Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia
Author(s)
Chin, Jia Min; Schrock, Richard Royce; Muller, Peter
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A potentially useful trianionic ligand for the reduction of dinitrogen catalytically by molybdenum complexes is one in which one of the arms in a [(RNCH2CH2)3N]3− ligand is replaced by a 2-mesitylpyrrolyl-α-methyl arm, that is, [(RNCH2CH2)2NCH2(2-MesitylPyrrolyl)]3− (R = C6F5, 3,5-Me2C6H3, or 3,5-t-Bu2C6H3). Compounds have been prepared that contain the ligand in which R = C6F5 ([C6F5N)2Pyr]3−); they include [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, [(C6F5N)2Pyr]MoOTf, and [(C6F5N)2Pyr]MoN. Compounds that contain the ligand in which R = 3,5-t-Bu2C6H3 ([Art-BuN)2Pyr]3−) include {[(Art-BuN)2Pyr]Mo(N2)}Na(15-crown-5), {[(Art-BuN)2Pyr]Mo(N2)}[NBu4], [(Art-BuN)2Pyr]Mo(N2) (νNN = 2012 cm−1 in C6D6), {[(Art-BuN)2Pyr]Mo(NH3)}BPh4, and [(Art-BuN)2Pyr]Mo(CO). X-ray studies are reported for [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, and [(Art-BuN)2Pyr]MoN. The [(Art-BuN)2Pyr]Mo(N2)0/− reversible couple is found at −1.96 V (in PhF versus Cp2Fe+/0), but the [(Art-BuN)2Pyr]Mo(N2)+/0 couple is irreversible. Reduction of {[(Art-BuN)2Pyr]Mo(NH3)}BPh4 under Ar at approximately −1.68 V at a scan rate of 900 mV/s is not reversible. Ammonia in [(Art-BuN)2Pyr]Mo(NH3) can be substituted for dinitrogen in about 2 h if 10 equiv of BPh3 are present to trap the ammonia that is released. [(Art-BuN)2Pyr]Mo−N═NH is a key intermediate in the proposed catalytic reduction of dinitrogen that could not be prepared. Dinitrogen exchange studies in [(Art-BuN)2Pyr]Mo(N2) suggest that steric hindrance by the ligand may be insufficient to protect decomposition of [(Art-BuN)2Pyr]Mo−N═NH through a variety of pathways. Three attempts to reduce dinitrogen catalytically with [(Art-BuN)2Pyr]Mo(N) as a “catalyst” yielded an average of 1.02 ± 0.12 equiv of NH3.
Date issued
2010-07Department
Massachusetts Institute of Technology. Department of ChemistryJournal
Inorganic Chemistry
Publisher
American Chemical Society
Citation
Chin, J. M., R. R. Schrock, and P. Müller. “Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia.” Inorganic Chemistry 49.17 (2010): 7904–7916.
Version: Author's final manuscript
ISSN
0020-1669
1520-510X