Brokerage and investment adviser Stifel Financial will buy Thomas Weisel Partners Group in a deal valued at $300 million in stock, the companies said on Monday.

The combined group aims to build a middle-market investment bank with "enhanced investment banking, research and wealth management capabilities."

The new company is expected to bring in annual revenue of $1.6 billion.

Each Thomas Weisel share will be exchanged for 0.1364 shares of Stifel stock. Thomas Weisel had about 32.8 million shares outstanding as of March 31.

The deal, approved by the boards of both companies, is expected to close before July.

Thomas W. Weisel, the chairman and CEO of Thomas Weisel Partners Group Inc., and Ronald J. Kruszewski, the chairman, president and CEO, will serve as co-chairmen of the board and Kruszewski will remain president and CEO of Stifel Financial.

Shares of Stifel Financial Corp. closed Friday at $4.36. Shares of Stifel had closed at $55.74.