Bentley, who joined CDR as financial controller in 2000, left the financial comms shop last Friday and is set to join direct marketing and advertising holding company Cello Group as finance director.
Prior to joining CDR, Bentley was financial project manager for Hodder Headline, the educational publishing company later acquired by WH Smith.
He became chief operations officer of CDR in 2002.
CDR chief executive Jonathan Clare said finance director Paul Baker, who joined last April, had taken over Bentley's responsibilities but would not immediately have the chief operating officer title.
Clare added that Bentley had been promoted from finance director to reflect his other responsibilities, which included property and outside suppliers.
CDR staff and those in other parts of the Incepta group are awaiting more details to emerge of the proposed merger with Huntsworth, which are to be put to shareholders at the end of this month.