Besides the office and hotel, Liberty Center includes a 25,000-square-foot retail shopping arcade and underground parking for 479 cars.

Starwood plans to substantially renovate the lobbies, hotel rooms, restaurants and other common areas of the complex.

The company's Jeff Shuster said, "The Pittsburgh economy is experiencing a renaissance, with broad based growth in multiple sectors, including energy, healthcare, technology, education and financial services. This economic expansion has helped raise the downtown Class A office occupancy rate to be among the best in the nation."

Also, Suril Shah of Starwood said the Westin is well-positioned for continuing room demand, because of its connection to the convention center. “When combined with the city's projected job and population growth,” Shah said the hotel is expected to offer “meaningful upside to the investment on behalf of our partners."

A recent analysis of 13 high-end building sales downtown and on the North Shore since 2011, conducted by the Pittsburgh Post-Gazette, found that 10 of them involved out-of-town buyers. The landmark U.S. Steel Tower and the PPG Place complex are now held by companies based elsewhere.

Starwood, which calls Greenwich, CT., home has invested $16 billion since its founding in 1991, representing over $41 billion in assets. It currently has $26.3 billion of assets under management around the globe, in nearly every class of commercial real estate.