Ok, I solved my own problem. I should have researched this a bit more.
select c.ItemID, c.Name, SUBSTRING(c.Path, (CHARINDEX('}',c.Path) + 1), 100) AS [Path]
from catalog c (nolock)
left join ExecutionLogStorage e (nolock)
on c.ItemID = e.ReportID
where c.ItemID not in
(select ReportID from ExecutionLog)