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Engineering Organometallic Femtosecond Chemistry: Photochemistry and Dynamics of Ultrafast Chelation of Cyclopentadienylmanganese Tricarbonyl Derivatives with Pendant Benzenecarbonyl and Pyridinecarbonyl Groups

Published

Author(s)

Edwin J. Heilweil, Jermaine O. Johnson, Karen L. Mosley, Phillipe P. Lubet, Webster E. Charles, T J. Burkey

Abstract

A new method was developed to prepare three cyclopentadienyl manganese tricarbonyl derivatives 1, 4, and 5 with different side chains (Mn{ 5-C5H4CH2COR}(CO)3, R = 2- pyridyl 1, phenyl 4, and 4-pyridyl 5). Steady-state UV-vis, FTIR, and NMR studies in heptane show that chelates 2, 6, and 7 are formed, respectively, with the side-chain oxygen but decay on the minute timescale. A side chain chelate 3 with nitrogen is also observed in competition with 2. The rearrangement of the O-chelate 2 to the nitrogen chelate 3 is a unimolecular process (a non-dissociative linkage isomerization) that is faster than the decay observed for the O-chelate 6 (phenyl instead of a 2-pyridyl side chain), even in the presence of 0.1 M pyridine for the latter. Ultrafast chelation is observed with the side-chain oxygen following irradiation of 4 and 5 during timeresolved infrared (TRIR) studies in heptane. Ultrafast chelation is also observed for both side-chain nitrogen and oxygen following irradiation of 1. The lack of ultrafast solvent coordination following irradiation of 1 indicates that the formation of these chelates is a sub-picosecond process. A split in the degenerate stretching bands 4 and 5 in FTIR spectra suggests that there is a significant electronic communication between the side chain and the metal carbonyl groups. These results suggest that ultrafast chelation is favored by side-chain conformations that position a functional group near the metal center.
Citation
Organometallics
Volume
30

Keywords

manganese tricarbonyls, molecular design, photoswitch, time-resolved infrared, ultrafast chelation

Citation

Heilweil, E. , Johnson, J. , Mosley, K. , Lubet, P. , Charles, W. and Burkey, T. (2011), Engineering Organometallic Femtosecond Chemistry: Photochemistry and Dynamics of Ultrafast Chelation of Cyclopentadienylmanganese Tricarbonyl Derivatives with Pendant Benzenecarbonyl and Pyridinecarbonyl Groups, Organometallics (Accessed April 17, 2024)
Created October 24, 2011, Updated January 27, 2020