can you kill yeast by adding it to to hot of wort?
Yes. You should pitch the yeast when the wort is down to fermenting temperature. 70F is good... you probably won't kill it unless you get over 100F, but it's really best to pitch at 70F or lower (for ale yeast).
I used a white labs Trappist ale yeast and pitched at around 85 90*?
That's really too hot to pitch yeast, but you're probably okay. Just take it down to 70F first next time.
You'll be OK. I've done the same in a rush.