title: Activation of the sulfhydryl group by Mo centers: kinetics of reaction of benzyl radical with a binuclear Mo(micro-SH)Mo complex and with arene and alkane thiols.
abstract: This paper provides evidence from kinetic experiments and electronic structure calculations of a significantly reduced S-H bond strength in the Mo(micro-SH)Mo function in the homogeneous catalyst model, CpMo(micro-S)(2)(micro-SH)(2)MoCp (1, Cp = eta(5)-cyclopentadienyl). The reactivity of 1 was explored by determination of a rate expression for hydrogen atom abstraction by benzyl radical from 1 (log(k(abs)/M(-)(1) s(-)(1)) = (9.07 +/- 0.38) - (3.62 +/- 0.58)/theta) for comparison with expressions for CH(3)(CH(2))(7)SH, log(k(abs)/M(-)(1) s(-)(1)) = (7.88 +/- 0.35) - (4.64 +/- 0.54)/theta, and for 2-mercaptonaphthalene, log(k(abs)/M(-)(1) s(-)(1)) = (8.21 +/- 0.17) - (4.24 +/- 0.26)/theta (theta = 2.303RT kcal/mol, 2sigma error). The rate constant for hydrogen atom abstraction at 298 K by benzyl radical from 1 is 2 orders of magnitude greater than that from 1-octanethiol, resulting from the predicted (DFT) S-H bond strength of 1 of 73 kcal/mol. The radical CpMo(micro-S)(3)(micro-SH)MoCp, 2, is revealed, from the properties of slow self-reaction, and exclusive cross-combination with reactive benzyl radical, to be a persistent free radical.
authors.affiliation: The Pacific Northwest National Laboratory, PO Box 999, Richland, Washington 99352, USA. james.franz@pnl.gov
authors.forename: James A
authors.initials: JA
authors.lastname: Franz
authors.forename: Jerome C
authors.initials: JC
authors.lastname: Birnbaum
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Kolwaite
authors.forename: John C
authors.initials: JC
authors.lastname: Linehan
authors.forename: Donald M
authors.initials: DM
authors.lastname: Camaioni
authors.forename: Michel
authors.initials: M
authors.lastname: Dupuis