In a large mixing bowl, combine brown sugar, ketchup, chicken broth, soy sauce, and garlic. Measure out 1 1/3 cups marinade and pour into a quart-size zip-top bag.
Place chicken into a gallon-size zip-top bag and pour remaining marinade from the bowl over chicken. Place both bags into another gallon-size zip-top bag. Label and freeze.
When ready to cook, thaw in refrigerator 1 - 2 days.
Drain chicken and discard marinade. Grill chicken, covered, over medium heat 6 - 8 minutes on each side. During the last five minutes of cooking, baste with additional marinade. Or bake in a 375°F oven 20 - 25 minutes or until done.