Lexapro is a SSRI for depression, in the same class as Zoloft and Prozac. It a clean drug with few drug-drug interactions and few side effects, so it has become popular. I know some people take it for OCD and anxiety as well as depression. Klonipin is a benzodiazapine like Valium or Xanax. It is not as addicting as Xanax because it is longer acting but its also not as effective as Xanax for panic attacks because it has a longer onset of action. All benzos carry a risk of addiction and need to be used with care and under careful supervision. Some docs hand out benzos like they are nothing and some are so cautious they never use them. They have a place as long as they are used judiciously.
The lexapro will take 4-6 weeks before the effect is really felt but the Klonipin will work the first day. I personally wouldn't take Klonopin for sleep. There are better sleep drugs that are less addicting. There are other meds for the ADD, too. Its worth investigating and if you have depression compounded by the ADD, I would see a psychiatrist who has experience in handling adult ADD. Or pehaps you already are...anyways, goodl luck!
Amy