You need to stop. Do not de-index your site ! Do not proceed with this scheme !
If you have done your proper research and vetted the domain, then redirect that domain to you money site. Understand if you have not vetted this domain you could be unleashing a world of hurt and make things much more worse than they are. This domain is expired for a reason, so check carefully for any sort of penalty it may have.
After you have vetted the domain, you need to make sure that existing backlinks pointing to this new domain get redirected to the appropriate pages on your money site. Do not just redirect everything to the home page.
This is not something for an amature to indulge in lightly.