Heat 2 teaspoons oil in a large skillet over medium-high heat. Add greens and cook, stirring often, until wilted, about 4 minutes. Stir in garlic, capers and 1/4 teaspoon pepper; cook, stirring occasionally, until fragrant, about 30 seconds. Add beans, broth and wine and bring to a simmer. Reduce heat to maintain a low simmer, cover and cook for 5 minutes. Remove from heat and stir in butter. Cover to keep warm.