The Red Sox received right-handed pitcher Clayton Mortensen in return. Mortensen, 26, is a former first-round sandwich pick in 2007 by St. Louis, who sent Mortensen to Oakland in the deal for outfielder Matt Holliday. The Rockies acquired Mortensen for a minor league player last January; the Red Sox become his fourth big league organization.
Last season, he was 2-4 with a 3.86 ERA in 16 games, six of them starts.
Scutaro was projected as Boston's starting shortstop but will play second base and bat second in Colorado, where the Rockies also have added Michael Cuddyer and Ramon Hernandez in an offseason makeover following last year's disappointing slide.
The 22-year-old Iglesias appeared in 10 games for the Red Sox last year, getting two hits in six at-bats. A slick fielder who has struggled at the plate as a pro, he batted .235 with a homer and 31 RBIs in 101 games for Triple-A Pawtucket last year. In two minor league seasons since he defected from Cuba, Iglesias has a paltry .308 on-base percentage and .316 slugging percentage.
Still, his defense is considered outstanding and the Red Sox have been grooming him as their shortstop of the future.
The Red Sox had exercised the $6 million option they held on Scutaro's contract for the 2012 season, in what Red Sox general manager Ben Cherington termed a "significant acquisition" just two days ago. But with the Red Sox still looking to improve their starting pitching depth, and Carl Crawford's wrist surgery leaving them thin in the outfield, the decision was made to move Scutaro.
Also Saturday, the Red Sox reached a one-year, non-guaranteed contract for 2012 with pitcher Daniel Bard, avoiding arbitration.
Scutaro hit .299 in 113 games last season for the Red Sox, reclaiming the starting job at short he lost to Lowrie in the season's first month.
Gordon Edes covers the Red Sox for ESPNBoston.com. ESPN.com's Jerry Crasnick and The Associated Press contributed to this report.