During their first observational run, the two Advanced LIGO detectors attained an unprecedentedsensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-massbinary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) frommerging intermediate mass black hole binaries (IMBHBs). The combined results from two independentsearch techniques were used in this study: the first employs a matched-filter algorithm that uses a bank offilters covering the GW signal parameter space, while the second is a generic search for GW transients(bursts). No GWs from IMBHBs were detected; therefore, we constrain the rate of several classes ofIMBHB mergers. The most stringent limit is obtained for black holes of individual mass 100 M⊙, withspins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained tobe less than 0.93 Gpc−3 yr−1 in comoving units at the 90% confidence level, an improvement of nearly 2orders of magnitude over previous upper limits.