The Brookline Chamber of Commerce is preparing to hold a farewell party for executive director Harry Robinson, who has taken a position as a history teacher at Wakefield High School. The special “after-hours’’ networking session will take place from 5:30 to 7:30 p.m. Sept. 16 at the Barcelona Wine Bar, 1700 Beacon St. Robinson has overseen the chamber’s operations for five years, and has initiated several projects, including a business breakfast with Governor Deval Patrick, two expos showcasing environmentally friendly business technologies, and a “cash mob” to bring in consumers to the St. Mary’s area. The chamber has also collaborated with the Brookline Rotary Club on an annual fund-raising golf tournament. In an announcement on his move by the local business organization, Robinson said his departure is bittersweet. “I have thoroughly enjoyed working with the chamber for the past five years and yet am thrilled to be embarking on a new adventure,” he said. Admission to the event is $20, or $10 for chamber members; because of limited space, participants are asked to preregister online at www.brooklinechamber.com.