No. In political science, a government where a sub-national polity has the de jure ability to succeed is called a "Confederation" and there is presently no extant Confederation in the world at this time (The "Swiss Confederation" doesn't count because the term "Confederacy" has had some linguistics drift from when the "Swiss Confederacy" became the official name of Switzerland and what Confederacy means today. Back then, Confederation meant the same thing as the modern term Federation does today).
The closest example to what you are looking for is the Eurpoean Union as their charter does give member-states the right to leave (Brexit anyone?) although there's nothing compelling the EU to make it a smooth and easy process. That said, the EU is not really considered a nation similar to the United States but a Super-national organization like NATO or the UN (though Germany and France have some ambitions to make the EU a more Federal polity like the United States... though there is some push back given how things went the last time Germany tried to Unite Europe under one national banner.).
EDIT: Forgot the historically brief nation of Gran Colombia, which was a Federal Nation in South America which broke apart. At it's height, it contained the present day territory of Colombia, Venezuela, and Ecuador. The three "nations" were united during their indepences war against Spain and the Gran Colombia-Peru war, but these two events happened rather quickly before the nation could draft formal constitutional documents and by the time the second war concluded, regional issues within the three states led to the peaceful dissolution of Gran Colombia... the term "Gran Colombia" was actually never used during the "nations" existence but was coined by historians to distinguish this nation with the Republic of Colombia, one of the three nations following the separation.