If you may have
John (no space)
John Brown (1)
John A. Brown (2+)
Then try this
Create 2 new columns instead
In the first =LEFT(A2,Find(" ",A2&" ")-1)
In the second =MID(A2,Len(B2)+2,255)
Select B2 and C2, double-click bottom right little black square of C2 (fill handle)
Select B:C (entire columns)
Copy
Right-click, paste special, choose Values, then OK.
All done!
(change A and B to where the full name and first column will be)