At the MAC, press and hold down the OPTION key, and click on the LrC startup icon.
That should start LrC, but with a dialog screen asking about what catalog to open, select new catalog.
If LrC starts, before it can crash, and hoping it does not, collect the System Information as LrC reports it
In LrC click on Help, then System Info, then Copy. Paste that information into a reply. Please present all information from first line down to and including Plug-in Info. Info after Plug-in info can be cut as that is just so much dead space to us non-Techs.
So 2 things, does LrC behave with a new catalog, What is the Sys Info (highly interested in plug-ins by the way)
As you probably know, googling on this is not very usefull for some reason.