This is what I do.
Its not a sync so much as a neater way of working, keeping your location shooting separate from your archival at the office.
I take a portable drive with me, and make new catalogs for each shoot, then simply import everything into the main archive using the import from catalog and copy the images to wherever I want.
I'm not sure whether you are using the same computer in the office and on location, lets assume you are using 2 computers.
Either way, to ensure all the presets etc are kept from catalog to catalog and from computer to computer I'd do this.
1. plug the portable hard drive into the main computer where you also access the archives
2. ensure that you have the "store presets with catalog" is checked before part 3
3. select one photo and export that to a new catalog on the portable drive, ensuring export selected photo is checked
4. open that new catalog on the portable drive and check your keywords, presets etc are in the catalog.
5. go on location with laptop and shoot, open the catalog on the portable drive, delete that photograph and import all the photos into that catalog
6. edit / tag / comment etc as needed
7. back at the office, plug the portable drive into the main system, open your main lightroom catalog and import the catalog
, you will have to dictate where the new shoot images are going to, but that is no hardship.
8. once done and you are happy, do your back up from your main archive as you would, then delete all the photographs from your portable drive, so the catalog is effectively empty, and repeat from 5 the next time you go on location.
I'd not use finder / explorer to move photos. You get all sorts of error messages saying can't find photos etc.
Use this method and you'll be sorted. Its simple its easy and it works, very well.
Even if you are using the same computer for office and location, I'd still make the catalog on the external drive, then you have everything in one place, keeps it neat and tidy.
Hope this works for you.
So, if I understand what you're saying, you want to edit on the portable, then, when you get home, import the changes onto your main computer. Basically then, you have two different catalogs that are "the same" for our purposes.
Okay. This works. I do this sometimes as well, and it's easy.
If you are editing a subset of your main catalog, export the images as a catalog to the portable, and copy the originals. Make sure your portable disk mounts to the same file name / place on your laptop as it does on your desktop.
Then edit on the laptop. Make changes, whatever, etc.
Plug the portable back into your desktop, and "import from catalog", but do _not_ select the copy negative function (since they are already in the main computer's catalog). One minor warning: If you've added images (imported) them onto the portable, I would import the same images onto the desktop FIRST, then import your metadata (catalog) changes.
If you make changes on the desktop that you want reflected on the portable, just do the same thing again. Open the portable's catalog, and import from catalog from the main disk.
That's what I consider to be the "built in" functions within LR.
The other way to do this is with an external sync program, but it will actually replace the entire catalog each time, so if you edit on both, then import, you'll most certainly lose the changes on one of them.