Alfredsson said he made the move because he believes Detroit is closer to winning the Stanley Cup.
"I've played 18 years and I haven't won a Stanley Cup. ... I'm really excited to get this opportunity at this stage of my career to go for a Stanley Cup and fulfil a long-time dream," the 40-year-old said.
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With the departure of Alfredsson, the Sens acquired four-time 30-goal scorer Bobby Ryan from the Anaheim Ducks. Ottawa gave up Jakob Silfverberg, prospect Stefan Noesen and a first-round pick in 2014 to get Ryan, a 26-year-old who plays right wing.
The Sens also signed forward Clarke MacArthur to a two-year deal.
The Toronto Maple Leafs have landed free agent David Clarkson from New Jersey and retained Tyler Bozak. Bozak has spent four seasons with Toronto.
"It's an honour to be here," said Clarkson, 29, who is a native of Toronto. "I wore that jersey as a kid. I was a big Leafs fan when I was little so it'll be pretty special to put it on. And for my family, it's a big day."
"I believe he has a lot of good years left in him," Leafs GM Dave Nonis said in regard to Clarkson's seven-year deal that is worth a reported $36.75 million US.
The Boston Bruins signed 36-year-old Jarome Iginla to a one-year deal — just months after he spurned the team at the trade deadline in favour of the Pittsburgh Penguins.
Forward Nathan Horton, who spent the last three seasons with the Bruins, agreed to a seven-year deal with the Columbus Blue Jackets.
"He was the No. 1 guy on our list," said Blue Jackets general manager Jarmo Kekalaine.
The Edmonton Oilers signed another former Bruin, defenceman Andrew Ference, to a four-year deal.
The Oilers signed centre Boyd Gordon for three years and goaltender Jason Labarbera to a one-year contract. Both players are former Coyotes.
In Calgary, the Flames acquired Red Deer, Alta. native Kris Russell in a trade with St. Louis, and signed Finnish netminder Karri Ramo to a two-year deal.
Goaltender Ray Emery, fresh off earning a Stanley Cup with the Chicago Blackhawks, gets his second tour of duty with the Philadelphia Flyers, who have signed him to a one-year deal. Emery went 17-1-0 with Chicago this past season while sharing goaltending duties with Corey Crawford.
The Montreal Canadiens added some heft by acquiring six-foot-five 228-pound enforcer George Parros from the Florida Panthers. The Habs sent prospect Philippe Lefebvre and a 2014 seventh-round pick to the Panthers.