By Isla Binnie and Svea Herbst-Bayliss

NEW YORK, July 25 (Reuters) - Citigroup's C.N global head of clean energy transition investment banking is leaving the U.S. lender for a role advising on mergers and acquisitions at boutique bank Moelis MC.N, people familiar with the matter said on Friday.

Serge Tismen is expected to formally join Moelis in September, following a period known as gardening leave. He will advise the bank's clients on dealmaking broadly and will report to Anton Sahazizian, Moelis' head of mergers and acquisitions, one of the sources added.

Reuters was unable to contact Tismen for comment.

Spokespeople for Citi and Moelis declined to comment.

Tismen has worked within Citi's investment bank for more than two decades, according to his LinkedIn account.

In 2021, he stepped in to lead a new unit to capture more business from companies working on reducing carbon emissions through developing hydrogen fuel, vehicle charging infrastructure, carbon capture and sequestration and biofuels.

Clean energy has recently come under pressure from U.S. President Donald Trump. His administration has sought to roll back environmental regulations and measures put in place by former President Joe Biden, to encourage renewable energy.

Trump has moved to cancel tax credits supporting renewable power generation, and ordered the Department of the Interior to review whether any regulations favor wind and solar over other energy sources.

While broader dealmaking was also subdued in the first half of 2025, as companies and financial markets navigated volatility triggered by Trump's trade war, sentiment is buoyant for the rest of the year, with forecasts for significant deal flow and a host of mega-mergers.

(Reporting by Isla Binnie in New York; Editing by David French and David Gregorio)

((isla.binnie@thomsonreuters.com; Reuters Messaging: isla.binnie.thomsonreuters.com@reuters.net/))