The Museum of Modern Art has received more major help with its $400 million renovation and expansion project — this time from the billionaire collector Steven A. Cohen and his wife, Alexandra. The couple’s philanthropic foundation has donated $50 million to the museum’s capital campaign, and MoMA’s largest contiguous gallery will be named the Steven and Alexandra Cohen Center for Special Exhibitions, the museum announced Tuesday.

Last year, the media mogul David Geffen donated $100 million to the project.

MoMA has raised the money to cover the construction, and is now focused on building the endowment.

The museum’s overhaul aims to increase exhibition space and to improve circulation in the museum. Mr. Cohen is a hedge fund manager who joined MoMA’s board last year.

“Alex and I have always believed that the arts can, and should, enrich all people’s lives,” Mr. Cohen said in a statement. “We are excited to see how this gift and the Cohen Center will allow the museum to bring new and even greater artistic experiences to visitors.”