Can I use toggle bolts to mount a tv on a barnwood wall?
No, you can not mount the TV the way you have described. Since you want the TV to articulate out from the wall, most of the force will be pull-out instead of shear. The barn boards are not attached to the wall in such a way to support your TV. It's likely you would rip the barn boards right off the wall, or break one where you drill for the toggle bolts.

You need to find the studs. There is no other way forward for you if you must mount it to the wall. Some ways to find studs include:


Remove the face plates from any outlets or switches on the wall. The outlet box is likely mounted to a stud, which you can see, or probe for with a screwdriver.
What's on the other side of the wall? If it's drywall, use a stud finder. Then measure off a common point to transfer the location to the barn board side, or use a long drill bit to drill all the way through the wall next to the stud.
Remove one barn board.
How are you going to power the TV and get any cabling to the TV? If you want to hide the cabling, you're going to have to cut a hole in the wall anyway. Use the hole to locate the studs.
Drill one hole, but point it severely to the left or right. Using a cut coat hanger, probe the wall to find the stud.
Use a magnet locate the fasteners holding the firing strips to the studs. This has a low chance of working in your situation.


Also, a good way to repair a hole in your wall is to make it look like a knot by painting the inside of the hole with black or brown paint. It helps if you carefully choose where to drill the hole to begin with so that it looks natural. Drilling the hole tilted down also helps with the realism and makes it harder to see through the hole.