As long as you publish in print, the solution is easy:
- Keep the whole opus in one main file (maybe using \include etc.)
- Compile the file with TOC
- Save your TOC as a extra PDF (e.g. by sending only the TOC pages to a PDF printer and the like)
- Now split your main file in two and set the first pagenumber of the second part to the pagenumber it had before.
- Before this first page include the TOC-PDF, using the pdfpages package.
You know how to switch between roman pagenumbers for the frontmatter and arabic pagenumbers of the mainmatter? But this depends on the documentclass.
So you need to find out how to deal with pagenumbering. We can help you, as soon as you tell us more about the documentclass and maybe give us an MWE. Minimal working examples for large documents are easy with the blindtext package and the command
If you publish a PDF, things are more complicated, because you'll probably wish to have hyperlinks from the TOC to the chapters and sections.