Bb Dominant 11th, 2nd inversion (E# in the bass)
Notes, from the bass up
E# (bass)G#B#D#A#D
The same notes as Bb Dominant 11th (E#, G#, B#, D#, A# and D), rearranged so E# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.