Merrill Lynch & Co. reshuffled a number of senior executives on Thursday, tapping Sam Chapin to succeed Daniel H. Bayly as co-head of global investment banking.

Mr. Bayly, 53, was promoted to chairman of Merrill’s investment banking division and will join the office of the chairman, the company said.

A Merrill spokesman said that Mr. Bayly’s promotion would let him refocus from running the division on a day-to-day basis to developing and maintaining key investment banking clients. Analysts said Merrill is looking to boost its underwriting and mergers and acquisitions advisory business.

Mr. Chapin, 43, will co-head global investment banking with Kevan Watts. Mr. Chapin had previously co-headed Merrill’s global industries investment banking group.

The company’s chairman and chief executive, David Komansky, 61, has indicated that he plans to name a successor by the end of the year. Mr. Komansky had previously said that he plans to work until age 65.

None of these executives are thought to be in the race, but Mr. Bayly and Mr. Chapin report to one of the top contenders for the post, Thomas W. Davis, who heads Merrill’s investment banking and capital markets divisions.

However, E. Stanley O’Neal, who heads Merrill’s huge brokerage division, is seen by many on Wall Street as the front-runner to succeed Mr. Komansky.

The New York financial services giant also said that it had named Claudio Aguirre to head investment banking for Europe, the Middle East, and Africa. Mr. Aguirre had headed the international private client group for those regions.

Mr. Aguirre is succeeding Justin Dowley and Huston McCullough. Both are leaving Merrill but plan to maintain ties with the company, the spokesman said.

The company also said that Jacob A. Frenkel has been named as president of Merrill Lynch International.

Jose Malbran, who will succeed Mr. Aguirre, will also succeed Ben Lorenz as chairman of Merrill Lynch International Bank, who is retiring.

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