Are labile tetrahedral [Mabcd] complexes optically active?
In a labile complex, ligands are detaching and attaching to the metal centre at extremely high rates. This means the solution will racemise quickly.  Therefore, even if the complex is truly optically active, you have equal proportions of each enantiomer and thus equal rotations of the polarised light plane - in opposite directions.
The end result is that rotation cancels and so none is observed.