U.S. stocks opened mixed on Monday as investors feared a sooner-than-excepted Fed rate hike. Boston Fed president Eric Rosengren told the Financial Times over the weekend that the economy is 'on the verge' of meeting conditions that warrant a rate hike during the central bank's next meeting in June. Plus, Bayer bid $62 billion for Monsanto  (MON)  in an all-cash deal, valuing Monsanto at $122 a share, which represents a 37 percent premium to the company's closing stock price on Friday. Monsanto shares surged some 8 percent Monday morning. Finally, VietJet Aviation is purchasing 100 Boeing (BA - Get Report)  737 MAX 200 jets in a deal valued at $11.3 billion.