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 PDF Download

Author: Thiruvengadam Munisamy
Publisher:
ISBN:
Category : Charge exchange
Languages : en
Pages : 203

Get Book Here

Book Description
The complexes Cp'Mo(CO)3X (X = Cl, Br, I; Cp' = C5H4CH3) 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 = C5H5) 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)2X 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([mu]-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(PPh3)I, [{Cp'Mo(CO)3}2([mu]-I)]BPh4, [Cp'Mo(CO)3(CH3CN)]BF4, [Cp'Mo(CO)3(C5H5N)]BPh4 andcis-[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.