SANTA CLARA, Calif. -- The San Francisco 49ers couldn't pry the ball from Anquan Boldin in the Super Bowl, but on Monday they were able to dislodge the veteran receiver from the Baltimore Ravens for a sixth-round pick.

The trade won't become official until Boldin returns from a charity mission to Senegal and passes a physical. But it was confirmed by Boldin's agent, and it gives the 49ers a big-bodied and strong-willed receiver who was a critical component in the Ravens' Super Bowl campaign.

Boldin, 32, caught 22 passes for 380 yards in four postseason contests, including a team-high 104 receiving yards against the 49ers in the Super Bowl. His catches in last month's game in New Orleans included the Ravens' first touchdown, which occurred on Baltimore's opening drive, and a crucial third-and-one snag along the sideline that came despite tight coverage by cornerback Carlos Rogers, who had a hand on the ball.

The 49ers do not acknowledge deals until they are complete, but quarterback Colin Kaepernick, appearing on ESPN's NFL Live, welcomed Boldin to the team.

"We need another receiver," Kaepernick said. "We have great wide receivers already, but he's another great addition. I think everybody saw what he was capable of this past year and what he did in the Super Bowl. So that's just another playmaker on our team."

As Kaepernick noted, the 49ers ended the 2012 season with gaps at the position.

Michael Crabtree, who the team compared to Boldin when he was drafted in 2009, will line up at one spot. But two other options, Randy Moss and Ted Ginn, are pending free agents who aren't expected back, while two others, Mario Manningham and Kyle Williams, are coming off late-season knee injuries.

Manningham, a free-agent acquisition last year, is not expected to be ready for training camp, and his injury could linger into the season.

In Boldin, the 49ers get a receiver they have admired -- and who has given them fits -- since he was taken by the division-rival Cardinals in the second round of the 2003 draft.

In 15 games against the 49ers, Boldin has 90 catches for 1,157 yards and eight touchdowns.

The 49ers currently have two picks in the sixth round and are expecting 15 selections overall in the upcoming draft once Alex Smith is traded to the Kansas City Chiefs.

That trade also will create enough salary-cap space to accommodate Boldin, who is due to earn a base salary of $6 million in the upcoming season.

Pressed against their own salary cap, the Ravens could not afford to pay Boldin that much, and they had asked him to take a $2 million salary cut.

Meanwhile, the 49ers on Monday extended the contract of one of their young players, nose tackle Ian Williams.

The two-year extension is worth $3.5 million, it locks in Williams through 2015 and is an acknowledgment that the 49ers will lose Ricky Jean Francois or Isaac Sopoaga -- or perhaps both -- when free agency begins Tuesday. Jean Francois has received attention from five teams, including the Eagles, Titans and Browns.

Williams played only a handful of snaps this past season but played well in his brief appearances.

"They signed me for an extension for two years, so I think I did something right," said Williams, who went undrafted out of Notre Dame in 2011.

The 49ers also appear to be in the market for a big cornerback and are one of the teams most interested in Miami free agent Sean Smith, who at 6-3, 218 pounds is one of the biggest cornerbacks in the league.

The 49ers have had trouble covering big receivers -- Boldin is a good example -- which is Smith's specialty. The Eagles, Buccaneers, Chiefs and Raiders also have shown interest in Smith.

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