Russian tycoon Alexander Nesis' investment company ICT Group has closed a deal to buy about 25 percent of real estate investment firm O1 Properties from owner Boris Mints, a source close to the deal said.
The source said the deal could be valued at about $350 million.
Nesis, who with a fortune of $3.3 billion ranks as the country's 30th richest man according to Forbes magazine, owns a minority stake in Russian precious metals miner Polymetal, and his ITC group has assets in industries including finance and engineering.
Last year, he sold his 5.1 percent stake in potash producer Uralkali.
Mints is ranked 130th richest Russian by Forbes with a wealth of $0.9 billion.
A representative for O1 declined to comment but confirmed talks are ongoing with ITC. A representative of ICT confirmed there were talks about the purchase of a stake but gave no further details.
It is unclear how much of a stake Mints has in O1 but he is the main shareholder.