Understanding a certain catalysis paper

Hello, I don't know if this is the right place for this, didn't seem fitting to post this to r/chemhelp.

Well, I'm having trouble understanding what a particular constant in a paper means (that is kobs). If someone read this paper before or is willing to help me out, I'd be very grateful. http://pubs.acs.org/doi/abs/10.1021/ja010624k

EDIT: Forgot to add link to the paper.