James S. McDonald, president and chief executive of investment management firm Rockefeller & Co., has died of an apparently self-inflicted gunshot wound, Massachusetts authorities said Tuesday. McDonald, 56, was found in his vehicle at about 3 p.m. Sunday behind a car dealership in Dartmouth, about 50 miles south of Boston, said Gregg Miliote, a spokesman for the Bristol district attorney's office. There was no note, but McDonald "made a phone call to his wife earlier in the day," Miliote said Tuesday, without getting into specifics of the call. The death is still under investigation.