Energetics and Ultrafast Ring Closure Dynamics of Cyclopentadienyl Manganese Tricarboyl Derivatives

Published

September 1, 1998

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

Pub Type

Journals

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 July 17, 2024)