The newspaper, citing league sources with knowledge of the situation, said the 32-year-old Boldin was on the verge of being released by the reigning Super Bowl champions due to a contract impasse before he was dealt.
The Ravens were asking him to take a $2 million cut in his $6 million base salary, the newspaper said.
The reported deal has instead sent Boldin to the team the Ravens defeated in last month's Super Bowl XLVII, who are coached by Jim Harbaugh, the brother of Ravens Coach John Harbaugh.
Boldin hauled down 65 passes for 921 yards with four touchdowns this past season. He also played a big role for Baltimore in the post-season, making 22 grabs for 380 yards with four scores in four playoff games.
He made six grabs for 104 yards with a score in the Super Bowl.
Over 10 NFL seasons with Arizona and the Ravens, Boldin has 772 receptions for 10,165 yards with 58 touchdowns.