An art collector and hedge fund manager are suing a high-end art gallery for $14.6 million, claiming the gallery, known for its extensive Renaissance and Baroque art collections, violated a contract regarding joint purchases of several paintings.

According to the complaint filed in state Supreme Court on Wednesday, the collector, Roy Lennox, said he and the Salander-O’Reilly Galleries’s owner, Lawrence Salander, together began buying Renaissance and contemporary paintings in 2003 under an agreement that they were investments and the gallery would resell them, with Mr. Lennox receiving a portion of the profits. The suit alleges Mr. Lennox rarely saw those returns.

While the arrangement initially went as planned, it turned sour after Mr. Salander went on a 2006 purchasing trip to Italy, according to the suit. When Mr. Lennox claimed he hadn’t seen his returns a year later, the art dealer instead offered to offset the payment with other works from the gallery, including a relief sculpture by the Renaissance artist Donatello worth more than $800,000, according to the complaint. When it arrived, Mr. Salander instead insisted Mr. Lennox pay for it in full, the suit said.

Since the deals began in 2003, Mr. Lennox claims to have invested $3.6 million to the gallery but received only $1 million in returns, according to the suit.

Mr. Salander declined to comment directly to the suit, referring to it in an e-mail message as a “dispute between friends.”

The gallery is involved in several other lawsuits filed in state and federal court that allege similar tactics.