Klenau never achieved full recognition as a composer in Denmark, but he held a number of important conducting positions.
In 1912, he led the concerts of the Bach Society Frankfurt, but already the following year he returned to the conductor position at the Freiburg Opera.
He took up permanent residence in Bavaria, where he owned a country house, but as a conductor he traveled extensively, both in Germany and the United Kingdom.
After the first orchestral period that lasted until around the outbreak of the First World War, Klenau shifted his focus to musical drama.
Between 1933 and 1939, Klenau composed three major twelve-tone operas: Michael Kohlhaas (after Kleist), Rembrandt van Rijn and Elisabeth von England.
[5] According to Schoenberg,[6] Klenau once defended his use of the twelve-tone technique as the basis of an opera as an example of National Socialist art, making an analogy with the Führerprinzip, where everything in the piece needed to follow the leader.
Klenau's musical output, some of which is undergoing recording revival, includes nine symphonies (spanning the year 1907-1945),[3] three string quartets, and a setting (1919) of Rainer Maria Rilke's "Die Weise von Liebe und Tod des Cornets Christoph Rilke"[3] among other works.