US EPA

8437668 

Journal Article 

Cis Labilization of Ligand Dissociation. I. 13CO Monoxide Exchange and Phosphorus Ligand Substitution with Mn(CO)5Br and Re(CO)5Br 

Atwood, JD; Brown, TL 

1975 

Yes 

Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 

97 

12 

3380-3385 

English 

10.1021/ja00845a017 

The exchange of 13CO with Mn(CO)5Br and Re(CO)5Br in hexane has been measured using infrared spectral techniques. A complete accounting of the time dependencies of all isotopically labeled species and comparison with the results of phosphorus ligand substitution rates lead to the following conclusions, (a) The rate-determining process is CO dissociation. (b) The rate constant for cis CO dissociation is at least ten times that for trans. (c) The five-coordinate intermediate formed in the dissociation is fluxional. (d) The rate constant for cis CO dissociation in Mn(CO)5Br is 2.8 × 10-5 sec-1 at 23°; for Re(CO)5Br at 30°, 5.1 × 10-7 sec-1. The labilization of CO toward dissociation by cis ligands which are weaker π acceptors than CO seems general. © 1975, American Chemical Society. All rights reserved.