Coat a large oven-proof skillet with olive oil and place over medium-high heat. Add chicken to pan and saute for about 2 minutes per side, seasoning with salt and pepper as it cooks. Remove chicken from pan. Add broth, syrup, thyme, and garlic to pan; bring to a boil, scraping pan to loosen browned bits. Cook 2 minutes, stirring frequently. Add vinegar and mustard; cook for 1 minute, stirring constantly. Return chicken to pan, and spoon mustard mixture over chicken.