Preheat oven to 400°F. Season chicken pieces with salt. Heat 1 ½ tablespoons oil in a large oven-proof skillet over high. Add chicken pieces, skin sides down, and cook undisturbed until skin is browned and crisp, about 10 minutes. Remove from heat, and transfer chicken to a plate. Add grapes, garlic cloves, and rosemary to skillet, stirring and scraping up any browned bits. Return chicken pieces to skillet, skin sides up, nestling between and atop grapes. Drizzle with remaining oil.
Roast in pre-heated oven until a meat thermometer inserted in chicken breast registers 155°F, 22 to 25 minutes. Let chicken rest 10 minutes; sprinkle with black pepper.
