(CO)2X (Cp = C 5H5) complexes. The self-exchange substitution reaction occurs between the [Cp'Mo(CO)3]- formed from the disproportionation reaction and Cp'Mo(CO)3X and L. 31P NMR was used to confirm the reaction mechanism. The self-exchange substitution reaction is inhibited at low temperature and under a CO atmosphere.;Complexes of the type [Cp'Mo(CO)3(L)]+ (L = CH3CN, CH3COCH3) showed an ECE-type reduction mechanism when studied using cyclic voltammetry and the electron transfer induced substitution formed [Cp'Mo(CO)3(PPh3)] + and [Cp'Mo(CO)2(PPh3)2] + as major products via an electron transfer chain pathway. These results confirm that cyclopentadienylmolybdenum carbonyl complexes can undergo an electron transfer chain reaction like the isoelectronic CpFe(CO)2 X when unhindered by factors such as large formation constants.;Electrospray mass spectrometry was used to characterize the complexes [Cp'Mo(CO)3(CH3CN)]PF6 and [{Cp'Mo(CO) 3}2(µ-I)]BPh4. The mass spectra showed the molecular ion peaks in addition to fragment ion peaks for [M-nCO]+ . Finally, X-ray crystal structures of cis-Cp'Mo(CO)2(PPh 3)I, [{Cp'Mo(CO)3}2(µ-I)]BPh4, [Cp'Mo(CO)3(CH3CN)]BF4, [Cp'Mo(CO)3 (C5H5N)]BPh4 and cis-[Cp'Mo(CO) 2(C5H5N)2]BPh4 were obtained and their bond lengths and bond angles were found to be in good agreement with those in related molybdenum complexes.