Usually not, unless you have enough time to learn it properly before you go. A new camera brings unfamiliar menus, focus controls, batteries, card formats and custom settings, and Antarctica is a poor place to meet all of that for the first time. Wildlife encounters are brief and operating a complicated camera in gloves is much harder than practising at home.
Before buying anything, use what you own. Photograph birds, dogs, sport, boats, white objects in bright sun and moving subjects. Practise changing settings without looking at the controls. If your existing kit consistently stops you making the photographs you want, then consider buying or renting.
Renting is a good option for someone who already understands photography but doesn't own a long lens or a backup body. Get the rental well before departure and confirm how autofocus works, how to change shutter speed and exposure compensation, how many batteries it needs, which cards it takes, how heavy it feels after an hour, whether it fits your dry bag, and whether your computer can read the files.
Renting unfamiliar professional gear two days before departure creates exactly the same problem as buying it.
The goal isn't arriving with the most advanced camera. It's arriving with one you can use confidently.