* Rhoen says CEO Pfoehler, CFO Hamann to leave
* Former Dresdner executive Neumann to be interim CFO
* Martin Siebert set to become new CEO - sources (Adds details, background)
By Andreas Kröner and Ludwig Burger
FRANKFURT, Sept 27 (Reuters) - The chief executive and chief financial officer of Rhoen-Klinikum are to step down after they were effectively sidelined by the German hospital chain's founder and chairman in a takeover bid by Fresenius that ultimately failed.
CEO Wolfgang Pfoehler will step down on Dec. 31 and CFO Erik Hamann will take a new job elsewhere after Sept. 30, both "on the best of amicable terms with the Supervisory Board", Rhoen said in a statement on Thursday.
Supervisory Board member Jens-Peter Neumann will become CFO but only for one year for regulatory reasons, the company said.
It did not say who would succeed CEO Pfoehler but two people familiar with the company said Martin Siebert, who was hired to join Rhoen's executive board on Oct. 1, was in the frame for the top job.
Earlier this month, German healthcare group Fresenius dropped plans for a 3.1 billion euro ($4.0 billion) takeover of Rhoen after other companies including Asklepios and medicals supplier B. Braun bought blocking stakes.
Rhoen founder and chairman Eugen Muench had championed the deal but did not involve his executive board in initial discussions with Fresenius.
Rhoen's top management remained on the fence about the offer for about a month and then endorsed it.
Reuters last week cited two people familiar with the matter as saying smaller rival Sana-Kliniken was looking to raise its stake in Rhoen-Klinikum in what eventually could result in a merger. Sources familiar with the matter said on Thursday that outgoing CFO Hamann was one of the driving forces behind Sana's approach.
CFO-designate Neumann had formerly been head of the capital markets division of Dresdner Bank, a lender that was taken over by Commerzbank, which was later subject to an 18.2 billion euro ($23.4 billion) government bailout after the financial crisis.
In 2009, Neumann won a legal fight with Commerzbank over a 3 million euro payout. ($1 = 0.7775 euros) (Reporting by Andreas Kroener and Ludwig Burger. Editing by Jane Merriman)