Not usually. Not usually. Diazepam works on certain parts of the brain which cause a anti-anxiety, and calming, and anticonvulsant effect. Medicines for adhd are very different, usually stimulants are prescribed which work differently on the brain.
No. Diazepam is used to reduce anxiety. If anxiety is interfering with your ability to focus and attend, it might be helpful, but your would be treating anxiety, not adhd. Diazepam would most likely make adhd symptoms worse. We know the chemistry of adhd and the chemistry of medications such as Ritalin (methylphenidate) and amphetamines that treat adhd symptoms.