The litigation trust established in the 2009 bankruptcy of chemical giant LyondellBasell is blaming a Brown Rudnick attorney for a tactical blunder that allegedly cost the trust $300 million.

In a malpractice suit filed in New York federal court Tuesday, the trust alleged that the firm had failed to demonstrate that a Lyondell subsidiary was insolvent when it paid back $300 million in credit to billionaire Leonard Blavatnik, just months before the Chapter 11 filing.