I would have said the key of this piece was G-minor, but since my piano is tuned flat, what I call a G might very well be an F# at concert pitch. I agree with the chord progression. However, the tonic sounds so strongly so much of the time in the bass that a case could be made that almost the entire piece is a pedal point on it. In that sense, there would be no chord but the tonic, with various 7ths, 11ths, and 13ths chords as variations of it.