Mechanistic study of hydrogen activation by cationic dinuclear ({mu}-sulfido)molybdenum complexes

Journal Article · Wed Jul 01 04:00:00 EDT 1992 · Organometallics

DOI:https://doi.org/10.1021/om00043a025· OSTI ID:567339

Lopez, L L; Bernatis, P; Birnbaum, J ^[1]

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1. Univ. of Colorado, Boulder, CO (United States); and others

The cationic derivatives have been synthesized and characterized spectroscopically. A single crystal has been studied by X-ray diffraction. The structure showed that the {mu}-thiophenethiolate ligand was oriented away from the adjacent sulfido ligand. The reactions of the cationic derivatives with hydrogen have been studied. The bromide salts reacted with hydrogen to form RH, (MeCpMoS){sub 2}S{sub 2}CH{sub 2}, and 1 equiv of HBr. In the presence of a nitrogen base, the reactions of the cations with hydrogen proceeded to form the neutral complexes (MeCpMo){sub 2}{sup -} (S{sub 2}CH{sub 2})({mu}-SR)({mu}-SH) and 1 equiv of protonated base. The kinetics of the latter hydrogen activation reaction have been studied over a range of temperatures, hydrogen pressures, and base concentrations. The kinetic data are consistent with a rate law which is first order in cation and first order in hydrogen. For the cation where R = CH{sub 2}CO{sub 2}Me, the deuterium isotope effect, k{sub H}/k{sub D}, was found to be 2.5 at 50 {degrees}C and the following activation parameters were determined: {Delta}H{sup {double_dagger}} = 84 kJ/mol and {Delta}S{sup {double_dagger}} = -9 J/(mol K). The data seem most consistent with a heterolytic mechanism for the activation of hydrogen. Several possible mechanisms for hydrogen addition to the cation are discussed. Attempts to model the initial hydrogen addition product have been made by reacting the related neutral complexes (CpMo){sub 2}({mu}-SMe)({mu}-SR) with 1 equiv of strong anhydrous protic acid. The reactions with acid involved either protonolysis of thiolate ligands or oxidation of the dimer, depending on the nature of thiolate substituents. However, no protonated intermediates were detected. 30 refs., 5 figs., 4 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 567339
• Journal Information: Organometallics, Journal Name: Organometallics Journal Issue: 7 Vol. 11; ISSN 0276-7333; ISSN ORGND7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
CATIONS
CHEMICAL ACTIVATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CLEAVAGE
DEUTERIUM
DIMERS
HYDROGEN
ISOTOPE EFFECTS
LIGANDS
MOLYBDENUM COMPLEXES
MOLYBDENUM SULFIDES
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
OXIDATION
REDUCTION
STRUCTURAL CHEMICAL ANALYSIS
SYNTHESIS
X-RAY DIFFRACTION