When 2011 began, Boston Properties was coming off a buying spree that really turned heads in the slow-to-recover local commercial real estate market. Its biggest purchase was in Boston’s Back Bay neighborhood, where it snapped up the John Hancock Tower for $930 million - a perfect example of the company’s ability to seize an opportunity at a critical moment. The company took ownership of the city’s most prized office property just as rents were beginning to rise.