Bb 7sus2, 2nd inversion (E# in the bass)
Also written as Bb7sus2/E#.
Notes, from the bass up
E# (bass)G#A#B#
The same notes as Bb 7sus2 (E#, G#, A# and B#), rearranged so E# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.