Citi's CEO joins others caught in the credit crunch

— -- With firm determination, Citigroup CEO Charles Prince declared earlier this year that 2007 was going to be the "year of no excuses."

Now he's run out of them.

Amid growing losses from subprime mortgages at the giant financial services firm, Prince, 57, retired under pressure on Sunday. He said it was "the only honorable course for me to take." Former Treasury secretary Robert Rubin, a board member and chairman of the company's executive committee, will serve as chairman of the board. Sir Win Bischoff, chairman of Citi Europe, will serve as acting CEO, the company said.

Rubin, 69, may be a reluctant leader for Citi. A senior executive at Goldman Sachs before he joined President Clinton's Cabinet as Treasury secretary, he has resisted calls to head Citigroup since joining its board in 1999.

In this new role, he'll be part of a committee to find a new permanent CEO. Rubin said the group intends to complete the search "as expeditiously as possible."

Prince's departure was not a complete surprise. It was the second major resignation at a Wall Street firm in a week, and is part of a tightening crunch for those at the top of financial services firms.