Publications [#234085] of Michael J. Therien

Papers Published

1. Therien, MJ; Trogler, WC; Ni, CL; Anson, FC; Osteryoung, JG, Kinetics of Disproportionation of Tricarbonylbis(phosphine)iron(I) Cation Radicals Probed by Double Potential Step Chronocoulometry, Journal of the American Chemical Society, vol. 108 no. 14 (January, 1986), pp. 4037-4042, American Chemical Society (ACS), ISSN 0002-7863 [doi]
   (last updated on 2026/01/15)

   Abstract:
   Rates of substitution of carbon monoxide in a series of iron(I) radical complexes were measured by using double potential step chronocoulometry, a transient electrochemical technique. Carbon monoxide substitution in Fe(CO)3L2⁺ (L = a phosphine) radicals proceeds solely by a second-order process that is first order in both the metal radical and the entering pyridine nucleophile. The rate of substitution depends on the basicity and size of the Lewis base, as seen in the L = PPh3 system, where kxvaries over 400-fold from 0.27 to 1.01 X 10² M“^l s’¹. Hammett analysis of the rate data shows that log k1 correlates well with the 3(PCy3)2⁺ is 10⁶ times slower than at Fe(CO)3(PMe3)2⁺, presumably because increased phosphine ligand size inhibits the associative pathway. Activation parameters further support the proposed associative mechanism: for L = PPh3, nucleophile = pyridine, AH* = 9.8 ± 0.3 kcal mol’¹ and AS’ = -21 ± 1 cal mol^-1 K’¹; for L = PCy3, nucleophile³⁵ 3, 4-dimethylpyridine, AHt - 14 ± 1.5 kcal mol’¹ and AS* = -27 ± 5 cal mol’¹ K”¹. After substitution of carbon monoxide by a nitrogen Lewis base, these complexes disproportionate via an outer-sphere electron-transfer process to yield Fe(II) and Fe(0) products. Comparison of the reactivities of Fe(CO)3(PPh3)2 and its 17-electron analogue, Fe(CO)3(PPh3)2⁺, shows that the cation radical is about 10⁹ more reactive toward pyridine than its 18-electron precursor. © 1986, American Chemical Society. All rights reserved.