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Energetics and Ultrafast Ring Closure Dynamics of Cyclopentadienyl Manganese Tricarboyl Derivatives

Published

Author(s)

T Jiao, Zhiyu Pang, Theodore J. Burkey, R F. Johnston, T Heimer, V D. Kleiman, Edwin J. Heilweil

Abstract

Ring closures following flash photolysis in alkane solvents has been detected for several complexes in the series η5-C5H4R)Mn(CO)3 where R = COCH3 (1), COCH2SCH3 (2), CO(CH2)2SCH3 (3), COCH2OCH3 (4), (CH2)2CO2CH3 (5), and CH2CO2CH3 (6). In each case where ring closure occurs a metal CO is ultimately substituted by the side chain functional group. Photoacoustic calorimetry studies reveal that ring closures occur with rate constants faster than 107s^-1u^ or between 106 and 107s-1. or in some cases the ring closure is biphasic with rate constants in both ranges. The enthalpies of CO dissociation followed by ring closure for 2 and 3 are the same (12kcal/mol) and more favorable than those for 4-6 (25-15 kcal/mol). Studies of 1-3 by transient picosecond to microsecond infrared spectroscopy confirm biphasic dynamics for 2 and 3: ring closure occurs immediately (k > 5 x 109 s^-1u^) and at slower rates (k = 108 to 106 s^-1^). We purpose that some ring closure occurs before solvent coordination and that the remaining ring closure, resulting in the displacement of solvent, is much slower. The relationships of the rates and energetics of ring closure to structure and quantum yields is discussed.
Citation
Journal of the American Chemical Society
Volume
121
Issue
No. 19

Keywords

manganese tricarbonyl, metal carbonyls, photoacoustic spectroscopy, photochemical reactions, reaction dynamics, selfassociation, solvent coordination, transient infrared, vibrational spectroscopy

Citation

Jiao, T. , Pang, Z. , Burkey, T. , Johnston, R. , Heimer, T. , Kleiman, V. and Heilweil, E. (1998), Energetics and Ultrafast Ring Closure Dynamics of Cyclopentadienyl Manganese Tricarboyl Derivatives, Journal of the American Chemical Society (Accessed May 21, 2024)

Issues

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Created August 31, 1998, Updated October 12, 2021