A giant insurer is preparing to complete 2 big changes.[@@]

MetLife Inc., New York, has agreed to sell 1 Madison Avenue, and it has passed an important milestone on the path to closing on Travelers Life & Annuity.[@@]

SL Green Realty Corp., New York, a real estate investment trust, has agreed to pay MetLife $918 million for 1 Madison Avenue, the old Metropolitan Life Insurance Company Tower.

MetLife used the 50-story, 700-foot tower as its corporate headquarters from 1909 to 2004, and the building was the tallest building in the world from 1909 to 1913, according to EarlyOfficeMuseum.com.

Napoleon Brun & Sons, the architects, based the design of the building’s famous clock and bell tower on the clock and bell tower at St. Mark’s Church in Venice, Italy, according to NYC-architecture.com.

In 2004, MetLife moved its headquarters to the former Pan-Am Building, at 200 Park Ave., New York, and many of the employees who had worked at 1 Madison Avenue to new offices in Long Island City, N.Y., a company spokesman says.

The SL Green deal should result in a gain of about $420 million, but it will have no material effect on operating earnings, MetLife says.

Once the deal closes, MetLife will no longer have any ownership interest or significant lease presence at 1 Madison Avenue, the company says.

“Given what this property has meant to MetLife for nearly 100 years, we are pleased that this unique asset will be owned by a company of SL Green’s stature,” says Robert Merck, head of real estate investments for MetLife.

In a separate announcement, MetLife today reported the termination of the 30-day antitrust waiting period triggered by its efforts to acquire Travelers Life from Citigroup Inc., New York.

“MetLife anticipates that the transaction, which is still subject to certain conditions, including other regulatory approvals, will close this summer,” the company says.