Without knowing what you/they are into, here's a couple of top-of-my-head suggestions. I avoided places at which you can't make reservations (like avec & Purple Pig), since reservations for a business dinner are usually a must. I like Girl & the Goat a lot, but agree that you may have trouble getting in with only a week's notice.
For Foodies:
The Publican (but be warned, this place is REALLY loud for a business dinner)
Blackbird
Sepia
Vera
For Scenesters:
Mercat a la Planxa
Nellcôte
The Pump Room
For "Quintessential" Chicago (if there is such a thing):
Your Chinatown idea is great if they're up for it
Topolobampo (especially if they're impressed with celebrity chefs)
North Pond (maybe better for a date than business, but a truly unique Chicago dining experience)
If they don't want to venture out, there are tons of places close by that are good. Naha (my favorite of the nearby places), Sable, GT Fish & Oyster, Graham Elliott, and all those steakhouses that Khaopaat mentioned...