Chrysler Group says its top purchasing executive, Peter Rosenfeld, has decided to exit the auto maker after 25 years of service.

Simon Boag, who will rejoin Chrysler following a 15-month stint as head of production planning for the Mercedes Car Group, will replace Rosenfeld as executive vice president-Procurement and Supply.

Before joining Mercedes, Boag was vice president-Assembly and Stamping Operations for Chrysler. A former General Motors Corp. executive, Boag initially came to Chrysler in 2005.

Chrysler did not give a reason for Rosenfeld’s decision to leave the auto maker, which is expected to come under majority ownership of Cerberus Capital Management LP in the third quarter.

Rosenfeld was appointed to his current position in December 2003. He will remain with the auto maker over the next month to help with the management transition.